Converting 3Ø to1Ø using the Scott ‘T’ in Transformers

Dr. Transformer:  Myth-busters 101 today: Are we on TV? No? OK, well today we are talking about converting: your thinking, and 3 phase to 2 phase!

There is a recurring myth in the electrical industry that it is advantageous to convert three phase (3Ø) to single phase (1Ø) using the Scott ‘T’ (refer to last week’s article).  Nothing can be further from the truth.  This typically comes up for us when talking to manufacturers purchasing our Furnace Transformers who have used this configuration from other suppliers for a long time.  Bad practice ‘baked in’ over time if you allow me to use a pun!

The way the connection would be made is tying two legs of the 2Ø output together to make a 3 wire connection and putting the 1Ø load across the other two lines. See diagram.


Scott T Furnace Transformers, Single Phase Transformer

Single Phase 1PH and Three Phase 3PH Alternative Connections


The expected result is that the input currents would be lower than what they would if just a 1Ø Transformer was used.  What actually results is one high current leg and two lower, but the high leg current is worse than it would be with a 1Ø Transformer.  So not only is the current higher but the Scott Transformer is significantly more expensive than the 1Ø (with more loss also). Thus this old style of thinking and product design works against you in a number of ways:

  • The primary line currents are higher
  • The transformer is going to cost more
  • It will be physically larger
  • It will weigh more
  • It will be significantly less efficient
  • The controller will be more expensive

In summary, the old solution adds to both the acquisition cost of your product and operational cost of your product over time.

The smarter solution is to use a well engineered single phase transformer for your product: The Power Magnetics single phase Furnace Transformer will be smaller, lighter, more efficient, cost less, operate for less, reduce your product cost for controller and connections, and be more reliable than any other solution.  Smarter and less expensive all around! Converted yet? Give us a call about your transformer needs in particular, Furnace Transformers or any other specialty power magnetics.

Scott ‘T’, beam me up!  Till next week!

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