Electrical Calculators

AC High Voltage Test

1. Objective

Before the RMU can be energised and put into operation, a power frequency AC high voltage test is carried out to verify that the dielectric strength of its components, the insulating medium and all other parts are sound and within their required limits so that the switchgear can operate safely on the system voltage without breakdown.

2. Method

Use an appropriate AC hi-pot tester suitable for the voltage rating of the RMU.

3. Safety Precaution

Barricade off the test area with red-white tape and display warning lights and danger signs.
Ensure all safety protocols are in place.
Make sure the area is only accessible to the authorised persons.

4. 11kV Ring Main Single Line Diagram.

1G1 - Incomer Feeder
1G2 - Transformer Feeder
1G3 - Transformer Feeder

5. Test Configuration 1

5.1 Configure the test circuit as show in above figure

5.2 Carry out an insulation resistance test of 10kV on L1 phase with the two other phase earthed and record the reading.

5.3 Repeat 5.2 for L2 and L3 Phase.

5.4 Connect the hi-pot tester's output lead to the conductor being tested and the return lead to ground. Gradually increase the test voltage to the specified level (e.g., 20kV as per PE/LEW during my time), hold it for one minute, and record the leakage current.

5.5 Watch for any signs of insulation breakdown, such as sudden current increases or audible discharges. The test is considered passed if there is no disruptive discharge throughout the test duration.

5.6 Discharge the switchgear and repeat step 5.4 for L2 and L3 phase.

5.7 Carry out the insulation resistance test again after high voltage test is done.

6. Test Configuration 2 to 6

Below procedure is applicable to test configuration 2 to 5.

6.1 Configure the test circuit as show in above figure

6.2 Carry out an insulation resistance test of 10kV on L1-L2-L3 stressed to Earth and record the reading.

6.3 Connect the hi-pot tester's output lead to the conductor being tested and the return lead to ground. Gradually increase the test voltage to the specified level (e.g., 20kV as per PE/LEW during my time), hold it for one minute, and record the leakage current.

6.6 Discharge the switchgear.

6.7 Carry out the insulation resistance test again after high voltage test is done.

For Configuration 6,

The procedures are the same other than the injection voltage. Please see test report.

7. Test Report

Below is the test result for your reference.