The speed of a synchronous motor is dependent on the frequency of the power source and the number of poles the stator has. … The motor will run at synchronous speed and will not have the slip required by the other three-phase induction motors. Varying loads within the rating of the motor will not cause the RPM to change.
Why does speed of synchronous motor remain constant even under variable load?
In the synchronous motor, rotor too have a DC excitation, so it produces a constant flux forming the electromagnetic poles on rotor which initially are stationary. … Even on loading, the speed is always constant but the torque angle (between stator and rotor magnetic poles) may vary.
What happens to the speed of a synchronous motor if the load is increased?
The load on the shaft is increased. The rotor slows down momentarily, as it required some time to take increased power from the line. In another word, it can be said that even if the rotor is rotating at synchronous speed, the rotor slips back in space because of the increase in the load.
What determines the speed control of a synchronous motor?
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. Some motors are designed to operate at synchronous speed.
What speed does a synchronous motor run at full load?
The synchronous speed is 1500 rpm and the typical full load speed is 1450 rpm. The slip is the difference between synchronous and load speed – 50 rpm.
Why the speed of synchronous motor is constant?
The rotor of a synchronous motor moves at the same speed as the changing, rotating field in its stator. The rotor’s magnetic field is “synchronized” with the stator’s field. … Their speed is dependent on the number of poles and the supply frequency. They have a constant speed at a given supply frequency.
How can you reduce the speed of a synchronous motor?
Changing the number of poles is not easy, so we do not use that method. However, with the invention of solid-state devices, the frequency of the current fed to the synchronous motor can be varied. We can control the speed of the synchronous motor by changing the frequency of the supply to the motor.
What happens when motor load increases?
As the load is increased, the motor will slow down, and the torque will increase. Current into the motor will also increase. … The peak torque occurs at relatively high speed for efficient motors. Certain applications use less efficient induction motors which are designed to have maximum torque occur at stall speed.
What is 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.
Does the excitation affect the synchronous motor speed?
why speed decreases as field excitation increases in synchronous machine. why the speed of the synchronous motor remains constant on any load. why with the change of excitation of a synchronous motor the magnitude of armature current first decrease and then increase.
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 is relation between synchronous speed and frequency?
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.
What is the difference between synchronous speed and rotor 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.
When a synchronous motor is running at synchronous speed?
Synchronous motors are inherently not able to self-start on an AC power source with the utility frequency of 50 or 60 Hz. As stated in Chapter 1, this is because synchronous motors can develop a torque only when running at the synchronous speed.
What happens to the V curve when a synchronous motor is loaded?
V curve is a plot of the stator current versus field current for different constant loads. If now, the field current is increased further, the armature current increases and the motor starts operating as a leading power factor. …
How can you increase the power output of a synchronous motor?
To change the power output of a synchronous generator, one has to change the amount of torque being provided to the generator–by the prime mover driving the generator. And, this is all done at relatively constant speeds (frequency) on most AC power systems (grids) around the world.