MO Surge Arresters: Stresses and Test Procedures

Abstract

EXECUTIVE SUMMARY The Cigré Technical Brochure TB 60 was published in 1991 describing effects on gapless metal oxide surge arresters (MO arresters) from various electrical stresses encountered in 3-phase AC systems. Since then, continued improvements in equipment technologies coupled with the interest of the de-regulated power industry to maximize utilization of the existing infrastructure has revolutionized the MO arrester applications and the expected performances in an environment, characterized by higher stress levels. Today?s proven confidence in the reliability and capability of modern MO arresters offers new possibilities of overvoltage protection and improved management of power system disturbances. The Working Group A3.17 of SC A3 took the task to evaluate the stresses on MO arresters and to review the existing test procedures. Further on, the actual state of MO arrester designs was investigated, as well as the various applications in different types of electrical networks. Emphasis was given to the MO resistors as the active part of the MO arresters. A research project was started to experimentally investigate the energy handling capability of the MO resistors, which is a key design criterion for a reliable arrester application. The resulting Technical Brochure covers and describes the actual MO resistor and arrester technology and the results of the first part of the research project on the energy handling capability of MO resistors. Electrical stresses on MO arresters can be divided into stresses at power frequency, which can have long time durations, and transient stresses of short time duration resulting from switching and lightning. IEC 60071-4 proposes some recommendations for the evaluation of overvoltages, based on the use of numerical programs.