Induced voltage behaviour analysis of an un-grounded outer layer semi-conductive coating of a 400 kv power cable system

Summary

It is standard practice to include semi-conductive layers within high voltage cables where the purpose is primarily focused around equalising the electric field strength around the conductors (core and metallic sheath). When a semi-conductive coating is present in the outer fire barrier layer, the complexity of additional induced voltages should be considered. When considering induced voltages, the primary concern is related to sheath voltages. During steady state and transient conditions, sheath voltages should be considered for potentially dangerous over-voltages. Usually these concerns are addressed with sheath bonding techniques and sheath voltage limiter arresters. During the initial phases of cable commissioning, the energisation of cables could pose significant problems if the bonding technique of the outer semi-conductive coating is not efficiently executed. Transient over-voltages might have adverse effects on all the connected feeder cables during the energisation of one cable. When the differential voltage between the semi-conductive coating and earth is driven beyond the withstand capability of the gap between the coating and supporting brackets, flashovers are likely to occur. The main insulation is expected not to be excessively stressed and the integrity is expected to be intact. This leads to the study where the cable outer layer is evaluated in terms of induced voltages specifically during transient conditions. It is imperative that safe touch voltages are achieved at all times. The induced voltages during switching are evaluated in an electromagnetic transient computer program to understand the problem that will ultimately lead to ensure the safety of personnel and to protect the equipment. It is also important to gain an understanding in the modelling of such a system. The study includes the simulation of the system to evaluate the problem and to propose a recommendation for a workable solution.

Additional informations

Authors

MARSHALL, SANTAMARIA

Keywords

Transient over-voltage, switching surge, insulation coordination, cable, high voltage