Introduction
Transformers are an essential part of any power system. Their primary function is to step up or step down the voltage levels as required. However, before commissioning, it is necessary to perform several tests to verify the transformer's electrical and mechanical suitability. One such test is the impulse voltage test. This article will provide you with a complete guide on the impulse voltage test of transformer.
What is Impulse Voltage Test?
An impulse is a high voltage, low duration voltage waveform applied to the transformer winding, terminals or bushings. The impulse voltage test is performed to verify the ability of the transformer insulation structure to withstand high voltage surges. The test is also known as the lightning impulse test and is performed in accordance with international standards.
Why Perform the Impulse Voltage Test?
Transformers operate under harsh environments, and their insulation may deteriorate over time due to aging, overheating, mechanical stress, or moisture ingress. The impulse voltage test provides a method to assess the insulation's ability to withstand lightning strikes and other high voltage surges that may cause insulation breakdown and result in transformer failures.
Types of Impulse Voltage Test
There are two types of impulse voltage tests - full wave and chopped wave. The full-wave test is a high voltage impulse of both polarities, while the chopped wave test is a unidirectional impulse voltage. The full-wave test is more severe and determines the transformer insulation's withstand capability under realistic operating conditions.
Preparation for the Test
Before the test, the transformer must be checked to ensure all connections are tight, and there are no open circuits. The winding's temperature should be below the rated temperature to prevent thermal stress during the test. Safety measures must be taken, and appropriate personal protective equipment should be used.
Test Procedure
The transformer is connected to a test circuit, and the impulse voltage wave is applied to the winding. The voltage level and duration of the impulse wave are specified in international standards. The test is repeated at multiple points in the transformer to ensure the insulation's uniformity.
Interpretation of Results
The impulse voltage test results are recorded and compared with the acceptance criteria. The results should show that the transformer insulation withstands the impulse voltage without any failure. If the impulse voltage test results are satisfactory, the transformer is considered suitable for operation.
Precautions
The impulse voltage test delivers high energy to the transformer, and safety precautions must be taken. The test should only be performed by trained personnel. The transformer should be grounded through the entire test, and no part of the transformer should be touched during the test.
Conclusion
The impulse voltage test of transformer is a vital requirement to ensure the transformer's suitability to withstand harsh environments. This test provides valuable information on the transformer's insulation withstand capability to high voltage surges, preventing transformer failures and ensuring safety. Adhering to international standards and taking proper safety precautions during the test is essential to obtain reliable results.