Composite System Reliability Evaluation Research Articles

Bulk load points reliability evaluation using a security based model

Existing composite system reliability evaluation models typically calculate the reliability indices based on the events that lead to load curtailment. These indices do not reflect whether or not a system is on the edge of being in trouble. A power system, however, operates under different degrees of stress and strain throughout a period. This paper presents an approach to quantify a power network into several operating states in terms of the degree to which adequacy and security constraints are satisfied. The probabilistic indices calculated in this paper to quantify the power network at bulk load points and at system level reflect the actual operating behaviour of a power system. The algorithm proposed can be easily incorporated in any composite system reliability model that uses enumeration techniques for reliability evaluation.

Reliability analysis of electric utility SCADA systems

Electric utility SCADA systems must be highly reliable given the potential for the SCADA system to directly contribute to load curtailment. This paper presents an analysis of SCADA system reliability in terms of its expected, aggregate contribution to load curtailment on the power system. Expressing this aggregate in system minutes and applying an appropriate damage cost function then provides an annual cost measure of SCADA system reliability worth. A composite generation and transmission system reliability evaluation technique is used to perform the numerical analysis of the joint SCADA and power system model. This performs a Monte Carlo simulation and includes an optimal power flow for enumerating grid load curtailment states and analysis of SCADA system component connectivity to determine availability of SCADA control. The application of this analysis is illustrated in a comparison of two alternative SCADA architectures. Trans Power (New Zealand) has adopted a subtransmission SCADA architecture which utilises terminals operating off its national SCADA system. These terminals have replaced separate systems located in each area. The objective of the evaluation being to quantify the increased exposure to financial losses due to joint load curtailment.

The effects of voltage collapse problems in the reliability evaluation of composite systems

This paper describes an approach to calculate voltage collapse related bulk reliability indices as well as their impact on the adequacy reliability indices of power systems. In this approach, the adequacy analysis of each selected system state is carried out in two steps. In the first, the minimum load shedding to restore system solvability is computed, neglecting operational constraints such as bus voltage levels and circuit power flows. In the second, the additional minimum load curtailment to alleviate any operating limit violations is calculated. In each step, optimal power flow is solved by a direct interior point algorithm, and related reliability indices are evaluated. The proposed methodology can be used in both enumeration and Monte Carlo methods. Case studies with a practical 11-bus network (the Brazilian Reduced Mato Grosso system) and with a 1600-bus network derived from the Brazilian South/Southeast/Central West system are presented and discussed.

Composite system reliability evaluation using state space pruning

This paper presents a method of computing the reliability indices of a composite generation-transmission system by performing Monte Carlo simulation selectively on those regions of the state space where loss of load states are more likely to occur. These regions are isolated by performing state space decomposition to remove coherent acceptable subspaces. It is shown that this method results in a significant reduction in the number of sampled states, thereby reducing the computational effort required to compute the system and bus indices. The method assumes a DC flow model, and is tested using the IEEE Reliability Test System. The proposed method is not intended to replace existing variance reduction techniques; in fact, such techniques may be used in conjunction with the proposed method to further improve its efficiency.

Modeling the base load generating units with derated states in composite power system reliability evaluation

A novel approach for the construction of the equivalent two-state models for base load generating units with derated states is suggested in order to reduce the computational burden in composite power system reliability (adequacy) evaluation. The proposed equivalent is conceived in such a way to preserve the invariance of the failure probability of the generation system taken alone, under assumption that the network effects upon the generating units models are slight and can be ignored. The equivalent model suggested has been successfully tested and compared with the EFOR based model for the IEEE RT System.

Enhanced adequacy equivalent for composite power system reliability evaluation

The paper presents a technique for studying the adequacy of a selected area in a power network in which the remaining network is modelled as an adequacy equivalent. This approach can be very useful for evaluation of large composite power systems as it is often necessary in practice to perform adequacy analysis of selected relatively small regions in the network. It is useful in conducting adequacy studies of interconnected areas where one area can be replaced by its equivalent, thus reducing the size of the overall system. The paper presents a new approach and shows that annual adequacy indices can be efficiently calculated using this technique, leading to greatly decreased computation times.

Security evaluation of composite power systems

An approach to the security evaluation of a composite power system is proposed which uses probability techniques for quantitative power system reliability analysis. This approach incorporates both steady-state and transient-state considerations in the reliability evaluation of composite power systems.

A new method for reliability evaluation of composite power systems

Abstract The increase in size and complexity of composite power systems, coupled with present day financial constraints, have made the use of probabilistic methods and reliability indices a necessity in order to maintain the continuity and quality of service to customers. This paper presents a new technique to obtain the loss of load probability(LOLP) and expected demand not served(EDNS) of a composite power system, that is not doomed by the ‘state space explosion’ problem. It considers only specified number of most probable states. Since the system operates in these states most of the time, we can get upper and lower bounds and hence, a good approximation of the system LOLP and EDNS without analysing all possible states. The applicability of the proposed algorithm has been tested for various systems. IEEE reliability test system is used for comparison of results. It is observed that the proposed algorithm is fast and approximates the LOLP and EDNS to acceptable accuracy.

Inclusion of weather effects in composite system reliability evaluation using sequential simulation

The studies reported in the paper describe the development of a new technique to accommodate the modelling of weather events in composite system reliability evaluation using a sequential simulation technique. Although considerable effort has been made to include weather impacts, all the available techniques neglect the moving or traversing nature of weather events. The technique described not only takes into account a comprehensive range of weather severities and attributes, it also accommodates the traversing nature of weather events. The sequential Monte Carlo simulation approach travels through time chronologically, and this unique concept allows it to be used for tracking the effects of nonstationary weather events within the evaluation procedure of transmission systems. Eventually this approach leads to an improved representation of a composite system. The approach is demonstrated by sensitivity studies conducted on the IEEE Reliability Test System. These results show the applicability of the algorithms for evaluating the reliability of a composite power system.

Composite power systems reliability evaluation based on demand‐side reserve

AbstractThis paper proposes new demand‐side reliability indices and useful computational methods for reliability evaluation of composite power systems. These new indices are based on the active power which can reach each demand spot under generating and transmission network constraints. This conception is defined as “reachable power,” and it leads the reserve margin on each demand spot, which is called as “demand‐side reserve.” If the reachable power is insufficient to satisfy the demand, load curtailment is required.In the proposed approach, the conception of the load curtailment area is defined, and the estimate method of load curtailment area is indicated. In case the reachable power exceeds the demand, system reliability is evaluated by the demand‐side reserve, and the power system is divided into several reliability zones according to the demand‐side reserve levels. Small system examples are used to illustrate principles of the proposed approach, and middle system examples show the effectiveness and practicality.

需要端予備率に基づく発電・送電系統の信頼度評価

This paper proposes new demand-side reliability indices and useful computational methods for reliability evaluation of composite power systems. These new indices are based on the active power which can reach each demand spot under generating and transmission network constraints. This conception is defined as “reachable power,” and it leads the reserve margin on each demand spot, which is called as “demand-side reserve.” If the reachable power is insufficient to satisfy the demand, load curtailment is required. In the proposed approach, the conception of the load curtailment area is defined, and the estimate method of load curtailment area is indicated. In case the reachable power exceeds the demand, system reliability is evaluated by the demand-side reserve, and the power system is divided into several reliability zones according to the demand-side reserve levels. Small system examples are used to illustrate principles of the proposed approach, and middle system examples show the effectiveness and practicality.

A system state transition sampling method for composite system reliability evaluation

The authors present a new Monte Carlo simulation technique for composite system reliability evaluation. The method is based on a system state transition sampling approach which can be used to calculate an actual frequency index without requiring an additional enumeration procedure and the associated approximate assumptions. The approach presented does not require sampling the up and down component cycles and storing chronological information of system states. Generating unit derated states can also be easily included without additional calculations. The effectiveness of the method presented is demonstrated by application to the IEEE Reliability Test System. A comparison study between a state sampling based technique and the proposed method is presented using the IEEE Reliability Test System.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Consideration of multi-state generating unit models in composite system adequacy assessment using Monte Carlo simulation

Presents a Monte Carlo method for reliability evaluation of large-scale composite generation-transmission systems. The method is based on combining the basic random sampling technique with a direct analytical approach for system analysis, and the utilization of a minimization model for load curtailment. The technique is particularly suited to simulating large-scale systems and multiple states of generating units. Many utilities are now using multi-state models to assess capacity adequacy. The utilization of multi-state models in a composite generation and transmission study can create considerable computational difficulties when a conventional contingency enumeration approach is used. The Monte Carlo method can be used to assess the effects of multi-state modelling in composite system adequacy assessment. The technique is illustrated by application to two test systems in order to demonstrate the effectiveness of the method.

A security based approach to composite power system reliability evaluation

An electric power network containing generation and transmission facilities can be divided into several states in terms of the degree to which adequacy and security constraints are satisfied in a reliability evaluation of the composite system. The composite system is classified into different system states for which probabilistic indices are calculated. Both annualized and annual indices using a seven-step load model are presented for two test systems. Selection methods are used to detect problem-creating contingencies. A linear programming model for generation rescheduling and minimization of the amount of load shed is presented. A linear programming model for correcting the voltage problem is presented. >

Sequential simulation applied to composite system reliability evaluation

The paper extends the application of sequential simulation to the analysis of composite generation and transmission systems. Most previous papers have described the application of sequential simulation to the generation system only. The paper summarises the basic characteristics of sequential simulation and describes theoretical and computational techniques that include models for the transmission system within the simulation process itself. It shows how the very nature of sequential simulation can be used with advantage to reduce significantly the computational effort that the simulation of composite systems originally involves. Algorithms based on the sensitivity of system busbars to overloads have been developed to simulate generation redispatch and load-shedding procedures. The feasibility of these reliability assessments for composite systems is demonstrated by applying the techniques to single and multiple IEEE reliability test systems.

Hybrid approach for reliability evaluation of composite generation and transmission systems using Monte-Carlo simulation and enumeration technique

A hybrid approach using Monte-Carlo simulation and an enumeration technique for the reliability evaluation of large scale composite generation-transmission systems is presented. The Monte-Carlo method is based on combining the basic random sampling technique with a direct analytical approach for system analysis and the utilisation of a minimisation model for load curtailment. The method presented is suited to the analysis of large systems and can be used to include multi-state representation of generating units. Studies presented illustrate that derating-adjusted two-state models for generating units can lead to pessimistic appraisals of composite system adequacy. Variability in system load can be incorporated by using a chronological load representation or by an aggregated load model. The accuracy of the load representation and the required computation time increases with the utilisation of more steps in the annual load duration curve. The adequacy indices of different composite systems have different sensitivities to the number of steps in the load curve. A procedure for establishing a set of ratios of generation-transmission adequacy indices which can be used to judge the sensitivities of composite system adequacy indices to the number of steps in the load duration curve is presented. It is only necessary in the case of sensitive composite systems to use many steps in the load model to obtain accurate annual indices and fewer steps can provide sufficiently accurate annual indices in the case of non-sensitive composite systems. A non-uniform load increment step model can effectively improve the accuracy of the calculated annual indices for sensitive composite systems. These conclusions are supported by application of the concepts proposed to two test systems.

Effect of bus load uncertainty and correlation in composite system adequacy evaluation

A tabulating technique of normal distribution sampling is used to simulate bus load uncertainty and a correlation sampling technique is utilized to simulate bus load correlation including those situations in which bus loads are completely dependent or independent. These techniques have been incorporated in the MECORE computer program developed at the University of Saskatchewan for composite system reliability evaluation. Case studies include comparisons between the normal distribution sampling technique and a discrete interval enumeration model, effects of bus load uncertainty and correlation on annualized and annual indices for different systems, and effects of different load uncertainty standard deviations and different degrees of bus load correlation on the inadequacy indices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Reliability Test System for Educational Purposes-Basic Data

The IEEE Subcommittee on the Application of Probability Methods (APM) published the IEEE Reliability Test System (RTS) [1] in 1979. This system provides a consistent and generally acceptable set of data that can be used both in generation capacity and in composite system reliability evaluation [2,3]. The test system provides a basis for the comparison of results obtained by different people using different methods. Prior to its publication, there was no general agreement on either the system or the data that should be used to demonstrate or test various techniques developed to conduct reliability studies. Development of reliability assessment techniques and programs are very dependent on the intent behind the development as the experience of one power utility with their system may be quite different from that of another utility. The development and the utilization of a reliability program are, therefore, greatly influenced by the experience of a utlity and the intent of the system manager, planner and designer conducting the reliability studies. The IEEE-RTS has proved to be extremely valuable in highlighting and comparing the capabilities (or incapabilities) of programs used in reliability studies, the differences in the perception of various power utilities and the differences in the solution techniques. The IEEE-RTS contains a reasonably large power network which can be difficult to use for initial studies in an educational environment.

A technique for reducing computational effort in Monte-Carlo based composite reliability evaluation

The authors describe a novel technique for reducing the number of samplings in Monte-Carlo-based composite power system reliability evaluation. The proposed technique uses analytical information from simple models (such as a generation reliability model) as regression variables to reduce the variance of LOLP (loss-of-load probability) and EPNS (expected power not supplied) estimates with the complete (composite) model. Sample size reductions of up to two orders of magnitude were obtained in case studies with a 24 bus modified reliability test system and a 124 bus reduced Brazilian system. Speed-ups of 6.1 to more than 40 were obtained for the estimate of the EPNS and of 2.1 to 3.8 for the LOLP estimate. In all cases, the EPNS index required more samplings to converge to the required tolerance (5% relative uncertainty) than the respective LOLP index (for the same tolerance). As a consequence, the higher speedups prevail in the overall convergence if a uniform criterion is adopted.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Composite system reliability evaluation

At present there is a significant interest in composite generation and transmission system reliability evaluation for use in bulk power system planning. Methods and computer programs for composite system reliability evaluation have been reported in the industry, though their applications in electric utilities are still very limited. Some improvements in the methods and education in applying them are required for system planners to gain confidence in these methods. This paper concentrates on the purpose and philosophy of composite system reliability evaluation.