Vibration Expert Systems | Consulting | System Design
AIRGAP MONITORING ON
HYDRO GENERATORS AND
RELATED CASE STUDIES
28.05.2020
Ozren Oreskovic
AGENDA:
- Introduction to Air Gap Monitoring
- Sensor Configuration in Offline and Online Air Gap
Measurements
- Measured and Calculated Values
- Tolerances, Standards and Recommendations
- Real-life Scenarios/Case Studies
- Integration with Other Monitoring Technologies
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Introduction to Air Gap Monitoring
Why monitor air gap?
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Hydro Measurements and supported diagnostics
Supported Diagnostics:
Rotor dynamics (relative shaft and
bearing vibrations)
Stator and end windings vibrations
Air gap and flux
Turbine cover vibrations
Process quantities
Electric quantities
Partial Discharge
Hydraulic quantities
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Fault identification and diagnostics
·
Faults analysis process:
- Cross correlation of signal vector components in different
operating modes (e.g. Run up, steady state, partial load etc.)
- Comparison to reference data in different operating modes
- Change detection
- Fault analysis
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measuring point / sensor
1x – Vibration signal component on
first harmonic frequency of rotation
2x – Vibration signal component on
Second harmonic frequency of
rotation
DC – static signal component
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Air Gap monitoring
+
+
Photos: Voith
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Air Gap monitoring - SENSORS
Optional (but important)
Phase refernce
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Air Gap
Magnetic Field
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Air Gap monitoring - How to measure and obtain the right data?
Any type of
signal connected
(sensor is
required)
Custom tailored
analysis applied
Recognize
Machine
operating
conditions (Stop,
run up…)
Custom tailored
GUI
Flexibility to adopt the monitoring strategy to specific machine problem!
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Sensor Configuration in Offline and
Online Air Gap Measurements
Phase reference
Phase is measured as phase lag φ, from the key phasor pulse to the positive peak of the
vibration first harmonic.
Also used to identify pole profile for air gap and flux monitoring
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Capacitve Gap Sensor
Interface Unit
CGL – Capacitive gap
Linearization module
CGP – Capacitive Gap Probe
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Capacitve Gap Sensor
TYPE
CGP-01
CGP-02
CGP-03
CGP-04
DIMENSIONS
80x17x1mm
135x32x1.7mm
230x32x2.4mm
250x40x3.2mm
CABLE LENGTH TO INTERFACE UNIT
1.2m
1.2m
2.0m
2.0m
RANGE
2 to 10mm
3 to 15mm
5 to 25mm
10 to 50mm
•
•
•
•
•
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Operational Temperature Range: -15 to 125C
Linearity of outputs: maximum +/- 3% of reading
Temperature drift: <300ppm/C at mid-range
EMC: Probe withstands magnetic field up to 2 Tesla (50/60 Hz)
Material: Non-conductive and semi-conductive
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Capacitve Gap Sensor
• Frequency response:
0...1000Hz, (-3dB)
• Power input:
+18 to 36VDC, 220mA max.
• Operating temperature:
-15 to 70C
• Relative humidity:
95% max, non condensing
• Dimensions:
220×120×80mm w/o cable inlets
• Cable length from Interface Unit:
10m
• Case protection class:
IP64
• Material:
Aluminum
• Outputs (factory set):
Current (0 to 20mA, 4 to 20mA)
Voltage (0 to 10V, 2 to 10V)
CGP and CGL when serialized pair
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Accuracy below 1%
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Sensor installation
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Sensor installation
Pole image
Inter poles (signal saturation)
Pole profile waveform signal
Profile of two poles - zoomed
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On-line monitoring – number and location of probes
• GUIDELINES for installing the PROBES considering the number and position
• Number of PROBES is dependent on the Generator diameter
• 4 SENSORS for <7.5m diameter
• 8 SENSORS for 7.5 to 12m diameter
• 12 to 16 SENSORS for larger
• Place PROBES on Top of Stator
• Top and Bottom if stator core height is >2m
Monitor the air gap and related changes
DURING CONTINUOUS OPERATION
Observing the dynamic signals and their
correlations
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Off-line monitoring – number and location of probes
• GUIDELINES for installing the PROBES considering the number and position
• Number of PROBES for rotor shape in slow roll
• 2 SENSORS in two planes on same line on the stator
(up and down)
• Number of PROBES for stator shape in slow roll
• 2 SENSORS in two planes on same line on the rotor
(up and down)
• Number of PROBES for eccentricity in slow roll
• 4 SENSORS in same plane
Monitor the air gap when machine is standstill
MANUALLY TURNING THE ROTOR
Observing the real stator and rotor shape
after installation
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Tolerances, Standards and
Recommendations
Air Gap Related Tolerances, Standards and Recommendations
• IEC 60034-33 / Under development
• ISO 19283:2018 / Chapter 7 Monitoring and diagnostic techniques – draft, in making
ISO 19283:2018 will be is the first standard to assess this important monitoring technique adequately
• air gap monitoring only briefly mentioned in IEEE 1129
• recommendation to include air gap data given in ISO 20816-5
• CEATI recommendations (Parts I-V): Hydroelectric Turbine Generator Units - Guide for
Erection Tolerances and Shaft System Alignment
• and more (e.g. USBR ALIGNMENT OF VERTICAL SHAFT HYDROUNITS)
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Air Gap Related Tolerances, Standards and Recommendations
CEATI recommendations (Parts I-V): Hydroelectric Turbine Generator Units - Guide for Erection Tolerances and Shaft System Alignment
Tolerances as % of nominal air gap
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Air Gap Related Tolerances, Standards and Recommendations
IEC 60034-33 : Rotating electrical machines – Part 33: Specific technical requirements for hydro generators (WD
Edition 3)
Should contain structural tolerances related to the air gap:
•
•
•
•
•
•
Maximum air gap variations
Stator circularity
Stator concentricity
Rotor circularity
Rotor concentricity
Minimum air gap
in 4 categories: GOOD, ACCEPTABLE, HIGH, CRITICAL
expressed in percentage of nominal air gap
Structural tolerances – obtainable from air gap measurements.
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Monitoring technique
Air Gap Related Tolerances, Standards and Recommendations
Monitoring and diagnostic techniques (chapter 7)
ISO 19283:2018 / Chapter 7
Generator Component - example
• Air Gap
• Magnetic flux
Found in Annex C
• Partial discharge analysis
• Stator frame and core vibration, core temperature
• Stator end winding vibration
The new techniques which have not (so far) been included in the standards are framed
• Primary descriptors and plots
• Correlation measurements
correlation with processing parameters (active, reactive
power, temperatures, water level, flow etc.) is important
(similar data is compared)!
• Adaptive monitoring strategy
setting of ALARMS according to operating regime (speed, active power,...)
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Air Gap Related Tolerances, Standards and Recommendations
ISO 19283:2018 / Chapter 7
Annex C: Primary monitoring and diagnostic techniques
Informations – dependent on the number of installed sensors
Possible result of applied analysis procedure
Number of installed sensors
1
2
4+
Minimum/Maximum/Average air gap (AGmin) – measured
from each sensor
●
●
●
Maximum neighboring poles difference (AGdiff)
●
●
●
Rotor poles profile
Rotor centre position
Rotor rotation centre position
Rotor dynamics
Stator shape – stator deformation
Stator centre position
Minimal air gap with stator shape impact
●
●
●
●
●
●
●
●
●
●
●
●
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Air Gap Related Tolerances, Standards and Recommendations
ISO 19283:2018 / Chapter 7
Annex C: Primary monitoring and diagnostic techniques
Descriptors important for air gap monitoring
calculated for each sensor (signal processing must be involved)!
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Measured and Calculated Values
Air Gap Related measured and calculated values
ONE TURN
CGP1
Pole No 1
CGP2
Pole No 1
CGP3
Pole No 1
Pole No 1
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CGP4
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Air Gap Related measured and calculated values
CGP1
CGP2
CGP3
CGP4
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Air Gap Related measured and calculated values
pole #1
trigger
pole #29
trigger
• Showing pole profile in one revolution (minimum of signal)
• Upper trace is raw signal at one sensor
• Lower trace shows air gap at each pole at that sensor
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Air Gap Related measured and calculated values
Air gap and Magnetic field raw signal
Pol profile / Air gap
Pole profile / Magnetic field
Comparison of Air Gap with Magnetic Flux can point to electrical or mechanical nature of magnetic unbalance
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Air Gap Related measured and calculated values
Ideal Rotor/ Stator
Eccentricity – Rotor/ Stator
without dynamic compensation
Protruding Pole (10%)
with dynamic compensation
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Air Gap Related measured and calculated values
Waveform (AG + trigger)
Pole profile
Average (DC) gap
s1n Amplitude
STATOR AND
s1n Phase
ROTOR SHAPE (*)
DYNAMIC ROTOR ECC.
(*) multiple sensors needed
AG max - Value + pole #
AG min - Value + pole #
AG min – Value + pole #
AG max – Value + pole #
RUB DETECTION/PROTECTION
s2n Amplitude
(AG max – AG min)
s2n Phase
LOOSE RIM INDICATION LOOSE RIM
AGdiff
AGdiff
without vibrations/ ecc.
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with vibrations/ ecc.
AGdiff Value + pole #
LOOSE POLE
Adjacent pole difference / pole
Looseness detection over long time
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Air Gap Related measured and calculated values
Air Gap Polar View: Screen from CoDiS-PDS
stator shape
rotor shape
stator center
Air Gap Related measured and calculated values
Rotor circularity
Rotor concentricity
rotor statical center +
precession (orbit)
Stator circularity
Stator concentricity
minimum AG @ angle for pole #
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- Real-life Scenarios/Case Studies
- Integration with Other
Monitoring Technologies
Typical problems detectable by air gap
Loose rotor rim
Overshrunk rotor rim
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Eccentric rotor rim
Blocked stator soleplates
Stator concentricity offset
Protruding pole
Stator circularity offset
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Case Study / Loose (oval) rotor rim
unit A
Maximum AG
Average AG
Minimum AG
Maximum AG
Average AG
Minimum AG
Two similar units in the same power
plant
unit A: NO loose rim detected (lines in
parallel)
unit B
unit B: Loose rim detected (lines
separated, due to unequal stretching)
Air gap by pole number (one sensor)
Maximum AG
Average AG
Minimum AG
Air Gap descriptors (slide)
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Case Study / Loose (oval) rotor rim
60% RPM / Rotor circularity = 1.9 %
100% RPM/ Rotor circularity = 6.3 %
Full load / Rotor circularity = 8.2 %
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Case Study / Loose rotor rim segment + eccentric rotor rim
Before calculating circularity 1X must be compensated
Large 1x rotor
NOMINAL SPEED
1x not compensated
Increasing rotor 1x
OVERSPEED
1x compensated
LOOSE RIM SEGMENT
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Case study / Stator concentricity offset (stator to rotor eccentricity)
Stator concentricity offset in tolerance ~6%
Bearing overheating with field flash
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Case study / Stator concentricity offset (stator to rotor eccentricity)
NO FIELD
FIELD FLASHED
Shaft centerline moves excessively with excitation – causing the rub and bearing heating
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Case study / Core circularity offset – segment joint gap
Extremestator
statorcore
corevibrations
vibrations– –32mm/s
32mm/s@@100Hz
100Hz
Extreme
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Increasing PD on one of the phases (3x in 4 years)
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Case study / Core circularity offset – segment joint gap
Three-segmented stator
(*) Air gap sensors magnetically attached to
the stator core / pole; measured in cold state
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Stator shape measured from rotor
Rotor shape measured from stator
•
•
stator circularity offset: 22.1 %;
rotor circularity offset: 7.9 %
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Case study / Core circularity offset – segment joint gap
Stator core vibrations reduced <4mm/s @ 100Hz
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PD reduced to nominal values
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Conclusion
1) Air Gap monitoring is very important tool in understanding dynamic
behavior of hydrogenerators
2) To monitor air gap one needs to install the right sensor configuration,
depending on the machine design
3) Extract the right parameters and correlate with other measurements
(flux, shaft displacement and bearing vibrations, stator frame and core
vibrations etc.)
4) Correlate the data in different operating conditions (run up, field flash,
overspeed, run down)
5) Pin point a root cause of a problem
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THANK YOU
ANY QUESTIONS?