## 4 Results of an Experimental Study with Power-Line Communication and Selected End-User Equipment
The magnitude of the transmission signal was also adapted to worse connection conditions and increased from 90 dB\(\mu\)V (reference condition) to 95-97 dB\(\mu\)V.  
Statistics of the connection in the presented case are expressed by:  
* Total number of the connections: 103 (including 83 successful and 20 failed connections). * Duration of failed connections in one hour: 187 s.  
Case 4 (Supply Voltage Scenario 4, Load Condition 1) Operation of the Tested PRIME PLC System with LED Light Sources during Distorted Supply Voltage Referring to Immunity Test Limits  
The final scenario of the supply voltage distortion represents harmonic contribution used in low-frequency immunity tests, according to IEC 61000-4-13 [30] addressed to the equipment of the third class of the immunity. Details of the harmonic contents are presented in Table 3. The distorted supply voltage waveform obtained using the programmable source is depicted in Figure 10a. The waveform is characterised by the total harmonic distortion index equals 25.69%. This scenario can be treated as a case that exceeds the normal operating condition of the equipment significantly. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**The Harmonic Order** & \multicolumn{2}{c}{**Class 3**} & \multicolumn{2}{c}{**The Harmonic Order**} & \multicolumn{2}{c}{**Class 3**} \\ \cline{2-4}
**h = 3n + 1** & **Test Levels in \%U1** & **h = 3n** & **Test Levels in \%U1** \\ \hline
5 & 12 & 3 & 9 \\
7 & 10 & 9 & 4 \\
11 & 7 & 15 & 3 \\
13 & 7 & 21 & 2 \\
17 & 6 & 27 & 2 \\
19 & 6 & 33 & 2 \\
23 & 6 & 39 & 2 \\
25 & 6 & & \\
29 & 5 & & \\
31 & 3 & & \\
35 & 3 & & \\
37 & 3 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The magnitude of particular harmonics of the supply voltage used in low-frequency immunity tests according to IEC 61000-4-13 [30] addressed to the equipment of third class of the immunity. In contrast to the previously described scenarios, Figure 10b shows a significant impact of the distorted supply voltage on the non-intentional emission at the point of the connection of the LED and energy meter. The characteristic time packages of the broadband transmission signal in the range 42-89 kHz are not recognized now. It can be generally concluded that the non-intentional emission \"covered\" the intentional transmission signal. A comparison of the characteristic spectra of the intentional and non-intentional emission is presented in Figure 10c. Following signal parameters in the point of the 42-89 kHz transmission band can be identified as:  
* Local maximum of the non-intentional emission level (noise, background): \(N_{max}\) = 89.82 dB\(\mu\)V.
* The intentional transmission signal level related to \(N_{max}\): \(S(N_{max})\) = 92.96 dB\(\mu\)V.
* Local minimum signal-to-noise ratio: \(SNR_{local}\) = 3.14 dB. * Signal-to-noise ratio in the full transmission band: \(SNR_{band}\) = 7.61 dB. In point of the transmission statistics, the transmission was effective in the majority of trials. However, similar to the previous case, when the distorted supply voltage referring to permissible levels of harmonics in a public grid was considered, using supply waveform distortion basing on IEC 61000-4-13 kept increasing number of the connection between  
Figure 10: Case 4: results of the analysis of PRIME PLC system operation with LED light sources at distorted supply voltage referring to permissible limits for low-frequency immunity tests defined in IEC 61000-4-13 [30]; **(a)** supply voltage waveform; **(b)** time-frequency representation in the range 2–150 kHz using 100 ms window during the 20 s observation; **(c)** comparison of the spectrum of the corresponding PRIME PLC transmission (black) and the spectrum of the voltage in the connection point of the load (grey) with the relation to the normative curves (ul—line voltage in the point of the equipment connection, which is also the point of energy meter connection with PRIME PLC). concentrator and energy meters. The maximum time of failed connection extends the acceptable 180 s in one hour.