Abstract
Power, stations are unevenly distributed and located far from the main loads that are concentrated in a few large cities. Electric power networks are heavily loaded. One of normalization policies of power supplies is power network linkage interconnecting with different alternating frequency power sources. Reflecting rapid advances in thyristor valves, there are frequency converters. In order to achieve a economical design of insulation coordination, it needs to adopt high performance surge arresters. In this case, AC 275kV/AC 56/DC 125kV metal oxide arresters have been developed. High performance surge arresters help to realize small, lightweight, low-cost, converter and substation equipments.
But, as the applied voltage ratio (=continuous operating voltage/reference voltage) of zinc oxide elements in high performance surge arresters is high, they are inclined to absorb surge energies of frequency resonance temporary overvoltage, Therefore, it is important to watch the conditions of surge arresters on line. On the other hand, the spike current flows through the arrester across thyritors valves A-K terminals corresponding with the commutation voltage, and also arresters terminal ends are insulated from the ground. It is difficult to use a conventional current monitoring method.
This paper adopts the temperature rise of zinc oxide elements to watch the degradation and thermal runaway of surge arresters on line. The relation between the temperature rise and leakage curent of zinc oxide elements in parallel connection is obtained by tests. From these results, monitoring equipments of surge arresters in AC-DC converter stations were developed. These equipments are very useful for operation and diagnosis assistance functions of surge arresters.
