rectifier failure question

[niall]

this is relation to friends mill , a fortis machine thats grid tied with an Aurora invertor

he wants to incorporate a secondary voltage monitoring circuit using an omron v sensing relay to trigger a secondary dump system ( belt and braces kind of thing )

the omron is set up to detect grid failure and/or mill overvoltage ...that bit seems fair enough

but on the subject of redundancys , what are the chances of the invertor rectifier failing in such a way that it might allow a  ac surge through to the invertor ?

i,ve had some small home made rectifiers fail but they usually went short circuit , which generally is just like a short circuit to the mill ....(the ac gets fed back into the mill ?)

he,s trying to keep all his bases covered as its a 4k machine which will be left unattended for  periods of time .....

i,m kinda curious if a failed rectifier can let pure ac through ...

[rossw]

but on the subject of redundancys , what are the chances of the invertor rectifier failing in such a way that it might allow a  ac surge through to the invertor ?

i,ve had some small home made rectifiers fail but they usually went short circuit , which generally is just like a short circuit to the mill ....(the ac gets fed back into the mill ?)

he,s trying to keep all his bases covered as its a 4k machine which will be left unattended for  periods of time .....

i,m kinda curious if a failed rectifier can let pure ac through ...

The chances are very slim. You'd need half the diodes to go short and the other half to go open.
The easiest way to mitigate such a problem would be one very beefy diode across the bridge output such that if you ever DID get AC out, it would be clamped to -0.7V.

In over 35 years working in electronics, I can't recall ever seeing a bridge (much less a 3-phase bridge) fail in the manner you fear.

[niall]

thanks for that ....i,ve passed on the info...