On Transformer Winding DC Resistance Test and Defects Site Treatment Method
The measurement of the DC resistance of the power transformer windings is an indispensable preventive test item in transformer overhaul. Through the comprehensive analysis of the measured data and its differences, the preliminary analysis of the connection between the phases of each winding of the tap leads and the welding of the leads of each phase, and the connection between the tap lead and the tap changer should be connected with fasteners. The quality of the contact status between the contact points of the switch, and according to the standard, can accurately determine whether there is fault and hidden trouble in the transformer winding.
In the field test work for many years, I fully realized that if the DC resistance data of the power transformer windings is abnormal, regardless of whether the difference exceeds the standard, it must be carefully analyzed to carefully find the cause of the abnormal fault and eliminate the fault. Otherwise, it will affect the safe operation and economic benefits of the equipment.
Transformer winding DC resistance test process 1, according to the test equipment nameplate, factory data, the previous test report to determine the approximate range of the test equipment DC resistance to select the DC resistance tester and test current size. The accuracy of the measuring instrument should not be lower than 0.5.
2. Measure the temperature. In order to compare with the factory and previous measurements, the DC resistance at different temperatures should be converted to the same temperature for comparison.
3, the connection wire should have enough cross-section, and the contact must be good, in the measurement of small resistance should be tested through the wiring to eliminate the impact of the lead contact resistance on the measurement results, the voltage lead should be close to the test equipment connector. Avoid the impact of test results due to the wiring, resulting in misjudgment.
4. Precautions for on-site testing The measured resistance is too large or extremely small. It may be caused by poor contact of the leads. After the contact is improved, the test is performed. Measure transformers and other large-inductance equipment, measure and connect DC power supply, need to consider enough charging time, let the resistance stabilize before reading. After the measurement is completed, it must be fully discharged before changing the test wiring.
5, test standard DL/T596-996 "electric power equipment preventive test procedures" for the transformer winding DC resistance: a. 1.6MVA transformer, the phase winding difference should not exceed 2% of the three-phase average, no The difference between the windings from the point of origin and the difference between the lines shall not be greater than 1% of the three-phase average; b. For transformers of 1.6MVA and below, the difference between the phases is generally not greater than 4% of the three-phase average value. The difference between the lines is generally not more than three-phase The mean value of 2%; c. Compared with the previous measured value of the same site, the change should not exceed 2%.
To accurately determine and deal with the defects, we must first ensure the accuracy of the measured resistance of DC resistance, remove the measurement factors of the instrument in order to prevent misjudgment; and then rely on everyone's years of work experience to discuss, from the tedious data Find out the rules and find out where the faults are; then formulate corresponding treatment methods and measures, deal with defects in a timely manner, reduce the time for equipment outage, and ensure the safe operation of the equipment.
Second, testers must have a high sense of responsibility when they work on site. It is also necessary to improve the technical quality of the on-site test personnel, perform comprehensive analysis on various data and various phenomena occurring in the test using various means, find out the key points of the defect, apply the right medicine to the disease, solve the problem in time, and let the transformer Safe and stable operation ensures economic benefits.
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