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On 3/7/14 8:03 AM, David Rieben wrote:
Hey guys,
Bumfuzzeld,
David
You need a fuse or circuit breaker in your ARSG power..that, at least,
will protect the control panel's variac.
but, to why it's shorted..
Is there a short from winding to case in your motor? Does it fail only
after turning on the sparks? There could be a hole in the insulation
and it doesn't short until you actually have HV transients running around.
I had some 10HP 460V motors running off 3 phase PWM motor drives.. they
kept tripping with a fault after a while, and it was because of the
spikes from the drive which had punctured the insulation on the
windings. They ohmed out fine, and ran fine at full speed with the
motor drive out of the circuit, but would trip instantly with the drive.
Doing a hi=pot test on the motor afterwards showed that it would fail hipot.
If you have access to someone who can hipot test your ARSG that would be
convenient. You can also rig one up a test set using a NST and a
variac.. (you want only a few kV.. not the full 15kV)
What might be happening is a transient causes a breakdown (at HV) which
then provides a conductive path to ground that carries enough current to
kill the diodes.
The other thing is whether you're getting inductive kickback from the
motor into the bridge.. but that would have killed your bridges in the
past..(although the electrolytic might have damped that out too..