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Harmonic resraint

Harmonic resraint

Harmonic resraint

(OP)
I had a question concerning harmonic restraint for differential relaying. The question concerns an auto transformer with a delta tertiary. I was told that there would be no need to have harmonic restraint for this particular transformer due to the presence of the delta tertiary. I do not see how the two are similar. I thought that harmonic restraint was for energizing a transformer and restraining for second and fifth harmonic current. I thought the only purpose of a delta tertiary in an auto transformer was to reduce fundamental harmonic.  Any clarification would be appreciated. Thanks

RE: Harmonic resraint

Agree. I don't think the tertiary will affect the need for restraint on inrush. I don't see the tertiary changing that. Harmonic restraint normally uses 2nd harmonic.

Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.

RE: Harmonic resraint

MRTECH, you are right. Tertiary winding is for separation of zero sequence impedances of primary and secondary networks only. It has nothing to do with charmonic restrain.
By the way, if you have in your relay setting option "cross blocking" for charmonic restrain, don't forget to ckeck it. I had a case in the past when left it unchecked and old 25 MVA transformer tripped when level of 2-nd charmonic of 2 from 3 phases dropped under setting level.

------------------------
It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant
 

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