HYDROTHERMAL POWER FLOW SCHEDULING ACCOUNTING FOR HEAD VARIATIONS

We treat the problem of optimal economic operation of hydrothermal electric power systems with variable head hydro plants employing the power flow equations to represent the network. Newton's method is used to solve the problem for a number of test systems. A comparison with solutions withe fixed head is presented. In general the optimal schedule requires higher slack bus and thermal power generation and cost in the case of variable head hydro plant than that required by the fixed head hydro plant in all demand periods. Correspondingly, the hydro generation is less in the case of variable head hydro plant compared to fixed head hydro plant. A negligible difference in voltage magnitudes in all the time intervals, but it is observed that slightly higher voltages occur in the case of the fixed head hydro plant. Higher power and energy losses occur in the case of variable head hydro plants compared to the fixed head hydro plants. Lower CPU time is required by the polar formulation than the rectangular formulation for all systems except for the case of the 14 bus system. For the 118 bus system, the rectangular formulation requires more than twice the CPU time required by the polar formulation.