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Due to this difference in flux, the rotor will experience a torque and will start to rotate at speed less than synchronous speed due to lagging. So, theoretically, the Induction motor can never run at synchronous speed. This will result in no torque on the rotor, and it will stop moving due to this.
What happens if induction motor runs above synchronous speed?
If an external mechanical system drives the rotor above synchronous speed, the induction machine acts as a generator. If the rotor is rotating below synchronous speed, the induction machine is a motor. The relationship between rotor speed and synchronous speed is defined using the terms slip and slip speed.
Can an induction motor run at synchronous speed state reasons?
The induction motor can’t run at synchronous speed because it is not possible to run the motor without load. Even the motor is at no load, there would be core loss,copper loss and air friction loss.In a nut shell, the motor slip can not be zero in any case.
Which motor runs at synchronous speed?
Synchronous speed is a significant parameter for the rotating magnetic field-type AC motor. It is determined by the frequency and the number of magnetic poles. A collective name for the motors that run at the synchronous speed is the synchronous motor.
What is standstill rotor EMF?
When rotor is stationary i.e. s = 1, the frequency of rotor e.m.f. is the same as that of the stator supply frequency. The value of e.m.f. induced in the rotor at standstill is maximum because the relative speed between the rotor and the revolving stator flux is maximum.
What happens if fifth harmonics is given to induction motor?
It will rotates in normal operation. Either short circuit or open circuit occurs. The sinusoidal components having frequency five times of fundamental are known as fifth harmonics. Hence induction motor will rotates in reverse direction because of reverse phase sequence of fifth harmonics.
Why synchronous motors are not self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator. Once the rotor nears the synchronous speed, the field winding is excited, and the motor pulls into synchronization.
What is the difference between rotor speed and synchronous speed?
Induction motor with squirrel cage rotor has two different speeds. The synchronous speed refers to the stator rotating magnetic field, which depends on the number of poles and frequency. The other speed is the rotor’s. The rotor speed will be always slower than the stator speed, we call it slip.
What are the two types of induction motor?
Single-phase induction motors and three-phase induction motors are the two main types of induction motors.
Why is it called synchronous speed?
The synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. Thus, an AC machine in which the rotor moved at a speed and built a constant relationship between the frequency of the voltage in the armature winding and the number of poles is called a Synchronous Machine.
Can the IM run at the synchronous speed?
The Induction Motor cannot run at Synchronous speed because the Slip is never zero in an Induction Motor.
What is synchronous and asynchronous speed?
The synchronous motor is a type of AC motor that runs at synchronous speed. The asynchronous motor is a type of AC motor that runs on speed less than the synchronous speed. It operates on the principle of magnetic interlocking between rotor and stator field.
What happens when slip is zero?
Zero slip means that rotor speed is equal to synchronous speed. If rotor is rotating at synchronous speed in the direction of rotating magnetic field the, there will be no flux cutting action, no emf in the rotor conductors, no current in rotor bar conductor and hence no development of electromagnetic torque.
What is slip at standstill?
At standstill, induction motor slip s is 1, hence the frequency of induced EMF in the rotor of the induction motor is same as that of supply frequency and reduces with increase in speed (due to the reduction in slip).
Which type of Induction motor is best for emf?
10. Which type of Induction motor is best for e.m.f injection method? Explanation: E.M.F injection method is used to control the speed of Induction motor. It is only applicable for WRIM because WRIM rotor consists of copper windings connected in star connection.
Which induction motor has maximum speed?
Synchronous and full load speed of amplitude current (AC) induction motors Speed (rpm) Number of Poles Frequency (Hz, cycles/sec) Synchronous Full Load 2 3600 2900 4 1800 1450.
What is slip in synchronous motor?
Slip is the difference between the synchronous speed of a motor and its actual speed. Mathematically it is determined by. Slip = Synchronous Speed − Actual Speed. Using the example above for synchronous speed of a motor with four poles operating at 60 hertz, the value was calculated to be 1800 RPM.
What is the condition for maximum torque?
Equation of Maximum Torque The maximum torque is directly proportional to square of rotor induced emf at the standstill. The maximum torque is inversely proportional to rotor reactance. The maximum torque is independent of rotor resistance. The slip at which maximum torque occur depends upon rotor resistance, R2.
Which motors are not self starting?
Above a certain size, synchronous motors are not self-starting motors. This property is due to the inertia of the rotor; it cannot instantly follow the rotation of the magnetic field of the stator.
What is the main disadvantage of synchronous motors?
Disadvantages or Demerits: Synchronous motors requires dc excitation which must be supplied from external sources. Synchronous motors are inherently not self starting motors and needs some arrangement for its starting and synchronizing. The cost per kW output is generally higher than that of induction motors.
Are asynchronous motor self starting?
The current carrying rotor being placed in a magnetic field experiences a torque and hence begins to rotate in the direction of rotating magnetic field. Thus we see that Induction Motor is self-starting. It does not require nay external mean to rotate.
