Contribution to the Evaluation of Silicon Carbide Surge Arresters

Abstract

Basically, there are two types of surge arresters installed in the power system: the silicon carbide (SiC) surge arresters and the zinc oxide (ZnO) ones. The SiC surge arresters are being replaced by the latter but a large number are still operating in the electrical system. Due to high costs and operational difficulties it is not possible to replace all the SiC surge arresters in a short term and the utilities have to manage both technologies (Carneiro, 2000). Therefore, in order to avoid failure, it is very important to know the level of degradation of the SiC surge arresters, most of them with 20 or more years of service. The diagnostic techniques applied to the ZnO surge arresters have been developed for many years and they are presented in (Heinrich & Hinrichsen, 2001) and (Kannus & Lahti, 2005). The main techniques are: thermovision and leakage current measurement. The leakage current measurement can give valuable information about the degradation of the ZnO surge arresters. The level of degradation is proportional to the magnitude of the resistive component of the total leakage current. Regarding the SiC surge arresters, there is no recommendation according to the (IEC-60099-5, 2000) standard. This chapter is focused on the application of the leakage current aiming the diagnostic of the SiC surge arresters. In the electrical utilities, the thermovision technique is also applied to the SiC surge arresters but it is very difficult to conclude, among several arresters, which of them are more degraded in order to replace them and to avoid failure (Almeida et al., 2009). This chapter describes the methodology and the results of the investigation that was performed aiming the application of the leakage current technique to the SiC surge arresters. The basic idea was to correlate the level of degradation of the SiC surge arresters with the magnitude of the third harmonic (3a H) of the total leakage current. Laboratory tests were performed in arresters that had been replaced in the substations. The characteristics of the leakage current showed a good correlation with the degradation of the arresters. Some of them were disassembled in order to verify their internal components. Afterwards, measurements were carried out in substation aiming to verify the feasibility of the technique in the field. Another substation was also evaluated, and based on the leakage current measurements obtained some SiC arresters were replaced. The results obtained in the investigation might help the utilities to develop more adequate maintenance programs. 12