GB2174245A - Switchgear operating mechanism - Google Patents

Abstract

A switchgear operating mechanism has a bell-crank lever 9 linked to a drive lever and a contact actuating shaft S by a toggle mechanism 1,2 effective in its straight condition to hold the switch contacts closed against a spring, trip means 6 operable to cause the toggle mechanism to collapse and cause the switch contacts to open, and a reset lever 10 which acts on the bell-crank lever 9 to straighten the toggle mechanism 1,2 and reset the trip against a further spring 15 which is capable of closing the contacts against the action of the first spring when the bell crank lever 9 is released from the reset lever 10. <IMAGE>

Description

SPECIFICATION Switchgear operating mechanism This invention relates to switchgear operating mechanisms for use in circuit breakers, and especially, though not exclusively, to such mechanisms arranged to form part of flameproof switchgear of the kind incorporating vacuum interrupters.

According to the invention a switchgear operating mechanism comprises a drive shaft coupled to, so as to actuate, the switch contacts, a drive lever fixed to the drive shaft, a bell crank lever linked to the drive lever by a toggle mechanism which, in the straightened condition is effective to hold the switch contacts closed against a first spring means, a trip mechanism effective when operated to cause the toggle mechanism to collapse and thereby to allow the switch contacts to open, a reset lever capable of acting on the bell crank lever in a manner which produces a straightening of the toggle mechanism and resetting of the trip against a further spring means, and then arranged to release the bell crank lever, the further spring means being capable of closing the switch contacts against the action of the first spring means.

For use-on three-phase supplies the drive shaft will normally be similarly coupled to, so as to actuate, three switches, such as vacuum interrupters, disposed in respective phases of the supply, the further switch means of the operating mechanism in accordance with the invention then being arranged to apply sufficient force to the operating lever to effect the closure of the contacts of all three switches.

Tripping of the mechanism, for effecting the opening of the switch or switches, can be arranged to be effected automatically in response to fault conditions in an associated circuit, but means are preferably also provided for achieving this manually.

One form of switchgear operating mechanism in accordance with the invention for use in a vacuum circuit breaker will now be described by way of example with reference to Figs. 1 to 4 of the accompanying schematic drawings, in which Figure 1 illustrates the mechanism with the circuit breaker in the closed condition, Figure 2 illustrates a part of the mechanism in more detail, Figure 3 shows the mechanism after the circuit breaker has been tripped to the open position, and Figure 4 shows a stage in the subsequent closure of the circuit breaker.

Referring to the drawings, the mechanism comprises a drive shaft S, suitably coupled by any convenient means (not shown) to the movable contacts of three vacuum interrupter units designed to be urged to the open condition by appropriate spring means (also not shown).

A drive lever L is fixed to the drive shaft S, and is coupled by means of links 1, 2 of a toggle lever mechanism to a bell crank lever 9 rotatable about a pivot 28. The pivot pin 19 at the junction of the links 1, 2 is connected by means of a further link 3 to an toggle actuating lever 4 pivotable about a fixed pin 20 and carrying a roller 5 at its free end. In the closed condition of the circuit breaker the links 1, 2 of the toggle mechanism are substantially straight as shown in Fig. 1, and the toggle actuating lever 4 extends generally upwards from the pin 20, being held in this position by a stop lever 6 engaging the roller 5, the stop lever, which is carried by a pivot pin 22, being held in this position against a stop (not shown) by means of a spring 42 (Fig. 2).

The mechanism also incorporates a trip lever 8, pivotable about a pin 23, and carrying a trip roller 7 at its free end. The position of the trip lever 8 is determined by a shunt trip device (not shown) which acts through a shunt trip rod 44 (Fig. 2), or alternatively by an undervoltage device.

A hand trip lever 45 also turns about the pin 23, and carries with it a hand trip boss 46, which engages the end of a hand trip bar 47. The opposite end of the latter is pivotally coupled by means of a pin 25 to an operating lever 10 which turns on a shaft 24 and also carries a drive pawl 11 whose function will be described later. The motion of the hand trip bar 47 is regulated by a fixed guide pin 48 acting in a longitudinally-extending slot 50 in the bar. Also mounted on the operating lever 10 is a stop screw 12 secured by a locknut 13.

A compression spring 15 extends between a fixed arm 30 and a pin 27 carried by the bell crank lever 9 urging the latter in the anticlockwise direction, as illustrated in the drawings, against a buffer 16. A further pin 26 carried by the bell crank 9 supports a roller 14.

Thus, in the circuit breaker closed position of the operating mechanism as illustrated in Fig. 1, the breaker opening springs are trying to turn the main drive shaft S clockwise and this force is transmitted to the mechanism by the lever L.

Since the pins 19 and 29 lie directly in line with the fixed pivot pin 28, there is no torque exerted on bell crank lever 9 and the linkage cannot move horizontally to the right of the illustration. Even should pins 19, 28 and 29 be slightly out of line, the bellcrank buffer 16 and closing spring 15 will prevent the bell crank lever 9 from turning.

The pin 19 is also prevented from being displaced vertically by the toggle link 3. The toggle link 3 is held stationary until the toggle formed by toggle lever 4 and toggle link 3 is able to unfold. The mechanism is therefore held stationary with the breaker in the CLOSED position until tripping is initiated.

Anti-clockwise movement of the trip lever 8 or hand trip lever 45 produces a clockwise movement of the stop lever 6 about the bias spring 42, thus releasing the toggle roller 5.

This allows the toggle lever 4 to pivot downwards in a clockwise direction, and the toggle link 3 is then able to descend, carrying with it the pin 19 and breaking the toggle lever mechanism 1, 2.

All this occurs under the pressure of the breaker opening springs which force the drive shaft S and drive lever L to turn clockwise, as seen in the drawings, until the drive lever comes up against a drive buffer 17. The position of the linkage is now as shown in Fig. 3 the breaker now being OPEN.

From this position, moving the operating lever 10 to the right causes the drive pawl 11 to engage with the operating roller 14 on the bell crank lever 9. Moving the operating lever 10 to the left will now cause the bell crank lever 9 to be forced clockwise. This action will compress the closing spring 15, straighten out the links 1 and 2, refold the toggle formed from toggle lever 4 and toggle link 3 and allow the stop lever 6 to move, under the action of its return spring 42, back into its place behind the roller 5. The mechanism will now be in its RESET position, as shown in Fig. 4, the breaker still being OPEN.

When the operating lever 10 is moved a little further to the right, the operating roller 14 will escape from the drive pawl 11. The closing spring 15 will now force the bell crank lever 9 anti-clockwise until it meets the bellcrank buffer 16. The aligned links 1 and 2 will be forced to the left, turning the drive lever L and drive shaft S anti-clockwise to close the breaker.

The mechanism is therefore back in position shown in Fig. 1 with the breaker CLOSED.

The operation of the tripping assembly is shown more clearly in Fig. 2. When the shunt trip is initiated, the shunt trip rod 44 is raised thereby turning the trip lever 8 about the pivot pin 23. The trip roller 7 will strike the inclined lower face of a trip boss 60 at the top of the stop lever 6, forcing the toggle lever to turn about the pivot pin 22 against the action of its return spring 42. The toggle roller 5 is freed from restraint and the rest of the mechanism linkage is tripped.

If an undervoltage trip has been supplied instead of a shunt trip, the trip lever 8 will be in a position with the trip roller 7 slightly above the stop lever 6. When the undervoltage trip operates the trip lever 8 will again turn about pivot pin 23, but in the opposite direction to that described for the shunt trip.

The trip roller will strike the upper face of the trip boss 60 of the stop lever 6, initiating the same sequence as before.

Manual tripping is initiated by moving the operating lever 10 away from the breaker CLOSED position. This causes the hand trip bar 47 to move to the left. The cam shaped projecting upper surface of the hand trip bar 47 strikes the hand trip boss 46 on the hand trip lever 45. This causes the hand trip lever 45 to rotate until the end 53 distant from the pivot pin 23 strikes the trip boss 60 on the stop lever 6. Movement of the stop lever has the same effect as that of tripping by the shunt trip.

Claims (9)

1. A switchgear operating mechanism comprising a drive shaft coupled to, so as to actuate the switch contacts, a drive lever fixed to the drive shaft, a bell crank lever linked to the drive lever by a toggle mechanism which, in the straightened condition is effective to hold the switch contacts closed against a first spring means, a trip mechanism effective when operated to cause the toggle mechanism to collapse and thereby to allow the switch contacts to open, a reset lever capable of acting on the bell crank lever in a manner which produces a straightening of the toggle mechanism and resetting of the trip against a further spring means, and then arranged to release the bell crank lever, the further spring means being capable of closing the switch contacts against the action of the first spring means.

2. A switchgear operating mechanism according to Claim 1 for use on a three-phase alternating current supply in which the drive shaft is similarly coupled to, so as to actuate three switches disposed in respective phases of the supply, the further spring means being arranged to apply sufficient force to the operating lever to effect the closure of the contacts of all three switches.

3. A switchgear operating mechanism according to Claim 2 wherein the switches are vacuum switches.

4. A switchgear operating mechanism according to any preceding Claim wherein the toggle mechanism is held in the straightened condition by a further lever operatively held in position by a spring loaded stop lever, and the trip mechanism incorporates means for rotating the stop lever against its spring so as to cause it to allow the toggle mechanism to collapse.

5. A switchgear operating mechanism according to Claim 4 wherein the stop lever acts on a toggle actuating lever pivotally coupled to said further lever such as to hold the latter in its operative position unitl the stop lever is rotated against its spring, release of the actuating lever by the stop means permitting the actuating lever to rotate and move said further lever into a position which allows the toggle mechanism to collapse.

6. A switchgear operating mechanism ac cording to Claim 5 wherein the means for rotating the stop lever against its spring comprises a trip lever movable to release the stop lever, either manually, or automatically in response to a fault condition.

7. A switchgear operating mechanism according to Claim 6 wherein for manually moving the trip lever comprises a trip bar slidably movable by a hand-operated lever and having a cam surface which, on movement of the trip bar, causes the trip lever to rotate and release the stop lever.

8. A switchgear operating mechanism according to Claim 7 wherein the hand-operated lever carries a pawl which is capable of engaging the bell-crank lever when the circuit breaker contacts are open, and on movement of the hand-operated lever into the switch closed position, the pawl causes the bell-crank lever to rotate so as to straighten the toggle mechanism and compress the further spring means, the subsequent release of the bellcrank lever causing the straightened toggle mechanism to reset the drive lever and drive shaft and thereby close the switch contacts under the action of said further spring on the bell-crank lever.

9. A switchgear operating mechanism substantially as shown in and as hereinbefore described with reference to Figs. 1 to 4 of the accompanying drawings.