Generator Synchronization Problem

Not my field, but what happens when you start #1 and then try to start and synch #3?

Both fault scenarios that you describe involve trying to sync #1 and #3. There may be a cable fault or similar in that set of connections.

As I said earlier, not my field, just a guess!

When we synch #1 & #2, no problem but if synch #3, #1 will trip loss of field relay,

If synch only #1 & #2, #2 & #3 or #1 & #3, no problem in synch. The problem is when synch the 3 generator #1 will trip because of Loss of Field, every time we synch the 3 generator

Sounds like you may want to check your switch gear for ground faults.

https://cr4.globalspec.com/thread/69707/Droop-of-a-Generator

Vinu_Answers has a good response in the above thread.

Suggestion only: Google reactive load of transmission lines.

Are the generators the same size? Does 'size' matter?

Is the 3rd generator brought in because he first 2 are on full load? , or are all three brought online before the load is applied?

They are the same capacity 6MW, they operate only during power interruption of the Utility. The question is, why Genset 1 will trip after it is synchronize to other 2 generator, it only operates normally if we use only 2 generator. For example, if we synchronize Genset #1 and Genset #2 or Genset #1 and Genset #3 it operates normally, problem occurs when we synchronize the 3 generator, Generator #1 will trip after we synchronized with 2 others with some delay not instantly. The cause of tripping is "Loss Of Field". Why it is only Genset #1 having problem. The two others operate normally.

I take it you have read posts #3, #4, #5??

It seems you agree that the problem is with Genset #1.

You have answered the post that asked if generators were all same size.

It is most possible the voltage regulator on Genset #1 has a fault, but it could be that it has a "wrong" selection from the plant control, even a "breaker closed" contact not working. It might be that Genset #1 "Loss of Field" protection is set wrong or has a fault.

Since #1 is able to synchronise and connect it is unlikely that "Loss of Field" protection which checks actual field current is faulty - it could be saying FAULT but its contact is disconnected from trip relay until Genset #1 is on-line. A look at the circuit diagram for "Trips" might find an "arming" contact [e.g. Generator to Line breaker auxiliary contact or "Breaker Closed" relay contact] in series with "Loss of Field".

However, Genset #1 would operate normally (same as other units when they start & load) before trip.

Normally, a generator will take some current & MW as soon as it connects - synchronisers do not have to be perfect. Power factor could be lead or lag and MW positive or negative. The governor will be given a raise demand at connection & MW will ramp up.

If the generator field current stayed constant, the power factor meter would indicate a falling leading power factor as MW increased until the generator loses synchronism with parallel gensets at much less than full MW.

In a historic system, the operator would increase the field current as MW increased, field current at full MW would be several times that to synchronise.

When 3 phase & Automatic Voltage Regulator [AVR] became common, it was realised that a current transformer could be made to put a voltage in series with voltage sensed by AVR, so that a leading power factor current reduced voltage to AVR proportionally, making it increase field current. If the volts setting was not altered, full MW would be got at high leading power factor.

With that in mind, some questions.....

1. What are the MW and Power Factor [cosφ] meters on Genset #1 reading at time intervals after connection & before/at trip? How do readings compare with "OK" gensets.
2. If you have an "Excitation Current/Field Current" meter, what does it read just before connection & how does it change after? What do the same meters on "good" sets read for each MW load up to full load for comparison?
3. Can you operate in a "manual" mode, with Genset #1 governor and AVR settings made by operator using switches/buttons to Raise or Lower? This could bypass a defective load sharing system.
4. Does your AVR have an MVR or excitation current regulator selection for testing? This could avoid faulty AVR parts & show Genset #1 can work without "Loss of Field".
5. What is the usual power factor of your load [on two Gensets?] and its MW when you are making tests for this problem?
6. What make and type are your AVRs? It may be possible to get data & suggest which modules can be swapped from genset to genset to see "if problem moves with module XX".

67model

Another question...

7. Is the "Loss of Field" detection <a relay on a "Generator Protection Panel">?

If it is, they are often in a glass front case or rack and can be unplugged to swap them from Genset to Genset.

67model