Successful operation of an interconnected power system requires the matching of total generation with total demand and associated system losses. With time as the operating point of a power system changes, and hence, these systems may experience deviations in nominal system frequency and scheduled power exchanges to other areas, which may yield undesirable effects. The two variables are considered for the evaluation of the system performances namely, frequency and tie-line power exchanges. In this two-area symmetrical thermal reheat system with stiff and elastic tie lines are considered for simulation controllers using proportional and integral are designed and the simulated results are analyzed for better performance.