C1,C2,C3,C8 burned out after one year working (3*230Vac power supply line). C1,C2,C3,C8 are all ceramic capacitor, 103Z/1kV.

The resistance of these failure caps is all about 30R.

Dose the quality of these capacitor be the root cause for this failure? or the selection of these capacitors in designing stage was not so suitable. Maybe we should pick a capacitor which has much high rated voltage, for example 2kV ?

And i can't work out why C8 was damaged. I thinks there is no much electric stress on C8.

 

Well, you might've had some kind of hefty transient spike (like lightning) that took them all out at once.

You might consider using MOVs or TVRs from the phase A,B,C inputs to Neutral.

Interesting about C8 - what's the difference between GND and GNDH?

 

Are the MOVs in parallel with the capacitors still good? If the caps failed due to high voltage I would change the MOVs since they have undoubtably been stressed.

 

MOVs are still good. Did you mean that I have to choose a MOV which have a lower varistor voltage? so MOV can work in time to protect the capacitor.

The spike damaged the capacitor, but not enough to make MOVs to start working.

 

Well, you might've had some kind of hefty transient spike (like lightning) that took them all out at once.

You might consider using MOVs or TVRs from the phase A,B,C inputs to Neutral.

Interesting about C8 - what's the difference between GND and GNDH?

i have used MOVs parallel with capacitor---VDR1,VDR2,VDR3 in schematic.
MOVs are good, not damaged. So, i think transient spike is not root cause.

I don't know exactly the difference of GND and GNDH. Maybe they are the Digital ground and Analog ground.

 

The caps should be X caps, or Y if only going to ground (the schematic indicates X rated needed). They are typically packaged in a plastic box, rather than the usual epoxy dip.

 

A full wave three phase rectifier generates third, fifth and higher order current harmonics on the input side of the bridge. The capacitors are there to shunt the harmonics to the neutral. The capacitive reactance goes down as the frequencies increase which is usually not a problem since the voltages for the higher orders are low. But if the three phase input is un-balanced or a diode is open then the harmonic voltages would increase and cause the capacitors to overheat.