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How to Do the Polarity Test of Transformer?

We can do three phase supply by a single-phase transformer banking system. While transformer banking it’s necessary to have the right polarity. Today we will discuss how to do the polarity test of transformer?

What is the Transformer Polarity test? 

Transformer polarity means the way of the induced voltage in the primary and secondary coil of the transformer.

Why We Will Do the Transformer Polarity Test?

When two transformers are connected in parallel in the transformer banking system, we need to know the polarity for the right connection. There will be a problem if the polarity is not right.

  • There is circulating current through the transformers. Which causes heat and loss.
  • There will be a short circuit in the transformer. 
  • The whole transformer can be damaged.
  • There will be no current flow in the connected load.

Types of Transformer Polarity Test 

There are two types of polarity for transformer winding connections.

  • Additive Polarity
  • Subtractive Polarity
Types of polarity
Types of Polarity

Additive Polarity 

If primary and secondary winding is connected in the same terminal, it is called additive Polarity.

Subtractive Polarity 

If the different side is connected to the primary and secondary winding, it is subtractive polarity. 

Definition of polarity from the picture

  • In the picture, each primary and secondary winding terminal can be positive or negative by the changing way of AC current.
  • Suppose, according to the primary side, A1 and A2 are respectively positive and negative terminal. And a1 and a2 are positive and negative according to the secondary side.
  • If A1 from the primary side and A1 from the secondary side, and A2 and A2 are connected, it means both terminals same sides are connected. This is additive polarity. 
  • If A1 from the primary side is connected with A2 from the secondary side, and A2 is connected with A1 then it’s subtractive polarity.
  • For additive polarity nit voltage will be V1+V2 and for subtractive polarity, not voltage will be V1-V2.
polarity connection
Polarity Connection

Steps of Polarity Test / How to do the polarity test of transformer?

  • Make a circuit according to the picture above and set up the autotransformer in zero position.
  • Start single-phase supply.
  • Measure voltage from different sides by connecting voltmeter.
  • If the primary voltage is V1 and secondary voltage is V2, then the total voltage of additive polarity will be V3= V1+V2.
  • And for subtractive polarity, the reading of the voltmeter will be V3= V1-V2.

That’s all for today’s article on how to do the polarity test of transformer?

Hope now the topic is clear for you how to do the polarity test of transformer?

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Md. Nazmul Islam
Md. Nazmul Islam
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