A 3000KW generator is tripping on " Rotor protection operated" during its startup for black start (island mode) and also while synchro with the grid in parallel mode.

recently i changed the set of diodes, but in vain the same tripping protection still occurring.

any further step? or any idea?

thanks

 

Azzam... can you be more specific as to the identity of the "Protective Device Number" that initiated the trips(s)?

 

Er, ..., Um, ... Are you sure there isn't a real problem with "the rotor"? Do you know precisely all the conditions this alarm may be indicating? It's likely this single alarm may be annunciated for any of several possible fault conditions, not just failed diodes (which, if they are for a brushless exciter) may not be at all related to a rotor fault condition (unless there was a ground--which may or may not be resolved by replacing the diode(s)).

Many times a fault is truly a fault, and not just that confounded instrumentation! So, if you are certain the alarm is related to the diodes, and you are certain the diodes (and their grounding, or lack of a ground) are not the problem, then the problem might be a real rotor fault.

Unless of course it's the stationary portion of the rotor fault indicator that's the problem--in which case it WOULD be the darned instrumentation.

But from the information provided, it doesn't seem like you've eliminated all possible causes of the alarm.

Please write back to let us know what you find.

 

Thanks Phil,

The alarm is initiated by MRR1-Relay SEG Woodward for generator rotor protection. the failure diode protection Ir=(Ie,max-Ie,min)/Ie is tripping the generator. however all the diodes are ok. if Ir=15..20%, one diode is open if Ir#110% and one diode short if Ir#200% during our test Ir is reaching 80..90%. This relay is F40-64R.

Prior to diodes replacement, insulation test on the rotor was performed giving high value 417MOhm.

Thanks again Phil I appreciate your contribution.

 

> Er, ..., Um, ... Are you sure there isn't a real problem with "the rotor"?

Actually the tripping of the generator is caused by the "diode failure protection" Ir, which based on the measurement of the ripple component of the excitation current related to the mean value of the excitation current as follows Ir=100x(Ie,max-Ie,min)/Ie initiated by MRR1-SEG Woodward relay. and moreover another test was carried out yesterday for further investigation and testing. however the test was ok as the generator synchronized with the grid for 10min, and then during the unloading phase as it reached 0.9MW. the generator tripped by the same protection Ir for the first time (all tripping occurred during loading). that confused me and have suspicion on the relay itself??!
Insulation of the rotor is high.

 

Azzam… three follow-up questions:

1) Your original post mentioned the relay tripped under two operating conditions: a) during startup; and b) while synchronized with the grid. Do you have the corresponding V, A, kW, kVAr, and Pf, for the pre-disturbance condition, as well as those during the disturbance, for both conditions?

2) Your test showed 417 MOhms with the test leads positioned in one direction! What are the corresponding resistance values with the test leads positioned in the opposite direction!

3) Had you ever carried out the same tests with the Diodes in situ?

Regards, Phil

 

Azzam... additional questions:

4) What is time-delay setting of the Ir relay?

5) Has the problem appeared recent, for example, updating of generator's protective relaying system?

Phil

 

I'll suggest record with a fast acquisition data device the actual value of Ie and check if the ripple really appear or not.

 

Hi...

Did you manage to resolve this problem? What did you find to be the problem? I have a similar problem with a 2MW generator tripping on rotor diode protection (Same protection relay) when the machine gets excited. All checks on the rotor and diode shows all is well.

Kindly revert back to me even off-line on [email protected].

Thanks.