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Today an average transmission line is loaded more heavily than ever before and this has given rise to serious problem of voltage instability. A noble method for power system voltage instability estimation and improvement using ANN is presented The method is based on the fan that reactive power injections at critical buses of the power system help to steer the system away from a developing voltage collapse. The location and quantum of reactive power support has been computed based on sensitivity. The sensitivity matrix is formulated by cascading the output/input sensitivity of multiplayer perceptron model with that of input features versus reactive power injections. The effectiveness of the proposed method is demonstrated on Ward-Hale 6-bus, IEEE14-bus and IEEE 30-bus test systems. The method can be effectively used to make the system secure against voltage collapse condition in system planning and on-line operation.

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Electrical Engineering

(SoE) School of Engineering

Journal of the Institution of Engineers (India): Electrical Engineering Division

Sensitivity based approach for voltage instability alleviation using ANN

Today an average transmission line is loaded more heavily than ever before and this has given rise to serious problem of voltage instability. A noble method for power system voltage instability estimation and improvement using ANN is presented. The method is based on the fact that reactive power injections at critical buses of the power system help to steer the system away from a developing voltage collapse. The location and quantum of reactive power support has been computed based on sensitivity. The sensitivity matrix is formulated by cascading the output/input sensitivity of multiplayer perceptron model with that of input features versus reactive power injections. The effectiveness of the proposed method is demonstrated on Ward-Hale 6-bus, IEEE 14-bus and IEEE 30-bus test systems. The method can be effectively used to make the system secure against voltage collapse condition in system planning and on-line operation. © 2003 Elsevier Science Ltd. All rights reserved.

International Journal of Electrical Power and Energy System

Sensitivity based voltage instability alleviation using ANN

This paper presents computationally efficient artificial neural network technique for assessing the security of the power system against line outages. Performance index (PI), which accounts for various line limit violations per contingency, is defined. The basic purpose of ANN is to assess the severity of line outages in terms of PI, based on training examples from off-line analysis. The selection of input signals for ANN is influenced by the operating state of the system and the contingency in question which determines the extent of line power limit violations. In an attempt to attain perfection in PI prediction, suitable architecture and topology for the network is investigated. To expedite learning process, saturating linear coupled neuron model (sl-CONE) is also tried out. The effectiveness of proposed technique is demonstrated on 5-bus (7-line) and IEEE 14-bus (21-line) test systems. Computation efficiency of the method makes it potential candidate for inclusion in on-line comprehensive security analysis package. © 2002 Elsevier Science Ltd. All rights reserved.

International Journal of Electrical Power and Energy Systems

ANN for transmission system static security assessment

This paper presents a comparative performance evaluation of SVS auxiliary controllers for transient stability enhancement of long transmission lines. A new controller, namely, the Combined Reactive Power and Frequency (C.R.P.F.) auxiliary controller, has been developed for the SVS located at the middle of the transmission line. The application of auxiliary controllers considerably enhances the system damping, and unstable system modes are stabilized. A digital computer simulation study has been performed to illustrate the comparative effectiveness of the auxiliary controllers under disturbance conditions, and the superiority of the C.R.P.F. auxiliary controller has been established.

International Journal of Power and Energy Systems

Application of SVS auxiliary controllers for power system control

Owing to frequent black-outs world wide, voltage collapse has received much attention in the electric utilities industry. This paper presents an artificial neural network based method for on-line voltage collapse margin estimation. Homotopy Continuation based Newton-Raphson method is used to drive system operating point to knee of nose curve. The distance of operating point from critical point, measured in terms of system loading may be regarded as margin to voltage collapse. This paper utilizes Kohonen classifier to estimate margin so that computational efforts are reduced compared to conventional methods. Also there is ample of saving in training time compared to error back propagation for parameter estimation. Kohonen neural network classifier transforms input patterns into neurons on the 2-dimensional grid. Power system conditions are assigned to neurons on the grid based on self-organized feature mapping. Finally these neurons are allocated voltage collapse margins corresponding to their system conditions representation. The effectiveness of the proposed technique is tested on sample systems. © 1997 Taylor & Francis.

Electric Machines and Power Systems

Kohonen neural network classifier for voltage collapse margin estimation

With the growing stress on today's power system, it is operated much closer to its stability limit. Under such circumstances it is highly desirable that one must be able to assess the security and stability of the electric power system when exposed to disturbances/faults. In the post-fault transient analysis of interconnected systems, the transient energy margin which is a complex function of prefault system conditions, structure of fault (type and location) and network topology at the specified fault clearing time gives a quantitative idea about the stability of the system. High adaptation capabilities of artificial neural networks make them capable of synthesizing the complex mapping that transform the input features in to a single-valued space of energy margin. Appropriate input feature selection has a direct bearing on the consistency and accuracy of mapping. This issue has been addressed in the present paper by comparing the prediction results based on approaches (Sobajic and Pao, 1989), (Sobajic and Pao 1992), (Jeyasurya, 1993) in the time domain, energy domain and its corresponding time domain calibration. Subsequent to the above comparison, the much haunting question of whether to train the network in the energy or time domain has been answered satisfactorily. It has been observed that fault clearing time is a key parameter that anticipates the success of possible calibration of energy margin results into the time domain. Test cases for prediction have been collected from many different operating conditions in power systems. Multilayer perceptron model with ADAPTIVE LEARNING ALGORITHM is used to carry out the present studies. © 1997 Taylor & Francis.

Input-features based comparative study of intelligent transient stability assessment

In the present work, an artificial neural network technique is applied to determine the distance from system operating point to voltage collapse. The distance is measured in terms of the existing loading/generating scenario. The critical/bifurcation point is approached in steps while moving along the nose curve. Generation resheduling is done at each step to ensure economical operation of the system. The homotopy continuation-based Newton Raphson load flow method takes care of numerical instabilities associated with the singularity of Jacobian while approaching critical point. Proximity to critical loading of present operating point is a complex function of operating point attributes and loading/generating pattern followed to approach voltage collapse. The high adaptation capabilities of artificial neural networks make it feasible to synthesize the function that maps system state attributes (bus power injections and tap settings of transformers) to distance from, voltage collapse for uniform dispatch strategy. A three-layer (one hidden layer) feed-forward artificial neural network (ANN) is trained to predict the nearness of current operating point to voltage collapse in terms of existing loading condition. It has been demonstrated here that the predicted values are well in tune with their actual ones. The technique is tested on a Ward-Hale 6-bus system and an IEEE 14-bus system.

Ann-based voltage collapse proximity prediction

In the present paper the coordinated application of the controlled series compensation (CSC) and the SVS auxiliary controllers has been demonstrated for the dynamic and transient performance enhancement of a series compensated long transmission line. SVS controller, known as the combined reactive power and frequency (CRPF) auxiliary controller, has been developed and incorporated in the SVS control system located at the middle of the transmission line. The application of the auxiliary controllers, considerably, enhances the system damping and the unstable system modes are stabilized. To improve the transient performance, the CSC having bang-bang control characteristics has been incorporated. A digital simulation study, using a nonlinear system model, has been performed to illustrate the comparative effectiveness of the CSC and the SVS auxiliary controllers developed.

Application of CSC and SVS auxiliary controllers for flexible ac transmission systems

The steady state and dynamic performance of a flexible AC transmission system (FACTS) with midpoint located SVS has been presented with and without series compensation. The maximum capacitor of SVS branch in case of line without series compensation, is split into two locations. Two third of it is at the sending end for the purpose of series compensation and one third remains at SVS branch. This has the advantage of reduced ‘δ’ without upsetting greatly the cost economy of equipment. The degree of series compensation thus obtained is used to evaluate the steady state and dynamic performance of series compensated transmission line. The results are then compared over a wide operating range. The line reactive power auxiliary controller and bus frequency auxiliary controller are employed in the SVS control system to stabilize the unstable system modes and the performance of the two auxiliary controllers is also compared over wide operating conditions. It has been established here that such a series capacitor compensated line can give improved static and dynamic performance at a reduced value of δ. © 1996 Taylor & Francis.

A flexible ac transmission system “steady state and dynamic performance analysis”

This paper presents a robust artificial neural network technique to assess the on-line dynamic stability of power system. Efforts have been made to minimize the error in dynamic stability assessment by optimising the size and introducing more sensitive information in training vector. The problem has been attempted with Kohonen's self-organising feature map (SOFM) to classify the states of power system. The main reason which inspired the authors to apply Kohonen's SOFM technique is to avoid local minima that saturate the learning process in back-propagation algorithm. Conventional QR algrithm in conjunction with S-matrix method is used to allocate dynamic stability indices to output neurons. © 1996 Taylor & Francis.

A robust artificial neural network technique for dynamic stability assessment

In the present paper a comparative performance of the SVS auxiliary controllers for the dynamic performance enhancement of long transmission lines with and without series compensation has been evaluated. A new controller, namely, combined reactive power and frequency (CRPF) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of the transmission line. The proposed SVS auxiliary controllers, considerably, enhances the system damping and the unstable system modes are stablized. A digital computer simulation study, using a nonlinear system model, has been performed to illustrate the performance of the proposed controller.

SVS Auxiliary Controllers to Improve the Dynamic Performance of Long Transmission Lines with and without Series Compensation

In this paper a novel concept of a static var system (SVS) auxiliary controller application for damping subsynchronous resonance in power systems has been proposed and demonstrated. An SVS controller, known as the combined reactive power and frequency (CRPF) auxiliary controller has been developed and incorporated in the SVS control system located at the middle of a series compensated long transmission line. The studies are conducted on a system having a similar spread of the torsional modes as the first IEEE benchmark model. The proposed SVS auxiliary controller stabilizes all the torsional modes over a wide operating range. A digital computer simulation study has been performed, using a nonlinear system model, to illustrate the effectiveness of the proposed SVS auxiliary controller.

Electric Power Systems Research

Application of an auxiliary controlled static var system for damping subsynchronous resonance in power systems

In this paper the coordinated application of the controlled series compensation (CSC) and the SVS auxiliary controllers has been demonstrated for the dynamic and transient performance enhancement of a series compensated long transmission line. An SVS controller, known as the combined reactive power and frequency (C.R.P.F.) auxiliary controller, has been developed and incorporated in the SVS control system located at the middle of the transmission line. A digital computer simulation study, using a nonlinear system model, has been performed to illustrate the comparative effectiveness of the CSC and the SVS auxiliary controllers developed.

Proceedings of the IEEE International Conference on Power Electronics, Drives & Energy Systems for Industrial Growth, PEDES

Auxiliary controlled SVS and controlled series compensation for flexible AC transmission systems

The paper presents a comparative performance evaluation of SVS auxiliary controllers for transient stability enhancement of long transmission lines over a wide operating range. The SVS has been considered located at the middle of the transmission line. The application of the auxiliary controllers considerably enhances the system damping and unstable system modes are stabilized. A new controller, namely Combined Reactive Power and Frequency (C.R.P.F.) auxiliary controller, has been developed for the SVS located at the middle of the transmission line. To illustrate the comparative effectiveness of the auxiliary controllers under disturbance condition, a digital computer simulation study has been performed. © 1996 Taylor & Francis.

Static var system auxiliary controllers for transient stability improvement of power systems

The paper presents a comparative assessment of the static var system (SVS) bus frequency and line reactive power auxiliary controllers for the transient performance enhancement of series compensated long transmission lines. A new controller, namely, the combined reactive power and frequency (CRPF) auxiliary controller, has been developed and incorporated in the static var control system located at the middle of the transmission line. The series compensation is provided at the sending end of the line. The application of the auxiliary controllers considerably enhances the system damping and the unstable system modes are stabilized. A digital computer simulation study has been performed to compare the effectiveness of the auxiliary controllers under disturbance conditions and the superiority of the (CRPF) auxiliary controller has been established over the other auxiliary controllers. © 1995.

Application of static var system auxiliary controllers to improve the transient performance of series compensated long transmission lines

A static VAR system has been considered located at the middle of a long transmission line, and the effect of the SVS auxiliary controllers on the system dynamic performances has been examined over a wide range of operating conditions. The performance of auxiliary controllers has been studied when a reduced order network model, represented by a lumped parameter T-circuit, is used. The performance is compared with a system having a network model represented by single lumped parameter π-circuit on either side of SVS. It is observed that the size of the system matrix reduces significantly when the reduced order model is used. Also The accuracy of the eigenvalues of the system Is not much affected. The application of the auxiliary controllers, considerably, increases the system damping and unstable system modes are stabilized. © 1995 Taylor & Francis Group, LLC.

Auxiliary control of static var system to improve the dynamic performance of long transmission lines

The transient stability of a turboalternator, connected to an infinite busbar through a reactive tieline, is investigated through Liapunov's direct method. The machine is fitted with an automatic voltage regulator (AVR) sensing the machine terminal voltage and its first time derivative. The AVR time lag is ignored and it feeds the machine directly. The governor is actuated by the load-angle deviation and its first two derivatives, and is represented by a differential equation involving one or two time lags only. The variation in the rotor direct, and quadrature-axis flux linkages has been included in the system model. Under different approximations, mathematical models for the AVR are suggested. Liapunov functions are proposed and the effect of variation in parameters of the AVR and governor on the critical fault clearing time, for a three-phase fault, is studied.

TRANSIENT STABILITY OF TURBOALTERNATOR THROUGH LIAPUNOV'S DIRECT METHOD.

The paper presents 0-1 integer programming models for the control of maintenance expenditure on thermal generating units. Choosing a sound and effective maintenance policy reduces the system down-time and thus increases the revenue to the utility. The objective is aimed at selecting that sot of proposals which will maximize the not present value of its total expected return. The alternative proposals, the forecasts of the net present value of the returns associated with the alternatives, the number of repairmen required for each alternative, and cash outflow required over the next 5 years are available for the analysis. The problem is discussed both under conditions of certainty and uncertainty. A new, simple and efficient tree search method is developed for the solution of the problems. A computer algorithm is developed and results of computation are presented for sample applications. © 1976 Taylor and Francis Group, LLC.

International Journal of Systems Science

Optimal maintenance budgetary control in generating systems

In a recent letter by Phan and Kim,A a new definition of the multiple-root sensitivity is given. However, it may be pointed out that exactly the same definition was given some time agoB and is also included in some text books,Cand is used for the same reasons as advanced by the authors. © 1973, The Institution of Electrical Engineers. All rights reserved.