US3113191A

US3113191A - Operating mechanism for an electric circuit breaker

Info

Publication number: US3113191A
Application number: US89233A
Authority: US
Inventors: Edward J Frank
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-02-14
Filing date: 1961-02-14
Publication date: 1963-12-03
Anticipated expiration: 1980-12-03
Also published as: DE1280967B; DE6604201U; GB930195A

Description

E. J. FRANK 3,

OPERATING MECHANISM FOR AN ELECTRIC cmcurr BREAKER 2 Sheets-Sheet 1 Dec. 3, 1963 Filed Feb. 14, 1961 a m M 6 I I P L m :"9 V 1.6 n Mr N all w a a? V? t 4 1mm M M. NW0 m H. .5

Dec. 3, 1963 E. J. FRANK 3,113,191

OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Feb. 14, 1961 2 Sheets-Sheet 2 Inventor: Edward J. -Frank,

by 611cm,

Attovneg.

United States Patent 3,113,191 OPERATING MECHANESM FOR AN ELECTREC tCIRCUlT BREAKER Edward J. Frank, Springfield, Pa, assignor to General Electric Company, a corporation oft New York Filed Feb. 14, 1961, Ser. No. 89,233 7 Claims. (Cl. Mitt-$2) This invention relates to an operating mechanism for an electric circuit breaker and, more particularly, to an operating mechanism in which large amounts of kinetic energy are stored during the initial and intermediate stages of circuit-breaker closing motion, so as to be available for overcoming the high opposing forces that may be encountered during the final stages of closing motion.

In the type of operating mechanism that this invention is concerned with, there is a rotatable cam driven through reduction gearing by an electric motor. This cam is utilized for imparting circuit breaker closing forces to a linkage coupled to the usual movable contact of the circuit breaker. As the circuit breaker closing operation progresses through the initial and intermediate stages, the motor accelerates to a relatively high speed, thereby storing large amounts of kinetic energy in the moving parts of the mechanism connected to the cam. This stored energy is available to overcome any opposing forces that may be enecountered near the end of the closing stroke. Upon completion of the closing stroke, the unused kinetic energy stored behind the cam continues rotating the cam independently of the linkage. After a slight amount of such overtravel, however, the cam is stopped by braking means which dissipates the unused kinetic energy.

In a mechanism of this character it is highly desirable that overtravel of the cam be limited to a rather narrow range. Otherwise, continued motion of the cam could carry it into positions in which it would interfere with the ability of the mechanism to perform a subsequent closing operation. This problem of precisely controlling the amount of overtravel is complicated by the fact that there may be widely varying amounts of kinetic energy to dissipate from one operation to the next. For example, the breaker could be closed either on a deenergized power line, which would involve no magnetic opposing forces, or on a short circuit, which would involve very large magnetic opposing forces; and the amount of excess energy remaining to be dissipated would be widely different for these two cases. As another example, the source of voltage for the motor may be subject to wide variations that could produce appreciable differences in the motor speed and, hence, the kinetic energy to be dissipated under diferent voltage conditions. Prior braking schemes of which I am aware have not been as precise as desired in controlling the amount of overtravel under such widely varying kinetic energy conditions, particularly where the maximum permissible amount of overtravel is small and the maximium amounts of kinetic energy are relatively large.

Accordingly, an object of my invention is to precisely control such overtravel under widely varying kinetic energy conditions, even where the maximum permissible amount of overtravel is quite small and the amounts of kinetic energy involved may sometimes be quite large.

Another object is to provide braking means which can compensate for varying amounts of kinetic energy by applying a braking force that automatically varies in magnitude directly with respect to the amount of kinetic energy to be dissipated, so that when relatively large amounts of kinetic energy are to be dissipated, relatively large braking forces will automatically be available.

Another object is to incorporate such braking means in such a manner that it will not interfere with attaining the high-speed travel of the cam that is required to develop 3-,l 13,191 Patented Dec. 3, 1963 ice the large amounts of kinetic energy that might be necessary for closing.

Another object is to provide braking means of the above character which requires no special brake-releasing means when it is desired to resume motor operation after braking has been completed.

In carrying out my invention in one form, I provide a linkage for transmitting force for closing a circuit breaker and a rotatable main cam'for transmitting circuit-breaker closing force to the linkage. The rotatable main cam is coupled to motor means that is operable upon energizaton to supply closing force to the main cam. After the motor means has driven the main cam into a predetermined position following initiation of a closing operation, the motor means is deenergized and braking force is thereafter applied to the motor means when the closing operation is completed. This braking force is derived from braking means comprising an auxiliary cam coupled to the main cam for rotation at the same angular speed as the main cam. The braking means also includes a dashpot having a reciprocable piston that is retarded during motion in one direction. Rotary motion of the auxiliary cam drives the dashpot piston in its direction of retarded motion during travel of the auxiliary cam occurring after the motor is deenergized and after closing of the circuit breaker is completed, whereby to dissipate the kinetic energy stored in the motor means and to stop the main cam in a terminal position. Reclosing of the circuit breaker is effected by causing the motor to drive the main cam through continued rotary motion past said terminal position into said predetermined position.

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

FIG. 1 is a schematic view of one form of circuit breaker operating mechanism embodying my invention. In FIG. 1 the operating mechanism is shown in its open position.

FIG. 2 illustrates the operating mechanism of FIG. 1 shortly after it has been tripped to open from its closed position.

FIG. 3 shows the operating mechanism of FIG. 1 in its closed position.

Referring now to FIG. 1, the circuit breaker shown therein comprises a set of stationary contacts 12, connected in a power line 14 and a movable bridging contact 16, movable into and out of engagement with said stationary contacts 12. The movable bridging contact 16 is secured to the left-hand end of a reciprocable operating rod 18 of insulating material, which is pivotally connected at its right-hand end to a crank 20. This crank 20 is pivotally mounted on a stationary pivot 22. The mova ble contact 16 is biased toward its open position of FIG. 1 by means of a suitable opening spring 21, shown as a tension spring connected to the crank 20.

For transmitting closing thrust to the operating rod 13 the contacts 16, there is provided a conventional trip-free linkage L which comprises a pair of toggle links 23 and 24-, pivotally joined together at a knee 25. One of the toggle links 23 is pivotally connected at its opposite end to the lower end of crank 20 by means of pivot pin 27. The other toggle link 24 is pivotally connected by pivot pin 28 to the upper end of a guide link 29. This guide link 29 is pivotally supported at its lower end on a fixed fulcrum 30. The pivot pin 28 carries a latch roller 31 which cooperates with a suitable trip-latch 32, which is arranged to be operated in response to predetermined circuit conditions by means of a suitable conventional tripping solenoid 34. In the disclosed embodiment, the coil of this solenoid 34 is shown connected across the secondary 35 of a current transformer inductively coupled to the power line 14 so as to cause operation of the solenoid in response to over-currents in the power line 14. Other conventional tripping schemes could, of course, be used. So long as the trip latch remains in the latched position shown in FIG. 3, the

toggle

23, 24 is capable of transmitting thrust to the movable contact-actuating rod 18. Thus, when the knee 25 is lifted from the position shown in FIG. 1, the

toggle

23, 24 is extended and drives the crank in a clockwise direction about its pivot 22 and the rod 18 to the right toward closed position against the bias of opening spring 21.

This lifting of knee is produced by the action of a rotatable main cam 40 cooperating with the usual roller 42 which is mounted at the knee 25. When the main cam 40 is rotated clockwise from its solid line position of FIG. 1 into its dotted line position of FIG. 3 by means soon to be described, it lifts the knee 25, thereby extending the

toggle

23, 24 and closing the breaker. The position occupied by the parts of the linkage L when the breaker is in its fully-closed position is shown in solid lines in FIG. 3. It will be apparent from FIG. 3 that closing action has resulted in the knee 25 of the toggle being driven slightly past a dead center position, i.e., past a reference line connecting the axes of

pivots

28 and 29, so that there is no tendency of

toggle

23, 24 to return to its retracted position of FIG. 3 when the application of closing force to the roller 42 is discontinued. There is a slight tendency for the

toggle

23, 24 to collapse upwardly, but this is resisted by a suitable stop 44 co-acting with the roller 42.

Tripping open of the circuit breaker is effected by energizing the solenoid 34 sufliciently to drive the triplatch 32 clockwise about its stationary pivot 46 against the bias of a suitable reset spring 47. Should the latch 32 be tripped when the circuit breaker is closed, or even during the closing stroke, the pivot 28 will be freed by such tripping action, thus no longer serving as a stationary reaction point for the

toggle

23, 24. This will render the

toggle

23, 24 inoperative to transmit thrust to the movable contact rod 18, and, as a result, the opening spring 21 will be free to drive the movable bridging contact 16 into its open position.

The position of the parts shortly after such tripping of latch 32 has occurred is shown in FIG. 2. The latch 32, having been moved off the latch roller 31, is no longer capable of restraining the pivot 28 in its fixed position of FIG. 3. This has permitted the opening spring 21 to drive the crank 26 counterclockwise about its stationary pivot 22, forcing the

entire toggle

23, 24 to the right. The roller 42 rolls along the stop 44 until the toggle knee 25 shifts to a position below the reference

line connecting pivots

27 and 28, at which time the knee 25 of the toggle is free to move downwardly, allowing the

toggle

23, 24 to collapse downwardly at the knee toward its dotted line position of FIG. 2. Such collapse of the

toggle

23, 24 allows the crank 22 to move further counterclockwise under the influence of opening spring 21, thus allowing for further circuit breaker opening. A typical final position of the linkage at the end of the opening operation is shown in dotted lines in FIG. 2.

For returning the linkage to a thrust-transmitting condition after it has been tripped open, a reset spring 49 is provided. This reset spring 49 cooperates with theguide link 29 to return the guide link to its latched position of FIG. 1 after tripping has occurred. Thus, in FIG. 1, the linkage L is shown in an open and reset position.

For driving the main cam 49 through a ciosing cycle, e.g., in a clockwise direction from its solid line position of FIG. 1 into its dotted line position of FIG. 3, an electric motor 59 is provided. This motor 5 acts through suitable reduction gearing 52 to drive in a clockwise direction a rotatable shaft 54 to which the main cam 49 is secured. The motor accelerates the cam 49 to a relatively high speed as the closing stroke progresses so that large amounts of kinetic energy are stored in the moving parts coupled to the cam. This kinetic energy is available to overcome the increasing opposition of the opening spring 21 and also the high magnetic opposing forces that would be encountered at the end of the closing stroke should a fault be present on the power line 14. When the main cam 40 enters its dotted line position of FIG. 3 and thus completes a breaker-closing operation; the motor is deenergized by means of a suitable limit switch 56 (controlled by a cam 107 secured to shaft 54). But any unused kinetic energy that remains after the motor 50 is deenergized acts to continue rotation of the main cam 40 clockwise past its dotted line position of FIG. 3.

One of the problems that the present invention is concerned with is dissipating this excess kinetic energy and stopping the main cam 40 within a rather narrow range of angular positions. Unless this overtravel of the main cam is precisely controlled, the cam can move into positions where it would interfere with the ability of the mechanism to perform a subsequent closing operation. For example, the main cam d0 might move into a position that would block resetting of the linkage L to its thrust-transmitting condition, or it might move into an excessively advanced final position just ahead of the dotted line position of FIG. 3 that would interfere with a subsequent closing operation. With respect to this latter condition, if, on a subsequent closing operation, cam travel prior to reaching the closing position is excessively restricted, there will be insufficient opportunity to attain the speeds needed for closing under all conditions.

For stopping the main cam 49 within the required narrow range of angular positions, I provide braking means in the form of a dashpot 60 and an auxiliary cam 62 for transmitting energy from the main cam 46 to the dashpot 6 The dashpot 69 comprises a cylinder 63 filled with a suitable liquid to a level above the highest position of the piston and a reciprocable piston 64 slidably mounted in the cylinder. Downward motion of the piston 64 is retarded by the liquid in the cylinder disposed beneath the piston, with the extent of such retardation being controlled by a small metering opening 65 extending through the piston. Upward motion of the piston can take place without significant retardation due to a large port 66 extending through the piston. A suitable check valve 67 controlling the flow of liquid through port 66 allows liquid to flow freely thereth-rough from the top side to the bottom side of the piston 64 during such upward piston motion. This check valve 67 blocks flow in a reverse direction through the port 66, thereby preventing liquid from flowing downward motion of the piston. A piston reset spring 68 positioned beneath the piston 64 acts independently of the auxiliary cam to quickly return the piston to its uppermost position (against shoulder 69) when downward force is no longer being applied to the piston. This quick reset action assures that the piston will be in its uppermost position in readiness for a braking operation whenever the main cam 46 enters its dotted line position of FIG. 3.

For transmitting energy from the auxiliary cam 62 to the piston 64, a roller 70 coupled to the piston rod 71 is provided. This roller 76 is rotatably mounted on a pin 72 carried by a link 73 that is pivotally connected at 74 to the upper end of piston rod '71. A guide link 75, pivotally connected atone end to the pin 72 and pivotally mounted at its other end on a stationary fulcrum 76, serves to guide the roller 70 and to maintain it in thrusttransmitting relationship relative to the piston rod 71.

In the illustrated embodiment of my invention, the auxiliary cam 62 is contoured in such a manner that all but about 60 degrees of its outer periphery is generally uniformly spaced from its axis of rotation. This generally uniform radius portion of the auxiliary cam 62 is referred to hereinafter as the dwell portion of the cam. The remaining 6 0 degrees of periphery contains a projecting cam portion 79 having a gradually curved contour through the port during on one side of a high point 80 and an approximately radially-extending contour on the other side of a high point 8t Shortly after the main cam 4t passes clockwise through the dotted line position of :FlG. 3 during a closing operation, the projecting portion 79 of the auxiliary cam 62 is just beginning to depress the roller 70 and dashpot piston 64 connected thereto. As described hereinabove, this downward motion of the dashpot piston 64- is opposed by the liquid beneath the piston, and a powerful retarding force is thus applied to the main cam 40 through the dashpot piston 64', and the auxiliary cam '62. The magnitude of this retarding force varies as a direct function of the square of the piston velocity. Hence, the higher the speed of the main cam 46 as it passes through the dotted line position of FIG. 3, the greater will be the retarding force developed by the dashpot. The dashpot, in effect, compensates for variations in the amount of kinetic energy to be dissipated by applying a [retarding force that varies in magnitude as a direct function of the amount of kinetic energy. Thus, the tendency for the higher amounts of excess kinetic energy to produce greater amounts of overtravel is effectively offset by the greater retarding force. This compensating effect enables the dashpot to stop the cam within a narrow range of angular positions for all magnitudes of excess kinetic energy that will normally be encountered.

The magnitude of the excess kinetic energy depends primarily upon the voltage that is applied across the terminals of the motor 51) and upon the magnitude of current encountered upon closing. in one typical application of my circuit breaker, the motor voltage can vary between normal limits of 90 and 130 volts, and the magnitude of the current encountered upon closing can vary from zero to heavy short circuit currents corresponding to the rated making current of the circuit breaker. It will therefore be apparent that the braking means 62, 60 might be called upon to dissipate widely varying amounts of excess kinetic energy. In one typical embodiment of my invention, the disclosed braking means has been capable of limiting the final position of the cam under all normally encountered excess energy conditions to a range of 45 degrees. The auxiliary cam 62 is so shaped that for maximum excess kinetic energy conditions, i.e., closing with maximum voltage on a deenergized power line, motion of the auxiliary cam 62 is terminated appreciably before the high point 80 of the cam 62 reaches the roller '70.

Assume now that the breaker has been tripped open and has thereafter reset into its position of FIG. 1 under the influence of its reset spring 49 and that it is desired to reclose the circuit breaker. The motor 50 would be energized by closing a switch 85 (in a manner soon to be described), and such switch-closing would complete an energizing circuit for the motor through switch 85 and motor 59 across the terminals 86 and $7 of a control voltage source. The motor would respond to completion of this circuit by driving the main cam 45} clockwise from its initial solid line position of FIG. 1, through its dotted line position of FIG. 1, and then into its dotted line position of FIG. 3. Until the high point 80 of the auxiliary cam 62 moves past the roller 76 during this clockwise closing motion, the dashpot 60 would have a tendency to retard such closing motion. This tendency is considerably lessened, however, by the fact that the initial speed of the main cam 40 is relatively low inasmuch as some initial travel is required before the motor can bring its load up to an appreciable speed. Since this initial travel is at a relatively low speed, the retarding force exerted by the dashpot is also quite low, thus permitting the motor to develop some initial speed without excessive retardation from the dashpot. When the high point 80 of the auxiliary cam 62 passes the roller 70, the dashpot piston 64 is released from driven relationship with the auxiliary cam 62 and further clockwise motion of the main cam 4d can occur without opposition from the dashpot 6th until the closing operation is essentially completed. It will be apparent that no special brake-releasing means is needed to enable the motor to drive the auxiliary cam 62 past the dashpot roller 70 during this early portion of a closing operation. Even though no such brake-release has occurred, the motor is able to drive the auxiliary cam 62 past the dashpot without undue opposition due to the low retarding forces that the dashpot exerts when the speed of its piston 64 is low.

During the above-described clockwise motion when the auxiliary cam 62 is contacting the roller 70 and during about degrees of added clockwise rotation, no appreciable opposing force is being transmitted through the link-age L to the main earn 4% of the circuit breaker. This follows from the fact that the effective working surface of the main cam 40 during this extended interval is substantially uniformly spaced from the axis of rotation of the main cam. More specifically, just past the highest point $8 on projecting portion 89 of the main cam there is a generally uniform radius dwell portion 90 of approximately degrees which is arranged to contact the roller 4-2 of the linkage L during this period. Since, by reason of this dwell 9i), no effort is being made to lift the roller 42 during this interval, no appreciable amount of power is being transmitted to the linkage L and thus no appreciable opposing force is transmitted through the linkage L to the main cam 4% during this interval. The absence of such opposing force contributes in an important manner to the ability of the motor to develop the required speed and kinetic energy before closing is attempted. When the dwell portion of the cam has finally been driven clockwise past the roller 42 of the linkage L, a cam portion of gradually increasing radius comes into operation and lifts roller 42 to close the breaker. The kinetic energy that the cam and its driving means 54}, 52 had acquired prior to this lifting action and the additional kinetic energy developed as the lifting action progresses provides sufficient kinetic energy to close the breaker positively and firmly even against heavy short circuit currents. As the cam moves through the dotted line position of FIG. 3 upon completion of the closing operation, the motor is deenergized by the limit switch 56 and the excess kinetic energy that remains after the closing operation is dissipated by the dashpot 60, all as described hereinabove.

A significant feature of my braking means 60, 62 is that it is applied to the driven end of the power transmission between the motor 5%) and the main cam 40'. Since this driven end of this power transmission makes only one revolution during each circuit-breaker closing operation, the braking means 6t), 62 applies its retarding force only during the portion of the closing operation when it is needed. On the other hand, had the braking means been applied directly to the motor shaft, which makes numerous revolutions during each closing operation, the braking force would have been applied and released repetitively during the closing operation, thus interfering with attainment of the desired high speeds. Additionally, the fact that the brake means 6%), 62 is on the driven shaft makes it easier to provide a precise angular relationship between the auxiliary cam 62 and the main cam 40, so that braking force can be applied at a precisely-located angular position of the main cam 40.

It is to be noted that the braking function is involved in only about 60 degrees of the total 360 degrees available for the closing operation inasmuch as the dashpot 6% is applying braking force only during this limited interval. Since only this relatively small portion of the total 360 degrees available for closing is consumed by the braking function, a relatively large portion of the remaining angular motion remains available to permit the motor to accelerate the cam d0 unopposed by the linkage L so that it can develop the high speed and kinetic energy needed for closing under severe short circuit conditions, particularly when the motor voltage is relatively low. Thus, because the brake means 60, 62 is exceptionally effective and requires only a small amount of angular 7 movement to perform its intended function, the duty imposed on the motor in closing is considerably reduced.

It is important, however, that the braking force not be applied so suddenly as to cause damage to the reduction gearing 52 or other parts of the mechanical transmission through excessive loads resulting from sudden dissipation of the stored kinetic energy. To this end, the auxiliary cam 62 is so contoured that the maximum braking torque developed by the braking means 60, 62 does not exceed the maximum torque that can be developed by the motor at the completion of a closing operation, i.e., the torque developed at the cam shaft 54 by the motor upon closing on a deenergized power circuit With maximum control voltage applied to the motor. For example, in one typical embodiment of my invention the maximum motor torque at the cam shaft 54 is 600 pound-inches whereas the maximum braking torque is 500 pound-inches.

The electric control for the motor 50 may be of any suitable conventional form. In the illustrated embodiment of the invention, however, this control comprises a motor control relay 190 that is arranged to close its contacts 85 when energized. If the circuit breaker is open, as shown in FIG. 1, closing of the contacts 85 completes an energizing circuit through the motor that extends from the positive terminal 86 of the source of control voltage, through the contacts 85 of the motor relay, then through the motor 50 and a normally closed limit switch 106 to the negative terminal 87 of the control voltage source. Completion of this energizing circuit causes the motor to drive the main cam 40 clockwise from its solid line position of FIG. 1 through its dotted line position of FIG. 1. By this time, a seal-in circuit has been completed around the contacts 35 of the motor relay 1% by means of the limit switch 56 controlled by cam Hi7 secured to the cam shaft d. Thus, when the contacts 35 of the motor relay drop out (as soon to be described), the motor 50 remains energized through the limit switch 56. When the motor drive the main cam 40 clockwise through its dotted line position of FIG. 3, the limit switch 56 opens, thereby deenergizing the motor, as described hereinabove. The other limit switch 106, which is opened by closing of the circuit breaker, opens immediately thereafter, thereby providing assurance that the motor 51) will be deenergized as soon as the breaker is closed.

For establishing an energizing circuit for the motor control relay 1%, there is provided a closing control switch 110 that is operable either manually or by suitable means capable of producing automatic reclosing of the main circuit breaker. This closing control switch 110 is connected in a circuit 111 that extends from the positive terminal of the control voltage source, through the closing control switch 119, an anti-pump device 112, a [2 switch 114 sensitive to position of the breaker, and the coil of the motor starting relay 100 to the negative terminal of the control voltage source. When the closing control switch 110 is closed, it completes this energizing circuit 111, thereby picking up the motor relay 1% and initiating motor operation. The motor begins the breaker closing operation and as the breaker approaches closed position, the b switch 114 opens, interrupting this operation-initiating circuit 111 and dropping out the motor relay 100. The motor operation continues, however, because the sealin circuit through limit switch 56 is then closed. When the motor has completely closed the breaker, the limit switches 56 and 106 open to deenergize the motor, as previously described.

The anti-pump device 112 serves to prevent inadvertent repetitive closing operations should the closing control switch 110 be held closed when the breaker trips open upon being closed on a fault. This device 112 serves to maintain the closure-initiating circuit 111 open after it has produced one circuit breaker closing, so long as the closing control switch lit) is held closed. This anti-pump device 112 may be of any suitable conventional form, such as, for example, that shown in US. Patent 2,381,336,

Coggeshall, assigned to the assignee of the present invention.

In some applications of my operating mechanism, it may happen that if the dashpot reset spring 68 is heavy enough to effect the desired high speed resetting of the piston 64 to its uppermost position after being released, then such spring would also be heavy enough to slowly rotate the auxiliary cam 62 and the other mechanisms 40, 52, Sit back toward its dotted line position of FIG. 3 after completion of a braking operation. An undesirable condition could result from allowing this reverse rotation to carry the cam 40 completely into the dotted line position of FIG. 3 inasmuch as resetting of the linkage L could be hampered by the presence of the cam 40 in the dotted line position of FIG. 3. My mechanism is arranged to prevent this condition from occurring by reason of the fact that upward motion of the dashpot piston 64 is blocked by the stop 69 substantially ahead of the point that the piston 64 would be required to reach in order to completely return the cam 40 to its dotted line position. When the piston 64 reaches the stop 69, the cam 44) still has not reached a position where it could interfere with resetting of the linkage L should such resetting be required. Additionally, when the piston 64 reaches the stop 6%, the control cam Hi7 still has not reached a position that would permit closing of the motor control switch 56. Closing of this control switch 56 under these conditions is desirably avoided since such closing could lead to an undesirable hunting condition.

Although in the illustrated mechanism the motor cutoff switch 56 is arranged to deenergize the closing motor 50 at about the time the closing stroke is completed, it is to be understood that this switch could be arranged to deenergize the motor considerably ahead of this point, with reliance being placed on the relatively great inertia of the motor 50 and reduction gearing 52 to carry the circuit breaker through its complete stroke. Thus, in a modified embodiment of my invention, the cut-off switch 56 is opened ahead of the point in the closing stroke at which a prestrike could occur between the main contacts 16, 12 of the breaker when closing on a fault. The inertia of the moving parts of motor 59 and gearing 52 is sufiicient to complete the closing stroke, even against heavy short circuit currents. Arranging the cut-off switch 56 to operate at this earlier point in the closing stroke provides even further assurance that the dashpot reset spring 68 will not accidentally cause reclosing of the switch 56 as a result of its above-described tendency to produce reverse rotation after the braking operation.

The fact that my braking scheme requires no electrical control power for its proper operation is another highly desirable feature. In this regard, should electrical control power he lost during a closing operation, the brake would still be capable of acting in its intended manner. With regard to the operation of motor 50 under such conditions the inertia of the parts connected to the cam 40 is high enough to assure successful completion of a closing operation should control power be lost during the latter stages of the closing operation. Thus, even if electrical control power would be so lost, successful completion of the closing operation and subsequent braking in the desired manner would still occur.

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. A circuit breaker operating mechanism comprising a linkage for transmitting force for closing said circuit breaker, means including a rotatable main cam for trans mitting circuit-breaker closing force to said linkage, mo-

tor means operable upon energization to supply closing force to said rotatable main cam, means for deenergizing said motor means upon movement of said main cam into a predetermined position following initiation of a circuitbreaker closing operation, an auxiliary cam mechanically coupled to said main cam for rotation at the same angular speed as said main cam, a liquidcontaining dashpot having a reciprocable piston that is retarded by said liquid during motion in one direction, means for causing rotary motion of said auxiliary cam to drive said dashpot piston in its direction of retarded motion during travel of said auxiliary cam occurring after deenergization of said motor means and after closing of said circuit breaker is completed whereby to dissipate the kinetic energy stored in said motor means and stop said main cam in a terminal position, and means for causing said motor means to produce reclosing of said circuit breaker by driving said main cam through continued rotary motion past said terminal position into said predetermined position, said dashpot piston being free from driven relationship with said auxiliary cam during the major portion of movement of said main cam between said terminal position and said predetermined position.

2. The operating mechanism of claim 1 in which said piston has a normal initial position that it occupies when said main cam passes through a preselected position at which closing of said circuit breaker is completed and in which means is provided for resetting said piston to said normal initial position during a closing operation, said piston-resetting means acting essentially independently of said auxiliary cam once said dashpot piston is released from driven relationship with said auxiliary cam, said piston being essentially unretarded during piston-resetting movement to enable said resetting means to restore said piston substantially to said initial position by the time said main cam enters said preselected position at which closing is completed.

3. The operating mechanism of claim 1 in which said main cam is so shaped that no substantial closing force is applied to said linkage during predetermined initial travel upon energization of said motor means, said predetermined initial travel acting to release said dashpot piston from driven relationship with said auxiliary cam and being sufliciently extensive to drive said auxiliary cam into a position wherein said dashpot is ineffective to retard continued rotary motion of said main cam until said main cam has driven said linkage substantially into the circuit-breaker closed position.

4. The operating mechanism of claim 1 in which said main cam is so shaped that no substantial closing force is applied to said linkage during predetermined initial travel upon energization of said motor means, said predetermined initial travel acting to release said dashpot piston from driven relationship with said auxiliary cam and being sufiiciently extensive to drive said auxiliary cam into a position wherein said dashpot is ineffective to retard continued rotary motion of said main cam until sai dmain cam has driven said linkage substantially into the circuit-breaker closed position, said predetermined initial travel also being sufficiently extensive to allow said motor means to drive said main cam a substantial distance past the point at which said dashpot becomes ineffective to retard said main cam.

5. The operating mechanism of claim 1 in which said piston has a normal initial position that it occupies when braking is initiated; in which resetting means is provided for returning said piston to said normal initial positon during a closing operation, said resetting means tending after a braking operation and before a subsequent closing operation to return said main cam toward a position in which said main cam could interfere with resetting of said linkage to a thrust-transmitting condition after an opening operation; and in which means is provided for blocking return movement of said main cam into said interfering position.

6. A circuit breaker operating mechanism comprising a linkage for transmitting force for closing said circuit breaker, means including a rotatable main cam for trans mitting circuit breaker closing force to said linkage, motor means adapted to be energized from a source of voltage that is subject to variations between predetermined minimum and maximum values, means for transmitting closing power from said motor means to said main cam, means for deenergizing said motor means after initiation of a closing operation and upon movement of said main cam into a predetermined position, an auxiliary cam mechanically coupled to said main cam for rotation at the same angular speed as said main cam, a liquid-containing dashpot having a reciprocal piston that is retarded by said liquid during motion in one direction, means for causing rotary motion of said auxiliary cam to drive said dashpot piston in its direction of retarded motion during travel of said auxiliary cam occurring after said main cam has driven said linkage into the circuit-breaker closed position whereby to dissipate the kinetic energy stored in said motor means and stop said main cam, said auxiliary cam being so shaped that said dashpot continues to oppose rotary motion of said main cam until said ro tary motion is terminated even when said circuit breaker is closed against no electrical load with said maximum value of voltage on said motor means and means for causing said motor means to produce reclosing of said circuit breaker by driving said main cam through continued rotary motion past said terminal position into said predetermined position, said dashpot piston being free from driven relationship with said auxiliary cam during the major portion of movement of said main cam between said terminal position and said predetermined position.

7. The operating mechanism of claim 6 in which the maximum braking torque applied by said dashpot to said main cam is less than the maximum torque that said motor applies to said cam when closing under maximum voltage conditions on a deenergized power line.

References Cited in the file of this patent UNITED STATES PATENTS 1,376,436 Hipple May 3, 1921 2,053,961 Linde Sept. 8, 1936 2,307,567 Coggeshall et al. Jan. 5, 1943 2,361,739 Bobst Oct. 31, 1944 2,680,164 Lennox June 1, 1954 2,895,570 Kury July 21, 1959 2,920,607 Barkan Jan. 12, 1960

Claims

1. A CIRCUIT BREAKER OPERATING MECHANISM COMPRISING A LINKAGE FOR TRANSMITTING FORCE FOR CLOSING SAID CIRCUIT BREAKER, MEANS INCLUDING A ROTATABLE MAIN CAM FOR TRANSMITTING CIRCUIT-BREAKER CLOSING FORCE TO SAID LINKAGE, MOTOR MEANS OPERABLE UPON ENERGIZATION TO SUPPLY CLOSING FORCE TO SAID ROTATABLE MAIN CAM, MEANS FOR DEENERGIZING SAID MOTOR MEANS UPON MOVEMENT OF SAID MAIN CAM INTO A PREDETERMINED POSITION FOLLOWING INITIATION OF A CIRCUITBREAKER CLOSING OPERATION, AN AUXILIARY CAM MECHANICALLY COUPLED TO SAID MAIN CAM FOR ROTATION AT THE SAME ANGULAR SPEED AS SAID MAIN CAM, A LIQUID-CONTAINING DASHPOT HAVING A RECIPROCABLE PISTON THAT IS RETARDED BY SAID LIQUID DURING MOTION IN ONE DIRECTION, MEANS FOR CAUSING ROTARY MOTION OF SAID AUXILIARY CAM TO DRIVE SAID DASHPOT PISTON IN ITS DIRECTION OF RETARDED MOTION DURING TRAVEL OF SAID AUXILIARY CAM OCCURRING AFTER DEENERGIZATION OF SAID MOTOR MEANS AND AFTER CLOSING OF SAID CIRCUIT BREAKER IS COMPLETED WHEREBY TO DISSIPATE THE KINETIC ENERGY STORED IN SAID MOTOR MEANS AND STOP SAID MAIN CAM IN A TERMINAL POSITION, AND MEANS FOR CAUSING SAID MOTOR MEANS TO PRODUCE RECLOSING OF SAID CIRCUIT BREAKER BY DRIVING SAID