US3585449A

US3585449A - Circuit interrupter with triggered vacuum gap

Info

Publication number: US3585449A
Application number: US884147A
Authority: US
Inventors: Rolf Dethleisen
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1969-12-11
Filing date: 1969-12-11
Publication date: 1971-06-15
Anticipated expiration: 1988-06-15

Abstract

An electrical system in which a current zero occurs comprises a pair of circuit breaker contacts between which an arc is established during contact separation. A triggerable vacuum gap is arranged in parallel with the separable contacts and means responsive to system conditions trigger the gap and cause it to break down while arcing occurs between the contacts but shortly before current zero thereby starving the circuit breaker arc and permitting rapid extinction of the spark gap arc.

Description

United States Patent [72] 2,610,231 9/1952 Wettstein 317/11 N w n. s- 2,789,253 4/1957 Vang 317/11.4 [21] Appl. No. 884,147 3,243,656 3/1966 Baude 317/11 [22] Filed Dec. 11, 1969 3,275,891 9/1966 Swanson.. 317/16 [45] Patented JIIM 15, 1971 3,309,575 31196? Lee 317/50 [73] Assignee Allis-Chalmers Manufacturing Company 3,328,632 6/1967 Robinson 317/62 Milwaukee, Wis. 3,430,016 2/1969 l-lurtle 317/11 3,454,832 7/1969 Hurtle 317/11 541 CIRCUIT INTERRUPTER wm1 TRIGGERED Primary Hammer-Milton Hirshfield VACUUM GAP Assistant Exammer- Ulysses Weldon I 7 Chin 2 Drawing Figs Attorneys--Thomas F. Kirby, Lee H. Kaiser and Robert B.

Benson [52] US. Cl 317/11, 307/136 h 1 Int. An electrical system in a current zero 0e. of Search l, 16, curs com rises a pair of circuit breaker contacts between 1 7L 50; 200/146 which an arc is established during contact separation. A triggerable vacuum gap is arranged in parallel with the separable [56] References cued contacts and means responsive to system conditions trigger UNITED STATES PATENTS the gap and cause it to break down while arcing occurs 3,087,092 4/1963 Lafferty 315/330 between the contacts but shortly before current zero thereby 3,515,940 6/1970 Hobson,.1r. 317/11 starving the circuit breaker arc and permitting rapid extinc- 1,595,768 8/1926 Eschholz 317/1 1 tion of the spark gap arc.

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CIRCUIT INTERRUPTER WITH TRIGGERED VACUUM GAP BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to means for interrupting electric circuits and, particularly, to such means which employ triggered vacuum gaps in conjunction with circuit interrupters.

2. Description of the Prior Art Efforts are continually underway to upgrade the interrupting performance of electric circuit interrupters, particularly those handling high voltage alternating current or DC interrupters with artificially introduced current zeros. For example, U.S. Pat. No. 3,243,656 owned by the same assignee as the present application teaches, among other things, a control for a circuit interrupter whereby the interrupter contacts are opened shortly before a predictable current zero to reduce contact erosion and increase the interrupting capacity of the breaker.

Conventional circuit breakers, such as oil, air and gas blast, air magnetic, and other types, develop a relatively high are voltage ranging from about 100 volts to several kilovolts. These breakers have a relatively long dielectric recovery time after the arc has been extinguished at current zero. The advantage of conventional'br'eakers is that they can handle the very high short circuit currents which are encountered in modern high power electric circuits. Yet, the relativelylong dielectric recovery time makes them susceptible to restrike after current zero. It is known that a vacuum arc is characterized by a low arc voltage and by an extremely short dielectric recovery time..A vacuum spark gap can be fired with high precision in time either by an electric signal or by a laser beam pulse, for example. In accordance with the present invention, the rather high arc voltage developed by conventional breakers allows a transfer of the arc from the conventional breaker to a vacuum spark gap at a certain time interval before current zero.

SUMMARY OF THE INVENTION In accordance with the present invention, there is provided an electrical system or circuit in which a current zero condition exists. The current zero condition may be natural, as in the case of alternating current, or it may be artificially introduced into a direct current system for interruption purposes. The system comprises a pair of circuit breaker contacts between which an arc is established upon contact separation. A triggerable vacuum gap is arranged in parallel with the separable contacts and means responsive to system conditions trigger the gap and cause it to break down while arcing occurs between the contacts but shortly before current zero, thereby starving the circuit breaker arc and permitting rapid extinction of the vacuum-gap arc.

In accordance with the present invention, the characteristics of conventional breakers and of vacuum spark gaps are combined in order to utilize their individual strengths while overcoming their individual weaknesses and providing new, improved and unobvious results. Conventional breakers are well developed for handling high short circuit currents. Their weakness is a relatively long dielectric recovery time. They develop a relative high are voltage. This allowsthe transfer of the arc to a vacuum spark gap within a short time interval before current zero. This time interval is chosen so that the transferred arc current is on the order of some desired value of kiloamperes. The extremely short dielectric recovery time of the vacuum gap may thus be utilized withoutsu bjecting the vacuum arc to the full magnitude of current to be switched.

2 OBJECTS OF'THE INVENTION It is an object of the present invention to provide improved means to upgrade the arc interrupting ability of electric circuit breakers, to reduce contact erosion therein, and to increase breaker ratings.

Another object is to provide improved means of the aforesaid character which are adaptable for use with many types of circuit breakers, including oil breakers, air or gas blast breakers, and air magnetic breakers.

Another object is to provide improved means of the aforesaid character which employ components which have already been developed and are commercially available.

Another object is to .provide means of the aforesaid character which are relatively inexpensive, reliable in use and have a long working life.

Other objects and advantages of the invention will hereinafter appear. 1

DESCRIPTION OF THE DRAWING The accompanying drawing illustrates a preferred embodiment of the invention but it is to be understood that the embodiment illustrated is susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 shows a schematic diagram of an electric circuit embodying the present invention; and

FIG. 2 is a graph of current conditions in the circuit during interruption.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 of the drawing, there is shown a circuit wherein the numeral 10 designates a source of high voltage current from which a load 12 is energizable through a powerline 14.

In accordance with the invention, the electrical system or circuit is one in which a current zero condition exists. For example, the current zero condition may be natural, as in the caseof alternating current from source 10, or it may be artificially introduced into a direct current supply from source 10 for interruption purposes by well-known means.

Connection and disconnection of load 12 to and from source 10 is controlled by circuit interrupting means such as a circuit breaker 16 which comprises a pair of separable relatively movable contacts 16a and 16b which are connected in line 14. Contact 16b (shown in open condition) for example, is movable to contact closed and contact open positions by contact operating means, such as a contact operating mechanism 18. It is to be understood, for example, that operating mechanism 18 effects opening of the contacts 16a and 16b in response to operation of a condition responsive means 20 which senses faults and other conditions, such asexcessive current flow, in line 14 when the systemis in operation. When contacts 16a and 16b of circuit breaker 16 are separated by operating mechanism 18 in response to a fault condition in line 14 sensed by condition responsive means 20, an arc is established between the contacts which must be extinguished as rapidly as possible.

In accordance with the present invention, a trig'gerable spark gap device 22, having a lower arc voltage characteristic than main breaker l6 and fast dielectric recovery, preferably of the vacuum type, is connected in parallel circuit with circuit breaker l6. Spark gap device 22 comprises a pair of spacedapart electrodes 22a and 22b which are disposed in a housing 22d in which a vacuum is maintained. Spark gap device 22 further comprises triggering means 220 to effect breakdown of the gap between the electrodes 22a and 22b. US. Pat. No. 3,303,376 teaches a triggered vacuum gap device of a type suitable for use in the present invention but other triggerable vacuum gap devices could be used. Spark gap device 22 is connected in parallel with.circuit breaker 16. More specifically, electrodes 22a and 22b of device 22 are electrically connected to contact 16a and 16b, respectively, of circuit breaker 16. The triggering means 220 of spark gap 22 is connected to a condition responsive means 24 which is adapted to sense conditions, such as current flow conditions, in line 14 and effect firing or breakdown of spark gap device 22 slightly before zero current while arcing exists between

contacts

160 and 16b of circuit breaker 16. US. Pat. No. 3,243,656 teaches a control for sensing line conditions and for providing a control signal at a predetermined point in the current or voltage waveform, such as at current zero or other desirable point, which control is adaptable to fire or trigger a device such as device 22. Condition responsive means 24 effects breakdown of trigger device 22 at some point in the interval of one-quarter of a cycle (4.1 milliseconds) before current zero, but preferably shortly before current zero when the current magnitude does not exceed the value of some predetermined value of KA,

such as IOKA, for example, as shown in the graph FIG. 2.

A system in accordance with the invention operates as follows. Assume that contacts 16a and 16b of circuit breaker 16 are closed and that load 12 is being energized from source 10. Further assume that a fault condition occurs in line 14 and that condition responsive means 20 senses the fault and thereby causes operating mechanism 18 to effect opening of

contacts

160 and 16b of circuit breaker 16. As the contacts 16a and 16b separate, a high current arc accompanied by high are voltage is established therebetween. Further assume that condition responsive means 24 also senses the fault condition and produces an output signal which effects breakdown of the gap between the electrodes 22a and 22b of spark gap device 22 sometime within one-quarter of a cycle before the first current zero and preferably at the point shown in the graph in FIG. 2. When this occurs, the arc voltage in device 22 is much lower than that in circuit breaker l6 and, thus, the are between contacts 16a and 16b of the circuit breaker is completely starved and extinguished and, in effect, transferred to device 22. However, because the vacuum gap device 22 has excellent dielectric recovery characteristics, the arc therein is readily extinguished when the current zero condition is reached in device 22. After the arcs in circuit breaker l6 and device 22 have been extinguished, the contacts 16a and 16b of the circuit breaker are ready to be reclosed by operating mechanism 18 in readiness for subsequent circuit interrupting operations.

In the embodiment shown, condition responsive means 20 and 24 are shown as separate elements. However, it is to be understood that at least some portions of these elements perform similar functions and could be combined, such a means common to both for sensing current flow conditions in line 14, for example. 1

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

lclaim: 1. In combination, an electrical circuit in which a current zero condition occurs, at least a pair of separable contacts in said circuit, triggerable spark gap means shunting said pair of contacts and having a lower arc voltage characteristic and shorter dielectric recovery time than said pair of separable contacts, first means to effect separation of said pair of contacts whereupon arcing occurs between said pair of contacts, and second means for sensing and responding to conditions in said alternating current circuit to effect triggering of said spark gap means to effect full transfer thereto of arcing which occurs between said pair of contacts at a point in time less than one-quarter cycle prior to occurrence of a current zero in the are. 2. A combination according to claim 1 wherein said triggerable spark gap means comprises spaced-apart electrodes which are disposed in a vacuum.

. A combination according to claim 2 wherein said first means is responsive to conditions in the electrical circuit and effects contact separation of said pair of contacts in response to a fault condition.

4. A combination according to claim 3 wherein said first means and second means have common means for sensing conditions in said circuit.

5. A combination according to claim 3 wherein said circuit comprises a source of current, a line and a load, wherein said pair of separable contacts are comprised in a circuit interrupting device and are disposed in said line between said source and said load, wherein each one of said spark gap electrodes is electrically connected directly to one of said contacts, and wherein said spark gap means comprises a trigger electrode responsive to an output signal from said second means.

6. A combination according to claim 5 wherein said second means is adapted to provide an output signal to said trigger electrode at a selectable predetermined time within onequarter cycle prior to the occurrence of the first current zero.

7. A combination according to claim 1 wherein triggering of said spark gap and transfer of the arc thereto from said pair of contacts occurs at a time within said one-quarter cycle when current magnitude does not exceed IOKA.

Claims

1. In combination, an electrical circuit in which a current zero condition occurs, at least a pair of sepaRable contacts in said circuit, triggerable spark gap means shunting said pair of contacts and having a lower arc voltage characteristic and shorter dielectric recovery time than said pair of separable contacts, first means to effect separation of said pair of contacts whereupon arcing occurs between said pair of contacts, and second means for sensing and responding to conditions in said alternating current circuit to effect triggering of said spark gap means to effect full transfer thereto of arcing which occurs between said pair of contacts at a point in time less than one-quarter cycle prior to occurrence of a current zero in the arc.

2. A combination according to claim 1 wherein said triggerable spark gap means comprises spaced-apart electrodes which are disposed in a vacuum.

3. A combination according to claim 2 wherein said first means is responsive to conditions in the electrical circuit and effects contact separation of said pair of contacts in response to a fault condition.

6. A combination according to claim 5 wherein said second means is adapted to provide an output signal to said trigger electrode at a selectable predetermined time within one-quarter cycle prior to the occurrence of the first current zero.

7. A combination according to claim 1 wherein triggering of said spark gap and transfer of the arc thereto from said pair of contacts occurs at a time within said one-quarter cycle when current magnitude does not exceed 10KA.