Magnetic actuator arrangement

Abstract

 A magnetic actuator arrangement, principally for a vacuum switching apparatus, employs, instead of precision ball-joint bearings (16) supporting the armature (14), simple bushes (40) with an inside diameter deliberately greater than the outside diameter of the armature spindle (15), such that the armature (14) is a loose fit inside the bushes (40). The effect of this is to enable the armature (14) to make non-rotational movements in the plane perpendicular to the spindle (15), and so automatically to assume a properly seated position with respect to the pole pieces (21, 22) of the magnets (10, 11) when the latter are energised, thereby eliminating an undesirable vibration at the magnet-armature interface. With conventional bearings having negligible play, this can only be done after time-consuming manual adjustment of the bearing locations by skilled technical personnel.

Description

[0001] The invention concerns a magnetic actuator arrangement comprising one or more electromagnets attached to a frame and an armature pivotably attached to the frame, and in particular, but not exclusively, a magnetic actuator arrangement for operating one or more vacuum switching devices.

[0002] A known magnetic actuator arrangement is shown in Figure 1. This magnetic actuator arrangement, which is part of a vacuum contactor chassis developed by the applicants, comprises a pair of electromagnets 10, 11 fixed to a frame 12 on a transverse member 13 thereof, and an "L"-shaped armature 14 with a welded- or brazed-on spindle 15 resting in a pair of ball-joint bearings 16 fixed to respective vertical members 17 of the frame 12.

[0003] The electromagnets 10, 11 each have a pole piece 21, 22 and a vertical portion 18 of the armature 14 is positioned so that, in an unenergised state of the actuator, it is spaced apart from the pole pieces 21, 22, the necessary gap being maintained by a pair of springs 23, 24 which are fixed to the transverse member 13 and act against the vertical portion 18 of the armature 14.

[0004] The horizontal portion 19 of the armature 14 is linked by a suitable linkage arrangement (not shown) to the actuator rods 25 of a group of three vacuum switches 26 (shown only very schematically), one for each phase of an AC system with which the switching apparatus is to be used. The switches 26 are mounted on a subframe 20, which is fixed to the vertical members 17, and are equipped with high-voltage terminals 27, 28 for connection to the AC system.

[0005] In operation, current is supplied to the electromagnets 10, 11 and the armature portion 18 is attracted against the springs 23, 24 towards the pole pieces 21, 22 of the electromagnets. The armature pivots in the bearings 16 at each side of the frame 12, so that the horizontal portion 19 of the armature is moved downwards, moving the actuator rods 25 of the switches 26 from an "open" to a "closed" position of the contactor. At the same time, a further linkage arrangement (not shown) actuated by the armature 14 operates two auxiliary switches 29 (shown only in plan view), thereby providing auxiliary signals and power for use in other, external equipment.

[0006] One potential problem with the arrangement just described is that, unless the face of the armature portion 18 sits exactly square against the pole pieces 21, 22 when the actuator is energised, a noticeable vibration manifesting itself in the form of a buzzing sound will result which can be very annoying for personnel working in the same environment as the switching apparatus and may be detrimental to its long-term operation. Because of this, the actuator design shown in Figure 1 employs an accurately adjustable bearing system in the form of the ball joints 16 (see Figure 2), each of which is attached to a side 30 of the vertical member 17 by a thread-and-nut arrangement 31, this arrangement allowing fine backward and forward adjustment of the armature relative to the pole pieces 21, 22. In order to allow such movement of the ball joints, the hole 34 in the frame member 17 through which the spindle 15 passes is arranged to be significantly larger than the diameter of the spindle.

[0007] Because the ball joints 16 are secured not to the main faces of the members 17 but to the sides 30 thereof, it is necessary to strengthen this part of the frame by the addition of screwed rods 32 and associated nuts 33 close to the ball-joint fixing points.

[0008] In practice, it is often necessary to adjust both bearings to achieve perfect seating of the armature against the pole pieces, and this is almost invariably the case when two magnets are employed, as here. Such adjustment requires the intervention of skilled technical personnel and this, together with the need for the precision ball-joints 16 and the reinforcing items 32, 33, adds to the cost of the chassis.

[0009] In accordance with a first aspect of the invention, there is provided a magnetic actuator arrangement, comprising one or more electromagnets attached to a frame and an armature pivoted in one or more bearings disposed in said frame, a portion of said armature being attracted to said electromagnets when the latter are energised, said armature having a spindle which is a loose radial fit in said bearings.

[0010] Each of said bearings may be constituted by a bush located in said frame.

[0011] The actuator arrangement may comprise two electromagnets and two bushes, said bushes being disposed at opposite ends of said frame.

[0012] The total clearance between the spindle and the bush may be greater than 0.2mm.

[0013] In accordance with a second aspect of the invention, there is provided an electrical switching apparatus, comprising a magnetic actuator arrangement as described above, in which said apparatus to be actuated is one or more switching devices. These devices may be vacuum, air, oil or SF₆ switches, for example.

[0014] An embodiment of the invention will now be described, by way of example only, with reference to the drawings, of which:

Figure 1 shows front, side and plan views of a vacuum contactor chassis incorporating a known magnetic actuator arrangement;

Figure 2 is a section along the line II-II in Figure 1;

Figure 3 is a section along the line II-II in Figure 1 for an equivalent vacuum contactor chassis incorporating a magnetic actuator arrangement according to the invention;

Figure 4 is a view of the section of Figure 3 looking from the right, and

Figure 5 shows a typical lie of the armature of a magnetic actuator arrangement according to the invention for (a) an unenergised and (b) an energised state of the actuator.

[0015] Referring now to Figures 3 and 4, the magnetic actuator arrangement of the present invention employs, instead of the expensive ball joints 16 of the known arrangement, a simple plain bearing in the form of a bush 40 inserted as an interference fit in a hole 41 in each of the frame members 17. The lip 42 of the bush 40 is situated inside the frame 12 so that, when the armature with its spindle 15 is in place, the bushes are kept from being dislodged by the presence of the armature.

[0016] The bushes 40 have an inside diameter 43 which is significantly larger than the diameter of the spindle 15. The difference may be of the order of 0.5mm. In an unenergised state of the actuator, due to the restoring action of the springs 23, 24 the spindle 15 will lie approximately in the position shown in Figure 5(a); however, when current is supplied to the electromagnets 10, 11, the attractive force on the armature 14 will tend to lift the spindle while it is turning, so that the spindle will assume a new position approximately as illustrated in Figure 5(b). This ability of the spindle to move inside the bearing in the plane of the principle face of the frame member 17 (i.e. radially with respect to the bushes 40) enables the armature to take up a properly seated position relative to the pole pieces 21, 22 of the electromagnets 10, 11, while at the same time executing its normal rotating movement within the bearing.

[0017] The amount of allowable non-rotational movement of the spindle inside the bearing is always arranged to be significantly less than the amount of vertical movement available (e.g. 3-4mm) at the point of action of the portion 19 of the armature on the actuator rods 25, so that correct switching operation of the contactor chassis is not impaired.

[0018] In contrast to the conventional bearing arrangement, the spindle 15 is never in full contact with the bush bearing 40 and wear on the latter is therefore minimal. Indeed, using a nylon composition as a preferred material for the bush 40, it has been found that in a test chassis of the above-described design which has been subjected to over 3,000,000 operating cycles, the bushes have exhibited virtually no wear at all.

[0019] The armature shape so far described is a preferred one, since it allows a fairly compact switching unit to be produced. However, it is possible to have an armature of any shape (e.g. straight instead of "L"-shaped) to suit a particular application, provided the armature always performs its required relay action, i.e. is able to translate the attractive movement of the portion of the armature near the magnets into some other desired movement at a distant point.

[0020] Also, although the use of two electromagnets has been assumed, it may, depending on the particular application, be possible to use only one electromagnet or, on the other hand, even more than two. Use of more than two magnets, however, may well require a greater clearance between the bushes and the armature spindle than would be the case with only one or two magnets.

Claims

1. A magnetic actuator arrangement, comprising one or more electromagnets (10, 11) attached to a frame (12) and an armature (14) pivoted in one or more bearings (40) disposed in said frame (12), a portion of said armature (14) being attracted to said electromagnets (10, 11) when the latter are energised, said armature (14) having a spindle (15) which is a loose radial fit in said bearings (40).

2. A magnetic actuator arrangement as claimed in Claim 1, in which each of said bearings is constituted by a bush (40) located in said frame.

3. A magnetic actuator arrangement as claimed in Claim 2, comprising two electromagnets (10, 11) and two bushes (40), said bushes (40) being disposed at opposite ends of said frame (12).

4. A magnetic actuator arrangement as claimed in any one of the preceding claims, in which an outside diameter of said spindle (15) is at least 0.2mm less than an inside diameter of said bush (40).

5. An electrical switching apparatus, comprising a magnetic actuator arrangement as claimed in any one of the preceding claims, in which said apparatus to be actuated is one or more switching devices.

Drawing