how a delta connected primary winding of three phase distribution transformer tackle unbalanced load of three phase 4 wire unbalanced load(unbalanced load is quite common due to supply of single phase equipment using neutral wire)?

  • \$\begingroup\$ It tackles it a lot better than a star primary. \$\endgroup\$
    – Andy aka
    Sep 17, 2021 at 10:53
  • \$\begingroup\$ Zarzis - are we done here now? Is there something you still don't understand with my answer? \$\endgroup\$
    – Andy aka
    Sep 19, 2021 at 12:32
  • \$\begingroup\$ Thank you dear Andy. You have helped me in a lot of thinking. Just one thing I am not clear, when there is unbalance current in the secondary star then that unbalance current should be reflected to primary phase winding(lets assume it is delta connected) and cause unbalanced current in the power system. Is it normal that power system run with unbalance current? \$\endgroup\$ Sep 20, 2021 at 13:09
  • \$\begingroup\$ Yes, quite significant imbalance currents can occur but, with multiple users of electricity, statistically the imbalance gets less problematic but, there can be occasions when it appears bad. \$\endgroup\$
    – Andy aka
    Sep 20, 2021 at 13:12

1 Answer 1


....three phase 4 wire unbalanced load

That implies a star wound secondary so, with star connected secondary, each load is exclusively connected across one of the limbs in the star output. This, of course, means between a phase voltage and the neutral-point (the forth wire). This also means that whatever load current is taken on one phase has no impact on the load currents of the other two windings.

delta connected primary winding of three phase distribution transformer

With a delta primary, each winding directly connects across an incoming line voltage AND, importantly, the relevance of all of this is that each phase of the transformer can be regarded as equivalent to a single phase transformer.

So, if you are happy that a single phase transformer can "tackle" a range of loads and, will do so irrespective of the other two phases that might be working along side it then you have your answer.

A better question would be why a star connected transformer primary might be appalling at dealing with unbalanced loads but, you didn't ask that and nobody likes folk changing their mind on questions so fundamentally.


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