Tripping of 33kV Feeders

Is there enough load inductance in the system to balance out all that capacitance?

Also look for a resonance condition between your inductance and capacitance, especially likely since you describe some of the signs; sparking (overvoltage) and fuses blowing (overcurrent) during switching. You may also now have hidden equipment insulation damage due to all these transient overvoltages.

You can now Google for much more info on the subject.

What you are experiencing is called transient overload. Have your client at the other end shutdown all of their inductive equipment BEFORE you switch. They can leave on their resistive loads.

When you pull the switch, you remove the primary EMF, and leave the inductive loads to supply. Now, the power supply is the spin-down power of the inductive loads at the other end of the circuit. Those inductive loads will induce their own "supply" voltage, BUT, those supplys are no longer in phase with each other. So, as each motor and transformer "spins down", there will be peaks in supply voltage that will cause arcing at your end, mainly the switch. The capacitors will supply what EMF they have stored up and whatever current they might have stored for one phase, BUT, again, the phase is no longer in sync, and so the capacitors at both ends may momentarily reach a much higher charge than they usually do. If the inductive loads are shut down before the switching takes place, then, ONLY the capacitors will supply current to the circuit, but NOT any more voltage than they were charged with initially.

For further study of this phenomenon, you should study Eric Dollard and Charles Steinmetz.

The problem is in rush current while switching which have to be contolled to avoid tripping.When capacitors are connected in parallel to a group of loads that are connected in parallel, switching on/off have to be carried out depending on requirement of compensation . When more capacitor banks are connected in parallel the parameters should be carefully studied especially regarding the inrush switching current across the capacitor bank at the time of switching when other capacitor bank(s) connected in parallel are already in energized condition. Generally capacitors can withstand up to 100 times the rated current at the instant of switching. In case this inrush current is more than the limit specified above it would be necessary to provide 0.2% series reactor on the neutral end of the capacitor bank for limiting the switching inrush current within permissible limits.

Try to switch off load on user side and then switch on the transformer and subsequent sequential switching on the user load for idnetifictaion of teh problem. May be capacitive and inductive laod are not balanced if the capcitors are not on AUTO mode.

check the capacitor condition in capacitor bank

i think problem was in capacitor bank

The amount of electrical current required to charge the capacitors in addition to the operating circuit load is greater than the system overload protection will allow.

Have a competent protection engineer evaluate your settings and correct any errors.

If the system protection settings are already correct for your application, you must decrease the amount/number of capacitors being switched into the circuit(s).

Again this will require the services of competent electical system protection engineer to perform the calculations and solve your issue(s).

Inrush surge current and voltage cause failure of capacitor banks and hence these factors have to be tackled with safe tripping VCB to avoid damage. Majority of failures of capacitors are due to switching surges and tripping is a safety device.It is advisable to provide surge arresters in the capacitor circuit preferably it is recommended to use Metal Oxide, Gap less type Surge Arresters with discharge class III. Double earthing pits to be provided exclusively for surge arresters. Check up weather these provisions are made.

The huge inrush current anticipated during back-to-back capacitor switching