DC resistance is the resistance that appears after the components on the power and electrical equipment are connected to DC, that is, the static resistance that already exists on the components, such as the transformer coil. The resistance presented by DC and AC respectively is different. Coil Alternating current has both direct current resistance and reactance. This phenomenon reflects the cooperation of resistance and reactance, also called impedance.

Why do we need to detect DC resistance? Take the transformer coil as an example. This is to check whether there is an inter-turn short circuit inside the three-phase winding. Because there is a short-circuit between phases inside the transformer, excessive short-circuit current will easily cause the transformer to burn out. The phenomenon of the fault is very obvious, and the appearance is easy to judge. However, if a short-circuit occurs between the turns of one phase winding and the short-circuit current value is too small, the transformer will be in the province. Trip protection action, but the appearance is difficult to judge whether the transformer itself is faulty, so we need to use a DC resistance tester to detect the DC resistance of electrical equipment.