HCPV Tracker Accelerated Reliability Tests
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Transcript of HCPV Tracker Accelerated Reliability Tests
© SolFocus, Inc. 2010Patents Pending
HCPV TrackerAccelerated Reliability TestsJon G. Elerath, Ph. D.Santa Clara Valley Chapter, IEEE Reliability SocietySeptember 28, 2010
Slide 2© SolFocus, Inc. 2010; Patents Pending
Agenda
Hardware
Acceleration Profile
Test Setup
Statistical Basis of Test
Results and Conclusions
Slide 3© SolFocus, Inc. 2010; Patents Pending
CPV system
Hardware
Power unit
CPV panel
Slide 4© SolFocus, Inc. 2010; Patents Pending
Two Axes of Movement Azimuth: Controlled by Slew Drive Elevation: Controlled by Screw Jack
Tracker Test Units/Systems 10 test systems with dummy
weights to create same forces and mechanical moments, fully accelerated
2 systems, fully accelerated 1 system, semi-accelerated
Tracker Moving Mechanical Parts
Tracker is programmed to “track” thesun based on its longitude, latitude and earth movement.
Slide 5© SolFocus, Inc. 2010; Patents Pending
Acceleration Profiles
Why do Accelerated Tests? We can’t wait 25 (calendar) years to assess tracker reliability Accumulate 25 years experience in 1.25 to 1.5 (calendar) years
Acceleration Process Reduces “Dead-Time” Fully-Accelerated
• Approximately 20 “days” of operation in one calendar day• No power produced
Semi-Accelerated• Approximately 10 “days” of operation in one calendar day• Power is produced during daylight hours• Accelerated mode during non-power producing hours (night)
Slide 6© SolFocus, Inc. 2010; Patents Pending
Acceleration Profiles
Acceleration process reduces “dead-time”
"Dead-time" between AZ or EL movements during power production
Short movement durations don't change
Reduced "dead-time" between movements in accelerated mode
Slide 7© SolFocus, Inc. 2010; Patents Pending
Test Setup
For Both AZ and EL Tests 8 accelerometers 4 voltages 1 motor current 5 thermocouples
Characterization Tests Fixed start and end points (travel) Run continuously from start
to end Record accelerations, current,
voltages, and temperatures
Analyze as Functions of: Time Frequency
Look for Changes in: Amplitudes Frequencies
Slide 8© SolFocus, Inc. 2010; Patents Pending
The “Bathtub Curve” Mechanical hardware usually fails
according to a “bath-tub” curve...which is really three different curves.
a = characteristic lifeb = shape parametert = time
Failure rate direction depends on bb < 1.0 → decreasing b = 1.0 → constantb > 1.0 → increasing
Typical High
Ball Bearings 1.3 3.5
Roller Bearings 1.3 3.5
Couplings, Gear 2.5 4.0
Gears 2.0 6.0
…For the Statistical People
bb
aaab tttf exp)(
1
0 5 10 15 20 250
0.000001
0.000002
0.000003
0.000004
0.000005
0.000006
Decreasing Constant Increasing "Bathtub"
WEIBULL SHAPE FACTOR b
Slide 9© SolFocus, Inc. 2010; Patents Pending
Tests when b ≠ 1.01) Two variables, a and b2) Select a confidence level (90%
lower one-sided confidence limit)3) Assume a b 4) Establish a life (t = 25 yrs) and a
probability of failure for that life5) Calculate the resulting a6) Calculate the number to test and
number permitted to fail7) After the test, calculate beta to
validate assumption #3
…For the Statistical People
bb
aaab tttf exp)(
1 a = characteristic lifeb = shape parametert = time
Slide 10© SolFocus, Inc. 2010; Patents Pending
Example Test Results
Elevator motor current and array motion speed
Current decrease and speed increase indicate decreased forces (friction)
Decreases in vibrations (15 Hz and 2.2 Hz) indicate mechanical wear-in
50 100 150 200Time [sec.]
0
0.5
1
0 94 188 282 376 470Time [sec.]
0
0.5
1
1.5
0
0.1
0.2
0.3
Speed
Current
- At 0 Years
- After 5 Years
- At 0 Years
- After 5 Years
50 100 150 200Time [sec.]
0
0.5
1
curr
e nt
[ Am
p s /
1 0]
0 94 188 282 376 470Time [sec.]
0
0.5
1
1.5
curr
e nt
[ Am
p s /
1 0]
0
0.1
0.2
0.3
Spee
d, A
rbitr
ary
S cal
e
Speed
Current
- At 0 Years
- After 5 Years
- At 0 Years
- After 5 Years
5 years accelerated time occurred in 3 months calendar time
Slide 11© SolFocus, Inc. 2010; Patents Pending
Example Test Results
Azimuth Motor Vibration A change in amplitude that
peaks at 283 sec. Possible causes are:
• Increased friction in AZ movement based on AZ position
• Motor bearings wear Amplitudes of many
frequencies increased Two tear-downs to determine
causes• 10 years (August 2010)• 25 years (end of test)
0 2000 4000 6000 8000 10000Frequency [Hz]
0
0.01
0.02
0.03
0.04
0.05
0 94 188 282 376 470Time [sec.]
-40
-30
-20
-10
0
10
20
30
40 - At 0 Years- After 5 Years
- At 0 Years- After 5 Years
0 2000 4000 6000 8000 10000Frequency [Hz]
0
0.01
0.02
0.03
0.04
0.05
0 94 188 282 376 470Time [sec.]
-40-30
-20
-10
0
1020
30
40 - At 0 Years- After 5 Years
- At 0 Years- After 5 Years
Slide 12© SolFocus, Inc. 2010; Patents Pending
Test Results
Elevator Rod-End Bearing Still accurately tracking, but high
vibrations at ends of motion FFT for lowest vibrations (3rd
quintile) and highest vibrations (5th quintile) for the test with bad rod-end
Significantly different frequencies dominate and common frequencies have higher amplitude for 5th quintile
Torn-down and analyzed. Component problem, not a design issue
0 85 170 255 340 425Time [sec.]
-100
-75
-50
-25
0
25
50
75
100
Ch
7 [m
/s^2
]
Ch 7 (TDMS: X:\PAW\EL_091124_13_25_54.tdms / Accelerations)Ch 8 (TDMS: X:\PAW\EL_091009_16_44_34.tdms / Accelerations)
0 2000 4000 6000 8000 10000Frequency [Hz]
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
Am
plitu
d ePe
ak4
[m/s
^2]
AmplitudePeak4 (: acceleration7 / X:\PAW\EL_091124_13_25_54.tdms / )AmplitudePeak2 (: acceleration7 / X:\PAW\EL_091124_13_25_54.tdms / )
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5thQuintile
3rdQuintile
1stQuintile
2ndQuintile
5thQuintile
4thQuintile
3rdQuintile
Slide 13© SolFocus, Inc. 2010; Patents Pending
Conclusions
Test method is rigorous and effective Six years of testing and no failures One rod-end bearing “issue”
• Tracker still tracked and produced guaranteed power• Defective component, not design issue• Will be carefully monitored
Bearings and gears showed changing accelerations• decreasing amplitudes: wear-in• increasing amplitudes: wear, but no failures
Motor bearings show greatest vibration increases
Slide 14© SolFocus, Inc. 2010; Patents Pending
Next Steps
Rod-end bearings• Continue to monitor in tests• Confirm adequate reliability from remainder of test
Tear down worst1 motor/gearboxes to see wear levels • Ten year teardown August 2010• Twenty-five year teardown May 2011
Determine failure distributions as possible Relate damage levels to life
1 greatest changes in vibration amplitude