PNNL-13501 - Pacific Northwest National Laboratory

Study Control Number: PN00075/1482
Probabilistic Assessment of Power System Security
Chi-Hung Kelvin Chu
Domestic utility systems are vulnerable to disruption from many types of threat including natural events and malicious
action. Tools are needed to protect our nation’s electric power generation and delivery systems. This project is
developing new approaches to reduce the vulnerability of the electric power infrastructure to internal and external threats.
Project Description
The goal of this research was to integrate both power
system adequacy and security evaluation into a single
framework. The scope of work focused on the security
aspect of the power system. Specific objectives included:
1) validate existing techniques for the fast detection of
power system instability; 2) develop a reusable computer
code to implement the selected technique, this segment of
the project is used to screen, rank, and select system
contingencies before conducting probabilistic system
security assessment; and 3) develop a prototype digital
computer program to implement and conduct probabilistic
power system security evaluation.
This project will quantify the system stability
performance by providing information such as the
probability of instability, and other useful and available
indices. Once the approach is successfully developed and
implemented, the overall goal of integrating both power
system adequacy and security evaluation under one single
framework can then be achieved.
Introduction
Power system security evaluation involves the
determination of the stability of a power system under
different contingencies. The common system planning
approach is the use of a deterministic criterion such as
“N-1” criterion. The system is designed to withstand and
continue to function within established guidelines for any
single contingency such as the outage of a line or the loss
of a generator. The use of the N-1 criterion reduces the
amount of time necessary to evaluate and simulate the
performance of the system. This criterion was adequate
for the North American interconnected transmission
system because of the significant amount of transmission
reserve in the system. As the economy grows, energy
consumption also increases. In addition, as the electric
industry moves into a deregulating and competitive
environment, more energy is transmitted across the
national grid and at longer distances. The power system
has become more susceptible to instability as the load
grows and the transmission reserve diminishes.
The stability of a power system depends on a large
number of factors and conditions at the time of the
contingency. Factors such as the load level at the time of
the contingency, location and the type of the contingency,
the conditions of the network, and the components that
are required to clear the problem at the time of
contingency can all affect the stability of the system. The
factors are stochastic in nature. The deterministic N-1
criterion does not take into account the probabilistic
nature of these factors. These, together with the addition
of new players into the energy market and the
unpredictable energy transactions across the nation, all
contribute more uncertainties to the planning and
operation of the modern power system. The ability to
incorporate these uncertainties into the planning and
operating processess and the ability to quantify the
various risks and their consequences are therefore greatly
needed.
Approach
The proposed project is divided into three stages:
1. Validation of existing techniques. The traditional
approach to determine system stability has been the
use of step-by-step simulation using the system swing
equation. Faster stability detection is often done
using various energy functions. The traditional
approach is computationally expensive and slow, and
the use of energy functions requires the development
of appropriate energy functions. Currently, the “Fast
Second Kick” technique seems to be the most
promising. The first phase is to select and validate
the latest techniques for the determination and
detection of power system stability. The selected
technique will be used in the second phase.
2. Implementation of the selected techniques. The
selected technique will be implemented in the second
Energy Technology and Management 269