Power cables are expected to be reliable conductors of electrical power. It is therefore vital that the correct test procedures are followed and that these cables are correctly installed, diagnosed and maintained. The following tests are offered:
Cable systems must withstand not only the rated voltage which corresponds to the highest voltage of the system, but also an overvoltage. Overvoltages are caused by lightning discharges, switching disturbances, pollution and fault conditions on the system. The magnitude and type of test voltage depends on the type of cable, the application and the rated voltage. To assess the ability of the cable system insulation to withstand the overvoltages, various test apparatus have been developed. The options available for overvoltage pressure testing can be summarized as follows:
Tangent delta (TD) is the tangent of the angle between resistive and capacitive leakage currents. By using a computer and VLF testing it is possible to make these measurements and detect the bad segments of water treed cables. The tan delta measurement allows the Utility or user to plan for the replacement or repair of water tree degraded cables. PD measurements must be done on all newly installed cables to ensure that the installation has been done correctly. It is possible to measure the level of PD in a cable on site and the distance to the point of PD using the time of flight of the PD waves.
A 5kV DC sheath test should be applied to test the integrity of the sheath (to avoid future water ingress). This test is applied between the armouring and the mother earth.
Most faults occur between the core and the armoring or concentric earth (neutral). Cable faults are identified by their resistance and type of fault. Resistive faults are the most common. High resistance faults do occur occasionally and these faults can become very difficult to find due to the fact that no flash can occur. A DC pressure tester will highlight these faults. The following services are also offered:
All cable accessories (Jointing and Terminations) are vital components, and when correctly installed they are absolutely necessary to ensure the effective performance under a great variety of environmental service conditions. Distribution power cables are in many ways the backbone of a power network.
The varieties of electrical power cables that are installed to complete the supply of power to all areas are manufactured in accordance with stringent specifications. It is therefore of utmost importance that the electricians and or people working with electrical power cables are properly trained and familiarized with all aspects cable jointing and termination of cables and the related cable accessories.
The difficulties in routing overhead lines in crowded human habitats are some of the reasons for the growth of cable technology. Where the batteries at a substation are the heart of the station, so are the cables the heart of the power supply to the customer.
A failed joint in the ground is much more difficult to locate and repair than an overhead line.
The quality of the joint termination depends on the skill and workmanship of the jointer, electrical and mechanical. The joint or termination must be as good as the cable itself (electrical properties).