Page 58 - Basic PD Theory
P. 58
PD Investigations
7.4 Summary - Failure Processes
Failure mechanism Polarity Load Effect Temperature Effect Phase Location
Internal delamination No predominance None Inverse 45° and 225°
Thermal cycling Negative None Inverse 45°
No or negative
Manufacturing defect None Inverse 45° and 225°
predominance
Bar/coil movements Positive Direct Inverse 225°
Electrical slot discharge Positive None Direct 225°
Contamination or No predominance None Unpredictable 15°, 75°, 195°, 255°,
Electrical tracking can be erratic
225°,
Interface problem Mostly positive None Direct
can be 0°/180°
Gap-type discharge 0° - 90°,
(Open air) No predominance Unknown Unknown 180° - 270°
Vibration sparking * No predominance Direct Inverse Erratic
Sometimes 0°/180°,
Broken strands * No predominance Direct Unknown
can be erratic
* Will only be seen in PD measurements if it is occurring at or near the phase line ends or it is
near the neutral connection and an EMC is installed there.
Endwinding Vibration No PD associated with this process
Internal Water Leak No PD associated with this process
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