US3873950A

US3873950A - Air circuit breaker

Info

Publication number: US3873950A
Application number: US365102A
Authority: US
Inventors: Vladislav Yakovlevich Guschin
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-05-30
Filing date: 1973-05-30
Publication date: 1975-03-25
Anticipated expiration: 1992-03-25
Also published as: DE2328971B2; DE2328971C3; FR2239755B1; GB1432794A; FR2239755A1; DE2328971A1; BE800292A

Abstract

An air circuit breaker for interrupting short-circuit currents and which interrupts short-circuit currents up to a predetermined value with a time delay and, at currents exceeding the predetermined value open the associated electric circuit without any time delay.

Description

United States Patent [1 1 [111 3,873,950 Guschin 1 Mar. 25, 1975 AIR CIRCUIT BREAKER 3,593,234 7/1971 Chabonneau 335/176 [7 In entor: vladislav Yakovlevich Guschin, 3,777,293 12/1973 TLlZUkl 335/176 Moskovsky prospekt 96, kv. 23,

Kharkov Primary Examiner-G. Harris [22] Filed: May 30, 1973 [211 App]. N0.: 365,102

[57] ABSTRACT [52] U.S. Cl. 335/42, 335/176 An air circuit breaker f interrupting shormircuit [51] Int. Cl. HOlh 77/06 Currents and which interrupts h t i it Currents up [58] Field of Search 335/24, 42, 175, 176 to a predetermined v l with a time delay and, at currents exceeding the predetermined value open the 1 References Clted associated electric circuit without any time delay.

UNITED STATES PATENTS 3,525,959 8/1970 Eusworth et a1 335/24 X 4 Claims, 2 Drawing Figures Z/ Ij' PATENTEU 3 3,873,950

snmauFz 1 AIR CIRCUIT BREAKER be disconnected and that all other circuits remain connected to supply. To this end, the air circuit breaker nearest to the source of supply is furnished with a device producing a time delay longer than the operating time of any of the circuit breakers located between it and the load.

When the circuit breaker nearest the load is capable of interrupting the short-circuit current within a period of time shorter than a part of the time delay, usually ranging from 70 to 90 per cent of the circuit breaker nearest to the source of supply, the latter breaker will not open at all.

If the circuit breaker nearest the load is unable to interrupt the short-circuit current in the course of the indicated period of time, the faulty circuit will be opened by the circuit breaker nearest to the source of supply on expiration of the time delay of the latter breaker. Such a method of circuit protection is known as selective protection, and air circuit breakers operating with a current-independent time delay are referred to as selective circuit breakers.

It is apparent from the above-said that one of the main requirements to be met by selective circuit breakers is their capability to withstand the injurious effect of short-circuit current throughout a considerable time delay.

Air circuit breakers used for operation under selective duty conditions are designed to carry a considerably heavier rated current than is required according to normal conditions of operation of the electric circuit in which the given circuit breaker is included.

Such air circuit breakers possess a high electrodynamic and thermal stability due to the high contact pressure and large cross-sectional area of their currentcarrying parts.

This high contact pressure calls for a large size of the breaker mechanism, and current-carrying parts oflarge cross-sectional area increase both the weight and the cost of such air circuit breakers. These disadvantages set limits on the use of air circuit breakers of high current ratings as selective breakers.

Also known in the art are small-size selective circuit breakers wherein a high electrodynamic stability is attained by use of an electrodynamic device for balancing the forces of repulsion arising between the breaker contacts during the passage of short-circuit currents rather than resorting to a high contact pressure.

An air circuit breaker intended for operation under selective duty conditions is already known. This air circuit breaker comprises a manual operating mechanism, a system of contacts, and electrodynamic device for balancing the electrodynamic forces of repulsion acting on the contacts, emergency tripping devices and a freetrip mechanism. The device used for balancing the electrodynamic forces of repulsion acting on the contacts during the passage of a short-circuit current through the conductors of the device gives rise to electrodynamic forces that act upon one of the circuit breaker contacts and balance the force of contact repulsion. These additional balancing forces are transmitted through links of the free-trip mechanism to the system of engaged elements of the free-trip mechanism.

The size of the overcurrent tripping device is reduced by using a free-trip mechanism requiring a small actuating force for its operation. For this purpose, one or more lever-type intermediate elements that allow reducing the force transmitted to the element actuated by the overcurrent tripping device are introduced between the main tripping element and the element acted upon by the overcurrent tripping device.

A disadvantage of air circuit breakers of this type is that they trip only after full expiration of the pre-set time delay on occurence of a short circuit located directly after the circuit breaker. Therefore, the crosssectional area of the current-carrying parts of the circuit section contiguous to the air circuit breaker has to be selected based on the thermal and electrodynamic effect of the longitudinal short-circuit current over the entire duration of the circuit breaker time delay.

Moreover, the mechanical effect of the short-circuit current upon the current-carrying parts of the air circuit breaker itself and the mechanical forces transmitted by the elements of the operating mechanism also act over the full time delay of the circuit breaker.

As a result, the current-carrying parts and operating mechanism elements of the air circuit breaker are designed to withstand the continuous thermal and mechanical action of the maximum short-circuit current liable to flow in the protected electric circuit, this circumstance leading to a considerable increase in the cost and size of the air circuit breaker as compared with circuit breakers that clear the short circuit without any time delay and, consequently, hindering standard' ization of the circuit breaker sizes.

It is a general object of the present invention to eliminate the above-mentioned disadvantages of known air circuit breakers.

A further object of the herein described invention is to provide an air circuit breaker adapted to open the protected circuit without any time delay as soon as the short-circuit current reaches a predetermined value.

These and other objects are attained in a novel air circuit breaker comprising a manual operating mechanism, a system of moving contacts, a device for balancing the electrodynamic forces of repulsion acting upon the mentioned contacts, emergency tripping devices and a free-trip mechanism provided with a latch and a tripping rod, so that the latch on being engaged with the tripping rod holds the free-trip mechanism in position corresponding to the closed position of the circuit breaker contacts, characterized according to the present invention by that the latch of the free-trip mechanism is mounted on a shaft within a support and is capable of travelling together with the shaft in respect to said support in the direction of disengagement of the latch with the tripping rod, said latch being provided with a device for keeping the latch engaged with the tripping rod.

The device for keeping the latch engaged with the tripping rod may be in'the form of a spring mounted so that it acts upon the latch in a direction opposite to the travel of the latch on its disengaging with the tripping rod.

The device for keeping the mentioned latch engaged with the tripping rod is preferablyfurnished with an adjusting device made, for example, in the form of a screw attached to one end of a tensioning spring.

The adjusting device allows the pull of the spring that keeps the latch engaged with the tripping rod to be varied, thus providing for accurate setting of the circuit breaker operating current.

In order to disengage the latch and tripping rod with minimum displacement of the latch in the direction of disengagement and, consequently, to shorten the time of disengagement, the air circuit breaker is preferably furnished with an arrester that prevents the tripping rod from rotating in the direction of increase of its engagement with the latch due to the effedt of frictional'forces acting at the point of engagement.

The present invention will further be described by drawings, wherein:

FIG. 1 is a general schematic representation of the aircircuit breaker in accordance with the present invention; and

FIG. 2 is an enlarged view of assembly A of the air circuit breaker in accordance with the present invention.

The automatic air circuit breaker of the invention comprises a system of contacts including a moving conductor 1, a carrying contact 2, a contact 3 directly connected with a device 4 that serves for balancing the electrodynamic forces of repulsion. The device 4 comprises a coil built up of two conductors made so that a conductor 5 of the coil is fixed to the circuit'breaker, whereas a conductor 6 is free to move a coupling shaft 7 of both conductors and carries the contact 3 that establishes an electrical contact with said contact 2 when the air circuit'breaker closes. A spring 8 produces the required contact pressure at closure of the air circuit breaker.

The moving conductor 1 and the coil moving conductor 6 have extended ends that perform the function of arcing contacts. The moving condutor l is hinged with a system of

collapsible links

9 and 10 and a tripping lever ll.

The manual operating mechanism of the air circuit breaker comprises an operating handle 12 and a spring 13, one end of which is attached to the handle 12 while the other end is coupled with the common joint (not shown in the drawing) of

links

9 and 10. When the air circuit breaker is in closed position, the lever 11 is engaged with a latch 14.

The latch 14 is hinged to a rest 15 and with the air circuit breaker in closed position is engaged with a tripping rod 16. A hole 17 ofthe rest 15 holding a shaft 18 of the latch 14 is elongated in the direction of displacement of the shaft 18 and the latch 14 corresponding to decrease of engagement of the latch 14 with the tripping rod 16.

When the air circuit breaker is in closed position, a spring 19 keeps the shaft 18 of the latch 14 in the extreme position within the rest 15 at which the latch 14 is engaged with the tripping rod' 16. The other enriZ-bl' the spring 19 is attached to an adjusting screw 20 used for varying the pull of the spring 19. The tripping rod 16 is hinged with a support 21 wherein an arrester 22 is provided to prevent the tripping rod 16 from rotating in the direction of increase of its engagement with the latch 14.

An overcurrent tripping device 23 meant for emergency tripping of the air circuit breaker is fitted with a moving rod 24 that serves for rotating the tripping rod 16 in the direction of its disengagement with the latch 14. The moving conductor 1 is connected electrically with a terminal 25 of the air circuit breaker by means of a flexible lead 26.

The air circuit breaker operatesin the following manner.

In the event of a shortcircuit thathas to be cleared without any time delay, the short-circuit current passing through the closed contacts 2 and 3 produces electrodynamicforces of repulsion that tend toseparate the contacts and are caused by narrowing of the current elementary lines at the point of contact. At a maximum value of the short-circuit current, these forces are much greater than the pull exerted by the spring 8.

Passage of the same current through the conductors of the device 4 gives rise to electrodynamic forces between the fixed conductor 5 and the moving conductor 6. As this takes. place, the upper part of conductor 5 and the conductor 6 in which the current flows in one and the same direction experience a force of attraction, whereas the lower part of conductor 5 and the conductor 6 in which the current flows in opposite direction experience a force of repulsion. The net force acting between the conductor 5 and the conductor 6 of device 4 prevents separation of the contacts 2 and 3,'whatever the magnitude of the short-circuit current. The magnitude of the force varies directly with the value of the short-circuit current. The force is applied to the moving conductor 1 via the contacts 2 and 3. In consequence, the moving conductor 1 acts through the

links

9 and 10 upon the lever 11,.the latch 14 and the tripping rod 16 with which it is engaged.

With the short-circuit current at predetermined value, the force acting upon the latch 14 exceeds the pull exerted by the spring 19 and the latch 14 moves together with the shaft 18 coupling it with the rest 15 within the elongated hole 17 of rest 15. As a result, the latch 14 and the tripping rod 16 become disengaged.

After the latch 14 has been released, it disengages the lever 11. The action of spring 13 upon the lever 11 on its disengagement from the latch 14 causes the lever to rotate counterclockwise about its shaft as far as it will go. As a result, the shaft coupling the link 9 and the lever 11 will be to the left'of the axis of spring 13, the

links

9 and 10 turn in respect to each other, and the moving conductor 1 coupled with the link 10 moves upwards, thus opening the contacts 2 and 3 of the air circuit breaker.

The air circuit breaker should preferably be provided with an adjusting device for setting the required value of the circuit breaker operating current interrupted without any time delay.

FIG. 2 illustrates the embodiment of the adjusting device.

One end of the spring 19 is attached to the adjusting screw 20, and the other end is held by the shaft 18 of the latch 14. A nut 27 is fitted on the screw 20 so as to keep the latter in fixed position. The pull of spring 19 is varied by moving the nut 27 along the screw 20.

The latch 14 during its movement within the hole 17 of the rest 15 may rotate the tripping rod 16 counterclockwise due to the action of frictional forces present at the point of engagement of the latch 14 and the tripping rod 16. This is an undesirable effect as it prevents disengagement of the latch 14 and the tripping rod 16.

To avoid this effect, the air circuit breaker should preferably be provided with the arrester 22 that limits the rotation of the tripping rod16 in the direction at which the magnitude of its engagement with the latch 14 does not diminish.

In accordance with the present invention, when the automatic air circuit breaker of the present embodi' ment interrrupts short-circuit currents and it is desired to have a time delay, the circuit breaker operates as an ordinary selective circuit breaker.

In this case, the force developed by the device 4 is insufficient to overcome the pull of spring 19. The latch 14 and its shaft 18 remain in the lower extreme position within the elongated hole 18 of rest 15 throughout the entire period of passage of the short-circuit current.

On expiration of the time delay, a rod 24 of the overcurrent tripping device 23 acts upon the tripping rod 16 and turns it through an angle required for disengagement from the latch 14. Further the air circuit breaker opens in the same way as described above.

The herein described air circuit breaker operates selectively up to a certain predetermined value of the short-circuit current and, at passage of short-circuit currents exceeding the predetermined value, the air circuit breaker opens the electric circuit without any time delay and current limitation.

Use of the proposed air circuit breaker allows reducing the size of the electric power distribution circuits selected according to the maximum value of the shortcircuit current and in conjunction with current-limiting circuit breakers improve the protection of the power supply transformers of switchgear installations.

What we claim is:

1. An air circuit breaker comprising: a manual operating mechanism; a system of moving contacts having open and closed positions; first means for balancing the electrodynamic forces of repulsion acting upon said moving contacts; emergency tripping devices; a freetrip mechanism adapted to effect control of said contacts;

said free-trip mechanism including a latch for action on said first means and a tripping rod;

said latch on being engaged with said tripping rod holding said free-trip mechanism in position corresponding to the closed position of said moving contacts, a support, a shaft displacably supported by said support, said latch being mounted on said shaft and being capable of travelling together with said shaft in a direction effecting disengagement of said latch from the tripping rod; second means resiliently tending to keep said latch engaged with said tripping rod; said second means including an adjusting means;

said adjusting means providing for adjustment of the magnitude of the force keeping said latch engaged with the tripping rod, thus allowing selection of a value of circuit breaker operating current.

2. An air circuit breaker according to claim 1, wherein said second means is in the form of a spring mounted so that said spring acts upon said latch in a direction opposite to the movement of said latch on its disengaging from said tripping rod.

3. An air circuit breaker according to claim 2,.

wherein said adjusting means comprises a screw attached to said spring and adjustable for providing for various degree of pull of said spring.

4. An air circuit breaker according to claim 1 wherein said tripping rod is rotatable, including an arrester that prevents said tripping rod from rotating under the action of the frictional forces present at the point of engagement with said latch in the direction of increase of its engagement with said latch.

l= l l= i

Claims

1. An air circuit breaker comprising: a manual operating mechanism; a system of moving contacts having open and closed positions; first means for balancing the electrodynamic forces of repulsion acting upon said moving contacts; emergency tripping devices; a free-trip mechanism adapted to effect control of said contacts; said free-trip mechanism including a latch for action on said first means and a tripping rod; said latch on being engaged with said tripping rod holding said free-trip mechanism in position corresponding to the closed position of said moving contacts, a support, a shaft displacably supported by said support, said latch being mounted on said shaft and being capable of travelling together with said shaft in a direction effecting disengagement of said latch from the tripping rod; second means resiliently tending to keep said latch engaged with said tripping rod; said second means including an adjusting means; said adjusting means providing for adjustment of the magnitude of the force keeping said latch engaged with the tripping rod, thus allowing selection of a value of circuit breaker operating current.

3. An air circuit breaker according to claim 2, wherein said adjusting means comprises a screw attached to said spring and adjustable for providing for various degree of pull of said spring.