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BSI PD IEC TS 62882:2020

BSI PD IEC TS 62882:2020

$215.11

Hydraulic machines. Francis turbine pressure fluctuation transposition

Published By Publication Date Number of Pages
BSI 2020 156
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IEC 62882, which is a Technical Specification, provides pressure fluctuation transposition methods for Francis turbines and pump-turbines operating as turbines, including:

  • description of pressure fluctuations, the phenomena causing them and the related problems;

  • characterization of the phenomena covered by this document, including but not limited to inter-blade vortices, draft tube vortices rope and rotor-stator interaction;

  • demonstration that both operating conditions and Thoma numbers (cavitation conditions) are primary parameters influencing pressure fluctuations;

  • recommendation of ways to measure and analyse pressure fluctuations;

  • identification of potential resonances in test rigs and prototypes;

  • identification of methods, to transpose the measurement results from model to prototype or provide ways to predict pressure fluctuations in prototypes based on statistics or experience;

  • recommendation of a data acquisition system, including the type and mounting position of model and prototype transducers and to define the similitude condition between model and prototype;

  • presentation of pressure fluctuation measurements comparing the model turbine and the corresponding prototype;

  • discussion of parameters used for the transposition from model to prototype, for example, the peak to peak value at 97 % confidence interval, the RMS value or the standard deviation in the time domain and the relation of main frequency and the rotational frequency in the frequency domain obtained by FFT;

  • discussion of the uncertainty of the pressure fluctuation transposition from model to prototype;

  • discussion of factors which influence the transposition, including those which cannot be simulated on the model test rig such as waterway system and mechanical system;

  • establishment of the transposition methods for different types of pressure fluctuations;

  • suggestion of possible methods for mitigating pressure fluctuation;

  • definition of the limitations of the specification.

This document is limited to normal operation conditions. Hydraulic stability phenomena related to von Karman vortices, transients, runaway speed and speed no load are excluded from this document.

This document provides means to identify potential resonances in model test rigs and prototype turbines. Scaling-up resonance conditions are not treated in this document. When resonance exists, the transposition methods identified in this document do not apply. Under these conditions, the relationship between model and prototype pressure fluctuations cannot be determined.

This document is concerned neither with the structural details of the machines nor the mechanical properties of their components, so long as these characteristics do not affect model pressure fluctuations or the relationship between model and prototype pressure fluctuations.

PDF Catalog

PDF Pages PDF Title
2 undefined
4 CONTENTS
11 FOREWORD
13 INTRODUCTION
14 1 Scope
15 2 Normative references
3 Terms, definitions, symbols and units
3.1 General terms and definitions
3.2 Units
16 3.3 Overview of the terms, definitions, symbols and units used in this document
17 3.3.1 Subscripts and symbols
18 3.3.2 Geometric terms and definitions
Figure 1 – Reference diameter of Francis turbine
19 3.3.3 Physical quantities and properties terms and definitions
3.3.4 Discharge, velocity and speed terms and definitions
Figures
20 3.3.5 Pressure terms and definitions
3.3.6 Specific energy terms and definitions
21 3.3.7 Height and head terms and definitions
Figure 2 – Reference level of the Francis turbine
22 3.3.8 Power and torque terms and definitions
Figure 3 – Flux diagram for power and discharge
23 3.3.9 Efficiency terms and definitions
3.3.10 General terms and definitions relating to fluctuating quantities
25 Figure 4 – Illustration of some definitions related to fluctuating quantities
26 3.3.11 Fluid dynamic and scaling terms and definitions
3.3.12 Dimensionless terms and definitions
27 4 Description of pressure fluctuation phenomena
4.1 General
29 Tables
Table 1 – Pressure fluctuation overview matrix
32 4.2 Pressure fluctuations overview
Figure 5 – Discharge range for the various fluctuation modes
33 Figure 6 – Efficiency hill chart with pictures of swirling flow
34 4.3 General description of draft tube flow in Francis turbines
Figure 7 – Example of a waterfall diagram of pressure amplitudes measured in the draft tube cone
35 Figure 8 – Velocity triangles at inlet and outlet of the runner blade
36 4.4 Detailed description of pressure fluctuation phenomena
4.4.1 Mode 1: Pressure fluctuation in high load
Figure 9 – Influence of the discharge on the circumferential component of the absolute velocity
37 4.4.2 Mode 2: Pressure fluctuation in best operation range
4.4.3 Mode 3: Pressure fluctuation in upper part load
38 4.4.4 Mode 4: Pressure fluctuation in part load
Figure 10 – Elliptical vortex rope precessing in the draft tube cone at upper part load
39 Figure 11 – Decomposition between the synchronous and asynchronous component of part load draft tube pressure fluctuations
40 4.4.5 Mode 5: Pressure fluctuation in deep part load
Figure 12 – Example of inter-blade vortex
41 4.4.6 Modes 6.a and 6.b: Rotor-stator interaction (RSI) pressure fluctuation
Figure 13 – Modulation process between runner blade flow field and guide vanes flow field
42 Figure 14 – Diametrical modes shapes representation according to k values
43 5 Specifications of pressure fluctuation measurement and analysis
5.1 General
5.1.1 Overview
5.1.2 Purpose of the measurements
44 5.1.3 Procedures and parameters to record
45 5.1.4 Locations of pressure fluctuation test transducers
Figure 15 – Suggested locations of pressure transducers
46 5.1.5 Data acquisition for pressure fluctuation measurements
Table 2 – Locations of pressure fluctuations transducers
47 5.1.6 Transducers and calibration
5.2 Pressure fluctuation on a model turbine
5.2.1 General
Figure 16 – Turbine hill-chart with exploration paths
48 5.2.2 Homology and limitations
5.2.3 Detailed procedures
49 Figure 17 – Schematic of the axial aeration device
50 5.3 Special requirements and information for a prototype turbine
5.3.1 General
5.3.2 Source of information
5.3.3 Important aspects
51 5.4 Analysis, presentation and interpretation of results
5.4.1 General
5.4.2 Time-domain analysis
Figure 18 – Schematic arrangement for pressure fluctuation transducers
52 5.4.3 Frequency-domain analysis
5.4.4 Non-dimensional frequency and pressure
5.4.5 Presentation and interpretation of pressure fluctuations
53 6 Identification of potential resonances in test rig and prototype
6.1 General
Figure 19 – Typical plot showing pressure fluctuation coefficient versus relative discharge
54 Figure 20 – Elementary hydroacoustic oscillator
55 6.2 Identify resonance in test rig
6.3 Possible resonance and self-excited pressure fluctuation in prototype
6.3.1 General
6.3.2 Draft tube vortex related resonances and self-excited pressure fluctuation in prototype
56 Figure 21 – Part load vortex rope in the draft tube and its fluctuation frequency range and corresponding risk of resonance with the generator local mode of oscillation valid for both Fgrid = 50 Hz and Fgrid = 60 Hz
57 6.3.3 Rotor-stator interaction (RSI) related resonance
6.3.4 Resonance with fluctuation modes not treated in this document
58 7 Transposition method and procedure
7.1 General
7.2 Parameters influencing transposition
7.2.1 Model test head
7.2.2 Thoma number
59 7.2.3 Froude number
7.3 Relevant quantities for transposition
7.3.1 Fluctuation frequency
7.3.2 Fluctuation amplitude
7.4 Transposable types of fluctuations
Figure 22 – Waterfall diagram of the pressure fluctuations as function of the frequency and Froude number for a given Thoma number
60 7.5 Statistical analysis of model and prototype transposition accuracy
Table 3 – Accuracy for transposition of fluctuation amplitude in draft tube cone
Table 4 – Accuracy for transposition of fluctuation amplitude in vaneless zone
61 8 Mitigations
8.1 Draft tube vortex phenomena
8.1.1 General
8.1.2 Draft tube fins
Table 5 – Accuracy for transposition of fluctuation amplitude in spiral case
62 8.1.3 Draft tube with a central column
Figure 23 – Example of fins in the draft tube and influence on the pressure fluctuations
63 8.1.4 Air admission
Figure 24 – Example of the draft tube with central column extension
Figure 25 – Typical runner cone extensions used for reducing draft tube pressure fluctuations
64 8.1.5 AVR or PSS parameter tuning
Figure 26 – Central and peripheral air admission locations for draft tube pressure fluctuations on a radial flow turbine
Figure 27 – Central air admission
65 8.2 Runner inter-blade vortex
8.3 Blade interaction
8.4 Operation restriction
66 Annexes
Annex A (informative) Example of pressure fluctuation records
68 Figure A.1 – Example 1: a case corresponding to mode 1 (a limited high load)
70 Figure A.2 – Example 2: a case corresponding to mode 1 (a large overload)
72 Figure A.3 – Example 3: a case corresponding to mode 2
74 Figure A.4 – Example 4 : a case corresponding to mode 3
76 Figure A.5 – Example 5 : a case corresponding to mode 4.a and 4.b
78 Figure A.6 – Example 6: a case corresponding to mode 4.a and 4.b
80 Figure A.7 – Example 7: a case corresponding to mode 4.c
82 Figure A.8 – Example 8: a case corresponding to mode 5.b
84 Figure A.9 – Example 9: a case corresponding to mode 6.a
85 Annex B (informative) Typical pressure fluctuation transducers parameters for model test
86 Annex C (informative) Pressure transducer dynamic calibration
C.1 Fast valve opening method
C.2 Rotating valve method
Figure C.1 – Pressure transducer dynamic calibration schematic diagram with fast open valve method
87 C.3 Electrical spark method
Figure C.2 – Pressure transducer dynamic calibration with rotating valve method
Figure C.3 – Spark plug used as to generate an impulse excitation in water for pressure transducer dynamic calibration
88 Annex D (informative) Proposed remote pressure measurement fluctuation correction
D.1 General
D.2 Correction method theory
89 D.3 Measuring and estimating tube frequency response
90 Figure D.1 – Typical results obtained by shutting off drainage valve
Table D.1 –and calculated for p1 to p4
91 D.4 Pressure fluctuation correction
Table D.2 – Estimated frequencies based on tubing mechanical characteristics
92 Figure D.2 – Signal and spectrum of four remote sensors and one local sensor
Table D.3 – Peak-to-peak value on the raw signals
Table D.4 – Wave speed and damping ratio
93 Figure D.3 – Signal and spectrum of four remote sensors (corrected) and one local sensor
94 D.5 Limitations
Table D.5 – Peak-to-peak value on the corrected signals
95 Annex E (informative) Forced response analysis for Francis turbines operating in part load conditions
E.1 General
E.2 Systematic methodology based on detailed modelling of hydroelectric power plant
E.2.1 Description of the test case
96 E.2.2 Modelling of the hydraulic power plant
Figure E.1 – SIMSEN model of the test case
Figure E.2 – Performance hill chart of the Francis turbine for different guide vane openings
Table E.1 – Francis turbine parameters
98 Figure E.3 – Elementary hydraulic pipe of length dx and its equivalent circuit
99 E.2.3 Forced response analysis of the test case
Figure E.4 – Forced response for a = 50 m/s (left) and a = 60 m/s (right)
100 Figure E.5 – Forced response for a = 70 m/s (left) and a = 80 m/s (right)
Figure E.6 – Forced response for a = 90 m/s (left) and a = 100 m/s (right)
Figure E.7 – Damping and eigenfrequency for a = 50 m/s (left) and a = 60 m/s (right)
Figure E.8 – Damping and eigenfrequency for a = 70 m/s (left) and a = 80 m/s (right)
101 Figure E.9 – Damping and eigenfrequency for a = 90 m/s (left) and a = 100 m/s (right)
Figure E.10 – Eigenmode for a = 50 m/s and eigenfrequency f = 4,18 Hz
Figure E.11 – Eigenmode for a = 50 m/s and eigenfrequency f = 3,67 Hz
Figure E.12 – Eigenmode for a = 100 m/s and eigenfrequency f = 2,61 Hz
102 E.3 Simplified approach based on the hydroacoustic properties of the hydraulic system
E.3.1 General
E.3.2 Cavitating draft tube first natural frequency
Figure E.13 – Draft tube modelled with cavitation compliance and draft tube inductance
103 E.3.3 Hydraulic circuit natural frequencies
Figure E.14 – Simplified model of a cavitation draft tube connected to a tailrace pipe composed by cavitation compliance of the draft tube and downstream inductance of the tailrace pipe
104 E.3.4 Example of applications
Figure E.15 – Hydraulic system modelled by an equivalent pipe and corresponding modes shapes for the first and second natural frequencies
105 Figure E.16 – Hydraulic systems 1, 2 and 3
Table E.2 – Parameters of the hydraulic systems 1, 2 and 3
106 Table E.3 – Parameters of the equivalent pipe of the hydraulic system 1
107 Table E.4 – Estimation of the natural frequencies f0 to f6 of the hydraulic system 1 based on Formulae (E.9) and (E.11) and comparison with results obtained with eigenvalue calculation and corresponding errors
Table E.5 – Parameters of the equivalent pipe of the hydraulic system 2
Table E.6 – Estimation of the natural frequencies f0 to f6 of the hydraulic system 2 based on Formulae (E.10) and (E.11) and comparison with results obtained with eigenvalue calculation and corresponding errors
108 Table E.7 – Parameters of the equivalent pipe of the hydraulic system 3
109 E.3.5 Limitations of the methodology
Table E.8 – Estimation of the natural frequencies f0 to f6 of the hydraulic system 3 based on Formulae (E.10) and (E.11) and comparison with results obtained with eigenvalue calculation and corresponding errors
Table E.9 – Pressure mode shape obtained by eigenvalue and eigenvector calculation for the three first natural frequencies f1, f2 and f3 of the hydraulic systems 1 and 2
110 Annex F (informative) Influence of Thoma number on pressure fluctuation
Figure F.1 – Influence of Thoma number on pressure fluctuation
111 Figure F.2 – Example of waterfall diagram of the pressure fluctuations as function of the frequency and Thoma number
112 Annex G (informative) Transposition of synchronous pressure fluctuations from model to prototype for Francis turbines operating at off-design conditions
G.1 General
G.1.1 Overview
Figure G.1 – Peak-to-peak value of pressure fluctuations as a function of the discharge factor measured on the model and the corresponding prototype
113 Figure G.2 – Layout of EPFL test rig PF3 1-D hydroacoustic model
Figure G.3 – Electrical T-shaped representation of the cavitation vortex rope developing in Francis turbine draft tube in part load conditions
115 Figure G.4 – Excitation system and 3D cut-view of the rotating valve
116 Figure G.5 – Strouhal number of the precession frequency as a function of the swirl number computed with Formula (G.6)
117 Figure G.6 – Strouhal number of the first eigen frequency of the test rig as a function of swirl number (a), the wave speed in the draft tube determined in the 1-D model (b)
118 Figure G.7 – Predicted values of precession frequency and first eigenfrequency at the prototype scale as a function of the output power of the generating unit
119 Figure G.8 – Comparison between observed and predicted values of the precession frequency frope and the first eigenfrequency f0 of a 444 MW hydropower unit (HYPERBOLE project test case)
120 Figure G.9 – Hill chart comparing the measured and the predicted resonance conditions assuming a constant pressure value in the draft tube cone of the prototype
121 Annex H (informative) Statistical analysis of pressure fluctuation data
H.1 Normalizing step for the comparison of data
122 Figure H.1 – Pressure fluctuations versus discharge factor
Figure H.2 – Normalized discharge of pressure fluctuations
Figure H.3 – Normalized pressure amplitude of pressure fluctuations
Figure H.4 – Comparison of pressure fluctuations of model and prototype
123 H.2 Collected data
H.3 Draft tube zone phenomena
Figure H.5 – Set of pressure fluctuation of models and prototypes for draft tube analysis
Table H.1 – World hydropower plant references
124 Figure H.6 – Difference between pressure fluctuations between the model and the prototype
Figure H.7 – Standard deviation of difference of pressure fluctuation
125 Figure H.8 – Transposition accuracy for draft tube cone
128 H.4 Vaneless zone phenomena
Figure H.9 – Transposition of each power plant test case for the draft tube cone
129 Figure H.10 – Set of pressure fluctuation of models and prototypes for vaneless zone analysis
Figure H.11 – Difference between pressure fluctuations between the model and the prototype
130 Figure H.12 – Standard deviation of difference of pressure fluctuation
Figure H.13 – Transposition accuracy for vaneless zone
131 Figure H.14 – Transposition of each power plant test case for vaneless zone
132 H.5 Spiral case phenomena
Figure H.15 – Set of pressure fluctuation of models and prototypes for spiral case analysis
133 Figure H.16 – Difference between pressure fluctuations between the model and the prototype
Figure H.17 – Standard deviation of difference of pressure fluctuation
134 Figure H.18 – Transposition accuracy for spiral case
135 Figure H.19 – Transposition of each power plant test cases for spiral case
136 Annex J (informative) Gathering worldwide pressure fluctuation data
J.1 Chinese test cases
137 J.2 France test case
Figure J.1 – Comparison of pressure fluctuations on the draft tube for 10 Chinese model and prototype references
138 Figure J.2 – Comparison of pressure fluctuations on the draft tube for one France model and prototype reference
Figure J.3 – Comparison of pressure fluctuations on the spiral case for one France model and prototype reference
139 J.3 Norway test case
Figure J.4 – Comparison of pressure fluctuations on the draft tube for one Norway model and prototype reference
140 Bibliography

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BSI PD IEC TS 62882:2020
$215.11