Why do the transformer winding leakage current test

Winding leakage current test purpose DC leakage test voltage is generally higher than the megger voltage, and can be adjusted, so it is more effective than the megger found defects, can be sensitive to reflect the porcelain insulation cracks, interlayer insulation Internal moisture and local loose fracture of insulating oil degradation, insulation along the surface of carbonization.
The polemounted transformer core and other accessories are in the electric field around the winding, if not grounded, the core and other accessories must sense a certain voltage, under the action of the applied voltage, when the induced voltage exceeds the discharge voltage to ground, Will produce discharge phenomenon. In order to avoid the internal discharge of the 37.5kva transformer, so the core ground.