Distribution systems analysis employs a set of techniques that allow engineers to simulate, analyse, and optimise power distribution systems. Combined with automation, these techniques underpin the emerging concept of the 'smart grid', a digitally-enabled electrical supply grid that can monitor and respond to the behaviour of all its components in real time. Distribution System Analysis and Automation provides a comprehensive guide to these techniques, with coverage including smart grid for distribution systems; introduction to distribution automation; network and radial load flow analysis; determination of the optimal topology for power electric systems; voltage VAR control and capacitor application; power quality and harmonics in distribution systems; harmonic filter design; distribution system restoration; short circuit analysis; arc flash concepts; numerical relaying and feeder protection; communication and control centres; and distributed energy resources. The book is based on over 30 years of experience in the field of power systems and combines theoretical concepts with real-world applications and MATLAB exercises.
Inspec keywords: power distribution protection; voltage control; smart power grids; power engineering computing; power system harmonics; control engineering computing; harmonic analysis; power distribution reliability; open systems; power distribution control
Other keywords: short circuit calculation; distribution automation function; volt-VAR control; harmonic analysis; distribution system analysis; interoperability concept; power distribution protection; smart grid; reliability
Subjects: Control of electric power systems; Mathematical analysis; General and management topics; Power engineering computing; Control engineering computing; General electrical engineering topics; Power systems; Power system protection; Distribution networks; Power supply quality and harmonics; Reliability; Mathematical analysis; Voltage control
Smart Grid (SG) is a rather new concept that includes aspects of energy generation, transmission and distribution and aims for a more reliable service, higher efficiency, more security, two-way utility-user communications, and promotion of green energy, among other goals. When the term 'Smart Grid' was first used, some people associated it with remote metering, which was later called AMR (automatic meter reading). The activities of AMR were encompassed within those of a broader field that was eventually called AMI (advanced metering infrastructure). Clearly, the metering system is one of the major elements of the Smart Grid, but certainly is not the only one. Many elements are included in the overall field of Smart Grids. Those pertaining to distribution systems and in particular to the automation of distribution systems (or distribution automation) will be considered in this book.
Distribution automation started in the 1970s. It allows utilities to implement modern techniques in order to improve the reliability, efficiency, and quality of electric service. Distribution automation is also referred to as feeder automation. It has been defined by the IEEE as follows: 'Distribution Automation is a system that enables an electric utility to remotely monitor, coordinate and operate distribution components in a real-time mode from remote locations'. Distribution automation, commonly known as DA, has evolved into advanced distribution automation, known as ADA, which incorporates advanced communication schemes, new computer technology, state-of-the-art equipment technologies and high-speed power electronic devices.
Distribution automation requires a deep knowledge of the system to where it is applied. For this, a proper handling of analysis techniques is very important. Distribution system analysis is a part of a broader concept referred to as power system analysis. In distribution system analysis only some fields of the overall picture are studied, and, of course, those referring mainly to feeders and radial systems. The main topics to be analyzed correspond to the modeling of the elements, the analysis of load flows for ring and radial systems, and short circuit conditions. Load flows are applied for different applications involving not only the analysis of power flows and voltage regulation but also feeder reconfiguration and loss reduction. Short circuit as always is essential in sizing equipment and protective relay setting. Studies of transient and small signal stability are not usually conducted at distribution levels and therefore will not be considered in this book.
Calculation of short circuit values is essential in power system analysis. The results are used in a number of applications like sizing of breakers and other elements of power systems, designing grounding grids, setting protective equipment, evaluating Total Harmonic Distortion (THD) of harmonic currents, and performing arc flash analysis.
Each distribution system component can be described by a set of reliability parameters. Simple reliability models are based on component failure rates and component repair times, but sophisticated models make use of many other reliability parameters.
For decades, distribution systems were designed with rigid topologies and limited possibilities for change in configuration. Improvements achieved by the manufacturers in recent years have prompted the use of feeder reconfiguration to modify the topology of distribution networks. These improvements include remotely controlled switches and breakers for pole installation, numerical protection, and appropriate communication systems Prior to determining the location of switches to allow changes in configuration, it is highly recommended to find the best topology for a distribution system. Under normal operating conditions, feeder reconfiguration aims for a more efficient operating condition of the network. Under faulty conditions, feeder reconfiguration aims to restore the service to the maximum number of users in the shortest time.
The term 'VVC' stands for Volt/VAR control and refers to the technique of using voltage regulating devices and reactive power controls to maintain voltage levels within the accepted ranges at all points of the distribution system under all loading conditions. Modern software techniques and the progress on communication technologies allow nowadays achieving these goals and therefore the service quality has improved remarkably in most utilities throughout the world.
Harmonics have become one of the most critical issues in power systems due to the high penetration of them and the magnitudes. This is particularly critical in distribution systems. Harmonics create problems that affect considerably the power quality of a system and therefore are treated in that field. Power quality can be defined as the goodness of the electric power quality supply in terms of its voltage waveshape, its current waveshape, its frequency, its voltage regulation, as well as level of impulses and noise, and the absence of momentary outages. Other definition defines power quality as the measure, analysis, and improvement of bus voltage, usually a load bus voltage, to maintain that voltage to be a pure sinusoid and at rated levels of voltage and frequency. A proper quality level is ultimately a compromise of the utility, the end user, and the equipment manufacturer. Power quality involves several categories of phenomena, which are better presented in Table 8.1. The categories and characteristics are presented in Table 8.2 taken from the IEEE Standard 1159-2009. Category 5 deals with waveform distortion that includes the harmonic handling, which is the topic developed in this chapter.
Overcurrent relays are the most common form of protection used to operate only under fault conditions. They should not be installed purely as a means of protecting systems against overloads. The relay settings that are selected are often a compromise in order to cope with both overload and overcurrent conditions. Overcurrent relays can be classified as definite current, definite time, and inverse time as shown in Figure 9.1(a-c). The time delay units can work in conjunction with the instantaneous units as shown in Figure 9.1(d).
For years, analog communication networks have provided channels that allowed long-distance information exchange. However, with the arrival of digital communications it was possible to employ physical mediums that have their own capacity to transfer large data packets in a reliable and efficient manner. Digital communication networks and data services have provided solutions that optimize thousands of processes worldwide. In the smart network environments such solutions have proved successful. A good example of this is the application on protective relaying. It is known that protection functionalities have maintained the theoretical foundations since they were first developed. However, the operation of protective relaying has been greatly improved in time response due to the availability of much faster relays based on the numerical technology as well as the wonderful development of communication capabilities that have been attained in recent years. The standardization of protocols brought a convergent platform to implement solutions based on open and flexible solutions. However, since high levels of reliability, availability, and security are required by electrical system networks, the protocols needed to be adapted to offer lower levels of latency and larger broadband. In the following sections reference will be made to important topics pertaining to the effect of communications on distribution automation and in general on Smart Grid, including the OSI model, the most popular protocols, and the transmission mediums. Special attention is given at the end of the chapter to the IEC 61850 Standard, considering its huge impact in all aspects of power system automation handling.
To achieve the objectives of the Smart Grid efficiently, it is necessary to integrate all the components of the power system from generation to the end user. They should relate to each other in a transparent manner, i.e. independent of their technologies and protocols. This concept applied to Smart Grid networks ensures efficient communication whether the information systems are used on different types of infrastructure or even at a distance. For this, the use of the concept of ontology from computer science helps greatly. Ontology is the philosophical study of the nature of the basic categories and their relationships. Ontology-based strategies applied to interoperability constitute a framework for organizing information and are used in the representation of components of power systems.
The maturity model helps utilities to implement Smart Grid application by prioritizing tasks and measuring the progress achieved. It also helps to identify the characteristics of the organization by designing a roadmap and by promoting the exchange of common terms among internal and external actors.changes. Maturity models, very common in IT organizations, help an organization assess its methods and processes according to management criteria. The key to achieving a maturity model is a good strategy and a good vision in the Smart Grid context. The maturity model covers three major elements: communications, IT, and electrical components. This chapter discusses the joint efforts among different entities which have come together to produce interesting procedures and schemes to aid organizations in using the most appropriate solutions for their requirements.
