Amendment 1
IEEE Power and Energy Society
STANDARDS
IEEE Guide for the Application of
Capacitance Current Switching for
AC High-Voltage Circuit Breakers
Above 1000 V
Developed by the
Switchgear Committee
IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
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IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
IEEE Guide for the Application of
Capacitance Current Switching for
AC High-Voltage Circuit Breakers
Above 1000 V
Amendment 1
Developed by the
Switchgear Committee
of the
IEEE Power and Energy Society
Approved 4 June 2020
IEEE SA Standards Board
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IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
Abstract: Covered in this amendment are changes in di/dt limitations for non-oil circuit breakers.
A section has been added describing possible delayed current zeros when doing a rapid close—
open of a line circuit breaker (CO) when shunt reactors are connected to a line or cable. Some
minor errors have been corrected and references have been updated.
Keywords: capacitive current switching, circuit breaker capacitive inrush/outrush limitations,
IEEE C37.012a, switching reactor compensated lines
•
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IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
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IEEE Std C37.012a™-2020
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IEEE Std C37.012a™-2020
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IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
Participants
At the time this draft guide was completed, the C37.012a Working Group had the following membership:
Roy Alexander, Chair
Brian Roberts, Vice Chair
Lucas Collette, Secretary
Anne Bosma
Arben Bufi
David Caverly
Michael Christian
Jason Cunningham
Raymond Frazier
John Hall
Helmut Heiermeier
Victor Hermosillo
Edward Hester
Roy Hutchins
Hua Ying Liu
Steven May
Neil McCord
Dave Mitchell
Craig Polchinski
Jon Rogers
Carl Schuetz
Sushil Shinde
Michael Skidmore
James van de Ligt
John Webb
Casey Weeks
Jan Weisker
Marcus Young
Wei Zhang
Jim Zhong
The following members of the individual Standards Association balloting group voted on this guide.
Balloters may have voted for approval, disapproval, or abstention.
Roy Alexander
Thomas Barnes
Anne Bosma
Demetrio Bucaneg Jr.
Arben Bufi
Ted Burse
Eldridge Byron
Paul Cardinal
Steven Chen
Lucas Collette
Sergio Flores
Edwin Goodwin
Lou Grahor
John Hall
John Harley
Helmut Heiermeier
Victor Hermosillo
Werner Hoelzl
Robert Hoerauf
Todd Irwin
Richard Jackson
Joseph Jasinski
Laszlo Kadar
Thomas Keels
Peter Kelly
Yuri Khersonsky
James Kinney
Boris Kogan
Jim Kulchisky
R. Long
Omar Mazzoni
Neil McCord
Charles Morse
Thomas Mulcahy
Dennis Neitzel
Arthur Neubauer
Joe Nims
Mary Owens
Bansi Patel
John Phouminh
Reynaldo Ramos
Samala Santosh Reddy
Charles Rogers
Surya Santoso
Bartien Sayogo
Daniel Schiffbauer
Carl Schuetz
Nikunj Shah
Devki Sharma
Michael Sharp
Sushil Shinde
Gary Smullin
Jon Spencer
Gary Stoedter
Donald Swing
James van de Ligt
John Vergis
Keith Waters
John Webb
Jan Weisker
Terry Woodyard
Jian Yu
Wei Zhang
Xi Zhu
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IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
When the IEEE SA Standards Board approved this guide on 4 June 2020, it had the following membership:
Gary Hoffman, Chair
Jon Walter Rosdahl, Vice Chair
Jean-Philippe Faure, Past Chair
Konstantinos Karachalios, Secretary
Ted Burse
J. Travis Griffith
Grace Gu
Guido R. Hiertz
Joseph L. Koepfinger*
John D. Kulick
David J. Law
Howard Li
Dong Liu
Kevin Lu
Paul Nikolich
Damir Novosel
Dorothy Stanley
Mehmet Ulema
Lei Wang
Sha Wei
Philip B. Winston
Daidi Zhong
Jingyi Zhou
*Member Emeritus
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IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
Introduction
This introduction is not part of IEEE Std C37.012a-2020, IEEE Guide for the Application of Capacitance Current
Switching for AC High-Voltage Circuit Breakers Above 1000 V.
Recent work has demonstrated that for vacuum, SF6 and other gas switchgear, the inrush current frequency
on capacitor energization or restrike is much less important than the current magnitude and often does not
need to be limited. Also, the inrush current magnitude alone may not need to be limited. The limiting
parameter is the ICI (Inrush Current Integral) during the pre-arc time of a making operation, before
galvanic contact of the contacts is achieved. As a result, the formerly used i × f product (or di/dt) as a
limitation for switchgear is less of a concern. Therefore, IEEE Std C37.012 has been amended to provide
guidance in applications where the formerly used i × f limitation is exceeded. At this time, it is deemed
appropriate to retain the inrush current magnitude limits with less emphasis on the importance of the
natural frequency of the inrush current until such time as the impact of the ICI is better understood and
reducible to an easily computed form suitable for an application guide.
Also, a few other corrections have been addressed (i.e., Ferranti rise numbers, added clauses on reactor
compensated lines and cables, delayed current zero possibility, and the discharge capability of capacitor
units with no internal fuses, etc.). References have been updated, and IEEE Std C37.100.2 was added to the
normative references.
7
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IEEE Std C37.012a™-2020
(Amendment to IEEE Std C37.012-2014)
Contents
2. Normative references.................................................................................................................................. 9
4. Capacitor bank switching ..........................................................................................................................10
4.3 Energizing capacitor banks .................................................................................................................10
5. Unloaded cable switching ..........................................................................................................................11
5.2 De-energizing unloaded cables ...........................................................................................................11
5.3 Energizing unloaded cables ................................................................................................................11
6. Switching of no-load transmission lines ....................................................................................................11
6.1 De-energizing uncompensated transmission lines ..............................................................................11
6.4 Switching the charging current of long transmission lines .................................................................12
6.5 Switching of reactor compensated lines and cables ............................................................................12
7. Voltage factors for capacitive current switching tests ...............................................................................12
8. General application considerations ............................................................................................................12
9. Capacitance current switching application considerations ........................................................................12
9.1 General ...............................................................................................................................................12
9.4 Rated capacitive current .....................................................................................................................13
9.5 Voltage and grounding conditions of the network ..............................................................................13
9.6 Restrike probability ............................................................................................................................13
9.7 Class of circuit breaker .......................................................................................................................14
9.10 No-load transmission lines ...............................................................................................................15
9.11 Capacitor banks ................................................................................................................................16
9.12 Insulated cables.................................................................................................................................21
9.14 Unusual circuits ................................................................................................................................22
10. Considerations of capacitive currents and recovery voltages under fault conditions ..............................23
10.1 Voltage and current factors ...............................................................................................................23
10.4 Switching transmission lines under faulted conditions .....................................................................23
10.5 Switching capacitor banks under faulted conditions.........................................................................23
10.7 Examples of application alternatives ................................................................................................24
Annex A (informative) Bibliography ............................................................................................................25
8
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IEEE Std C37.012a-2020
IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
IEEE Guide for the Application of
Capacitance Current Switching for
AC High-Voltage Circuit Breakers
Above 1000 V
Amendment 1
NOTE—The editing instructions contained in this amendment define how to merge the material contained therein into
the existing base standard and its amendments to form the comprehensive standard.
The editing instructions are shown in bold italic. Four editing instructions are used: change, delete, insert, and replace.
Change is used to make corrections in existing text or tables. The editing instruction specifies the location of the
change and describes what is being changed by using strikethrough (to remove old material) and underscore (to add
new material). Delete removes existing material. Insert adds new material without disturbing the existing material.
Insertions may require renumbering. If so, renumbering instructions are given in the editing instruction. Replace is used
to make large changes in text, subclauses, tables, figures, or equations by removing the existing material and replacing
it with new material. Editing instructions, change markings, and this NOTE will not be carried over into future editions
because the changes will be incorporated into the base standard.
2. Normative references
Change the following references in Clause 2:
IEEE Std C37.04™, IEEE Standard Rating Structure for AC High-Voltage Circuit Breakers for Ratings
and Requirements for AC High-Voltage Circuit Breakers with Rated Maximum Voltage Above 1000 V.2,3
IEEE Std C37.09a™-2005, IEEE Standard Test Procedures for AC High-Voltage Circuit Breakers Rated
on a Symmetrical Current Basis — Amendment 1: Capacitance Current Switching with Rated Maximum
Voltage Above 1000 V.
IEEE Std C37.010™, IEEE Application Guide for AC High-Voltage Circuit Breakers > 1000 Vac Rated on
a Symmetrical Current Basis.
Delete the following references in Clause 2:
IEEE Std C37.04a™-2003, IEEE Standard Rating Structure for AC High-Voltage Circuit Breakers Rated
on a Symmetrical Current Basis Amendment 1: Capacitance Current Switching.
9
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IEEE Std C37.012a-2020
IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
IEEE Std C37.06™, IEEE Standard for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current
Basis—Preferred Ratings and Related Required Capabilities for Voltages Above 1000 V.
Insert the following reference in Clause 2 in alphanumeric order:
IEEE Std C37.100.2™, IEEE Standard for Common Requirements for Testing of AC Capacitive Current
Switching Devices over 1000 V.
4. Capacitor bank switching
4.3 Energizing capacitor banks
4.3.3 Back-to-back energization
Change the following paragraphs in sublause 4.3.3:
Typical amplitudes of the inrush currents for back-to-back energization of capacitor banks are several tens
of kiloamperes with frequencies of from 2 kHz to 5 kHz (distribution banks) to 15 kHz (EHV transmission
banks).Higher frequencies may be possible for compact capacitor bank designs. Typical values are given in
IEEE Std C37.06. Capacitors can normally withstand amplitudes up to 100 times their charging current
Banks with internally fused capacitors can withstand inrush currents up to 100 times the bank charging
current. Capacitor units without internal fuses can withstand inrush currents of 10 kA (300 kvar and smaller
capacitor units), 15 kA for units 301 kvar – 599 kvar, or 20 kA (capacitor units 600 kvar and larger). The
bank inrush/outrush current capability can be determined by multiplying the inrush capability of one unit
by the number of units or strings in parallel in one phase of the capacitor bank. See IEEE Std 1036 for
guidance.
If the inrush current amplitude and frequency exceed those stated in IEEE Std C37.06 C37.04, it may be
necessary to limit them. However, for vacuum, SF6, and other gas switchgear if the inrush current
magnitude (i) is within that stated in IEEE Std C37.04 (ibb) it is acceptable for the inrush current frequency
(f) to exceed the tested frequency (fbb) as long as the product of i × f is less than 4 times the product of ibb ×
fbb. Also if i < 0.1 × (ibb) (i.e. less than 10% of ibb) there is no need for an upper limit on the inrush current
frequency. If the inrush current magnitude is greater than that stated in IEEE Std C37.04, the manufacturer
could be consulted to determine if a higher inrush current is acceptable. Such limitation can be done by
insertion of additional series inductance in the circuit (reactor or pre-insertion inductor), or by using preinsertion resistors (see 6.3, and NOTE below). Another possibility is to use controlled Limitation of the
inrush current can be accomplished with a fixed transient limiting inductor (TLI), preinsertion inductor,
preinsertion resistor, or controlled switching. Detailed studies are necessary to evaluate the effectiveness of
inrush current mitigation measures.
10
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IEEE Std C37.012a-2020
IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
5. Unloaded cable switching
5.2 De-energizing unloaded cables
5.2.1 Cable charging current
Change the following in subclause 5.2.1:
Using the shunt capacitive reactance, the cable charging current can be calculated and compared with the
rated cable charging current of the circuit breaker given in IEEE Std C37.06 C37.04. If the calculation
exceeds the rating, the manufacturer should be consulted. Before an application can be made, the inrush
current rating should also be checked (see 9.12.1 9.12.2).
5.3 Energizing unloaded cables
5.3.2 Energizing single cables
5.3.2.2 Single cable inrush current
Change the following in subclause 5.3.2.2:
The initial rate-of-rise of the inrush current (dii/dt at t = 0) is [um-ut]/L. For application purposes ii peak
should be compared to the value given in IEEE Std C37.06 C37.04. If the value is higher than given in
C47.04, the manufacturer should be consulted to see if the higher value is acceptable.
6. Switching of no-load transmission lines
6.1 De-energizing uncompensated transmission lines
6.1.1 Line charging current
Change the following in subclause 6.1.1:
Due to the distributed nature of the inductance and the capacitance of the line, the peak value of the power
frequency voltage at the remote (or receiving) end is higher than that at the circuit breaker (sending) end of
the line. This effect is called the Ferranti effect. For a 500 kV line with a length of 500 km the voltage
increase is approximately 4 approximately 24%, and for a line length of 200 km the voltage increase is
approximately 1 approximately 4%. That is why the Ferranti effect is not considered for line lengths below
200 km. The small magnitude of the Ferranti effect for line lengths less than 200 km justifies it not being
considered in these cases.
11
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IEEE Std C37.012a-2020
IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
6.4 Switching the charging current of long transmission lines
Change the following in subclause 6.4:
Transmission lines in excess of 300 km, even those of simple design, present a special case not covered by
the requirements of 4.10.7 of IEEE Std C37.09a-2005 C37.09-2018 or its notes. Where such long lines are
to be switched, consideration should be given to the higher value of peak recovery voltage present on
interruption. If the circuit breaker was tested for switching an ungrounded capacitor in the presence of a
fault (kc = 1.7) test data will provide insight on the capability of the circuit breaker to switch a long
transmission line. Additional testing, such as completing the capacitive current switching requirements of
4.10 of IEEE Std C37.09a-2005 C37.09-2018, but to the elevated values required by the specific
application may be desired.
Insert subclause 6.5 after 6.4:
6.5 Switching of reactor compensated lines and cables
When switching a line or cable whose charging current is more than 50% compensated with shunt reactors,
and those shunt reactors are connected to the line or cable before it is energized, it needs to be understood
that a rapid opening (within a few seconds) after a closing operation can result in delayed current zeros, and
should be avoided by the operator This can be a simple switching operation or a fault reclose operation.
Several reports of circuit breaker failure have been attributed to this phenomenon.
7. Voltage factors for capacitive current switching tests
Change the following in Clause 7:
In 4.10.7 of IEEE Std C37.09a-2005 C37.09-2018 the voltage factors (shown in Table 1, below) are given
for single-phase tests. IEEE Std C37.09a-2005 C37.09-2018 requires that the test voltage measured at the
circuit breaker location prior to interruption shall not be less than the product of the rated voltage Ur/√3 and
the voltage factors given in Table 1.
8. General application considerations
Change the following in Clause 8:
See Clause 5 Clause 4 of IEEE Std C37.010-2016.
9. Capacitance current switching application considerations
9.1 General
Change the following in subclause 9.1:
Caution should be exercised when applying older circuit breakers that have not been tested to IEEE Std
C37.09a-2005 C37.09-2018 or IEEE Std C37.100.2.
12
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IEEE Std C37.012a-2020
IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
9.4 Rated capacitive current
Change the following in subclause 9.4:
The preferred values of the rated capacitive switching current are given in IEEE Std C37.06 C37.04. Not all
actual cases of capacitive current switching are covered by IEEE Std C37.06 C37.04. The values for lines
and cables cover most cases, the values of the current for capacitor banks (single and back-to-back) are
typical and representative of actual values in service are presented as a preferred value and three alternate
values. These are intended to cover the majority of in service values, but cannot cover every case.
9.4.1 Transmission lines and cables
Change the following in subclause 9.4.1:
When very long lines and cables are considered, the no-load current may exceed that given in IEEE Std
C37.06 C37.04. The manufacturer should be consulted in such cases. Often currents up to the continuous
current rating of the breaker are acceptable.
The following may serve as an example: The no-load current of a 550 kV transmission line is
approximately 1.1 A/km at 50 Hz and 1.3 A/km for 60 Hz. Without considering the Ferranti effect (see
6.1.1), the charging current of a 500 km line would be 605 A at 50 Hz and 715 A at 60 Hz. Ferranti rise on
a 500 km on the line would increase the charging current by about 4% at 50 Hz and 6% at 60 Hz. This
which is not covered by IEEE Std C37.06 C37.04.
9.4.2 Capacitor and filter banks
Change the following in subclause 9.4.2:
The same remark as given under 9.4.1 applies to capacitor and filter bank currents. The current is
depending on the size of the capacitor bank and in certain cases the capacitor bank considered may have a
current rating higher than that given in IEEE Std C37.06 C37.04. The current is dependent on the size of
the capacitor banks and line lengths to the capacitors are often short, so Ferranti effect is negligible. In
certain cases, the capacitor bank considered may have a current rating higher than that given in IEEE Std
C37.04. Experience has shown that capacitive current is not a limiting parameter for circuit breakers up to
the continuous current rating.
9.5 Voltage and grounding conditions of the network
Change the following in subclause 9.5:
4.10.7 of IEEE Std C37.09a-2005 C37.09-2018 gives the multiplication factors for single-phase tests for
the different conditions (see also Clause 7). They range from 1.0 for effectively grounded systems to 1.7 for
ungrounded systems in the presence of single- or two-phase-to-ground faults.
9.6 Restrike probability
Change the following in subclause 9.6:
As all circuit breakers have a certain some restrike probability in service, it is not possible to define a
restrike-free circuit breaker. It is more logical to introduce the notion of a restrike classification associated
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IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
with a dedicated specific test procedure (see IEEE Std C37.04a-2003 C37.04-2018 and IEEE Std
C37.100.2).
The level of the restrike probability depends also on the service conditions (e.g., number of operations per
year, network condition, maintenance policy of the user). Therefore, it is impossible to introduce a common
probability level related to service condition.
A restrike classification has been introduced is included in IEEE Std C37.04a-2003 C37.04-2018 as
follows: class C0 (undetermined probability of restrike), class C1 (low probability of restrike), and class C2
(very low probability of restrike).
NOTE—It is anticipated that a class C0 will be introduced in a future revision of IEEE Std C37.04. Class
C0 corresponds to the General Purpose circuit breaker specified in IEEE Std C37.06.
9.7 Class of circuit breaker
Change the following in subclause 9.7:
TwoThree classes of circuit breakers are defined for capacitive current switching in 3.4 and 3.5 5.8 of IEEE
Std C37.04a-2003 C37.04-2018.
a)
Class C0: Undetermined probability of restrike
b)
Class C1: Low probability of restrike
c)
Class C2: Very low probability of restrike
The standard introduces the term of restrike probability during the design tests, corresponding to a certain
probability of restrike in service, which depends on many parameters. For this reason, the term cannot be
quantified in service.
The intent is for class C2 to have an order of magnitude lower probability of restrike than C1.
The main differences between the design tests and criteria for the two classes are given in 4.10.9.1 and
4.10.9.2 of IEEE Std C37.09a-2005 C37.09-2018 as well as IEEE Std C37.100.2. Tests in accordance with
class C2 are performed on preconditioned contacts. Preconditioning consists of three interruptions with
60% of the rated short-circuit current. The number of tests for class C2 is higher than that of class C1. The
number of tests conducted near minimum arcing time are much higher for the C2 test program compared to
the C1 test program.
It must be noted that the behavior of the circuit breaker after the first restrike during design test may be
different than under real network conditions since the energies involved in a laboratory test circuit will be
different compared to the real network conditions. The overvoltage protection on the capacitor bank used
for the type test may be different from the overvoltage protection in the network. This may result in
different voltage stresses to the test object. This may also influence possible damages within the
interrupting unit.
The choices for the user betweenIt must be noted that selection by the user among classes C0, C1, and C2
depends on the following:

The service conditions

The number of capacitive current switching operations expected per year

The operating frequency
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IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1

The number of circuit breakers in service, for system stability

The consequences of any restrike for:

The network (for cable distribution systems, the influence of restrikes is usually negligible
compared to the influence of restrikes in transmission lines systems)

For the circuit breaker (very difficult to evaluate in service)
Class C0 may be acceptable where restrikes are not a concern.
Class C1 is often considered acceptable for circuit-breakers with a voltage rating of 52 kV 100 kV and
below and circuit-breakers applied for infrequent switching of transmission lines and cables.
Class C2 is recommended for capacitor bank circuit-breakers and those used on frequently switched
transmission lines and cables.
NOTE—The class C0 anticipated to be introduced in a future revision of IEEE Std C37.04 is considered acceptable for
applications at rated voltages of 52 kV and below where restrikes are not a concern.
9.10 No-load transmission lines
9.10.3 Compensated transmission lines
Change the following in subclause 9.10.3:
As described in 6.2, very long transmission lines (> 200 km) and underground cables are often may be
compensated with shunt reactors to reduce the amount of charging current required of the system.
If the circuit breaker rating is chosen based on the compensated line charging current Ilc, the line could not
be switched without the compensating reactor(s) connected. The voltage rise caused by the Ferranti effect
and also the location of the reactor(s) will change the line current slightly.
Insert the following at the end of subclause 9.10.3:
When switching a line or cable whose charging current is more than 50% compensated with shunt reactors,
and those shunt reactors are connected to the line or cable before it is energized, it needs to be understood
that a rapid opening (within a few seconds) after a closing operation can result in delayed current zeros.
This can either be a switching operation or a reclose after fault clearing. When an alternating-current (ac)
circuit breaker opens a current zero must exist within a certain time after contact parting for successful
current interruption to occur. The delayed current zeros associated with switching lines and reactors
together can potentially lead to a failure for the circuit breaker to interrupt which can result in equipment
damage or other system related concerns. Such a rapid opening after closing should be avoided by a
tripping delay, or the shunt reactor should be disconnected before the line circuit breaker is opened. An
appropriately sized preinsertion resistor may be another solution.
Figure 21a shows an example for a case where an 80 km overhead line (43.3 Mvar charging at 345 kV) and
shunt reactor (25 Mvar at 345 kV) are energized together. When energizing the line/reactor at a voltage
zero point on wave, the transient inrush current from the capacitance of the line will be a high frequency
current that damps quickly to a steady-state current that is 90° out of phase (leading) with the voltage with a
magnitude equal to the charging current of the line. The inrush current through the shunt reactor will have a
dc offset which slowly decays based on the X/R ratio of the reactor and is 90° out of phase (lagging) with
the voltage. Because of the dc offset, the peak of the inrush current through the reactor can be up to two
times the shunt reactor rated current.
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IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
The total current through the line breaker which closed to energize the line/reactor combination will be a
sum of the capacitive current from the line and the inductive current through the reactor which will be
approximately 180° out-of-phase with each other (i.e., capacitive current is 90° leading and inductive
current is 90° lagging). If the shunt reactor compensates the line charging by 50% or more, a potential
concern exists for delayed current zeros because with the dc offset in the shunt reactor current (which will
now be greater than the capacitive current) will more than offset the capacitive current as shown in
Figure 21a which results in no current zeros because the inductive component magnitude will be greater
than the capacitive component.
It is important to note that if no current zeros exist within a certain time period after contact parting (i.e.,
within the interrupting time window of the concerned breaker), the breaker may fail to interrupt the current.
Detailed studies are often required to determine the recommended mitigation solution for delayed current
zeros. Example solutions include adding a delay to tripping or utilizing circuit breakers with pre-insertion
resistors.
Figure 21a—Example of delayed current zeros from energizing a compensated line
9.11 Capacitor banks
9.11.2 Methods for calculating transient inrush currents
9.11.2.3 Considerations for transient inrush currents
Replace subclause 9.11.2.3 with the following:
The inrush currents of different types of compact multi-section banks with minimum spacing between the
individual sections may differ by as much as 20%. These inrush currents can be reduced significantly by
increasing the lengths (i.e., inductance) of the circuits between the sections.
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IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
Another effective measure to reduce transient inrush currents is to add fixed inductance TLIs in the circuit
between the capacitor banks and the circuit breaker.
Traditionally, the capability of circuit breakers to handle inrush current had been expressed as the inrush
current peak times the natural frequency of the inrush current (i × f). The i × f (or di/dt) limit for back-toback switching was developed for shock wave limited devices such as oil circuit breakers as described in
5.8.5 of IEEE Std C37.04-2018. During closing, the breaker experiences a prestrike arc in which current
flows before galvanic contact is made between the contacts. In devices with an incompressible dielectric
medium, such as oil circuit breakers, this rapidly increasing current (high di/dt) creates a shock wave that
can damage the interrupter. Recent work and 40 years of experience with SF6 and vacuum circuit breakers
has shown these technologies are much less sensitive to shock waves than the formerly used oil circuit
breakers which had determined the i × f limits used before 2009. The i × f limits for class C2 circuit
breakers had been accepted to be approximately 100 kA × kHz. A set of tests with 2400 operations with
discharge currents of 100 kA @ 25 kHz (2500 kA × kHz) on a 72.5 kV SF6 breaker showed no indication
of shock wave damage. A series of capacitive inrush tests was also done on a 12 kV vacuum breaker with
inrush frequencies as high as 23.8 kHz, one pole had an inrush with 69 kA peak at 14.7 kHz. It appeared
that the ICI was the quantity that needed to be limited, not so much the peak current, and definitely not the
frequency. This supports the understanding that the natural frequency of the inrush current is a lesser
concern with SF6 and vacuum interrupters. CIGRE WG A3.38 arrived at the same conclusion that for
vacuum and gas interrupters, higher frequency of the inrush current is a lesser concern. In some cases,
frequency below the tested value can be more damaging in terms of contact erosion. Another set of tests
was done with 20 kA inrush currents at 81 kHz (1620 kA × kHz), 22 kHz (440 kA × kHz), and 6 kHz
(120 kA × kHz). Each of the tests was performed with 2500 operations. None of these showed evidence of
shock wave damage, however, contact erosion was more evident at the lower frequencies due to the larger
inrush current integral (ICI).
SF6 and vacuum circuit breakers do not require the degree of inrush current mitigation as oil circuit
breakers. The limitation seems to be more with control system transients, and in some cases the capacitors
themselves. If the peak currents in IEEE Std C37.04 are exceeded, the circuit breaker manufacturer should
be consulted to see if their breaker can withstand the higher inrush current peak.
NOTE—In determining the inrush current peak and frequency, the currents i1 and i2 as used in Table 2 should include
the effect of operating the capacitor bank at a voltage above nominal operating voltage and the effect of a positive
tolerance of the capacitance. However, because inrush current depends on the inductive reactance in the circuit, the
presence of higher frequency harmonics will only serve to decrease the inrush current slightly and thus can be
conservatively ignored.
The following example will illustrate the use of the equations in Table 2.
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Amendment 1
Figure 23—Example of 138 kV system
The capacitor banks shown in Figure 23 have a nominal rating of 32.4 Mvar. Nominal current per bank is
136 A. In determining the continuous current rating of the circuit breaker required, the increase in current
due to applied voltage, capacitance tolerance, and harmonics should be considered. The increase in current
at maximum rated voltage is: maximum voltage to capacitor rated voltage = 145/138 = 1.05. Assume a
positive tolerance of capacitors of +10%, yielding a multiplier to the current of 1.1, and a multiplier for
harmonic content for an effectively grounded neutral bank of 1.1.
The total multiplier used to determine the single and back-to-back continuous current rating is 1.05 × 1.1 ×
1.1 = 1.27, giving a current of 1.27 × 136 = 173 A. With capacitor banks 2 and 3 energized, the current
through CB2 is 346 A.
The circuit breakers intended for this duty have the following ratings: rated voltage 145 kV, rated current
1600 A, rated short circuit current 40 kA, rated single and back-to-back capacitive switching current 400 A.
The transient inrush current and frequency can be calculated using the equations in Table 2. In the example,
L1', L2', and L3' are the inductances between the respective capacitor banks and the circuit breakers,
including the inductance of the capacitor bank. Lbus is the inductance of the bus between the circuit
breakers.
The inductance values in Table 3 can be used, or values can be calculated for the actual bus configuration
used. In the example given below, the added inductance between the circuit breaker and capacitor bank is:
L1' = L2' = L3' = 15.2 µH
The inductance of the busbar Lbus = 15.6 µH
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Amendment 1
In determining inrush current and frequency, the currents i1 and i2 as used in Table 2 should include the
effect of operating the capacitor bank at a voltage above nominal rating of the capacitors and the effect of a
positive tolerance of capacitance. The multiplier for harmonics should not be included in the inrush current
calculation. In the example, the multiplier to be used is 1.051.1  1.155 . The currents are
i1  1361.155  157 A and i2 = 157 A or 314 A, depending on whether bank 2 or bank 3 or both banks
are energized.
Case I. Energization of capacitor bank 1 with bank 2 and bank 3 not energized (single or single bank
switching).
ii peak  1.4142 I sc i1  1.4142 18 000157  1.4142 282.6104  2377 A
I sc
18 000
 60
 642 Hz
i1
157
fi  fs
The calculated rate of change of current for the single bank switching is
 dii 
 
 dt 
 2π f i ii peak  2π  (642 Hz)  (2377 A)  10106 A/s  9.6 A/μs
max
This value is less than the maximum rate of change for a rated short-circuit current of 40 kA, which is equal
to 2π f s 2 I sc  21.3 A/μs , and therefore meets the requirements of single capacitor bank switching.
Case II. Energization of bank 1 with bank 2 energized on the bus (back-to-back switching against an
equal-size bank).
ii peak  9545
U r i1
f s Leq
The equivalent inductance Leq is the sum of L1  Lbus  L2  15.2  15.6  15.2 μH = 46.0 μH .
ii peak  9545
f i  13.5
145157
 9545 8.248  27413 A peak
60 46
f sU r
60145
 13.5
 14.8 kHz
Leq i1
46157
The calculations above are a simple way to estimate the inrush current peak and frequency for a back-toback capacitor bank switching application. Another method to obtain the inrush current is through the
means of detailed simulations in an electromagnetic transients software. For illustration, the capacitor bank
shown in Figure 23 was modeled in an electromagnetic transients program at a 138 kV substation with four
connected transmission lines and four connected step-down transformers as shown in Figure 23a. Note the
values for Ur, Ls, L1’, L2’, L3’, and Lbus shown in Figure 23 were used for the detailed simulations.
Figure 23b shows a plot of the inrush current through circuit breaker CB1 when energizing bank 1 with
bank 2 energized and bank 3 offline.
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IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
Figure 23a—Example 138 kV system used for simulation
Figure 23b—Example plot of inrush current from simulation
The calculated or simulated back-to-back inrush current amplitude must be compared to the back-to-back
current (ibb) listed in IEEE Std C37.04 or found on the breaker nameplate. The simulated inrush current
peak is 26.5 kA, which exceeds the preferred rating peak value of inrush current of 16 kA, thus some form
of mitigation is needed. Possible forms of mitigation may include the addition of a fixed inductor in series
with the capacitor bank and/or utilizing a switching device equipped with pre-insertion resistors/inductors
or controlled closing. Table 3a shows a comparison of the inrush current for different mitigation solutions
quantified through simulation using the model shown in Figure 23a.
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IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
Table 3a—Example comparison of inrush current mitigation solutions
Inrush current through CB1
Mitigation solution
ii peak
(kApeak)
fi
(kHz)
i×f
(kA × kHz)
Multiple of tested
i×f
No mitigation
26.5
15.6
41.3
6.0
Fixed inductor
(45 µH each bank)
15.6
9.1
14.2
2.1
Pre-insertion resistor
(150 Ω, 6 ms insertion time)
6.4
15.6
10.0
1.5
Controlled closing
(RDDS = 90 kV/ms, +/- 0.5 ms scatter)
6.0
15.6
9
1.4
NOTE 1—RDDS = rate of decay of dielectric strength for the switching device.
NOTE 2—As described in 4.4.2.1 of IEEE Std C37.011-2019, the addition of a fixed inductor to limit inrush current
may result in a high-frequency transient recovery voltage, which could exceed the standardized TRV values.
Case III. Energization of bank 1 with bank 2 and bank 3 energized on the bus.
For this case, assume the equivalent inductance of bank 2 and bank 3 equal to one half of L2' or (15.2)/2 =
7.6 µH. The total current of bank 2 and bank 3 is 314 A, which is under the assumed single bank switching
capability of 400 A as listed in IEEE Std C37.04. For this case, i1 = 157 A, i2 = 314 A, and the equivalent
inductance between the capacitor bank being energized and the banks already energized is the sum of:
L2 / 2  Lbus  L1  7.6  15.6  15.2  38.4 μH .
ii peak  13 500
U r i1i2
145157 314
 13 500
 34648A peak
f s Leq (i1  i2 )
6038.4 471
and
f i  9.5
f sU r (i1  i2 )
60145 471
 9.5
 14.0 kHz
Leq i1i2
38.4157 314
The calculated values of inrush current and frequency of 34.6 kA and 14.0 kHz exceed the preferred backto-back switching capability of 16 kA and 4.3 kHz listed in IEEE Std C37.04. While the 14 kHz frequency
is not a concern on its own, the peak current of 34.65 kA exceeds the preferred rated ibb value of 16 kA. As
in the previous case of switching identical banks, mitigation solutions should be considered to reduce the
inrush current peak.
Change the title of subclause 9.12 as follows:
9.12 Insulated cables
Delete the following paragraph from subclause 9.12:
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IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
In the application of circuit breakers for cable switching duty, consideration must be given to the rated
single cable switching current, the rated back-to-back cable switching current, and the rated transient inrush
current, both amplitude and frequency.
Insert subclause 9.12.1 as follows:
9.12.1 General
Insert the following paragraph in subclause 9.12.1:
In the application of circuit breakers for cable switching duty, consideration must be given to the rated
single cable switching current, the rated back-to-back cable switching current, and the rated transient inrush
current amplitude and frequency. In extreme cases with high transient inrush currents, as long as the ibb is
below the rated value, the i × f product is acceptable up to four times the tested value for vacuum, SF6, and
other gas switchgear.
Renumber subclause 9.12.1 as follows:
9.12.2 9.12.1 Cable inrush current
Delete the following paragraph from subclause 9.12.1:
For proper circuit breaker application, feq should be less than the rated inrush current frequency. Additional
inductance may be added in series with the inductances making up L to meet the rated inrush frequency
requirement. Such inrush reactors are common.
Renumber subclause 9.12.2 as follows:
9.12.3 9.12.2 Alternate configurations
9.14 Unusual circuits
9.14.2 Exposure to total capacitor bank discharge current (outrush current)
Change subclause 9.14.2 as follows:
For class C0 circuit breakers exposed to capacitor bank discharge current, in addition to the checking of the
crest current, it may be necessary also to check the rate of change of the discharge current with the
manufacturer (generally oil circuit breakers should be treated as class C0). For class C1 and class C2 circuit
breakers as long as the peak current does not exceed the close and latch peak current rating of the breaker
such a discharge is permissible up to two times in the life of the breaker without additional maintenance
being required. Generally, the ringing frequency of the discharge is not a concern for the circuit breaker,
but this should be confirmed with the manufacturer.
The transient discharge current passing through a circuit breaker must also be examined for its effects upon
the linear couplers and bushing current transformers. The discharge currents may substantially exceed the
magnitudes and the frequency of the inrush currents given in IEEE Std C37.06 C37.04. This occurs because
the contribution may come from a number of capacitor banks and is not limited by the inrush impedance
seen when energizing a bank of capacitors. Determination of the induced voltages in the linear couplers or
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Amendment 1
in bushing current transformers also may be used for assessing the effects of the discharge currents.
Induced voltages in high-voltage current transformer or linear coupler circuits can be mitigated with metal
oxide varistors [B2].
10. Considerations of capacitive currents and recovery voltages under fault
conditions
10.1 Voltage and current factors
Change subclause 10.1 as follows:
Some requirements, general ratings, and tests for capacitive current switching are based on switching
operations in the absence of faults. The presence of a fault can increase the value of both the capacitive
switching current and recovery voltage. This is recognized in 4.10.7 of IEEE Std C37.09a-2005 C37.092018, by the specification of two voltage factors when breaking in the presence of faults. These voltage
factors apply to single-phase tests as a substitute of three-phase tests and are given in Clause 7. They are
1.4 for effectively grounded systems and 1.7 for ungrounded systems. Tests for these conditions are not
mandatory. An example of such a fault is a circuit breaker switching a transmission line that interrupts fault
current in one phase and capacitive current in the other two phases.
The fact that the capacitive switching current increases in the presence of ground faults is recognized in
4.10.9.3 of IEEE Std C37.09a-2005 4.10.9.4 of IEEE Std C37.09-2018, where the line and cable charging
currents are multiplied by 1.25 for effectively grounded neutral systems and 1.7 for ungrounded systems.
The number of tests is reduced to reflect the fact that such operations do not occur frequently.
10.4 Switching transmission lines under faulted conditions
Change subclause 10.4 as follows:
The voltages and currents that occur when switching a faulted transmission line are affected by the circuit
parameters and the sequence in which the three phases interrupt. IEEE Std C37.09a-2005 C37.09-2018 lists
the maximum value of recovery voltage for switching an unfaulted transmission line as
21.2
Ur 2
3
 2.4 p.u.
When switching a faulted line this value may be exceeded, as may be the rated capacitive switching current
value as listed in IEEE Std C37.06 C37.04 (see also [B5]).
10.5 Switching capacitor banks under faulted conditions
Change subclause 10.5 as follows:
The voltages and currents that can occur when switching a faulted capacitor bank depend upon the
grounding conditions, whether the fault is to the bank neutral or to ground, and on the sequence in which
the three phases interrupt. IEEE Std C37.09a-2005 C37.09-2018 lists the maximum value of recovery
voltage in switching an unfaulted shunt capacitor bank as 2.8 p.u. When switching a faulted bank, this
value may be exceeded, as may the rated capacitive switching current value. In the sections below, a
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Amendment 1
comparison is given between the recovery voltages and currents of a reference condition and two faulted
conditions: a fault to neutral in the capacitor bank and a fault to ground in one phase.
It is also possible to have an evolving fault where the capacitor bank faults in the process of being switched
off, and the circuit breaker then cannot interrupt.
The factor 2.8 for the maximum recovery voltage specified in IEEE Std C37.09-2018 is valid when
switching an ungrounded capacitor bank where the second and third phases clear 90° after the first. This is
true for modern circuit breakers. For certain older circuit breakers (or other switching devices), where the
second and third phases do not clear 90° after the first, this factor is 4.1.
NOTE— The factor 2.8 for the maximum recovery voltage specified in IEEE Std C37.09a-2005 is valid when
switching an ungrounded capacitor bank where the second and third phases clear 90 o after the first. This is true for
modern circuit breakers. For older circuit breakers, where the second and third phases do not clear 90o after the first,
this factor is 3.0.
10.5.1 Reference condition
10.5.1.1 Recovery voltage
Change subclause 10.5.1.1 as follows:
The voltages and currents obtained with this reference condition (i.e., unfaulted balanced system) agree
with the 2.8 p.u. voltage listed in IEEE Std C37.09a-2005 C37.09-2018. Although the voltage across the
last poles to interrupt when at least one of the neutrals (source or bank) is ungrounded can reach 2 × Ur √2
= 2.828 × Ur = 3.46 p.u., the two phases are in series so that neither is stressed to much more than 1.73 p.u.
10.5.2 Fault to neutral in one phase (one capacitor bank phase short-circuited)
10.5.2.1 Recovery voltage
Change subclause 10.5.2.1 as follows:
The highest recovery voltage (i.e., 2 × Ur √2 = 3.46 p.u.) is obtained when at least one neutral is
ungrounded and the first pole-to-clear clears a healthy phase. This is in agreement with the voltage factor of
1.7 specified in 4.10.7 of IEEE Std C37.09a-2005 C37.09-2018. If the first pole-to-clear interrupts an
unfaulted phase, it is subjected to a recovery voltage of 3.46 p.u. until the second and third phases interrupt.
10.7 Examples of application alternatives
Change subclause 10.7 as follows:
Other application options available are as follows:

Use a circuit breaker of a higher rating in those cases of ground faults on ungrounded systems
where the recovery voltage and current, or both, exceed the requirements of IEEE Std C37.09a2005 C37.09-2018.

Reduce the capacitance of the existing capacitor bank size so that the current under faulted
conditions does not exceed the rated capacitive switching current of the circuit breaker.

Use a high-speed switch to ground the source or capacitor bank neutral before switching the
capacitor bank under faulted conditions.
24
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IEEE Std C37.012a-2020
IEEE Guide for the Application of Capacitance Current Switching for AC High-Voltage Circuit Breakers Above 1000 V
Amendment 1
Annex A
(informative)
Bibliography
Insert the following references and footnote in Annex A in alphanumeric order:
[B1] CIGRÉ Technical Brochure 624, “Influence of Shunt Capacitor Banks on Circuit Breaker Fault
Interruption Duties,” June 2015.
[B2] CIGRE Technical Brochure, “Shunt Capacitor Switching in Distribution and Transmission Systems:
Verification by Tests and Performance in Service,” 2020. 1
[B3] IEEE PES-TR16, “Transient Limiting Inductor Application in Shunt Capacitor Banks.”
1
A brochure is expected to be published by the end of 2020 documenting the work of CIGRE WG A3.38.
25
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