Measurement and Analysis of the Low Voltage Network Impedance in the Supraharmonic Range

The supraharmonic distortion levels and their propagation in low voltage networks are determined by the supraharmonic- or frequency-dependent network impedance (FDNI). Knowledge of the FDNI is limited and mainly based on assumptions, measurements to determine the actual values are uncommon and not readily available. In this research, a current injection-based measurement system is developed to measure the impedance from 10 to 150 kHz at low voltage installations. The measurement system is validated using lab measurements and a measurement campaign at different residential- and office installations is carried out to quantify the network impedance. It is found that both the amplitude of the impedance and the resonant frequencies are highly influenced by devices connected locally. The results provide typical ranges of the FDNI in low-voltage installations and contribute to the assessment of supraharmonic impact and propagation.

I. Introduction

Supraharmonic (SH) distortions are waveform distortions between 2 and 150 kHz and can be present in low- and medium voltage grids. They are mainly caused by small converters in all kinds of household appliances and, on a larger power level, by electric vehicle (EV) chargers and photo-voltaic (PV) installations. Supraharmonics can cause several unwanted effects like failures and breakdown of devices, interference with appliances using power line communication and can reduce the lifetime of grid assets [1]. Research assessing the impact of SHs on distribution grid components and devices connected to it is still ongoing and mainly focuses on characterizing emission. There is an increasing interest in studying the impact of SHs, as SH distortions in low-voltage grids are expected to increase and resonances can contribute to their amplification [2].