System Operation 1 Introduction to System Operation, Optimization, and Control James D. McCalley, Iowa State University [email protected] 1.0 Introduction The energy control center (ECC) has traditionally been the decision-center for the electric transmission and generation interconnected system. The ECC provided the functions necessary for monitoring and coordinating the minute-by-minute physical and economic operation of the power system. In the continental U.S., there are only three interconnected regions: Eastern, Western, and Texas, but there are about 130 balancing areas (previously known as control areas), with each one having its own ECC. Figure 0.a illustrates the three interconnections, and Fig. 0.b provides a map of all balancing areas within the US. Fig. 0.a: The three North American interconnectionsSystem Operation 2 Fig. 0.b: North American balancing areas Balancing areas should not be confused with regional transmission organizations (RTOs) indicated in Fig. 0.c (and are generally also independent system operators or ISOs).System Operation 3 Fig. 0.c A balancing area is an electric power system or combination of power systems bounded by interconnection metering and telemetering, which has automatic generation control and performs the following functions: - Balance Supply and Demand within metered area - Maintain Interchange Power with other Balancing Areas - Maintain frequency of Interconnection within reasonable limits Below are some pictures of ECCs.System Operation 4 Fig 0.d: Energy control centers Generally, most utility companies that owned significant transmission and generation also owned and operated an ECC. This began to change during the latter half of the 1990’s, however. A major part of the “deregulation” movement, perhaps better said as the “industry restructuring,” consisted of changing the organizational structure of the regulated utility from a vertically integrated, single organization having responsibilities for generation, transmission, operation, and distribution, into a number of different organizations, each one with a separate function. Now, within what was a single balancing area operated by a single utility company, there may exist generation plants and transmission circuits having ownership from a variety of different organizations. The process by which this took place is sometimes called “functional disaggregation.” The motivation for doing so was to create conditions conducive for competition within the electric power industry. One of the reasons why the electric power and energy industry was regulated under a monopolistic organizational structure, with a single utility company responsible for each control area, was that maintaining the integrity and the economy of the interconnected system required significant coordinated decision-making. So a single organization, having unified and consistent objectives, could achieve this very well. InSystem Operation 5 bringing marketplace competition to the industry, it was necessary to disaggregate these functions, in order to have multiple players to compete against one another without giving any one of them too much market power; yet the need for coordination remains. The independent system operator (ISO) and the real-time and day-ahead electricity markets have resulted from recognition of this need. The ISO function is to monitor and regulate the physical operation of the interconnected grid, and the electricity market function is to provide a fair way to facilitate competition while maintaining reliable and economic operation of the interconnected grid. Our objective in this introduction to gain some perspective regarding system operation and energy trading as it is done in the industry today. In order to achieve this objective, it is useful to study the role of the ECC and associated technology used in the regulated, traditional industry. This we will do in Section 1.1, because many of these same technologies still exist today, and newer technologies are typically an evolution of the traditional ones. In Section 1.2, we identify the way the traditional system control functions have been distributed to accommodate the restructured industry, and we describe some of the technologies that have been developed to facilitate this distribution. A final comment is in regards to the phrase power systems operation on which our course is focused. We will define it in two ways, what it is, and what it is not. - Power systems operation is the decision-making associated with use of existing equipment to generate, transmit, and deliver energy. It typically revolves around the ECC and the electric energy markets. Associated decision horizons (the time between the moment the decision must be made and the time in which it takes effect) are from real-time (milliseconds to seconds) to as much as 1-2 years. - Power systems operation is not the decision-making associated with the planning of future new equipment. This is an area thatSystem Operation 6 more typically comes under the heading of power system planning. We have another course for this topic. It should be said, however, that there are many inter-relationships between operations and planning, and there are some decisions that are not cleanly in just one area or the other, and there are some tools that are used in both areas. But the terms are used heavily (and many companies are organized accordingly) and you should have some appreciation of what these terms mean. 1.1 System control for a vertically integrated utility The system control function traditionally used in electric utility operation consisted of three main integrated subsystems: the energy management system (EMS), the supervisory control and data acquisition (SCADA), and the communications interconnecting the EMS and the SCADA (which is often thought of as part of the SCADA itself). Figure 1 [1] provides a block diagram illustration of these three integrated subsystems. The SCADA and communications subsystems are indicated in the dotted ovals at the top left hand corner of the figure. The rest of the figure indicates the EMS. We will describe each one in