VCM-E Grounding Current Traces Show Evidence of Core Damage
CORE LAMINATION SHORTING CASE HISTORY
| An MPS VCM-E was installed, along with a reliable shaft grounding brush. Recording was set up to chart the VCM-E Grounding current activity (peak-top and average-bottom) and was left running for several weeks. |
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VCM-EN Figure 1A & Figure 1B |***| |
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Peak and Average grounding current traces of a large Turbine-Generator, at Central Engineering indicated possible unit developing problems. In Figures 1A, 1B upper trace Ipeak and lower trace Iavg don’t track at one zone in Figure 1B. |
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The Trace (Figure 2A) showed erratic current behavior periodically, which would settle down, usually at a slightly higher constant level than before. |
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The customer confirmed that no changes to any of the systems or the operating unit were performed during this time period. Upon reviewing the traces MPS predicted that the incipient source was either shorted rotor turns or core lamination shorting. The unit tripped out of service on a stator coil ground fault. |
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Figure 2A Figure 2B
| Examination found that a top bar failure was precipitated by core end lamination shorting (Figure 2B). The coils were removed, the core was repaired and the stator was rewound. |
Copyright 2012 |
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Magnetic Products And Services, Inc. |
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www.gaussbusters.com |