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Transformer differential protection

Transformer differential protection

Transformer differential protection

(OP)
There is a 10 MVA transformer, 46kV/4.2kV, delta-delta with available bushings CTs in the LV side. New dead tank breakers with CTs are installed in the 46kV.
It is possible to use the existing CTs in the transformer to implement a differential protection?

Thanks

RE: Transformer differential protection

yes, it is possible to use CT's on the secondary side of the TX and CT on the high side circuit breaker to do a transformer differential scheme.

RE: Transformer differential protection

If they're decent CTs there shouldn't be any problem. The biggest issue is that your bushings aren't in the diff zone.  

RE: Transformer differential protection

Sure.  The zone is just not as complete as you would like, as David said. It's much better than nothing.

But it is frustrating when the squirrel gets across the transformer bushings and the differential doesn't trip, subjecting the transformer to a 50 cycle through-fault at a very high current level.  Speaking hypothetically, of course.  looking around

David Castor
www.cvoes.com

RE: Transformer differential protection

Of course you'd also use those same CTs for a bus zone, now wouldn't you?

On the other hand, the arrestors on that side of the transformer aren't going to trip the differential.

If the feds really wanted to protect the electrical system against terrorists, they'd be after those suicidal squirrels and not worry nearly so much about much more complex and difficult attacks.  

RE: Transformer differential protection

CTs for 4.2kV shouldn't be too expensive - have you no option to retrofit them at the LV switchgear?

Re. comments above: Does this transformer have cable boxes or air bushings? Over here it would be unusual to see an open terminal substation at such a low voltage, and bus duct is usually confined to very heavy loads.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Transformer differential protection

One has to be especially diligent in watching out for the jihadist-trained squirrels...  I've had two instances where the squirrels made it to the bus tie breaker or switch before suiciding and managing to take out both halves of the sub.

RE: Transformer differential protection

We had one case where the gap between buses was too large for the jihadist squirrels and they had to recruit a racoon martyr to take out both sides of the substation.machinegun
 

RE: Transformer differential protection

And then there are the larger type of vermin: cable thieves. Those occasions you kinda hope that the protection will be a bit slow to respond, just to be sure that they are well-done. evil
 
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Transformer differential protection

Scotty,

We've had some changes in the laws regarding sale of scrap metal and it seems to have reduced cable theft quite a bit in my little part of the world.  Or the meth addicts have found something more valuable to steal.  

 

David Castor
www.cvoes.com

RE: Transformer differential protection

david beach
arrestors , terrorists,  suicidal squirrels, attacks...
my god, I do not understand anything of what you said!

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