The Importance and Procedure of lightning impulse test of transformer
Transformers are an essential component of power transmission and distribution systems. Lightning impulse test is a vital aspect of transformer testing that determines the transformer's ability to withstand lightning surges. This test finds out transformer's insulation strength against lightning overvoltage. In this article, we will explore everything about the lightning impulse test of transformers, from its importance to testing procedures.
What is Lightning Impulse Test of Transformer?
Lightning impulse test is a high voltage test to determine the ability of transformer insulation to withstand lightning surges. Lightning impulses are a sudden and high voltage surge that can occur due to lightning strikes. During a lightning impulse test, a high voltage impulse is applied to the transformer winding and earthed parts to check the insulation and equipment's strength. The test voltage waveform is a 1.2/50-microsecond positive steep wave and a 50% virtual front time.
Importance of Lightning Impulse Test of Transformer
Lightning impulses can damage transformer insulation and equipment, which can cause significant power outages and result in costly repairs or replacement. Therefore, it is crucial to test transformer insulation strength against lightning surges. Lightning impulse testing ensures that transformers are reliable and can withstand voltage surges, which maintains the power system's stability and reduces the risk of power outages.
Lightning Impulse Testing Standards
Lightning impulse testing follows international standards such as IEC 60076-3 and IEEE C57.12.00. These standards provide guidelines for equipment preparation, test voltage, test duration, and pass/fail criteria. Testing facilities must have certified equipment to conduct the test under the standard.
Equipment Required for Lightning Impulse Test of Transformer
The equipment required for lightning impulse testing includes impulse voltage generator, impulse voltage divider, sphere gap, and oscilloscope. The impulse voltage generator produces the high voltage surge, and the impulse voltage divider measures the voltage. A sphere gap ensures that the voltage level remains constant at a given distance, and the oscilloscope is used to measure the voltage waveform.
Testing Procedure for Lightning Impulse Test of Transformer
Before the test, the transformer should be inspected for any damage or defects. The equipment should be prepared as per the standard guidelines, and any safety precautions must be taken. During the test, the high voltage surge is applied to the winding and earthed parts of the transformer. The voltage waveform is measured using an oscilloscope, and voltage readings are recorded. The test is conducted multiple times, and the occurrence of any damage or breakdown is noted. The test results are compared with the standard pass/fail criteria for the transformer.
Interpretation of Test Results
The lightning impulse test results are evaluated based on the recorded voltage waveform and any observed damage or breakdown. The recorded waveform is analyzed to ensure that it meets the standard guidelines for voltage level and waveform shape. The test results should not indicate any breakdown or flashover, and the transformer should withstand the test voltage without any damage.
Frequency of Lightning Impulse Test of Transformer
Lightning impulse testing should be conducted during transformer commissioning, and it should also be periodically conducted to ensure the transformer's ongoing reliability. The frequency of testing depends on various factors such as the age of the transformer, maintenance history, and the severity of environmental conditions. Typically, lightning impulse testing is performed every five years, but it can be increased or decreased based on the above-mentioned factors.
Precautions for Lightning Impulse Test of Transformer
Lightning impulse testing involves a high voltage surge, which can be dangerous and can cause equipment damage or injury. Therefore, it is essential to take necessary precautions, which includes proper training, using certified equipment, following standard guidelines, and wearing personal protective equipment.
Conclusion
Lightning impulse testing is a vital aspect of transformer testing that measures transformer insulation's ability to withstand high voltage lightning surges. It ensures the transformer's reliability, maintains the power system's stability, and reduces the risk of power outages. The testing equipment required includes impulse voltage generator, impulse voltage divider, sphere gap, and oscilloscope. The testing procedure follows international standards, and necessary precautions should be taken to ensure safety.