Transformer burnt while installing cap banks

[calabala]

Hi,
We were adding a step capacitor bank (each 600KvAr) to one of our customers. Out technician was installing it was stepping in and out Capacitors simultaneously in a way that did burns the main transformer. Is there any suggestion what can be the cause of that?
Note that the customer did have this transformer working for 5-7 years with no problem, and he has some nonlinear loads in his system.

 

[jghrist]

One or more steps of capacitors may be in resonance with the transformer. This could cause high voltages and/or currents in the transformer if there are high harmonic currents.

 

[calabala]

In that case, what can we do? do we need to measure harmonics in the facility and then try to get the frequency resonance and then add somehow a line reactor or what?

 

[magoo2]

What voltage level are you working with, what is the transformer rating and what type of breaker/switch is used for the capacitor bank?

How long have the capacitor banks been on before the transformer failed?

 

[MxGxK]

Stepping in and out simultaneously. Not sure what you mean. Did the capacitors have internal discharge resistors? Was the technician waiting 5 minutes prior to re-energization of capacitors?

 

[UtilityDave]

Capacitors are capable of building up charges through repeated switching w/o sufficient discharge time. If seen it referred to as "pumping". If your technician was switching frequently that is a possibility. The solution is don't do that. Wait a few (5) minutes between.

Second when swiching back to back capacitor banks there is some inrush between the banks. The energized bank can discharge into the energizing bank very quickly. There could be some issues with that. These banks seem small for that but it is a possibility. You could intorduce some resistance in the switch to limit that inrush.

 

[calabala]

Thx a lot for the useful info. This seems to be the problem (not waiting for 5 min to discharge capacitors)