Generator Synchronization Issue

Why would you not believe the supplier?

What is the model of the controller? Anyhow; I have doubt that the Gen Sets will be synchonized under loading condition if they cannot with no load.

symap - bcg,

Is it passive synchronizer?

http://www.voltex.com.au/wp-content/uploads/2012/05/SYMAP-Brochure.pdf

model bcg

The solution is to activate 25A(not only 25). That should sort the problem out.

My understanding of the differential protection trip circuit is that you are measuring the neutral current and also the vector sum of the three phase currents. If all is well within the "protected zone", they should sum to zero, or if not, some of the current is returning through ground and the power is shut down.

I understand that if either generator is run by itself, there is no problem, but if they are parallel, then it trips. Is this a new installation, or did it once work properly and is now faulty? A simple schematic would be helpful. If it has never worked, perhaps it is not set up properly. Finally, are you sure it's the differential protection that is causing the shutdown and not another issue like phase reversal on one of the generators?

Just some thoughts. I hope I have not belabored the obvious.

thanks, its new installation, under commissioning, it trips in both differential and reverse power. differential protection is individual for each set. if there is any leakage it should trip when it running individually also but it doesnt happens. that means abnormality is only after paralleling. the relay gives closing signal only after checking the parameters and its correct also.

Are you sure it's the differential that's tripping it?

Two things come to mind which come into play when generators are connected in parallel.

Governor droop allows the generators to share the "real" load (KW). When paralleled, one generator governor should be in "droop" mode. If both governors are "isochronous", a small misadjustment in the throttle settings will allow one generator to assume the whole load and even motorize the other generator.

Cross current compensation in the voltage regulators allows the generators to share the "reactive" load. Reactive load is where the current is out of phase with the voltage, and is not only due to the characteristics of the load, but also can be a result of the voltage levels (excitation) of the two generators not being set to the same value. A possible problem would be if current sensors (CTs) were not wired with the correct polarity for the cross current compensation.

If you have a large amount of current circulating between the two machines, possibly one or more of the current transformers in the differential protection circuit are saturating. If this is happening, it would appear as a ground fault (current imbalance) and trip the circuit.

I hope these ideas are helpful. (It's been a long while since I have worked on generators.)

its not only differential but also the reverse power. i will check it. but since it is not loaded yet no any chance to become ct saturated, if any ct polarity is changed tht time also diffntl will work. the cts are tested also prior to the commissioning. because to saturate at least full load current to be flown once it didnt happen yet. any way they will continue next then will come to know.

thanks

I was thinking not current flowing towards the load but between the alternators due to unequal governor settings (real current) or unequal excitation (reactive current) or both. Just guessing here.

We can throw out ideas of what we think might be going on, but someone on site really needs to look into it. (I've done troubleshooting remotely on equipment I was intimately familiar with and it's still tricky.) If your vendor "owns" it until it's accepted, you're best to go along with his suggestions, imho.

Synchronisation is half the story load sharing is the other.....

When the gensets are synchronised and tied they should both be feeding into the dummy load bank on the bus, no?

We need more information about the synchro panel and controller you are using.

Let them try.

the relay is symap BCG. pls refer

http://www.voltex.com.au/wp-content/uploads/2012/05/SYMAP-Brochure.pdf

since there is one common load bank only for both gensets it cant be loaded during parallel operation, there is interlock. thanks

and hand speed control

Synchronisation not possible.

Trips on breaker close.

Is it certain sets have same phase sequence at the breaker generator sides?

Unloaded gensets certainly can be paralleled.

Does the differential relay indicate which phase?

Have you tried synchronising lamps; synchroscope, or other elementary check with breaker close coil disconnected and hand speed control before trying actual close?

we done the synchronisation using symap relay in auto and by sychroscope in manual also (control panel having both mode of operation. its working fine prblm happens only after parallel operation. any way we stopped the testing and CAT will send their experts to sort out the issue. as you said they also confirmed that sets can be paralleled in no load. thanks

you are right sir cross wiring in ct circuits always operate unbalance relays. we faced in another 415V stand alone set. as you said it was clueless statement, we stopped the testing and they will send their experts to solve it. thanks

dear sir, would you please reply for a question. there are 4nos 3.3kv 2000kva gensets are running in parallel no load, while running on no load what is the permissible current in each genset. because while connecting gen-1 and 2 it works fine no current or power. but if the 3 or 4 are added to this, or 3 and 4 only connected and runs parallelly, the meter shows current up to 100A and power 2 to 30kw it varies also. its cat genset. all 4 sets are having the same ratings and parameters. the supplier says its normal and doesnt make any harm to the system.

thank you

If only sets 3 and 4 behave like this and all units are identical, then 3 and 4 have the same fault or most likely, wrong wiring again. It is not normal and it will do harm if left.