THREE-PHASE FLAT COILS

Abstract: There is provided a three-phase flat coil having coil portions each including output terminals (a₁, b₁, c₁, a₂, b₂, c₂) constituting winding-in and winding-out portions on an outer periphery (L₁-L₂) of an insulating plate and an electrical conductor positioned radially on front (o) and back (B) sides of said insulating plate and having bent-over portions (R) on outer (L₁-L₂) and inner (L₃-L₄) peripheries thereof, three-­ phase coil windings including a-phase, b-phase and c-phase windings each wound in a wave form in the same direction and ends (b, b₂) of the b-phase winding at said output terminals being different in polarity from ends (a₁, a₂, c₁, c₂) of the a-phase and c-phase windings to form an aggregation of said coil portions, and a gangway or bridging wiring member (4) including intersections (X′) provided intermedi­ ate said three-phase coil windings and collectively posi­ tioned at substantially one point of the outer periphery (L₁-L₂) of said insulating plate, and said intersections (X′) being three-dimensionally intersected with one another and connected to the respective a-phase, b-phase and c-phase coil windings. The bridging wiring member (4) having the intersections (X′) is not provided on the inner periphery (L₃-L₄) of the insulating plate and is not disposed dispersedly on a plurality of points of the peripheries thereof, but said member is collectively provided only at substantially one point of the outer periphery of the insulating plate thereby rendering the manufacture and wiring arrangement much easier.

Description: THREE-PHASE FLAT COILS Background of the Invention This invention relates to a three-phase alternating current coil and particularly to a three-phase flat coil having flat coil windings for three-phase alternating current for use in, for example, a printed circuit motor or a three-phase alternator. Hitherto, in three-phase alternating current coils, a coil winding for one has been wound in an opposite direction to that of the remaining two coil windings for simplifying the end treatment or working. Fig. 1 is a winding diagram of a conventional threephase alternating current coil in which a coil winding for a phase b is wound in an opposite direction to coil windings for phases a and c to provide a close arrangement of their positive and negative terminals in the end treatment or working. In order to provide a printed coil formed by such a conventional winding methods as shown in Fig. 1, however, there are disadvantages that because of the opposite winding direction of the coil winding for the phase b this coil winding intersects the coil windings for phases a and c at portions X, and thus electrical insulation has to be provided at the portions X. This will hereunder be descried more in - detail. References 1 to 12 shown in Fig. 1 designate numbers of disposition of coil portions. Furthermore, in case of a printed coil, there is strictly required no slot (coil containing groove), different from a ringlike core. For simplification, however, the disposition of coil portions corresponding to the number of 1 to 12 is numbered as slots7 which will be referered to as slot number hereinbelow. In Fig. 1, a disc-like printed coil is shown in a web-like development. Therefore, a line L1 L2 shows an outer periphery of an effective area of the disc-like printed coil, and a line L3 - L4 shows an inner periphery of the effecive area of the coil. This will be apparent when referring to Fig. 8 showing the outer configuration of a practical printed coil. In Fig. 1, a coil portion P1 is provided on a front side of the disc-like winding and bent at the inner periphery thereof so that a portion P2 extends on a back side of the disc. In this way, portions P3 and P4 are also provided on the front side of the disc-like winding, and portions P5 and P6 are on the back side thereof. In this case, a coil portion P7 of a noneffective area on the inner periphery is on the front side, and a portion P8 is on the back side. A portion P9 is on a boundary between the front and back sides and passes through an inner periphery L5 of the disc of Fig. 8. As described above, there are portions provided on the front and back sides. In Fig. 1, the portions provided on the front side are referred to by (0), and the portions provided on the back side are also referred to by (B). It is thus apparent that there are intersections X at which two front winding portions are intersected with each other or two back winding portions are intersected with each other. Such portions have to be fomred in three-dimentional intersections to provide electrical insulation therebetween, but such insulation will be difficult and the size will become large and bulky. Moreover, the wiring arrangement of Fig. 1 must have the intersections X positioned dispersedly throughout the inner and outer peripheries of the printed coil. To solve this problem, it is thikable to use a winding (magnet wire) having an insulating coating thereon, but this will render the intersections thick in size and make it impossible to manufacture a thin and flat printed coil. It is a first object of the present invention to provide a three-phase flat coil in which such intersections are reduced in number to the utmost and the reduced intersections are collectively provided at substantially one point or in a far smaller area. A second object of the present invention is to provide a three-phase flat coil having a sold and firm insulating construction of the intersections manufactured easily. A third object of the present invention is to provide a three-phase flat coil having a high output by overlapping a plurality of coil discs in layer. A fourth object of the present invention is to provide a multi-layered three-phase flat coil having an easy connection between the coil discs and thus capable of being manufactured easily. Another object of the present invention is to provide a three-phase flat coil comprising coil portions each including output terminals constituting winding-in and winding-out portions on an outer periphery of an insulating plate and an electrical conductor positoned radially on front and back sides of said insulating plate and having bent-over portions on outer and inner peripheries thereof, threre-phase coil windings including a-phase, b-phase and c-phase windings each wound in a wave form in the same direction and ends of the b-phase winding at said output terminals being different in polarity from ends of the a-phase and c-phase windings to form an aggregation of said coil portions, and a gangway or bringing wiring member including intersections provided intermediate said three-phase coil windings and collectively positioned at substantially one point of the outer periphery of said insulating plate, and said intersections being three-dimensionally intersected with one another and connected to the respective a-phase, b-phase and c-phase coil windings, so that the bringing wiring member having the intersections is not provided on the inner periphery of the insulating plate and is not disposed dispersedly on a plurality of points of the peripheries thereof, but said member is collectively provided only at substantially one point of the outer periphery of the insulating plate thereby rendering the manufacture and wiring arrangement much easier. A further object of the present invention is to provide a three-phase coil in a generally flat and thin form, even if the size of the bringing wiring member is increased. A still further object of the present invnetion is to reduce air gap or the like of the magnetic circuit of a rotary electric machine incorporating a three-phase thin and flat coil according to the present invention to minimize the magnetic resistance and increase the output. Brief Description of the Drawings Fig. 1 is a development showing a winding Fig. 2 is a development showing the principle of a winding arrangement of a three-phase coil in accordance with the present invention; Figs. 3 and 4 are vector diagrams showing the generating conditions of electromotive forces in the three-phase coils of Figs. 1 and 2; Fig. 5 is a.development of a first embodiment of the three-phase flat coil in accordnace with the present invention; Fig. 6 is a wiring diagram of a bringing wiring member area of the three-phase coil of Fig. 5; Fig. 7 is a wiring diagram of the coil in star connection of Fig. 5; Fig. 8 is a front view of a second embodiment of the coil of the present invention just before the finished-product thereof; Fig. 9 is a rear view of the coil of Fig. 8; Fig. 10 is a development of the second embodiment of the coil; ; Fig. 11 is a diagrammatic represnetation of the coil in the finished condition of Fig. 10; Fig. 12 is a practaical wiring diagram of a bringing wiring member area to be assembled with the coil of Fig. 10; Fig. 13 is a part-sectional view of a threephase alternator incorporated with the second embodiment of the coil; Fig. 14 is a fragmentary section of a part of a housing of the alternator of Fig. 13; Fig. 15 is a section of the bringing wiring member as viewed in a direction of an arrow XV of Fig. 13. Fig. 16 is a section taken along a line XVI-XVI of Fig. 15; Fig. 17 is a simple and diagrammatic representation of electrical connection of the winding of Fig. 10; Fig. 18 is a diagrammatic representation of electrical connection of a multi-layered three-phase coil with increased windings, which is a third embodiment of the present invention; Figs. 19 to 21 show the construction of the third embodiment, Fig. 19 being a section taken along a line XIX-XIX of Fig. 21, Fig. 20 being a fragmentary section taken along a line XX-XX of Fig. 21, and Fig. 21 being a section similar to that of Fig. 15 and showing the bringing wiring member area; Fig. 22 is a front view of a fourth embodiment of the present invention; Fig. 23 is a fragmentary section taken along a line XXIII-XXIII of Fig. 22; Fig. 24 shows a strip in a manufacturing step; ; Fig. 25 shows the strip of Fig. 24 in its finished condition; Fig. 26 is a section taken along a line XXVI-XXVI of Fig. 25; Fig. 27 is a front view of a fifth embodiment of the present invention; Fig. 28 is a fragmentary section in an enlarged scale of a portion shown by a circle XXVIII-XXVIII of Fig. 27; Fig. 29 is a section taken along a line XXIX-XXIX of Fig. 28; Fig. 30 is a sectional side view of the coil of Fig. 27; and Fig. 31 is a section taken along a line XXXI-XXXI of Fig. 30. Detailed Description of the Embodiment Fig. 2 is a development similar to that of Fig. 1 and shows a winding arrangement which is designed by and applied to the present invention. The arrangement of Fig. 2 has a b-phase winding wound in the opposite direction to that of the b-phase winding of Fig. 1, and a-phase, b-phase and cphase windings are all wound in the same direction in a wave form. Instead, the polarity of ends of the b-phase coil winding is reversed so that the direction of flow of current through the b-pahse winding of Fig. 2 is opposite to the direction of flow of current through the b-phase winding of Fig. 1. In the drawings, the references + and - designate positive and negative polarities, respectively. In other words, the pahse of the b-phase winding of Fig. 2 is deflected by an angle of 180 from the phase of the b-phase winding of Fig. 1. In order to remove this deflection of phase, the positive and negative polarities of the ends of the b-phase winding are changed to each other, that the same phase condition can be established by changing the end b+ of the b-phase winding of Fig. 1 to the end b- of the b-phase winding of Fig. 2. The electromotive forces generated in a threephase alternator are shown in Fig. 3 in the case of star connection and in Fig. 4 in the case of delta connection. In Figs. 1 and 2, a reference (U) designates a pole of N- or S-polarity of the magnetic field and moves through the slots at angles of 0 , 60 /P, 120 /P ..... 360 /P, where P designates a number of pole pairs. Figs. 3 and 4 show the directions of generation of the electromotive forces at the individual angles in the a-phase, b-phase and c-phase coil win dings. (In Fig. 3, outward arrows designate currents from positive to negative, and in Fig. 3 clockwise arrows designate currents from positive to negative.) In the conventional windings of Fig. 1, the electromotive forces are generated as shown in Fig. 3 in the case of star connection, and as shown in Fig. 4 in the case of delta connection. The windings of Fig. 2 used with the present invention also generate the same electromotive forces as shown in Fig. 3 in the case of star connection and as shown in Fig. 4 in the case of delta connection. In the winding system of Fig. 2, apparent intersections are causd in portions Y. Howeer, all the intersections are formed on the front and back sides of the coil portions as referred to by (0) and (B), respectively. Therefore, it is not necessary that the portions Y are provided with sepcific insulation to be interposed between-the coil portions. In the windings shown in Figs. 1 and 2, a part of slots positioned on the front and back sides of the disc-like flat coil is not used. For example, the portions of the slot numbers 2, 3 and 4 are provided with coil portions only on their front side, and no coil portion is provided on the back side of the disc-like coil corresponding to the slot numbers 2, 3 and 4. In the portions of the slot numbers 5, 6 and 7, only the back side is utilized. Particularly, such a winding system using only either the front or back side is very inefficient. Therefore, the coil of the present invention has windings shown in Fig. 5. The coil of Fig. 5 which is a first embodiment of the present invention has twelve slots which are all contained with conductors. The number of the pole pairs P is two in this case. In Fig. 5, references a1, b1, c1, a2, b2 and C2, designate output terminals, and t and e designate the polarity, and (R) designates a bent-over portion. In this Fig. 5, furthermore, the coil portion positioned on the front side of the disc-like flat coil is referred to by (0), and the portion positioned on the back side is referred to by (B). The lines L1-L2 and L 3-L4 designate the outer and inner peripheries, respectively, of the disc-like coil. As will be apparent from Fig. 5, coil portions are provided on the front and back sides of slot numbers 10, 11 and 12, but electrical connection should be provided from the back side of the slot numbers 10, 11, and 12 to the back side of the slot numbers 1, 2 and 3. Among the slots positioned as ... 7, 8, 9, 10, 11, 12, 1, 2, 3, 4, 5, 6 ... circumferentially along the outer periphery of the disc-like coil, three electrical connections for a-phase, b-phase, and c-phase from the slots 10, 11 and 12 to the slots 1, 2, and 3 should be made through three three-dimensional intersections X' as diagrammatically shown in Fig. 6, wherein the coil portions are mutually insulated. In Fig. 6, references 1T, 2T, 3T 10T, llT and 12T designate bridging terminals provided on the outer periphery of the coil portions connected to the coil portions positioned in the slot numbers 1, 2, 3, 10,. 11 and 12, respectively, and 2 is a coil portion and 3a is a projection of the insulating plate. In this manner, the coil of the present invention has the intersections X' but they are reduced in number and collectively provided substantially at one point of the outer periphery of the disc-like coil. The intersections X' are shown as a bridging wiring portion 4 in Fig. 5. It is, therefore, apparent that the construction of Fig. 6 is much more simple than that of Fig. 1 wherein a larger number of intersections are dispersedly provided on both the inner and outer peripheries. Fig. 7 is a more diagrammatical and simple representation of the wiring diagram of Fig. 5, and, for example, lines shown by dotted lines are added as bridging lines to form a neutral output terminal (NT) and the terminals al, bl, and cl are provided as three-phase alternating current output terminals to form a threephase flat coil having star connection usable as an armature coil for a three-phase alternator. The second embodiment will now be described. This embodiment has eight pole pairs and forty eight slots and is shown in Fig. 8 in a front view and in Fig. 9 in a back view. As will be apparent from these figuares, no such a bridging wiring portion 4 with the tersections as is shown in Fig. 5 is provided in the printed coil of Figs. 8 and 9. Fig. 10 is a development of the printed coil having eight pole pairs and forty eights slots but having no bridging wiring portion. In Fig. 10, references 1 to 48 are slot numbers. In order to form a three-phase coil as diagrammatically shown in Fig. 11 from the coil of Fig. 10 by making electrical connection with a bridging wiring portion similar to the coil of Fig. 5, terminals all' bl' and c1' connected to coil portions on the back side of . . . the slots 46, 47 and 48 of Fig. 10 and terminals a2', b2' and c2' connected to coil portions on the back side of . . . the slots 1, 2 and 3 have to be connected by bridging wiring portion. Fig. 12 is a diagrammatic representation of such bridging wiring portion 4. The construction of the coil of Figs. 8 and 9 will be described below. Figs. 8 and 9 show front and back sides of a single layered three-phase flat coil. In these drawings, 2 designates coil portions particularly made of copper strips, and 3 designates an insulating resin plate, such as a mica plate or an insulating resin plate, having an opening 3c at its center portion. The copper strips 2 are made in a quite same shape and welded on the front and back sides across the insulating plate 3, and gaps between adjacent copper strips 2 are filled with an insulating silicone resin material 15 to fix the strips 2, thereby forming a three-phase alternating current coil. 3a is a part of the insulating plate 3 slightly projecting outwardly from the outer periphery. Provided adjacent to this projecting portion 3a of the insulating plate is a bridging wiring member 4 shown in Fig. 12. A three-phase alternator incorporated as an armature coil with the three-phase flat coil of the second embodiment in which the coil portions are provided in all the slots of the front and back sides and which has eight pole pairs P and forty eight slots will be described by referene to Figs. 13 to 16. In Fig. 13, 2 designates copper strips on the front and back sides of the printed coil to constitute coil portions, 3 being an insulating plate for insulating the copper strips on the front and back sides, and the three-phase flat coil of the present invention being mainly formed by the strips 2 and the plate 3. 4 designates a bridging wiring member constituting a single intersecting portion which corresponds to the portion diagrammatically shown in Fig. 12. 5 is a connector, 6 is a shaft rotatably supported by bearings 7a and 7b. 8a and 8b are rotors fixed to the shaft 6, and 9a and 9b are permanent magnets incorporated in the rotors 8a and 8b. 10a and 10b are housing portions and 11 is a known thyrister bridge for commutating the three-phase current. Fig. 14 is a section showing a fitted portion between the front and rear housing portions 10a and 10b, and 14 is the fitted portion, 12 is a fixing throughbolt, and 13 is an insulating plate for holding the coil portions 2. Figs. 15 and 16 are sectional view showing more in detail the bridging wiring member 4 constituting the single intersection portion of Figs. 12 and 13, and Fig. 15 is as viewed in the direction of the arrow XV of Fig. 13, and Fig. 16 is a section taken along the line XVI-XVI of Fig. 15. The references designating the terminals in Fig. 15 are same as those shown in Fig. 12. In Fig. 15, 15 is an insulatinag silicone resin material for fixing the copper strips 2, and 4a is an insulating member, such as an insulating resin or ceramic, and 4b, 4c and 4d are connecting copper webs or bus bars made of a metal. The bridging wiring member 4 having the intersecting portion is located within the front housing portion 10a as shown in Fig. 13. The third embodiment of the invention will be described below. The third embodiment is made by overlapping a plurality of disc-like flat coils having such an outer configuration as shown in Figs. 8 and 9 to generate an increased output. The third embodiment is described with the aid of Figs. 8, 9 and 10 showing the second embodiment. It has been described hereinabefore that the wiring diagram of the single disc-like coil of Figs. 8 and 9 can be shown by Fig. 10. A more simplified representation of the circuit of Fig. 10 is seen in Fig. 17. Therefore, if three discs as shown in Figs. 8 and 9 are overlapped with and electrically connected in series to one another, the connection will be as shown in Fig. 18. As will be apparent from this figures, each of the discs has six output terminals al, bl, cl, a2, b2, and c2 and six gangway or bridging terminals awl', bull' C111 a311 b21 and c211 and those terminals are all positioned substantially at one point of the outer periphery of the disc, i.e., on the front and back sides of the projecting portion of the insulating plate. In order to connect the three discs in series, therefore, the output terminals a1, bl, cl of the first disc 51 are connected as the output of the three-phase coil to the output line member 54 through output wiring 56, and the bridging terminals all' bull' ... c21 of the frist disc 51 may be connected to the output terminals al, bl, ... c2 of the second disc 52. In this case, the bridging terminals al', bl', ... c2' of the first disc-like coil and the output terminals al, bl, ... c2 are located back to back and connected as shown in Fig. 20 described hereinlater. Moreover, the other portions of the insulating plate than the projecting portions 3a need not be fixed between the discs as shown in Fig. 19. Fig. 19 is a section (taken along the line XIX-XIX of Fig. 21) of a part of a multi-layered disclike coil formed of three coil discs overlapped. 51, 52 and 53 are first, second and third discs, respectively. Fig. 20 is a section (taken along the line XX XX of Fig. 21) of the projecting portions 3a of the insulating plates of the multi-layered disc-like coil. In Fig. 20, c2 is an output terminal of the first disc, and c21 is a bridging terminal of the third disc 53 and connected to the bridging wiring member 4. 55 is spot-welded portions to which the coil portion 2 on the front and back sides of the insulating plate 3. are connected. 30 is inter-layer insulating members which may be made of the same material as that of the insulating material 3, but are different in shape from the latter. Namely, as shown in Figs. 19 and 20, the inter-layer insulating members 30 are depressed at the position in which the projecting portions 3a of the insulating plates 3 are projected. As described above, by overlapping a plurality of coil discs and electrically conencting them in series, a relatively high voltage can be derived from output termianls ° 2 and t3 of the output wiring member and thus the output can be increased. Furthermore, use of this three-phase flat coil in a motor results in increase in the output thereof. A fourth embodiment of the flat coil according to the present invention is shown in Fig. 22 in which a reference numeral 61 designates copper strips for forming portions of the coil windings, 62 designates an electrically insulating plate, such as glass cloth or mica plate, and 63 designates adhesive agent, such as heatresisting and electrically insulating resin or ceramics. Each of the strips 61 is shaped into an overall configuration as shown in Figs. 24 and 25, and inculdes an effective area 61a, and first and second ineffective areas 61b and 61c. The strips 61 are welded to one another at their outer and inner ends 61d and 61e and fixed by the adhesive agent 63 to the front and back sides of the plate 62. 64 is ventilating holes. Terminal portions S1, S S3, 4, S and 6 of the coil are formed by laterally bending outer free ends of the second ineffective areas 61c of the strips 61 to shape them into hook-like or L-shaped portions 61d' as shown in Fig. 26. Fig. 27 shows a fifth embodiment of the coil of the present invention in which rings 65a, 65b, 66a and 66b are fixed to the o#uter and inner peripheries of the flat coil as shown in Fig. 22. The outer rings 65a, 65b are secured by welding at their inner surfaces facing the coil windings by way of interposed insulators 67, such as polyimide films, asbestos, mica or epoxy resing sheets. The inner rings 66a, 66b are fixed by caulking the ring 66b by way of insulator 67, so that radial gaps are provided for accomodating strain caused by heat. Terminal portions S1, , S2, S3, S4, S5 and are formed by laterally outwardly bending outer ends of the strips 61. The bent terminal portions are electrically connected to ends of terminals molded in a bridging wiring member 68 made of a heat-resisting and electrically insulating material, in such a manner that as shown in Figs. 30 and 31 a terminal 68a of the member 68 is connected to the terminal portions S1 and S4, a terminal 68b of the member 68 to the terminal portions and S5, and a terminal 68c of the member 68 to the terminal portions S3 and With the above-mentioned arrangement, the connection between the bent terminal portions of the strips and ends of the terminals of the briding wiring member 68 is easily made by, for example, welding. Although the example shown in Fig. 13 is a three-phase alternator, the coil of the present invention can be applied to a three-phase alternating current motor. Furthermore, the three-phase flat coil of the present invention can be manufactured by pressing operation to form the copper strips followed by adhesion of a coper disc on the insulating plate to form a plurality of radially extending conductive strips. In other words, the plurality of radially extending copper strips 2 may be printed and formed by etching operation on the insulating plate 3 or by punching and pressing operation of a dosc-like coper plate. Moreover, the coil can be made by winding a magnet wire, then pressing and flattening it.

Claims: CLAIMS 1. A three-phase flat coil having a quality of coil portions positioned on front and back sides of a disc-like insulating plate so that an aggregation of said coil portions forms the three-phase coil, comprising: a disc-like insulating plate having an opening at its center portion; coil portions each including output terminals constituting winding-in and winding-out por tions on an outer periphery of an insluating plate and an electrical conductor positioned radially on front and back sides of said insulating plate and having bent-over por tions on outer and inner peripheries thereof; ; three-phase coil windings including a-phase, b-phase and c-phase windings, each wound in a wave form in the same direction and ends of the b-phase winding at said output terminals being different in polarity from ends of the a-phase and c-phase windings to form said aggregation of the coil portions; and a gangway or bridging wiring member including intersections provided intermediate said three-phase coil windings and collectively positioned at substantialy one point of the outer periphery of said insulating plate, and said intersections being three dimensionally intersected with one another and connected to the respective a-phase, b phase and c-phase coil windings. 2. A three-phase flat coil as set forth in Claim 1, wherein a part of the outer peripheral portion of said insulating plate is radially projected to form a projecting portion for providing insulation between coil portions provided on the front and back sides of said insulating plate which coil portions constitute said out put terminals or are connected with said bridging wiring member. 3. a three-phase flat coil as set forth in Claim 1 or 2, wherein said bridging wiring member includes an insulating member containing metal connecting members intersecting three-dimensionally on the outer peripheries of said coil portions. 4. A three-phase flat coil having a plurality of coil portions positioned on front and back sides of a disc-like insualting plate, a plurality of coil discs each formed by an aggregation of said coil portions and said discs being overlapped with one another to form the three-phase coil, comprising: a disc-like insulating plate having an opening at its center portion; a plurality of coil discs formed by coil por tions and overlapped with one another, each of said coil portions including output ter minals constituting winding-in and winding out portions on an outer periphery of an insulating plate and an electrical conductor positioned radially on front and back sides of said insulating plate and having bent over portions on outer and inner peripheries thereof; inter-layer insulating members located between said discs; three-phase coil windings including a-phase, b-phase and c-phase windings formed by con necting between the output terminals of said respective discs and wound in a wave form in the same direction and the b-phase terminal of said output terminals inputting or out putting thrtee phase current being different in polarity from the a-phase and c-phase terminals to form said aggregation of the coil portions; and a gangway or bridging wiring member including intersections provided intermediate said three-phase coil windings and collectively positioned at substantially one point of the outer periphery of said insulating plate, and said intersections being three dimensionally intersected with one another and connected to the respective a-phase, b phase and c-phase coil windings. 5. A three-phase flat coil as set forth in any of Claims 1 to 4, characterized in that the radially outward ends of such coil portions as are connected with said bridging wiring member and constitute said output terminals are bent in L-shape to provide electrical connection to said bridging wiring member.

Inventors: KANAYAMA, KENJI, SUGI, HIDEKUNI
Applicants: NIPPONDENSO CO., LTD.
Application year: 1983
Main classification: H02K3
IPC codes: H02K3