The responsibility of power system is to ensure that adequate power generation with good quality and more economic power delivery to all consumers. Hence, proper control strategy is required to maintain a continuous power balance between power generation and surplus. So it is necessary to implement Automatic Generation control for more efficient control performance. In this paper , three area reheat thermal power is considered for the investigation and each generating unit equipped with either Single Reheat Turbine (SRT) or Double Reheat Turbine (DRH) with Proportional-Integral-Derivative(PID) controller. Optimal controller gain values are obtained using both conventional and Artificial Intelligence (AI) optimization technique. Finally, performances of AI-PID controller are compared with conventional optimized PID controller. Simulation result shows that contribution of AGC with AI PID controller more superior to conventional controller.