Academic literature on the topic 'Reliability Assessment of Power Systems'

The first part of this dissertation presents an innovative method for the assessment of generation system reliability. In this method, genetic algorithm (GA) is used as a search tool to truncate the probability state space and to track the most probable failure states. GA stores system states, in which there is generation deficiency to supply system maximum load, in a state array. The given load pattern is then convoluted with the state array to obtain adequacy indices. In the second part of the dissertation, a GA based method for state sampling of composite generation-transmission power systems is introduced. Binary encoded GA is used as a state sampling tool for the composite power system network states. A linearized optimization load flow model is used for evaluation of sampled states. The developed approach has been extended to evaluate adequacy indices of composite power systems while considering chronological load at buses. Hourly load is represented by cluster load vectors using the k-means clustering technique. Two different approaches have been developed which are GA parallel sampling and GA sampling for maximum cluster load vector with series state revaluation. The developed GA based method is used for the assessment of annual frequency and duration indices of composite system. The conditional probability based method is used to calculate the contribution of sampled failure states to system failure frequency using different component transition rates. The developed GA based method is also used for evaluating reliability worth indices of composite power systems. The developed GA approach has been generalized to recognize multi-state components such as generation units with derated states. It also considers common mode failure for transmission lines. Finally, a new method for composite system state evaluation using real numbers encoded GA is developed. The objective of GA is to minimize load curtailment for each sampled state. Minimization is based on the dc load flow model. System constraints are represented by fuzzy membership functions. The GA fitness function is a combination of these membership values. The proposed method has the advantage of allowing sophisticated load curtailment strategies, which lead to more realistic load point indices.

Abstract The goal of this research is to advance the state of the art in bulk power system reliability assessment. Bulk power system reliability assessment is an important procedure at both power system planning and operating stages to assure reliable and acceptable electricity service to customers. With the increase in the complexity of modern power systems and advances in the power industry toward restructuring, the system models and algorithms of traditional reliability assessment techniques are becoming obsolete as they suffer from nonrealistic system models and slow convergence (even non-convergence) when multi-level contingencies are considered and the system is overstressed. To allow more rigor in system modeling and higher computational efficiency in reliability evaluation procedures, this research proposes an analytically-based security-constrained adequacy evaluation (SCAE) methodology that performs bulk power system reliability assessment. The SCAE methodology adopts a single-phase quadratized power flow (SPQPF) model as a basis and encompasses three main steps: (1) critical contingency selection, (2) effects analysis, and (3) reliability index computations. In the critical contingency selection, an improved contingency selection method is developed using a wind-chime contingency enumeration scheme and a performance index approach based on the system state linearization technique, which can rank critical contingencies with high accuracy and efficiency. In the effects analysis for selected critical contingencies, a non-divergent optimal quadratized power flow (NDOQPF) algorithm is developed to (1) incorporate major system operating practices, security constraints, and remedial actions in a constrained optimization problem and (2) guarantee convergence and provide a solution under all conditions. This algorithm is also capable of efficiently solving the ISO/RTO operational mode in deregulated power systems. Based on the results of the effects analysis, reliability indices that provide a quantitative indication of the system reliability level are computed. In addition, this research extends the proposed SCAE framework to include the effects of protection system hidden failures on bulk power system reliability. The overall SCAE methodology is implemented and applied to IEEE reliability test systems, and evaluation results demonstrate the expected features of proposed advanced techniques. Finally, the contributions of this research are summarized and recommendations for future research are proposed.

<p>A stable and reliable electric power supply system is an inevitable pre-requisite for the technological and economic growth of any nation. Due to this, utilities must strive and ensure that the customer’s reliability requirements are met and the regulators requirements satisfied at the lowest possible cost. It is known fact around the world that 90% of the of the customer service interruptions are caused due to failure in distribution system. Therefore, it is worth considering reliability worth assessments as it provides an opportunity to incorporate the cost or losses incurred by the utilities customer as a result of power failure and this must be considered in planning and operating practices. The system modeling and simulation study is carried out on one of the district’s distribution system which consists of 33kV and 11kV network in Bhutan. The reliability assessment is done on both 11 and 33kV system to assess the performance of the present system and also predictive reliability analysis for the future system considering load growth and system expansion. The alternative which gives low SAIDI, SAIFI and minimum breakeven costs are being assessed and considered. The reliability of 33kV system could be further improved by installation of load break switch, auto recloser and connecting with line coming from other district (reserve) at reasonable break even cost. The decision base could be further improved by having Bhutan’s context interruption cost. However, the questionnaire’s which may be used in Bhutan to acquire interruption costs from the customers are being proposed. The utility should have their own reliability improvement strategy depending upon their needs and requirements of the regulators. Although there is no magic bullet in managing power quality issues, utilities can maximize network performance and better serve customers by diligently addressing trouble prone areas. In order to achieve this objective, a computer program NetBas/Lesvik is used to run load flow and reliability analysis, thus selecting the alternatives either based on reliability indices or on cost benefit ratio.</p>

Recent major electrical disturbances highlight the extent to which modern societies depend on a reliable power infrastructure and the impact of these undesirable events on the economy and society. Numerous blackout models have been developed in the last decades that capture effectively the cascade mechanism leading to a partial or complete blackout. These models usually consider only the state of the electrical part of the system and investigate how failures or limitations in this system affect the probability and severity of a blackout.However, an analysis of the major disturbances that occurred during the last decade, such as the North America blackout of 2003 and the UCTE system disturbance of 2006, shows that failures or inadequacies in the Information and Communication Technology (ICT) infrastructure and also human errors had a significant impact on most of these blackouts.The aim of this thesis is to evaluate the contribution of these non-electrical events to the risk of power system blackouts. As the nature of these events is probabilistic and not deterministic, different probabilistic techniques have been developed to evaluate their impact on power systems reliability and operation.In particular, a method based on Monte Carlo simulation is proposed to assess the impact of an ICT failure on the operators’ situation awareness and consequently on their performance during an emergency. This thesis also describes a generic framework using Markov modeling for quantifying the impact of insufficient situation awareness on the probability of cascading electrical outages leading to a blackout. A procedure based on Markov modeling and fault tree analysis is also proposed for assessing the impact of ICT failures and human errors on the reliable operation of fast automatic protection actions, which are used to provide protection against fast-spreading electrical incidents. The impact of undesirable interactions and the uncoordinated operation of these protection schemes on power system reliability is also assessed in this thesis.The simulation results of these probabilistic methods show that a deterioration in the state of the ICT infrastructure and human errors affect significantly the probability and severity of power system blackouts. The conclusion of the work undertaken in this research is that failures in all the components of the power system, and not just the “heavy electrical” ones, must be considered when assessing the reliability of the electrical supply.

The problem of optimum restoration after occurrence the outages in a distribution network is an important issue in smart grids. In this kind of networks remote-controlled switches, alternative sources and grid-connected distributed generators (DG) are employed. Therefore, the reliability of the system (corresponding to the frequency of failures and the duration of interruptions) is improved by operating the switches to resupply a part of interrupted system during the repair time. To evaluate the reliability indices in smart grids, neglecting the restoration during the repair time causes the wrong assessment of the network. Thus, considering the rerouting the power during the interruptions seems necessary to calculate the reliability indices. The problem of restoration is formulated as a non-linear integer programming problem with the assistance of the network graph. The circuit graph method is also used to pre-evaluate the feasible interchanging operations to enhance the efficiency of the computations. The topological and operational constraints in this formulation can be found and resolved with the assistance of fundamental cut-set matrix. The optimum restoration schemes is obtained by considering the optimal islanded mode of operation of the DGs which implies maximizing the loading of DGs while not violating their generation capacities. The optimum restoration policies lead us to find the optimum number and location of those manual switches that should be upgraded to the remote-controlled switches. This is a multi-objective problem that contains the contribution of each restoration policy in the reliability improvement and the cost of those switching operations. The proposed algorithm is applied to different standard test systems and the results are compared to the results obtained from other methods and algorithms.

Power companies around the world are incorporating wind power into their electricity networks. Wind power is an intermittent source of energy and its technical and financial impacts on the transmission and distribution networks are not yet totally investigated. This thesis investigates the impact of wind power on power system reliability evaluation. The investigation includes long-term system planning and short-term operational planning on reliability evaluation taking into accounts different penetration levels of wind power. This thesis presents a Wind-Hydro Cooperation (WHC) method for reducing the effects of wind power fluctuations on system operation and maintaining similar power system reliability level at different wind penetrations. The thesis starts by gaining insights into methodologies of power system reliability evaluation. These methodologies are described and discussed in details. Then, relations between the wind speed and the wind turbine power output are explored fo r modelling the wind farm output. The output fluctuation of wind power affects the power system operation. The system requires additional operating reserve to maintain the original system reliability. To mitigate these effects of wind output fluctuation, the study explores the use of Pump-Hydro technology to cooperate with wind power to meet the increased operating reserve requirements. In order to verify and analyze the validity of the WHC method on reducing the effect of wind power fluctuation on power output and maintaining the system reliability, an extensive set of case studies are performed. Following this, the reliability analyses focus on three aspects: a) a small system for initial validation of the idea; b) a larger system for analysing the effects of the WHC method on long-term system planning and short-term operational planning; c) application of a real practical system. All the above tests involve investigation of wind penetration at different level starting from 10% to 40%. The period of investigation ranges from one day, one week, one month and then extending it to one full year.