DC resistance test of transformer winding transformer in transition, overhaul and change the tap switch, the necessary pilot projects. By measuring DC resistance in transformer winding, welding can check out leads or connection quality, winding inter-turn short circuit or open circuit-free, and tap the contact is good, and so on. Measurement of DC resistance in the past using QJ44 double bridge to measure, and this sort of bridge measurement current for the Ma-level, measure up and takes a long time, and the accuracy is low.