Effects of voltage and reactive power constraints on power system reliability

The paper deals with a method for the reliability evaluation of a power generation and transmission system, when considering, together with the constraints on the active power capability of elements, the voltage constraint in network nodes. The approach suggested is an extension of a previous method for the reliability evaluation when considering only the active power capability constraints. The method is based on the approximate evaluation, by means of linear computation methods, of the reactive power flows and of the consequent voltage values in network nodes. This evaluation is performed starting from the approximate evaluation of the active power flow derived with the classic method of d.c. load-flow computation. The system performance, as a consequence of voltage constraints, is quantitatively evaluated by means of two indices: the first being the power disconnected in the nodes as a consequence of unacceptable voltage values or lack of reactive generation, the second being the irregularity of the voltage Service.