Transformer Differential Protection. Homopolar component compensation
Transformer Differential Protection. Homopolar component compensation
(OP)
Hi colleagues,
Actually we have a 3 bank power transformer with the following data sheets:
3 x 420 +-2.5+-5% kV / 20 kV
YNd11
3x420MVA - OF AF
The 87TG protection has conected an old design (dated from 1970) to compensate the homopolar component in the low voltage side, that include three CT in every winding phase conected in parallel and an auxiliary CT open delta / Wye used to conect to the 87 relay. Does anybody know this way to compensate the homopolar component ? Has anybody references about it?
The point is that now we are working to replace this relays and the actually digital differential transforme relay has features to filter the secuence zero component (on high voltage side) and this complex circuit shouldn't necesary.
Thanks
Actually we have a 3 bank power transformer with the following data sheets:
3 x 420 +-2.5+-5% kV / 20 kV
YNd11
3x420MVA - OF AF
The 87TG protection has conected an old design (dated from 1970) to compensate the homopolar component in the low voltage side, that include three CT in every winding phase conected in parallel and an auxiliary CT open delta / Wye used to conect to the 87 relay. Does anybody know this way to compensate the homopolar component ? Has anybody references about it?
The point is that now we are working to replace this relays and the actually digital differential transforme relay has features to filter the secuence zero component (on high voltage side) and this complex circuit shouldn't necesary.
Thanks






RE: Transformer Differential Protection. Homopolar component compensation
RE: Transformer Differential Protection. Homopolar component compensation
RE: Transformer Differential Protection. Homopolar component compensation
The relay could also accept CTs in wye on the delta side of the power transformer and in delta on the wye side, but you will get better information from the relay if you have wye connected CTs. You can also do ground differential (REF) if you have the CTs on the wye side of the power transformer in wye but you can't if you have delta connected CTs.
RE: Transformer Differential Protection. Homopolar component compensation
Anayway thank you so much
RE: Transformer Differential Protection. Homopolar component compensation
If you're indeed using GE STD's, then the instruction books are available on the GE website. In the manual for the STD15C, several representative diagrams are shown which depict the correct CT configurations for various transformer types. These should be followed to present these single-phase relays with currents in the proper relationships for proper operation. If the CT configuration cannot be followed as depicted due to other conflicts, then auxilliary CT's may be used to present the proper phase relationships, but this complicates the installation.
In my experience with commissioning many transformer installations, the improper connection of CT's for these relays was probably the most common one I caught. Many designers and engineers do not totally understand the circuits. The pictures in the book are correct.
The second most common problem was connecting the current inputs to the proper terminals of the relay, or incorrectly assigning the tap values. It's confusing because Winding 1 currents go to terminal 6 and Winding 2 goes to terminal 4.
New electronic relays do not require the external configuration of the CT's. Everything is connected in wye and brought to the relay, and the phase shifting and conversion is performed by the relay based on parameters the engineers enter into the relay program. Makes life easier in many ways.
old field guy
RE: Transformer Differential Protection. Homopolar component compensation
RE: Transformer Differential Protection. Homopolar component compensation
RE: Transformer Differential Protection. Homopolar component compensation
RE: Transformer Differential Protection. Homopolar component compensation
I don't see an open wye/delta CT connection, but this is how CTs were generally connected to electro-mechanical relays to get both differential and restricted earth fault (also known as ground differential)protection. To analyze, apply an SLG fault in zone and out of zone and trace the currents.
RE: Transformer Differential Protection. Homopolar component compensation
Somewhere there is FAQ on this site that explains how to post images. Try a search for image post faq.
RE: Transformer Differential Protection. Homopolar component compensation
Murillo: Like indicated by previous posters, modern differential relays do not need extra equipment (zero sequence shunts, interposing CTs, etc) to keep the zone stable. You can take all those stuff out, connect the CTs in star, and take it into your relay. Just ensure your internal settings are correct, and there you go. You might need adding metrosils, if your relay is using a high impedance principle for a REF-scheme.
Can you just clarrify:
Have you already changed the electromechanical relay with a modern relay? (Seems not)
What kind of trip do you experience? (Seems like a LV REF trip, high impedance principle)
Regards
Ralph
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RE: Transformer Differential Protection. Homopolar component compensation
I try to answer us:
David: The STD were brought up, twenty years ago, every year the Maintenance Dpt. test it to ensure that works correctly, in other case replace it for a new one.
David&Ralph: I can't use the www.tinypic.com that show the FAQ238-1161, my server filter some pages.
Ralph:
No, we have not change the electromechannical relay, we are in design process step. We will use a new digital relay with all the features that we are talking about in previous posters, and for this we launched the original question, we won't use the CT that we are talking about, and like it is a very strange CT differential conection I am trying to know more about it.
The trips that we are experienced are due to external faults.