Handbook of Small Electric Motors MAZ Part 14 doc

CHAPTER 7 SYNCHRONOUS MACHINES Chapter Contributors Chris A. Swenski William H. Yeadon 7.1 This chapter covers some of the ac synchronous motors commonly encountered in the industry. While it could be said that the electronically commutated motors dis- cussed in Chap. 5 are also synchronous motors, this chapter is confined to the typical ac versions.While larger polyphase machines are well covered by others, little infor- mation is available on these smaller motors. 7.1 INDUCTION SYNCHRONOUS MOTORS* These motors are built in a manner very similar to that for induction motors. They may have polyphase windings or be designed as single-phase motors, such as capacitor-start, split-phase, or shaded-pole types. The rotors have a dual construction that allows for induction motor starting char- acteristics and salient-pole synchronous running conditions. These rotors may be made from induction motor stampings with some of the teeth removed, as shown in Fig. 7.1.They are then die-cast in the same manner as an induction motor rotor (Fig. 7.2). Some motors use a permanent magnet in conjunction with an induction motor rotor. Figures 7.3 and 7.4 show such a motor. This is a four-pole shaded-pole motor. Here the field coils are connected such that they directly produce two like poles and induce two opposite poles at 90° in the unwound space between the coils. In these * Sections 7.1 to 7.3 contributed by William H. Yeadon, Yeadon Engineering Services, PC. figures, the rotor is shown to be enclosed by the stator. Figure 7.3 shows the permanent-magnet part of the rotor, while Fig. 7.4 shows the induction rotor end. The rotor is shown alone in Figs.7.5 and 7.6,with a piece of magnetic viewing film over the permanent-magnet portion. Figure 7.5 demonstrates the position of the magnetic poles, of which there are four on the rotor. Figure 7.6 shows that the induc- tion rotor portion is a laminated structure with copper-wire bars swedged over copper-plate end rings. 7.2 CHAPTER SEVEN FIGURE 7.1 Induction synchronous motor lami- nation. FIGURE 7.2 Four-pole induction synchronous rotor assembly. SYNCHRONOUS MACHINES 7.3 FIGURE 7.3 Shaded-pole synchronous motor, permanent-magnet rotor end. FIGURE 7.4 Shaded-pole synchronous motor, induction rotor end. 7.4 CHAPTER SEVEN FIGURE 7.5 Shaded-pole synchronous motor showing magnetized poles. FIGURE 7.6 Shaded-pole synchronous motor rotor showing induction motor bars and end rings. 7.2 HYSTERESIS SYNCHRONOUS MOTORS These motors have a rotor made of a cobalt alloy or another material that can be magnetized semipermanently by the stator field. They have a rather weak second- quadrant demagnetization curve which can be easily demagnetized.The demagneti- zation curves of some of these materials are shown in Figs. 7.7, 7.8, and 7.9. Figure 7.10 shows a motor utilizing a wound-field distributed stator (Fig. 7.11) and a cobalt hysteresis ring rotor (Fig. 7.12).This motor is connected and run like a permanent-split-capacitor (PSC) motor. It produces a speed-torque curve like the one shown in Fig. 7.13. SYNCHRONOUS MACHINES 7.5 FIGURE 7.7 0.32-MGOe hysteresis material. BR = 10.4 kG,BD = 7.0 kG,HC = 88 Oe, HD = 45 Oe, BH max = 0.315 MGOe, BD/HD = 155.6. (Courtesy of Arnold Engineering Company.) 7.6 CHAPTER SEVEN FIGURE 7.8 0.054-MGOe hysteresis material: hardened A151050. BR = 37.00 kG, BD = 2.0 kG, HC = 56 Oe, HD = 27 Oe, BH max = 0.054 MGOe, BD/HD = 24.1. (Courtesy of Arnold Engineering Company.) SYNCHRONOUS MACHINES 7.7 FIGURE 7.9 0.36-MGOe hysteresis material. BR = 9.5 kG,BD = 6.0 kG,HC = 116 Oe, HD = 60 Oe, BH max = 0.360 MGOe, BD/HD = 100.0. (Courtesy of Arnold Engineering Company.) 7.8 CHAPTER SEVEN FIGURE 7.10 Wound-field motor. FIGURE 7.11 Distributed wound stator. Many timer motors and value actuators use a hysteresis ring but use the shaded- pole type of stator to provide starting torque. Figures 7.14, 7.15, and 7.16 show a timer motor which utilizes this principle. The shaded-pole stator provides the start- ing torque, but it also makes the motor unidirectional. 7.3 PERMANENT-MAGNET SYNCHRONOUS MOTORS Many of these motors are used in clocks or timing devices. Figure 7.17 shows a typi- cal clock motor. Note that the stator portion has an uneven distribution of magnetic poles (Fig. 7.18). The purpose of this is to give the rotor a preferred starting point while providing an apparent shift in field during starting due to the uneven reluc- tance of the stator. Some of these motors have a spring return mechanism to reverse the rotation just in case it starts turning the wrong way. Other PM synchronous motors are essentially PM stepper motors run as PSC motors.The motor shown in Fig. 7.19 has a stator consisting of two sets of coils with the teeth offset from each other by one-half tooth pitch (Fig. 7.20). The rotor has magnetized poles along its length, as shown by magnetic viewing film (Fig. 7.21). One stator half serves as the main field winding. The other serves as the auxiliary phase.They are connected as in PSC motors, with a capacitor in series with the aux- iliary winding. SYNCHRONOUS MACHINES 7.9 FIGURE 7.12 Cobalt hysteresis ring rotor. 7.10 FIGURE 7.13 Synchronous motor speed-torque curves: Oz ⋅ in versus (a) rpm, (b) W in ,(c) PF, (d) amps, (e) horsepower, and (f) efficiency. (a) (b) (c) [...]... mean end-turn length of coil Ls = stator stack length lg = effective length of air gap Lt1 = length of teeth Ly1 = length of yoke MTL = mean turn length m = number of phases me = length of remaining portion of coil extension Ns = synchronous speed n = coils per group Pb = belt leakage permeance factor PF = power factor p = number of poles * Section contributed by Chris A Swenski, and William H Yeadon,... MACHINES FIGURE 7.20 Half-tooth-pitch offset consisting of two sets of coils with offset teeth FIGURE 7.21 Rotor with magnetized poles 7.15 7.16 CHAPTER SEVEN 7.4 PERFORMANCE CALCULATION AND ANALYSIS* P H Trickey suggests a method for calculating the performance of these synchronous motors which is summarized here Generally, this method applies to motors using cobalt ring rotors Motor parameters are calculated... FIGURE 7 .14 Rhodes, Inc.) Timer or actuator motor by Cramer Motor Company (Courtesy of MH FIGURE 7.15 Timer stator (Courtesy of MH Rhodes, Inc.) SYNCHRONOUS MACHINES FIGURE 7.16 Timer rotor FIGURE 7.17 Typical clock motor 7.13 7 .14 CHAPTER SEVEN FIGURE 7.18 Uneven distribution of magnetic stator poles FIGURE 7.19 Permanent-magnet synchronous motor SYNCHRONOUS MACHINES FIGURE 7.20 Half-tooth-pitch offset... methods as for ac induction motors, except for rotor losses Winding resistance, iron losses, friction and windage losses, and stator leakage reactance use exactly the same methods as induction motors Air gap leakage reactance is calculated as one-half the value of zigzag and one-third the value of belt leakage that would have been obtained using a rotor with the same number of slots as the stator The... saturation factor SFd = direct axis saturation factor SFq = quadrature axis saturation factor Str = number of strands of wire in parallel s1 = stator (primary) slots s2 = rotor (secondary) slots T = torque, oz⋅in Tp1 = primary tooth pitch Tp2 = secondary tooth pitch Tf1 = width of primary tooth face Tf2 = width of secondary tooth face Vph = volts per phase Win = total input, W WL = Loss, W Wout = output, W 7.17... I2r1 plus core losses Parasitic losses include hysteresis and eddy current losses of minor loops resulting from flux variation at tooth slot openings, losses resulting from harmonics of a nonsinusoidal winding distribution, and double-frequency backward field hysteresis and eddy current losses Variables B = slot span, ° electrical b = slot opening C = series conductors per phase C1 = flux form coefficient... portion of end-turn extension I = primary current (assumed) Id = direct axis current Iq = quadrature axis current kd = distribution factor kg = gap factor kp = pitch factor ks = slot leakage constant kw = total winding distribution factor kzz = zigzag leakage coefficient k1 = stator (primary) slot constant k2 = secondary slot constant Lg = physical length of air gap Lmet = mean end-turn length of coil... used in the following equations Calculation of Constants Pitch factor kp: kp = sin (pitch ⋅ 90°) where pitch is expressed as a fraction of the full pitch, such as 5⁄6, etc Distribution factor kd: sin (B/2) kd = ᎏᎏ n sin (B/2n) Total winding distribution factor kw: kw = kpkd Slot correction coefficient F: ΄ ΂ ΃΅ + ᎏᎏ + 0.08 2.87(y /y ) + 0.08 y1 F = 0.28 − 0 .14 ᎏ y2 d3/y2 1 2 Slot leakage constant ks:... variable descriptions k1 represents the primary (stator) slot constant, while k2 represents the secondary (rotor) slot constant They are found using the same set of equations, being careful to use the equation which most closely resembles that of the slot in question Round-bottom slot constant k1 or k2 (note that F is different for the two constants): Slot shape A (see Fig 7.23) d1 2d2 k1 or k2 = F +... for three-phase ΂ D1 Pb = 0.95 ᎏ pmk1 ΃ for two-phase 7.21 SYNCHRONOUS MACHINES FIGURE 7.30 Rotor cross section showing θpd and θpq Dimensions in inches, not degrees, measured along the circumference of the rotor Quadrature axis pole pitch θpq (see Fig 7.30): 20pks θpq = ᎏ + 1.25 s1 4πD1Sp(1.1 + 0.1p) (sin 1.5)[(Sp + pπ)/s1] ΄΂ ᎏ ΃ k ΅ + ᎏᎏᎏ + ᎏᎏᎏ s 2s L k 20pCx zz 1 1 s p 2.03θp(Ls + 2G1) + Q ᎏᎏ G1k1Ls) . way. Other PM synchronous motors are essentially PM stepper motors run as PSC motors. The motor shown in Fig. 7.19 has a stator consisting of two sets of coils with the teeth offset from each other. length of air gap L met = mean end-turn length of coil L s = stator stack length l g = effective length of air gap L t1 = length of teeth L y1 = length of yoke MTL = mean turn length m = number of. infor- mation is available on these smaller motors. 7.1 INDUCTION SYNCHRONOUS MOTORS* These motors are built in a manner very similar to that for induction motors. They may have polyphase windings