Role of Metal Oxide Surge Arrester for Power System Protection Against Lightning Overvoltage

Overvoltage is one of the major factors for the insulation failure in the power system. Thus, it is basic role of system designed to protect the insulation system against such voltage surges. Main reason of overvoltage in the power system is natural lightning as well as switching operations of large loads. Overvoltage generated due to switching operations are called switching overvoltage and generated due to natural lightning are called lightning overvoltage. Lightning overvoltage is very unpredictable as it does not depend on system voltage. As the overhead lines and substation equipment are exposed to open environment, it is important to protect the system against lightning overvoltage. Substation equipment such as transformer, cables, insulator etc. must be designed withstand against lightning overvoltage. Also, system must be protected from such overvoltage. Various methods such as shield wire; rod gaps and surge arresters are provided in the power system for protection against overvoltage. Surge arresters are one of the best measures for lightning overvoltage. Now, Metal Oxide Surge Arrester (MOSA) consisting of ZnO element are used in system due to its excellent nonlinear characteristics. However, location of MOSA in substation is critical and must be evaluated for its fast and reliable operation for system protection. For effective operation of MOSA, it must be grounded through lowest possible earth resistance. Also, tower footing resistance (TFR) plays important role for overvoltage magnitude. In this paper effective performance of MOSA with different TFR and different location of MOSA from equipment to be protected is analyzed. Analysis of lightning surge on different magnitude for 132 kV and 66 kV system has been evaluated and presented. The effect of MOSA on transferred voltage on secondary winding of transformer has been also computed considering effect of cable. EMTP-RV software has been used for the analysis of MOSA operations and results of the same has been presented in this paper.