IEC 62256:2008

IEC 62256
Edition 1.0 2008-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Hydraulic turbines, storage pumps and pump-turbines – Rehabilitation and
performance improvement
Turbines hydrauliques, pompes d'accumulation et pompes turbines –
Réhabilitation et amélioration des performances

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: csc@iec.ch
Tél.: +41 22 919 02 11
Fax: +41 22 919 03 00
IEC 62256
Edition 1.0 2008-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Hydraulic turbines, storage pumps and pump-turbines – Rehabilitation and
performance improvement
Turbines hydrauliques, pompes d'accumulation et pompes turbines –
Réhabilitation et amélioration des performances

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XF
CODE PRIX
ICS 27.140 ISBN 2-8318-9332-1
– 2 – 62256 © IEC:2008
CONTENTS
FOREWORD.6
INTRODUCTION.8

1 Scope and object.9
2 Nomenclature .9
3 Reasons for rehabilitating.10
3.1 General .10
3.2 Reliability and availability increase .12
3.3 Life extension and performance restoration .13
3.4 Performance improvement.13
3.5 Plant safety improvement .13
3.6 Environmental, social and regulatory issues .13
3.7 Maintenance and operating cost reduction.14
3.8 Other considerations .14
4 Phases of a rehabilitation project.14
4.1 General .14
4.2 Decision on organization .16
4.2.1 General .16
4.2.2 Expertise required .16
4.2.3 Contract arrangement.17
4.3 Level of assessment and determination of scope.17
4.3.1 General .17
4.3.2 Feasibility study – Stage 1.18
4.3.3 Feasibility study – Stage 2.18
4.3.4 Detailed study .18
4.4 Contractual issues.24
4.4.1 General .24
4.4.2 Specification requirements .24
4.4.3 Tendering documents and evaluation of tenders.24
4.4.4 Contract Award(s).25
4.5 Execution of project.25
4.5.1 Model test activities.25
4.5.2 Design, construction, installation and testing .26
4.6 Evaluation of results and compliance with guarantees .26
4.6.1 General .26
4.6.2 Turbine performance evaluation .27
4.6.3 Generator performance evaluation.27
4.6.4 Penalties and/or bonuses assessment.27
5 Scheduling, cost analysis and risk analysis .27
5.1 Scheduling .27
5.1.1 General .27
5.1.2 Scheduling – Assessment, feasibility and detailed study phases.28
5.1.3 Evaluating the scheduling component of alternatives .28
5.1.4 Scheduling specification and tendering phase .29
5.1.5 Scheduling project execution phases .30
5.2 Economic and financial analyses.30

62256 © IEC:2008 – 3 –
5.2.1 General .30
5.2.2 Benefit-cost analysis .31
5.2.3 Identification of anticipated benefits.32
5.2.4 Identification of anticipated costs and benefits.33
5.2.5 Sensitivity analysis .34
5.2.6 Conclusions.35
5.3 Risk analysis .35
5.3.1 General .35
5.3.2 Non-achievement of performance risk.36
5.3.3 Risk of continued operation without rehabilitation .36
5.3.4 Extension of outage risk .36
5.3.5 Financial risks .37
5.3.6 Project scope risk .37
5.3.7 Other risks.38
6 Assessment and determination of scope of the work.38
6.1 General .38
6.2 Assessment of the site .39
6.2.1 Hydrology .39
6.2.2 Actual energy production .39
6.2.3 Environmental social and regulatory issues .40
6.3 The assessment of the turbine .41
6.3.1 General .41
6.3.2 Turbine integrity assessment .70
6.3.3 Residual life .79
6.3.4 Turbine performance assessment .80
6.4 The assessment of related equipment .102
6.4.1 General .102
6.4.2 Generator and thrust bearing.107
6.4.3 Turbine governor .109
6.4.4 Turbine inlet and outlet valves, pressure relief valve. 109
6.4.5 Auxiliary equipment .109
6.4.6 Equipment for erection, dismantling and maintenance . 110
6.4.7 Penstock and other water passages .110
6.4.8 Consequences of changes in plant specific hydraulic energy (head).111
7 Hydraulic design and performance testing options .111
7.1 General .111
7.2 Computational hydraulic design. 112
7.2.1 General .112
7.2.2 The role of CFD.
...