Generator Overvoltage

[joan271273]

Has anyone experienced the following:

In a "island" type facility, power is supplied from three (3) 12.47kV generators in the moment we close the breaker of the first gen set against the "dead bus" we getting overvoltage reading of 25,000 volts for a few cycles. this value was maesured with some test isntrumentation ( & Easy power ). Problem came to evidence when the fuse ( at 480V bus )that serves the elevator started to blow. After reviewing everything related to the elevator is was pretty clear that the problem was elsewhere. Once it was determined that everytime we started the plant gensets we proceeded with the measurements that showed that overvoltage condition.

If the gen-set is OK, what can be the cause for this

 

[dpc]

It could be ringing due to a capacitor bank being energized or distributed capacitance of the cabling system.

Do you have a way to determine the frequency of the voltage spike?

I'm assuming the generator voltage is nominal before you close the breaker?

 

[joan271273]

Voltage was nominal, I was thinking that the cable distribution ( Impedance) might be the culprit. I will try to see if the charts have the frequency not one 100% sure. Do you know of any mitigation systems

 

[DirectCurrent]

How much of the system are you trying to energise in one go?

Is it possible to connect the first generator to the main bus and then re-energise parts of the system after that?

 

[busbar]

It may be possible that a 'ferroresonant' condition occurred. Recently discussed at: thread238-33645