example, electromagnetic transient programs generality, which made it so successful, is also a handicap and it quires good programming skill to utilize it fully. This has lead to several commercial programs that are loosely based on the methods of analysis first used in by the electromagnetic transient program. They have the advantage of a much improved user interface. Not all software is run on PCs. Apart from the Macintosh, which has a similar capability to a PC but which is less popular with engineers, more powerful workstations are available usually based on the Unix operating system. Mini computers and mainframe computers are also still in general use in universities and industry even Hardware and software for power system operation and control required at utility control centers is usually sold as a total package. These systems, although excellent, can only be alluded to here as the information is proprietary. The justification for a particular configuration requires input from many diverse groups within the utility. graphics Two areas of improvement that stand out in this second wave of generally available programs are both asso with the graphical capabilities of computers. A good diagram can be more easily understood than many of text or tables The ability to produce graphical output of the results of an analysis has made the use of computers in all engineering fields, not just power system analysis, much easier. Tabulated results are never easy to interpret. They are also often given to a greater degree of accuracy than the input data warrants a graph of the results, where appropriate, can make the results very easy to interpret and if there is also an ability to graph any variable with any other, or two if three dimensions can be utilized, then new and possibly significant information can g New packages became available for business and engineering which were based on either the spreadsheet or atabase principle. These also had the ability to produce graphical output. It was no longer essential to know programming language to do even quite complex engineering analysis. The programming was usually inef- ficient and obtaining results was more laborious, e.g., each iteration had to be started by hand. But, as engineers had to use these packages for other work, they became very convenient tools A word of caution here--be careful that the results are graphed in an appropriate manner. Most spreadsheet packages have very limited x-axis(horizontal)manipulation. Provided the x-axis data comes in regular steps, the results are acceptable. However, we have seen instances where very distorted graphs have been presented Apart from the graphical interpretation of results, there are now several good packages that allow the analy to enter the data graphically. It is a great advantage to be able to develop a one-line, or three-phase, diagram of a network directly with the computer. All the relevant system components can be included. Parameter data ill require entry in a more orthodox manner but by merely clicking on a component, a data form for that component can be made available. The chances of omitting a component are greatly reduced with this type of data entry. Further, the same system diagram can be used to show the results of some analyses An extension of the network diagram input is to make the diagram relate to the actual topography. In these cases the actual routes of transmission lines are shown and can be geographical maps. The lines in these cases have their lengths automatically established and, if the line char- acteristics are known, the line parameters can be calculated These topographical diagrams are an invaluable aid for power reticulation problems, for example, the minimum route length of reticulation given all the points of supply and the route constraints. Other optim zation algorithms include determination of line sizes and switching operations The analysis techniques can be either linear or nonlinear. If successful, the nonlinear algorithm is more accura ate but these techniques suffer from larger data storage requirements, greater computational time, and possible divergence. There are various possible optimization techniques that can and have been applied to this problem. There is no definitive answer and each type of problem may require a different choice The capability chart represents a method of graphically displaying power system performance. These charts are drawn on the complex power plane and define the real and reactive power that may be supplied from a c 2000 by CRC Press LLC© 2000 by CRC Press LLC example, electromagnetic transient program's generality, which made it so successful, is also a handicap and it requires good programming skill to utilize it fully. This has lead to several commercial programs that are loosely based on the methods of analysis first used in by the electromagnetic transient program. They have the advantage of a much improved user interface. Not all software is run on PCs. Apart from the Macintosh, which has a similar capability to a PC but which is less popular with engineers, more powerful workstations are available usually based on the Unix operating system. Mini computers and mainframe computers are also still in general use in universities and industry even though it had been thought that they would be totally superseded. Hardware and software for power system operation and control required at utility control centers is usually sold as a total package. These systems, although excellent, can only be alluded to here as the information is proprietary. The justification for a particular configuration requires input from many diverse groups within the utility. Graphics Two areas of improvement that stand out in this second wave of generally available programs are both associated with the graphical capabilities of computers. A good diagram can be more easily understood than many pages of text or tables. The ability to produce graphical output of the results of an analysis has made the use of computers in all engineering fields, not just power system analysis, much easier. Tabulated results are never easy to interpret. They are also often given to a greater degree of accuracy than the input data warrants. A graph of the results, where appropriate, can make the results very easy to interpret and if there is also an ability to graph any variable with any other, or two if three dimensions can be utilized, then new and possibly significant information can be quickly assimilated. New packages became available for business and engineering which were based on either the spreadsheet or database principle. These also had the ability to produce graphical output. It was no longer essential to know a programming language to do even quite complex engineering analysis. The programming was usually inef- ficient and obtaining results was more laborious, e.g., each iteration had to be started by hand. But, as engineers had to use these packages for other work, they became very convenient tools. A word of caution here—be careful that the results are graphed in an appropriate manner. Most spreadsheet packages have very limited x-axis (horizontal) manipulation. Provided the x-axis data comes in regular steps, the results are acceptable. However, we have seen instances where very distorted graphs have been presented because of this problem. Apart from the graphical interpretation of results, there are now several good packages that allow the analyst to enter the data graphically. It is a great advantage to be able to develop a one-line, or three-phase, diagram of a network directly with the computer. All the relevant system components can be included. Parameter data still require entry in a more orthodox manner but by merely clicking on a component, a data form for that component can be made available. The chances of omitting a component are greatly reduced with this type of data entry. Further, the same system diagram can be used to show the results of some analyses. An extension of the network diagram input is to make the diagram relate to the actual topography. In these cases, the actual routes of transmission lines are shown and can be superimposed on computer generated geographical maps. The lines in these cases have their lengths automatically established and, if the line char￾acteristics are known, the line parameters can be calculated. These topographical diagrams are an invaluable aid for power reticulation problems, for example, the minimum route length of reticulation given all the points of supply and the route constraints. Other optimi￾zation algorithms include determination of line sizes and switching operations. The analysis techniques can be either linear or nonlinear. If successful, the nonlinear algorithm is more accurate but these techniques suffer from larger data storage requirements, greater computational time, and possible divergence. There are various possible optimization techniques that can and have been applied to this problem. There is no definitive answer and each type of problem may require a different choice. The capability chart represents a method of graphically displaying power system performance. These charts are drawn on the complex power plane and define the real and reactive power that may be supplied from a