Time-domain modeling of distribution and transmission line protection
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Power system protective relay and fuse models have been used to evaluate performance of new and existing designs and schemes, and to assist in designing new relays. Normally, to evaluate relay performance, relay manufacturers and utility distribution and transmission industry users perform expensive and time consuming tests. The testing of electromechanical and microprocessor based relays requires costly equipment to inject analog current and voltage waveforms into the relay. As an alternative, a model of the protective device can be tested in a timedomain power system model to predict relay behavior. Time-domain modeling is ideal for this task since it is capable of modeling transient events. Data from the power system model provides input signals for the relay model, removing the need for expensive equipment. In this thesis, new time-domain models have been developed to predict behavior of distribution protection such as fuses, reclosers, and sectionalizers. Existing dynamic testing of distribution protection models from literature are based on steady-state phasor solutions and ignore any transient effects. Simple relay components already exist in time-domain simulation software. These can be used to create a basic distance relay model. However, the existing components are insufficient for modeling distance protection accurately as their performance suffers under real world conditions such as the presence of fault resistance and load current. In this thesis, a more realistic model that closely emulates the physical operation of a distance relay is developed than is currently documented in the literature. The model described in this thesis significantly reduces the amount of underreach when fault impedance is present by incorporating the polarizing voltage used in real-world electromechanical and microprocessor based distance protection. Testing of the new relay model under a variety of fault and load conditions showed improved reach accuracy. Other benefits of time-domain protection models include the ability to extensively test a variety of scenarios and generate waveform data for power system studies.