General Discussion This part presents papers that offer excellent overviews of the power system restoration process. They provide background and introductory material for those who want to become familiar with the key aspects of restoration. More importantly, they also include in-depth discussions of the overall restoration process. They help to illustrate the careful balance that will be required between different objectives, components, constraints, and operations to ensure a successful restoration. II. Discussion of Reprints 1.01 Power System Restoration-A Task Force Report, 1987, p. 3 The first paper offers a comprehensive discussion of the restoration process by first introducing the essential steps in restoration. It then examines restoration considerations for systems with specific types of generation, as well as considerations that are common to all systems such as switching operations timing and cold load inrush. To help address these concerns and plans for restoration, the paper discusses database requirements for generators, particularly with respect to hot restarts. It also provides background on generator mechanical, electrical, and frequency control systems; and how they impact restoration. The paper also discusses the importance of balancing reactive power and controlling voltage during restoration. It goes on to illustrate how load and generation need to be balanced as restoration proceeds, and how controlled islanding and generation isolation may develop. Finally, the paper compares the philosophies of sequential versus parallel restoration in terms of backup power supply problems, blackstart capability, and sectionalizing subsystems.

1. Power System Restoration
Methodologies & Implementation Strategies
John Wiley & Sons
ISBN: 0-7803-5397-8
Chapter One
Restoration Overview
I. General Discussion
This part presents papers that offer excellent overviews of the power system
restoration process. They provide background and introductory material for those who
want to become familiar with the key aspects of restoration. More importantly, they
also include in-depth discussions of the overall restoration process. They help to
illustrate the careful balance that will be required between different objectives,
components, constraints, and operations to ensure a successful restoration.
II. Discussion of Reprints
1.01 Power System Restoration-A Task Force Report, 1987, p. 3
The first paper offers a comprehensive discussion of the restoration process by first
introducing the essential steps in restoration. It then examines restoration
considerations for systems with specific types of generation, as well as considerations
that are common to all systems such as switching operations timing and cold load
inrush. To help address these concerns and plans for restoration, the paper discusses
database requirements for generators, particularly with respect to hot restarts. It also
provides background on generator mechanical, electrical, and frequency control
systems; and how they impact restoration. The paper also discusses the importance of
balancing reactive power and controlling voltage during restoration. It goes on to
illustrate how load and generation need to be balanced as restoration proceeds, and
how controlled islanding and generation isolation may develop. Finally, the paper
compares the philosophies of sequential versus parallel restoration in terms of backup
power supply problems, blackstart capability, and sectionalizing subsystems.

2. 1.02 Power System Restoration-The Second Task Force Report, 1987, p. 10
This paper investigates specific restoration problems that occurred following major
disturbances. These 19 studies identified such problems as faulty synchronization
equipment, resynchronization failures, lightning arrester failures due to switching
overvoltages, lack of adequate data, and switching errors. The paper then distills these
problems into seven general restoration problem categories: (1) reactive power
imbalance, (2) load-generation imbalance, (3) lack of load-generation coordination,
(4) lack of communication, (5) impediments caused by protective systems, (6) loss of
emergency backup power, and (7) lack of restoration plans. Each of these is followed
by suggested solutions and then by overall suggestions to help enhance restoration.
1.03 Analytical Tools for Power System Restoration-Conceptual Design, 1988, p. 17
The paper looks at the restoration process as a series of analyses and decisions to meet
a set of operating constraints. It proposes a conceptual framework for computeraided
monitoring and assessment during restoration. It also describes a knowledge-based or
expert system to help guide restoration. That system would evaluate monitored
conditions; suggest an appropriate sequence of actions for assessment; define the
problem and select software to be used in an analysis; and then validate the results of
the analysis. Based on these results, the system could modify the suggested sequence
of actions to help arrive at an improved restoration.
1.04 System Operation Challenges, 1988, p. 24
This paper includes a set of five reports that address various problems that can impact
the restoration process. The first involves the general issue of Energy Management
System (EMS) software and hardware slowly progressing towards obsolescence,
which affects normal operations as well as restoration. The second deals with the
difficulty involved in determining EMS requirements. The third raises the concern
that EMS alarm systems are designed for normal and limited emergency conditions,
and therefore, may need to be modified for restoration conditions. Under these
circumstances, only essential alarms should be activated to avoid overwhelming the
system. The fourth addresses restoration training concerns such as instructional
design, development of performance standards, and inadequacy of resources. Finally,
the fifth lists a series of restoration problems in the context of restoration planning,
actions during system degradation, and restoration of a stabilized system.
1.05 Power System Restoration Issues, 1991, p. 31
This paper lists major considerations that need to be dealt with during restoration,
such as switching transients, remote cranking power, damage assessment versus cause

3. identification, phase angle differences, and generator startup times. The paper then
lists the fundamental steps that need to be included in the development of a restoration
plan. It goes on to discuss exploration of more advanced methods such as expert
systems to aid in restoration and operator training.
1.06 Special Considerations in Power System Restoration, 1992, p. 37
This detailed paper addresses several important restoration issues. It discusses the
problem of excessive alarms that may occur, and it suggests that a more confined set
of alarms should be used during restoration. It then reviews restoration switching
problems and strategies, including the need to consider backup power systems and
cold weather problems. In addition, the optimal sequencing of generator startups is
discussed in detail. Next, the special problems associated with underground
transmission cable are illuminated. Finally, the paper lists the capabilities and
limitations of both public and private telecommunication systems during restoration.
1.07 New Approaches in Power System Restoration, 1992, p. 46
This paper looks at how the computer can be used to aid the restoration process. What
are the strengths and weaknesses of restoration that is fully computer automated,
computed aided, or simply shared cooperatively by both computer and operator? What
are the key steps in developing and implementing an expert system? What are the
requirements for an Operator Training Simulator (OTS) for use in restoration
preparation, and for what typical restoration scenarios would OTS be applicable?
1.08 A Hierarchical Interactive Approach to Electric Power System Restoration,
1992, p. 52
This paper begins with the argument that the use of general guidelines for restoration
lacks specificity. It proposes that these guidelines be framed more tightly in terms of
multiple, albeit conflicting, objectives; variables that can be controlled; and
constraints that need to be honored. The paper recommends a hierarchical interactive
control approach such that restoration control actions are decomposed into direct (or
localized), optimizing (centralized and global), and adaptive (alternative strategy)
layers. The paper then proceeds to explain these concepts to illustrate how they can be
used to improve the restoration process.
1.09 Special Consideration in Power System Restoration-The Second Working Group
Report, 1994, p. 61
This paper details four restoration issues. The first discusses different types of loads
and addresses modeling of cold load pickup both heuristically and through use of

4. physical models. The second looks at variations that may occur in cold load pickup on
low-voltage networks. The third discusses the unique role that gas turbines can play in
contributing to rapid system restoration. The fourth describes reactive power
balancing from the perspectives of transmission line charging, generator capabilities,
power-plant auxiliary requirements, and voltage control techniques.
1.10 Steam Plant Startup and Control in System Restoration, 1994, p. 68
This paper indicates the complexity of steam plant restarts following a major system
shutdown. It first discusses normal steam unit startups and shutdowns in detail. It then
explains how this orderly controlled process differs markedly from a unit that trips
and abruptly shuts down following a major disturbance. Finally, it offers methods to
improve generator operation during major disturbances through changes in design and
operator training.
1.11 An AGC Implementation for System Islanding and Restoration Conditions, 1994,
p. 75
This paper begins with an excellent background description of Automatic Generation
Control (AGC). From that base, it describes the development of an Island AGC
system on the Virginia power system to help improve the restoration process by
maintaining a constant frequency. It then shows options that would be available to
operators if Island AGC were invoked. It concludes with an analysis of actual test
results from the Virginia power system.
1.12 Analytical Tool Requirements for Power System Restoration, 1994, p. 86
This work presents an overview of restoration analytical tools (AT) and serves as a
valuable reference because it also addresses practical issues pertaining to restoration.
It explains the need for AT in preparing restoration plans and training, but it also
implies the need for general restoration guidelines that do not rely on AT. For each
type of AT restoration software, the authors indicate: (1) what needs to be studied; (2)
specific restoration features needed; (3) recommended preparatory work; (4) study
procedures; and (5) why restoration studies are needed.
1.13 A Framework for Power System Restoration Following a Major Power Failure,
1995, p. 96
The last paper in Part I is an organized summary of many of the other restoration
papers. As such, it can serve as a general restoration guide for operators, an outline to
help prepare a more specific restoration plan, and a guide to help evaluate and
improve restoration preparedness. The paper provides a framework for restoration by

5. outlining: (1) recommended goals and objectives of restoration; (2) responses that
should be initiated at the onset of abnormal conditions; (3) the sequence of restoration
actions that should be taken; and (4) steps that can be taken to enhance restoration
preparedness.
POWER SYSTEM RESTORATION - A TASK FORCE REPORT
Contributing Members: M. Adibi (Chairman), P. Clelland, L. Fink, H. Happ, R.
Kafka, J. Raine, D. Scheurer, and F. Trefny
Abstract - The IEEE PES System Operation Subcommittee has established the Power
System Restoration Task Force to: review operating practices, conduct a literature
search, prepare relevant glossaries and bibliographies, and promote information
exchange through technical papers. This is the first report of the Task Force.
The problem of bulk power system restoration following a complete or partial
collapse is practically as old as the electric utility industry itself. Many electric
utilities have developed over the years system restoration schemes that meet the needs
of their particular systems. These plans provide a great deal of insight into how the
restorative process is viewed by operating and planning personnel and what concerns
and constraints any plan must operate under.
The body of the report consists of notes prepared by members of the Task Force. It
should not be inferred that a complete reporting on Power System Restoration is
undertaken here. The intent is to report upon work of the Task Force to date. The
report also reviews several different restoration plans and shows their common
concerns and constraints.
I. INTRODUCTION
Today's bulk power systems provide a highly reliable supply of electric power.
However, due to a combination of unforeseen circumstances, there is the remote
possibility of a system wide outage. It is therefore prudent to be prepared for such an
unlikely eventuality by developing an up-to-date, readily accessible, and easily
understood power system restoration plan to allow a quick and orderly recovery from
a system outage, with resultant minimum impact on the public.
The bulk power supply major disturbances are primarily caused by transient faults and
mainly originate in the transimission systems. A very large number of these initiating
causes of supply interruptions are due to temporary faults, such as lightning, which
are immediately cleared by fast and selective protective relays, leaving the system in
an unfaulted condition. In many cases, however, these temporary initiating causes

6. produce subsequent effects which are "permanent," including loss of generation, load
and interconnections. These subsequent effects result in a partial to complete collapse
of unfaulted power systems. Thus, searching for the originating fault in power failures
may be futile, although identifying the status of the collapsed system components
would enhance restoration.
The major portion of the initial effort in restoring bulk supply is in restart and
reintegration procedures for generation and transmission systems. Load pick-up
during these initial phases, i.e. restart and reintegration, is necessary for (a) bringing
generators to their stable, minimum generation levels and (b) maintaining satisfactory
voltage conditions.
This paper first reviews three different restoration plans. It then describes the power
system characteristics relevant to restoration. This is followed by power system
considerations. Finally, it provides a bibliography covering 1940 to 1984.
II. REVIEW OF RESTORATION PLANS
1. Thermal Systems
The system restoration plan developed for all thermal systems serving metropolitan
areas is based on:
Sectionalization of the system into two or more subsystems and simultaneous
reintegration of generation and transmission in each subsystem. Selection of
subsystems is based on black-start capability within each subsystem and steam
generators with hot restart capability, and any transmission and loads required to
interconnect them.
Division of the restoration procedure into restart, reintegration, load pick-up and
interconnection phases. The restart phase begins with providing station service for the
restart of steam units within each subsystem. In the reintegration phase generating
stations are interconnected. During these two phases only the necessary loads are
picked-up as dictated by generation and transmission requirements. These two phases
end when the subsystems are synchronized and firmly interconnected. During the load
pick-up phase loads are picked-up in small increments to avoid excessive
underfrequency deviations. Due consideration is given to reactive power balance,
voltage conditions and stability of the system. With the start of large steam units and
availability of ample reactive absorbing capabilities, the EHV lines are energized and
the interconnections are reestablished.
2. Hydro-Thermal Systems

7. The system restoration plan developed for hydrothermal systems serving metropolitan
areas is based on energizing the entire bulk power transmission system in one step and
providing station service to all thermal generating stations. This approach uses the
ability of large hydro stations to absorb the charging currents of the complete
transmission system, and it is an attempt to avoid the time consuming line
sectionalization and switching operations which are normally required in system
restoration. The high voltages at the receiving end of lines are avoided by manual
operation of hydro's voltage regulators far below normal.
With the availability of large hydros, the interconnection phase can also precede the
load pick-up phase.
3. Primarily Hydro Systems
The system restoration plan developed for all hydro or primarily hydro systems
emphasize the switching operation and the response of prime movers to a sudden load
pickup. In this plan, due consideration is given to the time it takes to isolate and
energize the necessary lines by using central control systems to execute the switching
operation programs. The off-line dynamic programs are used to determine responses
of the system and provide guidelines for load pick-up based on the prevailing
generation on-line, transmission configuration and system loading.
4. Common Characteristics of Restoration
Review of the above and several other system restoration plans show a number of
common concerns even though their strategies are different:
1. Immediate resupply of station service.
2. Time consuming nature of switching operation.
3. Start-up timings of thermal units.
4. Voltage rise problems of energizing unloaded transmission lines.
5. Frequency response of prime movers to a sudden load pick-up.
6. Cold load inrush, power factors and coincident demand factors.
(Continues...)

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