Technical Report

NREL/TP-500-47203

May 2010

Wind Turbine Generator System 

Duration Test Report for the 

ARE 442 Wind Turbine

Jeroen van Dam, Don Baker, and David Jager
National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393

303-275-3000 • www.nrel.gov

NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

Contract No. DE-AC36-08-GO28308

Technical Report

NREL/TP-500-47203

May 2010

Wind Turbine Generator System 

Duration Test Report for the 

ARE 442 Wind Turbine

Jeroen van Dam, Don Baker, and David Jager

Prepared under Task No. WE10.2211
NOTICE

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iv

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operated for the United States Department of Energy (DOE) by the Alliance for 

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NREL is a DOE Laboratory, and as an adjunct of the United States government, cannot 

certify wind turbines. The information in this report is limited to NREL’s knowledge and 

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and the results shown in this test report have been determined in accordance with the 

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Approval By: _________________________________________________________________

Jeroen van Dam, NREL Test Engineer Date

Review By: __________________________________________________________________

Arlinda Huskey, NREL Test Engineer Date
v

Table of Contents

Background................................................................................................................................................... 1

Test Objective and Requirements............................................................................................................... 1

Description of Test Turbine......................................................................................................................... 2

Description of Test Site ......................................................................................................................... 6

Description of Instrumentation ................................................................................................................... 7

Results ........................................................................................................................................................... 8

Operation Time .......................................................................................................................................... 8

Months of Operation .................................................................................................................................. 8

Hours of Power Production ....................................................................................................................... 9

Operational Time Fraction ........................................................................................................................ 9

Failed IGBT’s .......................................................................................................................................... 10

Over-temperature faults........................................................................................................................... 10

Over-voltage faults................................................................................................................................... 10

Remaining TN ........................................................................................................................................... 10

Environmental Conditions ....................................................................................................................... 10

Power Degradation Checks ..................................................................................................................... 10

Dynamic Behavior.................................................................................................................................... 11

Tear-Down Inspection.............................................................................................................................. 11

Uncertainty.................................................................................................................................................. 14

Hours of Power Production ..................................................................................................................... 14

Operational Time Fraction ...................................................................................................................... 14

Highest Instantaneous Wind Speed.......................................................................................................... 14

Deviations and Exceptions......................................................................................................................... 14

Deviations from the Standard .................................................................................................................. 14

Deviations from Quality Assurance ......................................................................................................... 14

Appendix A: Instrument Calibration Certificates................................................................................... 16

Appendix B.: Turbine Commissioning Checklist .................................................................................... 31

Appendix C: Post-Test Teardown Inspection Report ............................................................................. 33

Nose cone ................................................................................................................................................. 33

Blades....................................................................................................................................................... 33

Alternator................................................................................................................................................. 33

Yaw head.................................................................................................................................................. 33

Tail assembly............................................................................................................................................ 33

Tower....................................................................................................................................................... 34

Voltage clamp .......................................................................................................................................... 34

Diversion loads........................................................................................................................................ 34

Inverters................................................................................................................................................... 34
vi

Table of Figures

Figure 1. The ARE 442 wind turbine ............................................................................................................. 4

Figure 2. General electrical arrangement........................................................................................................ 5

Figure 3. Map of the test site .......................................................................................................................... 6

Figure 4. Location of the data acquisition sensors.......................................................................................... 7

Figure 5. Diversion loads on exterior of data shed ....................................................................................... 12

Figure 6. Operational time fraction for each month ..................................................................................... 12

Figure 7. Scatter plot of power versus wind speed (10-minute averages).................................................... 13

Figure 8. Power level in several wind speed bins (in m/s) as a function of time.......................................... 13

Figure A.1. Power transducer calibration sheet............................................................................................ 17

Figure A.2. Primary anemometer calibration sheet I.................................................................................... 18

Figure A.3. Primary anemometer calibration sheet II .................................................................................. 19

Figure A.4. Wind vane calibration report..................................................................................................... 20

Figure A.5. RTD-Probe calibration sheet I................................................................................................... 21

Figure A.6. RTD-Probe calibration sheet II ................................................................................................. 22

Figure A.7. Pressure transmitter calibration sheet........................................................................................ 23

Figure A.8. Pressure transmitter calibration sheet II .................................................................................... 24

Figure A.9. NI 9217 data acquisition module calibration sheet I ................................................................. 25

Figure A.10. NI 9229 data acquisition module calibration sheet I ............................................................... 26

Figure A.11. NI 9205 data acquisition module calibration sheet I ............................................................... 27

Figure A.12. NI 9229 data acquisition module calibration sheet II.............................................................. 28

Figure A.13. NI 9217 data acquisition module calibration sheet II.............................................................. 29

Figure A.14. NI 9205 data acquisition module calibration sheet II.............................................................. 30

Figure C-1. Remnants of trip strip on one of the blade tips.......................................................................... 35

Figure C-2. Crack in trailing edge of one of the blades................................................................................ 35

Figure C-3. Crack in leading edge near blade root of blade #2. ................................................................... 36

Figure C-4. Crack in leading edge of blade #2............................................................................................. 36

Figure C-5. Cracked tail stop bumper........................................................................................................... 37

Figure C-6. Bent furl stop............................................................................................................................. 37

Figure C-7. Tail hinge pin ............................................................................................................................ 38

Figure C-8. Bent tower diagonal .................................................................................................................. 38

Figure C-9. Chipped coating on diversion loads .......................................................................................... 39

List of Tables

Table 1. Test turbine configuration and operational data ............................................................................... 3

Table 2. Equipment List for Duration Test..................................................................................................... 8

Table 3. Monthly and overall results of the ARE 442 duration test ............................................................... 9
1

Background

This test is being conducted as part of the U.S. Department of Energy’s (DOE) 

Independent Testing project. This project was established to help reduce the barriers of 

wind energy expansion by providing independent testing results for small turbines. In 

total, four turbines are being tested at the NWTC as a part of this project. Duration testing 

is one of up to 5 tests that may be performed on the turbines, including power 

performance, safety and function, noise, and power quality tests. The results of the testing 

provide manufacturers with reports that may be used for small wind turbine certification.

The test equipment includes a grid connected ARE 442 wind turbine mounted on a 30.5 

meter (100 ft) lattice tower manufactured by Abundant Renewable Energy. The system 

was installed by the NWTC Site Operations group with guidance and assistance from 

Abundant Renewable Energy. 

Test Objective and Requirements

The objective of this test is to assess the following aspects of the ARE 442 wind turbine 

with Windy Boy US 6000 inverters in accordance with Clause 9.4 of the International 

Electrotechnical Commission’s (IEC) standard, Wind turbines - Part 2: Design 

requirements for small wind turbines, IEC 61400-2 Ed. 2.0:2006-03 (throughout the 

report referred to as the Standard).

• Structural integrity and material degradation 

• Quality of environmental protection 

• The dynamic behavior

The wind turbine will pass the duration test when it has achieved reliable operation for:

• 6 months of operation

• 2,500 hours of power production in winds of any velocity

• 250 hours of power production in winds of 1.2Vave (10.2 m/s) and above

• 25 hours of power production in winds of 1.8Vave (15.3 m/s) and above.

Reliable operation means:

• Operational time fraction of at least 90%

• No major failure of the turbine or components in the turbine system

• No significant wear, corrosion, or damage to turbine components 

• No significant degradation of produced power at comparable wind speeds
2

Based on the parameters defined in the Standard for small wind turbine classes, Abundant 

Renewable Energy identified the test turbine to be a class II. This corresponds to a Vave of 

8.5 m/s.

In addition, NREL has conducted this test in accordance with our quality system 

procedures such that this report will meet the full requirements of our accreditation by 

A2LA. Our quality system requires that we meet all applicable requirements specified by 

A2LA and ISO/IEC 17025 or to note any exceptions in the test report.

Description of Test Turbine

The test turbine (Figure 1) is a three bladed, upwind, furling turbine with a rated power of 

10kW. Table 1 lists basic turbine configuration and operational data. Figure 2 shows the 

one-line diagram for the test turbine installation.

The following components were considered part of the test turbine system:

1. The turbine system includes a tower and foundation that have been designed for 

installation at the NWTC test site 3.3a. 

2. The turbine system is connected to the electrical grid at the test site through a 

subpanel. All wiring and components on the turbine side of this subpanel are 

considered part of the turbine system.

3. The turbine system includes all control components including wiring between the 

up-tower components and the down-tower control panel.
3

Table 1. Test turbine configuration and operational data

General Configuration:

Make, Model, Serial Number Abundant Renewable Energy , ARE 442, Y08-001C

Rotation Axis (H / V) Horizontal

Orientation (upwind / downwind) Upwind

Number of Blades 3

Rotor Hub Type Fixed

Rotor Diameter (m) 7.2

Small Wind Turbine Class II

Hub Height (m) 30.9

Performance:

Rated Electrical Power (kW) 10

Rated Wind Speed (m/s) 11

Cut-in Wind Speed (m/s) 2.2

Cut-out Wind speed (m/s) N/A

Rotor:

Swept Area (m2) 40.7

Blade Pitch Control None

Direction of Rotation Clockwise viewed from up wind

Rotor Speed 0 – 200

Power Regulation (active or passive) Passive

Tower:

Type Freestanding Lattice Valmont U4.5 x 100’

Height (m) 30.5 (100ft)

Control / Electrical System:

Controller: Make, Type Combination of side furling with gravity return, VCL 442-

HV voltage clamp and Windy Boy US6000 inverter 

software.

Electrical Output: Voltage 240 VAC, single-phase

Yaw System:

Yaw control Passive
4

Figure 1. The ARE 442 wind turbine

The test configuration consists of the turbine mounted on a lattice tower, the controller, 

the meteorological tower, associated wiring and junction boxes, and a data shed 

containing the data acquisition instrumentation. The turbine is installed on a freestanding

30.5 meter, lattice tower. The wire run from the base of the tower to the data shed is 

approximately 98 meters of #6 AWG wire. Inside the data shed there is a voltage clamp, 

and two inverters. Those are wired to a sub panel which in its turn is hooked up to a 

disconnect switch. Figure 2 shows the general electrical arrangement.
5

Figure 2. General electrical arrangementTower base 

J-box

Uptower 

J-box

Foundation 

junction box

Met tower 

j-box

Voltage 

clamp

Resistive 

dump 

load

Resistive 

dump 

load

inverterinverter

Sub panel

Power 

measure

ment box

60A 600V 

disconne

ct

kWh 

meter

Power panel 3-3L 

120/240V

2*10AWG

L1

datashed

3*6AWG

4*14AWG

AWG 4* 3

AWG 14 * 4

LP 14106 

surge 

suppressor

) AWG 4( Ground 

Ground (6AWG)

LP 14106 

surge 

suppressor

Ground rod on the 

southeast corner

G

L1

L1L2

G

Ground rod on the north 

side of datashed

ZD16100 

surge 

suppressor

L2

2 pole 30A 

breaker 3*10AWG

3*10AWG

1*10AWG

2*14AWG

2*10AWG

1*10AWG

2*14AWG

2 pole 30A 

breaker

1 pole 15A 

breaker

2 pole 60A 

breaker 

no.27-29

Everything between subpanel and panel 

3-3 L 6AWG

L

N

2

8AWG

8AWG

NREL 

grid 2*12AWG

2 pole 30A 

breaker

60A 600V 

disconnect

Shorting switch

SOW
6

Description of Test Site

The test turbine is located at site 3.3a at the National Wind Technology Center, located 8 

miles south of Boulder, Colorado. The terrain primarily consists of mostly flat terrain 

with short vegetation. The test site has prevailing wind bearing 292 degrees relative to 

true north. For measurements where it is important to accurately measure wind speed, 

NREL use data obtained when wind direction is between 214° and 74° degrees true. In 

this measurement sector, established in accordance with IEC 61400-12-1, the influence of 

terrain and obstructions on the anemometer and turbine are small. Figure 4 shows the 

turbine and meteorological tower locations. This figure also shows nearby obstructions 

and topographical features of the site. A circle indicating 20 rotor diameters is drawn in 

the map.

Figure 3. Map of the test site

N
7

Description of Instrumentation

Equipment used for duration testing differs only slightly from that used for power 

performance testing. Normal power performance requires measurements of wind speed, 

wind direction, turbine power, air temperature, air pressure, precipitation, and overall 

turbine system availability. For duration testing, NREL added a signal to monitor the 

brake resistors in the yaw head as an indication of turbine availability (0V means brake 

applied; 5V means not applied). Figure 4 gives the location of the met tower instruments

and Table 2 gives an equipment list that provides the specifications for each of the 

instruments used. The primary anemometer was sent out for recalibration after the test 

period. The difference between the two calibrations was within the tolerances allowed by 

IEC 61400-12-1.

Figure 4. Location of the data acquisition sensors
8

Table 2. Equipment List for Duration Test

Instrument Make, Model Serial Number Calibration Due Date

Power transducer Secondwind Phaser 5FM-4A20 02663 28 Apr 2009

Current transducers OSI 12974 001235408

001235411

Calibrated with power 

transducer 

Primary anemometer Thies, First Class 0707886

0707888

28 Feb 2009

2 Feb 2010

Reference anemometer NRG, Max 40 179500049022 In situ

Wind vane Met One, 020C with aluminum 

vane

G4706 28 Feb 2009

Pressure sensor Vaisala, PTB101B C1020015

T4730007

29 Oct 2008

26 Aug 2009

Temperature sensor Met One, T-200 0673552

0789020

29 Oct 2008

10 Oct 2009

Precipitation sensor Campbell Scientific, 237 None In situ

Data acquisition system Compact DAQ w/LabView-based 

data acquisition

cDAQ-9172

NI 9229

NI 9217

NI 9205

12EAE14

12A2037

12C73B4

12ECB77

31 May 2008

3 Aug 2008

9 Oct 2008

The data acquisition system ran out of calibration during the test. It was sent out for post 

test calibration and found within specification. The calibration sheet of the post test 

calibrations are also inserted in Appendix A.

The wind vane calibration also expired during the test. In field calibration checks were 

performed to verify validity of the calibration.

The power transducer was out of calibration for the last two days of the test. These two 

days do not significantly affect the test results.

Results

Operation Time

The test turbine system was installed on 9 and 10 June 2008. It was ready for testing on 

12 June 2008. On 13 June 2008 during a power outage IGBT’s in the voltage clamp 

failed. These were replaced and the duration test officially started on 7 July 2008. The 

duration test was completed on 30 April 2009, after enough data was collected to 

demonstrate sufficient hours of operation as required by the standard. The commissioning 

checklist from the installation can be found in Appendix B. 

Months of Operation

The duration test was conducted over a period of a little over 9.5 months from July 7th, 

2008, to April 30th, 2009 (6 months were required). The turbine has continued to operate 

since then until it was shut down for removal on 10 December 2009.
9

Hours of Power Production

The hours of power production at any wind speeds: 3,240 hours (2,500 hours required)

The hours of power production above 1.2*Vave (10.2 m/s): 552 hours (250 hours 

required)

The hours of power production above 1.8*Vave (15.3 m/s): 156 hours (25 hours 

required)

Thus the turbine met the requirements for hours of power production during the test. 

Table 3 shows the overall and month-by-month results of the duration test.

Table 3. Monthly and overall results of the ARE 442 duration test

Operational Time Fraction

The operational time fraction is defined as follows:

×100% − −

− − − =

T U E

T N U E

T T T

T T T T O

where:

TT is the total time period under consideration,

TN is the time during which the turbine is known to be non-operational,

TU is the time during which the turbine status is unknown,

TE is the time which is excluded in the analysis.

The overall operational time fraction of the combined wind turbine system (wind turbine, 

tower, and controller) in the total test period was 91.2%. Figure 6 and Table 3 show the 

operational time fraction per month. 

The main reasons for wind turbine system downtime (TN) during the test period were 

failed IGBT’s, over-temperature faults and over-voltage faults. These faults are described 

in more detail below. 

Max Gust TI @ 15 # Data T T T U T E T N O

Month 0 m/s 10.2 m/s 15.3 m/s (m/s) m/s (%) Points (hours) (hours) (hours) (hours) (%)

Overall 3240.6 552.6 156.7 42.9 18.9 325 7249 99.7 214.8 612.0 91.2

Jul 2008 295.8 7.5 0.0 27.8 15.8 3 735 3.1 152.2 0.0 100.0

Aug 286.8 9.5 0.0 26.5 16.9 1 739 26.0 4.0 0.0 100.0

Sep 217.5 8.8 0.7 23.2 13.8 8 687 16.6 5.3 0.3 99.9

Oct 279.7 35.7 6.7 34.0 16.9 13 744 0.9 5.0 9.5 98.7

Nov 156.0 8.2 0.0 34.3 19.5 44 720 0.0 0.1 332.8 53.8

Dec 379.2 131.8 41.8 42.9 18.2 72 744 1.0 10.2 124.2 83.1

Jan 2009 466.5 146.3 44.3 42.9 20.0 93 744 0.7 1.8 79.8 89.2

Feb 389.3 104.5 46.3 39.5 19.7 33 672 4.0 31.7 42.3 93.3

Mar 416.8 68.3 13.2 34.9 18.4 44 744 3.9 1.5 20.3 97.2

Apr 353.0 32.0 3.7 28.4 18.0 14 720 43.5 3.0 2.8 99.6

Hours of Power Production Above:
10

Failed IGBT’s

On November 5, a grid outage was simulated in 6-7 m/s winds by opening the disconnect 

switch. The turbine shut down but upon reconnection to the grid the turbine would not 

start up again. It was found that the IGBT’s in the voltage clamp had failed. New chopper 

boards were received on 19 November 2008. The period from 5 through 19 November 

2008 is counted as TN.

Over-temperature faults

At the start of the test, the diversion loads were installed inside the data shed per the 

manufacturers installation instructions. The data shed was unable to disperse the heat 

which caused the turbine to experience over temperature faults in high winds. The ten 

minute periods in which the turbine was faulted for more than 300 seconds were counted 

at TN. On 10 and 11 February 2009, the diversion loads were moved to the exterior of the 

data shed (Figure 5) to avoid further over temperature faults.

Over-voltage faults

After the diversion loads were moved to the exterior of the building no more overtemperature faults were observed. Instead, in high winds, the turbine would fault to overvoltage faults. The ten minute periods in which the turbine was faulted for more than 300 

seconds were counted as TN.

Remaining TN

Occasionally the turbine’s controller would get stuck in “Test” mode, even though the 

winds were above cut-in wind speed. This was resolved by cycling power to the voltage 

clamp. From the time when the turbine was last running to the time the power was cycled 

was counted as TN.

The main reasons for excluding time (TE) in the duration test were:

• Time during power outages that prevented the turbine from running

• Noise or safety and function testing that required the turbine to be shut down

If no reliable measurements were available, the time was classified as TU since the 

turbine’s status was unknown. 

Environmental Conditions

As an indication of the environmental conditions during the duration test, the standard 

requires reporting of the highest instantaneous wind speed gust and the average 

turbulence intensity at 15 m/s. The highest instantaneous wind speed was 42.9 m/s at 

16:41 on 7 January 2009. The average turbulence intensity at 15 m/s during the duration 

test was 18.9%.

Power Degradation Checks

A factor of reliable operation is that the turbine should experience no significant power 

degradation. During the power degradation analysis, the average power level for each 

wind speed bin was plotted as a function of time over the whole test period. This plot is 

analyzed for any obvious trends in power production.
11

Figure 8 shows the power degradation plot, which gives the power level in individual 

wind speed bins for each month. Variations in the power levels from season-to-season are 

caused by air density variations.

Dynamic Behavior

The turbine has been observed over a wide range of wind speeds. The turbine did not 

exhibit excessive vibration during any of the recorded observations. The following are 

paraphrased examples of dynamic behavior observations made in the logbook: 

26 August 2008 – Observed turbine in 5-6 m/s. The turbine tracks the wind’s direction 

but always seems to be 20 degrees off (due to the offset tail). The generator hums 

audibly, and there was occasional noise of sheet metal vibrations, with the likely cause as 

the cover of the electrical box. There was no excessive vibration

24 February 2009 – The turbine was observed for 20 minutes in 8-12 m/s. There was no

observable excessive vibrations. The turbine tracks wind well.

26 February 2009 - Throughout the day (9:30 to 17:00), the turbine was observed in 

winds from 25 m/s to 3 m/s. At high winds, the rotor operated at high yaw errors (30-40°) 

and the furl movements excited the tower lightly. At low wind speeds (<10 m/s), there 

was hardly any vibration noticeable. At the cut in, metal boxes or sheet metal resonates. 

Overall, there did not appear to be any excessive vibrations present. Observation times

were one hour below 10 m/s, and one hour above 15 m/s

Tear-Down Inspection

The tear down inspection was performed on 15 December 2009. The results are 

documented in Appendix C. The main finding was a leading edge crack in one of the 

blades.
12

Figure 5. Diversion loads on exterior of data shed

Figure 6. Operational time fraction for each month

0

10

20

30

40

50

60

70

80

90

100

Jul-08 Aug-08 Sep-08 Oct-08 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09 Apr-09

Operational Time Fraction [%]

Month
13

Figure 7. Scatter plot of power versus wind speed (10-minute averages)

Figure 8. Power level in several wind speed bins (in m/s) as a function of time

-2000

0

2000

4000

6000

8000

10000

12000

0 5 10 15 20 25

Power [W]

Wind speed [m/s]

0

2,000

4,000

6,000

8,000

10,000

12,000

Jul-08 Aug-08 Sep-08 Oct-08 Nov-08 Dec-08 Jan-09 Feb-09 Mar-09

Power [W]

4

5

6

7

8

9

10

11

12

13

14

15

16
14

Uncertainty

The uncertainty is estimated for the following parameters:

• Hours of power production 

• Operational time fraction

• Highest instantaneous wind speed

No uncertainty analysis was done for the power degradation results. These results were 

used only to find relative trends which might indicate hidden faults in the turbine.

Hours of Power Production

NREL assumes that the turbine is producing power for the entire 10-minute period 

whenever the average power for that period is positive. This method overestimates time 

for power production in wind speeds between 4 and 6 m/s. At these wind speeds the 

turbine may have been producing power for about half of the time recorded by NREL. At 

higher wind speeds, this method would produce less of an overestimate. NREL estimates 

that the reported time of power production in wind speeds greater than 0 m/s may be 20% 

less than calculated. However, the turbine continued to run through December 2009. 

Thus, NREL is confident that it achieved the 2,500 hours required by the standard. 

For the hours of power production above 10.2 and 15.3 m/s, the uncertainty in the wind 

speed was assumed to be the dominant factor. Assuming an uncertainty in wind speed of 

0.3 m/s, the hours of power production reduce to 512 (above 10.5m/s) and 147 (above 

15.6 m/s) well exceeded the 250 and 25 hours that the standard requires.

Operational Time Fraction

The total test time is 7,249 hours. Even if the classification of TN was wrong by 5% 

(which is a conservative assumption), the operational time fraction would be 90.7%. 

Highest Instantaneous Wind Speed

The uncertainties in the wind speed measurements were 0.009 m/s calibration 

uncertainty, 0.052 m/s + 0.52% operational characteristics, 1% mounting effects, and 2% 

terrain effects. For the maximum instantaneous gust of 42.9 m/s, the uncertainty was 

0.99 m/s.

Deviations and Exceptions

Deviations from the Standard

None.

Deviations from Quality Assurance

The data acquisition modules were used beyond the calibration due date. They were posttest calibrated and found to be in compliance within the specifications. Appendix A 

includes the post-test calibration sheets.
15

The wind vane was used beyond its calibration due date. In field calibration verification,

checks were performed by pointing the vane at known distant landmarks. It should be 

noted that the wind vane is not a critical or required instrument for the duration test.

The power transducer was used two days beyond its calibration due date. These two days 

do not significantly impact test results.
16

Appendix A: Instrument Calibration Certificates

Figures A.1 through A.14 show the calibration sheets for the instruments used during the 

duration test. 
17

Figure A.1. Power transducer calibration sheet
18

Figure A.2. Primary anemometer calibration sheet I
19

Figure A.3. Primary anemometer calibration sheet II
20

Figure A.4. Wind vane calibration report
21

Figure A.5. RTD-Probe calibration sheet I
22

Figure A.6. RTD-Probe calibration sheet II
23

Figure A.7. Pressure transmitter calibration sheet
24

Figure A.8. Pressure transmitter calibration sheet II
25

Figure A.9. NI 9217 data acquisition module calibration sheet I
26

Figure A.10. NI 9229 data acquisition module calibration sheet I
27

Figure A.11. NI 9205 data acquisition module calibration sheet I
28

Figure A.12. NI 9229 data acquisition module calibration sheet II
29

Figure A.13. NI 9217 data acquisition module calibration sheet II
30

Figure A.14. NI 9205 data acquisition module calibration sheet II
31

Appendix B: Turbine Commissioning Checklist
32
33

Appendix C: Post-Test Teardown Inspection Report

The ARE 442 turbine was taken down from site 3.3a on December 15 after NREL 

completed all testing activities as part of the Independent Testing project. A tear down 

inspection is performed as a part of the duration test. This report describes that teardown 

inspection.

Nose cone

The nose cone did not show any signs of wear. No cracks were found near any of the bolt 

holes.

Blades

All the blades had the trip strip missing on the high pressure side (Figure C-9). All three 

blades also had some cracking in the trailing edge bond line in the root area (Figure C10). Blade 2 also had some more severe cracking in the leading edge near the root (Figure 

C-11 and Figure C-12). All blade roots showed signs of light rubbing on the clamping 

plates and alternator.

Alternator

The coils of the alternator were visually inspected. No signs of overheating were found. 

Also no traces of rubbing between the stator and rotor were found. The alternator spins 

smoothly and no damage to the main bearing was evident.

Yaw head

All welds on the yaw head were visually inspected. No cracks were found. 

Tail assembly

The tail vane was inspected visually, no cracks were found. The tail boom did not have 

any cracks or signs of wear. The tail stop bumper was found to be cracked (Figure C-13). 

This bumper gets hit by the tail when the turbine comes out of furl. This may have been 

caused by over-torquing of the mounting bolts by ARE during the turbine production.

The plate that contacts the tail stop bumper when the turbine comes out of furl was found 

to be bent (Figure C-14).

The tail hinge pin and bronze sleeve bearings showed very little wear. Most wear was 

likely caused by the disassembly process. See Figure C-15.

Yaw system

The turbine is free yaw; the turbine was manually yawed. The turbine yaws smoothly. No 

play in the bearing was observed.
34

Up-tower Electrical components

The electrical components up-tower consist of:

1. Brake resistors. The brake resistors were visually inspected. They did not 

show any signs of overheating or any other wear

2. Contactor operating the brake resistors. The contactor box was opened and 

one of the contactors was disassembled. No damage or wear was observed.

3. Slipring assembly. The slipring assembly did not show any unexpected wear.

4. Terminal block. The terminal block was intact. However one of the wires was 

not tight. NREL has found it very hard to tighten any wires in the terminal 

block in the yaw head. According to ARE this issue has been addressed in a 

design change.

Tower

The tower was visually inspected. No cracked welds were found. All fasteners were 

present. A couple of diagonal supports were found to be bent (Figure C-16). Although no 

clear evidence is present, this was most likely caused by shipping and did not occur 

during the test.

Voltage clamp

The voltage clamp was opened and inspected for any discoloration, loose wires, etc. 

Nothing was noted that looked unexpected.

Diversion loads

The enclosure was taken apart and inspected for cracks or deformation, neither were 

found. 

The diversion loads were opened and the resistors and wires were inspected. No cracks or 

discoloration was found. Some of the coating was chipping off the resistors, where drips 

had formed from dipping the resistors in the coating during manufacturing (Figure C-17).

Inverters

The inverters were opened and visually inspected. No sign of wear, overheating or 

damage was found.
35

Figure C-9. Remnants of trip strip on one of the blade tips

Figure C-10. Crack in trailing edge of one of the blades
36

Figure C-11. Crack in leading edge near blade root of blade #2.

Figure C-12. Crack in leading edge of blade #2
37

Figure C-13. Cracked tail stop bumper

Figure C-14. Bent furl stop
38

Figure C-15. Tail hinge pin

Figure C-16. Bent tower diagonal
39

Figure C-17. Chipped coating on diversion loads
F1147-E(10/2008)

REPORT DOCUMENTATION PAGE Form Approved

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

May 2010

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Wind Turbine Generator System Duration Test Report for the 

ARE 442 Wind Turbine

5a. CONTRACT NUMBER

DE-AC36-08-GO28308

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

J. van Dam, D. Baker, and D. Jager

5d. PROJECT NUMBER

NREL/TP-500-47203

5e. TASK NUMBER

WE10.2211

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

8. PERFORMING ORGANIZATION

REPORT NUMBER

NREL/TP-500-47203

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR'S ACRONYM(S)

NREL

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AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service

U.S. Department of Commerce

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13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

This test is being conducted as part of the U.S. Department of Energy's (DOE) Independent Testing project. This 

project was established to help reduce the barriers of wind energy expansion by providing independent testing results 

for small turbines. In total, four turbines are being tested at the NWTC as a part of this project. Duration testing is one 

of up to 5 tests that may be performed on the turbines, including power performance, safety and function, noise, and 

power quality tests. The results of the testing provide manufacturers with reports that may be used for small wind 

turbine certification. The test equipment includes a grid connected ARE 442 wind turbine mounted on a 30.5 meter 

(100 ft) lattice tower manufactured by Abundant Renewable Energy. The system was installed by the NWTC Site 

Operations group with guidance and assistance from Abundant Renewable Energy.

15. SUBJECT TERMS

wind turbines; independent testing; duration testing; ARE 442; Abundant Renewable Energy wind turbine

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