• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

How Engineering Works

  • Home
  • About Us
  • Electrical Engineering
    • Interview Questions
  • Privacy Policy
  • Disclaimer
  • Contact Us
  • Blog

Why are 3-phase induction motors self-starting, but 3-phase synchronous motors are not?

February 5, 2018 by Lal Singh

DWQA Questions › Category: Induction Motor & Generator › Why are 3-phase induction motors self-starting, but 3-phase synchronous motors are not?
0 Vote Up Vote Down
Lal Singh asked 5 years ago
2 Answers
0 Vote Up Vote Down
admin Staff answered 5 years ago

3 Phase Induction Motor-
Expression for Torque-
T=
(V^2)* (R2)/(w syn)((R eq)^2 +(Xeq)^2)s
Where V- Equivalent Thevenin resistance
R2- Rotor resistance referred to stator
w syn- Synchronous angular speed
R eq- Equivalent Thevenin Resistance plus Rotor resistance at given slip s
X eq- Equivalent Thevenin Reactance plus Rotor Reactance

3 phase Synchronous Motor/Generator
Torque T= V*Ef*sin(∆)/ Xs
Where
V- Applied Voltage
Ef- Induced Voltage
∆- Load/Torque Angle
Xs- Synchronous reactance

Thus when field excitation(Ef) is zero, then T for synchronous machine is zero but for induction machine T isn’t equal to zero!
Thus induction machines are self starting wheres Synchronous machines aren’t!

You can also Read :
Interview Questions
MCQ or objective

0 Vote Up Vote Down
admin Staff answered 5 years ago

Yes, it is self starting. A magnetic field is induced in the Rotor which tries to catch up with that of the stator and makes the Rotor rotate.The Rotor is of Squirrel cage construction and produces magnetic Poles. Yes ! 3 phase induction motors are self starting and we need to incorporate a suitable starter device .

You are welcome to read more Important Interview Questions and MCQs.

Primary Sidebar

Related Questions

  • Why star delta starter is preferred with induction motor? asked by
  • What is RDOL starter? asked by
  • What happens if a capacitor is connected to a generator load? asked by admin
  • What is the diffrence between DOL & RDOL starter? asked by

INTERVIEW QUESTIONS

MCQ or Objective





Recommended Post

Mechanical Engineering MCQ’s

Demo timer

MCQs on Transmission and Distribution

MCQs on DC Motor

MCQs on Induction Motor

Categories

  • Electrical Articles (19)
  • Electrical MCQ (75)
  • Electrical Questions (11)
  • Interviews Questions (7)
  • IQ Test (1)
  • Uncategorized (12)

Join Our Whatsapp Group


About Us | Privacy Policy | Disclaimer


Copyright@2017-2022