2. 6/30/2016EMC: AC Motors Roger Enns1 AC

3. 6/30/2016EMC: AC Motors Roger Enns2 AC Motors Summary

4. 6/30/2016EMC: AC Motors Roger Enns3 AC

5. 6/30/2016EMC: AC Motors Roger Enns4 AC Motor Theory Rotating flux field created by alternating field current. Rotating field induces current within copper conductors in rotor. Rotor rotates due to torque exerted on conductors.

6. 6/30/2016EMC: AC Motors Roger Enns5 Induction Motor: Stator

7. 6/30/2016EMC: AC Motors Roger Enns6 Induction Motor: Rotor

8. 6/30/2016EMC: AC Motors Roger Enns7 Single-Phase AC Motors Used for low-hp applications only (typically less than 5 hp). Low operating efficiency (typ. 60-80%). Same basic operating principles as 3-phase, but field alternates rather than rotating. Direction of rotation not defined as startup. Must use supplemental method to create rotating field.

9. 6/30/2016EMC: AC Motors Roger Enns8 Single Phase Induction Motors 1.) Resistance Split Phase Motor –Secondary winding of fine high resistance wire used. –Change in inductive characteristics causes AC phase shift between primary and secondary windings, creating a rotating field. –I 2 R losses in secondary winding overheat quickly, suited for low loads only. –Centrifugal switch used to disconnect start winding once motor reaches about 75% of synchronous speed.

10. 6/30/2016EMC: AC Motors Roger Enns9 Single Phase Induction Motors 2.) Capacitor Start Motor –Motor wired with two identical windings 90 degrees apart. –Capacitor places in series with one winding, creating phase shift to generate rotating magnetic field –Lower I 2 R losses during start –Better suited to starting high inertial loads –Utilizes a centrifugal switch to drop start winding when motor speed reaches 75% of synchronous speed.

11. 6/30/2016EMC: AC Motors Roger Enns10 Single Phase Induction Motors 3.) Shaded Pole Motor –Part of pole surrounded by copper ring. –Ring delays formation of magnetic field in that portion of the pole, causing rotor to turn in that direction. –Fixed direction of rotation, cannot be changed after mfg. –Very inefficient, as start function cannot be disconnected once motor is as speed. –Used for fractional horsepower motors only (typ <.05hp)

12. 6/30/2016EMC: AC Motors Roger Enns11 Shaded Pole Motor Cont’d

13. 6/30/2016EMC: AC Motors Roger Enns12 Universal Motors Operate on single phase AC or DC power Essentially a series-wound DC motor, complete with armature, commutator, and brushes. Operates on AC as both field and armature reverse, rotating in the same direction. Applications: Vacuum cleaners, jig saws, drills … High-speed at no-load, similar to the series DC motor. Low efficiency

14. 6/30/2016EMC: AC Motors Roger Enns13 Synchronous Motors Runs at synchronous speed, no slip. Magnets on rotor ‘lock-on’ to rotating flux Motor must used external start assist such as: –External start motor –Squirrel cage built into rotor, to start as an induction motor –Variable frequency supply – slowly increase speed. Very high power (200 – 20,000 hp). –Rock crushers, rolling mills, paper mills. Very low power –Timing devices (wall and oven clocks) –Sheet feed devices Well suited to high-torque, low rpm applications – may eliminate the need for speed reducers

15. 6/30/2016EMC: AC Motors Roger Enns14 Reading the Nameplate – AC Induction Motors

16. 6/30/2016EMC: AC Motors Roger Enns15 Reading the Nameplate 1.Design NEMA specifies minimum values of locked-rotor, breakdown, and pull-up torque.

17. 6/30/2016EMC: AC Motors Roger Enns16 3 Phase Motor Design

18. 6/30/2016EMC: AC Motors Roger Enns17 Torque Curve Terminology

19. 6/30/2016EMC: AC Motors Roger Enns18 Reading the Nameplate– cont’d 2.Insulation Indication of motors resistance to temperature. NEMA ratings A,B,F, or H, A being lowest resistance, H being highest. Operating temperature is a result of ambient temperature (air temp in area surrounding motor) and heat generated by motor itself (I 2 R losses, startup losses). Altitude limits may also be specified in combination with thermal limits due to reduced heat rejection capability at higher altitudes. “Motors run cooler at lower altitudes.” 3.Max. Ambient. Maximum ambient temperature, degrees C, at which motor can operate at nameplate ratings with nameplate insulation class.

20. 6/30/2016EMC: AC Motors Roger Enns19 Reading the Nameplate– cont’d 4.Supply Voltage, Frequency, Phase Voltage – designed operation voltage for motor. May be single or multiple-voltage design. Most motors are designed to operate with a supply voltage tolerance of +- 10%, but nameplate ratings are only achieved with nameplate supply conditions. Typical supply voltages: 208, 230, 460, 575 Frequency – Input frequency of AC supply. North American standard is 60 Hz (cycles per second). In Europe 50 Hz is more common. Phase – Number of AC supply lines powering motor. Typically 3 or 1. 5.F.L.A. Full-Load Amps – Current required to operate at its nameplate horsepower with nameplate supply voltage and frequency.

21. 6/30/2016EMC: AC Motors Roger Enns20 Reading the Nameplate– cont’d 6.Duty Cycle % On-Time Allowed Continuous, or 15, 30, 45 minutes per hour operation. Most smaller motors are designed for continuous duty.. 7.Service Factor Continuous overload capability of motor. If motor is kept within temperature limits, and electrical supply can maintain nameplate voltage level, motor may be run beyond nameplate power output safely. 1.15 indicates 115% service factor, or 15% overload capability.

22. 6/30/2016EMC: AC Motors Roger Enns21 Reading the Nameplate– cont’d 9.Mounting C-Face – Motor is mounted to machine face of motor. Rigid Base – Motor has feet integral to the motor body that allow it to be rigidly fastened to the machine. Resilient Base – Motor has rubber-isolated feet integral to the motor body that allow it to be mounted but isolated from the machine. 10. Enclosure Frame size indicates dimensional standard to which motor was manufactured. Standards specify external dimensions, mounting, shaft diameter and length, c-face or foot mounting dimensions, etc. 11. Frame ODP – Open Drip-Proof – Motor open, free exchange of cooling air, enclosure provides protection against liquid within 15 degrees of vertical. TEFC – Totally Enclosed-Fan Cooled – Better protection against external contamination, and includes an integral fan to force cooling air across motor.

23. 6/30/2016EMC: AC Motors Roger Enns22 C-Face Capacitor Start/Run Motor

24. 6/30/2016EMC: AC Motors Roger Enns23 Foot-Mount