Generator or also called the alternator is the main tool in the power plant system because it serves to convert mechanical energy into electrical energy. In the process of generating electrical energy there is an important process called excitation system. Excitation system is a process of reinforcement in the form of excitation currents flowing to the field coil found on the rotor in the generator. Excitation currents flowing on this field coil, generate magnetic flux. The excitation system of PLTU units 1 and 2 at PT PJB UP Gresik uses a static excitation system. This excitation type uses a carbon brush to deliver excitation current, static excitation systems take advantage of the output of the generator. Problems that can occur in this excitation system is a disruption of under excitation or over excitation that can damage generators or other devices, in addition, the excitation system should always be properly considered so that the disorder can be prevented. Damage generators can be prevented or avoided by understanding the characteristics of excitation systems which include excitation currents, anchor currents, generator voltages and loading. Changes in the value of the load greatly affect the value of the injected excitation current, because the injection of this excitation current serves to maintain the stability of the generator terminal voltage to remain in nominal conditions.