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ABSTRACT
The protection system in the 330kV of Nigeria Transmission Network is investigated in this study. The study has reviewed the existing protection system as practiced and discovered common factors that often lead to power outages and blackouts to include; lack of co-ordination of system protection scheme control strategies and low power generation. The present status of the 330kV Transmission network is presented and new transmission lines to strengthen the existing network against system instability are proposed. The thesis also discussed the causes of system collapses, provides an overview of the existing system protection schemes and proposed wide area monitoring, protection and control scheme.
This thesis has modelled the Nigerian 330kV grid system transmission network using NEPLAN power software programme which has been used for the calculation of three-phase and single-phase to earth short-circuit fault currents at each of the substations, and apparent impedance of the network. The results obtained from these studies are used for the co-ordination of distance relays and settings of inverse definite minimum time overcurrent relays, and earthfault relays. The results also form the basis for the selection of circuit breakers from the manufacturer’s tables.
Various types of relay characteristics used in transmission line protection with specific emphasis on distance protection schemes are also analyzed. An algorithm and flowchart for setting, testing and commissioning of numerical (microprocessor) distance relays have been developed. Results obtained from the tests carried out on the setting of microprocessor based on distance relays on Benin-Oshogbo transmission line are presented. Additionally, the philosophies of differential and restricted earth fault protection schemes, guidelines for proper selection of current transformers and setting of relays, testing and commissioning of differential and restricted earth fault protection schemes with practical examples are also presented. This thesis has therefore achieved the characterization of the protection schemes of the Nigerian electrical supply power industry at 330kV level and also provides for the improvement of additional protection schemes whenever there is a need to expand the network.
