## 8 Discussion  
Communications networks are of capital importance in Smart Grids. PLC technologies are especially relevant in these scenarios since they provide benefits to DSO, such as that they use the power lines themselves as communications medium, so deployment costs are dramatically reduced. In particular, NBPLC technologies are being widely used in the \"last mile\" or NAN of many AMI deployments especially in Europe, since they fit the characteristics of European low voltage networks and meet the communications requirements of the application. All these NBPLC technologies operate in the CENELEC A band (between 35 and 90 kHz), where a wide range of devices radiate unwanted emissions mainly due to their power electronics. As a result, the frequency disturbances in the range from 2 to 150 kHz (the so-called supraharmacics) have become a hot topic both in research and standardization [75; 76]. Hence, some recent research works have investigated the effects associated to consumer electronics [77], to PV inverters [78; 79] or to EV charging [80] in this frequency range. However, there are just a few studies that investigate the effects of such unwanted emissions in the NBPLC network performance based on actual experiments and measurements. Reference [81] presents a great study along this research line, addressing the impact of several DER (namely, hydropower turbine and pump, PV inverters, and storage equipment) on NBPLC PRIME communications based on a set of experiments carried out at the Spanish CEDER (Center for the Development of Renewable Energies). Reference [82] also addresses this issue by investigating the impact of changes in impedance related to PV production on the quality transmission of FSK NBPLC networks by means of field measurements, simulations and measurements taken from a simple laboratory setup. This paper represents another contribution along this research line, presenting some features which stand out among current state of the art. The overview of noises in NBPLC networks represents a very comprehensive study, including normative noises, noises coming from consumer electronics that prevent actual operational PRIME networks from working properly, as well as noises coming from PV inverters and EV charging. In addition, the paper reviews different noise mitigation techniques, paying special attention to passive filters, which is in practice the preferred solution of DSO for this purpose, with the main aim of coming up with a filter that presents a fair enough performance and can be massively deployed. Thus, based on a set of experiments carried out in the LINTER of Union Fenosa Distribucion and using own-developed hardware and software tools (namely, a configurable filter and the network forensics tool PRIME Analytics [40]), the paper also evaluates the impact of some relevant sources of noise on PRIME communications, together with the effectiveness of different passive filter configurations to mitigate such an impact. The analysis of the traffic traces performed with PRIME Analytics shows that the considered sources of noise affect to PRIME network performance to different extent, provoking certain instabilities. Figure 49: Traffic traces analysis for the PV inverter noise tests. The spectral measurements show that the most effective filter configuration in terms of mitigating the noise is filter 9 (a low pass differential-type filter which presents an attenuation in PRIME band of more than 48 dB, c.f., Figures 23 and 35). However, this type of filter has an important drawback: it does not allow the reconnection of the breaker (power control) embedded in the smart meter by infinitive impedance detection because the filter presents a low capacitive impedance at 50 Hz if the capacity to neutral is not controlled. This problem could be solved by using an active element, but DSO are reluctant to this option since it increases the complexity of managing the filter (e.g., the active element may fail, consumes energy, and requires certain maintenance tasks).