Contingency analysis in Power SystemsContingency analysis is a steady state analysis of power system...
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RESEARCH POSTER PRESENTATION DESIGN © 2015 www.PosterPresentations.com An electric power system consists of generation, transmission and distribution subsystems that connects power providers and customers. It is a large and critical infrastructure, and it has an essential influence on functioning of society and economy. A big interruption in power system, named blackout, effects a large portion of society functioning and makes a lot of problems for a large number of customers that may extend significant time periods. Such disruptions result in direct and indirect losses. The security of electrical power system is the first priority both in power system planning and operation, and contingency analysis is an important tool used to assess security under both topological changes and component failures. Power system operators extensively use contingency analysis for deciding preventive and corrective control actions. A contingency analysis tool, using power flow analysis of power system, alerts the operators to maintain the system's security under any violation of any component due to contingency in the power system. Power system N-K contingency analysis is a hard analysis technique because of the complexity of power system network, high computational cost and various system operating conditions. Therefore determining specific set of N-K contingencies with high cascading risk is required, in terms of computational requirements. Abstract Introduction Contingency analysis is a steady state analysis of power system while on or more of system component are failed to be in service. AC power flow analysis is the accurate steady state model of the power system. On the other hand DC power flow analysis is a linear approximation of power system steady state performance. Although contingency analysis using AC power flow predicts system’s state accurately but the solution is nonfunctional because of fast system changes and low speed coverage of AC power flow. On the other hand, contingency analysis using DC power flow is useful although it is not accurate as AC power flow is. Therefore DC power flow makes online contingency analysis more practical in contrast with AC power flow while calculation inaccuracy may leads to blackout and voltage collapse in worst case. Linear sensitivity factors are used as an indices to evaluate line active power flow under generation and line outages. These factors are calculated using DC power flow analysis [1-2]. - Power Transfer Distribution Factors (PTDFs): line flow changes due to power shift between two buses - Line Outage Distribution Factors (LODFs): line flow changes due to the line outages. Using linear sensitivities, in general using DC power flow, to select contingencies with high potential of making component constraints violation (line flow overload or voltage limit) and then using the AC power flow to analysis selecting contingencies are the feasible solution for contingency analysis problem. In order to explain and compare the contingency analysis methods, a seven bus system is simulated with PowerWorld software [5] and the results are shown through figures (1-4). The accuracy of DC power flow comparing to AC power flow is discussed. Contingency analysis methods Case study Conclusion Contingency analysis is an essential tool in power system steady state analysis. Power system state estimation after line or generator outages enables the operator of the system to do preventive and corrective actions to keep the system in a normal operation. Steady state modeling of the power system is done by using either AC or DC power flow. AC power flow is the accurate model for steady state analysis, but it is no fast enough to estimate system states after forced outage which makes it nonfunctional for contingency analysis. On the other hand DC power flow is a useful estimator of the system states provided the assumptions are satisfied by system conditions. All in all, the best procedure for contingency selection is first using DC power flow to find out possible harmful contingencies then after using AC power flow to examine these contingencies deeply to rank them accurately. References [1] A. Wood, B. Wollenberg, “Power Generation, Operation and Control,” 3rd Ed. New York, NY, USA: Wiley, 2014. [2] G. Poyrazoglu, H. Oh, “Optimal topology control with physical power flow constraints and N-1 contingency criterion,” IEEE Trans. Power Syst., vol. 30, no. 6, pp. 3063–3071, Nov. 2015. [3] Y. Jia, K. Meng, Z. Xu, “N-k induced cascading contingency screening,” IEEE Trans. Power Syst., vol. 30, no. 5, pp. 2824–2829, Sep. 2015. [4] C. Matthew Davis, Thomas J. Overbye, “Multiple element contingency screening,” IEEE Trans. Power Syst., vol. 23, no. 2, pp. 1294–1300, Aug. 2011. [5] PowerWorld simulator, http://www.powerworld.com. The N-1 security criterion is a common standard for the security of power system for many years. According to this criterion, planned power system should have withstand against any single component failure without any violation in other component constraints while supporting all the loads. N-1 contingency criterion refers to the ability of system to move from one stable operation to another without any violation after the contingency (the loss of a transmission line or a generator) occurs. The N- 1 contingency criterion may not be sufficient when multiple component failures take place simultaneously or consecutively. The N-K contingency analysis seems to be inevitable considering serious blackouts due to multiple component failures [1-4]. Faculty of Engineering and Applied Science, Memorial University of Newfoundland, St. John’s, NL, Canada, A1B 3X5 Graduate student : Younes Salami Supervisor: Professor Benjamin Jeyasurya Contingency analysis in Power Systems Figure.1: Power flow result of 7 bus system in normal operation mode using AC power flow analysis. Figure.2: Line outage between bus one and two leads to and line flow violation between bus one and three. This figure shows N-1 contingency in the system which leads to a system constraints violation. Contingency analysis arise an alert for the operator. If the operator does not take an either preventive or corrective actions to relieve the overload line, the line’s protection disconnects the line which may lead to another violation in the system. This outage may lead to chain of outages which may lead to a blackout. Figure 3: this figure shows exactly the same condition as figure (2) but using DC load flow analysis. In this case, DC load flow analysis is able to distinguish which line flow violates correctly, but the severity of the violation is different. DC load flow results accuracy depend on how the assumptions are correct. In contingency analysis, the inaccuracy resulting from DC power flow may leads both line power flow inaccurate calculation and contingency screening misleading. Figure.6: generator outage in bus seven leads to an emergency condition in line between bus two and five, then line protection disconnect this line, after that the line between bus tow and six gets overloaded. With the protection system action of this line the system goes blackout. This simulation shows how contingency analysis important to predict and hence prevent cascading failure and in the worst case blackout.
Transcript of Contingency analysis in Power SystemsContingency analysis is a steady state analysis of power system...
RESEARCH POSTER PRESENTATION DESIGN © 2015
www.PosterPresentations.com
An electric power system consists of generation, transmission and distribution subsystems that connects power providers and customers. It is a large and critical infrastructure, and it has an essential influence on functioning of society and economy. A big interruption in power system, named blackout, effects a large portion of society functioning and makes a lot of problems for a large number of customers that may extend significant time periods. Such disruptions result in direct and indirect losses. The security of electrical power system is the first priority both in power system planning and operation, and contingency analysis is an important tool used to assess security under both topological changes and component failures. Power system operators extensively use contingency analysis for deciding preventive and corrective control actions. A contingency analysis tool, using power flow analysis of power system, alerts the operators to maintain the system's security under any violation of any component due to contingency in the power system. Power system N-K contingency analysis is a hard analysis technique because of the complexity of power system network, high computational cost and various system operating conditions. Therefore determining specific set of N-K contingencies with high cascading risk is required, in terms of computational requirements.
Abstract
Introduction
Contingency analysis is a steady state analysis of power system while on or more of system component are failed to be in service. AC power flow analysis is the accurate steady state model of the power system. On the other hand DC power flow analysis is a linear approximation of power system steady state performance. Although contingency analysis using AC power flow predicts system’s state accurately but the solution is nonfunctional because of fast system changes and low speed coverage of AC power flow. On the other hand, contingency analysis using DC power flow is useful although it is not accurate as AC power flow is. Therefore DC power flow makes online contingency analysis more practical in contrast with AC power flow while calculation inaccuracy may leads to blackout and voltage collapse in worst case. Linear sensitivity factors are used as an indices to evaluate line active power flow under generation and line outages. These factors are calculated using DC power flow analysis [1-2]. - Power Transfer Distribution Factors (PTDFs): line flow changes due to power shift between two buses - Line Outage Distribution Factors (LODFs): line flow changes due to the line outages. Using linear sensitivities, in general using DC power flow, to select contingencies with high potential of making component constraints violation (line flow overload or voltage limit) and then using the AC power flow to analysis selecting contingencies are the feasible solution for contingency analysis problem. In order to explain and compare the contingency analysis methods, a seven bus system is simulated with PowerWorld software [5] and the results are shown through figures (1-4). The accuracy of DC power flow comparing to AC power flow is discussed.
Contingency analysis methods
Case study
Conclusion
Contingency analysis is an essential tool in power system steady state analysis. Power system state estimation after line or generator outages enables the operator of the system to do preventive and corrective actions to keep the system in a normal operation. Steady state modeling of the power system is done by using either AC or DC power flow. AC power flow is the accurate model for steady state analysis, but it is no fast enough to estimate system states after forced outage which makes it nonfunctional for contingency analysis. On the other hand DC power flow is a useful estimator of the system states provided the assumptions are satisfied by system conditions. All in all, the best procedure for contingency selection is first using DC power flow to find out possible harmful contingencies then after using AC power flow to examine these contingencies deeply to rank them accurately.
References
[1] A. Wood, B. Wollenberg, “Power Generation, Operation and Control,” 3rd Ed. New York, NY, USA: Wiley, 2014. [2] G. Poyrazoglu, H. Oh, “Optimal topology control with physical power flow constraints and N-1 contingency criterion,” IEEE Trans. Power Syst., vol. 30, no. 6, pp. 3063–3071, Nov. 2015. [3] Y. Jia, K. Meng, Z. Xu, “N-k induced cascading contingency screening,” IEEE Trans. Power Syst., vol. 30, no. 5, pp. 2824–2829, Sep. 2015. [4] C. Matthew Davis, Thomas J. Overbye, “Multiple element contingency screening,” IEEE Trans. Power Syst., vol. 23, no. 2, pp. 1294–1300, Aug. 2011. [5] PowerWorld simulator, http://www.powerworld.com.
The N-1 security criterion is a common standard for the security of power system for many years. According to this criterion, planned power system should have withstand against any single component failure without any violation in other component constraints while supporting all the loads. N-1 contingency criterion refers to the ability of system to move from one stable operation to another without any violation after the contingency (the loss of a transmission line or a generator) occurs. The N-1 contingency criterion may not be sufficient when multiple component failures take place simultaneously or consecutively. The N-K contingency analysis seems to be inevitable considering serious blackouts due to multiple component failures [1-4].
Faculty of Engineering and Applied Science, Memorial University of Newfoundland, St. John’s, NL, Canada, A1B 3X5
Graduate student : Younes Salami Supervisor: Professor Benjamin Jeyasurya
Contingency analysis in Power Systems
Figure.1: Power flow result of 7 bus system in normal operation mode using AC power flow analysis.
Figure.2: Line outage between bus one and two leads to and line flow violation between bus one and three. This figure shows N-1 contingency in the system which leads to a system constraints violation. Contingency analysis arise an alert for the operator. If the operator does not take an either preventive or corrective actions to relieve the overload line, the line’s protection disconnects the line which may lead to another violation in the system. This outage may lead to chain of outages which may lead to a blackout.
Figure 3: this figure shows exactly the same condition as figure (2) but using DC load flow analysis. In this case, DC load flow analysis is able to distinguish which line flow violates correctly, but the severity of the violation is different. DC load flow results accuracy depend on how the assumptions are correct. In contingency analysis, the inaccuracy resulting from DC power flow may leads both line power flow inaccurate calculation and contingency screening misleading.
Figure.6: generator outage in bus seven leads to an emergency condition in line between bus two and five, then line protection disconnect this line, after that the line between bus tow and six gets overloaded. With the protection system action of this line the system goes blackout. This simulation shows how contingency analysis important to predict and hence prevent cascading failure and in the worst case blackout.
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