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CHAPTER 1

INTRODUCTION

1.1 GENERAL

Energy efficiency and renewable energy are said to be the “twin

pillars” of a sustainable energy policy. Both strategies must be developed

concurrently in order to stabilize and reduce carbon dioxide emission in our

lifetime.

In India, promotion of energy efficiency and energy conservation,

which is found to be the least cost option to augment the gap between demand

and supply, is a part of the strategy developed to make power available to all

by 2012. Nearly 25,000 MW of capacity creation through energy efficiency in

the electricity sector alone has been estimated.

Energy conservation measures are of significance not only to

developing countries like India, but for developed countries also.

Electric motor systems account for roughly 70% of industrial and

35% of tertiary sector electricity demand worldwide. The energy efficiency of

motor systems typically can be improved by 20 to 30% of the losses. Thus,

they represent a huge, untapped potential for cost-effective energy savings

and are a major driver for reduction of electricity demand and associated local

pollutant and greenhouse gas emissions from power plants.

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At this juncture, it is better to review the known efficiency

improvement measures in electric drive systems. Hence, a brief outline of the

same is provided. A detailed review of the literature on conventional energy

efficiency improvement / energy conservation measures in electric drive

systems, referred by the research scholar, are categorised and their significant

contribution are highlighted in the Review of literature, which forms

Chapter 2 of this thesis.

1.2 CONVENTIONAL EFFICIENCY IMPROVEMENT

MEASURES IN ELECTRIC DRIVE SYSTEMS

The following is a comprehensive list of the conventional measures

of efficiency improvement and electricity demand reduction in industrial and

agricultural motor systems.

Figure 1.1 shows the efficiency improvement opportunities in

electric drive systems.

1.2.1 Electrical Power Quality

In Figure 1.1, this measure is mentioned as opportunity 1. The

measures available to maintain acceptable levels of power quality and to

reduce electrical losses include:

Maintaining the supply voltage level as close as possible to

nameplate level, with a maximum deviation of 5%.

Minimizing phase imbalance within a tolerance of 1%, as the

deviation of one phase voltage from average phase voltage

will result in increased winding temperature.

Avoiding excessive harmonic content in the power supply

system that will increase motor temperature

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Opportunity 1 Electrical

Distribution Correction

Opportunity 3 Better Motor Mechanical

Subsystem Matching

Opportunity 4 Process

Optimization

Power Supply System

3 Phase input power

Motor Control System

Motor

System Coupling

Driven Load

Process

Opportunity 2 Motor

Efficiency Improvement

Figure 1.1 Efficiency improvement opportunities in electric drive

systems

1.2.2 Motor Efficiency Improvement

In Figure 1.1, this measure is mentioned as opportunity 2. It is a

traditional approach. The following are a few of the measures available to

improve motor efficiency:

If a motor is running at partial load, then, the connection of

the motor can be changed from delta to star. This will

improve motor efficiency.

Replacing rewound induction motor (operating at reduced

efficiency) with new energy-efficient motor.

If process demands oversized motor, then, possibility of use

of Variable Frequency Drives (VFD) may be explored to save

energy. This is also applicable in the case of varying load

duty cycle motor application.

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1.2.3 Better Motor Mechanical Subsystem Matching

In Figure 1.1, this measure is mentioned as opportunity 3. The

measures available include:

Proper sizing of the motor to the load requirement (many

motors are over-sized and thus run at sub-optimal load factors,

which reduces efficiency and power factor drastically).

1.2.4 Driven Load and Process Optimization

In Figure 1.1, this measure is mentioned as opportunity 4. The

measures available to optimize the process and its operation include:

Changing or reconfiguring the process or application so that

less input power is required.

Installing more efficient mechanical subsystems. Checking

that coupling, gearbox, fan or pumps are energy-efficient.

1.2.5 Miscellaneous Measures to Improve Motor Efficiency

Energy savings of 10 to 15 percent of motor energy consumption

can typically be realized, by following proper maintenance and repair. These

include:

Proper lubrication: It will minimize wear on moving parts.

Correct shaft alignment: It ensures smooth, efficient

transmission of power from the motor to the load. Incorrect

alignment puts strain on bearings and shafts, shortening their

lives and reducing system efficiency.

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Proper alignment: Belts and pulleys must be properly aligned

and tensioned when they are installed, and regularly inspected

to ensure that alignment and tension stay within tolerances.

Painting of motor: Painting of motor housing is to be avoided

because paint acts as thermal insulation, which increases

operating temperatures and shortens the lives of motors. One

coat of paint has little effect, but paint buildup accumulated

over years may have a significant effect.

Following Good rewinding practices (e.g., poor rewinding

practices can damage motors and lower their efficiency

significantly).

Thus, in order to reduce the electric motor drive energy cost, it is

essential to have a system approach rather than to attack on any one portion of

the motor drive system. This will not only reduce the energy consumption but

also increase the System / Plant efficiency.

The increased cost of electrical energy and increased demand for

efficient production of manufactured goods has been a motivating factor that

made it imperative to examine the electric motor that has been the basic

machine common to all manufacturing processes.

Bonnett (1994) summarized the measures that can be taken by

those who design Electric Machines to improve the efficiency. These

measures result in High-Efficiency (Energy-efficient) Machine, which is

available at a premium. However, High-Efficiency Motors (HEM) and motor

systems are cost-effective. Experience from pilot studies for new and

replacement motors worldwide report that the additional upfront investment

cost of HEMs and motor systems is paid back within one to three years

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through savings in electricity bills. HEMs reportedly also work more reliably

and are more durable (as they operate at lower temperature).

The idea of Higher Efficiency cage induction motors, which could

be sold profitably at Standard efficiency motor prices, was conceived by

Brook Hansen. The research and development work for the attempt that has

taken the idea into the reality of the new ‘W’ series motors is detailed out by

Williams et al (1996).

International Energy Association (IEA) (2006) reports that there

was broad agreement among participating experts that: “The major barriers to

market penetration of efficient motor systems include: higher up-front capital

investment required for efficient equipment; unclear motor Efficiency

Standards, labels and efficiency classification; split incentives / diverging

motivations for purchasers (mostly Original Equipment Manufacturers) of

motor system components versus those who pay life-cycle energy bills (and

hence a lack of awareness of energy-saving and cost-saving potential of high

efficiency equipment); reluctance to replace operational systems with new

equipment that might adversely affect operations; focus of policies and

incentive programs on motors alone, rather than on systems”.

Therefore, it recommends a suite of policies and measures required

to overcome the known barriers. These include mandatory Minimum Energy

Performance Standards (MEPS); Measures to improve access to information

and market transparency (e.g., Labeling schemes, Standards harmonization

efforts); Financial and Non-financial incentives (e.g., audit programs,

calculation tools); Training and education; Organizational innovation by

companies and educational institutions (e.g., introduction of energy

management systems).

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To illustrate a few of the barriers for market penetration of efficient

motor drive systems, the Indian scenario is taken as an example. Table 1.1

gives the comparison of motor-efficiency values of various Indian Standards.

The details of the minimum efficiency levels for induction motors according

to Indian Electrical Equipment Manufacturers’ Association (IEEMA)

Standards and various Standards of the Bureau of Indian Standards (BIS) are

provided. If a Standard efficiency motor that adheres to IS 325/IS 7538 is

replaced by a more Energy-efficient motor that adheres to IS 12615, there is

energy efficiency improvement of one percentage point in the case of

0.37 kW rating and 3 percentage points in the case of 15 kW rating.

Additional efficiency improvement may be obtained by using Energy-

efficient motors that adhere to the IEEMA 19 Standards. There is also some

confusion as to what is called an Energy-efficient motor. While IS 12615

requires higher efficiency than IS 325/IS 7538, a motor complying with it is

not normally called an “Energy-efficient” motor. The latter definition is

applied to those motors that comply with the IEEMA 19 Standard, also

denominated EFF1 Standard.

Internationally, there are Standards for even higher efficiency

levels. The International Electro-technical Commission (IEC) Standards

classify motors into four classes: Standard efficiency (IE1), High efficiency

(IE2), Premium efficiency (IE3), and Super premium efficiency (IE4).

Figure 1.2 depicts the proposed Internationally harmonized energy efficiency

classes in IEC 60034-30 (SEEM, 2007). Standards for Energy Efficiency in

Electric Motor Systems (SEEEM) is an independent, multi-stakeholder effort

to promote rapid market diffusion of High Efficiency Motor component

technologies and systems worldwide. One measure widely promoted by

SEEEM for improving the efficiency of the electric motor itself is through

Energy Efficiency Standards applicable to new motors). The IE1 Standard is

somewhere between IS 325/IS 7538 and IS 12615, whereas IE2 is similar to

the IEEMA 19 Standard.

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Table 1.1 Comparison of motor-efficiency values of various Indian

Standards

Sl. No. Rating in kW IS 325/ IS 7538

IS 12615 IEEMA 19 /

EFF1

1 0.37 64.0 65 73.0

2 0.55 69.0 70 78.0

3 0.75 71.0 73 82.5

4 1.10 73.0 75 83.8

5 1.50 76.0 77 85.0

6 2.20 79.0 80 86.4

7 3.70 83.0 84 88.3

8 5.50 84.0 85 89.2

9 7.50 85.0 87 90.1

10 9.30 85.5 87 90.5

11 11.00 85.5 88 91.0

12 15.00 86.0 89 91.8

Applicability conditions:

IS 325 (1996) : Standard for three phase induction motors for general purposes

IS 7538 (1996) : Standard for three phase induction motors for agricultural purposes

IS 12615 (1989) : Standard for Energy-efficient Induction motors

IEEMA 19/EFF1 (2000): Standard for Energy-efficient Induction motors

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Figure 1.2 Proposed Internationally harmonized energy efficiency classes in IEC 60034-30

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SEEEM (2007) expected that according to the new IEC efficiency

classes and time line for countries to have mandatory Minimum Energy

Performance Standards (MEPS) agreed upon, India, China, Brazil, Costa

Rica, Israel, and Taiwan were expected to stick to Standard efficiency design

by 2008 and Europe is expected to stick to the High-efficiency Standard by

2011.

Until now, the various measures related to efficiency improvement

in motors were discussed. The need for energy conservation is a motivating

factor to explore various possibilities for energy efficiency reduction and the

ways to avoid them. This thesis tries to analyse possible ways of efficiency

improvement in an electric motor that forms the major component of the

electric drive system and the basic machine common to all manufacturing

processes today.

1.3 MOTIVATION FOR THE THESIS

Central Electricity Authority, India (CEA) (2007) shows that in

India, during 2003-04, the amount of electricity consumed in industry and

agriculture was 154 TWh and 114 TWh respectively, out of a total of

524 TWh. Both are expected to increase substantially, with consumption

forecast to be 318 TWh and 187 TWh for 2011-2012 in these sectors

respectively.

Bonnett (1993) illustrated that the ability to increase generating

capacity is a very difficult and slow process. It is estimated that a typical

electric power plant will cost $3-4 billion and will require 12 to 15 years to

implement. Hence, he opined that even if the cost of energy can be controlled,

the need for additional capacity will continue to drive the need for

conservation and more efficient products at an accelerated pace during the

next decade. Even today, the time for building up a generating capacity

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remains almost the same and the amount of money to be spent to develop a

new generating capacity is still higher. Thus, in order to cater to growing

demand, there exists a need for conservation and more efficient products.

Energy Asia (2006) provides the statistics that in the Indian

agricultural sector, energy is consumed mainly for pumping water. Mathur

(2007) provides the statistics that in India, about 12 million electrical pump-

sets used in agriculture consume 28% of its electricity. And in Indian

industry, about 70 % of the total electricity demand is in electric drive

systems. Hence, motors are the largest single consumers of electricity in both

these sectors.

Even a small improvement in the operating-efficiency or avoidance

of unwarranted energy consumption by quality assurance of motors, which

form the major component of the motor-drives or pump systems, will

significantly contribute towards energy efficiency improvement of the system,

to enormous energy conservation and can lead to reduction of green house gas

emissions. This thesis analyses possible ways of unwarranted efficiency

reduction in electric motor, which forms the major component of the electric

drive system as well as the basic machine common to all manufacturing

processes today. It proposes a few non-traditional approaches for operating-

efficiency improvement in them to achieve the original operating-efficiency

level achieved through the original design or, in certain possible cases, a

higher operating-efficiency level.

A few of the possible means of efficiency reduction, life-time

reduction and undesirable performance change occur in the three phase

squirrel cage induction motors due to improper windings. They are:

Custom-designed three phase squirrel cage induction motors

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Rewound three phase squirrel cage induction motors operating

at end-user’s site.

Before, proceeding to discuss further, it is better to review the

relationship that exists between motor winding variables and performance of

the motor. These are some of the fundamentals necessary for the measures

dealt with in this thesis to avoid unwarranted energy consumption, to achieve

efficiency improvement by making the motor attain the original operating-

efficiency level arrived at through design or by achieving operating-efficiency

levels higher than the Standard efficiency design level (prescribed by BIS or

IEC Standards) in three phase squirrel cage induction motors.

1.4 RELATIONSHIP BETWEEN MOTOR WINDING VARIABLES AND PERFORMANCE

Hasuike (1983) describes 12 variable elements, which affect the

improvement in Efficiency of a 3.7 kW, three phase cage induction motor.

“The variable elements are: stator bore, length of the stack, air gap length,

diameter of the stator conductors, number of stator conductors per slot, size of

the stator slot, material of the rotor bar, size of the rotor bar, length of stator

coil end-connection, size of the end ring, the grade of electrical steel sheets,

the friction and windage losses”.

If the motor was designed according to an efficiency level (such as

Standard efficiency or High efficiency) at the design stage, the designer has

already specified all the variables. A change in the specified value of winding

variable in the form of diameter of the stator conductor, number of stator

conductors per slot, number of parallel circuits in each phase may occur when

proper managerial procedures are not followed during manufacture or rewind.

Umans (1989) explains the fact that: “Induction motor design is an

integrated process and that it is not in general possible to adjust one motor

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design parameter (such as the winding turns distribution) without changing a number of performance parameters (Torque, Efficiency, etc.)”.

Hasuike (1983) has studied, by design computations, the effect of

change in the winding variables individually from the original design and its

effect on the performance of the motor of 3.7 kW rating. The graphs provided

by Hasuike (1983) depicts that a decrease in the stator conductor size will

result in decrease in efficiency, space factor, locked rotor current and starting

torque; whereas increased heating occurs; while power factor remains almost

constant. A decrease in the number of stator conductors per slot will result in

a decrease in power factor, efficiency and stator conductor’s space factor. It

could also be deciphered that there is an increase in the locked rotor current,

starting torque and operating temperature, when there is a reduction in the

number of stator conductors in each slot than the original design.

Umans (1989) elaborates that “…if the motor was not designed for

optimal efficiency, increase in conductor area during a rewind may, in fact,

improve the efficiency. This will result from well understood phenomenon.

Perhaps, the motor has been rewound with the same turns distribution, but,

with larger wire size (resulting in lower winding resistance and hence lower

ohmic losses). In this case, the result will simply be an improvement in

efficiency…”.

1.5 PERFORMANCE REDUCTION DUE TO IMPROPER

WINDING

This thesis deals with undesirable performance changes that occur

in:

Custom-designed three phase squirrel cage induction motors

Rewound three phase squirrel cage induction motors operating

at end-user’s site

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1.5.1 Performance Reduction in Custom-Designed Motors

While manufacturing motors of regular designs, the stators in the

manufacturing line are compared with a standard stator, during Surge

Comparison Test (SCT), to check that the winding in the manufactured stator

is exactly the same as the winding present in the standard stator. The other

routine tests carried out on the stator under test will, then, assure that the

stator produced will have the same winding parameters as per the designer’s

specification to the winder. The surge comparison test needs a standard stator

as a pre-requisite for comparison. However, in a custom-designed motor, this

is not possible. Hence, the quality of stator winding of a custom-designed

motor cannot be assured thoroughly.

Further, the research scholar could not find a method in the

reported literature to select a standard stator from among a consignment of

stators in the manufacturing line. Such a method would be of much

significance when winding work is sub-contracted and when preference for

low winding cost is dominant in the market. Hence, as of now, SCT on

custom-designed motors will be useful only to detect any winding

dissymmetry. It will not be able to ensure that the stator winding adheres to

designer’s specification.

Actually, there might have been a deviation in the winding

configuration from the value of winding variable arrived at by the designer,

which might have led to performance reduction. Even after contemporary

end-of-line manufacturing test, a motor with a value of winding variable

different from the designer-specified value may pass unnoticed. In fact, the

efficiency and life achieved could be better in a motor with proper winding

than that obtained in a motor with improper winding.

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It may be thought that the manufacturer can develop a model

motor, test it and then start the manufacture of custom-designed motors.

However, this will take a lead time. Further, it is not possible to have a

benchmark motor, especially, when winding is sub-contracted by the

manufacturer with the intent of reducing overheads.

Hence, it is good to discuss the need for regulatory compliance tests

in custom-designed three phase cage induction motors to assure their quality.

It may be found from the personal communication with the Senior Design

Manager, Large Machines division, Kirloskar Electric Company Limited that

such a method will be of value when custom-designed motors are

manufactured (Prakash 2009a).

1.5.2 Operating-Efficiency Reduction in Rewound Motors

One of the items in the SEEEM (2006) list of potential energy

efficiency improvements refers to poor rewinding practices.

Darby (1986) discusses why efficiency reduction occurs during

rewind of motors including conductor size reduction and drop in number of

turns. He reports that “there are several ways to reduce the time required for

winding which reduces the cost of rewinding for those who only look at the

price of a rewind. If a smaller diameter wire is used, the wires can be inserted

in the slots much more easily and quickly, but this is a very detrimental

practice and should not be permitted. And as the cross-sectional area of the

conductor is reduced, the resistance will go up and the I2R losses will go up. It

raises stator losses with no corresponding beneficial effect. Another bad

winding practice is to drop turns. This makes winding easier and faster, and it

is true that it reduces winding resistance, but it increases the starting current,

starting torque and full-load torque and will increase stator core loss due to

increased flux densities”.

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Darby (1986) shares his experience that “the original winding was

usually duplicated until we began to look more closely at motor efficiency.

The practice of verifying the winding data in each motor that were rewound

started several years ago. The verification is done by calculating the flux

densities in the iron at the tooth, the air gap and the back iron. The circular

mills per ampere of the winding, the slot space available and the slot space

required are calculated. The present data was also compared with the master

file of the original winding data, which we receive from Electrical Apparatus

Service Association, which is our trade association...”.

However, the Indian scenario even today is quite different. No such

practice of verifying the winding data in each motor that is rewound exists

with most of the rewinders even today.

Energy Asia (2006) estimates that 50% of the operational motors in

Indian industry are Rewound motors. The agricultural power tariff is highly

subsidised and in certain states of India, it is free of charge. Hence, farmers

find little incentive for efficient use of electricity. Sant and Dixit (1996) report

that the end-use efficiency of agricultural pump-sets is dismally low in India.

Normally, in Indian small and medium scale industries as well as agriculture,

rewinding is done by winders who are not well-informed about the

significance of various winding variables. They normally rewind as per the

winding that was present in the ‘burnt’ motor. The commercially available

motors of Standard efficiency designs (not of Energy-efficient design) are as

per design for lower capital cost and not for lower life cycle costs. Moreover,

many Rewound motors of Standard efficiency design operate with windings,

which do not even stick to the winding as per design that minimised capital

cost, let alone the winding design that would lower life-cycle cost. Further,

preference for low cost is dominant in the market, while opting for rewinding.

Hence, rewinders make compromises in the quality of rewinding.

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Typically, either the conductor cross-sectional area is less or the number of

turns fewer than required by the original design. Such deviation in winding

data from its designer’s specifications will result in performance reduction,

which includes efficiency reduction. Thus, there is an unnecessary increase in

the Consumption of Energy. Hence, there is a significant potential for

operating-efficiency improvement in rewound motors by rectifying such

improper winding.

The above discussions on improper rewinding will be applicable to

motors with three phase windings irrespective of their original design. Hence,

such reductions take place in Rewound motors of both Standard efficiency

and Energy-efficient designs.

1.6 NECESSITY OF NON-DESTRUCTIVE APPROACHES

Two possible means of operating-efficiency reduction in three

phase squirrel cage induction motor were detailed in the earlier section.

Rectification to avoid the efficiency and life-time reductions that occur in the

motors requires:

The value of winding variables in the Custom-designed

motors need be ensured in the manufacturing line to be as per

the designer’s winding specification.

The winding data in a Rewound motor operating at the end-

user’s premises need be non-destructively determined.

The winding variables / winding data that have to be ascertained

include: (i) Type of the winding, (ii) Number of Layers, (iii) Coil Span,

(iv) Number of parallel circuits in each phase, (v) Number of turns per coil

and (vi) Conductor cross-sectional area.

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Of the above-said winding parameters, Type of winding, Number

of layers, and Coil span can be ascertained by observing the winding

overhang.

Conventional Quality assurance tests employed by motor

manufacturers include High potential test, Surge comparison test and

Resistance measurement test.

High potential test is useful to determine the insulation strength of

the winding.

Moses and Harter (1957) describe how Surge test can compare the

adjacent phases of motor windings. Zotos (1994) discusses about an

electronic and portable device “Surge Tester” used to locate insulation faults

and winding dissymmetry. It discusses about motor failures due to steep

fronted switching surges, and the need for surge protection.

Surge Comparison Test (SCT) cannot give any quantitative

information and at its best, it can only indicate whether the phases compared

are similar or not. The pre-requirement for the test to be carried out, in the

manufacturing line, on a stator to assure the quality of its winding is a

standard stator with winding variables as per design specifications. The

criterion to assure the quality is that the stator under test be identical to the

standard stator. However, in the two cases under consideration in this thesis, it

is difficult, if not possible, to have a standard stator.

IEEE Standard 118 (1978) presents methods of measuring electrical

resistance that are commonly used to determine the characteristics of electric

machinery and equipment. Resistance per phase of the winding depends upon

Number of turns per coil, Number of parallel paths, Number of in-hands and

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Conductor cross-sectional area. However, simple resistance determination

will not be sufficient to determine each of these winding data.

The inductance measurement on a wound stator cannot be

performed, as there is no accepted Standard for inductance measurement of

wound machines. Personal correspondence by the research scholar with

Technical support specialist of Electrical Apparatus Service Association

(EASA) puts forth the fact (Prakash 2009b).

Visual inspection alone cannot accurately determine the conductor

cross-sectional area present in the winding.

Combined resistance measurement and visual inspection is also not

enough to determine the unknown winding data under consideration in an

induction motor stator, whose winding configuration may have Number of

parallel circuits in each phase more than one.

Reduction in performance, which includes efficiency, due to

improper winding can, then, be detected only by performing end-of-line tests

carried out by machine manufacturers. IEEE Standard 112 (2004) covers

instructions for conducting and reporting the more generally applicable and

acceptable tests of poly phase induction motors. The end-of-line tests

recommended are load test on low horse power motors and pre-determination

tests on motors of large power ratings. However, these tests can be performed

only after the entire machine is assembled.

The other possible option for determination of the above said

winding data is by physical examination involving destruction. Such invasive

procedure can only be adopted by rewinders to determine the winding data of

a ‘burnt’ motor. However, this procedure is not advisable for the applications

considered in this thesis, and hence, cannot be adopted.

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Hence, by conventional practice and from literature, as far as the

knowledge of the research scholar, a way to determine non-destructively the

Number of Turns per Coil, Conductor cross-sectional area and Number of

parallel circuits in each phase is not available.

Walters (1999a) describes that, in typical 1.5 kW and 15 kW

motors, copper loss (and particularly the stator copper loss) dominates.

Therefore, it is imperative to develop Non-destructive methods to

assure the quality of Custom-designed motors, as well as to ascertain the

actual Number of Turns per coil (NTPC), Conductor Cross-sectional area

(CA) and Number of parallel circuits in each phase (NPCP) of stator winding

of Rewound low horse power three phase squirrel cage induction motors.

1.7 PROBLEM STATEMENT

This thesis, based primarily on experimental work, aims to avoid

unwarranted Energy consumption and performance deterioration caused

By improper windings, which may ensue during manufacture,

in Custom-designed low horse power three phase squirrel cage

induction motors.

By improper windings in Rewound low horse power three

phase squirrel cage induction motors, operating at end-user’s

site.

The aims are accomplished respectively by

Evolving an approach to assure the quality of Custom-

designed three phase squirrel cage induction motors non-

destructively, before the assembly of the motor, as the stator

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passes through the manufacturing line. The solution provided

by this approach is to choose a standard stator, which is a pre-

requisite for conducting Surge comparison test by using a

proposed method that includes a forward algorithm. This

standard stator will then be used for performing Surge

comparison test on other stators of the custom-designed stator

consignment. By adopting this approach, only the stators that

have the Number of Turns per coil, Conductor cross-sectional

area and Number of parallel circuits in each phase of the

winding adhering to the winding specification provided by the

designer, will pass through the manufacturing line for final

assembly.

Evolving an approach for non-destructive analysis to detect

improper winding in Rewound three phase squirrel cage

induction motors of a particular rating operating at low

efficiencies at the end-user’s site. The solution provided by

this approach is to determine the Number of Turns per coil,

Conductor cross-sectional area and Number of parallel circuits

in each phase of the winding in the stator, by means of a

proposed reverse algorithm. The winding data ascertained, are

compared with the manufacturer’s original design data

supplied to major service providers. If there are deviations,

then necessary rectification can be done by adopting one of

the suitable corrective measures suggested by this approach. A

corrective measure is to improve the efficiency of the motor to

the operating-efficiency level achieved through the original

design by rewinding, so that the winding adheres to the

original design data. Another corrective measure in the case of

Standard efficiency design is to improve the

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operating-efficiency of the motor above the original design

level, by rewinding the motor using a conductor area higher

than the designer-specified conductor cross-sectional area in

the original data. Care should be taken, however, to follow

recommended practices for rewinding.

1.8 METHODOLOGICAL BASIS

The non-destructive methods employed by the proposed approaches

should essentially deal with the three unknowns i.e. Number of Turns per coil

(NTPC), Conductor Cross-sectional area (CA) and Number of parallel circuits

(NPCP) in each phase of the stator winding.

For quality assurance of the three unknown winding variables or for

ascertaining that the three data are as per original winding data, three

independent relations / constraints involving those variables / data are needed.

The three relations are:

The relation between the EMF measured in the proposed EMF

tests and its theoretical relation to the Number of Turns Per

coil (NTPC), Number of Parallel Circuits in each Phase

(NPCP).

The relation between the resistance measured per phase / line

during the resistance measurement test and its theoretical

relation to the NTPC, Conductor cross-sectional Area (CA)

and the NPCP.

The constraint in the form of the CA, though approximate,

obtained from visual inspection of the stator winding

overhang conductors.

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The NPCP can assume only possible integer values depending upon

the number of poles and number of layers of the winding. The NTPC can

assume only integer values. The winding conductor area is specified by the

Standard for the winding conductor that is in vogue in the region of

manufacture / rewind of the motor. The conductor area also takes only

discrete values. Given the conditions, a unique solution is obtained from the

three relations / constraints. Necessary mathematical proof, which is

elaborated in the Results and Discussion chapter (Chapter 6), is developed to

show the same. Hence, in this case, the values of the three unknown variables

or the three winding data can be determined.

1.9 ORGANISATION OF THE THESIS

The chapters of this thesis are organised in the following way:

Chapter 1 deals with the various possibilities of efficiency

reduction / performance deterioration, necessity of non-destructive

approaches for finding the solution to the problem, the problem statement and

the methodological basis for the methods in the approaches.

Chapter 2 deals with the Review of Literature, the research scholar

has made prior to proposing the non-traditional efficiency improvement

measures and the proposed non-destructive methods that are imperative for

the measures.

Chapter 3 deals about the various tests necessary for: (i) Non-

destructive method to determine the standard stator to assure the quality of

custom-designed low horse power three phase squirrel cage induction motors.

(ii) Non-destructive method to be employed to determine the unknown

winding in a motor with low operating-efficiency at the end-user’s site.

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Chapter 4 deals with the approach to assure the quality of custom-

designed three phase squirrel cage induction motor. This approach includes a

method to determine the standard stator for Surge comparison test of a

custom-designed three phase cage induction motor consignment.

Chapter 5 deals with the proposed approach for operating-

efficiency improvement of three phase squirrel cage induction motor. This

approach includes a method for determination of unknown winding data

present in operational motors (brand new / rewound) in the field.

Chapter 6 provides the mathematical proof for the theoretical

validity of the method for determination of standard stator in the Quality

assurance approach and the method for determination of the three unknown

winding data in Rewound motors. It presents the results of the experimental

work of the proposed measures for Quality assurance and discusses the same.

It also presents the results of the experimental work to determine the winding

data present in motors and discusses corrective measures for unwarranted

efficiency reduction in the motors operational in the field. Further, simplified

cost benefit analysis for the end-user, as a result of the proposed efficiency

improvement measure in three phase induction motors, is also discussed.

Chapter 7 is provides the conclusion for the research work carried

out within the scope taken up for this thesis. It gives the recommendations to

be followed to achieve energy efficiency in three phase induction motors. The

future scope of the work is also provided.