Testing Insulation Resistance of Power Cables with a Megohmmeter
1. Preparations for Measuring Insulation Resistance of Power Cables with a Megohmmeter
A 2500V megohmmeter (equipped with test leads) shall be selected for measuring the insulation resistance of 10kV power cables.
Before measurement, inspect the megohmmeter: check whether the pointer works normally and whether the connections between clip leads and terminals are in good condition. The measuring wires shall be insulated wires with a shielding layer.
Prepare an earthing rod for discharging at any time. After the power cable is de-energized, discharge it first before measurement.
Check the markings on the power cable, for example, verify whether the rated insulation voltage specified in the model matches the voltage class of the megohmmeter. Understand the insulation value range of the equipment before testing.
Wipe off dirt near the cable conductor core with a dry and clean soft cloth.
Before starting measurement, hoist the tested cable end to about 1.5 m using ropes. The other end of the cable shall also face upward and preferably be erected to prevent the cable terminal from touching the wall and earthing. Assign dedicated personnel for on-site supervision.
2. Test Procedures for Measuring Insulation Resistance of Power Cables with a Megohmmeter
The test items mainly include insulation resistance between phases and phase-to-earth insulation resistance, namely U-V, W, Earth; V-U, W, Earth; W-U, V, Earth, three tests in total.
Make wiring strictly as required to ensure correctness. When measuring phase-to-earth insulation resistance, connect the shield of the tested phase to the G terminal of the megohmmeter.
Connect the two conductor cores of the non-tested phases together, then connect them to the metal sheath of the cable and earth them jointly. Connect this common earthing wire to the E terminal of the megohmmeter. Connect one test lead to the L terminal of the megohmmeter; the other end of this test lead (Line L) is not connected to the conductor core at this moment, as shown in the figure.
