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 determines the speed of 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.
How are synchronous machines controlled by?
Synchronous machine is a constant speed Machine and independent on load. In some industrial applications speed control is necessary. The synchronous machine speed is controlled by varying the frequency. Speed control of synchronous machine is achieved by voltage fed inverters, current fed inverters or cyclo converter.
How do you control the speed of a synchronous generator?
The torque must generally be provided at a specific frequency, which is directly proportional to the speed the prime mover is spinning the generator rotor. The speed of the prime mover can be controlled by the prime mover governor.
What is self control of synchronous motor?
In self controlled mode, the supply frequency is changed so that the synchronous speed is same as that of the rotor speed. Hence, rotor cannot pull-out of slip and hunting eliminations are eliminated. For such a mode of operation the motor does not require a damper winding. Fig (5.4 )Self Controlled Mode.
Why the speed of synchronous motor is constant?
Why does a synchronous motor rotate at a constant speed? The stator magnetic field rotates at synchronous speed (which depends upon the frequency of supply) and hence the rotor follows it and rotates at synchronous speed as well. The stator is excited from supply which produces a rotating magnetic field in the air gap.
What two factors determine synchronous speed?
The frequency of the power supply and the number of poles of the machine determine the synchronous speed. A synchronous motor is one in which the rotor turns at the same speed as the rotating magnetic field in the stator.
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.
What is true synchronous mode?
In true synchronous mode, the stator supply frequency is controlled from an independent oscillator. … This allows rotor speed to track the changes in synchronous speed. When the desired synchronous speed (or frequency) is reached, the rotor pulls into step, after hunting oscillations.
What are the application of synchronous motor?
Synchronous motors are normally used in applications in which a constant and precise speed is required. Typical applications of these low power motors are positioning machines. They are also used in robot actuators. Synchronous motors are also used in ball mills, watches, record players, and turntables.
Why the synchronous motor is 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.
Why does generator slow down load?
Mechanical issue such as fuel injection clogged or fuel filters clogged causing the machine to be under fuelled to handle load application and may cause machine to slow down, which in turn would drop Hertz and Volts.
What are the advantages of self control of synchronous motor?
Advantages… The cycloconverter are inherently capable of power transfer in both the directions. Therefore the direction reversal of the synchronous motor are possible. In other words four quadrant operation is possible.
What are the advantages of synchronous motor?
The advantages of the synchronous motor are the ease with which the power factor can be controlled and the constant rotational speed of the machine, irrespective of the applied load. Synchronous motors, however, are generally more expensive and a d.c. supply is a necessary feature of the rotor excitation.
What is another word for self control?
SYNONYMS FOR self-control
self-discipline, self-restraint, willpower, levelheadedness.