Optimal reactive power planning

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This dissertation presents a new method for optimal long-term reactive power planning. The planning problem is divided in two parts- short-term and long-term planning. In the short-term reactive power planning problem, the real and reactive power is optimally dispatched for the economic operation of a power system. As in other methods, the problem is decomposed into a P-optimization module and a Q-Optimization module, but in this method both modules use the same generation cost objective function. The control variables are generator real power outputs for the real power module and generator reactive power outputs, shunt capacitors/reactors, and transformer tap settings for the reactive power module. The constraints are the operating limits of the control variables, power line flows, and bus voltages. Mathematical models are developed to represent the sensitivity relationships between dependent and control variables for both real and reactive power optimization modules, and thus eliminate the use of B-coefficients. Results of two test systems are presented and compared with conventional methods. The long-term planning is to determine the required investment in reactive power compensation devices. The method economically determines the required compensation to keep system voltage profiles within a prescribed range which may change due to load increase over a number of years. This goal is achieved by reducing the operation cost (fuel cost) and investment cost in the system. The algorithm uses discrete optimal control theory to optimally determine the required annual investment in new reactive power compensation. The optimization problem is solved using the gradient projection method (GPM) which is used for the first time in the power systems study. The GPM allows the use of functional constraints without the need of penalty functions or Lagrange multipliers among other advantages.

Reactive power (Electrical engineering)