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How to test the electrical cables?

 Testing of Electrical cables(HV, MV, LV) :



The following shall be the guidelines for the testing personnel during the inspection and testing of LV, MV and HV cables.

1.Phase identification test:

Use safety grounding devices to discharge any trapped charges before connecting /disconnecting any test leads or other connections to/from the cable.

Disconnect the cable under test from any electrical circuit.

Connect the battery box, at one end of the cable :

           - 0V to earth

           - 4.5V to L1

           - 9V to L2

           - 13.5V to L3

Using a multimeter, check if at the other end of the cable, the voltages for each phase are correct according to drawings and specifications.

2.Shield continuity test:

Use safety grounding devices to discharge any trapped charges before connecting /disconnecting any test leads or other connections to/from the cable.

Using a multimeter, measure the resistance of the shield.

Investigate the shields with resistance of more than 10 ohms per 1000ft of cable.

3.Insulation Resistance test :

Measure and record the ambient temperature and humidity.

Discharge all stored capacitance in the cable by grounding it before testing.

Disconnect the cable to be tested from other equipment and circuits.

Test voltage should be as recommended by the manufacturer.

The test duration should be one minute.

Measure the insulation resistance of each phase to ground and between phases. The guard terminal of the megaohmmeter can be used to eliminate the effects of surface leakage across exposed insulation or leakage to ground.

After completing the test, ground all conductors in order to discharge the stored energy.

The measured insulation resistance must be compared the value recommended by the manufacturer. An insulation resistance field acceptance limit of:

         IR=1000(KV+10)/L

         Where,

          IR - is insulation resistance Mega ohms per 1000ft

          KV - is insulation voltage rating

          L - is the cable length in feet.

4.Before system Energization the following test shall be performed :

Megger test insulation on all feeder.

Continuity check conductive systems.

Ground(earth resistance) test at main service and separately derived system grounds. Megger and earth tester shall be used.

Ground system continuity check.

5.After system Energization the following test shall be performed :

Phase rotation and phase consistency test at panel board, switch bords and motor control centre.

Voltage, current and load balance tests at panels, motor control centers, switch board and equipment.

Verify and record voltage, phase to phase, phase to neutral at main switchboard.

Any defects notice during the test shall properly resolve the testing shall be done again until satisfactory results.

Proper documentation and quality record shall be done in accordance with approved ITP during the test.

All test instruments used must have a calibration.


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