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Generator rotor insulation resistance
2

Generator rotor insulation resistance

Generator rotor insulation resistance

(OP)
On a 200MW generator, the rotor insulation resistance displayed on REG316*4(with REX 010 and 011) is variable in operation,between 4 and 30kohm.
The rotor insulation resistance measured with rotor not in rotation is very good.
The rotor and the relay were checked and seem to be ok.
The problem appeared from rehabilitation of the unit, when the protection and control system was replaced with a digital one.
Does anyone encountered such a problem?

RE: Generator rotor insulation resistance

Does the unit have a static exciter? It can be the ripple is affecting the new digital relay, but did not the old.

If you check the opn of the new REG using a resistance decade box (unit at standstill) do you get correct operation ?

What are the Mohm readings of the rotor at standstill?

I am not familiar with that particular relay, but would imagine it must have a filter to remove the ripple from the static exciter built in, if that is what you have.

rasevskii

RE: Generator rotor insulation resistance

This type of relay works better on a static excitation system.  It's very difficult to get the relay (capacitance bridge) to reflect the actual rotor resistance to ground.  Mostly you can only balance it so it's not in alarm.  So if you have a brushless excitation system, you may have to live with it.  If you have a static exciation system you need to have it balanced.

Looking at your numbers I'm guessing that you are running sometimes in alarm

RE: Generator rotor insulation resistance

Hi lednas.
Please attach a wiring diagram of REG316 and REX( what type), and capacitors (2 or 4mF ?).
Do you provide commissioning according to commissioning procedure.
Please attach graph of test.
 Usually problem with wiring, check connection of cpacitors, check capacitors.
Check connection of grounding wire.

Possible some real problem and you have some temprary contact between plus or minus with grounding.

RE: Generator rotor insulation resistance

You could also try, balancing the relay while the generator is at full speed no load, with excitation on instead of only at standstill.  Sometimes makes a difference but trickier to do.

Also try changing the bridge supply phases.  For example if it's supplied by A and B, try A and C or B and C.  Not sure why this works but it's recommended in the manual and I've had some success with it.

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