What is the relationship between synchronous speed and frequency?
The synchronous speed of the motor remains constant if the number of poles and the frequency are constant. The synchronous speed of the motor can be changed by changing the number of poles or by changing the frequency….Synchronous speed Formula.
| No. of Poles | Frequency (50 Hz) | Frequency(60 Hz) |
|---|---|---|
| 16 | 375 | 450 |
| 20 | 300 | 360 |
What is the relationship between field current and power factor in a synchronous motor?
The fact that the field poles of a synchronous motor are magnetically in line with the stator flux allows dc current on the field to replace ac magnetizing current on the stator. Since power factor is determined by the magnetizing current, the power factor is adjustable by changing the field current.
How does the power capability of a synchronous motor relate to its speed?
The speed of a synchronous motor is dependent on the frequency of the power source and the number of poles the stator has. RPM increases directly with frequency and inversely as the number of poles. The same formula used to calculate the speed of the induction motor is used to determine the speed of this type of motor.
What is the power factor of a synchronous motor?
Synchronous motors are designed to operate at unity (1.0) power factor or 0.8 leading power factor. By varying the DC excitation of the motor, the power factor of the motor can be varied widely. Overexcited synchronous motors operate at leading power factor and provide reactive kVAR-like capacitors.
How can the power factor of a synchronous motor be reduced?
Another way to improve the power factor is to use a 3 phase synchronous motor which is over excited and runs on no load. This setup is known as the synchronous condenser. The interesting part is that the synchronous motor can operate under leading, lagging or unity power factor.
How does frequency affect a motor?
Varying the voltage frequency affects both the motor speed and the strength of the magnetic field. When the frequency is increased (for higher motor speed), the magnetic field decreases, and lower torque is produced. In order to keep the magnetic flux constant, the V/Hz ratio must remain constant.