Electricity Transmission, Distribution and Storage Systems

Ziad Melhem

• Publisher: Woodhead Publishing
• Year: 2013
• ISBN:
  9780857097378
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Electricity transmission and distribution systems carry electricity from suppliers to demand sites. During transmission materials ageing and performance issues can lead to losses amounting to about 10% of the total generated electricity. Advanced grid technologies are therefore in development to sustain higher network efficiency, while also maintaining power quality and security.Electricity transmission, distribution and storage systems presents a comprehensive review of the materials, architecture and performance of electricity transmission and distribution networks, and the application and integration of electricity storage systems.The first part of the book reviews the fundamental issues facing electricity networks, with chapters discussing Transmission and Distribution (T&D) infrastructure, reliability and engineering, regulation and planning, the protection of T&D networks and the integration of distributed energy resources to the grid. Chapters in part two review the development of transmission and distribution system, with advanced concepts such as FACTS and HVDC, as well as advanced materials such as superconducting material and network components. This coverage is extended in the final section with chapters reviewing materials and applications of electricity storage systems for use in networks, for renewable and distributed generation plant, and in buildings and vehicles, such as batteries and other advanced electricity storage devices.With its distinguished editor, Electricity transmission, distribution and storage systems is an essential reference for materials and electrical engineers, energy consultants, T&D systems designers and technology manufacturers involved in advanced transmission and distribution.

• Presents a comprehensive review of the materials, architecture and performance of electricity transmission and distribution networks
• Examines the application and integration of electricity storage systems
• Reviews the fundamental issues facing electricity networks and examines the development of transmission and distribution systems

Part 1

Fundamentals of electricity transmission and distribution

1

Introduction to transmission and distribution (T&D) networks: T&D infrastructure, reliability and engineering, regulation and planning

L. Willis, Quanta Technology, USA

Abstract:

Power transmission and distribution systems have evolved over the past twelve decades into vast interconnected systems of equipment built around large centralized generation plants. In the twenty-first century the evolution will begin to include significant portions of de-centralized, distributed generation and storage, much of it based on renewable and ‘micro-grid’ technologies. Power utilities will not evolve their systems completely to this type of configuration, but instead pragmatically combine their old central-station systems with additions and augmentation based on distributed generation and micro-grids when and where most suitable to their needs. Future power systems will be an amalgamation of old and new types providing considerably more flexibility as to reliability, economy and fit to extreme aesthetic and user demand requirements than traditional systems, but often requiring considerably more context-responsive and dynamic control than in the past.

Key words

power systems

power transmission

power distribution

micro-grids

distributed generation

renewable generation

distributed storage

future of power systems

electric utilities

electric load

electric demand

1.1 Introduction

For over a century, an increasing portion of the world’s population has enjoyed the benefits of electric power – a clean, controllable, and economical energy source that leads to material improvements in quality of life and industrial efficiency. At present, there are few places of economic importance on this planet that do not have utility-supplied electric power. Along with roads and bridges, telephone, and water and sewer, electricity has become part of the very foundation upon which first-world countries have built their quality of life and economic prosperity. During the past century, electric power has been produced and delivered to electrical energy consumers in all nations over electrical power systems that are almost all based on the same ‘central-station’ paradigm: power is produced in bulk at relatively few places but consumed at many. The power system serving a city or region is dominated by a few large central generating stations, each consisting of from one to perhaps half a dozen industrial-scale power production machines (generators) along with the ancillary equipment needed to operate and maintain them in good working order. Transmission lines carry the power in bulk quantities to points throughout the region, where it is passed to smaller-capacity lines (distribution) on which it is routed through neighborhoods and eventually to individual homes, businesses, and other energy users (Fig. 1.1), which each use only a tiny fraction of the power produced by the average-size generator. Typically, there are several orders of magnitude more points of consumption – perhaps 100 000 times as many – as power generation points. Engineering standards, which here will be taken to mean the institutionalized and documented ‘way of doing things,’ vary, sometimes significantly, from one continent or region of the world to others, but the vast majority of utility and industrial power systems on earth have been built to be, and continue to be, operated within this overall central-station system concept.

1.1 The structure of a traditional power system, dominated by several large central-station generator plants and the bulk transmission system connecting them. That transmission not only moved the bulk power around the system but in many ways determined the character of the power system itself.

A power T&D system is that portion of the power system that moves power from where it is produced to where it is consumed: basically, it is the entire power system sans generators. The T&D system interconnects all the disparate parts of the power system and thus to a great extent determines the character of that system.

Beginning in the late twentieth century and continuing into the twenty-first century, significant changes – advances if perhaps not true breakthroughs – began to occur in several of the technologies that made up electric power systems. It became possible to build electric power systems fed by many more, but individually smaller, generating sites (Fig. 1.2). No longer would there be thousands of times fewer generating stations than energy consumers: conceivably, the ratio could be one to one. Such distributed power systems, in which power production is dispersed widely throughout the energy consumer base rather than concentrated at a few generating stations as in a traditional power system, had different reliability, maintainability, and operability characteristics, as well as different economies of scale, etc., which shaped their use differently from traditional power systems. Neither type of system, traditional or distributed, is necessarily better. They are merely different. What seems clear is that the power system of the future will be neither one, but instead a hybrid mix of both.

1.2 The overall structure of a distributed power system, in which individual customers may have generation and the ‘power system’ may only be a local micro-grid connecting a number of local consumers together for power and reliability sharing.

This chapter focuses on the delivery part of the system, the T&D systems. It will review and summarize the overall structure, function, design, and performance of modern electric power T&D systems. At times it will present and discuss at an almost elementary level, basic concepts behind system design and operation, when these basics play into the differences between traditional and modern distributed power systems. These basics are among the factors that once required the traditional type of design solution, but can now be accommodated by something different, and thus they are a key to understanding how the transition from one to the other, or the hybrid melding of the two, can be accomplished.

This chapter begins in Section 1.2 with a look at the traditional power system, a power delivery paradigm dominated by large central-station generators and composed of a network of high-voltage transmission lines, medium voltage primary feeder systems, and low-voltage service lines to customers. Section 1.3 then takes a look at three technology changes and the smart distributed power systems they enable, and discusses how and why the distribution power systems that they enable differ from traditional designs, and what that can mean in terms of cost and performance.

Regardless of type, power systems must be planned, engineered, designed, built, and operated. Their parts and subsystems must be regularly maintained, repaired when broken and replaced when they fail or wear out. Someone must pay for all of that, and that is usually done by charging consumers for the power they according to well-established principles that basically price it per unit of use. Finally, the entire system must be managed, which is the job of utility companies, either public or private as the case may be, or the owner in the case of large industrial power systems. Section 1.4 summarizes these aspects of power systems.

Finally, whatever the advantages of distributed power systems, most developed nations around the world have traditional power systems in place, woven into the fabric of every city and town and region, and without which the local society and economy could not function. While there are often serious concerns related to reliability, pricing, or environmental issues, for the most part these traditional systems function well, or at least well enough. Most tellingly, they are in place and paid for – almost always an overwhelming reason to keep them despite any problems they may present. But distributed systems offer considerable advantages that are important to modern society and increasing individuals, companies, and governments are turned to them to meet their expanding power needs. Section 1.5 looks at electric infrastructures and the forces and factors in favor of retaining the traditional power system, as against moving to the newer distributed paradigm.

1.2 Characteristics of traditional and nontraditional power systems

Whether traditional or distributed, an electrical power system consists of equipment interconnected and operated in a coordinated fashion in order to route power from where it is produced to where it is consumed. Strictly speaking this simple definition could describe a flashlight, which includes a power source (battery), conducting ‘power transmission’ pathways (often the body of the flashlight itself) to route power to the electrical load: in this case a light bulb that consumes the power, and a control system (switch) in command of the operation. However, as normally used, power system is reserved for more powerful and expensive assemblages of equipment and generally does not include the end-use equipment (the light bulb in the case of the flashlight) but only the production, transmission, control, and hand-off points to the demands. With exceptions too rare and specialized to go into here, all power systems anywhere on the planet, and of either traditional or distributed types, have the following characteristics discussed below:

1.2.1 Constant supply voltage

For whatever reason, mankind has chosen to build constant-voltage power systems. The perfect constant-voltage power system would provide an unvarying, identical voltage at each electric consumer’s location, not varying at all regardless of time, system operating conditions, or the amount of usage. In practice, voltage is permitted to vary with time and conditions by small amounts – for example up to 3% during short periods of time. But despite this, the concept of use is: vary the amount of power drawn from the system by varying the current drawn from the system. For example, a device that needs 12 watts – a small light bulb – is designed to draw 0.1 amps from a source of 120 V. By contrast a device needing 120 watts, say a small motor, would be design...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributor contact details
• Woodhead Publishing Series in Energy
• Dedication
• Preface
• Part 1: Fundamentals of electricity transmission and distribution
• Part II: Advances in materials and technologies for electricity transmission and distribution
• Part III: Electricity storage technologies
• Index