## 1 Introduction  
Modern power grids are undergoing constant changes toward more reliable and efficient smart structures, especially in terms of how energy is produced, consumed, and transported. This development presents new and unexpected challenges as well as benefits. An important requirement for future power grids is the provision of a satisfactory quality of power. In normal conditions, the mains voltage level provided by the low-voltage distribution networks follows time-varying patterns within permissible limits. The need to ensure a satisfactory quality of the supplied power has been identified as a key requirement for future power grids [1]. However, power quality can be compromised by new technologies and changing conventional equipment to power-electronic-driven appliances. Low-voltagedistribution networks have been experiencing increasing penetration of distorting loads over the past few decades [2; 3; 4; 5; 6]. Modern electrical loads contain electronic power circuits in their topology, which can produce conducted emissions (propagated via power or signal wires into the electromagnetic environment) as they interact with power grid elements, such as loads, cables, transformers, etc. [7; 8; 9]. The topic of wide spectra waveform distortions has become challenging, since the emissions introduced into the power grid by electrical equipment may be responsible for severe malfunctioning and loss of efficiency [10; 11; 12]. Household devices, industrial-size converters, photovoltaic inverters, electric vehicle chargers, and energy-efficient lighting are examples of devices that can become sources of non-intentional disturbances if electromagnetic compatibility (EMC) requirements are not taken into account during the designing stage [13]. There are guidelines for acceptable levels of harmonic emissions introduced to the grid by electrical loads. Usually, the severity of harmonics in the frequency range up to 2 kHz is determined by the total harmonic distortion (THD) factor. There are two major international standards (sometimes with specific local adaptations): EN50160 [14] and IEEE519 [15]. The standard EN50160 describes a wide range of power quality measurements, including harmonics but also voltage dips, swells, unbalance, interruptions, and flicker severity. The IEEE519 standard focuses only on harmonics and pays particular attention to load currents waveform distortion. Although these standards have some differences, both documents reference the harmonics standards EN61000-4-3 [16], EN61000-4-7 [17], the flicker standard EN61000-4-15 [18] and the standard [19] that describes power quality testing and measurement techniques. Compared to their low-frequency cousins, the spectral components in the 2-150 kHz range have received far less research. In analogy to the total harmonic distortion factor, the total supraharmonic distortion (TSHD) index is introduced. The normative documents are still imprecise in this regard [20]. The standard EN55015 [21] contains limit values and methods for measuring radioelectric disturbances generated by lighting devices and similar equipment. According to this standard, lighting sources where the active electronic components are placed should be tested before releasing them into the market. Precise normative techniques for monitoring electromagnetic emissions in low voltage networks in the frequency range between 2 and 150 kHz are still lacking. Distribution system operators ought to encourage research in this field and make use of the most recent analysis to take proactive measures to stop degradation and raise the standard of power quality supply [22; 23; 24; 25]. The fundamental motivation for this work is the relatively sparse number of research studies concerning the influence of mains voltage level variation on the non-intentional conducted emission in the wide frequency range that electric equipment introduces into the power grid.