GB2129617A - Electrical isolating switch - Google Patents

Abstract

An electrical isolating switch has the movable contact (28) mounted on a generally circular cam (12) which may be manually rotated between forward, isolating and reverse contact positions. A vacuum interrupter (42) is connected electrically in series with the isolating switch contacts and is mechanically coupled with the cam (12) via a crank (58) so that the interrupter is open circuit during both closing and opening of the isolating contacts <IMAGE>

Description

SPECIFICATION Electrical isolating switch This invention relates to electrical isolating switches and in one important example to an isolating switch which can be positioned alongside or within a piece of electrical machinery or plant to enable rapid isolation and immobilisation of the machinery or plant in an emergency.

Because they offer a means of isolation which is both visible and measurable, air gap switches are conventionally used in both isolators and isolating switches. It is recognised however that air gap switches have no current breaking capabilities despite their ability to carry high current. It has been suggested (see for example United States Patent Specification No. 3,824,355 or United States Patent Specification No. 3,671,696) that an air gap switch should be connected in parallel with a vacuum interrupter. In such an arrangement, the air gap switch provides the high current carrying capability and-when open-the important visible and measurable degree of isolation. The vacuum interrupter serves to provide the necessary current breaking capability, provided of course that the vacuum interrupter and air gap switch are actuated in the correct sequence.Mechanisms of some mechanical complexity have been suggested for ensuring this correct sequence of actuation.

In GB Patent No. 1 599 677, there is described a vacuum interrupter and isolator combination in which the vacuum interrupter, in addition to providing the above described current breaking capability, is able to interrupt fault currents automatically and can trip under low voltage conditions. For the vacuum operator to provide such additional functions, it clearly has to be connected in series and not in parallel with the air gap interrupter. For the purposes which the device is intended to serve it is essential that separate means be provided for actuating the vacuum interrupter and air gap isolator, respectively, and this leads to a device which is of significant bulk and of some mechanical complexity.

It is an object of this invention to provide an improved electrical isolating switch which has the relatively high current breaking capacity associated with a vacuum interrupter as well as the visible and measurable isolation provided by an air gap switch, the device however being of relatively small bulk and of straight forward and economic construction.

Accordingly, the present invention consists in an electrical isolating switch comprsing a non-arcing interrupter connected electrically in series with an air gap switch, and a hand operated actuating mechanism serving in one movement to operate the interrupter and air gap switch sequentially such that the interrupter remains open circuit during both open ing and closing of the air gap switch.

Advantageously, the mechanism comprises a manually rotatable member carrying a mov able contact of the air gap switch and includ ing a cam surface, there being provided a cam follower cooperating with said cam sur face and so linked with the interrupter as to actuate the same on rotation of said member.

In another form of the invention, there is provided an electrical isolating switch compris ing a manually displaceable actuating member formed with a cam surface; an air gap switch having a movable contact carried on the actu ating member and at least one fixed contact positioned as to engage a movable contact on displacement of the actuating member; a non arcing interrupter connected electrically in series with the air gap switch and a cam follower cooperating with said cam surface and so linked with the interrupter as to actu ate the interrupter on displacement of the actuating member, the cam and cam follower being so adapted that the interrupter and air gap switch are actuated in sequence with the interrupter remaining open circuit during both opening and closing of the air gap switch.

This invention will now be described by way of example with reference to the accom panying drawings in which: Figure 1 is a front view of an electrical isolating switch according to this invention; Figure 2 is a cross section through the isolating switch of Fig. 1; Figure 3 is a diagram showing the electrical connections within the isolating switch; and Figures 4 a), b) and c) show in diagramma tic form respective operating stages of a pre ferred operating mechanism.

The isolating switch shown in the drawings comprises an operating shaft 10 on which is mounted a generally circular cam 1 2. This cam is formed integrally with and lies axially between two flanges 14 and 16. The isolating switch is enclosed by front and rear walls 1 8 and 20, a cover 22 and a base 24. The front wall 1 8 includes a conducting earth screen 26.

The cam 1 2 carries a contact blade 28 which projects radially of the operating shaft.

This contact blade can be brought, through rotation of the cam, into engagement with either of two contact clips 29 and 30. These contact clips are secured respectively to a forward load terminal 32 and a reverse load terminal 34 which are in turn supported in any suitable manner from respective mounting blocks 36 and 38. Mounting block 38 in cludes an upstanding and inclined arm 40 to which is bolted one end of a vacuum inter rupter 42 which is of conventional internal construction requiring no further explanation.

This end of the interrupter is provided with a terminal 44 which is connected with the fixed internal contact (not shown) of the interrupter and which forms the incoming supply terminal of the isolating switch. Towards the end opposite the terminal 44, the interrupter is provided with a cross piece 46 which is connected with the movable internal contact (not shown) of the interrupter and to which are secured two connecting braids 48. These connecting braids extend on opposite sides of the cam 1 2 and establish electrical connection with the contact blade 26 through studs 50 and nut 52.

Mounting block 36 is formed with a projection 54 having a pin 56 extending therethrough generally parallel with the operating shaft 10. On this pin 56 are mounted two parallel crank plates 58, one each side of the projection 54. The crank plates 58 are free to rotate as an assembly about the axis of pin 56. The generally vertical limb 60 of the crank plate assembly is connected with a slide 62 forming part of the interrupter and being mounted on a rod 64 such that movement of the slider toward and away from the body of the interrupter is effective to bring the movable internal contact of the interrupter into and out of engagement with the fixed internal contact. Between the slider 62 and the cross piece 46, a compression spring 66 is mounted on the rod 64.The effect of this compression spring is to bias the slider 62 away from the body of the interrupter, this corresponding with the open circuit position of the interrupter.

In the generally horizontal limb 68 of the crank arm assembly there is provided a roller 70 supported between the two crank plates 58 and cooperating with the surface of cam 1 2. It will be seen from Fig. 1 that the surface of cam 1 2 is shaped to provide two spaced slots 72 which lie along parallel chords and extend into the cam a distance approximately equal to half the cam radius.

Between the slots 72 there is formed a land surface 74 which lies on a radius which is approximately three-quarters of the cam radius.

The operation of the described isolating swich can now be understood. In the position shown in full outline in Fig. 1, both the vacuum interrupter and the air gap switch formed by contact blade 28 and contact clips 29 and 30, are open circuit. This corresponds with the position shown in the circuit diagram of Fig. 3. If the cam 1 2 is then rotated manually in a clockwise direction, contact blade 28 will move towards and then engage contact clip 29. During this initial movement, roller 70 remains on the land surface 74 and there is consequently no rotation of crank plates 58. With continued rotation of the cam, roller 70 will be caught in slot 72 and drawn downwardly so causing a clockwise pivoting action of crank plates 58 about the axis of pin 56 and a movement of slider 62 inwardly of the interrupter against the action of spring 66.This movement of the slider serves to close the internal contacts of the interrupter. This final rotation of the cam is at the same time forcing contact blade 28 into closer engagement with the clip 29.

When the contact blade first comes into engagement with the clip, the blade is electrically isolated from the supply by the open circuit interrupter. There is therefore no risk of arcing between the blade and the clip. Only after electrical contact has been made between the blade and the clip is the interrupter closed and the circuit connection completed between incoming supply terminal 44 and forward load terminal 32.

If the cam 1 2 is rotated in an anti-clockwise direction, that is to say in a direction to effect isolation, the roller 70 will be permitted to rise out of the slot 72 under the action of spring 66. The pivoting action of the crank plates 58 and consequential movement of the slider 62 away from the interrupter will open the internal interrupter contact. At this stage, the blade 28 is still in electrical contact with the clip 29 although it has of course moved a short distance away from its fully home position. Continued rotation of the cam will move the blade out of electrical contact with the clip and into its central, fully isolated, position shown in Fig. 1.Again, it will be appreciated that at the instant of electrical separation of the blade and the clip, the interrupter has already moved to the open position so that there is no risk of arcing between the blade and the clip.

Movement of the cam in an anti-clockwise direction from the position shown in full outline in Fig. 1 will serve to complete a circuit between the incoming supply terminal 44 and reverse load terminal 34. The sequence of events is exactly that described above, with the roller of course cooperating with the other one of the two slots 72. The use of the isolating switch in this way to provide load reversal is useful but the device could of course operate with a single pair of air gap switch contacts.

The described isolating switch is arranged so that a number of units can be combined on a single shaft to effect switching of any desired number of phases.

The current breaking and-if required current making capabilities of the isolating switch are dependent upon the speed of actuation of the vacuum interruptor and accord ingly upon the speed of rotation of the operat ing shaft 1 0. According to one advantageous feature of the invention, mechanism is inter posed between the operating shaft and the manually operable handle, whereby the speed of actuation of the vacuum interrupter is made independent of the manner of operation of the handle. Reference is made to Figs. 4 a), b) and c) which show, in diagrammatic form, a driven block 100 mounted to rotate with the operating shaft 10 and a drive block 102 carrying a handle 104 and arranged to rotate about the axis of the operating shaft.Lying between the driven and drive blocks is a cage 106 again rotatable about the axis of the operating shaft. This cage 106 includes two drive bars 108 which extend axially in both directions so as to be engagable with both the driven and the drive blocks. Compression springs 110 are mounted between the cage 106 and respective fixed points 11 2.

In the position shown in Fig. 4 a), which corresponds to the OFF position of the isolating switch, the compression springs 110 are in a relatively uncompressed state though they serve nonetheless to restrain any uncontrolled movement. As the handle 104 is moved downwardly and the drive block 102 rotated anti-clockwise, the drive bars 108 are engaged and the cage 106 rotates with the handle. In this movement, the two springs 110 are compressed. After approximately 120 of movement, the position shown in Fig.

4 b) is reached with the drive bars 108 coming into contact with the driven block 100 and the two springs just pushed over-centre.

The stored energy in the springs then serves to continue the rotating movement with the drive bars 108 forcing the driven block 100 to the ON position as shown in Fig. 4 c).

The sequence of operations from the ON to the OFF positions is analogous and requires no further description.

Since the rotation of the driven block 100, and hence of the operating shaft, is under the action of the compression springs, the speed of actuation of the vacuum interrupter is independent of the speed of movement of the handle. This applies to both making and breaking of current though in applications where a current making capability is not required a more compact mechanism might be employed. Similarly, a modified mechanism would be used where both an isolating action and a load reversing action were required.

A mechanical latch can be provided to ensure that the isolating switch is positively held in the closed position against the action of the interrupter compression spring. This latch may be incorporated in an over-centre spring arrangement as described above.

It should be understood that this invention has been described by way of example only and many variations are possible without departing from the scope of the invention. The described rotating cam represents a particularly advantageous way of actuating the interrupter and air gap switch in sequence, but other alternatives are possible such as a linearly displaceable wedge providing an inclined cam surface. The use of over-centre spring arrangements and mechanical latches is usually desirable but these will not be essential in all applications. Again, those skilled in the art will be able to devise obvious variants of the example described. The arrangement according to this invention enables a load reversing capability to be incorporated by the simple addition of a further contact clip and a slot in the cam surface. This is an important advantage but the invention can of course be used in cases where simple isolation is required and no load reversal.

Claims (9)

1. An electrical isolating switch comprising a non-arcing interrupter connected electrically in series with an air gap switch and a hand operated actuating mechanism serving in one movement to operate the interrupter and air gap sequentially such that the interrupter remains open circuit during both opening and closing of the air gap switch.

2. An isolating switch according to Claim 1, wherein the mechanism comprises a manually rotatable member carrying a movable contact of the air gap switch and including a cam surface and so lined with the interrupter as to actuate the same on rotation of said member.

3. An electrical isolating switch comprising a manually displaceable actuating member formed with a cam surface; an air gap switch having a movable contact carried on the actuating member and at least one fixed contact positioned as to engage the movable contact on displacement of the actuating member; a non-arcing interrupter connected electrically in series with the air gap switch and a cam follower cooperating with said cam surface and so linked with the interrupter as to actuate the interrupter on displacement of the actuating member, the cam and cam follower being so adapted that the interrupter and air gap switch are actuating in sequence with the interrupter remaining open circuit during both opening and closing of the air gap switch.

4. An isolating switch according to Claim 3, wherein said actuating member is rotatably mounted.

5. An isolating switch according to Claim 2 or Claim 4, wherein said cam surface includes a rest portion which is of arcuate form centered on the axis of rotation of the actuating member, the cam follower cooperating with said rest portion over a range of rotation corresponding with engagement or disengagement of the fixed and movable air gap switch contacts, the cam surface further including at least one operating portion adapted to displace said cam follower and thereby actuate the interrupter after initial engagement or prior to final disengagement of the fixed and movable contacts.

6. An isolating switch according to Claim 5, wherein the or each said operating portion of the cam surface comprises a slot.

7. An isolating switch according to any one of Claims 2 to 6, wherein the air gap switch comprises two fixed contacts which engage the movable contact on displacement of the actuating member in respective oppo site senses.

8. An isolating switch according to any one of Claims 2 to 7, further comprising a handle coupled to said actuating member by an over-centre spring arrangement serving to ensure full displacement of the actuating member on movement of the handle.

9. An electrical isolating switch substantially as hereinbefore described with reference to and as shown in the accompanying drawings.