BATTERY,POWER PLANT & EARTHING

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The power plant of any telecommunication system is usually referred as the ‘heart’ of the installation since the communication system can function only as long as power supply is available. Failure of power supply system in any installation renders the communication facilities offered by it to be instantly paralyzed.

 

  GENERAL INTRODUCTION

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The support power system in BSNL• Power plant:

To convert ac input into desired dc output (-48 V dc)

• Battery system:To give a back up supply load in case commercial supply is not available.

• DG Set: Alternative supply to battery

backup. The power plant has the capability

to recharge the battery once as discharged.

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Reliability of the components of the power plant and continuity of the power supply.

The power fed to the exchange equipment should be free from noise or hum and to telegraph equipment from large ripple harmonics.

Requirement of Power Supply:

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SECONDARY CELL CONSTRUCTION

(Lead Acid Accumulator)

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Maintenance free, valve-regulated lead-acid (VRLA) batteries ensure a reliable effective and user friendly source of power. It is spill proof and explosion resistant and there is no need to add water or to clean terminals. It has low self-discharge rate which eliminates the need for equalizing charges.

VRLA Technology – A brief review of Chemical Reaction

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The electrode in all lead acid batteries, including VRLA battery is basically identical. As the battery is discharged the lead dioxide positive active material and the spongy lead negative active material react with the sulphuric acid electrolyte to form lead sulphate and water. During charging, this process is reversed.

VRLA Technology – A brief review of Chemical Reaction

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120 AH, 400 AH, 600 AH, 1000AH, 1500 AH,

2000 AH, 2500 AH, 3000 AH, 4000 AH & 5000 AH.

VRLA Technology – Various capacities of

Batteries

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VRLA works on the principle of constant voltage charging

Normally the voltage per cell is set at 2.23 V (Total float voltage is 53.5V)and boost charge volt is set at 2.3 V per cell (55.2 V).

Battery capacity(AH) = Discharge current (A ) × Discharge Duration time(hours).

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Periodic physical inspection of each cell of the battery for cracks and leaking etc.

Discharge of battery for a short duration and recording the voltages of each cell in the string.

Measurement of a mark deviation (>30%) in the impedance or conductance of the cell as compared to the one recorded at the time of commissioning.

MONITORING OF VRLA BATTERIES

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Measurement & recording of cell temp. periodically.

Float Voltage of cells & its comparison with the mid point voltage.

Float current in fully charged battery.

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Float voltage of cells and its comparison with the mid point voltage. The float voltage should be set to 2.25V per cell and change to 2.3V per cell taking the adjustment factor of 3 mV/cell per degree centigrade

MONITORING OF VRLA BATTERIES

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CURRENT IN FULLY CHARGED BATTERY SHALL NOT DRAW A CURRENT MORE THAN 400mA at 27 DEGREE CENTIGRADE. IF IT DRAWS MORE THEN 400mA, it needs investigation

MONITORING OF VRLA BATTERIES

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Life of Assets was revised in the year 2001and the present norms for life of battery is:

Batteries upto 200 AH: 4 years Batteries more than 200 AH: 6

years

Life of Battery

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Surge protection feature is available in new power plants. Old p/ps were to be upgraded through respective manufacturers.

Implementation of low voltage cut off and surge protection features in power plants

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Maintenance Schedule of VRLA batteries Daily: Temperature and voltage of a pilot cell and all

the cells as far as possible. The pilot cell should be cyclically selected on

monthly basis. Monthly: Voltage of each cell during partial discharge. Float current measurement Physic al verification Quarterly: Ensure the tightness of terminal bolts to

11Nm /100Lb inch Conductance measurement Apply boost charge for 24Hrs. Yearly : Test discharge the batteries @ C10 and

measure the time battery sustains the load till any of the cells fallls to 1.75V.

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Some Do’s and Dont’s for the maintenance of VRLA Batteries

Do’s• Clean the batteries as and when dust accumulates.• Keep the batteries away from heat source, sparks, fire etc.,• Keep the battery room neat and clean• Charge the batteries once in every six months @ 2.30 vpc for 24hrs, if stored for longer periods• Wherever cables are used ensure using proper cable size andcrimping of the lug to the cable.

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Do’s

• Tighten all terminal bolts to 11 Nm (100 Lb.-inch)

• Re- torque all the terminal bolts once in every six months.After any discharge, recharge the batteries when power restores.

• Always use calibrated instruments for measurements.

• Keep the batteries in Air-conditioned environment, wherever possible.

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. Don’ts

• Do not add water or acid.• Do not tamper the safety valves.• Do not over tighten the terminal bolts.• Do not allow any metal objects to rest on the battery or

fall across the battery terminals.• Do not mix the batteries of different capacities or makes.• Do not combine ordinary conventional batteries with

VRLAbatteries.• Do not install physically damaged cells.• Do not dump any waste materials in the battery room.

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The power plant is used to rectify the ac input supply to desired output dc (-48v). The conventional power plants which were in use earlier were based on SCRsor Ferro-resonant techniques..

Conventional Power plant

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Problems of the conventional types of power plant :

1. Very large size, 2. Large weight 3. Lower efficiency. 4. No scope for modular expansion

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The salient feature of SMPS PP-

To get rid of all these problems now SMPS power plant are used.

In these systems, the conversion of AC to DC is accomplished in two stages

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The salient feature of SMPS PP- First Stage conversion:

The input AC voltage is directly rectified to high voltage DC.

Second Stage Conversion:• Rectified high voltage DC is stored in a capacitor.• High voltage DC is then converted into a very high frequency AC (20 KHz and higher) by means of very powerful and fast semi-conductor switching devices.

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The salient feature of SMPS PP-

• High frequency AC is stepped down to the required level, by means of a small high frequency transformer.

• Stepped down AC is rectified to DC of desired voltage and filtered by means of high frequency filters.

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Advantages of SMPS Power Plant:

1. Due to high frequency the size of transformers and chokes is reduced to 10 to15% of the conventional SCR/Thyristor controlled power plants. This makes the power plant compact due to which a lot of saving in floor area is achieved.

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Advantages of SMPS Power Plant:

2. The batteries (both VRLA as well as flooded Lead acid) are more prone to temperature variations . As most of the SMPS Power Plants employ microprocessor control techniques, the introduction of temperature compensation logic for batteries has become simple and easier.

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Advantages of SMPS Power Plant

3. Being small and light in weight, fit perfectly in modular concept.Up-gradation of the capacity in modular system is easy; simply plugging-in the additional modules adds to the capacity, with the limit of ultimate capacity and does not require the replacement of existing Power Plant as in the case of conventional Power Plants.

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Advantages of SMPS Power Plant

4.These Power Plants have very high reliability and therefore are less prone tofaults, which result in low operating cost.

5. SMPS offer a very improved Power Factor (near unity) making the system more efficient and make easy to comply with state electricity board’s P.F.norms.

6. These power systems are suitable for VRLA batteries.

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Every 10 degree rise in battery temperature doubles the chemical reaction in the battery & capacity becomes half. The SMPS power plant takes care of the temperature by reducing the charging voltage but still it is important to measure individual cell temp. There is temperature compensation in SMPS PP and it is 3mV per degree raise in temp.

Temperature:-

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Static p/p: 15 years SMPSp/p :15 years

SMPS(Switched Mode Power Supply)

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EARTHING

PPurposes of Earthing AApart from protection from hazardous stray

currents in electrical equipment in Telecom. circuits and equipments, earthing is provided for

the Following purposes: 11. Reduction of Crosstalk and Noise

22. Used as return path for the conductors in some circuits.

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EARTHING 

3 3. Protection of costly apparatus and persons against foreign voltages and leakage currents from power wirings to the metallic frame of the equipment

  4. Protection of buildings and equipments from lighting strikes. 5. It is used to effect reliability of power as it helps to provide stability of voltage conditions preventing excess fluctuations and providing a measure of protection against lighting.

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Three types of earth electrodes are commonly used for earthing systems.

1)   Rod electrodes 2)    Plate electrodes 3)     Strip electrodes

Earth Electrodes :

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As per the instruction:

•E/R is to be measured every six months.

•Earth resistance should be less than 0.5 Ώ for electronic xges

•One dry season must be included in these two occasions.

•For lightning prone area, it should be measured every month.

 

 

Instruction for monitoring of earth resistance were issued from Corporate office.

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•Wherever, it is beyond limits, it should be immediately brought within limits.

•Procedure for laying earth resistance may be followed as prescribed in the latest issue of EI on Protection earthing I-001.

•Reduction in card failure has been observed by improving the earth resistance.

 

 

 

As per the instruction:

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Thank You