ECN Forum Forums Technical Discussion Electrical Theory and Applications Polarity Test 3

This Schematic demonstrates how to find relative polarities of two individual and separate 1 phase 2 wire transformers.

The series connection between the Secondary Windings is a "Test Jumper", which is used only during the test procedures.
Test equipment consists of a common DVM [Digital Voltage Meter] - which is represented by the "E" in the circle.

**NOTE** Both Transformers need to be identical for Pri/Sec voltage, KVA and Z.

Any Comments???

Scott SET - posted 07/02/01

This is a great pair of diagrams!

It shows how when voltages are of the same polarity, they subtract; but of opposite polarity, they add.

Dspark,

Thanks for the reply!!! Glad the schematics are of use to the members of this forum.

As you said, the schematic demonstrates how relative polarity can either add voltages ["in phase" connections], or subtract voltages ["out of phase" connections].

It's all according to the direction of current flow on the secondary coil[s] - Vs - the magnetic flow in the core.

These polarity test schematics are really aimed more at the "How-To" or the "FYI" angle of things, rather than at anything that is trade applicable [except that anyone performing "in the field transformer connections" would benifit from this info.].

This particular schematic would be helpful if someone was planning to connect two separate transformers for a common output [Parallel Primary connections, Parallel, Series, or even "Multiwire" Secondary connections].

Transformers need to be exactly the same - even as much as being "Cloned" from the other - in order to function properly.
This meaning that not just the input/output voltage being the same, but the core material, winding density, KVA, %Z, reflected Z and all that jazz. Otherwise one winding will circulate a large level of current.

*** NOTE ***
The NEC does not allow the permanent usage of Paralleled Transformers!!! I can understand the reason[s] why!!!
so much for the disclaimer!

Once again, thank you!!! Glad these schematics are of interest.

P.S. Do you have any drawings, or similar tech. data that you could post here???
If you have any suggested item[s]. let me know. Feel free to contact me directly via E-Mail.
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Scott SET