Optimal reactive power control for industrial power networks

In addition to process steam and real power demands, manufacturing processes also have a varying reactive power demand that must be satisfied. Reactive power affects line currents and bus voltages, as well as power factor of the tie-line bringing power into the industrial plant from the local utility. The local utility applies a penalty if the tie-line power demand exceeds an agreed value and often imposes a low power factor penalty as well. Stable system operation requires that bus voltages are maintained within assigned limits, that transformers and connecting cables do not become overloaded, and that generators and synchronous motors run within their reactive capabilities. There can be many acceptable combinations of the settings of generator and synchronous motor excitations, of transformer taps and capacitor banks, all of which lie within the set of electrical system constraints. There are so many variables to manipulate that is very difficult for an operator to make optimal decisions, even under steady-state conditions. It is an even more complicated task during system upsets. This paper discusses a program that runs on a plant's distributed control system that resolves alternatives and presents to the operator the best combination of settings for implementation. The program can be adopted for direct online implementation. The paper discusses cases of three plants where online implementations have been employed.