ABSTRACT
Reliability of power equipment in Ajaokuta Steel Company Limited (ASCL), Ajaokuta, Kogi State is as important as the company as a whole. The study presents the reliability analysis of critical Power Equipment in Ajaokuta Steel Company Limited (ASCL), using one of the distribution substation, 7DS (Engineering Shops & Auxiliaries including Housing Estates) as a case study, for the purpose of assessing how frequent the failure of power equipment were experienced within the period of January to December 2020. To achieve this, failure data of power equipment like 11kV, 630A Oil Circuit Breakers (OCB) of Incoming Feeder to the substation as well as Outgoing Feeder Cubicle 32 and Outgoing Feeder Cubicle 5, Earth Fault Relay PTN, Overcurrent Relay PT3, Current Cut-off Relay PT1, Pole Discrepancy Protection Relay (for Single Phasing Fault), Voltage Transformer, 3-phase, 11/0.415kV Sub Service Transformer, Current Transformers, Manual isolator on Outgoing Feeders, 110V DC Battery Unit and Rectifier Unit were calculated using Microsoft Excel software and analysed using Fault Tree Analysis method. The Reliability of the distribution substation was determined using exponential distribution model. A model was developed using the reliability block diagram (RBD) method. A 10-year prediction using the exponential distribution model and the RBD model was obtained and comparison between the models was carried out. The outages/unavailability records were obtained from the Logbook of MSDS 1 Control Room. The Case Study Substation, 7DS is an unmanned Distribution Substation under MSDS 1. As a result, all data regarding 7DS Substation were obtained from MSDS 1 Control Room. Results show that the outgoing feeder 32 (Township Feeder 1) has the highest annual outage time/unavailability, thus contributing most to the interruptions in the substation with a failure rate of 0.021474607 per hour and annual outage time of 0.9141 hour. Another major contributor to interruptions in the substation thereby affecting delivery of electricity to the customers was earth fault failures having a failure rate of 0.016765799 per hour and outage time of 0.5676 hour, followed by current cut-off failures 0.012860225 per hour and 0.42996 hour and the outgoing feeder 5 (Township feeder 2), 0.014417382 per hour and 0.38268 hour respectively. Subservice transformers 1SST & 2SST, voltage transformers 1VT & 2VT as well as current transformer had the same failure rates of 0.000112007 per hour. The least contributor to interruption within the period under review was the sub-service transformer 1SST & 2SST with a value of 0.00000233348 hour. The reliability of the entire substation obtained using the exponential distribution model was 91.77%. Using reliability block diagram, the substation has a reliability of 95.22%. The reliability of the substation is low compared to the IEEE standard of 99.99% for distribution substation. Hence with the value calculated for this substation, the reliability is low. Comparing the result obtained with the available reliability benchmarks, it is obvious that the substation has performed poorly and needs to be improved upon to increase its reliability indices. Routine maintenance and right of way clearance on all outgoing feeders should be carried out to reduce the rate of earth fault and current cut off system tripping.
