GB2226451A - Limiting travel of circuit breaker operating lever - Google Patents

Abstract

Apparatus contacting the handle arm 62 of a circuit breaker when moveable contact(s) 19 of the circuit breaker is welded to its fixed contact thereby preventing operating lever 62 from being moved to the full off position comprises a lock 70 elevated by a cam 72 when the moveable contacts are in the closed position. If operating lever 62 is moved towards the off position, a locking surface 74 of a handle arm 75 which is connected to lever 72 engages a projecting member 76 of lock 70 thereby preventing the handle arm 75 and thus operating lever 62 from advancing to the full off position. This prevents operating lever 62 from falsely assuming the off position when the contacts of the circuit breaker are closed and also provides a visual indication of the closed contact condition. <IMAGE>

Description

APPARATUS FOR LIMITING THE TRAVEL OF A CIRCUIT BREAKER OPERATING LEVER Backaround of the Invention Field of the Invention This invention relates to electrical circuit breakers and, more particularly, to electrical circuit breakers which incorporate apparatus for directly contacting the handle arm of the breaker and restricting the travel of the operating handle when the contacts of the circuit breaker are closed.

Description of the Prior Art Electrical circuit breakers have been employed for many years. Typically, they are serially connected between an electrical power source and an electrical circuit to interrupt the flow of current in the electrical circuit when the electrical circuit is experiencing an overcurrent condition wherein the circuit is carrying excessive currents for prescribed periods of time. An operating mechanism is employed to trip open separable electrical contacts within the circuit breaker during such overcurrent conditions thereby stopping current flow through the electrical circuit.

The operating mechanisms of circuit breakers employ a manual operating device which enables a person to open and close the contacts of the circuit breaker as desired. Such manual operating devices are rendered inactive when the circuit breaker has tripped due to an electrical circuit overcurrent condition, thereby preventing the person from reclosing the contacts of the circuit breaker until the overcurrent condition has subsided.

The operating mechanism is designed to rapidly move the separable contacts between the open and closed positions thereby preventing the moveable contact from stopping at any position which is intermediate the fully open or fully closed position. This accomplishes two purposes. First, when the contacts are quickly closed, the resultant force with which the moveable contact strikes the fixed contact helps to ensure good electrical conduction since impurities which may become positioned between the contacts, such as dust and dirt, are dislodged. Second, when the contacts are quickly .opened, the opportunity for electrical arcing between the fixed contact and the moveable contact is minimized since the contacts are quickly separated through an arc suppressor by a distance which is sufficient to suppress the arcing and open the electrical circuit.

The moveable electrical contact is designed not only to strike the fixed contact, when closed, but also to slide across the surface of the fixed contact. This sliding action further aids in dislodging impurities from between the contacts.

Despite the aforementioned features which are built into the circuit breaker to ensure good electrical conduction, small amounts of debris may, nevertheless, become interposed between the fixed contact and the moveable contact. Under such circumstances, the possibility exists that the fixed member of the contact will weld to the moveable contact thereby preventing the circuit breaker from opening either during an overcurrent condition or during manual operation. Contact welding may also occur if the circuit breaker mechanically fails, thereby reducing the force applied by the moveable contact to the fixed contact.

It is possible for one or more of the contacts of the circuit breaker to weld closed thereby preventing all of the contacts for all of the poles from opening when the circuit breaker is tripped or when the lever is moved to the off position. However, the operating lever of the circuit breaker may still be manually moved to the off position even when the electrical contacts are welded closed and, hence, the electrical circuit is energized.

This is because the moveable contacts are mechanically connected to the operating lever through biasing springs. By applying a force of enough magnitude, the lever may be moved to the off position by overcoming the biasing force of the springs.

This can create a dangerous condition if, for example, a person were to move the operating lever to the off position, thereby believing that the electrical contacts are open and that the electrical circuit is, therefore, de-energized when in actuality it is not. This has a disadvantage in that a person could attempt to manually access energized portions of the circuit and unexpectedly receive an electrical shock. It is an object of the present invention to reduce the risk of such occurrence by providing apparatus which mechanically limits the travel of the operating lever so that it may not be moved fully to the off position when the electrical contacts are closed, such as when they are welded.

Summarv of the Invention The present invention provides apparatus for limiting the travel of the operating lever of an electrical circuit breaker to a predetermined position which includes electrical contacts which may assume a closed position and an open position, an operating lever which may be moved between an on position and an off position and a handle arm which moves in unison with the operating lever. The apparatus includes lever lock apparatus for directly contacting the handle arm of the electrical circuit breaker and limiting the travel of the operating lever to a predetermined position intermediate the on position and the off position when the lever is moved from the on position toward the off position and the electrical contacts of the electrical circuit breaker are in the closed position.

An advantage lies in the fact that the apparatus of the present invention provides an effective means for preventing the operating lever of the circuit breaker from assuming the full off position, when one or more of the moveable contacts of the circuit breaker is welded to its respective fixed contact and for providing a positive visual indication that the contacts of the breaker are closed.

Brief Description of the Drawings The invention may be better understood and further advantages and uses thereof are readily apparent, when considered in view of the following detailed description of the preferred embodiment taken with the accompanying drawings in which: Fig. 1 is a sectional side elevational view of an electrical circuit breaker which incorporates the apparatus of the present invention; Fig. 2 is a front elevational view of the circuit breaker of Fig. 1; Fig. 3 is a rear elevational view of the circuit breaker of Fig. 1; Fig. 4 is a perspective view of the circuit breaker of Fig. 1; Fig. 5 is a sectional side elevation view of the circuit breaker of Fig. 1; Fig. 6 is an exploded view of the arc suppressor of Fig. 4; Fig. 7 is a sectional view of the apparatus of Fig. 1; and Fig. 8 is a perspective view of the crossbar of Fig. 1.

Detailed Description of the Preferred Embodiment Figs. 1 through 8 show a circuit breaker which incorporates the preferred embodiment of the present invention. Circuit breaker 2 includes housing 4 which is, preferably, molded plastic. Housing 4 comprises base 6 and removable cover 8. Removable cover 8 is mechanically attached to base 6 through the use of screws (not shown) which engage base 6 through openings 10.

Circuit breaker 2 employs contact arms 12, 14 and 16 which open and close the three current paths, or poles, of circuit breaker 2. Contact arms 12, 14 and 16 are mechanically connected to crossbar 18 so that they move in unison and are either all in the closed position or all in the open position. Contact arms 12, 14 and 16 support moveable contacts 17, 19 and 23, respectively.

Moveable contact 19 is designed to mechanically contact fixed contact 20 for closing the electrical current path through center pole 24. Contact 20 is supported by support 21. Similar fixed contacts (not shown) are provided for opening and closing the electrical current paths through left pole 26 and right pole 28. The operation of circuit breaker 2 will be described with respect to center pole 24. Poles 26 and 28 employ apparatus identical to that of pole 24.

Electrical conductor 30 is engaged by clamp 32 which is raised and lowered by bolt 34. Electrical conductor 30 supplies the electricity which will be transmitted through center pole 24. Contact 36 is held in tight engagement with electrical conductor 30 by the force exerted by clamp 32. Current flows from conductor 30, through terminal 36 and line copper 60, which is electrically connected to fixed contact 20. Fixed contact 20 is mechanically attached to support 21. Current then flows from fixed contact 20, through moveable contact 19, contact arm 14 and conductor 52 to bimetal 48. Conductor 52 is, preferably, a braided copper conductor which can be bent repeatedly without breaking.

Bimetal 48 then conducts the current to electromagnet assembly 40. Electromagnet assembly 40 includes fixed members 42 and 43, spring 47 and pivoting member 44. As electrical current flows through electromagnet 40, a magnetic flux is generated between magnet frame 43 and pivoting member 44 which applies a force on pivoting member 44 in the direction of arrow 46.

The electrical current then flows through heater 38, which is electrically connected to bimetal 48 and to terminal 37 which is connected to the electrical circuit.

Heater 38 and bimetal 48 both have known electrical resistance properties which cause heat to be generated when electrical current flows therethrough. The heat generated in heater 38 and bimetal 48 elevates the temperature of bimetal 48 causing it to bend in the direction of arrow 50.

When contact arm 14 is in the closed position, as shown in Fig. 1, moveable contact 19 is pressed in tight engagement with fixed contact 20 through force exerted by springs 56 and 58. The electrical current, originating from conductor 30, can flow through pole 24 when contact 19 is so engaged with contact 20.

When contact arm 14 is raised to the open position, as shown in Figs. 5 and 7, no current can flow through center pole 24 and the serially connected electrical circuit is de-energized. Since contact arms 12 and 16 move in unison with contact arm 14, poles 26 and 28 also stop electrical current flow therethrough.

As shown by the solid lines in Fig. 1, operating lever 62 is in the on position. Handle arm 75 is mechanically connected to lever 62 and pivot pin 100 and is positioned against stop member 64. Springs 56 and 58 are in tension and exert a force on lower link 66 through pivot pin 100 which is both upward and to the left. Lower link 66 is mechanically connected to both crossbar 18 and contact arm 14. The upward and leftward force exerted on lower link 66 causes moveable contact 19 to be secured in tight engagement with fixed contact 20.

Fig. 7 shows circuit breaker 2 in the open position with contact 19 separated from contact 20 and operating lever 62 in the off position. Moveable contacts 17 and 23 are also separated from their respective fixed contacts since they move in unison with moveable contact 19.

As described above, any one of moveable contacts 17, 19 and 23 may become welded in the closed position to its respective fixed contact. Under this condition contact arms 12, 14 and 16 and lower link 66 will be positioned as shown in Fig. 1. Springs 56 and 58 will apply a biasing force on operating lever 62 moving it to the on position. However, the biasing force of springs 56 and 58 may be overcome by applying a suitable force to lever 62 thereby allowing it to be moved to the off position. The present invention prevents this from occurring.

The present invention includes lock 70, cam 72 and locking surface 74. When moveable contacts 17, 19 and 23 are in the closed position, crossbar 18 and cam 72 assume the position shown in Fig. 1. Cam 72 is positioned to elevate lock 70, which is held in place by plate 71, to the position shown in Fig. 1.

If operating lever 62 were then moved toward the off position, as shown in shadow in Fig. 1, locking surface 74 of handle arm 75 would engage projecting member 76 of lock 70 thereby preventing handle arm 75 and, thus, operating lever 62 from advancing to the full off position as shown in Fig. 7. Lever 62 would move back to the on position once the manual force overcoming the biasing force of springs 56 and 58 were removed.

The present invention, therefore, provides the dual advantages of preventing operating lever 62 from falsely assuming the off position when the contacts of circuit breaker 2 are closed and, hence, the associated electrical circuit energized, and moving operating lever 62 to the on position to provide a positive, visual indication of the closed contact condition.

If operating lever 62 would be moved from the on position toward the off position when none of moveable contacts 17, 19 and 23 are welded to their respective fixed contacts, springs 56 and 58 would exert a force on lower link 66 which is both upward and to the right causing it to pivot about crossbar 18 in the direction of arc 78. As operating lever 62 is further moved toward the off position, and before it reaches the position shown in shadow on Fig. 1, the force exerted by springs 56 and 58 on lower link 66 will cause crossbar 18 and contact arms 12, 14 and 16 to quickly pivot in the direction of arrow 78 thereby opening the contact of circuit breaker 2.

As crossbar 18 rotates in the direction of arrow 78, cam 72 is rotated out of contact with lock 70 allowing lock 70 to pivot downward to the position shown in Fig. 7.

Projecting member 76 is, thus, rotated to a position where it cannot engage locking surface 74 thereby allowing operating lever 62 to be further advanced to the full off position as shown in Fig. 7.

The apparatus of the present invention also functions effectively if circuit breaker 2 is tripped open by the bimetal or electromagnet overcurrent protection devices. If the magnitude of current flowing through any pole of circuit breaker 2 exceeds the rating of breaker 2 by between 10 percent and 500 percent for a prescribed period of time, end 80 of bimetal 48 will move in the direction of arrow 50 and press against end 82 of trip bar 84. That in turn causes trip bar 84 to pivot about arc 86.

Similarly, if the magnitude of current flowing through circuit breaker 2 exceeds the rating of breaker'2 by more than 500 percent, pivoting member 44 will immediately move under the influence of the magnetic force generated by electromagnet assembly 40 in the direction of arrow 46. Pivoting member 44 is mechanically attached to trip bar 84. When pivoting member 44 moves in the direction of arrow 46, trip bar 84 pivots about arc 86. Therefore, when either the bimetal overcurrent protection or the electromagnet overcurrent protection detects an overcurrent condition, trip bar 84 is pivoted about arc 86.

Trip bar 84 is mechanically connected to latch 88. Latch 88 is normally biased by spring 90 in the direction of arrow 92. However, both bimetal 48 and pivoting member 44 can exert sufficient force on trip bar 84 to overcome the biasing force of spring 90, under overcurrent conditions, to move latch 88 in the direction of arrow 94.

As shown in Fig. 1, a portion of cradle 96 projects through opening 98 which is formed in latch 88.

The portion of cradle 96 which projects through opening 98 hooks onto latch 88 and prevents cradle 96 from moving under the biasing force which spring 56 applies to cradle 96 through pivot pin 100.

Since cradle 96 is mechanically connected to pivot pin 100 and pivot pin 100 is mechanically connected to contact arms 12, 14 and 16, cradle 96 prevents pin 100, and parts mechanically attached thereto, from moving upward under the influence of the biasing forces of springs 56 and 58. However, when latch 88 is moved in the direction of arrow 94 by trip bar 84, latch 88 becomes disengaged from cradle 96 thereby causing pin 100, cradle 96, lower link 66 and contact arms 12, 14 and 16 to move upward. Also, crossbar 18 moves in the direction of arrow 78 due to the biasing forces of springs 56 and 58. Such upward motion of contact arms 12, 14 and 16 separates moveable contacts 17, 19 and 23 from their respective fixed contacts thereby opening all three poles of circuit breaker 2.

If, however, breaker 2 is tripped when one of the moveable contacts is welded to its respective fixed contact, contact arms 12, 14 and 16 cannot be raised and, therefore, crossbar 18 will not rotate out of the position shown in Fig. 1. Lock 70 will be elevated, as shown in Fig. 1, and contact locking surface 74 of handle arm 75 if an attempt is made to move operating lever 62 to the off position. Therefore, the present invention prevents operating lever 62 from being moved to the full off position anytime contacts 17, 19 and 23 are closed.

When circuit breaker 2 is tripped, operating lever 62 moves from the on position, as shown in Fig. 1, to an intermediate position approximately half way between the on position and the off position. This provides a visual indication that circuit breaker 2 has been tripped by an overcurrent condition. Circuit breaker 2 is reset by moving operating lever 62 to the reset position thereby rèengaging cradle 96 with latch 88. Such resetting can occur only if the contacts of the breaker are opened since the apparatus of the present invention prevents lever 62 from being moved to the reset position when the contacts are closed. Operating lever 62 is then moved to the on position thereby pivoting contact arms 12, 14 and 16 downward so that moveable contacts 17, 19 and 23 are in contact with their respective fixed contacts, closing all three poles of breaker 2.

Arc suppressor 102 includes a plurality of Ushaped plates 104 which are relatively positioned by insulating members 106, 108 and 110. Arc suppressor 102 quickly extinguishes any arc formed as the result of the moveable contacts being separated from their respective fixed contacts. Two additional arc suppressors (not shown) are provided for the other two poles of breaker 2.

Manual trip button 112 is provided to allow for the manual tripping of breaker 2. When button 112 is depressed it exerts a force through a mechanical linkage (not shown) which rotates trip bar 84 through a sufficient angle to trip breaker 2.

Thus, it may be seen that the apparatus of the present invention provides an effective means for preventing the operating lever of the circuit breaker from assuming the full off position, when one or more of the moveable contacts of the circuit breaker is welded to is respective fixed contact and for providing a positive visual indication that the contacts of the breaker are closed.

It may not be appreciated that, for purposes of illustration, certain optional items, such as particular terminal equipment, has been shown. Such optional items are not mandatory for the operation of the present invention and may be deleted or modified without compromising the effectiveness of the invention.

Whereas particular embodiments of the invention have been described for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details may be made without departing from the invention as defined in the appended claims.

Claims (2)

CLAIMS:

1. Electrical circuit overcurrent protection apparatus comprising, electrical contacts capable of assuming an open position for interrupting the flow of electrical current in the electrical circuit and capable of assuming a closed position for allowing electrical current to flow in the electrical circuit; handle arm connected to at least one of said electrical contacts for manually moving said electrical contact between said open position and said closed position; an operating lever connected to said handle arm and capable of assuming an on position and an off position for moving said handle arm; an overcurrent protection'device mechanically connected to said at least one electrical contact for moving said at least one electrical contact to said open position when the electrical current in the electrical circuit exceeds predetermined values for predetermined periods of time; characterized by a lever lock relatively positioned with respect to said handle arm for directly contacting said handle arm and limiting the travel of said operating lever to a predetermined position intermediate said on position and said off position when said operating lever is manually moved from said on position toward said off position and said electrical contact is in said closed position.

2. The apparatus of claim 1 wherein: said handle arm defines a recessed engagement surface; and said lever lock defines a pivoting latch which engages said engagement surface and limits the travel of said operating lever to said predetermined position when said operating lever is moved from said on position toward said off position and said electrical contacts are closed.