Generator synchronization problem

[madomankh]

How long i can synchronize two generators each 2MW without loads?
Is there is condition to connect generators in parallel without load or the synchronization will fail due to no-load operation.

 

[edison123]

I don't see any problem synchronizing two generators without load.

Any reason you want to run the 2 generators without load ?

 

[madomankh]

Yea,we are at the pre-commissioning phase and there is no actual load and we arleady did the test and one of the generators fail by reverse power 10seconds after synchro.
and we still investigating up to now.

 

[waross]

Hi Edison. I have had to do that prior to starting a large motor.
You may have to set the reverse power relay a few percent higher.

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

 

[waross]

If you are synchronizing manually, the synchro-scope needle may have been moving a little too fast when you closed the breaker. To sync with no load, you should adjust the governor control so that the synchro-scope is almost stopped before closing the breaker.

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

 

[edison123]

Thanks Bill. I get it.

moustafa

When you say "one of the generators fail by reverse power 10 seconds after synchro", do you mean the generator winding failed or simply the reverse power relay tripped ?

 

[madomankh]

Yea Simply the reverse power was activated and associated with under frequency.

and for Mr.waross
the synchro was on auto mode and the schenchro was already done but one generator trip after 10 seconds
and another clarification required the reverse power is will known for the generators but what do you mean by prior to starting a large motor.
You may have to set the reverse power relay a few percent higher.

 

[edison123]

What is RPR threshold setting ? If I remember right, it should be at least 5% of forward current.

 

[madomankh]

The setting is 10% for 2 sec.

 

[edison123]

What is your prime mover ? RPR is meant for protecting the prime mover mainly rather than the generator.

Here's a good ABB pdf link on their RPR's.

http://library.abb.com/global/scot/...and_protection_assemblies_RXPPK_2H__RAPPK.pdf

 

[edison123]

The link still works. Just click on the pdf file on the ABB page.

 

[waross]

We had to start a large motor at a mill. Typically,we would start and synchronize the generators and then start the motor. When the motor was successfully started, we would start the other loads.
Also, at a small power plant, when going back online after an outage, if the anticipated load was more than one set could handle we would start and sync two sets prior to picking up the load.
If there is any variation of the governors at no load, you will have reverse power. If the load will be applied within a few minutes, it may be safe to bypass the reverse power protection until some load is added.
Reverse power damage usually takes some time to develop.
What type of prime movers do you have.

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

 

[nawao]

Is possible, during pre-commissioning test without load that this kind of tripping occurs.
IMHO is not necessary to vary the protection settings calculated for normal operation.
Possibly in your case you are paralleling with governors in isoch mode. If is so, change to droop mode and set droop at 3 to 4% to avoid generators to be motorised each other.

 

[trikker79]

Hello, I posted an inquiry but i think this might be related. we want to test to manually disconnect one of our diesel generator from the busbar. the capacity is 1750KW and 6.6KV, what would be the minimum safest load this generator is carrying before we start testing it?

 

[madomankh]

Our priemover is diesel and the generator capacity is 2000KW and 6.6KV

 

[YuriSarcas]

You should be able to have two generators online with no load without tripping anything out. What kind of regulators are you using? What synchronizer and load control do you have? Make sure your voltages are spot on between the two. Even a half of volt difference on secondary could really mess with your cross currents and cause you to get reverse power. Are you using a droop CT? Verify proper polarity going to your regulator.

You need to make sure they will share together with no load before you try to load them in parallel.

 

[itsmoked]

trikker79; If things are balanced correctly, as this thread is describing, "no load" would be the answer.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[rbulsara]

Is any manufacturer's field service engineer working on this? This is a very common issue at the commissioning and any reasonably good field tech will resolve the "reverse power" tripping issue. All it needs is some tweaking to AVR and governors. This is assuming all protective CT and relay wiring is flawless.

 

[trikker79]

itsmoked; thank you for the reply. at least i have an idea. im avoiding the load going to other generators instantly. might cause a black out with the whole ship.

 

[waross]

trikker79;
Look at the watt meter, not the ammeter. Back off the governor until one generator shows zero watts. If the ammeter is showing a lot of current, adjust the voltage until the current drops. Then trip the breaker open.

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