IEC 62256:2017

Hydraulic turbines, storage pumps and pump-turbines - Rehabilitation and performance improvement

IEC 62256:2017 covers turbines, storage pumps and pump-turbines of all sizes and of the following types: Francis; Kaplan; propeller; Pelton (turbines only) and bulb turbines.
This document also identifies without detailed discussion, other powerhouse equipment that could affect or be affected by a turbine, storage pump, or pump-turbine rehabilitation. The object of this document is to assist in identifying, evaluating and executing rehabilitation and performance improvement projects for hydraulic turbines, storage pumps and pump-turbines. This document can be used by owners, consultants, and suppliers to define: needs and economics for rehabilitation and performance improvement; scope of work; specifications and evaluation of results. This document is intended to be: an aid in the decision process; an extensive source of information on rehabilitation; an identification of the key milestones in the rehabilitation process; and identification of the points to be addressed in the decision processes. This document is not intended to be a detailed engineering manual nor a maintenance document. This second edition cancels and replaces the first edition published in 2008. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: Tables 2 to 23 modified, completed and moved to Annex A; 7.3.2: subclauses moved with text changes; new subclauses on temperature, noise, galvanic corrosion, galling and replacement of components without assessment; 7.3.3: complete new subclause on residual life; Tables 29 to 32 moved to Annex C; New Annex B with assessment examples.
Key words: Turbines, Storage pump, Pump turbines, Rehabilitation, Performance.

Turbines hydrauliques, pompes d'accumulation et pompes-turbines - Réhabilitation et amélioration des performances

Spécifie comment préparer les spécifications particulières pour les transformateurs de puissance pour alimentations à découpage. Comprend une spécification particulière  cadre, qui montre la présentation et indique les essais appropriés  à considérer pour ce type de composant.

General Information

• Status: Published
• Publication Date: 29-May-2017
• ICS: 27.140 - Hydraulic energy engineering
• ICS: 29.100.10 - Magnetic components
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 4 - Hydraulic turbines
• Drafting Committee: MT 31 - TC 4/MT 31
• Current Stage: PPUB - Publication issued
• Start Date: 30-May-2017
• Completion Date: 26-May-2017

Relations

• Revises: IEC 62256:2008 - Hydraulic turbines, storage pumps and pump-turbines - Rehabilitation and performance improvement
• Effective Date: 05-Sep-2023

Overview - IEC 62256:2017 (Hydraulic turbines, storage pumps and pump-turbines)

IEC 62256:2017 provides guidance for the rehabilitation and performance improvement of hydraulic turbines, storage pumps and pump-turbines of all sizes and the following types: Francis, Kaplan, propeller, Pelton (turbines only) and bulb turbines. It is intended as a decision‑support and project‑planning document - helping owners, consultants and suppliers to identify needs, assess economics, define scope of work, develop specifications and evaluate results. This edition (2017) is a technical revision of the 2008 standard and adds assessment examples and new technical subclauses (e.g., temperature, noise, galvanic corrosion, galling, residual life).

Key topics and technical requirements

• Assessment and decision process
  • Phased approach: feasibility (stage 1 & 2), detailed study, procurement, execution and evaluation.
  • Identification of key milestones and decision points in rehabilitation projects.
• Turbine integrity and residual life
  • Systematic evaluation of runner, guide vanes, stay rings and related components.
  • Procedures for assessing structural condition and estimating remaining life.
• Hydraulic performance
  • Options for hydraulic design: computational (CFD) and physical model tests.
  • Guidance on prototype performance testing and accuracy considerations.
• Economic, schedule and risk analysis
  • Benefit–cost analysis, sensitivity studies, outage scheduling and financial risk assessment.
• Related equipment & plant integration
  • Assessment of generators, governors, bearings, valves, penstocks, auxiliaries and grid integration impacts.
• Procurement and contractual guidance
  • Specification content, tender evaluation and compliance/guarantee verification.
• Annexes and checklists
  • Practical checklists for turbine and equipment evaluation and worked assessment examples to aid implementation.

Practical applications - who uses IEC 62256:2017

• Hydropower plant owners and operators - to decide whether to rehabilitate, extend life or improve plant output.
• Consulting engineers - to structure feasibility and detailed studies, define scopes and produce specifications.
• Equipment suppliers and contractors - to prepare tenders, design rehabilitation solutions, and validate guarantees.
• Asset managers and financiers - to quantify economic benefits, outage impacts and project risks.

Related standards and references

IEC 62256 is part of the broader IEC corpus for electrotechnical and hydro equipment. Users typically apply it alongside relevant IEC and national standards for generators, controls, testing and materials, and with industry best practices for CFD/model testing and structural assessment.

Keywords: Turbines, Storage pump, Pump turbines, Rehabilitation, Performance, CFD, model tests, residual life, hydropower rehabilitation.

Standards Content (Sample)

IEC 62256 ®
Edition 2.0 2017-05
INTERNATIONAL
STANDARD
colour
inside
Hydraulic turbines, storage pumps and pump-turbines – Rehabilitation and
performance improvement
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.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland 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.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished

Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC 62256 ®
Edition 2.0 2017-05
INTERNATIONAL
STANDARD
colour
inside
Hydraulic turbines, storage pumps and pump-turbines – Rehabilitation and

performance improvement
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.140 ISBN 978-2-8322-4340-4

– 2 – IEC 62256:2017 © IEC 2017
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions and nomenclature . 10
4 Reasons for rehabilitating . 12
4.1 General . 12
4.2 Reliability and availability increase. 14
4.3 Life extension and performance restoration . 14
4.4 Performance improvement . 14
4.5 Plant safety improvement . 14
4.6 Environmental, social and regulatory issues . 15
4.7 Maintenance and operating cost reduction . 15
4.8 Other considerations . 15
5 Phases of a rehabilitation project . 15
5.1 General . 15
5.2 Decision on organization . 17
5.2.1 General . 17
5.2.2 Expertise required . 17
5.2.3 Contract arrangement . 17
5.3 Level of assessment and determination of scope . 18
5.3.1 General . 18
5.3.2 Feasibility study – Stage 1 . 19
5.3.3 Feasibility study – Stage 2 . 19
5.3.4 Detailed study. 19
5.4 Contractual issues . 23
5.4.1 General . 23
5.4.2 Specification requirements . 24
5.4.3 Tendering documents and evaluation of tenders . 24
5.4.4 Contract award(s) . 25
5.5 Execution of project . 25
5.5.1 Model test activities . 25
5.5.2 Design, construction, installation and testing . 25
5.6 Evaluation of results and compliance with guarantees . 26
5.6.1 General . 26
5.6.2 Turbine performance evaluation. 26
5.6.3 Generator performance evaluation . 27
5.6.4 Penalties and/or bonuses assessment . 27
6 Scheduling, cost analysis and risk analysis . 27
6.1 Scheduling . 27
6.1.1 General . 27
6.1.2 Scheduling – Assessment, feasibility and detailed study phases . 28
6.1.3 Evaluating the scheduling component of alternatives . 28
6.1.4 Scheduling specification and tendering phase . 29
6.1.5 Scheduling project execution phases . 29
6.2 Economic and financial analyses . 29

6.2.1 General . 29
6.2.2 Benefit-cost analysis . 30
6.2.3 Identification of anticipated benefits . 31
6.2.4 Identification of anticipated costs and benefits . 32
6.2.5 Sensitivity analysis . 33
6.2.6 Conclusions . 34
6.3 Risk analysis. 34
6.3.1 General . 34
6.3.2 Non-achievement of performance risk . 34
6.3.3 Risk of continued operation without rehabilitation . 35
6.3.4 Extension of outage risk . 35
6.3.5 Financial risks . 35
6.3.6 Project scope risk . 36
6.3.7 Other risks . 36
7 Assessment and determination of scope of the work . 37
7.1 General . 37
7.2 Assessment of the site . 37
7.2.1 Hydrology . 37
7.2.2 Actual energy production . 38
7.2.3 Environmental, social and regulatory issues . 38
7.3 The assessment of the turbine . 39
7.3.1 General . 39
7.3.2 Turbine integrity assessment . 39
7.3.3 Residual life. 52
7.3.4 Turbine performance assessment . 61
7.4 The assessment of related equipment . 83
7.4.1 General . 83
7.4.2 Generator and thrust bearing . 84
7.4.3 Turbine governor . 84
7.4.4 Turbine inlet and outlet valves, pressure relief valve . 85
7.4.5 Auxiliary equipment . 85
7.4.6 Equipment for erection, dismantling and maintenance . 86
7.4.7 Penstock and other water passages . 86
7.4.8 Consequences of changes in plant specific hydraulic energy (head) . 86
7.4.9 Grid integration . 87
8 Hydraulic design and performance testing options . 87
8.1 General . 87
8.2 Computational hydraulic design . 88
8.2.1 General . 88
8.2.2 The role of CFD . 88
8.2.3 The process of a CFD cycle . 89
8.2.4 The accuracy of CFD results . 89
8.2.5 How to use CFD for rehabilitation . 90
8.2.6 CFD versus model tests . 91
8.3 Model tests . 91
8.3.1 General . 91
8.3.2 Model test similitude . 92
8.3.3 Model test content . 93
8.3.4 Model test application . 93

– 4 – IEC 62256:2017 © IEC 2017
8.3.5 Model test location . 95
8.4 Prototype performance test . 96
8.4.1 General . 96
8.4.2 Prototype performance test accuracy . 97
8.4.3 Prototype performance test types . 97
8.4.4 Evaluation of results . 98
9 Specifications . 99
9.1 General . 99
9.2 Reference standards . 99
9.3 Information to be included in the tender documents . 100
9.4 Documents to be developed in the course of the project . 101
Annex A (informative) Check-list for evaluation of existing turbine . 103
Annex B (informative) Assessment examples . 136
B.1 General . 136
B.2 Runner (applicable to Francis, Kaplan, propeller and Pelton) . 136
B.2.1 Documentation – available data . 136
B.2.2 Design review . 137
B.2.3 Inspection items . 137
B.2.4 Assessment of inspection results . 138
B.2.5 Current condition assessment . 140
B.2.6 Scope of work . 140
B.3 Stay ring . 142
B.3.1 Documentation – available data . 142
B.3.2 Design review . 142
B.3.3 Inspection items . 142
B.3.4 Assessment of inspection results . 143
B.3.5 Current condition assessment . 143
B.3.6 Scope of work (possible action to be taken) . 144
B.4 Guide vanes . 144
B.4.1 Documentation – Available data. 144
B.4.2 Design review . 145
B.4.3 Inspection items . 145
B.4.4 Assessment of inspection results . 146
B.4.5 Current condition assessment . 147
B.4.6 Scope of work . 147
B.5 Real life example: Pelton runner with severe crack . 148
B.5.1 Data of the Pelton runner . 148
B.5.2 Fatigue analysis . 148
B.5.3 Fracture-mechanics analysis . 150
B.5.4 Results for the Pelton runner . 150
Annex C (informative) Checklist for evaluation of related equipment . 152
Bibliography . 156

Figure 1 – Flow diagram depicting the logic of the rehabilitation process . 16
Figure 2 – Critical zones for cracks “A” and “B” in Pelton runner buckets . 51
Figure 3 – Bathtub curve . 53
Figure 4 – Process of residual life estimation . 54
Figure 5 – Schematic behaviour for the different stages in the fatigue process . 55

Figure 6 – Start-up and full load strain gauge signal on Francis blade . 60
Figure 7 – Relative efficiency versus relative output – Original and new runners . 63
Figure 8 – Relative efficiency versus output – Original and new runners – Outardes 3
generating station . 64
Figure 9 – Efficiency and distribution of losses versus specific speed for Francis
turbines (model) in 2005 . 65
Figure 10 – Relative efficiency gain following modification of the blades on the
La Grande 3 runner, in Quebec, Canada . 67
Figure 11 – Potential efficiency improvement for Francis turbine rehabilitation . 71
Figure 12 – Potential efficiency improvement for Kaplan turbine rehabilitation . 72
Figure 13 – Cavitation and corrosion-erosion in Francis runner . 74
Figure 14 – Back side erosion of the entrance into a Pelton bucket . 75
Figure 15 – Leading edge cavitation erosion on a Francis pump-turbine caused by
extended periods of operation at very low loads . 76
Figure 16 – Severe particle erosion damage in a Francis runner . 78

Table 1 – Expected life of a hydropower plant and its subsystems before major work . 13
Table 2 – Typical routine inspections . 41
Table 3 – Example of a rating system for the inspection results . 58
Table 4 – Example of a typical list of turbine components for Francis and Kaplan with
different weight factors X to X based on relative importance . 59
1 7
Table 5 – Example of rating of a single component assessment including three
assessment criteria . 59
Table 6 – Francis turbine potential efficiency improvement (%) for runner profile
modifications only . 66
Table 7 – Potential impact of design and condition of runner seals on Francis turbine
efficiency with new replacement runner or rehabilitated runner (%) . 69
Table 8 – Potential total gain in efficiency from the replacement of a Francis turbine
runner including the blade profile improvements, the restoration of surface condition
and the reduction of seal losses . 69
Table 9 – Potential additional efficiency improvement by rehabilitation/replacement of
other water passage components on a Francis turbine (%) . 70
Table A.1 – Assessment of turbine embedded parts – Stay ring . 103
Table A.2 – Assessment of turbine embedded parts – Spiral or semi-spiral case . 104
Table A.3 – Assessment of turbine embedded parts – Discharge ring . 105
Table A.4 – Assessment of turbine embedded parts – Draft tube . 107
Table A.5 – Assessment of turbine non-embedded, non-rotating parts – Headcover . 109
Table A.6 – Assessment of turbine non-embedded, non-rotating parts – Intermediate
and inner headcovers . 112
Table A.7 – Assessment of turbine non embedded, non-rotating parts – Bottom ring . 113
Table A.8 – Assessment of turbine non embedded, non-rotating parts – Guide vanes . 115
Table A.9 – Assessment of turbine non embedded, non-rotating parts – Guide vane
operating mechanism . 117
Table A.10 – Assessment of turbine non embedded, non-rotating parts – Operating ring . 118
Table A.11 – Assessment of turbine non embedded, non-rotating parts – Servomotors . 119
Table A.12 – Assessment of turbine non embedded, non-rotating parts – Guide
bearings. 120

– 6 – IEC 62256:2017 © IEC 2017
Table A.13 – Assessment of turbine non embedded, non-rotating parts – Turbine shaft
seal (mechanical seal or packing box) . 122
Table A.14 – Assessment of turbine non embedded, non-rotating parts – Thrust
bearing support . 122
Table A.15 – Assessment of turbine non embedded, non-rotating parts – Nozzles . 123
Table A.16 – Assessment of turbine non embedded, non-rotating parts – Deflectors
and energy dissipation . 124
Table A.17 – Assessment of turbine rotating parts – Runner . 125
Table A.18 – Assessment of turbine rotating parts – Runner . 128
Table A.19 – Assessment of turbine rotating parts – Runner . 130
Table A.20 – Assessment of turbine rotating parts – Turbine shaft . 131
Table A.21 – Assessment of turbine rotating parts – Oil head and oil distribution pipes . 132
Table A.22 – Assessment of turbine auxiliaries – Speed and load regulation system
(governor) . 133
Table A.23 – Assessment of turbine auxiliaries – Turbine aeration system . 134
Table A.24 – Assessment of turbine auxiliaries – Lubrication system (guide vane
mechanism) . 135
Table C.1 – Assessment of related equipment – Governor . 152
Table C.2 – Assessment of related equipment – Generator and thrust bearing . 153
Table C.3 – Assessment of related equipment – Penstock and turbine inlet valves . 154
Table C.4 – Assessment of related equipment – Civil works . 155
Table C.5 – Assessment of related equipment – Crane, erection equipment . 155

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HYDRAULIC TURBINES, STORAGE PUMPS AND PUMP-TURBINES –
REHABILITATION AND PERFORMANCE IMPROVEMENT

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 62256 has been prepared by IEC technical committee 4: Hydraulic
turbines.
This second edition cancels and replaces the first edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– Tables 2 to 23 modified, completed and moved to Annex A;
– 7.3.2:
• subclauses moved with text changes;
• new subclauses on temperature, noise, galvanic corrosion, galling and replacement of
components without assessment;
– 7.3.3: complete new subclause on residual life;
– Tables 29 to 32 moved to Annex C;

– 8 – IEC 62256:2017 © IEC 2017
– new Annex B with assessment examples.
The text of this standard is based on the following documents:
FDIS Report on voting
4/323/FDIS 4/326/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The '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
Hydro plant owners make significant investments annually in rehabilitating plant equipment
(turbines, generators, transformers, penstocks, gates etc.) and structures in order to improve
the level of service to their customers and to optimize their revenue. In the absence of
guidelines, owners may be spending needlessly, or may be taking unnecessary risks and
thereby achieving results that are less than optimal. This document is intended to be a tool in
the optimisation and decision process.
Edition 1 of this International Standard was based on the IEA document Guidelines on
Methodology for Hydroelectric Francis Turbine Upgrading by Runner Replacement.

– 10 – IEC 62256:2017 © IEC 2017
HYDRAULIC TURBINES, STORAGE PUMPS AND PUMP-TURBINES –
REHABILITATION AND PERFORMANCE IMPROVEMENT

1 Scope
This document covers turbines, storage pumps and pump-turbines of all sizes and of the
following types:
• Francis;
• Kaplan;
• propeller;
• Pelton (turbines only);
• bulb turbines.
This document also identifies without detailed discussion, other powerhouse equipment that
could affect or be affected by a turbine, storage pump, or pump-turbine rehabilitation.
The object of this document is to assist in identifying, evaluating and executing rehabilitation
and performance improvement projects for hydraulic turbines, storage pumps and pump-
turbines. This document can be used by owners, consultants, and suppliers to define:
• needs and economics for rehabilitation and performance improvement;
• scope of work;
• specifications;
• evaluation of results.
This document is intended to be:
• an aid in the decision process;
• an extensive source of information on rehabilitation;
• an identification of the key milestones in the rehabilitation process;
• an identification of the points to be addressed in the decision processes.
This document is not intended to be a detailed engineering manual nor a maintenance
document.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and nomenclature
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

Wherever turbines or turbine components are referred to in the text of this document, they
shall be interpreted also to mean the comparable units or components of storage pumps or
pump-turbines as the case requires.
For the purpose of this document, the term “rehabilitation” is defined as some combination of:
• restoration of equipment capacity and/or equipment efficiency to near “as-new” levels;
• extension of equipment life by re-establishing mechanical integrity.
The term “performance improvement” means the increase of capacity and/or efficiency
beyond those of the original machine and may be included as part of a rehabilitation.
Many other terms are in common use to define the work of “rehabilitation” and “performance
improvement”, however use of the above terms is suggested. Some of the terms considered
and discarded for their lack of precision or completeness include:
• upgrade or upgrading – restoration of mechanical integrity and efficiency;
• uprating – increase of nameplate capacity (power) which may result in part from efficiency
restoration or improvement;
• overhaul – restoration of mechanical integrity;
• modernization – could mean performance improvement and replacement of obsolete
technologies;
• redevelopment – term frequently used to mean replacement of the powerplant and could
involve changes to the hydraulics and hydrology of the site usually implying a change in
mode of operation of the plant;
• refurbishment – restoration of mechanical integrity usually with restoration of performance
(closely resembles “rehabilitation”, the preferred term);
• replacement – usually refers to specific components but may involve the complete
hydraulic machine in the case of small units.
The nomenclature in this document is in accordance with IEC TR 61364, which provides the
“Nomenclature” in six languages to facilitate easy correlation with the terminology of this
document.
Here is a list of the acronyms used throughout this document:
• AGC: automatic generation or direct frequency control
• B/C: benefit/cost ratio
• CFD: computational fluid dynamics
• ETA: event tree analysis
• FEA: finite element analysis
• FFT: fast Fourier transform
• FMA: failure mode analysis
• FMECA: failure modes effects and criticality analysis
• FTA: fault tree analysis
• HAZOP: hazard and operability study
• IRR: internal rate of return
• MT: magnetic particle inspection technique
• NDT: non-destructive testing
• NPV: net present value
• PCB: polychlorinated biphenyl

– 12 – IEC 62256:2017 © IEC 2017
• PT: liquid penetrant inspection technique
• RSI: rotor-stator interactions
• SNL: speed no load
• UT: ultrasonic inspection technique
• VAR: Volt-Ampere Reactive
4 Reasons for rehabilitating
4.1 General
Hydroelectric generating facilities are among the most robust, reliable, durable structures and
equipment ever produced. The robustness of the equipment permits owners to continue
operating these facilities without major rehabilitation for relatively long periods. As shown in
Table 1, the reliable life for a turbine prior to a major rehabilitation being necessary is typically
between 30 and 50 years depending on type of unit, design, quality of manufacturing, severity
of service, and other similar considerations. However, all generating equipment will inevitably
suffer reduced performance, reliability and availability with time, which leads owners to the
fundamental question of what to do with an aging plant. This crucial question cannot be
answered easily since it involves many interrelated issues such as revenue, operating and
maintenance cost, equipment performance, reliability, availability, safety and mission of
generating facilities within the entire system. Ultimately, an owner will have to decide to
rehabilitate the plant or eventually to close it. At some point in time, delaying a major
rehabilitation ceases to be an option. This may come about as the result of a major
component failure or as the result of an economic evaluation. Cessation of commercial
operation does not necessarily relieve an owner of the responsibility for the maintenance of
the civil structures, regulation of the flows and any other issues which have an impact on an
owner’s liability for the plant.
The governing reason for rehabilitation is usually to maximize return on investment and
normally includes one or more of the following:
– reliability and availability increase;
– life extension and performance restoration;
– performance improvement:
• efficiency;
• power;
• reduction of cavitation erosion;
• enlargement of operating range;
– plant safety improvement;
– environmental, social or regulatory issues;
– maintenance and operating cost reduction;
– other considerations:
• modified governmental regulations;
• political criteria;
• company image criteria;
• modified hydrology conditions;
• modified market conditions.
The opportune time for starting a rehabilitation is prior to the plant being beset with frequent
and severe problems, such as generator winding failures, major runner cracking, cavitation or
particle erosion damage, bearing failures and/or equipment alignment problems due to
foundation or substructure movement or distortion. When a generating plant has reached such

a stage, it is obvious that a technical and an economic assessment of the equipment should
have been conducted years before. If the time frame of rehabilitation studies is too close to
the end of the useful life of the plant and its equipment, the owner may lose the option of
evaluating a range of alternatives. Catastrophic failures with potential major damage and loss
of life are, at some stage of the plant life, real risks. If significant improvements can be made
in the revenue generating capabilities of the plant by replacement of deteriorated equipment
with state-of-the-art equipment or components, there may be justification for performing
rehabilitation earlier than the date at which it would be required for purely reliability or life
extension reasons.
Typically, the renewed life of a turbine following rehabilitation would be more than 25 years
with normal maintenance. The residual life of the generating plant is dependent on the
collective residual lives of each individual component group and therefore can be determined
only by assessing all of the component groups including the civil structures.
Rehabilitation should result in a unit which is very close to its as-new condition.
Table 1 – Expected life of a hydropower plant and its subsystems before major work
Plant subsystems Expected Considerations
lifetime
(years)
Civil works
Dams, canals, tunnels, caverns, reservoirs, 60 to 80 Duration of water rights, quality of work, state of
surge chambers deterioration, safety, loss of water.
Powerhouse structures, water control 40 to 50 General condition, imposed stresses, quality of
structures, spillways, sand traps, material, state-of-the-art, safety, quality of steel,
penstocks, steel linings, roads, bridges corrosion, maintenance.
Mechanical installations
Hydraulic machines
Kaplan and Bulb turbines 25 to 50 Safety of operation, loss of water, cavitation
damage, erosion, corrosion, cracks, deterioration
Francis, Pelton and Fixed-blade Propeller 30 to 50
of efficiency, performance improvement.
turbines
Pump turbines (all types) 25 to 35
Storage pumps (all types) 25 to 35
Heavy mechanical equipment and

auxiliaries
Flat gates, radial gates, butterfly valves, 25 to 40 Quality of material, operating condition, safety
spherical valves, cranes, auxiliary considerations, quality of equipment, imposed
mechanical equipment stresses, performance improvement.
Electrical installations
Generators, transformers 25 to 40 Winding and iron core condition, cleanliness,
safety of operation, state-of-the-art, general
condition, quality of equipment, maintenance.
High voltage switchgear, auxiliary electrical 20 to 25
equipment, control equipment
Batteries, DC equipment 10 to 20
Energy transmission lines
Steel towers 30 to 50 Right of way, corrosion, safety of operation,
climatic conditions, quality of material, state-of-the-
Concrete towers 30 to 40
art, capacity vs. service conditions.
Wooden poles 20 to 25
Lines and cables 25 to 40
– 14 – IEC 62256:2017 © IEC 2017
4.2 Reliability and availability increase
A thorough rehabilitation can significantly increase reliability and availability of the units.
Following a thorough and well executed rehabilitation, an availability of approximately 98 %
can be expected. This normally results in less lost revenue associated with having the units
out of service for planned outages and fewer unplanned outages. By their nature, forced
outages for unplanned repairs usually cost significantly more than would a similar planned
repair, particularly when the consequential impacts are evaluated.
4.3 Life extension and performance restoration
The useful life of the turbine can be greatly extended by the rehabilitation or replacement of
turbine compo
...

IEC 62256 ®
Edition 2.0 2017-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Hydraulic turbines, storage pumps and pump-turbines – Rehabilitation and
performance improvement
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.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland 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.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC 62256 ®
Edition 2.0 2017-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Hydraulic turbines, storage pumps and pump-turbines – Rehabilitation and

performance improvement
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.140 ISBN 978-2-8322-4433-3

– 2 – IEC 62256:2017 RLV © IEC 2017
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions and nomenclature . 10
4 Reasons for rehabilitating . 12
4.1 General . 12
4.2 Reliability and availability increase. 14
4.3 Life extension and performance restoration . 14
4.4 Performance improvement . 14
4.5 Plant safety improvement . 14
4.6 Environmental, social and regulatory issues . 15
4.7 Maintenance and operating cost reduction . 15
4.8 Other considerations . 15
5 Phases of a rehabilitation project . 15
5.1 General . 15
5.2 Decision on organization . 17
5.2.1 General . 17
5.2.2 Expertise required . 17
5.2.3 Contract arrangement . 17
5.3 Level of assessment and determination of scope . 18
5.3.1 General . 18
5.3.2 Feasibility study – Stage 1 . 19
5.3.3 Feasibility study – Stage 2 . 19
5.3.4 Detailed study. 19
5.4 Contractual issues . 23
5.4.1 General . 23
5.4.2 Specification requirements . 24
5.4.3 Tendering documents and evaluation of tenders . 24
5.4.4 Contract award(s) . 25
5.5 Execution of project . 25
5.5.1 Model test activities . 25
5.5.2 Design, construction, installation and testing . 25
5.6 Evaluation of results and compliance with guarantees . 26
5.6.1 General . 26
5.6.2 Turbine performance evaluation. 26
5.6.3 Generator performance evaluation . 27
5.6.4 Penalties and/or bonuses assessment . 27
6 Scheduling, cost analysis and risk analysis . 27
6.1 Scheduling . 27
6.1.1 General . 27
6.1.2 Scheduling – Assessment, feasibility and detailed study phases . 28
6.1.3 Evaluating the scheduling component of alternatives . 28
6.1.4 Scheduling specification and tendering phase . 29
6.1.5 Scheduling project execution phases . 29
6.2 Economic and financial analyses . 29

6.2.1 General . 29
6.2.2 Benefit-cost analysis . 30
6.2.3 Identification of anticipated benefits . 31
6.2.4 Identification of anticipated costs and benefits . 32
6.2.5 Sensitivity analysis . 33
6.2.6 Conclusions . 34
6.3 Risk analysis. 34
6.3.1 General . 34
6.3.2 Non-achievement of performance risk . 34
6.3.3 Risk of continued operation without rehabilitation . 35
6.3.4 Extension of outage risk . 35
6.3.5 Financial risks . 35
6.3.6 Project scope risk . 36
6.3.7 Other risks . 36
7 Assessment and determination of scope of the work . 37
7.1 General . 37
7.2 Assessment of the site . 37
7.2.1 Hydrology . 37
7.2.2 Actual energy production . 38
7.2.3 Environmental, social and regulatory issues . 38
7.3 The assessment of the turbine . 39
7.3.1 General . 39
7.3.2 Turbine integrity assessment . 39
7.3.3 Residual life. 53
7.3.4 Turbine performance assessment . 63
7.4 The assessment of related equipment . 85
7.4.1 General . 85
7.4.2 Generator and thrust bearing . 86
7.4.3 Turbine governor . 87
7.4.4 Turbine inlet and outlet valves, pressure relief valve . 87
7.4.5 Auxiliary equipment . 87
7.4.6 Equipment for erection, dismantling and maintenance . 88
7.4.7 Penstock and other water passages . 88
7.4.8 Consequences of changes in plant specific hydraulic energy (head) . 89
7.4.9 Grid integration . 89
8 Hydraulic design and performance testing options . 89
8.1 General . 89
8.2 Computational hydraulic design . 90
8.2.1 General . 90
8.2.2 The role of CFD . 91
8.2.3 The process of a CFD cycle . 91
8.2.4 The accuracy of CFD results . 92
8.2.5 How to use CFD for rehabilitation . 92
8.2.6 CFD versus model tests . 93
8.3 Model tests . 94
8.3.1 General . 94
8.3.2 Model test similitude . 94
8.3.3 Model test content . 95
8.3.4 Model test application . 96

– 4 – IEC 62256:2017 RLV © IEC 2017
8.3.5 Model test location . 97
8.4 Prototype performance test . 98
8.4.1 General . 98
8.4.2 Prototype performance test accuracy . 99
8.4.3 Prototype performance test types . 99
8.4.4 Evaluation of results . 100
9 Specifications . 101
9.1 General . 101
9.2 Reference standards . 101
9.3 Information to be included in the tender documents . 102
9.4 Documents to be developed in the course of the project . 103
Annex A (informative) Check-list for evaluation of existing turbine . 106
Annex B (informative) Assessment examples . 140
B.1 General . 140
B.2 Runner (applicable to Francis, Kaplan, propeller and Pelton) . 140
B.2.1 Documentation – available data . 140
B.2.2 Design review . 141
B.2.3 Inspection items . 141
B.2.4 Assessment of inspection results . 142
B.2.5 Current condition assessment . 144
B.2.6 Scope of work . 144
B.3 Stay ring . 146
B.3.1 Documentation – available data . 146
B.3.2 Design review . 146
B.3.3 Inspection items . 146
B.3.4 Assessment of inspection results . 147
B.3.5 Current condition assessment . 147
B.3.6 Scope of work (possible action to be taken) . 148
B.4 Guide vanes . 148
B.4.1 Documentation – Available data. 148
B.4.2 Design review . 149
B.4.3 Inspection items . 149
B.4.4 Assessment of inspection results . 150
B.4.5 Current condition assessment . 151
B.4.6 Scope of work . 151
B.5 Real life example: Pelton runner with severe crack . 152
B.5.1 Data of the Pelton runner . 152
B.5.2 Fatigue analysis . 152
B.5.3 Fracture-mechanics analysis . 154
B.5.4 Results for the Pelton runner . 154
Annex C (informative) Checklist for evaluation of related equipment . 156
Bibliography . 160

Figure 1 – Flow diagram depicting the logic of the rehabilitation process . 16
Figure 2 – Critical zones for cracks “A” and “B” in Pelton runner buckets . 52
Figure 3 – Bathtub curve . 54
Figure 4 – Process of residual life estimation . 55
Figure 5 – Schematic behaviour for the different stages in the fatigue process . 57

Figure 6 – Start-up and full load strain gauge signal on Francis blade . 62
Figure 7 – Relative efficiency versus relative output – Original and new runners . 65
Figure 8 – Relative efficiency versus output – Original and new runners – Outardes 3
generating station . 66
Figure 9 – Efficiency and distribution of losses versus specific speed for Francis
turbines (model) in 2005 . 67
Figure 10 – Relative efficiency gain following modification of the blades on the
La Grande 3 runner, in Quebec, Canada . 69
Figure 11 – Potential efficiency improvement for Francis turbine rehabilitation . 73
Figure 12 – Potential efficiency improvement for Kaplan turbine rehabilitation . 74
Figure 13 – Cavitation and corrosion-erosion in Francis runner . 76
Figure 14 – Back side erosion of the entrance into a Pelton bucket . 77
Figure 15 – Leading edge cavitation erosion on a Francis pump-turbine caused by
extended periods of operation at very low loads . 78
Figure 16 – Severe particle erosion damage in a Francis runner . 80

Table 1 – Expected life of a hydropower plant and its subsystems before major work . 13
Table 2 – Typical routine inspections . 41
Table 3 – Example of a rating system for the inspection results . 60
Table 4 – Example of a typical list of turbine components for Francis and Kaplan with
different weight factors X to X based on relative importance . 61
1 7
Table 5 – Example of rating of a single component assessment including three
assessment criteria . 61
Table 6 – Francis turbine potential efficiency improvement (%) for runner profile
modifications only . 68
Table 7 – Potential impact of design and condition of runner seals on Francis turbine
efficiency with new replacement runner or rehabilitated runner (%) . 71
Table 8 – Potential total gain in efficiency from the replacement of a Francis turbine
runner including the blade profile improvements, the restoration of surface condition
and the reduction of seal losses . 71
Table 9 – Potential additional efficiency improvement by rehabilitation/replacement of
other water passage components on a Francis turbine (%) . 72
Table A.1 – Assessment of turbine embedded parts – Stay ring . 106
Table A.2 – Assessment of turbine embedded parts – Spiral or semi-spiral case . 107
Table A.3 – Assessment of turbine embedded parts – Discharge ring . 108
Table A.4 – Assessment of turbine embedded parts – Draft tube . 110
Table A.5 – Assessment of turbine non-embedded, non-rotating parts – Headcover . 112
Table A.6 – Assessment of turbine non-embedded, non-rotating parts – Intermediate
and inner headcovers . 115
Table A.7 – Assessment of turbine non embedded, non-rotating parts – Bottom ring . 116
Table A.8 – Assessment of turbine non embedded, non-rotating parts – Guide vanes . 118
Table A.9 – Assessment of turbine non embedded, non-rotating parts – Guide vane
operating mechanism . 121
Table A.10 – Assessment of turbine non embedded, non-rotating parts – Operating ring . 122
Table A.11 – Assessment of turbine non embedded, non-rotating parts – Servomotors . 123
Table A.12 – Assessment of turbine non embedded, non-rotating parts – Guide
bearings. 124

– 6 – IEC 62256:2017 RLV © IEC 2017
Table A.13 – Assessment of turbine non embedded, non-rotating parts – Turbine shaft
seal (mechanical seal or packing box) . 126
Table A.14 – Assessment of turbine non embedded, non-rotating parts – Thrust
bearing support . 126
Table A.15 – Assessment of turbine non embedded, non-rotating parts – Nozzles . 127
Table A.16 – Assessment of turbine non embedded, non-rotating parts – Deflectors
and energy dissipation . 128
Table A.17 – Assessment of turbine rotating parts – Runner . 129
Table A.18 – Assessment of turbine rotating parts – Runner . 132
Table A.19 – Assessment of turbine rotating parts – Runner . 134
Table A.20 – Assessment of turbine rotating parts – Turbine shaft . 135
Table A.21 – Assessment of turbine rotating parts – Oil head and oil distribution pipes . 136
Table A.22 – Assessment of turbine auxiliaries – Speed and load regulation system
(governor) . 137
Table A.23 – Assessment of turbine auxiliaries – Turbine aeration system . 138
Table A.24 – Assessment of turbine auxiliaries – Lubrication system (guide vane
mechanism) . 139
Table C.1 – Assessment of related equipment – Governor . 156
Table C.2 – Assessment of related equipment – Generator and thrust bearing . 157
Table C.3 – Assessment of related equipment – Penstock and turbine inlet valves . 158
Table C.4 – Assessment of related equipment – Civil works . 159
Table C.5 – Assessment of related equipment – Crane, erection equipment . 159

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HYDRAULIC TURBINES, STORAGE PUMPS AND PUMP-TURBINES –
REHABILITATION AND PERFORMANCE IMPROVEMENT

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.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.
International Standard IEC 62256 has been prepared by IEC technical committee 4: Hydraulic
turbines.
This second edition cancels and replaces the first edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– 8 – IEC 62256:2017 RLV © IEC 2017
– Tables 2 to 23 modified, completed and moved to Annex A;
– 7.3.2:
• subclauses moved with text changes;
• new subclauses on temperature, noise, galvanic corrosion, galling and replacement of
components without assessment;
– 7.3.3: complete new subclause on residual life;
– Tables 29 to 32 moved to Annex C;
– new Annex B with assessment examples.
The text of this standard is based on the following documents:
FDIS Report on voting
4/323/FDIS 4/326/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The '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
Hydro plant owners make significant investments annually in rehabilitating plant equipment
(turbines, generators, transformers, penstocks, gates etc.) and structures in order to improve
the level of service to their customers and to optimize their revenue. In the absence of
guidelines, owners may be spending needlessly, or may be taking unnecessary risks and
thereby achieving results that are less than optimal. This document is intended to be a tool in
the optimisation and decision process.
IEC TC 4 wishes to thank IEA for providing its document “Guidelines on Methodology for
Hydroelectric Francis Turbine Upgrading by Runner Replacement” as a starting point for the
writing of this document. IEC TC 4 appreciates this contribution and acknowledges that the
IEA document provided a good foundation upon which to build this IEC document.
Edition 1 of this International Standard was based on the IEA document Guidelines on
Methodology for Hydroelectric Francis Turbine Upgrading by Runner Replacement.

– 10 – IEC 62256:2017 RLV © IEC 2017
HYDRAULIC TURBINES, STORAGE PUMPS AND PUMP-TURBINES –
REHABILITATION AND PERFORMANCE IMPROVEMENT

1 Scope and object
This document covers turbines, storage pumps and pump-turbines of all sizes and of the
following types:
• Francis;
• Kaplan;
• propeller;
• Pelton (turbines only);
• bulb turbines.
This document also identifies without detailed discussion, other powerhouse equipment that
could affect or be affected by a turbine, storage pump, or pump-turbine rehabilitation.
The object of this document is to assist in identifying, evaluating and executing rehabilitation
and performance improvement projects for hydraulic turbines, storage pumps and pump-
turbines. This document can be used by owners, consultants, and suppliers to define:
• needs and economics for rehabilitation and performance improvement;
• scope of work;
• specifications;
• evaluation of results.
This document is intended to be:
• an aid in the decision process;
• an extensive source of information on rehabilitation;
• an identification of the key milestones in the rehabilitation process;
• an identification of the points that should to be addressed in the decision processes.
This document is not intended to be a detailed engineering manual nor a maintenance
document.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and nomenclature
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

Wherever turbines or turbine components are referred to in the text of this document, they
shall be interpreted also to mean the comparable units or components of storage pumps or
pump-turbines as the case requires.
For the purpose of this document, the term “rehabilitation” is defined as some combination of:
• restoration of equipment capacity and/or equipment efficiency to near “as-new” levels;
• extension of equipment life by re-establishing mechanical integrity.
The term “performance improvement” means the increase of capacity and/or efficiency
beyond those of the original machine and may be included as part of a rehabilitation.
Many other terms are in common use to define the work of “rehabilitation” and “performance
improvement”, however use of the above terms is suggested. Some of the terms considered
and discarded for their lack of precision or completeness include:
• upgrade or upgrading – restoration of mechanical integrity and efficiency;
• uprating – increase of nameplate capacity (power) which may result in part from efficiency
restoration or improvement;
• overhaul – restoration of mechanical integrity;
• modernization – could mean performance improvement and replacement of obsolete
technologies;
• redevelopment – term frequently used to mean replacement of the powerplant and could
involve changes to the hydraulics and hydrology of the site usually implying a change in
mode of operation of the plant;
• refurbishment – restoration of mechanical integrity usually with restoration of performance
(closely resembles “rehabilitation”, the preferred term);
• replacement – usually refers to specific components but may involve the complete
hydraulic machine in the case of small units.
The nomenclature in this document is in accordance with IEC TR 61364, which provides the
“Nomenclature” in six languages to facilitate easy correlation with the terminology of this
document.
Here is a list of the acronyms used throughout this document:
• AGC: automatic generation or direct frequency control
• B/C: benefit/cost ratio
• CFD: computational fluid dynamics
• ETA: event tree analysis
• FEA: finite element analysis
• FFT: fast Fourier transform
• FMA: failure mode analysis
• FMECA: failure modes effects and criticality analysis
• FTA: fault tree analysis
• HAZOP: hazard and operability study
• IRR: internal rate of return
• MT: magnetic particle inspection technique
• NDT: non-destructive testing
• NPV: net present value
• PCB: polychlorinated biphenyl

– 12 – IEC 62256:2017 RLV © IEC 2017
• PT: liquid penetrant inspection technique
• RSI: rotor-stator interactions
• SNL: speed no load
• UT: ultrasonic inspection technique
• VAR: Volt-Ampere Reactive
4 Reasons for rehabilitating
4.1 General
Hydroelectric generating facilities are among the most robust, reliable, durable structures and
equipment ever produced. The robustness of the equipment permits owners to continue
operating these facilities without major rehabilitation for relatively long periods. As shown in
Table 1, the reliable life for a turbine prior to a major rehabilitation being necessary is typically
between 30 and 50 years depending on type of unit, design, quality of manufacturing, severity
of service, and other similar considerations. However, all generating equipment will inevitably
suffer reduced performance, reliability and availability with time, which leads owners to the
fundamental question of what to do with an aging plant. This crucial question cannot be
answered easily since it involves many interrelated issues such as revenue, operating and
maintenance cost, equipment performance, reliability, availability, safety and mission of
generating facilities within the entire system. Ultimately, an owner will have to decide to
rehabilitate the plant or eventually to close it. At some point in time, delaying a major
rehabilitation ceases to be an option. This may come about as the result of a major
component failure or as the result of an economic evaluation. Cessation of commercial
operation does not necessarily relieve an owner of the responsibility for the maintenance of
the civil structures, regulation of the flows and any other issues which have an impact on an
owner’s liability for the plant.
The governing reason for rehabilitation is usually to maximize return on investment and
normally includes one or more of the following:
– reliability and availability increase;
– life extension and performance restoration;
– performance improvement:
• efficiency;
• power;
• reduction of cavitation erosion;
• enlargement of operating range;
– plant safety improvement;
– environmental, social or regulatory issues;
– maintenance and operating cost reduction;
– other considerations:
• modified governmental regulations;
• political criteria;
• company image criteria;
• modified hydrology conditions;
• modified market conditions.
The opportune time for starting a rehabilitation is prior to the plant being beset with frequent
and severe problems, such as generator winding failures, major runner cracking, cavitation or
particle erosion damage, bearing failures and/or equipment alignment problems due to
foundation or substructure movement or distortion. When a generating plant has reached such

a stage, it is obvious that a technical and an economic assessment of the equipment should
have been conducted years before. If the time frame of rehabilitation studies is too close to
the end of the useful life of the plant and its equipment, the owner may lose the option of
evaluating a range of alternatives. Catastrophic failures with potential major damage and loss
of life are, at some stage of the plant life, real risks. If significant improvements can be made
in the revenue generating capabilities of the plant by replacement of deteriorated equipment
with state-of-the-art equipment or components, there may be justification for performing
rehabilitation earlier than the date at which it would be required for purely reliability or life
extension reasons.
Typically, the renewed life of a turbine following rehabilitation would be more than 25 years
with normal maintenance. The residual life of the generating plant is dependent on the
collective residual lives of each individual component group and therefore can be determined
only by assessing all of the component groups including the civil structures.
Rehabilitation should result in a unit which is very close to its as-new condition.
Table 1 – Expected life of a hydropower plant and its subsystems before major work
Plant subsystems Expected Considerations
lifetime
(years)
Civil works
Dams, canals, tunnels, caverns, reservoirs, 60 to 80 Duration of water rights, quality of work, state of
surge chambers deterioration, safety, loss of water.
Powerhouse structures, water control 40 to 50 General condition, imposed stresses, quality of
structures, spillways, sand traps, material, state-of-the-art, safety, quality of steel,
penstocks, steel linings, roads, bridges corrosion, maintenance.
Mechanical installations
Hydraulic machines
Kaplan and Bulb turbines 25 to 50 Safety of operation, loss of water, cavitation
damage, erosion, corrosion, cracks, deterioration
Francis, Pelton and Fixed-blade Propeller 30 to 50
of efficiency, performance improvement.
turbines
Pump turbines (all types) 25 to 35
Storage pumps (all types) 25 to 35
Heavy mechanical equipment and

auxiliaries
Flat gates, radial gates, butterfly valves, 25 to 40 Quality of material, operating condition, safety
spherical valves, cranes, auxiliary considerations, quality of equipment, imposed
mechanical equipment stresses, performance improvement.
Electrical installations
Generators, transformers 25 to 40 Winding and iron core condition, cleanliness,
safety of operation, state-of-the-art, general
condition, quality of equipment, maintenance.
High voltage switchgear, auxiliary electrical 20 to 25
equipment, control equipment
Batteries, DC equipment 10 to 20
Energy transmission lines
Steel towers 30 to 50 Right of way, corrosion, safety of operation,
climatic conditions, quality of material, state-of-the-
Concrete towers 30 to 40
art, capacity vs. service conditions.
Wooden poles 20 to 25
Lines and cables 25 to 40
– 14 – IEC 62256:2017 RLV © IEC 2017
...

IEC 62256 ®
Edition 2.0 2017-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
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 l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland 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.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) 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 IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient 20 000 termes et définitions en anglais
Spécifications techniques, Rapports techniques et autres
et en français, ainsi que les termes équivalents dans 16
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC - www.iec.ch/searchpub
Glossaire IEC - std.iec.ch/glossary
65 000 entrées terminologiques électrotechniques, en anglais
La recherche avancée permet de trouver des publications IEC
en utilisant différents critères (numéro de référence, texte, et en français, extraites des articles Termes et Définitions des
comité d’études,…). Elle donne aussi des informations sur les publications IEC parues depuis 2002. Plus certaines entrées
projets et les publications remplacées ou retirées. antérieures extraites des publications des CE 37, 77, 86 et

CISPR de l'IEC.
IEC Just Published - webstore.iec.ch/justpublished

Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just
Published détaille les nouvelles publications parues. Si vous désirez nous donner des commentaires sur cette
Disponible en ligne et aussi une fois par mois par email. publication ou si vous avez des questions contactez-nous:
[e-mail].
IEC 62256 ®
Edition 2.0 2017-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
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
INTERNATIONALE
ICS 27.140 ISBN 978-2-8322-5201-7

– 2 – IEC 62256:2017 © IEC 2017
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions and nomenclature . 10
4 Reasons for rehabilitating . 12
4.1 General . 12
4.2 Reliability and availability increase. 13
4.3 Life extension and performance restoration . 13
4.4 Performance improvement . 14
4.5 Plant safety improvement . 14
4.6 Environmental, social and regulatory issues . 14
4.7 Maintenance and operating cost reduction . 15
4.8 Other considerations . 15
5 Phases of a rehabilitation project . 15
5.1 General . 15
5.2 Decision on organization . 17
5.2.1 General . 17
5.2.2 Expertise required . 17
5.2.3 Contract arrangement . 17
5.3 Level of assessment and determination of scope . 18
5.3.1 General . 18
5.3.2 Feasibility study – Stage 1 . 18
5.3.3 Feasibility study – Stage 2 . 19
5.3.4 Detailed study. 19
5.4 Contractual issues . 23
5.4.1 General . 23
5.4.2 Specification requirements . 23
5.4.3 Tendering documents and evaluation of tenders . 24
5.4.4 Contract award(s) . 24
5.5 Execution of project . 24
5.5.1 Model test activities . 24
5.5.2 Design, construction, installation and testing . 25
5.6 Evaluation of results and compliance with guarantees . 25
5.6.1 General . 25
5.6.2 Turbine performance evaluation. 25
5.6.3 Generator performance evaluation . 26
5.6.4 Penalties and/or bonuses assessment . 26
6 Scheduling, cost analysis and risk analysis . 26
6.1 Scheduling . 26
6.1.1 General . 26
6.1.2 Scheduling – Assessment, feasibility and detailed study phases . 27
6.1.3 Evaluating the scheduling component of alternatives . 27
6.1.4 Scheduling specification and tendering phase . 28
6.1.5 Scheduling project execution phases . 28
6.2 Economic and financial analyses . 29

6.2.1 General . 29
6.2.2 Benefit-cost analysis . 29
6.2.3 Identification of anticipated benefits . 30
6.2.4 Identification of anticipated costs and benefits . 31
6.2.5 Sensitivity analysis . 32
6.2.6 Conclusions . 32
6.3 Risk analysis. 32
6.3.1 General . 32
6.3.2 Non-achievement of performance risk . 33
6.3.3 Risk of continued operation without rehabilitation . 33
6.3.4 Extension of outage risk . 34
6.3.5 Financial risks . 34
6.3.6 Project scope risk . 34
6.3.7 Other risks . 35
7 Assessment and determination of scope of the work . 35
7.1 General . 35
7.2 Assessment of the site . 36
7.2.1 Hydrology . 36
7.2.2 Actual energy production . 36
7.2.3 Environmental, social and regulatory issues . 37
7.3 The assessment of the turbine . 37
7.3.1 General . 37
7.3.2 Turbine integrity assessment . 38
7.3.3 Residual life. 49
7.3.4 Turbine performance assessment . 58
7.4 The assessment of related equipment . 78
7.4.1 General . 78
7.4.2 Generator and thrust bearing . 79
7.4.3 Turbine governor . 79
7.4.4 Turbine inlet and outlet valves, pressure relief valve . 80
7.4.5 Auxiliary equipment . 80
7.4.6 Equipment for erection, dismantling and maintenance . 81
7.4.7 Penstock and other water passages . 81
7.4.8 Consequences of changes in plant specific hydraulic energy (head) . 81
7.4.9 Grid integration . 82
8 Hydraulic design and performance testing options . 82
8.1 General . 82
8.2 Computational hydraulic design . 83
8.2.1 General . 83
8.2.2 The role of CFD . 83
8.2.3 The process of a CFD cycle . 84
8.2.4 The accuracy of CFD results . 84
8.2.5 How to use CFD for rehabilitation . 85
8.2.6 CFD versus model tests . 85
8.3 Model tests . 86
8.3.1 General . 86
8.3.2 Model test similitude . 87
8.3.3 Model test content . 87
8.3.4 Model test application . 88

– 4 – IEC 62256:2017 © IEC 2017
8.3.5 Model test location . 90
8.4 Prototype performance test . 90
8.4.1 General . 90
8.4.2 Prototype performance test accuracy . 91
8.4.3 Prototype performance test types . 92
8.4.4 Evaluation of results . 92
9 Specifications . 93
9.1 General . 93
9.2 Reference standards . 93
9.3 Information to be included in the tender documents . 94
9.4 Documents to be developed in the course of the project . 95
Annex A (informative) Check-list for evaluation of existing turbine . 98
Annex B (informative) Assessment examples . 131
B.1 General . 131
B.2 Runner (applicable to Francis, Kaplan, propeller and Pelton) . 131
B.2.1 Documentation – available data . 131
B.2.2 Design review . 132
B.2.3 Inspection items . 132
B.2.4 Assessment of inspection results . 133
B.2.5 Current condition assessment . 135
B.2.6 Scope of work . 135
B.3 Stay ring . 136
B.3.1 Documentation – available data . 136
B.3.2 Design review . 137
B.3.3 Inspection items . 137
B.3.4 Assessment of inspection results . 137
B.3.5 Current condition assessment . 138
B.3.6 Scope of work (possible action to be taken) . 138
B.4 Guide vanes . 139
B.4.1 Documentation – Available data. 139
B.4.2 Design review . 139
B.4.3 Inspection items . 139
B.4.4 Assessment of inspection results . 140
B.4.5 Current condition assessment . 141
B.4.6 Scope of work . 141
B.5 Real life example: Pelton runner with severe crack . 142
B.5.1 Data of the Pelton runner . 142
B.5.2 Fatigue analysis . 142
B.5.3 Fracture-mechanics analysis . 143
B.5.4 Results for the Pelton runner . 144
Annex C (informative) Checklist for evaluation of related equipment . 145
Bibliography . 149

Figure 1 – Flow diagram depicting the logic of the rehabilitation process . 16
Figure 2 – Critical zones for cracks “A” and “B” in Pelton runner buckets . 48
Figure 3 – Bathtub curve . 50
Figure 4 – Process of residual life estimation . 51
Figure 5 – Schematic behaviour for the different stages in the fatigue process . 52

Figure 6 – Start-up and full load strain gauge signal on Francis blade . 57
Figure 7 – Relative efficiency versus relative output – Original and new runners . 60
Figure 8 – Relative efficiency versus output – Original and new runners – Outardes 3
generating station . 61
Figure 9 – Efficiency and distribution of losses versus specific speed for Francis
turbines (model) in 2005 . 62
Figure 10 – Relative efficiency gain following modification of the blades on the
La Grande 3 runner, in Quebec, Canada . 64
Figure 11 – Potential efficiency improvement for Francis turbine rehabilitation . 68
Figure 12 – Potential efficiency improvement for Kaplan turbine rehabilitation . 69
Figure 13 – Cavitation and corrosion-erosion in Francis runner . 70
Figure 14 – Back side erosion of the entrance into a Pelton bucket . 71
Figure 15 – Leading edge cavitation erosion on a Francis pump-turbine caused by
extended periods of operation at very low loads . 72
Figure 16 – Severe particle erosion damage in a Francis runner . 73

Table 1 – Expected life of a hydropower plant and its subsystems before major work . 13
Table 2 – Typical routine inspections . 39
Table 3 – Example of a rating system for the inspection results . 55
Table 4 – Example of a typical list of turbine components for Francis and Kaplan with
different weight factors X to X based on relative importance . 56
1 7
Table 5 – Example of rating of a single component assessment including three
assessment criteria . 56
Table 6 – Francis turbine potential efficiency improvement (%) for runner profile
modifications only . 63
Table 7 – Potential impact of design and condition of runner seals on Francis turbine
efficiency with new replacement runner or rehabilitated runner (%) . 65
Table 8 – Potential total gain in efficiency from the replacement of a Francis turbine
runner including the blade profile improvements, the restoration of surface condition
and the reduction of seal losses . 66
Table 9 – Potential additional efficiency improvement by rehabilitation/replacement of
other water passage components on a Francis turbine (%) . 66
Table A.1 – Assessment of turbine embedded parts – Stay ring . 98
Table A.2 – Assessment of turbine embedded parts – Spiral or semi-spiral case . 99
Table A.3 – Assessment of turbine embedded parts – Discharge ring . 100
Table A.4 – Assessment of turbine embedded parts – Draft tube . 102
Table A.5 – Assessment of turbine non-embedded, non-rotating parts – Headcover . 104
Table A.6 – Assessment of turbine non-embedded, non-rotating parts – Intermediate
and inner headcovers . 107
Table A.7 – Assessment of turbine non embedded, non-rotating parts – Bottom ring . 108
Table A.8 – Assessment of turbine non embedded, non-rotating parts – Guide vanes . 110
Table A.9 – Assessment of turbine non embedded, non-rotating parts – Guide vane
operating mechanism . 112
Table A.10 – Assessment of turbine non embedded, non-rotating parts – Operating
ring . 113
Table A.11 – Assessment of turbine non embedded, non-rotating parts – Servomotors . 114

– 6 – IEC 62256:2017 © IEC 2017
Table A.12 – Assessment of turbine non embedded, non-rotating parts – Guide
bearings. 115
Table A.13 – Assessment of turbine non embedded, non-rotating parts – Turbine shaft
seal (mechanical seal or packing box) . 117
Table A.14 – Assessment of turbine non embedded, non-rotating parts – Thrust
bearing support . 117
Table A.15 – Assessment of turbine non embedded, non-rotating parts – Nozzles . 118
Table A.16 – Assessment of turbine non embedded, non-rotating parts – Deflectors
and energy dissipation . 119
Table A.17 – Assessment of turbine rotating parts – Runner . 120
Table A.18 – Assessment of turbine rotating parts – Runner . 123
Table A.19 – Assessment of turbine rotating parts – Runner . 125
Table A.20 – Assessment of turbine rotating parts – Turbine shaft . 126
Table A.21 – Assessment of turbine rotating parts – Oil head and oil distribution pipes . 127
Table A.22 – Assessment of turbine auxiliaries – Speed and load regulation system
(governor) . 128
Table A.23 – Assessment of turbine auxiliaries – Turbine aeration system . 129
Table A.24 – Assessment of turbine auxiliaries – Lubrication system (guide vane
mechanism) . 130
Table C.1 – Assessment of related equipment – Governor . 145
Table C.2 – Assessment of related equipment – Generator and thrust bearing . 146
Table C.3 – Assessment of related equipment – Penstock and turbine inlet valves . 147
Table C.4 – Assessment of related equipment – Civil works . 148
Table C.5 – Assessment of related equipment – Crane, erection equipment . 148

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HYDRAULIC TURBINES, STORAGE PUMPS AND PUMP-TURBINES –
REHABILITATION AND PERFORMANCE IMPROVEMENT

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 62256 has been prepared by IEC technical committee 4: Hydraulic
turbines.
This second edition cancels and replaces the first edition published in 2008. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– Tables 2 to 23 modified, completed and moved to Annex A;
– 7.3.2:
• subclauses moved with text changes;
• new subclauses on temperature, noise, galvanic corrosion, galling and replacement of
components without assessment;
– 7.3.3: complete new subclause on residual life;
– Tables 29 to 32 moved to Annex C;
– new Annex B with assessment examples.

– 8 – IEC 62256:2017 © IEC 2017
This bilingual version (2017-12) corresponds to the monolingual English version, published in
2017-05.
The text of this standard is based on the following documents:
FDIS Report on voting
4/323/FDIS 4/326/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
The French version of this standard has not been voted upon.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The '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
Hydro plant owners make significant investments annually in rehabilitating plant equipment
(turbines, generators, transformers, penstocks, gates etc.) and structures in order to improve
the level of service to their customers and to optimize their revenue. In the absence of
guidelines, owners may be spending needlessly, or may be taking unnecessary risks and
thereby achieving results that are less than optimal. This document is intended to be a tool in
the optimisation and decision process.
Edition 1 of this International Standard was based on the IEA document Guidelines on
Methodology for Hydroelectric Francis Turbine Upgrading by Runner Replacement.

– 10 – IEC 62256:2017 © IEC 2017
HYDRAULIC TURBINES, STORAGE PUMPS AND PUMP-TURBINES –
REHABILITATION AND PERFORMANCE IMPROVEMENT

1 Scope
This document covers turbines, storage pumps and pump-turbines of all sizes and of the
following types:
• Francis;
• Kaplan;
• propeller;
• Pelton (turbines only);
• bulb turbines.
This document also identifies without detailed discussion, other powerhouse equipment that
could affect or be affected by a turbine, storage pump, or pump-turbine rehabilitation.
The object of this document is to assist in identifying, evaluating and executing rehabilitation
and performance improvement projects for hydraulic turbines, storage pumps and pump-
turbines. This document can be used by owners, consultants, and suppliers to define:
• needs and economics for rehabilitation and performance improvement;
• scope of work;
• specifications;
• evaluation of results.
This document is intended to be:
• an aid in the decision process;
• an extensive source of information on rehabilitation;
• an identification of the key milestones in the rehabilitation process;
• an identification of the points to be addressed in the decision processes.
This document is not intended to be a detailed engineering manual nor a maintenance
document.
2 Normative references
There are no normative references in this document.
3 Terms, definitions and nomenclature
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
Wherever turbines or turbine components are referred to in the text of this document, they
shall be interpreted also to mean the comparable units or components of storage pumps or
pump-turbines as the case requires.
For the purpose of this document, the term “rehabilitation” is defined as some combination of:
• restoration of equipment capacity and/or equipment efficiency to near “as-new” levels;

• extension of equipment life by re-establishing mechanical integrity.
The term “performance improvement” means the increase of capacity and/or efficiency
beyond those of the original machine and may be included as part of a rehabilitation.
Many other terms are in common use to define the work of “rehabilitation” and “performance
improvement”, however use of the above terms is suggested. Some of the terms considered
and discarded for their lack of precision or completeness include:
• upgrade or upgrading – restoration of mechanical integrity and efficiency;
• uprating – increase of nameplate capacity (power) which may result in part from efficiency
restoration or improvement;
• overhaul – restoration of mechanical integrity;
• modernization – could mean performance improvement and replacement of obsolete
technologies;
• redevelopment – term frequently used to mean replacement of the powerplant and could
involve changes to the hydraulics and hydrology of the site usually implying a change in
mode of operation of the plant;
• refurbishment – restoration of mechanical integrity usually with restoration of performance
(closely resembles “rehabilitation”, the preferred term);
• replacement – usually refers to specific components but may involve the complete
hydraulic machine in the case of small units.
The nomenclature in this document is in accordance with IEC TR 61364, which provides the
“Nomenclature” in six languages to facilitate easy correlation with the terminology of this
document.
Here is a list of the acronyms used throughout this document:
• AGC: automatic generation or direct frequency control
• B/C: benefit/cost ratio
• CFD: computational fluid dynamics
• ETA: event tree analysis
• FEA: finite element analysis
• FFT: fast Fourier transform
• FMA: failure mode analysis
• FMECA: failure modes effects and criticality analysis
• FTA: fault tree analysis
• HAZOP: hazard and operability study
• IRR: internal rate of return
• MT: magnetic particle inspection technique
• NDT: non-destructive testing
• NPV: net present value
• PCB: polychlorinated biphenyl
• PT: liquid penetrant inspection technique
• RSI: rotor-stator interactions
• SNL: speed no load
• UT: ultrasonic inspection technique
• VAR: Volt-Ampere Reactive
– 12 – IEC 62256:2017 © IEC 2017
4 Reasons for rehabilitating
4.1 General
Hydroelectric generating facilities are among the most robust, reliable, durable structures and
equipment ever produced. The robustness of the equipment permits owners to continue
operating these facilities without major rehabilitation for relatively long periods. As shown in
Table 1, the reliable life for a turbine prior to a major rehabilitation being necessary is typically
between 30 and 50 years depending on type of unit, design, quality of manufacturing, severity
of service, and other similar considerations. However, all generating equipment will inevitably
suffer reduced performance, reliability and availability with time, which leads owners to the
fundamental question of what to do with an aging plant. This crucial question cannot be
answered easily since it involves many interrelated issues such as revenue, operating and
maintenance cost, equipment performance, reliability, availability, safety and mission of
generating facilities within the entire system. Ultimately, an owner will have to decide to
rehabilitate the plant or eventually to close it. At some point in time, delaying a major
rehabilitation ceases to be an option. This may come about as the result of a major
component failure or as the result of an economic evaluation. Cessation of commercial
operation does not necessarily relieve an owner of the responsibility for the maintenance of
the civil structures, regulation of the flows and any other issues which have an impact on an
owner’s liability for the plant.
The governing reason for rehabilitation is usually to maximize return on investment and
normally includes one or more of the following:
– reliability and availability increase;
– life extension and performance restoration;
– performance improvement:
• efficiency;
• power;
• reduction of cavitation erosion;
• enlargement of operating range;
– plant safety improvement;
– environmental, social or regulatory issues;
– maintenance and operating cost reduction;
– other considerations:
• modified governmental regulations;
• political criteria;
• company image criteria;
• modified hydrology conditions;
• modified market conditions.
The opportune time for starting a rehabilitation is prior to the plant being beset with frequent
and severe problems, such as generator winding failures, major runner cracking, cavitation or
particle erosion damage, bearing failures and/or equipment alignment problems due to
foundation or substructure movement or distortion. When a generating plant has reached such
a stage, it is obvious that a technical and an economic assessment of the equipment should
have been conducted years before. If the time frame of rehabilitation studies is too close to
the end of the useful life of the plant and its equipment, the owner may lose the option of
evaluating a range of alternatives. Catastrophic failures with potential major damage and loss
of life are, at some stage of the plant life, real risks. If significant improvements can be made
in the revenue generating capabilities of the plant by replacement of deteriorated equipment
with stat
...