MCCB Failure on harmonic filter

[AusPowEng]

I have an MCCB with extensive internal arcing that doesn't make sense.

The breaker supplies a module in a 600V active harmonic filter (module 2 of 4). The prospective fault level is (say) 25kA @ 600V but there has been no fault that we can see. The breaker is a modern european design, 400A MCCB and it appear it has opened in anger..attempting to clear a very large fault. There has been no flashover internally in the breaker.

The active filter module runs at 250A with IGBT's immediately downsteam of the breaker switching at 9kHZ.

My question is this. The undervoltage release coil on the breaker has been playing up. If the U/V release activated whilst under full load, would the 9kHZ current switching lead to arc-extinguishing problems in the breaker; the breaker is a standard product (50/60Hz)?

As far as arc quenching goes ; the moving contacts move past the arc chutes based on 50/60Hz design. Of course the supply voltage is still 50Hz, but the active filter is switching current very fast.

I would appreciate any advice.

 

[rbulsara]

Possibilities:

1. Bad breaker (contacts not making properly)

2. If the filters have large capacitors, it may not be rated for its charging current.

3. You could have the case of parallel capacitor switching.

Since you mentioned 4 modules, and if they are in parallel look into possiblity of item 3. If one module (capacitive filter) is already charged and you turn on other, the first one will try to discharge thru the other as it (charging current) see it as a short circuit.