## 2 Literature Review  
### Gap in the Research Related to Influence of Supply Voltage Distortion on Supraharmonics Emission  
The phenomenon of electromagnetic emission occurring in the frequency range 2-150 kHz was termed \"supraharmonics\" in the literature (hereinafter SH) [2; 3; 4; 5; 6; 7; 8]. The lower limit of the SH range (2 kHz) is taken as the upper limit of traditional energy quality standards covering emission up to 40 th harmonic order. The upper limit of the SH (150 kHz) range is the lower limit of the electromagnetic compatibility (EMC). This division indicates that there is an area of insufficiently regulated standards. Hence, several standardisation committees are currently working on a description of emission and immunity limits and methods for emission testing in this frequency range. The scientific reports on the SH problem show that there are three lines of research in this area. The first concerns research into the impact of emissions generated by different types of loads on the level of current emissions [8; 22; 25], which should be considered as primary emissions. This group of research provides an overview of the types of noises that affect smart metering using power line communications, including noises coming from common electronic devices (compact fluorescent lamp (CFL) and light emitting diode (LED) light sources) and noises coming from photovoltaic inverters or electric vehicle charging spots, measured in a controlled environment. The previously mentioned studies, however, ignore the secondary emission in load currents, which is understood as the part of the current of a tested load that does not originate from its primary emission, but is transferred through parallel connections from another load. In order to describe the primary and secondary emission, a simplified model in a system of two loads is presented in Figure 2. Load 1 is represented by a constant current source I\({}_{\text{h1}}\) and impedance z\({}_{1}\). The primary emission from load 1 is denoted as I\({}_{1}\). Impedances z\({}_{1}\) and z\({}_{2}\) are the internal impedances of load 1 and 2 respectively, and z\({}_{\text{g}}\) is the network impedance. The primary emission (I\({}_{1}\)) flows partially into the grid and partially through the impedance of load 2. Thus, the total emission of load 2 consists of its primary emission I\({}_{2}\) superimposed on the secondary emission caused by load 1 (I\({}_{1,2}\)). Described relations are true, assuming the sinusoidal rated voltage. In practice, such conditions are hard to achieve. It is worth noting that, in [24], the authors noticed the influence of harmonics on the operating of electrical energy meters in a network with nonlinear loads. It is shown that electronic static meters of active energy are tested in the presence of distortions, and electronic static meters of reactive energy accuracy requirements do not take into account the possible presence of harmonics. The second line of research focuses on the so-called resultant emission of loads, resulting from the simultaneous primary emission of multiple appliances connected to the same subnetwork. In paper [16], among others, the authors presented interesting results of research on the effect of gradual incorporating of 1, 10, and 48 compact fluorescent lamps into one connection point, which shows that the level of current emission at the connection point does not increase linearly with the growth of loads of the same type. The authors observed the effect of decreasing the share of low frequencies 0-2 kHz in the total current while increasing the number of fluorescent lamps. It was observed that in the case of SH emissions above 2 kHz, some frequency components of currents close through input  
Figure 2: A simplified model, describing primary and secondary emissions in a system of two loads, assuming a sinusoidal rated voltage. circuits of adjacent loads and some frequency components of currents close through supply circuits and neutral wires.