In-service condition monitoring of polymer housed surge arrester within eThekwini Electricity

Abstract

The primary objective of this research was to investigate the failures occurring in the family of surge arresters used within EThekwini Electricity, making use of different diagnostic methods, such as leakage current testing (LC), infrared scanning (IR), and partial discharge (PD) measurements. The different diagnostic tests were used to assess the degradation process of the polymer housed surge arresters and their failure.

The measurements were used for diagnosis of 120 kV/65 kA surge arresters of different brands. Tests were performed on surge arresters that were still in the system and these test results were compared with results from tests performed on failed units. Results obtained from the different tests were compared to the test results for different families or designs. An imperfect arrester will exhibit excessive heating when an electrical surge is discharged. The aforementioned tenets are the primary factors influencing degradation and causing failure of Metal Oxide Surge Arrester (MOSA) in a system.

These factors can decrease creepage and flashover distance on insulation, which could result in a substantial increase in resistive leakage current, (which is a few microamperes in ideal condition), overheating, and PD formation on the zinc oxide varistor element. Therefore, it is extremely important to assess the status of the surge arresters whilst they are in service, firstly so that they can be removed from the system before they fail and, and secondly, to verify their condition, and their ability to effectively protect the substation apparatus.

Using infrared inspection, valuable information of condition of surge arresters was obtained, heat inside the surge arresters was detected and this shows that IR analysis can therefore be considered as an additional method to assess the condition of polymer housed surge arresters. It was observed that partial discharge activity is an indication of degradation in arrester varistor. LC test, IR, and PD measurement were valuable in obtaining sufficient information for failure of surge arresters. In additional, during the visual internal inspection of arresters, evidence of punctures, treeing, tracking, and moisture masks were noted on ZnO blocks and seals. These results indicate that the moisture ingress through the sealing collar can cause unnecessary outages.