excursion into the time domain for modeling this interaction. When the fundamental (load flow) is also included, thus simulating the interaction between fundamental and harmonic frequencies, it is termed a harmonic power flow. The most advanced technique, which is still only a research tool, is the harmonic domain In this iterative technique one Jacobian is built-up that represents all harmonic frequencies. This allows coupling between harmonics, which occurs, for example, in salient synchronous machines, to be represented There are many other features that need to be considered, such as whether the algorithm uses symmetrical components or phase coordinates, or whether it is single-or three-Phase. Data entry for single-phase typically requires the electrical parameters, whereas three-phase analysis normally requires the physical geometry of the overhead transmission lines and cables and conductor details so that a transmission line parameter program or cable parameter program can calculate the line or cable electrical parameters The communication link between the monitoring point and the control center can now be very sophisticated and can utilize satellites. This technology has led to the development of systems to analyze the power quality of a system. Harmonic measurement and analysis has now reached a high level of maturity. Many different pieces of information can be monitored and the results over time stored in a database Algorithms based on the fast Fourier transform can then be used to convert this data from the time domain to the frequency domain. Computing techniques coupled with fast and often parallel computing allows this information to be displayed in real time. By utilizing the time stamping capability of the global positioning system(GPS), information gathered at remote sites can be linked together. Using the GPS time stamp, samples taken exactly simultaneously can be feed to a harmonic state estimator which can even determine the position and magnitude of harmonics entering the system as well as the harmonic voltages and currents at points not monitored (provided enough initial monitoring points exist One of the most important features of harmonic analysis software is the ability to display the results graphically. The refined capabilities of present three-dimensional graphics packages has simplified the analy considerably. Finite element analysis Finite element analysis is not normally used by power system engineers although it is a common tool of high voltage and electrical machine engineers. It is necessary, for example, where accurate machine representation is required. For example, in a unit connected HVdc terminal the generators are closely coupled to the rectifier ridges. The ac system at the rectifier end is isolated from all but its generator. There is no need for costly filters to reduce harmonics. Models of the synchronous machine suitable for a transient stability study can be obtained from actual machine tests For fast transient analysis, a three-phase generator model can be used but it will not account for harmonics. A finite element model of the generator provides the means of allowing real time effects ch as harmonics and saturation to be directly included. Any geometric irregularities in the generator can be accounted for and the studies can be done at the design stage rather than having to rely on measurements or extrapolation from manufactured machines to obtain circuit parameters. There is no reliance on estimated machine parameters. The disadvantages are the cost and time to run a simulation and it is not suitable at present to integrate with existing transient stability programs as it requires a high degree of expertise. As the nite element model is in this case used in a time simulation, part of the air gap is left unmeshed in the model. At each time step the rotor is placed in the desired position and the missing elements in the air gap region formed using the nod ch side of the gap. grounding The safe grounding of power system equipment is very important, especially as the short circuit capability of power systems continues to grow. Programs have been developed to evaluate and design grounding systems in areas containing major power equipment, such as substations and to evaluate the effects of fault current on remote, separately grounded equipment. c 2000 by CRC Press LLC© 2000 by CRC Press LLC excursion into the time domain for modeling this interaction. When the fundamental (load flow) is also included, thus simulating the interaction between fundamental and harmonic frequencies, it is termed a harmonic power flow. The most advanced technique, which is still only a research tool, is the harmonic domain. In this iterative technique one Jacobian is built-up that represents all harmonic frequencies. This allows coupling between harmonics, which occurs, for example, in salient synchronous machines, to be represented. There are many other features that need to be considered, such as whether the algorithm uses symmetrical components or phase coordinates, or whether it is single- or three-phase. Data entry for single-phase typically requires the electrical parameters, whereas three-phase analysis normally requires the physical geometry of the overhead transmission lines and cables and conductor details so that a transmission line parameter program or cable parameter program can calculate the line or cable electrical parameters. The communication link between the monitoring point and the control center can now be very sophisticated and can utilize satellites. This technology has led to the development of systems to analyze the power quality of a system. Harmonic measurement and analysis has now reached a high level of maturity. Many different pieces of information can be monitored and the results over time stored in a database. Algorithms based on the fast Fourier transform can then be used to convert this data from the time domain to the frequency domain. Computing techniques coupled with fast and often parallel computing allows this information to be displayed in real time. By utilizing the time stamping capability of the global positioning system (GPS), information gathered at remote sites can be linked together. Using the GPS time stamp, samples taken exactly simultaneously can be feed to a harmonic state estimator which can even determine the position and magnitude of harmonics entering the system as well as the harmonic voltages and currents at points not monitored (provided enough initial monitoring points exist). One of the most important features of harmonic analysis software is the ability to display the results graphically. The refined capabilities of present three-dimensional graphics packages has simplified the analysis considerably. Finite Element Analysis Finite element analysis is not normally used by power system engineers although it is a common tool of high voltage and electrical machine engineers. It is necessary, for example, where accurate machine representation is required. For example, in a unit connected HVdc terminal the generators are closely coupled to the rectifier bridges. The ac system at the rectifier end is isolated from all but its generator. There is no need for costly filters to reduce harmonics. Models of the synchronous machine suitable for a transient stability study can be obtained from actual machine tests. For fast transient analysis, a three-phase generator model can be used but it will not account for harmonics. A finite element model of the generator provides the means of allowing real time effects such as harmonics and saturation to be directly included. Any geometric irregularities in the generator can be accounted for and the studies can be done at the design stage rather than having to rely on measurements or extrapolation from manufactured machines to obtain circuit parameters. There is no reliance on estimated machine parameters. The disadvantages are the cost and time to run a simulation and it is not suitable at present to integrate with existing transient stability programs as it requires a high degree of expertise. As the finite element model is in this case used in a time simulation, part of the air gap is left unmeshed in the model. At each time step the rotor is placed in the desired position and the missing elements in the air gap region formed using the nodes on each side of the gap. Grounding The safe grounding of power system equipment is very important, especially as the short circuit capability of power systems continues to grow. Programs have been developed to evaluate and design grounding systems in areas containing major power equipment, such as substations and to evaluate the effects of fault current on remote, separately grounded equipment