Sandia 2014 Wind Turbine Blade Workshop- Newman

1. Ground Based Inspection of
Wind Turbine Blades
John Lindberg, PE
EPRI Program Manager, NDE Innovation
John Newman
President, Digital Wind Systems Inc.

2. 2© 2014 Electric Power Research Institute, Inc. All rights reserved.
“ The wind industry has traditionally believed value creation is
concentrated in manufacturing and wind farm development
since…turbine performance is generally 93-94% available and
cash flow will be stable and predictable.
Our research…suggests improved O&M could account for
nearly a 20 percent increase in the equity internal rate of
return (IRR).”
McKinsey& Company
“How to Operate and Maintain Wind Assets”
Number 1, Winter 2008
Ground Based Inspection of
Wind Turbine Blades

3. 3© 2014 Electric Power Research Institute, Inc. All rights reserved.
The current wind energy tower count at approximately
50,000 USA and 60,000 European makes blade health
monitoring with retro fitted instrumentation impractical and
expensive.
There is an industry need to:
1. drive down blade maintenance costs and improve
reliability and service life
2. implement better, faster, cheaper blade inspection to
better manage blade repairs uptower vs rotor removal
repairs/replacement.
Ground Based Inspection of
Wind Turbine Blades

4. 4© 2014 Electric Power Research Institute, Inc. All rights reserved.
EPRI in collaboration with Digital Wind Systems, Inc. are testing and
validating the “SABRE™” ground based, high speed inspection technology, for
inspection and monitoring the structural integrity of wind turbine blades.
SABRE™ Features:
• Inspects wind turbine blades from the ground for detection of surface and
subsurface structural defects in operating wind turbine blades.
• No uptower access required.
• Towers may be inspected in less than 30 minutes (50m Blades), in good
weather.
• Incorporates multiple proprietary sensors including: Thermal Imaging, Wide-
Band Acoustic Spectral Analysis and Phase Imaging Photography
• Detects blade anomalies such as: propagating fatigue cracks, disbonds,
breaking, weak or missing adhesive joints, fiber waves, damage, gel-coat
cracking, LE erosion, delaminations, poor repairs.
Ground Based Inspection of
Wind Turbine Blades

5. 5© 2014 Electric Power Research Institute, Inc. All rights reserved.
SABRE™ Technical Overview
IR Imaging of Rotating Blades (Patent Pending)
• A specialized IR camera developed by DWS detects thermo-elastic and
frictional heating from damaged blade material due to cyclic loads. (hot
spots)
• In addition, cool air flow exiting the blade through blade perforations
such as cracks, crush damage and lightning strikes are also detected.
(cool spots)
• Damage and delaminations block thermo-elastic blade emission from
rotating blades. (cool spots)
Fiber Wave defects
in 49M blade carbon
fiber spar caps
during operation

6. 6© 2014 Electric Power Research Institute, Inc. All rights reserved.
Image of thermo-elastic emission from an operating 49m blade (at left)
IR Imaging
Multiple varying loads on blades
created generates internal heat
by the viscoelastic effect.
After blades reach thermal
equilibrium with air, the
temperature profile corresponds
to the sum of all of the principal
stresses.

7. 7© 2014 Electric Power Research Institute, Inc. All rights reserved.
IR Imaging- Fiber Waves Carbon Fiber Spar Cap
A turbine blade is
shown during normal
operation. No defects
present.
A similar wind turbine
blade with fiber wave
defect indications
located in the carbon
fiber spar cap.

8. 8© 2014 Electric Power Research Institute, Inc. All rights reserved.
Identifying IR reflections is critical to
eliminating false calls. Blades are excellent
IR reflectors.
Sequential frame analysis shows the
emissions are coming from the blade and
are not reflections of the tower or nacelle.
.
SABRE DWS
SABRE DWS
IR Imaging- Fiber Waves Carbon Fiber Spar Cap
Indication on blade falsely identified
as a defect in published paper.
ECNDT 2006 – Tu.1.5.3 P. Meinlschmidt

9. 9© 2014 Electric Power Research Institute, Inc. All rights reserved.
Infrared Results: Blade 1, FW indications are located on the HP Spar Cap
@ 32.1 and 37.8m
Evaluation:
1. Blades 1, a severe fiber wave (FW) defect
located on spar cap HP side, approximately
37.8m from root. Size is 0.5x0.5m
2. Indications can be graded by area , location
and signal to noise ratio (S/N)
FW1 FW2Reflection of Spar
Tower/Nacelle
37.8m32.1m
SABRE DWS
Single
Frame
Multiple
Sequential
0.33msec
Frames

10. 10© 2014 Electric Power Research Institute, Inc. All rights reserved.
IR Imaging- Delaminations near blade tip
Delamination or crush damage blocks heat emission from the blade during rotation.
Two damaged areas near
blade tip, LP Side

11. 11© 2014 Electric Power Research Institute, Inc. All rights reserved.
IR Imaging- Blade Anomaly
• 2 indications on 2 blades, 26.5 ft. from the hub
• Tap Test was un-revealing, eliminating transportation damage and
suggests the anomalies are deeper than 0.5 inch

12. 12© 2014 Electric Power Research Institute, Inc. All rights reserved.
IR Imaging- Blade Anomaly, Up Tower Tap Test

13. 13© 2014 Electric Power Research Institute, Inc. All rights reserved.
IR Imaging- Small Lightning Strikes
Multiple indications on one blade only.
Not the same blade

14. 14© 2014 Electric Power Research Institute, Inc. All rights reserved.
IR Imaging- Bolted Repairs
Bolted RUK
repair, typical
Dark indications show lowered
Stress concentration at typical
successful bolted repairs.
SABRE
Left: The SABRE IR camera can detect thermo-elastic
emissions from cyclical stress loading of structures such as
operating wind turbine blades (Patent Pending). The high
stress concentration near the TE on the HP side of this blade
is an anomaly.
Up-tower inspection revealed all bolts in this repair to be
loose or broken, but no blade failure.

15. 15© 2014 Electric Power Research Institute, Inc. All rights reserved.
SABRE™ Technical Overview
Acoustic Spectral Analysis (Pat. Pending)
• Operating wind turbine blades generate up
to 3 psi pressure inside at the blade tip due
to centripetal acceleration.
• This compressed air, escaping through
cracks, lighting strike holes generate both
sonic and ultrasonic signals, which to a
sensor on the ground, are Doppler shifted
as the turbine rotates.
• Our wide band sensor detects these
Doppler shifted signals
• Digital spectral analysis and software
algorithms determine the location of
these acoustic sources on the blade.
@17.4 rpm

16. 16© 2014 Electric Power Research Institute, Inc. All rights reserved.
• Acquires all the data to inspect all three turbine blades
in less than 30 seconds.
• Calculates sound source location on blade.
Detects:
1. breaches in blade outer mold line due to leading or
trailing edge splits, cracks, lightning strikes, damage
2. aerodynamic changes due to improper blade pitch
angle/control, changes to the blade shape
such as spar web to spar disbonds, disrupted airflow
due to damage
3. corona discharge due to degraded electrical insulation
4. mechanical noise from worn bearings, machinery
SABRE™ Acoustic Spectral Analysis

17. 17© 2014 Electric Power Research Institute, Inc. All rights reserved.
Approaching
Blade
Receding
Blade
TIME
Signal
Frequency
Acoustic Spectral Analysis

18. 18© 2014 Electric Power Research Institute, Inc. All rights reserved.
#16 (17.14 RPM)
#8 (9.61 RPM)
New Blades
10 Year Old Blades
Acoustic Spectral Analysis

19. 19© 2014 Electric Power Research Institute, Inc. All rights reserved.
Acoustic Spectral Analysis- TE Split
Acoustic spectrum data is collected by a sensor located at bottom center of wind turbine.
In the example shown below, a signal (arrow) is seen in the spectrum of blade pass (1).
The spectrum below shows three consecutive blade passes, labeled (1, 2 & 3), as
recorded at a location in the plane of the turbine disk at bottom dead center. The signal
parameters are measured and entered into the SABRE software to calculate the position
of the sound source anomaly on the blade.
1 2 3
Trailing Edge Split at Blade Tip
The SABRE calculation determined the source location, shown
above, to be 129 ft. from the hub. Up-tower rope access technicians
found the trailing edge split shown at left, 130.7 ft. from the hub.

20. 20© 2014 Electric Power Research Institute, Inc. All rights reserved.
Acoustic Spectral Analysis- Corona Discharge
High frequency 60Hz. Spikes detected in the nacelle from the ground
consistent with corona discharge due to insulation breakdown.

21. 21© 2014 Electric Power Research Institute, Inc. All rights reserved.
SABRE™ - Phase Imaging
Photography
Regular Tele-photo
image of blade
SABRE Phase Image
Photography provides
very high contrast to
detect surface damage,
erosion, damaged
gel coat.
(Patent Pending)

22. 22© 2014 Electric Power Research Institute, Inc. All rights reserved.
EPRI Wind Turbine Blade Guide
• EPRI Blade Maintenance Guideline:
– Level 1 Minor Cosmetic
– Level 2 Major Cosmetic
– Level 3 Minor structural (defect does not exceed 200mm
x 200mm)
– Level 4 Moderate structural (defect does not exceed
1000mm x 1000mm)
– Level 5 Major structural (repair to be scheduled asap)
– Level 6 Catastrophic (secure rotor immediately)

23. 23© 2014 Electric Power Research Institute, Inc. All rights reserved.
Table 1. Blade Grade Evaluation Key: Repair Priority Action
Level 0 No Indications NA Run, Re-inspect 1 yr.
Level 1 Minor cosmetic, GC, LG NA Run, Re-inspect 1 yr.
Level 2 Major cosmetic, LG, LG Low Run, Re-inspect 1 yr.
Level 3 Minor structural (DL, LG defect does not exceed 200x200mm) Low Run, Re-inspect 6 months
Level 4 Moderate structural (defect does not exceed 1000mmx1000mm) Med Run, Re-inspect 3 months
Level 5 Major structural: All splits, open cracks, IB & M fiber waves Hi Take Off Line Repair /Replace
at spar cap or blade root,
Table 2. Defect Key:
FW = Fiber Wave (Wrinkle) Defect
DL = Delamination, Crush Damage
LG = Lightning Strikes
CR = Crack
SC = Stress concentration
TES= Trailing Edge Split
LES= Leading edge Split
GC = Degraded Gel Coat
Blades are graded per Table 1 below. Defect Type abbreviations are shown in Table 2. Result Grades are
given only for areas inspected, abbreviations listed in Table 3.
Defect abbreviations used in this
report are defined in Table 2. below.
Abbreviations for Areas of
blades inspected
Table 3. Blade Area Key:
LE = Leading Edge
TE = Trailing Edge
IB = inboard 1/3
M = middle 1/3
OB= outboard 1/3
HP = High Pressure Side
LP = Low Pressure Side
W = whole blade
Proposed Blade Maintenance Priority based on
Indication Size/Location /Type

24. 24© 2014 Electric Power Research Institute, Inc. All rights reserved.
Summary
• The Digital Wind System SABRE™ ground based inspection
system for wind turbine blades integrates three complementary
technologies:
• First, a specialized IR camera is used to detect the very slight
thermo-elastic and friction generated emissions from damage or
propagating defects when they are subjected to cyclic
gravitational loads as the turbine rotates.
• Second, acoustic spectral analysis to detect and locate cracks
and other breaches of the blade shells as well as to detect
irregular surfaces such as missing gel coat areas and leading
edge erosion.
• Finally, Phase Image Photography capability to detect and locate
surface anomalies.

25. 25© 2014 Electric Power Research Institute, Inc. All rights reserved.
Summary
EPRI Supplemental Project Notice
Product ID: 3002001487 - Advanced
Inspection of Wind Turbine Blades
• Perform field demonstrations to assess
the reliability and ease of deployment of
IR Imaging and acoustic spectral analysis
techniques and equipment to detect flaws
in operating wind turbines.
• Correlation of the IR and acoustic data to
the actual field conditions will be
performed for technique assessment and
validation, when available.
• Field Demonstration at a wind power site
SABRE can provide operators
valuable information to:
• Data base to assist maintenance
planning
• Enable identification and
categorization of
blade anomalies to repair up tower.
• Survey potential wind farm
acquisitions

26. 26© 2014 Electric Power Research Institute, Inc. All rights reserved.
The authors would like to thank:
Jeff Hammitt, NextEra Energy
Maya Nissin, formerly EDPR
Mark Rumsey, Sandia (retired)
Scott Hughes, Mike Desmond
National Wind Technology Center
Ground Based Inspection of
Wind Turbine Blades

27. Together…Shaping the Future of Electricity
John Lindberg, PE
EPRI Program Manager, NDE Innovation
Jlindberg@EPRI.com
John Newman
President, Digital Wind Systems Inc.
JWNewman50@aol.com