Voltage Collapse Steady state analysis of the problem of voltage instability and voltage collapse are often based on load flow analysis programs. However, time solutions can provide further insight into the problem A transient stability program can be extended to include induction machines which are associated with many of the voltage collapse problems. In these studies, it is the stability of the motors that are examined rather than the stability of the synchronous machines. The asynchronous nature of the induction machine means that rotor angle is not a concern, but instead the capability of the machines to recover after a fault has depressed the voltage and allowed the machines to slow down. The re-accelerating machines draw more reactive current which can hold the terminal voltage down below that necessary to allow recovery. Similarly starting a machine will depress the voltage which affects other induction machines which further lowers the voltage. However, voltage collapse can also be due to longer term problems. Transient stability programs then need to take into account controls that are usually ignored. These include automatic transformer tap adjustment and generator excitation limiters which control the long-term reactive power output to keep the field currents nin their rated values The equipment that can contribute to voltage collapse must also be more carefully modeled. Simple imped ance models for loads(P=PoVQ=Q V2)are no longer adequate. An improvement can be obtained by replacing the (mathematical) power 2 in the equations by more suitable values. Along with the induction machine models, the load characteristics can be further refined by including saturation effects. SCADA SCADA(Supervisory Control And Data Acquisition)has been an integral part of system control for many years. A control center now has much real time information available so that human and computer decisions about system operation can be made with a high degree of confidence. In order to achieve high quality input data, algorithms have been developed to estimate the state of a system based on the available on-line data ( state estimation). These methods are based on weighted least squares techniques to find the best state vector to fit the scatter of data. This becomes a major problem when conflicting information is received. However, as more data becomes available, the reliability of the estimate can be improved. ower Quality One form of poor power quality which has received a large amount of attention is the high level of harmonics that can exist and there are numerous harmonic analysis programs now available Recently, the harmonic levels of both currents and voltages have increased considerably due to the increasing use of non-linear loads such as arc furnaces, HVdc converters, FACTS equipment, dc motor drives, and ac motor speed control. Moreover, commercial sector loads now contain often unacceptable levels of harmon due to widespread use of equipment with rectifier-fed power supplies with capacitor output smoothing(e.g computer power supplies and fluorescent lighting). The need to conserve energy has resulted in energy efficient designs that exacerbate the generation of harmonics. Although each source only contributes a very small level of harmonics, due to their small power ratings, widespread use of small non-linear devices may create harmonic problems which are more difficult to remedy than one large harmonic source Harmonic analysis algorithms vary greatly in their algorithms and features; however, almost all use the frequency domain. The most common technique is the direct method (also known as current injection method Spectral analysis of the current waveform of the non-linear components is performed and entered into the program. The network data is used to assemble a system admittance matrix for each frequency of interest. Thi set of linear equations is solved for each frequency to determine the node voltages and, hence, current flow hroughout the system. This method assumes the non-linear component is an ideal harmonic current source. The next more advanced technique is to model the relationship between the harmonic currents injected by a component to its terminal voltage waveform. This then requires an iterative algorithm, which does require c 2000 by CRC Press LLC© 2000 by CRC Press LLC Voltage Collapse Steady state analysis of the problem of voltage instability and voltage collapse are often based on load flow analysis programs. However, time solutions can provide further insight into the problem. A transient stability program can be extended to include induction machines which are associated with many of the voltage collapse problems. In these studies, it is the stability of the motors that are examined rather than the stability of the synchronous machines. The asynchronous nature of the induction machine means that rotor angle is not a concern, but instead the capability of the machines to recover after a fault has depressed the voltage and allowed the machines to slow down. The re-accelerating machines draw more reactive current which can hold the terminal voltage down below that necessary to allow recovery. Similarly starting a machine will depress the voltage which affects other induction machines which further lowers the voltage. However, voltage collapse can also be due to longer term problems. Transient stability programs then need to take into account controls that are usually ignored. These include automatic transformer tap adjustment and generator excitation limiters which control the long-term reactive power output to keep the field currents within their rated values. The equipment that can contribute to voltage collapse must also be more carefully modeled. Simple imped￾ance models for loads (P = PoV2 ; Q = QoV2) are no longer adequate. An improvement can be obtained by replacing the (mathematical) power 2 in the equations by more suitable values. Along with the induction machine models, the load characteristics can be further refined by including saturation effects. SCADA SCADA (Supervisory Control And Data Acquisition) has been an integral part of system control for many years. A control center now has much real time information available so that human and computer decisions about system operation can be made with a high degree of confidence. In order to achieve high quality input data, algorithms have been developed to estimate the state of a system based on the available on-line data (state estimation). These methods are based on weighted least squares techniques to find the best state vector to fit the scatter of data. This becomes a major problem when conflicting information is received. However, as more data becomes available, the reliability of the estimate can be improved. Power Quality One form of poor power quality which has received a large amount of attention is the high level of harmonics that can exist and there are numerous harmonic analysis programs now available. Recently, the harmonic levels of both currents and voltages have increased considerably due to the increasing use of non-linear loads such as arc furnaces, HVdc converters, FACTS equipment, dc motor drives, and ac motor speed control. Moreover, commercial sector loads now contain often unacceptable levels of harmonics due to widespread use of equipment with rectifier-fed power supplies with capacitor output smoothing (e.g., computer power supplies and fluorescent lighting). The need to conserve energy has resulted in energy efficient designs that exacerbate the generation of harmonics. Although each source only contributes a very small level of harmonics, due to their small power ratings, widespread use of small non-linear devices may create harmonic problems which are more difficult to remedy than one large harmonic source. Harmonic analysis algorithms vary greatly in their algorithms and features; however, almost all use the frequency domain. The most common technique is the direct method (also known as current injection method). Spectral analysis of the current waveform of the non-linear components is performed and entered into the program. The network data is used to assemble a system admittance matrix for each frequency of interest. This set of linear equations is solved for each frequency to determine the node voltages and, hence, current flow throughout the system. This method assumes the non-linear component is an ideal harmonic current source. The next more advanced technique is to model the relationship between the harmonic currents injected by a component to its terminal voltage waveform. This then requires an iterative algorithm, which does require