The Vanguard WRM-40 winding resistance meter is designed to accurately measure the winding resistance of highly inductive power transformers. The unit’s dual resistance-reading input channels can measure two winding resistances simultaneously. Four-wire (Kelvin) connections provide high accuracy voltage reading and require no lead compensation. The WRM-40 provides stable resistance readings of very large transformers by utilizing a 36 VDC power supply capable of outputting up to 40A. The resistance reading of a 100MVA transformer can be achieved in 5 minutes or less. The unit’s power supply is cooled by heavy-duty fans designed for continuous operation. For greater flexibility in the field, the WRM-40 comes with a built-in 2.5 inch wide thermal printer used for printing test reports.

Since the WRM-40 can accurately measure resistances ranging from 1 micro-ohm to 500 ohms, it can also be used to measure EHV circuit-breaker contact resistance, motor winding resistance, or any low resistance. In addition to measuring the resistance value, the WRM-40 also checks the “make-before-break” tap-switching sequences of voltage regulators and load tap changers. This unit can store test results in Flash EEPROM. Test results can be printed on the built-in printer or can be transferred to a PC via the RS-232C interface.