US3842225A

US3842225A - High voltage circuit breaker utilizing insertion of a fixed resistance during opening and closing

Info

Publication number: US3842225A
Application number: US00324949A
Authority: US
Inventors: W Leeds
Original assignee: Westinghouse Electric Corp
Current assignee: ABB Inc USA
Priority date: 1973-01-19
Filing date: 1973-01-19
Publication date: 1974-10-15
Anticipated expiration: 1991-10-15
Also published as: JPS553772B2; JPS49103170A

Abstract

A high voltage circuit interrupter, such as a circuit breaker is provided with a fixed resistance used for damping both closing and opening voltage transients. The high voltage circuit breaker is provided with back-to-back gallium ignitrons, in series with the damping resistance, having suitable controls for applying ignitron triggering voltage at preselected times during opening and closing of the circuit breaker. The gallium ignitrons are triggered and the fixed resistance is inserted just before the main contacts close and just after the main contacts open. Suitable controls are provided for interrupting the current flowing through the damping resistance during the opening stroke by removing the ignitron''s triggering potential, after the main contacts are open.

Description

United States Patent 1 1 3,842,225

Leeds Oct. 15, 1974 HIGH VOLTAGE CIRCUIT BREAKER UTILIZING INSERTION OF A FIXED RESISTANCE DURING OPENING AND CLOSING Inventor: Winthrop M. Leeds, Pittsburgh, Pa.

Westinghouse Electric Corporation, Pittsburgh, Pa.

Jan. 19, 1973 Assignee:

Filed:

Appl. No.:

References Cited UNITED STATES PATENTS 1/1954 Weinfurt 200/144 AP Beatty i. 200/ 144 AP Brunner 200/144 AP Primary ExaminerR0bert S. Macon Attorney, Agent, or Firm-H. G. Massung [5 7] ABSTRACT A high voltage circuit interrupter, such as a circuit breaker is provided with a fixed resistance used for damping both closing and opening voltage transients. The high voltage circuit breaker is provided with back-to-back gallium ignitrons, in series with the damping resistance, having suitable controls for applying ignitron triggering voltage at preselected times during opening and closing of the circuit breaker. The gallium ignitrons are triggered and the fixed resistance is inserted just before the main contacts close and just after the main contacts open. Suitable controls are provided for interrupting the current flowing through the damping resistance during the opening stroke by removing the ignitrons triggering potential, after the main contacts are open.

6 Claims, 2 Drawing Figures PAIENTEUum 1 51914 FIG! FIG.2

BACKGROUND OF THE INVENTION This invention relates generally to circuit interrupters and more particularly to high voltage circuit breakers having a means for synchronously inserting a switching surge damping resistor during the breaker closing stroke and then inserting the same resistor on the opening stroke.

In determining the insulation requirements for transmission equipment, consideration must be given to the voltage levels to which various insulation systems will be subjected. Normal operating voltages, switching surges and lightning surges must all be considered. When an open transmission line is energized by closing or reclosing a power circuit breaker, the switching surge voltage can be quite high. This is especially true for the extra high voltage class (EHV) and the ultrahigh voltage class (UHV). Switching surge voltages developed can easily flashover insulators or destroy the line insulation system. To construct an insulating system to withstand high surge voltages, the cost may become prohibitive or may even be impossible to attain physically in the case of 765 kv or 1,100 kv class, unless some-means are provided to control the switching surge voltage level. Switching surges in EHV and UHV systems when energizing a transmission line by closing a circuit breaker can reach undesirable values of three or more per unit amplitude, especially if a trapped charge is present on the line being reenergized. One means of limiting such surges is to insert a resistance in the circuit in the half cycle preceding the breaker contacts closing, and then shorting out the resistor after the contacts are closed. Under the most unfavorable conditions, switching surges as high as two per unit are still possible with a closing resistor.

Another solution to the problem would be to synchronize the breaker contacts so that they are close at or near the point at which the instantaneous bus voltage equals the voltage on the line, that is, when the voltage across the open breaker contacts is essentially zero. This is the most direct method for controlling the switching surge level. The synchronous closing can be achieved with or without preinsertion of closing resistance. However, the closing of large power circuit breakers involves the motion of heavy masses and ultra-high speed contact movement. In practice, synchronous closing of the main power contacts is not possible.

Another solution to the problem of limiting switching surge levels, is the combination of synchronously closing the circuit breaker and the preinsertion of resistance. If the circuit breaker can be closed when the voltage across breaker contacts is essentially zero, switching surges will be minimized. However, it is difficult to close the circuit breaker at exactly a voltage zero. As the closing of the breaker contacts deviates from a voltage zero, the switching surge level increases. It has been determined statistically that in order to obtain a switching surge level of 1.5 per unit or less 95 percent of the time, with a maximum level of 1.65 per unit, the standard deviation for the closing without re sistance must be limited to about 13 (0.602 milliseconds). Whereas, to obtain the same switching surge 1evels utilizing perinsertion of a 450 ohm resistance, the allowable standard deviation is approximately 30 (1.39 milliseconds). By preinsertion of a closing resistor and approximate synchronous closing of the circuit breaker, the permissible deviation of circuit closing from voltage zero, that will still limit surge voltage levels to an acceptable magnitude can be greatly increased.

Another problem in the construction of EHV and UHV circuit breakers is the increasing demand for breakers of higher interrupting capacity. Higher interrupting capacity becomes especially difficult to achieve during short line fault conditions when the rate of rise of recovery voltage (RRRV) is very high. The circuit rate of rise of recovery voltage of a short line or kilometric fault; where the fault is located a relatively short distance away from a circuit breaker, on a transmission line, can be reduced by providing an interrupting arrangement in which a shunting resistor is first inserted in parallel with the main contacts during opening and then the residual resistor current is cleared in a second interrupting operation. If a resistance of suitable value is inserted in parallel with the arc during circuit openings, the rate of rise of recovery voltage can be greatly reduced, making possible higher current interruption. However, after the main arc is extinguished, there is still a residual resistor current flowing which requires a separate interruption to open the circuit.

SUMMARY or THE INVENTION In accordance with the invention, an EHV or UHV circuit interrupter or circuit breaker is provided including a resistor which is substantially synchronously inserted in the circuit to limit the switching surge voltage during closing, and which is also inserted during circuit opening to reduce the rate of rise of recovery voltage. By reducing RRRV, the interrupting capability of the circuit breaker can be greatly increased. in the preferred embodiment of this invention, a triggered gallium ignitron is used to first insert a switching surge damping resistor during the breaker closing stroke and then to insert the same damping resistor to reduce the rate of rise of recovery voltage on the opening stroke. Although this invention is described for use with a gallium cathode ignitron, it is to be understood that it can be practiced with other triggered conducting devices such as silicon controlled rectifiers, Triacs, spark gaps or the like. A gallium cathode ignitron is especially suitable for closing the circuit breaker at or near a voltage zero due to its fast activation time. The gallium cathode ignitron can be activated consistently within two microseconds after triggering. The gallium cathode ignitron also has the advantage of having a high withstand voltage, necessary for use in an EHV circuit breaker. The gallium cathode ignitron used in the present invention has a gallium pool cathode, a triggering electrode, and a molybdenum anode, all disposed in an evacuated housing having a high vacuum below 2 X 10" Torr. An experimental model has been built having a withstand voltage between anode and cathode of greater than 120,000 volts. Practical devices having a withstand voltage greater than 300,000 volts can be built. It has been shown experimentally that triggering can be attained consistently within 2 microseconds. For a more detailed description of a satisfactory gallium cathode ignitron see copending application Ser. No. 357,437,

filedMay 4, 1973 (Westinghouse Case No. 40,160.)

In a closing operation, the circuit breaker contacts move from an open position toward a closed position. A suitable operating mechanism for moving the contacts between an open and closed position is described in detail in US. Pat. No. 3,291,947 issued Dec. 13, 1966 to R. C. Van Sickle and assigned to the assignee of the present invention. When the breaker contacts are still separated, a triggering pulse is sent to the gallium cathode ignitron at a voltage zero on the bus side of the breaker, during the half cycle in which the breaker contacts will close. When the gallium cathode ignitron is triggered, a closing resistor is inserted in parallel with the closing main contacts. Not so much damping action from the closing resistor is required since approximate synchronous insertion helps keep switching surges within an acceptable level.

When the main contacts are fully closed, the resistance inserted during closing is shorted out and transmission line charging current or load current can flow. With the triggering pulse removed, the gallium cathode ignitron will conduct only during the half cycle when energized. With the main contacts closed and the triggering pulse removed from the gallium cathode ignitron the resistance inserted during closing is electrically removed from the circuit.

When a circuit breaker clears a single phase fault, the deenergizing of the unfaulted phases usually leaves a trapped charge on the line which does not have time to leak off if high speed reclosing of the breaker is provided.

In such a case of a trapped D.C. charge voltage on the line, sensing of both line and bus voltages is necessary to send the triggering pulse when the voltage across the breaker terminals is near zero. That is, the gallium cathode ignitron is triggered at the instant when the bus voltage is approximately equal to the voltage existing on the open line, so that the voltage across the circuit breaker contacts is very nearly zero.

In order to reduce the rate of rise of recovery voltage of a kilometric or short line fault, the resistor used during closing is connected in the circuit to be interrupted during the opening operation. When the circuit breaker is opened, just after the contact tips have separated a triggering voltage is applied to the gallium cathode ignitron, inserting the damping resistor in parallel with the arc across the opening circuit breaker contacts. When the arc current in the main contact gap reaches zero, the bypass current through the resistors and ignitrons will. damp the recovery voltage buildup and help the circuit breaker to interrupt higher powers than would otherwise be possible. After the main current zero, the ignitron triggering circuits are deenergized so that when the resistor current reaches zero, about onequarter cycle after the main current zero because of the difference in power factor, the ignitrons will no longer conduct and the resistor circuit current is interrupted.

In the disclosed invention, a high voltage circuit breaker is provided with resistors used for damping both the closing and opening voltage transients. The high voltage circuit breaker is provided with back-toback gallium ignitrons in series with the damping resistors and with suitable controls for applying ignitron triggering voltage as preselected times, just before the main contacts close and just after the main contacts open with provisions for interrupting the resistor current during the opening stroke by removal of the ignitron triggering potential.

Although resistors have been used in prior art for both opening and closing voltage transient controls it is known that a single resistance value cannot be optimum for the two functions. In this invention, the resistance value can be chosen to be optimum for the opening function since the approximate synchronous insertion upon closing makes the closing resistance value less critical. This invention has the advantage of the dual use of the ignitrons performing both the synchronous closing function and also interrupting the resistor current during opening.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference may be had to the preferred embodiments exemplary of the invention shown in the accompanying drawings in which:

FIG. 11 is a side view partially in section and partially in elevation of a high voltage circuit interrupter embodying the principal features of the present invention; and

FIG. 2 is a schematic representation of the circuit interrupters shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and FIG. 1 in particular, there is shown a high voltage circuit breaker l0 utilizing the teaching of the present invention. High voltage circuit breaker 10 is connected to a high voltage alternating current supply, and the output of the breaker 10 is connected to a transmission line which feeds electrical loads. As shown in FIG. 1, the circuit interrupter 10 comprises a metal housing 12, and a rocker cross arm 13 which is rotatably mounted on a generally cylindrical bearing support, movable between an open and a closed position. Movable main contacts 26 are attached to the opposite ends of the rotatable cross arm 13. Stationary contacts 24, attached to terminal bushings 22 which extend through the ends of the housing 12, are disposed within the housing 12. As rocker cross arm 13 moves from the closed to the open position, movable contacts 26 separate from stationary contacts 24 to establish an arcing gap therebetween. A hollow vertically disposed insulating column 23 supports thehousing 12 of the interrupter unit 10.

Terminal bushings 22 which are attached to the ends of housing 12 are of the type suitable for extra high voltage service. Electrical circuit connections are made to the outer ends 21 of terminal bushings 22. The stationary contacts 24 are supported at the foot of terminal bushings 22.

Gallium ignitrons 20 are disposed within the housing 12 of the high voltage circuit breaker 10. Bus voltage is present on the source or bus side of the high voltage breaker 10 while the transmission line voltage can be measured on the opposite or line side of the high voltage breaker 10. Potential sensing devices 18 are connected to monitor, and to supply a signal proportional to, the source voltage or the line voltage. Potential sensing device 18 feeds a voltage proportional to the bus voltage to control device 19, which is designed to have a low burden. The closing control portion of control device 119 can be similar to the timed closing device described in IEEE paper 71 TP 571- PWR, entitled EHV Breaker Rated for Control of Closing Voltage Switching Surges to 1.5 Per Unit. Because of the low burden of control device 19, capacitive or inductive low power potential sensors can supply the reference voltage. The low power reference voltage can also be supplied from existing sources, such as potential transformers or capacitive bushing taps. At the beginning of the one-half cycle during which the main contacts 26 will close, control device 19 sends a triggering pulse through the gallium cathode ignitron 20 initiating conduction. Triggering of the gallium cathode ignitrons can normally be obtained consistently within two microseconds of a voltage zero. As can be seen in FIG. 1, the gallium cathode ignitron 20 is connected in parallel with the main contacts 26 so that the circuit completed by high voltage breaker can be closed very near a voltage zero by proper triggering of the gallium cathode ignitron 20. Synchronous closing of the high voltage circuit breaker can thus be accomplished, as described in more detail in copending application Ser. No. 357,437 Westinghouse Case 40,l60).

The

main contacts

24 and 26 thus close when a gallium cathode ignitron is conducting. The only voltage across contacts 26 during final closing is the small voltage drop across the conducting gallium cathode ignitron. The voltage drop across the gallium cathode ignitron 20 during conduction is approximately 20 volts. The gallium ignitron 20 starts conducting rapidly so that the circuit through the high voltage circuit breaker 10 is closed at approximately a voltage zero.

In order to reduce the rate of rise of the recovery voltage of a kilometric or short line fault, a pair of resistors 34 are connected in the circuit to be interrupted during an opening operation. The tubular resistors 34 are mounted around the base of bushings 22. One terminal of tubular resistor 34 is electrically connected to the stationary contact 24, which is mounted on the foot of bushing 22 and the other end is connected to the gallium cathode ignitrons 20. A resistor 34 is provided on each terminal bushing 22. In addition to reducing the rate of rise of recovery voltage, the resistors 34 also function as damping resistors to prevent restrikes during the opening if line charging current and prevent excessive over voltages during closing.

Capacitor dividers 33 are connected from each internal terminal to the tank 12 so as to bridge the contact breaks and thus substantially equalize the voltage appearing across each of the two interrupter breaks.

During the closing operation, energizing of the closing valve on the pneumatic operator (not shown) causes the

breaker contacts

24 and 26 to move from the open position towards the closed position. At a predetermined time, when the

contacts

24 and 26 are still separated, the synchronous control box 19 applies, at a moment selected when the voltage on the bus side of the breaker is close to zero, an impulse voltage to each of the capacitor dividers 30. The voltage surge, traveling up the capacitor stack 30, causes a potential to build up across impedance 32 applying a voltage pulse to the trigger of each of the ignitrons 20. Depending on the polarity of the potential difference across the circuit breaker 10 one of the ignitrons 20 will fire, inserting the resistors 34 in parallel with the

main closing contacts

24 and 26. Not much damping action from the resistor 34 is required since the approximate synchronous insertion will assure that the potential difference across the breakers is minimized. When the

main contacts

24 and 26 are fully closed the resistance 34 is shorted out and a transmission line charging current or load current can flow.

In the case of a trapped charge voltage on the line, an additional potential sensing device 18 is required. The signal from line potential device 18 is fed to control device 19 so that the triggering pulse to the gallium ignitrons can be transmitted near a zero terminal voltage across

circuit breaker contacts

24 and 26. Control device 19 compares signals from potential device 18 and sends a signal to the gallium ignitron 20 so that they begin to conduct at or near a point where the instantaneous bus voltage equals the voltage on the line. Triggering of ignitrons 20 occurs when the voltage across the

open breaker contacts

24 and 26 is essentially zero, in the onehalf cycle before the closing of the

main contacts

24 and 26.

On an opening operation, energizing of the breaker trip coil (not shown) allows accelerating springs to start contacts 26 toward the open position. Just after the contact tips have separated, drawing an arc and developing a little arc voltage, control device 19 applies a triggering signal to both ignitrons 20. Depending on the polarity of the arc voltage drop, one of the ignitrons will start to conduct. Conduction through one of the ignitrons will continue as long as the triggering signal is applied. When the current through the

main circuit contacts

24 and 26 reaches zero, the bypass current through the resistors 34 and ignitrons 20 will dampen the recovery voltage buildup and help the circuit breaker interrupt higher power levels than would otherwise be possible. By reducing the rate of rise of recovery voltage, the interrupting capability of circuit breaker 10 is enhanced. After the main current zero, the triggering signal is removed from the trigger of ignitrons 20 so that when the resistor 34 current reaches zero, about one-quarter cycle after the main current zero because of the difference in power factor, ignitrons 20 will no longer conduct and the damping resistor 34 circuit current is interrupted.

In the disclosed invention, a high voltage circuit breaker 10 is provided with resistor 34 for damping both closing and opening voltage transients. The high voltage circuit breaker I0 is provided with back-toback gallium ignitrons 20 in series with the damping resistors 34 and with suitable controls 19 for applying ig nitron 20 triggering voltages at preselected times just before the

main contacts

24 and 26 close and just after the

main contacts

24 and 26 open, with provisions for interrupting the current through the resistor 34 during the opening stroke by removal of the ignitron 20 triggering potential after main current interruption.

I claim:

1. A high voltage alternating current circuit breaker, comprising:

a housing;

main contact means disposed in said housing, movable between an open and a closed position; means for opening and closing said main contact means;

a damping resistor;

resistor insertion means disposed in parallel with said main contact means for synchronously connecting said damping resistor around said main contact means at a voltage zero of the alternating current wave just prior to main contact closing, and for connecting said damping resistor around said main contact means as said main Contact means move to the open position during circuit interruption; and

damping resistor current interruption means for interrupting the current flowing through said damping resistor after said main contact means are open and current through said main contact means is substantially zero.

2. A high voltage circuit breaker as claimed in claim I, wherein:

8 open position.

4. A high voltage circuit breaker as claimed in claim 1, wherein said resistor insertion means comprises:

a plurality of gallium cathode ignitrons, and said damping resistor is connected in series with said plurality of gallium cathode ignitrons.

5. A high voltage circuit breaker as claimed in claim 4, including:

triggering means for said gallium cathode ignitrons, said triggering means being capable of triggering said gallium cathode ignitron into conduction at a voltage zero across said main contact means, and said triggering means being capable of triggering said gallium cathode ignitron into conduction as said main contact means separate during circuit opening.

6. A high voltage circuit breaker for interrupting an electrical circuit as claimed in claim 5, wherein said triggering means comprises voltage sensing means electrically associated with said electric circuit for sensing the potential across said main contact means.

Claims

1. A high voltage alternating current circuit breaker, comprising: a housing; main contact means disposed in said housing, movable between an open and a closed position; means for opening and closing said main contact means; a damping resistor; resistor insertion means disposed in parallel with said main contact means for synchronously connecting said damping resistor around said main contact means at a voltage zero of the alternating current wave just prior to main contact closing, and for connecting said damping resistor around said main contact means as said main contact means move to the open position during circuit interruption; and damping resistor current interruption means for interrupting the current flowing through said damping resistor after said main contact means are open and current through said main contact means is substantially zero.

2. A high voltage circuit breaker as claimed in claim 1, wherein: said resistor insertion means is connected in series with said damping resistor; and said resistor insertion means comprises, disconnecting means for electrically disconnecting said damping resistor from parallel connection with said main contact means after said main contact means are fully closed.

3. A high voltage circuit breaker as claimed in claim 1, wherein said damping resistor current interruption means interrupts the current through said damping resistor only after said main contact means are in the fully open position.

4. A high voltage circuit breaker as claimed in claim 1, wherein said resistor insertion means comprises: a plurality of gallium cathode ignitrons, and said damping resistor is connected in series with said plurality of gallium cathode ignitrons.

5. A high voltage circuit breaker as claimed in claim 4, including: triggering means for said gallium cathode ignitrons, said triggering means being capable of triggering said gallium cathode ignitron into conduction at a voltage zero across said main contact means, and said triggering means being capable of triggering said gallium cathode ignitron into conduction as said main contact means separate during circuit opening.