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Introduction to monitoring and Introduction to monitoring and diagnosis of electrical machines and
apparatusapparatus
2nd lessonFaults in Electrical Machines
Ewen Ritchie Krisztina Leban
1. Introduction to course
2. Introduction to diagnosisg
3 O i f f l i id 3. Overview of fault incidence
4. Detection Methods
Lesson 1 5. Monitoring MethodsLesson 1
6 S & T d
g
6. Sensors & Transducers2
Lesson 2 ObjectivesLesson 2- Objectives• In Lesson 2, the student should learn about:
– Faults to be diagnosed on electrical machinesMeasurements to be made– Measurements to be made
– Diagnostic methods– Diagnostic IndicatorsDiagnostic Indicators– Examples of Results– Towards Reliable Diagnosisg
• A closer look at the different faults that mayA closer look at the different faults that may arise and the influence they may have on the signals collected.
2010-10-20 Ewen Ritchie and Krisztina Leban 3
Agenda – Lesson 2Agenda – Lesson 2• Induction machines
– Stator– Stator– Rotor
• Synchronous machines– StatorRotor– Rotor
• Mechanical faults
• Diagnosis by observing only one variable for instance:variable, for instance:– Current– Flux linkagesg
2010-10-20 Ewen Ritchie and Krisztina Leban 4
Induction Machines
Invented by Nikola Teslay1856‐1943
Induction machines – Stator faults arisingInduction machines – Stator faults arising• In the traditional induction machine, the
stator comprises a laminated iron core, with l tslots– An insulated winding is fitted in the slots– The individual turns of the winding are
insulated from each other• There is a winding for each phase
– Coils belonging to each phase winding are insulated from those of the other phase windingswindings
• All three phase windings are insulated from Earth
• Usually, the first sign of an insulation failure i h d d bl fis a shut‐down due to a blown fuse or a tripped earth fault protection relay
• This is a catastrophic failure as it causes unplanned downtimep
• Tesla’s version shown here, was a two phase system
2010-10-20 Ewen Ritchie and Krisztina Leban 6
What is a Short Circuit Fault?What is a Short Circuit Fault?
• One fault that occurs regularly is a short circuit in the stator• One fault that occurs regularly is a short circuit in the stator winding
• It is important to understand the mechanism of a "short‐circuit fault "circuit fault.
• A short‐circuit fault in an electrical machine winding is an abnormal condition where one or more coils unintentionally makes contact with another coil or earthmakes contact with another coil or earth.
• Due to the abnormal conditions, excessive current may flow in the short circuit fault causing local heating and insulation damagedamage
• An internally generated or induced EMF drives current in the short circuited portion of the winding and the impedance of the short circuitthe short circuit
• To understand the mechanism, we need to evaluate the EMF and the Impedance
2010-10-20 Ewen Ritchie and Krisztina Leban 7
Induction machines – Stator faults arisingg• A model may help us to
visualise and consider thevisualise and consider the problem
• At IET we considered a short circuit arising in a statorcircuit arising in a stator winding
• iDwas flowing in the short D circuited portion of the winding
• i’Dwas flowing in the shorti D was flowing in the short circuit
• We wanted to model the fault and to verify thefault and to verify the model
2010-10-20 Ewen Ritchie and Krisztina Leban 8
Induction machines – Stator faults arisingg
• We modelled the fault as an i di lextra winding electro‐
magnetically linked with the actual phase windings
iB
actual phase windings
• The short circuit is electro‐magnetically linked with ALL
i’D
magnetically linked with ALL other windings in the machine
iC
iA
2010-10-20 Ewen Ritchie and Krisztina Leban 9
Sample of simulation results – 1.5% of 1 stator phase shorted – No Load Load
• The 3 phase currents are f i l i il i li dfairly similar in amplitude– Around 5 Amp
• The fault current amplitude• The fault current amplitude is much larger– Around 50 AmpAround 50 Amp
• It is difficult to diagnose a stator winding short circuit gfault by measuring the supply current
2010-10-20 Ewen Ritchie and Krisztina Leban 10
Sample Experimental Results – 1.5% of 1 stator phase shorted
– No Load • Experimental verification gives a
similar resultsimilar result– Except the phase current is
much smaller
• The measured amplitude of theThe measured amplitude of the fault current is about 50 Amp
• But the unbalance in amplitude of the line current is about 0 5 Aof the line current is about 0.5 A
• Unbalance in the line current may be caused by many different problems external to the motorproblems external to the motor– e.g. unbalanced supply voltage
• Read [03‐01] Extract from Report St d f th Eff t f Sh tStudy of the Effects of Short Circuits in Stator Winding of Induction Machine
2010-10-20 Ewen Ritchie and Krisztina Leban 11
Experiment to study the effect of external faults on doubly fed induction machines
• Read reference [03‐2 and 03‐3]• Many wind generators employ doubly fed
i d ti hiinduction machines• Generators are subject to external faults
e.g. on distribution and transmission lines• Under normal duty, power is taken both
f h d d hfrom the stator winding and the rotor winding
• However, an external fault may cause unbalanced loading
• Rotor current supplied to the fault may be controlled by the power electronics converter
• It may be difficult to control the stator current
• Therefore it becomes interesting to study the effect of external faults in the doubly fed induction generator
• Some researchers propose that current signature analysis may be useful for detecting faults in the stator circuit
2010-10-20 Ewen Ritchie and Krisztina Leban 12
At IET we studied current signal analysis to diagnose faults in wind generator systems. wind generator systems.
– Experimental arrangementsL =(15 & 50) mHV ( )
Switch on / off
B
A
DFIGB
C
One stator phase inductive unbalance
A
Simulated turn-to-turn fault in one stator phase
DFIG
Switch on / off
B
one stator phase
One stator phase resistive unbalance
COne rotor phase resistive unbalance
2010-10-20 Ewen Ritchie and Krisztina Leban 13
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
• Experimental Results, stator inductive and resistive unbalance
The stator currents acquired by TDS 540 under Stator currents acquired by TDS 540 under one stator The stator currents acquired by TDS-540 under inductive unbalance-Lv=50 mH at P=2 kW. The
unbalance stator current is on channel 2. Scaling factor is 4 [mV / A].
Stator currents acquired by TDS-540 under one stator phase resistive unbalance (Rv=10 ) at P=2kW and n=1475 rpm. The unbalance stator current is configured on channel 2. Scaling factor is 4 [mV / A].
2010-10-20 Ewen Ritchie and Krisztina Leban 14
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
The degree of unbalance exhibited in one stator phase, obtained by Introducing
th i d ti b l f 50 H (10 ti th th t t h i d t ) the inductive unbalance of 50 mH (10 times more than the stator phase inductance),
may be observed very clearly in the stator current.
2010-10-20 Ewen Ritchie and Krisztina Leban 15
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
– Experimental results, turn‐to‐turn fault
The rotor currents acquired by TDS-540 under turn-to-turn fault in one stator phase (Lv=50 mH in parallel ) at P=2 kW and n=1475 rpm. Scaling
factor is 4 [mV / A].
The stator currents acquired by TDS-540 under turn-to-turn fault in one stator phase (Lv=50 mH in parallel ) at P=2 kW and n=1475 rpm. Scaling
factor is 4 [mV / A].
2010-10-20 Ewen Ritchie and Krisztina Leban 16
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
The rotor current observed during this type of turn to turn fault exhibits almost balanced amplitude ,while the unbalance created in the stator currents is greater This indicates that the stator current may be a good indicator for the detection of rotor faults.
2010-10-20 Ewen Ritchie and Krisztina Leban 17
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
– Experimental results, rotor unbalance
The rotor speed and stator currents of DFIG acquired by ICS-645 under the resistive unbalance of 1.2 Ω in one rotor phase at 2kW.
The rotor currents of DFIG acquired by TDS 540 under the resistive unbalance of 1.2 Ω in one rotor phase at 2 kW. Scaling factor is 4 mV/A
2010-10-20 Ewen Ritchie and Krisztina Leban 18
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
MCSA to detect DFIG faults– Machine current signature analysis (MCSA) is a non‐invasive, online or offline monitoring technique for the
diagnosis of problems in induction machines, such as turn‐to‐turn fault, broken rotor bars, static or / and dynamic eccentricity;
– Due to its powerful technique merits in diagnosis and detection of faults the MCSA monitoring technique was chosen as a fault detection methodchosen as a fault detection method.
– The stator and rotor currents monitoring system that has been developed consists of three main sub‐systems. These include: signal conditioning, data acquisition and data analysis.
– Data acquisition and data analysis sections are accessed by Matlab software package run from a PC. The controlling software allows the operator of the system to store the data in data files for future processing.controlling software allows the operator of the system to store the data in data files for future processing.
2010-10-20 Ewen Ritchie and Krisztina Leban 19
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
– MCSA to Diagnose Stator Turn‐to‐Turn Faults
n=1,2,3,..;k=1,3,5,..
2010-10-20 Ewen Ritchie and Krisztina Leban 20
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
– The obvious change between balance and turn‐to‐turn fault is that completely new current components exist around 125 Hz (k=1, n=3) and 375 Hz (k=1, n=13) . In addition, if we follow the trajectory of the current phase angle (Is1), we may observe that it has changed around 125 Hz, where a new faulty component exist as well.
2010-10-20 Ewen Ritchie and Krisztina Leban 21
At IET we studied current signal analysis to diagnose faults in wind generator systems.
– MCSA to Diagnose Stator Winding Unbalance
2010-10-20 Ewen Ritchie and Krisztina Leban 22
At IET we studied current signal analysis to diagnose faults in wind generator systems.
• Comparison of the stator current spectra for resistive unbalance in one stator phase (R=10 Ω) and for inductive unbalance in one stator phase (L=50 mH) reveals that the inductiveand for inductive unbalance in one stator phase (L=50 mH), reveals that the inductive unbalance causes new components to appear in the stator current spectrum at around 175 Hz and 425 Hz, while the resistive unbalance introduces new components at around 125 Hz, 325 Hz and around 375 Hz
2010-10-20 Ewen Ritchie and Krisztina Leban 23
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
– MCSA to Diagnose Rotor Winding Unbalance
Frequency spectrum of stator currents and rotor currents of DFIG for rotor unbalance at 2 kW. FFT was computed and current spectrum were plotted using MATLAB software and getting via ICS 645.
2010-10-20 Ewen Ritchie and Krisztina Leban 24
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
The rotor line current spectrum, for unbalance in one rotor phase, contains more information about the effect of this fault than the stator line current spectrum does Either may be useful as an the effect of this fault than the stator line current spectrum does. Either may be useful as an indicator for detection of rotor winding unbalance. For resistive and inductive unbalance in one stator phase and simulated turn-to-turn fault in one stator phase, the stator line current spectrum holds more information.
2010-10-20 Ewen Ritchie and Krisztina Leban 25
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
– MCSA versus Instantaneous Power
Frequency spectrum of partial and total instantaneous power and stator current of DFIG for stator unbalance (a) and rotor unbalance (b) at 2 kW. FFT was computed and power
and current spectrum were plotted using MATLAB software and getting via ICS 645.
2010-10-20 Ewen Ritchie and Krisztina Leban 26
Study of current signal analysis to diagnose faults in DFIG wind generator systems.
• Conclusion– The experimental results indicate that monitoring line currents in stator and
rotor ma be useful in identifying the presence of unbalance in one stator and rotor phase and exhibit the presence of harmonics related to a specific type of fault;
– The article indicates that the detection of different kind of faults may be possible using time and frequency domain analysis
– The spectrum of stator and rotor line currents gave promising results.Th i t l lt d t t th t MCSA b f l t di– The experimental results demonstrate that MCSA may be useful to diagnose turn‐to‐turn faults
– MCSA may also be useful to diagnose other problems in induction generators such as inductive and resistive unbalance in one stator and rotor phase.
– The instantaneous power seems to be an alternative diagnostic medium for the machine signature analysis.As this study was limited to simulating turn to turn fault placing an– As this study was limited to simulating turn‐to‐turn fault, placing an inductance in parallel to one phase winding, research intothe effect of real short circuits is certainly needed.
2010-10-20 Ewen Ritchie and Krisztina Leban 27
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine Read reference [03-2]
M h i l d l f h d bl f d i d i– Mathematical model of the doubly fed induction generator
asi'di di
asi
did d
bsi
csibsi
csi
2010-10-20 Ewen Ritchie and Krisztina Leban 28
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
– Mathematical model of the doubly fed induction generator
LL
lTT
ULILdRLI
1
)( 11
rrrs
srss
LLLL
L
ADACABAA
MMLMMMML
le TTJ
rsrT
se IdLdIT
DDDCDBDA
CDssCA
BDssBAss
LMMMMLMMMMLM
L
Tcrbrardcsbsas iiiiiiiI
rrr
rrr
rrr
rr
LMMMLMMML
L
Tcrbrarcsbsas uuuuuuU 0
Trs
CcCbCa
BcBbBa
AcAbAa
sr LMMMMMMMMM
L
DcDbDa
CcCbCa
MMM
rrrDssA rrrrrrrdiagR ,,,,, ,
2010-10-20 Ewen Ritchie and Krisztina Leban 29
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
– Calculation of circuit element values
NN s
DA r
NNNr
1
1
AsD rrr
2MMMM sBAAB
3MMMM sCAAC
,3,
2,
1
210
2
22
1
2
pppk
ykDs
DDD k
kp
lNL
NN
L
14 kklNN
DDDAAD LMMM 1
DDDBBD LMMM 2
,5,3,1
12
1102
1
21
cos4
1k
wkykD jq
kkkk
plNN
M
12
1102
1
32
21
cos4
2 wkykD jq
kkkklNN
M
DDDCCD LMMM 3
22
11
2210
221
21
21cos2 wkwk
CbBbqqrk
kkk
plNNMM
,5,3,1
22 32k kp
,5,3,1
12
1102
1
32
21
cos4
3k
wkykD jq
kkkk
plNN
M
,5,3,1 22k kp
,5,3,1
22
12210
22
21cos2
k
wkykDDa
qjrkkkk
plNNM
DDsmsD
AA LMLLN
NNL
1
2
1
1
2010-10-20 Ewen Ritchie and Krisztina Leban 30
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
– Generator parameters
Parameter Value
Rated Power 11 kW
Rated Voltage 400 V
Frequency 50 Hz
Stator resistance 1.1
Rotor resistance 0.908
St t l k i d t 3 82 HStator leakage inductance 3.82 mH
Rotor leakage inductance 4.593 mHRotor leakage inductance 4.593 mH
Mutual inductance 99.77 mH
2010-10-20 Ewen Ritchie and Krisztina Leban 31
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
SIMULATION RESULT OF INTER TURN SHORT CIRCUIT FAULT
di
– SIMULATION RESULT OF INTER‐TURN SHORT CIRCUIT FAULTi d
i a s
i (A) di
as i
t(s) a) Three phase current and short circuit current id a)Three phase currents and short circuit current
st
dB
f(Hz) b) Sp ectrum curve of phase A current
b) Spectrum curve of phase A current
Hzf
Simulation result of inter-turn
short circuit fault ( α = 3.125%)
b) Spectrum curve of phase A currentSimulation result of inter-turn
Short circuit fault( )%25.6
2010-10-20 Ewen Ritchie and Krisztina Leban 32
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
SIMULATION RESULT OF INTER TURN SHORT CIRCUIT FAULT– SIMULATION RESULT OF INTER-TURN SHORT CIRCUIT FAULT• Phase angle difference analysis under inter-turn fault
Phase angle
Condition
AB BC CA
Condition
Healthy 120° 120° 120°
3 125 % 130 8° 113 6° 115 6°3.125 % 130.8 113.6 115.6
6.25 % 131.6° 110.6° 117.7°
9.375% 134.8° 108.7° 116.4°
12.5 % 135.6° 108.6° 115.8°
1. Short circuit current id is very large, and decreases along with fault percentage increasing.1. Short circuit current id is very large, and decreases along with fault percentage increasing.2. 150Hz and 450Hz current components appear in spectrum curve.3. The phase angle difference becomes unbalance.
2010-10-20 Ewen Ritchie and Krisztina Leban 33
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
• EMULATED STATOR INTER-TURN SHORT CIRCUIT FAULT
Phase A stator winding is parallel with a resistance R=25Ω.
) Th h ta) Three phase currents ia R
ib
ic
b) Phase A current spectrumSimulation result of emulated inter-turn
short circuit fault (R=25Ω)
Diagram of emulated inter-turn short circuit fault
2010-10-20 Ewen Ritchie and Krisztina Leban 34
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
• EKSPERIMENTAL SETUP
Freq.conv22kW
Grid
I d ti motor
Frequency converter
Control box of DFIG
DC link
22kWBack-to-backconverter
IG
Testsystem
u,i
ω
ω
Gear box
Gear boxInduction cage motorControl PC
IM Gear Gear
Model of windModel of wind generator
DFIG
Simple diagram of experimental
turbine Model of wind generator
Speed transducer
p g psystem
Fig.8 Laboratory Experimental system
2010-10-20 Ewen Ritchie and Krisztina Leban 35
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
• EKSPERIMENTAL RESULTSDFIG healthy
DFIG phase A parallel with R=25
i(A)
y
a) Three phase currentst(s)
a) Three phase currentst(s)
a) Three phase currents a) Three phase currents
dB
Frequency (Hz)Frequency (Hz)
b) Phase A line current spectrum analysis
Frequency (Hz)b) Phase A line current spectrum analysis
2010-10-20 Ewen Ritchie and Krisztina Leban 36
Model of Stator Inter-turn Short Circuit fault in Doubly-fed Induction Generators for Wind Turbine
– CONCLUSION– A complete model to simulate inter‐turn faults have been set up
Emulation of inter turn faults are done by setting a resistance in parallel with– Emulation of inter‐turn faults are done by setting a resistance in parallel with phase A
• This is shown both by simulations and experimental results– Both simulation result and experimental result have two changes:
• 150Hz and 450Hz current components appear in spectrum curve.
• The phase angle difference becomes unbalance• The phase angle difference becomes unbalance.
2010-10-20 Ewen Ritchie and Krisztina Leban 37
Asynchronous machines – Rotor faults yarising
• In the squirrel‐cage rotor of an asynchronous machine the current links the magnetic polesg p
• A cracked or broken rotor bar or end‐ring will disturb this patternTh t b d ll d• The rotor may be modelled as a mesh of current paths
• These current paths induce magnetic fields that link with gall other windings on the machine
• It has been very popular to conduct research to detectconduct research to detect rotor faults in squirrel cage induction machines
2010-10-20 Ewen Ritchie and Krisztina Leban 38
Asynchronous machines – Rotor faults arisingarising
• In the squirrel‐cage rotor of an asynchronous machine the current links the magnetic polesthe magnetic poles
• A cracked or broken rotor bar or end‐ring will disturb this pattern
• The rotor may be modelled as a mesh of current pathscurrent paths
• The mesh may be rearranged to reflect local changes regarded as faults
• The magnitude and frequency of the rotor t d d th t l l fcurrents depend on the actual value of
the slip• The rotor mesh currents link and interact
with the air‐gap main flux
2010-10-20 Ewen Ritchie and Krisztina Leban 39
Asynchronous machines – Rotor faults yarising
• Fault currents in the rotor cause characteristic frequencies to appear in both the current and the flux linkageto appear in both the current and the flux linkage waveforms
• Experimental flux spectra are shown for a motor with and without broken rotor bars s 0 05 f 50 Hzwithout broken rotor bars, s = 0.05, f = 50 Hz
• The amplitude of the harmonic of order (1‐2s)f exhibits a marked increase with the quantity of rotor faults.
2010-10-20 Ewen Ritchie and Krisztina Leban 40
Asynchronous machines – Rotor faults yarising
• As the order of the new frequency caused by the fault is governed by the expression (1‐2s)f the possibility of detection is dependent on thethe expression (1 2s)f the possibility of detection is dependent on the actual value of slip
• For a small slip, the new frequency may be masked by the fundamental frequency if the discrimination of the FFT is insufficientlyfundamental frequency if the discrimination of the FFT is insufficiently fine
• Read [03‐4] Dynamical Model of Three‐Phase Squirrel‐Cage Induction Motor with Rotor FaultsInduction Motor with Rotor Faults
2010-10-20 Ewen Ritchie and Krisztina Leban 41
Synchronous machines
Synchronous machines – Stator faults arisingarising
• Stator faults arising in a synchronous machine are similarsynchronous machine are similar to those arising in an induction machine
• However the current excited
iBHowever, the current excited rotor will supply energy to the fault– As long as the field current flows
i’D
As long as the field current flows– As long as there is kinetic energy
stored in the rotor
• This is a different situation fromThis is a different situation from the Induction machine where the magnetising energy is supplied from the faulted stator system
iCfrom the faulted stator system– Here the fault may contribute to
dissipation of the magnetisationiA
2010-10-20 Ewen Ritchie and Krisztina Leban 43
Synchronous machines – Rotor faults yarising
• Faults arising on the rotor of a synchronous machine may includey– Loss of magnetising current
Short circuits arising in the magnetising winding– Short circuits arising in the magnetising winding
– Short circuits arising in the damper winding
2010-10-20 Ewen Ritchie and Krisztina Leban 44
Mechanical faults• Mechanical faults arising in
rotating electrical machinesrotating electrical machines are chiefly related to:– Bearings– Eccentricity
• Rolling bearings may become damaged or worn
C2
become damaged or worn• Eccentricity may arise
because of manufacturing C1gfaults, external accidental damage, or bending of shafts due to unsuitableshafts due to unsuitable mounting arrangements
2010-10-20 Ewen Ritchie and Krisztina Leban 45
Mechanical faults - eccentricityy• The eccentricity must be below
5% of the air gap in order to5% of the air gap in order to eliminate vibration problems due to magnetic pull.
• Eccentric machine– C1 is the centre of the rotor, and
C2 is the centre of the statorC2
– With static eccentricity, C1 is the centre of rotation
– With dynamic eccentricity, C2 is C1With dynamic eccentricity, C2 is the centre of rotation
– With mixed eccentricity, centre of rotation may be anywhereof rotation may be anywhere between C1 and C2.
2010-10-20 Ewen Ritchie and Krisztina Leban 46
Mechanical Faults - bearingsg
• Bearings may be plain b i lli b ibearings or rolling bearings
• Rolling bearings are widely used in industrialused in industrial applications
• We will consider only faults• We will consider only faults that may arise in rolling bearingsg
2010-10-20 Ewen Ritchie and Krisztina Leban 47
Mechanical faults - bearingsg• Many rotating electrical machines
are provided with rolling bearingsare provided with rolling bearings
• Rolling bearings are a complicated structure
• The outer ring or race is supported in a bearing housing
• The rolling elements are• The rolling elements are supported in a cage
• The inner guide ring or race is fitted to the shaft
• The seals keep dirt out and lubrication grease ing
2010-10-20 Ewen Ritchie and Krisztina Leban 48
Mechanical faults - bearingsg
• Any or all components of a lli b i ffrolling bearing may suffer
damage
• This damage may progress• This damage may progress from being incipient to being serious, and further,being serious, and further, to being catastrophic
• The photos show spherical p proller bearings with damage to the inner race and rollers
2010-10-20 Ewen Ritchie and Krisztina Leban 49
Diagnosis by observing only one Diagnosis by observing only one variable
As an example, we take the caseAs an example, we take the case of a short circuit in the stator winding of an induction motor g[03‐01]
Schematic diagram of the experimental systemsystem
• To observe any variable we need an experimental systemT i ll d t k th ti f ti
Phase 3
Frequency (Hz) 50• Typically we need to know the time function
of the machine supply variables, voltage current, torque, speed, etc.
• A typical experimental arrangement is as shown below
Output power [kW)
1.5
Efficiency 82%
Voltage (V)220-240shown below
• In this case we wanted to monitor what happened if a short circuit arose in the stator winding of an induction motor
Voltage (V)380-415 Y
Current (A)3.4-3.75Y5.9-6.5
Speed (r/min) 2860-2890
Power factor 0.85-0.79
Motor details
2010-10-20 Ewen Ritchie and Krisztina Leban 51
Schematic diagram of the experimental systemsystem
• An induction motor was provided with taps to enable partial short circuit of the
Phase 3
Frequency (Hz) 50p pstator winding to be applied at will
• All accessible signals were measured• The data acquisition system was with
Output power [kW)
1.5
Efficiency 82%
Voltage (V)220-240
simultaneous sampling on all channels– A signal conditioning box was used to
match the probes to the D/A converter
Voltage (V)380-415 Y
Current (A)3.4-3.75Y5.9-6.5
Speed (r/min) 2860-2890
Power factor 0.85-0.79
Motor details
2010-10-20 Ewen Ritchie and Krisztina Leban 52
Schematic diagram of the experimental psystem
P5200 i diff ti l lt
• All values were measured as functions of time for various fault• P5200 is a differential voltage
probe• PR30 is a current probe
functions of time for various fault values and motor loads
• This enabled a relationship to be drawn between the severity of
• RGF 75 is a current probey
the fault and any one of the various measured values
• Or a combination of these
2010-10-20 Ewen Ritchie and Krisztina Leban 53
Diagnosis by observing only one variable, e g Currente.g. - Current
• It was found that a short circuit producing a violently large short circuit current gave rise to a modest increase in the amplituderise to a modest increase in the amplitude of the shorted phase
• The current unbalance produced could easily come from other, comparatively harmless sourcesharmless sources
• It is clear that the winding cannot tolerate continuous operation when carrying the large fault current
• It would be interesting to reliably detect• It would be interesting to reliably detect even the smallest short circuit by observing the terminal values of current and voltage
• In this way catastrophic failures causingIn this way catastrophic failures causing loss of not only the motor itself, but also costly product, may be avoided
• Reliable detection is required to prevent spurious operation of the alarm/spurious operation of the alarm/ shutdown system as spurious operation would also cost loss of valuable product
2010-10-20 Ewen Ritchie and Krisztina Leban 54
Diagnostic Indicators
A diagnostic indicator is the time function of i bl l d f i ia variable selected for monitoring
This may be the current, the voltage, the flux linkages etcflux linkages, etc.
Current Signal Analysis (CSA) and Symmetrical Component Analysis
• Many researchers have ychosen to monitor the current as the diagnostic indicator
• Current is directlyCurrent is directly measurable thus simplifying the p y gmathematical calculations necessary yto obtain a diagnosis
• E.g. ref. [03‐5]g [ ]
2010-10-20 Ewen Ritchie and Krisztina Leban 56
Diagnosis by observing a derived variable, e g Fluxe.g. - Flux
• Researchers have also considered that derived variables makingthat derived variables, making use of two or more measured variables may carry more i f ti th b f d iinformation than may be found in a single variable
• One example of this is the flux ( )v i R dt linkages
• Here coherent measurements of both the voltage and the current
( )v i R dt both the voltage and the current are required in order to estimate the flux‐linkages
• This technique was used by Xiaolan Deng in ref. [03‐8]
2010-10-20 Ewen Ritchie and Krisztina Leban 57
ReviewReview
• Many different faults may arise in rotating electrical machines
• These may be electrical faults such as short circuits and open i it i th i di th b h i l f lt hcircuits in the windings, or they may be mechanical faults such as eccentricity or damaged bearings
• Research shows that many faults may be detected and• Research shows that many faults may be detected and identified by interpretation of measurements of the current and voltage, etc. made during normal operation of the g , g pmachine
• Later in this course you will consider some of the methods used to interpret the information held in the current or voltage measurement signals
2010-10-20 Ewen Ritchie and Krisztina Leban 58