Meggering of Dry-type or liquid-filled transformers

[unclebob]

For years I have meggered all transformers at 1000 Vdc for 1 minute. From 600 V thru 120 kV, dry type or oil liquid filled, 1000 V is the voltage, in our maintenance procedure.
Now this morning I learn that higher voltages can/must be used. Was I wrong for all these years?

 

[prc]

It is always better to use a higher voltage rated megger to test transformers so that any insulation weakness will come out. Meggers are available up to a voltage of 15kV DC, but popular voltage for HV and EHV range is 5 kV. But the voltage of Megger shall always be less than the rated voltage of the winding for voltages above 500 V.

 

[OffTap100]

!000v for 600v transformers is the suggested megger voltage.

Obviously transformers rated at a higher voltage require 5kv, 10kv and much higher.