What is the purpose of a surge arrester, and how is its health assessed in substation maintenance?

A surge arrester, also known as a surge protector or lightning arrester, is a protective device used in substations to protect electrical equipment from transient overvoltages caused by lightning strikes, switching operations, or other system disturbances. The purpose of a surge arrester is to limit the magnitude and duration of these overvoltages, diverting the surge current to ground and preventing damage to the protected equipment, such as transformers, circuit breakers, and insulators. Surge arresters are typically connected between the phase conductor and ground. Under normal operating conditions, the arrester acts as an insulator, allowing only a small leakage current to flow. When an overvoltage occurs, the arrester's internal components rapidly change from a high-impedance state to a low-impedance state, providing a path for the surge current to flow to ground. After the surge has passed, the arrester quickly returns to its high-impedance state, resuming its normal insulating function. Assessing the health of surge arresters is a crucial part of substation maintenance. Several methods are used to evaluate their condition. Visual inspection involves checking for signs of physical damage, such as cracks, chips, or corrosion. Leakage current measurement measures the current flowing through the arrester under normal operating conditions. An increase in leakage current indicates degradation of the arrester's internal components. Resistance grading current measurement is a more advanced technique that measures the distribution of current along the arrester's grading resistors. This can identify localized areas of degradation. Power factor testing measures the power factor of the arrester's insulation. An increase in power factor indicates insulation degradation. Online monitoring systems continuously monitor the arrester's leakage current and other parameters, providing early warning of potential problems. Periodic testing using specialized test equipment is also performed to verify the arrester's performance. This testing may involve applying high-voltage impulses to simulate lightning strikes and measuring the arrester's response. The results of these tests are compared to baseline data and manufacturer specifications to determine the arrester's condition. Damaged or degraded surge arresters are replaced to ensure continued protection of the substation equipment. Therefore, regular assessment of surge arrester health is essential for maintaining the reliability and safety of substations.