reports
industry
CIGRE
Session 2008
Paris, France. 24 - 29 August
B5 is one of 16 Study
committees of CIGRE.
Its scope is to facilitate
and promote the progress of protection and
automation.
by Klaus-Peter Brand
79
The CIGRE Session 2008 includes a discussion meeting on Protection and
Automation.
These meetings are based on a “Special Reporter” system.
The session papers that have been submitted and accepted for inclusion in the conference
are actually not presented by the authors during the meeting. Instead, they are discussed by
the delegates as responses to the questions formulated in Special Reports.
Protection and automation subjects are covered by Study Committee B5, focused on
“Principles, design, application and management of power system protection, substation
control, automation, monitoring and recording – including associated internal and external
communications, substation metering systems and interfacing for remote control and
monitoring..”
PAC.SUMMER.2008
CIGRE B5
industry reports
80
Special reports are prepared by
industry experts and are available
in advance at the CIGRE web site in
order to allow participants to prepare
and submit their contributions for
the Discussion Meeting.
A zipped file containing all special
reports can be downloaded at :
http://www.cigre.org/gb/events/
session.asp
The file is:
B5_Special_Report_2008.pdf.
For the CIGRE 2008 Session the
protection and automation papers
are focused on two preferential
subjects:
PS1: Impact of process-bus
(IEC61850-9-2) on protection and
substation automation systems
PS2: Life Cycle Management
of Protection and Control Systems
Summary of the PS1 Special
Report
prepared by Christoph Brunner,
Switzerland
The title of preferential subject
1 was "Impact of process-bus
(IEC61850-9-2) on protection and
substation automation systems".
It was asked, to cover aspects
like system reliability, system
architecture and experience so far.
A total of 6 papers with authors
from 8 countries where submitted
in response to this subject. In
addition, 1 paper allocated to
preferential subject 2 (B5-206) is
discussing the testing aspects of
an IEC 61850 based process bus.
The discussion is grouped in the
following five main topics:
System architect ure
considering system reliability
Benefits of the technology
Practical experience
Condition monitoring of
primary equipment
Testing of a process bus based
system
A special thank is given to Fred
Steinhauser for his assistance in the
evaluation of the submitted papers
and in the writing of this special
report.
One introductor y remark
1 The Congress Palace in Paris
Discussion meetings
are based on a
"Special Reporter"
system.
needs to be made related to the
preferential subject and the term
process bus. The term process bus
does not exist officially in the norm
since the norm is open concerning
the structure of the communication
network. It originates from the
view of a substation automation
system with three hierarchical levels
(station, bay and process) and two
levels of communication network
connecting these hierarchical levels –
the station bus and the process bus.
In that view, the process bus is the
communication network connecting
the bay level to the process level. IEC
61850-9-2 defines the mapping
of one specific set of services
required on the process bus: the
transmission of sampled values as
it is used typically between voltage
and current transformers and bay
level devices as a replacement for
the analogue signal. A process bus
normally will support services
defined in IEC 61850-9-2 as well
as in IEC 61850-8-1. From the
papers that have been submitted,
some of them focus on connections
to current and voltage transformers
using IEC 61850-9-2 only, others
address the complete process bus,
i.e. all connections between bay
level devices and process equipment
including breakers and switches.
Summary of the PS1 Special
Report
prepared by Iony Patriota de Siqueira,
Brazil
This repor t rev iews the
contributions for the 42th Cigré
Session related to Preferential
Subject 2 of Study Committee B5 Protection and Automation, on Life
PAC.SUMMER.2008
Cycle Management of Protection
and Control Systems. Fifteen
countries (Austria, Brazil, Canada,
China, France, Germany, Japan,
Malaysia, Romania, Slovenia, Spain,
Switzerland, The Netherlands,
UK and USA) have submitted
seventeen papers covering a wide
range of issues on asset and life
cycle management of protection
and control systems (PCS). For
discussion the papers and associated
questions are organized in five
general topics common to Life Cycle
Management.
Protection and control systems
must be managed considering that
they have a finite life cycle, like
any other asset of modern power
systems. Obsolescence or end of
life of PCS devices may stem from
different causes, ranging from
physical deterioration or functional
inadequacy up to market inability
to provide sufficient spare parts for
maintenance.
Asset management, as applied to
PCS, comprises the set of technical
and administrative actions taken
to maximize return on investment
and to exploit asset full capacity
during the whole life cycle while
minimizing cost and risk to power
systems. Return can be measured in
economic terms or other technical
aspects like reliability, dependability,
security etc.
The papers submitted to this
session cover different aspects of
the subject. For the purpose of
discussion, they are organized in
five key topics:
Testing methods for protection
and control systems
Impact of IEC 61850 on
testing and asset management
Lifetime management of
protection and control systems
Remote management of
protection and control systems
Exploitation of protection and
control systems.
Ten questions have been raised
to motivate the discussion on these
topics, after a brief summary of each
paper.
Performance of
Relaying during
Wide-Area Stresby Damir Novosel, Quanta Technologies, USA
Recent wide-area electrical
dis turbances have clearly
demonstrated the vulnerability of
the interconnected power system
when operated outside its intended
design limits and have shown that
protective relay systems are very
often involved in major wide area
perturbations. This important
topic was recently addressed by
the IEEE Power System Relaying
Committee (PSRC). The working
group C12 has created a report on
Performance of Relaying during
Wide-Area Stressed Conditions.
The report addresses key aspects
of relaying schemes dur ing
wide-area disturbance conditions
such as: performance; equipment
rating; settings and coordination;
dependability vs. security; and
maintenance. It describes key
stressed system conditions that
affect conventional protection
schemes, analyzes field experiences
under stressed conditions, and
suggests proven methods and
solutions to improve protection
per for mance and minimi ze
disturbance propagation.
The report includes analysis of
wide area phenomena affecting
protec t ion, such as volt age
instability, collapse and
The Power System
Relaying Comettee is
in the Power & Energy
Society of IEEE.
excursions, angular and small-signal
inst abilit y, high equipment
loadings and power transfers,
frequency excursions and high
system unbalance.
The behavior of different
protection functions under the
stressed operating conditions listed
above has been analyzed.Sample
examples from the report are
described below.
Off-nominal frequenc y
a f f e c t s r el ay m e a s u r e m e n t
for all t ypes and designs of
relays. Microprocessor-based
relays are typically designed to
measure fundamental frequency
component s in their input
signals. Straightforward phasor
estimation algorithms such as
the generic Fourier algorithm
work well under nominal system
frequenc y. If the frequenc y
c han g e s , the me a surement
becomes less accurate in a manner
similar to measuring circuits of
analog relays. To remain accurate
under off-nominal frequency
conditions, microprocessor-based
relays either apply a variable
sampling frequenc y scheme
(frequency tracking), or apply a
constant sampling frequency but
compensate mathematically the
PAC.SUMMER.2008
by Damir Novosel, Quanta Technologies, USA
IEEE PES PSRC
industry reports
82
measured phasors for the difference
between the nominal and actual
system frequencies (frequency
compensation). Both methods,
although implemented differently,
are quite similar: they measure the
actual system frequency and adjust
either the sampling clock or the
raw phasor measurements for the
difference in frequency.
As experienced during a number
of disturbances, transmission
protective relays that may operate
for non-fault conditions such as:
Power swing/Angular instability
Load encroachment
Frequency deviation
Voltage instability
Combination of the above
Problems are exacerbated by
the significant pressure to increase
the transfer limits to serve the
increasing demand. For example, an
increased load jeopardizes security
of the distance function, having
increased resistive coverage such
as memory-polarized (expanding)
mho, self-polarized mho under
long reach settings, or quadrilateral
functions if the resistive reach
stretches too far.
Using load encroachment
character ist ics, blinders, or
quadrilateral functions with less
aggressive resistive coverage
goals solves the problem, and
allows retaining dependability of
protection under excessive load. In
conclusion, modern microprocessor
relays provide solutions for the
conditions above.
Protective devices applied for
generator and system backup
protection have often tripped
during a system disturbance. These
relays need to be applied properly so
that they protect the generator, but
help preserve the system integrity
by not tripping unnecessarily
during a disturbance. For example,
a loss-of-field (LOF) relay can trip
on a recoverable transient swing
that may enter its operating zone.
Different power swing scenarios
should be run to find out how long a
stable power swing locus is likely to
remain in the LOF operating zone.
Initially leading generator power
factors, slow/no voltage regulator
response, low system impedance,
and close-in three-phase faults
cleared almost at critical clearing
time are factors contributing to the
worst stable swing conditions. The
time delay for this relay should be
set depending on the worst-case
results to avoid operation during
stable swings. The settings of LOF
relays built in static exciters should
be reviewed to ensure that they
coordinate with the corresponding
LOF relay protections.
The design and maintenance
of protection schemes have a
significant effect on the overall
performance during wide area
disturbances and other abnormal
system conditions. Different
protection solutions offer different
advantages and disadvantages that
need to be considered during the
protection scheme design and
1 Adaptive control of protection system 2 Load Encroachment
power system state based on wide-area
measurements
Zone 2
sample-based
percentage differential output
relaying
phasor-based
output
percentage differential
relaying
Zone 3
X
Z Line
OR
Control
AND
Logic
output
directional comparison
relaying
PAC.SUMMER.2008
To circuit
Z Arc
breakers
Vote
maintenance process. In general,
the art of protective relaying is a
constant balance between capacity
to detect abnormal conditions in a
protected asset, and the ability to
restrain from operation under all
the other conditions. Considered
separately, dependability and
security of protection are easy
targets. It is the necessity to
s at isf y both requirement s
simult aneously that makes
protective relaying a challenging
technical field. The protection
function faces both security and
dependability problems when
pushed beyond their regular design
limits, particularly under severe
system-wide conditions, calling
for more sophisticated relaying
methods. Such methods in turn
are more difficult to set and verify.
Moreover, they do not provide the
same high level of performance,
but rather avoid impairing the
protection system response too
much. A solution could be Increase
the security of protection design in
the areas vulnerable to blackouts or
during stressed conditions.
From recent major events it
also appears that a large number
of protection system failures are
caused by human errors such
as wiring, inadequate design,
errors during maintenance or VT
switching, incorrect settings and
use of type test results as opposed
to comprehensive field and system
simulation testing
Implementing review and
certification of the processes, as
well as adequate testing procedures,
can reduce the number and severity
of human errors causing outages.
It is recommended to read the
report that could be found on the
PSRC committee web site:
http://www.pes-psrc.org.
ZLoad
R
Key stressed system
conditions are analyzed
in the PSRC report.