SIST EN 62256:2017

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Wasserturbinen, Speicherpumpen und Pumpturbinen - Modernisierung und Verbesserung der Leistungseigenschaften (IEC 62256:2017)Turbines hydrauliques, pompes d'accumulation et pompes turbines - Réhabilitation et amélioration des performances (IEC 62256:2017)Hydraulic turbines, storage pumps and pump-turbines - Rehabilitation and performance improvement (IEC 62256:2017)27.140Vodna energijaHydraulic energy engineeringICS:Ta slovenski standard je istoveten z:EN 62256:2017SIST EN 62256:2017en01-oktober-2017SIST EN 62256:2017SLOVENSKI
STANDARDSIST EN 62256:20081DGRPHãþD

EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 62256
September 2017 ICS 27.140
Supersedes
EN 62256:2008
English Version
Hydraulic turbines, storage pumps and pump-turbines - Rehabilitation and performance improvement (IEC 62256:2017)
Turbines hydrauliques, pompes d'accumulation et pompes turbines - Réhabilitation et amélioration des performances (IEC 62256:2017)
Wasserturbinen, Speicherpumpen und Pumpturbinen - Modernisierung und Verbesserung der Leistungseigenschaften (IEC 62256:2017) This European Standard was approved by CENELEC on 2017-07-04. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung CEN-CENELEC Management Centre: Avenue Marnix 17,
B-1000 Brussels © 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 62256:2017 E SIST EN 62256:2017

This document supersedes EN 62256:2008. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights. Endorsement notice The text of the International Standard IEC 62256:2017 was approved by CENELEC as a European Standard without any modification. In the official version, for Bibliography, the following notes have to be added for the standards indicated: IEC 60041 NOTE Harmonized as EN 60041. IEC 60193 NOTE Harmonized as EN 60193. IEC 60609 (Series) NOTE Harmonized as EN 60609 (Series). IEC 60994 NOTE Harmonized as EN 60994. IEC 62097 NOTE Harmonized as EN 62097. IEC 62364 NOTE Harmonized as EN 62364.
IEC 62256 Edition 2.0 2017-05 INTERNATIONAL STANDARD
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 SIST EN 62256:2017

IEC 62256:2017 © IEC 2017 – 3 – 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 SIST EN 62256:2017

– 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
(informative)
Check-list for evaluation of existing turbine . 103 Annex A (informative)
Assessment examples . 136 Annex BB.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
(informative)
Checklist for evaluation of related equipment . 152 Annex CBibliography . 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 SIST EN 62256:2017

IEC 62256:2017 © IEC 2017 – 5 – 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 X1 to X7 based on relative importance . 59 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 SIST EN 62256:2017

– 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
IEC 62256:2017 © IEC 2017 – 7 – 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; SIST EN 62256:2017

– 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.
IEC 62256:2017 © IEC 2017 – 9 – 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 SIST EN 62256:2017

IEC 62256:2017 © IEC 2017 – 11 – 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 SIST EN 62256:2017

– 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 SIST EN 62256:2017

IEC 62256:2017 © IEC 2017 – 13 – 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 lifetime (years) Considerations Civil works
Dams, canals, tunnels, caverns, reservoirs, surge chambers 60 to 80 Duration of water rights, quality of work, state of deterioration, safety, loss of water. Powerhouse structures, water control structures, spillways, sand traps, penstocks, steel linings, roads, bridges 40 to 50 General condition, imposed stresses, quality of material, state-of-the-art, safety, quality of steel, 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 of efficiency, performance improvement. Francis, Pelton and Fixed-blade Propeller turbines 30 to 50 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, spherical valves, cranes, auxiliary mechanical equipment 25 to 40 Quality of material, operating condition, safety considerations, quality of equipment, imposed 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 equipment, control equipment 20 to 25
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-art, capacity vs. service conditions. Concrete towers 30 to 40 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 components. The operating characteristics and the mechanical integrity of the machine can be restored to nearly “as-new” condition, guaranteeing safe and r
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