ABSTRACT

The third of the five aspects of aging T&D infrastructure discussed in Chapter 1 is Engineering Paradigms and Approaches. Traditional power system engineering methods, and the paradigms built around them, are as much a part of existing power systems and their strengths and weaknesses, as old equipment and obsolete system layouts. Many of the key concepts and engineering approaches used in “modern” power systems were created in the mid-20th century, at a time when electric consumer demands, societal expectations, and engineering criteria were far different from today’s. Like all engineering methods, the mid-twentieth century’s had their limitations and advantages. Those limitations were for the most part well understood by their developers, but were far outweighed by their advantages, among the most important being that the methods could be implemented with the very limited computing resources available at the time. The power industry has carried many of these engineering methods and the concepts built around them through several generations of power system engineers. Not only are these methods in widespread use, but several of these paradigms have become dogma. This chapter will begin by examining the traditional power system reliability engineering tool: the N-1 criterion and the contingency-based planning approach. This method was first used in the mid-20th century and had been developed into

efficient computerized form by the late 1960s. It, and the conceptual approach to power system planning that goes along with it, are at the core of nearly every utility’s overall power delivery planning and reliability engineering procedures. Similarly, many of the core concepts and criteria concerning the layout of distribution feeder systems were developed in the 1930s through the 1960s, and are largely unchanged in their application as the electric utility industry enters the 21st century. These will be covered in Chapter 10. These traditional power system-planning methods proved more than adequate to meet the industry’s needs through the 1950s to early 1990s. However, as experience has shown, and this chapter will explain, they are less than completely adequate for application to aging infrastructure areas in some of today’s high-stress utility systems. This is due to an incompatibility between these traditional planning methods and the way that modern utilities need to plan, design, and operate their systems. As a result, systems planned and designed along proven but traditional lines, using tools that engineers could once confidently use, often provide poor customer service reliability and experience severe operating problems. This chapter begins in Section 9.2 with an examination of the basic N-1 contingency-based reliability design criterion and the typical methods of its application. Section 9.3 then explores this methodology’s limitations with respect to modern needs, and discusses how they interact with the characteristics of modern utility systems, and discusses how that often results in a system that does not provide the expected level of reliability. Section 9.4 looks at some other planning-related issues that have created real challenges for aging infrastructure utilities, most notably load forecasting errors and the way they interact with system reliability. Section 9.5 provides a reminder that high utilization rates and cost-reductions, per se, are not the reason that modern power systems and particularly aging systems, tend to give poor results – rather it is the inability of traditional planning tools to fully analyze the reliability implications of design in those areas. Section 9.6 rounds out the chapter by summarizing key points and gives five recommendations for effective planning procedures to be applied to aging infrastructure areas.