## 4 Results of an Experimental Study with Power-Line Communication and Selected End-User Equipment
The green line in Figure 7c represents the non-intentional emission limit values, according to EN 50065 [3]. It can be noted that using the proposed laboratory setup, it is possible to obtain conditions representing the permissible range of non-intentional emission in the public grid. The black line in Figure 7c represents the identified spectrum of intentional emission introduced by PRIME PLC transmission. From the graph, the following PLC transmission parameters in the 42-89 kHz band can be identified:  
* Local maximum of the non-intentional emission level (noise, background): \(N_{max}\) = 65.72 dB\(\upmu\)V.
* The intentional transmission signal level related to \(N_{max}\): \(S(N_{max})\) = 87.51 dB\(\upmu\)V.
* Local minimum signal-to-noise ratio: \(SNR_{local}\) = 21.79 dB. * Signal-to-noise ratio in the full transmission band: \(SNR_{bound}\) = 31.21 dB. Such conditions guarantee the correct operation of the PRIME PLC system in the 42-89 kHz band, which has been confirmed by the observation of meter-concentrator communication PLC statistics. Communication statistics have been also checked during a continuous system operation for 2 h. The correct transmission between the concentrator and the energy meters was confirmed. Case 2 (Supply Voltage Scenario 1, Load Condition 1): Operation of the Tested PRIME PLC System with LED Light Sources during Sinusoidal Supply Voltage  
The measurements were then repeated for the condition when the sinusoidal voltage supplied the LED light sources. Figure 8 represents: (a) investigated voltage, (b) time-frequency plane of 20 s observation of the transmission including non-intentional component, (c) comparison of the spectrum of the transmission and non-intentional emission signals (noise, background for the transmission). In comparison to the no-load condition, the spectrum of voltage measured in the connection point of the LED and the energy meter is characterised by an additional narrowband non-intentional component around 60-80 kHz. However, the magnitude of this component did not affect the transmission signal. Details of the characteristic parameters of the spectrum component in the PRIME PLC transmission band 42-89 kHz are as follows:  
* Local maximum of the non-intentional emission level (noise, background): \(N_{max}=75.63\) dB\(\mu\)V.
* The intentional transmission signal level related to \(N_{max}\): \(S(N_{max})=92.67\) dB\(\mu\)V.
* Local minimum signal-to-noise ratio: \(SNR_{local}=17.04\) dB. * Signal-to-noise ratio in the full transmission band: \(SNR_{band}=30.63\) dB. Figure 7: Case 1: Results of the analysis of PRIME PLC system operation without loads at pure sinusoidal supply voltage (reference case); (**a**) supply voltage waveform; (**b**) time-frequency representation in the range 2-150 kHz band 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 and energy meter (grey) with 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). Communication statistics have been also simultaneously checked. During a continuous system operation for 2 h, correct transmission between the concentrator and the energy meters was confirmed. * Statistics of the connection in the presented case are expressed by:
* Total number of the connections: 53 (including 44 successful and 9 failed connections). * Duration of failed connections in one hour: 2 s.  
Case 3 (Supply Voltage Scenario 2, Load Condition 1): Operation of the Tested PRIME PLC System with LED Light Sources during Distorted Supply Voltage Referring to Permissible Limits for Public Grid EN 50160  
The tests presented in the previous section have been repeated under operating conditions with a distorted supply voltage with the maximum harmonic content allowed by EN 50160:2015 [3] (see Table 2).