single phase Induction Motor-types, construction working.pptx

single phase Induction Motor-types, construction working

1. AC current reverses direction Two parts: stator and rotor Stator: stationary electrical component Rotor: rotates the motor shaft Two types Synchronous motor Induction motor AC Motors

2. AC Motors

3. Most common motors in industry Advantages: Simple design Inexpensive High power to weight ratio Easy to maintain Direct connection to AC power source AC – Induction motor

4. AC – Induction motor How induction motors work Electricity supplied to stator Magnetic field generated that moves around rotor Current induced in rotor Electromagnetics Stator Rotor Rotor produces second magnetic field that opposes stator magnetic field Rotor begins to rotate

5. Single-phase induction motor One stator winding Single-phase power supply Squirrel cage rotor Require device to start motor Up to 3 to 4 HP Household appliances: fans, washing machines, dryers AC – Induction motor

6. Shaded-pole motor The shaded pole delays the creation of the magnetic field in that portion of the stator poles. This produces a magnetic field in the shaded portion that is approximately 90 ° apart from the magnetic field produced in the main portion of the pole. Considered a nonreversible motor.

7. Split-phase motor Start winding Many turns of heavy-gauge wire Centrifugal switch opens after start-up removing the start winding from the circuit. Reverse direction of rotation by interchanging run winding or start winding connections (preferred).

8. Three Types of Capacitor Start Motors Capacitor Start (disconnects capacitor after motor speed picks up) Capacitor Run (Keeps the capacitor connected during the operation of the motor, in order to keep the electric power consumption low) Capacitor Start-Run (uses two capacitors, one for starting and one for running. This further improves Power Consumption)

9. Capacitor-start motor Start circuit has: Centrifugal switch Start winding Start capacitor This produces higher starting torque . Run winding Reverse direction of rotation by interchanging run winding or start winding connections (preferred).

10. Capacitor-run motor The capacitor shifts the phase on one of the windings so that the voltage across the winding is at 90° from the other winding Run capacitor produces higher running torque. Start winding stays as part of the circuit Run winding Reverse direction of rotation by interchanging run winding or start winding connections (preferred).

11. Capacitor-start/capacitor-run motor Start circuit: Start winding Centrifugal switch Start capacitor Larger value produces higher starting torque. Run winding Run capacitor Smaller value produces higher running torque. Reverse direction of rotation by interchanging run winding or start winding connections (preferred).

12. Capacitor start-run reverse connections

13. Winding(s) which produce the magnetic field(s) necessary to cause the rotor to turn. 3 Phase; 2 Pole Motor What are Poles in a Motor?

14. Requires DC voltage for starting excitation Has low starting torque S uited for low load applications Rotor of the synchronous motor travels at the same speed as the rotating magnetic field AC - Synchronous motor

15. Synchronous motor Three-Phase Motors Parts Rotor with single winding Slip rings and brushes Three-phase stator windings

16. Constant speed fixed by system frequency Used where there is a need to improve the power factor Synchronous speed (Ns): AC - Synchronous motor F = frequency of the voltage source supplied P = number of poles

17. Synchronous speed P 50 Hz 60 Hz 2 3000 3600 4 1500 1800 6 1000 1200 8 750 900 10 600 720 12 500 600

18. 4-Pole stator winding Each AC phase has 4 stator windings Each winding is in opposite direction from preceding winding, making a N-S-N-S field Field strength rotates with AC current of each phase

19. Three-phase induction motor Three-phase supply produces magnetic field Squirrel cage or wound rotor Self-starting High power capabilities Fractional to 100’s of HP Applications : pumps, compressors, conveyor belts, grinders 70% of motors in industry! AC – Induction motor

20. Aka: Asynchronous motor The induction ac motor is a common form of an asynchronous motor Is basically an AC transformer with a rotating secondary AC – Induction motor

21. Components Rotor Squirrel cage: conducting bars in parallel slots Wound rotor: 3-phase, double-layer, distributed winding AC – Induction motor Stator Stampings with slots to carry 3-phase windings Wound for definite number of poles

22. 3-phase I nduction Motor Operation Arrows shows stator magnetic field vector Stator field precedes the rotor’s induction field http://en.wikipedia.org/wiki/File:3phase-rmf-noadd-60f-airopt.gif

23. Interchange any two of the three stator leads. The industry standard is to switch T 1 and T 3 . The wound-rotor induction motor is considered to be a variable-speed motor. Initial cost is higher and maintenance costs are higher than for a squirrel-cage induction motor. Reversing Direction of a 3 Phase Motor

24. Reversing Direction of a 3 Phase Motor A B C

25. Changing AC Motor Speed Voltage – Hertz Ratio: Operating motor in a range different from rated frequency and voltage affects both torque and current .

26. Changing AC Motor Speed Voltage – Hertz Ratio: Maintaining the ratio gives a constant torque range For a synchronous motor rated for 3 phase, 460 volts, 60 Hz and 3600 rpm, what will be the operating frequency and voltage if the motor controller commands the motor to run at 2750 rpm? 7.67 2 poles 45.83 Hz 351.52 volts

27. Squirrel-cage induction motor Parts : Rotor Stator The squirrel-cage induction motor is considered to be a fixed-speed motor.

28. Speed and slip Motor never runs at synchronous speed but lower actual rotor speed Difference is “slip” Install slip ring to avoid this Calculate % slip: Ns = synchronous speed in RPM N R = rotor speed in RPM AC – Induction motor

29. Wound-rotor induction motor The rotor contains windings. Slip rings and brushes provide an electrical connection to the rotor windings. The wound-rotor induction motor is considered to be a variable-speed motor. Initial cost is higher and maintenance costs are higher than for a squirrel-cage induction motor.

30. Relationship: load, speed and torque Starting Torque (aka LRT): high torque and low speed “Pull-up ” torque: lower torque and increasing speed “Breakdown” torque: 75% speed and highest torque = 178.6 ft -#’S Full load torque: motor operates at rated voltage, frequency and load and stator current are zero 30 HP 1765 RPM

31. Torque Curve Calculate: Speed at 100% full load current % Slip

32. AC Motor Data Plate

33. Types of Motor Enclosures ODP – Open Drip Proof TENV – Totally Enclosed Non-Ventilating TEFC – Totally enclosed Fan Cooled XP – Explosion Proof

34. Types of Motor Enclosures ODP – Open Drip Proof Air flows through motor (fan blades help flow) Used in environments free from contaminants

35. Types of Motor Enclosures TENV – Totally Enclosed Non-Ventilating Protect motor from corrosive and harmful elements Frame fins help to dissipate heat

36. Types of Motor Enclosures TEFC – Totally enclosed Fan Cooled Similar to TENV except has external fan for cooling

37. Types of Motor Enclosures XP – Explosion Proof Similar to TEFC but enclosures are cast iron

38. Hazardous Locations Division I – Hazardous material present in the air as a norm Division II - Hazardous material present in the air as an abnormal event

39. Summary DC motors are: p ermanent magnet series-wound , shunt-wound , compound-wound AC single phase motors are: the shaded-pole, split-phase , capacitor-start , capacitor-run , capacitor-start / capacitor-run

40. Questions Name two motors that do not need brushes for their rotor windings. Which motor supplies the highest output torque to weight ratio? Why is it not recommended to use dc motors in artificial hearts? In an environment that contains explosive gases, such as in mines, which motor do you recommend using: a) series dc motor b) shunt dc motor c) induction motor d) universal motor