GeFS9001E unable to be back to service due to generator differential relay lockout and generator rotor field ground fault. This was the only process alarm on our operator interface display as at the time of the shutdown, that generator differential lockout.

Ge FS9001E gas turbine generator was shutdown normally due to inability of our gas supply company to deliver adequate gas pressure to us, but after sometimes there was gas restoration. however it was observed on the generator control panel in attempt to bring the unit generator differential lockout operation and at the ex2000 cubicle the generator field ground detector relay also operated but attempt made to clear these alarms were not successful. What one do when these the conditions prevailed. What positive response and suggestion shall be highly appreciated. Thanks.

 

H2G... what tests have you carried out, thus far?

Regards, Phil Corso

 

>H2G... what tests have you carried out,
>thus far?
>
>Regards, Phil Corso

We have carried IR test on both the stator and rotor.

Stator IR were okay but that rotor were giving 0megaohm but as the carbon brush and slip ring holder was it improve to 608megaohm. But after connection it 0megaohm. We then applied the generator space heater but the value still remain the same. What can be done then.

 

H2G... what are readings with brushes lifted?
Phil

 

The proper way to handle this kind of situation is to look at the unit's protection relay logic diagram. Look at all the inputs that goes to the generator diff lockout. From there, check individual relay operation.

Try to perform hard reset on the EX2k as well. Good Luck

 

> H2G... what are readings with brushes lifted?

With the brushes the readings was 0megaohm. Also with the brush holder removed completely, the rotor IR was 0megaohm.

Thanks.

 

> The proper way to handle this kind of situation is to look at the unit's
> protection relay logic diagram. Look at all the inputs that goes to the
> generator diff lockout. From there, check individual relay operation.

It seen to be you have a good understanding of the GE fs9001. We megger the generator rotor it was giving us 0megaohm with or without the carbon brush holder.

How one check the protection relay logic diagram?

Thanks.

 

H2G... lifting the brushes will separate the field-winding from the exciter!

Have you tested resistance using an ohmmeter instead of the IR meter?

A very common source of ground-failure is inadvertent grounding of the slip-ring mounting itself. It must be isolated from the shaft! What is the Ohm value between the slip-ring and the shaft?

Phil

 

How is the rotor ground detection wired? We had a similar issue when meggering the rotor only to find that the megger was going to ground via the ground detection LED. No real ground existed.