Reverse power protection for a transformer

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mbrooke

mbrooke

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Any tips on what the reverse power settings should look like- or what to consider?


Basically I am contemplating this as a last resort backup if you were to loose bus bar protection. Ie, 345 to 115kv substation with bus bar protection disabled. A bus fault on the 345kv side would be cleared via zone 2, but how would you get the interconnecting 345-115kv transformers to trip their breakers? Unless of course someone believes ANSI 21 (step impedance) would be better.
 
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GoldDigger

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mbrooke said:
In simplified terms a relay that operates with current flowing only in one direction and not the other. Ie, current flowing forward above the trip threshold will cause a trip, current flowing in the reverse direction above the tripping threshold will do nothing. ....
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Which of course actually means current flowing in the same direction as the applied voltage or the opposite direction. Current will always alternate. It is the power (energy flow) that has a definable direction.
 
ATSman

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Not sure I understand what you are trying to achieve.
I have only seen reverse power protection used for either gens in parallel or gens & utility.
For transformer winding protection, xfmr differential relays were the norm.
 
mbrooke

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GoldDigger said:
Which of course actually means current flowing in the same direction as the applied voltage or the opposite direction. Current will always alternate. It is the power (energy flow) that has a definable direction.
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Correct, power flowing into the 345kv faulted bus but not the 115kv bus.
 
mbrooke

mbrooke

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ATSman said:
Not sure I understand what you are trying to achieve.
I have only seen reverse power protection used for either gens in parallel or gens & utility.
For transformer winding protection, xfmr differential relays were the norm.
Click to expand...



Normally a 345kv (or 115kv) bus fault is cleared via bus bar differential protection which opens all the breakers connected to that bus. But picture a scenario where the bus bar protection is out of service (or fails)- you need a last resort backup. For 345kv lines entering the station the last resort for a fault on the 345kv bus bar will be cleared via Zone 2 step distance at the remote substations. However, Id like to have some type of means to remove the transformers.
 
mbrooke

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Phil Corso said:
What's stopping you from using the 67?

Phil
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Nothing, other than the thought that 21 might coordinate better. With 21 all I need is the positive and zero sequence impedance of the transformer itself, the right zone time delays, and the correct facing MHO circles. However, a typical 487E does not contian any 21 elements so 21 would require a separate 311C relay. The 487E on the other hand does have 67, so I can use that no questions asked. However, I am unsure what vales to use for the 67 elements. I do not need exact numbers, but rather general guidance from the senior pros.
 
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Phil Corso

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mbrooke;... said:
I have to admit since there are no requirements that transformers have such backup protection, material on the subject are sparse (down load the link to read)...
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Caveat: I have a vague recollection that Prof. Blackburn warned, that on Xfmr feeders, Qty-3 and not just Qty-2 phase relays are required! If I can find it I'll get back to you!

Phil
 
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mbrooke

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Phil Corso said:
3-units, one per phase!:roll:

I looked back thru all my Westinghouse Directional-Relay Application Bulletins and personal job files! None ever used 2-units! And, no, I can't recall the reason for Prof. Blackburn's admonition!

Phil
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I have to admit I don't know much about that- as I am unfamiliar with electro mechanical relays. I know that meant something in the induction disk world, but I for one am not sure how that translates to the microprocessor world.
 
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Phil Corso

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mbrooke said:
I have to admit I don't know much about that- as I am unfamiliar with electro-mechanical relays. I know that meant something in the induction disk world, but I for one am not sure how that translates to the microprocessor world.
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Kept digging and found another piece of the puzzle! It had nothing to do with relay, but related to there being 2, phase 67's, a 67N, and double-phase to grnd fault!

Phil
 
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