On-line Security Assessment Research Articles

An advanced control system for the optimal operation and management of medium size power systems with a large penetration from renewable power sources

An advanced control system for the optimal operation and management of autonomous wind-diesel systems is presented. This system minimises the production costs through an on-line optimal scheduling of the power units, which takes into account the technical constraints of the diesel units, as well as short-term forecasts of the load and renewable resources. The power system security is maximised through on-line security assessment modules, which enable the power system to withstand sudden changes in the production of the renewable sources. The control system was evaluated using data from the island of Lemnos, where it has been installed and operated since January 1995.

An extended ward equivalent approach for power system security assessment

A complete extended Ward equivalent approach is proposed for on-line security assessment of a power system. This new approach combines the off-line topological modelling of the extended Ward equivalent with on-line updating of the parameters of the equivalent model for representing real time topology changes of the external system. Test results indicate that the new equivalent model has an excellent response from the external system to the contingencies of the internal system.

Power System Planning and Operation in a Competitive Environment: the Contributions of Artificial Intelligence

Abstract Technical and economic reasons, as well as political decisions, are pushing for the restructuring and introduction of competition in the electricity industry. In this framework, new technical challenges arise, concerning power system planning and operation. Artificial intelligence can provide efficient solutions for some of these new problems: improved modelling of uncertainty, accurate on-line security assessment, customer modelling and control, decision-support systems for trading operations, etc.

DETERMINATION, BY KOHONEN NETWORK, OF THE GENERATOR COHERENCY IN DYNAMIC STUDIES

ABSTRACT For on-line security assessment, mere is a need for a tool which, during a disturbance, will quickly recognize impacted system components. A Kohonen artificial neural network is described which can be used for coherency identification among generators. Additional information provided by this method makes it better than the conventional approach used to identify coherency for dynamic equivalencing. The method is tested on two representative power systems.

On-line steady-state security assessment of power systems

Steady-state security assessment primarily addresses the question of the adequacy of generating and transmission capacity to meet load demand. In security assessment, there are two aspects of system failure that should be considered, namely, load curtailment and system collapse. The study of steady-state security has become essential, specially in modern large interconnected power systems. In this paper, a comprehensive conceptual framework and technique for on-line steady-state security assessment is suggested. As security of a power system is characterized in terms of power injections, namely, load demand and generation, the technique mainly depends on the idea of the partial solution of the electric power system. It assumes a subsystem built from three concentric tiers of buses around the faulted component while the rest of the power system outside the third tier is represented by the active and reactive power injections whose values are those before the contingency occurrence. The basic idea of the conceptual framework and technique for the unified approach to steady-state security assessment assumes that the changes are concentrated only inside the subsystem and those changes outside the third tier are small and can be neglected. The accuracy of the technique is compared with the exact solution, the full AC and DC solutions, of the selected IEEE 30-bus power system model with the same contingency cases and is found satisfactory.

A decision tree method for on-line steady state security assessment

In this paper the application of an inductive inference method to online steady state security assessment of a power system is proposed. For each contingency a number of decision rules in the form of a decision tree (DT) is built offline from a preclassified learning set consisting of operating points of the system. For the real time application of the method the DTs corresponding to the foreseen contingencies are searched online to provide optimal guidelines for preventive control of the system. The algorithm developed is applied to the steady state security assessment of a realistic model of the Hellenic interconnected power system comprising 240 busbars, 270 branches, 57 transformers and 30 equivalent generators. >

Parallel computation of power system dynamics using multistep methods

There is considerable interest in speeding up the dynamic simulation of power systems for on-line security assessment purposes. While software is being developed for automatically detecting parallelism in an otherwise serial code, research in developing parallel numerical algorithms is also useful. In this paper we develop a sequential algorithm that can be automatically converted (autotasked) to execute in parallel. We have also adapted an explicitly parallel algorithm for simulating the dynamics of a multimachine power system. Both were multistep predictor corrector algorithms and were implemented on a Cray 2 machine with four processors. Simulations were performed on four test systems (3, 10, 17 and 50 machines). While the speedups by both techniques are comparable, it is believed that continued research in numerical algorithms and their practical implementation is warranted. Autotasking may not always ensure the desirable spedups, since it may run into difficulties in certain instances.

Real-time data exchange for online security assessment-A report by the IEEE Task Force on Data Exchange for Security Assessment

The current status and near-term future goals of real-time data exchange for online security assessment of power systems in several regions of the United States are described from the viewpoint of the end-user application, namely, security assessment. An overview of the issues concerning data exchange for external network modeling is presented. Several data exchange systems are discussed. The following information is provided: description, justification of data exchange, uses for the data, types and quantities of the data exchanged, frequency of data exchange, impact of data exchange on system modeling detail, feasibility of implementing online security assessment without data exchange, exchange of supporting static data, efforts to establish and maintain data exchange, and problems/solutions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Application of Pattern Recognition in Transient Security Assessment

ABSTRACT One of the primary requirements of reliable service in electric power systems is to retain the synchronous machines running in parallel with adequate capacity to meet the load. In the normal operation of power systems, there may be faults or other large disturbances which have the potential of shifting the system operating point. Transient security assessment consists of determining whether the system oscillations, following the occurrence of a fault or a large disturbance from a contingency set, will cause loss of synchronism among the system generators. In order to have a highly reliable service, the system operating point has to be monitored and as soon as the system becomes vulnerable to a fault or disturbance, the control center should change the operating point of the system in a way to enhance its security. Pattern recognition is one of the promising methods for power system transient security assessment. The main objective of this method is to reduce the on-line computational requirement to a minimum. This paper is a review of the progress in the application of pattern recognition to power system transient security assessment. The recent results indicate that this method has reached a level of maturity that could be considered for on-line transient security assessment of real systems.

A conceptual ANN-ES scheme for power system security assessment and preventive control

Proposes a coupled artificial neural network-expert system (ANN-ES) scheme for on-line security assessment and preventive control of power systems. A conceptual scheme for this purpose is presented.

CQR: a hybrid expert system for security assessment

An offline prototype, called CQR, of a system for online security assessment has been built and tested in conjunction with a western Pennsylvania utility. CQR is a hybrid of rule-based programs written in OPS5 and numerical tools written in FORTRAN. CQR uses the utility's full power system model, accepts arbitrary operating conditions, evaluates the base case, evaluates a small number of AC contingency list using distribution factors, selects and evaluates a small number of AC contingencies, makes an explicit assessment of power system security, and presents results to the operator in a compact and understandable report. Security is decomposed into components that are evaluated independently, allowing separate criteria to be applied to the base case and contingencies. Transient stability is dealt with through dynamically imposed operating limits. CQR's strong points are the correctness, consistency, and compactness of its reports. Run times are acceptable for real time operation. >

Direct stability evaluation of power systems with detailed generator models using structure-preserving energy functions

Energy-based direct methods for transient stability analysis are potentially useful both as offline tools for planning purposes as well as for online security assessment. In this paper, a novel structure-preserving energy function (SPEF) is developed using the philosophy of structure-preserving model for the system and detailed generator model including flux decay, transient saliency, automatic voltage regulator (AVR), exciter and damper winding. A simpler and yet general expression for the SPEF is also derived which can simplify the computation of the energy function. The system equations and the energy function are derived using the centre-of-inertia (COI) formulation and the system loads are modelled as arbitrary functions of the respective bus voltages. Application of the proposed SPEF to transient stability evaluation of power systems is illustrated with numerical examples.

On-Line Transient Stability Assessment and Enhancement by Pattern Recognition Techniques

Abstract This paper presents a new candidate method for on-line transient security assessment and enhancement based on Pattern Recognition techniques. Transient state variables are used as primary features and the classifier is obtained in two phases, through the combination of an optimum discriminant transformation together with a probabilistic procedure. The proposed security functions can be further refined by means of a second level classifier based on an optimal discriminant plane and using a weighted K nearest neighbour rule. Finally it is shown that this method provides also an efficient and simple tool for on-line preventive control. Extensive results obtained for several contingencies in the CIGRE test system are presented and discussed.

A Fast Loop-Based Algorithm for Automatic Contingency Selection

In order to speed up on-line security assessment, a fast loop-based automatic contingency selection algorithm is presented in this paper. A linearized active power flow model is built up and loop analysis method with introduction of series potential compensation is used to compute the distribution of the flows after occurance of outages, thereby the change of active power performance index due to outage is calculated, and from which an outage list is constructed. Instead of using detailed AC (or DC) load flow calculation for each outage case, only one m-dimensiona1 forward/backward substitution solution is required to construct the outage list, where m is the number of loops which is much less than the number of buses. Therefore, this method is very fast in speed in contrast with the node-based method. Several digital examples are carried out and the calculated results show that the proposed method is more accurate than that by using a single P-Q iteration of FDLF, at the same time, the calculation speed is hundreds of times faster than the latter. Simultaneous multi-outages can also be simulated and their formulas for calculation are also given.

Power system self-excitation online security assessment

Power system online security assessment is a significant new approach for power system operation. A new pattern-recognition-based application for power system security assessment is described. Here, the method is applied to the power system self-excitation operating problem. The security function used has the learning capacity to adapt to different network configurations and to new load and generation schedules. This paper relates to online security assessment and the corrective actions required. The system under study is the northern collector system for Manitoba Hydro, where self-excitation is a serious operating problem.

Fast Transient Security Assessment

The growth of large interconnected power systems demands a high degree of security for normal operation. This requirement emerges from the fact that the possible disturbances in large power systems could have catastrophic results. Therefore it is the duty of power system control center to retain the operating point within secure boundaries. In order to control the security of system, one has to monitor and analyze the level of system security and enhance it in case it does not fulfill the system security requirement. The pattern recognition technique which is proposed in this paper is a method suitable for fast, on-line security assessment. Most of the literature in this area concerns the use of steady state variables for identification pruposes; the use of transient measurements, however, has been found to be better suited for the fast classification of operating points with minimal error. One of the salient conclusions of this paper is that the pattern recognition technique is a serious candidate for on-line applications. This favorable conclusion is based on the inclusion of transient state variables in the feature vector. The main objective of the pattern recognition method in transient security assessment is to reduce the computational requirement to a minimum. This is done at the expense of elaborate off-line computations. The classical methodology of pattern recognition consists of defining a pattern vector x whose components consist of all significant variables of the system.

An Improved Method of Digital Load Flow for On-Line Security Assessment

In this paper the effectiveness of the fast decoupled load flow method in rectangular coordinates is demonstrated both for planning and for on-line security assessment purposes. A computational saving of 10-20 percent is possible. Several numerical test results are given.

On-Line Observability Determination for Power System Monitoring

Prerequisites for on-line state estimation in electric power systems include the determination of the electrical connectivity of the system (i.e. its configuration), based on the status of circuit breakers and isolators, and the determination of the ‘measurement’ connectivity of the system (i.e. its observability) based on the type and availability of measurement devices.The observability problem is to a large extent unexplored and appears from recent literature to be inadequately defined.The present paper concentrates on the definition of the terminology regarding ‘observability’ of the network, and presents an ‘algorithm’ which is currently implemented in an on-line security assessment installation.

Transient Security Assessment of Power Systems by Pattern Recognition – A Pragmatic Approach

In this paper, transient security assessment is formulated as a two-class classification problem of pattern recognition. The fundamental elements of pattern recognition are described. Features obtained from the physical understanding of the transient phenomena are used here to represent the operating states (samples). The results reported here are encouraging and show that the pragmatic approach introduced. In this paper is very valuable for on-line transient security assessment by pattern recognition techniques.

Security monitoring systems including fast transient stability studies

This paper relates to on-line security assessment and determination of optimal preventive measures of power system, which the authors have developed by using two methods, digital and digital-analog hybrid. The description includes the power system of the Tokyo Electric Power Co., Inc. (TEPCO) for the security assessment; the software configuration for the on-line security assessment; fast calculating methods for the assessment, with emphasis on the study of transient stability; methods for determinating optimal preventive measures to improve transient stability; performance test of the digital method for an actual bulk power system; and a model hybrid security monitoring system for a comparatively small power system and its performance test.