This research is to analyze the effect of excitation changes on reactive power of generators operated in power plant unit. The excitation system is a system used in every power generation. Excitation system is a process where direct current will flow to the generator as a reinforcement current, resulting in the electrical voltage and the amount of electricity generated by the generator depends on the amount of excitation current. In the power generation system, excitation system holds the main function to maintain the stability. Because if at the time of generation and fluctuation occurs, the excitation system will immediately work as a regulator of output generator in order to balance the stability.The excitation system also affects the reactive power that is channeled to the system. When the excitation current is high, the value of the reactive power increases, and vice versa. If in the generation of excitation current in the drain is too small then the reactive power will reverse back from the system to the generator. This situation would be dangerous because it could cause excessive warming of the generator. The excitation system on Wonogiri hydroelectric generation uses a static excitation system where the excitation currents can be utilized by a carbon brush.