Answer / kj

See extract from service manual for HV alternator.

A 5000V motorised megger or similar instrument should be
used. Separate the three neutral leads,
ground V and W leads and megger U to ground. Repeat for V
phase with U and W grounded and W
phase with U and V grounded. Minimum acceptable limits
after 1 minute for each phase are:
New machine 300 M

In-service machine 150 M

The insulation resistance should not be less than specified
and the polarisation index should be in the
order of 2 or greater at 20 ºC.
(PI = IR10min / IR1min)

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