US3533024A - Electric circuit breaker with undervoltage responsive trip means - Google Patents

Description

1970 M. L. HEINTZ 3,533,024

ELECTRIC CIRCUIT BREAKER WITH UNDERVOLTAGE RESPONSIVE TRIP MEANS Filed March 25, 1969 2 Sheets-Sheet 1 nws/vron: M/LTON L. HE/N 7'2,

ATTORNEY 0a. 6, 1970 M L. HEINTZ 3,533,024

ELECTRIC CIRCUIT BREAKER WITH UNDERVOLTAGE RESPONSIVE TRIP MEANS Filed March 25, 1969 2 Sheets-Sheet B /N VENTOR. MILTON L. HE/NTZ,

av A/daw 731m ATTORNEY United States Patent 3 533,024 ELECTRIC CIRCUIT BREAKER WITH UNDER- VOLTAGE RESPONSIVE TRIP MEANS Milton L. I-Ieintz, Newtown Square, Pa., assignor to General Electric Company, a corporation of New York Filed Mar. 25, 1969, Ser. No. 810,149 Int. Cl. H01h 83/12 US. Cl. 335-20 4 Claims ABSTRACT OF THE DISCLOSURE An undervoltage trip device comprising an undervoltage linkage connected to the trip latch of a circuit breaker and biasing means biasing the linkage in a direction to effect release of the trip latch. The undervoltage linkage is normally held in an inactive position against the force of said biasing means by an auxiliary latch of the offcenter type which is urged out of its latching position by force from said biasing means. Voltage-responsive mag netic means acts to hold the auxiliary latch in its latching position with a force varying directly with voltage but is overcome by the force from said biasing means when the voltage drops to a predetermined level.

This invention relates to an electric circuit breaker and, more particularly, relates to improved means for tripping the circuit breaker in response to a predetermined drop in voltage on the power line being controlled by the circuit breaker.

Prior undervoltage trip devices have been complicated, expensive, and difiicult to accurately adjust. An object of my invention is to provide a simple, inexpensive, and easily-adjustable undervoltage trip device that is automatically reset after tripping by the opening operation of the circuit breaker.

In carrying out my invention in one form, I provide, for releasing the trip latch of a circuit breaker, an undervoltage trip device comprising an undervoltage linkage operatively connected to said trip latch and biasing means biasing said linkage in a direction to effect release of said trip latch. For holding said undervoltage linkage in an inactive position against the force of said biasing means, an auxiliary latch is provided. This auxiliary latch has a latching surface engaged by a portion of said undervoltage linkage and so shaped that the force exerted thereon by said biasing means through said undervoltage linkage acts in a direction to release said auxiliary latch. Voltage responsive magnetic means acts to hold said auxiliary latch in its latching position with a force varying directly with the voltage on the power line. The releasing force on the auxiliary latch from the biasing means acts to overcome the force from the magnetic means when the voltage on the line drops to a predetermined level, thus releasing said auxiliary latch and allowing said biasing means to operate the undervoltage linkage to release said trip latch.

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

FIG. 1 is a partially schematic showing of a circuit breaker embodying one form of the invention. The circuit breaker is shown in closed position.

FIG. 2 is a view similar to that of FIG. 1 except showing the circuit breaker in a position through which it passes near the end of an opening operation.

FIG. 3 is an enlarged view of a portion of FIG. 1.

FIG. 4 is a sectional view along the line 4-4 of FIG. 3.

Referring now to FIG. 1, there is shown a power line 10, the current through which is controlled by an electric circuit breaker 12 having a set of normally-closed contacts 13, 14 connected in the power line 10. Contact 14 is a movable contact that is biased toward open position by an opening spring 16 but is normally held in closed position by a trip latch 18. When trip latch 18 is released, as will soon be described, the spring 16 drives the movable contact 14 upwardly to open the circuit breaker and interrupt the current in line 10'. The opening spring 16 is connected to the movable contact 14 through a crank 20 that is pivotally mounted on a stationary pivot 21 and has one end pivotally connected at 23 to an insulating operating rod 24 that is connected to the movable contact.

Force for closing the circuit breaker is imparted thereto through a conventional trip-free mechanism 25. This mechanism comprises a pair of toggle links 26 and 27 pivotally joined together at a knee 28. One of the toggle links 26 is pivotally connected at its opposite end to the right hand end of crank 20 by a pivot pin 29. The other toggle link 27 is pivotally connected by a pivot pin 31 to the upper end of a guide link 32. This guide link 32 is pivotally supported at its lower end on a fixed fulcrum 34. The pivot pin 31 carries a latch roller 34a which cooperates with the trip latch 18. Trip latch 18 is pivotally mounted on a stationary pivot 35 and is biased into its latching position of FIG. 1 against the stop 38 by a suitable reset spring 39. For preventing the toggle 26, 27 from collapsing at its knee 28, a suitable prop 39 is provided. This prop 39 is pivotally mounted on a fixed axis shaft 50 and is biased into its position of FIG. 1 against stop 51 by a suitable spring '52. The knee 28 bears against the upper surface of pro 39.

Trip latch 18 can be released in response to an overcurrent condition in power line 10 by means of a conventional tripping solenoid 40, Solenoid 40 is shown connected across the secondary winding 42 of a current transformer connected in the power line. When current through power line 10 exceeds a predetermined value, the current transformer supplies sufficient secondary current to solenoid 40 to cause it to operate, thereby driving latch .18 into its released position of FIG. 2.

Release of latch 18 frees pivot pin 31 and thus renders the toggle 26, 27 incapable of transmitting continued closing force to crank 20. Accordingly, opening spring 16 drives crank 20 clockwise from its position of FIG. 1 into its position of FIG. 2, thereby opening the circuit breaker. Such movement forces the entire toggle linkage 26, 27 downwardly and to the right, causing guide link 32 to pivot clockwise about its fulcrum 34. When knee 28 moves off prop 39, toggle 26, 27 is capable of collapsing to allow further opening movement into the position of FIG. 2.

After an opening operation, guide link 32 is reset to its position of FIG. 1 by a suitable reset spring 54. The reset spring drives guide link 32 counterclockwise into its dotted line position of FIG. 2 and, in doing so, further cFtillcapses the toggle 26, 27 into its dotted line position of Closing of the circuit breaker is effected by lifting the toggle knee 28 from its dotted line position of FIG. 2, thereby extending the toggle 26, 27 and returning it to its position of FIG. 1. The force for lifting toggle knee 28 is derived from a motor-driven cam 58. When cam 58 is rotated clockwise from its position of of FIG. 2, it lifts the toggle knee 28 and returns the toggle to its position of FIG. 1, thereby closing the breaker. The cam continues rotating until it returns to its original position of FIG. 2, but the toggle 26, 27 is prevented from collapsing after the cam leaves the knee 28 by the prop 39, which is moved by spring 52 into its restraining position of FIG. 1 under the knee.

The mechanism as described in detail up to this point is conventional. The present invention is concerned with tripping such a mechanism in response to a drop in voltage on power line to a predetermined level. For effecting such tripping, I provide an undervoltage trip device shown at 60. This trip device 60 comprises an actuating lever 64 biased by a spring '65 in a direction to trip the circuit breaker but restrain from so acting -by an auxiliary latch 62. The actuating lever 64 is pivotally mounted at 67 and is normally prevented from moving clockwise past its inactive position of FIG. 1 by the auxiliary latch 62 engaging a latch roller 68 carried by lever 64. Lever 64 is connected to the main trip latch 18 by a link 71 having its upper end pivotally connected to lever 64 by a pivot pin 71a. The lower end of link 71 has a slot 73 therein that receives a pin 74 on the main trip latch. When auxiliary latch 62 is released, as will soon be described, the spring 65 drives the lever 64 clockwise from its inactive position of FIG 1, lifting link 71 to pivot trip latch 18 clockwise, thus tripping the circuit breaker.

Referring to FIG. 3, the auxiliary latch 62 comprises two basic components 70 and 72 that are adjustably secured together. Component 70 performs the actual latching function, and component 72 forms a pivot for the component 70 and is itself pivotally connected at 75:: to the armature 75 of an undervoltage-sensitive electromagnet 76. For adjustably securing the parts 70 and 72 together, a slot 77 is provided in part 70; and this slot received a laterally-extending hub 78 fixed to the other part 72. A pin 79 extends through hub 78 to serve as a stationary pivot for latch 62. A screw 80 extending through a slot 82 in the part 72 and threaded into part 70 is used for clamping the parts 70, 72 together in a desired position of adjustment. When it is desired to adjust part 70 relative to part 72, the screw 80 is loosened, part 70 is moved laterally, shifting its slot 77 with respect to hub 78, and thereafter the screw 82 is tightened.

The auxiliary latch 62 has a latching surface 84 at its upper end that has its center of curvature at a point 86. It is important to note that this center of curvature is laterally offset from the actual pivot of the latch, formed by pin 79 through hub 78. The force from the tripping spring 65 acts on latch 62 through a line of action 87 passing through its center of curvature 86, thus exerting an overturning moment on the latch tending to pivot it clockwise about stationary pivot 79. This clockwise motion of latch '62 is opposed by the voltage-sensitive solenoid 76, which, when energized, pulls upwardly on its armature 75 against a light compression spring 89 to normally hold latch 62 in its position of FIG. 3 against a stop 88. But when the holding force from solenoid 76 falls below a predetermined value, the overturning moment is suflicient to pivot the latch 62 clockwise about pivot pin 79, thus releasing the actuating lever 64. Upon such release, spring 65 drives the actuating lever 64 clockwise about pivot 67, thereby tripping the breaker, as above described.

The overturning moment exerted on latch 62 by tripping spring 65 is directly proportional to the distance d between the actual pivot 79' of the latch and the center of curvature 86. By adjusting the part 70 with respect to part 72, as described hereinabove, this distance d can be varied, thus varying the overturning moment exerted by tripping spring 65 on the latch '62. It is to be understood that the actual pivot 79 remains stationary during this adjustment. It is only the position of the center of curvature 86 that is changed.

The force exerted by the electromagnet 76 in opposition to the above described overturning moment is directly dependent upon the line-to-ground voltage. In this respect, a potential transformer 90 is provided having its primary winding 91 connected between line 10 and ground on the source side of the breaker contacts 14 and its secondary winding 92 connected across the solenoid 76. When the line-to-ground voltage drops below a predetermined level, the above-described overturning moment on latch 62 overcomes the holding force of the electromagnet, thus tripping the circuit breaker. The voltage at which the overturning moment will predominate depends upon the distance d, and adjustments in this distance will, of course, change the voltage at which the auxiliary latch releases the actuating lever 64 to trip the breaker.

For resetting the undervoltage trip device after it has tripped the circuit breaker, a reset linkage is provided. This reset linkage comprises a first link 101 pivotally connected to actuating lever 64 by pivot 71a and a second link 102 pivotally connected to crank 20 by a pivot pin 29 extending through a slot in link 102. A normally unstressed compression spring 104 is dis posed between the two links 101 and 102.

When the circuit breaker opens in response to tripping, the pivot pin 29 on crank 20 moves downward into its position of FIG. 2, driving the reset linkage 100 down wardly. Downward movement of reset linkage 100 pivots the actuating lever 64 counterclockwise about its pivot 67 into its solid-line position of FIG. 2. This allows the then-energized solenoid 76 to pivot the latch 62 counterclockwise back to its latching position of FIG. 3. The solenoid will be capable of holding the latch in this position so long as the voltage on line 10 is above the predetermined value referred to above.

When the circuit breaker is operated to close its position from its dotted line position of FIG. 2, the pin 29 on the crank 20 moves upwardly, eventually moving link 102 upwardly to decompress spring 104 and remove the downward force on link 101. This allows tripping spring 65 to drive lever 64 clockwise a short distance until its roller 68 (FIG. 3) engages the surface 84 of auxiliary trip latch 62. The parts are then in their reset position of FIGS. 1 and 3.

If the circuit breaker is tripped open by the overcurrent solenoid 40, the undervoltage trip device will be actuated from its position of FIG. 1 into its position of FIG. 2 upon opening of the circuit breaker. The slot 73 in the link 71 and the pivotal connection at 71a allow overcurrent tripping to take place without interference from the undervoltage trip device 60. For limiting the extent to which actual opening of the circuit breaker affects the undervoltage trip device, the slot 105 and spring 104 are provided in the reset linkage 100. These parts allow the in 29 on crank 20 to move downwardly during an opening operation without causing anything more to occur in the undervoltage trip device 60 than the slight counterclockwise movement of actuating lever 64- from its position of FIG. 1 to its position of FIG. 2.

By using an off-center latch 62 in my undervoltage trip device, I have been able to considerably simplify the trip device. Instead of providing a separate operator for tripping the latch 62 when the voltage drops, I use the same spring (65) to trip auxiliary latch 62 as is used for tripping the main latch 18. Moreover, the construction of my undervoltage trip device makes it a simple matter to adjust the voltage level at which tripping will occur. This adjustment can be made simply by varying the distance d in FIG. 3, as described hereinabove.

While I have shown and described a particular embodiment 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. In a circuit breaker for interrupting current through a power line when the voltage on said power line falls to a predetermined level, said breaker comprising opening means biasing the breaker toward open position, a trip latch for holding said breaker in closed position and re leasable to permit said opening means to open the breaker, and an undervoltage trip device for releasing said trip latch comprising:

(a) an undervoltage linkage operatively connected to said trip latch,

(b) biasing means biasing said undervoltage linkage in a direction to effect release of said trip latch,

(c) an auxiliary latch having a latching position wherein said auxiliary latch is effective to hold said undervoltage linkage in an inactive position against said biasing means,

((1) said auxiliary latch having a latching surface engaged by a portion of said undervoltage linkage and so shaped that the force exerted thereon by said biasing means through said undervoltage linkage acts in a direction to release said auxiliary latch,

(e) voltage-responsive magnetic means for holding said auxiliary latch in said latching position With a force varying directly with the voltage on said power line,

(if) the releasing force on said auxiliary latch from said biasing means acting to overcome the force from said magnetic means when the voltage on said line drops to a predetermined level, thus releasing said auxiliary latch and allowing said biasing means to operate the undervoltage linkage to release said trip latch.

2. The arrangement of claim 1 in which said auxiliary latch has a stationary pivot axis and said latching surface has a center of curvature through which the line of action of the force from said biasing means acts on said auxiliary latch, said center of curvature being laterally offset from said stationary pivot axis in a direction wherein said force from said biasing means acts on said auxiliary latch in a direction to release said auxiliary latch.

3. The arrangement of claim 1 in which:

(a) said auxiliary latch has a stationary pivot axis and said latching surface has a center of curvature through which the line of action of the force from said biasing means acts on said auxiliary latch, said center of curvature being laterally offset from said stationary pivot axis in a direction wherein said force from said biasing means acts on said auxiliary latch in a direction to release said auxiliary latch,

(b) said auxiliary latch comprising two components which are adjustahly secured together, the first of said components determining the location of the center of curvature of said latching surface and the second of said components determining the location of the pivot axis of said latch,

(c) satd first component being movable with respect to said second component to shift said center of curvature and change the distance between said pivot axis and said center of curvature.

4. The circuit breaker as defined in claim 1 and further comprising:

(a) a part that moves in one direction through a predetermined stroke in response to an opening operation of said circuit breaker and in an opposite direction through said stroke in response to a closing operation of said circuit breaker, and

(b) means comprising a reset linkage connected between said part and said undervoltage linkage for restoring said undervoltage linkage to said inactive position in response to an opening operation of said circuit breaker in the event said undervoltage linkage had previously operated to release said trip latch.

References Cited UNITED STATES PATENTS 3,009,034 11/1961 Barkan 335-26 3,162,740 12/1964 Klein 335-26 3,402,373 9/1968 Werner 335-73 3,453,568 7/1969 Murphy 335-20 GEORGE HARRIS, Primary Examiner H. BROOME, Assistant Examiner Us. (31. X3, 3 5- 6,

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