PROTECTION OF CROSS-BONDED CABLE SYSTEMS USING NON-LINEAR INDUCTIVE DEVICE

Mohammad  Mahmoud  ABDUL GHANI

The adoption of cross‑bonding in single‑cored cable systems virtually eliminates sheath power losses (with their heating effects). Nonetheless, cross‑bonding is associated with high over‑voltages across sheath interrupts. These over‑voltages are due to the reflection of travelling wave from the cross‑bonded points. Protection of sheath interrupts is accomplished in practice by using ZnO non‑linear resistors.

The present work proposes non‑linear inductive device as an alternative to the ZnO resistor. The performance of this device, when connected to the sheath circuit of a single‑phase cable system is tested experimentally under steady‑state and impulse current transient conditions. Computational results are shown to conform to the experimental ones. This indicates that the mathematical models used, for both the cable and the protective device, provide a reasonable presentation of the system.

A mathematical model of a single major section of cross‑bonded cable system is developed, and an outline of the Z‑transform method for determining transient over‑voltages in the system is presented. Cross‑bonded cables are analyzed in terms of the parameters of constituent homogeneous sections. These parameters are compounded by using a rotation matrix at each cross‑bonding point. Sheath voltages to ground and voltages across sheath interrupts are calculated at various points along typical system comprising one major section. Finally, the effect of the non‑linear device on the prospective sheath over‑voltages, under different switching conditions, is investigated.