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Omer

differential protection on 3 phas TXR

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cos90    3

My apologies for starting this discussion. Here's how you would solve this problem before microprocessor relays came onto the scene:

rrXwCMX.png

 

@TNPE  you would see a wye-delta transformer applied for Generator Step Up (GSU), the tertiary of a large autotransformer, and at interconnection sites where two systems are operating at a different phase angle. For distribution you typically see a Wye-Wye or Delta-Wye transformer.

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cos90    3

A GSU is a delta-wye. I misspoke.

The LV winding is the primary on a GSU transformer.

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cos90    3

You could also see a wye-delta used as a grounding bank, used like a zigzag transformer.

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TNPE    15

That's my point, it is almost impractical to use this winding configuration on the utility scale when other more practical, existential options are available.  Most transmission step-downs (e.g. 161-69kV or similar) are wye-wye grounded with a delta tertiary.  The tertiary serves two purposes, trapping zero sequence and providing station service to a 13.2 kV bus (typically). Generally speaking, to pick up ground faults, you want your down line sections to be looking back at a grounded secondary.  Without this, you have to use a more expensive alternate approach to detect "ground" faults.  Whether you accomplish this by beefing up the relays or adding a zigzag.  Why even go that route when it's not necessary?

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rg1    4
4 hours ago, cos90 said:

My apologies for starting this discussion. Here's how you would solve this problem before microprocessor relays came onto the scene:

rrXwCMX.png

 

@TNPE  you would see a wye-delta transformer applied for Generator Step Up (GSU), the tertiary of a large autotransformer, and at interconnection sites where two systems are operating at a different phase angle. For distribution you typically see a Wye-Wye or Delta-Wye transformer.

Yes it will. Thanks Cos90 for sharing this, you seem to have good stuff. When I look back the reason of zero sequence - I was right and then solution is different from what I suggested. In my suggestion 30 degree phase angle  problem, will again appear which need to be resolved by ICTs ( Intermediate CTs connected in delta). Here they are using a delta connected trap for resolving  zero sequence currents. But as mentioned by the t60 manual- it is not true that the conventional relaying system were not able to tackle this problem.

Still I fail to understand when you chose and  need an ungrounded system why you need grounding. Should have gone for star-star Xmer. To be honest my practical knowledge of an ungrounded system is nil.

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TNPE    15

Dodge the problem entirely by doing what I mentioned in other posts.  No need to complicate it and make it more expensive at the same time.   

I have yet to see a scenario where this configuration would be needed, at least with regards to HV, MV and distribution utility applications.

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