Certification Testing for Small Wind Turbines
Contents
1. Golden CO 80401 Tim Sasseen Southwest Windpower 2131 N First St Flagstaff AZ 86003 1 0 Background This paper describes the testing procedures for obtaining type certification for a small wind turbine Southwest Windpower SWWP is seeking type certification from Underwriters Laboratory UL for the AIR 403 wind turbine UL 1s the certification body and the National Renewable Energy Laboratory NREL 1s providing technical assistance including conducting the certification testing This 1s the first small turbine to be certified in the United States therefore standards must be interpreted and test procedures developed 2 0 Description of the Turbine The AIR 403 is a small battery charging turbine rated to produce 400 watts in a 12 5 meters per second m s 28 mph wind speed The turbine is generally used either as a stand alone battery charging system or in conjunction with a small photovoltaic PV array as a wind PV hybrid system to power loads such as lighting TV and small household appliances The AIR 403 turbine is also very popular on sailboats for on board power The AIR 403 uses a brushless permanent magnet alternator to produce three phase variable alternating current AC output that is then rectified to direct current DC The rectifier and charge controller for the turbine are housed in the nacelle of the turbine and are directly heat sinked to the turbine body The turbine rotor diameter is 1 15 meters 4 ft the we2. W 400 Rated Wind Speed m s 12 5 28 mph Cut in Wind Speed m s 2 7 6 mph Rotor Swept Area m 1 8 19 4 ft Blade Pitch Angle deg 2 5 Direction of Rotation Clockwise Type Tubular schedule 40 pipe guyed tilt up Height 13 7 m 40 ft with 1 5 m 5 ft adapter Control and Electrical System Controller Make Type Autobrake rectifier charge controller Electrical Output Voltage Nominal 12 volts 24 and 48 volt versions available 3 0 Certification Testing Overview Figure 2 shows an overview of the requirements for small wind turbine type certification Specific tests are required under type testing Optional but desirable tests are shown under type characteristics measurements However the blade tests and load measurements required under type testing for large turbines can be waived in lieu of a duration test per IEC 61400 22 Annex E Also required under type testing 1s a safety and function test SWWP chose to certify a power curve for their turbine therefore a power performance test is being conducted according to the requirements of IEC 61400 12 The safety and function duration and power performance tests are the three main tests required for the certification of the AIR 403 NREL has written a detailed test plan for each test being conducted that describes the testing approach configuration and procedures NREL is also obtaining some additional data on the SWWP turbine s characteristics in o
3. power curve will be an average of the three voltages If voltage has a significant effect on the power curve output e g greater than 5 then the power curves corresponding to the three voltage settings may be shown separately The AIR 403 is available in three different nominal voltages 12 24 and 48 volts It 1s anticipated that the power output will be slightly higher as the nominal turbine voltage increases hence three separate power performance tests will be conducted corresponding to the three nominal voltage versions of the turbine It 1s anticipated that the nominal voltage rating of the turbine will have a larger impact on the power curve than the voltage variation corresponding to battery state of charge Hence the data requirements for voltage variations as a function of battery state of charge may be relaxed for tests of 24 volt and 48 volt AIR 403 turbine versions A second change from the IEC 61400 12 standard is accommodation of the charge controller The power performance test will be conducted so that the charge controller does not have any effect on the power output This will be done by setting the charge controller voltage above that of the load so that the charge controller never regulates current Voltage control of the load will be maintained using Alternative Engineering s Enermaxer load controller configured to maintain voltage within 2 of the desired setting The Enermaxer load controller uses pulse width modulation
4. to control current to a dump load and thereby maintain voltage control Per IEC 61400 12 the anemometer must be located between 2 and 4 rotor diameters from the turbine In this test the anemometer will be mounted 2 5 rotor diameters from the turbine Another anemometer is located approximately 15 m 50 feet from the turbine tower as a check on the primary anemometer An assessment will be made to determine if there are any significant anemometer wake effects on the turbine from the primary anemometer Figure 4 shows the layout for the power performance test Turbine Tower Anemometer ATR403 Wind Speed Wind Direction Barometric Pressure Temperature Wetness Sensor Load 140001 Voltage Sensing Current Sensor Batteries FIGURE 4 TURBINE CONFIGURATION FOR POWER PERFORMANCE TEST 3 4 Verification of Design Assumptions The three main certification tests for small turbines shown in Figure 2 fall under type testing and type characteristic measurements However the design evaluation process according to IEC 61400 2 is based on assumptions and or measurements of the following parameters rated and maximum rotor speed and power and maximum yaw rate As part of the duration and or power performance test these parameters will be measured The maximum and rated rpm can be calculated by measuring the frequency of the AC ripple downstream of the rectifier on the DC bus and calculating wind turbine rpm base
5. EL staff note any problems with the turbine the switch 1s thrown and an entry is made in the log This method avoids the undesirable loss of availability when the turbine is shut down for instrumentation changes or special tests The arrangement for the AIR 403 duration test including the measured parameters for the data acquisition system is shown in Figure 3 The battery bank voltage in the duration test is varied by means of applying a constant resistance load in series with a low voltage disconnect LVD The load will be used to lower the battery bank voltage to the LVD set point equal to about 40 state of charge at which point the load will automatically disconnect The reset voltage of the LVD will correspond to full battery state of charge SOC Hence the LVD will keep the load disconnected until the turbine recharges the batteries back to the 100 SOC When the batteries are once again charged the LVD will reconnect the load and the batteries will again discharge The load will vary about 15 because it is a fixed resistance and the voltage changes with battery SOC In addition the discharge rate of the batteries will vary depending on the turbine output The turbine charge controller will regulate current when the batteries reach 100 SOC and hence the charge controller will be tested every time the batteries reach 100 SOC Also included in the type certification for the turbine is the tower for the AIR 403 The tower is a guyed t
6. d on frequency and the number of poles in the generator The maximum yaw rate will be estimated by using a video camera at slow speed to measure yaw in degrees for a given time interval Simplifying the yaw rate measurement by using a video camera as opposed to instrumenting the turbine with an expensive yaw sensor set up helps to reduce the complexity and costs for small certification testing 4 0 Future Work in Small Wind Turbine Certification Testing Small wind turbine certification testing 1s just starting with the AIR 403 certification test being the first certification test in the United States Work is now beginning on a revision of IEC 61400 22 Lessons learned from the current certification testing will be incorporated in the IEC 61400 22 revision and into future certification testing protocols NREL will continue to develop small wind turbine testing capabilities and to share information References Standard IEC 61400 22 International Electrotechnical Commission IEC Draft Wind Turbine Generator Systems Part 22 Wind Turbine 88 102 CD 18 Dec 1998 Standard IEC 61400 2 International Electrotechnical Commission IEC Wind Turbine Generator Systems Part 2 Wind Turbine 18 Dec 1996 04 Standard IEC 61400 22 International Electrotechnical Commission IEC Wind Turbine Generator Systems Part 12 Wind Turbines Power Performance Testing Wind Turbine 88 66 CDV 1997 10 03 AIR 403 Owner s Manual Southwest Windpower F
7. ight is 5 85 kilograms 13 lb and the turbine is available in 12 24 and 48 volt configurations The cut in wind speed of the turbine is 2 7 m s 6 mph The turbine has a brake switch that shorts the turbine output wires together and results in the turbine stopping The turbine blades are made from injected molded carbon fiber In winds above about 18 8 m s 42 mph the carbon fiber blades will go into flutter to protect the turbine from overspeeding This is called aeroelastic stall in the user s manual Southwest Windpower 1999 During normal turbine operation 1 e turbine connected to batteries the turbine regulator will brake the turbine to a very slow rotational speed when the batteries are fully charged During open circuit operation of the turbine 1 e turbine disconnected from the batteries the turbine regulator will brake the turbine to prevent overspeed and to prevent the output voltage from rising above double the rated voltage of the turbine Figure 1 shows a picture of the AIR 403 Table 1 lists the basic turbine specifications and operational data FIGURE 1 THE AIR 403 TABLE 1 TEST TURBINE CONFIGURATION AND OPERATIONAL DATA Test Turbine General Configuration Make Model Serial Number Southwest Windpower AIR 403 19825 Rotation Axis H V Orientation upwind downwind Upwind Number of Blades Rotor Diameter m 1 15 m 4 ft Hub Height as tested m 13 7 m 45 ft Operation Rated Electrical Power
8. ilt up tower made from schedule 40 pipe The turbine will be tested with this tower to ensure that the tower is designed for all the loads encountered during the duration test including the 25 hours of wind speeds greater than 15 m s 33 mph Southwest Windpower Southwest Windpower AIR 403 Duration Test Layout AIR 403 Wind Module Wind speed Wind Vane Turbine DC Volts Turbine DC Amps ith Lightning Turbine DC Power J pl Arrestor Wind Speed direction Voltage taps Brake Status DAS l la al i Brake EN LE Battery Bank Trojan L 16 700 Ah FIGURE 3 AIR 403 DURATION TEST SCHEMATIC 3 3 Power Performance Test The power performance test follows the IEC 61400 12 standard except that changes are required to account for the effect that battery state of charge 1 e voltage variation in the load has on power output The electrical load is controlled at voltages corresponding to a battery SOC of approximately 40 70 and 100 and 60 hours of operation is required for each SOC voltage In addition for each of the three voltage settings 30 minutes of data is required for each 0 5 m s 1 mph wind speed bin Because this is the first power performance test for a small wind turbine certification the variation of the power curve as a function of voltage will be evaluated to determine the sensitivity of the power curve to battery SOC If the voltage variation has a small effect on the power output then the final
9. lagstaff AZ 1999
10. ly energy production would indicate a problem with yaw bearings blades bearings generator or the rectifier To compare energy production both the expected energy production and measured energy production are determined Expected energy production is the energy that would have been produced under the measured wind conditions 1f the turbine operated on its power curve as measured during the first month Measured energy production is energy that the turbine actually produced as measured by the power transducer The comparison uses data obtained when turbine and anemometer are clear of wakes from any obstacles and when the winds are within the range of the power curve measured during the first month of duration testing Another requirement by NREL for the duration test 1s that the turbine maintains its ability to reduce power output when the batteries are fully charged NREL has developed a procedure to test the charge controller to verify that it operates during the entire duration test The turbine is connected to the battery bank near full SOC and current output from the turbine observed as the battery approaches the voltage set point of the turbine charge controller Upon reaching the charge controller voltage set point the turbine current output is verified to be reduced below 3 amps This test will be conducted at least three times including the beginning middle and end of the duration test The final requirement by NREL for the durati
11. o zero Over speed protection Verify blade aeroelastic stall reduces current output The above tests are contained in a checklist and capture the intent of the IEC 61400 2 Annex D requirements without making the testing so burdensome and expensive that small turbine manufacturers would be unable to afford the it For example visual inspection of adequate yaw control is relatively inexpensive compared to instrumenting recording and analyzing yaw and wind direction signals 3 2 Duration Test As mentioned previously the duration test may replace the blade tests and load measurements required under type testing for small turbines This variance from the large turbine standard can help reduce the cost of testing small turbines because it is usually easier to conduct a duration test as opposed to blade and load tests The IEC 61400 2 Annex E requires that the turbine undergo testing for 1 500 hours of power generation and six months test duration as well as operation in winds greater than 10 m s 22 mph for 250 hours and operation in winds greater than 15 m s 33 mph for 25 hours The operating requirements per IEC 61400 2 Annex E are that the turbine achieve at least 90 availability In addition to the availability requirement NREL requires that the turbine s monthly energy production throughout the test be no less than 20 of the first month s energy production after correction for wind resource differences A 20 change in the month
12. on test is that there is no abnormal wear Abnormal wear will be noted in the final component wear and durability assessment At the completion of the duration test the turbine will be taken down from the tower and a detailed component wear and durability checklist for the entire turbine will be conducted It will include an assessment of the physical integrity of the blades noting any cracks or abnormal surface conditions the mechanical alignment of the rotor and an analysis of the charge controller including any signs of thermal degradation The following measurements will be taken during the duration test power production turbine availability wind speed consisting of 10 minute average 3 second gust and turbulence intensity and wind direction NREL has included wind direction to avoid using data obtained when upwind obstacles affect the turbine or anemometer Power is measured by a power transducer and also calculated from current and voltage measurements for the duration test Voltage measurements are taken at the top of the wind turbine tower and also at the battery bank so that the line losses can be calculated The AIR 403 is available in a 12 24 and 48 volt version the 12 volt version was selected for the duration test because it produces the highest current and therefore the highest thermal loading Turbine availability is determined from the test log and supplemented by a manual switch connected to the data acquisition system If NR
13. rT a rT an a a a a a a a a rT rT rT a s s e E _ QDD o L eet 0 EE EE O E OA ieee 0 E eet E eet lees eet bees E E lee ea meane a za ee O ioe A A A A eee eee lt E o za a O O oe O ODO DES LEO A eet oot et ere oy i Ltt SERPS eee oa B sa roa one iea ee a 1 A gen a a a a A ee ee ee a ee ee a a eee o ae eee fa a a a a a a a i a a a a a oa a a a a Sat e a a o earan I E N ee a ee a 1na a a pl i EEE NIT HOT rit A MEAN TILL TT TL A AT ae A EEE ILLIC LILILO MAA 00 O O O O O A O O SS NN TITTILILLE T TT LCCC rTTILILILLe AAA AA A A BREE BENNEN NNN nN Trt BETEREN REE EREREREE O DD O NENE p O E O E E E a MAA AAA A A Ml ERE A EII a a es ee ee ee ee ee z E g Ei y oja EILIT ttt tt p a 4 F f 1 i a z a October 1999 NREL CP 500 27062 Certification Testing for Small Wind Turbines D Corbus H Link S Butterfield C Stork and C Newcomb National Renewable Energy Laboratory T Sasseen Southwest Windpower Presented at Windpower 99 Burlington Vermont June 20 23 1999 4s i L eg mieku aan Energy Laboratory 1617 Cole Boulevard Golden Colorado 80401 3393 NREL is a U S Department of Energy Laboratory Operated by Midwest Research Institute e Battelle e Bechtel Contract No DE AC36 98 GO10337 NOTICE This report was prepared as an account of work sponsored by an agency of the United Sta
14. rder to provide inputs to the design evaluation process Design Type Manufacturing F oundation Type Evaluation Testing Evaluation Design Characteristic Evaluation Measurement Safety and Function Test Final Evaluation Duration Test Report Power Performance Test Type Certificate FIGURE 2 TESTS REQUIRED FOR SMALL WIND TURBINE CERTIFICATION 3 1 Safety and Function Test The purpose of the safety and function test is to verify that the turbine has adequate provisions to operate safely under all conditions It 1s conducted in accordance with provisions listed in IEC 61400 22 Annex D For larger turbines this testing focuses on the control system for the turbine However the control systems for small turbines are very simple and often passive For the AIR 403 turbine the safety and function test consists of the following Emergency shutdown operation Conduct a brake test to ensure the turbine stops in high winds when the brake is applied Power and speed control Verify that the aero elastic stall mechanism of the blades limits speed and power and verify that the charge controller limits current in high winds when the battery voltage is greater or equal to the charge controller voltage set point Yaw control Visual inspection if problems are noted a test plan will be developed Grid loss behavior Open circuit test includes 4 Hz sampling of current to verify internal braking mechanism of turbine controller reduces current t
15. tes government Neither the United States government nor any agency thereof nor any of their employees makes any warranty express or implied or assumes any legal liability or responsibility for the accuracy completeness or usefulness of any information apparatus product or process disclosed or represents that its use would not infringe privately owned rights Reference herein to any specific commercial product process or service by trade name trademark manufacturer or otherwise does not necessarily constitute or imply its endorsement recommendation or favoring by the United States government or any agency thereof The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof Available to DOE and DOE contractors from Office of Scientific and Technical Information OSTI P O Box 62 Oak Ridge TN 37831 Prices available by calling 423 576 8401 Available to the public from National Technical Information Service NTIS U S Department of Commerce 5285 Port Royal Road Springfield VA 22161 703 605 6000 or 800 553 6847 or DOE Information Bridge http www doe gov bridge home html Sa ae Printed on paper containing at least 50 wastepaper including 20 postconsumer waste CERTIFICATION TESTING FOR SMALL WIND TURBINES Dave Corbus Hal Link Sandy Butterfield Christof Stork Charles Newcomb National Renewable Energy Laboratory 1617 Cole Blvd
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