Fault current can be used as a basis for selectivity only where there is an abrupt difference between its magnitude for a fault within the protected section and a fault outside it, and these magnitudes are almost constant. Where this is so, a current magnitude device can be used, such as a fuse or an instantaneous relay or trip device and selectivity can be obtained by grading current. A typical case where current grading can be used is shown in fig. 4.1, where there is a high impedance unit such as a transformer which makes the fault much less for faults beyond the transformer.
KeywordsFault Current Protective Relay Ground Fault Zero Sequence Directional Unit
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- 17.Sonnemann, W. K. and Glassburn, W. E. ‘Principles of Induction-type Relay Design’, Transactions A.I.E.E., 72, Part III, 1953, pp. 23–27.Google Scholar
- 18.Sonnemann, W. K. ‘A New Inverse Time Overcurrent Relay with Adjustable Characteristics’, Transactions A.I.E.E., 72, Part III, 1953, p. 360.Google Scholar
- 21.Gross, E. T. B. ‘Sensitive Ground Relaying of a.c. Generators’, Transactions A.I.E.E., 71, 1952, paper No. 51–371.Google Scholar
- 32a.McConnell, A. J. ‘A Single Element Polyphase Directional Relay’, Transactions A.I.E.E., 113; No. 8, 1937 pp. 1025–1028.Google Scholar
- 33.Sonneman, W. K. ‘A Study of Directional Element Connections for Phase Relays’, Transactions A.I.E.E., 69, Part II, 1950. Also Disc, ibid., pp. 1450–1451.Google Scholar
- 34.Barnes, H. C. and McConnell, A. J. ‘Some Utility Ground Relay Problems’, Transactions A.I.E.E., June, 1955.Google Scholar
- 35.Wilson, R. M. and Cannon, C. E. ‘Fundamentals of Co-ordinating Fuses and Relays’, Electrical West., 87, July, 1941, pp. 30–31.Google Scholar
- 36.Steeb, G. ‘Relay Inverse Time Characteristic Doubled’, Electrical World, 118, October, 1942, p. 1484.Google Scholar
- 39.Morris, W. C. ‘Dual-polarised Directional Ground Relays’, Distribution, April, 1952, pp. 8–9.Google Scholar
- 40.Pratt, M. G., Audlin, L. J. and McConnell, A. J. ‘New Relay Assures Feeder Resumption After Outage’, Electrical World, Part I, September 10th, 1949, pp. 99–103; Part II, September 24th, 1949, pp. 95–98.Google Scholar
- 49.Ramsaur, O. ‘A New Approach to Cold Load Restoration’, Electrical World, October, 1952, pp. 101–103.Google Scholar
- 71.Salzmann, A. ‘Co-ordination of Phase Fault Protection’, Electrical Energy, December, 1958, pp. 480–487.Google Scholar
- 118.Kreekon, N. and Powchroski, D. W. ‘A New Static Overcurrent Relay’ Allis-Chalmers Review, April, 1960.Google Scholar