Phenix WRM-10N-230 10A Max Current, 1 Micro Ohm Range (230V)

Winding resistance testing is an important part of a power transformer maintenance or a manufacturing quality assurance program. Transformers and large motors are subject to vibrations, overloading and environments with large temperature variations. Winding resistance measurements can assure that the connections are made correctly and that no opens or shorts are present. Tap changers of power transformers are a particularly critical element of a power system. The WRM-10N is very effective in detecting tap changer abnormalities.

The WRM-10N injects a DC current through the windings and measures the voltage drop. The instrument calculates the resistance R= E / I. The challenge in winding resistance measurements is that the voltage across an inductor is defined by V= L (di/dt), where L is the inductance of the winding and (di/dt) is rate of change of current. Therefore, small changes in the current, as may be caused by ripple or poor regulation, can make it impossible to measure the DC resistance. The highly regulated and filtered current output of the WRM-10N allows for winding resistance measurements on very large power transformers.