US2331740A - Circuit breaker - Google Patents

Description

Oct. 12, 1943. w I H T AL 2,331,740

CIRCUIT BREAKER Filed Jan. 13, 1943 I, 46 2a a 15 47 43 211i fi l7 59m e k j w F at ,9 &\\\\\\\\\\\\\\\\\\\\\\\ 0 l L I Q l' z [43/ W um i\\\\\\' ,9

In ventors: Robert W. Smith, Joseph W Seaman,

b3 JV fJ TheiZ Attorne s.

v Patented Oct. 12, 1943 CIRCUIT panama Robert W. Smith, Aidan, and Joseph W. Seaman, Thornton, Pa., assignors to General Electric Company, a corporation or New York Application January 13, 1943, sci-n1 No. 412,226

(01. zoo-as) 9 Claims.

Our invention relates to circuit breakers or relays, more particularly to alternating current responsive trip means for circuit breakers, and has for its object simple and reliable tripping means which is responsive instantly to a shortcircuit current to trip the breaker but responsive to lower currents in accordance with an inverse time relation.

More specifically, our invention has for its ob- Ject a breaker tripping means or relay which is not only instantly responsive to currents of shortcircuit magnitude, but also is responsive to excessive load currents after a time interval during which the temperature of the protected lines or electric apparatus approaches their maximum safe operating temperatures whereby the unnecessary interruption of continuity of service is avoided.

In carrying out our invention in one form, we provide a current responsive electromagnet whose armature is normally held in an unattracted position by means of a floating arm, one point of which is held by springs to be compressed by the attractedarmature in the event 01 a short-circuit current, and another point of which is held by a time delay overcurrent responsive device and released in inverse time relation to the magnitude of the overcurrent. Thus one point or the other of the floating arm moves in the event of an overcurrent to provide for movement of the armature to its attracted position and operation by the armature of the circuit breaker tripping means.

For a more complete understanding of our invention, reference should be had to the accompanying drawing, Fig. 1 of which is a side elevation view with the cover removed of a circuit breaker tripping device embodying our invention; Fig. 2 is a sectional view along the line 2-2 of Fig. 1 looking in the direction of the arrows; Fig. 3 is a simplified view in perspective oi the device shown in Figs. 1 and 2; Fig. 4 is a diagrammatic view showing tripping means embodying my invention applied to a circuit breaker; while Figs. 5 and 6 are fragmentary views showing details of construction.

Referring to the drawing, in one form of o invention we provide a current responsive electromagnetic operating device comprising a U- shaped magnet core ll) having a current coil I i surrounding its central leg and an armature l2 so that the coil ii is responsive to the current flowing through the circuit breaker.

The armature l2 has enough force exerted on it by a comparatively low current in the coil II to pull the armature to its attracted position so that under all conditions of either very light overcurrent or short circuit current the armature is biased to its attracted position by the magnetic force. It is prevented normally from moving to its attracted position by afloating arm I! having a pin ll which extends across and in front of the armature and which is engaged by the armature through a flexible or spring connection. As shown clearly in Fig. 3, the floating pivoted at its lower end on the lower leg of the arm i3 is made up of two parallel side members in and lib which are connected together rigidly by three cross members consisting oi the rod or pin it intermediate its ends, a top rod l5 and a bottom strip l6. This floating arm is supported pivotally at one point, as shown its upper end, on the rod it the ends of which project at each side beyond the members Ito and lit) to form pivots l1 and it which lie respectively on bearing surfaces (not shown) provided for them in opposite sides of the supporting casing ll. These bearing surfaces for the pivots l1 and II extend in a horizontal direction, as seen in Fig. 1, to provide for movement horizontally of the pivots, and hence horizontal movement of the upper end of the floating arm it toward the left hand, as seen in Fig. 1, against compression springs 20 and 2041 thereby to permit the armature II to move to its attracted position. The bearing surfaces for the pivots l1 and is may be provided by the lower walls of horizontal slots in opposite sides of the supporting casing. This movement of the upper end of the floating arm ll occurs only in response to very heavy overcurrent, such as a current of short circuit magnitude, which applies an attractive force to the armature l2 sumcient to compress the springs 20 and 20a.

For the purpose of interrupting electrically the short-circul-ted loops formed by the two side members and the three cross members forming the floating arm ii, the rod I4 is provided at one end with a cylindrical electric insulator Ila which insulates that end of the rod ll from the a side member lib. This, it will be-observed, open circuits the two otherwise electrically closed loops through which the magnetic flux passes or interlinks in passing through the armature II. The

magnetic induction of electric currents in these mechanically closed circuits is thereby prevented.

Secured to the armature I2 is a bracket 2| projecting from a suitable aperture (not shown) ment of the arm about its pivots I1 and an adjusting screw 30 end a cross bar in the casing and carrying on its upper end an adjustable trip pin 22 in position to engage a trip arm 23 secured to a trip shaft 24. Thus when the armature is attracted, the shaft 24 is turned in a counterclockwise direction, as seen in Fig. 1, thereby to trip open the circuit breaker. Obviously, the armature may be arranged to operate various types oi circuit breaker tripping mechanism other than the shaft 24. We particularly contemplate using our device to operate a trip shaft such, for example, as provided in the circuit breaker described and claimed in Patent 2,152,453, issued on March 28, 1939, to Winfield A. Atwood and George Rudolph. Thus the shaft 24 and arm 23 are the shaft 26 and the arm 36 of the Atwood and Rudolph patent.

At another point, as shown it lower end, the floating arm l3 normally is secured by a latch 25, one end of which is in abutting engagement with the cross bar l6 and the other end of which is mounted on a pivot pin 26. Preferably as shown, as a further prevention of chattering, a spring strip 25a (Figs. 1 and is secured to the strip IS in spaced relation therewith and in such position that the middle of the strip 25a engages the end of the latch 25. The latch 25 is moved downward out of engagement with the bar I6, thereby to release the lower end of the arm l3, in response to over currents of low'small magnitude in inverse time relation with the magnitude of the current. Thus this release of the lower end of the arm l3 permits pivotal move- I8 thereby to allow the armature to move to its attracted position and trip the circuit breaker.

For moving the latch 25, a straight bimetallic strip thermostat 21 is provided having its lefthand end pivotally mounted on the pivot pin 26 by means of an arm 28 mounted on the pin 26 and extending upward, as seen in Fig. 1, where the thermostat is rigidly secured to it as by rivets or by a brazed or welded joint. Secured to the arm 28 is a trip projection 29 which extends over carried by the latch 25. the latch 25 includes at its left-hand 3| and two parallel projections 32 and 33 which are pivoted at their ends on the pin 26. Y

The opposite or right-hand end of the thermostat 21 bears against a rotatable cam 34 mounted on a shaft 35 extending through the casing l9 and having on it outer end an adjustment handle or knob 36. A helical compression spring 31 supported by the casing I9 is provided for forcing the end of the thermostat upward against the lower edge of the cam 34. By turning the came 34 by means of the knob 36, the position of the end of the thermostat can be varied in a vertical direction, as seen in the drawing, thereby to adjust the amount of flexing of the thermostat required to move the latch 25 downward out of engagement with the arm 13.

For the purpose of heating the thermostat 21 in response to the current in the coil l l and hence the current in the circuit breaker, a secondary winding 38, shown as a single turn or loop, is provided on the magnet core l0, encircling the lower leg of the core. This winding 38 as shown is made of a suitable electrically conducting material, such as copper, in the form of a strap or strip bent into a rectangle with its ends electrically connected with each other so as to form As shown,

a single turn short-circuited secondary winding;

At its lower side the winding 38 is connected to the thermostat in good thermal relation therewith as by a brazed or welded joint, In the operation of the device, a voltage is induced in the secondary winding 38 which voltage produces a current in the winding proportional to the current in the coil ll whereby the winding is heated and transmits heat by conduction, radiation and convention to the thermostat 21.

Preferably the two ends of the strap forming the winding 38 are separately brazed or welded to the bimetallic thermostat 21 in spaced relation with each other so that a portion of the thermostat itself is included in the electric circuit of the winding, as described and claimed in a copending application of Charles H. Titus, Serial No. 485,491, filed May 3, 1943, and assigned to the same assignee as this application. Thus, as seen in Fig. 2, the two ends 38a and 38b of the strap 38 are secured to the bimetallic strip 21 in abutting spaced relation with each other so as to be electrically connected together through the portion of the thermostat between the ends in the electric circuit of the secondary winding. This has the advantage of more efiiciently heating the thermostat by generating at least a portion of the heat directly in the thermostat itself, the material of which has a higher electrical resistivity than the material of the strap 38. Also, by varying the spacing between the ends of the strap and thereby varying the rate of heat generation in the thermostat itself, the time response of the thermostat can be varied to suit the apparatu to be protected.

The thermostat, moreover, forms a support for the secondary coil 38 and the coil moves with the thermostat upon flexing of the thermostat. To provide for this movement, the coil is rectangular in shape, as shown, so as to conform to the rectangular outline of the core leg which it surrounds, and it i considerably larger than the core leg so as to leave space for movement oi the secondary coil relative to the core leg. The.

thermostat 21 extends in substantial parallel relation with the lower leg of the core I0, while the coil 38 is at right angles with the thermostat and core leg.

In the operation of the device, an overcurrent greater than a predetermined current in the coil l l induces enough voltage in the secondary winding 38 to drive a current therethrough that will heat it and thereby heat the thermostat. Thus with a relatively small overcurrent the rate of heat generation in the secondary winding is correspondingly low, and with a relatively large overcurrent correspondingly high thereby to heat the thermostat to a predetermined operatingtemperature in time intervals having an inverse relation to the current in the coil ll. As the thermostat becomes heated, its central portion moves downward, the thermostat flexing into a bowed shape. This bowing downward of the middle of the thermostat rotates the supporting arm 28 for the thermostat slightly in a clockwise direction, as seen in Fig. 1, about the pivot 26 whereby the arm 29 is moved downward and moves the latch 25 downward out of engagement with the cross member 16 after the elapse of the required interval of time for the heating of the thermostat to a predetermined temperature. It will be observed that the secondary winding 38 is secured to an intermediate point of the thermostat so that heat is transmitted fromthe secondary directly to a flexing portion of the thermostat.

By means of a helical tension spring 40, the floating arm I3 is given a bias in a counterclockwise direction about its supporting pivots I1 and I8. The lower end of the spring is connected to an arm 4| secured to the lower end of the floating arm I3 while the upper end of the spring is secured adjustably to the casing or support I9. This spring provides for automatic reset of the floating arm I3 after the circuit breaker has opened automatically in which case the coil II is deenergized and the armature I2 is released from the magnet ID. The spring 40 then moves the lower end of the arm I3 back to the position shown in the drawing so that when the thermostat cools, the latch 25 returns to its latching position behind the bar l6. A spring 42 is provided for biasing the latch 25 upward to this position as the thermostat cools and thereby maintaining the screw 36 in engagement with the arm 29.

Additional supporting and guiding means for the upper end of the floating arm I3 is provided by means of pins or plungers 43 and 44 secured to the cross bar I and slidably fitting into tubular supports 45 and 46. These supports 45 and 46 bear at their left-hand ends as shown against the inner side of the supporting casing. They carry ring seats 41 and 48 for the ends of the springs and 20a.

The cross bar I4 lies in a large notch 49 provided in the armature, and for the purpose of preventing humming or chattering a resilient connection is provided between the bar I4 and the armature. This connection consists of two spring plates 50 and 50a (Fig. 6) between which the cross bar I4 is clamped. The spring plates are secured to the armature by means of two bolts 5| passing through them and through the armature, a helical compression spring 5Ia being provided around each of the bolts between the two plates. Also, a shoulder 5Ib is provided in the bottom of the notch against which the lower ends of the two plates are clamped by the bolts. Thus by turning up the nuts on the bolts the compression springs are compressed and the two plates are drawn together in frictional engagement with the cross bar I4. Also, preferably, to cushion the movement of the armature a layer of resilient material 5Ic is inserted between the free end of the plate 50a and the adjacent surface of the armature, space for this layer being provided by the shoulder 5Ib. This resilient layer may be made of rubber, leather or felt, but preferably it is made of leather.

A chatter-free pivot mounting is provided for the lower end of the armature consisting of a spring strip 52 having its ends secured as by rivets and screws respectively to the end of the core and the lower end of the armature thereby to secure the'lower end of the armature to the core in a predetermined spaced relation therewith. This spring strip is furthermore connected as shown to the lower end of the armature in such manner as to bias the armature to its unattracted position in which an adjustable stop 52a carried by the armature engages the casing I9.

Referring to Fig. 4, the switch or circuit breaker may comprise a switch arm 53 movable between its open and closed circuit positions by means of a coil 54 connected to toggle links 55 and 56. As shown, the toggle links are held in their nearly straightened or made position by energization of the coil 54 whereby the circuit breaker is held closed. Upon the occurrence of an overcurrent or short circuit, the shaft 24 in rotating releases a latch arm 51 which in turn releases a link 56 connected to the outer end of the link 55. Thus the links 55 and 56 are free to move toward the left to allow the switch arm 53 to open in accordance with its bias. If the 5 coil 54 is now deenergized, the link 58 and latch arm 51 are returned by their weight or by a biasing spring (not shown) to the position shown ready to be secured by the shaft 24.

An extension arm 59 is provided on the arm 26 for operation to its closed position of a suitable signal switch 60, this switch being closed to close a circuit for operation of a signal 6 I, Fig. 4, shown as a bell just before the thermostat flexes sufflciently to release the floating arm I3. This operation of the bell before the breaker is tripped open gives an indication of an overload condition before the breaker is opened. If the overload decreases the thermostat cools and the switch 60 opens.

The switch 60 is a suitable snap action switch biased to its open circuit position and operable between its open and closed positions by a small amount of movement by means of an operating arm 62 connected to the arm 59. A suitable switch for this purpose is described and claimed in Patent No. 2,230,720 issued on February 4,

1941 to Samuel F. Jarvis. As shown, this switch 60 is mounted on the outside of the casing I9 on a suitable pivot 63. The switch contacts are mounted in a rectangular casing 64 of electrically insulating material to one side of which is secured an arm 65. The pivot pin 63 is secured to this arm and extends into a suitable pivot bearing aperture in the casing I9. A tension spring 66 connected between the end of the arm 65 and a lug 61 secured to the outside of the casing biases the switch downward against an adjustable stop screw 66. Thus when the thermostat flexes upon an increase in temperature, the end of the arm 62 moves upward and engages a suitable operating button (not shown) for the switch extending through the casing 64 thereby to operate the switch to its closed circuit position. The spring 66, after closure of the switch, yields to provide for pivotal movement of this switch and casing 64 about the pivot 63 in the event of continued deflection of the thermostat 21 to release the floating arm I3 after the switch ha been operated. When the thermostat cools and releases it, the switch snaps in accordance with its bias back to its open circuit position.

While we have shown a particular embodiment of our invention, it will be understood, of course, that w do not wish to be limited thereto since many modifications may be made, and we therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of our invention.

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

1. An overcurrent responsive release mechanism for circuit breakers comprising a current coil, an armature for said coil, release means operated by movement of said armature, a floating arm connected to said armature for normally restraining said armature, time delay current responsive means normally pivotally securing a first point of said arm against movement by said armature but releasing said first point after a time interval in response to a predetermined current in said coil for pivotal movement of said arm by said armature about a second point of said arm, and means mounting said second point of said arm for movement about said first point by said armature in response to a predetermined high current in said coil.

2. An overcurrent responsive release mechanism for circuit breakers comprising a magnet core member, a current coil on said core member, an armature for said core member, release means operated by movement of said armature, a floating arm connected to said armature for normally restraining said armature, a latch normally pivotally securing a first point of said arm against movement by said armature, a thermostat connected to said latch, a Secondary winding surrounding a leg of said core member for inducing current for heating said thermostat in response to a predetermined overcurrent in said current co-il thereby to cause said thermostat to move said latch and release said first point for pivotal movement of said arm by said armature about a second point of said arm, and means mounting said second point of said arm for movement about said first point by said armature in response to a predetermined high current in said coil.

3. An overcurrent responsive release mechanism for circuit breakers comprising a. magnet core member, a current coil on said core member, an armature for said core member, release means operated by movement of said armature to its attracted position, a floating arm having an intermediate point pivotally connected to said armature, thermal current responsive means normally securing one end of said arm against movement by said armature but releasing it in response to a predetermined current in said coil for pivotal movement about its other end, and means mounting said other end of said arm for instantaneous pivotal movement about said one end by said armature in response to a predetermined higher current in said coil.

4. An overcurrent responsive release mechanism for circuit breakers comprising a magnet core member, a. current coil on said core member, an armature for said core member, release means operated by movement of said armature to its attracted position, a floating arm having an intermediate point pivotally connected to said armature, latch means normally securing one end of said floating arm against movement by said armature, a bimetallic thermostat operating when heated to move said latch means to release said floating arm, a secondary winding surrounding a leg of said core member and mounted on said thermostat in good thermal relation therewith for producing heating currents for said thermostat, and means mounting said other end of said floating arm for instantaneou pivotal movement about said one end by said armature in response to a predetermined high current in said coil.

5. Current responsive switch release means comprising a magnet core member, a current coil on said core member, an armature for said core member biased away from said core member to an unattracted position and movable toward said core memberto an attracted position in response to a predetermined low value of current in said coil, switch release means operated by said armature, a floating arm extending lengthwise of said armature, a connection between intermediate points of said armature and said arm, means responsive to the current in said coil normally holding one end of said arm to prevent movement of said armature to its attracted position but releasing said arm for pivotal movement about its other end in response to a predetermined low overcurrent, and resilient means holding said other end of said arm normally in a predetermined position but yielding in response to a predetermined high overcurrent in said'coil to permit pivotal movement of said arm about said first end and movement of said armature to said attracted position.

6. The combination with an electric switch provided with a. latch for holding the switch in a closed circuit position of current responsive means for moving said latch to release said switch comprising a magnet core member, a coil on said core member connected in an electric circuit with said switch, an armature for said core member biased away from said core member to an unattracted position and movable toward said core member to an attracted position in response to a predetermined low overcurrent in said coil, means operated by said armature for moving said latch to release said switch when the armature is moved to its attracted position, a floating arm extending lengthwise of said armature, a connection between intermediate points of said armature and said arm, thermal means responsive to the current in said coil normally holding one end oi said arm to prevent movement of said armature to its attracted position but releasing said arm for pivotal movement about its other end in response to an overcurrent at least as great as said predetermined current, and resilient pivotal supporting means for the other end of said arm yielding in response to a higher current in said coil to permit pivotal movement of said arm about said first end and movement of said armature to said attracted position.

7. The combination with an electric switch provided with a latch for holding the switch in a closed circuit position, of overcurrent responsive mechanism for moving said latch to release said switch comprising a magnet core member, a coil on said core member connected in an electric cir cuit with said switch, an armature for said core member biased away from said core member toan unattracted position and movable toward said core member to an attracted position in response to energization of said coil, means operated by said armature for moving said latch to open said switch when said armature is moved to said attracted position, a floating arm extending lengthwise of said armature, a pivotal connection between said armature and an intermediate point of said arm, a pivot support for one end or said arm mounted for movement with said armature to its attracted position, a spring biasing said pivot support in the opposite direction to a. predetermined normal position said spring being overcome by said armature in response to a predetermined overcurrent in said coil to provide for movement of said armature to said attracted position, a pivoted second latch for normally holding the other end of said arm and forming a pivot for said arm upon said movement of said armature to its attracted position, a bimetallic strip thermostat having a first end connected to said second latch, an adjustable support for the other end of said thermostat, a single turn secondary winding on said core in thermal relation with said thermostat for heating said thermostat in response to the current in said coil whereby said first end of said thermostat turns said latch about its pivot to release said arm in response to a pre determined low overcurrent in said coil thereby to release said armature for movement to its attracted position to trip said switch.

8. An overload responsive release mechanism comprising a magnet core member, a current coil on said core member, a bimetallic thermostat, a secondary winding surrounding said core leg, a mechanical and thermal connection between said winding and said thermostat whereby said winding is supported by said thermostat, said winding being larger than said core leg to provide for freedom of movement of said winding with respect to said core leg upon fiexure of said thermostat, a pivot mounting for one end of said thermostat, means adjustably securing the other end of said thermostat against movement on said pivot mounting, and latch means moved to a released position by rotation of said pivot mounting in response to flexure of said thermostat.

9. An overload responsive release mechanism comprising a magnet core member, a current coil on said core member, a substantially straight bimetallic thermostat extending parallel with one leg of said core member, a single turn secondary loop surrounding said core leg made of a strap of electrically conducting material, a mechanical and thermal connection between one side of said loop and an intermediate point of said thermostat whereby said loop ls supported by said thermostat and said thermostat is heated by currents induced in said loop, said loop being stiff enough 'to be self-supporting on its Side secured to said I thermostat and said loop being larger than said core leg to provide for freedom of movement of said loop with respect to said core leg upon flexure of said thermostat, a pivot mounting for one

Images