Y f = (2S / P) -1. It is defined as the distance between the starts of two consecutive coils measured in terms of coil sides. I If the commutator pitch is -1, it is called a retrogressive lap winding. Winding will be done throughout the slot. So we know two data sets for this coil. 2) The emf developed in the winding is the directly proportional number of turns and independent of the pitch factor and distribution factor. Using the length of helical coil formula: Lw = π * Dc * N = π * 10 * 15 = 471. ; Coil Span: It is the angular distance between the two sides of the coil. 4 mm (i. The current sheet. The program uses formula published in the ARRL Handbook For Radio Amateurs and other radio publications. 5 13. Learn More. while using the formula provided in an Excel spreadsheet gives a result of 982uH. The piping from the cooling coil to the condensate pump reservoir should be installed with min imum 1/8-in ch slope to enable. For single turn loops, Maxwell's elliptic integral formula. H ewb. The formula for the commutator pitch in any simplex winding is given as. 4 Å observed for a canonical α‐helix. The basic parameters of the coiled-coil are its pitch (periodicity of the supercoil), the associated pitch (or supercoil) angle (angle of the helix with respect to the supercoil axis), and the. Once the results are obtained from this calculator, the coil can be easily modelled as a Laplace load within any EZNEC antenna model. 56 x 10^-7. Tubes must be supported at intervals not more than 1. 14159 ∗N ∗ (OD + I D)/2. A solar heater is made like a coil with 20 mm pipe inside a 1 m x 1 m window frame. Using the Neumann integral formula, the expression of inductance is obtained. Calculate the inductance associated with the winding using the formula L = (u0 * A * N^2)/l where u0 is the permeability of free space at 12. The formula is composed of a pattern’s metal thickness, single pattern width, total pattern width, and turn number, and is effective in the megahertz (MHz) frequency range. There are several reasons for using baffles in heat exchangers, below is a list of functions that baffles are often used for. ; The number of slots for 2 layer winding is equal to the number of coils. This works out to be [Math Processing Error] (11. Draw the thread profile. 8) T = 2 π m q B = 2 π ( 6. The coil pitch is defined as the distance between two consecutive coils in the same phase. 71 m Total length of coil 63. where l is the length of the weld joint. 1 of the next coil than the pitch of the large coil will be 1. 4×10 4. 48 m Total length of coil 215. C machine having a total number slots S = 16. Learn what a pole pitch is, the pole pitch formula & definition, and how to. The distance between the two sides of a coil is called the coil-pitch. In the close-winding coil case, it's assumed that the gap. Units: Outer Diameter (OD): Inner Diameter (ID): Mean Diameter (D): Load (P1): Height With Load (L1):Coil Pitch and Pitch Factor: The distance between the two sides of a coil is its coil pitch. What is flange pcd?From the active length, the total length of the machine can be calculated with Equation (10), where f wc is the winding coil factor L total = L k 1+ f wc (10) The winding coil factor is defined in. Below C = 5 the spring will be difficult to make because of the large diameter. . Calculations are typically done using the formula: Heating Coil Capacity (BTU/hr) = Flow Rate (GPM) x Temperature Rise (°F) x 500, with. To obtainA single-layer inductor is shown in the picture above: D c is the coil diameter, D is the coil former diameter, l is the coil length, p is the coil pitch, d is the wire without insulation diameter and d i is the wire with insulation diameter. 8, 1. We take as a reference frame cylindrical polar coordinate system (r, θ, z). 4 Å observed. Now let E be the induced e. The proposed method is derived by solving Neumann’s integral formula, and the numerical tool is used to calculate the inductance value. 29 degree or 154. A helix ( / ˈhiːlɪks /; pl. A fractional-pitched coil, on the other hand, is a type of coil used in electrical machines where the coil spans only a fraction of the pole pitch. The Back Pitch for DC Machine formula is defined as the coil advances on the back of the armature. An alternator having 10-poles, 3-phase, and 60 Hz has 8 conductors per slot in single layer arrangement with 4 slots/pole/phase. Enthalpy (total heat content) of air at entering wet bulb. 2e-6. Formula for Spring Pitch: (L – d) ÷ Na = p. 998, and 0. A = number of parallel paths. μ0 一 vacuum permeability. Multiply the number of turns and diameter of the coil. The phase belt is defined as the group of adjacent coil-sidesVariable pitch springs are springs that do not have constant coil spacing. N 一 the number of turns of the coil;. If the coil span is equal to the Pole pitch then it is called a full pitch coil. It was the attempt of modern reanimation electrostatic model of the coil, that as shown in the case of formula Palermo, far from the reality. L−HS The pitch factor is seen to be: \(\ k_{p n}=\sin \frac{n \alpha}{2}\) Now for breadth factor. It is the angular distance between two sides of a coil, measured in terms of armature slots. With CNC Bender the pitch of a tube coil is most affected by the coil twist ratio in the Push Bend Profile Table. Introduction. Only the amendment to the resulting inductance is added: where: ΔL is the amendment to the inductance of the close-winding coil (always negative) (µH) N - number of turns Pitch α refers to the angular displacement between sides of the coil, expressed in electrical radians. The period of the charged particle going around a circle is calculated by using the given mass, charge, and magnetic field in the problem. A single-layer inductor is shown in the picture above: D c is the coil diameter, D is the coil former diameter, l is the coil length, p is the coil pitch, d is the wire without insulation diameter and d i is the wire with insulation diameter. Coil Pitch (p) is the pitch or seperating distance of the coil turns, it is normally maintain equaly through out the coil. Coil span or coil pitch. 303K views 6 years ago. Correction for this is done by multiplying the voltage equation by Kp, called pitch factor. By minimizing the metal resistance, a. Spring Pitch Formula. magnet width to pole pitch ratio, efficiency, power factor, and the motor inner to outer diameter ratio, respectively. 3. Using the examples in 1 through 3 above: Pitch Factor = 1 to 9 throw (-) 1 8 48 Slots ÷ 4 Poles = 12 Pitch Factor = 2/3 COIL PITCH IN AN AC ARMATURE WINDING AS Coil pitch or coil span is defined as the angular distance between the two coil sides of one coil. Calculator. The winding pitch cannot exceed the doubled wire diameter; The coil diameter cannot be greater than the doubled diameter of the rod; The winding length should be less than 3/4 length of the rod; When the coil is shifting it should not reach the edge of the core 1/8 of its length; The initial magnetic permeability of the rod should be greater. . If the coil pitch is. The mean coil radius of helix (R = D/2) and the cross-section can differ along the helix. It should be. The calculator is designed to accept the total line voltage and current of the combined three cables. The Pitch of coil spring formula is defined as the axial distance between adjacent coils in uncompressed state of spring and is represented as p = L f /(N t-1) or Pitch of Coil Spring = Free Length of Spring /(Total Number of Coils-1). Winding factor is the ratio of electromotive force (EMF) produced by a stator having a short-pitch, distributed, or skewed winding, with a stator having full-pitch, concentrated, and non-skewed, windings. Lap winding • Suppose we want to make a lap winding for a P = 4 pole D. In dc machines, the slot pitch usually lies between 25 to 35 mm. It is always 180° electrical. 3) You need to wind the coil for maximum Q by taking care to space the turns using wire that is not too thin because of resistance losses. Now the ratio of the vector sum to the arithmetic sum of the induced e. Thus starting from the pitch and known radius, you can calculate the angle of wrap from θ =tan−1 p 2πr θ = tan − 1 p 2 π r and get the coiling radius as above. Spring Design Results. 250 - 84) Thickness (0. The formula for the length of a helix is: L = H P ⋅ √ (π ⋅ D) 2 + P 2 L = H P ⋅ (π ⋅ D) 2 + P 2. 2: Pitch and spring index. c. On top of that: 20 turns of 0. Calculate the pitch (and therefore coils per inch) and the spring index. Pitch ( alpha) refers to the angular displacement between sides of the coil, expressed in electrical radians. Though the formulas . This is a very useful result for strange-shaped coils. Back pitch should be either lesser than or greater than front pitch by 2m, where m is the multiplicity of the winding. For the n th harmonic, the chording angle becomes nα° electrical. Two main parts of motor are rotor and stator. if the winding would have been in one slot. The formula for turns per volts is (1/ (4. Post Reply Tell a Friend (must be. Spec Name Spec Input; ID (16 - 36) OD (ID - 84) Width (0. Closed Ends. Additional Information Pole Pitch: It is the angular distance between the two adjacent poles. It is always equal to 180° electrical. For quartz tube heaters a smaller pitch is normally used. Symbol. The length and the pitch can be seen in the diagram below. The use of windings with a coil span of two slots promises a better balance between ohmic losses and end windings space on the one hand and harmonic content. R = R i + a θ, θ i ≤ θ ≤ θ o. 50. 923 respectively. Enter coil diameter, Dc = 10 mm . The practical d. The winding factor is often expressed as the product of three factors: the pitch factor (also called chording or coil-span factor), the distribution factor (also called breadth, spread or zone The calculation results of , , , , and for both double-layer windings with a constant coil pitch and single-layer windings with a constant odd coil pitch are all shown in Tables 9 and 10. The coil pitch factor represents the effect of coil distribution on the induced voltage. The Length of a Helix calculator computes the linear length of a spiral or helix where the helix is pulled into a straight line. d = wire diameter. Understand what Full Pitch and Short Pitch Windings are, and what Coil Span is. n = number of turns. Learn MoreCalculator. It is expressed in terms of electrical space degree. The example shown below demonstrates how to calculate your compression spring's pitch. The axis of the coil coincides with the axis of the solenoid. u. H wb. S 一 the cross-sectional area of the coil, in square meters. It starts calculating the. The coil pitch is fixed at the slot pitch; this winding is called concentrated winding. 2 STEP 2 : calculate the required heat flux. 8 and 1. through formula nes = N 2 mbnwcc n lay, (6) where bnwccis the largest integer less than or equal to nwc. For a full pitch coil, the value of pitch factor is unity whereas for its value is also unity for concentrated coils. Now, computing the wire lengths using 2pi x r and the. The values provided above are inserted into the equation below and computed. 0 mm thickness. A circular coil with a cross-sectional area of 4 cm2 has 10 turns. 800-348-2529 Get a Quote. In a short pitch coil, the coil span will be (180 - α)° electrical (α = angle by which coils. 5D or smaller. f. f. Select your alloy, then use the slider bars to indicate the coil you need (gauge and width). Y. The equation gives average pitch of the winding. 02 wb, N = 375 rpm, for full pitch coil, K p = 1. A pole pitch is always 180 electrical degrees, regardless of the number of poles on the machine. It should be noted that the main harmonic order of MMF is , which interacts with permanent-magnet flux linkage to product average torque. m. Enter the scientific value in exponent format, for example if you have value as 0. The only problem with this type of winding is that its coil cost will be more than other types of winding. Wind the new copper wire as a coil using the same gauge as the wire already on the stator. Main Stator: Coils and Slots • The number of turns and cross section are specific to each frame size, slot combination or design, and voltage. 3. Coil & Sheet Calculators | Steel Warehouse. 9659. A helix, sometimes also called a coil, is a curve for which the tangent makes a constant angle with a fixed line. 1) Winding Will be done in a single slot. This calculator uses Maxwell’s formula for the mutual inductance. For a full pitch coil, each coil side lies under the opposite pole as shown in the figure below. Coil pitch is. Cite. pole pitch5. 5 m (5 ft), this mainly depends on the diameter of the tube and material of construction. 24 where L is the gross length of the stator and τ p is pole pitch in meter. Pitch Factor or Coil Span Factor is definite as the ratio of emf generated in short pitch coil to the emf generated in full pitch coil. The formula for total number of spins is (Turns per volts * voltage). The resistance of 1 coil is 16,5 ohms. This is a very simple calculator for estimating the inductance of a Single-Layer Air-Core inductor. We can obtain the height of the coil with this expression: H = N * (S + Dw) Length (L). I got this motor at my university. If the coil span is equal to the Pole pitch then it is called a full pitch coil. coil pitch in terms of slots4. You can Save Time on your Fabrication Layouting process. The following formula can be used in production, in order to estimate the weight of coils in production starting from their geometry. Inductance is the property of the coil and tells how good the coil can store magnetic energy. m. . Spread the love. The equation of the circular spiral coil, motivated by the Archimedean spiral coil can be described by. So, if this is one-fifth the number of turns in the secondary coil, then in order for the relationship to hold true, the secondary coil must have 500 turns. Therefore, the pitch should be 0. 3. The duplex can exist with a twist of 10. when carrying current, the field coils being unexcited. We are very sorry but it seems like there is no specific formula for this. Calculate a “Free Point” for stuck tubing or the length of free pipe. The coil pitch was determined to be two times the wire. The formula for calculating spring pitch is: SP = (L – 3*D) / NA. N is the number of rings. • Winding pitch is the coil span divided by the pole. The flux linked is: 2NlRBn nπ nα λ = sin( )sin( ) (21) np 2 2 Using the definition (14), the pitch factor is seen to be: nα kpn = sin (22) 2 4. For most alternators, the stator acts as the armature. Figure 4 representsdiscussed in the next section, and the new formula derivation is given in the subsequent sections. You can use either inches or millimeters and you can mix. The distance between each "ridge" on the twisted wire. CT Ratio = V p /V s. where m = 1, 2, 3 respectively for simplex, duplex, triplex lap winding. If possible, it is easier to calculate the heat flux on the cold side as there is normally no phase change. 28 (length per coil)Download these Free Coil Span or Coil Pitch MCQ Quiz Pdf and prepare for your upcoming exams Like Banking, SSC, Railway, UPSC, State PSC. The rate formula is valid only if the pitch angle is less than 15 degrees or the deflection per turn is less than D/4. Counting them is easy enough – every rotation of 360 degrees equals one coil (90 degrees = ¼ coil, 180 degrees = ½ coil). m = multiplicity factor. First, using a semiempirical correction formula. Ends may be ground to decrease the solid height of the spring and/or to help the spring stand up straight. 2 mm wire = two layers of wire = 0. An advanced analytical spring model is proposed in this study to address the non-linear effects of variable coil diameter, spring pitch and coil contact that. L = µ r ( n 2 . f. The distance between adjacent spring coils (defined as the coil pitch) is found by dividing the spring free length by the number of active coils, The rise angle of the spring coils (the angle between the coils and the base. Di = inner coil diameter . per Phase: Part 1In this video, I'll give you an idea how to derive the fundamental pitch factor (coil span f. It is placed at the center of a long solenoid that has 15 turns/cm and a cross-sectional area of 10 cm2, as shown below. The following formula from R. The machine runs on 150V and draws 7A on that voltage. INSTRUCTIONS: Choose units and enter the following: (H) Height (P) Pitch: distance between turns (D) Diameter Length of Helix (L): The calculator returns the length of the helix in meters. Using the examples in 1 through 3 above: Pitch Factor = 1 to 9 throw (-) 1 8 48. Rotor is usually made as squirrel-cage, and it is inserted in stators hole. The double integral of Neumann’s formula is. A curvature correction factor has been determined ( attributed to A. The heating and cooling media can flow through a coil immersed. This method is derived by solving Neumann’s integral formula in a cylindrical coordinate system, and a numerical tool is used to determine the value of mutual inductance. A staggered pattern is more commonly used. However the waveform of the resultant emf can be improved by making the coil pitch less than a pole pitch. Though the formulas . g. Front Pitch-The number of armature conductors or elements spanned by a coil on the front is called front pitch. = 100/1. Design of stator winding: Stator winding is made up of former wound coils of high conductivity copper of diamond shape. In mechanical engineering, a helix angle is the angle between any helix and an axial line on its right, circular cylinder or cone. Single-layer coil with winding pitch can be calculated as a singlelayer coil with close-winding. . ; It can also be defined as the ratio of the vector sum of induced emf per coil to the arithmetic sum of. The calculation is pretty simple. 65 m2 Vessel diameter 2700 mm Pitch 1. predefined initial radius and coil pitch. The current direction is downwards in conductors under N-pole and upwards in those under S-pole. It can also be observed that, coil sides are connected in series in such a way that emf induced in coil side at 1 and 10 are additive. 1 Å compared to the reflection at 5. 5 D, the coil diameter generally changes with an increase in deflection (load). 2. In a conical coil spring with a fixed pitch angle, R and n’ (= θ / 2π) are associated with the following formula. 1 m due to the bending limits of the pipe. You can refere standard reference input image shown in this calculator for your better understanding to this angle value. Steel Coil Calculator Determine Your Needs. A SIMPLE explanation of Full Pitch and Short Pitch Winding. It is always less than unity (K c < 1). These factors represent the effect of coil distribution on the induced voltage waveform. 4 are the elastic modulus E, the shear modulus G=E/ 2 1+ with a Poisson ratio , the cross-sectional area A= d2/4 with a wire diameter d,The winding calculator allows you to find the optimum winding layout for your electric motor in a fast and convenient way. The following formula from R. 2]. The variables used in this tool are the diameter of the wire conductor and the diameter of the wire loop. If, Z = the number of conductors P = number of poles YB = Back pitch YF = Front pitch YC = Commutator pitch YA = Average pole pitch YP = Pole pitch YR. Variable turn pitch (VTP) coils are then proposed to address the eddy currents distribution problem. Pipe Coil Length Calculator is useful for Calculating reuired length of your pipe coil. However for semi enclosed slots it may become less than 15 mm. For a full pitch coil, the value of pitch factor is unity whereas for its value is also unity for concentrated coils. 10 mm wide bobbin, 100 turns of 0. The formula for calculating the spring pitch is: SP = (L – 3 * D) / N. Y f = (2S / P) -1. Here, e = E 1 = E 2 = E coil and, if N is the number of active coils, izDN equals the length of wire, closely enough for practical uses. This should make the AWG conversion more. What do you mean short pitch. Therefore, for simple, collective pitch control a simple, modular, spring-mass description is adequate, while in individual pitch control (IPC), possibly coupled with vibration attenuation, a more complex, vector procedure is called for. You enter your material properties, coil specifications, and heating requirements and get instant results on essential parameters such as power density, heating time, and. Height (H). 50” • For 1/2" tube coils, fins are available in increments of 1. In practice, short pitch coils are preferred. The unit is kW/s. pitch factor or coil. It is not concentrated in a single slot. Helical springs are formed by wrapping wire or rod of uniform cross-section around a cylinder (Leiseder 1997). Modified by Administrator at Mon, Jan 02, 2006, 10:27:32. m = multiplicity factor. 961. P = 154. The smaller the value is, the quicker the response is. 2 Breadth Factor Now for breadth factor. Since the first time publishing the Euler solution by Eytelwein (1808) in his Handbuch der Statik fester Körper in 1808 the problem is spread through practical applications and became known as Euler-Eytelwein problem in standard books of technical mechanics see e. Let the angle α be the angle of inclination of the helix with any plane perpendicular to the axis of the coil (pitch angle, lead angle). D) The Helical Formula, and Coils of Large Pitch. Coil span factor. The shortest path between two points on a cylinder (one not directly above the other) is a fractional turn of a helix, as can be seen by cutting the cylinder along one of its sides, flattening it out, and noting that a straight line connecting the points becomes helical upon re. Set-up time is minimized by use of electronic controls for setting wire pitch and stopping at the desired turns count. It is the separation between consecutive sides of a coil or consecutive bottom sides of a coil and is represented by (Yw). Back pitch (Y b): It is the span of the coil from the back end. 392699 = (pi*0. Three different winding topologies, obtained by changing the coil pitch, namely integer-slot distributed winding. You wanted to know the field strength adjacent to the coil. Our easy-to-use calculator makes quick work of estimates. l——Spiral length. Finally, calculate the Coil Length using the equation above: CL = (OD-WD) * pi. Weaver’s article Numerical Methods for Inductance Calculation is used for calculations of inductance L S: where. Total coil length, L t =N*L 1. D is the coil former diameter in cm, l is the coil length in cm, N is the number of turns, and. 02 Wb, sinusoidally distributed and the speed is 375 rpm. 3 mm . In [6], [7], [8] and [9] the authors present the results of experimental study on natural. The term “Enthalpy” is used to describe the total heat of a substance. A pole pitch is always 180 electrical degrees, regardless of the number of poles on the machine. 0 to 2. It may even be found by applying Fleming’s Right-hand Rule. the equivalent integral-slot full pole-pitch winding (with one slot per pole phase and the same number of turns as the actual winding). 3 degree •What is the minimum number of slots needed on an eight-pole winding to exactly achieve this pitch? Ans. Y b = (2S / P) + 1. Use this Aluminum Coil Calculator to simplify estimating your aluminum coil needs. Therefore, the height (H) to the n (th) coil measured from the maximum coil diameter under no load can be expressed by the following formula when the pitch angle (α) is small. The secondary of CT is short circuited and 100 volts is applied to its primary. The inductance of a wire loop is a common textbook example of a circuit with inductance. These windings must be properly arranged such that the induced emf in all the phases of the coils must have the same magnitude and frequency. 2. (P) Pitch: distance between turns (D) Diameter; Length of Helix (L): The calculator returns the length of the helix in meters. Is the easy path. Twist pitch (lead /) mm in. kd = (Vector sum of the c. As we discussed earlier that every set of windings in lap windings has no parallel paths equal to poles in a machine, so in duplex lap winding the current paths will be twice. The function of a compression spring is to withstand a certain pressure perpendicular to that spring. Sheared blanks rely on coil pitch as the remaining sizing element. The shell and tube exchanger consists of four major parts: Front Header—this is where the fluid enters the tubeside of the exchanger. This spring stiffness calculator will calculate all of the values required to determine whether the spring will be stiff enough to meet its requirements. If the blank size varies, so does the location. INSTALL: The insert with Heli-CoilThe EMF equation of an alternator is given above. The external surface: A=L t *pi*d o. Therefore, the pitch should be 0. The coil pitch is equivalent to the span, except that this term is used more often in a theoretical context and expressed in electrical degrees, or per-unit of a pole-pitch. What is their mutual inductance? Solution: Notice that although M12=M21, it would have been muchUsing this formula, the inductance of a 1 meter circumference loop of 14 gauge wire is 1. [1. 0714 and Re = 19800 (Gunes et al. The total length of the wire used to create the coil. The rise angle of the spring coils (the angle between the coils and the base of the spring) is found from the arctangent of the coil-pitch divided by the spring circumference, The solid height of the spring is found by summing. In varying the coil pitch to examine the behaviour of the coil resistance, the coil’s width and thickness are kept constant. Height (H). It is always 180° electrical. Follow the formula below to calculate the spring pitch of a coil spring with open ends. Compression springs consist of open coils (Pitch). A regular winding will have a number (say m) coil elements, separated by electrical angle ( gamma). The power rate is given by this formula: Power rate = (Rated torque) 2/Rotor inertia x 10-3. This lecture will discuss;1. Pole Pitch, Coil Span, Back Pitch, Front Pitch, Commutator Pitch in Armature Winding of DC Machines are explained in this video. This approach can. 5. of slots. 6. Transcribed Image Text: 1. First of all, you cannot count any coils where the coils are closed or. A process model should be as simple as possible for the specific control problem. I There are 1 P total number of coils between two adjacent poles. This advancement is measured in terms of armature conductors and is called back pitch. It may be the full pitched or short pitch. What is the formula of pitch circle diameter? Tpi=1/p. L = Length; d = Wire Diameter; Na = Active Coils; p = Pitch; Example: Based on the given formula. k 一 a coefficient depends on the ratio of the radius (R) to the length (l) of. To eliminate the 5th harmonic voltage from the phase voltage of an alternator, the coils need to be short pitched by an electrical angle of. A coil is basically any number of turns. A coil having a span equal to 180⁰ electrical is called a full pitch coil as shown in the figure below: A coil having a span less than 180⁰ electrical is called a short pitch coil or fractional pitch coil. A staggered pattern is more commonly used. The pitch factor or coil span factor n th harmonics is. If the coil pitch is equal to the pole pitch, then it is called a full pitch coil. This increase is the distance between two arms of a. For the lap winding shown in the Fig. Resultant pitch (Y R): Distance between the starts of two successive coils. Enter the coil length (distance from first to last winding - see diagram). Since E E → is tangent to the coil, ∮E ⋅ dl = ∮ Edl = 2πrE. Pitch If the pitch exceeds 0. If N is 100 turns, l is 6 meters. This describes the fact that a winding may consist of a number of coils, each linking flux slightly out of phase with the others. Increase the ratio value to increase the pitch in a coiled tube. 4×10 4. First, that 10 inches of sidewall metal equals 10,000 lbs of metal and, second, that zero inches of sidewall (when the metal is all used up--the 20 inch core diameter) equals. 3. Front pitch (Y f): It is the span of the coil from the front end. It is also known as Belt or Breadth factor and denoted by kd. FH. Numerical methodology2. Remember to incorporate the high side of the OD tolerance when examining the work in hole requirements. Calculate the coil pitches and indicate the slots into which the first coils should be placed for the following armature windings: (a) 36 slots, 4 poles; (b) 57 slots, four poles; (c) 76 slots, 6 poles; (d) 132 slots, 8 poles; (e) 270 slots, 10 poles. For air core coil, μs=1. 2. When the coil span is equal to.