Why do we use capacitor-start induction motors in applications requiring high starting torque in preference to repulsion induction motors?

1 Answer

Answer :

Capacitors are easily available, cheaper and reliable. Repulsion-induction motors posses a special commutator and brushes that require maintenance. Most manufacturers have stopped making them.

Related questions

Description : Why do we use capacitor-start induction motors in applications requiring high starting torque in preference to repulsion induction motors?

Last Answer : Ans : Capacitors are easily available, cheaper and reliable. Repulsion-induction motors posses a special commutator and brushes that require maintenance. Most manufacturers have stopped making them.

Description : Why is the starting torque of a capacitor start induction motor high?

Last Answer : Ans: The capacitor C in the starting winding is so chosen that Is leads Im by 75 degree. Since the starting torque is directly proportional to Sin Ф, and it is quite high in capacitor-start induction motor.

Description : Give applications of Capacitor start Induction run motors.

Last Answer : Drilling machine, centrifugal pump, grinders , refrigerator etc

Description : Why capacitor –start induction motors advantageous?

Last Answer : In capacitor start induction motors capacitor is connected in series with the auxiliary winding. When speed of the motor approaches to 75 to 80% of the synchronous speed the starting winding gets ... torque is proportional to phase angle ά and hence such motors produce very high starting torque.

Description : Why is the starting torque of a resistance split-phase induction motor not high?

Last Answer : The starting torque is given as, Ts = K Im Is Sin Ф Where K = constant whose magnitude depends upon the design of the motor (i) The angle between Is and Im is small ... Im are not equal in magnitude, the rotating magnetic field is not uniform and the starting torque produced is small.

Description : Differentiate between “capacitor start “and “capacitor start capacitor run“ induction motor?

Last Answer : In capacitor start motor, capacitor is connected in series with the starting winding. But it will be disconnected fro m the supply, when the motor picks up its speed. But ... capacitor are not disconnected, but always connected in the supply .so it has high starting and running torque.

Description : Give application of capacitor start capacitor run Induction motor

Last Answer : Ceiling fan, air conditioner, blowers, table fans, conveyors etc

Description : How is the direction of a capacitor start Induction motor be reversed?

Last Answer : The direction of rotation can be reversed by interchanging the terminals of either the main winding or the starting winding.

Description : Where do we require single-phase induction motors?

Last Answer : Single-phase induction motors are required where (i) 3 phase supply is not available (ii) Efficiency is of lesser importance (iii) Rating is less than one H.P. (iv) Equipment is portable

Description : Which type of torque is developed in single phase motors?

Last Answer : Pulsating torque is produced.

Description : How the starting winding produce rotation in a single phase resistance start induction motor?

Last Answer : The starting winding is highly resistive and the main winding is inductive. So the phase difference between the two currents becomes nearly 90 degree and hence the motor start as two phase motor.

Description : Give applications of resistance start Induction run motor?

Last Answer : Fans, Lathe machines, blowers, refrigerator , separators, washing machine etc

Description : Why are centrifugal switches provided on many 1-phase Induction motors?

Last Answer : Centrifugal switches are provided on many 1-phase Induction motors to disconnect the starting / auxiliary winding from the supply when the motor reaches about 70% of its synchronous speed.

Description : Name types of 1-phase induction motors.

Last Answer : Based on the method of starting arrangement provided, the 1-phase Induction motors are classified as follows (i) Split-phase motor (ii) Shaded pole motor (iii) Resistor start Induction run ... iv) capacitor start Induction run single phase IM (v) capacitor start Capacitor run single phase IM

Description : Name the two different theories with which principle of 1-phase induction motors are explained

Last Answer : The two different theories are · Double revolving field theory · Cross field theory

Description : What is the function of capacitor in single phase induction motor?

Last Answer : To make phase difference between starting and running winding, to improve PF and to get more torque

Description : Which of the following is a characteristic of fractional horsepower repulsion start motors? A. They start with a rotating stator field. B. The short circuiting ring is removed from the commutator while ... brushes are removed from the commutator while starting. D. They have a low starting torque.

Last Answer : Answer: B

Description : Why shaded-pole single phase induction motor does not need any special starting technique like capacitors and auxiliary winding etc.

Last Answer : Because it is inherently self started motor. The construction of the poles is such that they give a sweep to the magnetic flux and motor starts rotating.

Description : What is the function of centrifugal starting switch in a single-phase induction motor?

Last Answer : Ans: The centrifugal switch is connected in series with the starting winding. The primary function of the centrifugal switch is to produce rotating flux in conjunction with main winding at the time of ... has no function to perform and is removed from the circuit by a centrifugally operated switch.

Description : What are methods available for making single phase induction motor a self starting?

Last Answer : By slitting the single phase, by providing shading coil in the poles.

Description : Why single phase induction motor is not a self starting one?

Last Answer : When motor fed supply from single phase, its stator winding produces an alternating flux, which doesn’t develop any torque.

Description : Is there any relation between the capacitances of two capacitors used in two value capacitor start capacitor run motor?

Last Answer : Ans: Starting capacitor has about 10 – 15 times high capacity than the value of running capacitor.

Description : How speed control is made in single phase motors?

Last Answer : It is usually controlled by applying a variable voltage from tapped transformers, variacs, potentio meters, and tapped reactors.

Description : What kind of motors used in ceiling fan and wet grinders?

Last Answer : Ceiling fan # Capacitor start and capacitor run single phase induction motor, wet grinders# Capacitor start capacitor run single phase induction motor.

Description : Why are resistance split-phase inductions motors most popular?

Last Answer : These motors are most popular due to their low cost. They are used where moderate starting torque is required and where the starting periods are not frequent. They drive fans, pumps, washing machines, small machine tools etc. They have power rating between 60 watts and 250 watts.

Description : Which type of rotor is used in single phase motors?

Last Answer : Squirrel cage type

Description : A single-phase induction motor having a relatively high starting torque, is the ___________. A. shaded pole motor B. wound-rotor motor C. capacitor-start motor D. resistance-start motor

Last Answer : Answer: C

Description : How the speed of rotation of a split phase induction motor is reversed?

Last Answer : The terminal connections of the starting windings are reversed with respect to main running windings..

Description : what is the type of induction motor used in wet grinders?

Last Answer : Capacitor start capacitor run single-phase induction motor.

Description : What is the draw back of the resistance split-phase induction motor?

Last Answer : The starting winding has a relatively small number of turns of fine wire and its resistance is higher than that of the main winding. Therefore the current density is high and the winding heats up quickly. ... begins to smoke and may burn out unless the motor is protected by a built-in-thermal relay.

Description : why single-phase induction motor has low power factor?

Last Answer : The current through the running winding lags behind the supply voltage by a very large angle. Therefore power factor is very low.

Description : Name the two winding of single phase induction motor?

Last Answer : Running and starting winding.

Description : what is the application of shaded pole induction motor?

Last Answer : Because of its small starting torque, it is generally used for small fans, toys, instruments, hair driers, tape recorder, advertising display, ventilators, electric clock etc.

Description : What is the principle of operation of shaded-pole induction motor?

Last Answer : A shaded-pole motor is basically a small single-phase squirrel cage motor in which the starting winding is composed of short-circuited copper ring (called shading coil) surrounding one-third of each pole ... rotating magnetic field. As a result, the rotor is set in motion due to induction principle.

Description : What are the inherent characteristics of plain 1-phase Induction motor ?

Last Answer : 1-phase Induction motor is not used in practice due to the following inherent characteristics · 1-phase Induction motor does not have any starting torque · However, if the rotor is initially ... up its speed in a direction at which the initial torque is given and deliver the required output

Description : what do you mean by single phase induction motor?

Last Answer : A machine that converts 1 phase ac electrical power into mechanical power by using a electromagnetic induction phenomenon is called a 1 phase induction motor.

Description : How the starting winding is made resistive?

Last Answer : It consists of only few turns of smaller diameter.

Description : What happens when the centrifugal starting switch fails to open?

Last Answer : Ans: If the starting switch fails to open when needed, then the starting winding will overheat and burn out and motor will not start next time.

Description : Autotransformer starters or compensators are sometimes used with polyphase induction motors to _____________. A. reduce the voltage applied to the motor during the starting period B. increase the voltage for ' ... to be either stepped up or down, depending on the application, to ensure full torque

Last Answer : Answer: A

Description : An across-the-line starter is typically used for which of the following applications? A. Reduced-current starting of large motors B. Low torque starting of small motors C. Low resistance starting of DC motors D. Full-voltage starting of motors

Last Answer : Answer: D

Description : The rotor slots of a repulsion-type motor are generally skewed (placed nonparallel to the rotor axis) to _________. A. produce a constant starting torque B. permit a greater air gap with the starter C. permit a smaller air gap with the starter D. reduce eddy current losses

Last Answer : Answer: A

Description : Reduction in the capacitance of a capacitor-start motor, results in reduced (A) Noise. (B) Speed. (C) Starting torque. (D) Armature reaction.

Last Answer : Ans: C Reduction in the capacitance reduces starting voltage, which results in reduced starting torque.

Description : What is the use of shading ring in a pole motor?

Last Answer : The shading coil causes the flux in the shaded portion to lag behind the flux in unshaded portion of pole. This gives in effect a rotation of flux across the pole face and under the influence of this moving flux a staRting torque is developed.

Description : After servicing a single phase fan it was found to run in reverse direction. What could be the reason?

Last Answer : The connection to the starting/ auxiliary winding would have reversed.

Description : If a single phase motor is driven in any direction by any means, it starts running in that direction. Explain why?

Last Answer : Actually a pulsating torque has two components which are equal in magnitude and rotate in opposite direction with synchronous speed at unity slip. Now if the motor rotates in any direction, the ... component in this direction increases than the other component and hence motor runs in that direction.

Description : what kind of motor is used in mixie?

Last Answer : Single-phase ac series motor is used in mixie.

Description : What is size of shaded-pole motor?

Last Answer : These are usually built in small fractional H.P, not exceed 1/4 H.P.

Description : In which direction does a shaded pole motor run?

Last Answer : The rotor starts rotation in the direction from unshaded part to the shaded part.

Description : what do you mean by shaded pole motor?

Last Answer : These motor have projected pole with 1/3 pole part rapped with a copper strip. This portion of the pole is called shaped part of the pole because of this a revolving field is set up in the Stator and torque is developed.

Description : What are the conclusions from Double revolving field theory?

Last Answer : Forward component of flux produce forward torque while backward component produce backward torque. At start, magnitude of both torque are equal but their directions are opposite. hence resultant torque is zero Thus single phase Induction motor isnt self starting.