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This ability to selectively control power factor can be exploited for power factor correction of the power system to which the motor is connected. Since most power systems of any significant size have a net lagging power factor, the presence of overexcited synchronous motors moves the system's net power factor closer to unity, improving efficiency.
The minimum at unity power factor () is due to the general formula for the power P of a synchronous motor, = . In order to keep the power constant, with the line voltage at the terminals of the armature V A {\displaystyle V_{A}} also constant, any decrease in power factor has to be accommodated by a corresponding increase in the armature ...
Power-factor correction increases the power factor of a load, ... The reactive power drawn by the synchronous motor is a function of its field excitation.
The zero power factor curve (also zero power factor characteristic, ZPF, ZPFC) of a synchronous generator is a plot of the output voltage as a function of the excitation current or field using a zero power factor (purely inductive) load that corresponds to rated voltage at rated current (1 p.u.).
An over-excited synchronous motor has a leading power factor. This makes it useful for power-factor correction of industrial loads. Both transformers and induction motors draw lagging (magnetising) currents from the line. On light loads, the power drawn by induction motors has a large reactive component and the power factor has a low value. The ...
Therefore, it is necessary to either snap the motor and connect it momentarily to a live grid or to add capacitors charged initially by residual magnetism and providing the required reactive power during operation. Similar is the operation of the induction motor in parallel with a synchronous motor serving as a power factor compensator.
is the resistive power loss (SI unit: watt) The motor constant is winding independent (as long as the same conductive material is used for wires); e.g., winding a motor with 6 turns with 2 parallel wires instead of 12 turns single wire will double the velocity constant, , but remains unchanged.
The brushless wound-rotor doubly fed motor is a synchronous motor that can function exactly at the supply frequency or sub to super multiple of the supply frequency. Other types of motors include eddy current motors, and AC and DC mechanically commutated machines in which speed is dependent on voltage and winding connection.