Transcript Slide 1

December 5th , 2012
Uri Livnat
Electrical engineering
department
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Published in 2003, Iowa State University
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Vijay Vittal, IEEE fellow
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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
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OL-RBSA provides rapid online quantification of
security level associated with existing or forecasted
operating condition
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Probabilistic approach
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Advantage : condenses contingency likelihood and
severity into indices reflecting probabilistic risk
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Using indices in control room decision making
Increased understanding of potential network
problems and improved decision making
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Overload
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Cascading Overload
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Low voltage
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Voltage instability
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Today : competitive supply system and the
organizational separation of supply, transmission and
system operators have significant implications
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Highly stressed and unpredictable operating conditions
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Vulnerable networks
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Increased need to monitor security level
Cause : natural load growth coupled with an increase
in long-distance transmission usage which results in:
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Heavy transmission circuit loading
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Depressed bus voltage magnitudes
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Closer proximity to voltage instability
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Result : operators make control room complex
decisions to alleviate stressed network conditions
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How to act?
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To what extent?
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Decisions usually increase the cost of supply
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Tradeoff between security and economics
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Today’s systems enable operators to monitor network
condition through the following :
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Data acquisition
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State estimation
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Deterministic contingency analysis
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Useful techniques, but require a huge
amount of subjective assessment
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How many overloads or voltage violations exist?
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How severe are they?
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How close is the system to voltage instability?
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Is cascading possible?
In order to answer these questions, risk
indices are computed on line and used
efficiently
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Provides ability to compute risk associated with
conditions up to several hours ahead
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Performs security assessment on a near future
conditions in contrast to performing security
assessment on a past condition (traditional systems)
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Decision is based on information that corresponds to
time frame in which it is effective
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Explanation on computing the indices
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My enhancement to the risk calculations
The risk index is an expectation of
severity, computed by summing over all
possible outcomes the product of the
outcome probability and its severity
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Uncertainty of contingency
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Uncertainty of opening conditions
~
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Provide a quantitative evaluation of what would
happen to the power system in terms of severity,
impact, consequences or cost
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One of the most difficult problems in probabilistic
security assessment
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Many reasons for choosing these functions
(simple, deterministic …)
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I will try to enhance the severity functions and
make them more realistic
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Overload : per circuit
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Voltage instability : per the system
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Two main steps
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Calculate the risk indices per contingency for a given
contingency state
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Combine the risks of all contingencies for each security
problem, weight them and sum.
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18 cases were tested, representing 2 days over
nine hours each day
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17 contingencies
Severity
functions are
used to quantify
severity
State
Estimation
Models of
Uncertainty and
Probability of
conditions
Indices are computed based on probabilistic risk
Control room to assess system security level
On Line decisions that affect the network
1. More realistic low voltage severity
function
2. Voltage rise problem due to renewable
Feeder
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|v|=1
|v |≠ 1