In the world of power equipment maintenance, transformers are like the heart, and their “health condition” directly affects the stable operation of the entire power system. Today, let’s talk about how to “auscultate” the heartbeat of a transformer – testing the DC resistance of the transformer. This is not a small job, there are many tricks inside.
What is a transformer DC resistor?
Simply put, the DC resistance of a transformer refers to the resistance value of the transformer winding in the DC state. Although this value may seem insignificant, it directly reflects the cross-sectional area, material purity, and good connection of the winding conductor. Imagine, just like a water pipe, the thicker the pipe and the better the material, the smoother the water flow and the lower the resistance.
The ‘behind the scenes’ driving force that affects DC resistance
Temperature: This is the most easily overlooked but influential factor! As the temperature increases, the resistance of the conductor will also increase accordingly. So, during testing, accurately recording the temperature at that time and comparing it to the standard temperature is necessary to obtain meaningful results.
Poor contact: Poor contact in any part of the lead connections and tap changer contacts inside the transformer can greatly increase the resistance value and even cause local overheating, with unimaginable consequences.
Winding damage: If the winding is broken or burned, the resistance value will also undergo abnormal changes.
Measuring tool: Transformer DC resistance tester
Accurate measurement naturally relies on professional tools. The transformer DC resistance tester launched by HV Hipot Electric Co., Ltd. is our capable assistant for this work. They usually use advanced constant current discharge technology, which can quickly and accurately measure the DC resistance value and automatically perform temperature compensation, greatly improving work efficiency and measurement accuracy.
Why is this test so important?
Judging winding insulation: Abnormal changes in DC resistance are early signals of possible problems with winding insulation.
Evaluate connection reliability: Through measurement, poor contact issues can be identified in areas such as tap changers and lead connections.
Evaluating the performance of on load tap changers: For transformers with voltage regulating tap changers, the contact resistance of their dynamic and static contacts is particularly critical.
Related to other tests: The results of this test can also be mutually verified with other electrical parameters such as no-load tests and short-circuit tests of transformers, providing more comprehensive diagnostic information.
How can we do better?
Standardized operation: Strictly follow the instrument instructions and procedures to ensure correct testing wiring and avoid misoperation.
Multi point measurement: For on load voltage regulating switches, measurements should be taken for each gear and detailed data should be recorded.
Comparing historical data: Comparing and analyzing this test data with historical data is the key to identifying potential issues.
Professional instrument selection: Choose a reputable brand such as HV Hipot Electric Co., Ltd. to ensure the stability and accuracy of the testing instruments.
HV Hipot Electric Co., Ltd. has always been committed to providing efficient and reliable power testing solutions to assist in the safe and stable operation of the power system.
FAQ
Q: When is the best time to test the DC resistance of a transformer? A: It is usually carried out after the transformer has been powered off and cooled for a period of time to reduce the impact of temperature on test results and ensure personnel safety.
Q: What should I do if the tested DC resistance value is too high? A: Firstly, check whether the test wiring is secure. Then, based on the on-site situation, focus on checking whether there is poor contact or oxidation at the tap changer and lead connection parts. If necessary, clean or tighten them.
Q: How is temperature compensation carried out? A: Use the built-in temperature sensor of the instrument to measure the actual temperature of the transformer winding, and then convert the measured DC resistance value to the value at the preset standard temperature (such as 20 ° C) according to the standard conversion formula.
Q: What is the difference between DC resistance testing and AC resistance testing for transformers? A: DC resistance testing mainly reflects the resistance characteristics of the conductor itself, while AC resistance testing (such as winding AC resistance measurement) is also affected by factors such as eddy current losses. The focus of the two is different, but both are of great significance for transformer state evaluation.