IEC 60143-4:2010

IEC 60143-4 ®
Edition 1.0 2010-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Series capacitors for power systems –
Part 4: Thyristor controlled series capacitors

Condensateurs série destinés à être installés sur des réseaux –
Partie 4: Condensateurs série commandés par thyristors

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IEC 60143-4 ®
Edition 1.0 2010-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Series capacitors for power systems –
Part 4: Thyristor controlled series capacitors

Condensateurs série destinés à être installés sur des réseaux –
Partie 4: Condensateurs série commandés par thyristors

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XA
CODE PRIX
ICS 29.240.99; 31.060.70 ISBN 978-2-88912-242-4
– 2 – 60143-4 Ó IEC:2010
CONTENTS
FOREW ORD . 4
1 Sc o pe . 6
2 Normative references . 6
3 Terms, definitions and abbreviations. 7
3.1 Abbrev iations. 7
3.2 Definitions . 7
4 Operating and rating considerations . 11
4.1 General . 11
4.2 TCSC characteristics . 14
4.3 Operating range . 15
4.4 Reactive power rating . 16
4.5 Power oscillation damping (POD) . 16
4.6 SSR mitigation . 16
4.7 Harmonics . 17
4.8 Control interactions between TCSCs in parallel lines . 17
4.9 Operating range, overvoltages and duty cycles . 17
4.9.1 Operating range . 17
4.9.2 Transient overvoltages . 17
4.9.3 Duty cycles . 17
5 Valve control . 18
5.1 Triggering system . 18
5.2 System aspects . 19
5.3 Normal operating conditions . 19
5.4 Valve firing during system faults . 20
5.5 Actions at low line current . 20
5.6 Monitoring . 20
6 Ratings . 20
6.1 Capacitor rating . 20
6.2 Reactor rating . 21
6.3 Thyristor valve rating . 21
6.3.1 Current capability . 21
6.3.2 Voltage capability . 22
6.4 Varistor rating . 24
6.5 Insulation level and creepage distance . 24
7 Tests . 24
7.1 Test of the capacitor . 25
7.1.1 Routine tests . 25
7.1.2 Type tests . 25
7.1.3 Special test (endurance test) . 26
7.2 Tests of the TCSC reactor. 26
7.2.1 Routine tests . 26
7.2.2 Type tests . 26
7.2.3 Special tests . 26
7.3 Tests of thyristor valves . 27
7.3.1 Guidelines for the performance of type tests . 27
7.3.2 Routine tests . 29

60143-4 Ó IEC:2010 – 3 –
7.3.3 Type tests . 29
7.4 Tests of protection and control system . 38
7.4.1 Routine tests . 38
7.4.2 Type tests . 39
7.4.3 Special tests . 39
8 Guide for selection of rating and operation . 40
8.1 General . 40
8.2 Thyristor controlled series capacitor . 41
8.2.1 AC transmission system . 41
8.2.2 TCSC Operational objectives . 42
8.2.3 TCSC ratings . 42
8.3 Thyristor valves . 44
8.4 Capacitors and reactors . 44
8.4.1 Capacitor considerations . 44
8.4.2 Reactor considerations . 45
8.5 Fault duty cycles for varistor rating . 45
8.6 Valve cooling system . 46
8.7 TCSC control and protection . 46
8.7.1 Control . 47
8.7.2 Protection . 49
8.7.3 Monitoring and recording . 50
8.8 Precommissioning and Commissioning Tests . 50
8.8.1 Introduction . 50
8.8.2 Precommissioning Tests . 51
8.8.3 Station tests . 51
8.8.4 Commissioning (field) tests . 51
Bibliography . 53

Figure 1 – Typical nomenclature of a TCSC installation . 12
Figure 2 – TCSC subsegment . 13
Figure 3 – TCSC steady state waveforms for control angle α and conduction interval σ . 14
Figure 4 – TCSC power frequency steady state reactance characteristics according to
Equation (1) with λ = 2,5 . 15
Figure 5 – Example of TCSC operating range for POD (left) and SSR mitigation (right). 15
Figure 6 – Valve base electronics (VBE) . 18
Figure 7 – Valve electronics (VE) . 19
Figure 8 – Thyristor valve voltage in a TCSC . 23
Figure 9 – Typical block diagram of a real time TCSC protection- and control system
simulation environment . 40
Figure 10 – Example of operating range diagram for TCSC . 43

Table 1 – Peak and RMS voltage relationships . 13
Table 2 – Typical external fault duty cycle with unsuccessful high speed auto-reclosing . 45
Table 3 – Typical duty cycle for internal fault with successful high speed auto-reclosing . 45
Table 4 – Typical duty cycle for internal fault with unsuccessful high speed auto-
reclosing . 46

– 4 – 60143-4 Ó IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SERIES CAPACITORS FOR POWER SYSTEMS –

Part 4: Thyristor controlled series capacitors

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60143-4 has been prepared by IEC technical committee 33: Power
capacitors and their applications.
This part of IEC 60143 is to be used in conjonction with the following standards:
– IEC 60143-1:2004, Series capacitors for power systems – Part 1: General
– IEC 60143-2:1994, Series capacitors for power systems – Part 2: Protective equipment for
series capacitor banks
– IEC 60143-3:1998, Series capacitors for power systems – Part 3: Internal fuses

60143-4 Ó IEC:2010 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
33/472/FDIS 33/478/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of IEC 60143 series, under the general title Series capacitors for power
systems can be found on the iec website.
NOTE This standard contains excerpts reproduced from IEEE Std 1534-2002. IEEE Std 1534-2002 IEEE
Recommended Practice for Specifying Thyristor-Controlled Series Capacitors. Reprinted with permission from
IEEE, 3 Park Avenue, New York, NY 10016-5997 USA, Copyright 2002 IEEE.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
 reconfirmed,
 withdrawn,
 replaced by a revised edition, or
 amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – 60143-4 Ó IEC:2010
SERIES CAPACITORS FOR POWER SYSTEMS –

Part 4: Thyristor controlled series capacitors

1 Scope
This part of IEC 60143 specifies testing of thyristor controlled series capacitor (TCSC)
installations used in series with transmission lines. This standard also addresses issues that
consider ratings for TCSC thyristor valve assemblies, capacitors, and reactors as well as
TCSC control characteristics, protective features, cooling system and system operation.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
NOTE If there is a conflict between this part of IEC 60143 and a standard listed below in Clause 2, this standard
prevails.
IEC 60050-436, International Electrotechnical Vocabulary – Chapter 436: Power capacitors
IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60068-1, Environmental Testing – Part 1: General and guidance
IEC 60068-2-2, Basic environmental testing procedures – Part 2-2: Tests – Tests B: Dry heat
IEC 60068-2-78, Basic environmental testing procedures – Part 2-78: Tests – Tests C: Damp
heat, steady state
IEC 60071-1, Insulation co-ordination – Part 1: Definitions, principles and rules
IEC 60071-2, Insulation co-ordination – Part 2: Application guide
IEC 60076-1:1993, Power transformers – Part 1: General
IEC 60076-6:2007, Power transformers – Part 6: Reactors
IEC 60143-1:2004, Series capacitors for power systems – Part 1: General
IEC 60143-2:1994, Series capacitors for power systems – Part 2: Protective equipment for
series capacitor banks
IEC 60143-3:1998, Series capacitors for power systems – Part 3: Internal fuses
IEC 60255-5, Electrical relays – Part 5: Insulation coordination for measuring relays and
protection equipment – Requirements and tests
IEC 60255-21 (all parts), Electrical relays – Vibration, shock, bump and seismic tests on
measuring relays and protection equipment

60143-4 Ó IEC:2010 – 7 –
IEC 60270, High-voltage test techniques – Partial discharge measurements
IEC 61000-4-29, Electromagnetic compatibility (EMC) – Part 4-29: Testing and measurement
techniques – Voltage dips, short interruptions and voltage variations on d.c. input port
immunity tests
IEC 61954:1999, Power electronics for electrical transmission and distribution systems –
Testing of thyristor valves for static VAR compensators
NOTE Additional useful references, not explicitly referenced in the text, are listed in the Bibliography .
3 Terms, definitions and abbreviations
For the purposes of this document, the following terms, definitions and abbreviations as well
as those given in IEC 60143-1, IEC 60143-2, IEC 60143-3 and some taken from IEC 60050-
436 apply.
NOTE In some instances, the IEC definitions may be either too broad or too restrictive. In such a case, an
additional definition or note has been included.
3.1 Abbreviations
ETT Electrically triggered thyristors
FACTS Flexible ac transmission systems
FSC Fixed series compensation
LTT Light-triggered thyristors
MC Master control
MTBF Mean time between failure
MTTR Mean time to repair
POD Power oscillation damping
RAM Reliability, availability, and maintainability
RIV Radio influence voltage
RTU Remote terminal unit
SCADA Supervisory control and data acquisition
ER Events recorder
FR Fault recorder
RTDS Real time digital simulation
SSR Sub synchronous resonance
SVC Static var compensator
TCR Thyristor-controlled reactor
RMS Root mean square
3.2 Terms and definitions
3.2.1
thyristor valve
electrically combined assembly of thyristor levels, complete with all connections, auxiliary
components and mechanical structures, which can be connected in series with each phase of
the reactor or capacitor of a TCSC

– 8 – 60143-4 Ó IEC:2010
3.2.2
bypass current
the current flowing through the bypass switch, protective device, thyristor valve, or other
devices, in parallel with the series capacitor, when the series capacitor is bypassed
3.2.3
capacitive range
TCSC operation resulting in an effective increase of the power frequency reactance of the
series capacitor (See Figure 5)
3.2.4
temporary overload
short duration (typically 30 min) overload capability of the TCSC at rated frequency and
ambient temperature range
3.2.5
dynamic overload
short duration (typically 10 s) overload capability of the TCSC at rated frequency and ambient
temperature range. (See Figure 5 and Figure 10)
3.2.6
platform-to-ground cooling/air-handling insulator
an insulator that encloses cooling/air handling paths between platform and ground level
3.2.7
thyristor-controlled series capacitor bank
TCSC
an assembly of thyristor valves, TCSC reactor(s), capacitors, and associated auxiliaries, such
as structures, support insulators, switches, and protective devices, with control equipment
required for a complete operating installation
3.2.8
valve electronics
VE
electronic circuits at valve potential(s) that perform control functions
3.2.9
TCSC reactor
one or more reactors connected in series with the thyristor valve (see NOTE This figure contains material
reproduced from IEEE Std 1534-2002. IEEE Std 1534-2002 IEEE Recommended Practice for Specifying Thyristor-
Controlled Series Capacitors, Copyright 2002 IEEE. All rights reserved.
Figure 1, item 12)
3.2.10
thyristor valve enclosure
a platform-mounted enclosure containing thyristor valve(s) with associated valve cooling and
electronic hardware
3.2.11
valve varistor
an assembly of varistor units that limit overvoltages to a given value. In the context of TCSCs,
the valve varistor is typically defined by its ability to limit the voltage across a thyristor valve
to a specified protective level while absorbing energy. The valve varistor is designed to
withstand the temporary overvoltages and continuous operating voltage across the thyristor
valve
60143-4 Ó IEC:2010 – 9 –
3.2.12
valve blocking
an operation to prevent further firing of a thyristor valve by inhibiting triggering
3.2.13
valve deblocking
an operation to permit firing of a thyristor valve by removing valve blocking action
3.2.14
valve base electronics
VBE
an electronic unit, at earth potential, which is the interface between the control system of the
TCSC and the thyristor valves
3.2.15
voltage breakover protection
VBO
means of protecting the thyristors from excessive voltage by firing them at a predetermined
voltage
3.2.16
redundant thyristor levels
the maximum number of thyristor levels in the thyristor valve that may be short-circuited,
externally or internally, during service without affecting the safe operation of the thyristor
valve as demonstrated by type tests; and which if and when exceeded, would require either
the shutdown of the thyristor valve to replace the failed thyristors, or the acceptance of
increased risk of failures
3.2.17
capacitor current
I
C
current through the series capacitor (see Figure 2)
3.2.18
line current
I
L
power frequency line current (see Figure 2)
3.2.19
rated current
I
N
the RMS line current (I ) at which the TCSC should be capable of continuous operation with
L
rated reactance (X ) and rated voltage (U )
N N
3.2.20
valve current
I
V
current through the thyristor valve (see Figure 2)
3.2.21
capacitor voltage
U
C
voltage across the TCSC (see Figure 2)
3.2.22
protective level
U
PL
magnitude of the maximum peak of the power frequency voltage appearing across the
overvoltage protector during a power system fault

– 10 – 60143-4 Ó IEC:2010
NOTE The protective level may be expressed in terms of the actual peak voltage across a segment or in terms of
the per unit of the peak of the rated voltage across the capacitor.
3.2.23
rated TCSC voltage
U
N
the power frequency voltage across each phase of the TCSC that can be continuously
controlled at nominal reactance (X ), rated current (I ), frequency, and reference ambient
N N
temperature range
3.2.24
apparent reactance
X(α)
TCSC apparent power frequency reactance as a function of thyristor control angle (α) (see
Figure 4)
3.2.25
rated frequency
f
N
frequency of the system in which the TCSC is intended to be used
3.2.26
rated capacitance
C
N
capacitance value for which the TCSC capacitor has been designed
3.2.27
physical reactance
X
C
the power frequency reactance for each phase of the TCSC bank with thyristors blocked and
a capacitor internal dielectric temperature of 20 ˚C; X = 1(2πf ´C )
C N N
3.2.28
boostfactor
k
B
the ratio of X(α) divided by X ; k = X(α) / X
C B C
3.2.29
nominal reactance
X
N
the nominal power frequency reactance for each phase of the TCSC with rated line I and
N
nominal boost factor
3.2.30
conduction interval
σ
that part of a cycle during which a thyristor valve is in the conducting state, σ = 2β (see
Figure 3)
3.2.31
control angle
α
the time expressed in electrical angular measure from the capacitor voltage (U ) zero
C
crossing to the starting of current conduction through the thyristor valve. (see Figure 3)
3.2.32
internal fault
an internal fault is a line fault occurring within the protected line section containing the series
capacitor bank
60143-4 Ó IEC:2010 – 11 –
3.2.33
external fault
an external fault is a line fault occurring outside the protected line section containing the
series capacitor bank
4 Operating and rating considerations
4.1 General
Transmission line series reactance can be compensated by combinations of fixed series capacitors and TCSC
capacitors and TCSC banks (see NOTE This figure contains material reproduced from IEEE Std 1534-2002. IEEE
Std 1534-2002 IEEE Recommended Practice for Specifying Thyristor-Controlled Series Capacitors, Copyright 2002
IEEE. All rights reserved.
Figure 1). TCSC banks use one or more controllable modules to achieve the range of
performance requirements specified by the purchaser. This clause discusses requirements of
TCSC operating and rating considerations.
The TCSC circuit configurations discussed in this standard (see Figure 2) consider three
basic operating modes:
· BLK operation with thyristors blocked (no current through the thyristor valve)
· BP operation with continuous thyristor current
· CAP operation in capacitive boost mode.

– 12 – 60143-4 Ó IEC:2010
Phase A Phase B Phase C
11 11 11
10 10
1 1
6 9
9 9
2 2 2
10 11 10 11 10 11
Phase C
Phase A Phase B
Key
1 Segment (-phase) 9 External bypass disconnect switch
2 Switching step or module (3-phase) 10 External isolating disconnect switch
3 Capacitor units 11 External grounding disconnect switch
4 Discharge current limiting and damping equipment 12 TCSC reactor
5 Varistor 13 Thyristor valve
6 Bypass gap 14 Controllable subsegment (1-phase)
7 Bypass switch 15 Additional controllable subsegments when required
8 Additional switching steps when required 16 Additional FSC segment when required
NOTE This figure contains material reproduced from IEEE Std 1534-2002. IEEE Std 1534-2002 IEEE
Recommended Practice for Specifying Thyristor-Controlled Series Capacitors, Copyright 2002 IEEE. All rights
reserved.
Figure 1 – Typical nomenclature of a TCSC installation

60143-4 Ó IEC:2010 – 13 –
Figure 2 – TCSC subsegment
The definition of control angle (α) with reference to voltage zero crossing is selected to be
consistent with other power electronic devices (see Figure 3). However, it should be noticed
that many TCSC control systems use the line current wave form as an important control
reference.
When a TCSC is operating in CAP mode, the current in the thyristor valve branch can boost
the voltage across the capacitor, resulting in an apparent capacitive reactance larger than the
physical capacitor reactance, see Figure 4. In a TCSC application, the increased capacitive
reactance would increase the line current. The current pulses through the thyristor valve,
distorts the capacitor voltage (U ). The distorted waveform means that the capactor voltage
C
includes non-power frequency components and that the relationship between total RMS and
total peak voltage is not 2 as in the case for a pure sinusoidal waveform, see Table 1.
Table 1 – Peak and RMS voltage relationships
Boost Normalized Power Power frequency Total RMS Total peak
factor discharge frequency RMS peak voltage voltage voltage
frequency voltage
k
λ
B
1,0 2,5 1,0 1,41 1,00 1,41
2,0 2,5 2,0 2,83 2,02 2,55
3,0 2,5 3,0 4,24 3,05 3,70
1,0 3,5 1,0 1,41 1,00 1,41
2,0 3,5 2,0 2,83 2,03 2,54
3,0 3,5 3,0 4,24 3,07 3,67
– 14 – 60143-4 Ó IEC:2010
2,0 2,0
Boost factor 2,0
Boost factor = 1,0
~
1,5 1,5
I = I + I
C L V
I
L
1,0 1,0
I
L
0,5 0,5
b
s
0,0 0,0
a
a
-0,5 -0,5
I
V
-1,0 -1,0
U at a = 180°
C
U at a = 145°
C
-1,5 -1,5
-2,0 -2,0
0 90 180 270 360 0 90 180 270 360
Time  (°) Time  (°)
NOTE This figure contains material reproduced from IEEE Std 1534-2002. IEEE Std 1534-2002 IEEE
Recommended Practice for Specifying Thyristor-Controlled Series Capacitors, Copyright 2002 IEEE. All rights
reserved.
Figure 3 – TCSC steady state waveforms for control angle α and conduction interval σ
4.2 TCSC characteristics
NOTE This subclause contains excerpts reproduced from IEEE Std 1534-2002. IEEE Std 1534-2002 IEEE
Recommended Practice for Specifying Thyristor-Controlled Series Capacitors, Copyright 2002 IEEE. All rights
reserved.
TCSC characteristics are determined from the series capacitor (C) and reactor (L) circuit
parameters shown in Figure 2. The steady state TCSC power frequency reactance X(α) as a
function of thyristor control angle (α) can be calculated from Equation (1).
2 2
é ( ) ù
1 l 2b+ sin 2β 4l l´tan (lb) - tan (b)
X()a= 1 -  ´  +  ´cos()b´ (1)
ê ú
2 2 2
2pf C (l -1) p (l -1) p
N ë û
where
β is half the conduction interval (π-α);
α is control angle from capacitor voltage zero;
λ is the normalized discharge frequency ;
2pf LC
N
C is the series capacitor capacitance;
L is the TCSC reactor inductance.
Normalized units (Peak)
Normalized units (Peak)
60143-4 Ó IEC:2010 – 15 –
-1
-2
-3
-4
-5
90 100 110 120 130 140 150 160 170 180

Thyristor control angle  a (°)
Angle de contrôle du thyristor  [deg]

Figure 4 – TCSC power frequency steady state reactance characteristics
according to Equation (1), with λ = 2,5
4.3 Operating range
The operating range is one of the most important factors for rating of a TCSC. It has a major
impact on the main circuit components stresses and must therefore be clearly specified by the
purchaser. The TCSC shall be designed to withstand operation with the different reactances
and line currents within the specified operating range. The required operating range shall be
defined by system studies performed by the purchaser and be clearly stated in the
specification with a set of curves of the apparent fundamental frequency TCSC reactance or
boost factor (k ) versus the line current as indicated in Figure 5. The required operating range
B
depends on the purpose of the TCSC. Generally a TCSC for power oscillation damping (POD)
requires a larger operating range than a TCSC for SSR-mitigation.

3,5 3,5
CAP: Continuous CAP: Continuous
CAP: 30 min overload CAP: 30 min overload
3,0 3,0
CAP: 10 s overload CAP: 10 s overload
BP: Continuous BP: Continuous
BP: 30 min overload BP: 30 min overload
2,5 2,5
BP: 10 s overload BP: 10 s overload
2,0 2,0
1,5 1,5
1,0 1,0
0,5 0,5
0 0
-0,5 -0,5
0 0,5 1,0 1,5 2,0 0 0,5 1,0 1,5 2,0
Line current  (pu) Line current  (pu)

Figure 5 – Example of TCSC operating range for POD (left) and SSR mitigation (right)
The operating range does not extend all the way to zero line current because steady-state
firing of a thyristor valve is not possible at very low thyristor valve voltages and currents. All
thyristors and associated firing and monitoring electronics have a minimum voltage below
which firing and condition monitoring is not possible. In addition, some thyristor valves have
power supplies for the firing circuits that may place additional constraints on the firing of the
Boost factor k
B
Boost factor k
B
– 16 – 60143-4 Ó IEC:2010
thyristor valve when the line current is low. This results in a minimum line current and boost
factor (k ) below which operation in CAP mode is not feasible. This can have implications on
B
the application and operation of the TCSC. The impact of series compensation is of limited
value at low line currents. If SSR is a concern, it is recommended that the TCSC be bypassed
at line current levels below which operation in CAP mode cannot be maintained.
4.4 Reactive power rating
When a TCSC is operating in capacitive boost mode the reactive power seen by the power
system differs from the reactive power of the capacitors. The reactive power output of a TCSC
and the reactive power of the capacitors are given by
Q = 3´ k ´ ´I
TCSC B
L
wC
2 2
Q = 3´ k ´ ´ I
CAP
B L
wC
The nominal reactive power rating of the TCSC shall be defined as the reactive power output
given by Q in the above expressions with nominal boost and nominal line current.
TCSC
4.5 Power oscillation damping (POD)
Power oscillation damping (POD) is a specialized subset of closed loop reactance control
which can be realized by modulating the TCSC reactance in response to transmission system
conditions to dampen power system oscillations. By using BP mode during power oscillations,
the damping performance of a TCSC can be increased significantly since this extends the
reactance range of a TCSC to a lower inductive reactance.
A TCSC for POD applications shall fulfil the following fundamental requirements:
· The POD controller shall be able to handle system disturbances that results in power
oscillations through zero and be insensitive to the direction of the average power flow.
· The POD controller shall be able to handle large system disturbances. This means that the
structure of the POD controller must be such that the desired phase shift between the
input and output signal of the TCSC is maintained independently of the magnitude of the
power oscillation.
· The TCSC control system shall be able to handle mode switching from CAP to BP and BP
to CAP during power oscillation damping.
4.6 SSR mitigation
When properly designed and applied, TCSC can provide a degree of SSR mitigation when
operated with a boost factor greater than one. The TCSC can help mitigate the resonant SSR
series combination that results from fixed series capacitors.
If the TCSC application requires that SSR concerns be addressed, it is recommended that
studies be performed involving detailed models of the power system, the nearby turbine
generators and the TCSC. This recommendation is heightened in situations when the power
system includes a combination of fixed series capacitors and TCSC and the combined series
compensation exceeds 50 %. If the studies indicate that fixed series capacitors with the
desired level of compensation will result in an SSR problem, the TCSC supplier shall be
actively involved in the SSR studies.
A TCSC can only provide SSR mitigation if the valves are firing on a continuous basis. The
result is that for the TCSC to meet the SSR mitigation objectives its operating region must be
constrained to a boost factor equal to or greater than the minimum value at which it provides
the desired SSR-mitigation. The degree of mitigation can be a function of the control angle

60143-4 Ó IEC:2010 – 17 –
but it is desirable that the TCSC control system can provide a sub-synchronous impedance
that depends as little as possible on the boost factor.
In an application where SSR mitigation is critical, the operation of the TCSC under low line
current condition must be reviewed, see 4.3.
4.7 Harmonics
A TCSC operating in CAP mode will produce harmonics. The magnitude of the harmonics
depends on the operating point in terms of line current and boost factor.
In application where TCSC is used for SSR-mitigation or power oscillation damping purposes,
the TCSC normally operates with the nominal boost factor and only temporarily during system
disturbances operates with a higher boost factor. Therefore harmonic requirements on such
TCSC installation shall be given for nominal operation i.e. rated line current and nominal
boost factor.
Harmonic requirements for a TCSC shall be given in terms of maximum allowed voltage
distortion caused by the TCSC at the busses connecting the series compensated line
segment. Harmonic studies for a TCSC installation requires detailed transmission line data of
the series compensated line together with harmonic network equivalents for the line ends to
be supplied by the purchaser.
4.8 Control interactions between TCSCs in parallel lines
In situation where two TCSC are located on parallel lines, there is a risk for control
interactions between the TCSC’s during system disturbances. To reduce the risk for harmful
interactions between parallel connected TCSC’s the following is recommended:
· The POD controllers to use the same input signals, i.e. the sum of the power flow on the
parallel circuits.
· The POD controllers to have similar dynamics.
· The reactance controllers to have similar dynamics and respond in similar ways when
hitting limits.
· The degree of compensation of a line segment at maximum boost factor should be well
below 100 %.
4.9 Operating range, overvoltages and duty cycles
4.9.1 Operating range
The TCSC shall be capable of withstanding the operation within the specified continuous and
temporary operating ranges. The operating range is generally specified by the purchaser.
4.9.2 Transient overvoltages
The TCSC shall be suitable for repeated operations at transient overvoltages caused by
power system faults, with the highest possible value U that is expected to occur across the
PL
TCSC terminals. The transient overvoltage is normally limited by a varistor overvoltage
protector.
4.9.3 Duty cycles
The TCSC equipment shall be designed to withstand the required sequences of faults,
dynamic overload, temporary overload, and continuous currents as specified by the
purchaser. These sequences form the duty cycles that all of the components of the TCSC
bank shall be designed to withstand. The duty cycle shall be consistent with the manner in
which the surrounding power system will be operated for both internal and external line faults.
The purchaser shall define duty cycles for faults of normal and extended duration and for

– 18 – 60143-4 Ó IEC:2010
faults of
...