Evaluation of Lightning Protection Efficacy on Nigerian Installations High Voltage Installations Using Screen and Cone of Protection Methods

This study evaluated lightning protective system efficacy on 11kV-132kV substation-power line installation in Ikorodu, Lagos State, Nigeria with reference to cloud to ground(C-G) lightning strike (LS) events. It focus on interception of lightning strikes and its protection with reference to direct lightning strike (DLS) and indirect lightning strike (IDLS). Data were collected from Ikorodu 132/33 kV Transmission Substation and its four major injection stations. This work was carried out using physical measurement of raw data obtained from the high voltage substation. Installations were scaled down and modelled dimensionally using AutoCAD software in order to measure spatial parameters in order to measure the screening of the existing substations and connected lines, as well as the existing cone angles of protection. Probability of lightning efficiency of lightning protective level (LPL) are used for screening evaluation while spike and sky wire angle of protection are used for cone of protection evaluation. Physical measurement of six substations (33/11 kV and 132/33 kV substations) in the studied area were also carried out to evaluate the effectiveness of the installed lightning arresters with respect to the protected devices using applicable standard. The results under the prevailing lightning protective system, LPS, (screening method), revealed that the existing 33/11 kV and 132/33 kV substations are not adequately protected against lightning strike; 132/33 kV substation is more vulnerable to lightning strike than 33/11kV substation and that the incoming 132kV power lines to the substation are adequately protected. The evaluation of the installed distances of all lightning arresters are within standard range and would adequately protect substation transformers against travelling waves (Indirect Stroke) events. The installed lightning arresters (LAs) would adequately protect substation transformers against travelling waves (Indirect Stroke) events. The adequate protection should be reinforced with proposed design scheme in further study in order to mitigate the disastrous effects of lightning strike. Any proposed design of protective system for electric power installations in Nigeria should be simulated using computer aided design software for scaled validation of dimensional and spatial design values in order to mitigate reported failures and uncertainties in identifying causes of observed failures in the system.