t
Texas A&M University
College Station , TX 77840
Phone: 979 845 7476
Fax:
Email: huang@ee.tamu.edu


Power Systems Engineering Research Center

This is a project report from the Power Systems Engineering Research Center (PSERC). PSERC
is a multi-university Center conducting research on challenges facing a restructuring electric
power industry and educating the next generation of power engineers. More information about
PSERC can be found at the Centers website:
http://www.pserc.wisc.edu
.

For additional information, contact:

Power Systems Engineering Research Center
Cornell University
428 Phillips Hall
Ithaca, New York 14853
Phone: 607-255-5601
Fax: 607-255-8871


Notice Concerning Copyright Material

Permission to copy without fee all or part of this publication is granted if appropriate attribution
is given to this document as the source material. This report is available for downloading from
the PSERC website.




2002 Washington State University. All rights reserved
.

ACKNOWLEDGEMENTS


The work described in this report was sponsored by the Power Systems Engineering
Research Center (PSERC). We express our appreciation for the support provided by
PSERCs industrial members and by the National Science Foundation under grant NSF
EEC 0001880 received under the Industry / University Cooperative Research Center
program.

The industry advisors for the project were Mani Subramanian, ABB Network
Management; Don Sevcik, Center Point Energy; Bruce Dietzman, Oncor. Their
suggestions and contributions to the work are appreciated.
EXECUTIVE SUMMARY

Increasingly, within the deregulated power systems, voltage stability issues are becoming
significant in the way we plan, operate and maintain the system. The involvement of
newer players to the electricity power business has led to the proliferation of intra-area
and inter-area transactions of electricity in the transmission network. Typically, these
transactions are of considerably shorter duration and larger variety than that in vertically
integrated utility (VIU) structures, where utilities controlled power generation,
transmission and distribution. Not only does this lead to frequent and significant changes
in system operating points and load flow patterns, but also result in increasing volatility
in the system. This leads to potential security and reliability degradation in the existing
electric power system operations. One of the most affected security degradation, that is
being witnessed, is the voltage stability issue.

There is a need to evolve procedures to incorporate voltage stability effectively into the
operational aspects of deregulated power systems. To achieve this aim one needs to
quickly assess, from measurable quantities, the operational state of the system from
viewpoint of voltage stability. At the same time in case of stability problems, the
responsibility evaluation procedures need to be distinctly identified in the spirit of
deregulation.

The objective of this project was to evolve a framework, within the context of the
restructured power market operation, to incorporate voltage stability assessment into the
power system security, accountability and utilization factors for control devices.

In course of completing the objective of this project, we have come up with various new
and practical algorithms and procedures that can effectively address the incorporation of
voltage stability into the deregulated power system operation. We summarize the
significant outcomes of our work as given below.

Dynamic Modeling of generators, governors, ULTC, switched capacitor and loads
using EUROSTAG have been carried to study dynamic voltage stability and the
importance of dynamic reserves to maintain stability.
[8]
Detecting dynamic voltage
collapse using state information has been investigated for a variety of dynamic
disturbances.
[4]
Static modeling of FACT devices in investigating voltage stability
studies also has been carried out. It is observed that usage of devices like TCSC and
SVC could improve stability margin significantly.
[3]


A new way of using bifurcation analysis, using the unreduced jacobian matrix,
[7]
that
avoids singularity induced infinity problem and being computationally attractive has
been formulated.



Within the context of deregulated market the responsibility evaluation, in a potential
voltage collapse, assumes significance. Using the bifurcation analysis a procedure to
allocate contribution of generators, transmission and control elements in voltage
stability has been evolved.
[6]
This could be used as the basis for evaluating the
utilization factors and the pricing of control elements in power system.

An algorithm to compute Optimal Power Flow incorporating voltage stability has
been proposed.
[1]
The voltage stability constraint is computed from the power flow
state variables and the network topology. This algorithm has been applied further to
evaluate reliability indices in planning stages.
[2]
The incorporation of voltage stability
enhancement devices like FACTS, into the algorithm, has also been formulated.
[3]


The framework for transaction based power flow analysis for transmission utilization
allocation has been proposed.
[10]
The methods to model transaction for both pool type
and point-to-point long term bilateral type has been designed. This analysis has been
used to address the approach to equitable loss allocation in a deregulated market.
[11]

The approach has been applied to congestion management and responsibility
evaluation in the competitive, deregulated energy markets.
[9]


A new way to evaluate voltage stability responsibility in a composite market model
framework having both the pool type spot market and the bilateral long-term
transactions has been devised.
[5]
This decomposition approach has the potential to
address voltage stability usage, voltage security pricing and responsibility settlement
in a transaction based deregulated operation of electrical markets






TABLE OF CONTENTS


1.0 VOLTAGE STABILITY STUDIES AND MODELING ISSUES

1.1
Typical two bus system for voltage stability studies
1.2.1 Test Case for a 2-bus system
1.2.2 Effects Studied
1.2.3 Software used for Simulation
1.3
Power factor issues on static voltage collapse limits
1.4
Modeling of TCSC in static voltage stability analysis
1.5
Modeling of SVC & its effect on voltage stability analysis
1.6
Modeling of load and its effect on voltage stability margins
1.7
Summary of observations for the 2-bus case study

2.0 STABILITY INDEX FOR STATIC VOLTAGE SECURITY ANALYSIS

2.1.1 Voltage collapse point at load bus using a two bus model
2.1.2 Formulate a stability indicator
2.2.1 Numerical
Verification
2.2.2 Another Example: (Index L for the TCSC scenario discussed in 1.4)
2.3
Extension of the two bus voltage stability index L theory to a Multi-bus system
2.4.1 Test Case
2.4.2 Details of Case Scenarios Presented
2.5
Results
2.6
Summary for the multi-bus case scenarios

3.0 DYNAMIC VOLTAGE STABILITY ISSUES

3.1
Investigation towards applying index L for dynamic voltage stability studies
3.1.1 Simulation set-up details
3.2.1 Objective 1: Contribution of other load buses towards index at local bus
3.2.2 Observations
3.3.1 Objective 2: The index L information at first dip on voltage after a load change
3.3.2 Observations
3.4.1 Objective 3: Index variations at all buses following a load change
3.4.2 Observations
3.5.1 Objective 4: The index L information immediately after line outage
3.5.2 Observations
3.6.1 Objective 5: Approximate L evaluation after line outage based on pre-outage data
3.6.2 Observations
3.7 Publications

4.0 VOLTAGE STABILITY CONSTRAINED OPF ALGORITHM

4.1.1 Algorithm
4.1.2 Proposed incorporation of voltage stability index constraints
4.2 A sample run
4.3 Observations
4.4 Publications

5.0 TRANSACTION BASED STABILITY MARGIN AND UTLIZATION
FACTORS EVALUATION

5.1 Theory behind Transaction based power flow
5.2
Transcation based power flow algorithm
5.2.1 Assumptions
5.2.2 Step-wise procedure for decomposition
5.3
Transaction based voltage security margin allocation algorithm
5.4.1 Test case for demonstrating voltage security margin allocation algorithm
5.4.2
Results for various scenarios
5.5 Publications

6.0 CONCLUSION

7.0 REFERENCES

1
VOLTAGE STABILITY STUDIES AND MODELING
ISSUES



1.1 Typical two bus system for voltage stability studies

We have taken a sample 2 bus system which is generally used to evaluate static voltage
stability limit and simulated the effects which we were interested in evaluating. The
following subsections gives details of our case, the methods used for analysis and the
results obtained in our simulations


Consider the typical representation for studying voltage stability where the power
transmission model with one end without voltage support is as shown in Fig 1.


jX


V1
V2
I



SD







As shown in the figure