PLTU Suralaya unit 3 is a steam power plant with capability of 400 MW generation. As the larger power plant unit, it is a must to have a generator with a large capacity to be able to evoke or produce electrical power. The generator can evoke the power because it is supported by the excitation system where can be functioned to afford the inline direction on terrain found of the rotor and will be able to produce a fluxs of magnet. When the anchor coils field distributed with stator excitation plays with a certain speed, the coil in the stator anchor will be induced by the magnetic fluxs, so that it will be generated voltage-back and forth. The production of a system voltages depends on the magnitude of the excitation provided on the rotor. In order to avoid damage on the generator, the thecnician or Labor have to understand the characteristics of excitation system, current excitation, and the percentage voltage supply on the generator. Excitation system greatly affects the loading on the generator. When the load is increase, the voltage will drop the chain that causes the generator voltage slowing down. Based on the calculation of the percentage voltage supply, the highest voltage value of the generator calculated on the point of IE +2.83% where the value loading 265.18 MW and voltage generator 23.65 kV, and the lowest value recorded minus 1.87% where the value of loading 399.19 MW and voltage generator 22.57 kV. From those condition it can be inferred that the supply voltage synchronous generators in Suralaya PLTU unit 3 are in safe condition based on standard PLN i.e. on condition -5% and +10%. Therefore, by understanding the characteristics and parameters of the voltage supply generator percentages, can be conclude that, the excitation influence on the performance of the generator were under the condition of over excitation.