Accounting for a positive, negative and zero sequences power in a three-phase unbalanced electrical system

Abstract

Purpose. Based on the instantaneous electrical power of a three-phase asymmetric system of sinusoidal periodic current, to determine positive, negative, zero-sequences active and reactive power, as well as invariance power factor. Methodology. In the unbalance case in three-phase electrical system, the electrical energy quality is evaluated by means on voltage and current positive, negative, zero-sequences. At the same time, similar components of active and reactive power have not received practical distribution. But it is precisely in terms of power that electricity is accounted for. The instantaneous power orthogonal components in the time domain are determined using the symmetrical components of voltage and current. Active, reactive powers of positive, negative and zero-sequences are allocated. The result obtained has the property of representativeness, which most of the known results lack. Findings. The three-phase system’s instantaneous power components are analytically determined, including the amplitudes of the oscillating power components. The need to take into account the oscillating instantaneous power components has been proven by means of a graphical interpretation of a special case of the three-phase system mode. As an integral indicator that takes into account the oscillating components of the three-phase system instantaneous power, its root-mean-square value over the repetition period is used. Originality. By calculating the transformer efficiency of the studied model according to the active power positive sequence and the same indicator according to the active power as a whole, it was established, that the component sequence separation affects the results of calculating the generalized indicators, including the power transmission system objects. This can lead to erroneous judgments about the efficiency of the specified facilities functioning. Practical value. The invariance power factor was used to characterize the electrical energy quality level of a three-phase sinusoidal current system in an unbalanced mode.