SUMMARY

BOILER1. Energy Audit on Ships: Audit of Marine Boiler2. Energy Conservation in Boilers and Making a Boiler Report 3. What to do When Flame Failure or Fuel Pump Tripping in Marine

Auxiliary Boilers Occurs?4. Understanding Boiler Feed Water Contamination5. MAN B&W’s Dual Fuel Marine Engine : A General Overview6. Boiler Mountings: A Comprehensive List7. Important Points for Boiler Cleaning on a Ship8. Boiler Operation Made Easy : Procedure for Starting and Stopping a Boiler9. Blow-Down Procedure for Marine Boilers10. The Science behind Marine Boiler Water Circulation on Ships11. Boiler Starting Failure – Troubleshooting12. Procedure for Boiler Gauge Glass Maintenance on a Ship13. Everything You Ever Wanted to Know About Scavenge Fires14. How to Prevent Crankcase Explosion on a Ship?15. What is Turbocharger Surging?16. Everything You Ever Wanted To Know About Crankcase Inspection on a

Ship17. What is Steam Hammering in Ship’s Steam System?

REFRIGERATION1. What are the Safety Devices on the Refrigeration System of a Ship?2. Construction and Working of Ships Refrigeration plant3. Guidelines on Quality of Refrigerant Used on Ships4. Understanding Capacity Control in Ship’s Air Conditioning and

Refrigeration System5. How to Charge Refrigeration Plant on Ships?6. Everything You Ever Wanted to Know About Container Refrigeration Unit

ELECTRICAL1. How is Power Generated and Supplied on a Ship?2. Preferential Trips on Ship : Construction and Working3. Single Phasing in Electrical Motors: Causes, Effects, and Protection

Methods4. Construction and Operation of Megger Explained5. Permanent Magnet Moving Coil Instrument (PMMC) – Working and

Application on Ship6. What are the Main Safety Devices for Main Switch Board on Ship?7. Electrical Safety Device: Air Circuit Breaker (ACB)8. Understanding Rectifier and Rectifier Circuits on Ship

9. Amplifier Circuit or Operational Amplifier (op amp) Used on Ship10. Construction and Working of 3 Phase Induction Motor on Ship11. Maintenance of Electrical Relay on Ships Electrical Circuit12. How to Find an Earth Fault On board Ships?13. Why are Transformer and Alternator Ratings in kVA on Ships?14. Reasons for Using High Voltage Systems On board Ships15. How to Install Electronic Circuits on Ship?16. Electric Propulsion System for Ship: Does it have a Future in the Shipping?17. Electrical Propulsion System in Ships18. What is Alternate Marine Power (AMP) or Cold Ironing?19. Important Points to Consider While Carrying out Alternator Maintenance

of Ship’s Generator20. How to Minimize the Risks of an Electrical Shock on a Ship?21. Hazards Related to Electric Cable Insulation in Case of Fire22. Importance of Insulation Resistance in Marine Electrical Systems23. Thermocouples: The Most Common Pyrometer on Ship24. What is Lambda Control in Ships?25. Electric Propulsion System for Ship: Does it have a Future in the Shipping?26. Electrical Propulsion System in Ships

Energy Audit on Ships: Audit of Marine BoilerIn continuation with the last article on energy audit on ships, we discuss the energy audit of the ship’s boiler. One of the major and important machinery on the ship, a marine boiler comes under special emphasis in an energy audit due to many well marked and potential energy saving areas.

A well maintained boiler is not only safe but is also fuel efficient.

Basic Steps of Boiler Audit

As discussed earlier, the steps involved in an energy audit are data collection, data analysis and making report.

Data Collection: Finding how the ship uses steam, costs of fuel consumed per day and issues by reducing steam consumption for utilities. For example reduction of domestic hot water temperature or reduction of accommodation heating etc.

Data Analysis: Identifying measures that would lead to energy conservation. These include measures with no investment, with medium investment and with large investment.

Audit Report: The report has to be presented to the owners with the economic viability to enable making decision.

Instruments Required for Boiler Audit

In any energy audit the use of proper calibrated instruments is essential. The instruments that are required to carry out an in depth boiler energy audits are as follows:

Portable Oscilloscope: It’s an all in one tool. It is used for visual display and interpretation of data, trend analysis, data logger, spectrum analyzer and measuring capacitance, resistance, continuity, AC and DC voltage, power measurement for single phase and three phase, total power, apparent power, reactive power, power factor, frequency and current etc.

Infrared Remote Thermometer: It is used for temperature measurement and for finding hot spots.

Tachometer: For speed measurement of motors and shafts as slippage of belts and lowering of speeds can cause improper air fuel ratio.

Master Pressure and Temperature Calibrator: For calibrating the online instruments and sensors in the boiler control panel.

Infrared Camera: This camera can take infrared photographs thus indicating trouble areas and hot spots.

Flue Gas Analyzer: For analyzing flue gas and measuring concentration of O2, CO2, CO, NOx, and SOx etc.

Ultra Sonic Leak Detector: It is used for checking steam traps that are leaking and pin-hole leakages of steam.

Other Instruments: The other instruments that are used are digital manometers, calibrated pressure gauges, Multi meter, Clamp ammeter, Contact thermometer, Non contact water flow meter, power analyzer etc.

Pre-audit Precautions

Before carrying out energy audit on the boiler some precautions must be taken to ensure accuracy and reliability of measurement.

The boiler load should be kept constant during the audit. No soot blowing should be done during the audit. No blow down should be done during the audit.

Energy Conservation and Optimization opportunities

Depending on the layout of the ship, make of the boiler, the quality of maintenance and the condition of the boiler there may be some ship specific problems and

recommendations; but in addition to these there are some common areas where generally loss of heat occurs and there is scope of energy conservation

Excess air in combustion: Specified quantity of air is required as per stoichiometric air fuel ratio for combustion. However as metering in inadequate some extra air is always supplied to avoid incomplete combustion. Excess air lowers efficiency because it does not take part in the combustion and takes away the heat of the furnace.

Less air in combustion: If the air is less than the recommended stoichiometric air fuel ratio, incomplete combustion will result. Carbon will not fully burn to carbon-di-oxide but will partially burn to form carbon monoxide. This will cause loss of energy.

Maximum Waste Heat Recovery: The funnel stack temperature must be as low as possible but with sufficient margin to be above the dew point to avoid sulphur corrosion. Generally a funnel temperature of 165 to 195 deg C when using Fuel Oil is considered optimum. In any case when the funnel (Exhaust Stack) temperature is higher than 200 deg C, a more stringent waste heat recovery program should be required.

Feed Water Preheating: If the funnel temperature is higher than 200 deg C it can be utilized for feed water preheating, thus increasing the waste heat recovery. It will increase the overall efficiency of the plant

Combustion Air Preheating: In case there is still a margin in funnel temperature combustion air preheating may be considered.

Blow- Down Optimization: The blow down of the boiler is required for controlling the amount of TDS in the boiler. Blow down must be calculated and

done after measuring the TDS amount. Some engineers merrily blow down the boiler excessively without need even when the parameters are in control and it results in loss of precious water and heat. Blow down must be done in response to the conductivity and the pH.

 

In the next article we will look into the areas of energy conservation and optimization opportunities and audit report.

Energy Conservation in Boilers and Making an Audit ReportIn the last article in this series on the energy audit of the ships boiler, we discussed the instruments required for ship’s audit, pre audit precautions and the energy conservation and optimization opportunities. In this article we discuss the other opportunities for energy conservation and also layout of the final audit report.

Read the first two parts of the series here:

1. Energy Audit on Ships

2. Audit of Marine Boilers

Energy Conservation and Optimization Opportunities

The other areas where energy conservation and optimization opportunities exist are as follows:

 

Performance of Heat Transfer Areas: The heat transfer areas of the boiler must be monitored. The soot blowing of the boiler must be done religiously as build up of soot acts like an insulator and reduces the heat transfer rate. That means for generating the

same amount of steam more fuel will be needed. The same goes for the buildup of scale in the tubes. The stack temperature must be monitored regularly and any increase in it means that heat recovery is not optimum. If the funnel temperature increases about 40 deg C after last cleaning it indicates that boiler cleaning must be done.

Read important points on boiler cleaning here.

Heat Loss Due to Inadequate Insulation: The boiler and steam lines along with condensate return to the hot well must be well insulated. Over a period of time insulation is damaged or worn out. Any analysis by an infra red camera or infra red thermometer can identify the hot spots and optimize fuel consumption.

 Optimum Hot Well temperature: The hot well temperature must be maintained at temperature specified by manufacturers which is generally about 80 to 85 deg C. A lower temperature will cause colder feed water to enter the boiler thus increasing the fuel cost due to loss of sensible heat. An overheated hot well will cause vapor lock in the feed pump and loss of suction.

Learn how to troubleshoot marine boiler starting failure here.

Steam Trap Losses: Steam traps are used to discharge condensate once it is formed, to prevent live steam from escaping and to remove air and non condensable gases from the line. However it is a largely neglected part of the steam piping. Steam traps that are stuck open allow live steam to escape thus resulting in loss of heat and also increasing the load of the condenser. Steam trap that is stuck shut results in reduced capacity of the equipment it is being supplied to.

 Radiation and Convection Losses: The boiler body loses lots of heat from the exposed surfaces to the surroundings. In cold climate the loss is greater. Effective insulation can reduce these losses.

 Optimize Boiler Steam pressure: Running a boiler at lower pressure after optimizing steam usage will lower the fuel consumption.

Installation of variable speed drives: The air dampers use throttling to obtain capacity control. These old methods of capacity control lack accuracy and have poor control characteristics at the top and bottom of the operating range. In case the steam demand of the boiler is variable and changes from time to time, then replacing the damper type air register with the new electronically controlled variable speed drive forced draught fan should be considered.

Understand marine boiler water circulation here.Reducing Steam Leakage: Though this is a simply understood principle that steam leakage leads to energy and fuel loss, it is common to see many leakages of steam unattended due to either fear or apathy. Just by controlling the leakages many of the boiler operational problems can be avoided.

Audit Report on Energy Saving Measures

The audit report of the boiler must indicate the energy opportunities that can be availed, the investment required, the fuel saving and returns. The owner must be provided with the economic viability and feasibility of the project. The energy measures recommended are of three types.

Immediate Returns: Those energy saving measures that give immediate returns and require no investment. For example overhauling the burner, calibrating the air register, cleaning the tubes of soot, repairing steam traps etc.

Medium Term return:  Those energy saving measures that require moderate investment and give returns in a medium time frame.  For example these can be equipment modification like change of burner and air register, change of insulation, retrofitting the furnace with a new burner etc.

Long term return: These require considerable investment and will benefit in long term only. For example if the boiler is old and unusable, under or over sized. Replacing an old boiler with an energy efficient new boiler may be a good strategy. It is only recommended if the company has plans for keeping the ship for a long time.

Financial analysis of the energy saving measures is the most important part of a boiler energy audit. Annual cost savings from the upgrades, retrofits and replacements must be provided to enable the owner make correct decision.References:

Boiler Operations  By M P Murgai and Ram Chandra

Training Manual for Energy Efficiency By Asian Productivity Organization, 2010

Presentation on Energy Audit in Thermal Power Stations by H.S.Bedi

Hand Book on Energy Audit and Environment Management by Y.P.Abbi and Shashank Jain

Working manual on Energy Auditing in Industries By Asian Productivity Organization

What to do When Flame Failure or Fuel Pump Tripping in Marine Auxiliary Boilers Occurs?Auxiliary Boiler is only used in port and the exhaust Boiler caters for all heating and steam needs while at sea. Generally if the burner routines are carried out religiously and the filters are cleaned, there is no major maintenance or routine that needs to be done

In this article the author is relating a problem faced on one ship and the troubleshooting done.

Scenario:

One day the boiler shut down after flame failure alarm came.  After many futile attempts to restart the boiler on HFO, the boiler was changed over to diesel and manually fired. The auto firing mode was non operational and the FO pressure low alarm was coming and fuel pumps stopping.

 

The following checks were done that helped to restart the boiler:

Correct pressure setting of the boiler: Generally the Fuel Oil pressure at the burner must be between 2 to 4 bars. In case the pressure is too high more fuel will be sent and the air fuel ratio disturbed. Less fuel pressure will give a lean mixture and flame will be unsteady and fail.

The fuel pump might trip on overload. Check the pump for mechanical damage and jamming. It should be free to turn by hand.

The over current relay may be at fault. Check the OCR setting and try increasing it if not correct. There is generally a test lever at back of OCR for testing.

The fine filter also called as dirt trap on the burner may be dirty.

The pressure transmitter may be giving wrong pressure feedback, check the wires.

The pressure transmitter for DO is normally different from FO line, Check this pressure transmitter.

The PLC will give command to stop due to pressure transmitter fault. Try calibrating the transmitter with the Master calibrator and check output. Output should be between 4 to 20 mA.

The fuel oil line may be choked and blocked. This can be ascertained by high back pressure.

The fuel oil temperature should be around 90 deg C. Check heater for correct functioning. High temperature can cause vapor lock that can lead to ignition failure.

The PLC (Programmable Logic Controller) has a reset buttons and resetting it restores the default values, often solving the problem.

Check any error code flashing on the display of the PLC or logic module and consult the manufacturer.

                 

If a fuel oil (FO) low pressure alarm is generated it may be due to restriction in the line going to the pressure transmitter. There are also valves for isolation, they must be open.

Local FO pressure gauge may be replaced with a new / calibrated one to get correct picture.

If the boiler is firing on diesel oil (DO) then the burner should be generally ok, however if filters are partially dirty or the nozzle is partially choked, it may lead to this problem. Overhauling the burners may give correct picture. If the nozzle is choked it will create a back pressure.

There are two fuel oil (FO) pumps, try starting the second pump.

Check supply and return lines for correct functioning of valves.

Check the megger reading of the pump motor.

Check the suction line change over and return line change over valves.

In case the system includes separate pressure control valves for HFO and MDO, change over the three way valve from MDO position to HFO position or close the stop valve before the MDO pressure control valve.

Near the FO change over valves and near the burner assembly, there are pressure regulating valves on MDO and HFO line, try to adjust the pressure within 3 to 4 bars for HFO. Moreover there may be another pressure regulating valve near the pressure gauge of burner assembly. Use this for fine adjustment.

If the fuel pumps are tripping in manual firing then there is pump problem or back pressure.

In manual mode PLC should not be involved and as still pump is tripping there is some other fault.

Check the input voltage to the pump and also the current by clamp meter.

If both the pumps are tripping then it indicates Pressure switch or back pressure problem.

The information was related to Saacke boiler on board but may slightly differ with the make of the boiler and the piping system and automation on board.

Understanding Boiler Feed Water ContaminationThe quality of boiler water plays an important role in deciding the overall marine boiler efficiency. Contamination of boiler water leads to several types of problems, including the main ones – corrosion and scale formation. To eradicate the problem from the roots, it is important to understand the boiler water chemistry and how contaminants enter boiler feed water.

Inside the boiler system, the boiler feed water passes through a series of pipelines, tanks, and equipment. The feed water is always chemically treated to reduce the effects of harmful minerals and gases. However, the boiler feed water is not the only one responsible for problems related to boiler water contamination and boiler efficiency. The boiler feed water is always clean and chemically treated, and is mainly affected by the corrosion of the boiler system, which is mostly harmless.

The main problem starts when a lot of this boiler feed water is lost through leakages and processes such as boiler blow down, soot blowing etc., and make-up water is needed to be introduced to compensate this loss. It is this make-up water that brings in a majority of the impurities into the boiler system.

How the make-up feed water is more contaminated?

The new feed water is taken into the boiler system by two ways

1. From fresh water tanks whose water is meant for drinking purpose2. From sea water distillation plan or fresh water generator

Boiler feed water is mainly taken from the fresh water generator. The sea water contains a large amount of salts and other dissolved minerals and gasses. Moreover, the fresh water generated in the fresh water generator would often carry small droplets of salt water from the vapours. Salt droplets are also a result of salt water leaks in the distillate condenser. The feed water thus contains several dissolved minerals and salts.

Also, the dissolved gases in the seawater which are either absorbed from the air or are a result of decayed plant and animal bodies are also carried over with the vapour to the distilled water. Many of these gases and impurities are harmful, and which eventually lead to boiler problems.

 

Problems Due to Contaminated Boiler Feed Water

The problems arising due to contaminated boiler feed water can be classified into two main types:

1.  Corrosion

2. Scale formation

Technically, both the above mentioned problems are interlinked. Both of them results in loss in boiler efficiency and can cause boiler tube failures and inability to produce steam.

Corrosion

One of the most common reasons for boiler corrosion remains the action of dissolved oxygen in the make-up and feed water. Corrosion leads to failure of machinery from inside also reduces over all boiler efficiency.

Scale Formation

Scale formation or deposits in the boilers results from hardness contamination of feed water.

The primary minerals in the water that make the feed water “hard” are Calcium (Ca++) and Magnesium (Mg++).

These minerals form a scale over the surface of piping, water heaters, and on everything it comes in contact with. Hardness contamination of the feed water may also result from either deficient softener systems or raw water in leakage of the condensate.

This kind of scale/ deposits act as insulators and lower the heat transfer rate.

The insulating effect of deposits also causes the boiler metal temperature to rise and lead to tube-failure by overheating.

Large amounts of such deposits throughout the boiler would reduce the heat transfer enough to drop the overall boiler efficiency.

MAN B&W’s Dual Fuel Marine Engine : A General OverviewToday the maritime industry is on the verge of a major change, from conventional methods of propulsion to modern and more economical and environment friendly methods.

In order to reduce fuel consumption in ships such as gas carriers, MAN B&W’s duel fuel or bi fuel ME- GI engines works both on conventional marine fuels and also on gas fuels.

Gas carrier cargo tanks are specially built, designed, and insulated to carry the liquefied cargo at a temperature as low as -161 °C. However, 0.1 to 0.17% of the total cargo boil off per day which is a natural phenomenon. This means if a ship is carrying total cargo of 20000 m3 in a voyage of 10 days, then the cargo that will boil off will be approximately 300000 liters.

This waste gas is used in the main propulsion engines of the ship, which reduces the overall fuel consumption of the ship, saving huge amount of money.

Construction of MAN B&W’s duel fuel ME- GI engines

ME-GI engines are designed to burn very low temperature gas cargo. As they handle gas as fuel, following safety features and equipments are used;

Conventional or Pilot Fuel Injection System:

The conventional fuel injection system is similar to that found in other MAN – 2 stroke engine.

Two fuel valves are provided on top of cylinder head, supplied via high pressure pipes from fuel pumps.

Gas Injection System:

Two gas injection valves are provided on top of the cylinder head along with two fuel injection valves.

The gas supplied is through double walled, jacketed pipe made of suitable material like stainless steel to withstand the low temperature if there is a gas leak.

Electronic Gas Injection Control (ELGI):

ELGI controls the gas injection in the cylinder by controlling the opening and closing of the gas injector valve.

Fuel Injection Valve Actuator (FIVA):

The FIVA valve controls the fuel oil quantity when the engine is used on both the fuels.

 

Different Modes of operation

The Duel fuel engines are always started in conventional diesel fuel oil. The ME GI engine can be operated in three basic modes-

1)      Only gas mode- Constant gas injection when enough and constant gas supply is available, with fuel oil quantity for injection depends upon engine load.

2)      Fuel and Gas mode-Both oil and gas fuel is used in the cylinder liner with oil fuel about 6 to 8 % depending upon the load of the engine.

3)      Only fuel mode- When maneuvering or when no gas fuel is available, the engine is run on conventional fuel system.

Safety Incorporated in the System:

The space in the double jacketed gas injection is filled with air with an extraction providing 30 air changes per hour, which maintains inside pressure less than the engine room pressure to avoid leakage.

Hydro carbon sensor is fitted in the jacketed space for leak sensing.

The gas pipes are pressure tested at 1.5 times the working pressure.

The outer shield of the double layer pipe is made of stainless steel material to withstand low temperature.

Sealing oil is supplied in injector with pressure 20-25 bar above gas pressure to avoid leakage.

An accumulator at valve block is provided in the gas line for shutting down the system at low pressure. If the injector is stuck in open position, the pressure within the accumulator will fall and the pressure sensor will shut down the gas system.

An inert gas purging line connects to the gas injection line when the system is not in use.

If there is a non combustion inside the cylinder due to fuel not injected or not burning, the gas system shut downs and inert gas fills the line.

 

Advantages of Duel Fuel Engine

The boil off cargo can be utilized as a fuel for propulsion of ship, thus saving money and energy.

No need of costly re-liquefaction plant.

Fuel consumption of the ship reduces.

It produces less air pollution.

Boiler Mountings: A Comprehensive ListJust installing a boiler on a ship doesn’t guarantee efficient working of a boiler. There are several mountings and attachments required to be fitted on the boiler to ensure its safety and quality performance. The article describes a comprehensive list of boiler mountings without which a boiler cannot operate on a ship.

 

Boiler operation can be carried out safely and efficiently by only using the mountings described below:

1)     Main steam Stop Valve: The steam generated in the boiler is supplied to the main system through this v/v. It is normally non-return type of valve.

2)     Auxiliary steam Stop Valve: If there is separate steam line provided for small auxiliary system, it is supplied through this valve. The valve is smaller in size and usually of a non-return type.

3)     Safety valve: In the event of unsafe excessive pressure inside the boiler, the safety valve comes in action to release the overpressure. The lifting pressure of the valve is set prior to its installation and locked in the presence of a surveyor so that it not changed later on. Safety valves are generally installed in pairs.

4)     Water level gauge glass: Gauge glasses are also fitted in pairs for manually checking the water level inside the boiler drum. It is on the basis of the boiler pressure that the construction of the gauge glass is decided.

5)     Air release valve or boiler vent: This valve is fitted in the headers, boiler drum etc, to avoid imploding of boiler when it is depressurized or when initially raising the steam pressure.

6)     Feed check and control v/v: This valve controls the supply of steam supply as per the demand and is fitted in both main and aux steam line after the stop valve. They are non-return valves with a visible indication of open and close position.

7)     Pressure gauge connection: This pressure gauge can be fitted in super heater, boiler drum and wherever it is necessary to read the pressure reading.

8)     Blow down valve: It is used to empty the boiler completely for maintenance purpose or for water treatment of boiler when the chloride level becomes very high.

9)     Scum blow down valve: It’s a shallow dish type arrangement fitted at the normal water level which allows the blow down of floating impurities, oil foaming etc from the water surface.

10)  Sampling connection: Generally, a sampling water cock arrangement is also fitted with cooler in series so that water sample can be collected at any time for feed water analysis.

11)  Whistle valve: If there is a provision for steam whistle in the ship, then steam is supplied directly from the boiler through a small bore type non-return valve known as whistle valve.

12)  Low Level alarm: A device used to initiate audible warning at low water level condition.

13)  Soot blowers: Required to blow the soot and the combustion products from the tube surfaces. It is operated by steam or compressed air.

14)  Automatic feed water regulator: Device which is essential to ensure appropriate water level in all load conditions and is fitted in the feed line. Multiple element feed water control system is used in boilers with high evaporation rate.

Important Points for Boiler Cleaning on a ShipBoiler cleaning is one of the most important processes that are to be performed routinely on marine boilers on a ship. Boiler cleaning is done to prevent and remove carbon and particle deposits from the boiler.

However, there are certain important points that are to be kept in mind while doing boiler cleaning. In this article we learn about these important points.

Boiler Cleaning: Important Points

If the boiler water is treated properly with chemicals and the concentration of chemicals is within the acceptable range then the deposits on the walls of water and steam side of the boiler will be minimal.

If boiler is operating on fresh water rather than heavy water the deposits inside the tubes will also be minimal and can be removed by boiling out. The hard

deposits inside the tubes are removed with the help of scrubber and brush from the upper drum.

If the boiler oil burner is functioning properly and proper maintenance is being carried out from time to time then the soot deposits inside the oil fired boiler will be minimal. But the soot deposits cannot be completely avoided as during starting of boiler soot formation is more and over a period of time it collects inside the boiler space.

The soot deposits can be removed with the help of water washing with 10 percent soda solution through the inlet door in the uptake with the help of water hose.

Necessary precautions are to be taken during water washing. It is to be noted that the refractory present inside the boiler does not get wet.

During water washing the refractory should be covered with the plastic sheet and water should be drained off continuously through the drain provided at the bottom.

In case the refractory gets wet, the lighting of boiler should be done very slowly, otherwise the refractory will crack and drop down and finally cause overheating and deformation inside.

The above mentioned points are the basic things to be kept in mind while doing boiler irrespective of the type boiler or ship.

Boiler Operation Made Easy : Procedure for Starting and Stopping a BoilerA boiler is one of those machineries that gets the ship going. A boiler is something, which though not required continuously in operating a ship, cannot be done away with. Moreover, it’s a dangerous equipment which generates steam at extremely high pressure, and it is for this reason that proper care should be taken while operating it.

In this article we have brought to you a step-by-step procedure for starting and stopping a boiler on a ship. With this procedure you can never go wrong, as far as boilers are concerned. Starting and stopping a boiler was never so easy.

 

Starting a Boiler

It is to note that the following steps may not apply to all types of boilers and each boiler requires some additional steps to be followed as per its system design. However, the basic steps remain the same:

1. Ÿ  Ensure that the vent valve on the boiler is open and check there is no pressure in the boiler.

2. Ÿ  Check that the steam stop valve is closed.3. Ÿ  Check that all the valves for fuel are open, and let the fuel circulate through

the system until it comes to the temperature required by the manufacturer recommendation.

4. Ÿ  Check and open the feed water valves to the boiler and fill the water inside the boiler drum to just above the low water level. This is done because it is not possible to start the boiler below the low water level due to safety feature which prevent boiler from starting. Also, the level is not filled much because if filled too much, the water inside the boiler might expand and over pressurize the boiler.

5. Ÿ  Start the boiler in automatic mode. The burner fan will start the purging cycle which will remove any gases present in the furnace by forcing it out through the funnel.

6. Ÿ  After the pre-set purge time the pilot burner will ignite. The pilot burner consists of two electrodes, through which a large current is passed, via the transformer, producing the spark between the electrodes. The pilot burner is supplied with diesel oil and when the oil passes over, the former ignites.

7. Ÿ  The main burner which is supplied by heavy oil catches fire with the help of pilot burner.

8. Ÿ  Check the combustion chamber from the sight glass to ensure the burner has lit and the flame is satisfactory.

9. Ÿ  Keep a close eye on the water level as the pressure increases and open the feed water when the level of water inside the gauge glass is stable.

10. Ÿ  Close the vent valve after the steam starts coming outside.11. Ÿ  Open the steam stop valve.12. Ÿ  Once the working steam pressure is reached, blow down the gauge glass and

float chambers to check for the alarms.

 

Stopping a boiler

1. Ÿ  If the boiler is needed to be stopped for longer duration for maintenance or opened up for survey, change the fuel to distillate fuel.

2. Ÿ  If separate heating arrangement for heavy oil is present then there’s is no need to change over to distillate fuel and the oil is kept on circulation mode.

3. Ÿ  Stop the boiler automatic cycle.4. Ÿ  Close the steam stop valves.5. Ÿ  Close the boiler feed water valves.6. Ÿ  When the boiler pressure is just reduced to over atmospheric pressure the

vent valve is kept open to prevent vacuum formation inside the boiler.

Blow-Down Procedure for Marine BoilersBoiler is one of the most important machinery on the ship. An economic and efficient working of a marine boiler on a ship requires timely maintenance and special care in starting and stopping the boiler. Routine cleanup is extremely helpful in increasing the working life of a marine boiler. In this article we have brought to you one such important procedure – boiler blow down, which has to be performed at regular interval of times in order to increase the performance of the boiler.

 Boiler blow down

Boiler blow down is done to remove carbon deposits and other impurities from the boiler. Blow down of the boiler is done to remove two types of impurities – scum and bottom deposits. This means that blow down is done either for scum or for bottom blow down. Moreover, the reasons for boiler blow down are:

1.       To remove the precipitates formed as a result of chemical addition to the boiler water.

2.       To remove solid particles, dirt, foam or oil molecules from the boiler water. This is mainly done by scum valve and the procedure is known as “scumming.”

3.       To reduce the density of water by reducing the water level.

4.       To remove excess water in case of emergency.

Procedure for Scumming and Bottom Blow Down

Below is the procedure for boiler blow down using the blow down valve located at the bottom of the boiler. In order to do scumming, instead of bottom blow down, the scum valve is to be opened.

Steps for blow down procedure are as follows:

Kindly refer the diagram to understand the blow down procedure properly.

1.       Open the overboard or ship side valve(1) first.

2.       Open the blow down valve (2), this valve is a non-return valve.

3.       The blow down valve adjacent to the boiler (2) should be opened fully so as to prevent cutting of the valve seat.

4.       The rate of blow down is controlled by the valve (3).

5.       After blow down close the valve in reverse order.

6.       A hot drain pipe even when all valves are closed indicates a leaking blow down valve.

The Science behind Marine Boiler Water Circulation on ShipsThe most important aspect of any marine boiler is maintaining the correct water level. As the boiler fires, steam liberates from the surface of the water and thus as the steam gets consumed, there is subsequent drop in water level inside the boiler.

Steam gets produced only when there is an effective circulation of water within the boiler. For tank type boilers, circulation is not distinct and the water circulates within the tank of the boiler itself. For water tube boilers, circulation is necessary within each and every tube and headers.

This happens naturally if both the steam and water drums are connected with tubes. But there is some basic design reason which has to be emphasized on.

 

Natural Circulation within a Water Tube Boiler:

The steam drum and water drum may or may not be separated depending upon the boiler design. To understand the water circulation principle, we will assume the following components to be separate. A steam drum at the top is connected to the water drum at the bottom through down comers outside the boiler shell and risers inside the boiler shell.

Cold water is fed to the top drum/steam drum, by water feed pump through a screw down non-return valve and a check valve. As we all know, hot water stays on top and relatively cold water (being denser) travels to the bottom of the drum.

The steam/water drum has down comers connecting to the water ring at the bottom of the boiler. The down comers are located outside the boiler shell and are large in diameter when compared to the water tubes.

As the cold water from the down comers reach the water ring in the bottom, the circulation starts within the tubes and drums. As the water particles enter the water tubes, which are inside the boiler furnace, they start to heat up and become wet steam with some bubbles. As they are less dense, they immediately rise up to the steam drum and thus are continuously being replaced by relatively cold water from down comers. Thus circulation happens naturally inside a water tube boiler.

Design Aspect

If the circulation has to happen in a natural way, then there are some design considerations to be observed. Ratio between the amount of steam leaving the risers & the amount of water entering the down comers is of the order 4:1.

It is important to have more water than steam on the risers. If the riser at some point becomes completely full of steam, the tube would over heat and “BURN OUT”.

“BURN OUT” is where the tube metal over heats can no longer resist the pressure forces within the tube and thus ruptures.

 

Reasons for having External Down comers:

It is known that as the pressure and temperature increases, the density of water decreases. Thus the density difference between water and the steam reduces & thus at higher pressures, the natural circulation of water-steam is impaired.

Thus to maintain the natural circulation, external, unheated down comers are fitted. These external down comers are large bore tubes connecting the steam drum with the water drum.

Boiler Starting Failure – TroubleshootingFailure in boiler starting is a common phenomenon on ship. There can be several reasons for the failure in staring of a boiler. In this article we will learn about the most common reasons for not starting of boiler.

1)     Fuel inlet valve to the burner is in close position:

The fuel line for boiler’s burner consists of several valves located at fuel tank, pumps suction, discharge valve, or valve before the boiler burner. Any of these can be in closed position resulting in starvation of fuel.

2) Line filter at the inlet of the fuel line for burner is choked:

If the system runs in heavy oil then there are chances of filters in the line getting choke. To avoid this, boiler system are normally built for changeover from diesel to heavy oil during starting and heavy to diesel during stopping. This keeps the filter and the fuel line clean.

3)     Boiler fuel supply pump is not running:

There are two main reasons for fuel pump not running. Normally when the pumps are in pairs, the change over auto system is kept in manual position, and if the operating pump trips, the stand by pump will not start automatically. Another reason is tripping of pump due to short circuit in the system etc.

4)     Solenoid valve in the fuel supply line is malfunctioning

Nowadays most of the system adopts advance automation, but their can be a possibility wherein the solenoid in the fuel supply line is malfunctioning and not opening.

5)     Flame eye is malfunctioning:

A Flame eye is a photocell operated flame sensor fitted directly on the refractory to detect weather the burner is firing or not. If the flame eye unit is malfunctioning, then it will give a trip signal even before the burner starts firing.

6)     Air or Steam ratio setting is not proper

For proper and efficient combustion, air fuel ration is very important, if the supply of air is excess then there will be excess of smoke, and if it exceeds more than normal level the combustion will burn off causing flame failure.

7)     Forced draft fan flaps malfunctioning

For removing excess gases trapped inside the combustion chamber forced draft fan (FDF) are used for pre purging and post purging operation and are connected with a timer to shut the fan flaps. If the flaps are malfunctioning then continuous forced air will go inside the chamber, preventing the burner to produce flame causing flame failure of the boiler.

8) Any contactor switch inside Control panel is malfunctioning

Boiler control panel consist of several contactors and PLC cards. Even one contactor malfunctioning may result in trouble for boiler starting.

9)     Trip not reset

If any previous trips like low water level, flame failure, emergency stop etc. has not been reset than boiler will not start.

10)  Main Burner atomiser is clogged

Main burners consist of atomizer for efficient burning of fuel. If the atomizer is clogged by sludge and fuel deposits then burner may not produce flame and trip the boiler..

11)   Pilot Burner nozzle is choked :

A Pilot burner nozzle is very small and can be blocked by carbon deposits and sludge resulting in flame failure. Some pilot burner consists of small filter which can be clogged after continuous operation resulting in flame failure because of carbon accumulation.

12)  Electrodes are not generating spark

Initial spark for generating a flame is produced by electrode which may be due to carbon deposits on them or fault in the circuit of electrodes etc.

Procedure for Boiler Gauge Glass Maintenance on a ShipA gauge gauge is used at many places on a ship. Gauge glass is a kind of a level indicator which shows the amount of fluid in a tank or any other storage place on a ship. In this article we will learn as to how the maintenance of a gauge glass is done on a ship. Gauge glass are mainly used in boiler of the ship.

Before learning about boiler gauge glass maintenance lets take a quick look at the working of a gauge glass.

Working of Boiler Gauge Glass

A gauge glass has two different compartments – top side and bottom side, connected to two different sections of a boiler. The top side of the gauge glass is connected to the steam side of the boiler and the bottom side is connected to the water side of the boiler. The pressure on both sides will equalize and the level of water can be seen in the gauge glass.

Maintenance During service check up.

Refer the diagram for better understanding of boiler gauge glass.

Check the nut (1) and tighten if necessary. Bolts on the boiler flanges are to be checked, if loose tighten them. Check if union nuts are loose. Bolt from screw 7 with cocks in open position. If the leak can not be stopped from water side on the gauge glass by tightening

the screw 7 then the sealing surface of the cock plug 8 my be damaged or corroded.

Gauge glass blow down procedure

Gauge glass should be blown before lighting up of boiler, after stopping the boiler and regularly if the level in gauge glass is suspected to be wrong.

Cleaning the water side of gauge glass

Close the valve S and W as shown in the figure. Now open the cock W and see if the water is coming out of the drain valve D

indicating the drain line is clear. Now close the drain valve D and keep the cock W open and see if the water

level rises in the gauge glass; this indicates the line to gauge glass is also clear. Repeat the steps two to three times to remove nuds and deposits inside.

Cleaning the steam side of gauge glass

Close both the cocks S and W. Now open the cock S and open the drain valve D and see the steam is coming

out. The drain is opened only for 1-2 seconds only as steam may damage the sealing and service life decreases.

Putting the gauge glass in normal operating position

Close all the valves S, W and the drain valve D. Now open the cock W and let the water fill inside the gauge glass. Now open the cock S and then the level can be seen as the pressure equalizes.

Everything You Ever Wanted to Know About Scavenge FiresOne of the most common reasons for a fire in a ship’s engine room, scavenge fire is the deadliest of all fires. Scavenge fire has been the reason for several major accidents on ships in the past and it is for this reason that it is termed as the most dangerous cause for accidents on a ship.

In order to understand scavenge fire it is important to learn the basics. In this article we have brought to you everything you ever wanted to know about scavenge fires – from causes to actions. Understand and fight scavenge fires the way it should be.

Getting the Basics Right: What is Scavenge fire?

For any fire to occur we need three elements which make the fire triangle. The three important elements for any type of fire are:-

1. Oxygen -this is available plenty in the scavenge space.

2. Heat source- this could happen because of blowing by of gases between piston rings and liner or as a result of any rubbing between two surfaces.

3. Fuel- this can be from un-burnt fuel, carbon  or cylinder lubricating oil leaked into the space

 

When all these elements are present in a proportion ratio and lie within the flammable limit  inside the scavenge space the later become a hot spot for eruption of fire. The fire which thus results is known as the scavenge fire.

 

Causes of scavenge fire

There are many reasons for scavenge fire. However, the main ones are as below:

1.       Excessive wear of the liner.

2.       The piston rings might be worn out or have loose ring grooves.

3.       Broken piston rings or rings seized in the grooves.

4.       Dirty scavenge space.

5.       Poor combustion due to leaking fuel valves or improper timing.

6.       Insufficient or excess cylinder lubrication.

 

Indications of scavenge fire

There are a few signs which indicates a scavenge fire. One should be extremely cautious in case any of the below mentioned conditions are observed.

1.       Scavenge temperature will start increasing.

2.       The turbochargers will start surging.

3.       High exhaust temperature.

4.       Loss of engine power and reduction in rpm. This happens because a back pressure is created under the piston space due to fire.

5.       Smoke coming out of the scavenge drains.

6.       The paint blisters will be formed on the scavenge doors due to high temperature but this will occur only in large fires and extreme cases.

 

Actions to be taken

Action taken in case of a scavenge fire depends on the type of the fire, whether small or large. In case of large fire the following signs will be easily visible – the peeling or blistering of paint, large reduction in engine rpm and surging of turbocharger.

 

For small fires

1.       Start reducing the engine rpm and reduce it to slow or dead slow.

2.       Increase the cylinder lubrication of the affected unit. Special attention to be given for this as this does not feed the fire. In case of increase of fire do not increase the lubrication.

3.       The fire can be due to leaky fuel valves, so lift up the pump of the affected unit.

4.       Keep scavenge drain closed.

5.       Keep monitoring the scavenge and exhaust temperatures and let the fire starve and wait for it to burn itself out.

6.       After confirming that the fire is out start increasing the rpm slowly.

7.       Keep monitoring the scavenge temperature for any signs of re-ignition.

 

For large fires

1. Stop the engine immediately and engage turning gear, and keep engine rotating with turning gear.

2. Extinguish the fire with fixed fighting system for scavenge fire. This may be co2 system or a steam connection for smothering the fire.

3.  In case fixed system is not available on very old ships an external cooling is provided to prevent distortion due to heat.

4.  Once after confirming that the fire is extinguished. The scavenge space is allowed to cool down and later opened for inspection and cleaning of the scavenge space.

How to Prevent Crankcase Explosion on a Ship?Crankcase explosion is one of the most dangerous reasons that can lead to massive accidents and fires on a ship. It is therefore imperative to prevent all the reasons that can lead to crankcase explosion on a ship. In this article we will learn about the various methods to prevent crankcase explosion on a ship.

The first and foremost thing to avoid any type of explosion on a ship, it is necessary to take the preventive steps right from the basic roots. In a main engine crankcase also there are safety features provided to detect the causes of explosion.

There are two main features provided on the crankcase to prevent crankcase explosion. They are as follows:

1. Oil Mist Detector

The Oil mist detector takes continuous samples from the main engine crankcase and check whether the sample concentrations of mist are well below the level at which a crankcase explosion can take place. The oil mist is drawn into the instrument with the help of small fan which takes suction from each crankcase through sampling tubes provided on each crankcase.

The oil mist detector consists of a small rotator with which it takes sample from one cylinder at a time and the rotator then turns to the next after approximately 4 seconds. The sample from the rotator goes to the measured cell and the reference cell takes sample from rest of the crankcase to evaluate the difference in oil mist.

An overall mist density of the crankcase is also measured by comparing the samples with the fresh air once every rotation of the sampling valve is done. A beam of light from a common lamp is reflected through mirrors and output is measured from a photo cell.

Under normal conditions the output from the reference and measured contact is same and hence no deflection is measured. However, a deflection in the output gives an alarm indication and the valve rotator stops at position to know which chamber has high mist concentration.

Some engines are even fitted with slowdown alarms so that when the oil mist alarm rings, the engine automatically slows down to prevent crankcase explosion.

2. Crankcase relief doors

 

The Crankcase relief doors are also fitted to prevent any damage to the crankcase and ingress of fresh air inside the crankcase.

The crankcase doors are spring loaded valves which lift up in case there is any rise of pressure inside the crankcase. Once the pressure is released they re-seat to prevent any ingress of fresh air. This helps especially in case of any ingress of air that can lead to a secondary explosion followed by a lot of surge and damage to the crankcase.

The opening pressure and sizes of the valves are specified by different classification societies, depending on the volume of the crankcase. The number of doors to be present also depends on the bore of the cylinder.

What is Turbocharger Surging?A turbocharger is one of the most important parts of the main propulsion system of the ship. Turbocharger surging is a phenomenon of turbocharger which affects its performance and reduces the efficiency. In this article, we will learn everything about turbocharger surging.

Turbo charger surging may be defined as a high pitch vibration of audible level coming from the blower end or compressor end of the turbocharger. Whenever the breakdown of gas flow takes place, a reversal of scavenge air takes place through diffuser and impeller blades into the blower side which causes surging.Surging is to be avoided as it interferes with the combustion in the main engine and may cause damage to the thrust bearings.

Therefore, the turbochargers are needed to be matched properly with the engine air consumption rate and pressure across the operating range of the engine and they should not fall in the surge limits.

What are the Causes of Turbocharger Surging?

The following are the causes of turbocharger surging:

Improper power distribution between the main engine cylinders may cause turbocharger surging as one unit is producing more power and other is producing less. Due to this the air consumption required by both the turbochargers differs, which leads to surging.

Fouled compressor on turbine side – In this case if the inlet filters are dirty then enough air can not be supplied for combustion, which leads to surging. Similarly if the turbine side is also dirty i. e nozzle, blades etc enough air can not be produced for combustion.

Highly fouled exhaust i.e. economizer, if fitted may cause back pressure in the turbocharger and thus finally lead to surging.

Bad weather – This is one more reason for surging. Due to bad weather the engine suddenly starts racing and sudden load change takes place. This happens because during bad weather or pitching the propeller moves in and out of the water, causing the change in load on the engine.

How to Prevent Turbocharger Surging?

The following are the ways to prevent turbocharger surging. However, it is to note that some points may vary with design and construction of the turbocharger.

Keep the turbocharger intake filter clean. Water-wash the turbine and the compressor side of the turbocharger. Proper maintenance and checks should be done on turbocharger periodically. Soot blow should be done from time to time in case of economizer or exhaust

boiler. Indicator cards to be taken to assess cylinder and power distribution of

individual units.

Everything You Ever Wanted To Know About Crankcase Inspection on a ShipThere are several important factors that need to be taken care of for efficient running of the main engine on the ship, and one of them is the crankcase of the ship’s engine. The crankcase is one such part of the main engine which contains the most sensitive components of the main engine. Before doing crankcase inspection, are you confused as to what safety rules that are need to be followed or ever wondered what you should check and what not? If yes, then you have come to the right place. In this article we will learn the most important points that need to be considered for efficient working of the crankcase of the main engine. Learn the important checks on crankcase and what all things need to be included in crankcase inspection on a ship.

 

Checks Required and Done On board on Crankcase Lubricating Oil

The crankcase lubricating oil needs to be maintained in good condition for efficient running of the main engine. If not maintained and checked periodically, the crankcase lubricating oil can damage the bearings and other parts of the engine which can incur heavy loss and wastage of time in maintenance. Moreover if the damage is more, the ship might need to go off charter which is not acceptable in shipping activities.

Weekly Checks on Crankcase

In weekly test of crankcase, lubricating oil water test should be done. This is to ascertain that there is no leakage in the crankcase and it’s in fine condition. If water content is below 2 % of the total volume then it is acceptable and can be reduced with the help of purification.

However, if it is above 2% then investigation needs to be made if there is any leakage of water inside the crankcase. In case of any leakage, the cracks are to be checks and fixed and the causes of water ingress is to be found. Once this is done the oil in the crankcase has to be replaced completely.

Other checks also done during weekly checks are to ascertain TBN and viscosity of the oil. The crankcase must be topped up or change of oil needs to be done as per manufacturer’s recommendation.

Once every three months the oil has to be sent for laboratory analysis i.e spectrography analysis to ascertain that the amount of wear and fine metal particles are within acceptable limit. In case if it is off limit, the laboratory analysis report will recommend procedure or precautions to be taken to tackle the situation.

Crankcase Inspection in large Slow Speed Engines

The crankcase inspection is done every month whenever the ship is in port and there is sufficient time for inspection. Thorough inspection is required during this to analyze the condition inside and damage to the bearings.

Before inspection following procedures has to be followed:-

Permission has to be taken before reaching port to make sure that the authority is not having any problem with this. This is called Immobilization permission of the main engine.

After the permission is received the checklist has to be filled. Safety issues have to be discussed with the people taking part in the inspection. When the engine is in “stopped” condition, the lubricating oil pump and cross-

head oil pump have to be stopped and the breaker taken out so that it doesn’t start on its own or by any other person by mistake.

Proper sign and placards to be displayed regarding men at work. Since engine crankcase is an enclosed space, an enclosed space checklist is also

to be filled. After stopping the engine and the pumps the crankcase doors have to be opened

and sufficient time is to be given to cool and ventilate the space as the temperature inside is very hot and deprived of air.

After the cooling and ventilating the space, the person entering the space should be with proper personnel protective equipments like boiler suit, safety harness, and anti slipping pads for shoes.

Make sure there are no tools, pen etc in your pockets which might drop inside and cause damage to bearing and machinery parts

Before entering, the person has to be detailed as what needs be checked inside. Special attention is also given if any other issue is specified by technical department or any major problem found on other ships.

 

Inside Crankcase Following Checks are to be Made

1.     Check the overall quality of oil whether it is clean or dirty with carbon particles.

2.     Check for any distinguished smell, if found, this could be because of bacterial contamination of oil. The smell is generally of rotten eggs.

3.    Check for any metal particles near the grating in the crankcase.

4.   Check the condition and damage to the gratings.

5.    Check the slip marks on the web; they should be in the same line. If slip is found then report is to be made to the company and classification society regarding this.

6.    Check for any bluish dark patches, this indicates that hot spots are caused by friction of insufficient lubrication.

7.    Check cross head for any damages.

8.    Check cross head guides for damages and marks.

9.       Check the bed plate for any welding cracks etc.

10.   Check any metal seen near the bearings coming out due to wiping.

11.   Check for piping and any loose connections between them.

12.   Check the locking wires and locking washers on bolts of stuffing box.

13.   Make any other checks specified by technical department.

14.   Before coming out make sure there is nothing left inside.

What is Steam Hammering in Ship’s Steam System?Steam system is an important auxiliary system used for different purposes onboard ship. While working on ship or in steam system, one must have heard an abnormal banging and rattling sound from the steam pipe. This is known as Steam hammering.

Let’s understand the cause and remedies of the same.

Steam Hammering in Steam System

In a steam piping, when steam flow is suddenly stopped or condensed, then it results in gaseous shock wave, which are thermal shock wave resulting in to steam hammering.

Causes

Normally, if the steam piping system is not properly drained then the steam travelling in the pipe will come in contact with cold water and implode causing shock wave, developing thermal stress.

Understanding “Implode”

The term “implode” is similar to “explode” in meaning but opposite in functionality. When due to sudden drop in pressure vacuum is created and if this negative pressure or vacuum is not released, then it causes shock wave leading to implosion.

Hammering can occur when there is sudden change in the load or sudden increase in the steam pressure by ship’s boiler.

If the piping system has sharp bends then this will cause condensation of steam and thus hammering.

If the steam is used for heating purpose in a heater and if there is a leak then this will cause fluid to come in contact with high pressure steam causing hammering.

 

Effects of Hammering

As discussed, steam hammering will produce thermal shock and hence thermal stress on the piping system. This are already under high temperature stress and additional stress can reduce the working life.

If there is hammering due to sudden rise in the steam pressure, it may lead to cracking of steam pipes.

Due to the implosion effect, there can be cavity formation and erosion of the piping leading to thinning of the pipes.

Remedies

Drain the steam system at initial stage so that all the condensed water is removed.

Avoid sudden increase of the steam pressure.

Piping system and pipe design to be such that they are smooth and with minimum number of bends.

Sharp bending of pipes to be avoided.

What are the Safety Devices on the Refrigeration System of a Ship?A reefer system is the back bone of ships carrying refrigerated cargo. A malfunction of any of the components of the system can lead to degradation and wastage of perishable and cold storage cargo including provision for a ship. It is therefore important to maintain and run the refrigeration plant properly to avoid any breakdowns.

In this article we will learn about the safety feature of the refrigeration plant. Before that, you must read the construction and working of the ship’s refrigeration plant.

To have an efficient and hassle free operation of a ship’s refrigeration plant and its components, a good maintenance schedule and safety systems are adopted.

A safety system includes alarm, cut offs, and trips which safeguards the machinery and its parts from getting damage.

The main safeties adopted for refrigeration plants are

Low Pressure or LP cut off: This is a compressor safety which cut off the compressor in the event of pressure drop in the suction line. The pressure of the suction line is continuously sensed by the control unit and when it goes below the set value, which means the room is properly cooled, the LP cut out will auto trip the compressor. When the pressure rises, indicating there is flow of refrigerant in the line due to increase in room temperature, the LP switch will start the compressor.

High pressure or HP cut out: As the name suggests, the high pressure cut out activates and trips the compressor when the discharge side pressure increases above the limit value. The HP cut out is not auto reset and has to be done manually. The reason behind it is to manually attend the fault which is leading to rise in pressure, else this situation can lead to overloading of compressor parts and may damage the same

Oil differential cut out: This safety is again for compressor as it is the only machinery in the circuit having rotational parts which requires continuous lubrication. In the event of low supply or no supply of lube oil to the bearing, the differential pressure will increase and activates a trip signal to safeguard the bearing and crankshaft.

Relief valves: Relief valves are fitted in discharge side of compressor and will lift and safeguard the compressor in the event of over pressure. One relief valve is also fitted in the condenser refrigerant line to avoid damage to the condenser if there is high pressure in the discharge line.

Solenoid valves: Master solenoid valve is fitted in the common or main line after the condenser discharge. It closes when compressor stops or trips to avoid over flow of refrigerant in to evaporator. All holds or rooms are fitted with individual solenoid valve which control the flow of refrigerant to that room.

Oil heater: Oil heater is provided for the compressor crank case oil and prevents compressor from getting excessively cold which may effect the lubrication of the parts.

Construction and Working of Ships Refrigeration plantThe refrigeration plants on merchant vessels play a vital part in carrying refrigerated cargo and provisions for the crew on board. In reefer ships, the temperature of the perishable or temperature sensitive cargo such as food, chemical, or liquefied gas, is controlled by the refrigeration plant of the ship. The same plant or a smaller unit can be used for maintaining the temperature of different provision rooms carrying food stuffs for crew members.

The main purpose of ship’s refrigeration plant is to avoid any damage to the cargo or perishable material so that the cargo in transported in good and healthy condition. Refrigeration prevents growth of micro-organisms, oxidation, fermentation and drying out of cargo etc.

Main Components of Refrigeration plants

Any refrigeration unit works with different components inline to each other in series. The main components are:

1. Compressor: Reciprocating single or two stage compressor is commonly used for compressing and supplying the refrigerant to the system.

2. Condenser: Shell and tube type condenser is used to cool down the refrigerant in the system.

3. Receiver: The cooled refrigerant is supplied to the receiver, which is also used to drain out the refrigerant from the system for maintenance purpose.

4. Drier: The drier connected in the system consists of silica gel to remove any moisture from the refrigerant

5. Solenoids: Different solenoid valves are used to control the flow of refrigerant into the hold or room. Master solenoid is provided in the main line and other solenoid is present in all individual cargo hold or rooms.

6. Expansion valve: An Expansion valve regulates the refrigerants to maintain the correct hold or room temperature.

7. Evaporator unit: The evaporator unit act as a heat exchanger to cool down the hold or room area by transferring heat to the refrigerant.

8. Control unit: The control unit consist of different safety and operating circuits for safe operation of the refer plant.

Working of Ship’s Refrigeration Plant

The compressor acting as a circulation pump for refrigerant has two safety cut-outs- Low pressure (LP) and High Pressure (HP) cut outs. When the pressure on the suction side drops below the set valve, the control unit stops the compressor and when the pressure on the discharge side shoots up, the compressor trips.

LP or low pressure cut out is controlled automatically i.e. when the suction pressure drops, the compressor stops and when the suction pressure rises again, the control system starts the compressor. HP or high pressure cut out is provided with manually re-set

The hot compressed liquid is passed to a receiver through a condenser to cool it down. The receiver can be used to collect the refrigerant when any major repair work has to be performed.

The master solenoid is fitted after the receiver, which is controlled by the control unit. In case of sudden stoppage of compressor, the master solenoid also closes, avoiding the flooding of evaporator with refrigerant liquid.

The room or hold solenoid and thermostatic valve regulate the flow of the refrigerant in to the room to maintain the temperature of the room. For this, the expansion valve is controlled by a diaphragm movement due to the pressure variation which is operated by the bulb sensor filled with expandable fluid fitted at the evaporator outlet.

The thermostatic expansion valve supplies the correct amount of refrigerants to evaporators where the refrigerants takes up the heat from the room and boils off into vapours resulting in temperature drop for that room.

This is how temperature is maintained in the refrigeration plant of the ship.

Guidelines on Quality of Refrigerant Used on Ships

A major quality concern with regard to refrigerants is their purity. The moisture content in the refrigerant is of great importance since too much moisture can cause serious operational problems. Water can enter a system through sub-quality refrigerants during top-up.

Excessive moisture in refrigeration systems may lead to the following conditions:

Freeze ups

Freeze ups occur when moisture picked up by the refrigerant starts to freeze, building ice crystals that block the refrigerant passage in narrow passageways, for example in the expansion valve. This effect is called intermittent cooling, as the compressor stops after a while due to the blockage in the expansion valve. It starts again when the ice crystals have melted and allow the refrigerant to pass through again. This is a periodical process of constant freezing and melting of the moisture inside the system, causing a high frequency of stop/start for the compressor.

Corrosion

Moisture can cause corrosion. However, moisture in combination with a HCFC refrigerant containing chlorine (like for example R-22 or R-409A) creates much more serious corrosion, as the chlorine hydrolyses with the water to form hydrochloric acid (HCl) which is aggressive to most metals. Heat adds significantly to the problem by accelerating the acid-forming process. For HFC refrigerants (like R-404A or R-407C), it is the polyolester oils that are very hygroscopic and may decompose at high temperatures forming hydrofluoric acid with the moisture which could be introduced to the system through a sub-standard refrigerant.

Sludge formation

Acid content inside a system can emulsify with the compressor oil to form an aggressive oil sludge that reduces lubrication properties. This can lead to serious compressor damage. Sludge can also cause a variety of other problems in a system, such as blockages of strainers, expansion valves and other tiny passages.

Quality

The problems listed above do not normally happen overnight, but build up over time if allowed to by incorrect refrigerant handling by the ship’s crew. A system breakdown is costly and time consuming, especially if it results in a loss of refrigerant charge. The system will be repaired and get back into operation, but the repair does not eliminate the cause of the problem. It is therefore vital that refrigerants comply with appropriate quality standards with regards to purity and composition.

As the prices for more environmentally friendly alternatives are higher than traditional refrigerants like R-22, R-401A or R-409A it is feared that there will be more cases in the future where local companies cut corners on quality and deliver partly full cylinders.

In order to assure trouble-free and safe operation of onboard refrigeration machinery, all Unicool refrigerants supplied by Wilhelmsen Ships Service throughout the world comply with the ARI 700-2006 standard that defines and benchmarks the purity and composition of these substances.

Understanding Capacity Control in Ship’s Air Conditioning and Refrigeration SystemShip’s air conditioning and refrigeration system helps in lowering room temperature and in keeping perishable food items and refrigerated cargo at desirable temperature.

As discussed in our article about basics of refrigeration plant – Construction and Working of Ships Refrigeration plant on ships, the reefer and air conditioning systems are installed to handle fluctuating loads i.e. they are responsible for maintaining low temperature of several rooms or cargo holds at the same time.

The efficiency of the refer plant depends on its ability to maintain different rooms or holds at different temperature.

 

What is Capacity Control?

Capacity control of a refrigeration plant can be defined as a system which controls the output of the plant as per the load in demand. As the load (temperature) of one room is achieved, there will be no more need of the refrigerant for cooling. Hence, the solenoid valve supplying refrigerant to that room will shut. This functionality is called capacity control.

The refrigeration compressor consists of different units working in parallel to cope up with the load. As the load decreases, the capacity control system cut off one or more units (depending upon the load) and maintains the efficiency of the plant by reducing stresses on different parts.

 

Components and Working of Capacity control system

1.      Compressor lube oil pump supply

2.      Capacity control valve

3.      Capacity control regulating valve

4.      Un-loader assembly

 

The compressor lube oil pump supplies oil to all the bearings and one connection is provided to the capacity control valve.

 

The capacity control valve is provided with high pressure oil from the compressor lube oil supply pump. This valve has several grooves bored in to its periphery and connected to the un-loader mechanism of different units.

A spring piston is provided which controls the spreading of high pressure oil supply in to the bore chamber. The spring piston is pressed by the oil supplied through an orifice which pushes the piston and aligns the un-loader holes, supplying high pressure oil to the un-loader unit.

 

The un-loader assembly comprises of a un-loader piston held by a spring. The un-loader piston is connected to a rotating cam ring having lifting pins attached to th suction valve. The lifting pins always act on the suction valve i.e. un-loading the unit at stop condition.

When the bores on control valve aligns with the un loader bores, oil will pass and press the un-loader piston rotating the cam and releasing the un loader pins from the suction valve.

 

The capacity control regulating valve is responsible to control the pressure (opening and closing of capacity control valve ports with un-loader ports). Its one end is connected to the crankcase and other end to capacity control valve.

As the pressure in the crankcase drops due to reduction in load, oil in capacity control valve is drained into the crank case leading to closing of un-loader ports, lifting of the suction valve, and cutting of the cylinder unit.

How to Charge Refrigeration Plant on Ships?The main use of refrigeration plants on ships is to keep cargo and food provisions at low temperature to prevent them from spoiling. The reefer plant is a combination of various machines such as compressor, valves, heat exchangers etc., which are connected to each other through pipes and joints. 

While in operation, the refrigerant used in the refer plant gets consumed or is reduced in quantity because of leakage in the system. Reduction in quantity of refrigerant may lead to troubles in the plant such as-

Short Cycling of Compressor

Too low suction pressure

Difficult to maintain temperature of rooms and holds

Reduction in the efficiency of the plant

When the above mentioned problems occur, it indicates that the plant has to be charged with the refrigerant.

There are two methods for charging reefer plants: Liquid charging and Gas charging.

Now a day’s gas charging is preferred over liquid charging because it is more safe and simple.

 

Gas Charging of Refrigeration Plant:

For gas charging, a special T piece valve block with mounted pressure gauge is provided to combine three connectors inter-connecting:

-Vacuum pump

-Charging Cylinder

-Charging Point

 

Following steps are to be taken for charging gas into the reefer plant:

1. Connect gas bottle or charging cylinder, vacuum pump and charging point in the reefer system to the valve block.

2. The discharge of the vacuum pump is to be connected in the empty recovery bottle

3. First open the valve between vacuum pump and charging bottle located in the valve block without opening the main valve of the charging cylinder. This will remove all the air inside the pipe. Once vacuum is reached, close the valve of charge cylinder in the valve block

4. Now open the valve of the charging point pipe in the valve block and run the vacuum pump until the vacuum is reached. This will remove the trapped air from this pipe. Then shut the valve in the valve block

5. Now keep the system idle for 5 minutes to check there is no pressure drop. This will ensure there are no leakages in the system

6. Now open charging bottle pipe valve and the charging point pipe valve located in the valve block. This will set the line for charging. Ensure that the vacuum pump valve is shut

7. Now open the main valves in the charging cylinder and charging point of the reefer system

8. Do not overfill the system. Make sure the receiver has 5 % space for expansion

Ensure that no refrigerant is leaked out in the environment as these effects the ozone layer in the atmosphere.

Everything You Ever Wanted to Know About Container Refrigeration UnitA reefer container is an enclosed unit used for transporting temperature sensitive cargo. The container requires external power supply for its operation. The article describes everything you ever wanted to know about container refrigeration units. 

When reefer containers are loaded in ships, the power supply is provided from the power generated from the D.G sets of the vessel. Some important points about container refrigeration are:

-  Container Refrigeration unit is fitted in front of the container and it serves as container front wall.

-   Some units are dual voltage, designed to operate on 190/230 or 380/460 volts A.C, 3 phase, 50-60 hertz power.

-   Operating control power is provided by single phase transformer which steps down the A.C supply power source to 24 volts, 1 phase control power.

 

Understanding the Basic Sections of Refer Unit

1.  Compressor Section

-   Consist of compressor (with H.P switch) and power cable storage compartment. Power transformer may be an option where the ship supply differs.

-   It also contain modulating and suction solenoid valve (for controlling the quantity of gas flow).

-   Safety fittings in the section are- moisture liquid indicator, pressure relief valve, filter drier etc.

-   Safety of the system is further enhanced by electronic monitoring with the help of following sensors- Compressor suction and discharge sensor, supply air temperature sensor, supply recorder sensor, ambient sensor.

2. Condenser Section

-   The condenser section contains condenser fan and its motor, an air cooled condenser coil and condenser saturation sensor.

-   For air cooled condenser air is normally pulled from bottom and discharged horizontally through centre of the unit.

-    Some units consists of water cooled condenser /receiver. This unit is expensive.

3.Evaporator Section

- This section contains temperature sensing bulb, return recorder bulb sensor and a thermostatic expansion valve (for flow of refrigerant and maintenance of inside temperature).

-  Assembly consist of evaporator coil and heater, drain pan and heater, defrost and heat transmission switches.

-  The evaporator fan circulates air throughout the container by pulling air in top of refrigeration unit and directing air through evaporator coil where it’s either heated or cooled and is then discharged out at the bottom of refrigeration unit into the container.

4. Fresh air Make up Vent

-  Purpose of this vent is to provide ventilation for commodities that requires fresh air circulation and must be closed when transporting frozen foods.

-   Air exchange depends upon static pressure differential which will vary depending upon how container is loaded.

Safety and Operating Precaution

An injury, no matter how small, should never go unattended. Always obtain first aid or medical attention immediately.

a)   Always wear safety gloves and glasses while working on any unit and also when charging refrigerant.

b)   Keep hand, tools, and clothing clear from evaporator and condenser fan.

c)   No work should be performed on any unit until all circuit breaker and start stop switches are turned off and power supply disconnected.

d)  Do not bypass any electrical safety device.

e)  When performing arc welding on unit or condenser, disconnect all wire harness connection from the module in control box. Do Not remove wire harness from the module unless you are grounded to unit frame with a static safe wrist strap.

f)   In case of electrical fire, open circuit switch and extinguish it with CO2 extinguisher.

How is Power Generated and Supplied on a Ship?A ship is like a floating city with all the privileges enjoyed by any normal land city. Just like a conventional city, the ship also requires all the basic amenities to sustain life on board; the chief among them is power or electricity. In this article we will learn as to how power is generated and supplied on board a ship.

Power generation On board

Shipboard power is generated using a prime mover and an alternator working together. For this an alternating current generator is used on board. The generator works on the principle that when a magnetic field around a conductor varies, a current is induced in the conductor.

The generator consists of a stationary set of conductors wound in coils on an iron core. This is known as the stator. A rotating magnet called the rotor turns inside this stator producing magnetic field. This field cuts across the conductor, generating an induced EMF or electro-magnetic force as the mechanical input causes the rotor to turn.

The magnetic field is generated by induction (in a brushless alternator) and by a rotor winding energized by DC current through slip rings and brushes. Few points to be noted about power on board are :

AC, 3 phase power is preferred over DC as it gives more power for the same size.

3 phases is preferred over single phase as it draws more power and in the event of failure of one phase, other 2 can still work.

Power Distribution on board

The Power Distributed on board a ship needs to be supplied efficiently throughout the ship. For this the power distribution system of the ship is used.

A shipboard distribution system consists of different component for distribution and safe operation of the system. They are:

Ship Generator consisting of prime mover and alternatorMain switch board which is a metal enclosure taking power from the diesel generator and supplying it to different machinery.

Bus Bars which acts as a carrier and allow transfer of load from one point to another. Circuit breakers which act as a switch and in unsafe condition can be tripped to avoid breakdown and accidents. Fuses as safety device for machinery.

Transformers to step up or step down the voltage. When supply is to be given to the lighting system a step down transformer is used in the distribution system.

In a power distribution system, the voltage at which the system works is usually 440v. There are some large installations where the voltage is as high as 6600v. Power is supplied through circuit breakers to large auxiliary machinery at high voltage. For smaller supply fuse and miniature circuit breakers are used. The distribution system is three wires and can be neutrally insulated or earthed. Insulated system is more preferred as compare to earthed system because during an

earth fault essential machinery such as steering gear can be lost.

Emergency Power

In case of the failure of the main power generation system on the ship, an emergency power system or a standby system is also present. The emergency power supply ensures that the essential machinery and system continues to operate the ship.

Emergency power can be supplied by batteries or an emergency generator or even both systems can be used.

Rating of the emergency power supply should be made in such a way that it provides supply to the essential systems of the ship such as

a)     Steering gear system

b)    Emergency bilge and fire p/p

c)     Watertight doors.

d)    Fire fighting system.

e)     Ships navigation lights and emergency lights.

f)      Communication and alarm system.

Emergency generator is normally located outside the machinery space of the ship. This is done mainly to avoid those emergency situations wherein access to the engine room is not possible. A switch board in the emergency generator room supplies power to different essential machinery.

Preferential Trips on Ship : Construction and WorkingPreferential trip is a kind of electrical arrangement on ship which is designed to disconnect the non-essential circuit i.e. non-essential load from the main bus bar in case of partial failure or overload of the main supply.

The non-essential circuits or loads on ships are air conditioning, exhaust and ventilation fans, and galley equipments which can be disconnected momentarily and can be connected again after fault finding. The main advantage of preferential trip is that it helps in preventing the operation of main circuit breaker trip and loss of power on essential services and thus prevents blackout and overloading of  generator.

Construction and Working

The preferential trip circuit consists of an electromagnetic coil and a dashpot arrangement to provide some delay to disconnect the non-essential circuits. Along with this, there is also an alarm system provided, which functions as soon as an overload is detected and trips start operating. There are some mechanical linkages also in the circuit which instantaneously operates the circuit and completes the circuit for preferential trips.

The dashpot arrangement consists of a small piston with a small orifice and which is placed inside a small cylinder assembly. This piston moves up against the fluid silicon and the time delay is governed by the orifice in the piston.

Working of Preferential Trip

The current passes through the electromagnetic coil and the linkages are kept from contacting using a spring arrangement. As soon as the current value increases the limit, the electromagnetic coil pulls the linkage up against the spring force and operates the instantaneous circuit and the alarm system. The lower linkage completes the circuit for the preferential trip circuit.

The current passes through the coil in the preferential trip circuit  which pulls the piston in the dashpot arrangement. The movement of this piston is governed by the diameter of the orifice and the time delay made by the same. The preferential trip operates at 5, 10 and 15 seconds and the load is removed accordingly. If the overload still persists, then an audible and visual alarm is sounded.

Conclusion

The preferential trip is one of those important electrical circuit diagrams which help in removing the excessive load from the main bus bar, thus preventing situation like blackout which is a dangerous incident to ship, especially when the ship is sailing in restricted or congested waters.

Single Phasing in Electrical Motors: Causes, Effects, and Protection MethodsFor proper working of any 3 phase induction motor it must be connected to a 3 phase alternating current (ac) power supply of rated voltage and load. Once these three phase motors are started they will continue to run even if one of the three phase supply lines gets disconnected. The loss of current through one of these phase supply is described as single phasing.

Effect of Single Phasing

The following are the effects of single phasing:

1) Due to single phasing the current in the remaining two phases increases and it is approximately 2.4 times the normal current value.

2) Single Phasing reduces the speed of the motor.

3) The motor becomes noisy and starts vibrating due to uneven torque produced in the motor.

4) If the motor is arranged for standby and automatic starting then the motor will not start, and if the overload relay provided fails to function then the motor may burn.

5) The windings will melt due to overheating and can give a fatal shock to the personnel.

6) It may cause overloading of the generator.

Causes of Single Phasing

Single Phasing is usually caused when:-1) One of the three back up fuses blows (or fuse wire melts).

2) One of the contactor for motor is open circuited.

3) Single phasing might also be caused due to wrong setting of the protection devices provided on the motor.

4) Contactors are coated due to oxidation hence not conducting.

5) Relay contacts may be damage or broken.

How to Protect Motor from Damage Due to Single Phasing?

All motors above 500 KW are to be provided with protection devices or equipments to prevent any damage due to single phasing.

The rule stated above does not apply to motors of the steering gear system installed on the ship. Only on the detection of the single phasing an alarm will be sounded; however, the motor will not stop as it is essential for safety or propulsion of the ship.

The most commonly used protection devices for single phasing are:-

1) Electromagnetic Overload Device

In this device all the three phases of the motor are fitted with an overload relay. If there is any increase in the value of the current then this relay activates automatically and the motor trips.

This device works on the principle of electromagnetic effect produced due to the current.As the current value increases, the electromagnet in the coil also increases which pulls the relay and activates the trip relay and the motor is stopped.

The time delay is provided in this system because during starting the motor draws a lot of current which can trip the motor.

2) Thermistors

Thermistors are small thermal devices which are used together with an electromagnetic overload relay. The thermistors are inserted in the three windings of the motor. Any increase in the current will cause heating in the windings, which is detected by the thermistors that send signals to the amplifier.

The amplifier is connected to electromagnetic relay. As soon as a signal is received from thermistor about overheating, this amplifier increases the current value in the coil of electromagnetic relay which activates the trip and the motor stops or trips.

3) Bi-metal strip

In this method the bi metallic strip is placed in such a way that it detects the overheating in the circuit. As soon as overheating is detected, this bimetallic strip tries to expand due to two different metal used and because they have different coefficient of expansion. The strip tries to bend towards the metal having high coefficient of expansion and finally completes the trip circuit and the motor trips.

Construction and Operation of Megger ExplainedThe most important factor for the staff working onboard is personal safety and the safety features incorporated in machinery and systems. Electrical components and machinery systems present in the engine room are maintained by the electrical officer. The most important routine maintenance for electrical machinery involves checking of insulation resistance which is done by an instrument called “Megger” or “ohmmeter”.

Insulation Resistance:

Insulation resistance (I.R) is a critical parameter as it’s directly related to personal safety, safety of machinery and power reliability. The I.R value of an electric devise changes with aging, mechanical and electrical stresses, temperature, contamination, atmosphere, humidity etc. It is therefore important for the engineers to identify this detection to avoid any accidents on board due to electric shock.

Megger or Ohmmeter:

Megger is a portable instrument which is used to measure insulation resistance of the electrical machinery or system. It can be battery operated or mechanically operated (hand crank dc generator) and gives direct reading in ohms. For this reason it is also called as ohm meter. Onboard ship, different systems are present with large voltage ratings and therefore Megger comes in the range of 100V to 5000V.

Construction :

The important construction features of Megger consist of following parts:

1) Control and Deflecting coil: They are normally mounted at right angle to each other and connected parallel to the generator. The polarities are such that the torque produced by them is in opposite direction.

2) Permanent Magnet: Permanent magnet with north and south poles to produce magnetic effect for deflection of pointer.

3) Pointer and scale: A pointer is attached to the coils and end of the pointer floats on a scale which is in the range from “zero” to “infinity”. The unit for this is “ohms”.

4) D.C generator or battery connection: Testing voltage is supplied by hand operated D.C generator for manual operated Megger and a battery and electronic voltage charger for automatic type Megger.

5) Pressure coil and current coil: Provided for preventing damage to the instrument in case of low external source resistance.

Working: -

The voltage for testing is supplied by a hand generator incorporated in the instrument or by battery or electronic voltage charger. It is usually 250V or 500V and is smaller in size.

- A test volt of 500V D.C is suitable for testing ship’s equipment operating at 440V A.C. Test voltage of 1000V to 5000V is used onboard for high voltage system onboard.

- The current carrying coil (deflecting coil) is connected in series and carries the current taken by the circuit under test. The pressure coil (control coil) is connected across the circuit.

- Current limiting resistor – CCR and PCR are connected in series with pressure and current coil to prevent damage in case of low resistance in external source.

- In hand generator, the armature is moving in the field of permanent magnet or vice versa, to generate a test voltage by electromagnetic induction effect.

- With an increase of potential voltage across the external circuit, the deflection of the pointer increases; and with an increase of current, the deflection of pointer decrease so the resultant torque on the movement is directly proportional to the potential difference and inversely proportional to the resistance.

- When the external circuit is open, torque due to voltage coil will be maximum and the pointer will read “infinity”. When there is short circuit the pointer will read “0”.

Permanent Magnet Moving Coil Instrument (PMMC) – Working and Application on ShipSeveral electrical machines and panels are fitted onboard so that the ship can sail from one port to another, safely and efficiently. The electrical machinery and system require scheduled maintenance and checks to avoid any kind of breakdown during sailing.

Different instruments are used onboard for measuring several electrical parameters to analyze and keep these machinery in proper running condition. A permanent magnet moving coil (PMMC) is one such instrument which is popularly used onboard and has several applications.

Permanent Magnet Moving Coil: Principle of Working

When a current carrying conductor is placed in a magnetic field, it experiences a force and tends to move in the direction as per Fleming’s left hand rule.

Fleming left hand rule:

If the first and the second finger and the thumb of the left hand are held so that they are at right angle to each other, then the thumb shows the direction of the force on the conductor, the first finger points towards the direction of the magnetic field and the second finger shows the direction of the current in the wire.

Construction:

A coil of thin wire is mounted on an aluminum frame (spindle) positioned between the poles of a U shaped permanent magnet which is made up of magnetic alloys like alnico.

The coil is pivoted on the jewelled bearing and thus the coil is free to rotate. The current is fed to the coil through spiral springs which are two in numbers. The coil which carries a current, which is to be measured, moves in a strong magnetic field produced by a permanent magnet and a pointer is attached to the spindle which shows the measured value.

Working:

When a current flow through the coil, it generates a magnetic field which is proportional to the current in case of an ammeter. The deflecting torque is produced by the electromagnetic action of the current in the coil and the magnetic field.

The controlling torque is provided by two phosphorous bronze flat coiled helical springs. These springs serve as a flexible connection to the coil conductors.

Damping is caused by the eddy current set up in the aluminum coil which prevents the oscillation of the coil.

Applications:

The PMMC has a variety of uses onboard ship. It can be used as:

1)      Ammeter:

When PMMC is used as an ammeter, except for a very small current range, the moving coil is connected across a suitable low resistance shunt, so that only small part of the main current flows through the coil.

The shunt consists of a number of thin plates made up of alloy metal, which is usually magnetic and has a low temperature coefficient of resistance, fixed between two massive blocks of copper. A resistor of same alloy is also placed in series with the coil to reduce errors due to temperature variation.

2)      Voltmeter:

When PMMC is used as a voltmeter, the coil is connected in series with high resistance. Rest of the function is same as above. The same moving coil can be used as an ammeter or voltmeter with an interchange of above arrangement

3)      Galvanometer:

Galvanometer is used to measure small value of current along with its direction and strength. It is mainly used onboard to detect and compare different circuits in a system.

5)      Ohm Meter:

The ohm meter is used to measure resistance of the electric circuit by applying a voltage to a resistance with the help of battery. A galvanometer is used to determine the flow of current through the resistance. The galvanometer scale is marked in ohms and as the resistance varies, since the voltage is fixed, the current through the meter will also vary.

Advantages:

-  The PMMC consumes less power and has great accuracy.

-  It has uniformly divided scale and can cover arc of 270 degree.

-  The PMMC has a high torque to weight ratio.

-  It can be modified as ammeter or voltmeter with suitable resistance.

-  It has efficient damping characteristics and is not affected by stray magnetic field.

-  It produces no losses due to hysteresis.

Disadvantage:

-  The moving coil instrument can only be used on D.C supply as the reversal of current produces reversal of torque on the coil.

-  It’s very delicate and sometimes uses ac circuit with a rectifier.

-  It’s costly as compared to moving coil iron instruments.

-  It may show error due to loss of magnetism of permanent magnet.

What are the Main Safety Devices for Main Switch Board on Ship?The Main switch board is an intermediate installation in the ship’s power distribution circuit connecting the power generators and power consumers. The power generators on ships are auxiliary engines with alternators and the consumers are different engine room machineries such as motors, blowers etc.

It is very important to isolate any type of fault in an electrical system supplied from the main switch board (MSB) or else it will affect all the other system connected to the same. If such isolation is not provided then even a short circuit in a small system can cause blackout of the whole ship.

Therefore, different safety devices are used on board ship and installed on the main switch board (MSB) and electrical distribution panels. This ensures safe and efficient running of machineries and safety of the personal from electric shock even when one system is at fault.

The Important safety devices fitted on main switch board are:

Circuit breakers: A circuit breaker is an auto shut down device which activates during an abnormality in the electrical circuit. Especially during overloading or short circuit, the circuit breaker opens the supplied circuit from MSB and thus protects the same. Different circuit breakers are strategically installed at various locations.

Fuses: Fuses are mainly used for short circuit protection and comes in various ratings. If the current passing through the circuit exceeds the safe value, the fuse material

melts and isolates the MSB from the default system. Normally fuses are used with 1.5 times of full load current.

Over current relay: OCR is used mainly on the local panel and MSB for protection from high current. They are installed where a low power signal is a controller. Normally relays are set equivalent to full load current with time delay.

Dead front panel: It is another safety device provided on the Main switch board individual panels wherein you cannot open the panel until the power of that panel is switched off.

Apart from this, maintenance and operational safety plays an important part for the safety of main switch board.

Electrical Safety Device: Air Circuit Breaker (ACB)Generators onboard ships are the power suppliers for the entire vessel as they stand as the primary source of power to all running machineries including the propulsion plant. For this reason, safe and efficient running of the ship generator has to be given highest consideration. One of the important safety devices used for ship’s generator is Air Circuit Breaker (ACB).

Air circuit breaker is designed to overcome the defects and safeguard the machine before it breakdowns.

The main function of air circuit breaker is to:

-          Open and close a 3 phase circuit, manually or automatically.

-          Open the circuit automatically when a fault occurs. Faults can be of various types – under or over voltage, under or over frequency, short circuit, reverse power, earth fault etc.

-          The main feature of ACB is that it dampens or quenches the arcing during overloading.

Air Circuit Breaker (ACB) Construction & Working

ACB has two sets of contacts i.e. main and auxiliary contacts. Each set of contact consists of a fixed contact and a moving contact. The main contact normally carries most of the load current. All the contacts are made of cadmium-silver alloy which has very good resistance to damage by arcing.

When the ACB is closed, the powerful spring is energized and the ACB is than latched shut against spring pressure. The auxiliary contact makes first & breaks last i.e. when ACB is closed, the auxiliary contact closes first then the main contact follows.

When the ACB is open, the main contact open firsts and then auxiliary contact opens. Thus the auxiliary contacts are subjected to arcing during the opening of ACB and can easily be replaced.

The main contact closing pressure is kept high so that the temperature rise in the contacts while carrying current remains within limit. Closing coil operating on D.C voltage from a rectifier is provided to close the circuit breaker by operating a push button.

How Arc Quenching is Achieved?

Quenching of arc is achieved by:

1.Using arcing contacts made of resistance alloy and silver tips for the main contacts. Arcing contacts close earlier and opens later than the main contacts.

2.When opening contacts have long travelled at high speed to stretch the resultant arc, which is transferred to the arcing contact.

3.Cooling and splitting of the arc is done by arc chutes which draw the arc through splitters by magnetic action and quickly cool and split the arc until it snaps. The circuit breaker opens when the arc is quenched.

Understanding Rectifier and Rectifier Circuits on ShipApart from their small size, all electrical and electronic equipment or circuit on boards on ship play a vital role in operation of ship’s system and machinery. Different equipment onboard vessel utilizes alternating current, direct current or both depending upon the nature of operation. Some of the Very important circuits and setups are run through D.C current.

Since most of the ship generates A.C current from its alternator, it becomes essential to use a device, along with transformer, which can convert this A.C current into D.C current for the use of those equipment or circuit running on D.C.

Rectifier

Rectifier is a circuit which utilizes one or more semiconductor diode to convert an alternating current into a pulsating direct current.

This process of conversion is known as rectification.

 

Types of Rectifier

Half wave rectifier

Half wave rectifier consists of a single diode connected in series with load resistor.

 

During the positive half cycle of input voltage, the diode is forward biased and it conducts for all volts which is greater than its barrier potential.

During negative half of the cycle, the diode is reverse biased hence it does not conduct.

 

Full wave rectifier

Full wave rectifier circuit allows unidirectional current to flow to the load during the entire input cycle.

There are two types of single full wave rectifier:

1)      Two diodes connected back to back using a centre tapped transformer.

2)      Full wave bridge rectifier using four diodes connected in the form of bridge.

 

Bridge rectifier

A single phase bridge rectifier is used with four diodes connected in bridge with a non centre tapped transformer. Full wave rectifier has an advantage of converting both polarities of input A.C waveform in to D.C, hence it is more efficient.

A three phase rectifier circuit consist of six diodes which are in pair of three, connected in series (anode to cathode). It is commonly used in three phase circuits.

 

Application onboard

Some of the uses of rectifiers on board ship are;

Used in many marine electronic devices and circuits.

They are used for onboard battery charging from the ship supply.

Used in detection of radio signals.

They can be used in electroplating process.

They are used in ship construction for electrolyte refining of metals.

Used in operation of D.C motor.

Used in field excitation of three phase alternator.

Amplifier Circuit or Operational Amplifier (op amp) Used on ShipAn Amplifier or an operational amplifier (op-amp) circuit is commonly used in the automation, control and other electronic circuits for marine applications. The applied input signal is normally a voltage or a current signal. The purpose of an amplifier is to produce an output signal larger than that of the input signal.

 

Purpose of Amplifier Circuit

As the name suggest, the purpose of an amplifier or an op amp is to amplify or increase the input signal to produce an output signal which is much larger than that of the input, with a similar waveform as that of the input.The main change in the output signal will be the increase in the power level. This additional power is supplied by a D.C voltage which is externally provided. The output signal is controlled by the input signal in an amplifier.

 

Operation of Amplifier Circuit

The input of the amplifier consists of differential input voltage V+ input and V-input and this difference in the voltage is amplified to produce a large output. Therefore the op-amp equation can be given by

V o/p = [(V+)- (V-)] x A o/l

Where A o/l is open loop gain of the amplifier.

In an op-amp the magnitude of A o/l is very large which gives a large output even when the input differential is small.

The other important properties

It has a high output gain.

It has high input and low output impedance

The band width is in very high range.

Application of Amplifier Circuit

An amplifier circuit is popularly used in marine electrical and electronic circuits. They are:

It is used to amplify audio signal (loudspeaker, VHF)

It is used as voltage and current regulator.

It is used as analog to digital converter & vice versa

It is used as a servo amplifier in motor

The output signal from amplifier is supplied to a relay in a circuit.

Construction and Working of 3 Phase Induction Motor on ShipThe popularity of 3 phase induction motors on board ships is because of their simple, robust construction, and high reliability factor in the sea environment. A 3 phase induction motor can be used for different applications with various speed and load requirements.

The ship’s generator 3 phase AC supply can be connected to the AC induction motor via a starter or any other arrangement like auto transformer to improve the torque and current characteristics.

3 phase induction motors are used in almost all machinery system of the ship such as crane motor, propulsion motor, blower motor, sea water pump motor, and even small synchronous motor.

 

Construction

The main body of the Induction Motor comprises of two major parts:

 

Stator

Stator is made up of number of stampings in which different slots are cut to receive 3 phase winding circuit which is connected to 3 phase AC supply.

The three phase windings are arranged in such a manner in the slots that they produce a rotating magnetic field after AC supply is given to them.

Usually, windings are kept at different pitch circle with 30 % overlap to each other.

The windings are wound for a definite number of poles depending upon the speed requirement, as speed is inversely proportional to the number of poles, given by the formula:

Ns= 120f/p

Where Ns= synchronous speed

f  = Frequency

p = no. of poles

Rotor

Rotor consists of cylindrical laminated core with parallel slots that carry conductor bars.

Conductors are heavy copper or aluminium bars which fits in each slots. These conductors are brazed to the short circuiting end rings.

The slots are not exactly made parallel to the axis of the shaft but are slotted a little skewed for the following reason:

They reduces magnetic hum or noise

They avoid stalling of motor.

 

Principle and working

When 3 phase supply is given to the motor, the resulting current generates a magnetic flux “Ø”.

Due to the switching sequence of 3 phase current in R, Y and B, the generated flux rotates around the rotor conductor.

 

According to Faraday’s law which states that –“an emf induced in any closed circuit is due to the rate of change of magnetic flux through the circuit”.

Emf is induced in the Copper bar and due to this, current flows in the rotor. The direction of rotor can be given by Lenz law which states that – “the direction of induced current will be in the opposite of the motion causing it”

Here the relative velocity between the rotating flux and static rotor conductor is the cause of current generation; hence the rotor will rotate in the same direction to reduce the cause i.e. the relative velocity, thus rotating the rotor of the induction motor.

Maintenance of Electrical Relay on Ships Electrical CircuitA relay is an important electromechanical safety device in ship’s electrical circuit and is normally used to open the faulty circuit from the main supply when any kind of electrical fault occurs. A relay is fitted in the Main and Emergency switch board of the ship as a protective device.

Relay has to be kept operational and healthy at all times, else at the time of fault if it relay does not operate properly, the whole system may suffer loss of power or damage. The most common application of relays is for overload and short circuit protection.

A ship engineer or electrical officer has to make sure that relay is efficiently in operation and all the maintenance is carried out on the same as per schedule or as per continuous monitoring.

If during inspection, the relay is found out to be defective it must be replaced immediately with a spare one.

A simple electromagnetic Relay is shown in the below diagram and it will get activated when the magnetic effect of the iron core is sufficiently increased by the excess or high

current in the coil which will attract the iron armature held against the spring force to trip the circuit.

 

A brief maintenance for relay is given as follows-

Checks to be carried out on relay contacts for damage due to arcing.

Polish the contact with emery paper to remove rust and deposits.

Check the closing linkage for free movement.

Check the continuity of the contacts with multimeter.

There are arc chutes provided to quench the arcing. Check for burnout of the same.

Check the tension of the spring.

Open circuit and short circuit test to be performed on the coil by multimeter.

Check the continuity of the trip circuit by multimeter.

Check tightness of the supply terminals.

How to Find an Earth Fault On board Ships?Earth fault is considered very critical on board a ship. Some ships which operate at 440 V do not have any trip devices attached for a single earth fault. However when the operating voltage exceeds 3000V, it is mandatory to have a protection system which isolates when a machinery suffers an earth fault.

 

How to find out an Earth Fault?

The seriousness of the action to be taken on an Earth Fault depends on the part of the electrical system it affects. Conventional ships which operate on 3 Phase, 440V, have earth fault indicators installed on all three phases. Any earth fault on a 440V system is considered to be a serious trouble and immediate action is required to identify the faulty circuit. Any earth fault on 220V or any low voltage lighting circuit can be considered as important but need not require immediate attention. However, attention should be paid at the next earliest opportunity.

 

Finding Earth Fault on 440V circuit

Whenever there is an earth fault alarm, immediately inform to electrical officer (if he is on board). First action is to check the trueness of the alarm. Usually there will be a test button which when pressed, resets the alarm and rechecks the condition of the earth fault.

If the ship is having IAS (Integrated Automation System), check on the computer in the list of events after which the alarm has activated. If IAS facility is not available, there is only one option of isolating each and every machinery in the 440 V circuit and check whether the earth fault indication returns back to normal.

Isolation of all machinery, which operates on 440V, is not always possible. Certain critical equipment like steering gear and lubricating oil pumps cannot be isolated for when the ship is underway. However changeover can be done from running machinery to the standby one and thus the earth fault can be found.

 

Finding Earth Fault on 220V Circuit

Finding an Earth Fault on a 220V circuit is comparatively difficult than a 440V circuit. The main reason being the lighting circuits found all round the vessel. However, any earth fault alarm with respect to a 220V circuit is usually treated as important but not an emergency.

When a 220V earth fault alarm sounds, as said earlier, the trueness of the alarm is checked by pressing the test button and then investigation can be started on each and every 220V circuit.

 

Example: Earth Fault alarm sounds on a 220V panel

1. Check the trueness of the alarm.2. Isolate the complete Group start panel for a lighting division one by one.3. Check the Earth Fault indicator for status (still faulty or normal).4. If faulty, then put on the breaker which is put off earlier and isolate other group start

panel for lighting circuit.5. Once the group start panel is identified, then individual lighting switches are turned off

one by one and checked for the alarm condition.

6. When any switch when turned off and thus the condition becomes normal, then this lighting circuit is marked and then inspection is done on the particular light for abnormalities.

Ingress of moisture is most common reason for an earth fault.

 

Alternate Idea: Instead of turning off breakers one by one for the lighting circuit, I followed a method where I turned off all lighting circuit of a particular doubted area. This method helps usually when there are two or more earth faults in 220V lighting circuit. By turning off all the breakers of a particular area, then switching on the breaker one by one will eliminate multiple earth faults.

When I turned off lighting switches one by one, it was difficult for me to identify multiple earth faults.

Once the particular faulty circuit is spotted, then we have to further break them into individual dividable pieces and check them for earth faults. For this as usual, we use megger against earth.

By removing fuse of the two phase lines, each line can be tested and the fault pinned down.

Why are Transformer and Alternator Ratings in kVA on Ships?On ships, not only transformers, but also generators, protection devices etc., are mostly rated in kVA. A motor does mechanical work and thus has mechanical output expressed in kW. A transformer is a static device, which does not perform any mechanical work. But the main functions are stepping down and stepping up of voltage ratings. Invariably, while stepping up/down the voltage, it also steps down/up the current inversely.

 

Thus the rating of a transformer can only be expressed as a product of Volts and Amperes (V *A)

 

Amps Rating

The current flowing through the transformer can vary in power factor, from zero PF lead (pure capacitive load) to zero PF lag (Pure inductive load) and is decided by the load connected to the secondary. The conductor of the transformer winding is rated for a particular current beyond which it will exceed the temperature for which its insulation is rated irrespective of the load power factor.

 

Voltage Rating  

The maximum voltage which the primary winding can be subjected to, has also a maximum limit. If the applied voltage to the primary winding exceeds the maximum rated value, then this will cause magnetic saturation of the core leading to distorted output with higher iron losses.

Thus considering both the above ratings, it is usual for transformers to be rated in VA. It can further be understood as product of voltage (V) and Current (A). But this does not mean that one can apply a lower voltage and pass a higher current through the transformer contributing to the rated VA value. The VA value is bounded individually by the rated voltage and rated current.

All electrical equipments in connection with generation, transmission, distribution of a.c. power such as alternators, transformers, switch gear, cables etc are rated on k VA basis.

We know that

Cos φ = kW/ k VA.

Or

k VA = kW/ Cos φ.

It is evident from the above equation that the larger the Power factor, the smaller is the k VA requirement of the machinery. Therefore at low power factors, the K VA rating of the equipment has to be made more, making the equipment larger and expensive.

Thus k VA rating is so important and it is assigned at the design stage itself.

Reasons for Using High Voltage Systems On board ShipsWe all know about the voltages used on board a ship. It is usually a 3phase, 60Hz, 440 Volts supply being generated and distributed on board. Every day the owners and designers aim for bigger ships for more profitability. As the ship size increases, there is a need to install more powerful engines and other machineries.

 

This increase in size of machineries and other equipment demands more electrical power and thus it is required to use higher voltages on board a ship.

Any Voltage used on board a ship if less than 1kV (1000 V) then it is called as LV (Low Voltage) system and any voltage above 1kV is termed as High Voltage.

Typical Marine HV systems operate usually at 3.3kV or 6.6kV. Passenger Liners like QE2 operate at 10kV.

Why High Voltage?

Let us assume a ship generating 8MW of power at 440V, from 4 diesel generating sets of 2MW, 0.8 power factors each.

Each generator feeder cable and circuit breaker has to handle a full-load current of:

I = 2 * 106/ (√3 * 440 * 0.8)

I = 3280.4 Amps i.e. Approximately 3300 Amps.

The protection devices like circuit breaker should be rated at approximately 90kA for each feeder cable.

Let us now calculate the same if the generated voltage is 6600Volts.

I = 2 * 106 / (√3 * 6600 * 0.8)

I = 218.69 Amps, Approximately 220 Amps. Thus the protection devices can be rated as low as   9 k Amps.

 

Also Power Loss = I2 * r.

Where I is the current carried by the conductor,

R is the resistance of the conductor.

Thus power loss varies square of the current carried by the conductor. If the supply voltage is 440V, then the current carried by the conductor is 0.002P, and if the voltage is raised to 6600V, then the current carried for the same power is (1.515 *( 10^-4)) * P

Thus it implies that the power loss is reduced by a greater extent if the voltage is stepped up. Thus it is always efficient to transmit power at a higher voltage.

Conversely, the power loss can be reduced by reducing the resistance of the conductor.

r = ρ * l/a.

Thus by increasing the cross-sectional area of the conductor (diameter), the resistance of the conductor can be reduced and thus the power loss. But this involves huge increase in cost and heavy cables with supports. Thus this idea was not used to reduce the power loss during transmission and utilization.

Also a motor (let us assume a bow thruster), may be of a smaller size if it designed to operate on 6600 Volts. For the same power, the motor would be of a smaller size if it is designed for 6600Volts when compared to 440Volts.

Thus these are the major reasons why recent ships have shifted towards high voltage systems.

How to Install Electronic Circuits on Ship?With increase in modern technology and automation in ship’s machinery and operations, electronic circuits like printed circuit board or PCB along with signal transducer and transmission system are popularly used onboard. Since these are very small and vital circuits they require proper location and precaution for their installation.

What is Printed Circuit Board or PCB?

In ships, electronic system PCB plate or board is commonly used as it is compact in size and easy to replace.

PCB is an electrical interconnection of different electronic components using tracks, signal traces, conductive pathways etc., and the whole circuit is supported mechanically on a small board.

It is very important to properly locate the installation of electronic components as they are prone to damage if there is excessive change in the surroundings.

Important points to be kept in mind while installing electronic system:

The electronic circuits get affected by change in temperature or heat so component like transmitter should be installed in a place with good ventilation and with no gas or steam leakage.

Cable connecting the electronic component must be installed over perforated plates for good ventilation and should not lie on the hot surface.

The cable used must have proper insulation.

Circuits like PCB have more chance of getting damaged when exposed to high temperature. Therefore, they are installed in Engine control room (ECR) and air conditioning is provided in the control room to maintain the temperature of electronic and electrical components.

While installing the electronic component, drier or silica gel packets are used in the control box to avoid condensation of moisture over the circuit.

With moisture over the circuit due to humidity in the atmosphere, the electronic component will behave erratic.

The box or cabinet used to install electronic circuit must be properly secured with the surroundings to avoid vibration.

Vibration will cause loose or breaking of contacts.

All the components are to be tightly fitted in the cabinet as else loose fitting may lead to vibration and hence breaking of contacts and components.

Electronic circuit’s component cable should not be in the vicinity of 440 v high tension cable.

440 v cable produce electromagnetic field which will interact with the signal of the electronic circuit and lead to wrong input or output.

Electric Propulsion System for Ship: Does it have a Future in the Shipping? With the increase in demand for alternate propulsion systems that not only improve the overall efficiency of the ship but also reduce the carbon footprints, innovators in the shipping industry are leaving no stone unturned to find a solution to this grave problem. With all the options presently available at hand, electric propulsion system seems to have a promising future.

But as everything comes with a consequence, this system has its drawbacks too. Will or will it not make it to the engine room of every ship – this only time can tell. But what we can do is weigh its pros and cons and see if it has the very necessary “X” factor that everyone is talking about.

The Electrical propulsion system has got a lot of advantages over the conventional engine driven propulsion system, which is obviously increasing the demand for electrical propulsion for merchant vessels. With advancement in technology and research, electrical propulsion system is not limited to small boats and small vessels anymore.

We managed to list the main advantage of electrical propulsion system. They are as follows:

-          A large amount of power is generated by the system and the excess power can be utilised by supplying it to cargo pumps, fire pumps and other important auxiliary machineries.

-          The space required for installation of electrical propulsion machinery is very less and compact as compared to conventional system.

-          There is no direct connection of propeller shaft and prime mover and hence transmission of severe stresses such as torsional and vibration is restricted.

-          There is more flexibility in installation of machineries.

-          It provides improved maneuverability and high redundancy

-          Increased payload through flexible location of machinery components

-          Environmental benefits from lower fuel consumption and emissions

-          High performance in tough ice conditions due to maximum torque at zero speed

-          Reduces lifecycle cost by less fuel consumption and maintenance cost

-          Better comfort due to reduced vibration and noise

 

Yes, there are disadvantages of this system as well. They are:

-          The efficiency of electrical plant is less than that of conventional system.

-          The installation cost of electrical propulsion plant is much higher.

-          Different and improved training for ship’s crew as the system is completely different from mechanical system and involves major automation.

 

Putting advantages and disadvantages side by side, we can confidently say that the former easily surpasses the later ones. From a long term perspective, we feel that electric propulsion will not be a bad bet, keeping in mind the amount of initial investment that needs to be made, and which we think will definitely pay-off at a later stage.

Electrical Propulsion System in ShipsThe shipping industry has come a long way as far as R & D for reducing costs of propulsion without increasing marine pollution is concerned. The conventional propulsion system of the ship is efficient but requires high operating costs and increases the marine pollution. Among all the prospective alternate power sources, electrical propulsion system is one of the best tried out alternative in today’s time.

Electrical Propulsion

Understanding the System

The electric propulsion system consists of a prime mover which may be of two types:

-          Diesel driven

-          Turbine or steam driven

Both the systems produce less pollution as compared to conventional marine propulsion system, which involves burning of heavy oil.

The propeller shaft of the ship is connected to large motors, which can be D.C or A.C driven and are known as propulsion motors. Power for propulsion motor is supplied by the ship’s generator and prime mover assembly.

Arrangement or operation

The generator can be direct or alternating current type with diesel or steam driven prime mover, depending upon the requirement or demand of the owner/ship.

In the electrical propulsion system, the direction of the rotation of propeller is governed by either the electrical control of the motor itself or by changing the electrical supply.

Normally variable speed electrical motor is used for fixed pitch propeller system and constant or variable can be used for variable pitch propeller or CPP.

Applications

Normally electrical propulsion is used in small vessel but now a day shipping companies are adopting this system for big size cargo vessel as well.

Generally electrical propulsion is fitted in

-          Tug and trawlers

-          Dredgers

-          Dynamic positioning vessels

-          Cable laying ship

-          Ice breakers

-          Research ship

-          Floating cranes

-          Vessels for offshore industries

What is Alternate Marine Power (AMP) or Cold Ironing?Huge ships and tankers pollute the marine ecosystem considerably. The pollution caused includes acid rain because of sulphur oxide and smog because of nitrous oxide. In order to make sure that the levels of these pollutants do not increase further, there has emerged the concept of cold ironing or alternate marine power.

Alternate marine power or AMP, as the name suggests, refers to the usage of other power supply sources to feed power to the ship. Such AMP is used when the ship is halting at a port so that the engines of the ship (working on diesel) do not need to be used unnecessarily. This in turn reduces the emissions by the ships by a great margin. This process is also known as cold ironing.

The process of cold ironing can be explained with the help of a few simple steps:

When the ships and tankers are being loaded or unloaded in a port or dock, alternate marine power is supplied to them

This is done so with the help of supply cables that are plugged to an electricity supply board in the port on one end and to the ship’s power supply board on the other

The process is called cold ironing because in the olden days when the ship’s mainframe engines used to be rested, they used to get cold while the power was being transferred in this manner

The process leads not just preservation of the marine ecosystem but also contributes to lesser usage of diesel and other oily power supply materials

AMP provides power for lights, refrigerators, air-conditioners and other equipments on ship

The power coming from the shore can be from a separate power generation unit or from the power plant supplying power to the port city or town.

However, even as cold ironing has a lot of advantages, there are quite a few disadvantages to the process. The crucial disadvantages can be explained as follows:

Problems pertaining to cost. The consumption of electricity will be enormous owing to the size of the ships and tankers. This factor is the primary negative contributor to AMP

Every port and harbour where such tankers and ships halt for the loading and offloading of cargo and thereby for the cold ironing process, will require huge investment to set up the equipments for AMP

Even certain tankers are not compatible and suitable for the process of alternate marine power. The cost of equipping these tankers with the right kind of AMP gadget will also require an enormous investment

The reduction in pollution occurs only when the ship is stationary. When the ship is actually in the water, then because of the usage of conventional engines, pollution will still spread in the marine atmosphere

At present there are four different variations in the AMP that is provided from the port to a ship or a tanker. The same can be listed as follows:

11000 Volts of AC (Alternate Current) 6600 Volts of AC 660 Volts of AC 440 Volts of AC

The concept of AMP has come a long way. In the initial days, cold ironing was used just as a recharging accessory for the tankers. However, seeing that the usage has widened and grown so much in these past few years, it can be assumed and hoped that alternate marine power will become a tool far more vital and necessary than what it is today.

Important Points to Consider While Carrying out Alternator Maintenance of Ship’s GeneratorA ship cannot remain “Live” without a Generator – the lifeline and power production plant of the vessel. A generator on ship is a combination of two separate systems – an alternator and a prime mover whose capacity depends upon the number of machinery or power consuming items fitted on the ship.

What is Alternator?

An alternator is an electro-mechanical device comprising of stator, rotor winding and an external exciter for supplying excitation voltage. Alternator generates electricity when coupled with a prime mover.

Alternator on a ship is exposed to harsh weather and sea conditions, due to which, its capacity and efficiency tends to reduce. It is very important to have proper maintenance on the alternator part of the generator as per planned maintenance or as and when required.

 

Following Points are to be considered while Carrying Out Maintenance on Alternators:

Before starting any maintenance work on the alternator, all safety precaution should be taken and the alternator should be shut and locked down. Also, post notice and ply cards on relevant places and alternator heater to be isolated.

Clean the alternator ventilation passage and air filter.

Check the Insulation resistance of stator and rotor winding.

Air gap between stator and rotor to be checked and maintained between 1.5 to 2 mm.

Slip rings to be checked for even wear down to be renewed if required.

Carbon brushes to be clean and checked for free movement.

The brush contacting pressure to be checked by spring balance.

Automatic Voltage Regulator to be checked and cleaned off oil and dust.

The lube oil level of pedestal bearing to be maintained and renewed as per planned maintenance.

A vacuum cleaner can be used to remove dust accumulated in the inner parts of alternator.

The terminal box cover gasket to be checked for proper oil and water tightness.

All the connection in the terminal box to be tightened properly.

Cable gland to be checked for integrity.

Forced Ventilation around alternator must be maintained all the time.

Check heater for proper operation.

The foundation bolts of the alternator to be checked for tightness

After maintenance is performed, a no load test should be carried out and general condition such as noise, temperature, voltage generated etc. of the alternator should be observed and noted.

How to Minimize the Risks of an Electrical Shock on a Ship?If you are new to a ship, the first few days might leave you confused, lost, and extremely apprehensive as to how are you going to spend the rest of your days of your contract on the ship safely without confronting any accidents. The huge matrix of pipes, the complex machinery, and the massive bunch of wires which runs without any restrictions in different directions might leave you a bit messed up in your mind. It is during this vulnerable mindset, you can come across the worst accident that has happened to you.

When we talk about accidents on a ship, an electrical shock is the worst of all kinds. Electrical wires and connections are present everywhere on a ship and it is important to escape them to prevent yourself and others from getting a major electrical shock. Moreover, it is said that a person on board a ship gets an electrical shock mainly due to its negligence and unawareness. In this article we will learn as to how you can save yourself and others from an electrical shock on board a ship. Also find out what all precautions you should take to minimize the risk of an electrical shock on board.

 

Steps to Minimize the Risk of an Electrical Shock On board

1) Start with the first round of the day; check all electrical motors, wiring, and switches, for abnormal sounds, variation in temperatures, and loose connections.

2)    Ensure that all electrical connections are inside the panel box so that no one can touch them accidently.

3)    In accommodation area multiple socket plugs shouldn’t be used.

4)    Turn off the breaker before starting any work on an electrical system.

5)    Use ply card and notice board as much as possible to inform others about the ongoing work to avoid accidental starts.

6)    Double check the electrical tools like portable drills for any loose wires before attempting any job.

7)    Always wear protective clothing, rubber gloves, rubber knee pads and safety shoes to avoid risk of shock.

8)    Use electrically insulated handle tools for working or checking electrical system.

9)     Before working, remove jewellery wrist band and other conductive items.

10) When working or removing multiple wires, tape off all but the one wire you are working on.

11) Try as much as possible not to work on live system and even if you do so be a professional and work carefully with full concentration.

12)  During working in group or pair, organise a tool box meeting and discuss the procedure, risk and hazards of the job in hand.

13)  If you don’t know about the system, ask for assistance. Don’t work without knowing it.

14) Always think about your own safety and safety of fellow persons while carrying out any electrical work.

Hazards Related to Electric Cable Insulation in Case of FireThe insulation of the electric cable is generally made up of rubber or plastic. The amount of smoke generated by the plastic in case of fire is dependent on factors like nature of plastic, type of additive used, flame of fire and ventilation arrangement. In general most plastics produce a very dense smoke when heated. In this article we will learn about the hazards related to electric cable insulation in case of fire.

Some plastic burns very clearly when subjected to heat and flame, producing very less smoke. If insulation used is of urethane foam it produces a very dense smoke and visibility in the room is lost in a minute. Some plastic contains Poly Vinyl Chloride (PVC) which produces hydro chloride gas as a product of combustion. This is a very deadly gas and has a pungent, irritating odor.

Rubber when used for insulation produces a dense black, oily smoke and has some toxic qualities. The most common gases produced during combustion of rubber are hydrogen sulphide and sulphur di-oxide. These gases are both dangerous and can be fatal in certain cases.

Ways to Reduce these Hazards

The following steps should to taken as preventive measures

Cables having E.P.R (Ethylene Propylene Rubber) insulation with necessary sheathing of Poly Chloro Prene or Chloro Sulphonated Polyethylene ( PCP or CSP) may be used to protect the insulation against fire.

G.i armor may be used to protect insulation from fire and needs to be earthed.

By using cables having high oxygen index number, the number allotted to material depending on minimum percentage of oxygen required to sustain combustion. If the material used is having oxygen index number 27, it means that minimum percentage of oxygen required to burn the material is 27 % which is well above the normal atmospheric oxygen percentage of 21 %. Thus, the insulation material will not catch fire.

Important Precautions for Installation of Electric Cables

1)      The cables and wiring external to the equipment must have flame retardent properties and should be installed in such a manner that it should not interfere with the original flame retarding properties.

2)      Cables and wirings for emergency equipments, lightings, communication and signal should be kept away from spaces like galley, laundries, machinery space of category A & other high risk areas.

3)      Special precautions are to be taken for cable installation in hazardous area as it might lead to explosion in case of electrical fault.

4)      Terminations and joints are to be made in such a manner that it should retain its original fire resisting properties.

5)      Avoid cable for damage and chaffing during installation.

6)      Fireproof glands to be used in case of cable passing through the bulkhead as it would prevent fire from one compartment to other.

Importance of Insulation Resistance in Marine Electrical SystemsInsulation resistance is one of the important readings of marine electrical equipment systems and serves as the best guide to indicate the health of the equipment. Insulation resistance is measured between the insulated conductors and earth and between conductors.

The insulation resistance is measured by the equipment known as meggar, which is a high resistance meter with a test voltage of about 500 volts dc. The 500 V is produced with the help of a hand driven generator or with the help of batteries and electronic voltage charger.

The 500 V test charge is suitable for testing equipments which are rated for 440 volts AC. The equipments to be tested for insulation resistance must be disconnected from the live power supply and the supply to be locked down to prevent any accidents.

On ships, the insulation resistance of all the motors is checked from time to time and values are logged as a part of planned maintenance system. The insulation resistance of the machinery reduces with increase in temperature. The reasons for increase in temperature may be due to dust deposits on the windings or improper ventilation. The

resistance is checked between the windings U-V, V-W, W-U and between U & earth, V& earth, W& earth.

The readings are logged down and the graph is plotted and the trend of insulation resistance is checked. If the reading is reduced to a very low value then the windings have to be checked and cleaned and the readings are to be taken again.

Thermocouples: The Most Common Pyrometer on ShipThermocouple is a device which is widely used as a pyrometer on board ship for continuous measurement of temperature for various machineries like Main engine, Auxiliary engine, gas turbines etc.

It is absolutely important to choose the correct thermocouple material for different temperature range operation, depending upon the machinery and thermocouple location, where the parameter has to be measured.

 

Construction of Thermocouple

A thermocouple consists of two dissimilar homogeneous materials connected together. The materials used depend upon the application and usage. Normally, following materials are used for different temperature range:

Copper – constantan (copper nickel alloy) for range of -200 to 400 °C

Iron – constantan for temperature range of −40 to +750 °C

Chrome – alumel (alloy of nickel, manganese, aluminium and silicon) for temperature range of −200 to +1350 °C.

These materials are connected together in a ceramic sheath covered again by a metal sheath and fitted at desired locations like exhaust manifold etc. The one end of the thermocouple is placed in hot junction and other end is kept in a constant cold junction. These materials are led to a temperature indicator through amplifier and compensator lead. The amplifier and compensator lead (normally made up of copper and dose not effect the circuit) helps in transmitting the output to a remote location.

 

Principle & Working

Thermocouple works with the principle of “seebeck effect” which states that-“Temperature between two dissimilar metals in a circuit converts into electric current”

When two dissimilar metal wires joined, suppose iron and constantan, are coupled together and exposed to difference in temperature at both the ends, then emf is generated and current flows from hot to cold side.

The magnitude of the current depends on the temperature difference between the junctions.

If one junction is kept at constant temperature, then the value of temperature for the other junction can be easily determined.

 

Advantages of Thermocouple

Can be used for remote temperature sensing. It can be used for continuous temperature sensing. Temperature difference can be measured with high accuracy. They are inexpensive and easily interchangeable.

What is Lambda Control in Ships?With new stringent regulations against pollution being introduced, it is important for the manufacturers to build marine engine that satisfy these norms and do not hamper the normal operation of the engine. To achieve this, engines are provided with several automation systems, which not only reduce the pollution level but also increase the efficiency of the engine and reduce other operational cost.

One such introduced automation is lambda control which controls the fuel injection system of the marine engine according to the variation in the load on the same.

Purpose of Lambda Controller

The main function of any engine is to supply enough power so that it can handle the load put on it. The load may increase or reduce during the operation and to accompany this, some excess fuel may be given to keep up the performance.

Lambda controller is used to control the excess fuel injection in the combustion chamber of a marine engine when there is a change in the engine load i.e. during a momentary increase in the engine load.

This is done by controlling the two main elements which are responsible for combustion- fuel and air. This controller senses the relation between the charge air pressure and fuel index of the engine at that load.

Principle of Working

The working of Lambda controller can be understood with the help of the following diagram:

When there is a sudden momentary increase in the engine load, the lambda control will regulate the fuel through injection pump using the regulator arm. For this, (1) is turned on which in-turn commands the switch (2) to touch the Piston arm (3) and be pushed downward, where in the electric circuit will be closed.

Hence, solenoid valve (4) will open which will then actuate the jet system to accelerate the turbocharger resulting in increase in charged air pressure. This will result in pressing the piston (3) back in the lambda cylinder (5). When the lambda value or lambda ratio is satisfactory, then the solenoid valve will get closed, deactivating the jet system.

When the system is activated for more than 10 seconds, then the solenoid valve is signaled to shut off and there is an alarm for system failure

Fuel oil limiting during start

During the start procedure, the lambda controller is used as an index limiter.

Hereby heavy smoke formation is prevented during start procedure and the regulating device cannot over-react.

Advantages

It reduces the emission of excess visible smoke when there is a sudden increase in engine load.

The overall load efficiency of engine increases. The exhaust side of the engine .i.e. exhaust valve, exhaust gas way, exhaust uptake etc

are less fouled due to carbon deposits. The maintenance work reduces due to less fouling of parts.

Electric Propulsion System for Ship: Does it have a Future in the Shipping? 

With the increase in demand for alternate propulsion systems that not only improve the overall efficiency of the ship but also reduce the carbon footprints, innovators in the shipping industry are leaving no stone unturned to find a solution to this grave problem. With all the options presently available at hand, electric propulsion system seems to have a promising future.

But as everything comes with a consequence, this system has its drawbacks too. Will or will it not make it to the engine room of every ship – this only time can tell. But what we can do is weigh its pros and cons and see if it has the very necessary “X” factor that everyone is talking about.

The Electrical propulsion system has got a lot of advantages over the conventional engine driven propulsion system, which is obviously increasing the demand for electrical propulsion for merchant vessels. With advancement in technology and research, electrical propulsion system is not limited to small boats and small vessels anymore.

We managed to list the main advantage of electrical propulsion system. They are as follows:

-          A large amount of power is generated by the system and the excess power can be utilised by supplying it to cargo pumps, fire pumps and other important auxiliary machineries.

-          The space required for installation of electrical propulsion machinery is very less and compact as compared to conventional system.

-          There is no direct connection of propeller shaft and prime mover and hence transmission of severe stresses such as torsional and vibration is restricted.

-          There is more flexibility in installation of machineries.

-          It provides improved maneuverability and high redundancy

-          Increased payload through flexible location of machinery components

-          Environmental benefits from lower fuel consumption and emissions

-          High performance in tough ice conditions due to maximum torque at zero speed

-          Reduces lifecycle cost by less fuel consumption and maintenance cost

-          Better comfort due to reduced vibration and noise

 

Yes, there are disadvantages of this system as well. They are:

-          The efficiency of electrical plant is less than that of conventional system.

-          The installation cost of electrical propulsion plant is much higher.

-          Different and improved training for ship’s crew as the system is completely different from mechanical system and involves major automation.

 

Putting advantages and disadvantages side by side, we can confidently say that the former easily surpasses the later ones. From a long term perspective, we feel that electric propulsion will not be a bad bet, keeping in mind the amount of initial investment that needs to be made, and which we think will definitely pay-off at a later stage.

Electrical Propulsion System in ShipsThe shipping industry has come a long way as far as R & D for reducing costs of propulsion without increasing marine pollution is concerned. The conventional propulsion system of the ship is efficient but requires high operating costs and increases the marine pollution. Among all the prospective alternate power sources, electrical propulsion system is one of the best tried out alternative in today’s time.

Electrical Propulsion

Understanding the System

The electric propulsion system consists of a prime mover which may be of two types:

-          Diesel driven

-          Turbine or steam driven

Both the systems produce less pollution as compared to conventional marine propulsion system, which involves burning of heavy oil.

The propeller shaft of the ship is connected to large motors, which can be D.C or A.C driven and are known as propulsion motors. Power for propulsion motor is supplied by the ship’s generator and prime mover assembly.

Arrangement or operation

The generator can be direct or alternating current type with diesel or steam driven prime mover, depending upon the requirement or demand of the owner/ship.

In the electrical propulsion system, the direction of the rotation of propeller is governed by either the electrical control of the motor itself or by changing the electrical supply.

Normally variable speed electrical motor is used for fixed pitch propeller system and constant or variable can be used for variable pitch propeller or CPP.

Applications

Normally electrical propulsion is used in small vessel but now a day shipping companies are adopting this system for big size cargo vessel as well.

Generally electrical propulsion is fitted in

-          Tug and trawlers

-          Dredgers

-          Dynamic positioning vessels

-          Cable laying ship

-          Ice breakers

-          Research ship

-          Floating cranes

-          Vessels for offshore industries