Keywords

1 Introduction

The current electrical model is evolving from a strongly centralized architecture, both in power generation and in management and based on a radial transmission and distribution scheme, to a decentralized structure where new actors arise to develop new or complementary functionalities. Hence, the scheme of a unidirectional generation-transmission-distribution chain will be replaced by a distributed system.

Concepts such as Smart Grids and demand response will generate a different relation between power generation agents, utilities and final users. The user is expected to play an active role to become a prosumer due to the promotion of local power generation. The increasing introduction of distributed power generation systems and the active role of a growing number of prosumers will lead to the accomplishment of a real-time demand response. To achieve this goal, more flexible and complex management systems that allow a rapid, efficient and robust control of the electrical network will be required.

This scenario would not be possible without the use of advanced communications system that provide all the high-demanding requirements described in the previous sentences.

2 Automation and Control of the Electrical Grid: Historical Evolution

The proper performance of the electrical infrastructure is a critical factor, because power cuts cause serious economic, social and technical consequences [2]. Due to the expected radical changes in social, economic and demographic areas, the infrastructures of the cities require a radical change [1]. Due to the higher dependence on the electricity, and considering the new functionalities that are being proposed for the city of the future (Smart City, SC), the electric network infrastructure is a substantial and fundamental part of this process.

The modernization of the electrical infrastructure has not happened overnight. In the 1950s, analog communications were employed to collect real-time data of power outputs from power plants, and tie-line flows to power companies. To achieve this, operators used analog computers to conduct Load Frequency Control (LFC) and Economic Dispatch (ED) [3]. LFC was used to control generation in order to maintain frequency and interchange schedules between control areas, and ED adjusts power outputs of generators at equal incremental cost.

It is from 1960, with the advent of digital computing, when developing the Remote Terminal Units (RTUs), which were designed to collect voltage measurements, active and reactive power, and states of protection devices in substations. To make this measure possible, the use of dedicated transmission channels was necessary to interconnect the final devices with the computational center. As a consequence of the blackout of 1965 in the USA, a more extensive use of digital computers was highly recommended, in order to improve the real-time operations of the interconnected power systems. The use of computers and digital systems was considerably increased from 1970, with the introduction of the concept of system security, covering both generation and transmission systems [4].

The first control centers were based on dedicated computers, but in the subsequent years, they were gradually replaced by general-purpose computers. It is already from 1980 when the microcomputers were replaced by UNIX workstations, interconnected by means of Local Area Networks (LAN) [5]. These first networks of interconnected computers allowed a more rapid and efficient data exchange between different parts of the electrical grid.

The real revolution in the electrical system took place in the second half of 1990s, when the electrical industry launched the reorganization of the system. Since then, services ceased to be vertical and the generation, the transport and the distribution of the energy were separated. In addition, monopolies were replaced by competitive markets [6]. The combination of these both aspects marked a turning point in the evolution of the electrical system.

In this new scenario, three clearly differentiated segments were created in the electrical system: Energy Management System (EMS), Business Management System (BMS) and Market. The above-mentioned segments and the interaction between then are shown in the Fig. 1.

Fig. 1.
figure 1

Segments of the electrical system and interaction between them.

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3 The Role of the Communications in the Development of the Smart Grids

3.1 Evolution of the Communication Systems in the Electrical Infrastructure

One of the aspects that enable and foster the great evolution of the electrical system described in the previous section was the development of a robust communications layer. The communication systems used in the electrical infrastructure have also undergone great changes, in order to provide new functionalities adapted to both the evolution of the grid and to the new requirements of the companies in charge of the transmission and distribution services.

Regarding Power Line Communications (the communication technologies based on the use of the electrical cable), the electrical grid was not initially developed as a communication medium, and therefore, the high number of interferences and noise sources, together with the high variability with time and frequency, represent a great challenge for the proper performance of the data transmission.

The strong points for the use of wireless communications have been the higher flexibility, the better conditions of the propagation medium and the potential use of transmission technologies already tested. On the weak side, the difficulties to provide a complete coverage and the need of deploying the complete transmission-reception chain for each link. Nevertheless, these drawbacks were recently overcome by the use of advanced cellular technologies, such as GPRS (General Packet Radio Service) and LTE (Long Term Evolution or 4G), which provide good rates of coverage, availability, data rate and latency. Future Smart Grids functionalities and applications rely on the better performance of wireless technologies, mainly LTE and 5G.

The historical evolution of the wired and wireless communications in the electricity grid is shown in Table 1 [7, 8].

Table 1. Evolution of the communication systems in the electrical infrastructure.
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3.2 The Communication Systems in the Structure of the Electrical Grid

The performance of the a communication technology may vary depending on the conditions of the grid, such as the grid topology, the density of communication devices (users, data concentrators or substations) to be connected, the distance between them and the requirements of the communications (data rate, robustness, priority levels) and the presence of interfering electrical noise sources. For example, high-speed communications can be used for the connection of electrical substations in urban areas; however, this solution may not be feasible in other areas, such as rural environments or remote devices.

Accordingly, the network infrastructure can be separated into two zones [9]:

  • Last mile connectivity: it can be understood as the high-speed communications between the substations and the control center. There are wired communications (PLC and fiber optic) and wireless communications (via satellite and wireless in general).

  • High speed communication core network: this network can be private or public. A high-speed network for the automation of substations is Internet based on Virtual Private Network.

Although everything is important, perhaps the last mile communications are crucial for the operation of the electric network. In this sense, one type of communications or others will bring advantages or disadvantages, as can be seen in Table 2.

Table 2. Advantages and disadvantages of possible communication technologies for last mile connectivity.
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3.3 A Representative Example: Wireless Communications Applied to Automation Tasks

The Wireless Sensor Networks (WSN) can be used in automation tasks [14]. Specifically, WSN is used in Wireless Automatic Meter Reading (WAMR) systems, for reading consumption/generation in Smart Meters (SM). WSN presents some benefits in automation, namely:

  • The sensors used in WSN are reliable, self-configurable, robust and are not affected by climatic conditions (pressure, temperature, etc.).

  • The coverage of a sensor is low, but the entire network of sensors converts the network into an extensive communications network.

  • The WSN is a redundant network, due to the intervention of all the sensors.

  • The sensors perform a pre-filtering, so that the network presents an efficient data processing.

  • The WSN presents self-configuration and automatic organization of the devices.

  • The WSN has low installation and maintenance costs.

4 Conclusions

An essential feature in the evolution of the Smart Grids is the use of information and communications technology to gather different types of data from a distributed network of sensors and take fast decisions according to the analysis of this information. The final purpose is the improvement of the efficiency, reliability, economics, and sustainability of the production, transmission, and distribution of electricity.

The conversion of the user from a consumer to a prosumer, together with the new generated distribution systems, will change completely the architecture and the procedures to manage the electrical grid. This will lead to employ two-way communication systems in the smart grid.

In parallel, the recent developments on the wireless technologies, mainly in cellular systems, providing higher data rates, much lower latency values and the possibility to provide simultaneous service to a high number of devices, will open the door to innovative services for the users and the rest of the agents related to the electrical grid.