TY - BOOK
T1 - On-line Dynamic Security
Assessment in Power Systems.
AU - Weckesser, Johannes Tilman Gabriel
PY - 2014
Y1 - 2014
N2 - The thesis concerns the development of tools and methods for on-line dynamic
security assessment (DSA). In a future power system with low-dependence or even
independence of fossil fuels, generation will be based to a large extent on noncontrollable
renewable energy sources (RES), such as wind and solar radiation.
Moreover, ongoing research suggests that demand response will be introduced to
maintain power balance between generation and consumption at all times. Due to
these changes the operating point of the power system will be less predictable and
today’s stability and security assessment tools may no longer be feasible, since they
are generally based on extensive off-line studies.
A core component of an efficient on-line dynamic security assessment is a fast
and reliable contingency screening. As part of this thesis a contingency screening
method is developed and its performance is assessed on a set of test cases. The
developed method reliably assesses first-swing transient angular stability of a power
system in its current state with respect to a given set of contingencies. In order
to ensure fast performance of the screening method, first a review of existing transient
stability assessment (TSA) methods was carried out and their computational
complexity was investigated. This allowed to identify the single machine equivalent
(SIME) method as the potentially fastest assessment method and, hence, well
suited for on-line DSA. Means for further performance improvement of the SIME
method are investigated such as the reduction of the degree of model detail used in
time-domain simulation, which results in a recommendation for the required model
detail for synchronous generator. A challenging task when using the SIME method
is to early and reliably determine the critical machine cluster, which is the group of
generators likely to lose synchronism. Therefore, a novel approach to identify the
critical machine cluster is proposed in the thesis. This approach uses a new coupling
coefficient, which is a measure of the coupling strength of a pair of generators,
and a simple clustering algorithm to identify the critical group of generators.
In order to determine a system to be transient secure, it is not sufficient to solely
assess if all synchronous generator remain in synchronism, it is also required that
the bus voltages remain within acceptable limits. A transient disturbance and the
following angular divergence of a group of generators can cause critical voltage
sags at certain buses in the system. In this thesis assessment of such voltage
sags using two types of sensitivities, which are derived from the algebraic network
equations, is proposed. These sensitivities are derived after an in-depth study of the
mechanism causing the voltage sags. The first sensitivity type is called load voltage
i/xii
sensitivity and allows identifying which bus voltages are affected by a change in
rotor angle of a particular generator. The second proposed type is called generator
power sensitivity, which provides information on the effect of load variation on
the generator’s power injection. It is shown that the derived sensitivities can give
valuable information to identify critical generator-load pairs as well as locations for
applying preventive or remedial control measures. Furthermore, the development
of a method for early prediction of critical voltage sags is described. The method’s
performance is compared to other prediction approaches. The results show that the
proposed method succeeds in early, accurately and consistently predicting critically
low voltage sags.
An efficient on-line DSA not only identifies unstable or insecure operation, but also
proposes preventive or remedial control actions to restore stability and security
in the system. In this thesis a further development of a method for determining
real-time remedial action against aperiodic small signal rotor angle instability is described.
A real-time aperiodic small signal rotor angle stability assessment method
is employed to monitor the respective stability boundary and to compute the respective
stability margin of each generator in the system. In case that the stability
margin of a particular generator falls below a pre-defined security threshold, the
proposed method analytically determines power generation re-dispatch solutions,
which restore stable and secure operation in the system. The effectiveness of the
method is presented on two test cases in two different test systems.
AB - The thesis concerns the development of tools and methods for on-line dynamic
security assessment (DSA). In a future power system with low-dependence or even
independence of fossil fuels, generation will be based to a large extent on noncontrollable
renewable energy sources (RES), such as wind and solar radiation.
Moreover, ongoing research suggests that demand response will be introduced to
maintain power balance between generation and consumption at all times. Due to
these changes the operating point of the power system will be less predictable and
today’s stability and security assessment tools may no longer be feasible, since they
are generally based on extensive off-line studies.
A core component of an efficient on-line dynamic security assessment is a fast
and reliable contingency screening. As part of this thesis a contingency screening
method is developed and its performance is assessed on a set of test cases. The
developed method reliably assesses first-swing transient angular stability of a power
system in its current state with respect to a given set of contingencies. In order
to ensure fast performance of the screening method, first a review of existing transient
stability assessment (TSA) methods was carried out and their computational
complexity was investigated. This allowed to identify the single machine equivalent
(SIME) method as the potentially fastest assessment method and, hence, well
suited for on-line DSA. Means for further performance improvement of the SIME
method are investigated such as the reduction of the degree of model detail used in
time-domain simulation, which results in a recommendation for the required model
detail for synchronous generator. A challenging task when using the SIME method
is to early and reliably determine the critical machine cluster, which is the group of
generators likely to lose synchronism. Therefore, a novel approach to identify the
critical machine cluster is proposed in the thesis. This approach uses a new coupling
coefficient, which is a measure of the coupling strength of a pair of generators,
and a simple clustering algorithm to identify the critical group of generators.
In order to determine a system to be transient secure, it is not sufficient to solely
assess if all synchronous generator remain in synchronism, it is also required that
the bus voltages remain within acceptable limits. A transient disturbance and the
following angular divergence of a group of generators can cause critical voltage
sags at certain buses in the system. In this thesis assessment of such voltage
sags using two types of sensitivities, which are derived from the algebraic network
equations, is proposed. These sensitivities are derived after an in-depth study of the
mechanism causing the voltage sags. The first sensitivity type is called load voltage
i/xii
sensitivity and allows identifying which bus voltages are affected by a change in
rotor angle of a particular generator. The second proposed type is called generator
power sensitivity, which provides information on the effect of load variation on
the generator’s power injection. It is shown that the derived sensitivities can give
valuable information to identify critical generator-load pairs as well as locations for
applying preventive or remedial control measures. Furthermore, the development
of a method for early prediction of critical voltage sags is described. The method’s
performance is compared to other prediction approaches. The results show that the
proposed method succeeds in early, accurately and consistently predicting critically
low voltage sags.
An efficient on-line DSA not only identifies unstable or insecure operation, but also
proposes preventive or remedial control actions to restore stability and security
in the system. In this thesis a further development of a method for determining
real-time remedial action against aperiodic small signal rotor angle instability is described.
A real-time aperiodic small signal rotor angle stability assessment method
is employed to monitor the respective stability boundary and to compute the respective
stability margin of each generator in the system. In case that the stability
margin of a particular generator falls below a pre-defined security threshold, the
proposed method analytically determines power generation re-dispatch solutions,
which restore stable and secure operation in the system. The effectiveness of the
method is presented on two test cases in two different test systems.
M3 - Ph.D. thesis
BT - On-line Dynamic Security
Assessment in Power Systems.
PB - Technical University of Denmark, Department of Electrical Engineering
ER -