Protective relaying apparatus

• US 4,297,740 A
• Filed: 02/05/1979
• Issued: 10/27/1981
• Est. Priority Date: 02/05/1979
• Status: Expired due to Term

• Current Assignee: ABB Power T&D Limited (ABB Limited)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Hagberg, John E.
• Primary Examiner(s): Salce, Patrick R.
• Application Number:
  US06/009,012
• Time in Patent Office: 995 Days
• Field of Search: 361/67, 361/68, 361/62, 361/64, 361/78, 361/82, 361/84-87, 307/127, 324/86, 324/108
• US Class Current: 361/67
• CPC Class Codes: H02H 3/387 using phase-sequence analysing arrangements

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.

Claims

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.

2. The protective relaying apparatus of claim 1 wherein the ratio ground relays discriminate between an unbalanced load and a high impedance fault by being responsive to the magnitude of the zero sequence current, with a predetermined minimum magnitude being required to initiate delay timing, and with the magnitude required to initiate delay timing being increased by the predetermined phase current related quantity according to a ratio setting of the relay.

3. The protective relaying apparatus of claim 1 wherein the first ratio ground relay includes delay means which requires that the detected fault current persist for a time T1 before tripping the first circuit breaker, and the second ratio ground relay includes delay means which is responsive to the zero sequence directional relay, tripping the second circuit breaker when a fault on the load side persists for a time T2, which is shorter than time T1, and tripping the second circuit breaker when a fault on the source side persists for a time T3, which is longer than time T1.

4. The protective relaying apparatus of claim 1 wherein the predetermined phase current related quantity is the minimum of the phase currents.

5. The protective relaying apparatus of claim 1 wherein the predetermined phase current related quantity is the positive sequence component of the phase currents.

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:

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.

7. The protective relaying apparatus of claim 6 wherein each ratio ground relay compares the zero sequence current with each phase current, providing an output signal when the zero sequence current exceeds the selected minimum magnitude, and a predetermined percentage of the minimum of the phase currents.

8. The protective relaying apparatus of claim 6 wherein each ratio ground relay compares the zero sequence current with the positive sequence component of the phase currents, providing an output signal when the zero sequence current exceeds the selected minimum magnitude, and a predetermined percentage of the positive sequence component of the phase currents.