Propagation of Supraharmonics in Low-Voltage Networks

The need for measures towards a sustainable use of energy has incited the proliferation of devices and systems for the efficient use of electricity. Energy-efficient appliances, equipment for the electrification of transportation, electricity generators from renewable energy sources, and communication protocols, e.g., for smart metering are sources of supraharmonic distortion in electrical networks. Supraharmonics are voltage and current waveform distortion in the frequency range from 2 up to 150 kHz. The increase in sources of supraharmonics in the last decades and the propagation of this type of distortion have triggered a variety of unwanted consequences (interference) in the electrical networks. Interference associated to supraharmonics such as audible noise, degradation or failure in the operation of electrical equipment, and breakdown of insulation materials, have been reported around the world. A standardized framework for supraharmonics as a power quality phenomenon that involves both grid operators and equipment manufacturers is needed to limit these interferences. The limits to be set shall not hinder the modernization of the electrical system and the consequential energy transition. There are gaps in the standardization framework for supraharmonics as a power quality phenomenon. The study of supraharmonics as a power quality parameter should consider variables that affect emission levels and propagation of supraharmonics. At the same time, an assessment of the severity of given supraharmonics levels regarding their consequences is needed to settle realistic reference levels. Deterministic methods have been generally used to study supraharmonic propagation but they might not be suitable when considering many possible scenarios. This research introduces forefront methods and results on the study of supraharmonics emission, propagation, and consequences. The study has two focal points: 1) to study the impact of the impedance of the grid and low-voltage devices on the emission and propagation of supraharmonics; 2) to assess the severity of propagated supraharmonics in terms of the characteristics of the distortion and the probability of interference. Experimental and theoretical case studies are built to carry out the research. Measured and synthetic signals representative of supraharmonic distortion present in low-voltage networks are used. The main results of this research are summarized as: The levels of emitted and propagated supraharmonics depend on the impedance of the grid, the emitting device and the neighboring devices. Resonance can lead to significant levels of supraharmonics anywhere in the grid. The variability and diversity of low-voltage devices lead to high uncertainty in the estimation of their impedance. Stochastic methods are recommended to assess the probability of interference. Different attributes of supraharmonics are responsible for different interference phenomena. Indications of the severity of supraharmonics attributes are given for three phenomena: audible noise, negative impacton residual current devices, and light flicker of LED lamps. This research contributes to the establishment of supraharmonics as a power quality phenomenon with standardized solutions. It introduces methods for the assessment of: 1) supraharmonic emission from installations needed to recommend planning levels; 2) supraharmonic propagation in low-voltage networks, and 3) the probability of interference needed to define reference levels