Reliability investigation of the Nigerian Electric Power Authority transmission network in a deregulated environment

The paper presents the findings of reliability investigation carried out on the 330 kV high voltage transmission network of the Nigerian Electric Power Authority (NEPA). The system made up of three hydro generating stations in the north and four thermal stations in the south is loosely tied together by long transmission lines that are basically radial. The system was represented by a 24-bus, 39-transmission line and seven generating stations that made up the grid. The base load was taken as 1776 MW representing approximately 30% of installed capacity of about 6000 MW. Taking into consideration all available VAr injections and voltage control equipment the load was increased by 10% consecutively and the system generating voltages and. available VAr were controlled to make sure that all bus voltages were within tolerance of +5% and -10% of rated values The results show that the system was able to cope with the load demand without problems up to 3500 MW. Although some stations experienced low voltages, these were corrected when the generator voltages were adjusted via reactive power injection. But by the time the load was increased to 3800 MW, all the available VAr injection had been utilized and most stations were at their upper voltage limits. The system response for load above 4160 MW was completely unacceptable. Suggestions are given that will enable the network to cope should the installed generating capacity be increased in order to meet the increasing load demand.