Synchronization at 20 kV is Fail 2

[JonoJakarta]

Dear Experts,

Last 8 October 2019, we did synchronization between our generator and our grid in 20 kV networking. Our generator is 11 kV and step up by transformer 11/20 kV, 12/15 MVA.
The Synchronization is fail. And 87T relay in breaker (this breaker connected between our Transformer and grid) active also the breaker at grid side is active and tripped also.
My question:
1. Is that normal way when we do synchronization in 20 kV between the generator and grid with "MANUAL"? (MANUAL mean is we closed breaker with switch "OPEN-NEUTRAL-CLOSE" at our Synchro.Panel)
2. What is "UNEARTH" means in the picture (red circle)? (please, see attachment in this thread)

Any comments are welcome for me.
Thank you

Best Regards,

Jono Jakarta

 

[edison123]

Isn't 87T differential protection?

Many conditions to be met before synching the generator to the grid. Phase sequences match, CT polarity match for generator and block differential protection, correct speed/Hz, proper synchronizing at 12 O'clock etc.

A synch check relay will prevent you from wrongly synchronizing the machine to the grid.

Muthu

http://www.edison.co.in

 

[waross]

Is this an installation that has been successfully synchronized in the past or are you commissioning a new set?
Unearth? Probably a description of the cable armour. Nothing to do with synchronization.


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

 

[ScottyUK]

87T will be the GSU transformer differential, so it makes complete sense that the relay has tripped both breakers.

Generally an automatic synchroniser is provided, but it's certainly possible to synchronise a machine manually using the synchroscope. The synchroniser is backed up by an independent check-sync relay to prevent out-of-step closure.

 

[JonoJakarta]

Dear Bill,

this is commissioning new set, 1st time

 

[waross]

There are two possible causes.
Control wiring errors.
Reversed phase sequence.

Check your wiring.
Specifically PT polarities.
Then check phase rotation.
The old school method.
You should have Potential Transformers and on each generator phase and on each bus phase.
Follow the bus from one pole of the breaker used to synchronize the gen-set to the PTs on each side.
That is the generator PT and the bus PT.
Do the same for the other two poles.
IMPORTANT: You are looking for a wiring flaw. Do not assume that the numbering on the PTs is correct. Visually or by continuity verify the PTs. One or more PTs may be mislabeled.
Now connect a double voltage lamp or a voltmeter across the PTs for each phase.
You will see up to 220 Volts with 110 Volt PT secondaries.
Start and run the generator about 1 Hz faster than the grid.
The lamps should go bright and dark all together.
The synchroscope should be at the 12:00 o-clock position when all the lights are dark.
If the lamps do not go bright and dark together you may have reversed phase sequence. That is while the grid is ABC the generator is ACB.
If the lamps are bright and dark together, but the sync-scope is not at 12:00 o-clock when the lamps are dark you have a wiring error in the synchro-scope wiring.
The sync-check relay should only allow closure when the lamps are dark.

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

 

[ScottyUK]

Ideally disconnect the transformer from the system, then close the synchronising breaker. If the breaker is closed then the main bus is in synchronism with the generator feeder. From that state check your VT's signals match the state of the primary plant.

If the VT's check out OK look for a CT wiring error. With the GSU transformer is isolated from the system you should be able to arrange a balance shot through the diff scheme using a Variac or a rental LV generator with a directly-controlled field as a source of variable 3-phase AC current. Short together the terminals of whichever winding you don't inject current on, or use the earthing switches as the short. Be careful you don't inadvertently activate a breaker fail scheme!

 

[Rodmcm]

Isolate the generator and then manually close the incomer to the transformer
This should liven all of the Pts and show whether the running and incoming are phased matched
I do this for all synchronising checks