Winding Resistance Meter

By Author: millin lange
Total Articles: 10
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The winding Ohmmeter is a line-operated, field portable instrument designed specifically to measure the dc resistance of all types of magnetic windings safely and accurately. Its predominant use is the measurement of the dc resistance of all types of transformer windings within the defined ranges of current and resistance. It can also test rotating machine windings and perform low-current resistance measurements on connections, contacts and control circuits. Three features combine to make this instrument unique: dual measurement, load tap-changer testing and safety shutdown.

The winding Ohmmeter WRM-10 is designed to accurately measure the winding resistance of highly inductive power transformers. The units 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 winding ohmmeter WRM-10 provides stable resistance readings of very large transformers by utilizing a 36 Vdc power supply capable of outputting up to 10 Amperes. The resistance reading of a 100MVA transformer can ...
... be achieved in 5 minutes or less. The units power supply is cooled by heavy-duty fans designed for continuous operation.

Since the winding Ohmmeter WRM-10 can accurately measure winding resistances ranging from 1 micro-ohm to 2,000 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-10 also checks the make-before-break tap-switching sequences of voltage regulators and load tap changers.

The winding Ohmmeter WRM-10 is furnished with three 50-foot test cables, a ground cable, a power cord, and a cable carrying bag. Each test cable lead is terminated with a quick-disconnect test clip.

FUNCTIONAL DESCRIPTION

The winding ohmmeter WRM-10s operation is based on the electrical relationship described by Ohms law: R=V/I, where I is a known current and V is the DC voltage measured across the unknown resistance. The value of the unknown resistance is calculated by dividing the measured voltage by the current which is calculated by the microprocessor. Calculated winding resistance readings are then displayed on the units back-lit LCD screen.

A special current source allows the winding ohmmeter WRM-10 to output up to 10 Amperes of test current. The winding resistance test current is automatically adjusted depending on the load resistance. For added safety, the current source circuit is thermally protected. Also, a built-in discharge circuit automatically discharges the stored energy in the transformer at the end of each test.

APPLICATIONS

The Winding Ohmmeter is used:

1.To verify factory test reading.

2.As part of a regular maintenance program

3.To help locate the presence of defects in transformers, such as loose connections

4.To check the make-before-break operation of on-load tap-changers

A regular maintenance program that includes winding resistance measurements is the most effective way to use this instrument. Once a benchmark is established, subsequent test results can be compared to determine if changes are occurring in the transformers, instrument, transformers and associated control wiring, voltage regulators, motors, generators, breaker contacts, all types of connections (bolted, soldered, crimped, etc.).

The company which manufactures electrical equipment for measurement and maintenance of electrical substations offers customers reliable equipment. We have a wide range of products like winding ohmmeter, power analyzers, battery discharger, transformer test equipment or test equipment for relays. For further information about circuit breaker tester, please visit us online.