Scott ‘T’ Connections for Furnace Transformers, Auto Transformers and Distribution Transformers

Dr. Transformer:  Welcome back to PMI Institute for today’s discussion of Scott ‘T’ Connections!  Say what?  Social networking?  Not here!  And no Scotty beam me up, either! (Get it?)  No, this is about transformers!  Furnace Transformers, Auto Transformers and Distribution Transformers in particular and their connection options.  This is one part of the story.

The ‘Scott’ connection is the most popular way to connect three phase, 3Ø, to two phase, 2Ø (see diagram).  The Transformer consists of two coils; a ‘Main’ rated full line voltage with a center tap and a ‘Teaser’ rated at 86% line voltage connected from the line to the center tap (CT) of the ‘Main’.


Scott 'T'

Diagram of a Scott ‘T’ Connection, three phase to two phase for transformers by Power Magnetics, Inc. Trenton, NJ


The transformer can be constructed as one unit using a ‘2Ø Core Type Core’ (see diagram) with a 3 legged core utilizing an oversized center leg. It can also be made with two separate Single Phase Transformers, usually at a higher cost.   The reason one might do that is because the package is smaller, therefore more configurable and easier to have a single phase spare.

Furnace Transformers applications, (or any other) where the load can be divided into two separate but equal zones, lend themselves to the ‘Scott’ connection because it turns two balanced 1Ø Loads into a balanced 3Ø load on the input.  The connection is very versatile; used in Distribution Transformers that convert 2Ø to 3Ø and also as an Auto Transformer.

We have a lot of experience using the connection in a wide range of applications.   As always, we are happy to provide you with our expertise if we can be of help.

Please let me know if you have any questions about your application.   Until then, happy Scott ‘T’! CPT Kirk, out!…. Uh, oops!  Dr. Transformer signing off until next week.

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