## 2 Literature Review
### Gap in the Research Related to Influence of Supply Voltage Distortion on Supraharmonics Emission
The frequency range of these disturbances coincides with the PLC transmission frequencies; as a result, the useful signal of PLC transmission is \"covered\" by the spectrum of unintentional disturbances. The authors of [17] also analysed the operation of light sources in the band above 2 kHz. The analyses were performed in three frequency sub-ranges: 9-30 kHz, 30-95 kHz, and 95-150 kHz. Tests of a representative set of lamps, both compact fluorescent lampsand LED lamps, showed clear differences in the current emission not only between the two types of lamps, but also between lamps within the same type. The discussed results indicate the influence of the quality of the supply voltage on the content of higher frequencies in the current of LED lamps in the wide 30-95 kHz range, used by some narrowband and broadband PLC technologies. Hence, the conclusion that in the case of operation of these loads in conditions of supply other than sinusoidal, the share of unintentional disturbances introduced to the network by these loads may be greater than the results of emissivity obtained during standardized tests. This paper presents the results of the research devoted to the issue of the impact of harmonic content in the supply voltage, or more generally, the degree of distortion of the supply voltage waveform on non-intentional emission in the 2-150 kHz band by loads, which, according to literature, are responsible for most of the emission of the intentional PLC transmission. The methodology of the investigation is aimed to cover two issues: characterisation of the non-intentional emission under the different quality of the supply voltage as well as the assessment of its influence on continuity of the transmission in the selected PLC system. The Background of the Investigations--Identification of the Emission Limits, Compatibility Levels, and Immunity Levels for Conducted Disturbances and Signalling in the Frequency Range 2-150 kHz  
Due to the manner of interaction between the transmission systems (intentional emission, mains signalling) and the power grid including loads (non-intentional emission), it is worth analysing the contents of the standards in terms of permissible levels relating to:  
* Levels of non-intentional emission referring to individual equipment and the power grid (non-intentional emission). * Compatibility levels in the power grids (compatibility levels, environment characteristics). * Intentional emission (transmission levels and mains signalling). * Immunity test levels. For this reason, in Figure 3, several characteristics in the range 2-150 kHz were collected. Presented curves express limits defined in applicable standards. Details of selected standards are given in the legend of the figure. The prominent curve is related to intentional emission (i.e., mains signalling and power-line communication denoted in the figure by the lines described using the letter \"S\") and non-intentional emission (i.e., network distortions, denoted in the figure by the line described using the letter \"E\"). Additionally the compatibility level in an electrical network is also represented (denoted in the figure, using letter \"C\"). The boundary conditions are represented by the curve related to the immunity test of the communication systems in the range 2-150 kHz (denoted in the figure by the line described using the letter \"I\"). Additionally, the figure shows the frequency area 42-89 kHz, which represents the PRIME broadband power-line communication technology used in the research. Legend of the curves in Figure 3:  
Non-intentional emission referring to IEC 61000-3-8:1997 [4] adopted in the standard for PLC transmission EN 50065:2012 [2]--it can be treated as background emission, potentially affecting the communication by the power grid (solid line, green colour, letter \"E\"). * Compatibility levels referring to IEC 61000-2-2: AMD1:2017 [5] and AMD2:2018 (dashed line, pink colour, letter \"C\").