Power quality effects on the measurement of reactive power in three-phase power systems in the light of the IEEE Standard 1459–2000.

Abstract

Reactive power is a very important quantity in electric power systems since it affects the efficiency of these systems. Also, capacitive loads can produce over-voltages in electric transformers by Ferranti effect, which produces bad power quality, so it is necessary to measure the reactive power correctly. In this paper reactive phenomena in three-phase power systems with unbalanced voltages are expressed and measured in the light of the IEEE Std 1459-2000. For analyzing the reactive phenomena the positive-sequence fundamental frequency instantaneous reactive power is used. By comparing the expressions of this instantaneous power in three-phase systems with unbalanced voltages with those corresponding to balanced voltages, the reactive phenomenon due to the unbalances is obtained by separating of the traditional reactive power yield by the reactive loads in electric power systems. These reactive phenomena in three-phase power systems are formulated in the same way as Steinmetz defined reactive power in single-phase systems, by adding the amplitudes of each phase of its respective instantaneous reactive power. In the paper, this new formulation of the reactive phenomena has been applied on actual industrial and urban electric installations to obtain values of these reactive powers. Data registered express the following conclusions: a) reactive power is divided into two components: due to the reactive loads and caused by the unbalances, b) both reactive components can be inductive or capacitive quantities and, therefore, can be added or compensated, c) reactive power caused by the unbalances can exist even though in resistive systems, when there are unbalances at sources and at loads in the same time and, generally, when there is not any symmetry in the system.