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Why a pure single phase induction motor does not have starting torque but has running torque?
Wiki User
∙ 9y ago
A single-phase induction motor can be considered as running on two oppositely-rotating magnetic fields. In normal running just below synchronous speed, the slip is perhaps 0.05 on one of these rotating fields and 1.95 on the other. The first field supplies the major part of the torque.
When the motor is stationary with power supplied, both fields have a slip of 1 and they produce contrary torques so the motor remains stalled.
If the motor is spun in one direction, the slip becomes unbalanced and there is a net torque from the direction with the least slip, so the motor runs up in that direction.
Wiki User
∙ 9y ago
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How starting torque of an induction motor can be increased?
For a single phase motor, this can be done by connecting a capacitor in series with the starting windings. For three phase motors, this can be done by connecting starting resistors in the stator windings at starting. This reduces the stator current and hence it's flux density. Thus the rotor will have less opposition starting to rotate. Hence, the torque has increased.
What type of motor is used in centrifugal pump?
3 Phase induction motor because it produce high torque at starting
What is the maximum torque than an induction motor can develop known as?
Gross Torque
How does an induction motor develop torque?
The shaft of an AC induction motor rotates because of the torque created by the interaction between the magnetic field of the stator and the magnetic field of the rotor.
Why a single phase induction motor is not self starting?
Single phase induction motor is not self starting because, when the main winding is excited from a single phase supply, it produces an alternating magnetic field instead of rotating magnetic field in two phase and 3 phase induction motor. According to double field revolving theory any alternating vector can be resolved into two vectors rotating in opposite directions, each having magnitude equal to one half the magnitude of the actual vector. The vectors will be rotating in such a way that their resultant will be zero at every instant. Thus a single phase induction motor fails to produce a net starting torque, and is not self starting.It can be made self starting by any of the methods below1) By using an aux winding in series with a very high resistance2) using two capacitors,in series with the aux wdg,one with intermittent duty and the other one with continuous duty3) Using shaded poles
Why use clutch plate in single phase motor?
induction motors have very little starting torque as the motor come up to speed it reduces the torque load until it gets near synchronous speed
Performance curve of a single phase induction motor?
The performance curve can be a graph of torque versus speed. The torque is zero at zero speed and also at the synchronous speed. Normally an induction motor operates at 90-97% of the synchronous speed, where the slip is between 10% and 3%. In this region the torque is proportional to the slip. As the torque is increased the speed falls until the motor stalls and the speed drops to zero. Below the stalling speed the torque rises between zero speed and the stalling speed. Because the torque is 0 at 0, a single-phase induction motor needs a separate starting winding fed by a starting capacitor to produce a little positive torque that starts the motor.
What are the advantages of induction motor?
1. Induction motor has high starting torque, therefore use for operate pump which need high starting torque. 2. Induction motor operate on variable speed. 3. It can be used as generator when speed of motor is higher than synchronous speed.
Where theSlip ring induction motors are used?
The slip ring induction motors are usually used in the application requiring the low starting current or the high starting torque.
What is the use of double cage rotor in induction motor?
to obtain high starting torque
How starting torque of an induction motor can be increased?
For a single phase motor, this can be done by connecting a capacitor in series with the starting windings. For three phase motors, this can be done by connecting starting resistors in the stator windings at starting. This reduces the stator current and hence it's flux density. Thus the rotor will have less opposition starting to rotate. Hence, the torque has increased.
What are the advantages of single phase induction motor?
the torque requirement of single phase induction motor is less,and it is use for low power applications upto 1 to 10 kw.like in fans,mixiers
Disadvantages of a squirrel cage motor?
Squirrel Cage Induction Motor Disadvantages:Some of disadvantages or demerits of squirrel cage induction motors are listed below:Main disadvantage of squirrel cage induction motor is that they have poor starting torque and high starting currents. Starting torque will be in the order of 1.5 to 2 times the full load torque and starting current is as high as 5 to 9 times the full load current. In slip ring induction motors, higher starting torque can be attained by providing an external resistance in the rotor circuits during starting of the slip-ring induction motor. This arrangement in slip-ring induction motors also reduces the high inrush currents during starting of induction motor.Squirrel cage induction motors are more sensitive to the supply voltage fluctuations. When the supply voltage is reduced, induction motor draws more current. During voltage surges, increase in voltage saturates themagnetic components of the squirrel cage induction motor.Speed control is not possible in squirrel cage induction motor. This is one of the major diadvantages of squirrel cage induction motors.The total energy loss during starting of squirrel cage motor is more compared to slip ring motors. This point is significant if the application involves frequent starting
Why do some induction motors start at no load?
The motor might produce little torque when starting. Single-phase motors are particularly bad in this regard. So it is often necessary to remove the load while starting. Loads like fans or rotary driers do not need the load taking off while starting, because the demanded torque is small at low speeds.
What type of motor is used in centrifugal pump?
3 Phase induction motor because it produce high torque at starting
How do you increase starting torque in cage type 3-phase induction motor's?
by adding external resistance to the shaft of rotor
Disadvantages of 3 phase induction motor?
One of the disadvantages of the 3 phase induction motor is that it requires a three wire supply. The other disadvantage is that the 3 phase induction motors have poor starting torque and high have in the rush currents.
