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HCPV Tracker Accelerated Reliability Tests

HCPV Tracker Accelerated Reliability Tests. Jon G. Elerath, Ph. D. Santa Clara Valley Chapter, IEEE Reliability Society September 28, 2010. Agenda. H ardware Acceleration Profile Test Setup Statistical B asis of Test Results and Conclusions. Hardware. CPV system. Power unit.

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HCPV Tracker Accelerated Reliability Tests

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  1. HCPV TrackerAccelerated Reliability Tests Jon G. Elerath, Ph. D. Santa Clara Valley Chapter, IEEE Reliability Society September 28, 2010

  2. Agenda • Hardware • Acceleration Profile • Test Setup • Statistical Basis of Test • Results and Conclusions

  3. Hardware • CPV system • Power unit • CPV panel

  4. Tracker Moving Mechanical Parts Tracker is programmed to “track” the sun based on its longitude, latitude and earth movement. 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

  5. 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)

  6. 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

  7. 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 Changesin: • Amplitudes • Frequencies

  8. …For the Statistical People The “Bathtub Curve” • Mechanical hardware usually fails according to a “bath-tub” curve...which is really three different curves. a = characteristic life b = shape parameter t = time Failure rate direction depends on b b < 1.0 → decreasing b = 1.0 → constant b > 1.0 → increasing WEIBULL SHAPE FACTOR b

  9. …For the Statistical People Tests when b ≠ 1.0 • Two variables, a and b • Select a confidence level (90% lower one-sided confidence limit) • Assume a b • Establish a life (t = 25 yrs) and a probability of failure for that life • Calculate the resulting a • Calculate the number to test and number permitted to fail • After the test, calculate beta to validate assumption #3 a = characteristic life b = shape parameter t = time

  10. 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 5 years accelerated time occurred in 3 months calendar time

  11. 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)

  12. 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

  13. 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

  14. Next Steps • Rod-end bearings • Continue to monitor in tests • Confirm adequate reliability from remainder of test • Tear down worst1motor/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

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