Continuous harmonic analysis and power quality measurements in three-phase systems

A virtual instrument, named Power Quality Meter, is presented for (a) measuring power consumption and harmonics in three-phase systems, under non-sinusoidal and imbalance conditions (b) detecting, classifying and organizes power disturbance events. Measurement of the power consumption follows the formulation proposed by the members of the IEEE Working Group on Nonsinusoidal Situations (1996). So, definitions are based on the analysis of functions in the frequency domain, separating the fundamental terms from the harmonic terms of the Fourier series. The virtual instrument has been developed too for monitoring and measuring power disturbances, which are automatically classified and organized in a database while they are being recorded. Software tools use the database structure to present summaries of power disturbances and locate an event by severity or time of occurrence. Records of actual measurements are included to demonstrate the versatility of the instrument

Instantaneous current vectors in polyphase systems: two compensation concepts

6 páginas, 9 figuras, 24 referencias.-- Trabajo presentado al Modern Electric Power Systems (MEPS) International Symposium, celebrado del 20-22 de septiembre 2010, en Wroclaw, Polonia.According to the target of minimal line losses and a power factor equal to one, the present work studies two concepts of instantaneous compensation of nonactive current which are generally applied to polyphase systems. The analysis is defined both on the basis of the instantaneous value concept, for arbitrary voltage and current waveforms, and on the basis of the average value concept, for steady-state and periodic conditions. Results of using these concepts for instantaneous compensation are compared by simulation.Peer reviewe

Voltage quality factor for networks supplying unbalanced nonlinear loads

4 páginas, 3 figuras, 8 referencias.-- conferencia oral presentada en la Sesion 3: International Conference on Renewable Energy and Power Quality (ICREPQ'05), ceelebrada del 16-18 de marzo 2005, en Zaragoza, España.While the common term for describing the harmonic content and the unbalanced loading of the three-phase supply is power quality, it is actually the quality of the voltage that is being addressed in most cases. The power supply system can only control the quality of the voltage; it has no control over the currents that particular loads might draw. Therefore, the standards in the power quality area are devoted to maintaining the voltage within certain limits. In this paper, a voltage quality factor, designated VQF, is suggested that integrally assesses the voltage quality of a given three phase supply from the two aspects mentioned above.This work was supported by the ‘Comisión Interministerial de Ciencia y Tecnología ’ (CICYT) of the Spanish Minister of Education and Culture.Peer reviewe

DSP-based algorithm for electric power measurement

The paper describes a new approach to the design of digital algorithms for electric power measurements under nonsinusoidal conditions. Using the discrete Fourier transform of two sets of real data in one pass, the voltage and current spectra are obtained, simultaneously. Real and imaginary parts of both spectra are then processed to obtain the terms of the electric power components according to various definitions in both the time domain and the frequency domain. Some results of simulated measurements using an assembler program for the TMS 32010 micro-computer are given.Peer Reviewe

Measurement of apparent power components in the frequency domain

An algorithm and a digital signal-processing technique are proposed for the measurement of the apparent power components in the frequency-domain approach. The discrete Fourier transform (DFT) is applied to simultaneous samples of voltage and current waveforms to compare their respective spectra. The rms values of the harmonic currents flowing between the source and the load (resistive, reactive, and generated by the load nonlinearity) are calculated. The algorithm evaluates Vrms, Irms and the active power in both the time and frequency domains, and the resistive, reactive, and complementary power components in the frequency domain.Peer Reviewe

Power quality factor for networks supplying unbalanced nonlinear loads

A single indicator [i.e., the power quality factor (PQF)] in the range between 0 and 1 is suggested in this paper to integrally reflect the power transfer quality of a general three-phase network feeding unbalanced nonlinear loads. The prominent power quality aspects considered in the paper are the following: 1) the voltage and current harmonic levels; 2) the degree of unbalance; and 3) the phase displacement factor in the different phases at the fundamental frequency. A network that supplies balanced sinusoidal currents at balanced sinusoidal voltages with zero phase displacement between the corresponding currents and voltages yields a PQF of unity. The measurement of the PQF is discussed. Practical examples illustrate the use and relevance of the new quality factor.Peer Reviewe

Analysis of instantaneous nonsinusoidal voltage and current in polyphase systems

Multiline systems are analyzed into an orthonormal-coordinate system using the fundamental laws of polyphase systems and the condition of zero neutral-current. Current vectors are decomposed into three mutually orthogonal components; two of them are responsible of the active power. Without the condition of zero neutral-current, the current vector is decomposed into two mutually orthogonal components. The analysis shows the condition of line losses minimization after compensation with active power filters.Peer Reviewe

Power system frequency measurement under nonstationary situations

A new method for the measurement of the instantaneous power-system frequency is proposed. It is based on the frequency estimation of the voltage signal using three equidistant samples. An algorithm is developed that diminishes the variance of the estimation. The procedure is applied to the case of single- and three-phase networks, and uncertainty in the frequency estimation is obtained with simulated signal and severe conditions of signal quality. A frequency variation has been assumed as ±2 Hz around the nominal value, with a maximum rate of change of 1 Hz/s. The uncertainty of 25 mHz and 3.5 mHz has been obtained for single- and three-phase signals, respectively. A low-cost virtual instrument has been developed to make frequency measurements over the actual voltage signal.Peer Reviewe