Download SC34 Discussion Session - Cigré Brasil

Study Committee B5 Colloquium
2005 September 14 – 16
Calgary, CANADA
Preferential Subject #3
Protection and Control of
Series Compensated Networks
Special Reporter: Graeme Topham
South Africa
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Introduction
 Renewed interest in series compensation:
 Increasing need to obtain maximum
benefit of existing assets
 Economically increase transfer capability
of transmission lines
 Secure better system stability
 Challenges in application particularly for
protection engineers
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Introduction
 Series compensation in modern power
systems:
 influences power flow
 reduces active power losses
 connects more robustly, different subsystems to a stronger integrated network
 Thyristor controlled series capacitors (TCSCs)
can be used to damp system & subsynchronous oscillations
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Introduction
 Introduction of series compensation into
existing networks requires extensive studies
covering:
 expected performance of new systems
 the influence of its introduction on the
operation of existing protection, control
and monitoring systems
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Introduction
 Challenges:
 Voltage inversion
 Current inversion
 Low frequency transients
 High frequency transients
 Sub-synchronous resonance
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Cigré Working Group B5-10
 Formed and commenced work in 2002
 Focus is protection, monitoring and control of
series compensated networks
 protection, control and monitoring of series
capacitor banks
 protection of series compensated and
adjacent power lines
 4 regular and 10 corresponding members
 Target date for report: 2006
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Cigré Working Group B5-10
 International survey questionnaire distributed
in December 2004
 main objective to obtain better overview of
practices currently used in SC networks
 Questionnaire focuses on:
 technical issues
 economic aspects
 environmental aspects
 refurbishment and future trends
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Cigré Working Group B5-10
 Participants urged to respond
 utilities who have experience with series
compensated networks;
 those who are currently investigating the
possibility for implementation of series
compensation; and,
 those who have decided in the past
against incorporating SC for various
reasons
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Papers
 18 papers received from 15 countries
 Paper 301 by WG B5-10 provides overview
 Main themes covered by remaining papers:
 Distance protection
 Non-distance protection
 Auto-reclosing
 FACTS devices
 Informational analysis
 Shunt capacitor banks
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Paper 301
 Paper 301 gives an overview of:
 the intended structure of the WG B5-10
report
 the main primary components of Fixed
and Thyristor-controlled SC banks;
 the basic control philosophies;
 the fundamental elements of series
capacitor bank protection; and,
 the challenges which face the protection
of SC and adjacent transmission lines.
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Paper 301
 Question #1: What are the main utility
considerations when deciding to series
compensate a transmission line and/or what are
the challenges faced in the protection, control and
monitoring of the capacitor banks as well as of the
series compensated and adjacent transmission
lines?
 Question #2: What economic and/or environmental
issues deter the implementation of series
compensation?
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Distance protection
 The papers which had distance protection as the main
theme cover a number of different aspects namely:
 polarizing voltages, directionality and phase
selection;
 zero sequence mutual coupling and subsynchronous frequencies;
 weak infeed;
 fault locating and calculation of the series
capacitor voltage; and,
 settings and testing
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Distance protection: Polarizing voltages,
directionality and phase selection


Paper 302 (Brazil) describes
 study of the effect of different polarizing quantities and
their suitability for SC applications
 a detailed analysis of relay directionality difficulties
imposed by SC
Paper 304 (Canada) discusses
 possible inadequacy of some protection techniques
which function correctly in traditional SC applications
but which may perform inadequately in applications
such as long lines interconnecting a high capacity wind
farm
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Distance protection: Polarizing voltages,
directionality and phase selection
 Question #3: Are there any experiences of other
unique series compensation distance relay
applications where special adjustments to settings
and/or logic are required to ensure correct
protection performance?
 Question #4: What analysis tools are available to
utilities to assist in evaluating distance relay
performance on series compensated applications
prior to the purchase or choice of a particular relay
type?
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Distance protection: Zero sequence mutual
coupling and sub-synchronous frequencies


Paper 306 (Germany/USA/Brazil)
 presents calculation of sub-synchronous frequencies
caused by series capacitors and their influence on
measuring algorithms.
Paper 316 (UK)
 influence of sub-synchronous frequencies on distance
measurement as well as addressing the effect of mutual
coupling on distance measurement
 benefit of introducing zero sequence compensation on
parallel transmission lines to improve distance
calculation
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Distance protection: Zero sequence mutual
coupling and sub-synchronous frequencies
 Question #5: Besides utilizing zero sequence
current compensation, what other techniques have
been successfully applied to distance relays to
resolve the impedance measurement inaccuracy
on series compensated parallel lines caused by
the mutual zero sequence impedance?
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Distance protection: Weak infeed


The weak infeed function was developed to speed up the
operation of impedance relays operating in a permissive
intertripping mode for cases where there is a lack of, or
insufficient, fault current
Paper 318 (South Africa)
 some experiences of high-risk incorrect operations
resulting in overtripping of parallel lines
 investigation revealed two areas of possible lack of coordination, namely the timing co-ordination due to
unforeseen drop-off delays of relays and impedance
co-ordination due to a lack of required overlapping of
the remote forward zone 2 element by the local reverse
blocking element in the worst case scenario (series
capacitor does not bypass)
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Distance protection: Weak infeed
 Question #6: What are the current experiences
with using the weak infeed protection function,
particularly in series compensated line protection
applications?
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Distance protection: Fault locating and
calculation of the series capacitor voltage

Paper 307 (China)
 accurate and efficient calculation of the series
capacitor voltage is crucial for the reliable operation of
a distance relay and for the accurate results of a fault
locator applied on series compensated lines
 presents a simplified capacitor voltage calculation
algorithm which is based on three procedures and
requires no iteration
 influence of charging current is eliminated with a
charging current compensation algorithm based on
travelling wave theory
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Distance protection: Fault locating and
calculation of the series capacitor voltage
 Paper 309 (Japan)
 protection and fault location experiences of
the SC EHV line in Japan. After analysis of
incorrect fault location results, obtained for
faults without gap flashover, a two-terminal
type fault location scheme was proposed as
an effective solution.
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Distance protection: Fault locating and
calculation of the series capacitor voltage
 Question #7: What are the main technical
difficulties with accurate fault location on series
compensated lines and what fault location
techniques are currently being successfully
employed on series compensated lines?
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Distance protection: Settings and
testing
 Paper 308 (India)
 case study of line relay settings for a 400 kV SC
double-circuit line and adjacent lines in India.
Each line has 40 % fixed (FSC) and 5 to 15 %
variable (TCSC) compensation
 paper recommends that instantaneous tripping
zones need to be considerably reduced or even
disabled at the remote ends of the protected SC
lines and on lines adjacent to them
 authors point out the necessity for the suitability
of existing protection on adjacent lines to be
investigated and, if necessary, changed
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Distance protection: Settings and
testing
 Paper 315 (USA/Sweden)
 USA utility’s approach towards testing
different line protection relays to be used
within the utility’s 500 kV network
 special attention is paid to specific project
oriented tests which are performed on a
complete protection system before
installation
 Paper 306 (Germany/USA/Brazil)
 outlines performance verification of protection
for SC lines in Brazil using a fully digital realtime network analyzer
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Distance protection: Settings and
testing
 Question #8:
a) What methodologies are used to optimize
settings for series compensated line
applications?; and,
b) What are the requirements of utilities in terms of
certification tests for relays and/or protection
systems before applying these to series
compensated lines?
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Non-Distance protection
 Three papers focussed on the application of nondistance protection to series compensated lines
 Paper 309 (Japan)
 indicates that the Japanese utility uses
current differential protection as the main
protection (with impedance type protection
used as back-up)
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Non-Distance protection


Paper 314 (Sweden)
 challenge of detecting high resistance earth faults and
the determination of a suitable reference quantity for
directional measurement
 paper identifies the fact that SC of transmission lines
can further endanger the correct functioning of
directional earth fault protection as the magnitude and
phase angle of residual voltage and current is
influenced by the series capacitors
Paper 317 (USA/France/UK)
 presents a directional comparison protection scheme
with sub-cycle operating times.
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Non-Distance protection
 Question #9: What are utility experiences with nondistance protection applications on series
compensated transmission lines?
 Question #10: What are the advantages,
disadvantages, technical challenges and cost
implications of using non-distance protection
when compared to using distance protection on
series compensated line protection applications?
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Auto-Reclosing
 Paper 305 (Germany)
 a controlled auto-reclosing technique for
compensated transmission lines which uses the
‘Prony Method’ to determine the future voltage
shape over the circuit-breaker
 illustrates that using the conventional zero
crossing of the voltage over the circuit-breaker as
the switching instant does not produce the
smallest transient overvoltages at the end of the
transmission line
 paper defines a new additional criterion which
considers the influence of the resonance circuit of
the compensated transmission line.
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Auto-Reclosing
 Question #11:
a) What are the current experiences with autoreclosing on series compensated transmission
lines?; and,
b) What are the technical challenges and proposed
solutions?
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FACTS Devices
 Two of the submitted papers dealt with the influence of
Unified Power Flow Controllers (UPFCs) on protection
 Paper 310 (Korea)
 investigates the impedance variation caused by
the series voltage injected by the UPFC according
to different UPFC operating conditions under
steady- and transient- states in the Korean
network
 impedance variations seen by the distance
protection relay were reviewed under fault
conditions to investigate the possibility of relay
misoperation and the possible need for relay
protection setting modifications
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FACTS Devices
 Paper 311 (Poland)
 also points out the influence of the series
branch of UPFCs on the impedance
measurement
 paper also considers aspects relating to
current differential and phase comparison
protection and mentions that adaptive
distance protection is a reasonable solution to
ensure protection flexibility
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FACTS Devices
 Question #12: Have there been any problematic
protection issues relating to the use of UPFCs
experienced by other utilities and what solutions
are available to mitigate against the problems?
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Informational Analysis
 Two papers, 312 (Russia/Sweden) and 313
(Russia), deal with the subject of informational
analysis as a tool to analyse uncertainty and
ambiguity in the identification of fault conditions in
electrical systems
 Question #13: What other novel theoretical tools
are available to assist in the analysis and
understanding of series compensated networks?
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Shunt Capacitor Banks
 Paper 303 (Brazil/Switzerland)
 distance protection behaviour under extreme
system conditions in the shunt capacitor bank
compensated transmission network in Brazil
 system was simulated with different software
tools and extensive tests were performed on
two different model power system simulator
tools
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Shunt Capacitor Banks
 Paper 303 (Brazil/Switzerland) cont.
 based on the investigations and the
experience collected during the tests, the
paper summarizes how selected power
system fault conditions can affect distance
protection
 authors propose protection strategies, readjustment of protection concepts and readaptation of protection algorithms to deal
with the challenges of extreme network
conditions
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Shunt Capacitor Banks
 Question #14: What influences of shunt capacitor
banks on protection measurement are reported
and how are the effects mitigated?
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Conclusions
 Evidence of continued valuable work being done to
improve the performance of the protection, control and
monitoring of series compensated networks
 New challenges in protecting series compensated and
adjacent transmission lines are emerging and
innovative techniques to deal with such challenges and
also to enhance equipment performance continue to be
developed
 Encouraging to see the high level of co-operation
between manufacturers and utilities (evident from the
number of joint papers) to solving application
problems and also to improve protection equipment
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Conclusions
 It is also apparent that a thorough understanding
of the subject is advantageous in order to ensure
optimal application of the correct equipment for
particular applications
 The importance and value added by international
collaboration through international bodies and
working groups should not be underestimated.