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This paper focuses on the parameter estimation of transmission lines which is an essential prerequisite for system studies and relay settings. Synchrophasor measurements have shown promising potentials for the transmission line parameter estimation. Majority of existing techniques entail existence of phasor measurement units (PMUs) at both ends of a given transmission line; however, this assumption rarely holds true in nowadays power networks with few installed PMUs. In this paper, a practical technique is proposed for the estimation of transmission line parameters while the required data are phasor measurements at one end of a given line and conventional magnitude measurements at the other end. The proposed method is thus on the basis of joint PMU and supervisory control and data acquisition (SCADA) measurements. A non-linear weighted least-square error (NWLSE) algorithm is employed for the maximum-likelihood estimation of parameters. The approach is initially devised for simple transmission lines with two terminals; then, it is extended for three-terminal lines. Numerical studies encompassing two- and three-terminal lines are conducted through software and hardware simulations. The results demonstrate the effectiveness of new technique and verify its applicability in present power networks. [ABSTRACT FROM AUTHOR]

In this paper, a novel power-based algorithm to discriminate between switching and internal fault conditions in power transformers is proposed and evaluated. First, the differential power signal is scrutinized and its intrinsic features during inrush conditions are introduced. Afterwards, a combined time-domain-based waveshape classification technique is proposed. This technique exploits the suggested features and provides two discriminative indices. Based on the values of these indices, inrush power signals are identified after only half a cycle. This method is founded upon some inherent low-frequency features of power waveforms and is independent of the magnitude of differential power. The approach is also unaffected by power system parameters, operating conditions, noise and transformer magnetizing curves. Simplicity of the suggested features and equations describe how the proposed method can help make it a practical solution for the inrush problem. Extensive simulations carried out in PSCAD/EMTDC software validate the merit of this technique for various conditions, such as current-transformer saturation. Furthermore, real-time testing of the proposed method using real fault and inrush signals confirms the possibility of implementing this algorithm for industrial applications. [ABSTRACT FROM AUTHOR]

A novel control scheme for the dynamic voltage restorer (DVR) is proposed to achieve fast response and effective sag compensation capabilities. The proposed method controls the magnitude and phase angle of the injected voltage for each phase separately. Fast least error squares digital filters are used to estimate the magnitude and phase of the measured voltages. The utilized least error squares estimated filters considerably reduce the effects of noise, harmonics, and disturbances on the estimated phasor parameters. This enables the DVR to detect and compensate voltage sags accurately, under linear and nonlinear load conditions. The proposed control system does not need any phase-locked loops. It also effectively limits the magnitudes of the modulating signals to prevent overmodulation. Besides, separately controlling the injected voltage in each phase enables the DVR to regulate the negative- and zero-sequence components of the load voltage as well as the positive-sequence component. Results of the simulation studies in the PSCAD/EMTDC software environment indicate that the proposed control scheme 1) compensates balanced and unbalanced voltage sags in a very short time period, without phase jump and 2) performs satisfactorily under linear and nonlinear load conditions. [ABSTRACT FROM AUTHOR]