Vibration and stability problems in hydro generators

690
VIBRATION AND STABILITY PROBLEMS
MET IN NEW, OLD AND REFURBISHED
HYDRO GENERATORS:
ROOT CAUSES AND CONSEQUENCES
WORKING GROUP
A1.36
JULY 2017

Members
J. Ahtiainen, Convenor FI A. Tétreault, Secretary CA
G. Aalvik NO J. Balauntescu RP
M. Bruintjies ZA P. Eilebrechtr DE
J. Kangas FI T. Karlsson SE
C. Leiva AR G. Lopez AR
M. Maerke CH A. Merkhouf CA
Z. Milojkovic HR F. Neumayer AT
J. Rocha BR C. Roth AR
J Studir HR R. Tremblay CA
P. Wiehe AU E. Zulovic AU
WT Stokes UK J. Borrajo AR
WG A1.36
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VIBRATION AND STABILITY
PROBLEMS MET IN NEW, OLD
AND REFURBISHED HYDRO
GENERATORS: ROOT CAUSES
AND CONSEQUENCES
ISBN : 978-2-85873-393-4

VIBRATION AND STABILITY PROBLEMS MET IN NEW, OLD AND REFURBISHED HYDRO GENERATORS: ROOT
CAUSES AND CONSEQUENCES
3
EXECUTIVE SUMMARY
Non-optimal original design and/or errors caused by improper erection work or degeneration of
generator construction can cause excessive dynamic and static forces in a generating unit.
In some cases these forces can be recognized as increased vibrations or only as excessive stress and
fatigue loading in construction which can in the long run generate cracks and/or deformations. In
many cases these deviations can cause damage and further unplanned outages of machines and the
need for repairs or major refurbishments outside scheduled refurbishment programs.
Examples of such deviations are:
• Air gap deviations around the circumference
• Deviations of mean air gap from design air gap
• Stator roundness as a percentage of design air gap
• Eccentricity as a percentage of design air gap
• Rotor roundness as a percentage of design air gap
• Some specific deformation forms (ellipticity, tri-angularity, quad-angularity) can also influence
the operation of the generating unit.
The generator design also has an influence on machine behaviour. Items such as the stator and rotor
winding configuration including the stator slot number/slot pitch, type and connection of the stator
winding (diamond/wave, number of parallel branches), damper winding (number of damper bars and
slot pitch), form of rotor pole shoe, skewed slots and/or damper bars and also rotor poles with non-
centered damper bars.
This technical brochure describes recommendations for vibration measurements, limit values and
guidelines for evaluation of the unit shaft line, generator stator and rotor roundness and other
construction parameters which are deemed to be acceptable for new and old generators. It is
assumed that a certain amount of continuous degradation is present when a generator is in operation
and new generator designs include sufficient margin for degradation to allow reaching the intended
life expectancy.
The frequency of some problems and fault cases has been studied in the survey and the survey also
presents some of the typical problems encountered in hydro machinery.
Some dynamic stability calculations are normally carried out to verify the expected dynamic behaviour
of a unit. This brochure contains recommendations for which components should be included in a
dynamic model in addition to the rotating inertias. It also suggests other additional calculations that
may be carried out in some cases.
Only vertical hydro generators with a rotor construction that includes a rotor rim are considered in this
survey.

4

5
Contents
EXECUTIVE SUMMARY ............................................................................................................................... 3
1. METHODOLOGY AND DESCRIPTION ......................................................................................... 7
1.1 METHODOLOGY................................................................................................................................................................ 7
1.2 STRUCTURE OF THE QUESTIONNAIRE........................................................................................................................... 7
1.3 QUESTIONNAIRE ANSWERS ........................................................................................................................................... 7
2. BACKGROUND ................................................................................................................................ 9
2.1 THEORY................................................................................................................................................................................. 9
2.1.1 International Standards for Vibrations................................................................................................................. 9
2.1.2 Causes of vibration:.................................................................................................................................................. 9
2.2 INTRODUCTION TO THE SURVEY CONDUCTED.......................................................................................................15
2.3 GENERAL INFORMATION...............................................................................................................................................15
2.4 VIBRATIONS, MEASUREMENTS, TESTING AND DEFINED LIMITS...........................................................................15
2.5 STUDY OF MACHINE CONSTRUCTION DEVIATIONS..............................................................................................17
2.6 VIBRATION FAULT EXPERIENCE.....................................................................................................................................19
2.7 STUDY OF NUMERICAL VERIFICATION OF STABILITY AND VIBRATIONS...........................................................21
2.8 FAULT CASE STUDY .........................................................................................................................................................22
2.9 FUTURE STANDARDS .......................................................................................................................................................22
3. CONCLUSION................................................................................................................................23
APPENDIX
A.1. GENERAL TERMS...............................................................................................................................................................27
A.2. SPECIFIC TERMS................................................................................................................................................................27
C.1. QUESTIONNAIRE - NORWAY .......................................................................................................................................33
C.2. QUESTIONNAIRE – GERMANY .....................................................................................................................................49
C.3. QUESTIONNAIRE – FINLAND.........................................................................................................................................60
C.4. QUESTIONNAIRE – FINLAND.........................................................................................................................................76
C.5. QUESTIONNAIRE – SWEDEN ........................................................................................................................................84
C.6. QUESTIONNAIRE – GERMANY .....................................................................................................................................95
C.7. QUESTIONNAIRE – ROMANIA ................................................................................................................................... 110
C.8. QUESTIONNAIRE – SWEDEN ..................................................................................................................................... 125
C.9. QUESTIONNAIRE – ARGENTINA................................................................................................................................ 135
QUESTIONNAIRE – AUSTRALIA............................................................................................................................. 151C.10.

6
Figures and Illustrations
Figure 1 - Calculated radial forces in a Kaplan turbine in nominal operation (blue curve) and with
three over speeds (up to maximum 135% of nominal speed)......................................................... 11
Figure 2 - Vertical hydro unit with bearings and magnetic stiffness (unbalanced magnetic pull)....... 12
Figure 3 - Campbell diagram ....................................................................................................... 14
Tables
Table 1 - Surveyed Fleet Size ...................................................................................................... 15
Table 2 Expert opinions on which vibrations should be measured / monitored / included in protection:
.................................................................................................................................................. 16
Table 3 Expert opinions on which suitable measurement units to be used for vibration measurements:
.................................................................................................................................................. 16
Table 4 Expert opinion on which frequency components are to be measured: ................................ 16
Table 5 The maximum allowable deviation in the airgap is given as the range of value of all the
answers received. Values are assumed to be measured statically (unit stopped and cold):............... 17
Table 6 The maximum allowed limits for the stator roundness parameters (as a % of air gap) for
hydro generators is given as the mean value of all the answers received:....................................... 18
Table 7 The maximum allowed limits for the rotor roundness parameters (as a % of air gap) for
hydro generators is given as the mean value of all the answers received:....................................... 18
Table 8 The following table lists the problems reported most frequently and the frequency of the
vibrations experienced as a multiplier of the speed of rotation N. ................................................... 19
Table 9 Failures experienced related to vibration and stability:....................................................... 20
Table 10 Maximum allowed limits for stator roundness parameters (% of air gap): ........................ 24
Table 11 Maximum allowed limits for rotor roundness parameters (% of air gap):.......................... 24
App Table A.1 Definition of general terms used in this TB .............................................................. 27
App Table A.2 Definition of technical terms used in this TB ............................................................ 27

7
1. METHODOLOGY AND DESCRIPTION
1.1 METHODOLOGY
In May 2012 CIGRÉ's Technical Committee approved the Terms of Reference for the Working Group
A1.36 "Vibration and Stability Problems Met in New, Old and Refurbished Hydro Generators, Root
Causes and Consequences."
Following CIGRÉ’s tradition a questionnaire was prepared and sent to all regular members, observers
and technical experts in 2013 to gather experts’ opinions and experiences with Vibration and Stability
Problems Met in New, Old and Refurbished Hydro Generators, Root Causes and Consequences.
Specific questions included tests for factory and on site qualifications.
1.2 STRUCTURE OF THE QUESTIONNAIRE
The questionnaire had eight (8) sections and the report has been structured similarly:
• Introduction;
• Definitions;
• General Information;
• Vibrations measurements, testing and define limits;
• Study of machine construction deviations;
• Vibration fault experience;
• Study of numerical verification of stability and vibrations;
• Fault case study.
1.3 QUESTIONNAIRE ANSWERS
The questionnaire was answered by 10 Respondents from Power Generation Utilities (Users) /
Consultants and Manufacturers (Suppliers) from 7 countries, as follows:
Argentina: 1
Australia: 1
Finland: 2
Germany: 2
Norway: 1
Romania: 1
Sweden: 2
The questionnaires were answered by seven utility owners/consultants and by three manufacturers.

8

9
2. BACKGROUND
2.1 THEORY
2.1.1 International Standards for Vibrations
Measurement of rotor vibrations is the most common way of evaluating the mechanical operation of
rotating machines and determining the condition of the machine. Measured vibrations do not directly
present the stresses of the critical machine parts, but it can be reasonably assumed that similar types
of machines have approximately the same level of vibration responses to the forces which have been
found to cause damages for the same machine group members. This can justify the use of vibration
levels as criteria for safe or unsafe operation of the machine. Acceptable levels of vibration for
different types of machines are usually determined by reference to internationally recognised
standards such as:
→ ISO 7919-5 Mechanical Vibration of non-reciprocating machines - Measurements on rotating shafts
and evaluation criteria - Part 5: Machine sets in hydraulic power generating and pumping plants:
In the present edition of standard ISO 7919-5 the maximum allowed shaft relative vibration
displacement is given as a function of speed of rotation. Further in ISO 7919-5 possible causes of
vibration or of change of vibration are divided into three categories:
• Mechanical causes such as incorrect shaft alignment, residual unbalance, frictional forces, oil-
film instability in guide bearing etc.
• Electrical causes like magnetic pull on rotor or non-uniform airgap.
• Hydraulic causes like flow through waterways, draft tube flow instabilities, cavitation and self-
excited vibration.
ISO 7919-5 gives guidelines for applying shaft vibration evaluation criteria, under normal operating
conditions. Any transients such as sudden shut-downs and trips of the unit are not considered in this
context as there is no database of vibration levels that might be expected during such transients,
although they can also cause significant problems for unit operation.
Criteria in ISO 7919-5 refer to values of relative displacement. Measured relative shaft vibration
doesn't give exact stresses of the bearing and its supporting structures. To determine absolute
displacement it is necessary that absolute vibration of the support frame be measured with seismic
transducers (ISO 10816-5). Because seismic transducers are in many cases not reliable enough at low
frequencies, other type of transducers must be considered after it has been confirmed that the
required frequency range is available. Rotor movement in bearings as well as bearing housing
movements depend on the stiffness of bearing brackets and bearings and their interrelationship [B18].
These data are needed to be able to estimate stresses in the bearing assembly.
→ ISO 10816-5 Mechanical Vibrations - Evaluation of machine vibration by measurements on non-
rotating parts - Part 5: Machine sets in hydraulic power generating and pumping plants:
In standard ISO 10816-5 vertical hydro units are divided into groups depending on whether the
bearing housing (upper bracket) is braced against the foundation or not.
2.1.2 Causes of vibration:
2.1.2.1 Shaft Unbalance:
The maximum allowed unbalanced force for different types of units is defined in standard: ISO 1940-
1: Mechanical vibration -- Balance quality requirements for rotors in a constant (rigid) state.
In standard ISO 1940-1 the balancing class is defined as the maximum permissible residual unbalance
given as [g*mm]. Permissible residual unbalance is proportional to the rotor mass.
Balance quality grade G6,3 is typically applied for hydro units.

10
2.1.2.2 Shaft Allignment
In a number of guidelines for hydro unit installations, recommendations are given for shaft alignment
verticality, straightness of the shaft line and the maximum run-out of shaft line when turning the
shaft.
Definition for straightness of the shaft line is very similar in most of the guidelines. In the survey the
following are identified:
• ETRA Japan: Guide of installation and inspection for hydroelectric machines in hydropower
stations
• CEATI Report: Hydroelectric Turbine-Generator Units Guide for Erection Tolerances and shaft
system alignment
• United States Department of Interior Bureau of Reclamation, Denver, Colorado: Facilities,
Instructions, Standards, and Techniques Volume 2-1: Alignment of Vertical Shaft Hydro-units
• IEEE Std 1095-2012 Guide for Installation of Vertical Generators and Generator/Motors for
Hydroelectric Applications
Additionally there is also on-going work in IEC TC 4 (hydraulic turbines) WC 30 "Guide for Installation
procedures of hydropower machines"
The questionnaire issued in fulfillment of this Technical Brochure refers to the definitions given in
standard IEEE Std 1095-2012, which are assumed to be well known.
2.1.2.3 Magnetic pull at rotor and non-uniform airgap.
Unbalanced magnetic pull, which can be caused by deformations in stator and rotor form.
Eccentricity (or concentricity) of the stator causes a static unbalanced magnetic pull (UMP). The force
of this pull increases with decreasing air gap and the magnetic stiffness is therefore a destabilizing
phenomenon, which must be controlled by the bearings.
Static forces (UMP) can cause rubbing between the stator and rotor when the stiffness of the stator
core and frame is less than the magnetic force.
If Fmagn is exerted in a radial direction then magnetic stiffness (typically defined as negative value) can
be defined as follows:
=
ɛ
If kmech > kmagn the system is stable and if kmech < kmagn it is unstable
If the damping ratio is used to describe the stability of the system, a negative damping ratio will lead
to unstable operation and in a worst case scenario can lead to mechanical contact between the rotor
and the stator. A positive damping ratio limits the mechanical deflection amplitude to some finite
number, therefore this amplitude is a function of the damping ratio value.
Magnetic stiffness (magnetic pull) in the airgap can also be calculated as a function of whirling
frequency and it can be shown that magnetic stiffness is dependent on parallel branches in the stator
winding and damper windings in the rotor ([B1], [B2])
There are also variations of generator design parameters which can increase or decrease the influence
of UMP (Unbalanced magnetic pull):

11
Stator winding: Rotor poles:
- Number of parallel branches - Shape of rotor pole shoe
- Configuration of winding - Non-centralized rotor pole shoes
- Type of winding - Skewed slots (damper bars)
- Slot number and slot pitch - Non-centralized damper bars
- Skewed slots - Slot pitch in rotor pole (damper bars)
Different whirling frequencies, both backwards and forwards, can occur in large generators due to
deviations in the generator shape ([B3])
2.1.2.4 Hydraulic forces from waterways
There are different sources for the hydraulic and other vibration forces from the turbine and
waterways
• Hydraulic pressure fluctuation
• Eigen frequencies from draft tube
• Eigen frequencies of different turbine components
• Number of blades and guide vanes and their combinations
• Vibration behaviour caused by a load rejection
• Self-excited forces
Figure 1 - Calculated radial forces in a Kaplan turbine in nominal operation (blue curve) and with
three over speeds (up to maximum 135% of nominal speed)

12
Dynamic model of the generating unit is needed for studying the behaviour of the turbine-generator
and its response to different forced excitations.
Figure 2 - Vertical hydro unit with bearings and magnetic stiffness (unbalanced magnetic pull)
Guide bearings are modelled with stiffness and damping in the x-direction and the y-direction. In an
anisotropic case (non-symmetric) stiffnesses in x-direction and in y-direction are not equal. If cross
coupling between the x- and y-direction is taken into consideration, the stiffness of the bearing is
presented in matrix form. Magnetic stiffness in the airgap are presented as negative values.
The rotor dynamic model is typically constructed of a shaft line model which includes:
1. Shaft model (including shaft line, added inertias and masses of e.g. rotor and runner).
2. Model of bearings (damping and stiffness, non-linear).
3. Model of air gap forces and model of magnetic interaction between stator and rotor.
The model can include also additional components like:
4. Model of runner (stiffness, damping and added mass, different models for Kaplan and Francis
turbines) and runner / guide vane interaction.
5. Model of seals (especially for Francis turbines).
Stable operation means that shaft and bearing vibration levels are limited to a reasonable level as e.g.
defined in standard ISO 7919 and long term reliable operation is possible and also stresses and
fatigue loading in the machine structures is at an acceptable level.
An early calculation method to estimate eigenfrequencies was by using a simple supported beam as
the model for calculation. In the case of a simple supported beam a vibration/mass/spring analogy
can be used. When the mass is in the maximum displacement position all the energy is stored in the
spring as potential energy and when the mass has zero displacement all the energy is in the kinetic
energy of the mass. When the potential energy and kinetic energy are equal, the natural frequency
can be determined. This is often called Rayleigh’s method.
In this method no damping and gyroscopic forces are taken into consideration and calculated
eigenmodes are real so all masses are vibrating in the same phase.
In rotating shafts, damping and gyroscopic forces (which is also a type of damping) should be taken
into consideration.
Upper guide bearing
Lower guide bearing
Turbine guide bearing
Magnetic stiffnes in airgap

13
In vibrating systems, damping arises from a variety of sources. At least the following types of
damping can be distinguished:
• Coulomb damping (dry-friction damping, rubbing of stator and rotor)
• Viscous damping (generated by fluid interaction e.g. damping in bearings and seals)
• Structural damping (hysteric damping in steel structures etc.)
Damping can be divided into rotating and non-rotating damping.
When damping and gyroscopic forces are taken into consideration the eigenmodes will be complex. In
complex eigenmodes each part of the shaft has its own amplitude and own phase (eigenmodes are
travelling waves)
Now all the main components in the rotor dynamic model have been presented and we can see that
the equations of motion for the more general type of system might be expressed in the matrix form as
follows:
[ ]{ } [ ] [ ][ ]{ } [ ] [ ] [ ][ ]{ } { })()()( txEDixGCxM fK =Ω+++Ω++ &&&
where M is mass matrix
C is damping matrix
)G(Ω is gyroscopic matrix
K is stiffness matrix
D is structural (hysteretic) damping matrix
)E(Ω is internal damping matrix
Ω is speed of rotation
x is displacement vector
)(tf is force vector.
In these equations, the two speed-dependent matrices [G] and [E] are both skew-symmetric, while all
other matrices are symmetric. Solution of the equations will follow different routes depending upon
specific features in each case.
The solution of this matrix equation is typically a set of complex eigenvalues and can be expressed as
follows:
idii i ,ωτλ +=
where τi is the decay rate / damping ratio and ωd,i the damped eigenfrequency of the system. The
system is stable if all eigenvalues have a negative decay rate / damping ratio. The eigenvectors
contains information about whirling direction for each node and mode-shape
As mentioned above the eigenvectors are also complex. A complex mode is one in which each part of
the structure has not only its own amplitude of vibration but also its own phase.
Eigenfrequencies are functions of rotor spin speed due to induced gyroscopic effects and has enough
influence to allow separate forward and backward whirling modes to be distinguished, which can be
seen in a so called Campbell diagram. Also damping ratios of different eigenmodes are functions of
spin speed.

14
Only the forward whirling mode is excited by unbalance of the rotor, which is the main excitation
source in most cases.
Figure 3 - Campbell diagram
Substituting the eigenfrequency back into the matrix equation gives values for corresponding
eigenmodes.
Eigenmodes are orthogonal to each other.
Each and any displacement vector of shaft line can be presented as a linear combination of
eigenmodes.
When the excitation frequency is close to one of the system’s natural frequencies the operational
deflection shape will usually reflect the shape of a nearby mode.
Nonlinearities in the system can also cause response frequencies other than the excitation frequency.
There can also be excitation in other frequencies other than rotational speed which can also influence
responses in these frequencies.
Backward eigenmodes can be theoretically excited by forces acting against the direction of rotation.
Torsional interaction occurs when the induced sub synchronous torque in the generator is close to
torsional natural modes of the turbine-generator shaft. If this torque equals or exceeds the inherent
mechanical damping of the rotating system, the system will become self-excited. Typical frequency
range 10-40 Hz. This phenomenon is called sub-synchronous resonance (SSR) or sub-synchronous
torsional interaction (SSTI).
The most common example of the natural mode sub-synchronous oscillation is found in networks that
include series capacitor compensated transmission lines or at the rectifier side of an HVDC
transmission. Generally hydro generator systems are not as SSTI sensitive as turbomachinery [B6].
For Kaplan units, the torsional frequency between the turbine and the generator is around 10 Hz
(based on one case study between 6 Hz and 15 Hz [B5])
For Francis and Pelton wheel units the torsional frequency lies between 10 Hz and 24 Hz with an
average around 18 Hz (based on one case study between 7 Hz and 46 Hz [B5].

15
2.2 INTRODUCTION TO THE SURVEY CONDUCTED
The questionnaire was prepared and sent out to companies within the hydro power industry (asset
owners/operators (power utilities), OEM and consultants) to obtain information on vibration and
stability issues with hydro generators. The survey has been limited to vertical hydro generators with
rotor construction inclusive of a rotor rim so that answers are somehow comparable.
The questionnaire asked for information on vibration measurement/monitoring, maximum allowable
limits, machine configuration, machine erection tolerances, vibration testing, and experience with
vibration/stability problems and failures. Additional questions on the study and modelling of vibration
problems/failures also formed part of the questionnaire.
The information obtained from the questionnaire is summarised in this report. The aim of the report is
to use this information to help develop recommendations/limitations on different parameters and
identify allowable maximum limits for different types of machines in operation.
The questionnaire consists of two parts:
• Section A is to obtain general information on machine numbers and types in operation, which
vibration parameters are measured/monitored, what vibration limits are applied, machine
construction tolerances, and experience with vibration/stability problems and failures.
• Section B is to obtain detailed information on the study/modelling of machine vibration issues
as used by vibration specialists.
It was anticipated that all companies would be able to provide responses to most questions in Section
A, while Section B would be limited to those companies (larger power utilities, OEMs and specialist
consultants) who have vibration specialists or engineers with some experience in the modelling and
study of machine vibration.
2.3 GENERAL INFORMATION
The survey is based on the fleet of the size as follows:
Table 1 - Surveyed Fleet Size
Output in MVA 10 - 20 20 - 40 40 - 60 60 - 100
100 -
200 >200
Total
Number
Number if Units: 1055 739 402 380 307 226 3109
Speed of Rotation (rpm) 50 - 100
100 -
200
200 -
300
300 -
400
400 -
500 >500
Total
Number
Number of units: 562 1451 550 439 257 353 3612
Turbine type Kaplan Francis Pelton Total
Number of units: 462 585 129 1176
Only vertical hydro generators with rotor construction including rotor rim are included.
2.4 VIBRATIONS, MEASUREMENTS, TESTING AND DEFINED LIMITS
The survey asked for expert opinion on selected questions regarding vibrations, measurements of
vibrations, testing and limits for maximum allowed vibrations in different machine parts. The answers
are summarized in this report.
In cases where acceptable operational limit values were submitted by respondents, only values
supported by more than half of the respondents are published in this brochure.

16
Please note that the table below contains the mean value of all answers received for the specific
question. If more than half of the respondents have answered with the specific listed mean value, the
corresponding answer box is indicated as green, if exactly 50% of the respondents have answered
with a specific answer, the corresponding box is indicated as yellow, if less than 50% of the
respondents have answered with the specific answer, the corresponding boxes are not coloured.
Table 2 Expert opinions on which vibrations should be measured / monitored / included in
protection:
Table 3 Expert opinions on which suitable measurement units to be used for vibration
measurements:
Table 4 Expert opinion on which frequency components are to be measured:
Description YES NO
Comment /
Please
specify
During
commissi
oning
Periodical
Monitor
Permanent
Monitor
Included
in
protection
Radial / Lateral shaft vibrations 10 0 1 8 7 8 8
Radial / Lateral bearing housing vibrations 10 0 1 8 8 7 7
Radial / Lateral other vibrations Describe 4 4 1 3 3 3 2
Axial (longitudinal) shaft vibrations 7 2 2 5 3 5 3
Axial (longitudinal) thrust bearing housing vibrations 7 3 1 6 5 4 3
Stator frame 8 2 1 7 4 3 2
Stator core 6 4 0 7 3 2 1
Stator end winding 4 4 0 4 3 2 1
Head Cover axial vibration 5 4 1 5 2 3 2
Thrust Bearing axial vibration 6 4 0 6 3 4 3
µm /mils mm/s mm/s2
s_max mils/s G
pk to pk in/s
Shaft vibration at or near guide bearings 8 3 3 1 0
Bearing housing vibration 5 2 7 1 0
Thrust bearing axial vibration 5 2 7 1 1
Oil head 4 1 3 0 0
Shaft coupling 4 1 1 0 1
Stator frame radial 3 0 6 2 0
Stator core radial 3 0 6 2 0
Stator end winding 2 0 3 2 0
Head Cover axial Vibration 4 2 3 1 1
Description
µm /mils
pk to pk
Other?
Describe
harmonics
2N, 3N…
harmonics
N/2, N/3…
2 x 2f, 3 x
2f
Shaft vibration at guide bearings 8 6 9 8 2 1
Bearing housing vibration 7 8 9 8 3 2
Thrust bearing axial vibration 7 8 8 8 4 3
Oil head 4 4 6 5 1 0
Shaft coupling 3 1 4 3 0 0
Stator frame radial 3 5 6 4 7 5
Stator core radial 3 4 4 4 6 5
Stator end winding 2 3 3 2 5 3
Head Cover axial Vibration 4 3 3 4 0 0
Description
Overall
value
rms 1N 2f

17
According to the survey the location of the thrust bearing should be taken into consideration when
evaluating vibrations.
The most suitable vibration measurement unit according to the survey is maximum shaft vibration
given as % of guide bearing diametric clearance. The proposed acceptance values are 50% - 80% so
that for new and refurbished machines the maximum allowed value would be 50 - 60% if specified
separately and when not separately specified a maximum indicated value should be 80% (for old
machines).
In the case of bearing housing vibrations, vibration velocity in mm/s is clearly the most common
measurement unit. For maximum allowed vibration level specifications, Standard ISO 10816 should be
referred to, or a limit of 1.6 mm/s for new machines should be specified and values of 1.6 mm/s to 4
mm/s can be specified for older machines, this range can also be specified in general without
necessarily specifying if it should be for old or new machines.
For maximum thrust bearing axial vibrations, values from 0.8 - 2 mm/s are proposed but
recommendations from the bearing manufacturer should be taken into account.
For maximum shaft axial vibrations, values of 200 - 350 µm and 1.6 mm/s are proposed.
For stator end winding tangential vibration a maximum overall vibration of 6 mm/s is suggested
For the stator core vibration a maximum value in the range 2 mm/s to 6 mm/s is proposed (the base
frequency of the stator core vibration is 100 Hz in a 50 Hz system and 120 Hz in a 60 Hz system).
Impact (“bump”) testing of the stator end winding is not always carried out but where it is carried out,
the evaluation criterion is response frequency.
2.5 STUDY OF MACHINE CONSTRUCTION DEVIATIONS
In the study of the machine construction deviations the following results have been obtained.
Please note that the tables below contains the mean value of all answers received for the specific
question. If more than half of the respondents have answered with the specific listed mean value, the
corresponding answer box is indicated as green, if exactly 50% of the respondents have answered
with the specific answer, the corresponding box is indicated as yellow, if less than 50% of the
respondents have answered with the specific answer, the corresponding boxes are not coloured.
Table 5 The maximum allowable deviation in the airgap is given as the range of value of all the
answers received. Values are assumed to be measured statically (unit stopped and cold):
Value [%] Value [%] Value [%]
new
machines
refurbished
old
machines
(max
allowed)
Deviation of average airgap compared to nominal airgap
Deviation of minimum airgap compared to nominal
airgap
2 … 10 3 … 20
Deviation of minimum airgap compared to average
airgap
2 … 5 3 … 10 3 … 30
Description

18
Table 6 The maximum allowed limits for the stator roundness parameters (as a % of air gap) for
hydro generators is given as the mean value of all the answers received:
Table 7 The maximum allowed limits for the rotor roundness parameters (as a % of air gap) for
hydro generators is given as the mean value of all the answers received:
The values in the “Max acceptable for old unit” column, presented in Tables 6 and 7, are based on
mean values according to received answers to questionnaire. Because hydrogenerators vary
significantly, exact operational limits are very difficult to assess. It is possible that some generators
may have stator and rotor shape results which are beyond acceptable values compared to the
tolerances above.
In the results of the survey the experts made the following comments:
• The stator and rotor roundness should be measured at two or three different axial positions in
the length of the air-gap.
• At this time it is not possible to recommend a single value for the difference in axial position
of the stator and rotor.
• The difference between the inclination of the stator and rotor should not exceed 3% of the
airgap (verticality, plumb, maximum measured separate value of minimum eight
Value [%]
Description
Eccentricity *) 1,89 2,80 9,67
Concentricity *) 1,67 3,50 10,00
Ellipticity *) (ovalization) 1,93 2,75 12,60
Tri angularity *) 1,50 2,25 6,00
Four angularity *) 1,57 2,38 6,50
n-angularity *) 1,00 2,50 5,00
Circularity *) 2,20 4,00 10,00
New
After
refurbish
ment
Max
aceptable
for old unit
Value [%]
Description
n-angularity *) 1,00 2,50 5,00
Circularity *) 2,50 3,00 8,75
New
After
refurbish
ment
Max
aceptable
for old unit

19
measurement points and mean value of all the measurements). The inclination is for the
whole core.
• There is no clear limit on stator core waviness.
When evaluating the shaft line according to the definitions given in IEEE 1095 the experts made the
following comments:
• The maximum acceptable inclination of the shaft from vertical should be 0.02 mm/m for new
and refurbished machines and 0.05 mm/m for old machines still in operation.
• The experts could not agree on a value for the accepted straightness of the shaft measured
as the maximum runout from the shaft centre line. In some answers IEEE 1095 and IEEE 810
were quoted.
2.6 VIBRATION FAULT EXPERIENCE
When asked if respondents experienced vibration problems in the following areas the bold
alternatives got most votes and underlined alternatives also received several votes
• Core vibration
• Frame Vibration
• End Winding Vibration
• Head Cover axial Vibration
• Thrust Bearing axial vibration
• Half of rotor poles short circuit
• Rotor inter turn short circuit
• Stator winding short circuit
• Stator winding inter turn short circuit
• Faulty synchronization
• Runaway
Table 8 The following table lists the problems reported most frequently and the frequency of the
vibrations experienced as a multiplier of the speed of rotation N.
Among others the following sources for vibrations were also mentioned: pressure pulsations in
waterways, self-excited vibrations in Kaplan turbine, Draft tube (DT) wall vibrations caused by DT
pressure pulsations, Penstock resonance pressure pulsation and high vibrations, Shaft and structural
resonance, Foundation Concrete structure vibration.
Unbalance 4 6 0 0 0 0
Misalignment 3 5 2 0 0 0
Bow in shaft 4 5 1 0 0 0
Unbalance magnetic force static (stator eccentricity etc.) 3 6 2 1 0 0
Axial runout of thrust collar 4 5 0 0 0 0
Bearing journal runout in guide bearing 4 3 1 0 0 0
YES N/3Description NO YES 1N YES 2N YES 3N YES N/2

20
The summary of what failures related to vibrations and stability have been experienced are presented
in the following tables. The mean value of the number of cases that were experienced during the last
ten years as well as the mean value of what was the typical outage duration for the recovery is also
presented. Especially in the case of outage duration there was considerable variation in the answers,
so the calculated mean values can give only a rough idea of how difficult is was to fix the the
problem.
Table 9 Failures experienced related to vibration and stability:
Vibrations / stability problems caused by YES NO
Number
of cases
last 10
years
Typical
outage
duration
[weeks]
Misalignment (bow in shaft) 5 3 3.3 1
Misalignment (knee in shaft) 6 2 2.4 3
Misalignment (bearing centers misalignment) 3 5 4 3
Thrust bearing collar axial runout 4 3 1.7 4
Vibrations due to interturn short circuit in rotor
poles
2 5 3 8
Problems with critical speed in operation area (1N) 2 6 1.5 10
Problems with critical speed in runaway area 3 5 2 10
Problems with superharmonic vibrations with unit
at operational speed
4 4 4.5 10.5
Vibration problems from turbine (water pulsation
etc.)
6 3 3.5 7
Excitation system 3 5 3 1
Stator circularity 4 4 2.3
Stator concentricity 3 5 3
Stator verticality 2 6 2
Stator ovalisation due to magnetic forces 3 5 2.3 6
Stator distortion due to concrete movement 1 7 3
Stator distortion due to A.A.R. (Alkali Aggregate
Reaction)
2 6 2
Insufficient stator support from Power House
structure
1 7 3
Loose stator core clamping 4 4 2.5 4
Distortion due to stator core section issues 4 4 2 6
Stator foundation connection 3 5 2

21
Vibrations / stability problems caused by YES NO
Number
of cases
last 10
years
Typical
outage
time
[weeks]
Rotor circularity 1 6
Rotor eccentricity 2 6
Rotor rim looseness by design (floating rim) 2 6 1 10
Rotor rim looseness by failure (shrink fit rim) 2 6
Rotor rim over-shrinking 2 6
Rotor rim under-shrinking 2 5
Other rotor rim issues, please specify 0 6
Inadequate mechanical vs. magnetic stiffness 4 3 2
Rotor vs. stator vertical alignment 4 4 2 20
Rotor spider tilting / torsional stiffness 1 6 2 20
Rotor pole inter turn short circuit 3 3
According to the survey most of the problems which have been experienced were related to shaft
alignment and vibration problems from waterways. In the case of shaft misalignment the required
outage time to fix the problem was from 1 - 3 weeks. In the case of turbine vibration problems the
average outage time was 7 weeks.
A number of problems with stator cores have been experienced such as stator circularity, loose core
clamping, and distortion of core sections. In these cases the outage times expected were 4-6 weeks.
There have also been problems with inadequate mechanical vs. magnetic stiffness and rotor vs. stator
vertical alignment.
A number of problems have been identified related to thrust bearing collar axial runout which can be
obviously seen as a type of shaft alignment problem.
According to the survey more problems are related to stator shape and construction than to rotor
shape and construction if shaft alignment problems are considered separately from other rotor
problems.
2.7 STUDY OF NUMERICAL VERIFICATION OF STABILITY AND VIBRATIONS
The majority of experts consider that the following components should be included when building a
shaft model for calculating critical speeds:
• Inertias of all the rotating masses
• Bearing stiffness (guide bearing)
• Bearing damping (guide bearing)
• Cross coupling of stiffness and damping (guide bearings)

22
• Thrust bearing stiffness
• Magnetic stiffness in air gap
• Water mass from turbine runner
It is also considered that the bearing stiffness and damping values should be given in both the ‘x’ and
‘y’ directions.
When evaluating the results of dynamic stability calculations (critical speed calculations) the following
items are considered to be the most important:
• Verify that no forward whirl Eigen modes and frequencies are present under runaway
speed(off-cam) without magnetic pull.
• Verify that no backward whirl Eigen modes and frequencies are present under runaway speed
(on-cam or off-cam).
• Verify that the minimum required damping ratio for eigenmodes and frequencies is reached
(no specific minimum value is given in the survey).
• Verify that the minimum required damping ratio for super harmonic eigenmodes and
frequencies (eigenmodes above nominal speed of rotation) is obtained.
The majority of experts agree that the following items should also be verified:
• Torsional eigenmodes / eigenfrequencies.
• Axial / Longitudinal eigenmodes / eigenfrequencies.
• Stator core eigenfrequencies, harmonic/ transient response.
• Short-circuit and faulty synchronization influence calculations (stator and/or rotor).
2.8 FAULT CASE STUDY
Based on the survey the faulty cases caused by problems in turbine and waterways have no specific
reason and a specific root cause can't be identified. In the answers all the alternative fault cases have
received an equal number of hits. In the fault case study the most common problem has been rubbing
between static and rotating parts. In the questions which attempted to identify a root cause, several
cases of problems relating to problematic slot number and/or winding construction are mentioned.
None of the answers provided any detailed analysis or information about problem cases.
2.9 FUTURE STANDARDS
In the survey the need for the following additional standards was raised
Shaft / Bearing vibration 3 supports (of which one asked only for shaft vibration standard)
End winding vibrations 3 supports (one answer refers specially radial and tangential
vibrations)
Stator core vibration 5 supports
Stator frame vibrations 3 supports
Shaft / Bearing vibration 2 supports
Also the need for vibration standards for the draft tube wall, external penstock metal shell, turbine
inlet valve, turbine top cover, thrust bracket and exciter housing were additional items.
Based on this survey there is mostly need for a standard for stator vibrations.

23
3. CONCLUSION
The response to the survey on the ‘Vibration and Stability Problems Met in New, Old and Refurbished
Hydro Generators, Root Causes and Consequences’ was fair, with 10 responses received from 7
different countries. Responses were from utility owner/consultants (users) and manufacturers
(suppliers), with the majority being utility owner/consultants.
The responses covered mostly units with nominal rated output range of 10 to 200 MVA (93% of
answers) however some units with output above 200 MVA have been included as well. The fleet
studied in the survey covers mostly Kaplan and Francis turbines which typically have vertical low-
speed generators with a rotor rim construction.
The background for the study was to survey the expert opinion for the most feasible way to verify
dynamic stability of the unit with measurements and calculation. The survey also asked for experience
of the faults encountered in problem cases. In this conclusion we give some recommendations based
on the majority expert opinion obtained in the survey.
The most important vibrations to measure are the radial vibrations of the shaft and the bearing
housing. These measurements should be included in the commissioning tests and monitored
periodically (permanently if possible). These measurements should also be included in the protection
system. The survey did not specifically ask if this should be included for all machine sizes.
Other measurements which are important to include, at least to commissioning tests, are axial shaft
vibrations, axial thrust bearing housing vibrations as well stator frame and core vibrations.
The most suitable unit for the measurement of shaft vibration is displacement (in µm or mil). For the
bearing housing, thrust bearing axial vibration and stator frame vibration velocity is the preferred
option (mm/sec or mil/sec). For the bearing housing and thrust bearing there is also support for using
displacement.
In case of shaft vibrations, bearing housing vibrations and thrust bearing axial vibrations, the peak-to-
peak value, rms value, 1N and harmonic values should be measured. If measuring vibration at the top
of the shaft, where, in the case of Kaplan units, the oil head is located, only measurement of 1N is
enough.
When measuring stator vibrations of the frame and core, the 1N component should be measured as
well as the double grid frequency component (100 Hz or 120 Hz) and its harmonics. There is also
support for measuring the rms values and the values at the harmonics of rotational frequency.
The most important vibration measurement according to the survey is the maximum shaft vibration
given as % of guide bearing diametric clearance. For new and refurbished machines the maximum
allowed value are 50 to 60% and for old units the maximum value up to 70% and even 80%.
The most important parameters which should be taken into consideration when evaluating vibrations
are:
• Nominal speed of rotation
• Rated apparent power of the unit
• Location of thrust bearing
The maximum recommended bearing housing vibration according to ISO 10816 is 1.6 mm/s for new
machines and up to 4 mm/s for old machines.
In the absence of any manufacturer recommendations the maximum thrust bearing axial vibration
should not exceed 2 mm/s.
The shaft axial vibration should not exceed 350 µm or 1.6 mm/s while the stator end winding
tangential vibration should not exceed 6 mm/s.
Impact (“bump”) testing of the stator end winding is not normally required but in case where it is
performed, the suitable evaluation criteria is frequency.

24
The maximum allowed construction deviations in stator and rotor shape are given in the tables below.
Table 10 Maximum allowed limits for stator roundness parameters (% of air gap):
Table 11 Maximum allowed limits for rotor roundness parameters (% of air gap):
The values in the “Max acceptable for old unit” column, presented in Tables 6 and 7, are based on
mean values according to received answers to questionnaire. Because hydrogenerators vary
significantly, exact operational limits are very difficult to assess. It is possible that some generators
may have stator and rotor shape results which are beyond acceptable values compared to the
tolerances above.
The maximum allowed difference in the axial position of the stator and rotor centre line is 20% of the
air gap and the permissible inclination of stator and rotor is 3% of airgap.
According to standard IEEE 1095 the maximum inclination of the shaft line shall be 0.02 mm/m for
new and refurbished machines and 0.05 mm/m for old machines.
According to the survey most of the problems which have been experienced were related to shaft
alignment and vibration problems from waterways. In the case of shaft misalignment the required
outage time to fix the problem has been from 1 - 3 weeks. In the case of vibration problems
originating from the turbine, the average outage duration is 7 weeks. A number of problems have
been identified relating to the thrust bearing collar axial runout which can be obviously seen as a type
of shaft alignment issue.
Value [%]
Description
n-angularity *) 1,00 2,50 5,00
Circularity *) 2,20 4,00 10,00
New
After
refurbish
ment
Max
acceptable
for old unit
Value [%]
Description
n-angularity *) 1,00 2,50 5,00
Circularity *) 2,50 3,00 8,75
New
After
refurbish
ment
Max
aceptable
for old unit

25
In addition to vibrations in the shaft line and bearings, the following vibration problems has been
encountered most frequently: Stator core and frame vibrations, thrust bearing axial vibrations,
vibrations caused by rotor interturn short circuit and runaway.
According to the survey, more problem cases are related to stator shape and construction than to
rotor shape and construction if shaft alignment problems are analysed separately from other rotor
problems.
When constructing the shaft line model for dynamic stability calculations in addition to shaft line with
rotating inertias and masses, the following additional components should be also included in model:
• Bearing stiffness (guide bearing), shall be given in matrix form
• Bearing damping (guide bearing) shall be given in matrix form
• Cross coupling of stiffness and damping (guide bearings)
• Thrust bearing stiffness
• Magnetic stiffness in air gap
• Water mass from turbine runner
In dynamic stability calculations, at least the following shall be verified:
• Verify that no forward whirl eigenmodes and frequencies are present under runaway speed
(off-cam) without magnetic pull;
• Verify that no backward whirl eigenmodes and frequencies are present under runaway speed
(on-cam or off-cam);
• Verify that the minimum required damping ratio for eigenmodes and frequencies is reached
(no specific minimum value is given in the survey);
• Verify that the minimum required damping ratio for super harmonic eigenmodes and
frequencies (eigenmodes above nominal speed of rotation) is obtained.
Based on the study it can be said that eigenmodes and their damping also need to be calculated at
nominal speed of operation and at over-speeds which will be encountered in practise when a unit trip
occurs. The calculation of unbalanced response can be used in addition to damping factor calculation
to verify the possible level of vibrations reached when the unit has been modified.
Other eigenmodes / eigenfrequencies and stability which should be also verified:
• Torsional eigenmodes / eigenfrequencies;
• Axial / Longitudinal eigenmodes / eigenfrequencies;
• Stator core eigenfrequencies, harmonic/ transient response;
• Short-circuit and faulty synchronization influence calculations (stator and/or rotor)
According to the survey the most urgent requirement is for an up to date standard for stator
vibrations.
Note: We would like to thank all technical experts who answered the questionnaire and those who
sent us their comments. We also would like to thank the regular members and observer members of
many countries for the contribution they made to the success of this study.

26

27
APPENDIX A. DEFINITIONS, ABREVIATIONS
AND SYMBOLS
A.1. GENERAL TERMS
App Table A.1 Definition of general terms used in this TB
Acronym Phrase Definition
TB Technical Brochure A publication produced by CIGRÉ representing the
state-of-the-art guidelines and recommendations
produced by an SC WG. Hardcopy TBs can be
purchased [B1], or Individual Members, or staff of a
Collective Member can download the PDF for free
using their login credentials (copyright restrictions for
use within their own CIGRE Membership only)
SC Study Committee One of the 16 technical domain groups of CIGRE
WG Working Group A group formed by a SC to develop a TB on a
particular subject of interest
A.2. SPECIFIC TERMS
App Table A.2 Definition of technical terms used in this TB
N Speed Frequency of shaft rotation (rated speed)
2f Two times line (grid( frequency
Nominal Air Gap Air gap at nominal, steady state operation
Average air gap Average value of measured air gap values at each pole
Operational average air gap Average air gap measured during operation.
Stator profile measurement Measurement of air gap from one pole to several
stator positions when rotor is turned
Rotor profile measurement Measurement from one position in stator against
each pole when rotor is turned
Circularity Zone limited by two concentric circles having as
their common centre the best centre of the
components to be verified. Deviation is difference
between a maximum and a minimum radii form
the best centre.
Roundness See circularity
Type of roundness deviation :
eccentricity (also concentricity)
Harmonic content N = 1
ellipticity (also ovalization)
triangualrity
quadrangularity
Type of roundness deviation : n-
angularity
Harmonic content N = n

28
rms Root mean square computed in time or frequency
domain
pk-pk peak-to-peak Difference between maximum positive and
maximum negative peaks during a specified
interval
smax Maximum vibration displacement from time-
integrated mean position in the plane of
measurement (ref. ISO 7919)
Anisotropic support Uneven stiffness in different directions (eg. x-
and y-direction)
Non-linear support Stiffness is not linear in one or more directions
Rotor whirling Motion of a rotor in which individual elements of
the rotor are deformed form the static deflection
line
Oil whirl Whirling caused by hydrodynamic effects in fluid
film bearings
Oil whip Self-excited vibration of a rotor supported by fluid
bearings due to an increase in tangential force of
the fluid bearings
Forward whirl Shaft orbiting with sense of rotation
Backward whirl Shaft orbiting against sense of rotation
Cross coupling Consideration of cross stiffness and/or cross
damping terms
Critical speed Eigenfrequency of rotor bending eigenmode
considering speed depending stiffness and
damping effects, such as Coriolis damping
Natural frequency of a mechanical
system
The frequency of free vibration of a mechanical
system
Eigenfrequency of a mechanical
system
See natural frequency
Eigenmode of a mechanical system Mode shape associated to a particular natural
frequency
Synchronous amplification factor A measure of sensitivity of a rotor system to
unbalance when rotor speed is equal to a rotor
system natural frequency
Bistable vibration Vibration system with two stable vibration modes
Parametric instability Instability depending on particular vibration
parameter
Unstable unbalance The unbalance vector is not constant
Accelerance Ratio of acceleration to excitation according to
frequency-response function (ref. ISO 2041, table
1)
Verticality Difference of best centres of measured rotor or
stator profiles in two horizontal planes divided by
the offset of the two planes
Straightness Max. runout from centre line connecting top and
bottom of shaft

29
On-cam Turbine operation when runner blades and wicket
gates (guide vanes) are according to opening
defined by governor
Off-cam Worst case combination with runner blade
position and wicket gate opening reaching
highest speed of rotation
New generator Generators commissioned in the last ten years
Refurbished generator At least some of the major component replaced
(minimum rewinding of stator) and new
component integrated to old generator (generator
is partly renewed and partly old part reused). For
new components (for example stator) same
requirements as for new generators are applied.
Old generator Generators commissioned more than ten years
ago
Non symmetric / symmetric damper
bars
Damping bars are symmetrically located on pole
shoe / damping bars are not symmetrically
located on pole shoe
Centralized / non centralized rotor
pole shoes
Rotor pole shoe is symmetrically located on pole
body / rotor pole shoe is not symmetrically
located on pole body
Damper winding in different poles
directly connected
Damper segments in each pole are directly
connected electrically
Anisotropic linear support The support stiffnesses in the two principal and
orthogonal directions are both linear but differ in
value
Axisymmetric nonlinear support Axisymmetric support includes systems which
are axisymmetric but non-linear, i.e. systems
whose stator reaction force is not simply
proportional to the rotor deflection
Planar asymmetric support One support axis has an asymmetric stiffness
(softer for motion in one direction and harder for
motion in the opposite direction). The other has a
linear stiffness characteristic

30

31
APPENDIX B. LINKS AND REFERENCES
[B1] Low-order parametric force model for eccentric-rotor electrical machine equipped with
parallel stator windings and rotor cage , 2007, A. Burakov, A. Arkkio, IET Electric Power
Applications Vol. 1, Issue 4, pp. 532-542.
[B2] Mitigation of UMP components by the parallel stator windings in eccentric-rotor electrical
machines , The IEEE International Electric Machines and Drives Conference (IEMDC 2007),
2007, A. Burakov, A. Arkkio, Antalya Turkey, pp. 1638-1642.
[B3] Whirling frequencies and amplitudes due to deviations of generator shape, 2008, Niklas L.P.
Lundström, J.O. Jan-Olov Aidanpää, International Journal of Non-Linear Mechanics, Elsevier,
43 (9), pp. 933.
[B4] Linear and Nonlinear Rotor Dynamics , 2001, T. Yamamoto, Y. Ishida, Wiley.
[B5] Influence of Hydro Units' Generator-to-Turbine Inertia Ratio on Damping of Subsynchronous
Oscillations, G. Andersson, R. Atmuri, R. Rosenqvist, S. Torseng, 1984, IEEE Transactions on
Power Apparatus and Systems, Volume: PAS-103, Issue: 8.
[B6] Subsynchronous Torsional Behaviour of a Hydraulic Turbine-Generator Unit Connected to a
HVDC System, 2008, Australasian Universities Power Engineering Conference (AUPEC'08),
Yin Chin Choo, A. P. Agalgaonkar, K. M. Muttaqi and S. Perera, M. Negnevitsky, Paper P-177.
[B7] Determination of Journal Bearing Stiffness and Damping at Hydropower Generators Using
Strain Gauges, PWE2005, ASME Power, Chicago, Illinois, 2005, M L Lundström, J O
Aidanpää.
[B8] Modal Testing, theory, practise and application, 2000, D. J. Ewins, 2nd Edition, Wiley, 2000.
[B9] The influence of magnetic forces on the stability behavior of large electrical machines, 1996,
H. Sprysl, Vögele & H, G. Ebi, VDI Berichte, Nr.1285.
[B10] Dynamics of Rotating Systems, 2005, G. Genta, Springer.
[B11] Structural Dynamics and Probabilistic Analysis for Engineers, 2008, G. Maymon, Elsevier.
[B12] Dynamic stability of old vertical hydrounits with two guide bearings, 2015, J. Ahtiainen,
CIGRE SC A1 Colloquium, Madrid.
[B13] Mechanical vibrations of non-reciprocating machines - Measurements on rotating shafts and
evaluation criteria —Part 5: Machine sets in hydraulic power generating and pumping plants,
ISO 7919 -5.
[B14] Mechanical vibrations - Evaluation of machine vibrations by measurements on non-rotating
parts Part 5: Machine sets in hydraulic power generating and pumping plants, ISO 10816 -5.
[B15] Installation of Vertical Generators for Hydroelectric Applications , IEEE 1095-2012.
[B16] Standard for Hydraulic Turbine and Generator Integrally Forged Shaft Couplings and Shaft
Runout Tolerances, IEEE 810-1987.
[B17] Mechanical vibration, shock and condition monitoring – vocabulary, ISO 2041; 2009
[B18] Vibration Analysis – Force and Vibration Relationship,2011, CEATI report; 2011, HPLIG 0353

32

33
APPENDIX C. ANSWERED SURVEYS
C.1. QUESTIONNAIRE - NORWAY
Utility Owner
Country =NORWAY
Only vertical hydro generators with rotor construction including rotor rim are concerned
Answers are based on the fleet of size
Output in
MVA
Description
10
-
20
20
-
40
40
-
60
60 -
100
100 -
200
>
200
Total
number
number of units 43 52 30 34 32 12 203
Comment: 334 – 203 = 131 units below 10 MVA
Speed of
rotation rpm
Description
50
-
100
100
-
200
200
-
300
300 -
400
400 -
500
>
500
Total
number
number of units
number of units below 10 MVA
9 84 38 65 36 102 334
203
Turbine
type
Kaplan Francis Pelton Total
number of units
number of units below 10 MVA
154 120 60 334
203

34
Vibrations measurements, testing and define limits
In your opinion what vibrations should be measured / monitored /included in protection (S)
Description YE
S
NO Comment /
Please
specify
During
commissioning
Periodical
Monitor
Permanent
Monitor
Included in
protection
Radial / Lateral
shaft vibrations
Y Y Y
Radial / Lateral
bearing housing
vibrations
Y Y Y
Radial / Lateral
other vibrations
Describe
N
Axial
(longitudinal)
shaft vibrations
Y Y Y
Axial
(longitudinal)
thrust bearing
housing vibrations
N
Axial other
vibrations
Describe
N
Stator frame N
Stator core N Y
Stator end
winding
N
Head Cover axial
vibration
N
Thrust Bearing
axial vibration
N
Other vibrations
please specify (1)
N
Other vibrations
please specify (2)
Other vibrations
please specify (3)
Other vibrations
please specify (4)

35
In your opinion what is the suitable measurement unit for vibration measurement (S)
Description µm /mils µm /mils
s_max
mm/s
mils/s
in/s
mm/s2
G
Other? Describe
Shaft vibration at
or near guide
bearings
mm/s
Bearing housing
vibration
- mm/s
Thrust bearing
axial vibration
. mm/s
Oil head -
Shaft coupling -
Stator frame
radial
-
Stator core radial - mm/s
Stator end
winding
-
Head Cover axial
Vibration
-
Which frequency components are to be measured (please specify in columns where multiple choice
are given)
Description Overall
value
rms 1N harmonics
2N, 3N…
N/2,
N/3…
2f harmonics
2 x 2f, 3 x
2f
Other, please specify
Shaft vibration
at guide
bearings
Y
Bearing housing
vibration
Y
Thrust bearing
axial vibration
Y
Oil head
Shaft coupling
Stator frame
radial
Stator core
radial
Y Y
Stator end
winding
Head Cover
axial Vibration

36
What are the most important parameters when defining maximum levels for vibrations
Description YES NO Comments / Please
specify
Nominal speed of rotation X
Rated apparent power of the unit X
Rated reactive power X
Rated voltage X
Number of guide bearings X
Location of thrust bearing X
Construction type according to IEC 34 X
specify
Stiffness of the bearing brackets X
Turbine type X
Magnetic pull X
Other, please specify (1) X
What are the maximum allowable (permissible) vibrations levels according to your standards/practice?
If different max levels apply for new generators / refurbished generators / old generators; please
specify values for each row separated by backslash.
Description µm
peak-
peak
µm
s_max
mm/s
rms
mm/s2 % of
bearing
clearance
acc. standard,
which
Additional
info
Shaft vibration in upper guide
bearing (two generator guide
bearings) upper bracket not
braced against foundation
70 IEEE 1095
Shaft vibration in lower guide
70 id
bearings) with upper bracket
70 id
70 id
bearing (one generator guide
bearing)
70 id

37
Shaft vibration in top of the
shaft (lower guide bearing
only)
id
Description µm
peak-
peak
µm
s_max
mm/s
rms
mm/s2 % of
bearing
clearance
acc. standard,
which
Additional
info
bearing)
70 id
Bearing housing vibration in
upper guide bearing (two
generator guide bearings)
upper bracket not braced
against foundation
id
lower guide bearing (two
against foundation
id
generator guide bearings) with
upper bracket braced against
foundation
id
foundation
id
lower guide bearing (one
generator guide bearing)
id
Relative thrust bearing axial
vibration
id
Thrust bearing housing axial
vibration
id
Shaft axial vibration id
Oil head
Shaft coupling
Stator frame
Stator end winding tangential
Stator end winding radial
Stator core 2
Description µm
peak-
peak
µm
s_max
mm/s
rms
mm/s2 % of
bearing
clearance
acc. standard,
which
Additional
info

38
Slip rings
Head Cover axial Vibration
Other part
which______________
Other part
which______________
Other part
which______________
Do you perform impact (“bump”) testing on end winding? (E)
YES NO
X
Do you have limits for results of impact (“bump”) test? (E)
Description YES NO If yes please specify
Frequency
Accelerance
other
Study of machine construction deviations
What should be the allowable deviation in airgap
Description Value [%]
new
machines
Value [%]
refurbished
Value [%]
old machines
(max allowed)
Not important
Deviation of average airgap
compared to nominal airgap
2 5 10
Deviation of minimum airgap
2 5 10
compared to average airgap
2 5 10
According to your opinion what are max allowed limits for stator roundness
parameters (% of air gap) for hydro generators (S)
Value
[%]
Description
New After
refurbishmen
t
Max
aceptable for
old unit
Not
important
According to
standard / norm
Eccentricity *) 2 5 10
Concentricity *) 2 5 10
Ellipticity *) (ovalization) 2 5 10
Tri angularity *) 2 5 10

39
Four angularity *) 2 5 10
n-angularity *) 2 5 10
Circularity *) 2 5 10
Some other definition and criteria
*) - according to definitions given at beginning of questionnaire.
According to your opinion what are max allowed limits for rotor roundness
Value
[%]
Description
New After
refurbishmen
t
Max
aceptable for
old unit
Not
important
According to
standard / norm
Eccentricity *) 2 5 10
Concentricity *) 2 5 10
Ellipticity *) (ovalization) 2 5 10
Tri angularity *) 2 5 10
Four angularity *) 2 5 10
n-angularity *) 2 5 10
Circularity *) 2 5 10
How many levels of measurement should be performed (specify core height as
applicable) and how many measurements at one level (if discrete
measurement points)
1 level / <
core height
2 levels /
< core
height
3 levels /
> core
height
each level
evaluate
separate
mean
value of
all levels
Minimum
number of
discrete
points
Stator X = thrust bg.
bracket arms
Rotor X 2p
According to your opinion what is the max allowed difference in levels of stator and
rotor center lines axial positions (E)
Description % of
airgap
in
mm
% of
stator
core
height
Other
criteria
Max value
in given
criteria
Max difference in levels of stator and
rotor centre lines
10

40
According to your opinion what inclination of stator and rotor is permissible
(verticality, plumb, maximum measured separate value of minimum eight
measurement points) (E)
% of
airgap
in
mm
Other
criteria, what
Max value in
given criteria
No experience
Stator 3
Rotor 3
Max difference in verticality between
stator and rotor
3
According to your opinion what is max allowed value of stator core
% of
airgap
in
mm
Other
criteria, what
Max value in
given criteria
No experience
Stator core waviness % of wave
length
0,5
Vertical/angular distortion of the
cross-section
X
If evaluating shaft line according to definition given in standard IEEE 1095 what is
the max inclination of the shaft (from vertical line, shaft line plumb) you would
allow/accept
Description 0,01
mm/
m
0,02
mm/
m
0,03
mm/
m
0,04
mm/
m
other
mm/
m
Not
important
According to
standard / norm,
What
Shaft line plumb, New Generators X
Shaft line plumb, Refurbished
Generators
0,06
Shaft line plumb, Old Generators
(operation still allowed)
0,10
If evaluating shaft line according to definition given in standard IEEE 1095 what is
the required straightness of the shaft (max runout from centreline connecting top
and bottom of shaft )
Description 0,01
mm
0,02
mm
0,03
mm
0,04
mm
other
mm
Not
important
According to
standard / norm,
What
Straightness, New Generators X
Straightness, Refurbished
Generators
Straightness, Old Generators
(operation still allowed

41
Are there other assembly / machine construction parameters which are
essential according to your opinion?
Both upper and lower brackets shall be braced radially against foundation, in
order to ease satisfaction to critical speed criteria.
Vibration Fault Experience
Have you experienced problems related to the following vibrations? (S)
Description YES NO Comment / Please
specify
Core vibration X
Frame Vibration X
End Winding Vibration X
Head Cover axial Vibration X
Thrust Bearing axial vibration X
Have you experienced problems in vibrations related to the following? (S)
specify
Half of rotor poles short circuit X
Rotor inter turn short circuit X Usually not critical
Stator winding short circuit X Critical
Stator winding inter turn short circuit X Very critical
Faulty synchronization
X More often than we
expect/believe.
Runaway X But load rejection, yes.
What stability / vibration problems have you experienced with forced
excitation and what are the response frequencies compared to speed of
rotation N. If yes give number of separate cases (S)
Description NO YES
1N
YES
2N
YES
3N
YES
N/2
YES
N/3
YES
other
frequency
Unbalance X
Misalignment X
Bow in shaft X
Unbalance magnetic force static
(stator eccentricity etc.)
Resonance
100

42
Description NO YES
1N
YES
2N
YES
3N
YES
N/2
YES
N/3
YES
other
frequency
Axial runout of thrust collar X
Bearing journal runout in guide
bearing
X
Other, Describe
Other, Describe
Other, Describe
Other, Describe
What failures related to vibrations and stability have you experienced (specify if assembly problem is
concerned)(S)
Vibrations /
stability
problems caused
by
YES NO Number
of
cases
last 10
years
Typical
outage
time
[weeks]
Comment / Please
specify
Misalignment (bow in
shaft)
X 1 1
Misalignment (knee in
shaft)
X 1 2
Misalignment (bearing
centers misalignment)
X 2 3
Thrust bearing collar
axial runout
X 3 4
Vibrations due to
interturn short circuit
in rotor poles
X 3 8
Problems with critical
speed in operation
area (1N)
X 1 10
speed in runaway area
X 2 10
Vibrations /
stability
problems caused
by
YES NO Number
of
cases
last 10
years
Typical
outage
time
[weeks]
Comment / Please
specify
Problems with
superharmonic
vibrations with unit at
operational speed
X 3 12

43
Vibration problems
from turbine (water
pulsation etc.)
X 3 10
Excitation system X 1 1
Other, what (1)
Other, what (2)
Related to stator: have you experienced any vibration problems caused by issues such as (S)
Vibrations /
stability problems
caused by
YES NO Number
of
cases
last 10
years
Typical
outage
time
[weeks]
Comment / Please
specify
Stator circularity X
Stator concentricity X
Stator verticality X
Stator ovalisation
due to magnetic
forces
X
Stator distortion due
to concrete
movement
X
to A.A.R. (Alkali
Aggregate Reaction)
X
Insufficient stator
support from Power
House structure
x
Loose stator core
clamping
X
Distortion due to
stator core section
issues
X
Stator foundation
connection
(please specify
sliding/flexible/other
type)
X Hard solid connection

44
Related to the rotor, have you experienced any vibration problems caused by such issues as (S)
Vibrations /
stability
problems caused
by
YES NO Number
of
cases
last 10
years
Typical
outage
time
[weeks]
Comment / Please
specify
Rotor circularity X
Rotor eccentricity X
Rotor rim looseness
by design (floating
rim)
X
Rotor rim looseness
by failure (shrink fit
rim)
X
Rotor rim over-
shrinking
X
Rotor rim under-
shrinking
X
Other rotor rim
issues, please
specify
X
Inadequate
mechanical vs.
magnetic stiffness
X
Rotor vs. stator
vertical alignment
X
Rotor spider tilting
/ torsional stiffness
X
Rotor pole inter
turn short circuit
X
Have you ever experienced any failure(s) due to the above mentioned items.
Cracks, even ruptures, in welded constructions on rotor or/and bracket.
Is there need for any additional Standards concerning vibration like (S)
- Shaft / Bearing vibration
- End winding vibrations
- Stator core vibration
- General vibrations, other machine components
- Air gap
Stator core vibration 100 Hz resonance

45
Section B – Additional Questions for Vibration Specialists
Study of numerical verification of stability and vibrations
Which parameters would you have use when calculating critical speeds / eigenmodes
and frequencies (in addition to shaft line with rotating masses) (S)
specify
Bearing stiffness (guide bearing) X
Bearing damping (guide bearing) X
Bearing stiffness separate figures for x- and
y-direction (guide bearing)
X
Bearing damping separate figures for x- and
y-direction (guide bearing)
X
Cross coupling of stiffness and damping
(guide bearings)
X
Thrust bearing stiffness X
Magnetic stiffness in air gap and level of
excitation in definition of stiffness (please
specify)
X
Water mass from turbine runner X
Turbine shaft sealing X
Turbine runner band seals (Francis runner) X
Other, please specify (1)

46
According to your opinion what are the acceptance criteria to evaluate critical
speeds / eigenmodes and eigenfrequency calculations (E)
Description Need to
calculate
Need
criteria
YES NO YES NO Comment / Please
specify
No forward whirl eigenmodes and
frequencies under runaway speed, give
tolerance above runaway speed (on-cam)
without magnetic pull
X X 20 % above runaway speed
tolerance above runaway speed (on-cam)
with magnetic pull
X X
tolerance above runaway speed (off-cam)
without magnetic pull
X X
tolerance above runaway speed (off-cam)
with magnetic pull
X X
No backward whirl eigenmodes and
frequencies under runaway speed (on-cam
or off-cam)
X X
Minimum allowed damping ratio for
eigenmodes and frequencies, min allowed
value?
X X
Unbalance response X X
Min allowed damping ratio for subharmonic
eigenmodes and frequencies (N/2, N/3,
N/4… down to?) , min allowed value
X X
Min allowed damping ratio for
superharmonic eigenmodes and frequencies
(2N, 3N, 4N, 5N… up to?), min allowed value
X X
Forward whirl eigenmodes and frequencies
under rated speed, give tolerance above
rated speed
X X
Forward whirl eigenmodes and frequencies
under overspeed, give tolerance above
overspeed
X X

47
What other eigenmodes / eigenfrequencies and stability you normally verify
(E)
specify
Torsional eigenmodes / eigenfrequencies X
Stability against subsynchronous resonance X
Axial / Longitudinal eigenmodes /
eigenfrequencies
X
Stator core eigenfrequencies, harmonic/
transient response, please specify
X
End winding local eigenfrequencies, X
End winding global eigenfreguencies,
harmonic/ transient response, please specify
X
Short-circuit and faulty synchronization
influence calculations (stator and/or rotor)
X
Half of rotor poles short circuited influence
calculation (stator and/or rotor, coupled),
please specify
X
Other please specify (1)?
Have you encountered problems with different design deviations (E)
Problem in
design
details
of case
problematic
stator slot
number
Stator slot
number
and/or
winding
construction
Stator slot
number contra
rotor damping
bar / pole
shoe
other what
with new
generator
Complicated
but OK
Multiturn coils
instead of
possible
Roebel.
after
refurbishment
In a bid, which
we rejected.
with old
generator
extensive shaft
vibration
extensive
bearing vibration
extensive stator

48
vibration
Number of slots
per pole and
phase
Too close to a
whole.
Non symmetric /
symmetric
damper bars
Centralized / non
centralized rotor
pole shoes
Number of
damper bars
Open or closed
damper bar slots
Damper winding
in different poles
directly
connected
Have you encountered stability / vibration problem cases which you can describe in details (and
some background information of machine speed of rotation, output, type of machine,
type of winding, parallel branches, number of slots etc. ) (E)
• 100 Hz resonance in stator core, leading in most cases to stator
exchange (guarantee) if winding rearrangement is impossible (typically
on 750 rpm).

49
C.2. QUESTIONNAIRE – GERMANY
Utility Owner
Country: Germany
Output in
MVA
Description
10
-
20
20
-
40
40
-
60
60 -
100
100 -
200
>
200
Total
number
number of units 0 9 10 0 6 4 29
Speed of
rotation rpm
Description
50
-
100
100
-
200
200
-
300
300 -
400
400 -
500
>
500
Total
number
number of units 0 4 5 12 8 29
Turbine
type
number of units 0 29 0 29
Description YES NO Comment /
Please
specify
During
commissioning
Periodical
Monitor
Permanent
Monitor
Included in
protection
Radial / Lateral
shaft vibrations
X depends
on size
X X X X
Radial / Lateral
bearing
housing
vibrations
X depends
on size
X X X X
Radial / Lateral
other
vibrations
Describe
X
Axial
(longitudinal)
shaft vibrations
X
Axial
(longitudinal)
thrust bearing
X

50
housing
vibrations
Axial other
vibrations
Describe
X
Stator frame X
Stator core X
Stator end
winding
X
Head Cover
axial vibration
X
Thrust Bearing
axial vibration
X
Other
vibrations
please specify
(1)
X
Other
vibrations
please specify
(2)
X
Other
vibrations
please specify
(3)
X
Other
vibrations
please specify
(4)
X
s_max
mm/s
mils/s
in/s
mm/s2
G
Other? Describe
Shaft vibration at
or near guide
bearings
X X
Bearing housing
vibration
- X
Thrust bearing
axial vibration
. X
Oil head X -
Shaft coupling -
Stator frame -

51
radial
Stator core radial -
Stator end
winding
-
Head Cover axial
Vibration
-
are given)
Description Overall
value
rms 1N harmonics
2N, 3N…
N/2,
N/3…
2f harmonics
2 x 2f, 3 x
2f
Shaft vibration
at guide
bearings
X X X X X frequency x blade
runner
Bearing housing
vibration
runner
Thrust bearing
axial vibration
runner
Oil head X X X X X frequency x blade
runner
specify
Nominal speed of rotation depends on individual
unit
Rated apparent power of the unit depends on individual
unit
Rated reactive power depends on individual
unit
Rated voltage depends on individual
unit
Number of guide bearings depends on individual
unit
Location of thrust bearing depends on individual
unit
Construction type according to IEC 34 depends on individual
unit

52
specify
Stiffness of the bearing brackets depends on individual
unit
Turbine type depends on individual
unit
Magnetic pull depends on individual
unit
Other, please specify (1) depends on individual
unit
What are the maximum allowable (permissible) vibrations levels according to your standards/practice?
If different max levels apply for new generators / refurbished generators / old generators; please
specify values for each row separated by backslash.
Description µm
peak-
peak
µm
s_max
mm/s
rms
mm/s2 % of
bearing
clearance
acc. standard,
which
Additional
info
500 4
500 4
500 4
500 4
bearing)
Shaft vibration in top of the
shaft (lower guide bearing
only)
Description µm
peak-
peak
µm
s_max
mm/s
rms
mm/s2 % of
bearing
clearance
acc. standard,
which
Additional
info
bearing)
500 4

53
against foundation
500 4
against foundation
500 4
foundation
500 4
foundation
500 4
Do you perform impact (“bump”) testing on end winding? (E)
YES NO
X
Do you have limits for results of impact (“bump”) test? (E)
Description YES NO If yes please specify
Frequency X
Accelerance X
other X
Study of machine construction deviations
What should be the allowable deviation in airgap
Description Value [%]
new
machines
Value [%]
refurbished
Value [%]
old machines
(max allowed)
Not important
Deviation of average airgap
X
X
compared to average airgap
X

54
According to your opinion what are max allowed limits for stator roundness
Value
[%]
Description
New After
refurbishmen
t
Max
aceptable for
old unit
Not
important
According to
standard / norm
Eccentricity *) X
Concentricity *) X
Ellipticity *) (ovalization) X
Tri angularity *) X
Four angularity *) X
n-angularity *) X
Circularity *) X
According to your opinion what are max allowed limits for rotor roundness
Value
[%]
Description
New After
refurbishmen
t
Max
aceptable for
old unit
Not
important
According to
standard / norm
Eccentricity *) X
Concentricity *) X
Ellipticity *) (ovalization) X
Tri angularity *) X
Four angularity *) X
n-angularity *) X
Circularity *) X

55
Vibration Fault Experience
Have you experienced problems related to the following vibrations? (S)
specify
Core vibration X
Frame Vibration X
End Winding Vibration X
Head Cover axial Vibration X
Thrust Bearing axial vibration X
Have you experienced problems in vibrations related to the following? (S)
specify
Half of rotor poles short circuit X
Rotor inter turn short circuit X
Stator winding short circuit X
Stator winding inter turn short circuit X
Faulty synchronization X
Runaway X
What stability / vibration problems have you experienced with forced
rotation N. If yes give number of separate cases (S)
Description NO YES
1N
YES
2N
YES
3N
YES
N/2
YES
N/3
YES
other
frequency
Unbalance X
Misalignment X
Bow in shaft X
Unbalance magnetic force static
(stator eccentricity etc.)
X
Description NO YES
1N
YES
2N
YES
3N
YES
N/2
YES
N/3
YES
other
frequency
Axial runout of thrust collar X
Bearing journal runout in guide
bearing
Other, Describe

56
What failures related to vibrations and stability have you experienced (specify if assembly problem is
concerned)(S)
Vibrations /
stability
problems caused
by
YES NO Number
of
cases
last 10
years
Typical
outage
time
[weeks]
Comment / Please
specify
Misalignment (bow in
shaft)
X 4 fixed in planned
maintenance
Misalignment (knee in
shaft)
maintenance
Misalignment (bearing
centers misalignment)
maintenance
Thrust bearing collar
axial runout
X
Vibrations due to
interturn short circuit
in rotor poles
X
speed in operation
area (1N)
X
speed in runaway area
X
Problems with
superharmonic
vibrations with unit at
operational speed
X
Vibration problems
from turbine (water
pulsation etc.)
X
Excitation system X
Other, what (1)
Other, what (2)

57
Related to stator: have you experienced any vibration problems caused by issues such as (S)
Vibrations /
stability problems
caused by
YES NO Number
of
cases
last 10
years
Typical
outage
time
[weeks]
Comment / Please
specify
Stator circularity X
Stator concentricity X
Stator verticality X
Stator ovalisation
due to magnetic
forces
X
to concrete
movement
X
to A.A.R. (Alkali
Aggregate Reaction)
X
Insufficient stator
support from Power
House structure
X
Loose stator core
clamping
X
Distortion due to
stator core section
issues
X
Stator foundation
connection
(please specify
sliding/flexible/other
type)
X
Related to the rotor, have you experienced any vibration problems caused by such issues as (S)
Vibrations /
stability
problems caused
by
YES NO Number
of
cases
last 10
years
Typical
outage
time
[weeks]
Comment / Please
specify
Rotor circularity X
Rotor eccentricity X
Rotor rim looseness
by design (floating
rim)
X
Rotor rim looseness
by failure (shrink fit
X

58
rim)
Rotor rim over-
shrinking
X
Rotor rim under-
shrinking
X
Other rotor rim
issues, please
specify
X
Inadequate
mechanical vs.
magnetic stiffness
X
Rotor vs. stator
vertical alignment
X
Rotor spider tilting
/ torsional stiffness
X
Rotor pole inter
turn short circuit
X
Section B – Additional Questions for Vibration Specialist
Fault Case Studies
What kind of stability problems have you experienced with forced excitation
and what are the response frequencies compared to speed of rotation N. If
yes give number of separate cases (E)
Description NO YES
1N
YES
2N
YES
3N
YES
N/2
YES
N/3
YES
other
frequency
Von Karman Vortices in turbine parts X
Draft tube (eigenfrequency) X
Hydraulic unbalance force X
Unbalanced (non-symmetric)
hydraulic force
X
Pulsation in waterways X
Pressure Surge X
Sealing in runner (Francis) X
Number of guide vanes X
Number of runner blades X
Combination of number of runner
blades and guide vanes
X frequency
x blade
runner

59
What kind of stability problems have you experienced with self excited
rotation N. If yes give number of separate cases (E)
Description NO YES
1N
YES
2N
YES
3N
YES
N/2
YES
N/3
YES
other
frequency
Oil whirl X
Rubbing of static and rotating parts X
Labyrinth sealing X
Bistable vibration X
Unstable unbalance X
Parametric instability X
What kind of stability problems have you experienced with force vibration
response in nonlinear support and what are the response frequencies
compared to speed of rotation N. If yes give number of separate cases (E)
Description NO YES
1N
YES
2N
YES
3N
YES
N/2
YES
N/3
YES
other
frequency
Anisotropic linear support *) X
Isotropic (axi-symmetric non-linear)
support *)
X
Planar asymmetric support *) X
Other what (please explain below) X
Other what (please explain below) X

60
C.3. QUESTIONNAIRE – FINLAND
Utility owner
Country: Finland
Output in
MVA
Description
10
-
20
20
-
40
40
-
60
60 -
100
100 -
200
>
200
Total
number
Speed of
rotation rpm
Description
50
-
100
100
-
200
200
-
300
300 -
400
400 -
500
>
500
Total
number
Turbine
type
number of units 84 46 0 130
Description YES NO Comment /
Please
specify
During
commissioning
Periodical
Monitor
Permanent
Monitor
Included in
protection
Radial / Lateral
shaft vibrations
x x x
Radial / Lateral
bearing
housing
vibrations
x x x
Radial / Lateral
other
vibrations
Describe
Axial
(longitudinal)
shaft vibrations
x x
Axial
(longitudinal)
thrust bearing
x x

61
housing
vibrations
Axial other
vibrations
Describe
Stator frame x x
Stator core x x
Stator end
winding
Head Cover
axial vibration
x x
Thrust Bearing
axial vibration
x x
s_max
mm/s
mils/s
in/s
mm/s2
G
Other? Describe
Shaft vibration at
or near guide
bearings
µm
Bearing housing
vibration
- mm/s
Thrust bearing
axial vibration
. mm/s
Oil head µm -
Shaft coupling -
Stator frame
radial
- mm/s
Stator core radial - mm/s
Stator end
winding
-
Head Cover axial
Vibration
µm -

62
are given)
Description Overall
value
rms 1N harmonics
2N, 3N…
N/2,
N/3…
2f harmonics
2 x 2f, 3 x
2f
Shaft vibration
at guide
bearings
x x x x
Bearing housing
vibration
x x x x
Thrust bearing
axial vibration
Oil head x x x
Shaft coupling
Stator frame
radial
x x x x
Stator core
radial
x x x x
Stator end
winding
Head Cover
axial Vibration
x x x
specify
Nominal speed of rotation x
Rated apparent power of the unit x
Rated reactive power x
Rated voltage x
Number of guide bearings x
Location of thrust bearing x
Construction type according to IEC 34 x
specify
Stiffness of the bearing brackets x
Turbine type x
Magnetic pull x
Other, please specify (1) x

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