PhD viva voce Presentation

INVESTIGATIONS ON FAULT DETECTION OF
INVERTER FED THREE PHASE SQUIRREL CAGE
INDUCTION MOTOR
by
S.NAGARAJAN
(Reg. No. 2006319721 )
Part Time Research Scholar
Under the guidance of
Dr.S.RAMA REDDY,
Professor,
Dept. of Electrical and Electronics Engineering,
Centre for Collaborative Research with Anna University,
Jerusalem College of Engineering.
1

INTRODUCTION
Induction Motor for many years has been
regarded as workhorse in industrial applications.
In the last few decades induction motor has
evolved from being a constant speed motor to
variable speed, variable torque machine.
When the application requires large power and
torque specifications, the usage of induction
motor comes into demand.
2

With increased advantages and steady
responses, induction motor has acquired an
essential place in industrial applications.
With growing demands, a fault tolerant drive
system is the need of the hour.
So the fault detection in the machine and the
advantages of fault tolerant voltage source
inverter becomes more prominent and
necessary to enhance operations.
3

LITERATURE SURVEY
• N.M.Elkasabgyand,et. al (1992) dealt with broken bar and its detection
technique.The cross section of the machine was modeled with Finite
elements, and the field distribution and mechanical performance were
computed using a non linear complex stead state technique. Experimental
results show that analysis of the voltage induced in an external search coil
is adequate to detect the presence of broken bar.
• R.Burnett, et.al (1995), used a signal processing technique which obtains
the time frequency representation of multi-component non-stationary
signals to detect the presence of the non-stationary components within the
transient line current of a 3 phase induction motor supply which are
indicative of rotor faults such as broken rotor bars.
• A.Bentounsi,et. al (1998), proposed a local approach to tackle the problem
of breaking bars and end rings of squirrel cage in induction machines
based mainly on the signature of the local variables, such as the normal
flux density. This allows a finer analysis ,by use of a finite element based
simulation.
4

Literature Survey (contd.)
• J.F.Bangura,et. al (1999) computed the characteristic frequency
components which are indicative of rotor bar and connector breakages in
the armature current waveforms and developed torque profiles. He used
MCSA technique for the diagnosis of rotor breakages in induction
motor and Finite Element Method to calculate the parameters and
modeled using State Space Modeling approach.
• John.F.Watson ,et. al (1999) described how commercial finite element
packages may be used to simulate rotor faults and hence enhance the
capability of practical condition monitoring schemes. Accurate models of the
machine under faulted conditions were developed using both fixed mesh
and time-stepping finite element packages.
• N.Bianchi,et. al (1999) presented a comparison between two different finite
element analysis of three phase induction motors. The first method is
based on the equivalent circuit of the motor and the second method is
based on the field solution. Both approaches worked with 2D discretized
domain and implemented in Ansoft Maxwell and in Cedrat Flux 2D.
5

• Subhasis Nandi, et. al (2001) presented the effect of pole pair and rotor slot
numbers on the presence of different harmonics under healthy and
eccentric conditions. Other harmonics due to slotting, saturation and
asymmetry can also be predicted. But this simulation technique was not as
accurate as Finite Element Method.
• B. Mirafzal ,et. al (2004) presented new technique based on rotor magnetic
field space vector orientation which is used to diagnose broken-bar faults in
induction machines operating at steady state. In this technique stator
currents and voltages are used as inputs to compute and subsequently
observe thr rotor magnetic field orientations which has a more significant
“swing-Like” pendulous oscillations in case of broken bar faults than in
healthy operation.
• Jee-Hoon Jung,et. al (Dec 2006), proposed a corrosion rotor bar model
derived from electromagnetic field theory and simulated using Matlab
Simulink.the leakage inductance and resistance of a roto bar varies when
the roto bar rusts.From the proposed corrosion model, Motor current
signature analysis can detect the fault of a corrosive rotor bar as the
progress of a rotor bar fault
6

• Li Weili ,et. al (2007) developed the foundations of a technique for
diagnosis and characterization of effects of broken bars in squirrel cage
induction motors based on the time-stepping coupled finite-element
approach. These studies are performed by using the model to compute
healthy case, one broken bar fault and two adjacent broken bar fault
performance data, which contain stator starting current wave forms, the
current density on the bar, the magnetic force distribution on the rotor bar
and the distribution of magnetic field.
• Gennadi Y.Sizov,et. al (2009) described the effect of adjacent and
nonadjacent bar breakages on rotor fault diagnostics in squirrel-cage
induction machines. It also described how nonadjacent bar breakages result
in the masking of the commonly used fault indices and other problems and
the solution to overcome these problems.
• Manuel Pineda Sanchez,et. al (2010) proposed the optimization of the FrFT
to generate a spectrum where the frequency-varying fault harmonics
appears as a single spectral lines and therefore facilitate the diagnostic
process.
• T.W.Preston,et. al (1988) conveyed that the equivalent circuit approach
usually gives adequate predictions of torque and current but gives no
information on flux distribution. This deficiency was overcome by numerical
approach which uses 2D, nonlinear, time-stepping finite element method for
excitation from a constant voltage source. Comparison of stator current for
no load and other load conditions show good agreement with test values on
a large induction motor .
7

• A.J.Marques Cardoso, et. al (1997) presented the on-line detection and
location of inter-turn short circuits in the stator windings of three-phase
induction motors using a noninvasive approach, based on the computer-
aided monitoring of the stator current Park’s vector approach.
• S. Balamurugan,et. al (2004) dealt with the analysis of induction motor
behavior during transient periods using coupled electric circuit with 2D finite
element electromagnetic field analysis. The designed geometric dimension
of induction motor is modeled in the finite element domain and the transient
performance are found at the starting of motor with no load, the operation of
asymmetrical excitation of the stator and turn to turn fault condition .
• Ali.M.Osheiba, et. al (2006) presented an accurate mathematical model
for diagnosis of stator winding faults in induction motors. The model is
based on d-q axis theory and valid for both the transient and steady state
conditions. The model was not act well under no-load condition so the
simulation results were taken under loading conditions .
8

• B.Vaseghi,et. al ( 2008) presented a dynamic model for IM under inter-turn
insulation failure fault, derived using reference frame theory . Finite element
analysis is used for parameter determination of the machine in healthy and
faulty condition.
• S.E.Zouzou,et. al ( 2010) proposed the use of Partial Relative Indexes (PRI)
as a new fault indicators to ameliorate the reliability of fault detection task
and uses MCSA method.
• Michael J.Devaney,et. al (2004) monitored the induction motor current and
detecting bearing failure. Monitoring the induced current frequencies to
detect the characteristic bearing failure involves supporting the more
dominant power system harmonics and then analyzing the remaining
current spectrum.
• Irahis Rodriguez,et. al (2006) dealt with the application of CSA for detection
of rolling element bearing faults on induction motor by monitoring the stator
current.A fault model has been analyzed which considers fault related
airgap length variation.complete exprssions for the frequency content of the
stator current are obtained for the three types of fault.
• S.Williamson,et. al (1991) described about the conventional equivalent
circuit model to determine the equivalent circuit components for a three
phase squirrel cage induction motor using finite element model. The use of
minimal models leads to a fast execution time. The method used separate
finite element models for rotor and stator.
9

• William T. Thomson, et. al (2001) focused on the industrial application of
motor current signature analysis (MCSA) to diagnose the faults in the three-
phase induction motor drives.
• John.F.Bangura, et. al (2003) developed the foundations of a technique for
detection and categorization of dynamic, static eccentricities and bar,
end-ring connector breakages in squirrel-cage induction motors using Time-
Stepping Coupled Finite-Element–State-Space method to generate fault
case performance data, which contain phase current waveforms and time-
domain torque profiles .
• A new artificial immune based support vector machine algorithm for fault
diagnosis of induction motors was proposed by J.Aydin,et. al (2007).The
new feature vector is constructed based on parks vector approach. The
phase space of this feature vector is constructed using non linear time
series analysis.Broken rotor bar and stator short circuit faults are classified
in combined phase space using support vector machines.
• O.A.Mohammed,et. al (2007) examines the behavior of three phase
induction motors with internal fault conditions under sinusoidal supply
voltages. Discrete wavelet transform is used to extract the different
harmonic components of stator currents.
10

• Barain welchko et al (2004) compared the many fault tolerant three phase
ac motor drive topologies for inverter faults of switch short or open circuits,
phase leg short circuits and single phase open circuits.
• Shengming Li et al (2006) proposed fault tolerant operation strategies for
three level neutral point clamped pulse width modulation inverters in high
power safety-critical applications.
• André Mendes et al ( 2007) presentd the results of an investigation
regarding the thermal behavior of a three-phase induction motor when
supplied by a reconfigured three-phase voltage source inverter with fault-
tolerant capabilities. For this purpose, a fault tolerant operating strategy
based on the connection of the faulty inverter leg to the dc link middle point
was considered. The experimentally obtained results show that, as far as
the motor thermal characteristics are concerned, it is not necessary to
reinforce the motor insulation properties since it is already prepared for such
an operation.
• Aliyan chen et al (2007) presented on the fault tolerant potential of multilevel
inverters with redundant switching states such as cascade multilevel
inverters and capacitor self voltage balancing inverters.
11

• Jesus M. Corres, et. al (2006) proposed a new method to detect the
negative effects of a particular unbalanced voltage and inverter harmonics
on the performance of an induction motor using fiber sensors. A new in-line
fiber etalon accelerometer has been designed.
• Sayeed Mir et al (1998) presented direct torque control (DTC) of induction
machines used the stator resistance of the machine for estimation of the
stator flux. Variations of stator resistance due to changes in temperature or
frequency make the operation of DTC difficult at low speeds. A method for
the estimation of changes in stator resistance during the operation of the
machine is presented. The estimation method is implemented using
proportional-integral (PI) control and fuzzy logic control schemes. The
estimators observe the machine stator current vector to detect the changes
in stator resistance. The performances of the two methods are compared
using simulation and experimental results. Results obtained have shown
improvement in DTC at low speeds.
12

• Chan et al (1999) described a generalized model of the three-phase
induction motor and its computer simulation using MATLAB/SIMULINK.
Constructional details of various sub-models for the induction motor were
given and their implementation in SIMULINK is outlined.
• Benbouzid et al (2000) introduced a concise manner the fundamental
theory, main results, and practical applications of motor signature analysis
for the detection and the localization of abnormal electrical and mechanical
conditions that indicate, or may lead to, a failure of induction motors. The
paper is focused on the so-called Motor Current Signature Analysis (MCSA)
which utilizes the results of spectral analysis of the stator current.
• Bin Huo et al ( 2001) presented simple stator fault detector for ac motors,
based on the TMC320C243 DSP controller is presented. The detector
provides compensation of the constructional and supply voltage
imbalances, and senses the ripple of the compensated instantaneous
power. The power ripple is indicative of such stator faults as open and short
circuits in the stator winding . 13

• Don-Ha Hwang et al ( 2003) described the distribution characteristics of
switching the surge voltage in the stator windings of an induction motor
driven by IGBT PWM inverter. To analyze the voltage distribution between
turns and coils of the stator winding, an equivalent circuit model of the
induction motor including feeder cable is proposed and high frequency
parameters are computed by finite-element analysis.
• Mendes et al (2003) presented comparative analysis involving several fault
tolerant operating strategies applied to three phase induction motor drives.
The paper exploits the advantages and the inconveniences of using
remedial operating strategies under different control techniques, such as the
field oriented control and the direct torque control.
14

• Yushaizad Yusof et al ( 2003) presentd accurate stator flux estimation for
high performance induction motor drives is very important to ensure proper
drive operation and stability. Unfortunately, there is some problems
occurred when estimating stator flux especially at zero speed and at low
frequency. Hence a simple open loop controller of pulse width modulation
voltage source inverter (PWM-VSI) fed induction motor configuration is
presented. By a selection of voltage model-based of stator flux estimation, a
simple method Using artificial neural network (ANN) technique is proposed
to estimate stator flux by means of feed forward back propagation algorithm.
In motor drives applications, artificial neural network has several
advantages such as faster execution speed, harmonic ripple immunity and
fault tolerance characteristics that will result in a significant improvement in
the steady state performances. Thus, to simulate and model stator flux
estimator, Matlab/Simulink software package particularly power system
cblock set and neural network toolbox is implemented. A structure of three-
layered artificial neural network technique has been applied to the proposed
stator flux estimator. As a result, this technique gives good improvement in
estimating stator flux which the estimated stator flux is very similar in terms
of magnitude and phase angle if compared to the real stator flux. [37]
• Xiaomin et al (2004) presented a unique design for flying capacitor type
multilevel inverters with fault tolerant features. This paper will also
discuss the capacitor balancing approaches under fault conditions. [38]
15

• Liag Zhou et al (2005) presented fault tolerant control method for hexagram
inverter motor drive. This proposed method consists of fault detection, fault
isolation and post fault control method.[39]
• Luís Alberto Pereira et al (2005) presented the development and the
practical implementation of a system for detection and diagnosis of interturn
short-circuits in the stator windings of induction motors. Motor Current
Signature Analysis (MCSA) and Fuzzy Logic techniques are utilized in order
to achieve that. After a brief description of the MCSA, the causes of short
circuits are discussed and characterized with frequency relationships and
frequency spectra.[40]
• Martin Blodt et al (2006) presented the detection of small torque oscillations
in induction motor drives during speed transients by stator current analysis.
The proposed solution is time-frequency signal analysis. This work
particularly deals with the extraction of fault indicators that could be used in
a permanent and automatic condition monitoring system.[41]
16

• Jee-Hoon Jung et al (2006) described, an online induction motor diagnosis
system using motor current signature analysis (MCSA) with advanced
signal-and-data-processing algorithms is proposed. MCSA is a method for
motor diagnosis with stator-current signals. The proposed system
diagnoses induction motors having four types of faults such as breakage of
rotor bars and end rings, short-circuit of stator windings, bearing cracks, and
air-gap eccentricity. Therefore, advanced signal-and-data-processing
algorithms are proposed.
• Biswas et al (2009) dealt with harmonic analysis of motor current
signatures under different fault conditions of medium and high power
Variable Frequency Drive (VFD) systems. Computer simulation of a VSI fed
induction motor based on constant voltage/frequency (V/f) operation is
implemented using Powersim (PSIM) simulation software. Frequency
response characteristics of motor currents are compared to analyze
fault conditions in motor drive system.
17

• Debmalya Banerjee et.al (2009) proposed a CSI-fed induction motor drive
scheme where GTOs are replaced by thyristors in the CSI without any
external circuit to assist the turning off of the thyristors. Here, the current-
controlled VSI, connected in shunt, is designed to supply the volt ampere
reactive requirement of the induction motor, and the CSI is made to operate
in leading power factor mode such that the thyristors in the CSI are auto
sequentially turned off. The resulting drive will be able to feed medium-
voltage, high-power induction motors directly.
• Luigi Alberti et al (2011) described a set of experimental tests on a dual
three-phase induction machine for fault-tolerant applications. Different
winding configurations are investigated and compared in case of both open-
circuit and short-circuit faults. Experimental tests for each configuration are
reported at no-load and under load operating conditions.
• Marco Antonio Rodríguez-Blanco et al (2011) proposed a novel failure-
detection technique and its analog circuit for insulated gate bipolar
transistors (IGBTs), under open- and short-circuit failures. This
technique is applied to a three-phase induction motor (IM) drive system.
However, this technique required addition of extra voltage sensor in the
drive.
18

• Andrian Ceban et.al(2012) presented a new signature for detection of rotor
faults in induction motors, such as eccentricity and broken rotor bars, that
uses the external magnetic field analysis. The Proposed method is based
on the variations of axial flux density in the presence of these faults.
The low frequency part of the magnetic field spectrum is particularly
analyzed. The analysis is realized through a machine modeling based on
permeance circuit under eccentricity fault and also by machine modeling
based on coupled magnetic circuit theory under broken rotor bars fault. In
particular, an inverse stator cage induction machine have been used to
measure the bar currents under healthy and faulty cases.
• Bashir Mahdi Ebrahimi,et.al (2013) proposed new analytical method for
the calculation Ohmic and core losses in induction motors under broken
bar fault. In this method, new coefficients are introduced to consider non-
sinusoidal distribution effects of flux density due to bar breakage. Then,
core losses of induction motors in this condition are estimated. In order to
calculate Ohmic losses in faulty induction motors, impacts of the bar
breakage on the harmonic components of the stator currents are taken into
account. In this modeling approach, the effects of the nonlinear
characteristics of the core materials, stator, and rotor slots are taken into
account. The simulation results are verified by the 2-D time stepping finite-
element method and experimental results.
19

RESEARCH GAP
• Leg swap module is not used for induction motor
drive. This work proposes leg swap module for
VSI fed induction motor drive.
• The control logic for Fault tolerant VSI is not
present in the literature.This work aims to develop
control logic for Fault tolerant VSI system
20

OBJECTIVES
• To detect the rotor broken bars in a three phase squirrel cage induction motor
using finite element model of the induction machine.
• To model and simulate CSI fed induction motor drive of the three phase
squirrel cage induction motor to analyze Various faults.
• To model and simulate VSI fed induction motor drive of the three phase
squirrel cage induction motor to analyze Various faults.
• To develop control logic for leg swap module.
• To model and simulate fault tolerant voltage source inverter under fault
condition.
21

MODULES
Broken bar fault
CSI-fed Induction motor drive
Fault tolerant VSI-fed Induction Motor drive
Hardware implementation
VSI-fed Induction motor drive
22

Investigations on Fault detection of inverter fed 3Φ squirrel cage induction motor
Real time experimental studies
Modeling of 3Φ squirrel
cage induction motor
Fault detection of 3Φ squirrel
cage induction motor
VSI fed induction motor
Rotor broken
bar fault
VSI fed IM
inverter fault
CSI fed IM
inverter fault
Fault tolerant
VSI fed IM
Simulation studies
TREE DIAGRAM OF THE PRESENT WORK
23

MODULE-1
Broken Bar
Fault analysis
24

SPECIFICATIONS OF THREE PHASE SQUIRREL
CAGE INDUCTION MACHINE
Rated Power - 22 kW
Rated Voltage - 415V
Rated Frequency - 50Hz
Rated Speed - 1458 rpm
Number of Poles - 4
Number of Stator Slots - 36
Number of Rotor Slots - 28
Slip - 0.028
Efficiency - 0.85
Power Factor - 0.88
25

ASSUMPTIONS FOR DESIGN OF INDUCTION MOTOR :
For 50Hz machine of normal design,
the value of Bg lies between 0.55 to 1.15 Wb/m2.
Therefore, Bg = 1.15 Wb/m2
For good overall design, L/τ = 1
Slots per Pole per Phase, qs = 3
Slot pitch, yss = πD/Ss = 25mm
Winding Factor, Kws = 0.955
Air-gap length, lg = 0.5mm
26

DESIGN DATA FOR INDUCTION MOTOR :
Shaft Diameter = 5.5 (output in W / rps)1/3 mm = 50mm
Main Dimensions:
D = Ssyss/π = 286mm
L = τ = πD/p = 225mm
Flux per pole, Фm = BavπDL/p = 0.02274Wb
Stator turns per phase, Ts = Es/4.44KwsfФm = 86turns
Stator conductors per slot, Zss = 6Ts/Ss = 16conductors
Ampere conductors per metre, ac = IzZ/πD = 22000A.cond./m
27

no radial ventilating duct, therefore nd and wd are neglected.
Gross iron length, Ls = L - nd wd = 0.225m
Net iron length, Li = kiLs = 0.2025m
Depth of slot, dss = d0s + d1s + h = 33mm
Depth of stator core, dcs = Acs/Li = 42mm
Outer diameter of the stator, D0 = D + 2 (dss + dcs) = 436mm
Rotor diameter, Dr = D – 2lg = 285mm
28

2D MESH MODEL FOR THREE PHASE SQUIRREL CAGE INDUCTION MOTOR
29

FIELD DISTRIBUTION UNDER FULL LOAD CONDITION
HEALTHY CONDITION
MAXIMUM FLUX : 0.0225Wb
31

FLUX DENSITY UNDER FULL LOAD CONDITION
HEALTHY CONDITION
MAXIMUM FLUX DENSITY :1.227 Wb/m²
32

TWO BROKEN BAR CONDITION
FIELD DISTRIBUTION UNDER FULL LOAD AND FAULTY CONDITIONS
MAXIMUM FLUX : 0.0348 Wb
Faulted Slots 33

FLUX DENSITY UNDER FULL LOAD AND FAULTY CONDITION
Faulted Slots
MAXIMUM FLUX DENSITY :1.374 Wb/m²
34

FIELD DISTRIBUTION UNDER FULL LOAD AND FAULTY CONDITIONS
FOUR BROKEN BAR CONDITION
MAXIMUM FLUX : 0.0428 Wb
35

FLUX DENSITY UNDER FULL LOAD AND FAULTY CONDITION
MAXIMUM FLUX DENSITY : 1.483 Wb/m² 36

SUMMARY OF FLUX FUNCTION
Condition Flux Function(Wb) Percentage Change
No Load
Healthy 0.0023 -
2 broken 0.0025 8.69
4 broken 0.0032 39.13
6 broken 0.0034 47.82
8 broken 0.0035 52.17
Half Load
Healthy 0.0115 -
2 broken 0.0131 13.91
4 broken 0.0141 22.60
6 broken 0.0157 36.52
8 broken 0.0191 66.08
Full load
Healthy 0.0229 -
2 broken 0.0348 51.96
4 broken 0.0428 86.89
6 broken 0.0432 88.64
8 broken 0.0435 89.95 37

GRAPHICAL REPRESENTATION OF FLUX FUNCTION
The value of flux function increases as the number of broken bars
increases from 2 to 8.
Similarly, there is a increase in the percentage change as the
number of broken bars increases. 38

SUMMARY OF FLUX DENSITY
Condition Flux Density(Wb/m²) Percentage Change
No Load
Healthy 0.1229 -
2 broken 0.1250 1.70
4 broken 0.1298 5.61
6 broken 0.1363 10.90
8 broken 0.1401 13.99
Half Load
Healthy 0.8532 -
2 broken 0.9061 6.20
4 broken 0.9548 11.90
6 broken 1.0043 12.89
8 broken 1.0425 22.18
Full load
Healthy 1.2278 -
2 broken 1.3745 11.94
4 broken 1.4830 20.78
6 broken 1.4861 21.03
8 broken 1.5032 22.43 39

GRAPHICAL REPRESENTATION OF FLUXDENSITY
The value of flux density increases as the number of broken bars
increases from 2 to 8.
number of broken bars increases.
40

OBSERVATIONS
 The flux function and the flux density increases when
the number of broken bars increases. The simulated
value of flux and flux density correlates with the
theoretically calculated value.
HEALTHY
CONDITION
THEORETICAL
VALUE
SIMULATED
VALUE
Flux Function 0.0227 Wb 0.0229 Wb
Flux Density 1.15 Wb/m² 1.22 Wb/m²
41

MODEL OF INDUCTION MOTOR CIRCUIT DIAGRAM
TRANSIENT ANALYSIS
42

CURRENT : 40.46 A
HEALTHY CONDITION
-0.4
-0.2
0
0.2
0.4
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
Value
(Wb)
Time (ms)
FLUX LINKAGE = 0.1666 Wb
0
200
400
600
800
1000
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
Value
(J)
Time (ms)
INSTANTANEOUS MAGNETIC ENERGY : 174. 2153Joules 43

CURRENT : 49.47 A
-330
-230
-130
-30
70
170
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
Value
(A)
Time (ms)
FLUX LINKAGE = 0.1938 Wb
0
200
400
600
800
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
Value
(J)
Time (ms)
INSTANTANEOUS MAGNETIC ENERGY : 157.6726 Joules
44

CURRENT : 52.53 A
FLUX LINKAGE : 0.22034 Wb
INSTANTANEOUS MAGNETIC ENERGY : 125.8326 Joules
45

SUMMARY OF STATOR CURRENT
Condition Stator Current (A) *Percentage rise
No Load
Healthy 7.35 -
2 broken 9.99 35.86
4 broken 10.50 42.88
8 broken 11.15 51.79
Full load
Healthy 40.46 -
2 broken 49.47 22.25
4 broken 52.53 29.82
8 broken 61.44 51.84
*PERCENTAGE RISE WITH RESPECT TO HEALTHY CONDITION
46

SUMMARY OF FLUX LINKAGE
Condition Flux Linkage (Wb) *Percentage rise
No Load
Healthy 0.01104 -
2 broken 0.01327 20.19
4 broken 0.01791 62.22
8 broken 0.02205 99.72
Full load
Healthy 0.16668 -
2 broken 0.19386 16.30
4 broken 0.22034 32.19
8 broken 0.31012 86.05
*PERCENTAGE RISE WITH RESPECT TO HEALTHY CONDITION
47

GRAPHICAL REPRESENTATION OF FLUX LINKAGE
The value of flux linkage increases as the number of broken
bars increases from 2 to 8.
number of broken bar increases.
48

SUMMARY OF MAGNETIC ENERGY
Condition Magnetic Energy(Joules) *Percentage drop
No Load
Healthy 1.58446 -
2 broken 1.57958 0.307
4 broken 1.28950 18.61
8 broken 1.16965 26.17
Full load
Healthy 174.2153 -
2 broken 157.6726 9.49
4 broken 125.8326 27.77
8 broken 91.4319 47.51
*PERCENTAGE DROP WITH RESPECT TO HEALTHY CONDITION
49

GRAPHICAL REPRESENTATION OF MAGNETIC ENERGY
The value of magnetic energy decreases as the number of
broken bars increases from 2 to 8.
number of broken bar increases. 50

OBSERVATIONS
BROKEN BARS
 Broken bar saturate the magnetic force distribution on the rotor tooth
adjacent to the bars that where broken. Hence, the bars adjacent to broken
bars will become more susceptible to additional wear and eventual
breaking.
The flow of current in the stator phases and flux linkage produced in the
motor were increased.
The magnetic energy was decreased when the number of broken bars
were increased. The simulated value correlates with the calculated value.
HEALTHY
CONDITION
THEORETICAL
VALUE
SIMULATED
VALUE
Magnetic Energy 166.69 J 174.21 J
Flux Function 0.0227 Wb 0.0229 Wb
Flux Density 1.15 Wb/m² 1.22 Wb/m² 51

MODULE-3
Fault Analysis of CSI-fed Induction
Motor Drive
52

TYPES OF FAULTS
Open circuit of upper MOSFET of Phase-A in inverter
 Open circuit of MOSFETs in first leg of inverter
 Short circuit of upper MOSFET of Phase-A in inverter
 Short circuit of MOSFETs in first leg of inverter
53

SIMULATION CIRCUIT OF CSI-FED DRIVE
54

LINE VOLTAGE WAVEFORMS WITHOUT FAULT
HARMONIC SPECTRUM OF LINE VOLTAGE
55
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-1000
-500
0
500
1000
Time(s)
Vab(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-1000
-500
0
500
1000
Time(s)
Vbc(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-1000
-500
0
500
1000
Time(s)
Vca(V)

OPEN CIRCUITING OF UPPER MOSFET of PH-A IN INVERTER
56

LINE VOLTAGE WAVEFORMS WITH UPPER MOSFET OF PH- A OPEN CIRCUITED
57
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-4
-3
-2
-1
0
1
2
Time(s)
Vab(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-6
-4
-2
0
2
4
Time(s)
Vbc(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-4
-2
0
2
4
6
Time(s)
Vca(V)

OPEN CIRCUITING OF MOSFETs IN FIRST LEG OF INVERTER
58

LINE VOLTAGE WAVEFORMS WITH FIRST LEG OF INVERTER OPEN CIRCUITED
59
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-0.4
-0.2
0
0.2
0.4
Time(s)
Vab(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-1
-0.5
0
0.5
1
Time(s)
Vbc(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-0.4
-0.2
0
0.2
0.4
Time(s)
Vca(V)

SHORT CIRCUIT OF UPPER MOSFET OF PHASE A IN THE INVERTER
60

LINE VOLTAGE WAVEFORMS WITH UPPER MOSFET OF PH-A SHORT CIRCUITED
HARMONIC SPECTRUM OF LINE CURRENT
61
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-100
-50
0
50
100
150
200
Time(s)
Vab(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-200
-150
-100
-50
0
50
100
150
Time(s)
Vbc(V)
6 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.1
-150
-100
-50
0
50
Time(s)
Vca(V)

SUMMARY OF THDs AND VOLTAGE OF CSI-FED DRIVE
62
Conditions Parameters CSI
Vab(peak) Vbc(peak) Vca(peak)
Healthy Circuit
Line Voltage (v) 590.4 590.4 590.2
Voltage THD (%) 4.56 4.56 4.56
Open circuit fault
In ph-A MOSFET
Line Voltage (v) 1.99 2.33 2.7 9
Voltage THD (%) 47.12 35.58 19.59
Phase A open
circuited
Line Voltage (v) 0.15 0.21 0.12
Voltage THD (%) 60.48 33.75 48.04
Short circuit fault
In ph-A MOSFET
Line Voltage (v) 111.1 124.7 61.58
Voltage THD (%) 52.69 45.84 52.23

63
OBSERVATIONS
 Without Fault the THD is 4.56%. But for MOSFET open
circuit fault it increases to 47.12% and for MOSFET short
circuit fault it is 52.69%.
 Due to MOSFET open circuit fault, THD increases by 12
times .
 Due to MOSFET short circuit fault, the THD increases by 13
times. DC voltage is introduced. This results in failure of
inverter operation.

MODULE-4
Fault Analysis of VSI-fed Induction
Motor Drive
64

SIMULATION CIRCUIT FOR VSI-FED DRIVE
65

LINE CURRENT WAVEFORMS WITHOUT FAULT
66

OPEN CIRCUITING OF UPPER MOSFET OF PH-A IN INVERTER
67

LINE CURRENT WAVEFORMS WITH UPPER MOSFET OF PH-A OPEN CIRCUITED
68

OPEN CIRCUITING OF MOSFETs IN FIRST LEG OF INVERTER
69

LINE CURRENT WAVEFORMS WITH MOSFETs IN FIRST LEG OPEN CIRCUITED
70

SHORT CIRCUITING OF UPPER MOSFET OF PH-A IN INVERTER
71

LINE CURRENT WAVEFORMS WITH UPPER MOSFET OF PH -A SHORT CIRCUITED
72

SHORT CIRCUITING OF MOSFETs IN FIRST LEG OF INVERTER
73

SUMMARY OF THDs AND CURRENT OF VSI-FED DRIVE
Conditions Parameters
VSI
Phase A Phase B Phase C
Healthy Circuit
Line current (A) 4.676 4.676 4.718
Current THD
(%)
4.7 4.7 4.54
Open circuit fault
In ph-A MOSFET
Line current (A) 2.687 5.582 2.687
Current THD
(%)
50.83 23.48 50.83
Phase A open
circuited
Line current (A) 0 4.084 4.083
Current THD
(%)
81.01 4.59 4.59
Short circuit fault
In ph-A MOSFET
Line current (A) 0.356 0.507 0.656
Current THD
(%)
17.64 24.13 17.72
74

OBSERVATIONS
 Without Fault the THD is 4.7%. But for MOSFET open circuit
fault it increases to 50.83% and for MOSFET short circuit
fault it is 17.26%.
 Due to MOSFET open circuit fault, THD increases by 10 times.
Current direction gets reversed.
 Due to MOSFET short circuit fault, the THD increases by 4
times. DC current is introduced(nearly 15A).This
results in failure of inverter operation.
75

MODULE 5
INDUCTION MOTOR FED BY FAULT
TOLERENT VOLTAGE SOURCE INVERTER
76

IM FED BY FAULT TOLERENT VOLTAGE SOURCE
INVERTER
77

IM FED BY FAULT TOLERENT VOLTAGE SOURCE
INVERTER(during faults)
78

SIMULATION CIRCUIT OF IM FED BY FAULT
79

PHASE A
PHASE B
PHASE C
LINE CURRENT WAVEFORMS WITHOUT FAULT
80

SIMULATION CIRCUIT WITH OPEN CIRCUIT OF MOSFETS IN
FIRST LEG OF INVERTER
81

LINE CURRENTWAVEFORMS WITH OPEN CIRCUIT FAULT
82

HARMONIC SPECTRUM OF LINE CURRENT (phase A)
83

SIMULATION CIRCUIT OF IM FED BY FAULT TOLERENT
VOLTAGE SOURCE INVERTER WITH OPEN CIRCUITED
FIRST LEG
84

LINE CURRENT WAVEFORMS OF IM FED BY FAULT
85

HARMONIC SPECTRUM OF LINE CURRENT(phase A)
86

SUMMARY OF THD AND LINE CURRENT
Phase A open leg fault
THD Line current (A)
Fault tolerant VSI fed induction motor 23 1.5
87

OBSERVATIONS ON FAULT TOLERANT
VSI-FED DRIVE
 It is observed that for normal inverter fed drive due to
open circuit fault, the THD value is 81% whereas for
fault tolerant inverter fed drives it is 23%.
 For normal inverter fed drive due to open circuit fault
the line current is 0.00035 A whereas for fault
tolerant inverter fed drives it is 1.5 A.
88

FAULT TOLERANT INVERTER WITH AUXILIARY LEG
89

Control Logic for Leg swap module
Phase
Identifier
Logical Operator
90

CURRENT WAVEFORMS – Fault in Phase A
91

LINE CURRENT SPECTRUM OF PHASE A, B & C
92

A Comparison of fault operation of voltage source inverter and
fault tolerant inverter
PHASE HEALTHY VSI
Phase A Open Circuit
Fault in VSI
Phase A Open Circuit
Fault in Fault
tolerant inverter
Current (A)
THD
(%)
Current
(A)
THD
(%)
Current
(A)
THD
(%)
A 4.67 4.7 0.003 81.01 4.82 4.71
B 4.67 4.7 4.08 4.59 4.84 4.66
C 4.70 4.5 4.08 4.59 4.87 4.54
93

There is a reduction in the harmonic distortion
by 30%using fault tolerant VSI fed drive with
SPC configuration.
The fault tolerant inverter with leg swap Module
replicates the performance of a healthy VSI.
Leg swap module needs 3 more bidirectional
switches.
OBSERVATIONS
94

MODULE 6
HARDWARE IMPLEMENTATION
95

WAVEFORM OF LINE VOLTAGE UNDER HEALTHY
CONDITION
X-axis 1cm=2ms
Y-axis 1cm=200v 97

HARDWARE AND SIMULATED WAVEFORM OF Vab
WITH OPEN LEG FAULT
X-axis 1cm=2ms
Y-axis 1cm=200v 98

HAREWARE AND SIMULATED WAVEFORM OF V bc
WITH OPEN LEG FAULT
X-axis 1cm=2ms
Y-axis 1cm=200v
99

HARDWARE AND SIMULATED WAVEFORM OF Vac
WITH OPEN LEG FAULT
X-axis 1cm=2ms
Y-axis 1cm=200v 100

WAVEFORM OF LINE CURRENT UNDER HEALTHY CONDITION
x-axis 1 cm=2ms
y-axis 1 cm=3A
101

PH-A LINE CURRENT AND SPECTRUM UNDER OPEN LEG FAULT
x-axis 1 cm=2ms
y-axis 1 cm=3A
102

PH-B LINE CURRENT AND SPECTRUM UNDER OPEN LEG FAULT
x-axis 1 cm=2ms
y-axis 1 cm=3A 103

PH-C LINE CURRENT AND SPECTRUM UNDER OPEN CIRCUIT FAULT
x-axis 1 cm=2ms
y-axis 1 cm=3A
104

6.1 COMPARISON OF SIMULATION AND EXPERIMENTAL RESULTS
OF LINE VOLTAGE
Voltage
Healthy Open leg fault
simulation hardware simulation hardware
Vab 415 405V 320V 320V
Vbc 420 420V 639V 640V
Vca 415 405V 318V 320V
105

Parameters Healthy Open circuit fault
Simulation Hardware Simulation Hardware
amplitude THD amplitude THD amplitude THD amplitude THD
Ia 4.83A 4.71 4.81A 5.1 0.003A 80.4 0.004A 85.2
Ia
4.83A 4.71 4.78A 5.3 4.23A 4.57 4.24A 5.1
Ia
4.88A 4.52 4.82A 5.5 4.25A 4.58 4.51A 5.4
speed
1430 1420 0 0
COMPARISON OF SIMULATION AND EXPERIMENTAL
RESULTS OF LINE CURRENTS
106

under healthy condition the motor runs at a
speed of 1420 rpm.
During open leg fault condition, voltage waveforms
are distorted and the motor fails to run.
OBSERVATIONS
107

CONCLUSIONS
BROKEN BAR FAULT:
• The stored magnetic energy decreases when the
number of broken bars in the rotor increases.
• Similarly the flux function and the flux density
increases when the number of broken bars increases.
• The flow of current in the stator phases and the torque
produced in the motor were increased.
108

CONCLUSIONS(contd…)
VSI / CSI :
Due to faults there is an asymmetry in the line current
waveforms.
Due to open circuit fault only negative half is obtained for
Ph A line current i.e. the current direction gets reversed.
Due to short circuit fault D.C component is introduced
(15A for VSI & 45A for CSI). This results in failure of
inverter operation.
CSI fed drive introduces more harmonics than VSI fed
drive.
109

FAULT TOLERANT VSI-FED DRIVE
There is a 30% reduction in the harmonic distortion by
using fault tolerant VSI fed drive with SPC
configuration.
Fault tolerant inverter with leg swap module replicates
the performance of a healthy VSI.
But it needs 3 more bidirectional switches.
Hardware results of VSI fed drive are almost similar
to simulation results
110
CONCLUSIONS(contd…)

CONTRIBUTIONS
1. TRANSIENT MODELS FOR INDUCTION MOTOR ARE DEVELOPED
TO DETECT SIX AND EIGHT BROKEN BAR FAULTS .
2. TRANSIENT MODELS FOR INDUCTION MOTOR ARE DEVELOPED
TO DETECT 10%, 20%,& 30% OF INTER TURN SHORT CIRCUIT
FAULTS.
3. CONTROL LOGIC FOR LEGSWAP MODULE IS DEVELOPED FOR
FAULT TOLERANT VSI FED DRIVE SYSTEM.
111

SCOPE FOR FURTHER WORK
 This work can be further extended for Bearing & Eccentricity
fault.
 The signature analysis can be further done using the artificial
intelligence techniques like neural networks.
 There is a scope for fault Analysis of induction motor drive fed
from ZSI circuit and AC Chopper circuit.
 Control logic for five leg topology may be developed for
induction motor drive using two inverters.
112

113
WORK CARRIED OUT AFTER THESIS IS SUBMITTED
FAULT ANALYSIS OF Z - SOURCE INVERTER
FED INDUCTION MOTOR DRIVE

NEED FOR Z – SOURCE INVERTER
• For a traditional inverter, to obtain the output voltage of
230Vrms with modulation index of 0.7, 550V DC voltage is
required this is undesirable since it will require additional
voltage booster circuit.
• With Z-source inverter, input DC voltage applied to is 210V.
• Thus the input voltage (210V) is boosted (385V) and applied
as DC link voltage.
• The peak value of this DC link voltage appears as stator
voltage across the output.

DESIGN CALCULATIONS
• Shoot-through duty ratio,
• Capacitor voltage,
• Peak DC-link voltage,
• The output peak phase voltage,
• The boost factor,

SIMULINK MODEL OF ZSI FED IM
UNDER HEALTHY CONDITION
Z – source
network

OUTPUT CURRENT WAVEFORMS AND SPECTRUM
ANALYSIS UNDER HEALTHY CONDITION
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-4
-2
0
2
4
Time(s)
current(A)
Output current(phase A)
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-4
-2
0
2
4
Time(s)
current(A)
Phase B
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-4
-2
0
2
4
Time(s)
current(A)
Phase C

SIMULINK MODEL OF ZSI FED IM WITH
SINGLE DEVICE OPEN CIRCUIT FAULT

ANALYSIS
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-8
-6
-4
-2
0
2
Time(s)
current(A)
Output current(pahase A)
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-40
-30
-20
-10
0
10
20
30
40
Time(s)
current(A)
Phase B
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-40
-20
0
20
40
Time(s)
current(A)
Phase C

SINGLE LEG OPEN CIRCUIT FAULT

ANALYSIS
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-0.1
-0.05
0
0.05
0.1
Time(s)
current(A)
Output current(phase A)
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-40
-20
0
20
40
Time(s)
current(A)
Phase B
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-40
-30
-20
-10
0
10
20
30
40
Time(s)
current(A)
Phase C

SINGLE DEVICE SHORT FAULT

ANALYSIS
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-20
0
20
40
60
80
Time(s)
Ia(A)
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-50
-40
-30
-20
-10
0
10
Time(s)
Ib(A)
0.3 0.31 0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.4
-30
-20
-10
0
10
Time(s)
Ic(A)

OBSERVATIONS
• Due to faults third harmonics are introduced.
• Hence there will be fluctuations in the speed.
• Short circuit fault produces high DC component in the
current spectrum and this DC component produces
heating of the winding.

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138

PUBLICATIONS OF THE SCHOLAR
International Journals
1. Nagarajan. S. and Rama Reddy. S. (2010), “Modeling and Simulation of Faulty
Squirrel Cage Induction Motor using magnet” International Journal of
Computer and Electrical Engineering (IJCEE), Vol. 2, No. 5, pp.867-869, 2010,
Singapore.
2. Nagarajan. S. and Rama Reddy. S. (2011), “Simulation of fault detection in AC
to AC converter fed induction motor” International Journal of Electrical
Engineering, vol.4, No.6, 2011, Egypt.
3. Nagarajan. S. and Rama Reddy. S. (2012), “Detection of inter-turn fault in three
phase squirrel cage induction motor using magnet” Journal of Electrical
Engineering, Romania,Vol.58, No.3, pp.384-391, 2012.
139

4. Nagarajan. S. and Rama Reddy. S. (2014),“Fault Analysis on VSI fed
Induction Motor Drive with Fault Tolerant Strategy” Research Journal of
Applied Sciences, Engineering and Technology, U.K, Vol. 7, No. 10,
pp.2004-2016.
5. Nagarajan. S. and Rama Reddy. S. (2013),“Detection of Broken bars in
Three phase Squirrel Cage Induction Motor using Finite Element Method”
International Journal of Electrical Engineering, Taiwan, vol. 20, No.4,
pp.139-150.
140
PUBLICATIONS OF THE SCHOLAR

International Conference
1. Sudarvizhi.A, Nagarajan.S, Ramareddy.S (2012), ‘Detection and Analysis of Broken
Bar in Three Phase Squirrel Cage Induction Motor using FEM’, 2012 International
Conference on Computing, Electronics and Electrical Technologies (ICCEET) 978-1-
4673-0210-4/12/IEEE, pp.40-50, 2012.
2. Dhanya.B, Nagarajan.S, Ramareddy.S (2012), ‘Fault Analysis of Induction Motor Fed
by a Fault Tolerant Voltage Source Inverter’, 2012 International Conference on
Computing, Electronics and Electrical Technologies (ICCEET) 978-1-4673-0210-4/12/
IEEE, pp.51-58, 2012.
3. Nagarajan. S. and Rama Reddy. S (2012). “Embedded Controlled Fault Tolerant
Inverter with A Leg Swap Module For Induction Motor Drive”, IEEE International
conference on Power Electronics, Drives and Energy systems(PEDES 2012). 978-1-
4673-4508-8/12/IEEE-2012
141

Paper communicated
1.Nagarajan. S. and Rama Reddy. S (2012). “Modelling, Simulation and
Implementation of VSI fed induction motor drive with a leg swap module”,
IEEJ(JAPAN ).
142

143
Clarifications to the Queries made by the Indian Examiner
Q.1. In CONTENTS in pg XI in 5.3. ‘VSI FED FED Drive’ should be corrected as ‘VSI FED Drive’.
Ans. In the above mentioned sentence in page XI in 5.3, FED is deleted.
Q.2. In pg2, Literature Survey, MCSA should be specified in List of Abbreviations
Ans. MCSA is included in list of Abbreviations as suggested by the examiner.
Q.3. In pg 53, specify whether it is percentage change in torque or percentage change in flux
linkages.
Ans. It is percentage change in flux linkage. As suggested by the Examiner
it is specified in pg53 of the revised thesis
Q.4. In pg.57, present the basis for obtaining theoretical values.
Ans. The basis for theoretical calculations for flux and flux density are included in page57.
Q.5. In chapter 2 extensive discussion on effects of rotor broken bar fault on
torque harmonics and noise may be presented.
Ans. As suggested by the examiner the discussion on effects of rotor broken bar fault on
torque harmonics is added (pg.58). Noise analysis cannot be done using Magnet software.

144
Clarifications to the Queries made by the Foreign Examiner
Q.1. The unit of measurement of the magnetic flux density.
Wb/m2 instead of T for Tesla.
Ans: Wb/m2 is replaced by T as suggested by the examiner.(pg.30,38,45,59)
Q.2. Avoid a too dense scale of values for the time (fig.2.15, 2.16, 2.17, 2.18, 2.19, 2.20).
Ans: Time scale was reduced from 4000ms to 1000ms in Figs.2.15, 2.16, 2.17,
2.18, 2.19, 2.20 as suggested by the Examiner.

145
Questions for Oral Examination
1.What is the approximate percentage contribution of broken bar faults in interior faults?
Ans: 10% to 15%
2.How do you relate broken bar faults with the Thesis title?
Ans: we have consider both interior(induction motor fault) and exterior faults(inverter faults)
3.How do you validate the simulation results obtained with broken bar faults?
Ans: Simulations results are validated with design calculations. The simulated values of the
average flux density and flux function correlate with the theoretical values.
4.Normally flexibility for simulink model is less compared to equation model for operating
conditions beyond the specified ranges-justify in your case.
Ans:

146
5.Describe the causes of broken bar faults such as electromagnetic,thermal,dynamic
conditions, etc.
Ans: The causes of rotor bar and end-ring breakage include:
(a) magnetic stresses caused by electromagnetic forces,
(b) thermal stresses due to abnormal operating duty, including overload and unbalance,
(c) inadequate casting, fabrication procedures or overloading,
(d)contamination and abrasion of rotor because of poor operating conditions,
(e) lack of maintenance.
Most failures will increase the current and stress in the adjacent bars,
progressively deteriorating the rotor part and degrading the motor’s overall performance.

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