The lightning arrestors are those types of equipment which operate during high voltage lighting and switching pulses. It bypasses the surge current to the ground during overvoltage surge. It becomes a low impedance path for the surge current. In this way, it keeps the system voltage at a certain limit even during the high voltage surge impulses. So, we can understand the importance of a surge arrester in the electrical power system. Normally, a lightning arrestor remains idle in the maximum time of a year. Also, the number of operations is very few. Also, its operations are invisible. Because of that, the reliability of in time operation of an LA is extremely essential. To maintain this reliability of the equipment, proper maintenance of lightning arrestors is essential.
There is always a counter fitted with lighting arrestor. We call this counter as surge counter. Normally this counter counts 0 to 5 per year.
But if there are more than 10 counts then we can recheck it with the record of switching operation of the line to which the LA is attached.
But in any case, if the surge counter counts more than 100 in a year then we consider it as abnormal behavior. It indicates that the spark over voltage of the lightning arrestor has reduced. This may be due to internal defects of the arrestor. In that case, we must replace the LA by a new or a good one.
Schedule for Maintenance of Lightning Arrestors
- We need to clean the insulator body of an LA once in a year.
- After that, means after cleaning of the insulator rain shed surfaces, we must measure the IR value of the LA. We do this with the help of a 5KV megger. The recommended IR value is 400 MΩ with 5KV megger.
- We also need to measure the leakage current or third harmonic resistive current of an LA during maintenance of lightning arrestors.
If this leakage current is less than 300µA we may consider the LA as a healthy one. But if it is more than 300µA we need to take out ZnO block to the laboratory for testing. Here the test results determine the condition of the LA. If it reports badly, it needs to be replaced.
We need to perform the leakage current measurement after proper cleaning of the LA insulators.