Generator excitation control operation

Increasing the output voltage of a generator is achieved by adjusting the magnitude of the excitation current. This happens because as DC current is increased, the rotating magnetic field increases thereby increasing the generator  voltage induced in the stator conductor.     As the voltage is increased, the generator will transfer more MVAR into the power system.

Instead of collector rings, suppose that a  brushless generator above  is used in our example. The exciter is provided from the DC winding which is wound in the stator. The rotor produces ac current that is feed into the rectifier built in the shaft. The rectifier converts AC to  DC and feed the rotor windings.

To control of the rectifier  output in the field windings of the excitation generator, voltage regulator receives its command signal from the AC voltage controller which monitors the ac voltage of the monitor.


The limitation of the generator due to current in the stator should follow within the machine capability curve. Increasing the excitation current of the generator to deliver MVAR will produce heating in rotor winding. alternatively, if the excitation is reduced voltage and VARS will fall. then the machine will have weak magnetic field .

Technical Data for Generator 60WX18Z-090 with Static Excitation 158,8 MVA 13800 V 60 Hz p.f. = 0,85 Tcg = 33 °C Temp.-Cl. = 130(B

In the capability curve, the horizontal axis is the  reactive power in per unit quantity, where 1 pu =159 MVAR and the vertical axis is the active power per unit quantity.