IEC 62032:2012

IEC 62032
Edition 2.0 2012-06
™
IEEE Std C57.135
INTERNATIONAL
STANDARD
Guide for the Application, Specification, and Testing of Phase-Shifting
Transformers
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IEC 62032
Edition 2.0 2012-06
IEEE Std C57.135™
INTERNATIONAL
STANDARD
Guide for the Application, Specification, and Testing of Phase-Shifting

Transformers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 29.180 ISBN 978-2-83220-101-5

– ii – IEEE Std C57.135-2011
Contents
1. Overview . 1
1.1 Scope . 1
1.2 Purpose . 1
2. Normative references . 2
3. Definitions . 2
4. Application and theory of PSTs . 4
4.1 Introduction . 4
4.2 Basic principle of application—advanced and retard phase angle . 4
4.3 PST under load . 6
4.4 Power transfer . 8
4.5 Types of PSTs .10
4.6 Special on load tap changer (OLTC) features .16
4.7 Arrangement of more than one PST .20
4.8 Design criteria.20
5. Service conditions .21
5.1 Usual service conditions .21
5.2 Loading at other than rated conditions .22
5.3 Unusual service conditions .22
5.4 Protection .23
6. Rating data .26
6.1 Polarity, angular displacement, and terminal markings .26
6.2 Impedance .26
6.3 Name plates .27
7. Construction .27
7.1 Enclosed throat connections .27
7.2 Liquid insulation and preservation system .27
8. Short-circuit characteristics .28
8.1 Short-circuit requirements .28
9. Control system .29
9.1 Control equipment and accessories .29
9.2 Requirements .29
9.3 Test code for control systems .31
10. Testing of PSTs .32
10.1 General .32
10.2 Special tests for PSTs .33
11. Tolerances .34
11.1 General .34
11.2 Tolerances for ratio of series and exciting units .34
11.3 Tolerance for phase angle and impedance .34
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – iii –
12. Bid document checklist .35
12.1 Nontechnical information .35
12.2 Technical information .35
12.3 Special requirements or conditions .36
12.4 Additional information .36
Annex A (informative) Bibliography .38
Annex B (informative) IEEE List of Participants . 40

Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

– iv – IEEE Std C57.135-2011
Guide for the Application, Specification, and Testing of
Phase-Shifting Transformers
FOREWORD
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Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – v –
determination of the validity of any patent rights, and the risk of infringement of such rights, is entirely
their own responsibility.
International Standard IEC 62032/ IEEE Std C57.135-2011 has been processed through
IEC technical committee 14: Power transformers, under the IEC/IEEE Dual Logo
Agreement.
This second edition cancels and replaces the first edition, published in 2005, and
constitutes a technical revision.
The text of this standard is based on the following documents:
IEEE Std FDIS Report on voting
IEEE Std C57.135-2011 14/710/FDIS 14/714/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.
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
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At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

– vi – IEEE Std C57.135-2011
IEEE Std C57.135™-2011
(Revision of
IEEE Std C57.135-2001)
IEEE Guide for the Application,
Specification, and Testing of Phase-
Shifting Transformers
Sponsor
Transformers Committee
of the
IEEE Power & Energy Society
Approved 16 June 2011
IEEE-SA Standards Board
Abstract: Theory, application of phase-shifting transformers, and the difference of specification
and testing to standard system transformers are described in this guide. Various types of phase-
shifting transformers and how to select the optimal design to achieve required control of power
flow are covered. An understanding of the terminology, types, construction, and testing specific to
phase-shifting transformers is provided.

Keywords: advance phase angle, dual-core design, IEEE C57.135, main transformer, phase-
shifting transformer, power transfer, retard phase angle, series transformer, single-core design,
special tests
•
IEEE is a registered trademark in the U.S. Patent & Trademark Office, owned by the Institute of Electrical and Electronics
Engineers, Incorporated.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – vii –
IEEE Introduction
This introduction is not part of IEEE Std C57.135-2011, IEEE Guide for the Application, Specification, and Testing of
Phase-Shifting Transformers.
This guide describes the application, specification, and testing of phase-shifting transformers. It is intended
for the following:
 Organizations responsible for the application and specification of phase-shifting transformers
for electric transmission systems to control power flow.
 Organizations responsible for testing phase-shifting transformers.

This guide is designed to help organizations:
 Understand the various types of phase-shifting transformers and how to apply them to obtain
required control of power flow.
 Prepare specifications for the purchase of phase-shifting transformers.
 Standardize tests and test methods for phase-shifting transformers.

This guide is intended to satisfy the following objectives:
 Promote consistency within organizations for the application and specification of phase-shifting
transformers.
 Provide an understanding of the terminology, types, construction, and testing relating
specifically to phase-shifting transformers.
 Promote the standardization of testing procedures for phase-shifting transformers.
Since this guide was first published in 2001, several recommendations from users and manufacturers were
made to revise it to improve accuracy and applicability. Some of the revisions are as follows:
 Figure 1, Figure 3, Figure 4, Figure 7, and Figure 11 were improved.
 Equation (1) was divided into two parts to show the difference between advance and retard
operations.
 A new section on minimum information requirements for specifying a PST was inserted.
 Various editorial changes were made to clarify the contents of the guide.
Notice to users
Laws and regulations
Users of these documents should consult all applicable laws and regulations. Compliance with the
provisions of this standard does not imply compliance to any applicable regulatory requirements.
Implementers of the standard are responsible for observing or referring to the applicable regulatory
requirements. IEEE does not, by the publication of its standards, intend to urge action that is not in
compliance with applicable laws, and these documents may not be construed as doing so.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

– viii – IEEE Std C57.135-2011
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Attention is called to the possibility that implementation of this guide may require use of subject matter
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Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – 1 –
Guide for the Application,
Specification, and Testing of Phase-
Shifting Transformers
IMPORTANT NOTICE: This standard is not intended to ensure safety, security, health, or
environmental protection. Implementers of the standard are responsible for determining appropriate
safety, security, environmental, and health practices or regulatory requirements.
This IEEE document is made available for use subject to important notices and legal disclaimers.
These notices and disclaimers appear in all publications containing this document and may
be found under the heading “Important Notice” or “Important Notices and Disclaimers
Concerning IEEE Documents.” They can also be obtained on request from IEEE or viewed at
http://standards.ieee.org/IPR/disclaimers.html.
1. Overview
1.1 Scope
This guide covers the application, specification, theory of operation, and factory and field testing of single-
phase and three-phase oil-immersed, phase-shifting transformers (PSTs).
This guide is limited to matters particular to PSTs and does not include matters relating to general
requirements for power transformers covered in existing standards, recommended practices, or guides.
1.2 Purpose
The terminology, function, application, theory of operation and protection, and design of PSTs are not
covered by existing transformer standards and guides. The purpose of this document is to provide guidance
to those specifying, designing, and using PSTs.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

– 2 – IEEE Std C57.135-2011
2. Normative references
The following referenced documents are indispensable for the application of this document (i.e., they must
be understood and used, so each referenced document is cited in text and its relationship to this document is
explained). For dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments or corrigenda) applies.
IEC 60076-1, Power Transformers—Part 1: General.
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 60076-7, Power Transformers—Part 7: Loading Guide for Oil-Immersed Power Transformers.
2,3
TM
IEEE Std 693 , IEEE Recommended Practice for Seismic Design for Substations.
TM
IEEE Std C37.90.1 -1989, IEEE Standard for Surge Withstand Capability (SWC) Tests for Relays and
Relay Systems Associated with Electric Power Apparatus.
TM
IEEE Std C57.12.00 , IEEE Standard General Requirements for Liquid-Immersed Distribution, Power,
and Regulating Transformers.
TM
IEEE Std C57.12.80 , IEEE Standard Terminology for Power and Distribution Transformers.
TM
IEEE Std C57.12.90 , IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating
Transformers, and IEEE Guide for Short-Circuit Testing of Distribution and Power Transformers.
3. Definitions
For the purposes of this document, the following terms and definitions apply. The IEEE Standards
Dictionary: Glossary of Terms & Definitions should be consulted for terms not defined in this clause.
All other definitions, except as specifically covered in this guide, shall be in accordance with IEEE Std
TM
C57.12.80 .
advance phase angle: The phase angle expressed in degrees that results when the load (L) terminal voltage
leads the source (S) terminal voltage.
excitation-regulating winding: A two-core phase-shifting transformer (PST) design in which the exciting
unit has one winding operating as an autotransformer that performs both functions listed under excitation
and regulating winding of a two-core PST.

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IEEE publications are available from the Institute of Electrical and Electronics Engineers, 445 Hoes Lane, Piscataway, NJ 08854-
4141, USA (http://standards.ieee.org/).
The IEEE standards or products referred to in this clause are trademarks owned by the Institute of Electrical and Electronics
Engineers, Incorporated.
The IEEE Standards Dictionary: Glossary of Terms and Definitions is available at http://shop.ieee.org.
Information on references can be found in Clause 2.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – 3 –
excitation winding: The winding of a phase-shifting transformer (PST) that draws power from the source
to energize the PST.
excited winding of a two-core phase-shifting transformer (PST): The winding of the series unit that is
excited from the regulating winding of the exciting unit.
exciting unit of a two-core phase-shifting transformer (PST): The core and coils that furnish excitation
to the series unit.
L terminal: The L terminal is the terminal that is used to measure the voltage phase-shift angle when
compared to the S terminal of the phase-shifting transformer (PST).
primary winding of the exciting unit of a two-core phase-shifting transformer (PST): The winding on
the high-voltage side of the exciting unit.
phase-shifting transformer (PST): A transformer that advances or retards the voltage phase-angle
relationship of one circuit with respect to another.
rated kVA of a phase-shifting transformer (PST): The apparent power at rated voltage for which the
PST is designed.
rated phase angle of a phase-shifting transformer (PST): The phase angle measured between the S and
L terminals at maximum advance and/or retard tap position under no-load condition.
rated voltage of a phase-shifting transformer (PST): The phase-to-phase voltage to which operating and
performance characteristics are referred. The voltage ratings are to be defined at no-load and based on turn
ratios.
regulated circuit of a phase-shifting transformer (PST): The circuit on the output side of the PST in
which it is desired to control the voltage, the phase relation, or both.
NOTE—In the regulated circuit the voltage may be held constant, or may vary with or without relation to the phase
angle depending on the type of PST.
regulating winding: The winding of a single-core phase-shifting transformer (PST) or of the exciting unit
of a two-core PST in which taps are changed to vary the phase angle.
retard phase angle: The phase angle expressed in degrees that results when the L terminal voltage lags the
S terminal voltage.
series unit of a two-core phase-shifting transformer (PST): The core and coil unit that has one or more
windings connected in series with the line circuit.
series winding(s) of a two-core phase-shifting transformer (PST): The winding(s) of the series unit that
is(are) connected in series in the line circuit.
single-core design: A single-core phase-shifting transformer (PST) has all windings mounted on a single
core.
S terminal: The S terminal is the terminal that is used as the fixed reference point when measuring the
voltage phase angle of a phase-shifting transformer (PST).

Notes in text, tables, and figures of a standard are given for information only and do not contain requirements needed to implement
this standard.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

– 4 – IEEE Std C57.135-2011
two-core design: A two-core phase-shifting transformer (PST) consists of a series unit and a exciting unit.
The series and the exciting unit can be either in one tank or in separate tanks.
4. Application and theory of PSTs
4.1 Introduction
The development of large, high-voltage power grids has enabled power consumers to enjoy the benefits of
more reliable and efficient service and has allowed generation sources to be, in some cases, located long
distances from large load centers. Although large interconnected grids strengthen a power system’s
reliability, complications can arise with the control of steady-state power flow along certain segments of
the system. These complications can be attributed to several factors, including the impedance of parallel
paths in the power grid, variation in power generation output, and variation in loads and load center phase
angles.
4.2 Basic principle of application—advanced and retard phase angle
PSTs are used to control the power flow in electrical power systems. When power flows between two
systems, there is a voltage drop and a phase-angle shift between the source and the load that depends upon
the magnitude and power factor of the load current. If the systems are connected together in two or more
parallel paths so that a loop exists, any difference in the impedances will cause unbalanced line loading.
Figure 1 shows an example with the load side power factor assumed to be 1 and the system resistances
being negligible with respect to their reactances. An arbitrary power flow distribution can be obtained by
inserting a PST into one of the branches. Dependent upon whether the PST is installed in the branch with
the higher or lower impedance, an advanced or a retard phase angle is needed. Advanced means that the L
terminal voltage (V ) leads the S terminal voltage (V ); retard means that the L terminal voltage (V ) lags
L S L
the S terminal voltage (V ).
S
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – 5 –
Figure 1 —Load side power factor of 1
Equation (1a) and Equation (1b) illustrate the advance and retard operations shown in Figure 1.
(1a)
I * Z −∆V− I * Z = 0 ⇒ ∆V= I * Z − I * Z
2 2 1 1 2 2 1 1
(1b)
I 1 * Z 1+∆V− I 2 * Z 2= 0 ⇒ ∆V= I * Z − I * Z
2 2 1 1
A numerical example should illustrate this. If it is required that both systems are loaded with 50% of the
total transferred power 2xS and the impedances are assumed to be z = 0.02 and z = 0.30, related to S, the
1 2
necessary additional voltage becomes ΔV = 0.30 – 0.02 = 0.28. Hence, a load phase angle (advanced) of
about 15.6° (≈arctan(0.28)) is necessary. The total angle between source and load becomes minus 1.1°. In
case with z = 0.30 and z = 0.02, the same load phase angle (retard) would be needed, but the total phase
1 2
angle between source and load would become 16.7°. If no measures were taken, then the load distribution
between system 1 and 2 would be 0.9375 to 0.0625 instead of 0.5 to 0.5.
A second important application is the use of a PST to control the power flow between two large
independent grids. An advanced phase-shifting angle is necessary to achieve a flow of active power from
system 1 to system 2 (Figure 2).
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

– 6 – IEEE Std C57.135-2011
Figure 2 —Advanced phase-shifting angle
4.3 PST under load
So far an “ideal” PST (i.e., a transformer with an impedance z = 0) has been dealt with. To demonstrate
T
load conditions, an equivalent circuit phasor diagram is used as shown in Figure 3 with an ideal PST with
z = 0 and an additional transformer with a turns ratio of 1:1 and an impedance z = R + jX .
T T T T
where
V * is load-side voltage (no-load)
L
is load-side voltage (loaded)
V
L
V is source-side voltage (advanced)
S(a)
V is source-side voltage (retard)
S(r)
I is load current
L
cos φ is load power factor
L
z is transformer impedance
T
β is transformer load angle
α is phase-shift angle
+ advanced
– retard
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – 7 –
Figure 3 —Demonstration of load conditions
Next, the phasor diagram of the PST can be drawn. Starting with the load voltage V and calculating the
L
ohmic and reactive voltage drop in the 1:1 transformer, the load voltage V * can be obtained. The load
L
phase angle β can be calculated with Equation (2):
I × X× cosϕϕ− IR××sin Z × cosϕ
L LL L T L
β arctan ≅ arctan (2)
V × I × X×sinϕϕ+ I ××R cos 100+ Z ×sinϕ
LL L L L T L
The PST adds ±α, and so, finally, the load phase angles of the transformer α* and α* , respectively, are
(a) (r)
obtained as shown in Equations (3) and (4):
α* = α – β is phase-shift angle (loaded) advance (3)
(a)
α* = –(α + β) is phase-shift angle (loaded) retard (4)
(r)
On the one hand, to obtain an advanced phase angle α* under load, the no-load phase angle α has to be
(a)
chosen properly under consideration of the phase angle α* of the PST. On the other hand, the retard phase
(r)
angle α* is increased under load. This has an impact on transformer and tap changer as discussed in 4.8.4.
(r)
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

=
– 8 – IEEE Std C57.135-2011
4.4 Power transfer
A PST has two separate effects on power flow. First, the no-load phase angle creates an additional voltage
that drives additional current through the line. Second, the PST’s additional impedance is added to the
circuit. These two effects may work against each other. Therefore, a minimum phase angle is usually
required to compensate for the additional voltage drop across the PST’s impedance in the advanced
position. To ease the following considerations, the impedance of the PST has been assumed to be constant
over the whole regulating range, a tolerable approximation for two-core designs (the impedance of single-
core designs is commonly zero at 0° phase shift).
With the denotations used in Figure 3 and
P is active power transferred when α = 0 (preload)
Q is reactive power transferred when α = 0 (preload)
the power components at the source side are calculated using Equations (5) and (6):
V
S
PP(α)= ×cosαα−×Q sin+ ×sinα (5)
X
T
V
S
QP(α)= ×sinα+ Q× cosα+ × (1− cosα ) (6)
00 0
X
T
Figure 4 explains the effect of the introduction of the phase-shift angle α. In the formula, the first two terms
reflect the effect of the phase angle on the original power flow as easily can be derived from Figure 4. The
last term represents the additional power flow generated by the additional voltage ΔV across the impedance
jX of the PST. Taking into consideration that the real component of ΔV (–ΔV* cos(α/2)) drives a current
with a positive imaginary component and the imaginary component of ΔV (–ΔV*sin(α/2)) is a current with
a positive real component and that ΔV = 2*V * sin((α/2), the last terms in Equations (5) and (6),
s
respectively, can be confirmed without difficulties.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

IEEE Std C57.135-2011 – 9 –
Figure 4 —Effect of phase-shift angle α
Figure 5 shows the variation of the additional power flow (assumption: P = Q = 0, Z ≈ jX , V /X = 1)
0 0 T T s T
with the PST angle α.
0.5
0.4 Active Power    Reactive Power
__________    _ _ _ _ _ _ _ _ _
0.3
0.2
0.1
0 4 8 12 16 20 24
Phase angle (º)
Figure 5 —Variation of additional power flow with the PST angle α
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

Power (per unit)
– 10 – IEEE Std C57.135-2011
Figure 6 shows as an example the variation of the power flow at the source side with the phase angle α,
depending on different preload conditions. The maximum additional power transferred has been assumed to
be 1.
It can be seen how the power flow is influenced when the no-load phase angle of the PST is changed from
zero to maximum leading phase shift. The highest increase of active power for the same phase shift appears
when a negative reactive power flow exists, i.e., with high capacitive load. An inductive load (positive
reactive power) decreases the effect of the PST.
The reactive power flow is also influenced by the preload condition. The active power has a major impact
on the influence of the PST angle.
Power Flow
α=0º à α=40º
0.5
-0.5
-1
-1 -0.5 0 0.5 1 1.5
Active Power P (pu)
Figure 6 —Variation of power flow with the phase angle α depending on different
preload conditions
4.5 Types of PSTs
4.5.1 Introduction
The basic principle to obtain a phase shift is to connect a segment of one phase into another phase. Figure 7
shows an elementary arrangement; the phasor diagrams are drawn for a no-load condition. A PST is used
with the exciting winding delta connected. The regulating winding of phase V –V is connected to phase V
2 3 1
and so on. The scheme has been plotted for subtractive polarity of the windings, and the tap position has
been chosen so that the transformer produces an advanced phase angle. Under the no-load condition, the
regulation is symmetrical, i.e., the absolute values of source and load voltage are the same.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

Reactive Power Q (pu)
(Cap.)          (Ind.)

IEEE Std C57.135-2011 – 11 –
Figure 7 —Phasor diagram for the no-load condition
Equation (7) through Equation (9) can be used to calculate V , V , and V :
S L Δ
∆V
VV+ (7)
S1 10
∆V
V V− (8)
L1 10
V VV− (9)
∆1 20 30
With consideration of these formulas, the phasor diagram can be drawn and absolute values can be
determined using Equation (10) through Equation (15):
V V−V (10)
SL1 11
α
VV× cos (11)
10 1
α
∆VV= ××2 sin (12)
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

=
=
=
=
=
– 12 – IEEE Std C57.135-2011
α
V=V× 3=V× 3× cos (13)
∆ 10 1
(14)
I II
SL1 11
∆V αα2
II= × × cos=I× × sin (15)
∆ LL11
V 22
Λ
The rated throughput power of the PST is determined with Equation (16):
P=3××VI (16)
SL11
whereas the rated design power that determines the size of the unit is determined with Equation (17):
α
P 3×∆VI× P× 2× sin (17)
In practice, many solutions are possible to design a PST. The user’s electric power system requirements
and the manufacturer’s preference generally determine the design. The major factors determining the type
of PSTs are listed subsequently.
The factors specific to the PST design are as follows:
 PST purchasing price or the first cost
 Cost of capitalization of losses
 Impedance variation across the tap range
 Angle at full load
 Electrical arrangement of on-load tap changers
 On-load tap changers margins on step voltage, rated current, fault current and switching
capacity and duty of changeover selector [advance-retard switch (ARS)]
 Test capability
The factors specific to the project are as follows:
 Foundations and the space requirement in the substation
 Oil spill containment volume
 Shipping weights and shipping dimensions
 Protection and relay costs
These factors decide whether a single-core or a two-core type has to be chosen. These two types are
described in more detail in 4.5.2 through 4.5.3.
Published by IEC under license from IEEE. © 2011 IEEE. All rights reserved.

= =
==
IEEE Std C57.135-2011 – 13 –
4.5.2 Single-core design
The single-core design is less complex and has fewer winding segments than two-core designs but has
some disadvantages as follows.
The load tap changer (LTC) and the tapped winding are in the line end of the windings and are directly
exposed to the system overvoltages.
The short-circuit impedance of the single-core design PST is very low at tap positions near 0° phase shift.
Therefore, the ratio between external fault currents passing through the PST and rated current may become
very high, especially in systems with low fault current impedance. This has to be taken into account when
selecting the tap changers and when calculating the forces in the windings.
With the design outlined in Figure 7, symmetrical conditions are
...