Inter-Turn Fault Analysis of Three Phase Induction
Motor
Priyanka C P
Department of Electrical Engineering
National Institute of TechnologyCalicut
Kozhikode, Kerala, India
priyanka.cp03@gmail.com
Abstract—Induction motor is the most popular electric drive in
industrial and other applications because of its reliable and
rugged construction. As like the other motors induction motor
also subjected to different faults such as open winding stator
fault, short circuit stator fault, bearing fault etc. Among these
faults the most severe one is the short circuit fault which is first
developed as inter-turn fault across the stator winding.
Therefore, timely fault detection is necessary for the continuous
operation of the motor. Motor Current signature analysis is one
of the effective and commonly used method for the detection of
short circuit fault. But in Induction motor fed from PWM
Inverters MCSA cannot able to detect the fault. In this paper
the FEA analysis of inter turn fault is done in ANSYS Maxwell.
The Finite Element Analysis is performed for 16% and 25%
stator turns short are in Ansys Maxwell 2D. The
MATLAB/Simulink model of faulty motor is developed. The
results obtained in inter-turn faulty conditions are validated
experimentally.
Keywords— Fault Detection, Motor Current Signature
Analysis (MCSA), Finite Element Analysis (FEA)
I. INTRODUCTION
The most commonly used motor in Industries, Electric
vehicle and traction application is Induction motor because of
its rugged construction, low manufacturing cost, Ease of
maintenance, and low power to weight ratio compared with
the permanent magnet synchronous motors. It’s one of the
most reliable electric machines, but the chance of occurrence
of fault is same as that of other machines. In early days fault
diagnosis of machine is done by over voltage and over current
measurements. After detecting the fault, the machine has to
shut down for its clearance. But in Safety Critical and
automotive application it’s difficult to stop the machine and
it can’t be recommended for the fault mitigation. This
demands efficient Fault diagnosis and Mitigation strategies.
The primary objective in condition monitoring is the fast
detection of fault and its prediction of the severity and exact
location were the fault occurred. If the fault cannot be
identified within time it can result in huge damage to
machine.[1]-[3]
The faults of induction motors are can be classified into
two which are electrical and mechanical faults. These faults
are stator faults which include 1) stator faults which consists
of open phase fault, stator unbalance due to the short circuit of
winding 2) rotor electrical faults, which include rotor open
phase fault, rotor imbalance due to short circuits or increased
resistance in case of slip ring motor and broken bars which can
occur in squirrel cage induction machines 3) rotor mechanical
faults such as bearings damage, eccentricity fault, bent in shaft
and it’s misalignment[4]-[5]. Among these faults the
occurrence of short circuit fault is 20%. The short circuit fault
begins as inter-turn fault which caused due to insulation
Jagadanad G
Department of Electrical Engineering
National Institute of TechnologyCalicut
Kozhikode,Kerala, India
jagadanand@nitc.ac.in
degradation from and mechanical and thermal stress, Power
surges and external object interference. If it is not detected in
the beginning it will result is phase-phase or phase-ground
short circuit across the stator phase winding of the machine[6].
This further causes unbalance air gap flux distribution,
increase in torque harmonics and reduction in average torque,
vibration, losses and overall reduction in efficiency.
Different detection tests are there to determine the condition
of stator winding insulation. The offline test such as dielectric
dissipation test, dielectric spectroscopy, partial discharge,
insulation resistance is performed to analyse the condition of
stator winding insulation. But the limitation of these tests is
that in order to conduct the test the machine has to be shut
down. For monitoring the condition of stator winding online
test such as Temperature, Vibration and partial discharge
methods can be used[11]-[12]. The additional requirement of
sensors can increase the cost. The sensors for non-invasive
technique such as park vector approach, frequency spectrum
of current and power are utilised to determine the stator
insulation failure. The non-invasive method most commonly
choosing for stator winding fault detection is Motor Current
Signature Analysis (MCSA) which can be used for direct
online connected Induction motors. But in case of motors fed
from PWM inverter the MCSA technique is difficult due to
high switching frequency [7]-[9]. The existing fault diagnosis
method (MCSA) the limitation is that it is not considering
the effect of complex shape of the machine and the
electromagnetic impacts.
Finite Element Analysis is a method for doing the
electromagnetic analysis of motor both in healthy and in
faulty conditions. The Transient analysis is done in Maxwell
2D. FEA deals with the non-linear behaviour of induction
motor. The analysis using simulation tool helps for the fault
prognosis which is essential for application were the
continuity of operation is a criterion. The FEA analysis is an
easy method and the detection of fault can be inferred by
comparing the results of healthy and faulty conditions. The
advantage of Maxwell 2D is the ability to integrate FEA
generated models within a system simulation [10],[13]. The
internal fault modelling is the primary step in the design of
the fault diagnosis systems. For the analysis of internal faults,
the simulation using mathematical modelling is more
complex, and using FEA different internal faults in the motor
can be modelled and detection is easier.
This paper presents the transient analysis of Inter-turn fault
developed in a 3 phase 50 Hz 3 HP Induction motor, with 4
poles and 36 slots. The motor is designed using the basic
equations in RMxprt and the electromagnetic analysis is done
in Maxwell 2D. Section I describes the design of Induction
motor in healthy and 9%, 16% and 25% faulty condition and
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Section II explains the results obtained from the Maxwell 2D.
Section III deals about the transient analysis of healthy &
faulty motor. Section IV deals with the MATLAB Modelling
of Faulty motor and section V is hardware implementation
and results. Section VI is the conclusion.
II. FINITE ELEMENT ANALYSIS
A. Design of Three Phase Induction Motor
A 3HP, 415V, 50 Hz, 1440rpm , 4 pole three phase
Induction motor is designed using the basic equations of motor
and it has been modelled in RMxprt in Ansys Maxwell. All
the parameters such as stator diameter, length, number of
stator slots and specifications, Type of winding, dimensions,
Type of steel, Number of conductors/slot, No of Parallel
branches, rotor length, diameter, number of slots are given
from the calculated values. The performance characteristics is
analysed for both healthy and inter-turn short circuit fault of
three phase Induction motor. The inter-turn fault is modelled
for the same motor by short circuiting 16% and 25% of the
turns in one phase. The Transient analysis for healthy as well
as faulty induction motor is done in Ansys Maxwell 2D.
Fig.1 Short circuit Fault condition of Three Phase Induction motor
Table I Induction motor Specification
Sl no:
Parameter
Value
1.
Rated Power of motor
2.2KW
2.
Rated voltage(V)
415V
3.
Rated Speed(rpm)
1440 rpm
4.
No of poles
4
5.
Friction loss
10W
6.
Windage loss
10 W
7.
Number of stator slots
36
8.
Outer diameter of the stator
200mm
9
Inner diameter of the stator
124mm
10.
Length of the stator
126mm
11.
Length of the Rotor
126mm
12.
Outer diameter of the rotor
122mm
13.
Inner diameter of the rotor
55mm
14.
Stacking factor
0.95
15.
Rotor Slots
26
16.
Air gap
0.5mm
17.
Type of steel
Steel_1008
19.
Number of Parallel branch
1
20.
Conductors per slot
37
Fig. 2 Healthy Condition of Induction motor
Fig.3 16% Inter-turns Fault in Stator winding
Fig. 4 25% Inter-turn fault in stator winding
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III. TRANSIENT ANALYSIS OF MOTOR
The designed motor steady state characteristics are
analyzed in RMxprt in Maxwell. The Performance
characteristics of three phase Induction Motor shows that the
designed motor is efficient and reliable and can be exported
into Maxwell 2D for transient analysis.
Fig.8 Driver Circuit for Three Phase Induction Motor
Fig.5 Torque-Speed Characteristics
Fig. 9 Phase Voltage (vrn)
Fig.6 Power factor-output power
Fig. 10 Current waveform in healthy motor
Fig.7 Efficiency-Output Power
The electromagnetic analysis is done by exporting the
designed motor in Maxwell 2D. A Voltage Source Inverter
(VSI) of switching frequency 5 KHZ is used for driving the
motor. The VSI is modeled in MATLAB/Simulink and its
exported for driving the Maxwell model. The Speed, torque
and current curves are shown below. The transient
electromagnetic flux response indicates the healthy motor
condition with uniform distribution of flux.
Fig. 11 Torque of healthy motor
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equation containing the fault is also developed to represent the
faulty three phase induction motor completely.
1
∆
∆
2
∆
3
∆
4
∆
5
∆
6
Fig.12. Speed of healthy motor
∆
2
∆
2
∆
Fig. 13 Transient Flux plot of Healthy motor
2
2
3
2
3
3
3
2
7
2
8
3
9
∆
10
∆
11
The electromagnetic torque produced in a faulty motor is
given by
)
(12)
Where, k represents the short circuit constant, which is
equal to the ratio of numbers of short circuit turns to the total
number of turns available in stator winding. if and Lls, Lms
represent the fault current and leakage inductance,
magnetizing inductance of the stator winding respectively.
Fig. 14 Torque plot of motor with 25% fault
IV MATHEMATICAL MODEL OF FAULTY MOTOR
The mathematical modelling of faulty three phase induction
motor is developed in d-q-0 reference frame which can be
utilized for predicting the inter-turn fault across stator
winding. The inter-turn fault development across the stator
winding results the faulty phase which divides as two sub
windings located along the same magnetic axis. Thus four
voltage equations are made for the stator windings. The
assumption made for modeling the faulty motor is same as that
of healthy motor. The distribution of leakage inductance
between the two stator sub windings, originated by the
development of inter-turn short circuit fault, is directly
proportional to the square of the number of turns shortcircuited. The six voltage equations representing the three
stator and three rotor windings of the motor and a voltage
Fig.15 Simulink Model of faulty induction motor
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V HARDWARE IMPLEMENTATION
The experimental setup of faulty induction motor is is shown
below. The Intelligent Power Module (1000V, 25A, 3 Phase
IGBT inverter bridge) converts the 415 V AC supply from the
autotransformer into DC link voltage which is filtered and
then converted to ac to supply the three-phase induction
motor. The driver part is implemented with sinusoidal PWM
(open loop), using the OPAL-RT real time simulator. The
MATLAB –SIMULINK model is loaded in RT Lab 11.2
software of OPAL-RT real time simulator for generating the
switching pulse for the six leg inverter switches. The inter-turn
fault can be detected by observing the stator current which can
be done using the sensors available with Intelligent Power
Module.
Fig.16 Motor current of three induction motor
3 Phase Auto
Transformer
IP Based Power
Module IPM-01
Three PhaseTwoLevel
3HP Three Phase
Induction Motor
PWM Pulses
From opal-RT
Fig.17 speed of Three phase induction motor
Fig. 20 Block diagram of fault Analysis
Fig.18 Torque of three phase induction motor
Fig. 19 Stator Currents during 16% turns short
Fig.21 Experimental Set up of 3φ healthy and faulty condition
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and the transient electromagnetic plots obtained in Maxwell
2D shows the effect of inter-turn fault when different
percentage of stator windings are shorted across three phase
induction motor. The MATLAB/Simulink modelling of faulty
induction motor is also analyzed and from the experimental
setup validates the inter-turn fault 9% and 16% developed
across the windings in the stator.
REFERENCES
[1]
Fig. 22 Triggering Pulses from opalRT
[2]
[3]
[4]
[5]
[6]
Fig. 23 Stator Currents during 9% inter-turn fault
[7]
[8]
[9]
[10]
[11]
Fig. 24 Stator Currents during 16% inter-turn fault
[12]
VI CONCLUSION
The short circuit stator fault is the most severe fault
occurring in motors it begins as the Inter-turn fault which has
to be identified in the starting stage itself. This work analyses
the inter-turn fault developed across a 3 hp three phase 4 pole
Induction Motor. The motor is designed using basic equation
and the performance characteristics are analysed in RMxprt
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