33KV Capacitor Bank Cable Burst

[Masood Anzar]

Hi,
In one of my plant, we installed a capacitor bank in parallel with the load across 33 KV Line for power factor improvement.
The capacitors were connected to the 33 KV point of common coupling (PCC) with fuse in between.
When a fault occur, one of the capacitor bank cable got burst and the control panel which was providing the switching signal to the capacitor bank breaker got blown. But to my surprise the fuse did not blown which was connected between capacitor and 33KV Line
While, on the load side, our 33KV breaker got trip and some of the Electric Drives got the flash.
I want to know the possible cause of the fault. Either it must be at load end or at capacitor bank end. Can anyone suggest me.

 

[jghrist]

It would appear to be a fault in the cable. Where was the fuse? If the fuse was between the cable and the capacitor, that would explain why the fuse did not blow. Fault current did not flow through the fuse. Where was the 33 kV breaker? Between the cable and the PCC?

 

[RRaghunath]

It seems there was over voltage in the 33kV system that caused flashovers at different locations.
How fast the capacitor protection is able to sense overvoltage and isolate the capacitor bank? This is crucial for avoiding such flashovers.
Further, capacitor bank at 33kV level is a bad idea as it can cause ferro-resonance with associated flashovers / failures. Mind you, there is inductive reactance of the line, inductive reactance of transformers downstream.
The power factor correction is best done at the load end, be it 6.6kV or 415V always.