Simple judgment method for internal fault of transformer - Topics
1. Measure the DC resistance by using a bridge to check the resistance of each phase in both high and low voltage windings. Ensure that the resistance between phases is balanced and matches the manufacturer's factory data. If phase resistance cannot be measured, you can measure the line resistance instead. This test helps determine if the winding is intact, whether there are any short circuits or poor connections, and whether the tap changer contact resistance is normal. If the DC resistance changes after switching the tap position, the issue likely lies at the contact point rather than the winding itself. This test also checks the bushing guides, leads, and their connection to the windings for good electrical continuity.
2. Measure the insulation resistance using a megohmmeter to assess the resistance between each winding and ground, as well as the R60/R15 ratio. The measured values can help determine if the insulation on either side is damp or damaged, and whether there are any issues such as wear, breakdown, or flashover between the windings and ground.
3. Measure the dielectric loss using a GY-type Xilin bridge to determine the tan delta (tgδ) value between windings and between windings and ground. Based on these results, it can be determined whether the insulation is damp or experiencing overall degradation.
4. Conduct a simplified test on the insulating oil sample. Use a flash point meter to check if the flash point has dropped, and look for signs of carbon particles or paper fragments in the oil. Pay attention to the smell of the oil sample. If a gas chromatograph analyzer is available, you can measure the gas content in the oil to identify the type and nature of the fault.
5. Perform a no-load test on the transformer. Measure the three-phase no-load current and no-load loss to detect any faults in the core silicon steel sheets, magnetic circuit short circuits, or coil shorting phenomena. This test provides valuable insight into the internal condition of the transformer without applying load.
These tests are essential for maintaining the performance and safety of transformers, ensuring they operate efficiently and reliably over time. Regular testing can help identify potential issues early, preventing costly failures and downtime.
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