A DIGITAL FREQUENCY-CUM-RATE OF CHANGE OF FREQUENCY RELAY
Date
1978-11
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Degree Level
Masters
Abstract
Under-frequency relays are often used to detect deficiency of generation in a power system and to shed load to restore generation-load balance. These relays operate somewhat after the frequency falls to a prespecified level. The difference between the set frequency and the frequency at which load shedding is initiated depends on the rate at which the frequency continues to change. To eliminate this delay frequency-cum-rate of change of frequency relays have been proposed, developed and used. These relays are designed using analog electronic circuits.
The availability of digital processing devices has considerably increased during the last few years while the cost of these devices has been rapidly decreasing. The use of digital processors in system control and protection is at the verge of becoming economically competitive.
This thesis examines the presently used methods of measuring frequency and rate of change of frequency at a power system bus. A few new and novel approaches are then proposed. Also examined are the relative advantages and suitability of these approaches for use in relays based on digital processors. A relay design using the selected techniques of measuring frequency and rate of change of frequency is then outlined. Implementation of this design and relay tests performed in the laboratory are also described.
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Degree
Master of Science (M.Sc.)
Department
Electrical Engineering