US3538278A

US3538278A - High voltage electric circuit breaker

Info

Publication number: US3538278A
Application number: US736704A
Authority: US
Inventors: William H Rathbun
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1968-06-13
Filing date: 1968-06-13
Publication date: 1970-11-03
Anticipated expiration: 1987-11-03
Also published as: CH493922A; SE358768B; FR2010847A1; JPS4928545B1; GB1260545A; DE1929552A1

Description

Nov. 3, 1970 W. H. RATHBUN H HIGH VOLTAGE ELECTRIC CIRCUIT BREAKER Filed June 13, 1968 a4 34 as mm L H W ATTORNEY United States Patent Ofice Patented Nov. 3, 1970 3,538,278 HIGH VOLTAGE ELECTRIC CIRCUIT BREAKER William H. Rathbun, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Filed June 13, 1968, Ser. No. 736,704 Int. Cl. H01h 9/42 U.S. Cl. 200-144 7 Claims ABSTRACT OF THE DISCLOSURE A high voltage electric circuit breaker in which the same voltage-controlling resistors parallel the main contacts of the breaker during both the initial part of an opening operation and the final part of a closing operation. Auxiliary switch means is provided for reducing the efiective resistance of the resistors when the breaker is open and before connection of the resistors in parallel with the main contacts during the closing operation, whereby smaller elfective values of resistance parallel said contacts during the final part of closing than during the initial part of opening.

This invention relates to a high voltage electric circuit breaker and, more particularly, to ahig h voltage circuit breaker in which resistors are preinserted into the circuit during closing to reduce the severity of the switching surge produced by the closing operation.

When a circuit breaker is closed to energize or reclose a power line, voltage surges of relatively high magnitude can be produced. One well-known method of reducing the magnitude of such surges is to preinsert a resistance of suitable low value into the circuit during the closing operation just prior to the instant at which the main contacts engage. For example, see U.S. patent application 434,270Mi1ler, now Pat. No. 3,390,238, filed Feb. 23, 1965 and assigned to the assignee of the present invention, or the paper by Hedman et al. entitled Switching of EHV Circuits, IISurge Reduction With Circuit Breaker Resistor, IEEE Transactions on Power Apparatus and Systems, December 1964, pages 1196-1205; or U.S. Pat. 3,291,94-7Van Sickle.

It is well-known that the presence of a resistance shunting the contacts of the breaker can be beneficial during circuit-opening as well as during circuit-closing. During opening, the resistance can serve to limit the peak surge voltages developed and can also reduce the rate of rise of the recovery voltage, thereby making it easier for the circuit breaker to withstand the recovery voltage and thus to complete the interrupting operation.

Many circuit breakers which rely upon resistances during both closing and opening operations use the same resistor for both of these types of operations. See, for example, the circuit breaker of the aforesaid Miller application S.N. 434,270. While this approach results in a simpler circuit breaker, it is subject to the disadvantage that the resistance value must be a compromise between what is ideal for opening and what is ideal for closing. In general, a higher value of resistance is desirable for opening than for closing. In this regard, when the opening resistance is reduced to values approaching the ideal for closing, the resistor current on opening becomes so high that its interruption becomes difficult and costs unduly increase because of the need for dissipating the increased 1 R heating of the resistor.

In one prior circuit breaker that I am aware of, this general problem has been attacked by using two separate resistors for each main break, one for opening and one for closing. A disadvantage of this approach is that, for each main break, two separate resistor switches are also required, one for use in opening and one for use in closing, and both requiring very precise controls.

An object of my invention is to provide different values of resistance for use in opening and in closing, yet without requiring separate, precision-operated opening and closing resistor switches.

In carrying out the invention in one form, I provide resistance switch means which is closed during the initial part of the circuit-opening operation to connect re;- sistance means in parallel with associated main contacts, thereby providing first predetermined values of resistance in parallel with the gaps between the main contacts during this initial circuit-opening interval. Means is provided for opening the resistance switch means to interrupt the circuit through said resistance means following separation of the main contacts during the circuit-opening operation. Means is also provided for closing the resistance switch means during a circuitbreaker closing operation prior to main contact reengagement to connect at least a portion of said resistance means in parallel with their associate main contact gaps. Auxiliary switch means is also provided for reducing the resistance of the resistance means when the breaker is open and before said resistance switch means close during a breaker-closing operation, whereby smaller effective values of resistance parallel said gaps during the final part of closing than during the initial part of openmg.

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 schematic side elevational view partly in section of a circuit breaker embodying one form of my invention. The circuit breaker is depicted in fully open position.

FIG. 2 is a schematic showing of a portion of the circuit breaker of FIG. 1. The parts are shown in the positions they occupy just prior to the circuit breakers reaching fully-open position.

FIG. 3 is a schematic showing of a modified form of the invention.

Referring now to FIG. 1, there is shown a high voltage circuit breaker 10 comprising a metal tank 20 at a high voltage with respect to ground and a hollow insulating column 17 supporting the tank 20 and insulating it from ground. The circuit breaker is, for the most part, constructed in the manner disclosed and claimed in the aforesaid Miller application 434,270. Since many of the details of the circuit breaker form no part of the present invention, most of them have been omitted from the drawing, and those that are included are shown in simplified schematic form.

In the schematic showing of FIG. 1, a wiring diagram is provided to illustrate components of the circuit breaker that are located within tank 20. More specifically, there are shown two series-connected

pairs

22 and 24 of relatively-movable main contacts. Each pair of main contacts comprises a stationary contact 25 and a cooperating movable contact 26. The portion of the circuit between the movable contacts is electrically connected to the tank 20 through conductive structure diagramatically illustrated at 27. The two stationary contacts are supported on terminal bushings 28 projecting through opposite ends of metal tank 20. These bushings comprise conductive stud 29 for carrying current to and from stationary contact 25 and tubular insulator 30 for insulating conductor 29 and stationary contact 28 from tank 20 when the circuit breaker is open, as is shown in FIG. 1. When the main contacts of each

pair

22 and 24 are separated during a circuit-interrupting operation, arcs are established therebetween. To assist in extinguishing these arcs, a gas blast is directed through the arcing region. This gas blast is controlled by a conventional blast valve (not shown) which is operated to initiate the blast just prior to contact separation and to continue it until interruption is completed. Such an arrangement is shown and claimed, for example, in US. Pat. 2,783,338, Beatty, assigned to the assignee of the present invention.

Shunting each pair of main contacts in FIG. 1 is the series combination of a resistor 32 and a resistor switch 34. The resistor switch 34 comprises a stationary contact 36 and a movable contact 37. Resistors 32, when connected across the

main contacts

22 and 24, serve to control the peak value and the rate of rise of the surge voltages developed during a circuit-opening operation. When connected across the

main contacts

22 and 24, they also serve to control the peak value of the surge voltage developed during a closing or reclosing operation.

For enabling performance of the latter function, each resistor switch must be closed slightly ahead of the main contacts which it shunts. In addition, the resistor switches must be closed substantially simultaneously in order to reduce the chances for a flashover of the insulation paralleling the last switch to close. In this latter respect, it is required in certain circuit breakers that all the resistor switches 34 make contact within approximately two milliseconds of each other during a closing operation. In the aforesaid Miller application and in US. Pat. 3,333,071, Oppel et al., means are shown and claimed for eifecting this substantially simultaneous closing of the resistor switches at a point prior to main contact engagement.

It is to be understood that two or more circuit breaker units corresponding to that shown in FIG. 1 may be connected in series to accommodate higher voltage. The operating mechanism of the Miller application is suitable for use in such circuit breakers and can operate to elfect substantially simultaneous closing of all of the resistor switches in such a circuit breaker prior to engagement of the main contacts.

The operating mechanism of the aforesaid Miller application is also used during an opening operation. More specifically, it opens the main contacts substantially simultaneously, and a short time thereafter opens the resistor switch contacts substantially simultaneously. Arcs are' established between the resistor switch contacts, but these are quickly extinguished by a gas blast controlled in a suitable conventional manner, as by the blast valve of the Beatty patent referred to hereinabove.

By selecting suitable values for resistors 32, it is possible to limit the peak line-to-neutral surge voltage developed on closing to a maximum of 2.0 per unit, or even lower, under the most severe circuit conditions. Typically, the total value of resistance required to so limit the surge voltages on closing is quite low, and for various reasons, referred to hereinabove, it is desirable to use a higher value of resistance on opening. For example, in a typical air blast circuit breaker rated at 500 kv. and having eight main breaks in series, I may wish to provide 100 ohms across each main break on opening and 50 ohms across each main break on closing.

In the illustrated circuit breaker, I am able to provide a lower value of resistance for closing than for opening because I provide a pair of auxiliary switches 50 which are used for shorting out a portion of each of the resistors 32 after a circuit-breaker opening operation and prior to a circuit-breaker closing operation. Each auxiliary switch comprises a set of normally-open contacts 52 which are closable to establish a short circuit 53 around a portion of 32a of resistor 32, thus leaving only the resistor portion 32b for insertion in the power circuit when the

resistor switch contacts

36, 37 are closed. FIG. 1 illustrates the auxiliary switches 50 in the closed position they occupy when the circuit breaker is fully open.

The contacts of each auxiliary switch 50 are controlled by an operator 55 that may be of any suitable conventional form. FIG. 2 shows in schematic form an operator that is satisfactory. In FIG. 2 the parts are depicted at an instant occurring near the end of a circuitbreaker opening operation while the auxiliary switch 50 is still open. The operator 55 shown in FIG. 2 comprises a piston 60 coupled to the movable contacts of the auxiliary switch and an opening spring 62 biasing the movable contacts toward the open position shown. A normally-closed control valve 64 controls operation of piston 60. This control valve normally vents the space 65 above piston 60. When the main contact 26 of the circuit breaker reaches a suitable point near the end of its opening stroke, as depicted in FIG. 2, a part 66 attached thereto engages a control element 67, which responds by causing the control valve 64 to open. This causes pressurized gas to flow through valve 64 and line 68 into the space 65 above the piston 60, driving piston 60 downward, and closing the auxiliary switch 50. If necessary, the control valve 64 can be made to open with a slight time delay, e.g., several electrical cycles, to assure that the circuit breakers interrupting operation is completed when the auxiliary switch 50 closes.

The control valve 64 remains open and the auxiliary switch 50 remains closed, as shown in FIG. 1, until the main contacts 26 of the circuit breaker are operated from their open position of FIG. 1 into their fullyclosed position. When the main contacts of the breaker reach their fully-closed position, a second control element 69 is operated to cause the control valve 64 to again close and vent the space 65 above piston 60. This allows the auxiliary switch 50 to rapidly open under the influence of its opening spring 62. This opening operation of auxiliary switch 50 takes place before the main contacts can reopen, and thus the full resistance of resistor 32 is in parallel with the main contacts during an opening operation.

Each auxiliary switch 50 has a substantially identical operator 55, and the control valve 64 is relied upon to control the operators 55 for both resistor switches. Thus, both of these operators respond to operation of control valve 64 in the manner described hereinabove.

It will be apparent that the above-described operation of the auxiliary switches 50 makes available a reduced value of resistance for closing as compared to that used for opening. The instant at which the auxiliary switches 50 are closed to reduce the valve of shunting resistance 32 is not very critical inasmuch as this closing of the auxiliary switches can take place at any time following completion of interruption while the circuit breaker is open and before closing of the resistor switches 34 occurs during a closing operation. Less time is available for opening the auxiliary switches 50 at the end of a main contact closing operation, but this interval is still ample to permit this auxiliary switch opening operation to be accomplished in the available time with relatively simple operating means.

It will be apparent that the auxiliary switch 50 does not require any interrupting ability since it is operated to open when the main contacts are closed. Thus, there is a short circuit around the auxiliary switch contacts through the main contacts which prevents any arcing across the auxiliary switch contacts when operated open.

The absence of any need for interrupting ability permits the auxiliary switch 50 to be relatively simple and makes it unnecessary to associate therewith any gas blast to extinguish an arc or any blast valve for controlling such a blast. The fact that no blast valve needs to be operated as a condition precedent to opening of the auxiliary switch 50 facilitates rapid-opening of the auxiliary switch in the short interval available while the main contacts are closed.

As pointed out hereinabove, a gas blast is conventionally provided in association with each resistor switch 34 to enable it to interrupt the resistor current during the circuit-opening operation.

My invention is particularly useful in an automatic reclosing circuit breaker. In this type of application, reclosing is automatically effected within 40 cycles or less after opening, and substantially the full trapped charge may still be present on the line when the main contacts reengage. This condition tends to result in high surges being produced, but the presence of the low ohmic resistor across the contacts holds the peak surge voltage to the desired value. The illustrated circuit breaker is preferably of the automatic reclosing type and is therefore provided with suitable conventional reclosing control means, such as shown for example in US. Pat. 2,582,027, Goff, assigned to the assignee of the present invention.

FIG. 3 illustrates a modified form of the invention, differing from the preferred form of FIG. 1 by having both of its main-contact shunting resistors (32) located electrically between the two resistor switches (34), instead of on oposite sides of the resistor switches. An auxiliary switch 50 has relatively movable contacts 52 connected in a shunt circuit 53 that is closable to short out portions of the two resistors 32. The auxiliary switch 50 operates in the same manner as that of FIG. 1, closing when the circuit breaker nears fully-open position and opening while the main contacts of the breaker are in their engaged, closed position. Just as in FIG. 1, this operation of the auxiliary switch makes a lower value of resistance available for circuit-breaker closing than for circuit-breaker opening. Corresponding parts in FIGS. 3 and 1 have been assigned corresponding reference numerals.

Locating the resistors in the position shown in FIG. 3 has the advantage of enabling a single auxiliary switch 50 and operator 55 (instead of two, as in FIG. 1) to 'be used for controlling the effective value of resistance shunting each main break during an opening or closing operation. But a disadvantage of the arrangement of FIG. 3 over that of FIG. 1 is that a special mounting is required for the resistor and the resistor switches, as contrasted to the more conventional mounting shown in the aforesaid Miller application or in US. Pat. 2,911,546, Opel. This special mounting is needed in order to accommodate the voltages that are developed between the portion of the circuit between the two resistor switches 34 and the enclosing tank 20. In FIG. 1, this portion of the circuit is always at the same voltage as the tank and may be connected directly thereto at any point without interposed insulation.

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 in the appended claims 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:

1. In a high voltage circuit breaker for opening and closing the circuit through an alternating current power line,

(a) a plurality of series-connected pairs of main contacts the contacts of each pair being separable to establish a gap therebetween during a circuit-opening operation,

(b) closing means for reengaging said main contacts following a circuit-opening operation,

(0) resistance means respectively associated with said pairs of main contacts,

(d) resistance switching means closed during the initial part of a circuit-opening operation for connecting said resistance means in parallel with their associated intercontact gaps during a circuit-opening operation, thereby providing first predetermined effective values of resistance in parallel with said gaps,

(e) means for opening said resistor switch means to interrupt the circuit through said resistance means following separation of said main contacts during a circuit-opening operation,

(f) means for closing said resistor switch means during a circuit-breaker closing operation prior to main contact reengagement to connect at least a portion of said resistance means in parallel with their associated gaps,

(g) auxiliary switch means for reducing the effective resistance of said resistance means when said circuit breaker is open and before said resistance switch means close during a circuit-breaker closing operation, whereby smaller effective values of resistance parallel said gaps during the final part of closing than during the initial part of opening.

2. The high voltage circuit breaker of claim 1 in combination with means for opening said auxiliary switch means when said main contacts reengage and before said main contacts are separated during the next circuit-opening operation.

3. The high voltage circuit breaker of claim 1 in which said auxiliary switch means comprises an auxiliary switch having separable contacts connected in parallel with a portion of an associated resistance means and in series with the resistor switch means associated with said latter resistance means.

4. The high voltage circuit breaker of claim 1 in which said auxiliary switch means comprise a plurality of auxiliary switches respectively associated with said resistance means, each auxiliary switch having separable contacts connected in parallel with a portion of their associated resistor means and in series with the associated resistor switch means.

5. In a high voltage circuit breaker for opening and closing the circuit through an alternating current power line,

(a) a plurality of series-connected pairs of main contacts, the contacts of each pair being separable to establish a gap therebetween during a circuit-opening operation,

(b) closing means for reengaging said contacts following a circuit-opening operation,

(c) resistance means respectively associated with said pairs of contacts,

(d) resistance switch means closed during the initial portion of a circuit-opening operation for connecting said resistance means in parallel with their associated intercontact gaps during a circuit-opening operation, thereby providing first predetermined effective values of resistance in parallel with said gaps,

(e) means for opening said resistor switch means to interrupt the circuit through said resistance means following separation of said main contacts during a circuit-breaker opening operation;

(if) means for closing said resistor switch means during a circuit-breaker closing operation prior to main contact reengagement to connect at least a portion of said resistor means in parallel with their associated (g) and means for reducing the effective value of the resistances connected in parallel with said intercontact gaps by the closing of said resistor switch means References Cited during said circuit-breaker closing operation. UNITED STATES PATENTS 6. The high voltage circuit breaker of claim 1 in which: 730 108 6/1903 Girault 307 136 (a) the two resistance means paralleling adjacent inter- 1 563833 12/1925 christens'e'n'.

contact gaps are located electrically between the re- 5 1Z861:129 5/1932 Millikan sistor switch means paralleling said gaps, and 2,639,357 5 /1953 Kesselring 317 11 (b) said auxiliary switch means comprises a shunting 3,052,783 9/1962 Buron 2O0 143 circuit connection between intermediate points on 3,291,947 12 1 v Sickle said two resistance means and separable contacts 3,333,071 7 19 7 oppel et a1, 2Q(] 148 X closable to complete said shunt circuit and short out 10 adjacent portions of said two resistance means. ROBERT MACON, Primary Examine! 7. The circuit breaker of claim 1 in which means is provided for automatically reclosing said circuit breaker within 40 electrical cycles after an opening operation. 15 200145; 307136; 31711