[Transformer] Check polarity

Check polarity with DC pulse

Figure 1: Determine coil polarity using DC pulse

The polarity of the transformer can be determined by performing the following measurements:

The appropriate DC source to use is a 1.5V battery source.

Step 1: Connect the devices as shown in diagram figure 3.1. Connect the battery's positive power to terminal A, the negative power to terminal X of the high voltage coil.

Step 2: Apply a direct current pulse to the high voltage coil and observe the direction of rotation of the Ganvanometer.

·        When the needle turns in a positive direction, it is of the same polarity.

·        When the needle turns negative, the polarity is reversed.

Note:  For accurate results, the Ganvanomet must be connected to the correct polarity. The pulse is turned on and off quickly but must be enough to observe the direction of rotation of the indicator needle.

Check polarity using AC voltage:

For transformers with a transformer ratio of 30:1 or less, conductor A will be connected to the low voltage conductor (in figure 2).

Figure 2: Checking polarity using AC voltage

Value of AC voltage applied to the entire high voltage coil AX and read the index of the Voltmeter connected between the two terminals Xx.

– When the following voltage index is greater than the previous one, the polarity is opposite.

– When the following voltage index is smaller than the previous one, it is of the same polarity.

Check polarity by comparison method

Figure 3: Checking polarity using the comparison method

Step 1: Connect the high voltage windings of the two transformers in parallel by connecting the same conductors together.

Step 2: Connect the low voltage lead X1, of both transformers together, leaving lead X2 free.

Step 3: With this connection, apply voltage to the high voltage coils, measure the voltage between the two free wire ends. Voltmeter reading 0 or negligible value shows that the polarity of both transformers is relatively similar (see figure 3).

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Above are some commonly used methods to check the polarity of the transformer.