Case study on HV Induction motor, 6000 V, 8MW

1. DYNAMIC ON-LINE MOTOR ANALYSIS TEST
Case study on HV Induction motor, 6000 V, 8MW
www.koncar-institut.com

2. DynamicOn-lineMotorAnalysis
TEST RESULTSTEST ITEM
02
The latest generation of dynamic on-line
motor analysis test doesn’t require for a
motor to be stopped. The testing provides
comprehensive information on general
condition, operation, load, power supply
and drive of the motor.
HV Induction motor
Power [kW] 8000
Current [A] 880
Frequency [Hz] 50
Voltage [V] 6000
cos φ 0,91
Efficiency η [%] 96
Speed [r/min] 994
Synchronous speed [r/min] 1000
Slip [%] 0,6
Rotor bars 112
Stator slots 126
TEST VALUE STATUS CAUTION LEVEL WARN. LEVEL
Voltage Level (Over) [%] 98,72 Good 110,00 120,00
Voltage Level (Under) [%] 98,72 Good 95,00 90,00
Voltage Unbalance [%] 0,19 Good 2,00 3,50
THD [% of fund.] 0,24 Good 7,00 9,00
Total Distortion [% of fund.] 0,28 Good 10,00 12,00
Current Level [%] 61,31 Good 110,00 120,00
Current Unbalance [%] 0,14 Good 10,00 20,00
Load [%] 59,79 Good 110,00 125,00
Ef. Service Factor [p.u.] 0,60 Good 1,10 1,25
Rotor Bar [db] -67,68 Good -45,00 -36,00
Op. Point [%] 0,00 Good 20,00 30,00
Loss Difference [%] 0,00 Good 25,00 50,00

3. DynamicOn-lineMotorAnalysis
Voltage Level TestPOWER QUALITY DOMAIN
03
» Voltage Level Test
All voltages are around 99% of
the nominal value.
There is no over/under voltage
measured.
Voltage Level
The test detects presence of
overvoltage or undervoltage
with regard to rated voltage. The
presence of overvoltage stresses
the motor insulation,
undervoltage can cause current
increase above the nominal
values.

4. DynamicOn-lineMotorAnalysis
Voltage Level TestPOWER QUALITY DOMAIN
04
Voltage Unbalance
Unbalanced voltage condition
causes negative sequence
currents within the stator,
resulting in excessive heat.
NEMA derating curve specifies
maximum load for each
unbalance.
» Voltage Unbalance Test
Voltage unbalance is under
0,5%. If value above 3.5% is
reached, the asymmetry can
cause negative sequence
currents. This will increase
machine losses and additionally
heat the machine winding.

5. Voltage Level Test
DynamicOn-lineMotorAnalysis
POWER QUALITY DOMAIN
05
Total Harmonics Distortion and
Total Distortion
Total Harmonic Distortion (THD)
and Total Distortion (TD) deal
with quantifying the effect of
nonfundamental components to
the voltage and current
waveform. TD values must result
in higher values than THD.
Both, THD and TD values are low and do not indicate possible machine
performance problems.

6. Voltage Level Test
DynamicOn-lineMotorAnalysis
06
» POWER
POWER QUALITY DOMAIN
» HARMONICS
Power quality domain shows the quality level of motor
power supply by each phase.
Additional harmonic levels increase the losses
and machine heating.

7. DynamicOn-lineMotorAnalysis
Voltage Level TestMACHINE PERFORMANCE DOMAIN
07
Effective Service Factor
Effective service factor graphically
displays the estimated percentage
of load derated within the NEMA
derating factor. This test identifies
how closely the motor is
operating to its effective service
factor. The test predicts heat-
based deterioration.
» Effective Service Factor
Motor is operating “in green”
area, with NEMA derating factor 1.

8. DynamicOn-lineMotorAnalysis
Voltage Level TestMACHINE PERFORMANCE DOMAIN
08
Load and Losses
Motor efficiency is calculated
from operating load and
measured losses (mostly heat).
High losses can cause increase
of the motor temperature.
Motor is operating at high efficiency.
Motor Load Measured Losses

9. DynamicOn-lineMotorAnalysis
Voltage Level TestCURRENT DOMAIN
09
Current Level and Current
Unbalance
The overload of a motor heats
the machine and significantly
reduces the lifetime of the
insulation. It is very important
to monitor this regularly.
The motor is operating underloaded. There is no current unbalance in this case.

10. Voltage Level Testd
DynamicOn-lineMotorAnalysis
10
SPECTRUM DOMAIN
Order n
Lower sideband [Hz] Upper sideband [Hz]
Hz dB Hz dB
1 49,68 -67,68 50,32 -68,5
2 49,35 -64,1 50,65 -64,1
3 49,03 -75,5 50,97 -71,01
» ROTOR BAR
Broken rotor bar sidebands are low (>-60 dB).
The values indicate excellent rotor condition.
The graph shows stator current spectrum with broken
rotor bar sidebands marked. In case when there is a
rotor bar damage on a certain frequency, new
harmonics will appear showing abnormal values.

11. Voltage Level Testd
DynamicOn-lineMotorAnalysis
11
SPECTRUM DOMAIN
Order n
Lower sideband [Hz] Upper sideband [Hz]
Hz dB Hz dB
1 33,4 -78,39 66,6 -79,17
2 16,9 -81,29 83,1 -79,86
3 0,3 -83,6 99,7 -78,4
» ECCENTRICITY SIDEBANDS
Eccentricity sidebands are low. There is no
indication of static or dynamic eccentricity.
The graph shows stator current spectrum with eccentricity
sidebands marked. Here it is important to watch for
frequencies and corresponding harmonics that are present
because of the static/dynamic eccentricity.

12. Voltage Level Testd
DynamicOn-lineMotorAnalysis
12
SPECTRUM DOMAIN
» V/I Spectrum
Stator current spectrum with broken rotor bar
sidebands marked
Stator current spectrum with broken rotor bar
sidebands marked.
There are no significant sidebands in current spectrum up
to 500 Hz. Measurement was taken with 1 kHz for 120 sec.

13. DynamicOn-lineMotorAnalysis
Voltage Level TestTORQUE DOMAIN
13
Torque Ripple Results
Motor torque is slightly rippled.
There is no indication of serious
motor/load problem. Torque
ripple should be trended in
future.
Torque Ripple

14. DynamicOn-lineMotorAnalysis
Voltage Level TestTORQUE DOMAIN
14
Torque Spectrum
There are no significant
sidebands at critical frequencies
in torque spectrum. Typical
frequencies are marked.
Torque Spectrum

15. DynamicOn-lineMotorAnalysis
Voltage Level TestCONNECTION DOMAIN
15
Supply voltage is sinusoidal and
stator currents are slightly
rippled. Situation is normal for
induction motor operation.
Voltage/current phasors are
symmetrical and motor (as well
as measurement sensors) is
properly connected.
» WAVEFORMS » PHASORS
Voltage – Current waveforms

16. DynamicOn-lineMotorAnalysis
Voltage Level TestCONCLUSION
16
There is no evidence of
any faults. The motor is in
good condition. The
recommendation is to
repeat this test in two
years.
» Induction Motor is in good condition. Supply voltage is symmetrical.
There is no over/under voltage
» THD and TD values are low. Effective service factor is 1.08 and motor
is working with NEMA derating factor 1, with high efficiency
» There are no significant sidebands in stator current spectrum.
Sidebands for rotor bar faults are low as well as for eccentricity
» Motor torque is slightly rippled and it is advised to trend it in time.

17. CONTACT US TO ARRANGE A VISIT TO YOUR FACILITY
Fallerovo šetalište 22, PP 202
Zagreb 10002, Croatia
info-iet@koncar-institut.hr
KONČAR Electrical Engineering Institute
@
+3851 3667-315; 3851 3666-351
www.koncar-institut.com
+3851 3667-309
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