NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
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NOYAFA Electronic specializing in testing instruments and cable testers for 16 years
Author: Noyafa–CCTV Tester
Question: How to solve the problem that the resistance value exceeds the limit when using the three-channel magnetic flux direct resistance tester? Answer: The three-channel flux assist direct resistance tester is a new generation of fast tester that integrates the magnetic flux method test, three-phase test and degaussing functions. , is the problem of measuring large-scale power transformers: how to solve the problem of measuring the resistance value exceeding the limit by using the three-channel magnetic DC resistance tester? The integrated new generation of fast tester is an ideal device for measuring the DC resistance of large power transformers. Records can be edited and user information saved and printed. In actual use, if the measured resistance value of the three-channel magnetic DC resistance tester exceeds the limit, we can refer to the following solutions. 1. First consider whether there is a measurement error (such as whether the external lead is connected, whether the test lead is too long or too thin, whether the contact is good, whether the battery voltage in the bridge is insufficient).
2. The resistance value of a DC resistor is greatly affected by temperature, so it must be converted to the same temperature (usually 20℃, R20=(T+20)/(T+T), TCu=235) for comparison , and generally based on the oil temperature of the upper layer. 3. For the currently used three-phase distribution transformer, the high-voltage winding adopts Y-shaped wiring. When the resistance value exceeds the limit value, the following formula can also be used [RA = (RAB + rac-rbc) / 2, RB = (RAB + rac) -rac)/2, RC(RBC+rac-rab)/2] in order to find out the defect phase. 4. It is common for the tap changer to have poor contact, resulting in a high resistance value. For example, the switch is cleanly plated out, the spring pressure is insufficient, the stress is uneven, and the overvoltage contacts are deposited with carbon, which will lead to the conduction of the resistance value.
high end. At this time, the cover of the tap changer should be opened and turned several times, which can generally be eliminated. If the limit is still exceeded through the above methods, the cause of the failure is most likely to be the winding and lead welding, welding, wire breakage or layer short circuit or winding burnout.
Users can solve it according to the actual situation.
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