Transient Stability Evaluation Research Articles

On-Line Transient Stability Evaluation by System Decomposition-Aggregation and High Order Derivatives

An on-line transient stability evaluation method is presented in this paper. Under some classical assumptions, the change of generator rotor angles during the transient period is described by a set of second order differential equations. This set of equations is solved by single-step high order derivative explicit integration. A new system decomposition-aggregation technique is proposed to decompose the power system into subsystems and then to aggregate the subsystems by interconnection boundary conditions. Based on the aggregation model, the calculation of high-order derivatives is quite efficient to reduce the requirements of both computer memory and computational time for a large scale power system. The relation of memory and execution time requirements to the system decomposition is discussed. Two systems, the IEEE 118 bus test system with 34 generators and a 293 bus system with 63 generators, are tested by simulation on a CDC-6600 computer. The results demonstrate that the proposed method is effective for on-line application and may be faster than Liapunov's direct method.

On-Line Transient Stability Evaluation by System Decomposition-Aggregation and High Order Derivatives

On-Line Transient Stability Evaluation by System Decomposition-Aggregation and High Order Derivatives

Dynamic Performance Characteristics of North American HVDC Systems for Transient and Dynamic Stability Evaluations

Dynamic Performance Characteristics of North American HVDC Systems for Transient and Dynamic Stability Evaluations

Dynamic Performance Characteristics of North American HVDC Systems for Transient and Dynamic Stability Evaluations

This paper surveys the important dynamic performance parameters of two-terminal HVdc systems. Specific HVdc systems included are the Pacific HVdc Intertie, the Nelson River Bipoles 1 and 2, the Eel River and Stegall back-to-back ties, the CPA-UPA (CU) and the Square Butte HVdc systems and the Vancouver Island cable system. The parameters tabulated (Table 1) and the dynamic performance features described should be sufficient for dynamic performance evaluations of the corresponding ac/dc systems by means of generally available transient and dynamic stability programs. These characteristics of existing HVdc systems may influence the modeling and design of future HVdc systems for transmission planning studies.

Protection System Modelling in a Probabilistic Assessment of Transient Stability

The application of probability methods in the evaluation of power system transient stability has been demonstrated in recent papers1-3. A probabilistic index for transient stability was developed which in addition to considering the random variations in the operating conditions, included the probabilistic aspects associated with the type, location and clearance of the system faults. It was realized during these studies that there was a need to develop stochastic models for the protection system behaviour which include the actual design aspects. The operational behaviour of the protection system is an important component in the high degree of security and service continuity associated with bulk power systems. This paper illustrates an approach used to model the protection system in the probabilistic assessment of transient stability. The probability density functions of the operating times associated with the components of the protection system such as relays, breakers, etc. are used in conjunction with the reliabilities of the main and back-up protection schemes to obtain the probability density functions of the fault clearing time for different fault locations. These density functions are used together with the critical fault clearing time for a given fault type and location to obtain a probabilities index for transient stability. A simple distance impedance protection system is used to illustrate the procedure. Continuous as well as discrete density functions for the operating times of the protection system components are used. This paper illustrates the basic probabilistic nature of the fault clearing phenomenon and its importance in transient stability assessment.

A Structure Preserving Model for Power System Stability Analysis

A new model for the study of power system stability via Lyapunov functions is proposed. The key feature of the model is an assumption of frequency-dependent load power, rather than the usual impedance loads which are subsequently absorbed into a reduced network. The original network topology is explicitly represented. This approach has the important advantage of rigorously accounting for real power loads in the Lyapunov functions. This compares favorably with existing methods involving approximations to allow for the significant transfer conductances in reduced network models. The preservation of network topology can be exploited in stability analysis, with the concepts of critical and vulnerable cutsets playing central roles in dynamic and transient stability evaluation respectively. Of fundamental importance is the feature that the Lyapunov functions give a true representation of the spatial distribution of stored energy in the system

A probabilistic assessment of transient stability

Transient stability assessment deals with the performance of a system when subjected to large disturbances such as faults, sudden loss of load or generation, and line switching. Most of the work carried out in this area has been based on deterministic models. The probabilistic nature of the problem and a method for considering the probabilities associated with the type, location and clearance of system faults have been illustrated in recent papers. The present paper includes the probabilities associated with basic initiating factors in the stability evaluation. Two simple systems have been used to illustrate the results: a single machine, infinite bus system and a 6-bus multimachine system model based on the Saskatchewan Power Corporation transmission system. The impact of different fault types on the transient stability of the system is demonstrated, and a single index of the stability of the overall system for different faults is developed. The difficulties and possible methods of solving transient stability evaluation problems are indicated from a practical system viewpoint.

A Probabilistic Index for Transient Stability

Transient stability evaluation is normally done using fixed system criteria. A particular generation-load- transmission system is subjected to a predetermined perturbation, usually a single phase or three phase fault and the resulting response evaluated. This paper illustrates the inclusion of probabilistic considerations into the transient stability evaluation problem by application to a simple system. A stability index based upon the probabilistic nature of the system is developed and examined for sensitivity to selected system parameters.

Probabilistic considerations in transient stability assessment

Discusses transient stability evaluation of a power system from a probabilistic viewpoint. The random nature of the basic factor such as the type, location, and clearance of faults which affect the transient stability performance is demonstrated. Consideration of these aspects for simple single machine-infinite bus and multimachine systems is illustrated using two example systems. Methods of extending the basic approach to practical systems together with the difficulties and possible methods of solution in a comprehensive analysis are indicated.

Probabilistic evaluation of transient stability in a multimachine power system

There has been continuous development of better techniques for assessing transient instability in a power system. It has also been recognised that there is a need for additional indices of transient stability which more completely reflect all the factors that influence system stability. The bulk of the work in this area is based on deterministic models. The probabilistic nature of the basic factors which affect transient-stability performance of a power system has been demonstrated in recent papers.1,4 This paper illustrates the inclusion of probabilistic considerations in transient-stability analysis of a practical power system by application to a multimachine configuration. A relatively simple multimachine system is used to demonstrate the technique of considering the probabilities associated with the type, location and clearance of faults. The approach in this paper is not restricted by the simplifying assumptions made in Reference 4. Reliability levels for different fault types and fault locations are evaluated, and the effect of variation of selected system parameters on the overall reliability of the system is investigated.

Dynamic models and control strategies for wastewater treatment processes

Consideration of dynamic behavior and the incorporation of modern control systems can lead to substantial improvements in the performance of wastewater treatment plants. Other potential benefits include increased productivity, greater reliability, lower operational costs, more stable operation and faster start-ups. Several powerful tools are available for the study of dynamic behavior. Included among these are dynamic mathematical models, computer simulation, transient response analysis and process stability evaluation. Simple examples illustrating the theory and use of these tools are presented. The development of a control strategy is intimately related to the dynamic behavior of a process. Some of the basic questions which must be answered in developing a control strategy are: (1) What information should be collected? (2) How should the information be transmitted? (3) How should the information be processed? (4) What control actions should be taken? A wide variety of control algorithms are available for the processing of information for control. A discussion of several of these, on-off, PID. ratio, cascade, and feedforward, is presented and an example is given for the application of on-off control to a biological CFSTR. Digital computers are also being increasingly used for control of wastewater treatment plants and a discussion of computer control systems is presented. Examples of dynamic models and control strategies for two wastewater treatment processes, the step feed activated sludge process and the anaerobic digester, are presented and discussed, In addition, dynamic modeling and computer simulations are used to indicate those design and operational factors for the anaerobic digester which are effective in improving process stability. An effective control strategy for the activated sludge process is that provided by the step feed process which permits changing the points at which wastewater is added along the length of the reactor. Example control strategies for the anaerobic digester include the addition of base and the recirculation of the digested sludge. The effectiveness of the control strategy is dependent upon the type of forcing to which the digester is subjected.

Bibliography on the Application of Probability Methods In Power System Reliability Evaluation

This paper presents a bibliography of papers on the subject of power system reliability evaluation. Papers in such areas as: probabilistic load flow, probabilistic production costing, probabilistic transient stability evaluation, etc. have not been included except where they specifically address power system reliability evaluation. It includes material which has become available since the publication of the four previous papers. 'Bibliography on the Application of Probability Methods in Power System Reliability Evaluation', IEEE Trans. On Power Apparatus and Systems PAS-91, 1972, p.649-660; PAS-97, 1978, p.2235-2242; PAS-103, 1984, p.275-282 and IEEE Trans. On Power Systems, vol.3, no.4,p.1555-1564, 1984. The authors have endeavored to include papers which are readily archival on an international basis. Consequently, the proceedings of such conferences as: CIGRE, Inter-RAM, PMAPS, etc. are regretfully not included. Due to space constraints, only papers written in English were considered for inclusion in this bibliography. >