PROTECTIVE EQUIPMENT FOR AN ALTERNATING CURRENT POWER DISTRIBUTION SYSTEM

• US 3,660,721 A
• Filed: 02/01/1971
• Issued: 05/02/1972
• Est. Priority Date: 02/01/1971
• Status: Expired due to Term

• Current Assignee: Leslie L. Baird
• Original Assignee: Leslie L. Baird
• Inventors: Baird, Leslie L.
• Primary Examiner(s): Trammell, James D.
• Application Number:
  US05/111,236
• Time in Patent Office: 456 Days
• Field of Search: 317/26,11R,16,36TD,46,51
• US Class Current: 361/55
• CPC Class Codes: H01H 33/66 Vacuum switches
• CPC Class Codes: H01H 71/1081 Modifications for selective or back-up protection; Correlation between feeder and branch circuit breaker circuits H02H3/06, H02H7/26
• CPC Class Codes: H01H 79/00 Protective switches in which excess current causes the closing of contacts, e.g. for short-circuiting the apparatus to be protected H01H39/004 takes precedence
• CPC Class Codes: H02H 3/021 concerning the disconnection itself, e.g. at a particular instant, particularly at zero value of current, disconnection in a predetermined order disconnection at zero value in general H03K17/18
• CPC Class Codes: H02H 3/023 by short-circuiting
• CPC Class Codes: H02H 7/22 for distribution gear, e.g. bus-bar systems; for switching devices detecting mechanical or electrical defects in gas-insulated switchgears H02B13/065

Abstract

Protective equipment for an electric power distribution system comprising a bus, a supply circuit connected to the bus through a main circuit breaker, and feeder circuits connected to the bus through feeder circuit breakers. Should a high current fault occur on a feeder circuit, a short circuit is quickly established on the supply circuit on the bus side of the main breaker by means of a triggered vacuum gap device, which is triggered into conduction in response to the fault. This short circuit diverts current from the fault, thereby reducing the interrupting duty on the feeder breaker and enabling it to open on feeder faults producing fault current exceeding its interrupting capacity. After the feeder breaker has opened and before the main breaker can open, the triggered vacuum gap is returned to its normally non-conducting state, thus allowing power from the supply circuit to be restored to the bus.

Claims

1. In an electric power distribution system comprising a bus, a supply circuit for supplying power to said bus, and a plurality of feeder circuits for feeding power from said bus to loads, protective equipment comprising:

a. feeder circuit breakers adapted when closed to respectively connect said feeder circuits to said bus, b. a main circuit breaker adapted when closed to connect said supply circuit to said bus, c. means comprising a triggered vacuum gap device for establishing a short circuit on said supply circuit on the bus side of said main circuit breaker when said triggered vacuum gap device is triggered into conduction, d. means responsive to a fault on any one of said feeder circuits producing current through the associated feeder circuit breaker above the current-interrupting rating of said feeder circuit breaker for triggering said gap device into conduction, thereby diverting current from said fault, e. means responsive to said feeder circuit fault for tripping open said feeder circuit breaker and for causing opening to be completed while said gap device is conducting, thus completing opening of said feeder circuit breaker at a time when the current therethrough is limited by conduction through said gap device, f. means for terminating said conduction through said gap device after said feeder circuit breaker has completed opening, thus allowing power from said supply circuit to be restored to said bus, g. and means for maintaining said main circuit breaker closed during said conduction through said gap device and for at least a short period following termination of said conduction through said gap device, whereby power from said supply circuit can be immediately supplied through said main circuit breaker to said bus upon the termination of said conduction through said gap device.

2. The apparatus of claim 1 in which:

a. said bus and said supply circuit are polyphase circuits, b. said triggered vacuum gap device is connected across one pair of phases of said supply circuit and additional triggered vacuum gap devices are respectively connected across the remaining pairs of phases of said supply circuit, and c. said means responsive to a fault on any one of said feeder circuits effects triggering of all of said triggered vacuum gap devices.

3. The apparatus of claim 1 in which:

a. said main circuit breaker includes overcurrent-responsive means for opening the main circuit breaker after a predetermined time in response to fault current therethrough produced by a feeder fault, b. and said triggered vacuum gap is normally restored to its normally non-conducting state following inception of said feeder fault before said overcurrent-responsive means has had sufficient time to open said main circuit breaker.

4. The apparatus of claim 1 in which:

a. said main circuit breaker and said fEeder circuit breakers each include overcurrent-responsive means for opening the associated circuit breaker with a time delay varying in duration inversely with respect to current magnitude, b. for a given fault current, the time delay for opening of said main circuit breaker is greater than that for said feeder circuit breakers, and c. said triggered vacuum gap device is normally restored to its normally non-conducting state following inception of said feeder circuit fault before said main circuit breaker has had sufficient time to open.

5. The apparatus of claim 1 in which the means for triggering said gap device into conduction is also responsive to faults on said bus and is operable in response to said bus faults for triggering said gap device into conduction before said main circuit breaker can open, thereby reducing the damage from arcing at the point of said bus fault.

6. The apparatus of claim 1 in which:

a. said triggered vacuum gap device includes electrodes which are relatively movable into and out of engagement with each other, b. means is provided for producing engagement of said electrodes immediately following the triggering into conduction of said gap device, and c. the means for terminating conduction through said gap device comprises means for separating said electrodes.

7. The apparatus of claim 2 in which:

a. each of said triggered vacuum gap devices includes electrodes which are relatively movable into and out of engagement with each other, b. means is provided for producing engagement of the electrodes of all of said gap devices immediately following the triggering into conduction of said gap devices, and c. means is provided for terminating conduction through all of said gap devices after said feeder circuit breaker has opened, said last-mentioned means comprising means for separating the electrodes of all of said gap devices.

8. The apparatus of claim 1 in which said means for terminating conduction through said gap device comprises means for discontinuing triggering of said gap device.