IEC TS 63111:2025

IEC TS 63111 ®
Edition 1.0 2025-10
TECHNICAL
SPECIFICATION
Hydraulic turbines, storage pumps and pump-turbines – Hydraulic transient
analysis, design considerations and testing

ICS 27.140  ISBN 978-2-8327-0605-3

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CONTENTS
FOREWORD . 9
INTRODUCTION . 11
1 Scope . 12
2 Normative references . 13
3 Terms, definitions, symbols and units . 13
3.1 General . 13
3.2 General terminology . 14
3.3 Units . 14
3.4 Terms, definitions, symbols and units . 15
3.4.1 List of terms, definitions, symbols and units . 15
3.4.2 Subscripts and symbols . 15
3.4.3 Geometric terms . 16
3.4.4 Physical quantities and properties . 19
3.4.5 Discharge, velocity, speed terms and time symbols . 19
3.4.6 Pressure terms . 20
3.4.7 Specific energy terms . 20
3.4.8 Height and head terms . 21
3.4.9 Power and torque terms . 22
3.4.10 General terms relating to fluctuating quantities . 23
3.4.11 Fluid dynamic and scaling terms . 25
3.4.12 Dimensionless terms . 25
3.5 Abbreviated terms . 26
4 Hydraulic transient basics . 27
4.1 Elements related to hydraulic transient . 27
4.1.1 General . 27
4.1.2 Waterways system components . 27
4.1.3 Equipment . 31
4.1.4 Hydraulic machine . 35
4.1.5 Electro-mechanical equipment . 48
4.1.6 Other devices . 49
4.1.7 Opening and closing laws of flow control devices . 50
4.2 Hydraulic transient phenomena . 51
4.2.1 Waterhammer . 51
4.2.2 Mass oscillation . 51
4.2.3 Hydraulic machine transients . 51
4.2.4 Counter thrust and unit uplift . 54
4.3 Relevant hydraulic transient constant . 54
4.3.1 Water starting time T . 54
w
4.3.2 Unit acceleration constant T . 55
a
4.3.3 Small-signal stability indicator . 55
4.3.4 Penstock reflection time T . 55
r
4.3.5 Period of mass oscillations T . 56
mo
4.3.6 Thoma critical cross sections A . 56
Th
4.3.7 Ratio between surge tanks . 57
4.4 Types of transient load cases . 57
4.4.1 General . 57
4.4.2 Normal load cases (NOR) . 57
4.4.3 Exceptional load cases (EXC) . 59
4.4.4 Catastrophic load cases (C) . 60
4.4.5 Combination of load cases (CO) . 60
4.5 Depths of transient analysis at different project stages . 61
4.5.1 General . 61
4.5.2 New power plants . 61
4.5.3 Plant modification projects . 62
4.6 Limitations and exclusions of the specifications . 63
4.6.1 General . 63
4.6.2 Two phase flow. 64
4.6.3 Cavitation . 64
4.6.4 Water column separation . 64
4.6.5 Free surface flows . 64
4.6.6 Turbine governor . 64
4.6.7 Countries with extremely low temperatures . 65
4.6.8 Fluid structure interactions . 65
4.6.9 Unsteady friction . 65
4.6.10 Viscoelasticity . 65
4.6.11 Flow induced pressure fluctuations . 65
4.6.12 Variable-speed machines . 66
5 Modelling and computation methods . 66
5.1 Governing equations . 66
5.1.1 General . 66
5.1.2 Friction factor . 66
5.1.3 Wave speed . 68
5.2 Solution methods . 71
5.2.1 Analytical methods . 71
5.2.2 Graphical method . 73
5.2.3 Method of characteristics . 75
5.2.4 Finite difference method . 77
5.2.5 Remarks to the solution methods . 78
5.3 Wave speed adaptations and accuracy . 79
5.4 Hydraulic components modelling . 81
5.4.1 General . 81
5.4.2 Elastic column model of pipes . 81
5.4.3 Rigid water column model . 82
5.4.4 Equivalent pipes . 82
5.4.5 Singular head losses . 83
5.4.6 Valves . 84
5.4.7 Surge tanks . 85
5.4.8 Hydraulic turbines . 89
5.5 Limitations of the models for different purposes . 94
5.6 Validation (Performance) of transient analysis software . 96
6 Hydraulic transient calculation . 97
6.1 General . 97
6.2 Transient load case definition and computation methodology . 98
6.2.1 Transient load case definition . 98
6.2.2 Methodology for transient load case computation . 99
6.3 Short list of load cases . 109
6.3.1 General . 109
6.3.2 Normal load cases . 109
6.3.3 Exceptional load cases . 112
6.3.4 Catastrophic load case . 116
6.3.5 Load case combination . 117
6.4 Identification of load cases by critical values . 120
6.4.1 General . 120
6.4.2 Overspeed . 120
6.4.3 Water static pressure . 121
6.4.4 Water levels . 123
6.4.5 Additional values . 124
6.5 Identification of load cases by project stage . 124
6.6 Identification of load cases by machine type . 126
6.6.1 General . 126
6.6.2 Francis turbine . 128
6.6.3 Pelton turbine . 128
6.6.4 Kaplan turbine . 129
6.6.5 Reversible pump-turbine and pump . 129
6.7 Identification of load cases by plant layout . 129
6.7.1 General . 129
6.7.2 Single unit, single penstock . 130
6.7.3 Single unit, single penstock with surge shafts . 130
6.7.4 Multiple units, shared penstock, surge shafts and waterways . 130
6.7.5 Multiple units on same shaft . 130
6.7.6 "Complex plant" . 130
6.7.7 List of load cases by plant layout . 130
6.8 Identification of load cases corresponding to field tests or commissioning . 132
6.8.1 Plant first filling and reservoir maintenance . 132
6.8.2 Plant commissioning . 132
6.9 Example of how to build a table of load cases . 133
7 Prototype hydraulic transient test . 134
7.1 General . 134
7.2 Measurement quantities . 134
7.3 Measurement techniques . 135
7.4 Frequency range selection . 137
7.4.1 Calibration of the 1D model . 137
7.4.2 Frequency treatment and preparation of measured data for guaranteed
comparison . 138
7.4.3 Statistical treatment of measured data for guaranteed comparison . 139
7.4.4 Comparison with guarantees . 139
7.5 Uncertainties in measurements and presentation of results . 140
7.5.1 Definition of error . 140
7.5.2 Definition of uncertainty . 140
7.5.3 Types of error . 140
7.5.4 Total uncertainty . 142
7.6 Recommended tests . 142
7.6.1 General . 142
7.6.2 Site conditions and transposition of results . 143
7.6.3 Field test program and test protocol . 144
7.7 Field measurement report . 144
8 Comparison between site measurements and calculations . 145
8.1 General . 145
8.2 Direct comparison of transient results with guaranteed values . 145
8.3 Comparison of transient tests with numerical simulations results . 146
8.3.1 General . 146
8.3.2 Approach to calibrate and validate the model and determine numerical
model uncertainty . 146
8.3.3 Adjustment of the numerical transient model . 148
8.4 Considerations of the fluctuating quantities . 148
8.5 Adjustment of unit during field tests . 149
8.6 Comparison of simulated results with expected or guaranteed values . 150
8.7 Updated calculation report . 150
Annex A (informative) Example of load cases for different plant layouts and project
stages . 151
A.1 Disclaimer . 151
A.2 List of examples . 151
A.3 Francis turbine with PRV at offer phase . 152
A.3.1 Layout description . 152
A.3.2 Operating range definition . 152
A.3.3 Table of load cases . 153
A.4 Pelton turbine with a surge tank at feasibility phase . 160
A.4.1 Layout description . 160
A.4.2 Operating range definition . 160
A.4.3 Table of load cases . 161
A.5 Kaplan turbine at execution phase . 164
A.5.1 Layout description . 164
A.5.2 Operating range definition . 164
A.5.3 Table of load cases . 165
A.6 Bulb turbine at offer phase . 169
A.6.1 Layout description . 169
A.6.2 Operating range definition . 169
A.6.3 Table of load cases . 170
A.7 Reversible Francis pump-turbine at feasibility phase . 173
A.7.1 Layout description . 173
A.7.2 Operating range definition . 173
A.7.3 Table of load cases . 174
A.8 Ternary unit at execution phase . 182
A.8.1 Layout description . 182
A.8.2 Operating range definition . 182
A.8.3 Table of load cases . 183
Annex B (informative) Optional model tests and CFD analysis . 184
B.1 General . 184
B.2 Hydraulic machine characteristics . 184
B.3 Advanced valves characteristics . 188
B.4 Surge tanks . 188
B.4.1 General . 188
B.4.2 Steady state flow measurement . 188
B.4.3 Transient flow measurements . 189
B.5 Open channel flow . 190
B.6 Intakes and outlets. 192
B.7 Manifold model test . 193
B.8 Integrated model test of hydropower generating system . 194
B.8.1 Basic methodology and components of the integrated model . 194
B.8.2 Similarity law and model scale . 195
Annex C (informative) Examples of sample calculation of the value to be compared to
the guarantee . 197
Bibliography . 200

Figure 3-1 – Guide vane opening and angle . 17
Figure 3-2 – Reference diameter and bucket width . 18
Figure 3-3 – Flux diagram for power and discharge. 23
Figure 3-4 – Illustration of some definitions related to oscillating quantities . 25
Figure 4-1 – General schematic of a typical hydropower plant arrangement . 27
Figure 4-2 – Possible configurations of surge tanks – Sketches 1 to 4 . 29
Figure 4-3 – Schematic of a simple pressurised air chamber . 30
Figure 4-4 – Common valve designs . 32
Figure 4-5 – Schematic of sealing ring arrangement (left) and corresponding loss
characteristic of valve with sealing ring between 89,9 ° and 90 ° . 33
Figure 4-6 – Schematic of spherical valve with pressure balancing bypass . 34
Figure 4-7 – Hydraulic machine application diagram . 35
Figure 4-8 – Schematic view of water jet between nozzle and bucket . 36
Figure 4-9 – Schematic view of 6-jet vertical Pelton-type turbine. 36
Figure 4-10 – Schematic view of Pelton-type turbine runner and bucket . 37
Figure 4-11 – Schematic view of Pelton-type turbine deflector . 37
Figure 4-12 – Schematic view of Francis-type turbine for runner and spiral inlet . 38
Figure 4-13 – Francis typical discharge characteristics; lines of constant guide vane
opening (solid) and runaway curve (dashed) . 38
Figure 4-14 – Deriaz sketch and model runner (3 of 6 runner blades removed) . 39
Figure 4-15 – Deriaz typical discharge characteristics – lines of constant guide vane
opening (solid) and runaway curve (dashed) . 39
Figure 4-16 – Schematic view of Kaplan-type turbine . 40
Figure 4-17 – Kaplan typical discharge characteristics – lines of constant guide vane
opening (solid) and runaway curve (dashed) . 41
Figure 4-18 – Schematic view of a Saxo-type turbine . 42
Figure 4-19 – Schematic layout of a bulb (left) and pit (right) turbine . 42
Figure 4-20 – Schematic layout of a S-downstream (left) and S-upstream (right) turbine . 43
Figure 4-21 – Schematic view of (radial) pump-turbine . 43
Figure 4-22 – Pump-turbine typical 4-quadrant characteristics for a single-regulated
(radial) pump-turbine . 44
Figure 4-23 – Multi-stage pump (left), and 4-quadrant pump characteristics (right) . 45
Figure 4-24 – Schematic view of ternary set with Pelton type turbine and storage pump . 46
Figure 4-25 – Relationship between servomotor stroke and distributor opening angle . 46
Figure 4-26 – Schematic arrangement of PRV oil-hydraulically linked to hydraulic
machine . 47
Figure 4-27 – Schematic view of pressure relief valves . 48
Figure 4-28 – Example of ring gate valve discharge characteristics . 49
Figure 4-29 – Possible mode changes for pump-turbine . 52
Figure 5-1 – Nikuradse-Moody diagram for Darcy-Weisbach friction coefficient . 67
Figure 5-2 – Pressurized pipe subject to downstream flow control device closure
inducing waterhammer pressure wave . 71
Figure 5-3 – Pressurized pipe subject to downstream flow control device instantaneous
closure inducing direct waterhammer with steep pressure wave front . 72
Figure 5-4 – Pressurized pipe subject to downstream flow control device with closure
time equal to 2 × L/a inducing reduced waterhammer with linear pressure wave front in
case of linear discharge reduction over time . 72
Figure 5-5 – Negative waterhammer pressure wave downstream of a closing flow
control device . 73
Figure 5-6 – Set of characteristic line in [H-Q] plane (top) linked to characteristic line in
the [x-t] plane (bottom) for progressive waves and retrograde waves . 74
Figure 5-7 – Simple hydraulic system with upper reservoir, pressurized pipe and
downstream end valve considered for waterhammer calculation with graphical method. 74
Figure 5-8 – Head versus discharge diagram obtained from waterhammer calculation
of a valve closing in time of T = 4 × L/a using graphical method (left) and
closure
corresponding time domain evolution of the valve discharge and head (right) . 75
Figure 5-9 – Characteristic lines in the x-t plane . 75
Figure 5-10 – Wave speed adaptation of pipes . 80
Figure 5-11 – Schematic sketch of a pipe element . 81
Figure 5-12 – Equivalent pipe . 83
Figure 5-13 – Schematic sketch of a valve . 84
Figure 5-14 – Schematic representation of a free surface surge tank . 85
Figure 5-15 – Example of computation of a surge tank’s hydraulic inductance . 87
Figure 5-16 – Schematic sketch of a pressurized air chamber (air cushion surge
chamber) . 88
Figure 5-17 – Typical runner profiles of a Francis turbine depending on specific speed . 90
Figure 5-18 – Typical examples of performance characteristics for Francis turbines,
reversible Francis pump-turbines, Pelton turbines and axial turbines . 92
Figure 5-19 – Francis turbine reference diameter D and corresponding elevation to be
s
considered for draft tube pressure calculation . 93
Figure 6-1 – Sketch of typical load cases . 98
Figure 6-2 – Sketch of water level boundary conditions. 99
Figure 6-3 – Typical turbine operating range head versus discharge . 101
Figure 6-4 – Typical pump operating range head versus discharge . 102
Figure 6-5 – Example of a closing law of a reversible Francis unit in pump mode. 103
Figure 6-6 – Example of a typical guide vane closing law with two slopes . 104
Figure 6-7 – Example of guide vane closing law effect on overspeed and overpressure . 105
Figure 6-8 – Example of closing and opening laws of guide vanes and MIV . 106
Figure 6-9 – Example of the simultaneous closing sequence of blades, guide vanes
and downstream gate for a Bulb unit subjected to a load rejection . 107
Figure 6-10 – Example of final conditions of a transient computation case for
overpressure (top figure) and pressure drop (bottom figure) . 108
Figure 7-1 – Checking of instrument . 136
Figure 7-2 – Illustration of 97 % confidence level . 139
Figure 8-1 – Comparison between measured signal and simulated signal . 147
Figure 8-2 – Graph illustrating raw data and filtered data . 148
Figure 8-3 – Determination of the fluctuating quantity Y, the absolute difference
between the filtered data and the average data . 149
Figure A.1 – Hydraulic layout including Francis turbines with PRV . 152
Figure A.2 – Definition of Francis turbine operating points . 153
Figure A.3 – Hydraulic layout including Pelton turbines with a surge tank . 160
Figure A.4 – Definition of Pelton turbine operating points . 161
Figure A.5 – Hydraulic layout including Kaplan turbines . 164
Figure A.6 – Definition of Kaplan turbine operating points . 165
Figure A.7 – Hydraulic layout including Bulb turbines . 169
Figure A.8 – Definition of Bulb turbine operating points . 170
Figure A.9 – Hydraulic layout including reversible Francis pump-turbines . 173
Figure A.10 – Definition of Francis turbine operating points . 174
Figure A.11 – Definition of typical Francis pump-turbine operating points in pump mode . 174
Figure A.12 – Hydraulic layout including ternary unit . 182
Figure A.13 – Definition of Pelton turbine operating points . 183
Figure A.14 – Definition of pump operating points . 183
Figure B.1 – Comparison of pump-turbine four quadrant characteristics between high
sigma and sigma plant . 185
Figure B.2 – Example of influence of asynchronous opening of two guide vanes on the
pump-turbine hill chart (dashed lines are the original more pronounced S-shape
characteristic, solid lines are the new less pronounced S-shape characteristic
assuming two guide vanes operating asynchronously) . 186
Figure B.3 – Example of pump-turbine start-up failing to synchronise due to S-shape
instability . 187
Figure B.4 – Example of pump-turbine start-up with successful synchronisation and
loading with partially open main inlet valve . 187
Figure B.5 – Example of flow streamlines through a butterfly valve computed from CFD . 188
Figure B.6 – Example of flow physical model test of surge tank and related comparison
of CFD computation results with streamlines for surge tank inflow conditions . 189
Figure B.7 – Example of downstream surge tank transient physical model test to
evaluate the impact of free surface waves, possible air admission and slugs and
shocks phenomena . 190
Figure B.8 – Example of free surface flow physical model tests developing in tailrace
tunnel and comparison of related CFD results of hydraulic jump at bifurcation . 191
Figure B.9 – Example of the comparison between site disjunction wave and reduced
scale model tests (1/35) . 192
Figure B.10 – Example of free surface flow physical model tests of intake and
development of free surface vortex for extreme flow conditions . 193
Figure B.11 – Example of physical model tests of manifold and identification of flow
separation using ink injection . 193
Figure B.12 – Photo and overall illustration of an integrated physical model of
hydropower generating system . 194
Figure B.13 – Operating trajectories as dynamic loops in the S-shaped region of
hydraulic machine . 195
Figure C.1 – Penstock pressure – Fluctuating quantity. 197
Figure C.2 – Penstock pressure – Averaged measured value and simulation . 197
Figure C.3 – Draft tube pressure fluctuating quantity . 198
Figure C.4 – Draft tube pressure – Averaged measured value and simulation . 198

Table 5-1 – Pipe elasticity dA/(A·dp) depending on type of support for thin-walled pipes . 69
Table 5-2 – Pipe elasticity dA/(A·dp) depending on type of support for thick-walled
pipes . 69
Table 5-3 – Material properties of common materials in hydropower . 70
Table 5-4 – Typical wave speed in different pipe arrangements . 70
Table 5-5 – Example of wave speed adaptation for 3 different pipes . 81
Table 5-6 – Definition of head loss coefficients for valves . 85
Table 5-7 – Recommended minimum modelling complexity for different project stages . 94
Table 6-1 – Locations of interest and corresponding critical value to be assessed
through numerical simulations . 108
Table 6-2 – Load cases by critical values – Overspeed . 121
Table 6-3 – Load cases by critical values – Static pressure rise . 122
Table 6-4 – Load cases by critical values – Static pressure drop . 123
Table 6-5 – Load cases by critical values – Water levels. 123
Table 6-6 – Normal load cases . 125
Table 6-7 – Exceptional load cases. 125
Table 6-8 – Catastrophic load cases . 125
Table 6-9 – Combined load cases . 126
Table 6-10 – Normal load cases. 127
Table 6-11 – Exceptional load cases . 127
Table 6-12 – Catastrophic load cases . 127
Table 6-13 – Combined load cases . 128
Table 6-14 – Normal load cases. 131
Table 6-15 – Exceptional load cases . 131
Table 6-16 – Catastrophic load cases . 131
Table 6-17 – Combined load cases . 132
Table 8-1 – Typical model uncertainty (MU %) . 147
Table B.1 – Similarity law and model scale of integrated model test of hydropower
generating system . 196

INTERNATIONAL ELECTROTECHNICAL COMMISSION
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Hydraulic turbines, storage pumps and pump-turbines -
Hydraulic transient analysis, design considerations and testing

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