US3546641A

US3546641A - Electric circuit breakers

Info

Publication number: US3546641A
Application number: US707536A
Authority: US
Inventors: Alan Twemlow Freeman
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1967-03-09
Filing date: 1968-02-23
Publication date: 1970-12-08
Anticipated expiration: 1987-12-08
Also published as: ES351371A1; NL6803145A; GB1145959A; BE711942A; FR1555375A; DE1613974A1; SE326751B

Description

' D A. T. FREEMAN 3,545,641

ELECTRIC F CI RCU'IT BREAK RR R Filed Feb. 23, 1968 2 Sheers-Sheet l D .'1970 I A. T. FREEMAN 3,546,641

' ELECTRIC CIRCUIT BREAKERS Filed Feb. 23, 1968 z SheetsSheet z FIGB United States Patent US. Cl. 33516 13 Claims ABSTRACT OF THE DISCLOSURE An electric circuit breaker in which contact-separation is achieved by retracting one of a pair of co-operating contacts from the other by means of the force of repulsion between a conductive ring or disc and an electromagnetic coil in which a current is suddenly caused to flow in response to a trip signal, the retractable contact being mechanically connected to one of these members, preferably the ring or disc. Means for retaining the retractable contact in its retracted position and means for automatically releasing it on withdrawal of the other contact. A mechanical trip mechanism, responsive to the motion of the retractable contact, for initiating withdrawal of the other contact.

BACKGROUND OF THE INVENTION This invention relates to electric circuit breakers and is particularly, but not exclusively, applicable to socalled high speed circuit breakers whose purpose is to achieve contact separation as rapidly as possible on the occurrence of a trip signal, especially under overload or fault conditions, in order to be able to provide eflicient protection in high power, direct current, circuit applications.

An object of the invention is to provide in a circuit breaker means whereby contact separation may be achieved more rapidly and with less delay after the occurrence of a trip signal than is achievable by a known high speed circuit breaker, such as a high speed circuit breaker according to our British patent specification No. 934,210, in which a certain delay is inherent in the releasing of a mechanical latch in the operating mechanism and in which the acceleration of a movable contact away from a cooperating stationary contact is limited by the inertia of a relatively massive pivoted arm carrying the movable contact.

SUMMARY OF THE INVENTION The present invention makes use of the well-known principle that when a current is suddenly caused to flow in an electromagnetic coil a repulsive force will be exerted between the coil and a conductive ring or disc adjacent to and substantially coaxial with the coil.

According to one aspect of the present invention, in an electric circuit breaker comprising a pair of cooperating contacts one of the contacts of the pair is mechanically connected, for retraction from the other contact, to one member of a combination comprising an electromagnetic coil and conductive ring or disc which, on the occurrence of a trip signal in response to which a current is suddenly caused to flow in the coil, cooperate to repel one another and thereby exert an accelerating retraction force on the retractable contact. Preferably the member to which the retractable contact is connected is the ring or disc and the coil is restrained against movement, at least in the direction away from the ring or disc: this arrangement is conducive to fulfilling the desideratum of minimum inertia of parts connected to the retractable contact, as well as being more convenient for making electrical con- ICC nection to the coil, and will be assumed to subsist in order to facilitate the following description of certain other aspects of the invention.

It has been found that, if the ring or disc is subject to a restraining force inhibiting its movement away from the coil during a very short delay period corresponding to the inevitable time lag in the build up of electromag netic energy in the coil, the energy imparted to it will be many times greater than that which would be imparted to it if not so inhibited. Such restraint may be provided by applying to the ring or disc a biasing force which holds it against the coil and exceeds the opposing force on the ring or disc due to contact pressure exerted by the other contact. Such biasing force (provided it is not excessive) does not decrease the force available for accelerating the retractable contact, as might have been expected, but results in a manifold increase therein.

With the retractable contact arranged to move rectilinearly, which allows of a convenient arrangement with low inertia, a path for the current flowing through that contact under normal working conditions and during fault clearance is preferably provided by means of one or more sliding contacts.

Since the retraction force is transient the biasing force will return the contact to its closed-contact position unless means, such as a latch or toggle mechanism, is provided to retain it in a retracted position. The need for such means may be avoided by providing for withdrawal of the other contact of the pair from its closed-contact position prior to such return of the first-mentioned retractable contact; alternatively provision may be made both for such retention of said retractable contact and for withdrawal of the other contact in order to achieve further separation of the contacts. Withdrawal of the other contact may be initiated by a release mechanism which may be actuated by an electrical trip mechanism independently responsive to the trip signal or by a mechanical trip mechanism responsive to the motion of said retractable contact.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully understood, an embodiment thereof will now be described, by way of example, with reference to the accompanying drawings, in which FIG. 1 is a diagrammatic representation of a high speed electric circuit breaker in accordance with the invention and FIGS. 2 and 3 illustrate modifications thereof.

The circuit breaker represented by the drawings is of the kind previously mentioned with reference to our British patent specification No. 934,210 but with its stationary contact replaced by a retractable contact as hereinbefore defined. In the following description this contact, 2, will be referred to as the fast contact, while the normal movable contact 4 will be referred to as the slow contact.

The slow contact 4 is carried by a contact arm 6 which is pivoted at a fixed point 8 and has an operating mechanism 10, generally as described in said British patent specification, including a release mechanism constituted by a latch 12 which may be of the kind described in our British patent sepcification No. 849,658 with reference to FIG. 1 thereof but with the arm 14 carrying the-roller 16 inverted as shown in the present drawing. The latch 12 is releasable by the armature 17 of an electromagnetic trip mechanism 18 (responsive to an overload current in a connection 20 to the contact arm 6 via the pivot at 8) mechanically connected to the C-shaped catch 22 through the inermediary of a rod or wire 24.

In its closed posittion, as shown in the drawing, the slow contact 4 bears against the fast contact 2 which is secured coaxially to the end of a rod 26 slidably mounted in a stop 28 (fixed to the circuit breaker frame partly shown at 29) through which the rod passes. Beyond the stop, the rod passes through an electromagnetic coil 30 also fixed to the circuit breaker frame. To the other end of the rod 26 is secured, also coaxially, a copper ring 32 held as by a screw 34 and a clamping device 36. The clamping device has a flange 36A against which bears a spiral spring 38, the other end of which bears against a fixed abutment 40 on the circuit breaker frame. The spring may provide a force of, say, 150 lbs. pressing the fast contact to the left in the drawing, as shown by the arrow 42, against the coil 30. A main current connection 44 is connected to the fast contact 2 through the stop 28 and a plurality of radially spring loaded fingers 46 enabling the current path to be maintained while the contact 2 is retracted as will now be described.

The adjustment of the contacts and the closing mechanism are so arranged that the slow contact presses against the fast contact, as shown by the arrow 48, with a force which may be, say, 100 lbs. Thus there is a margin of, say, 50 lbs. for opposing movement of the fast contact, which takes place as follows in a preferred way of operating the circuit breaker.

An overload current, which will operate the electromagnetic trip mechanism 18 and thereby release the slow contact 4 by means of the latch12, also causes operation of sensitive quick-acting switching means S (such as a sensitive relay, thyratron or thyristor) which serves to discharge a previously charged capacitor C through the coil 30. The pressure of the spring 38 retains the ring 32 in close proximity to the coil until, after a time delay which may be less than 0.1 millisecond and is determined by the time constant of the LC circuit including the inductance of the coil 30 and the capacitance of the capacitor, a large repulsive force established between the coil and the ring causes the fast contact to move very rapidly away from the slow contact with an acceleration which may exceed l000G; thus there is little delay between the occurrence of the trip signal and the initial separation of the contacts and there is a high rate of increase of the distance between the contacts. The slow contact 4 initially attempts to follow the fast contact 2 under the force ap plied to it by the mechanism 10 but, owing to the inertia of the arm 6, it moves much more slowly than the fast contact. Before the slow contact has moved any appreciable distance and before the fast contact has returned from its excursion which may take milliseconds, the operating mechanism 10 (its latch 12 having been released by the trip mechanism 18) will have caused the slow contact 4 to move away from its closed position towards its open position so that contact is not re-established. The use of independent electrical trip means for the fast and slow contacts is feasible for interrupting rapidly rising fault currents, even though the trip settings may not be absolutely identical, because initiation of the retraction of the fast contact is followed by a period of arcing time during which current substantially in excess of the current level of the trip settings will continue to flow.

Contact erosion, due to wear or the effect of arcing known as burn (which would normally be accommodated by adjusting a fixed contact), is accommodated by the slow contact the closed position of which varies with such wear, since the repelling ring 32 connected to the fast contact must be maintained in its correct position relatively to the coil and with the correct pressure thereon.

The circuit breaker may incorporate a latch or toggle arrangement which engages the fast contact 2 (or one of the parts mechanically connected thereto) at the limit of its travel so as to prevent this contact returning to its normal position until the latch or toggle is released.

FIG. 2 shows such a latch arrangement in which the fast-contact rod 26 has an extension 26A which passes through the fixed abutment and through a conical hole 50A in another fixed member 50. This hole tapers in the direction of return motion of the rod, opposite to the direction (indicated by the arrow 52) of retraction of the fast contact. A ring of steel balls 54, surrounding the rod 26A and within the hole 50A, is pressed into the tapering aperture between the rod and the conical surface of the hole by a light spring 56. The rod 26A is free to move in the direction of the arrow 52 but will be gripped and held by the balls 54 as soon as it attempts to return in the opposite direction. This action will not be affected by any variation which may occur in the travel of the fast contact due, for example, to variation in the voltage to which the aforementioned capacitor is charged.

FIG. 2 also shows a means of releasing such a latch. The slow-contact arm 6, in moving to its contact-open position, strikes a pin 60 carried by a link 62 and thereby exerts a force in the link in the direction of the arrow 64. This force acts through a forked lever 66, pivoted at 68, to press a tubular member 70 against the ring of balls 54 in the direction to overcome the pressure of the spring 56. With the locking force of the balls 54 between the rod 26A and the fixed member 50 thereby removed, the retractable contact 2 is able to return to its closed-contact position.

Another feature with which the circuit breaker may be provided is a lever arrangement responsive to the motion of the fast contact 2 and arranged to trip the latch 12 of the slow contact mechanism at a predetermined point in the travel of the fast contact. This would enable the electromagnetic trip mechanism 18 itself to be dispensed with. Since the acceleration of the fast contact is very high, such lever mechanism would be subject to severe shock loading.

FIG. 3 shows such a lever arrangement comprising a forked lever pivoted at a fixed point 82. The forked end 80A of the lever (of which only one fork is shown in the cross-sectional drawing) is so shaped and positioned as to be acted upon, by the flange 36A against which the spring 38 bears, to rotate the lever clockwise (as indicated by the arrow 84) on retraction of the fast contact 2. The other end of the lever is coupled, by a Bowden cable 86 or other suitable means, to the slowcontact trip mechanism arm 17A which carries the armature 17, so that the rotation of the forked lever 80- will initiate release of the slow contact 4.

The discharging of the capacitor C is preferably achieved by means of a thyristor whose firing circuit PC is responsive to a signal representative of the value of current flowing in the main current circuit being controlled by the high speed circuit breaker, so that when the current exceeds a predetermined value the firing circuit produces a trigger pulse which fires the thyristor. With the circuit breaker controlling a direct current circuit, such signal may be the output of a D0. current transformer CT included in that circuit. The delay between the instant at which the main current reaches the trip value and the instant at which the thyristor is fired can be very short, typically less than one microsecond.

I claim:

1. An electric circuit breaker including a combination comprising an electromagnetic coil member and a conductive ring or disc member one of which members is repellably movable away from the other by sudden flow of current created in the coil member in response to a trip signal and a pair of co-operating circuit-breaking contacts one of which is mechanically connected to said one of said members, whereby consequently upon such flow of current said one contact will be subject to an accelerating retraction force for separating it from the other contact, including means for retaining the retractable contact in its retracted position on completion of retraction thereof, and wherein the retaining means comprises a rod connected to the retractable contact for movement therewith, a fixed apertured member having an inner surface defining a tapering aperture through which the rod extends and which tapers in the direction of movement of the rod accompanying return movement of the retractable contact to its closed-contact position, a ring of balls surrounding the rod and being so dimensioned as to be able to contact both the rod and said surface, and spring means urging the balls in said direction, the arrangement being such that when so urged the balls will co-operate with the rod and said surface to oppose movement of the rod in said direction, and wherein the release means comprises means for so urging the balls in the opposite direction to overcome the etfect of said spring means.

2. An electric circuit breaker, including, in combination: an electromagnetic coil member and a conductive ring or disc member, one of said member being repellably movable away from the other of said members by sudden flow of current created in the coil member, a pair of co-operating circuit breaking contacts one of which is retractable and is mechanically connected to said movable one of said members, a main source of current electrically connected to each of said contacts and flowing through said contacts when said contacts are closed, a trip signal source of current electrically connected to said coil member and to said main current source and adapted to create a sudden flow of current in said coil in response to undesirable variations in said main current source, whereby consequently upon such sudden flow of current in said coil said one mechanically connected contact is subjected to an accelerating retraction force for separating it from the other contact, including means connected to said other contact for withdrawing the other contact from its closed-contact position and means for actuating said withdrawing means in response to said undesirable variations and after commencement of retraction of the retractable contact.

3. A circuit breaker as claimed in claim 2, and including means for retaining the retractable contact in its retracted position on completion of such retraction thereof.

4. A circuit breaker as claimed in claim 2, wherein the circuit breaker includes automatic release means for releasing the retaining means in response to movement of said other contact on such withdrawal thereof.

5. A circuit breaker as claimed in claim 1, wherein means are incorporated for withdrawing the other con tact from its closed-contact position and automatic release means for releasing the retaining means in response to movement of said other contact on such withdrawal thereof, the release means comprising a tubular member surrounding the rod and capable of being urged against the balls in said opposite direction, pivotally mounted lever means for so urging the tubular member, and link means for transmitting to the lever means movement imparted to the link means by said other contact on withdrawal thereof, the movement being such as to cause such urging of the balls as to overcome the effect of said spring means.

6. The combination claimed in claim 5, wherein means are included for Withdrawing the other contact.

7. A circuit breaker as claimed in claim 6 including a mechanical trip mechanism, said mechanism responsive to the motion of the retractable contact on retraction thereof, and means for initiating the action of the withdrawing means.

8. The combination as claimed in claim 2, wherein there is included a trip mechanism operatively connected to said withdrawing means to initiate the action of the said withdrawing means before the return of said retractable contact to its closed-contact position.

9. The combination claimed in claim 8, wherein the said trip mechanism includes an electrical trip mechanism electrically connected to said trip signal source and a mechanical trip mechanism mechanically responsive to the motion of said retractable contact on retraction thereof, and wherein the electrical and mechanical trip mechanisms include a common lever for transmitting their initiating etfect to the withdrawing means.

10. The combination of claim 2 wherein the retractable contact moves rectilinearly.

11. The combination of claim 10 wherein there is included in cooperative electrical relation one or more sliding contacts, a stationary conductive member electrically connected to said one or more sliding contacts, said contacts providing an electrical connection between said retractable contact and said stationary conductive member.

12. The combination of claim 2 and including time delay circuit means electrically connected to said trip signal source and said coil and means for subjecting said movable member to a restraining force inhibiting movement thereof during the delay period of said time delay means.

13. The combination of claim 12 and wherein further first means are provided for forcing said withdrawable contact against said retractable contact and second means for forcing said retractable contact against said withdrawable contact, said second forcing means exceeding said first forcing means by an amount equal to said restraining force.

References Cited UNITED STATES PATENTS 1,818,801 8/1931 Herden 335-192 2,486,104 10/1949 Bohn 335-14 3,127,488 3/1964 Bodenschatz 335-174 3,178,533 4/1965 Lory 335-174 3,215,798 11/1965 Kesselring 335-38 3,384,845 5/1968 Johnson 335-16 FOREIGN PATENTS 740,568 1/1933 France 35-16 BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner US. Cl. X.R. 317-11