DESIGN AND IMPLEMENTATION OF A MICROPROCESSOR-BASED ADAPTIVE PROTECTION FOR A DISTRIBUTION NETWORK
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The development of microprocessor-based relays started in early 1970's. Many researchers have had the view that long range economic trend favours the use of microprocessors in protective relays. As a result, for the last 25 years an extensive research has been carried out on digital protection. The research, design and economics of microprocessor-based relays reached to a stage where commercial production began in the early 1980's. While microprocessor-based relays are being used by many utilities, the protection philosophy remains the same. In the present practice, abnormal operating conditions are analyzed a priori and relays are set considering all contingencies. Since it is difficult to identify all operating conditions in advance, and determine a set of relay settings that are optimum for all operating states, compromises are made in determining the settings. This results in the relays having inadequate selectivity, higher operating times and even failure to operate in some conditions. Researchers are now investigating whether the capabilities of microprocessor based relays can be fully utilized and dynamic conditions of power systems can be included in the protection system. This approach, known as adaptive protection, allows the utility engineers to change the settings of relays as the system conditions change. The work reported in this thesis includes the designs of two major software packages developed for adaptive protection of a distribution network. One software package is for performing the relaying tasks and the other software package is for relay settings and checking coordinations. The relaying software was implemented on TMS320C25 DSP microprocessors and relay setting and coordination software was implemented in a personal computer. Also, two communication application softwares were developed; these softwares used two commercial packages for communication between the relays, station controller and a central control computer. A small scale prototype was designed and built in the power system laboratory at the University of Saskatchewan. The thesis also examines the improvement that can be achieved by applying the adaptive protection approach to a distribution network. Results reported in the thesis demonstrate that the use of adaptive protection minimizes relay operating times and improves coordination between relays.