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ELECTRICAL POWER NETWORKS E9501

ELECTRICAL POWER NETWORKS E9501. December 5 th , 2012 Uri Livnat Electrical engineering department. Online Risk-Based Security Assessment. Published in 2003, Iowa State University Vijay Vittal , IEEE fellow

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ELECTRICAL POWER NETWORKS E9501

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  1. ELECTRICAL POWER NETWORKSE9501 December 5th , 2012 Uri Livnat Electrical engineering department

  2. Online Risk-Based Security Assessment • Published in 2003, Iowa State University • Vijay Vittal, IEEE fellow • Motivation : Increase in the frequency that power system operators are encountering high stress in bulk transmission systems and the corresponding need to improve security monitoring of networks • OL-RBSA provides rapid online quantification of security level associated with existing or forecasted operating condition

  3. Background • Probabilistic approach • Advantage : condenses contingency likelihood and severity into indices reflecting probabilistic risk • Using indices in control room decision making • Increased understanding of potential network problems and improved decision making • Overload • Cascading Overload • Low voltage • Voltage instability

  4. Introduction • Today : competitive supply system and the organizational separation of supply, transmission and system operators have significant implications • Highly stressed and unpredictable operating conditions • Vulnerable networks • Increased need to monitor security level • Cause : natural load growth coupled with an increase in long-distance transmission usage which results in: • Heavy transmission circuit loading • Depressed bus voltage magnitudes • Closer proximity to voltage instability

  5. Introduction • Result : operators make control room complex decisions to alleviate stressed network conditions • How to act? • To what extent? • Decisions usually increase the cost of supply • Tradeoff between security and economics • Today’s systems enable operators to monitor network condition through the following : • Data acquisition • State estimation • Deterministic contingency analysis

  6. Introduction • Useful techniques, but require a huge amount of subjective assessment • How many overloads or voltage violations exist? • How severe are they? • How close is the system to voltage instability? • Is cascading possible? • In order to answer these questions, risk indices are computed on line and used efficiently

  7. OL-RBSA - Characteristics • Provides ability to compute risk associated with conditions up to several hours ahead • Performs security assessment on a near future conditions in contrast to performing security assessment on a past condition (traditional systems) • Decision is based on information that corresponds to time frame in which it is effective • Explanation on computing the indices • My enhancement to the risk calculations

  8. Some Math: The Risk Concept The risk index is an expectation of severity, computed by summing over all possible outcomes the product of the outcome probability and its severity

  9. The Risk Concept

  10. The Risk Concept • Uncertainty of contingency • Uncertainty of opening conditions • ~

  11. Modeling Severity Function • Provide a quantitative evaluation of what would happen to the power system in terms of severity, impact, consequences or cost • One of the most difficult problems in probabilistic security assessment • Many reasons for choosing these functions (simple, deterministic …) • I will try to enhance the severity functions and make them more realistic

  12. Severity functions • Overload : per circuit • Voltage instability : per the system

  13. Calculating OL-RBSA Indices • Two main steps • Calculate the risk indices per contingency for a given contingency state • Combine the risks of all contingencies for each security problem, weight them and sum.

  14. Paper Numerical Results • 18 cases were tested, representing 2 days over nine hours each day • 17 contingencies

  15. Paper Summary Models of Uncertainty and Probability of conditions Severity functions are used to quantify severity State Estimation Indices are computed based on probabilistic risk Control room to assess system security level On Line decisions that affect the network

  16. Enhancements 1. More realistic low voltage severity function

  17. Enhancements 2. Voltage rise problem due to renewable Feeder |v|=1 |v|=1 |v |≠ 1

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