In this chapter, an overview of electric power systems is presented. The purpose is to describe the structure and operation of the power system and its evolution to the new smart grids. The first section gives an introduction about the electric grid and its evolution. Then, there is a section with a brief description of the different components of the electric power system: generation, transmission, distribution, and consumption. The third section is related to power system control, explaining why control actions are necessary in the power system to maintain the balance between supply and consumption and to keep constant the system frequency (at 50 or 60 Hz). In order to understand future applications of electric vehicles, it is important to present a fourth section related to fundamentals of the electricity markets. The chapter finishes with a description of the future power systems with high penetration of intermittent renewable energies, energy storage capacity, active demand management, and integration with telecommunication infrastructure.
TopIntroduction To Electrical Power Systems
Electricity is an important form of energy due to the versatility, immediacy, and cleanness in its use. According to the International Electrotechnical Commission (1985), an electrical power system is the set of “all installations and plants provided for the purpose of generating, transmitting and distributing electricity”. Although this broad definition can be applied to systems of very different size, from a simple load supplied by a hand-portable engine-generator to a complex nation-wide electrical network, this chapter focuses on interconnected networks linking generators to loads.
In a power plant, in general, a primary energy source (e.g., thermal energy from different kind of fuels or the sun, kinetic energy from water or the air) is converted (directly or through some successive transformations) into electrical energy. The generators are the devices at the end of the energy transformation chain in a power plant. They are mainly, but not only, rotating electrical machines. On the opposite part of the power system, the loads are the devices that make use of the electrical energy by converting it into another useful form of energy. The grid is the rest of the power system, and it comprises the lines, cables, transformers, switches, protections, and all the installations needed to convey the electrical energy from the generators to the loads. In some cases, the transmission of electrical energy is done with high voltage direct current (HVDC) links, but the majority of grids are three-phase alternating current (AC) based systems. Figure 1 shows a schematic overview with the main parts of a power system: a generator and its step-up substation, a high voltage transmission line, a distribution system with three successive step-down substations and two distribution lines, and four loads connected at different voltage levels.
Figure 1. Schematic overview of a power system
Apart from its many benefits, it is important to know some general issues related to the use of electricity as a form of energy that are important to understand the technical challenges that modern power systems have to face. First, electrical energy cannot be stored in a significant amount, thus, at every time instant, the power injected into the grid by all the connected generators has to be equal to the power consumed in the rest of elements of the system, including all the losses. Second, as it covers so many basic needs, it is almost irreplaceable, what, in economic terms, means that the electricity demand is very inelastic. Third, in an electrical grid, the power flows from generators to loads cannot be directed through specific paths, they are subjected to physical laws.
The objective of this chapter is to present a general overview of electrical power systems, their components, how are they operated and controlled, and its evolution to the new smart grids, helping non-specialist readers to understand these concepts.
TopComponents Of The Electrical Power System
As stated before, the four main parts of a power system are: generation, transmission, distribution and consumption. This section describes their main functions and components and introduces some basic tools for the analysis of power systems.