Power quality factor and line-disturbances measurements in three-phase systems

A power quality meter (PQM) is presented for measuring, as a first objective, a single indicator, designated power quality factor (PQF), in the range between zero to one, which integrally reflect the power transfer quality of a general three phase network feeding unbalanced nonlinear loads. PQF definition is based on the analysis of functions in the frequency domain, separating the fundamental terms from the harmonic terms of the Fourier series. Then, quality aspects considered in the PQF definition can be calculated: a) the voltage and current harmonic levels b) the degree of unbalance and c) the phase displacement factor in the different phases at the fundamental frequency. As a second objective, the PQM has been designed for detecting, classifying and organizes power line disturbances. For monitoring power line disturbances, the PQM is configured as virtual instrument, which automatically classifies and organizes them in a database while they are being recorded. The type of disturbances includes: impulse, oscillation, sag, swell, interruption, undervoltage, overvoltage, harmonics and frequency variation. For amplitude disturbances (impulse, sag, swell, interruption, undervoltage and overvoltage), the PQM permits the measurement of parameters such as amplitude, start time and final time. Measurement of harmonic distortion allows recording and visual presentation of the spectrum of amplitudes and phases corresponding to the first 40 harmonics. Software tools use the database structure to present summaries of power disturbances and locate an event by severity or time of occurrence. Simulated measurements are included to demonstrate the versatility of the instrument.