EVALUATION AND PLANNING OF LIGHTNING PROTECTION EFFICACY ON NIGERIAN HIGH VOLTAGE INSTALLATIONS: IKORODU 11 kV-132 kV SYSTEM AS CASE STUDY

Abstract

This study evaluated cloud to ground(C-G) lightning strike (LS) events and protective system for 11kV-132kV substation-power line installation in Ikorodu, Lagos State, Nigeria and proposed an effective lightning protection scheme specifically for the installations. Cloud-to-ground(C-G) lightning incidence data were obtained from Nigeria eteorological Agency (NIMET), Oshodi, Lagos, for the period of 2006 to 2012. Direct measurement of dimensions of installations were carried out in order to evaluate the protection of 11 kV -132 kV substation and connected power lines. Statistical methods were used to analyses the obtained data. Scaled models of installations were produced in AutoCAD in order to measure the screening of the existing substations and connected lines, as well as the existing cone angles of protection. Physical measurement of six substations (33/11 kV and 132/33 kV substations) in the studied area were carried out to evaluate the effectiveness of the installed lightning arresters with respect to the protected devices. Sizing of air terminal, down conductor and lightning protection earthing network of power substations and lines were carried out. The obtained results show that lightning strike events are significantly intense in the studied region and contribute to power outage, most especially at 33 kV and 132kV installations. There is correlation between lightning strike and power outage, and also lightning strike events and power outage frequency in the studied town. This results 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. This research also provided a model for effective protection schemes for 132/33 kV and 33/11 kV substations with associated lines. Under the proposed lightning protective scheme, all 23 and 33 elements3 of both 33/11 kV and 132/33 kV substations respectively are adequately protected against lightning strike by obtained coverage factor assessment values. It was established that the prevailing earthing system conductor size of 95 mm2 should be replaced with conductor size of at least 161 mm 2 in order to obtain effective earthing system protection. Planned maintenance for efficient operation of lightning protective systems in Ikorodu 11-132kV substations and power lines installations should be carried out during the dry season, preferably in December and January. Upgrading that will incorporate a hybrid design comprising screen, sky wire and spike schemes with adequate parameter values should be implemented. 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.