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Rotor Bar % Continuity Tests Using the El-Cid Equipment.
(Highlights of over 290 tests)
J McMurdo
The ‘Extreme’
Major Damage to:
• Rotor Winding
• Rotor Core
• Stator Core
• Stator Winding
Rotor Bar Types
Material: Copper Brass Aluminium Silicon-Bronze Steel
Bar profile: T L Rectangular Round Pyramid Square.
Approaching the ‘Extreme’
Bars de-brazed from s/c ring, eroded through the slot bridge,
Being rubbed down by contact with the stator core
Broken Rotor Bars
Numerous broken bars, erosion of slot bridges in progress
Inadequate Brazing [A]
Inadequate Brazing [B]
Bar % Continuity and Core Losses
0.00
20.00
40.00
60.00
80.00
100.00
120.00
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73
Rebrazed Bar continuity
Original bar continuity
El Cid Profile
No evidence of correlation between ‘in-phase’ bar % continuity and ‘quadrature’ measurement of core losses
Good
Rotor Bar % ContinuityAvg 98% - Lowest 93%
0.00
20.00
40.00
60.00
80.00
100.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49
Bar No
Perc
ent C
ontin
uity
One Low Indication *Localised Repair Possible
Rotor Bar % ContinuityAvg 95% - Lowest 33%
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59
Bar No
Per
cent
Con
tinui
ty
Numerous Low Indications*Major Repairs Indicated
Rotor Bar % ContinuityAvg 89% - Lowest 64%
11 Bars below 80%
60.00
65.00
70.00
75.00
80.00
85.00
90.00
95.00
100.00
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70
Bar No
Perc
ent C
ontin
uity
Steel Bars to Copper Short Circuit Rings [A]
Rotor Bar % ContinuityAvg 98% - Lowest 94%
N.B. Steel Bars
60.00
65.00
70.00
75.00
80.00
85.00
90.00
95.00
100.00
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76
Bar No
Per
cent
Con
tinui
ty
Rotor Bar % Continuity Re-testAvg 98% - lowest 91%
N.B. Steel Bars
60.00
65.00
70.00
75.00
80.00
85.00
90.00
95.00
100.00
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 64 67 70 73 76
Bar No
Per
cent
Con
tinui
tySteel Bars to Copper Short Circuit Rings [B]
Induction Techniques
Work using the ‘Wissink’ tester first performed at Bonnycan and refined during the Author’s continued development work at GEC / Alstom and Wadeville AW
Induction coil ‘growler’ combined with El-Cid equipment to qualify starting condition [50hz]
Die-Cast Aluminium Rotor *Outer Cage
Rotor Bar % ContinuityAvg 86% - 10 bars <80% - Lowest 70%
Outer Cage (Starting condition)
020406080
100
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49
Bar No
Per
cent
C
ontin
uity
Die-Cast Aluminium Rotor *Inner Cage
Rotor Bar % ContinuityAvg 93% -Lowest 84%
Inner Cage
0.0020.0040.0060.0080.00
100.00
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49
Bar No
Perc
ent
Conti
nuity
Die-Cast Rotor Bar*Combined Profile
Die-Cast Rotor Profile
40.00
50.00
60.00
70.00
80.00
90.00
100.00
12 3
45
67
8
9
10
11
12
13
14
15
16
17
18
19
2021
2223
242526
272829
3031
32
33
34
35
36
37
38
39
40
41
42
43
44
4546
4748
49 50 INNER
OUTER
El-Cid Technique
Direct applied current Measurement using the Rogowski coil
(Chattock potentiometer) coreless, non-inductively wound sensor.
In-phase measurement rather than quadrature
Technique differentiates between 1. broken bars and 2. poor ‘bar to short circuit ring’ joints
El-Cid Technique (cont’d)
Accuracy: Calibrated to within 0.5%Repeatability: Bar #1 hard stamped, bar
#2 stamped to confirm progression
El-Cid Technique
Phase Sensor
Conclusion
Rotor bar problems still occur
Testing at the assessment stage is of value in preventing the ‘Extreme’
Re-test to prove efficacy after repairs
End-user operational feedback is required to maximise value
The ‘Extreme’
Major Damage to:
Rotor Winding
Rotor Core
Stator Core
Stator Winding
Acknowledgement: This presentation was produced in collaboration with Ron Scollay
