Protective relaying apparatus
First Claim
1. Protective relaying apparatus for detecting and clearing high impedance faults on a polyphase electrical distribution circuit, comprising:
- a polyphase source of alternating potential,a polyphase distribution circuit,a load circuit,a first circuit breaker for controlling the connection of the distribution circuit to the source,a second circuit breaker for controlling the connection of the distribution circuit to the load circuit,first and second ratio ground relays at the first and second circuit breakers, respectively, for tripping the associated circuit breaker after a predetermined delay time when the ratio of zero sequence current to a predetermined phase current related quantity indicates a fault condition,an a zero sequence directional relay at the second circuit breaker for coordinating the first and second ratio ground relays by adjusting the trip delay time of the second circuit breaker relative to the trip delay time of the first circuit breaker, in response to the flow direction of a zero sequence quantity at the second circuit breaker.
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Accused Products
Abstract
A protective relaying system for detecting and clearing high impedance faults on a polyphase electrical distribution circuit. First and second ratio ground relays are located at first and second circuit breakers, respectively. The first circuit breaker is located at the substation, and the second circuit breaker is remote from the substation, usually operating with a reclosing relay. A zero sequence directional relay, located at the second circuit breaker, coordinates the ratio ground relays by adjusting the trip delay time of the second circuit breaker according to the flow direction of a zero sequence quantity at the second circuit breaker.
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Citations
8 Claims
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1. Protective relaying apparatus for detecting and clearing high impedance faults on a polyphase electrical distribution circuit, comprising:
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a polyphase source of alternating potential, a polyphase distribution circuit, a load circuit, a first circuit breaker for controlling the connection of the distribution circuit to the source, a second circuit breaker for controlling the connection of the distribution circuit to the load circuit, first and second ratio ground relays at the first and second circuit breakers, respectively, for tripping the associated circuit breaker after a predetermined delay time when the ratio of zero sequence current to a predetermined phase current related quantity indicates a fault condition, an a zero sequence directional relay at the second circuit breaker for coordinating the first and second ratio ground relays by adjusting the trip delay time of the second circuit breaker relative to the trip delay time of the first circuit breaker, in response to the flow direction of a zero sequence quantity at the second circuit breaker. - View Dependent Claims (2, 3, 4, 5)
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6. Protective relaying apparatus for protecting line sections of a polyphase electrical distribution circuit against high impedance ground faults, and broken conductors which do not result in ground fault conditions, comprising:
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a source of alternating potential, first and second line sections, first and second circuit breakers for controlling the connection of the first line section to the source, and the second line section to the first, respectively, first and second ratio ground relays responsive to the magnitudes of the phase currents and the zero sequence currents at the first and second circuit breakers, respectively, providing first and second output signals, respectively, when the zero sequence current exceeds a magnitude determined by a selected minimum magnitude, a selected ratio setting of the relay, and the magnitude of a phase current related quantity. first time delay means responsive to the first output signal, providing a trip signal for said first circuit breaker when the first signal persists for a time T1, second and third time delay means responsive to the second output signal, said second and third time delay means providing trip signals for the second circuit breaker when the second output signal persists for times T2 and T3, respectively, with times T1, T2 and T3 being selected to have the relationship T3>
T1>
T2,and a directional relay responsive to the flow direction of a zero sequence quantity at the second circuit breaker, said directional relay selecting the delay time T2 or T3 according to the flow direction of said zero sequence component, with the delay time T2 being selected when the flow direction indicates a fault in the second line section, and with delay time T3 being selected when the flow direction indicates a fault in the first line section. - View Dependent Claims (7, 8)
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Specification