bank capacitor

Unless this happens any and every time the capacitors are engaged, I think the problem stems from a lack of operator training.

thank you sir for comment but for further elaboration about the problem..the capacitor banking are all replaced with new same rating ..rewired all wirings and all protective devices are even replaced, every screws and bolts are re-tightened, the capacitor's contactors are also on and off due to demand.. its was one day old after installation the cable starts burning below the fuses..the operator keep on monitoring that's why we found out this discoloration of cable and stars burning..it happens many times and we keep on changing those burned cable and busted 100A fuses.

From what you've done it does seem like you've assembled the capacitor bank properly. So with a properly assembled package that repeatedly fails, this leads to only two other options, poor design or operation control. Both options require more information like a schematic, operational signal measurements and verification that the actual assembly is being used as the designer intended. In other words, a knowledgeable person on site to troubleshoot your repetitive failures.

Now if I was there, the first thing I would do would be to verify that the schematic agreed with the actual circuit assembled. Next I would measure the currents running through the circuit breaker and capacitor bank with a clamp on ammeter and oscilloscope. Then and only then might I have a suggestion which might be your cause of failure.

Is this capacitor bank switched on and off often ? If so, the switching-on transient current can play havoc on the switching and protection elements.

"the capacitor's contactors are also on and off due to demand.."

So the capacitor IS switched on and off frequently. Are these special capacitor-switching contactors ? Please note that one can get, at a worst-case scenario, a VERY HIGH transient current of ~ 180 times the rated capacitor current .. please see here...

ABB

You are saying 500Kva. No power factor. then why do u need capacitor bank?...Even it is in Kw , the 50 Kvar seems to be less as per thumb rule...please tell the capacitor bank internal wiring diagram and details of load.

oppss sorry i mis-spell the word..the load is 500Mva not "kva" ..but now there's new additional load reaches until 950 Mva..the load also supplying 4 chillers (400 tons total capacity) lots of different types of pumps ranging from 5hp to 30hp 3phase. some communication apparatus with UPS installed. sewage plant system, reverse osmosis system and other things.

500 MVA????.....fed from one panel????...and capacitor bank is 50 Kvar??????I think you are forced by somebody to join in this job regardless of level of knowledge required for the candidate.

Furthermore that 500 mva is the total connected load at site but as per Main distribution board (one panel) the total connected load is 950KVA and if diversified with PF correction during summer it goes to 620kva as per original computed plan..