Novel Method of Assessment of Healthiness of EHV Lightning Arrestors using Total Harmonic Distortion analysis of Leakage Current

Substation’s, which primarily help in protection of substation equipment from Lightning strikes. Ensuring healthiness of lightning arrestors is of paramount importance, so as to ensure that the arrestors do not conduct under normal operating conditions and conduct and protect the substation equipment’s only during lightning strikes/ abnormal voltage surges. As on today, the healthiness of a metal oxide lightning arrestor is assessed primarily through monitoring of the third harmonic resistive component (THRC) of the leakage current in a charged Lightning

Arrester, in addition to Insulation Resistance measurement of the Lightning Arrester during shutdown/ offline condition. However, despite the availability of the above monitoring techniques, there have been numerous instances of Lightning Arrester failures while in service, affecting the reliability of the grid. Further, in a number of cases, low Insulation Resistance (IR) of Lightning Arrester’s were detected during offline Insulation Resistance measurement during shutdown maintenance, thereby prolonging the planned maintenance time, which is not desired.

This paper introduces and establishes the Total Harmonic Distortion (THD) of the leakage current of the Lightning Arrestor, as a determining parameter for assessment of the health of the EHV Lightning Arrestor. Total Harmonic Distortion of the Lightning Arrester’s can be easily measured using commercially available Power Quality Analysers (PQ analysers). It is observed that, the Lightning Arrester’s with low Insulation Resistance value, especially of the top stack, show abnormally low values of Total Harmonic Distortion of leakage current while in service, when compared to a healthy Lightning Arrester in the same bay of the switchyard.

Using the proposed method, one can easily predict the insulation failure in the Lightning

Arrester and in case of exponential violation of the Total Harmonic Distortion of leakage current of the Lightning Arrester, immediate shutdown can be taken and Arrester can be replaced, thereby increasing system reliability. The Lightning Arrester, if not replaced, would otherwise fail and may lead to consequential damage to other equipment’s in addition to lost system availability. Further, shutdown planning can be done in a more efficient way as the maintenance engineer, using the above method, shall have a clear idea if the insulation of the

Lightning Arrester is healthy or not.

The method proposed above is an online technique, which, when used in conjunction with the existing Lightning Arrester health monitoring techniques (i.e online THRC and offline IR measurement) can provide wholesome solution to the EHV Lightning Arrestors health monitoring, thereby, greatly enhancing the reliability and availability of the Grid.