06 Chapter 1
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Transcript of 06 Chapter 1
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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.