>>
4 Symbols and abbreviations
5 Effect of loading beyond nameplate rating
5.1 General
5.2 General consequences
5.3 Effects and hazards of short-time emergency loading
5.4 Effects of long-time emergency loading
5.5 Transformer size
6 Relative ageing rate and transformer insulation life
6.1 General
6.2 Insulation life
6.3 Relative ageing rate
6.4 Loss-of-life calculation
7 Limitations
7.1 Temperature limitations
7.2 Current limitations
7.3 Specific limitations for small transformers
7.3.1 Current and temperature limitations
7.3.2 Accessory and other considerations
7.3.3 Indoor transformers
7.3.4 Outdoor ambient conditions
7.4 Specific limitations for medium power transformers
7.4.1 Current and temperature limitations
7.4.2 Accessory, associated equipment and other considerations
7.4.3 Short-circuit withstand requirements
7.4.4 Voltage limitations
7.5 Specific limitations for large power transformers
7.5.1 General
7.5.2 Current and temperature limitations
7.5.3 Accessory, equipment and other considerations
7.5.4 Short-circuit withstand requirements
7.5.5 Voltage limitations
8 Determination of temperatures
8.1 Hot-spot temperature rise in steady state
8.1.1 General
8.1.2 Calculation of hot-spot temperature rise from normal heat-run test data
8.1.3 Direct measurement of hot-spot temperature rise
8.1.4 Hot-spot factor
8.2 Top-oil and hot-spot temperatures at varying ambient temperature and load conditions
8.2.1 General
8.2.2 Exponential equations solution
8.2.3 Difference equations solution
8.3 Ambient temperature
8.3.1 Outdoor air-cooled transformers
8.3.2 Correction of ambient temperature for transformer enclosure
8.3.3 Water-cooled transformers
9 Influence of tap-changers
9.1 General
9.2 Load loss
9.3 Ratio of losses
9.4 Load factor
Annex A (informative) Insulation life expectancy and relative ageing rate considering oxygen and water effect
Annex B (informative) Core temperature
Annex C (informative) Specification of loading beyond rated power
Annex D (informative) Description of Q, S and H factors
Annex E (informative) Calculation of winding and oil time constant
Annex F (informative) Thermal model parameters
Annex G (informative) Oil and winding exponents
Annex H (informative) Practical example of the exponential equations method
Annex I (informative) Application of the difference equation solution method
Annex J (informative) Flowchart, based on the example in Annex H
Annex K (informative) Example of calculating and presenting overload data
Annex L (informative) Geomagnetic induced currents
Annex M (informative) Alternative oils
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GSO IEC 60076-7:2022Gulf Standard
GSO IEC 60076-7:2022
IEC 60076-7:2018
مواصفة قياسية خليجية
محولات القدرة – الجزء 7: دليل التحميل لمحولات القدرة المغمورة بالزيت
Gulf Standard
Power transformers - Part 7: Loading guide for mineral-oil-immersed power transformers
ICS: |
29.180
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© GCC Standardization Organization 2022 – All rights reserved
© هيئة التقييس لدول مجلس التعاون لدول الخليج العربية 2022 – جميع الحقوق محفوظة
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جميع الحقوق محفوظة لهيئة لتقييس لدول مجلس التعاون لدول الخليج العربية.
ما لم ينص على خلاف ذلك، لا يجوز إعادة إنتاج أي جزء من هذا المنشور أو استخدامه بأي شكل آخر أو بأي وسيلة، إلكترونية أو ميكانيكية، بما في ذلك التصوير، أو النشر على الإنترنت أو الإنترانت، دون إذن كتابي مسبق من هيئة التقييس لدول مجلس التعاون لدول الخليج العربية على العنوان أدناه أو الدول الأعضاء في الهيئة داخل بلدانهم.
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All rights reserved to GCC Standardization Organization (GSO). Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either GSO at the address below or GSO's member body in the country of the requester.
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GCC Standardization Organization (GSO)
P.O.Box: 85245 Riyadh 12511
Kingdom of Saudi Arabia
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إدارة التواصل، قسم إدارة المعرفة
هيئة التقييس لدول مجلس التعاون لدول الخليج العربية (GSO)
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Gulf Foreword
GCC Standardization Organization (GSO) is a regional organization which consists of the national standardization bodies of GCC member states. One of GSO main functions is to issue gulf standards and technical regulations through specialized technical committees.
GSO Technical Council
in its meeting number (52) held
on 10/10/1443 H,
which corresponds to 12/05/2022, has approved
the update of
Gulf
Standard
GSO IEC 60076-7:2022
titled "Power transformers - Part 7: Loading guide for mineral-oil-immersed power transformers" in
English
language
which was studied
and adopted
from
International Electrotechnical Commission
Standard
IEC 60076-7:2018
without any technical modifications
through
the technical program of
GSO Technical Committee for Electric Power Generation, Transmission and Distribution Equipment
(TC09)
in KUWAIT schedule
.
This document will cancel and replace the Gulf
Standard
GSO IEC 60076-7:2014.
| تقديم خليجي |
هيئة التقييس لدول مجلس التعاون لدول الخليج العربية هيئة إقليمية تضم في عضويتها أجهزة التقييس الوطنية في الدول الأعضاء ، ومن مهام الهيئة إعداد المواصفات القياسية واللوائح الفنية الخليجية بواسطة لجان فنية متخصصة.
قرر المجلس الفني
لهيئة التقييس لدول مجلس التعاون لدول الخليج العربية
في الاجتماع الـ (52)
بتاريخ 1443/10/10 هـ ،الموافق 2022/05/12م اعتماد
تحديث
المواصفة القياسية الخليجية
رقم GSO IEC 60076-7:2022
وعنوانها "محولات القدرة – الجزء 7: دليل التحميل لمحولات القدرة المغمورة بالزيت"
باللغة
الانجليزية
التي تم دراستها
وتبنيها
عن
اللجنة الدولية الكهروتقنية
رقم
IEC 60076-7:2018
بدون إدخال تعديلات فنية عليها
ضمن برنامج عمل
اللجنة الفنية الخليجية لمواصفات معدات توليد ونقل وتوزيع الطاقة الكهربائية
(TC09)
المدرجة في خطة دولة الكويت
.
على أن تلغي وتحل محل
المواصفة القياسية
رقم
GSO IEC 60076-7:2014
.
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Gulf StandardGSO IEC 60076-7:2022
Gulf StandardGSO IEC 60076-7:2022
Gulf StandardGSO IEC 60076-7:2022
GSO IEC 60076-7:2022Gulf Standard
| IEC 60076-7 |
INTERNATIONAL STANDARD | Edition 2.0 2018-01 | |
| Power transformers – Part 7: Loading guide for mineral-oil-immersed power transformers | ||
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Gulf StandardGSO IEC 60076-7:2022
GSO IEC 60076-7:2022Gulf Standard
 | THIS PUBLICATION IS COPYRIGHT PROTECTEDCopyright © 2018 IEC, Geneva, Switzerland |
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Gulf StandardGSO IEC 60076-7:2022
Gulf StandardGSO IEC 60076-7:2022
Gulf StandardGSO IEC 60076-7:2022
GSO IEC 60076-7:2022Gulf Standard
| IEC 60076-7 |
INTERNATIONAL STANDARD | Edition 2.0 2018-01 | |
| Power transformers – Part 7: Loading guide for mineral-oil-immersed power transformers | ||
INTERNATIONAL
ELECTROTECHNCIAL
COMMISSION
ICS 29.180ISBN 9782832250822Warning! Make sure that you obtained this publication from an authorized distributor.© Registered trademark of the International Electrotechnical Commission
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GSO IEC 60076-7:2022Gulf Standard
CONTENTS
4 Symbols and abbreviations
5 Effect of loading beyond nameplate rating
5.1 General
5.2 General consequences
5.3 Effects and hazards of short-time emergency loading
5.4 Effects of long-time emergency loading
5.5 Transformer size
6 Relative ageing rate and transformer insulation life
6.1 General
6.2 Insulation life
6.3 Relative ageing rate
6.4 Loss-of-life calculation
7 Limitations
7.1 Temperature limitations
7.2 Current limitations
7.3 Specific limitations for small transformers
7.3.1 Current and temperature limitations
7.3.2 Accessory and other considerations
7.3.3 Indoor transformers
7.3.4 Outdoor ambient conditions
7.4 Specific limitations for medium power transformers
7.4.1 Current and temperature limitations
7.4.2 Accessory, associated equipment and other considerations
7.4.3 Short-circuit withstand requirements
7.4.4 Voltage limitations
7.5 Specific limitations for large power transformers
7.5.1 General
7.5.2 Current and temperature limitations
7.5.3 Accessory, equipment and other considerations
7.5.4 Short-circuit withstand requirements
7.5.5 Voltage limitations
8 Determination of temperatures
8.1 Hot-spot temperature rise in steady state
8.1.1 General
8.1.2 Calculation of hot-spot temperature rise from normal heat-run test data
8.1.3 Direct measurement of hot-spot temperature rise
8.1.4 Hot-spot factor
8.2 Top-oil and hot-spot temperatures at varying ambient temperature and load conditions
8.2.1 General
8.2.2 Exponential equations solution
8.2.3 Difference equations solution
8.3 Ambient temperature
8.3.1 Outdoor air-cooled transformers
8.3.2 Correction of ambient temperature for transformer enclosure
8.3.3 Water-cooled transformers
9 Influence of tap-changers
9.1 General
9.2 Load loss
9.3 Ratio of losses
9.4 Load factor
Annex A (informative) Insulation life expectancy and relative ageing rate considering oxygen and water effect
Annex B (informative) Core temperature
Annex C (informative) Specification of loading beyond rated power
Annex D (informative) Description of Q, S and H factors
Annex E (informative) Calculation of winding and oil time constant
Annex F (informative) Thermal model parameters
Annex G (informative) Oil and winding exponents
Annex H (informative) Practical example of the exponential equations method
Annex I (informative) Application of the difference equation solution method
Annex J (informative) Flowchart, based on the example in Annex H
Annex K (informative) Example of calculating and presenting overload data
Annex L (informative) Geomagnetic induced currents
Annex M (informative) Alternative oils
Power transformers - Part 7: Loading guide for mineral-oil-immersed power transformers
FOREWORD
1)
The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely 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.
International Standard IEC 60076‑7 has been prepared by IEC technical committee 14: Power transformers.
This second edition cancels and replaces the first edition published in 2005. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a)
title has been updated from "oil-immersed power transformers" to "mineral-oil-immersed power transformers";
b)
insulation life is updated by considering latest research findings;
c)
temperature limits have been reviewed and maximum core temperature is recommended;
d)
number of fibre optic sensors is recommended for temperature rise test;
e)
Q, S and H factors are considered;
f)
thermal models are revised and rewritten in generally applicable mathematical form;
g)
geomagnetic induced currents are briefly discussed and corresponding temperature limits are suggested;
h)
extensive literature review has been performed and a number of references added to bibliography.
The text of this standard is based on the following documents:
| FDIS | Report on voting |
| 14/933/FDIS | 14/942/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.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60076 series, 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 website under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be
•
reconfirmed,
•
withdrawn,
•
replaced by a revised edition, or
•
amended.
A bilingual version of this publication may be issued at a later date.
IMPORTANTThe 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.
INTRODUCTION
This part of IEC 60076 provides guidance for the specification and loading of power transformers from the point of view of operating temperatures and thermal ageing. It provides recommendations for loading above the nameplate rating and guidance for the planner to choose appropriate rated quantities and loading conditions for new installations.
IEC 60076‑2 is the basis for contractual agreements and it contains the requirements and tests relating to temperature-rise figures for oil-immersed transformers during continuous rated loading.
This part of IEC 60076 gives mathematical models for judging the consequence of different loadings, with different temperatures of the cooling medium, and with transient or cyclical variation with time. The models provide for the calculation of operating temperatures in the transformer, particularly the temperature of the hottest part of the winding. This hot-spot temperature is, in turn, used for evaluation of a relative value for the rate of thermal ageing and the percentage of life consumed in a particular time period. The modelling refers to small transformers, here called distribution transformers, and to power transformers.
A major change from the previous edition is the extensive work on the paper degradation that has been carried out indicating that the ageing may be described by combination of the oxidation, hydrolysis and pyrolysis. Also, providing possibility to estimate the expected insulation life considering different ageing factors, i.e. moisture, oxygen and temperature, and more realistic service scenarios. The title has been updated from "oil-immersed power transformers" to "mineral-oil-immersed power transformers". The temperature and current limits are reviewed and the maximum core temperature is recommended. The use of fibre optic temperature sensors has become a standard practice, however, the number of installed sensors per transformer highly varies. This issue and the description of Q, S and H factors are now considered as well. The thermal models are revised and rewritten in generally applicable mathematical form. The geomagnetic induced currents are briefly discussed and corresponding temperature limits are suggested.
This part of IEC 60076 further presents recommendations for limitations of permissible loading according to the results of temperature calculations or measurements. These recommendations refer to different types of loading duty – continuous loading, normal cyclic undisturbed loading or temporary emergency loading. The recommendations refer to distribution transformers, to medium power transformers and to large power transformers. Clauses 1 to 7 contain definitions, common background information and specific limitations for the operation of different categories of transformers.
Clause 8 contains the determination of temperatures, presents the mathematical models used to estimate the hot-spot temperature in steady state and transient conditions.
Clause 9 contains a short description of the influence of the tap position.
Application examples are given in Annexes A, B, C, D, E, F, G, H, I and K.
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1Scope
This part of IEC 60076 is applicable to mineral-oil-immersed transformers. It describes the effect of operation under various ambient temperatures and load conditions on transformer life.
NOTEFor furnace transformers, the manufacturer is consulted in view of the peculiar loading profile.
2Normative 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.
IEC 60076‑2, Power transformers – Part 2: Temperature rise for liquid-immersed transformers
IEC 60076‑14, Power transformers – Part 14: Liquid-immersed power transformers using high-temperature insulation materials
3Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
small power transformer
power transformer without attached radiators, coolers or tubes including corrugated tank irrespective of rating
3.2
medium power transformer
power transformer with a maximum rating of 100 MVA three-phase or 33,3 MVA single-phase
3.3
large power transformer
power transformer with a maximum rating of greater than 100 MVA three-phase or greater than 33,3 MVA single-phase
3.4
cyclic loading
loading with cyclic variations (the duration of the cycle usually being 24 h) which is regarded in terms of the accumulated amount of ageing that occurs during the cycle
Note 1 to entry: The cyclic loading may either be a normal loading or a long-time emergency loading.
3.5
normal cyclic loading
loading in which a higher ambient temperature or a higher-than-rated load current is applied during part of the cycle, but which, from the point of view of relative thermal ageing rate (according to the mathematical model), is equivalent to the rated load at normal ambient temperature
Note 1 to entry: This is achieved by taking advantage of low ambient temperatures or low load currents during the rest of the load cycle. For planning purposes, this principle can be extended to provide for long periods of time whereby cycles with relative thermal ageing rates greater than unity are compensated for by cycles with thermal ageing rates less than unity.
3.6
long-time emergency loading
loading resulting from the prolonged outage of some system elements that will not be reconnected before the transformer reaches a new and higher steady-state temperature
3.7
short-time emergency loading
unusually heavy loading of a transient nature (less than 30 min) due to the occurrence of one or more unlikely events which seriously disturb normal system loading
3.8
hot-spot
if not specially defined, hottest spot of the windings
3.9
relative thermal ageing rate
for a given hot-spot temperature, rate at which transformer insulation ageing is reduced or accelerated compared with the ageing rate at a reference hot-spot temperature
3.10
transformer insulation life
total time between the initial state for which the insulation is considered new and the final state for which the insulation is considered deteriorated due to thermal ageing, dielectric stress, short-circuit stress, or mechanical movement (which could occur in normal service), and at which a high risk of electrical failure exists
3.11
per cent loss of life
equivalent ageing in hours over a time period (usually 24 h) times 100 divided by the expected transformer insulation life
Note 1 to entry: The equivalent ageing in hours is obtained by multiplying the relative ageing rate with the number of hours.
3.12
non-thermally upgraded paper
kraft paper produced from unbleached softwood pulp under the sulphate process without addition of stabilizers
3.13
thermally upgraded paper
cellulose-based paper which has been chemically modified to reduce the rate at which the paper decomposes
Note 1 to entry: Ageing effects are reduced either by partial elimination of water forming agents (as in cyanoethylation) or by inhibiting the formation of water through the use of stabilizing agents (as in amine addition, dicyandiamide). A paper is considered as thermally upgraded if it meets the life criteria defined in ANSI/IEEE C57.100 [1]1; 50 % retention in tensile strength after 65 000 h in a sealed tube at 110 °C or any other time/temperature combination given by the equation:
[2], but after the sealed tube test.
 | (1) |
Because the thermal upgrading chemicals used today contain nitrogen, which is not present in kraft pulp, the degree of chemical modification is determined by testing for the amount of nitrogen present in the treated paper. Typical values for nitrogen content of thermally upgraded papers are between 1 % and 4 % when measured in accordance with ASTM D-982 |
3.14
non-directed oil flow
OF
flow indicating that the pumped oil from heat exchangers or radiators flows freely inside the tank, and is not forced to flow through the windings
Note 1 to entry: The oil flow inside the windings can be either axial in vertical cooling ducts or radial in horizontal cooling ducts with or without zigzag flow.
3.15
non-directed oil flow
ON
flow indicating that the oil from the heat exchangers or radiators flows freely inside the tank and is not forced to flow through the windings
Note 1 to entry: The oil flow inside the windings can be either axial in vertical cooling ducts or radial in horizontal cooling ducts with or without zigzag flow.
3.16
directed oil flow
OD
flow indicating that the principal part of the pumped oil from heat exchangers or radiators is forced to flow through the windings
Note 1 to entry: The oil flow inside the windings can be either axial in vertical cooling ducts or zigzag in horizontal cooling ducts.
3.17
design ambient temperature
temperature at which the permissible average winding and top-oil and hot-spot temperature over ambient temperature are defined
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Bibliography
[1] | C57.100-2011, IEEE Standard Test Procedure for Thermal Evaluation of Insulation Systems for Liquid-Immersed Distribution and Power Transformers | |
[2] | ASTM D982, 16 Standard Test Method for Organic Nitrogen in Paper and Paperboard | |
[3] | IEC 60214‑1:2014, Tap-changers – Part 1: Performance requirements and test methods | |
[4] | IEC 60354:1991, Loading guide for oil-immersed power transformers2 | |
[5] | IEC 60076‑1:2011, Power transformers – Part 1: General | |
[6] | A.K. Bose and G.J Hulsink: Performance of the magnetic circuit of a transformer in service – Elektrotechniek 56 (1978)(7) | |
[7] | E. Binder und W. Felber: Rueckarbeitsverfahren mit zwei 500 MVA Transformatoren – ELIN-Zeitschrift 1978 Heft 1 | |
[8] | A.K. Bose, C. Kroon, J. Wildeboer: The loading of a magnetic circuit – CIGRE 1978 session, August 30 – September 7 | |
[9] | A.M. Emsley, X. Xiao, R.J. Heywood, and M. Ali: “Degradation of cellulosic insulation in power transformers. Part 3: Effects of oxygen and water on ageing in oil”, IEE Proceedings – Science, Measurement and Technology, vol. 147, pp. 115-119, 2000 | |
[10] | L.E. Lundgaard, W. Hansen, S. Ingebrigtsen, D. Linhjell, and M. Dahlund: “Aging of kraft paper by acid catalyzed hydrolysis”, in IEEE International Conference on Dielectric Liquids, 2005. ICDL 2005. pp. 381-384 | |
[11] | CIGRE TF D1.01.10 (L. Lundgaard): “Ageing of cellulose in mineral oil insulated transformers”, CIGRE Brochure No.323, 2007 | |
[12] | L.E. Lundgaard, W. Hansen, and S. Ingebrigtsen: “Ageing of mineral oil Impregnated cellulose by acid catalysis”, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 15, pp. 540-546, 2008 | |
[13] | CIGRE WG A2.24 (J. Declerec): Thermal performance of power transformers, CIGRE Brochure No.393, 2010 | |
[14] | N. Lelekakis, D. Martin, and J. Wijaya, “Ageing rate of paper insulation used in power transformers Part 1: Oil/paper system with low oxygen concentration”, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 19, pp. 1999-2008, 2012 | |
[15] | N. Lelekakis, D. Martin, and J. Wijaya, “Ageing rate of paper insulation used in power transformers Part 2: Oil/paper system with medium and high oxygen concentration”, IEEE Transactions on Dielectrics and Electrical Insulation, vol. 19, pp. 2009-2018, 2012 | |
[16] | Lampe, W., Petterson, L., Ovren, C., Wahlstrom, B., Hot-spot measurements in power transformers – CIGRE, Rep. 12-02, 1984 | |
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30mm
20mm
15mm
15mm
10mm
17mm
1Numbers in square brackets refer to the bibliography.
2Withdrawn. IEC 60354:1991 was cancelled and replaced by IEC 60076‑7:2005
3Withdrawn.