Why Demagnetization is Needed in Transformer Winding Resistance Test - Yangzhou Darui
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Why demagnetization is needed after transformer winding resistance test
If not demagnetized, on next power-up, if the magnetic fields happen to superimpose, causing core magnetic saturation, it will result in high primary current, damaging the transformer, and may also cause secondary voltage spikes, damaging the load or the transformer's own insulation.
Three-phase demagnetization DC resistance tester
The DC resistance of a transformer refers to the DC resistance value of each phase winding. The purpose of measuring DC resistance is to check whether there is inter-turn short circuit inside the three-phase windings. Because if a phase-to-phase short circuit occurs inside the transformer, the short-circuit current is very large, which can easily burn out the transformer, and the fault symptoms are obvious and easy to judge from appearance; however, if an inter-turn short circuit occurs in one phase winding, the short-circuit current is very small, and the transformer's gas protection will act to trip, but it is difficult to tell from the appearance whether the transformer itself has a fault. By measuring the DC resistance of each phase and comparing the three resistance values, it is easy to determine whether there is an inter-turn short circuit: if the resistance values differ greatly, the possibility of inter-turn short circuit is high; if they are basically similar, this fault possibility can be ruled out.
Three-phase demagnetization DC resistance tester
Because according to the transformer structure, the windings are almost insulated by the insulation medium of the insulated wires themselves. If there are defects in insulation treatment, coupled with heavy transformer load, weak insulation points are prone to inter-turn short circuits. Therefore, the purpose of measuring DC resistance is to determine whether the transformer has inter-turn short circuits, facilitating fault handling.
Note: The above information and technical parameters are compiled and released by Yangzhou Darui Electric Co., Ltd.
