How to test the impulse voltage withstand of a substation transformer?

Testing the impulse voltage withstand of a substation transformer is a crucial step to ensure its reliability and safety in the power grid. As a substation transformer supplier, I've been involved in numerous tests and know how important it is to get it right. In this blog, I'll share with you how we test the impulse voltage withstand of a substation transformer.

Why Test Impulse Voltage Withstand?

Before we dive into the testing process, let's understand why we need to test the impulse voltage withstand. Substation transformers are exposed to various transient over - voltages in the power system, such as lightning strikes and switching operations. These transient over - voltages can cause significant stress on the transformer insulation. If the transformer's insulation cannot withstand these impulse voltages, it may lead to insulation breakdown, which can result in equipment failure, power outages, and even safety hazards. So, testing the impulse voltage withstand helps us verify if the transformer can handle these transient over - voltages and ensure its long - term performance.

Preparation for the Test

First things first, we need to do some preparation work. We gather all the necessary test equipment, including impulse voltage generators, voltage dividers, oscilloscopes, and current sensors. The impulse voltage generator is the heart of the test setup, which can generate high - voltage impulses with specific waveforms and amplitudes.

We also need to make sure the transformer is in a proper condition for testing. It should be installed correctly in the test area, and all the connections should be tight and secure. The transformer should be clean, and there should be no visible damage to its insulation or other components.

Test Setup

Once the preparation is done, we set up the test. We connect the impulse voltage generator to the transformer terminals. The voltage divider is used to measure the voltage applied to the transformer accurately. The oscilloscope is connected to the voltage divider to record the voltage waveform during the test. The current sensor is used to measure the current flowing through the transformer during the impulse voltage application.

We also need to pay attention to the grounding of the test setup. A proper grounding system is essential to ensure the safety of the test personnel and the accuracy of the test results. All the equipment should be grounded properly, and the grounding resistance should be within the specified range.

Test Procedure

Now, let's talk about the actual test procedure. There are two main types of impulse voltage tests: the full - wave impulse test and the chopped - wave impulse test.

Full - Wave Impulse Test

In the full - wave impulse test, we apply a full - wave impulse voltage to the transformer terminals. The impulse voltage has a specific waveform, usually a 1.2/50 μs waveform, which means the time to reach the peak value is 1.2 μs, and the time to decay to half of the peak value is 50 μs.

We start the test with a low - amplitude impulse voltage and gradually increase the amplitude step by step. For each amplitude level, we apply a certain number of impulses, usually three. We carefully observe the oscilloscope to record the voltage and current waveforms during the impulse application. If there are any abnormal phenomena, such as excessive current flow or significant changes in the voltage waveform, it may indicate a problem with the transformer insulation.

Chopped - Wave Impulse Test

The chopped - wave impulse test is a more severe test. In this test, the impulse voltage is chopped at a certain time after reaching the peak value. The chopped - wave impulse can simulate a more severe transient over - voltage condition, such as a lightning strike near the transformer.

The test procedure for the chopped - wave impulse test is similar to the full - wave impulse test. We also start with a low - amplitude chopped - wave impulse voltage and increase the amplitude step by step. However, the chopped - wave impulse test requires more precise control of the test equipment to ensure the correct chopping time and waveform.

Evaluation of Test Results

After the tests are completed, we evaluate the test results. We compare the recorded voltage and current waveforms with the standard requirements. If the waveforms are within the specified range and there are no signs of insulation breakdown, such as flashovers or punctures, the transformer passes the impulse voltage withstand test.

However, if there are any abnormal waveforms or signs of insulation breakdown, we need to further investigate the cause. It could be due to manufacturing defects, damage during transportation or installation, or other factors. We may need to disassemble the transformer to check its internal insulation and components and take appropriate measures to repair or replace the defective parts.

Importance of Regular Testing

Regular impulse voltage testing is essential for substation transformers. Even if a transformer passes the initial test during manufacturing, its insulation performance may degrade over time due to aging, environmental factors, and operating conditions. By conducting regular tests, we can detect any potential insulation problems early and take preventive measures to avoid equipment failure.

Related Products

If you're interested in other substation - related products, we also offer Prefabricated Electrical Substation (E - House), Mobile Substations, and EU Type Prefabricated Compact Substation. These products are designed to meet different needs in the power grid and can be used in conjunction with our substation transformers.

Contact Us for Purchase

If you're in the market for substation transformers or any of our related products, we'd love to have a chat with you. We can provide you with detailed product information, pricing, and technical support. Contact us for more information and let's start a great partnership together.

References

• IEEE Standard for Tests for Liquid - Immersed Distribution, Power, and Regulating Transformers (IEEE C57.12.00 - 2010).
• IEC 60076 - 3: Power transformers - Part 3: Insulation levels, dielectric tests and external clearances in air.