2012

Nishat Mills LTD

[INTERNSHIP REPORT] Electrical Engineering (power)

Submitted by : Muhammad Gulraiz Ahmed

NFC Institute Of Engineering & Fertilizer

Research Faisalabad

(affiliated with UET LHR)

1

In the name of

ALLAH

The Gracious and The Benevolent

2

Acknowledgements

First of all the whole praise to ALMIGHTY ALLAH, the creator of

the universe and anything in this universe. He made us super creature,

blessed us to accomplish this work. We are very thankful to Allah

Almighty, Who has provided us such an opportunity to gain

knowledge in Ibrahim Fibers Limited. It was a great experience to do

internship over here. We learnt many things practically which we

have learnt theoretically earlier. We also pay our gratitude to the

Almighty for enabling us to complete this Internship Report within

due course of time.

Words are very few to express enormous humble obligations to our

affectionate Parents for their prayers and strong determination to

enabling me to achieve this job.

We would like to thank all the administration engineers, operators and

officials for helping us and for their kind behavior.

3

Introduction

Nishat Group

billion (US$ 5 billion), it ranks amongst the top five business houses

of Pakistan. The group has strong presence in three most important

business sectors of the region namely Textiles, Cement and Financial

Services. In addition, the Group also has reasonable market share in

Insurance (Adamjee and Security General), Power Generation, Paper

products ( Nishat Shoaiba Paper Mills) and Aviation

( Phonix Aviation). It also has the distinction of being one of the

largest players in each sector. The Group has a remarkable position in

the market as good as any multinationals operating locally in terms of

its quality of products, services and management skills.Nishat Group

is one of the leading and most diversified business groups in South

East Asia with fixed/ current assets of over Rs.300

Executive Summary

Nishat has grown from a cotton export house into the premier

business group of Pakistan with 5 listed companies, concentrating on

4 core businesses; Textiles, Cement, Banking and Power Generation.

Today, Nishat is considered to be at par with multinationals operating

locally in terms of its quality products and management skills.

I recently have done my internship in Nishat Mills Limited, in which I

got training from each of its department. The internship basically

revolved around the product knowledge training. The system, the

style of working & the commitment of the employees in NML is

really exemplary.

The difference between the success & failure is doing things right and

doing things nearly right, & NML has always tried for success & that

is why it is known to be one of the leading organizations in Pakistan.

Irrespective of all these positive points of Nishat Mills Limited, I have

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noticed a few areas where the improvement can really increase the

efficiency of NML.

In this report I have given a very brief review of what I have seen

during our internship I have mentioned all these as I have made an

internship as according to the schedule. I also mentioned about the

Textile industry in Pakistan and vision of its industry. Then I have

done a detailed SWOT analysis as well as PEST Analysis.

Then I have discussed about my learning in the whole internship that

is all about the Textile Terminologies and process of the productions.

I have made it possible to write each and every thing that I have learnt

there. I have all my practical efforts in the form of this manuscript

that’s the asset for my future career.

Vision Statement

To transform the Company into a modern and dynamic yarn, cloth

and processed cloth and finished product manufacturing Company

that is fully equipped to play a meaningful role on sustainable basis in

the economy of Pakistan. To transform the Company into a modern

and dynamic power generating Company that is fully equipped to

play a meaningful role on sustainable basis in the economy of

Pakistan.

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Mission Statement

To provide quality products to customers and explore new markets to

promote/expand sales of the Company through good governance and

foster a sound and dynamic team, so as to achieve optimum prices of

products of the Company for sustainable and equitable growth and

prosperity of the Company.

6

Company Profile

Nishat Mills Limited is the flagship company of Nishat Group. It was

established in 1951. It is one of the most modern, largest vertically

integrated textile company in Pakistan. Nishat Mills Limited has

198,120 spindles, 655 Toyota air jet looms. The Company also has

the most modern textile dyeing and processing units, 2 stitching units

for home texitle, one stitching unit for garments and Power

Generation facilities with a capacity of 89 MW. The Company’s total

export for the year 2011 was Rs. 36.015 billion (US$ 416 million).

Due to the application of prudent management policies, consolidation

of operations, a strong balance sheet and an effective marketing

strategy, the growth trend is expected to continue in the years to

come. The Company's production facilities comprise of spinning,

weaving, processing, stitching and power generation.

Quality Policy

We work together as a team for implementation and continual

improvement of total quality system in order to achieve satisfaction of

our internal and external customers.

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Board of Directors

As on April 05, 2012

Power Generation

(MESSAGE FROM CEO)

Mobilizing and generating affordable and environment-friendly

energy resources is one of the key challengers for any nation in

today's world. Today the top priority for Pakistan is Energy and

Power Generation. Presently, Out of around 162 million population

only 65-70% has access to electricity.

To Enter into power generation business is one of the diversified

decision of Nishat Group with the vision to enhance its Investment

into Energy Sector. Nishat Power Ltd. (NPL) a public limited

company was incorporated in February 2007 under the Companies

Ordinance for setting up power plant under the Power Policy 2002 on

Build, Own and Operate ("BOO") basis. Its a 200 MW Combined

Cycle Power Plant based on Reciprocating Engine Technology. The

1 Mian Umer Mansha Director/CEO/Chairman

2 Mian Hassan Mansha Director

3

Mr. Khalid Qadeer

Qureshi Director

4

Mr. Muhammad

Azam Director

5 Syed Zahid Hussain Director (Nominee NIT)

6

Ms. Nabiha

Shahnawaz Cheema Director

7 Mr. Maqsood Ahmad Director

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primary fuel of the Plant is Residual Furnace Oil ("RFO") and its

uninterrupted supply is guaranteed by SHELL Pakistan. The Plant

Configuration is eleven (11) proven Engine sets of type 18v46

manufactured by WARTSILA of Finland and eleven (11) generating

sets, One (1) Heat Recovery Steam Turbine with generator.As per the

Power Purchase Agreement, the NTDC has contracted to purchase the

total net generation capacity of 195.26 MW produced by NPL for a

period of 25 years at US cents 12.1253 per KWh. As the plant will

operate on residual furnace oil, a Fuel Supply Agreement ("FSA") has

been signed between the Company and Shell Pakistan Limited for a

period of ten years after the commencement of commercial

production.The entire plant, machinery and equipment required for

the project has been procured from Wartsila Finland Oy. Whereas,

Wartsila Pakistan (Private) limited has been appointed for the

construction, erection, installation testing and commissioning of the

entire project. We have also awarded Wartsila Pakistan an Operations

& Maintenance Contract for our Plant.The total cost of the project

including interest during the construction period is around PkR17.704

billion.

Major Consideration of the Project were:

The Project would offer significant relief locally in the transmission

system of Lahore, as it would bypass long transmission lines and

potential stepdown transformer bottlenecks. There is currently no

significant power generation inside this area

The plant generation would be consumed very close to the generation

site, thus also reducing substantial transmission losses

The Project has been finalized and commissioned on a fast-track basis

within 18 months as a power generation plant based on reciprocating

engine single fuel RFO fired technology

It is hoped that NPL's power project, the RFO based power plant

under Power Policy 2002, shall serve as role model for others to

follow.

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Safety Precautions

In order to avoid the hazards on the plant, company train their

employees for the Safe handling and operation of materials and units

installed on plant. So for this company follow following steps:

Authorization

Even a small mistake on the plant can cause a serious damage so

MMM (man, machine, material) is very important.

nting out and

also some

crossing the roads and also tanks with explosive materials are present

at different places and anything hitting them may cause a serious

danger.

workers and as a result, their work may be ignored.

for every unit some guider is provided for the specific period of time

and we are not allowed to go in any area according to our desire.

other to prevent injury of workers.

computer control

systems to prevent the tripping of systems as they are very sensitive.

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water in that area is of very high conductivity.

for the workers.

material for the safe handling and storage of the materials.

ded for the safe

operations.

overcoming fire.

Safety Measures:

Safety measures are activities and precautions taken to improve

safety, i.e. reduce risk related to human health. Common safety

measures include:

o Root cause analysis to identify causes of a system failure and

correct deficiencies.

o Visual examination for dangerous situations such as emergency

exits blocked because they are being used as storage areas.

o Visual examination for flaws such as cracks, peeling, loose

connections.

o Chemical analysis

o X-ray analysis to see inside a sealed object such as a weld, a

cement wall or an airplane outer skin.

o Destructive testing of samples

o Stress testing subjects a person or product to stresses in excess

of those the person or product is designed to handle, to

determining the "breaking point".

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o Safety margins/Safety factors. For instance, a product rated to

never be required to handle more than 200 pounds might be

designed to fail under at least 400 pounds, a safety factor of two.

Higher numbers are used in more sensitive applications such as

medical or transit safety.

o Implementation of standard protocols and procedures so that

activities are conducted in a known way.

o Training of employees, vendors, product users

o Instruction manuals explaining how to use a product or perform

an activity

o Instructional videos demonstrating proper use of products

o Examination of activities by specialists to minimize physical

stress or increase productivity

o Government regulation so suppliers know what standards their

product is expected to meet.

o Industry regulation so suppliers know what level of quality is

expected. Industry regulation is often imposed to avoid potential

government regulation.

o Self-imposed regulation of various types.

o Statements of Ethics by industry organizations or an individual

company so its employees know what is expected of them.

o Drug testing of employees, etc.

o Physical examinations to determine whether a person has a

physical condition that would create a problem.

o Periodic evaluations of employees, departments, etc.

o Geological surveys to determine whether land or water sources

are polluted, how firm the ground is at a potential building site,

etc.

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Different Safety Signs

Safety signs are used for indication of the hazard involved while

carrying out the certain action. They are very helpful in for the subject

as they give clear guideline about the hazard that one could face at the

site where they are erected. Some different safety signs are:

In safety there is a rule of triple M.

Man safety

Machine safety

Material safety

Man safety

In safety the first thing is man safety. Man safety is one of

the important things between the rules of safety. Man safety

means how to safe man in working area (plant).Mask, safe-

guard, gloves etc are provided for safety. Also no use of mobile

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Machine safety

Machine safety is also important. The trouble shoot,

maintenance of temperature is the important one. No use of

mobile near to machine because safety of tripping and matching

of frequency.

Material safety

The safety of material is also important. The thing like

sand is safe according to its way of safety. Other things like

PTA, MEG are store according to its conditions.

Power Distribution

The feeder lines are fed to the panels situated there which are

connected to each other with bus couplers along with VCB breakers.

From there, these lines are fed to Transformer Room where the

voltage is stepped down from 11KVA to 415V. The lines from the

transformers are fed to LVD Room in the form of bus wires. The bus

wires are fed to the panels in LVD Room where the panels are

connected in the form of Ring Main System along with Power Factor

Control and ACCB Breakers for safety purpose. From there, the

power is supplied further as per requirement.

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MCC Room

The purpose of this room is to control the speed of the motors hence

controlling the output of the SPG/DL-1 section. The speed is

controlled through inverters which in turn are controlled through

PLCs via Control Room.

The explanation of different terms and the equipment mentioned

above will be explained after giving the summary of each section.

MCC is the motor control centre which is controlling the all the

motors and pumps connected in the specific area. In MCC room the

panels which are controlling the Motors parameters the technology

which is using in MCC room is the one of the modern technology

which the inverters based.

The inverter work is converts the voltage waves into one form to the

other. The main two inverters are using in the MCC room of polyester

plant are the following:

AC to AC inverters

DC to AC inverters

The main purpose of the invertors is that many motors which are

using in the plant are proportional to the frequency and the power we

having the frequency of 50 Hz so that by using invertors we can vary

the frequency of the power given to the motor. We known t the speed

is directly proportional to the frequency we apply.

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UTILITIES

Soft Water

Fresh raw water is pumped from ground and is transported to the

water plant. In plant they are further pumped to gravel bed in a closed

vessel. Small portions of Hydro-chloric acid (HCl) are added to the

filtered water kill bacteria and to lower pH value. Then it passes

through bag filter which consists of series of fibers to deposit gravel

on them. The water that passes the laboratory test is termed as Soft

water, and this is the major production of plant. The soft water

produced is then decarbonised. Decarbonisation is a process in which

air is pumped into water to remove carbon content.

Daemon Water

The soft water is passed through the bed of mixed cation and anion

bed and it become demineralised. Daemon water is then stored in

another vessel (4010-V05). Daemon water is used in chilled water

circuit, boiler house etc.

Drinking Water

Soft water from the storage vessel and some small amount of raw

water is passed through the bed of calcium hydrolit. Drinking water

produced is then stored in drinking vessel.

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Boilers

Boiler house have 3 boilers. All boilers are of fire tube types

having three passes and a super heater. Water is accumulated in

the shell and it surrounds the tubes. Fire is passed through first

pass where combustion take place, from first pass end it enters

the second pass from behind, leave the second pass from front

and the fire rises to the super heater then it enters the third pass,

exhaust gases leave the boiler at boiler rear face to the exhaust

chimney erected outside the boiler house.

There are basically two types of boilers:

Fire tube boiler

Water tube boiler

Fire tube boiler

The name fire tube is very descriptive. The fire, or hot flue gases from

the burner, is channeled through tubes that are surrounded by the fluid

to be heated. The body of the boiler is the pressure vessel and

contains the fluid. In most cases this fluid is water that will be

circulated for heating purposes or converted to steam for process use.

Every set of tubes that the flue gas travels through, before it makes a

turn, is considered a "pass". So a three-pass boiler will have three sets

of tubes with the stack outlet located on the rear of the boiler.

Fire tube Boilers are:

Relatively inexpensive

Easy to clean

Compact in size

Available in sizes from 600,000 btu/hr to 50,000,000 btu/hr

Easy to replace tubes

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Well suited for space heating and industrial process

applications

Disadvantages of Fire tube Boilers include:

Not suitable for high pressure applications 250 psig and

above

Limitation for high capacity steam generation

Three pass Fire tube boilers are used in the IFL. There are 3 fire tube

boilers are used in IFL. One is stand by while 2 are in operation.

Water Tube Boiler

A Water tube design is the exact opposite of a fire tube. Here the

water flows through the tubes and are incased in a furnace in which

the burner fires into. These tubes are connected to a steam drum and a

mud drum. The water is heated and steam is produced in the upper

drum. Large steam users are better suited for the Water tube design.

The industrial watertube boiler typically produces steam or hot water

primarily for industrial process applications, and is used less

frequently for heating applications.

Water tube Boilers are:

Available in sizes that are far greater than the fire tube

design. Up to several million pounds per hour of steam.

Able to handle higher pressures up to 5,000 psig

Recover faster than their fire tube cousin

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Have the ability to reach very high temperatures

Disadvantages of the Water tube design include:

High initial capital cost

Cleaning is more difficult due to the design

No commonality between tubes

Physical size may be an issue

Fuel for boiler:

Natural gas (mostly used)

Furnace oil (stand by)

The steam at 25 bar pressure is then divided in to 3 different pressures

25-bar , 10-bar , 6-bar

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Parts Of Boiler:

Evaporator –

A liquid vapor refrigerant mixture enters the evaporator at state point

1. Liquid refrigerant is vaporized to state point 2 as it absorbs heat

from the system cooling load.The vaporized refrigerant flows into the

compressor first stage.

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Compressor first stage –

Refrigerant vapor is drawn from the evaporator into the first stage

compressor. The first stage

impeller accelerates the vapor increasing its temperature and pressure

to state point 3.

Compressor second stage –

Refrigerant vapor leaving the first stage compressor is mixed with

cooler refrigerant vapor from the economizer. This mixing lowers the

enthalpy of the vapor entering the second stage. The second stage

impeller accelerates the vapor, further increasing its temperature and

pressure to state point 4.

Condenser –

Refrigerant vapor enters the condenser where the system cooling load

and heat of compression are rejected to the condenser water circuit.

This heat rejection cools and condenses the refrigerant vapor

to a liquid up to point 5.

Economizer and refrigerant orifice system –

Liquid refrigerant leaving the condenser at state point 5 flows

through the first orifice and

enters the economizer to flash a small amount of refrigerant a an

intermediate pressure labeled P1. Flashing some liquid refrigerant

cools the remaining liquid to state point 8. Another benefit of flashing

refrigerant is to increase the total evaporator Refrigeration Effect from

RE’ to RE. The economizer provides around 4 percent energy savings

compared to chillers with no economizer. To complete the operating

cycle, liquid refrigerant leaving the economizer at state point 8 flows

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through a second orifice. Here refrigerant pressure and temperature

are reduced to evaporator conditions at state point 1. An innovative

design feature of the CVGF chiller is maximizing the evaporator heat

transfer performance while minimizing refrigerant charge

requirements. This is accomplished by the Trane-patented falling film

evaporator design. The amount of refrigerant charge required in

CVGF is less than that in comparably sized chillers of flooded

evaporator design.

Process

The evaporator is basically shell & tube heat exchanger in which the

chilled water is in the tube side & the refrigerant (Freon) is on the

shell side. The heat exchanger used here is a 1-2 pass heat exchanger.

The wc (chilled water) stream from the process (11-12oC) enters the

evaporator in the tubes & is discharged at a temperature of 6-7oC. It is

present in the liquid form & when the WC stream passes through the

evaporator tubes, the refrigerant gets heat from the water and

evaporates.

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The vapors of the refrigerant are sent to the two-stage compressor.

The compressor should be of such capacity that it should intake same

amount of vapors from the evaporator as being produced in it if the

capacity is low then the pressure in the evaporator will increase &

thus the saturation temperature of refrigerant will increase. When the

vapors are compressed their temperature & pressure increases.

The compressed stream is sent to the condenser in the tubes, where

cooling water is circulated for the cooling purpose in the shell side.

Here the vapors are discharged at the same pressure but at lower

temperature & sent to the economizer. A nozzle is fitted in the

economizer, which acts as an expansion valve. Here the vapors are

sprayed so their pressure decreases due to sudden expansion cooling

occurs & most of the vapors go to liquid form. From the economizer

these streams are discharged.

To the evaporator (in liquid form)

To the evaporator (in the vapor form)

To the 2nd stage of compressor as an inter cooler (in vapor form)

Cooling Tower

Types of cooling towers

Cooling towers are designed and manufactured in several types:

1. ATMOSPHERIC

2. MECHANICAL DRAFT

FORCED DRAFT

INDUCED DRAFT

1: Atmospheric

The atmospheric cooling towers utilize no mechanical fan to create air

flow through the tower; its air is derived from a natural induction flow

provided by a pressure spray.

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2: Mechanical Draft

Mechanical draft towers uses fans (one or more) to move large

quantities of air through the tower. They are two different classes:

Forced draft cooling towers

Induced draft cooling towers

The air flow in either class may be cross flow or counter flow with

respect to the falling water. Cross flow indicates that the airflow is

horizontal in the filled portion of the tower while counter flow means

the air flow is in the opposite direction of the falling water.

The counter flow tower occupies less floor space than a cross flow

tower but is taller for a given capacity. The principle advantages of

the cross flow tower are the low pressure drop in relation to its

capacity and lower fan power requirement leading to lower energy

costs.

Forced Draft

The forced draft tower, shown in the picture, has the fan, basin, and

piping located within the tower structure. In this model, the fan is

located at the base. There are no louvered exterior walls. Instead, the

structural steel or wood framing is covered with paneling made of

aluminum, galvanized steel or asbestos cement boards.

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During operation, the fan forces air at a low velocity horizontally

through the packing and then vertically against the downward flow of

the water that occurs on either side of the fan. The drift eliminators

located at the top of the tower remove water entrained in the air.

Vibration and noise are minimal since the rotating equipment is built

on a solid foundation. The fans handle mostly dry air, greatly

reducing erosion and water condensation problems

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MOTORS

Electromechanical device that converts electrical energy to

mechanical energy

Mechanical energy used to e.g.

• Rotate pump impeller, fan, blower

• Drive compressors

• Lift materials

Motors in industry: 70% of electrical load

Three types of Motor Load

Motor loads Description Examples

Constant torque

loads

Output power varies but

torque is constant

Conveyors, rotary kilns,

constant-displacement

pumps

Variable torque

loads

Torque varies with square

of operation speed

Centrifugal pumps, fans

Constant power

loads

Torque changes inversely

with speed

Machine tools

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Classification of Motors

DC motors

Speed control without impact power supply quality

• Changing armature voltage

• Changing field current

Restricted use

• Few low/medium speed applications

• Clean, non-hazardous areas

Expensive compared to AC motors

Electric Motors

Alternating Current (AC)

Motors

Direct Current (DC)

Motors

Synchronous

Induction

Three-Phase

Single-Phase

Self

Excited

Separately

Excited

Series

Shunt Compound

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Relationship between speed, field flux and armature voltage

Back electromagnetic force: E = KN

Torque: T = KIa

E = electromagnetic force developed at armature terminal (volt)

= field flux which is directly proportional to field current

N = speed in RPM (revolutions per minute)

T = electromagnetic torque

Ia = armature current

K = an equation constant

Separately excited DC motor: field current supplied from a

separate force

Self-excited DC motor: shunt motor

DC compound motor

AC Motors – Synchronous motor

Constant speed fixed by system frequency

DC for excitation and low starting torque: suited for low load

applications

Can improve power factor: suited for high electricity use

systems

Synchronous speed (Ns):

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F = supply frequency

P = number of poles

Most common motors in industry

Advantages:

• Simple design

• Inexpensive

• High power to weight ratio

• Easy to maintain

• Direct connection to AC power source

Components

Ns = 120 f / P

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Rotor

• Squirrel cage:

conducting bars

in parallel slots

• Wound rotor: 3-phase, double-layer, distributed winding

Stator

• Stampings with slots to

carry 3-phase windings

• Wound for definite

number of poles

How induction motors work

• Electricity supplied to stator

• Magnetic field generated that moves around rotor

• Current induced in rotor

• Rotor produces second magnetic field that opposes stator

magnetic field

• Rotor begins to rotate

Single-phase induction motor

• One stator winding

• Single-phase power supply

• Squirrel cage rotor

Electromagnetics

Stator

Rotor

(Reliance)

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• Require device to start motor

• 3 to 4 HP applications

• Household appliances: fans, washing machines, dryers

Three-phase induction motor

• Three-phase supply produces magnetic field

• Squirrel cage or wound rotor

• Self-starting

• High power capabilities

• 1/3 to hundreds HP applications: pumps, compressors,

conveyor belts, grinders

• 70% of motors in industry!

Speed and slip

• Motor never runs at synchronous speed but lower “base speed”

• Difference is “slip”

• Install slip ring to avoid this

• Calculate % slip:

Ns = synchronous speed in RPM

Nb = base speed in RPM

% Slip = Ns – Nb x 100

Ns

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Efficiency of Electric Motors

Motors loose energy when serving a load

• Fixed loss

• Rotor loss

• Stator loss

• Friction and rewinding

• Stray load loss

(US DOE)

Factors that influence efficiency

• Age

• Capacity

• Speed

• Type

• Temperature

• Rewinding

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• Load

Motor part load efficiency

• Designed for 50-100% load

• Most efficient at 75% load

• Rapid drop below 50% load

(US DOE)

Motor Load

• Motor load is indicator of efficiency

• Equation to determine load:

= Motor operating efficiency in %

HP = Nameplate rated horse power

Load = Pi x HP x 0.7457

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Load = Output power as a % of rated power

Pi = Three phase power in kW

Three methods for individual motors

• Input power measurement

• Ratio input power and rate power at 100% loading

• Line current measurement

• Compare measured amperage with rated amperage

• Slip method

• Compare slip at operation with slip at full load

Input power measurement

• Three steps for three-phase motors

Step 1. Determine the input power:

Pi = Three Phase power in kW

V = RMS Voltage, mean line to

line of 3 Phases

1000

3xPFxIxVPi

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I = RMS Current, mean of 3 phases

PF = Power factor as Decimal

Step 2. Determine the rated power:

Step 3. Determine the percentage load:

Pr = Input Power at Full Rated load in kW

hp = Name plate Rated Horse Power

r = Efficiency at Full Rated Load

Load = Output Power as a % of Rated Power

Pi = Measured Three Phase power in kW

Pr = Input Power at Full Rated load in kW

r

r xhpP

7457.0

%100xP

PiLoad

r

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Result

1. Significantly oversized and underloaded

2. Moderately oversized and underloaded

3. Properly sized but standard efficiency

Action

→ Replace with more efficient, properly sized models

→ Replace with more efficient, properly sized models when they fail

→ Replace most of these with energy-efficient models when they fail

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Energy Efficiency Opportunities

1. Use energy efficient motors.

2. Reduce under-loading (and avoid over-sized motors)

3. Size to variable load 4. Improve power quality 5. Rewinding

6. Power factor correction by capacitors 7. Improve maintenance

8. Speed control of induction motor

37

Use Energy Efficient Motors

• Reduce intrinsic motor losses • Efficiency 3-7% higher • Wide range of ratings • More expensive but

rapid payback • Best to replace when

existing motors fail

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Power Loss Area Efficiency Improvement

1. Fixed loss (iron) Use of thinner gauge, lower loss core steel

reduces eddy current losses. Longer core adds

more steel to the design, which reduces losses

due to lower operating flux densities.

2. Stator I2R Use of more copper & larger conductors

increases cross sectional area of stator

windings. This lower resistance (R) of the

windings & reduces losses due to current flow

(I)

3 Rotor I2R Use of larger rotor conductor bars increases

size of cross section, lowering conductor

resistance (R) & losses due to current flow (I)

4 Friction &

Winding

Use of low loss fan design reduces losses due to

air movement

5. Stray Load Loss Use of optimized design & strict quality

control procedures minimizes stray load losses

Use Energy Efficient Motors

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2. Reduce Under-loading

• Reasons for under-loading • Large safety factor when selecting

motor • Under-utilization of equipment • Maintain outputs at desired level

even at low input voltages • High starting torque is required

• Consequences of under-loading • Increased motor losses • Reduced motor efficiency • Reduced power factor

• Replace with smaller motor • If motor operates at <50% • Not if motor operates at 60-70%

• Operate in star mode • If motors consistently operate at <40% • Inexpensive and effective • Motor electrically downsized by wire

reconfiguration • Motor speed and voltage reduction but

unchanged performance

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X

3. Sizing to Variable Load

• Motor selection based on • Highest anticipated load: expensive and

risk of under-loading • Slightly lower than highest load:

occasional overloading for short periods • But avoid risk of overheating due to

• Extreme load changes • Frequent / long periods of overloading • Inability of motor to cool down

4. Improve Power Quality

Motor performance affected by

• Poor power quality: too high fluctuations in voltage and frequency

• Voltage unbalance: unequal voltages to three phases of motor

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Example 1 Example 2 Example 3

Voltage unbalance

(%)

0.30 2.30 5.40

Unbalance in current

(%)

0.4 17.7 40.0

Temperature increase

(oC)

0 30 40

Keep voltage unbalance within 1%

• Balance single phase loads equally among three phases

• Segregate single phase loads and feed them into separate line/transformer

5. Rewinding

• Rewinding: sometimes 50% of motors • Can reduce motor efficiency • Maintain efficiency after rewinding by

• Using qualified/certified firm • Maintain original motor design • Replace 40HP, >15 year old motors instead

of rewinding • Buy new motor if costs are less than 50-

65% of rewinding costs

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6. Improve Power Factor (PF)

• Use capacitors for induction motors • Benefits of improved PF

• Reduced kVA • Reduced losses • Improved voltage regulation • Increased efficiency of plant electrical

system • Capacitor size not >90% of no-load kVAR of

motor

7. Maintenance

Checklist to maintain motor efficiency

• Inspect motors regularly for wear, dirt/dust • Checking motor loads for over/under loading • Lubricate appropriately • Check alignment of motor and equipment • Ensure supply wiring and terminal box and

properly sized and installed • Provide adequate ventilation

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8. Speed Control of Induction Motor

• Multi-speed motors • Limited speed control: 2 – 4 fixed speeds

• Wound rotor motor drives • Specifically constructed motor • Variable resistors to control torque

performance • >300 HP most common

• Variable speed drives (VSDs) • Also called inverters • Several kW to 750 kW • Change speed of induction motors • Can be installed in existing system • Reduce electricity by >50% in fans and pumps • Convert 50Hz incoming power to variable

frequency and voltage: change speed • Three types

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Direct Current Drives

• Oldest form of electrical speed control • Consists of

• DC motor: field windings and armature • Controller: regulates DC voltage to armature

that controls motor speed • Tacho-generator: gives feedback signal to

controlled