Mention different types of speed control of slip ring induction motor?

Mention different types of speed control of slip ring induction motor?
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1 Answer

Answer :

a) By changing supply frequency b) By changing the number of stator poles c) By rotor rheostat control d) By operating two motors in cascade
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Related questions

Slip ring induction motor advantages and disadvantages compared to squirrel cage motors?

Description : Slip ring induction motor advantages and disadvantages compared to squirrel cage motors?

Last Answer : Advantages: High starting torque with low starting current Smooth acceleration under heavy loads No abnormal heating during starting Good running characteristics after external rotor resistances are cut out ... cage motors The speed regulation is poor when run with resistance in the rotor circuit

What is the purpose of connecting external resistors to slip ring Induction motor?

Description : What is the purpose of connecting external resistors to slip ring Induction motor?

Last Answer : It increases starting torque and decreases starting current.

What are the materials used to manufacture the brushes for slip rings of an induction motor?

Description : What are the materials used to manufacture the brushes for slip rings of an induction motor?

Last Answer : A:The slip rings are made of brass and phosphor bronze. The brushes are made of metal graphite which is an alloy of copper and carbon.

How the slip ring motor is started?

Description : How the slip ring motor is started?

Last Answer : The slip ring motor is started by using rotor resistance starter. The starter consists of star connected resistance to slip rings. While starting the full resistance is included in the rotor circuit to ... running condition the slip rings are shorted and so it is equivalent to squirrel cage rotor.

What are the advantages of slip ring motor over squirrel cage motor?

Description : What are the advantages of slip ring motor over squirrel cage motor?

Last Answer : 1. The starting torque can be varied by adding resistance to rotor. 2. The speed of the machine can be varied by injecting an emf through slip rings to the rotor.

Why Speed Control of Induction Motor is difficult compared to DC shunt motor?

Description : Why Speed Control of Induction Motor is difficult compared to DC shunt motor?

Last Answer : Answer: Speed Control of DC shunt motor can be possible by providing resistance in the armature and field circuits and varying the resistors speed changes can be carried out over a wide range. ... employed. Care should be taken that in the process efficiency and power factor should be maintained.

List out the methods of speed control of cage type 3-phase induction motor?

Description : List out the methods of speed control of cage type 3-phase induction motor?

Last Answer : a) By changing supply frequency b) By changing the number of poles c) By operating two motors in cascade

What are the different types of stator winding in induction motor?

Description : What are the different types of stator winding in induction motor?

Last Answer : The different types of stator windings are mush winding, lap winding and wave winding.

What types of slots are preferred for the induction motor?

Description : What types of slots are preferred for the induction motor?

Last Answer : Semi enclosed slots are preferred for induction motor. It results in less air gap contraction factor giving a small value of magnetizing currents, low tooth pulsation loss and much quieter operation(less noise)

State the types of Induction motor ?

Description : State the types of Induction motor ?

Last Answer : 1) Squirrel cage Induction motor 2) Wound or slip ring Induction motor.

What is slip speed?

Description : What is slip speed?

Last Answer : The difference between synchronous speed and rotor speed is called slip speed.

Explain the operation of induction motor in simple words?

Description : Explain the operation of induction motor in simple words?

Last Answer : Answer: When 3 phase ac supply is given to stator of the induction motor rotating magnetic field will be generated. This magnetic field (flux) cuts the stationary conductors of the rotor of ... be developed. If the torque generated is sufficient to overcome the load torque rotor starts rotating.

Why the efficiency of the Induction motor is less compared to transformer?

Description : Why the efficiency of the Induction motor is less compared to transformer?

Last Answer : Answer: Induction motor and Transformer operates on the same principle that power is transferred to secondary by mutual induction. But in transformer, flux will be traveled from primary to ... compared to transformer which also results in less efficiency for induction motor compared to transformer.

Disadvantages of Star-Delta Starting of Induction motor?

Description : Disadvantages of Star-Delta Starting of Induction motor?

Last Answer : In Star-Delta starting induction motor stator is connected in star connection for starting after picking up speed it is connected to delta connection. When induction motor is connected in star connection ... . This also results in reduced starting torque (1/3 times compared to delta connection).

What is the condition for maximum torque in induction motor?

Description : What is the condition for maximum torque in induction motor?

Last Answer : Starting torque will be maximum when the rotor resistance / phase is equal to standstill rotor reactance / phase

Induction Motor Operating Characteristics

Description : Induction Motor Operating Characteristics

Last Answer : All torques of an induction motor, at a given slip, vary approximately as the square of the voltage applied to its terminals Low rotor resistance results in high full load speed (low slip), ... voltage), the load torque is unchanged, and the ratio of accelerating torque to load torque is reduced

why the three phase induction motor draws heavy current at starting?

Description : why the three phase induction motor draws heavy current at starting?

Last Answer : At the time of starting, the rotor speed is zero hence slip is 1, the emf induced in rotor winding is very high. Hence rotor current is also very high. The starting current is 5 to 7 times more than its full load current.

What happens if the air gap flux density in an induction motor increases?

Description : What happens if the air gap flux density in an induction motor increases?

Last Answer : The increase in air gap flux increases iron loss and hence efficiency decreases.

What would happen if a 3 phase induction motor is switched on with one phase disconnected?

Description : What would happen if a 3 phase induction motor is switched on with one phase disconnected?

Last Answer : The motor is likely to burn .

In what respect does a 1-phase Induction motor differ from a 3-phase Induction motor?

Description : In what respect does a 1-phase Induction motor differ from a 3-phase Induction motor?

Last Answer : Construction wise a plain 1-phase Induction motor is more or less similar to a 3-phase squirrel-cage Induction motor except that its stator is provided with only 1-phase winding..

Why the air gap of an induction motor is made as small as possible?

Description : Why the air gap of an induction motor is made as small as possible?

Last Answer : The mmf and the magnetizing current are primarily decided by length of air gap. If air gap is small then mmf and magnetizing current will be low, which in turn increase the value of power factor. Hence by keeping small air gap, high power factor is achieved.

List out the methods to improve the power factor of the induction motor.

Description : List out the methods to improve the power factor of the induction motor.

Last Answer : The power factor of the induction motor can be improved by reducing the magnetizing current and leakage reactance. The magnetizing current can be reduced by reducing the length of air gap. The ... stator & rotor slots, by providing short chorded winding and reducing the overhang in stator winding.

What are the advantages and disadvantages of large air gap length in induction motor?

Description : What are the advantages and disadvantages of large air gap length in induction motor?

Last Answer : Advantage: A large air gap length results in higher overload capacity, better cooling, reduction in noise and reduction in unbalanced magnetic pull. Disadvantages: The disadvantage of large air gap length is that it results in high value of magnetizing current.

Which part of induction motor has the maximum flux density? What is the maximum flux density in that part?

Description : Which part of induction motor has the maximum flux density? What is the maximum flux density in that part?

Last Answer : The teeth of the stator and rotor core will have maximum flux density. The maximum value of flux density in the teeth is 1.7 wb/m

What are the advantages of 3-phase induction motor?

Description : What are the advantages of 3-phase induction motor?

Last Answer : a) It was very simple and extremely rugged, almost unbreakable construction b) Its cost is very low and it is very reliable c) It has been suffiently high efficiency .No brushes are needed and hence frictional losses are reduced d) It requires minimum of maintenance.

Explain why the no load current of an induction motor is much higher than that of an equivalent transformer.

Description : Explain why the no load current of an induction motor is much higher than that of an equivalent transformer.

Last Answer : In induction motor, due to the presence of the air gap, the magnetizing current that is required to set up the flux is much higher. The working component of the current has to meet the ... eddy current loss, friction and windage losses. Hence the no load current of induction motor is higher.

Why the induction motor is called asynchronous motor?

Description : Why the induction motor is called asynchronous motor?

Last Answer : Since the induction motor runs always at a speed lesser than synchronous speed, it is called asynchronous motor.

Why Induction motor is called rotating transformer?

Description : Why Induction motor is called rotating transformer?

Last Answer : Transformer has two sides: primary & secondary. Transformer transforms energy from primary to secondary by induction. Similarly, Induction motor has primary (stator) & secondary (rotor). Voltage is ... magnitude i.e. the process of induction Thus induction motor treated as a rotating transformer.

Name the materials used to insulate the laminations of the core of induction motor.

Description : Name the materials used to insulate the laminations of the core of induction motor.

Last Answer : The materials used to insulate the laminations are kaolin and varnish.

Why skewing is done in squirrel cage Induction motor?

Description : Why skewing is done in squirrel cage Induction motor?

Last Answer : i) For more uniform torque ii) Reduction in noise iii) To decrease magnetic locking tendency

Explain how Torque-Slip Characteristics vary when adding resistance to rotor circuit?

Description : Explain how Torque-Slip Characteristics vary when adding resistance to rotor circuit?

Last Answer : The addition of resistance to the rotor circuit does not change the value of maximum torque but it only changes the value of the slip at which the maximum torque occurs

What is the normal value of slip of an I M operating at full load?

Description : What is the normal value of slip of an I M operating at full load?

Last Answer : 3 - 5%

How the frequency of rotor emf is related to the slip in an I M?

Description : How the frequency of rotor emf is related to the slip in an I M?

Last Answer : Frequency of rotor emf/current fr=Sf

How the magnitude of rotor emf is related to the slip in an I M?

Description : How the magnitude of rotor emf is related to the slip in an I M?

Last Answer : Rotor circuit emf per phase E2’=SE2

What is Slip?

Description : What is Slip?

Last Answer : The difference between synchronous speed and rotor speed with respect to synchronous speed is called slip. S=Ns-N/Ns*100

What are slip rings?

Description : What are slip rings?

Last Answer : The slip rings are made of copper alloys and are fixed around the shaft insulating it. Through these slip rings and brushes the rotor winding can be connected to external circuits.

A degree of control over the speed of a slip ring induction motor can be obtained by _____________. A. adjusting governor linkage B. changing the number of phases to the motor C. inserting resistance into the stator circuit D. inserting resistance into the rotor circuit

Description : A degree of control over the speed of a slip ring induction motor can be obtained by _____________. A. adjusting governor linkage B. changing the number of phases to the motor C. inserting resistance into the stator circuit D. inserting resistance into the rotor circuit

Last Answer : Answer: D

What are the advantages and disadvantages of Induction Motors?

Description : What are the advantages and disadvantages of Induction Motors?

Last Answer : Advantages: It is simple and rugged in construction It is relatively cheap Induction motors require less maintenance Induction motor has high efficiency and reasonably good power factor 3-phase induction ... and its speed cannot be changed easily Its starting torque is inferior to dc shunt motor

Name the tests to be conducted for predetermining the performance of 3-phase induction machine.

Description : Name the tests to be conducted for predetermining the performance of 3-phase induction machine.

Last Answer : (a) No load test (b) Blocked rotor test

Methods to control speed of Wound Rotor Motors?

Description : Methods to control speed of Wound Rotor Motors?

Last Answer : The speed of wound rotor motors are changed by changing the slip of the motor. This can be achieved by: Varying the stator line voltage Varying the resistance in the rotor circuit Inserting and varying a foreign voltage source in the rotor circuit

What would happen if synchronous speed is equal to rotor speed?

Description : What would happen if synchronous speed is equal to rotor speed?

Last Answer : The rotor never obtained the synchronous speed because at that speed there would be no relative speed between rotor conductors and stator revolving field and induction phenomenon is not possible. Its speed is always less than synchronous speed.

What is Synchronous speed?

Description : What is Synchronous speed?

Last Answer : The speed at which rotating magnetic field of three Phase Induction motor rotates is called synchronous speed. Ns=120f/p

What are the types of starters?

Description : What are the types of starters?

Last Answer : Direct on line Autotransformer Star delta Rotor resistance starter Soft starter or Electronic starter

In a 3-phase slip-ring induction motor, the slip at some speed is 0.05. The speed is reduced by inserting an

Description : In a 3-phase slip-ring induction motor, the slip at some speed is 0.05. The speed is reduced by inserting an external resistance in the rotor circuit and the slip is 0.15. If the rotor winding resistance per phase is 0.2 Ω, the external resistance is (A) 0.2 Ω (B) 0.3 Ω (C) 0.4 Ω (D) 0.5 Ω

Last Answer : In a 3-phase slip-ring induction motor, the slip at some speed is 0.05. The speed is reduced by inserting an external resistance in the rotor circuit and the slip is 0.15. If the rotor winding resistance per phase is 0.2 Ω, the external resistance is 0.3 Ω

Develop power and control diagram for secondary frequency acceleration starter of slip ring induction motor.

Description : Develop power and control diagram for secondary frequency acceleration starter of slip ring induction motor. 

Last Answer : Power and Control Circuit diagram for secondary frequency acceleration starter of slip ring induction motor:

Draw power and control circuit for definite time-limit starter for slip-ring induction motor. Explain its working.

Description : Draw power and control circuit for definite time-limit starter for slip-ring induction motor. Explain its working.

Last Answer : Definite Time-limit Starter for Slip-ring Induction Motor: This starter is used for automatic control of acceleration of slip-ring induction motor at the time of starting. In this starter, the ... each phase, shorting the rotor winding terminals and final acceleration of the motor takes place. 

What are the effects of increasing rotor resistance on starting current and starting torque?

Description : What are the effects of increasing rotor resistance on starting current and starting torque?

Last Answer : The additional external resistance reduces the rotor current and hence the current drawn from the supply. It improves the starting torque developed by improving the power factor in high proportion to the decrease in rotor current..

What are the methods adopted to reduce harmonic torques?

Description : What are the methods adopted to reduce harmonic torques?

Last Answer : The methods used for reduction or elimination of harmonic torques are chording, integral slot winding, skewing and increasing the length of air gap.

What happens if the air gap length is doubled?

Description : What happens if the air gap length is doubled?

Last Answer : If the air gap of an induction motor is doubled then the mmf and magnetizing current approximately doubles. Also increase in air gap length increases the overload capacity, offers better cooling, reduces noise and reduces unbalanced magnetic pull.

Where mush windings are used?

Description : Where mush windings are used?

Last Answer : The mush windings are used in small induction motors of ratings below 5 HP.