SIST EN IEC/IEEE 60076-57-1202:2025

SLOVENSKI STANDARD
01-junij-2025
Močnostni transformatorji - 57-1202. del: Transformatorji s prečnim premikom
faze, potopljeni v tekočino (IEC/IEEE 60076-57-1202:2017)
Power transformers - Part 57-1202: Liquid immersed phase-shifting transformers
(IEC/IEEE 60076-57-1202:2017)
Leistungstransformatoren - Teil 57-1202: Ölgefüllte Phasenschieber (IEC/IEEE 60076-57
-1202:2017)
Transformateurs de puissance - Partie 57-1202: Transformateurs déphaseurs immergés
dans un liquide (IEC/IEEE 60076-57-1202:2017)
Ta slovenski standard je istoveten z: EN IEC/IEEE 60076-57-1202:2025
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC/IEEE 60076-57-1202

NORME EUROPÉENNE
EUROPÄISCHE NORM April 2025
ICS 29.180
English Version
Power transformers - Part 57-1202: Liquid immersed phase-
shifting transformers
(IEC/IEEE 60076-57-1202:2017)
Transformateurs de puissance - Partie 57-1202: Leistungstransformatoren - Teil 57-1202: Ölgefüllte
Transformateurs déphaseurs immergés dans un liquide Phasenschieber
(IEC/IEEE 60076-57-1202:2017) (IEC/IEEE 60076-57-1202:2017)
This European Standard was approved by CENELEC on 2025-03-26. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
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Comité Européen de Normalisation Electrotechnique
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© 2025 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC/IEEE 60076-57-1202:2025 E

European foreword
This document (EN IEC/IEEE 60076-57-1202:2025) consists of the text of document
IEC/IEEE 60076-57-1202:2017, prepared by IEC/TC 14 "Power Transformers".
The following dates are fixed:
• latest date by which this document has to be (dop) 2026-04-30
implemented at national level by publication of an
identical national standard or by endorsement
• latest date by which the national standards (dow) 2028-04-30
conflicting with this document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC/IEEE 60076-57-1202:2017 was approved by CENELEC as a
European Standard without any modification.

IEC/IEEE 60076-57-1202 ®
Edition 1.0 2017-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power transformers –
Part 57-1202: Liquid immersed phase-shifting transformers

Transformateurs de puissance –

Partie 57-1202: Transformateurs déphaseurs immergés dans un liquide

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-4258-2

– 2 – IEC/IEEE 60076-57-1202:2017
© IEC/IEEE 2017
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
2.1 IEC references . 7
2.2 IEEE references . 7
3 Terms and definitions . 8
4 Use of normative references . 11
5 Service conditions . 11
5.1 General . 11
5.2 Usual service conditions . 11
5.2.1 Switching arrangement . 11
5.2.2 Power flow . 11
5.2.3 Operation with two or more PSTs in series or parallel . 11
5.2.4 Phase unbalance . 12
5.2.5 Surge protection . 12
6 Rating and general requirements . 12
6.1 Rated power . 12
6.2 Loading at other than rated conditions . 12
6.3 Specification of buck capability . 12
6.4 Cooling modes . 13
6.5 Short circuit impedance and load phase angle capability . 13
6.5.1 Specification . 13
6.5.2 Short circuit impedance for asymmetric designs . 13
6.6 Neutral earthing (grounding) . 13
6.7 Rated voltage . 13
6.8 Voltage variation and asymmetric design . 13
6.9 Rated frequency . 14
6.10 Operation at higher than rated voltage and/or at other than rated frequency . 14
6.11 Highest voltage for equipment and dielectric test levels . 14
6.12 Taps . 14
6.13 Sound level . 14
6.14 Transport . 14
7 Construction . 14
7.1 General . 14
7.2 Liquid-filled connections between tanks . 15
7.3 Liquid insulation and preservation system . 15
7.4 Alignment between tanks . 15
7.5 Core and core frame earthing arrangements . 16
7.6 Test connections . 16
8 Short circuit capability . 16
9 Connection phase displacement symbols . 16
9.1 General . 16
9.2 Special symbols for PSTs . 16
9.3 Clock number notation . 17
9.4 Examples . 17
9.4.1 Single core phase shifting transformers . 17

IEC/IEEE 60076-57-1202:2017 – 3 –
© IEC/IEEE 2017
9.4.2 Two core phase shifting transformers . 19
9.4.3 Transformers incorporating a phase shifting element . 21
10 Rating plates (nameplates) . 22
11 Terminal markings and phase rotation . 23
12 Information to be provided by the manufacturer . 23
13 Tests . 24
13.1 General . 24
13.2 Routine tests. 24
13.3 Type (design) tests . 24
13.4 Special tests . 24
13.5 Winding resistance. 25
13.6 Measurement of voltage ratio, phase angle and check of phase
displacement . 25
13.7 Measurement of short-circuit impedance and load loss . 25
13.8 Temperature-rise test . 26
13.9 Measurement of no-load loss and current . 26
13.10 Determination of sound level . 26
13.10.1 General . 26
13.10.2 For PSTs with one combined cooling system . 26
13.10.3 For PSTs with separate exciting and series unit cooling systems . 27
13.11 Measurement of zero sequence impedance . 27
13.12 Dielectric tests . 27
13.12.1 General . 27
13.12.2 Induced voltage test with partial discharge measurement (IVPD) . 28
13.12.3 Switching impulse test (SI) . 28
13.12.4 Lightning impulse test . 28
13.12.5 Lightning impulses applied to multiple line terminals simultaneously
(LIMT) . 29
13.13 Tests on on-load tap-changers – operation test . 29
13.14 Leak testing with pressure . 30
13.15 Vacuum deflection test . 30
13.16 Pressure deflection test . 30
14 Tolerances . 30
14.1 General . 30
14.2 Tolerance for impedance and phase angle . 30
Annex A (informative) Check list of information to be provided with enquiry and order . 32
A.1 Rating and general data . 32
A.1.1 Normal information . 32
A.1.2 Special information . 33
A.2 Parallel operation . 34
Annex B (informative) Behaviour of a phase shifting transformer with non-symmetrical
fault currents. 35
Annex C (informative) Example specification of buck capability . 37
Annex D (informative) Additional noise measurements . 38
Annex E (informative) Calculation of phase angle under load . 40
Annex F (informative) Additional information on advance-retard switch . 44
F.1 Principle . 44
F.2 Classification within the international standardization system . 44

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© IEC/IEEE 2017
F.3 Requirements according to IEC 60214-1 and IEEE Std C57.131 . 44
Bibliography . 45

Figure 1 – Example A: DS0-3/9 . 18
Figure 2 – Example B: PS0-3/9 . 18
Figure 3 – Example C: DA0-3 . 19
Figure 4 – Example D: YNyn/IIId S0-3/9 . 20
Figure 5 – Example E: YNyn+d/IIId A0-3/9 . 20
Figure 6 – Example F: YNa0yn/dIII A0-3/9 . 21
Figure 7 – Example G: V A0-2/8. 22
Figure B.1 – PST with single phase fault and surge protection . 36
Figure E.1 – Phase angle diagram for a PST under load where α > 0 and φ < 0 . 40
0 L
Figure E.2 – Phase angle diagram for a PST under load where α < 0 and φ < 0 . 40
0 L
Figure E.3 – Phase angle diagram for a PST under load where α > 0 and φ > 0 . 41
0 L
Figure E.4 – Phase angle diagram for a PST under load where α < 0 and φ > 0 . 41
0 L
Table C.1 – Required PST capability in buck operation . 37
Table D.1 – Combinations of sound level measurements needed to represent different
loading conditions . 39

IEC/IEEE 60076-57-1202:2017 – 5 –
© IEC/IEEE 2017
POWER TRANSFORMERS –
Part 57-1202: Liquid immersed phase-shifting transformers

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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation.
IEEE Standards documents are developed within IEEE Societies and Standards Coordinating Committees of the
IEEE Standards Association (IEEE-SA) Standards Board. IEEE develops its standards through a consensus
development process, approved by the American National Standards Institute, which brings together volunteers
representing varied viewpoints and interests to achieve the final product. Volunteers are not necessarily
members of IEEE and serve without compensation. While IEEE administers the process and establishes rules
to promote fairness in the consensus development process, IEEE does not independently evaluate, test, or
verify the accuracy of any of the information contained in its standards. Use of IEEE Standards documents is
wholly voluntary. IEEE documents are made available for use subject to important notices and legal disclaimers
(see http://standards.ieee.org/IPR/disclaimers.html for more information).
IEC collaborates closely with IEEE in accordance with conditions determined by agreement between the two
organizations. This Dual Logo International Standard was jointly developed by the IEC and IEEE under the
terms of that agreement.
2) The formal decisions of IEC on technical matters express, as nearly as possible, an international consensus of
opinion on the relevant subjects since each technical committee has representation from all interested IEC
National Committees. The formal decisions of IEEE on technical matters, once consensus within IEEE Societies
and Standards Coordinating Committees has been reached, is determined by a balanced ballot of materially
interested parties who indicate interest in reviewing the proposed standard. Final approval of the IEEE
standards document is given by the IEEE Standards Association (IEEE-SA) Standards Board.
3) IEC/IEEE Publications have the form of recommendations for international use and are accepted by IEC
National Committees/IEEE Societies in that sense. While all reasonable efforts are made to ensure that the
technical content of IEC/IEEE Publications is accurate, IEC or IEEE cannot be held responsible for the way in
which they are used or for any misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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5) IEC and IEEE do not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or IEEE or their directors, employees, servants or agents including individual
experts and members of technical committees and IEC National Committees, or volunteers of IEEE Societies
and the Standards Coordinating Committees of the IEEE Standards Association (IEEE-SA) Standards Board,
for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect,
or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this
IEC/IEEE Publication or any other IEC or IEEE 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 implementation of this IEC/IEEE Publication may require use of
material covered by patent rights. By publication of this standard, no position is taken with respect to the
existence or validity of any patent rights in connection therewith. IEC or IEEE shall not be held responsible for
identifying Essential Patent Claims for which a license may be required, for conducting inquiries into the legal
validity or scope of Patent Claims or determining whether any licensing terms or conditions provided in
connection with submission of a Letter of Assurance, if any, or in any licensing agreements are reasonable or
non-discriminatory. Users of this standard are expressly advised that determination of the validity of any patent
rights, and the risk of infringement of such rights, is entirely their own responsibility.

– 6 – IEC/IEEE 60076-57-1202:2017
© IEC/IEEE 2017
International Standard IEC/IEEE 60076-57-1202 has been prepared by IEC technical
committee 14: Power transformers, in cooperation with the Transformers Committee of the
IEEE Power & Energy Society , under the IEC/IEEE Dual Logo Agreement.
This publication is published as an IEC/IEEE Dual Logo standard.
The text of this standard is based on the following IEC documents:
FDIS Report on voting
14/892/FDIS 14/902/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.
International Standards are drafted in accordance with the rules given in the ISO/IEC
Directives, Part 2.
The IEC Technical Committee and IEEE Technical Committee have decided that the contents
of this publication will remain unchanged until the stability date indicated on the IEC website
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.
_______________
A list of IEEE participants can be found at the following URL: http://standards.ieee.org/downloads/60076/60076-
57-1202-2017/60076-57-1202-2017_wg-participants.pdf

IEC/IEEE 60076-57-1202:2017 – 7 –
© IEC/IEEE 2017
POWER TRANSFORMERS –
Part 57-1202: Liquid immersed phase-shifting transformers

1 Scope
This part of IEC 60076 covers the requirements for phase-shifting transformers of all types.
The scope excludes transformers with an unregulated phase shift.
This document is limited to matters particular to phase-shifting transformers and does not
include matters relating to general requirements for power transformers covered in existing
standards in the IEC 60076 series or IEEE Std C57.12.00™ and IEEE Std C57.12.10™.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
2.1 IEC references
IEC 60050-421, International Electrotechnical Vocabulary – Chapter 421: Power transformers
and reactors (available at: www.electropedia.org)
IEC 60076-1, Power transformers – Part 1: General
IEC 60076-2, Power transformers – Part 2: Temperature rise for liquid-immersed transformers
IEC 60076-3, Power transformers – Part 3: Insulation levels, dielectric tests and external
clearances in air
IEC 60076-5, Power transformers – Part 5: Ability to withstand short circuit
IEC 60076-10, Power transformers – Part 10: Determination of sound levels
IEC 60076-18, Power transformers – Part 18: Measurement of frequency response
ISO 2178, Non-magnetic coatings on magnetic substrates – Measurement of coating
thickness – Magnetic method
ISO 2409, Paints and varnishes – Cross-cut test
2.2 IEEE references
IEEE Std C57.12.00™, IEEE Standard for General Requirements for Liquid-Immersed
Distribution, Power, and Regulating Transformers
IEEE Std C57.12.10™, IEEE Standard Requirements for Liquid-Immersed Power
Transformers
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© IEC/IEEE 2017
IEEE Std C57.12.70™, IEEE Standard for Standard Terminal Markings and Connections for
Distribution and Power Transformers
IEEE Std C57.12.80™, IEEE Standard Terminology for Power and Distribution Transformers
IEEE Std C57.12.90™, IEEE Standard Test Code for Liquid-Immersed Distribution, Power,
and Regulating Transformers
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
For the purposes of this document, the terms and definitions given in IEC 60050-421 and
IEC 60076-1 apply to IEC specified phase shifting transformers. For IEEE specified phase
shifting transformers the terms and definitions given in IEEE Std C57.12.80 apply. For all
phase shifting transformers the following apply and take precedence.
3.1
phase-shifting transformer
PST
transformer (or combination of transformers designed to work together) with two sets of line
terminals (S and L) which is capable of varying the voltage phase-angle relationship between
the S terminals and the L terminals
Note 1 to entry: The rated voltage of the S terminals and the L terminals may be the same or different. In addition
the PST may also be capable of varying the in-phase voltage.
Note 2 to entry: This note applies to the French language only.
3.2
S terminal
terminal that is used as the fixed reference point when measuring the voltage phase angle of
a phase-shifting transformer
3.3
L terminal
terminal that is used to measure the voltage phase angle when compared to the S terminal of
the phase-shifting transformer
Note 1 to entry: The designations of S and L to the terminals do not imply any particular direction of power flow.
3.4
zero phase shift tap position
tap position at which the no-load voltage phase angle is zero
3.5
rated power
output power at rated voltage and rated frequency that can be delivered at the L terminal
continuously without exceeding the specified temperature rise

IEC/IEEE 60076-57-1202:2017 – 9 –
© IEC/IEEE 2017
3.6
excitation winding
winding of a phase-shifting transformer (PST) that draws power from the source to energize
the PST
3.7
excited winding
winding of the series unit that is excited from the exciting winding
3.8
quadrature booster
asymmetric design phase-shifting transformer with the excitation winding connected to the
S terminal
3.9
symmetric design
phase-shifting transformer where the no-load voltage ratio between the S and L terminals is
constant
3.10
asymmetric design
phase-shifting transformer where the no-load voltage ratio between the S and L terminals
changes with the phase angle variation tap position
3.11
single-core PST
phase-shifting transformer that has all windings mounted on a single core
3.12
two-core PST
phase-shifting transformer consisting of a series unit and an exciting unit, located on two
separate cores
3.13
extreme tap
tap for maximum absolute value of no-load phase angle in the advance or retard direction
3.14
phase angle
electrical phase angle expressed in degrees between the S and L terminals with a sign such
that the angle is positive when the voltage at the L terminal leads the voltage at the S terminal
3.15
boost operation
operation when the PST is acting to increase the power flow in the circuit
3.16
buck operation
operation when the PST is acting to reduce or reverse the power flow in the circuit
Note 1 to entry: For example, in retard operation the load phase angle between the S and L terminals is made
more negative in buck operation relative to the no-load phase angle at the same tap position because both the no-
load phase angle and the phase angle change caused by the load are negative (see Annex E).
3.17
advance
mode of operation where the L terminal no-load voltage leads the S terminal no-load voltage,
giving a positive no-load phase angle

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© IEC/IEEE 2017
3.18
retard
mode of operation where the L terminal no-load voltage lags the S terminal no-load voltage,
giving a negative no-load phase angle
3.19
rated voltage
no-load phase-to-phase voltage at zero phase shift tap position to which operating and
performance characteristics are referred
3.20
tapping voltage of the S terminal
no-load phase-to-phase voltage based on turns ratio appearing at
the S terminal when rated voltage is applied to the L terminal at a particular tap position
Note 1 to entry: For an asymmetric design, the voltage at taps other than at the zero phase shift tap position will
be lower at the S terminal than the L terminal. This definition is used so that the series unit rated current is
constant with tap position to be compatible with the rating of the attached power system circuits.
3.21
series winding
winding connected between the S and L terminals
Note 1 to entry: The term series winding refers to any winding or set of windings that can be connected between
the S and L terminals. For example, this term refers to the tap winding of a single-core phase shifting transformer
where this winding is connected between the S and L terminals. In the case of a PST combined with a transformer
or autotransformer, the series winding of the PST may be connected to the S or L terminal indirectly through the
transformer or autotransformer series winding (see example 9.4.3.1).
3.22
series unit
core and windings of a two-core PST containing the series winding
3.23
exciting unit
core and windings of a two-core PST that provides excitation to the series unit
3.24
exciting winding
winding of a single-core PST or of the exciting unit of a two-core PST which supplies the
voltage required to change the phase angle
3.25
tap winding
winding in which taps are changed to vary the phase angle
Note 1 to entry: The tap winding is referred to as the regulating winding in some countries.
3.26
design value
expected value given by the number of turns in the design in the case of turns ratio and no-
load phase angle or calculated from the design in the case of impedance, no-load current or
other parameters
3.27
advance-retard switch
ARS
switch separate from any change-over selector associated with the on-load tap-changer that
allows a change of operation from advance to retard or from retard to advance at zero no-load
phase angle without interrupting the load current or de-energizing the PST

IEC/IEEE 60076-57-1202:2017 – 11 –
© IEC/IEEE 2017
Note 1 to entry: See Annex F.
Note 2 to entry: This note applies to the French language only.
4 Use of normative references
This standard can be used with either the IEC or IEEE normative references, but the
references shall not be mixed. The purchaser shall include in the enquiry and order which
normative references are to be used. If the choice of normative references is not specified,
then IEC standards shall be used, except for PSTs intended for installation in North America
where IEEE standards shall be used.
5 Service conditions
5.1 General
Unless otherwise specified by the purchaser, normal service conditions shall apply as stated
in IEC 60076-1 or IEEE Std C57.12.00.
5.2 Usual service conditions
5.2.1 Switching arrangement
Unless otherwise specified, the PST shall be designed for use with an on-load bypass device
connecting the respective L terminals and S terminals that will only be closed in service when
the PST is on the zero phase shift tap position for the time taken to complete a switching
sequence to place the PST into or out of service.
If the PST will never be used with the L and S terminals connected (no on-load bypass
device), this can be specified and the double ended impulse test may be omitted (see
13.12.5).
If the PST is to be used in the condition where an on-load bypass is closed in service with the
PST energized from both S and L terminals for longer than the time taken for switching, this
shall be specified.
Unless otherwise specified, the PST shall not be energized or operated with the L and S
terminals connected by a bypass unless it is on the zero phase shift tap position. If it is
required that the PST can be bypassed at other than zero phase shift tap position, this shall
be clearly stated by the purchaser in the enquiry.
The PST shall be suitable for energization from either the S or L terminals at any tap position.
5.2.2 Power flow
Unless otherwise specified, the PST shall be capable of transferring rated power in either
direction provided that the phase angle between the S and L terminals does not exceed the
maximum no-load phase angle.
NOTE If the PST is acting to reduce or reverse the power flow in the circuit, the phase angle will exceed the no-
load phase angle and, unless otherwise specified, there will be no power flow capability at the extreme taps under
these conditions. If this capability is required, see 6.3.
5.2.3 Operation with two or more PSTs in series or parallel
Unless otherwise specified, it may be assumed that the PST will not be installed in series or
parallel with another PST connected to the same circuit. If series or parallel operation is
required, this shall be stated by the purchaser in the enquiry and contract, and details of the
PST which will be in series or parallel given.

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© IEC/IEEE 2017
NOTE For parallel operation of PSTs it should be considered that if the PST has a low impedance at or close to
the no-load zero phase shift tap position then a short circuit or an extremely high circulating current can occur
during tap-change operations if no additional reactance is connected to the circuit. See IEC 62032 [1] or
IEEE Std C57.135 [2].
5.2.4 Phase unbalance
PSTs are intended to be used in a system where the voltages and currents in the three
phases are essentially balanced under normal conditions (see IEC 60076-1 or
IEEE Std C57.12.00 for normal levels of voltage balance). If the PST is to operate in a system
that has current unbalance of more than 5 %, the expected unbalance shall be stated by the
purchaser in the enquiry and order.
5.2.5 Surge protection
The PST shall be installed with adequate surge protection on both S and L terminals
irrespective of the characteristics of the connected system. Unless otherwise specified, this is
the responsibility of the purchaser.
NOTE A through fault short circuit condition on one phase is likely to produce induced voltages on the other
phases higher than the test voltage levels, see Annex B.
6 Rating and general requirements
6.1 Rated power
The rated power shall be specified by the purchaser and shall apply to the zero phase shift
tap and any tap in boost mode, but see 6.3 for rated power in buck mode.
6.2 Loading at other than rated conditions
Any requirements for loading beyond rated power or at other than rated conditions shall be
specified by the purchaser. See IEC 60076-7 [3] or IEEE Std C57.12.00, and
IEEE Std C57.91 [6]. See also 6.3.
NOTE PSTs have loading limitations due to thermal, magnetic induction and tap-changer considerations.
6.3 Specification of buck capability
If operation of the PST in buck mode is required, the minimum required power at each tap
position under buck loading conditions including any overloads shall be specified. Unless
otherwise specified, unity power factor, rated frequency and rated voltage at the L terminal
shall be assumed when calculating the PST capability. An example of such a specification is
given in Annex C.
If the minimum required power at each tap position under buck loading conditions is not
specified, then according to 5.2.2 the PST will have no buck loading capability at the extreme
tap position. Some buck capability (below rated power) at other tap positions will be available
depending on the no-load phase angle and impedance at that tap, but any capability will be
determined by the manufacturer.
The impedance used as the basis for the buck loading capability assessment shall become
the maximum guaranteed value (without tolerance) at that particular tap position. This figure
may be lower than the maximum impedance, but shall be higher than the minimum impedance
specified by the purchaser.
_______________
Numbers in square brackets refer to the Bibliography.

IEC/IEEE 60076-57-1202:2017 – 13 –
© IEC/IEEE 2017
6.4 Cooling modes
Requirements for cooling modes and minimum power under different cooling modes if any
shall be stated in the enquiry and order. See IEC 60076-1 or IEEE Std C57.12.00.
6.5 Short circuit impedance and load phase angle capability
6.5.1 Specification
The purchaser shall specify the load phase angle capability of the PST in one of the following
ways:
• the maximum and minimum impedance at the extreme taps and the minimum absolute no-
load phase angle at the extreme taps;
• the minimum absolute boost and/or buck phase angle at rated power. In this case the
manufacturer shall determine the no-load phase angle and impedance required to meet
this requirement. The purchaser shall also specify either a maximum impedance or voltage
drop (regulation) if required.
Unless otherwise specified, unity power factor, rated frequency and rated voltage at the
L terminal shall be assumed when calculating the PST capability.
NOTE In the case of certain asymmetric designs with both voltage and phase angle variation, it can be more
convenient by agreement to base the capability on the S terminal to avoid an apparent interaction between phase
angle tap position and voltage variation range.
If there is a minimum impedance requirement at the zero phase shift tap position, this shall be
specified by the purchaser. Otherwise the minimum impedance at the zero phase shift tap is
at the discretion of the manufacturer.
If the purchaser requires any particular limits on zero sequence impedance, for example to
avoid series resonance conditions, this shall be stated in the enquiry and order.
6.5.2 Short circuit impedance for asymmetric designs
In the case of an asymmetric design, the voltage ratio between the S terminal and the
L terminal and consequently the tapping voltage of the S terminal will vary with tap position.
Unless otherwise agreed, the impedance at each tap shall be based on the rated voltage and
rated power at the L terminal.
6.6 Neutral earthing (grounding)
The purchaser shall specify the neutral earthing arrangement for each neutral terminal;
whether directly connected to earth, earthed through an impedance or not earthed.
Any intermediate circuit or circuits that would otherwise have no galvanic connection to the S,
L or neutral terminals shall be connected to earth. Unless otherwise specified, intermediate
circuits shall be connected to earth externally to facilitate site testing. Unless otherwise
agreed, the connection to the tank earth shall be provided by the manufacturer.
6.7 Rated voltage
The purchaser shall specify the rated voltage for the S and L terminals.
6.8 Voltage variation and asymmetric design
Unless otherwise specified, the PST shall be designed so that the voltage ratio between the S
and L terminals does not vary with tap position. If an asymmetric design can be accepted by
the purchaser, this should be stated in the enquiry together with any limits on the voltage
variation at the L terminal.
– 14 – IEC/IEEE 60076-57-1202:2017
© IEC/IEEE 2017
Any requirements for voltage variation separate to or combined with phase angle variation
shall be specified.
6.9 Rated frequency
The rated frequency shall be specified by the purchaser to be the normal undisturbed
frequency of the network
6.10 Operation at higher than rated voltage and/or at other than rated frequency
If the PST is to be operated at V/Hz in excess of the provisions given in IEC 60076-1 or
IEEE Std C57.12.00, this shall be specified by the purchaser.
6.11 Highest voltage for equipment and dielectric test levels
The purchaser shall specify the highest voltage for equipment (maximum system voltage) and
the dielectric test levels. See IEC 60076-1, IEC 60076-3
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