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Motor Designs A, B, C, D. Cross-Sections of NEMA Motors. Induction Motor Applications. Design B Broadest field of applications Centrifugal pumps, fans, blowers, machine tools Design A Same characteristics as Design B, but with higher breakdown torque

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Presentation Transcript
induction motor applications
Induction Motor Applications
  • Design B
    • Broadest field of applications
    • Centrifugal pumps, fans, blowers, machine tools
  • Design A
    • Same characteristics as Design B, but with higher breakdown torque
    • Higher starting current limits applications

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induction motor applications continued
Induction Motor Applications continued
  • Design C
    • Higher locked-rotor torque but lower breakdown torque than Design B
    • Use to drive plunger pumps, vibrating screens, and compressors
  • Design D
    • Very high locked-rotor torque and high slip
    • Used for high-inertia loads such as elevators and hoists

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induction motor applications continued5
Induction Motor Applications continued
  • Design E
    • High-efficiency
    • Drive loads similar to Design B, but with lower locked-rotor, breakdown, and pull-up torque

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nema tables
NEMA Tables
  • Tables 5.1 – 5.7 give values of locked-rotor torque, breakdown torque, and pull-up torque for specific horsepower, frequency, and synchronous speed ratings.

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example 5 1
Example 5.1
  • Determine the values of locked-rotor torque, breakdown torque, and pull-up torque that can be expected from a 3-phase, 10-hp, 460-V, six-pole, NEMA design C motor whose rated speed is 1150 r/m.

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solution
Solution

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locked rotor torque
Locked-Rotor Torque
  • From Table 5.1, page 171 of the text, the minimum locked-rotor torque of a 10-hp design C motor with a synchronous speed of 1200 r/min should be 225% of full-load torque.

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breakdown torque
Breakdown Torque
  • From Table 5-3

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pull up torque
Pull-up Torque
  • From Table 5.6,

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motor performance as a function of machine parameters slip and stator voltage
Motor Performance as a function of Machine Parameters, Slip, and Stator Voltage
  • Use the “complete” equivalent circuit model, including both the rotor and stator.

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equivalent circuit for an induction motor with all parameters referenced to the stator
Equivalent Circuit for an Induction Motor with all parameters referenced to the stator

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approximate equivalent circuit for an induction motor
Approximate Equivalent Circuit for an Induction Motor

Move the magnetizing branch to the left of resistor R1.

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slip at which maximum torque occurs
Slip at Which Maximum Torque Occurs

Take the derivative of the expression for the developed torque

Solve for the value of slip that makes the derivative equal to zero.

Slip is directly proportional to the rotor resistance.

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slip at which maximum torque occurs23
Slip at Which Maximum Torque Occurs
  • Applications which require a very high starting torque are designed with enough resistance so that the maximum torque occurs at blocked rotor (s = 1).

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maximum torque
Maximum Torque

at maximum torque

Independent of Rotor Resistance!

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