Table of Contents
The three-phase synchronous motor is a unique and specialized motor. As the name suggests, this motor runs at a constant speed from no load to full load in synchronism with line frequency. This attraction exerts a torque on the rotor and causes it to rotate at the synchronous speed of the rotating stator field.
How does a 3 phase synchronous motor work?
Working of synchronous motors depends on the interaction of the magnetic field of the stator with the magnetic field of the rotor. The stator contains 3 phase windings and is supplied with 3 phase power. The rotor enters into the rotating Magnetic-Field produced by the stator winding and rotates in synchronization.
Why do we use 3 phase synchronous motor?
Three-phase synchronous motors find their major application in industrial situations where there is a large, reasonably steady mechanical load, usually in excess of 300 kilowatts, and where the ability to operate at leading power factor is of value.
What is a three-phase synchronous machine?
A synchronous motor is one in which the rotor normally rotates at the same speed as the revolving field in the machine. The stator is similar to that of an induction machine consisting of a cylindrical iron frame with windings, usually three-phase, located in slots around the inner periphery.
What is a 3 phase synchronous motor will always run at synchronous speed?
In synchronous Motor when 3 phase Ac supply is provided to the stator it produces a Rotating Magnetic Field which is rotating at a speed of Ns = 120f/p RPM and on the rotor we already have poles induced due to field winding which is energized by DC source, Now RMF locks this poles induced on the rotor and makes rotor.
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.
How does a 3 φ synchronous motor start?
A three-phase synchronous motor has no starting torque. Once up to speed, the rotor field can be excited with direct current and the rotor is, in effect, then dragged around at the same speed as the three-phase stator field. Its speed is synchronized with that of the stator field.
Why the speed of synchronous motor is constant?
When you supply 60 Hz (or 50 Hz), the motor will spin at one speed, which is dependent on the number of poles. This rotational speed will be constant with different mechanical loads, up to the point that the motor (or coupling) fails, hence it is a “constant speed” motor.
Is 3-phase induction motor is self-starting?
Three-phase induction motor is self-starting, because winding displacement is 120 degrees for each phase and supply also has 120 phase shift for 3-phase. It results in a unidirectional rotating magnetic field is developed in air gap which causes 3-phase induction motor to self-start.
Why it is called synchronous machine?
A synchronous generator is called “synchronous” because the waveform of the generated voltage is synchronized with the rotation of the generator. A synchronous generator is essentially the same machine as a synchronous motor. The magnetic field of the rotor is supplied by direct current or permanent magnets.
What is meant by synchronous speed?
: a definite speed for an alternating-current machine that is dependent on the frequency of the supply circuit because the rotating member passes one pair of poles for each alternation of the alternating current.
Is synchronous machine AC or DC?
In a synchronous motor, AC power is supplied to the stator to generate a rotating magnetic field. DC power is supplied to the rotor which results in discrete North (N) and South (S) poles.
How do you calculate synchronous speed?
The synchronous speed of an AC motor is determined by the frequency of the source and the number of poles. The RPM is calculated by multiplying the frequency times 60 and dividing by the number of pairs of poles. This was explained in Chapter 6.
Which synchronous motor will be smallest in size?
Which synchronous motor will be smallest in size ? (D) 10 HP, 375 rpm. Explanation: Q15.
How can a synchronous motor be self starting?
Answer: The synchronous motor itself does not have the ability to self-start. However, the addition of an additional winding known as damper winding (similar to squirrel cage motor) enables it to self-start. This damper winding is linked with the rotor, and works on the principle of induction motor.
How do you know if a motor is synchronous or asynchronous?
if the slip of the motor is zero or the rotor has the same rotational speed as the stator rotating field, the motor is called AC Synchronous motor. if an AC motor has a slip or there is a difference between the stator field speed and the rotor, the motor is called asynchronous motor.
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.
What 3 things are needed for an induction motor to work?
A 3-phase induction motor includes two essential components namely the stator & the rotor. In this motor, the stationary part is the stator whereas the rotating part is the rotor. In this motor, the load is connected to the shaft. Three-phase armature winding can be wound over the stator.
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.
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.
What is the principle of synchronous generator?
The principle of operation of synchronous generator is electromagnetic induction. If there exits a relative motion between the flux and conductors, then an emf is induced in the conductors.
