Winding Resistance Ohmmeter WRM40

Fast and Accurate Measurements

The WRM-40 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, and four-wire (Kelvin) connections provide high accuracy and require no lead compensation. The WRM-40 provides stable resistance readings of very large transformers by utilizing a 36Vdc power supply capable of outputting up to 40 Amperes. The resistance reading of a 500MVA transformer can be achieved in 5 minutes or less.

View an usage demostration

The unit's power supply is cooled by four 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 microohm to 500 ohms, it can also be used to measure EHV circuit-breaker contact resistance, motor winding resistance, or any low resistance. If the transformer winding temperature is entered, the WRM-40 can calculate the equivalent resistance value of the winding material (aluminum or copper) at any standard reference temperature. Also, a special test mode can run a test for up to 45 minutes while saving resistance readings at one-minute intervals. In addition to measuring the resistance value, the WRM-40 also checks the "make-before-break" tapswitching sequences of voltage regulators and load tap changers.

The WRM-40 can store test results in Flash EEPROM. Test results can be printed on the built-in 2.5-inch wide thermal printer or can be transferred to a PC via the RS-232C interface port.

The WRM-40 is furnished with three 50-foot test cables. Each test cable lead is terminated with a quick-disconnect test clip.

At the end of each test, the WRM-40 automatically dissipates the stored energy in the transformer. This discharge circuit will continue to work even if the supply voltage is lost. For added safety, the unit's power supply is thermally protected from over-load damage.

User Interface

The WRM-40 features a back-lit LCD screen (20 characters by 4 lines) that is viewable in both bright sunlight and low-light levels. A rugged, alpha-numeric, membrane keypad is used to control the unit.

Internal Test Record Storage

The WRM-40 can store 63 test records (up to 48 readings per test record) in Flash EEPROM. Test records can be retrieved and printed on the built-in thermal printer or can be transferred to a PC via the RS-232C interface port. A Windows® XP/Vista-based software application is provided with each WRM-40. This software can be used to retrieve test records from the WRM-40 and can also be used to export records in Microsoft® Excel format