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

© SolFocus, Inc. 2010; Patents Pending

Agenda

Hardware

Acceleration Profile

Test Setup

Statistical Basis of Test

Results and Conclusions


CPV system

Hardware

Power unit

CPV panel


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.


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)


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


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


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


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


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


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


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 / )

06/17/2010 of 15

5thQuintile

3rdQuintile

1stQuintile

2ndQuintile

5thQuintile

4thQuintile

3rdQuintile


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


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

hcpv tracker accelerated reliability tests

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