Page 23 - Basic PD Theory
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Basic PD Theory
2.4.7.4 Phase-to-phase Discharges
Contamination or Phase to phase * Phase-to-phase
phase-to-phase
50/60 Hz phase-to- voltage discharges in the end arm area can lead discharges are 30°
ground voltage to partial discharge activity. Unlike the phase-shifted from
previously described pulses that are classic positions
phase-to-ground voltage dependent, *
0 o 75 o 180 o 360 o these pulses are based on phase-to- * Inadequate spacing
Contamination
255 o phase voltages. Though these types of
pulses tend to be very erratic, it is sometimes possible to distinguish these
pulses from others by observing their location with reference to a phase-
Partial to-ground voltage. Typically, because of the phase-to-phase voltage
Discharges dependence there is a 30° phase shift from the classic phase positions
associated with pulses that are phase-to-ground voltage dependence as
Figure 16: Endwinding Discharges shown in Figure 16. That is endwinding pulses tend to clump at 15°, 75°,
195°, and 255°, based on the location of the pulses and the phase rotation of the machine. Sometimes, it is possible to determine
which two phases are involved, but more often, it is difficult to extract that information accurately from the quantity of pulses
detected.
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