The 4th Electronic International Interdisciplinary Conference August, 10. - 14. 2015, www.eiic.cz Computer design of electromagnets Łukasz Kolimas Przemysław Sul Warsaw University of Technology Warsaw University of Technology Institute of Electrical Power Engineering HVT&EMC Division Warsaw, Poland Warsaw, Poland Abstract—The article raises the question still relevant for the electromagnet design. The authors compared the analytical and FEM (finite element method) methods design electromagnets. The issue is targeted at designers and constructors of apparatus and electrical machines. Keywords- design of electromagnets, electrical apparatus I. INTRODUCTION The electromagnet is used for processing electrical energy into mechanical work. Each electromagnet drive consists of a magnetic core (magnetic circuit), the stationary part is the core Figure 2. Schematic diagram of the open plunger type solenoid: 1-backplate and the moving part is an armature and exciting winding which with the plunger foot, 2–frame with the front plate (housing), 3-plunger (armature), 4-electromagnetic flux field winding, wound on a carcass, 5-guide produces magnetic flux. There are also electromagnets without of the plunger of non-magnetic material, 6- bearing liner of the plunger guide the keeper. Examples are electromagnets in electromagnetic 7-the plunger bearing liner, F-the attraction force of the armature; (the cranes in which caught steel components comprise a keeper backplate-1, the housing-2 and the plunger-3 are made of soft-magnetic steel) (for example, scrap in steel smelters). DC electromagnets can [11]. be divided into two largest groups: hinged armature (fig. 1) and plunger type constructions (fig. 2) [3]. The solenoids can be supplied with AC or DC. Larger application, particularly in precision mechanics has DC power supply due to [3]: The need for exact repetition of the supply current in subsequent cycles, easy and very low cost of control by direct current using semiconductor devices (usually transistors), the possibility of direct cooperation of coil feeding systems with logical control systems, small eddy current losses generated in the magnetic core, most often required low supply voltage adapted to mobile energy sources, often high repetition rate cycle, many times higher than the frequency of the power grid, usually short time power supply in one cycle, usually in the Figure 1. Schematic diagram of the hinged armature type electromagnet: 1- range of about one-to tens of ms. movable part (armature) 2-fixed part (core), 3-field winding to produce Electromagnets acting quickly put the following magnetic flux under the current influence and F-the attraction force of armature s - gap in the magnetic core (personal elaboration). requirements [10]: constant time of current rise in the excitation winding should be as small as possible, typically less The armature in the hinged electromagnets during the than 1 ms, solenoid must be adapted to the rapid distribution of working motion does not penetrate into the coil windings, the heat released during the excitation winding, dimensions while plunger is dipped into it. Due to the nature of the should be as small as possible, as small as possible mass of armature movement electromagnets can be identified with an moving parts of the magnetic circuit (armature, plunger), armature performing angular (oscillation), rotary or linear magnetic circuit should be made of material having high movement (progressive). They are produced also specialty magnetic permeability, high saturation flux density, a narrow grades, e.g. polarized permanent magnet, double hysteresis loop, high mechanical resistance and impulse electromagnets, solenoids (without core) and others. The most withstand. popular are plunger type electromagnets with linear motion and II. PROJECT OF THE ELECTROMAGNET roller- armature [4]. Sources of the attraction forces of the electromagnet elements: the armature and the core, is the magnetic flux flowing through the air gap. Therefore, the electromagnet was Electrical and Electronic engineering eISSN: 1339-9977, cdISSN: 1338-7871 - 211 - ISBN: 978-80-554-1090-6 The 4th Electronic International Interdisciplinary Conference August, 10. - 14. 2015, www.eiic.cz made by a project that includes some assumptions: where: Bp - magnetic induction in the air gap, S - polar - The distance of the armature from the core is much smaller surface field to which the force is applied μ0 - vacuum than the average linear dimension of the pole cross section of permeability. the electromagnet, - A magnetic field in the gap of the magnetic core is uniform, In order to determine the magnetic induction in the air gap - The magnetic flux generated by the winding penetrates the formula (1) becomes: working air gap or without taking into account the scattering F 4 107 6 0 =0,289 T (2) flux. Bp 6 In the magnetic circuit designing process the strength causing S 91010 the armature attraction by the hinged armature type Using the formula BS calculated magnetic flux in the electromagnet was set at 6 N. The magnetic circuit concept is a gap: closed path in which the magnetic flux moves around.The electromagnet magnetic circuit was made of ferromagnetic iron B S 0,289 90 106 26,05106 Wb (3) Armco called Hyperm 0, and the field source was one p horizontal coil wound on the level core column. The designing According to the assumptions, ignoring leakage flux, was divided into two stages. The aim of the first stage was to magnetic flux in the gap, in the core and the armature is equal propose the dimensions of the core and windings producing a to Φ. The magnetic field strength in the gap was determined magnetic flux. At this stage the electromagnet was shown as from the formula: flat configuration using a circumferential electromagnetic Bp 0,289 phenomena model. The pre-selected parameters of the (4) H p 7 230329A/ m electromagnet having raised the requirements were used in the 0 4 10 second stage to design a model in the ANSYS environment. For this purpose a finite element method ANSYS was used to Induction in each section of the magnetic core elements formulate a flat model (2D) of the electromagnet. It allowed for was determined on the basis of the following relationships: more detailed analysis and comparison of the two models. The 6 - In the armature: 26,05 10 (5) following describes the two design stages: of the core and B1 6 0,289T windings. f b 10 9 10 - In vertical columns of the core: III. FLAT MODEL OF ELECTROMAGNET In the magnetic circuit analysis it is possible to distinguish 26,05106 B 0,289T (6) two types of tasks. Type I Task involves the determination of 2 c b 109106 the flow at a given magnetic induction. Type II task consists in determining the magnetic induction at a given flow. The - In a horizontal connector of columns: analysis aim was to determine the values of magnetic induction 26,05 106 in the working gap, and then the sum of the voltage drops equal (7) B3 0,289T to prerequisite magnetic flow. In practice, the elementary (d e) b (20 10) 9 106 circuit size is selected as estimated on the basis of electromagnetism laws knowledge and experience of the From the magnetization curve B = f (H) (fig. 4) for designer. The authors did a drawing No. 3 and suggested induction previously calculated field strength values were read: magnetic circuit dimensions. The dimensions are shown in H1 = H2 = H3 = 49 A/m (8) figure 3. For simplicity, it was assumed that the average magnetic path contour is composed of sections defined by the points P1 to P6. The constituent magnetic voltage drops are: - In the armature: -3 zI1=H1·(a – c + f) = 49∙(60-10+10)∙10 = 2,94 Az (9) - In vertical columns of the core: 3 (10) zI2 H2 e 491010 0,49Az Figure 3. The dimensions of the hinged construction (personal elaboration). - In a horizontal connector of columns: 3 (11) Under the assumptions stated earlier model that describes zI3 H3 (a c d e) 49(60 10 20 10)10 2,94Az the magnet strength (the force acting on pole) operating at two working gaps is [8]: - In the gap: 3 2 (12) Bp S (1) zI p H p s 230329110 230,329Az F 2 2 0 Electrical and Electronic engineering eISSN: 1339-9977, cdISSN: 1338-7871 - 212 - ISBN: 978-80-554-1090-6 The 4th Electronic International Interdisciplinary Conference August, 10. - 14. 2015, www.eiic.cz The total flow rate was calculated according to the formula 0,5 (m (d e)) 0,5 (20 (20 10)) (17) w INT 5,675 n z1 d p max 0,881 Hk lk = , where: Hk - the magnetic field strength along k and: the road lk, k - the number of the next section of magnetic 0,5 (r b) 0,5 (19 9) (18) circuit, - is the size named current linkage or magnetomotive wz2 INT 5,675 d 0,881 force expressed in the formula =z ∙ l (z - number of coils): p max Assumed Wz = 6. zI1 2 zI2 zI3 2 zI p 2,94 20,49 2,49 2230,329 467,029Az Maximum turns number on a carcass was calculated from the formula: zmax zwwwz 34 6 204 (19) The ratio of the predetermined coil number to a maximum coil number that a carcass can accommodate was calculated z 0,56 and it was also found that the winding selection zmax was proper, because the calculated value is in the range (0.5 ... 0.8). Taking into account the core dimensions at the coil location and the carcass dimensions, on which the coil was wound the average length of a single winding was set lśr = 94mm. Then the resistance R of the winding was set: Figure 4. Characteristics of Armco iron magnetization called Hyperm 0; B - magnetic induction, H - magnetic field strength [1].