# Smart Grid Architecture for Rural Distribution Networks: Application to a Spanish Pilot Network
## 3 Electrical Actuations to Evolve the Rural Grid
### New Telecommunications Network  
The SRG project explores the convergence between electricity and Telecommunications Networks (TN). A new infrastructure is proposed with the aim of guaranteeing the efficient integration and management of DGs, new back-up resources, and new protection and control devices through RTUs. TN is an essential infrastructure to support the new SRG, transmitting commands and setpoints for remote management and control, data obtained from measurements and smart meters, even speech signals. The TN is presented in Figure 4. As mentioned previously, the TN is comprised of two different environments: an inner TN and an outer TN for the network. At the lower layer of the open system interconnection, the solution adopted for inner TN implements a wireless area at the SS level, thus enabling DGs to connect directly to control devices. In the second step, a main channel that employs the PLC technology will be set up, allowing communications between SSs. Then, the wireless network can also be used as an alternative link channel if the main one is incapacitated [24]. On the one hand, the Worldwide Interoperability for Microwave Access (WiMAX) is the wireless standard chosen for creating the SS wireless area and the alternative point-to-point channel between SSs. The wireless technologies (e.g., WiMAX) do not require a core infrastructure to operate, which simplifies operations and reduces initial deployment costs [48; 49]. WiMAX communication standard is similar to the Wi-Fi, but the former has better capability to operate at higher speeds for users connected over a large area like rural environments, in particular, it can stretch up to a maximum range of 50 km. The WiMAX is the name of the wireless broadband standard IEEE 802.16, which is a wireless local area network technology for fixed and portable devices [49]. It is able to provide access at a maximum bit rate between 1 Mbps to 75 Mbps. It could be potentially deployed in a variety of spectrum bands such as 2.3 GHz, 2.5 GHz, 3.5 GHz and 5.8 GHz [39; 48; 49]. The adopted WiMAX service uses a dish antenna to connect straight to the nearest wireless tower, providing a strong and stable connection. On the other hand, the PLC technology deployed combines a spread spectrum for those parts of the TN where robustness is fundamental, and a modulation multicarrier for those parts of the TN where distances are shorter but higher capacity is required [24; 50]. The transmission rate reaches 3 Mbps to 30 Mbps at short and medium distances even in the presence of strong interfering signals (e.g., photovoltaic inverter) and 320 kbps at distance of 8 km. Nominal bandwidth is between 2 MHz and 30 MHz and the internal latency is between 4 ms to 6 ms. The solution adopted for the outer TN, which connects the PN with the SCADA and other exogenous agents, is based on two communications channels. The main channel connects the PN with the SCADA through new point-to-point links in order to cross the mountains using WiMAX communication standard to the private fiber optics network from Xarxa Oberta de Catalunya (XOC). The emergency channel uses a public wireless link based on General Packet Radio System (GRPS) to connect the PN to another fiber optics public telecommunications network. Radio technologies, like WiMAX and GPRS, deliver data access services at low cost [24]. GPRS, unlike WiMAX, provides a data rate significantly smaller between 56 kbps to 114 kbps [51]. GPRS is a wireless technology that distributes packets of data across multiple channels, making efficient use of the bandwidth and providing the minimum information a secure channel for the link [24]. Figure 4: The telecommunications network. The coexistence of such a heterogeneous group of technologies is justified by two main reasons: the existence of certain communications infrastructures, like XOC and public telecommunications network, at the time of modernizing the project; and geographical constraints that make it difficult to deploy wired communications in some parts of the PN.