• Document: High Voltage Surge Arresters for Protection of Series Compensation and HVDC Converter Stations
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The 4th International Conference on Power Transmission and Distribution Technology 2003 High Voltage Surge Arresters for Protection of Series Compensation and HVDC Converter Stations Kai Steinfeld, Reinhard Göhler, Daniel Pepper Siemens AG, Berlin Abstract The efficiency of overhead power lines can be increased by series compensation or HVDC transmission. These complex systems can be protected from overvoltages by metal oxide surge arresters. Both porcelain and polymer tube design surge arresters are used for these applications, however, polymer tube design surge arresters offer various advantages over porcelain arresters such as light weight, extremely high mechanical resistance and safe short circuit behaviour. Type and routine tests of surge arresters for series compensation and HVDC stations ensure the general functionality and quality of these devices. The rating of surge arresters for series compensation and HVDC stations follows different consideration as the rating of standard high voltage surge arresters. While the latter ones are rated by mainly taking standard lightning, switching and temporary overvoltages into consideration, the rating of surge arresters for series compensation and HVDC converter stations is given by internal overvoltages due to operating and fault conditions. 1. Introduction The transmission of electric energy over long distances by high voltage AC overhead transmission lines is limited by the inductance of the line. Above a certain length, the magnitude of which depends on the geometry of the system and its voltage, the voltage drop across the inductive impedance reaches a value which makes the system ineffective. There are two countermeasures to reduce or completely avoid the inductive current and thus to increase the efficiency of an overhead line: The installation of series compensation (SC) stations within the AC overhead line [1], or the transmission by high voltage direct current (HVDC). The equipment used in SC or HVDC stations, e.g. capacitors, reactors, transformers, filters or valves, are exposed to overvoltages of different origin. Lightning strokes into the electric power system, the station itself or into its vicinity lead to lightning overvoltages. Switching action within the system including the periodic switching of the HVDC converter valves cause switching overvoltages. Certain operating conditions due to load flow control cause temporary overvoltages. Finally, overvoltages may be caused by internal or external faults and subsequent short circuit current. Without countermeasures, occurrence of these overvoltages in the system can lead to breakdown of the equipment insulation and its failure. In order to protect the equipment from overvoltages, surge arresters are used within the system. The purpose is to always limit the voltage across the terminals of the equipment to be protected below its insulation withstand voltage. This is achieved by connecting elements with an extremely non linear voltage current characteristic in parallel to the terminals of the equipment. So called metal oxide (MO) surge arresters containing ceramic bodies mainly made from zinc oxide (ZnO) and bismuth oxide are used nowadays [2]. To some extend, there are differences in the design and testing, but particularly in the rating of surge arresters for protection of SC and HVDC stations as compared to arresters for standard AC high voltage applications. While the rating of standard surge arresters is mainly determined by standard lightning, switching and temporary overvoltages [3], the rating of SC and HVDC surge arresters is based on overvoltages by fault conditions or internal overvoltages. In this paper, the design, testing and application of surge arresters for protection of SC and HVDC converter stations will be explained. 2. Design, Rating and Testing of Surge Arresters In this chapter, the design, electrical rating as well as type and routine testing of surge arresters in general will be introduced. Since arresters for SC and HVDC stations are somewhat different from each other and different from standard surge arresters, only very brief information about some basic considerations will be given. More details about the design, rating and testing of high voltage surge arresters can be found in [4]. 1232 The 4th International Conference on Power Transmission and Distribution Technology 2003 2.1. Design of Surge Arresters In the past twenty years there were two major changes in the technology of surge arresters. Firstly, the gapped silicon carbide (SiC) arrester technology was replaced by the gapless metal oxide (MO) arrester technology in the late seventies to early eighties of the last century. As a consequence, the protection characteristic was improved, the reliability was dramatically increased to failure rates close to zero and the design became much easier. In the late ei

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