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Synchronous motors use electromagnets as the stator of the motor which create a magnetic field that rotates in time with the oscillations of the current. The rotor with permanent magnets or electromagnets turns in step with the stator field at the same rate and as a result, provides the second synchronized rotating magnet field.
If the field current is increased beyond this point, the armature current becomes leading, power factor decreases, and grows again. [4] The data from the V curves can be used to set up the synchronous motor to correct the power factor of the overall system, as the power factor of the motor can be changed by simply adjusting the field current. [3]
Synchronous speeds for synchronous motors and alternators depend on the number of poles on the machine and the frequency of the supply. The relationship between the supply frequency, f, the number of poles, p, and the synchronous speed (speed of rotating field), n s is given by: = .
In vector control, an AC induction or synchronous motor is controlled under all operating conditions like a separately excited DC motor. [21] That is, the AC motor behaves like a DC motor in which the field flux linkage and armature flux linkage created by the respective field and armature (or torque component) currents are orthogonally aligned such that, when torque is controlled, the field ...
This change in power factor is larger than the change in with increase in load. The phase of armature current varies with field excitation. The current has larger values for lower and higher values of excitation. In between, the current has minimum value corresponding to a particular excitation (see graph on right).
Synchronous impedance curve (short-circuit characteristic curve), showing armature current as function of field current. The curve is obtained by rotating the generator at the rated RPM with the output terminals shorted and the output current going to 100% of the rated for the device (higher values are typically not tested to avoid overheating ...
They may also be started as induction motors using a squirrel-cage winding that shares the common rotor: once the motor reaches synchronous speed, no current is induced in the squirrel-cage winding so it has little effect on the synchronous operation of the motor, aside from stabilizing the motor speed on load changes. Synchronous motors are ...
The synchronous reactances are exhibited by the armature in the steady-state operation of the machine. [8] The three-phase system is viewed as a superposition of two: the direct one, where the maximum of the phase current is reached when the pole is oriented towards the winding and the quadrature one, that is 90° offset. [9]