Synchronous generator connection to sybstation 3

[Grinc]

I found in this forum that there are many experts regarding synchronous generator so perhaps somebody will explain me. I would like to know how generator connection is made to switchgear in substation? In my country synchronous generator connection to switchgear in substation (110 kV/10 kV) is made using voltage transformer that is connected in parallel with the line that supply system with power. The connection is made to 10 kV switchgear and synchronous generator installed capacity is about 2 MW (Coogeneration). I would like get know why this voltage transformer is used. One explained me that it is needed for blocking the feeder that feeds substation from generator if suddenly the voltage appears on it. I think the reason why this voltage suddenly appears on this feeder is that generator doesn’t work or work for auxiliaries service. If there are no blocking system there will be a short circuit. Am I right? Or is it related to phase angle differencies between the grid and generator ? If the generator works only for auxiliaries services so it doesn’t synchronized with grid and difference in phase angle between grid and generator may lead to short-circuit. That’s why there are blocking system in the substation needed (??). I am little bit confused...

Grinc

 

[slavag]

Hi Grinc.

Please attached SLD of typical connection.

Are you have 3-ph autoreclosere on the 110kV lines , that feeded this substation.

Best Regards.
Slava

 

[Grinc]

Hi Slavag,
Thank you for your attention
I tried to find any scheme there was shown cogeneration connection to substation. I hope it will be usefull to uderstand the use of this voltage transformer...
Actually I working in distribution group and 110 kV line is in responsobility of transmission group. But I was taught in school that there must be a 3-ph autoreclosere on 110 kV line, that feeded this substation.

 

[slavag]

Hi Grinc.
One dwg always better than 1000 words .

This VT/PT for synchronization of generator to grid.
Possible, it is used for the protection functionality of generator too.

Also optoion, near to generator you have additional VT for synchronization with bus, and this additional VT for synchrocheck relay only, additional functionality: used for avoid close CB w/o voltages on the cogeneration cable, live line -dead bus.

Hope it help.
Best Regards.
Slava

 

[Grinc]

Hi Slavag

Thank you very much.
Yes it became me much more clearer and you found right words to describe VT function regarding the synchronization
I am not so familiar with english abbreviations so what is "w/o" in full text ? ... sorry for silly question.
Another question - how this VT avoided to close CB if there is any voltage on generator feeding cable ? CB operation is controlled by CT and in which stage is working this VT to avoid this CB close ?

Grinc

 

[slavag]

Hi Grinc.
Np problem, my english isn't perfect too .
w/o = with out.

Now about your Q's.
1. You have generator and grid.
2. On the generator you have automatic synchronization system.
3. You have VT in the generator set for the protection and autosynchronization. One voltage from BusBar and one from generator side.
4. You send close command to CB, control of CB usually include additional synchtocheck relay: voltage from Busbar and from your VT. Thsi relay privide close ebable in series with generator system close command.

Few option:
Generator is far from substation and you don't want cables from your substation to generator side, generator side is include GCB ( geneartor circuit breaker)
In this case possible toe option:
1. Firstly you close your CB, in this case synchrocheck check live bus-dead line mode and after generator guys will closed GCB.
2. Blackout situation , generator guys closed GCB on the live bus-dead line, and you close your CB live line -dead bus.

This is a diference between two cases. First, your CB have synchrochek relay with voltage check functionality and it's synchronization CB
Second case it's only voltage check functionality.
In both case you nedd this VT.

Hope it help.
Best Regards.
Slava

 

[waross]

Did you get a star for that explanation, Slava? Have one now.

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

 

[Grinc]

Hi Slavag,

Aha, now I know for what purposes this star is given to somebody. Of course this explanation is star worth from me, too. I hope you receive a star from me, too
Thank you for explanation. I think this man who explained me once the use of this VT meaned the situation to avoid blackout situation. He explained me in much more difficult way. Perhaps this VT is used for synchronization check in my country, too. Next time I will ask him
Thank you, Slavag, again.

And thanks to waross to understand the use of STARS

Grinc