Cable testing: General test, For high voltage and low voltage


#1

What is cable testing? Why is it Needed?

Cable testings are completed before the commissioning to ensure the cable condition. Copies of test certificate shall be provided as per project and requisition requirements. These tests shall be performed by the Vendor and in accordance with the IEC standards.

Cable test is done to check the:

  • Cable conformity
  • Cabling quality
  • Cable functionality

General cable test:

  • Qualitative and quantitative control of technical documentation given with cables and its compliance with the particular specifications.

  • Control of drums: quality of flanges, marking and labelling, cable designation, length, section, sizes and weight, observance of minimum curve radius, capping of terminations, packaging and protection against shocks.

  • Control of conformity with the technical documentation.

Non electrical test:

  • Visual Inspection

  • Verify Against Specifications

  • Measurement of the thickness of the insulating covering.

  • Test for flame retardant according to IEC 60332-3 (Test C) for bunched cables.

  • Test for fire resistance according to IEC 60331.

  • Control of the mechanical properties of the external protective sheaths.

  • Verification of the nature, composition and thickness of the metallic armor.

  • Measurement of the external dimensions of the complete cable.

Electrical tests:

There are high voltage and low voltage cable tests.

1 Low voltage tests:

  • Insulation Resistance (Megger) Test
  • Hi-Pot 2 kV DC Test
  • Cable Tensiometer (Strain Gage) and Pulling Devices
  • Point-to-Point Verification of Cables

Insulation Resistance (Megger) Test:

Megger test is conducted to directly measure the insulation resistance of the cable. The megohmmeter test is more useful for low voltage cables. In the megohmmeter test, the megger is used to configure an electromagnetic field, and the field that is created is used to produce leakage currents that will flow through the insulation between the cable conductor and the ground. The amount of leakage current flow that is detected by using the megger results in a reading of the megger meter of the insulation resistance.

Hi-Pot 2 kV DC Test:

The purpose of a dc high potential (hi pot) test on low voltage cables is to identify internal faults in or damage to the low voltage cable insulation system. The hi-pot test will identify these faults so that corrective action can be taken. The hi-pot test should be performed or conducted before initially energizing a cable but after a megohmmeter test.

Cable Tensionometer (Strain Gage) and Pulling Devices:

This device is used for check the damages in the cable because of curves and bends within the selected installation route. The maximum cable tensions are calculated for various extraction directions and cable lengths, and a final cable extraction schedule is determined. The suitable cables and the equipment of drag are staggered in the different points of traction along all the pull of the cable.

Point-to-Point Verification of Cables:

A point-to-point verification of the cable installation is performed before and during the cable installation process to ensure that the correct cable is being installed along the correct route.

2 High voltage tests:

  • Insulation Resistance (Megger) Test
  • DC Hi-Pot Test
  • Cable Tensionometer (Strain Gage) and Pulling Devices
  • Point-to-Point Verification of Cables

Insulation Resistance (Megger) Test:

The megohmmeter test that is performed on medium/high voltage cables is conducted in an identical manner to the megohmmeter test that is performed on low voltage cables. For medium/high voltage cables, the megohmmeter test voltage should be 5,000 V for cables that are rated for 5,000 V and above.

DC Hi-Pot Test:

The purpose of the dc hi-pot test that is performed on medium/high voltage cables is to identify internal faults in, or damage to, the medium/high voltage cable insulation system. The dc hi-pot testing technique that is used for medium/high voltage cables involves the measurement of increased dc voltage that is applied to the insulation under test. The major difference between the low and medium/high voltage cable dc hi-pot tests is the voltage values that are used during the test

Cable Tensionometer (Strain Gage) and Pulling Devices

The purpose of conducting an installation inspection of the cable pulling process is to ensure that the cable pulling methods are correct and that the cable pulling tensions do not exceed the maximum values that were determined during the design phase of the installation.

Cable tensiometer (strain gage) checks are performed throughout the pull (or pulls) to ensure that the maximum cable pulling tensions are not exceeded.

Point-to-Point Verification of Cables:

The purpose of performing the evaluation of the medium/high voltage cable terminations and splices is to determine whether the medium/high voltage cables have been correctly terminated or spliced. The main causes of cable failure are damage during installation and improper splices or terminations. An evaluation of cable splices and terminations can uncover problems or installation errors.