According to CIGRE A2.34, the dynamic resistance measurement or DRM (OFFLINE) is a test that offers diagnostics for several diverter or selector switch malfunctions such as: contact problems, broken springs, broken transition resistors, poor contact pressure, inadequate transition time, momentary open circuit, and synchronism motion issues.
Zensol’s DRM principle
Tap windings are powered with a DC voltage source. The current fluctuations are recorded during the switching process. The schematic below shows the principle of the dynamic resistance measurement.
“The TAP-4-PLUS with TAP-DRM accessory can perform dynamic resistance, vibration recordings, and motor current at the same time.”
Zensol advertisement in the issue:
“Zensol TAP-4-PLUS. The newest instrument for OLTC testing”