8 Standard Tests Performed on Power Transformers

Step-up transformers that increase voltage and step-down transformers that reduce electrical energy serve almost all commercial, residential, and industrial zones to regulate power. Voltage needs differ, and some countries use a higher voltage power supply than others. For instance, the U.S uses a voltage supply level of 120 volts for residential zones. The voltage supply level may differ across zones or even nations.

All transformers should get tested before use. The transformer installation team always conducts performance and specifications tests before putting any transformer to service. Proper transformer testing makes sure that the mechanical, thermal, and electrical specifications are suitable for the grid system that it serves. Read on to get a glimpse of the eight necessary transformer tests performed before the commissioning of any transformer, and the transformer testing equipment used.

1. The Turns Ratio Tester and Turns Ratio Testing

The turns ratio test is a specifications test done to ensure that the windings on the secondary and primary coils of the transformer are as per the transformer’s specifications. The examination reveals whether the transformer will provide the expected step-up or step-down voltage. In order to get the turns ratio, the primary coil’s turns get divided by the secondary coil’s turns. The acquired ratio defines the transformer output and the corresponding voltage. You can compute the turns ratio when the transformer is off by using a transformer testing equipment known as a turns ratio tester.

2. The Megohmmeter and Insulation Resistance Testing

The Megger test measures the quality of the insulation within the unit of the transformer. This test gets done by a transformer testing equipment known as a megohmmeter. This equipment is a measurement tool akin to the multi-meter, but it has a capacity that is higher than that of a multi-meter. To pass the test, the unit should have a resistance that is higher than the recommended international standards. There are variations in the performed tests in most cases or depending on the temperature, cleanliness, and moisture levels within the transformer unit.

3. Power Factor Testing

The power factor test shows how much power loss results from the insulation system of the transformer. You can get this measure by gauging the power angle between the resulting voltage and the applied AC voltage. This measure is also defined as the phase angle cosine between the current and voltage. The ideal angle should be 90 degrees. The power factor test uses the power factor test kit to gauge its level.

4. Transformer Ohmmeter and Resistance Testing

The transformer ohmmeter is one of the transformer test instruments used to perform resistance testing. The purpose of resistance testing is to find any resistance differences between the connections and the windings. The test gets done a few hours after the transformer gets shut down and after the temperature of the unit reaches the same level as the surroundings. The test tool for this task is a transformer ohmmeter.

5. The Voltmeter and Polarity testing

The polarity test determines whether the windings’ connections are towards the ideal ends to avoid short-circuiting. It’s a test of the direction of the current. Polarity is a crucial consideration if the transformers are to be bank-connected. Polarity can be subtractive or additive, and its tool of measure is the voltmeter.

6. Phase Relation Testing

The phase relation test detects whether two or more transformer units are in proper phase connection relationship.

7. Oil Tests

The transformer oil that cools and insulates the transformer unit gets tested before the transformer gets on or as part of the maintenance schedule. The test tool is a portable kit that applies a high voltage that reaches the oil’s breakdown point.

8. Visual Inspection

A visual inspection of the transformer is the simplest of all tests performed on the transformer units. Visual inspection needs no transformer testing equipment, and what to view and assess gets determined by the type of transformer under investigation.

These are some of the basic CT test and current transformer testing tools that determine whether the unit has the right specifications and performance. It’s mandatory to perform all these tests as stipulated in the national ANSI and IEEE standards.

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