Bissoy.com
Doctors Medicines MCQs Q&A

In a single-phase repulsion motor, torque is developed on the rotor when the brush axis is fixed:

In a single-phase repulsion motor, torque is developed on the rotor when the brush axis is fixed: Correct Answer at an angle with the stator field axis

Concept:

  • Repulsion Motor is a special kind of single phase AC motor which works due to the repulsion of similar poles.
  •  The stator of this motor is supplied with a single phase AC supply and the rotor circuit is shorted through a carbon brush.

Construction:

  • The main components of repulsion motor are stator, rotor and commutator brush assembly.
  •  The stator carries a single phase exciting winding similar to the main winding of a single phase induction motor.
  • The rotor has distributed DC winding connected to the commutator at one end just like in the DC motor. The carbon brushes are short-circuited on themselves.

Figure shows the construction of a repulsion motor:

[ alt="F1 Jai Prakash Anil 22.01.21 D4" src="//storage.googleapis.com/tb-img/production/21/01/F1_Jai%20Prakash_Anil_22.01.21_D4.png" style="width: 275px; height: 208px;">

Working principle of Repulsion motor:

  • When the stator winding of the repulsion motor is supplied with single-phase AC, it produces a magnetic flux along the direct axis as shown in the figure above by arrow mark.
  • This magnetic flux when link with the rotor winding, creates an emf. Due to this emf, a rotor current is produced.
  • This rotor current in turn produces a magnetic flux that is directed along the brush axis due to commutator assembly.
  • Due to the interaction of stator and rotor produced fluxes, an electromagnetic torque is produced.


[ alt="F1 Jai Prakash Anil 22.01.21 D3" src="//storage.googleapis.com/tb-img/production/21/01/F1_Jai%20Prakash_Anil_22.01.21_D3.png" style="width: 356px; height: 225px;">

  • In the above figure, the angle α between the stator produced field and brush axis is 90°.
  • This means, the brush axis is in quadrature with the direct. Under this condition, there will not be any mutual induction between the stator and rotor windings.
  • Therefore, no emf and hence no rotor current is produced. Thus no electromagnetic torque is developed.


[ alt="F1 Jai Prakash Anil 22.01.21 D5" src="//storage.googleapis.com/tb-img/production/21/01/F1_Jai%20Prakash_Anil_22.01.21_D5.png" style="width: 313px; height: 158px;">

  • In this condition, a maximum emf is induced across the brushes. This is because the rotor and stator magnetic flux coincides and hence there is a perfect mutual coupling between them


Conclusion:

  • Therefore torque is developed in the motor when the brush axis is aligned at an angle with the stator field axis.

Related Questions

In the following question, sentences of a paragraph have been jumbled and labelled as A, B, C and D. You are required to rearrange the jumbled sentences of the paragraph and mark your response accordingly by selecting the correct option. A: An induction motor can, therefore, be made without electrical connections to the rotor. B: Three-phase squirrel-cage induction motors are widely used as industrial drives because they are self-starting, reliable and economical. C: An induction motor's rotor can be either wound type or squirrel-cage type. D: An induction motor or asynchronous motor is an AC electric motor in which the electric current in the rotor needed to produce torque is obtained by electromagnetic induction from the magnetic field of the stator winding.
A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted. The maximum torque is twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit. An external resistance is now tripled in the rotor circuit. Then the slip at which maximum torque occur for the same load torque is?
An electromechanical energy conversion device has cylindrical stator but salient pole rotor. Rotor is not excited. If δ is the angle between stator field and rotor long axis, then average torque developed is proportional to (A and B are constants).
For a three phase induction motor, maximum torque is double the full load torque and starting torque is 1.6 times the full load torque. To get a full load slip of 5%, percentage reduction in the rotor resistance should be?
Consider the following statements: In the above figure, the curves pertain to the DC motor A. Speed vs Armature current characteristic of a DC shunt motor B. Torque vs Armature current characteristic of a DC shunt motor C. Speed vs Armature current characteristic of a DC series motor D. Torque vs Armature current characteristic of a DC series motor
In the following question below some statements are given followed by some conclusions. Taking the given statements to be true even if they seem to be at variance from commonly known facts, read all the conclusions and then decide which of the given conclusions logically follows the given statements. Statements: Only few bottles are brush All bottles are phone Conclusion: I. All brush can be phone II. No brush is phone
Consider the following statements: 1. A synchronous motor has no starting torque but when started it always runs at a fixed speed. 2. A single-phase reluctance motor is not self-starting even if path for eddy currents are provided in the rotor 3. A single-phase hysteresis motor is self-starting Which of these statement(s) is/are correct?
A 10 kW, 400 V, 3-phase, 4-pole, 50 Hz induction motor develops the rated output at rated voltage with its slip rings shorted. The maximum torque is twice the full load torque occurs at the slip of 10% with zero external resistance in the rotor circuit. An external resistance is now tripled in the rotor circuit. Then the stator current will _________
Which of the following statements are correct for dc shunt motor? 1. Speed of a shunt motor is sufficiently constant 2. For the same current input, its starting torque is not high as that of series motor 3. The motor can be directly coupled to a load such as fan whose torque increases with speed Select the correct answer using the code given below.
In case of synchronous motor, which of the following are true? a. Synchronous motor is not self-starting b. If the rotor poles are excited by field current and the stator terminals are connected to AC supply, motor vibrates. c. Variable frequency supply is used to start synchronous motor. d. By using frequency converter, a synchronous motor can be brought from standstill to its desired speed.