OVERCURRENT RELAYS: MODELLING OF CHARACTERISTICS AND FEASIBILITY OF A COMPUTER BASED DESIGN
Date
1978-02
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ORCID
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Degree Level
Masters
Abstract
Overcurrent relays are used to protect sub-transmission and distribution lines from phase to phase and phase to ground faults. The procedures of determining the settings of these relays include the rule of thumb, template and digital computer methods. The relay characteristics are defined by lookup tables or by mathematical equations.
The mathematical equations suggested in the past for representing the relay characteristics are qualitatively examined in this thesis. Most of the equations do not represent the relay characteristics adequately. Seven alternative equations are proposed and their adequacy is investigated by determining the models of CO type overcurrent relays manufactured by the Westinghouse Electric Corporation and by checking the models against the published data. The tests have revealed that five of the seven proposed, equations can adequately represent the relay characteristics at a selected time dial setting. These equations have also been extended to provide composite models which can adequately define the relay characteristics at different time dial settings.
The feasibility of designing a digital overcurrent relay using one of the proposed mathematical models is investigated in this thesis. A sample software for an overcurrent relay was developed and tested and is included in Chapter 6.
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Degree
Master of Science (M.Sc.)
Department
Electrical Engineering