| Summary: | The power utility industry in North America is quickly evolving from a
monopolistic environment to a competitive one. Traditional dynamic security assessment
methods and tools which have served the industry well in the past cannot provide the risk
analysis needed to extract more value out of existing assets. BC Hydro's current
deterministic practice is to study the "worst case", where all faults are assumed to be 3$
bus faults with unsuccessful reclosing, at a load factor of 100%. A review of historical
fault data from BC Hydro's 500 kV system over the past 20 years has shown these
assumptions do not reflect the true nature of the power system. However, they are in
place to ensure that minimum operating reliability mandated by regulatory agencies are
met.
Based on historical statistics, the probabilistic states of load factor, fault type,
fault location, fault clearing, and automatic reclosing were applied to a generation
rejection study on the Peace system and a transfer limit study on the Columbia system.
For each study, 1000 simulations were carried out on a full model of the BC Hydro
interconnected system, with the probabilistic states chosen via Monte Carlo techniques.
The results were quantified using a BC Hydro developed transient stability assessment
module in conjunction with a commercial load flow and dynamic simulation package
(PTI's PSS/E).
The results showed that BC Hydro's existing deterministic criteria are very
conservative, with a risk of instability between 0% and 0.2% in the Peace case and 0.1%
in the Columbia case. Although the risk of instability was calculated as 0% for the Peace
case, this an approximation error due to the number of samples used. The studies also
revealed that the deterministic criteria does not always correspond to the "worst case" as
normally assumed.
An analysis of the effectiveness of each probabilistic factor considered showed
that fault type and successful/unsuccessful reclosing were the more significant factors,
while fault location on the line was the least significant. This research has shown that
considering the probabilistic nature of the power system in dynamic security assessment
can lead to less remedial actions and increased transfer limits.
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