I know that if you have two transformers connected in parallel that are of slightly different turns ratios, then there will be a circulating flow of VARs.

I also know that if you have two transformers that are mutually phase-shifted, you will have a circulating flow of watts.

My question is: what is a circulating flow of watts? To my knowledge, having more VARs implies more current implies more losses. But, having a circulating flow of watts seems like the exact same thing to me.

So what is a circulating flow of watts?


  • 2
    \$\begingroup\$ I think you need to draw a picture of what you mean to minimize ambiguity. \$\endgroup\$
    – Andy aka
    Dec 10, 2018 at 10:25
  • \$\begingroup\$ Hi Andy, I don't really know how to do that. But perhaps I can explain it a little bit better. Imagine we have a three-phase grid and, connected to the grid, are two transformers in parallel. One of the transformers is a normal transformer of turns ratio N; the other is a phase-shifting (a small phase-shift, for example) transformer also with turns ratio N. If ideal, identical transformers are placed in parallel, they will share the current equally; a different turns ratio causes VARs to circulate; a different phase causes Watts to circulate. What does "circulating Watts" mean? \$\endgroup\$
    – Lerbi
    Dec 14, 2018 at 4:15
  • \$\begingroup\$ I don't know what a small phase shifting transformer is and I don't follow your words. Draw a circuit and name the components. \$\endgroup\$
    – Andy aka
    Dec 14, 2018 at 8:24
  • \$\begingroup\$ Well, if you don't know what a phase-shifting transformer is, I'm not sure you can help me. Thanks anyway! \$\endgroup\$
    – Lerbi
    Dec 14, 2018 at 18:05
  • \$\begingroup\$ A star delta transformer only shifts 30 degrees and 30 degrees aint small by any means. But you know best how to attract someone to answer your question. \$\endgroup\$
    – Andy aka
    Dec 14, 2018 at 18:16

1 Answer 1


"Power flow divides inversely with the relative impedances on a common base" RUS Design guide for substations - section 5.2.7 - Parallel Operation of Transformers


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.