Proceedings of the IMAC-XXVIII
February 1–4, 2010, Jacksonville, Florida USA
©2010 Society for Experimental Mechanics Inc.
ACOUSTIC AND MECHANICAL MEASUREMENTS OF AN
HYDRAULIC TURBINE’S GENERATOR IN RELATION TO POWER
LEVELS AND EXCITATION FORCES
F. Lafleur, S. Bélanger, L. Marcouiller and A. Merkouf,
Institut de recherche d’Hydro-Québec, IREQ
1800 boul.Lionel-Boulet
Varennes, Québec
Canada J3X 1S1
ABSTRACT
Recent measurements were performed on the existing generator of an hydraulic turbine to carry
out a power increase diagnostic. These measurements were performed on the rotor and stator of
the generator includes mechanical, thermal and air flow instrumentation. This paper will analyze
the acoustic and mechanical measurements relative to the power level produced. Frequency
analysis of noise, vibration and stress levels will be presented. The multi-channel analysis will
enable us to make correlation analyses between signals and to link the different excitation
frequencies to the electromagnetic or mechanical sources.
INTRODUCTION
A project aimed at increasing the power in existing generators is under way at Hydro-Québec’s
research institute (IREQ). This project combines thermal, electromagnetic, mechanical and fluid
numerical simulation and measurements in order to represent the generator behavior under
different conditions. The simulation results are compared to measurements to ensure that the
model of the generators represents reality. Once this exercise completed, an extrapolation is
made to evaluate the real power this generator can provide without going beyond its mechanical
and thermal limits. This approach will allow the utility to increase the nominal capacity of a
number of generators compared to their nameplate rating by reducing the margin and without
compromising their lifetime.
The first phase of the project concentrated on a thermal and electromagnetic assessment of the
stator of the generator. In order to extend the model to the full generator and to integrate a
multiphysics approach, mechanical measurements are essential. Measurements were therefore
performed recently on the rotor and stator of the generator using thermal, fluid, acoustic and
mechanical instrumentation.
This paper will describe the overall measurement setup with emphasis on details of the
mechanical measurements.
DESCRIPTION OF MEASUREMENTS
A newly refurbished hydraulic power generator was instrumented and monitored. Figure 1 shows
the rotor and stator of the generators during refurbishing. The generator’s specification is 65,000
and 74,750 kVA for summer and winter respectively. The power factor is 0.85; thus the output
power is 55 MW and 64 MW.
Figure 1: Rotor and stator of the hydraulic generator
Performance measurements
Performance measurements of the generator were taken in several operating conditions, namely:
Speed No Load (SNL), 0%, 70%, 85% and 100% of the nominal summer power specifications (55
MW).
Temperature measurements
Several temperature sensors (DTS fibers and thermocouples) were installed to measure the
stator and the stator frame temperature as well as the air temperature in the generator enclosure.
These temperature measurements were used to evaluate the temperature distribution for the
numerical simulation.
Flow measurements
The speed flow measurements of the stator cooling ducts and enclosure were performed using
specially designed static convergent cones with static pressure taps and flow meters [1]. These
measurements were used to evaluate the mass and volume flow for future numerical simulation
purposes.
Acoustic and mechanical measurements
Acoustic measurements were performed around the generator in all the above-mentioned
operating conditions (see Figure 2 for the sound meter positions). These measurements were
used to evaluate the overall noise level for monitoring the working environment and machinery by
non-contact sensing. Frequency analyses were also performed to correlate the acoustic signals
with the operating conditions.
Mechanical instrumentation was installed on the rotor and stator. The rotor instrumentation
includes 3 accelerometers installed in the axial, radial and tangential directions on one of the
rotor’s 16 cross arms and 16 strain gages (one per cross arm, with the position optimized by
finite-element analysis and previous measurements) (Figure 3). These signals were transferred to
the acquisition system by RF transmission. The stator instrumentation allows acceleration
measurements (radial and tangential) on the stator core and stator frame and relative
displacement of the stator core to the stator frame to investigate their relative displacement vs.
temperature and operating conditions (Figure 4). These mechanical measurements were used to
investigate the effect of operating conditions by frequency analysis.
Point 1
Point 8
Point 2
Measurement points are located
at 1.5 meter outside of the rotor
diameter
Point 7
dB(A):1/3 octave and overall
measurements and FFT
( 0-10 kHz and 0-2kHz)
Point 6
Point 3
Point 4
Point 5
Figure 2: Location of acoustic measurement points
Figure 3: Generator’s rotor instrumentation
Stator core and
stator frame
accelerometers
stator core and stator
frame relative
displacement laser
sensor
Figure 4: Stator instrumentation
ACOUSTIC MEASUREMENTS RESULTS
The overall noise level at a specific position vs. the operating conditions ranges from 80.7 dB(A)
in SNL conditions to 85.5 dB(A) at 55 MW (100% of summer generator’s power specification (55
MW) (Figure 5). The noise level slightly exceeds the prescribed value of 85 dB(A) for the power
generator. The maximum noise emission predominant frequency is 120 Hz (twice the line
frequency) but includes a large frequency content, as illustrated in Figure 6, which shows the
linear weighted noise level of the generator for the frequency range of 0-2 kHz under different
operating conditions. This frequency content allows us to identify mechanical signals (rotation
speed and harmonics, blade passing frequency, etc.) and electromagnetic excitation on the rotor
and stator of the power generator (twice the line frequency and harmonics, slot passing frequency
and harmonics, electromagnetic torque transmission between rotor and stator).
90,0
88,0
85,5
Noise level (dB(A))
86,0
84,5
84,7
84,0
82,0
80,7
81,3
80,0
78,0
Point 6
77,3
76,0
74,0
72,0
70,0
Bruit de
fond
SNL
0%
70%
80%
100%
Operating conditions
Figure 5: Noise level vs. operating conditions
100
SNL
90
0%
70%
Noise level (dB)
80
80%
70
100%
60
50
40
30
20
0
500
1000
1500
2000
Frequency (Hz)
Figure 6: Noise level (dB) vs. frequency, 0-2 kHz
MECHANICAL MEASUREMENTS RESULTS
Rotor mechanical instrumentation
The mechanical measurements taken on the rotor allowed us to evaluate the stress and vibration
level of the rotor cross arms. The strain analysis in the SNL and other operating conditions shows
that the strain level is low on the rotor structure. The average stress (for the rotor’s 16 cross
arms) at 100% operating conditions is 94.0 MPa with a standard deviation of 3.2 MPa. This
represents an increase of the stress from the SNL operating condition of 65.4 MPa cause by the
mechanical torque transmission at maximum power. At the measurement points, for this type of
material (carbon steel), the stress level is considered to be low and uniform over the rotor
structure. These stress levels include the static and dynamic stress. Figure 7 shows the
frequency spectrum of the dynamic part of the stress levels. The dominant frequencies are
components of the electromagnetic torque between rotor and stator at 94.74 Hz and harmonics at
189.5 Hz but the signal also includes some of the low-frequency rotation speed (94.7 RPM or
1.5783 Hz) harmonics.
Radial and axial acceleration levels were predominant on the rotor. The frequency analysis (0500 Hz) is shown in Figure 7 for the two signals at 100% operating condition in comparison with
all strain gauge signals in the same operating condition. The specific frequency content is
presented for the rotor measured signal, which represents the main electromagnetic torque
excitation but, also, at a lower level, the mechanical excitation.
Figure 7: Accelerometers and strain-gauges frequency analysis
Stator mechanical instrumentation
The mechanical measurements on the stator allowed us to evaluate the relative distance between
the stator and stator frame and to evaluate the vibration and displacement level of the magnetic
core of the stator. The distance between the stator and its frame is constantly changing because
of thermal expansion of the components. A new type of anchor for the stator core lamination to
the stator frame was used to refurbish the generator. The core laminations are aligned with a tube
in which a clamping stud is inserted: the theoretical gap between lamination and tube at room
temperature is 0.1875 mm. The temperature difference between the warm core lamination and
the colder stator frame in operation reduces this gap as the power is increased and creates
interference at rated power. The average, minimal and maximal distances between the stator and
its frame are given in Figure 8. The results show some interference between the core and the
frame but only at the active rated power of 55 MW (100%). At the 85% operating condition level,
the average value indicates interference but the minimum value shows that the contact is not
steady. These results comply with temperature simulations of the thermal expansion between
these two elements.
0,15
Interference
0,10
Distance (mm)
0,05
0,00
SNL
70%
85%
100%
-0,05
-0,10
-0,15
gap
-0,20
Figure 8: Relative displacement between the core and the frame of the stator
The displacement of the stator core in the radial direction was evaluated from double integration
of the accelerometer signal. The values recorded at 120 Hz ranged from 18 to 22 µm, in
compliance with the applicable limit of 30 µm for displacement of the stator core.
Spectral analysis of the radial stator vibration under different operating conditions (Figure 9)
shows that the predominant vibration level is 120 Hz and its harmonics. The 100% operatingcondition vibration presents a modulation of the 120 Hz at about 40 Hz. This low-frequency
vibration causes a higher displacement than the 120 Hz. The origin and effect of this vibration
need to be identified.
1
0,9
Acceleration (m/s2)
0,8
0,7
100%
0,6
80%
0,5
70%
0,4
SNL
0,3
0,2
0,1
0
0
500
1000
1500
2000
Frequency (Hz)
Figure 9: Spectral analysis of the stator radial vibration
RELATION OF ACOUSTIC AND MECHANICAL MEASUREMENTS TO EXITATION FORCES
The forces on the rotor and the stator of the power generator are a combination of mechanical
and electromagnetic excitation. Spectral analysis of the acoustic rotor and stator excitation shows
that one signal alone cannot give a complete diagnosis of the status of the power generator. The
frequency content at the stator shows a major contribution of the electrical excitation (120 Hz and
harmonics). The rotor excitation shows a frequency content that is governed by mechanical and
electromagnetic excitation (rotation frequency and electromagnetic frequencies). The acoustic
excitation shows a richer frequency content. For example, the acoustic spectrum includes all the
120 Hz and harmonics (present at the stator) and also frequencies present at the rotor
measurement points such as the electromagnetic torque between rotor and stator at 94.74 Hz
rotation speed harmonics.
CONCLUSION
A series of measurements were performed on a hydraulic power generator equipped with
mechanical instrumentation on the rotor and stator. Acoustic measurements were also performed.
Spectral analysis of the rotor and stator instrumentation signals shows that the different excitation
forces are not present on the all sensors. The rotor instrumentation shows principally the rotation
frequency and electromagnetic torque between the rotor and the stator. The results of the stator
measurements illustrate mainly the line frequency (120 Hz) and its harmonics. The acoustic
signal shows a richer frequency content that includes most of the electromagnetic and
mechanical excitation, which paves the way for development of a generator diagnostic by non
contact instrumentation. Further analysis of the complete set of mechanical and acoustic signals
could lead to a more complete hydraulic power generator diagnostic based on non contact
acoustic measurements.
ACKNOWLEDGMENTS
The authors acknowledge the technical staff of the Hydro-Québec research institute (IREQ) for
the quality of their work. This team includes Guillaume Chaput, Jean-Philippe Charest-Fournier,
Calogero Guddemi, Luc Martell, Benedicto Navarette, Jean Picard and Mathieu Soares.
REFERENCES
[1] IREQ-2009-0001-Méthode de caractérisation de l’écoulement à la sortie des évents du stator
[2] Hydro-Québec Production, GEME – Guide des exigences de maintenabilité et d'exploitabilité,
Module COM01- – Sécurité Technique, Mars 2009
[3] Hydro-Québec Production, GEME – Guide des exigences de maintenabilité et d'exploitabilité,
Module GR07 – Alternateur, revision in progress