eliability f constant concern to the operators of power systems is the reliability of equipment. This has become more aportant as systems are run harder In the past, reliability was ensured by building in reserve equipment which was either connected in parallel with other similar devices or could be easily connected in the event of a failure Not only that, knowledge of the capabilities of materials has increased so that equipment can be built with a more certain level of reliability. However, reliability of a system is governed by the reliability of all the parts and their configuration. Much work has been done on the determination of the reliability of power systems but work is still being done to fully model power system components and integrate them into system reliability models The information that is obtained from reliability analysis is very much governed by the nature of the sys tem The accepted breakdown of a power system containing generation, transmission, and distribution is into three hierarchical levels. The first level is for the generation facilities alone, the second level contains generation and transmission,while the third level contains generation, transmission, and distribution facilities. Much of the early work was focused on the generation facilities. The reasons for this was that, first, more information was available about the generation; second, the size of the problem was smaller; and, third, the emphasis of power systems was placed in generation. With the onset of deregulation, distribution and customer requirements are ed paramount. At the generation and transmission levels, the loss of load expectation and frequency and duration evaluation re prime reliability indicators. a power system component may well have several derated states along with the fully operational and non-operational states. Recursive techniques are available to construct the system models and they can include multi-state components The usual method for evaluating reliability indices at the distribution level, such duration per customer per year, is an analytical approach based on a failure modes assessment and the use of equations for series and parallel networks. Economic Dispatch and Unit Commitment Many programs are devoted to power system operational problems and the minimization of the cost of production and delivery of energy is of great importance. Two types of program which deal with this problem are economic dispatch and unit commitment. Economic dispatch uses optimization techniques to determine the level of power each generator(unit)must supply to the system in order to meet the demand. Each unit must have its generating costs, which will be nonlinear functions of energy, defined along with the units operational maximum and minimum power limits The transmission losses of the system must also be taken into account to ensure an overall minimum cost Unit commitment calculates the necessary generating units that should be connected (committed)at any time in order to supply the demand and losses plus allow sufficient reserve increase or accidental loss of a generating unit. Several operating restrictions must be taken into account when determining which machines to commit or decommit. These include maximum and minimum running times for a unit and the time needed to commit a unit. Fuel availability constraints must also be considered. For ample, there may be limited fuel reserves such as coal stocks or water in the dam. Other fuel constraints may be minimum water flows below the dam or agreements to purchase minimum amounts of fuel. Determining Init commitment for a specific time cannot be evaluated without consideration of the past operational con- figuration or the future operating demands. 68.3 The Second Generation of programs It is not the intention to suggest that only the above programs were being produced initially. However, most of the other programs remained as either research tools or one-off analysis programs. The advent of the PC gave a universal platform on which most users and programs could come together. This process was further assisted when windowing reduced the need for such a high level of computer literacy on the part of users. For c 2000 by CRC Press LLC© 2000 by CRC Press LLC Reliability Of constant concern to the operators of power systems is the reliability of equipment. This has become more important as systems are run harder. In the past, reliability was ensured by building in reserve equipment which was either connected in parallel with other similar devices or could be easily connected in the event of a failure. Not only that, knowledge of the capabilities of materials has increased so that equipment can be built with a more certain level of reliability. However, reliability of a system is governed by the reliability of all the parts and their configuration. Much work has been done on the determination of the reliability of power systems but work is still being done to fully model power system components and integrate them into system reliability models. The information that is obtained from reliability analysis is very much governed by the nature of the system. The accepted breakdown of a power system containing generation, transmission, and distribution is into three hierarchical levels. The first level is for the generation facilities alone, the second level contains generation and transmission, while the third level contains generation, transmission, and distribution facilities. Much of the early work was focused on the generation facilities. The reasons for this was that, first, more information was available about the generation; second, the size of the problem was smaller; and, third, the emphasis of power systems was placed in generation. With the onset of deregulation, distribution and customer requirements are now considered paramount. At the generation and transmission levels, the loss of load expectation and frequency and duration evaluation are prime reliability indicators. A power system component may well have several derated states along with the fully operational and non-operational states. Recursive techniques are available to construct the system models and they can include multi-state components. The usual method for evaluating reliability indices at the distribution level, such as the average interruption duration per customer per year, is an analytical approach based on a failure modes assessment and the use of equations for series and parallel networks. Economic Dispatch and Unit Commitment Many programs are devoted to power system operational problems and the minimization of the cost of production and delivery of energy is of great importance. Two types of program which deal with this problem are economic dispatch and unit commitment. Economic dispatch uses optimization techniques to determine the level of power each generator (unit) must supply to the system in order to meet the demand. Each unit must have its generating costs, which will be nonlinear functions of energy, defined along with the units operational maximum and minimum power limits. The transmission losses of the system must also be taken into account to ensure an overall minimum cost. Unit commitment calculates the necessary generating units that should be connected (committed) at any time in order to supply the demand and losses plus allow sufficient reserve capability to withstand a load increase or accidental loss of a generating unit. Several operating restrictions must be taken into account when determining which machines to commit or decommit. These include maximum and minimum running times for a unit and the time needed to commit a unit. Fuel availability constraints must also be considered. For example, there may be limited fuel reserves such as coal stocks or water in the dam. Other fuel constraints may be minimum water flows below the dam or agreements to purchase minimum amounts of fuel. Determining unit commitment for a specific time cannot be evaluated without consideration of the past operational con- figuration or the future operating demands. 68.3 The Second Generation of Programs It is not the intention to suggest that only the above programs were being produced initially. However, most of the other programs remained as either research tools or one-off analysis programs. The advent of the PC gave a universal platform on which most users and programs could come together. This process was further assisted when windowing reduced the need for such a high level of computer literacy on the part of users. For