Lectur Lecture 22: e 22: AC M AC Motor otors AC M AC Motor - - PowerPoint PPT Presentation

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Lectur Lecture 22: e 22: AC M AC Motor otors AC M AC Motor - - PowerPoint PPT Presentation

Jun 13, 2023 206 likes •477 views

Lectur Lecture 22: e 22: AC M AC Motor otors AC M AC Motor otors Two main types of AC Motors Induction (non-synchronous) Motors Workhorse of industry rugged, reliable, cheap Only stator externally excited Rotor spins

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SLIDE 1

Lectur Lecture 22: e 22: AC M AC Motor

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SLIDE 2

AC M AC Motor

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  • Two main types of AC Motors

– Induction (non-synchronous) Motors

  • Workhorse of industry – rugged, reliable, cheap
  • Only stator externally excited
  • Rotor spins at frequency less than excitation

– Synchronous Motors

  • Requires stator and rotor to be externally excited
  • Can provide power factor correction
  • Rotor spins at frequency equal to excitation
  • Other important types of AC Motors

– Universal Motors – Operate on DC or AC supply

  • Widely used in home appliances and power tools
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SLIDE 3

Recall: DC M Recall: DC Motor

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Operation ation

  • Simplest DC Motor – single loop coil

With Commutation

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SLIDE 4

Motor

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Commutation utation

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Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Construction - Stator

– Windings typically embedded in slots to produce electromagnets.

Rotor goes in here Both diagrams 2-pole 3-phase stators

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SLIDE 6

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Construction - Rotor

– Two general types of Rotor Construction

Squirrel-Cage Rotor Wound Rotor

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Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Operating Principle

– Three-phase source connected to motor windings – Produces rotating magnetic field in the stator – This var varying ying magnetic field induces voltage on rotor bars (squirrel cage) or windings (wound)

  • Same as operation of transformer secondary

– Voltage causes current to flow in rotor conductors – Force on conductors due to current flow in changing magnetic field – Rotor turns due to torque (force x distance) – NOTE: Speed of rotor less than that of rotating magnetic field

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Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Operation: Generating rotating magnetic field of

stator

Consider Resulting Magnetic Field every 30º

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Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 1:
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SLIDE 10

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 1:

Equivalent Magnetic Field

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SLIDE 11

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 2:
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SLIDE 12

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 2:

Equivalent Magnetic Field

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SLIDE 13

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 3:
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SLIDE 14

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 3:

Equivalent Magnetic Field

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SLIDE 15

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 3:
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SLIDE 16

Thr Three- ee-Phase Induction M Phase Induction Motor

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  • Time instance 3:

Equivalent Magnetic Field

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Full Cycle of Rotating Field Full Cycle of Rotating Field

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SLIDE 18

Speed of Rotating Field Speed of Rotating Field

  • Previous discussion on 2-pole 3-phase motor

– 1 electrical cycle corresponds to 1 magnetic field cycle

  • 60 Hz (3600 RPM)
  • More poles reduces speeds

– 4-pole → 30 Hz (1800 RPM) – 6-pole → 20 Hz (1200 RPM) – etc.

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SLIDE 19

Speed of Rotor Speed of Rotor

  • Rotor speed LESS

LESS than synchronous speed

– Percent difference called slip

  • Rotor “slips” because otherwise:

– No changing (relative to rotor) magnetic field – No currents induced in rotor – No force on rotor – Thus, rotor only spins because there is slip.

  • Typical slip between 1 and 5% of synch speed

– Depends on load.

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SLIDE 20

Standar Standard Squir d Squirrel Cage el Cage Motor

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Character acteristics istics

  • Torque and speed as functions of slip
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SLIDE 21

Standar Standard Squir d Squirrel Cage el Cage Motor

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Character acteristics istics

  • Speed, Efficiency, PF, Current and Torque as

functions of Load

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SLIDE 22

Quick Question Quick Question

  • How can you easily change the rotational direction
  • f an induction motor?
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SLIDE 23

Quick Question Quick Question

  • How can you easily change the rotational direction
  • f an induction motor?
  • ANSWER: Interchange two of the electrical phase-

leads.

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Other Other Types of Induction Types of Induction Motor

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  • Double squirrel-cage rotor

– Has two squirrel-cage windings – Inner winding has low resistance and high inductance

  • High Impedance (due to reactance) at startup
  • Low impedance at rated speed

– Outer winding has high resistance and low inductance

  • Low impedance startup
  • High impedance (due to resistance) rated speed

– High starting torque due to outer winding!

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SLIDE 25

Other Other Types of Induction Types of Induction Motor

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  • Wound-Rotor Induction Motor

– Windings connected to slip-rings (similar to brushes

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– Slip-rings connected to external variable resistors

  • Resistors used to optimize current

– High starting torque – Control speed when under constant load – Smooth acceleration

– Disadvantages

  • Higher costs
  • More maintanence
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SLIDE 26

Last bit of class Last bit of class

  • Project – due Monday 12/2
  • Optional HW 7 – Will be put on D2L by

Wednesday

  • Last week of class

– Monday 12/2 - Continue AC Motor Discussion – Wednesday 12/4 – In class review

  • Final 12/12 – Location TBA (but probably this

classroom)