EVALUATION OF SURGE PROTECTION IN UNDERGROUND DISTRIBUTION SYSTEMS USING ZINC OXIDE (METAL OXIDE) SURGE ARRESTERS

The application of zinc oxide arresters represents a significant development in surge protection. One area of distribution system protection where the new arrester technology can be immediately valuable is underground distribution system protection. Increasing system voltage levels and the economic advantages of lower basic insulation level (BIL) have led to increased interest in improving protection of underground distribution system equipment. Because conventional silicon-carbide surge arresters have not met the challenges imposed by system requirements, costly alternatives such as paralleling arresters have been used in an attempt to limit surges imposed on systems.; All surge protection studies performed until recently have been limited to the silicon-carbide arrester and the earlier types of surge arresters. The few surge protection studies which considered zinc oxide arresters involved single-line systems and only hypothetical data was used. In this thesis differences between the two types of arresters are reviewed and an evaluation of surge protection employing zinc oxide arresters in underground distribution systems is carried out.; In order to evalute zinc oxide surge arrester's performance under various conditions, transient phenomena of single- and multi-line underground distribution systems, with and without surge arresters, are studied. The conditions considered include; (i) low and high surge impedance systems, (ii) slow and fast front surges and (iii) different line terminations. Actual data obtained from a typical and operative underground distribution system is used in the study. In the multi-line model of the system attention is focussed on the ring busbar at a transmission substation which is exposed and therefore vulnerable to lightning strokes. Underground distribution systems are know to endure switching surges, therefore lightning strokes only are considered. System simulation is done by the Electromagnetic Transients Digital Computer Program.; In real life distribution systems are multi-line systems and the significance of studying the transient phenomena of multi-line systems is the high degree of accuracy achieved as opposed to only considering single-line systems. The results obtained in this research show the contrast in system response to overvoltages by single- and multi-line systems.