SIST EN 60076-19:2015

SLOVENSKI STANDARD
01-oktober-2015
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Power transformers - Part 19: Rules for the determination of uncertainties in the
measurement of the losses on power transformers and reactors
Leistungstransformatoren - Teil 19: Regeln für die Bestimmung von Unsicherheiten in
der Messung der Verluste von Leistungstransformatoren und Drosselspulen
Transformateurs de puissance - Partie 19: Règles pour la détermination des incertitudes
de mesure des pertes des transformateurs de puissance et bobines d’inductance
Ta slovenski standard je istoveten z: EN 60076-19:2015
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 60076-19

NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2015
ICS 29.180
English Version
Power transformers - Part 19: Rules for the determination of
uncertainties in the measurement of the losses on power
transformers and reactors
(IEC/TS 60076-19:2013 , modified)
Transformateurs de puissance - Partie 19: Règles pour la Leistungstransformatoren - Teil 19: Regeln für die
détermination des incertitudes de mesure des pertes des Bestimmung von Unsicherheiten in der Messung der
transformateurs de puissance et bobines d'inductance Verluste von Leistungstransformatoren und Drosselspulen
(IEC/TS 60076-19:2013 , modifiée) (IEC/TS 60076-19:2013 , modifiziert)
This European Standard was approved by CENELEC on 2015-06-25. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, 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: Avenue Marnix 17, B-1000 Brussels
© 2015 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60076-19:2015 E
Foreword
This document (EN 60076-19:2015) consists of the text of IEC/TS 60079:2013 prepared by
IEC/TC 14 "Power transformers", together with the common modifications prepared by
CLC/TC 14 "Power transformers".

The following dates are fixed:

(dop) 2016-06-25
• latest date by which this document has to be
implemented
at national level by publication of an identical
national standard or by endorsement
(dow) 2018-06-25
• latest date by which the national standards
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 [and/or CEN] 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.

Endorsement notice
The text of the International Standard IEC/TS 60079:2013 was approved by CENELEC as a
European Standard with agreed common modifications.
COMMON MODIFICATIONS
Introduction
Modify the first paragraph as follows:
The losses of the transformers (no- load and load losses) are object of guarantee and penalty
in the majority of the contracts and play an important role in the evaluation of the total
(service) costs and therefore in the investments involved. Furthermore, regional regulations,
such as the European Union directive for EcoDesign, may also pose requirements on
establishment of reliable values for losses.
Modify the third and fourth paragraphs as follows:
Corrections and uncertainties are also considered in IEC 60076-8 where some general
indications are given for their determination.
This European Standard deals with the measurement of the losses that from a measuring
point of view consist of the estimate of a measurand and the evaluation of the uncertainty that
affects the measurand itself. The procedures can also be applied to loss measurements on
power transformers and reactors as evaluation of the achievable performance of a test facility
in the course of prequalification processes, as estimations of achievable uncertainty in the
enquiry stage of an order or prior to beginning final testing at manufacturer´s premises and for
evaluations of market surveillance measurements.
Add before the fifth paragraph:
Evaluation of uncertainty in testing is often characterized as “top-down” or “bottom-up”, where
the first one relies on inter-laboratory comparisons on a circulated test object to estimate the
dispersion and hence the uncertainty. The latter method instead relies on the formulation of a
model function, where the test result y is expressed as a function of input quantities. This
function is often the formula used for the calculation of the result. The “bottom-up” method is
applied in this Document.
Replace the sixth paragraph by:
It is recommended that guarantee and penalty calculations should refer to the best estimated
values of the losses without considering the measurement uncertainties, based on a shared
risk concept, where both parties are aware of and accept the consequences of non-negligible
measurement uncertainty.
In cases where the losses are required to conform to stated tolerance limits, it is
recommended that the estimated uncertainty is less than the tolerance limit. This situation will
occur for example in market surveillance activities. In lieu of other specifications it can be
noted that 3 % is often used as estimate for the required uncertainty.
Modify the eighth paragraph as follows:
Standards mentioned in the text but not indispensable are listed at the end of the document.
Replace the last paragraph by:
This European document is based on IEC/TS 60076-19. The technical content of the TS was
not changed, but small numerical mistakes and consistent use of symbols in Annex A were
corrected. The introduction was modified to enhance clarity.
1 Scope
Modify the first paragraph as follows:
This European Standard illustrates the procedures that should be applied to evaluate the
uncertainty affecting the measurements of no-load and load losses during the routine tests on
power transformers.
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.
EN 60076-1:2011, Power transformers – Part 1: General (IEC 60076-1:2011)
EN 60076-2:2011, Power transformers – Part 2: Temperature rise for liquid-immersed
transformers (IEC 60076-2:2011)

Annex A
(informative)
Example of load loss uncertainty evaluation
for a large power transformer
A.4 Model function of the measurand and deviation correction (see 7.2)
A.4.2 Correction of known systematic deviations
Modify the paragraph after the first equation as follows:
The remaining corrective term is given by the following equation: (erroneous K replaced by
C
F )
D
Replace the second and the third equations by the following ones:
F =
∆
1−(∆ −∆ )⋅ tanϕ
ϕV ϕC
P = k ⋅ k ⋅ P ⋅ F
2 CN VN W ∆
A.5 Results of the measurements
A.5.1 Load loss measurements
Modify the paragraph after Table A.2 as follows:
The estimate of the phase angle between voltage and current results (see 7.2 and A.6.1):
Replace the first equation by:
 
P 6,625 0,09 0,11 180
 
W
ϕarccos −∆+∆ arccos − + 88⋅ ,782−0,11588,670°
 
ϕϕVC   
IU 3,608×86,60 100 100 π
  
 MM
Modify the paragraph after the first equation as follows:
The corresponding tanϕ is therefore equal to 43,087.
Replace the second equation by:
F 1,0943
∆
1− (0,09 /100+⋅0,11/100) 43,087
1− ∆ +∆ ⋅ tanϕ
( )
ϕϕVC
= ==
= = = =
Replace the third equation by:
P= k⋅ k⋅⋅PF= 60⋅200⋅6,625⋅1,0943=86 997 W
2 CN VN W D
Add after the third equation:
NOTE This result differs slightly from the result obtained with the full formula given in clause A.4.1 because of
the simplifications introduced in A.4.2.
A.6 Estimates of the single contributions to the uncertainty budget
A.6.3 Instrument transformer phase displacement uncertainties (see 10.3)
Replace the first, second and third equations by the following ones:
0,02
u = = 0,011 5 crad
∆ϕC
0,010
u 0,005 8 crad
∆ϕV
Add after the second equation:
and
22 2 2
u uu+= 0,0115+ 0,005 8 0,012 9
∆ϕ ∆∆ϕϕVC
NOTE In some cases, in the calibration certificates the uncertainty is directly indicated with a given confidence
level and therefore the standard uncertainties can be directly obtained from these data.
A.6.4 Power analyzer uncertainties (see 10.5)
Modify the first paragraph as follows:
According to the manual for the instrument used, the accuracy on power measurement is
obtained by the combination of a number of terms:
Modify the third paragraph after the first equation as follows:
The accuracy determined in accordance with the above relation resulted in ±0,91 %.
Modify the paragraph before the last equation as follows:
According to the manual for the instrument used, the accuracy for voltage measurement is
±0,18 %, which corresponds to the following standard uncertainty:

A.6.5 Corrective term uncertainty (see 10.3.2)
Modify the first paragraph as follows:
The uncertainty u related to the phase displacement correction can be evaluated with the
F∆
following simplified relations:
Replace the first and the second equations by the following ones:
u ≈ u ⋅ tanϕ
F∆ ∆ϕ
= =
==
u 0,012 9⋅=tanϕ 0,012 9⋅43,087 0,56 %
F∆
A.6.6 Uncertainty of the resistance at temperature θ (see 10.8)
Modify the first paragraph as follows:
The standard uncertainty due to the measuring instruments is assumed equal to 0,35 % and
that attributable to the winding temperature estimate equal to 2 K, with the latter deemed to
be negligible.
A.7 Uncertainty of the load loss measured at ambient temperature (see 7.4)
Modify the first paragraph and Table A.4, fifth row, last cell, as follows:
The uncertainties that affect the load loss at ambient temperature can be estimated using the
results of the previous elaborations and are summarized in Table A.4.
Table A.4 – Uncertainty contributions
Quantity Estimate Standard uncertainty Sensitivity Uncertainty
coefficient contribution
(%)
CT ratio error η u 1 -
C C
VT ratio error  1 -
η u
V V
Power meter 1 0,53
u
P
P
W
Phase displacement 1 0,56
u
F∆
1−(∆ϕv−∆ϕc)tanϕ
Ampere meter I u 2 0,24
M IM
Replace the equation by:
22 2 2 2 2
u= uu+ + u= 0,53+ 0,56+ 0, 24= 0,81 %
P2 P F∆ IM
A.8 Expanded uncertainty of the measured load loss (see 7.4)
Replace the first and second equations by the following ones:
Uu2 2 ⋅ 0,81 1,61 %
PP22
U 1,61
P2

UP 86,997 1,4 kW
P22
100 100
Modify the second paragraph after Equation 2 as follows:
= ==
= ==
= =
If the uncertainty is given in relative value, the load loss at ambient temperature 24,2 °C is to
be expressed as follows:
Replace the third and the fourth equations by the following ones:
87,0 kW±1,6 %
87,0 kW± 1,4 kW
Modify the last paragraph as follows:
The result shall be also completed with the indication of the coverage factor, which for the
example made was k = 2 (confidence level of about 95 %).
A.9 Uncertainty for reported load loss at reference temperature (see 7.5)
Replace the text under A.9 as follows:

The additional loss at ambient temperature is given by:
P= P−⋅I R= 86 997− 69 500=17 497 W
aN22 2
The absolute uncertainty of the measured loss and I R loss are obtained as follows:
N
u 0,80 u 0,35
P2 R2 2
 
uP 86 997 696 W and u IR 69 500 243 W
P22 R22N
100 100 100 100
The absolute uncertainty of the additional loss at temperature θ is given by (see Table 3):
2 2 2 2 2
 
u = u + (I R ⋅ u ) = 696 + 243 = 737 W
Pa2 P2 N 2 R2
The reported load loss at reference temperature is calculated for copper conductors with
t=235, reference temperature θ = 75 °C and ambient temperature θ = 24,2 °C is given by:
r 2
t+θ t+θ
t+θ
r 2 2 2
r
=1,196 = 0,836 I R ≅ 0,004 6 I R
N 2 N 2
t+θ t+θ (t+θ )
2 r 2
The reported loss at the reference temperature is thus given by:
P=1,196 IR+ 0,836 P= 83 122+14 627= 97 749 W
LL N 22a
The various contributions to the absolute uncertainty are calculated according to Table 4:
=== = ==
t+θ
2 r
For I R loss: I R u 1,196 ⋅ 69 500 ⋅=0,35 /100 291 W
N 2
NR22
t+θ
t+θ

For additional loss: u 0,836 ⋅ 737 616 W
Pa2
t+θ
r
t+θ
r 2
For mean winding temperature:
I R u = 0,004 6 x⋅ 69 500= 320 W
N r θ 2
(t+θ )
The combined absolute standard uncertainty is given by:
2 2 2 2 2 2 22

u (1,196 I Ru )+ (0,836 u )+ (0,004 6 I Ru ) 291+ 616+ 320 753 W
LL N 2 R2 Pa2 N 2 θ 2
The expanded absolute uncertainty is obtained as:

Uu2  2 ⋅ 0,753 1,51 kW
LL LL
which corresponds to a coverage probability of approximately 95 %.
The relative standard uncertainty is then:

u 753
LL
u 100 100 0,77 %
LL
P 97 749
LL
and the expanded relative uncertainty:
Uu=2 =2×≈0,77 1,5 %
LL LL
which corresponds to a level of confidence of approximately 95 %.
A.10 Presentation of the results
Modify the second and fourth paragraphs and replace the first and second equations as
follows:
If the uncertainty is given in relative value, the load loss at reference temperature 75 °C is
expressed as follows:
97,7 kW±1,5 %
97,7 kW±1,5 kW
The text shall be also completed with the indication of the coverage factor that for the
example made was k = 2 (coverage factor of about 95 %).
= ==
= ==
= = =
==
=
NOTE The probability that the loss is higher than (97,7+1,5) kW is therefore 2,5 %.
Annex B
(Informative)
Example of load loss uncertainty evaluation
for a distribution transformer
B.4 Model function of the measurand (see 7.2)
Modify the first paragraph as follows:
The model function for load loss referred to rated current and ambient temperature is the
following (considering that no voltage transformer is used):
Replace the first, second, third and the fourth equations by the following ones:
 
ε P I
 
C W N
P = k 1+ ⋅ ⋅
 
CN  
100 1+∆ tanϕ k × I
 
ϕC CN M
 
 
P
W
 
ϕ=ϕ +∆ = arccos +∆
M ϕC ϕC
 
I U
 M M
1+∆ tanϕ
ϕC
 
P I
W N
P = k ⋅ ⋅
2 CN  
1+∆ tanϕ k × I
ϕC  CN M
B.5 Results of the measurements
Replace the first, second and the third equations as follows:
 
 
P 337,5 0,035 180
W
 
 
ϕ= arccos +∆ = arccos + ⋅ = 83,63+ 0,02= 83,65 °
ϕC
 
 
I ⋅U 100 π
4,812⋅ 3⋅ 365,0
 M M
 
1 1
F = = = 0,997
∆
0,035
1+∆ tanϕ
ϕC
1+ ⋅ 8,99
P = k ⋅ P ⋅ F = 40 ⋅ 337,5 ⋅ 0,997=13 460 W
2 CN W ∆
B.6 Estimate of the single contributions to the uncertainty formation
Modify the title of B.6.2 as follows:
B.6.2 Power meter (see 10.5)
Replace the first, second and the third equations by the following ones:
0,57
u = = 0,33 %
PW
0,42
u = = 0,24 %
IM
0,25
u = = 0,14 %
UM
B.6.3 Current transformers (see 10.3)
Modify the second paragraph and Table B.3, second row, last cell, as follows:
For the type of transformer under test the values of the ratio error and displacement error
given by the calibration certificate can be considered, as indicated in Table B.3. Uncertainty
statements have been given as standard uncertainty in the table.
Table B.1 – Calibration of the current transformers
Ratio error Phase displacement
(%) (centiradians)
Rated ratio Accuracy class
u
ε u Value
c ∆ϕ
c
200/5 0,1 0,0 0,01 0,01
+ 0,035
NOTE The errors reported in the table are those measured including burden and connections corresponding to
the instrument used.
B.6.4 Corrective term uncertainty (see 10.3.2)
Replace the equation by:
u
∆
ϕC
u ≈ ⋅ tanϕ⋅100= 0,01 ⋅ 8,99= 0,09 %
F∆
B.7 Uncertainty of the load loss measured at ambient temperature (see 7.4)
Modify Table B.4, third row as follows:

Table B.2 – Uncertainty contribution
Quantity Estimate Standard uncertainty Sensitivity Uncertainty
coefficient contribution
Power meter P u 1 0,33 %
W P
Phase displacement u 1 0,09 %
F∆
1+∆ tanϕ
ϕC
Ampere meter I u 2 0,48 %
M IM
Modify the second paragraph and replace the equation as follows:
The combined uncertainty of load loss P measured at ambient temperature is given by:
LL
2 2 2 2 2 2
u = u + u + u = 0,33 + 0,09 + 0,48 = 0,59 %
LL P F∆ I
B.8 Expanded uncertainty of the load loss (see 7.4)
Replace the first and second equations by the following ones:
U = 2 u = 2 ⋅ 0,59=1,18 %
LL LL
U 1,18
LL

U = P = 13,5= 0,16 kW
LL LL
100 100
Modify the last paragraph as follows:
The result shall be also completed with the indication of the coverage factor that for the
example made was k = 2 (coverage factor of about 95 %).
Bibliography
Replace the bibliography by:
EN 61869-1, Instrument transformers – Part 1: General requirements (IEC 61869-1)
EN 61869-2, Instrument transformers – Part 2: Additional requirements for current
transformers (IEC 61869-2)
EN 61869-3, Instrument transformers – Part 3: Additional requirements for inductive voltage
transformers (IEC 61869-3)
EN ISO/IEC 17025:2005, General requirements for the competence of testing and calibration
laboratories (ISO/IEC 17025:2005)
CLC/TR 50462:2008, Rules for the determination of uncertainties in the measurement of the
losses on power transformers and reactors
IEC/TS 60076-19 ®
Edition 1.0 2013-03
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
Power transformers –
Part 19: Rules for the determination of uncertainties in the measurement of the

losses on power transformers and reactors

Transformateurs de puissance –

Partie 19: Règles pour la détermination des incertitudes de mesure des pertes

des transformateurs de puissance et bobines d’inductance

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 29.180 ISBN 978-2-83220-693-5

– 2 – TS 60076-19 © IEC:2013
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Symbols . 8
4.1 General symbols . 8
4.2 Symbols for uncertainty . 9
5 Power measurement, systematic deviation and uncertainty . 10
5.1 General . 10
5.2 Model function . 10
5.3 Measuring systems . 10
6 Procedures for no-load loss measurement . 11
6.1 General . 11
6.2 Model function for no-load losses at reference conditions . 11
6.3 Uncertainty budget for no-load loss . 12
7 Procedures for load loss measurement . 13
7.1 General . 13
7.2 Model function for load loss measurement at rated current . 13
7.3 Reporting to rated current and reference temperature . 14
7.4 Uncertainty budget for the measured power P reported to rated current . 14
7.4.1 General . 14
7.4.2 Uncertainties of measured load loss power P at ambient temperature
θ . 14
7.5 Uncertainty budget for reported load loss at reference temperature . 15
8 Three-phase calculations . 16
8.1 Power measurement . 16
8.2 Reference voltage . 17
8.3 Reference current. 17
9 Reporting . 17
9.1 Uncertainty declaration . 17
9.2 Traceability . 17
10 Estimate of corrections and uncertainty contributions . 18
10.1 Instrument transformers . 18
10.2 Uncertainty contributions of ratio error of instrument transformers . 18
10.3 Uncertainty contribution of phase displacement of instrument transformers . 19
10.3.1 General . 19
10.3.2 Complete reference procedure . 19
10.3.3 Class index procedure . 20
10.4 Voltage and current measurements . 21
10.5 Power meter . 21
10.6 Correction to sinusoidal waveform . 22
10.7 Winding temperature at load loss measurement . 23
10.8 Winding resistance measurement . 23
Annex A (informative) Example of load loss uncertainty evaluation for a large power
transformer . 25

TS 60076-19 © IEC:2013 – 3 –
Annex B (Informative) Example of load loss uncertainty evaluation for a distribution
transformer . 33
Bibliography . 37

Table 1 – Measured no-load loss uncertainties . 12
Table 2 – Measured load loss uncertainties at ambient temperature . 15
Table 3 – Absolute uncertainty of the additional losses at temperature θ . 15
Table 4 – Absolute uncertainty of load losses P reported at reference temperature . 16
LL
Table 5 – Procedures for the determination of phase displacement uncertainties . 19
Table A.1 – Transformer ratings . 25
Table A.2 – Loss measurement results (one phase) . 27
Table A.3 – Calibration of voltage and current transformers . 27
Table A.4 – Uncertainty contributions. 29
Table B.1 – Transformer ratings . 33
Table B.2 – Measured quantities . 34
Table B.3 – Calibration of the current transformers . 35
Table B.4 – Uncertainty contribution . 36

– 4 – TS 60076-19 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 19: Rules for the determination of uncertainties in the
measurement of the losses on power transformers and reactors

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-
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements 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.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC 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
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees 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 Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 60076-19, which is a technical specification, has been prepared by IEC technical
committee 14: Power transformers.
The text of this technical specification is based on the following documents:

TS 60076-19 © IEC:2013 – 5 –
Enquiry draft Report on voting
14/726/DTS 14/736A/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60076 series, published under the general title Power
transformers, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International Standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – TS 60076-19 © IEC:2013
INTRODUCTION
The losses of the transformers (no- load and load losses) are object of guaranty and penalty
in the majority of the contracts and play an important role in the evaluation of the total
(service) costs and therefore in the investments involved.
According to ISO/IEC 17025 the result of any measurement should be qualified with the
evaluation of its uncertainty. A further requirement is that known corrections shall have been
applied before evaluation of uncertainty.
Corrections and uncertainties are also considered in IEC 60076-8 were some general
indications are given for their determination.
This Technical Specification deals with the measurement of the losses that from a measuring
point of view consist of the estimate of a measurand and the evaluation of the uncertainty that
affects the measurand itself.
The uncertainty range depends on the quality of the test installation and measuring system,
on the skill of the staff and on the intrinsic measurement difficulties presented by the tested
objects.
The submitted test results are to be considered the most correct estimate and therefore this
value has to be accepted as it stands.
In the annexes to this document, two examples of uncertainty calculations are reported for
load loss measurements on large power and distribution transformers.
Standards, technical reports and guides mentioned in the text are listed at the end of the
document.
It is stated that guaranty and penalty calculations should refer to the best estimated values of
the losses without considering the measurement uncertainties.

TS 60076-19 © IEC:2013 – 7 –
POWER TRANSFORMERS –
Part 19: Rules for the determination of uncertainties in the
measurement of the losses on power transformers and reactors

1 Scope
This part of IEC 60076, which is a Technical Specification, illustrates the procedures that
should be applied to evaluate the uncertainty affecting the measurements of no-load and load
losses during the routine tests on power transformers.
Even if the attention is especially paid to the transformers, when applicable the specification
can be also used for the measurements of reactor losses, except large reactors with very low
power factor.
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.
IEC 60076-1:2011, Power transformers – Part 1: General
IEC 60076-2:2011, Power transformers – Part 2: Temperature rise for liquid-immersed
transformers
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60076-1 and
60076-2, as well as the following apply.
NOTE The following terms and definitions were taken from ISO/IEC Guide 98-3:2008.
3.1
uncertainty (of measurement)
parameter, associated with the result of a measurement, that characterizes the dispersion of
the values that could reasonably be attributed to the measurand
[SOURCE: ISO/IEC Guide 98-3:2008, 2.2.3]
3.2
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.1]
3.3
type A evaluation (of uncertainty)
method of evaluation of uncertainty by the statistical analysis of series of observations
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.2]

– 8 – TS 60076-19 © IEC:2013
3.4
type B evaluation (of uncertainty)
method of evaluation of uncertainty by means other than the statistical analysis of series of
observations
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.3]
3.5
combined standard uncertainty
standard uncertainty of the result of measurement when that result is obtained from the
values of a number of other quantities, equal to the positive square root of a sum of terms, the
terms being the variances or covariances of these other quantities weighted according to how
the measurement result varies with changes in these quantities
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.4]
3.6
expanded uncertainty
quantity defining an interval about the result of a measurement that may be expected to
encompass a large fraction of the distribution of values that could reasonably be attributed to
the measurand
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.5]
3.7
coverage factor
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain
an expanded uncertainty
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.6]
4 Symbols
4.1 General symbols
Parameter related to correction of power for phase displacement in measuring circuit

F
D
Current measured by the ammeter (preferably rated current)

I
M
Reference current (normally corresponding to rated current)

I
N
Rated transformation ratio of the current transformer

k
CN
Rated transformation ratio of the voltage transformer

k
VN
Power
P
Power measured at the load loss measurement corrected for known systematic deviations and referred

P
to the current I
N
Load loss at reference conditions

P
LL
No-load loss at reference conditions and corrected for known errors in the measurement
P
NLL
n Exponent related to the non-linear behaviour of no-load loss
Power measured by the power meter

P
W
Additional losses at reference temperature

P
ar
Additional losses at temperature
θ
P
a2
TS 60076-19 © IEC:2013 – 9 –
R
Equivalent resistance of the windings at temperature θ according to IEC 60076-1
Equivalent resistance of the windings at temperature
R θ
2 2
Equivalent resistance of the windings at reference temperature

R
r
t Parameter related to the thermal coefficient of winding resistance
Voltage measured with an instrument having average rectified mean response

U
avg
Voltage measured
U
M
Rated voltage
U
N
Voltage measured using an instrument with true r.m.s. response

U
rms
Temperature (expressed in degrees Celsius)
θ
Temperature of transformer winding at cold winding resistance test according to IEC 60076-1

θ
Temperature of transformer windings during load loss test (expressed in Celsius degrees)

θ
Reference temperature for transformer windings according to IEC 60076-1

θ
r
Actual phase displacement of the current transformer (rad)
Δ
ϕC
Actual phase displacement of the power meter (rad)

Δ
ϕP
Actual phase displacement of the voltage transformer (rad)
Δ
ϕV
Actual ratio error of the current transformer (%)

ε
C
Actual ratio error of the voltage transformer (%)

ε
V
ϕ
Actual phase angle between voltage and current (rad)
Phase angle between voltage and current measured with power meter (rad)

ϕ
M
4.2 Symbols for uncertainty
c Sensitivity factor for contribution to uncertainty
u
Standard uncertainty
 Absolute standard uncertainty
u
Expanded uncertainty
U

Absolute expanded uncertainty
U
Uncertainty of current transformer ratio (expressed in percent of the ratio)

u
C
Uncertainty of current measurement
u
IM
Uncertainty of the load loss at reference temperature

u
LL
Uncertainty of the no-load loss

u
NLL
Uncertainty of
u P
P2
Uncertainty of term
u F
FD
D
Uncertainty of the power indicated by the analyzer

u
PW
u Uncertainty of the equivalent resistance
R
R1
Uncertainty of the equivalent resistance
u R
R2
Uncertainty of voltage measurement

u
UM
– 10 – TS 60076-19 © IEC:2013
Uncertainty of voltage transformer ratio

u
V
Uncertainty of correction to sinusoidal waveform for no-load-loss

u
WF
Uncertainty of phase displacement for complete measuring system
u
Δϕ
Uncertainty of current transformer phase displacement
u
ΔϕC
Uncertainty of voltage transformer phase displacement
u
ΔϕV
5 Power measurement, systematic deviation and uncertainty
5.1 General
In the following, it is assumed that the transformer losses are measured in the conditions
prescribed by IEC 60076-1 by means of digital instruments.
For three-phase transformers, losses are intended to be measured using three independent
single-phase measuring systems. These systems may be made by separate instruments or a
combined in a three-phase instrument.
In general, losses are measured using current and voltage transformers in conjunction with a
power meter (power analyser).
The measuring system usually has a known systematic deviation (error) that can be corrected
for, or not, and the two cases ask for different approach in the uncertainty analysis.
Systematic deviations related to measuring equipment can be characterised by calibration.
If not negligible, systematic deviations introduced by the measuring system should be
corrected before the uncertainty estimate.
5.2 Model function
The uncertainty estimation includes uncertainties in the measuring system as well as in the
tested object (transformer or reactor).
Thus the model functions presented below includes both the measuring system and the test
object in one equation.
5.3 Measuring systems
Measuring systems can be characterized either by a stated overall uncertainty, or by
specifications of its components.
For systems characterized by an overall uncertainty, simplifications in the uncertainty analysis
are possible, but in this document this has not been utilized since calibration on the system
level are not generally available.
As a consequence, all type of measuring systems should be specified also on the component
level.
TS 60076-19 © IEC:2013 – 11 –
6 Procedures for no-load loss measurement
6.1 General
The test procedure is given in IEC 60076-1.
The no-load loss measurement shall be referred to rated voltage and frequency and to voltage
with sinusoidal wave shape.
The current drawn by the test object is non-sinusoidal, and this may cause a distortion in the
voltage that leads to erroneous values for the losses. A correction for the transformer losses
is prescribed in IEC 60076-1, as well as a limit for the permissible distortion.
6.2 Model function fo
...