Lectur Lecture 20: e 20: DC M DC Motor otors Exam Exam 2 - - PowerPoint PPT Presentation

lectur lecture 20 e 20 dc m dc motor otors exam exam 2
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Lectur Lecture 20: e 20: DC M DC Motor otors Exam Exam 2 - - PowerPoint PPT Presentation

Lectur Lecture 20: e 20: DC M DC Motor otors Exam Exam 2 Results 2 Results Most M ost Missed Questions: issed Questions: Most M ost Missed Questions: issed Questions: Most M ost Missed Questions: issed Questions: Exam Exam 2 M 2


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SLIDE 1

Lectur Lecture 20: e 20: DC M DC Motor

  • tors
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SLIDE 2

Exam Exam 2 Results 2 Results

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SLIDE 3

Most M

  • st Missed Questions:

issed Questions:

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SLIDE 4

Most M

  • st Missed Questions:

issed Questions:

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SLIDE 5

Most M

  • st Missed Questions:

issed Questions:

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SLIDE 6

Exam Exam 2 M 2 Make- ake-up up

  • Fix all your mistakes on the solution problems only.
  • Receive up to 1/3 of the points missed on solution problems.
  • No partial credit will be given.

Instructions:

  • For each problem you want to resubmit, rework each problem

in it's entirety on NEW paper (even if you only missed one part

  • f the problem).
  • Clearly identify each problem, subproblem, i.e. a, b, c, etc.,

and each answer.

  • Credit given by subproblem.
  • Must have correct and complete answers and must CLEARLY

show work to receive credit.

  • As a minimum, make sure you write down any/all equations

used in variable form prior to substituting numbers.

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SLIDE 7

DC M DC Motor

  • tors
  • DC Motor electromechanical energy conversion device.

– Uses DC electricity (obviously). – Converts electrical energy / power into mechanical energy / power.

  • Advantages:

– Easy use with batteries (transportation/portable applications) – Simpler / more precise speed and torque control than AC motors

  • Disadvantages:

– Requires “commutation” - mechanical (brushes) or power electronic based – Brushed systems require regular maintenance / replacement

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SLIDE 8

Elecr Elecrom

  • magnetic Fundam

agnetic Fundamentals entals

Ampere's Law – Moving charge (current) induces a magnetic field

`

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SLIDE 9

Right Hand Rule ( Right Hand Rule (Conductor Conductor)

  • Determines direction of

magnetic field

  • Imagine grasping conductor

with right hand

  • Thumb in direction of current

flow (not electron flow)

  • Fingers curl in the direction of

magnetic field DO NOT USE LEFT HAND RULE IN BOOK

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SLIDE 10

Right Hand Rule ( Right Hand Rule (Coil) Coil)

  • Imagine grasping coil with right hand
  • Fingers in direction of current flow (not

electron flow)

  • Thumb points in direction of magnetic

field through coil DO NOT USE LEFT HAND RULE IN BOOK Creates electromagnet

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SLIDE 11

Magnetic For agnetic Force on M ce on Moving

  • ving

Char Charge ge

  • A magnetic field has a force on a moving charge
  • Lorentz Force Law

Two right hand rules. Choose which one is best for you. I like the one on the right.

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SLIDE 12

DC M DC Motor

  • tor Oper

Operation ation

  • Consider simplest DC Motor – single loop coil

If No Commutation

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SLIDE 13

DC M DC Motor

  • tor Oper

Operation ation

  • Consider simplest DC Motor – single loop coil

With Commutation

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SLIDE 14

DC M DC Motor

  • tor Oper

Operation ation

  • Real DC Motors

– Rotor has multiple windings around ferromagnetic material core

  • Increase total force on wires (torque)
  • Smoother torque

Rotor – Rotating electromagnetic

  • component. In most DC machines,

this is the armature. Stator – Stationary electromagnetic (or just magnetic) component. In most DC machines, these are the field magnets.

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SLIDE 15

DC M DC Motor

  • tor Oper

Operation ation

Electrochemically generated rotor poles repelled by like stator poles, attracted to

  • pposite stator poles

If poles align, there is no force and thus no torque To have continuous torque, commutation required

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SLIDE 16

Motor

  • tor Com

Commutation utation

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SLIDE 17

Motor

  • tor Tor

Torque que

  • Torque is the product of force and distance:
  • Force per conductor:
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SLIDE 18

Motor

  • tor Tor

Torque que

  • Then, total torque exerted on rotor depends on:

– Number of conductors (individual windings) – Length of conductors – Strength of main field magnetic flux density – Magnitude of the current flowing in each conductor

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SLIDE 19

Motor

  • tor Tor

Torque que

Example: Find the torque developed by a motor with 20 armature conductors, each 10 in. in length, and radially 3 in. from the center of the armature. The current in each conductor is 20 A, and the flux density is 60,000 lines per square inch.

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SLIDE 20

Motor

  • tor Tor

Torque que

Example: Find the torque developed by a motor with 20 armature conductors, each 10 in. in length, and radially 3 in. from the center of the armature. The current in each conductor is 20 A, and the flux density is 60,000 lines per square inch.

F=8.85 B I l 10

8

B=60,000lines/in

2

I=20 A l=10in. F=1.062lb

Per conductor: Total armature torque:

R=3in. =F R =0.2655lb− ft 0.2655lb− ft x 20 5.31lb− ft

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SLIDE 21

Counter Counter EM EMF

  • Motor windings “cut” through magnetic fields
  • Equivalent of changing magnetic field
  • Generates voltage in windings: Counter

electromotive force (CEMF, aka Back emf)

  • Generated voltage in opposition to applied
  • voltage. Effect opposes current flow.
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SLIDE 22

Motor

  • tor Speed

Speed

  • CEMF is proportional to motor speed

– EMF proportional to derivative of change in magnetic flux, which is proportional to speed.

  • Actual motor speed can differ from rated speed

depending on load.

– Rated hp and speed given for a specific load

  • A motor is rated at its maximum horsepower and

speed at a constant load

  • Speed regulation: Motor speed changes by load
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SLIDE 23

Wednesday Wednesday

  • Continue discussion of DC Motors.

– Various types of motor electrical connections – Special types of DC motors

  • Distribution Project Assignment

– Due Monday 12/2