Generators

[gillson]

My question is.... Post generator fault, 10MVA unit, what tests would you run before putting it back into service? Consider a) internal fault such as stator ground b) external fault such as a slow clearing bus fault.

I have mainly transmission experience and am not sure what all to consider other than insulation integrity checks.

Thank you.

 

[gillson]

Can someone please give their 2 cents worth regarding generator testing post fault?

 

[MotorVib]

If I was you I would run it at rated voltage and if you can run full load amps. Also check the vib's of the unit. An over speed and Mager would also be a good check.

Chris

"In this house, we obey the laws of thermodynamics." Homer Simpson

 

[dpc]

If internal fault, you can assume it's probably going to stay broken. A quick megger test should be done. If that is successful, a PI can be done and possibly a high-pot. If these all pass (unlikely), you can try to bring it up to speed to check for vibration than apply the field gradually.

For an external fault, I wouldn't be too worried. The generator output in the long term is limited by the synchronous reactance and the field. Just keep your eye on the no-load current as the field is applied.

If it is solidly-grounded and you had an long external ground fault, I'd be a little more concerned, since the fault current will be higher than for a phase fault. But I'd really hope a 10 MVA unit was impedance-grounded.

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[waross]

Can you share with us the details of the fault?
You may want to do a few other tests before the full load/full voltage test.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

A lot depends on what type of fault occurred, what you know about the the nature and location of the fault, what protective devices operated, etc.

Less you know, more tests are required.

 

[nawao]

In case of internal fault, after the general overhauling and necessary repairs done including rotor dynamic balance, a high-pot test must pass. Bring it up to speed to check for vibrations. Make a load test applying the load gradually. Give us more details about the alternator characteristics and the type of fault.

 

[Denan]

dpc, can you please explain what is PI and high-pot from your post above:
"If that is successful, a PI can be done and possibly a high-pot."

Thanks!

 

[pwrengrds]

A PI is just a 10 minute megger test, the idea is to determine the capacitance of the winding. The 10 minute reading / 1 minute reading is the Polarization Index. Depending on the type of insulation it should be between 2-5.

 

[Denan]

Thank you for explanation, pwrengrds

 

[gillson]

Thanks guys, this question is due to an Aph-ground fault at the gen disconnect. The high voltage cables were not terminated at the same height, so the voltage gradient from the 7kV termination kit was less than an inch from the ground point (shield) of the adjacent Aph cable. An external fault, internal to the txf differential zone but cleared by the stator ground protection. So my guess was to high-pot, and check vibration at speed no load. Thanks