US3708638A

US3708638A - Vacuum type electric circuit breaker

Info

Publication number: US3708638A
Application number: US00097835A
Authority: US
Inventors: G Mitchell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1970-12-14
Filing date: 1970-12-14
Publication date: 1973-01-02
Anticipated expiration: 1990-01-02
Also published as: CA936612A

Abstract

Discloses a high voltage circuit breaker that comprises a main circuit interrupter of the vacuum-type, a voltage-controlling resistor shunting the main interrupter, and an auxiliary interrupter connected in series with parallel combination of the main interrupter and the resistor. During fault-current interruptions the main interrupter is opened first and the auxiliary interrupter thereafter. During capacitance-current interruptions the auxiliary interrupter is opened first and the main interrupter thereafter. The latter sequence enables the auxiliary interrupter to assume the capacitance-current interrupting duty and to relieve the main vacuum-type interrupter therefrom.

Description

Jan. 2, 1973 United States Patent [19] Mitchell Primary Examiner-Robert S. Macon [54] VACUUM TYPE ELECTRIC CIRCUIT BREAKER [75] Inventor:

Graham R. Mitchell, Willingboro, N.J.

[73] Assignee: General Electric Company [22] Filed:

ABSTRACT Discloses a high voltage circuit breaker that comprises Dec. 14, 1970 a main circuit interrupter of the vacuum-type, a voltage-controlling resistor shunting the main interrupter,

[2]] Appl. No.: 97,835

and an auxiliary interrupter connected in series with [52] US. Cl. B parallel combination of the main interrupter and the- Illt. 33/66 .200/144 A, 146 A, 146

resistor. During fault-current interruptions the main [58] Field of Search..............

interrupter is opened first and the auxiliary interrupter thereafter. During capacitance-current interruptions [56] References Cited UNITED STATES PATENTS the auxiliary interrupter is opened first and the main. interrupter thereafter. The latter sequence enables the auxiliary interrupter to assume the capacitance-cur- 2,032,l49 2/1936 Rawlins ............................200/146 A rent interrupting duty and to relieve the main vacuum- 3,287,531 100/144 AP type interrupter therefrom. 3,560,682

ll/l966 Yonezawa et al. 2/1971 Kohler..............................200/l46 R 6 Claims, 4 Drawing Figures OPERA T0)? CLOS/NG CONTROL l l TIME DELAY UN/T us I VACUUM TYPE ELECTRIC CIRCUIT BREAKER This invention relates to a high voltage electric circuit breaker which is rated to interrupt fault currents of tens of thousands of amperes and capacitance currents of hundreds of amperes. The invention is particularly concerned with a circuit breaker of this type that comprises one or more vacuum interrupters that are relied upon for interrupting fault currents.

Vacuum interrupters are typically rated to interrupt fault currents and capacitance currents at a predetermined voltage. If the vacuum interrupter could be employed for fault current interruptions only, its voltage rate could be very substantially increased. For example, tests have shown that for fault current interruptions alone, many high-current vacuum interrupters are capable of interrupting at twice their rated voltage. But such vacuum interrupters typically cannot interrupt capacitance currents at this higher voltage and would produce objectionable restrikes if used for this purpose at this higher voltage. This inability of such vacuum interrupters to interrupt capacitance currents at the higher voltage level necessitates a reduction in voltage rating of the interrupter down to the maximum voltage at which the interrupter can consistently interrupt rated capacitance currents without objectionable restrikes.

An object of the present invention is to provide a circuit breaker that is'able to rely upon a high-current vacuum interrupter to interrupt fault currents at a voltage appreciably above the maximum value at which it can consistently interrupt capacitance currents without requiring the vacuum interrupter to capacitance currents at this higher voltage.

Another object is to relieve the high-current vacuum interrupter from capacitance-current interrupting duty and yet to make it available for fault-current interrupting duty.

Another object is to provide a circuit breaker capable of performing as in the preceding two objects and also capable of preinserting a resistor during a closing operation to reduce the magnitude of the surge voltages produced by a circuit-breaker closing operation.

In carrying out the invention in one form I provide a main circuit interrupter of the vacuum type that comprises a pair of separable contacts and a highly evacuated insulating housing enclosing said contacts. Main operating means is provided for separating said contacts during a fault-current interrupting operation. A resistor is connected in parallel with said contacts for reducing the severity of the recovery voltage transient developed across said contacts when they are separated during a fault current interrupting operation. Auxiliary interrupting means is connected in series with the parallel combination of the vacuum interrupter contacts and the resistor. Auxiliary operating means is provided for operatingthe auxiliary interrupting means and is operable in response to initiation of the operation of said main operating means for opening the auxiliary interrupting means a few half-cycles after the main contacts are separated during a fault current interruption. The auxiliary interrupting means has sufficient capacitance-current interrupting ability to interrupt without assistance from the vacuum-type circuit interrupter the most severe capacitance currents for which the circuit breaker is rated. Capacitance-current interrupt interrupting operations are effected by causing said auxiliary operating means to open said auxiliary interrupting means while said vacuum interrupter contacts are still closed, whereby said auxiliary interrupting means assumes the capacitance-current interrupting duty and relieves said vacuum interrupter therefrom.

For a better understanding of the invention, reference may be had to the following description taken-in conjunction with the accompanying drawing, wherein:

FIG. 1 is a diagrammatic representation of a circuit breaker embodying one form of the invention.

FIG. 2 is a view of a portion of one of the interrupters contained in the circuit breaker of FIG. 1 shown in its open position.

FIG. 3 is a side elevational view in simplified form of a circuit breaker embodying the components of FIG. 1.

FIG. 4 is a schematic side elevational view, partly in section, of a modified embodiment of the invention.

Referring now to FIG. 1, there is shown a high voltage electric breaker 10 that is connected in a high voltage power circuit 12. This circuit breaker comprises two circuit-

interrupting devices

14 and 16 that are electrically connected in the power circuit 12 by means of a conductor 18 extending between them. The interrupting device 14 is a vacuum-type circuit interrupter that is capable of interrupting tens of thousands of amperes of fault current at the rated voltage of the circuit 12. The interrupting device 16, which is also shown as a vacuum-type circuit interrupter, has a much lower current-interrupting capacity, but still high enough to interrupt normal load currents and capacitance currents. Capacitance currents are typically no higher than several hundred amperes, and the interrupter 16 is designed to interrupt such currents at the rated voltage of the power circuit 12 without objectionable restrikes. More will be explained hereinafter about the interruption of capacitance currents.

The vacuum-type interrupter 14, which is referred to hereinafter as the main interrupter, is of a conventional design, such as shown, for example, in US. Pat. Nos. 3,462,572-S0fianek and 3,497,652-Horn et al., both assigned to the assignee of the present invention. The illustrated interrupter 14 includes a highly evacuated housing 19 which comprises a tubular casing 20 of insulating material and a pair of

end caps

22 and 24 sealed to the opposite ends of the casing. Within the highly evacuated housing 19 is a pair of

separable contacts

26 and 28. Contact 26 is a stationary contact joined to the lower end of a conductive contact rod 29 projecting through the top end cap 22 in sealed relationship. Contact 28 is a movable contact joined to the upper end of a movable conductive contact rod 30 projecting freely through the lower end cap 22. A flexible metal bellows 32 provides a seal about the contact rod 30 and permits longitudinal movement of the rod without impairing the vacuum inside housing 19.

Opening of the interrupter 14 is effected by driving the rod 30 downwardly to separate movable contact 28 from stationary contact 26. This develops an arc between the contacts which persists until the next natural current zero, after which it is prevented from reigniting by the high dielectric strength of the vacuum. A tubular shield 34 surrounds the contacts in spaced relationship thereto to condense the metal vapors generated by the arc. Shield 34 is suitably supported on casing to electrically isolate it from both contacts and is preferably at mid-potential with respect to the contacts when the interrupter is open. Additional shielding (not shown in the drawing but preferably of the form disclosed in the aforesaid Sofianek patent) is also provided within the interrupter housing to help in condensing the arc-generated metal vapors.

The other interrupting device 16 is illustrated as a vacuum-type interrupter; but it could, if desired, be of some other type which has good capacitance current interrupting ability. For example, an interrupter filled with an electronegative gas, such as sulphurhexafluoride. The illustrated interrupter 16 comprises a highly evacuated housing 39 comprising an insulating casing 40 and

end caps

42 and 44 sealed to its opposite ends. Within the housing 19 is a pair of

separable contacts

46 and 48. Contact 48 is a stationary contact joined to the lower end of a contact rod 49; and the other contact 28 is a movable contact joined to the upper end of a movable contact rod 50 projecting freely through the lower end cap and sealed thereto by a flexible bellows 62. A suitable tubular shield 64 surrounds the contacts to condense metal vapors generated by arcing between the contacts during an opening operation.

Auxiliary interrupter 16 has only a very limited amount of current interrupting ability compared to the main interrupter 14, but it is designed to have much superior voltage handling capabilities. More specifically, auxiliary interrupter 16 has a much longer stroke than main interrupter 14 and has a contact shield 65 behind which the movable contact 48 is withdrawn at the end of an opening operation (as shown in FIG. 2) to'locate it in a region of low dielectric stress. Shield 65 is a tubular member of cup form having an opening in its upper end through which a movable contact 48 is movable between its position of FIG. 1 and its position of PK]. 2. The main interrupter 14 cannot have such a long stroke since it will detract from its current-interrupting capacity. Another feature contributing to the superior voltage handling capability of interrupter 16 is its relatively small contacts as' compared to those of interrupter l4. lnterrupter 14 requires large contacts to enable it to interrupt high currents.

The movable contact rod 30 of interrupter 14 is connected to the conductor 18 by means of flexible conductive braid 70, and movable contact rod 50 of the other interrupter 16 is connected to conductor l8-by flexible conductive braid 71, thus connecting the two interrupters in series with each other by means of

conductive parts

70, 18, 71.

The

interrupters

14 and 16 are respectively provided with suitable

high speed operators

75 and 90 connected to their associated interrupters by operating rods schematically indicated at 76 and 91. Since these operators can be of any suitable conventional form, they are shown in block form for simplification purposes. Main operator 75 has two

input channels

77 and 78, either of which can be used for initiating an opening operation of the operator. An input signal delivered to the operator 75 through either of these

channels

77 or 78 causes operator 75 to immediately open interrupter 14. Channel 77 is normally deenergized by a set of normally open contacts'80, but closing of the contacts 80 causes an input signal to be supplied via channel 77 to the operator 75.

Auxiliary operator 90 has two

input channels

92 and 94 either of which can be utilized for initiating its opening operation. When an input signal is applied to either of these channels, operator 90 responds by immediately opening interrupter 19. Channel 92 is normally deenergized by a normally open switch 93, which is manually operable. When switch 93 is closed, an input signal is immediately delivered via channel 92 to the operator 90, thereby causing operator 90 immediately to open the interrupter 16.

The closing of switch 93 also causes channel 78 to deliver an input signal to the main operator 75, but this signal is delayed in reaching main operator by a suitable time delay unit 95. After a preset short interval determined by delay unit 95, the input signal reaches operator 75, causing it to immediately effect opening of interrupter 14.

Closing of the input channel 77 to main operator 75 causes channel 94 to deliver an input signal to auxiliary operator 90, but this signal is delayed in reaching operator by a suitable time delay unit 96. After a preset short interval determined by time delay unit 96, the input signal reaches operator 90, causing it to immediately effect opening of interrupter 16.

In the event of a short circuit or fault on the power circuit 12, it is desired to immediately open the main interrupter l4 and to operate the auxiliary interrupter 16a few half cycles thereafter. Such circuit-breaker opening is initiated by an overcurrent relay that is connected across the secondary winding 102 is inductively coupled to primary conductor 18, and in the event of an overcurrent, sufficient current is induced in the secondary winding to cause relay 100 to pick up and close its contacts 80. Thus, fault current through primary conductor 18 causes over-current relay 100 to immediately pick up and closes contacts 80. This causes an input signal to be immediately applied to main operator 75 through channel 77 and an input signal to be applied to the auxiliary operator 90 through channel 94 after a time delay. This results in main operator 75 immediately opening main interrupter 14 and auxiliary operator 90 opening auxiliary interrupter 16 after a time delay of a few half cycles.

For limiting the magnitude of the voltage surge appearing across the main interrupter during the interruption of fault current (and for other reasons soon .to be explained), a suitable resistor 104 is connected in parallel with the

contacts

26 and 28 of the main interrupter and in series with the auxiliary interrupter 16. This resistor is shorted out by the

contacts

26 and 28 when the interrupter 14 is closed (as shown-in FIG. 1), but when the

contacts

26, 28 are separated, the resistor is connected in parallel with them and serves in a known manner to limit the rate of rise and magnitude of the voltage transient appearing thereacross at any current zero following arcing in the main interrupter. A few half cycles after the

main contacts

26 and 28 have parted, when interruption at the main interrupter has been assured, the auxiliary interrupter 16 opens, as was described above, thereby interrupting the current then flowing through the resistor.

The usual high current vacuum interrupter (such as 14) can recover its dielectric strength extremely rapidly following high current arcing and, if used only for fault current interruptions, could be rated for much higher voltages than it is typically rated. This is true even where no shunting resistor such as 104 is present to limit the magnitude of the recovery voltage transient. The presence of resistor 104, with its ability to reduce the peak value of the recovery voltage transient, permits this voltage rating to be increased even further, assuming that the interrupter is to be used only for short-circuit current interruptions. But most high-voltage power circuit breakers must have, in addition to short-circuit current interrupting capability, the capability of interrupting several hundred amperes of capacitance current, such as encountered, for example, in switching an unloaded transmission line or some other predominantly capacitive load. As explained in US. Pat. No. 2,391,672-Boehne et al., the interruption of capacitance currents is a difficult type of duty because during the one-half cycle immediately following clearance at current zero, the voltage appearing across the contacts builds up to twice normal peak volt age; and if such voltage breaks down the gap between the contacts (i.e., causes a restrike), much higher voltages can be developed. The requirement that the breaker be capable of interrupting such capacitance currents without objectionable restrikes necessitates'a substantial reduction in the voltage rating of the con- .ventional high current vacuum circuit breaker as compared to the voltage rating possible if only fault currents are to be interrupted.

In accordance with the present invention, I relieve the main vacuum interrupter 14 from capacitance-current interrupting duty by relying upon the auxiliary interrupter 16 for such duty. This I accomplish, in a preferred form of my invention, by opening the auxiliary interrupter 16 prior to opening of the main interrupter 14 on all those opening operations that involve capacitance current interruption. Such opening operations are usually initiated at the will of the operator, as by closing the manually operable switch 93. Closing of switch 93 causes auxiliary operator 90 to immediately open the auxiliary interrupter 16, and then after a time delay determined by delay unit 95 causes main operator 75 to open the main interrupter 14. By preventing the main interrupter 14 from separating its contacts (26, 28) before the auxiliary interrupter 16 has opened during a capacitance-current interrupting operation, I can assure that no restrikes will occur across the contacts of the main interrupter during such a capacitance current interrupting operation. The recovery voltage is applied entirely to the auxiliary interrupter, and because of its special design, as described hereinabove, it can withstand this voltage with no objectionable restrikes.

l deliberately prevent separation .of the main contacts before the auxiliary contacts separate during the capacitance current interrupting operation. Preferably, as described hereinabove, l delay separation of the main contacts until after the auxiliary contacts have parted. But my invention, in its broader aspects, contemplates a circuit breaker which during capacitancecurrent interrupting operations separates the contacts of the main interrupter simultaneously with separation of the auxiliary contacts. Simultaneous separation of the contacts is satisfactory because the auxiliary interrupter is at least partially open when the recovery voltage builds up across the circuit breaker and the gap between its contacts is therefore available to bear this voltage and to prevent a restrike across the main interrupter. In the remote event that a restrike across the auxiliary interrupter should occur in this situation, the resistor 104 would be available to limit the follow current flowing immediately subsequent to the restrike.

Irrespective of the sequence of opening operations of the two

interrupters

14 and 16, when the circuit breaker is fully open, both interrupters are in their fully open position. Closing of the circuit breaker is effected by closing a switch 110 to supply an input signal through channel 112 to a closing control 114. Closing control 114 responds by supplying a closing signal through a channel 116 to the auxiliary operator 90 and through a time delay channel 118 to main operator 75. This causes auxiliary operator 90 to immediately produce closing of the auxiliary interrupter 16 and causes main operator after a short time delay determined by time delay unit 120 to produce closing of main interrupter 14. Closing of the auxiliary interrupter inserts the resistor 104 in series with the power circuit l2, and subsequent closing of main interrupter l4 establishes a short circuit around the resistor through the

contacts

26, 28 of interrupter 14. The abovedescribed preinsertion of the resistor 104 into the power circuit 12 prior to closing of the main interrupter acts in a known manner to reduce the magnitude of the voltage surges produced by circuit-breaker closing.

In addition to imparting capacitance-current interrupting ability, the auxiliary interrupter 16 serves, when the circuit breaker is open, to provide between its separated contacts 46 and 48 a long isolating gap of high dielectric strength in series with line 12. This gap can successfully withstand impulse and continuous voltages much higher than those that the main interrupter alone could withstand. This, of course, enables the illustrated circuit breaker to be rated for higher impulse and continuous withstand voltages than would be the case with only the main interrupter 14 present.

While I have shown the main interrupting means 14 as consisting of only a single interrupter, it is to be understood that for higher voltage circuit breakers, a plurality of such interrupters electrically connected in series and operable simultaneously with each other could instead be used. Similarly, for higher voltage applications, a plurality of auxiliary interrupters 16 electrically connected in series and operable simultaneously with each other could be used for the capacitance-current interrupting means instead of the single interrupter shown. In such a high voltage arrangement, the sequence of operations of the main interrupting means and the auxiliary interrupting means is the same as with the illustrated circuit breaker.

The actual circuit breaker in which the equipment diagrammatically shown in FIG. 1 is embodied can take various forms. One suitable form is shown in FIG. 3, where the two

interrupters

14 and 16 are shown mounted on a frame at a high voltage with respect to ground. A pair of spaced-apart tubular insulating

columns

121 and 122 support the frame 120. The operating

rods

76 and 91 for the two interrupters extend to ground through the supporting insulators, and the operating mechanisms are located at ground potential in

housings

125 and 126. A base 127 at ground potential supports the

columns

121, 122 and the

housings

125 and 126. The two interrupters are encapsulated in casings of suitable weatherproof insulating material which are illustrated in more detail in FIG. 1 at .130 and 132. The shunted resistor 104 of FIG. 1 is mounted in a separate housing (not shown in FIG. 3)

located adjacent interrupter 14.

To impart additional voltage handling capability to the circuit breaker, each of the interrupters, instead of being encapsulated as shown, can be located in a dielectric-filled porcelain housing of sufficient length to withstand without flashover the-relatively high voltages to which each interrupter may be subjected.

To reduce the total length of such insulation, I have in the embodiment of FIG. 4 located both interrupters 14 and 16in a single insulating housing 150 filled with a suitable dielectric. The interrupters are disposed in end-to-end relationship and are electrically interconnected by flexible conductive braid 152.

Terminals

154 and 156 are provided at opposite ends of housing 150 for connection to an external circuit. When the interrupter 14 is closed and the interrupter 16 is open, as during a capacitance-current interrupting operation, the portion of the insulating housing 150 surrounding the closed interrupter 14 is available to assume a portion of the voltage appearing across interrupter 16, thus providing additional insulation to reduce the chance for an external flashover. Similarly, when interrupter 16 is closed and interrupter 14 is open, as during a fault-current interrupting operation, the portion of the insulating housing 150 surrounding interrupter 16 is available to assume a portion of the voltage appearing across interrupter 14.

While I have shown an operating system for the two interrupters that comprises two separate sources (75 and 90) of motive power electrically coupled together, my invention is intended to comprehend other suitable forms of operating systems which are capable of producing operation of the interrupters in the claimed sequence.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects; and I, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A high voltage electric circuit breaker which is rated to interrupt fault currents of tens of thousands amperes and to interrupt capacitance currents of huntransient developed across said contacts when they are separated during a fault-current interrupting operation, auxiliary interrupting means having separable contacts connected in series with the parallel combination of said vacuum interrupter contacts and said resistor,

e. said auxiliary interrupting means having sufficient capacitance-current interrupting ability upon separation of its contacts to interrupt without assistance from said vacuum-type circuit interrupter the most severe capacitance currents for which said circuit breaker is rated,

f. auxiliary operating means operable in response to initiation of the operation of said main operating means for opening said auxiliary interrupting means to separate its contacts a few half-cycles after said main interrupters contacts are separated during a fault-current interrupting operation,

. and means operable during a capacitance-current interrupting operation for causing said auxiliary operating'means to separate the contacts of said auxiliary interrupting means while said vacuum interrupter contacts are still closed or simultaneously with separation of said vacuum interrupter contacts, whereby said auxiliary interrupting means assumes the capacitance-current interrupting duty and relieves said vacuum interrupter therefrom.

2. The electric circuit breaker of claim 1 in which during a capacitance-current interrupting operation said auxiliary operating means separates the contacts of said auxiliary interrupting means prior to separation of said vacuum interrupter contacts.

3. The electric circuit breaker of claim 1 in'which during a capacitance current interrupting operation said auxiliary operating means separates the contacts of said auxiliary interrupting means simultaneously with separation of said vacuum interrupter contacts.

4. The circuit breaker of claim 1 in combination with:

a. circuit breaker closing means for closing said auxiliary interrupting means and said vacuum interrupter to effect circuit breaker closing,

b. said circuit breaker closing means effecting closing of said auxiliary interrupting means prior to closing of said vacuum interrupter, thus completing a circuit through said resistor 'prior to closing of'said vacuum interrupter; f

5. The circuit breaker of claim 1 in which said auxiliary interrupting means comprises a second vacuumtype circuit interrupter, the contacts of said second vacuum interrupter beingrelatively movable through a substantially longer opening stroke than those of said main interrupter.

6. The circuit breaker of claim 1 in which said main circuit interrupter and said auxiliary interrupting means are disposed in end-to-end relationship in a single insulating housing that has a wall portion surrounding said main interrupter that assumes a portion of the voltage appearing across said auxiliary interrupting means when said auxiliary interrupting means is open and said main interrupter is closed.

Claims

1. A high voltage electric circuit breaker which is rated to interrupt fault currents of tens of thousands amperes and to interrupt capacitance currents of hundreds of amperes, comprising: a. a main circuit interrupter of the vacuum-type comprising a pair of separable contacts and a highly evacuated insulating housing enclosing said contacts, b. main operating means for separating said contacts to draw a fault current arc therebetween during a fault-current interrupting operation, c. a resistor connected in parallel with said contacts for reducing the severity of the recovery voltage transient developed across said contacts when they are separated during a fault-current interrupting operation, d. auxiliary interrupting means having separable contacts connected in series with the parallel combination of said vacuum interrupter contacts and said resistor, e. said auxiliary interrupting means having sufficient capacitance-current interrupting ability upon separation of its contacts to interrupt without assistance from said vacuum-type circuit interrupter the most severe capacitance currents for which said circuit breaker is rated, f. auxiliary operating means operable in response to initiation of the operation of said main operating means for opening said auxiliary interrupting means to separate its contacts a few half-cycles after said main interrupter''s contacts are separated during a fault-current interrupting operation, g. and means operable during a capacitance-current interrupting operation for causing said auxiliary operating means to separate the contacts of said auxiliary interrupting means while said vacuum interrupter contacts are still closed or simultaneously with separation of said vacuum interrupter contacts, whereby said auxiliary interrupting means assumes the capacitance-current interrupting duty and relieves said vacuum interrupter therefrom.

3. The electric circuit breaker of claim 1 in which during a capacitance current interrupting operation said auxiliary operating means separates the contacts of said auxiliary interrupting means simultaneously with separation of said vacuum interrupter contacts.

4. The circuit breaker of claim 1 in combination with: a. circuit breaker closing means for closing said auxiliary interrupting means and said vacuum interrupter to effect circuit breaker closing, b. said circuit breaker closing means effecting closing of said auxiliary interrupting means prior to closing of said vacuum interrupter, thus completing a circuit through said resistor prior to closing of said vacuum interrupter.

5. The circuit breaker of claim 1 in which said auxiliary interrupting means comprises a second vacuum-type circuit interrupter, the contacts of said second vacuum interrupter being relatively movable through a substantially longer opening stroke than those of said main interrupter.