One of the most important concerns in generators is their startup. The performance characteristic of synchronous machines is determined according to the output terminal voltage of the generator in no-load mode, this voltage value depends on the current of the magnetic field (starting current) and if this current changes, the performance characteristic of the generator will also change
Synchronous machine rotor needs a controllable direct current to create an excitation field. The source of this current is the excitation system that sends the excitation current to the synchronous machine (generator). This system consists of a group of feeders, regulators, controls and protection devices
The excitation system of synchronous machines has two main parts

A) The power system that includes the equipment that is responsible for producing the required current of the magnetic field of the rotor wire of the synchronous machine

B) The control system that has the task of controlling the amount of magnetic field current in normal operating conditions and in the event of an error