Research On The Characteristic Of Harmonic Impedance And Its Measure Methods In Electric Network

Non-linear loads were generally characterized by harmonic currents and therefore, it is often preferred to express the emission limits in term of currents rather than voltages, In recent years, a great attention has been devoted to probabilistic approaches for the prediction of the harmonic currents injected by loads and of the corresponding nodal harmonic voltages. In order to translate the injected harmonic currents into harmonic voltages through, need to know the harmonic impedance of system. In this framework, minor importance has been devoted to the variability of the system impedance.The principle of penetration was introduced in this paper. Single-phase analysis method and three-phase analysis method are discussed, and single-phase models and three-phase models of a. c power system main elements are presented in this paper.This paper also studied the power system harmonic impedance as a function of frequency in opportune conditions. The most critical conditions related to the presence of strong resonances are analysed. And the curves of impedance as a function of frequency, related to the series-parallel connection resonances are also discussed in this paper. The question of how to estimate the resonant frequencies in real power system was discussed in this paper. This article analysed the characteristic of harmonic impedance in network components of electric transmission line and capacitor, discussed the resonance and harmonic current amplification, which may be caused by capacitor.This paper studied measurement of harmonic impedance, presented open-short circuit measure method and measurement using voltage and current increments, which was implemented by measure the power system steady state. Practical implementation issues and their solutions were discussed in this paper, which present the theoretical basis for this two measure methods in practical application. In this paper, simulation for this two measure methods was performed using MATLAB/PSB module. This paper also analysed error produced in the simulation procedure. Simulation verified that this two measuremethods measuring harmonic impedance in specific condition is practicable.