By hvhipot 
Transformers will inevitably be affected by various short-circuit fault currents during operation. Especially the outlet short circuit and the near area short circuit are harmful to the transformer. The transformer windings will bear huge, uneven axial and radial electrical stress. When the internal mechanical structure of the winding is weak, the deformation of the winding is inevitable. Including changes in axial and radial dimensions, bulging, short circuit between turns, displacement of the device, and winding deformation. The following situations can occur after the transformer winding is deformed:
(1) The transformer was damaged immediately. We had a 110kV transformer in a near short circuit, and the reclose was successful. After the gas was activated, the winding deformation was checked after more than 20 seconds, and the winding was returned to the factory for rewinding;
(2) Transformer insulation material damage or winding deformation causes the insulation distance to change, resulting in a decrease in insulation strength. Under long-term normal voltage or overvoltage, insulation breakdown may eventually occur. In this case, insulation defects can be detected by conventional methods such as electrical tests and oil tests.
(3) After the winding is deformed, the insulation state is not damaged, but the mechanical strength of the coil will be reduced. When a short-circuit fault occurs again, it will not be able to withstand the huge electromotive force and be damaged. In this case, since the insulation is not damaged, the general There is no problem in the electrical test and the oil test. The correct conclusion can only be drawn through the winding deformation test. At the same time, this situation is more common. This is because many transformers will not be damaged just because of a short-circuit accident. The transformer in operation may suffer multiple short-circuit shocks, reduce mechanical strength, and even slightly deform. The test is unable to detect its internal deformation problem, unable to judge its state, which is a potential and major safety hazard.
Therefore, the transformer winding deformation tester should be used to detect the transformer winding deformation, which can detect and deal with the problematic transformer in time, and carry out the targeted lifting inspection, which plays an extremely important role in preventing the occurrence of transformer accidents.