EN 50708-1-1:2020
(Main)Power transformers - Additional European requirements: Part 1-1: Common part - General requirements
Power transformers - Additional European requirements: Part 1-1: Common part - General requirements
This document is part of the EN 50708 series which applies to transformers in compliance with EN 60076-1.
Leistungstransformatoren - Zusätzliche europäische Anforderungen - Teil -1-1: Allgemeiner Teil - Allgemeine Anforderungen
Transformateurs de puissance - Exigences européennes supplémentaires : Partie 1 - Partie commune
Le présent document fait partie intégrante de la série EN 50708 qui s’applique aux transformateurs conformes à l’EN 60076 1.
Močnostni transformatorji - Dodatne evropske zahteve - 1-1. del: Skupni del - Splošne zahteve
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-julij-2020
Nadomešča:
SIST EN 50588-1:2017
SIST EN 50629:2015
SIST EN 50629:2015/A1:2016
SIST EN 50629:2015/A2:2018
Močnostni transformatorji - Dodatne evropske zahteve - 1-1. del: Skupni del -
Splošne zahteve
Power transformers - Additional European requirements: Part 1-1: Common part -
General requirements
Transformateurs de puissance - Exigences européennes supplémentaires : Partie 1 -
Partie commune
Ta slovenski standard je istoveten z: EN 50708-1-1:2020
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN 50708-1-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2020
ICS 29.180 Supersedes EN 50588-1:2017 (PART), EN 50629:2015
(PART) and all of its amendments and corrigenda (if any)
English Version
Power transformers - Additional European requirements: Part 1-
1: Common part - General requirements
Transformateurs de puissance - Exigences européennes To be completed
supplémentaires : Partie 1 - Partie commune
This European Standard was approved by CENELEC on 2019-10-09. 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.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50708-1-1:2020 E
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Service condition . 10
5 Ratings and general requirements . 11
5.1 Rated power . 11
5.2 Rated frequency . 11
5.3 Energy performance . 11
5.3.1 Energy performance requirements . 11
5.3.2 Exclusion from energy performance requirements . 11
5.3.3 Reference conditions . 12
5.3.4 Technical documentation . 12
6 Rating plate . 13
7 Tolerances . 13
7.1 Tolerance during factory acceptance tests . 13
7.2 Tolerances for Market surveillance. 14
8 Tests . 14
8.1 General . 14
8.2 Measurement of cooling consumption . 14
9 Accessories and fittings . 14
10 Capitalization of losses . 14
11 Transformer overhaul . 15
Annex A (normative) Peak efficiency calculation . 16
A.1 Efficiency Index. 16
A.2 Peak Efficiency Index . 16
A.3 PEI calculation for transformers having more than two windings . 17
Annex B (informative) Capitalization of losses . 19
B.1 General Theory, Concept of Capitalization . 19
B.2 Impact of capitalization values . 19
B.3 Capitalization formula . 20
B.3.1 General . 20
B.3.2 Calculation of factor A . 20
B.3.3 Calculation of factor B . 21
B.3.4 Use of A and B for tender evaluation. 23
B.3.5 Determination of factors A and B . 24
Annex C (informative) A-deviations . 26
Annex D (informative) Additional considerations related to energy performances. 27
D.1 General . 27
D.2 Autotransformers . 27
D.3 Voltage and insulation level . 27
D.4 More than two windings. 27
D.5 Short-circuit impedance . 27
D.6 Tapping range . 27
D.7 Losses on taps different than rated tap . 28
D.8 Separate phases . 28
Annex E (informative) Transformer overhaul . 29
E.1 General . 29
E.1.1 Overview . 29
E.1.2 Energy performance. 29
E.1.3 Life expectancy . 29
E.2 Classification of overhaul activities . 29
E.2.1 Overview . 29
E.2.2 Repair. 30
E.2.3 Upgrade . 30
E.2.4 Refurbishment . 30
E.2.5 Retrofit . 31
Annex ZZ (informative) Relationship between this European Standard and the ecodesign
requirements of Commission Regulation (EU) No 548/2014 of 21 May 2014 and its
amendment No 2019/1783 of 1 October 2019 on implementing Directive 2009/125/EC of
the European Parliament and of the Council with regard to small, medium and large
power transformers aimed to be covered . 32
Bibliography . 33
European foreword
This document (EN 50708-1-1:2020) has been prepared by CLC/TC 14, “Power transformers”.
The following dates are fixed:
• latest date by which this document has (dop) 2020-11-22
to be implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2023-05-22
standards conflicting with this document
have to be withdrawn
This document supersedes EN 50588-1:2017 and EN 50629:2015 and all of their amendments and corrigenda
(if any).
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.
This document has been prepared under a mandate given to CENELEC by the European Commission and the
European Free Trade Association, and supports essential requirements of Commission Regulation (EC).
For the relationship with the Commission Regulation (EC) see informative Annex ZZ, which is an integral part
of this document.
Introduction
The EN 50708 series, “Power transformers – Additional European requirements” has been prepared by
CENELEC TC 14 to address specific European requirements of power transformers related EU Regulations
and local practices.
Technical requirements set by the EN 50708 series supplement, modify or replace certain requirements of the
other EN standards derived from equivalent IEC international standards.
This series contains general requirements on energy performance, accessories, fittings, tests, mechanical
requirements etc. structured as follows:
— Part 1 series - Common requirements;
— Part 2 series - Medium power transformers;
— Part 3 series - Large power transformers.
The EN 50708-X parts with X greater than 1 contain particular requirements for a different category of
transformers or transformer applications which are based on the requirements of the general parts of
EN 50708-1-1.
The EN 50708-X parts should be considered in conjunction with the requirements of the general part.
The particular requirements of these subparts of EN 50708 supplement, modify or replace certain requirements
of the general parts of EN 50708-1-1 and/or EN 50708-1-X being valid at the time of publication of this part. The
absence of references to the exclusion of a part or a clause of a general part means that the corresponding
clauses of the general part are applicable (undated reference).
Requirements of other -X parts with X greater than 1 being eventually relevant for cases covered by this part
also apply. This part may therefore also supplement, modify or replace certain of these requirements valid at
the time of publication of this document.
The main clause numbering of each subpart follows the pattern and corresponding references of EN 50708-1-1.
The numbers following the particular number of this part are those of the corresponding parts, or clauses of the
other parts of the EN 50708 series, valid at the time of publication of this part, as indicated in the normative
references of this document (dated reference).
In the case where new or amended general parts with modified numbering were published after the subpart
was issued, the clause numbers referring to a general part in subparts might no longer align with the latest
edition of the general part. Dated references should be observed.
It is acknowledged that environmental requirements including energy in the use phase are a significant aspect
that can be addressed through product design. As the material content increases to improve energy
performance, it is advisable to make a proper life cycle assessment including recycling of the extra raw material
and the overall energy used to produce and transport transformers. Some guidelines are given in EN 60076-1.
1 Scope
This document is part of the EN 50708 series which applies to transformers in compliance with EN 60076-1.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references, the
latest edition of the referenced document (including any amendments) applies
EN 50329:2003, Railway applications - Fixed installations - Traction transformers
EN 50708-2-1:2020, Power transformers - Additional European requirements: Part 2-1 Medium power
transformer - General requirements
EN 50708-3-1:2020, Power transformers - Additional European requirements: Part 3-1 Large power transformer
- General requirements
EN 60076 (all parts), Power transformers (IEC 60076 series)
EN 60310:2016, Railway applications - Traction transformers and inductors on board rolling Stock (IEC 60310)
EN 61378-1:2011, Convertor transformers - Part 1: Transformers for industrial applications (IEC 61378-1:2011)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 60076-1:2011 and the following 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
3.1
medium power transformer
MPT
power transformer with all windings having a rated power lower than or equal to 3 150 kVA, and highest voltage
for equipment greater than 1,1 kV and lower than or equal to 36 kV
Note 1 to entry: The definitions of power transformer and winding are given in EN 60076-1.
Note 2 to entry: The national practice of the Czech Republic could require the use of the highest voltages for equipment
in AC three-phase systems of 38,5 kV instead of 36 kV and 25 kV instead of 24 kV. These units have a rated power lower
than or equal to 3 150 kVA:
— with U = 38,5 kV are considered as U = 36 kV (ref. to EN 50708-2-1:2020);
m m
— with U = 25 kV are considered as U = 24 kV (ref. to EN 50708-2-1:2020).
m m
3.2
large power transformer
LPT
power transformer with at least one winding having either a rated power greater than 3 150 kVA or highest
voltage for equipment greater than 36 kV
Note 1 to entry: The definitions of power transformer and winding is given in EN 60076-1.
Note 2 to entry: The national practice of Czech Republic requires the use of the highest voltages for equipment in AC three-
phase systems of 38,5 kV instead of 36 kV and 25 kV instead of 24 kV. These units have a rated power greater than 3 150
kVA:
— with U = 38,5 kV are considered as U = 36 kV (ref. to EN 50708-3-1:2020);
m m
— with U = 25 kV are considered as U = 24 kV (ref. to EN 50708-3-1:2020).
m m
3.3
medium power pole-mounted transformer
power transformer with a rated power of up to 400 kVA suitable for outdoor service and specifically designed to
be mounted on the support structures of overhead power lines
Note 1 to entry: The definitions of power transformer and winding are given in EN 60076-1.
Note 2 to entry: For definitions of pole see IEV [466–07–01].
3.4
load factor
k
ratio of actual input current over the rated current of transformer
Note 1 to entry: Normally the ratio is 0 ≤ k ≤ 1.
3.5
transmitted apparent power
kSr
product of the load factor and rated power
3.6
Efficiency Index
EI
ratio of the transmitted apparent power of a transformer minus electrical losses to the transmitted apparent
power of the transformer
3.7
Peak Efficiency Index
PEI
maximum value of the ratio of the transmitted apparent power of a transformer minus the electrical losses to the
transmitted apparent power of the transformer
Note 1 to entry: PEI is the maximum value of EI that can be achieved at the optimum value of load factor.
3.8
load factor of Peak Efficiency Index
k
PEI
load factor at which Peak Efficiency Index occurs
Note 1 to entry: Alternative cooling modes can require an iterative calculation of the kPEI. In any case, the kPEI is defined
at the point where the highest PEI occurs.
3.9
declared value
values given in the technical documentation and where applicable, the values used to calculate these values
Note 1 to entry: The values given are pursuant to point 2 of Directive 2009/125/EC, Annex IV.
3.9.1
declared value of loss
loss measured by the manufacturer and written in the test report part of technical documentation and on the
rating plate
Note 1 to entry: This definition applies both to no-load loss and to load loss.
Note 2 to entry: Declared values and guaranteed values according to EN 60076-1 are two different concepts. Guaranteed
values are related to contract, whereas declared values are related to compliance verifications with Commision Regulation
(EU) No 548/2014.
Note 3 to entry: This definition complies with item g) of point 2 of Directive 2009/125/EC, Annex IV.
3.9.2
declared value of no-load loss
P
no-load loss measured by the manufacturer and written in the test report part of technical documentation and
on the rating plate
Note 1 to entry: For definition of no-load loss, see EN 60076-1.
3.9.3
declared value of load loss
P
k
load loss measured by the manufacturer and written in the test report part of technical documentation and on
the rating plate
Note 1 to entry: For definition of load loss see EN 60076-1.
3.9.4
declared value of electrical power required by the cooling system for no load operation
P
c0
electrical power required by fan and liquid pump motors for no load operation as derived from the transformer
type test certificates
Note 1 to entry: The electrical power required by the cooling system for no load operation is not measured all the time
because this is a type test according to EN 60076-1.
3.9.5
declared value of additional electrical power required by the cooling system for the load factor of k
P (k)
ck
additional electrical power required (in addition to Pc0) by the cooling system for continuous operation at k times
the rated load ensuring the compliance with the temperature rise derived from the transformer type test
measurements of the power taken by the fan and liquid pump motors
Note 1 to entry: The electrical power required by the cooling system for k times the rated load operation is not measured
all the time, because this is a type test according to EN 60076-1. It can be extrapolated from the temperature rise test.
3.9.6
declared value of PEI
PEI calculated from the declared values of no-load loss, load loss and power required by the cooling system for
load operation at k according to the above definitions
PEI
3.10
dual voltage transformer
transformer with one or more windings with two voltages available in order to be able to operate and supply
rated power at either of two different voltage values
3.11
acceptance test
contractual test to prove to the customer that the item meets certain conditions of its specification
Note 1 to entry: The test may be witnessed by purchaser or/and third party.
Note 2 to entry: The common IEC acceptance tests do not require witnesses. Routine tests are performed on every
transformer; for this reason the factory acceptance test shall be agreed between purchaser and supplier at the order stage.
[SOURCE: IEV ref 151-16-23]
3.12
witnessed testing
active observance of the physical testing of the product under investigation by another party, to draw conclusions
on the validity of the test and the test results and which may include conclusions on the compliance of testing
and calculations methods used with applicable standards and legislation
3.13
instrument transformer
transformer intended to transmit an information signal to measuring instruments, meters and protective or
control devices or similar apparatus even if it supplies energy for the operation of connected equipment
Note 1 to entry: The difference between the definition in Commission Regulation 548/2014 and the CENELEC one is in
the use of the word ‘supply’ rather than ‘transmit an information signal’.
[SOURCE: EN 61869-1:2009, 3.1.1, modified]
3.14
transformer with low-voltage windings specifically designed for use with rectifiers to provide a DC
supply
transformer specifically designed and intended to supply power electronic or rectifier loads specified according
to EN 61378-1:2011
Note 1 to entry: This definition covers transformers designed for use with rectifiers to provide a DC supply in certain
applications.
Note 2 to entry: The term “Low-voltage winding” refers to the winding having the lowest rated voltage as per EN 60076-1,
whatever its voltage level.
Note 3 to entry: This definition does not include:
— transformers which are intended to provide AC from DC sources such as transformers for wind turbine and
photo voltaic applications;
— transformers designed for DC transmission and distribution applications.
Therefore, they are part of the scope of this document and are expected to comply with Commission Regulation (EU)
No. 548/2014.
3.15
transformer specifically designed for offshore applications and floating offshore applications
transformer to be installed on fixed or floating offshore platforms, offshore wind turbines or on board ships and
all kinds of vessels
3.16
transformer specially designed for emergency installations
transformer designed to only provide cover for a specific time limited situation when the normal power supply is
interrupted either due to an unplanned occurrence such as failure or a station refurbishment, but not to
permanently upgrade an existing substation
Note 1 to entry: Such transformer could have some specific features that make it suitable for emergency or temporary use
as opposed to normal use. Example of some specific features:
— multiple windings making it suitable for use at several locations;
— special low weight or dimensions for easy transport, or special capability to be disassembled into smaller units
for transport;
— increased overload capability achieved by the use of special material;
— permanent mounting on a transporter arrangement.
3.17
transformers and auto-transformers specifically designed for railway feeding systems
transformer as defined in EN 50329:2003
3.18
earthing or grounding transformers, this is, three-phase transformers intended to provide a neutral
point for system grounding purposes
three-phase transformer or reactor connected in a power system to provide a neutral connection for earthing
either directly or via an impedance
[SOURCE: EN 60076-6:2008, 3.1.10, modified]
3.19
traction transformer
transformer installed on board of rolling stock inserted in the traction and auxiliary circuits of rolling stock and in
the scope of EN 60310:2016
3.20
starting transformers, specifically designed for starting three-phase induction motors so as to
eliminate supply voltage dips
transformer that is de-energized during normal operation, and used for the purpose of starting a rotating machine
3.21
Medium Voltage (MV) to Medium Voltage (MV) interface transformers up to 5 MVA
transformer used in network voltage conversion program and placed at the junction between two voltage levels
of two MV networks and which needs to be able to cope with emergency overloads
Note 1 to entry: Such units may or maybe not part of a packaged compact substation including also MV Reclosers and
protection equipment.
4 Service condition
See EN 60076-1.
5 Ratings and general requirements
5.1 Rated power
The reference rated power for any losses evaluation is the continuous rated power as stated in EN 60076-1.
If additional cooling system such as fans or pumps are to provide additional power for a situation limited in time
when the normal power supply is interrupted due to either an unplanned occurrence (such as a power failure)
or a station refurbishment, but not to permanently upgrade an existing substation, then such overloading rating
cannot be claimed to be the rated power.
5.2 Rated frequency
The rated frequency is the normal undisturbed frequency of the network where the transformer is installed,
unless otherwise specified the rated frequency is 50 Hz.
5.3 Energy performance
5.3.1 Energy performance requirements
The energy performance of a transformer in accordance with this standard is defined as follows:
a) Maximum no-load and load losses at rated power for three-phase MPT;
b) The Peak Efficiency Index and the load at which it occurs for LPT.
For Peak efficiency calculation see Annex A.
In case of forced cooling system, the consumption of the cooling system shall be considered together with the
losses according to the relative part of this series of standards.
NOTE Minimum energy requirements are based on the rated tapping, but real energy losses in service are affected
also by other variables like, for example, voltage regulation and loading factors. See Annex D of this document and
EN 50708-3-1:2020.
5.3.2 Exclusion from energy performance requirements
The following transformers are excluded from energy performance requirements for transformers specifically
designed and used for the following applications:
(a) instrument transformers, specifically designed to transmit an information signal to measuring instruments,
meters and protective or control devices or similar apparatus;
(b) transformers specifically designed and intended to provide a DC power supply to electronic or rectifier
loads. This exemption does not include transformers that are intended to provide an AC supply from DC
sources such as transformers for wind turbine and photovoltaic applications or transformers designed for
DC transmission and distribution applications;
(c) transformers specifically designed to be directly connected to a furnace;
(d) transformers specifically designed to be installed on fixed or floating offshore platforms, offshore wind
turbines or on board ships and all kinds of vessels;
(e) transformers specifically designed to provide for a situation limited in time when the normal power supply
is interrupted due to either an unplanned occurrence (such as a power failure) or a station refurbishment,
but not to permanently upgrade an existing substation;
(f) transformers (with separate or auto-connected windings) connected to an AC or DC contact line, directly
or through a converter, used in fixed installations for railway applications;
(g) earthing or grounding transformers specifically designed to be connected in a power system to provide a
neutral connection for earthing either directly or via an impedance;
(h) traction transformers specifically designed to be mounted on rolling stock, connected to an AC or DC
contact line, directly or through a converter, for specific use in fixed installations for railway applications;
NOTE Traction transformers (with separate or auto-connected windings) connected to an AC or DC contact line,
directly or through a converter, specifically designed for fixed installations or on rolling stock for railway applications;
(i) starting transformers, specifically designed for starting three-phase induction motors so as to eliminate
supply voltage dips and that remain de-energised during normal operation;
(j) testing transformers, specifically designed to be used in a circuit to produce a specific voltage or current
for the purpose of testing electrical equipment;
(k) welding transformers, specifically designed for use in arc–welding equipment or resistance-welding
equipment;
(l) transformers specifically designed for explosion-proof applications in accordance with Directive 94/9/EC of
the European Parliament and of the Council and underground mining applications;
(m) transformers specifically designed for deep water (submerged) applications;
(n) medium Voltage (MV) to Medium Voltage (MV) interface transformers up to 5 MVA used as interface
transformers used in a network voltage conversion programme and placed at the junction between two
voltage levels of two medium voltage networks and that need to be able to cope with emergency overloads;
(o) medium and large power transformers specifically designed to contribute to the safety of nuclear
installations, as defined in Article 3 of Council Directive 2009/71/Euratom;
(p) three-phase medium power transformers with a power rating below 5 kVA.
5.3.3 Reference conditions
For the energy performance calculation, the following reference temperature shall be considered:
a) For transformers with rated average winding temperature rise less than or equal to 65 K for OF or ON, or
70 K for OD, the reference temperature is 75 °C;
b) For transformers with other rated average winding temperature rise or not immersed in class O liquid, the
reference temperature is equal to the rated average winding temperature rise + 20 K, or rated winding
temperature rise + yearly external cooling medium average temperature, whichever is higher.
5.3.4 Technical documentation
Each power transformers shall have a technical file (technical documentation). This technical documentation
can be a printed document as well as an electronic document.
NOTE This clause has been included in this document to be aligned with the EU regulation. Other data and information
could be required in accordance with agreements between the manufactured and purchaser.
The following minimum information shall be included in the technical documentation of power transformers:
(a) manufacturer's name and address;
(b) model identifier, the alphanumeric code to distinguish one model from other models of the same
manufacturer;
(c) information on rated power, load loss and no-load loss and the electrical power of any cooling system
required at no load;
(d) for large power transformers, the value of the Peak Efficiency Index and the power at which it occurs;
(e) for dual voltage transformers, the maximum rated power at the lower voltage, according to
EN 50708-2-1:2020, Table 3 and Table 4;
(f) information on the weight of all the main components of a power transformer (including at least the
conductor, the nature of the conductor and the core material);
(g) For medium power pole mounted transformers, the disclaimer ‘For pole-mounted operation only’;
(h) the specific reason(s) why transformers are considered to be exempted from the EU Regulation on power
transformers in accordance with 5.3.2;
(e) rating plate data in accordance with Clause 6.
If (parts of) the technical documentation is based upon (parts of) the technical documentation of another model,
the model identifier of that model shall be provided and the technical documentation shall provide the details of
how the information is derived from the technical documentation of the other model, e.g. on calculations or
extrapolations, including the tests undertaken by the manufacturer to verify the calculations or extrapolations
undertaken.
6 Rating plate
In addition to EN 60076-1:2011 or EN IEC 60076-11:2018 requirements, the following values shall be included
in all cases on the rating plate:
For transformers with dual voltage, all values shown on the rating plate and in the technical documentation shall
refer to the highest rated voltage(s):
— P ;
— If not zero, P + P (k ), the electrical power required by the cooling system to operate at k ;
c0 ck PEI PEI
— P ;
k
— Conductor material and total mass of each material (for instance copper, aluminium, copper and
aluminium);
— Mass and material of the magnetic circuit;
— the PEI in % and k , the load factor at which PEI occurs for transformers when applicable;
PEI
— For dual voltage transformers, the rated power at the lower voltage.
For medium power pole mounted transformers, a visible display “For pole-mounted operation only”.
7 Tolerances
7.1 Tolerance during factory acceptance tests
During factory acceptance tests, the measured values of no load and load losses shall not exceed the respective
maximum values specified in EN 50708-2-1:2020 without tolerances, and the Peak Efficiency Index values
obtained from the measured values of no load and load losses shall not be below the respective minimum
values specified in EN 50708-3-1:2020 without tolerances.
For other test tolerances see EN 60076 series of standards.
7.2 Tolerances for Market surveillance
During market surveillance measurements, the individual measured values of loss can be up to 5 % higher than
the declared or calculated ones, in the case of PEI values.
During market surveillance measurements, the measured values of electrical power required by the cooling
system can be up to 5 % higher than the declared value of electrical power required by the cooling system.
8 Tests
8.1 General
List and procedures of additional tests are defined in relevant parts 2 or 3 of this series. Measurement methods
shall be in accordance with EN 60076-1:2011 or EN IEC 60076-11:2018.
8.2 Measurement of cooling consumption
The active electrical power required by the cooling system is allowed to be obtained from transformer type test
results.
If the active electrical power required by the cooling system shall be known for the energy performance and it
is not known from existing type test reports, a type test on the electrical power required by the cooling system
is to be done as described in this clause.
The active electrical power required by the cooling system (P and P (k )) shall be measured during a
c0 ck PEI
type test at rated frequency with rated voltage applied to the terminals of the cooling system feeder (for ONAN
cooling system P is always 0).
ck
The supplied voltage shall be within ± 3 % of the rated value and the frequency ± 1 % of the rated frequency.
The fans and pumps used for this test shall be identical (type and reference) and installed in the same position
as on the transformer in service.
The number of pumps and fans in service during this test shall be those needed at k and if the cooling mode
PEI
is not available at exactly k next higher number shall be used.
PEI
Before measurement of the cooling electrical power consumption, the fans and pumps shall have run
permanently for a time allowing them to be at a stable working temperature, by default this is considered as
achieved at the end of the total loss supply phase of the temperature rise test before the shut-down.
If the transformer is not subject to temperature rise test the cooling consumption, including pumps can be
measured at room temperature.
9 Accessories and fittings
List of accessories and fittings are under development in relevant parts.
10 Capitalization of losses
Capitalization of losses is considered to be the most economically correct method to optimize transformer design
in accordance with the purchaser needs. The method is described in Annex B.
It is recognized that to get the benefits of standardization of transformer design, the capitalization of losses is
normally considered over the fleet of transformers rather than for individual units.
If the efficiency of a transformer purchased using a loss capitalization formula exceeds the benchmark peak
efficiency proposed for that transformer, it should be used, as the benchmark simply sets a lower floor for
transformer efficiency – it does not attempt to set an optimal value.
11 Transformer overhaul
In case of overhaul, medium and large power transformers, regardless of when they were first placed on the
market or put into service, shall be reassessed for conformity, if they are subject to all of the following operations:
a) replacement of the core or part thereof;
b) replacement of one or more of the complete windings.
However, for all transformer overhaul to extend or maintain the life expectancy, consideration should be given
to the alternative option of replacing the transformer with a lower loss unit, in the context of Life cycle investment
appraisal. See Annex E for examples of different transformer overhaul activities.
Annex A
(normative)
Peak efficiency calculation
A.1 Efficiency Index
The Efficiency Index at load factor k is calculated in accordance with Formula (1):
kS - (P +−P )(k²P + P (k))
r 0 c0 k ck
EI k = (pu) (A.1)
( )
kS
r
Where:
S is the rated power of the transformer or autotransformer on which P is based;
r k
and for the other symbols see Clause 3.
NOTE 1 This approach respects the philosophy of EN 60076 (all parts), which refers the rated power to the rated voltage
and current of one of the transformer windings.
NOTE 2 The Efficiency Index includes the losses associated with the mode of the cooling system at the considered load
factor.
A.2 Peak Efficiency Index
The Peak Efficiency Index is the maximum value of the Efficiency Index obtained from Formula (A.1) by
replacing k with kPEI as defined in Formula (A.3).
The formula to be used for Peak Efficiency Index calculation is:
2(P +P +P (k ))
0 c0 ck PEI
PEI = 1 - =1- P +P +P (k ) P (%) (A.2)
( )
0 c0 ck PEI k
S
P +P +P (k )
r
0 c0 ck PEI
S
r
P
k
Where:
S is the rated power of the transformer or autotransformer on which P is based;
r k
and for the other symbols see Clause 3.
P +P +P (k )
0 c0 ck PEI
(A.3)
k = (pu)
PEI
P
k
The Peak Efficiency Index does not impose a particular load factor (which may vary greatly depending on the
application) and does not depend explicitly on the rated power of the transformer. Peak efficiency is an intrinsic
parameter of the transformer that does not depend on whether the transformer has alternative ratings depending
on cooling modes.
The Peak Efficiency Index includes the losses associated with the mode of the cooling system stated on the
rating plate at the load factor where PEI occurs. Any further additional cooling and associated cooling loss
necessary to achieve rated power is excluded.
The derivation of P at k involves establishing the total power consumption of the fans and the pumps (see
ck PEI
Clause 8.1) and then ascribing a proportion of this total cooling loss based on the cooling mode stated on the
rating plate. The proportion used is the ratio of the average electrical loss of the fans and pumps used at k
PEI
and average yearly ambient temperature (20 °C unless otherwise specified) to the total electrical loss of the
pumps and fans installed.
If fans and pumps have variable speed drives, an additional type test measurement may be required to
determine P at k .
ck PEI
NOTE 1 This applies to transformers equipped with heat-exchangers which need pumps and fans to provide heat
dissipation (e.g. ODAF, ODWF, OFWF, OFAF, OFAN).
If different values of apparent power are assigned under different circumstances, for example, with different
methods of cooling (ONAN/ONAF, AN/AF, etc…), all values shall be reported on the rating plate and the highest
of these values is the rated power. This applies also in case a provision for a future value of apparent power is
made (for example future ONAF, future AF
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.