We have a siemens master drive for blower application. The drive was indicating 'DC link under voltage' fault. The service engineer checked the rectifier module and found it to be ok. He replaced the PCC (power control card). The problem got solved, but, after 30 days the same fault is coming again.

I checked the input AC supply to the drive and found it to be ok. Can somebody suggest me that how to check the rectifier module (made up of thyristor)?

 

This sounds a lot like a power problem. And yes, right now the power is fine. But when motor A and motor D happen to start at the same time, the house power dips a bit and you get your fault. Before I spent a lot of time and money, I'd put a PQM (Power Quality Meter) on that circuit and see if your fault doesn't correspond to a power issue. The electrician _always_ thinks the power is fine :^) I've found several trips that worked like that. And you can rent one, probably for a lot less than renting the Siemens guy. I had one where a control problem would deadhead a large hydraulic pump and _lots_ of stuff tripped. The breaker for the branch never did because the electronics would dump load before it could respond.

Regards
cww