A Methodology to Assess and Rank the Effects of Hidden Failures in Protection Schemes based on Regions of Vulnerability and Index of Severity.

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A Methodology to Assess and Rank the Effects of Hidden Failures in Protection
Schemes based on Regions of Vulnerability and Index of Severity.


David C. Elizondo


Dissertation submitted to the Faculty of the
Virginia Polytechnic Institute and State University
in partial fulfillment of the requirements for the degree of


Doctor of Philosophy
In
Electrical Engineering


Jaime De La Ree, Chair
Arun G. Phadke
Yilu Liu
William T. Baumann
Antonio A. Trani
Reynaldo Nuqui

April 16, 2003
Blacksburg, Virginia

Keywords: Hidden Failures, Regions of Vulnerability, Index of Severity, Wide-Area
Disturbances, Power System Protection.

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A Methodology to Assess and Rank the Effects of Hidden Failures in Protection
Schemes based on Regions of Vulnerability and Index of Severity
David C. Elizondo
Abstract
Wide-area disturbances are power outages occurring over large geographical regions that
dramatically affect the power system reliability, causing interruptions of the electric supply to
residential, commercial, and industrial users. Historically, wide-area disturbances have greatly
affected societies.

Virginia Tech directed a research project related to the causes of the major disturbances in
electric power systems. Research results showed that the role of the power system’s protection
schemes in the wide-area disturbances is critical. Incorrect operations of power system’s
protection schemes have contributed to a spread of the disturbances. This research defined
hidden failures of protection schemes and showed that these kinds of failures have contributed in
the degradation of 70-80 percent of the wide-area disturbances. During a wide-area disturbance
analysis, it was found that hidden failures in protection schemes caused the disconnection of
power system elements in an incorrect and undesirable manner contributing to the disturbance
degradation.

This dissertation presents a methodology to assess and rank the effects of unwanted
disconnections caused by hidden failures based on Regions of Vulnerability and index of
severity in the protection schemes.

The developed methodology for the evaluation of the Region of Vulnerability found that the
indicator that most accurately reflects the relationship of the Region of Vulnerability with the
single line diagram is kilometers. For the representation of the Region of Vulnerability in the
power system, we found segments in the transmission line in which the occurrence of faults do
make the relay to operate, producing the unwanted disconnection caused by hidden failure. The

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results in the test system show that the infeed currents restrain the Region of Vulnerability from
spreading along power system elements.

Finally the methodology to compute the index of severity is developed. The index of severity has
the objective of ranking the protection schemes, considers the dynamics of the protection
schemes, and evaluates the overall disturbance consequence under the static and dynamic
perspectives.

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Acknowledgments
To describe five years full of learning experiences and valuable input from a number of people in
this section of the dissertation is complicated, but here is my attempt.

First of all I would like to thank my Lord, because now the second part of my dream has come to
reality.

The guidance, patience, and always vigorous talks with my advisor, Dr. Jaime De La Ree, were
an important factor in the achievement of this dissertation. I thank him for his contributions in
my integral growth as a person. Special thanks to the committee members: Dr. Phadke, Dr. Yilu
Liu, Dr. Antonio Trani, and Dr. William Baumann for their valuable feedback. Dr. Virgilio
Centeno and Dr. Antonio Nieto recommendations helped me to conceive my plans in the
appropriate perspective.

The Power Engineering staff, Carolyn Guynn and Glenda Caldwell helped in many ways during
these five years; they made me feel like home. The Power Engineering graduate students with
whom I had long discussions in our attempts to “find the truth” will always be in my memory.
The words included in Reynaldo Nuqui’s dissertation are precise: we could develop a
competitive but healthy academic environment in the Power Lab; efforts exist towards the
unification of the group after graduation. Special thanks to: Abdel Khatib, Reynaldo Nuqui, Bin
Qiu, Sebastian Rosado, Arturo Bretas, Dr. Aysen Arsoy, Juancarlo Depablos, Marcos Donolo, Q
Qiu, Liling Huang, Dr. Dong, and Ling Chen. The enthusiastic members of the “Aztec Night”
deserve to be mentioned; those meetings provided the escape from the routine and after enjoying
them we came back with a fresh mind, ready to reexamine the problems to solve.

This research work was made possible in part thanks to the National Council for Science and
Technology, CONACYT, Mexico, and a grant from EPRI-DoD.

Finally I would like to thank my family that provided support from my foreign country. Special
thanks to my wife: Leticia Alvarez. I thank you for all your patience and great help during these
five years; thanks for being part of this journey and take care of the two wonderful sons that were
born during our graduate studies. I am sure I could not have completed this project without you.

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For my wife: Leticia Alvarez