ELECTROMAGNET

Abstract: The invention relates to an electromagnet with a magnet coil (10, 11) and a magnetic circuit consisting of a fixed core (12, 13) and a rotating armature (16). In the rest position of the armature the magnetic circuit exhibits two series-connected air gaps (21, 22) located inside the magnet coil. The magnet is primarily intended to be used as a kicker for directly actuating the contact system of an electric switch to achieve rapid breaking and limitation of the current in case of a short circuit.

Description: Electromagnet TECHNICAL FIELD The present invention relates to an electromagnet of the kind described in the preamble to claim 1. The magnet, which is designed with a rotating armature, is primarily intended to be used for operation of current-limiting switching devices for rated operating voltages of up to about 1000 V. However, it may be used with advantage in other applications as well, in which a rapid operation is required. BACKGROUND ART Electromagnets with rotating armature are previously known. In most of the designs known up to now, the air gap of the electromagnet (the pole surface of the armature) lies out ¬ side of the magnet coil. This causes a considerable part of the magnetic flux to be closed through the air outside the core, which results in considerable magnetic losses and reduces the attractive force of the electromagnet, especi¬ ally in the case of saturation. From US-A-3 253 195 it is also known, in an electromagnet with a rotating armature, to design the magnetic circuit with two series-connected air gaps, which are both enclosed within the magnet coil. This results in the magnetic flux being utilized considerably more efficiently than in those embodiments in which the air gaps of the magnet lie outside the magnet coil. This entails a greater attractive force of the magnet. In the prior art embodiment the magnet coil is completely surrounded by the magnetic core, which con¬ sists of a circular hollow cylinder provided with end plates, from which pole ends of circular segment-shaped ' cross section extend into the coil bobbin at the end por¬ tions thereof. The space available for the magnet armature in this design is small in relation to the outer diameter of the magnet. Therefore, the design is not suitable to use in current-limiting three-phase circuit.breakers, in which one operating magnet in each phase is-required and in which the distance between the phases is limited. In such cases a relatively large cross section of the magne¬ tic circuit is desired in order to achieve high flux values and, hence, great operating force and operating speed. It is then advantageous for the armature to be as wide as possible. Increasing the thickness of the armature is no good solution, since this reduces the length of stroke of the magnet. Another disadvantage of the prior art design is that, because of the cylindrical or semicylindrical shape of the magnetic circuit parts, ' it is relatively expensive to manu¬ facture. SUMMARY OF THE INVENTION The primary object of the present invention is to provide an ultrarapid striking pin, a so-called kicker, for direct- ly actuating the contact system of a switching device to achieve a rapid breaking and limitation of the current in case of a short circuit. This is achieved with an electro¬ magnet-provided with a rotating armature, the magnetic cir¬ cuit of the electromagnet having two series-connected air gaps, like the described prior art design, which are both enclosed in the magnet coil. According to the invention, the magnetic core consists of a substantially rectangular frame or U-shaped yoke, which surrounds the coil in such a way that two opposite sides of the envelope surface of the coil are free. By not having any adjacently located iron mass on two opposed sides of the coil, the advantage is obtained that, in a three-phase circuit breaker with a kicker in each phase and with a limited distance between the phases, a relatively wide armature can be accomodated in the kicker. By increasing the cross section of the mag- netic circuit in this way, higher flux values are achieved, which entails a greater attractive force of the magnet, a faster opening movement of the switching device and hence a higher breaking capacity. An additional improvement in this respect can be obtained by constructing the core from magnetic sheets. The magnetic force can be transmitted from the armature to the contact carrier of the switching device with the aid of an operating arm fixed to the armature. Because of the rotating movement of the armature, a relativley large length of stroke with a relatively small air gap can be obtained with such a design. Otherwise, the design pro¬ vides great possibilities, among other things by changing the length of the operating arm, of trimming the tripping force, the contact speed and the contact distance. To avoid that the operating arm influences the magnetic flux in the magnet, the operating arm can be made of non-magne¬ tic material. The bearing arrangement of the rotating magnet armature is accomplished according to the invention with the aid of guiding surfaces on the inside of the coil bobbin. Since the armature is loosely located in the coil bobbin and is guided up by guiding surfaces thereon, the manufacture and the mounting will be simpler and less expensive than in the prior art designs using fixed bearing points. In addi¬ tion the armature can be made solid without holes for bear¬ ings, which makes possible a greater magnetic flux in the armature. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in greater detail, by describing a number of embodiments, with reference to the accompanying drawings, wherein Figures 1 and 2 show a first embodiment of an electromagnet according to the invention, Figure 1 being a section along the line I-I in Figure 2, and Figure 2 a section along the line II-II in Figure 1, Figure 3 shows separately the different parts inclu ¬ ded in the magnet according to Figures 1 and 2, the arrows showing how the parts are assembled together, Figures 4 and 5 show, in the same way as in Figure 1, a second and third embodiment, respectively, of an electromagnet according to the inven¬ tion, Figures 6, 7, 8 and 9 show a fourth embodiment of an elec ¬ tromagnet designed according to the inven¬ tion, Figure 6 being a view from the side, Figure 7 a view from above, Figure 8 a sec ¬ tion along the line VIII-VIII in Figure 7, and Figure 9 a section along the line IX-IX in Figure 6, and Figures 10, 11 and 12 show a fifth embodiment of an elec¬ tromagnet according to the invention, Figure 10 being a view from the side, Figure 11 a view from above, and Figure 12 a section along the line XII-XII in Figure 11. DESCRIPTION OF THE PREFERRED EMBODIMENTS The electromagnet shown in Figures 1 and 2 is built up of the parts shown in Figure 3. The magnet comprises a winding 10 of insulated copper wire arranged around a coil tube 11 of plastic. The coil consisting of parts 10 and 11 is surrounded by a frame-shaped iron core, which consists of two identical, substantially L-shaped parts 12, 13 made of iron plate by punching and bending. One leg of the core parts 12, 13 exhibits an inwardly-bent tongue 14 and 15, respectively. These tongues, which form the pole ends of the magnetic core, extend into the coil 10,-11, at the end portions thereof. The magnet has an armature 16 enclosed in the magnet coil, the armature being rotatable about an axis of rota ¬ tion oriented perpendicular to the longitudinal axis of the winding 10. The axis of rotation passes through the central portion of the armature, the central portion being journalled, via an operating arm which will be described below, between two ridge-formed wall portions 17, 18, directed against each other, in the coil tube 11. For guiding the armature during its rotary movement, the co.il tube is formed with diametrically located cylindrical guiding surfaces 19 » 20. The armature 16 is rotatable between a rest position in which the magnetic circuit exhibits two series-connected air gaps 21, 22, and an activated position in which the armature makes contact with the pole ends 14, 15 of the magnetic core. The movement of the armature is brought out from the magnet with the aid of an operating arm fixed to the armature. The operating arm consists of two arm parts 23, 24 of non-magnetic material, for example brass, stainless steel, plastic, etc., which are each arranged on a respective side of the armature. To fix the arm parts to the armature, the mid-portions of the arm parts are provided with square holes 25 fitting square shaft pins 26 on the armature. The arm parts are formed with circular mid-portions which together with shoulder surfaces on the wall portions 17, 18 of the coil tube form a bearing for the operating arm and the armature. The arm parts are joined together with the aid of two pins 27, 28 at the ends of the arm parts. In the case of a currentless magnetic winding, the arma- ture is kept in its rest position with the aid of a tension spring 30, one end of which is attached to the pin 27 and the other end of which is attached to a fixing projection 31 stamped on the magnetic core. --. 5 In the electromagnet shown in Figure 4, the iron core 12, 13 consists of two identical halves composed of ferromag¬ netic plates. Otherwise, this embodiment does not differ, in principle, from the design shown in Figures 1-3. By using a laminated iron core according to Figure 4, better 10 magnetic properties and a greater attractive force are achieved in the magnet. In the embodiment according to Figure 5, the operating arm 23 is an extension of the armature 16, the armature move ¬ ment thus being made available without any extra parts. In addition, in this embodiment the magnetic core 12 is made in one single sheet metal part, which has been com ¬ pletely bent after the mounting of the armature. The shape of the core before the bending is completed is shown in dashed lines. The bearing of the armature is integra- 0 ted with the coil tube, which for this purpose is formed with two laterally displaced support walls 32, 33. The armature is formed with two oppositely directed projec¬ tions 34, 35 cooperating with the support walls 32, 33 for fixing the armature in the axial direction. A com- 5 pression spring 36 maintains the armature in its rest position when the magnet coil is currentless or is tra¬ versed by current below a certain level. In the embodiment shown in Figures 6-9, the magnetic core consists of a substantially rectangular frame consisting of 30 two side plates 12, 13 and two cross-pieces 14, 15. The four parts 12-15 are joined together by pins on the cross- pieces being riveted into holes in the side plates. The cross pieces 14, 15 form the pole ends of the magnetic core, which pole ends in this case do not extend into the 35. magnet winding 10 but are located in immediate proximity to the ends of the winding. The side plates 12, 13 extend diagonally between the ends of the winding. In this way the operating arm 23, which in this case consists of an extension of the armature 16, will, in the rest position of the armature, lie at a greater distance from the mag- netic core. In this way it is not necessary to use a separate, non-magnetic operating arm, and, accordingly, a simpler and less expensive design is obtained without the attractive force of the magnet being reduced to any signi- ficant extent. From Figure 9 it is clear that the axial holes of the coil bobbin have a substantially rectangular cross section. In comparison with the prior art design according to US-A-3 253 195 mentioned above, this permits the use of a relatively wide armature with a great length of stroke. The embodiment shown in Figures 10-12 differs from that described with reference to Figures 6-9 in that the magne¬ tic core consists of a substantially U-formed yoke, the base portion 12 of which extends diagonally between the ends of the magnet coil and the legs 14, 15 of which form the pole ends of the magnetic core. Since this embo¬ diment consists of only a few parts, it will be relatively inexpensive to manufacture. The invention is not limited to the embodiments shown but several variants are possible within the scope of the claims.

Claims: CLAIMS 1. An electromagnet comprising a magnet ςoil (10,11) and a magnetic circuit partly surrounded by ' the magnet coil and consisting of a fixed core (12, 13) and a rota- tably arranged armature (16) positioned in the magnet coil, said armature being rotatable between a rest posi¬ tion, in which the magnetic circuit exhibits two series- connected air gaps (21, 22), and an activated position, in which the air gaps are at least approximately short- circuited, the two air gaps (21, 22) being located inside the magnet coil (10, 11) or in immediate proximity to the ends thereof, c h a r a c t e r i z e d in that the magnetic core (12, 13) consists of a substantially rectan¬ gular frame or a U-formed-yoke, which surrounds the coil (10, 11) in such a way that two opposed sides of the envelope surface of the coil are free. 2. An electromagnet according to claim 1, c h a r a c ¬ t e r i z e d in that the magnet coil (10, 11) consists of a winding (10) which is arranged on a coil frame (11) made of insulating material, the interior of said coil frame being provided with guiding surfaces (19, 20) for the movement of the armature. 3. An electromagnet according to claim 1 or 2, c h a r a c t e r i z e d in that the magnetic core (12, 13) is formed with pole ends (14, 15) extending into the coil at the en portions thereof. 4. An electromagnet according to claim 1, 2 or 3, c h a r a c t e r i z e d in that the core (12, 13) con¬ sists of two joined, identical parts made of iron sheet by punching and bending. 5. An electromagnet according to any of the preceding claims, c h a r a c t e r i z e d in that it is provided with an operating arm (23, 24) fixed to the armature and projecting from the coil (10, 11) at at least one of the ends of the coil. 6. An electromagnet according to any of the preceding claims, c h a r a c t e r i z e d in that the axis of rotation of the armature (16) is perpendicular to the longitudinal axis of the coil (10, 11). 7. An electromagnet according to any of the preceding claims, c h a r a c t e r i z e d in that it is provi¬ ded with a spring (30, 36) for returning the armature (16) to its rest position. 8. An electromagnet according to any of the preceding claims, c h a r a c t e r i z e d in that the operating arm (23) and the armature (16) are made in one piece. 9. An electromagnet according to any of the preceding claims, c h a r a c t e r i z e d in that that part (12, 13) of the magnetic core which extends along the magnet coil (10, 11) is obliquely directed in relation to the longitudinal axis of the coil. 10. An electromagnet according to any of claims 2-9, c h a r a c t e r i z e d in that the coil frame (11) has an axially through-going hole for the armature, which hole, at least at the end portions of the coil frame, has a sub¬ stantially rectangular cross section.

Inventors: ABRI ASSADOLLAH, NORDGREN ROBERT, ABRI, ASSADOLLAH, NORDGREN, ROBERT
Applicants: ASEA BROWN BOVERI, ASEA BROWN BOVERI AB
Application year: 1989
Main classification: H01F7
IPC codes: H01F7