3 Phase Scott-T transformers operation manual

[test11]

I'm looking for a good write-up on the operation of Scott-Ts to confirm what I think is going on. 3 Phase to 3 phase in particular. The most I get is a paragraph everywhere I look. Calculus involvement is ok. I'm not scared :)

[Kalbi_Rob]

I'm looking for a good write-up on the operation of Scott-Ts to confirm what I think is going on. 3 Phase to 3 phase in particular. The most I get is a paragraph everywhere I look. Calculus involvement is ok. I'm not scared :)

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/special-transformers-applications/

[test11]

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/special-transformers-applications/

Yeah same problem. 3 phase to 2 phase. Not 3 phase to 3 phase.

442

[Kalbi_Rob]

The Scott-T transformer connection may be also used in a back to back T to T arrangement for a three-phase to 3 phase connection. This is a cost saving in the smaller kVA transformers due to the 2 coil T connected to a secondary 2 coil T in-lieu of the traditional three-coil primary to three-coil secondary transformer. In this arrangement the Neutral tap is part way up on the secondary teaser transformer .
The voltage stability of this T to T arrangement as compared to the traditional 3 coil primary to three-coil secondary transformer is questioned.
It appears that you just get a cheap ferroresonant transformer for ground isolation, and/or UPS voltage transient suppression (but downfall is high neutral currents). There are a couple of white papers on IEEE.org, specifically "A comparison of three phase Scott-T and ferroresonant transformers" by Robert J. Kakalec.

[test11]

It appears that you just get a cheap ferroresonant transformer for ground isolation, and/or UPS voltage transient suppression (but downfall is high neutral currents). There are a couple of white papers on IEEE.org, specifically "A comparison of three phase Scott-T and ferroresonant transformers" by Robert J. Kakalec.

Thanks man! I always forget I have access to IEEE now. Been so long without it, I automatically look elsewhere.

Edit: Unfortunately, this configuration still utilizes 2 phase output. It's just comparing using a 3 phase ferroresonant transformer for a rectifier use vs Scott-T with a 2 phase output.

[Kalbi_Rob]

Thanks man! I always forget I have access to IEEE now. Been so long without it, I automatically look elsewhere.

Edit: Unfortunately, this configuration still utilizes 2 phase output. It's just comparing using a 3 phase ferroresonant transformer for a rectifier use vs Scott-T with a 2 phase output.

I think you are overthinking it, as they put 2 t-transformers back to back to produce the 3phase-3phase. Only math I cannot see is if the output is 180 or 0 degrees from the input since the 3ph-2ph Scott outputs a phase shift of 90 degrees. The 3-ph version just uses the same 2-ph output commoned between the 2 t-transformers.

[test11]

I think you are overthinking it, as they put 2 t-transformers back to back to produce the 3phase-3phase. Only math I cannot see is if the output is 180 or 0 degrees from the input since the 3ph-2ph Scott outputs a phase shift of 90 degrees. The 3-ph version just uses the same 2-ph output commoned between the 2 t-transformers.

I got ahold of a rep for a manufacturer who makes these. He gave me some textbooks to look at and confirmed my suspicions that it is pretty different from the 3 to 2 phase configuration. I haven't had time to look due to my newborn son, but I will post what I find for the fellow curious.