TRANSFORMER DIFFERENTIAL PROTECTION

[apprenteng]

I have a relay that has faulted on the digital to analogue converter circuit for the red phase, High voltage side. I can't get a replacement immediately but need to normalize the circuit urgently. I would like to connect the differential relay to work on red and blue phase currents only as I source for a replacement.

Will the connection provide adequate differential protection?

 

[cranky108]

No.

Take the equipment out of service or operate it without differential protection or find a replacment relay.

Rather blunt, but if the transformer is a delta wye, what you are proposing won't work. If it is a wye-wye or auto, than one phase won't be protected.

Depending on you application you may need differential protection for safty reasons. Or it may have been nice to install, which means you don't absulity need it.

 

[alehman]

No, it will not provide "adequate" differential protection.

What you propose might be possible to obtain partial protection, but would take some careful analysis of the relay and CT configuration.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[odlanor]

In a delta-star transformer with grounded source from both side, a diferential circuit connection
always have two differential relays in operation during a fault even thou for one fault-to-ground.
I guess this is possible.

 

[slavag]

Hi.
What cranky108 saied.
In urgently case, you have O/C protection-50/51 and all elktromechnical protections ( Buhollz, etc.).
What is a Xfr size?
Best Regards.
Slava

 

[apprenteng]

The transformer is 5 MVA and the relay is numerical, a micom P631

 

[odlanor]

If is a numerical relay forget everything I said !

 

[slavag]

Hi apprenteng.
I can't recommend something, it's your responsibility.
But, for this size of Xfr, you can leave Xfr with O/C ( two stages) and Buhholz only and urgently order spare relay.

Best Regards.
Slava

 

[oldfieldguy]

I agree with slava (as usual. he's good!). You have tow choices to explain to your managers: continue running with diminished protection (overcurrent, Buchholz) or take it off line until a replacement is installed.

If the transformer is in good health and not subject to adverse conditions, the first option is a relatively low-risk venture. The second is no risk to the equipment, but downstream loads may be subject to several undesirable situations.

old field guy

 

[xxjohnh]

Contact

http://www.selinc.com/

they can get you something in 48 hours.

 

[apprenteng]

Thank you guys.