Page 60 - Basic PD Theory

Off-line Testing

A. Off-line Testing

Test Description Detects Effectiveness Typical Test Test Precautions References
Frequency (Years)
AC High Potential Overvoltage Test Weakened ground Pass/Fail: Not effective for Factory test or as Potentially destructive IEEE 112 or NEMA
applied from conductor- insulation, severe cracks trending necessary following MG-1, IEEE 432
to-ground major maintenance
Capacitance AC test to measure Moisture and tape Single coils during Factory test IEEE 286
insulation capacitance delamination or improper manufacturing of medium
line-to-ground curing voltage generators.
Coil-to-ground Measure resistance from Detects problems with the Pass: <2000Ω QA test
resistance the coil to the core semicon or interference fit Fail: >5000Ω
DC High Potential Overvoltage Test Weakened ground Step Voltage or Ramp As necessary Potentially destructive IEEE 95 or NEMA
applied from conductor- insulation, severe cracks Method effective for trending MG-1
to-ground
Dissipation Factor AC test to measure Moisture and tape Single coils during 1-2 IEEE 286
& Tip-up - Medium dissipation line-to- delamination or improper manufacturing of medium
Voltage generators ground curing voltage generators. Possible
for trending.
Endwinding Measure frequency Loose or resonance of Look for high resonance at As needed
response response endwinding 100/120Hz
Insulation Insulation between Contamination, or Trending if corrected for 1-1.5 after outage IEEE 43
Resistance conductor and ground moisture temperature
Partial discharge AC test to measure Moisture and tape With some technologies 1-1.5 IEEE 1434
partial discharge line-to- delamination or improper possibly effective for
ground curing trending
Polarization Index Ratio of 10-minute IR to Wet or dirty insulation, Effective for trending 1-1.5 IEEE 43
1-minute IR possibly aged insulation
Power Factor & AC test to measure Moisture and tape Single coils during 1-2 IEEE 286
Tip-up - Medium power factor line-to- delamination or improper manufacturing of medium
Voltage generators ground curing voltage generators. Possible
for trending.

56 | P ag e