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

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Gearbox Reliability Collaborative

Phase 3 Gearbox 2 Test Plan

H. Link, J. Keller, and Y. Guo

National Renewable Energy Laboratory

B. McNiff

McNiff Light Industry

Technical Report

NREL/TP-5000-58190

April 2013 
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

Gearbox Reliability Collaborative

Phase 3 Gearbox 2 Test Plan 

H. Link, J. Keller, and Y. Guo

National Renewable Energy Laboratory

B. McNiff

McNiff Light Industry

Prepared under Task No. WE11.0301

Technical Report

NREL/TP-5000-58190

April 2013 
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i 

Acknowledgments

This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-

08GO28308 with the National Renewable Energy Laboratory. 
ii

List of Acronyms

CM condition monitoring 

COE cost of energy 

CRB cylindrical roller bearing

DAS data acquisition system

DLC design load case

DGBB deep groove ball bearing 

DOE Department of Energy 

EPO emergency power off 

FAST Fatigue, Aerodynamics, Structures, and Turbulence 

fcCRB full complement cylindrical roller bearing

GB gearbox 

gpm gallon per minute

GRC Gearbox Reliability Collaborative 

Fx thrust 

HS high speed 

HSS high-speed shaft

HS-ST high-speed stage

IEC International Electrotechnical Commission

IS intermediate speed

ISS intermediate-speed shaft

IS-ST intermediate-speed stage

kNm kiloNewton-meter 

LS low speed

LSS low-speed shaft

LS-ST low-speed stage

LVDT linear variable displacement transformer

Myy pitch moment 

Mzz yaw moment

NI National Instruments

NREL National Renewable Energy Laboratory 

NTL non-torque loads

NWTC National Wind Technology Center

PL Planet

PLC planet carrier

rpm revolutions per minute

RTD resistance temperature detector

SRB spherical roller bearing

TDC top dead center (spatial reference)

TRB tapered roller bearing 

VDC volts direct current

VFD variable frequency drive
iii

Table of Contents

List of Acronyms......................................................................................................................................... ii

Table of Contents....................................................................................................................................... iii

List of Figures ............................................................................................................................................. v

List of Tables .............................................................................................................................................. vi

1 Introduction and Background ............................................................................................................. 1

2 Test Article ............................................................................................................................................ 3

2.1 Test Turbine..................................................................................................................................... 3

2.2 Test Drivetrain ................................................................................................................................. 4

2.2.1 External Gearbox Configuration......................................................................................... 4

2.2.2 Internal Gearbox Configuration.......................................................................................... 5

2.2.2.1 Gear Arrangements....................................................................................................... 5

2.2.2.2 Bearing Arrangements .................................................................................................. 6

2.3 Coordinate System........................................................................................................................... 7

3 Test Environment ................................................................................................................................. 8

3.1 Dynamometer Configuration ........................................................................................................... 8

3.2 Dynamometer Control ..................................................................................................................... 9

3.3 Non-Torque Loading System......................................................................................................... 10

3.4 Data-Acquisition System ............................................................................................................... 12

4 Instrumentation ................................................................................................................................... 14

4.1 Non-Torque Loading System......................................................................................................... 14

4.2 Mainshaft and Gearbox Low-Speed Shaft..................................................................................... 14

4.3 Gearbox.......................................................................................................................................... 15

4.3.1 Housing............................................................................................................................. 15

4.3.2 Ring Gear.......................................................................................................................... 15

4.3.3 Planet Carrier.................................................................................................................... 16

4.3.4 Planetary Gears................................................................................................................. 16

4.3.5 Planetary Bearings............................................................................................................ 16

4.3.6 Sun Gear ........................................................................................................................... 17

4.3.7 Intermediate Stage ............................................................................................................ 17

4.3.8 High-Speed Shaft.............................................................................................................. 17

4.4 Brake Disk ..................................................................................................................................... 17

4.5 Generator ....................................................................................................................................... 18

4.6 Additional Measurements.............................................................................................................. 18

5 Test Sequence .................................................................................................................................... 18

5.1 Test Overview................................................................................................................................ 18

5.2 General Dynamometer Test Procedures ........................................................................................ 19

5.3 Recommissioning Test................................................................................................................... 20

5.4 Non-Torque Load Test................................................................................................................... 22

5.4.1 Static Bending Moment Test ............................................................................................ 22

5.4.1.1 Test Procedure............................................................................................................. 24

5.4.1.2 Torque and Non-Torque Bending Moments............................................................... 24

5.4.2 Dynamic Bending Moment Test....................................................................................... 26

5.4.2.1 Test Procedure............................................................................................................. 26

5.4.2.2 Torque and Non-Torque Bending Moments............................................................... 26

5.4.3 Static Thrust Test.............................................................................................................. 27

5.4.3.1 Test Procedure............................................................................................................. 28

5.4.3.2 Torque, Bending Moments, and Thrust ...................................................................... 28

5.4.4 Trunnion Mount Axial Locking Test................................................................................ 29

5.4.4.1 Test Procedure............................................................................................................. 30

5.4.4.2 Torque, Bending Moments, and Thrust ...................................................................... 30
iv

5.4.5 Dynamic Thrust Test ........................................................................................................ 31

5.4.5.1 Test Procedure............................................................................................................. 31

5.4.5.2 Torque and Non-Torque Bending Moments............................................................... 31

5.5 HSS Radial Misalignment Test...................................................................................................... 32

5.5.1.1 Test Procedure............................................................................................................. 33

5.5.1.2 Torque and Non-Torque Bending Moments............................................................... 33

5.6 Field Representative Test: Dynamic Torque and Non-Torque Loads.......................................... 34

5.7 Campbell Diagram Measurement Test .......................................................................................... 35

6 References .......................................................................................................................................... 39

Appendix A. Signal List............................................................................................................................ 40

Appendix B. Instrumentation Details ...................................................................................................... 45

Appendix C. Sample Design Load Cases............................................................................................... 92
v 

List of Figures

Figure 1. Ponnequin wind farm in northern Colorado (NREL PIX/19258) ............................................. 3

Figure 2. Gearbox Reliability Collaborative drivetrain configuration.................................................... 4

Figure 3. Torque arm and rubber mount detail........................................................................................ 5

Figure 4. Gearbox Reliability Collaborative gearbox internal component view................................... 5

Figure 5. Gearbox Reliability Collaborative gearbox internal nomenclature and abbreviations........ 6

Figure 6. Gearbox coordinate system....................................................................................................... 8

Figure 7. The NWTC 2.5-MW dynamometer test facility (NREL PIX/17398) .......................................... 9

Figure 8. Schematic of NWTC 2.5-MW dynamometer test facility and control block diagram ........... 9

Figure 9. Asynchronous generator control mode ................................................................................. 10

Figure 10. Upwind view of test article and NTL system components (thrust frame hidden)............ 11

Figure 11. Side view of system showing thrust components .............................................................. 11

Figure 12. Schematic of GRC data acquisition system during Phase 2 testing................................. 13

Figure 13. Data acquisition boxes for the GRC drivetrain (NREL PIX/24914) ..................................... 13

Figure 14. Effect of pitching moment (Myy) on ring gear load distributions ....................................... 23

Figure 15. Torque and bending moment distribution measured during the GRC field test.............. 23

Figure 16. Response of GRC mainshaft and gearbox to thrust load................................................... 28

Figure 17. High-speed coupling with flexible “dog bone” links........................................................... 32

Figure 18. Sample time series and vibration spectrum (Reproduced from

http://en.wikipedia.org/wiki/File:Voice_waveform_and_spectrum.png) ....................................... 36

Figure 19. Example of a Campbell diagram; BW and FW represent resonances that are slightly 

dependent upon spin speed and the origin-intersecting line represents frequencies at 1P. 

(Reproduced from http://en.wikipedia.org/wiki/File:Campbelldiagram.png) ............................... 37

Figure 20. Accelerometer locations for Phase 3 vibration testing ...................................................... 37

Figure B-1. Mainshaft torque ................................................................................................................... 45

Figure B-2. Mainshaft speed and azimuth.............................................................................................. 46

Figure B-3. Mainshaft Bending Z-axis..................................................................................................... 47

Figure B-4. Mainshaft Bending Y-axis .................................................................................................... 48

Figure B-5. Mainshaft axial motion ......................................................................................................... 49

Figure B-6. Gearbox motion, XX at trunnion.......................................................................................... 50

Figure B-7. Gearbox motion, YY at trunnion.......................................................................................... 51

Figure B-8. Gearbox motion, ZZ, at trunnion ......................................................................................... 52

Figure B-9. Gearbox motion, YY bottom rotation .................................................................................. 53

Figure B-10. Gearbox case triaxial strain, AA location......................................................................... 54

Figure B-11. Gearbox accelerometers .................................................................................................... 55

Figure B-12. Ring gear 0° face width load distribution ......................................................................... 56

Figure B-13. Ring gear 120° face width load distribution ..................................................................... 57

Figure B-14. Ring gear 240° face width load distribution ..................................................................... 58

Figure B-15. Ring gear external face width load distribution............................................................... 59

Figure B-16. Ring gear local distortion strain........................................................................................ 60

Figure B-17. Carrier-rim radial displacement......................................................................................... 61

Figure B-18. Carrier-rim axial displacement........................................................................................... 62

Figure B-19. Planet gear B rim deflection............................................................................................... 63

Figure B-20. Planet gear C rim deflection............................................................................................... 64

Figure B-21. Planet bearing radial load sensor arrangement............................................................... 65

Figure B-22. Planet bearing A radial load............................................................................................... 66

Figure B-23. Planet bearing B radial load............................................................................................... 67

Figure B-24. Planet bearing C radial load............................................................................................... 68

Figure B-25. Planet bearing inner ring temperature.............................................................................. 69

Figure B-26. Planet bearing outer ring temperature.............................................................................. 70

Figure B-27. Planet bearing slip .............................................................................................................. 71

Figure B-28. Sun pinion radial motion.................................................................................................... 72

Figure B-29. Mainshaft aft-end slip ring assembly................................................................................ 73

Figure B-30. Intermediate-shaft axial motion......................................................................................... 74

Figure B-31. Intermediate-shaft aft bearing temperature...................................................................... 75
vi 

Figure B-32. High-speed shaft bending and torque at location A........................................................ 76

Figure B-33. High-speed shaft bending and torque at location B........................................................ 77

Figure B-34. High-speed shaft bending and torque at location C........................................................ 78

Figure B-35. High-speed shaft pinion face width load distribution ..................................................... 79

Figure B-36. High-speed shaft downwind tapered roller bearing strain ............................................. 80

Figure B-37. High-speed shaft upwind tapered roller bearing strain .................................................. 81

Figure B-38. High speed shaft tapered roller bearing outer ring temperature ................................... 82

Figure B-39. Brake disk speed and azimuth........................................................................................... 83

Figure B-40. Brake disk axial motion...................................................................................................... 84

Figure B-41. Brake disk radial motion .................................................................................................... 85

Figure B-42. Axial motion of generator upwind face............................................................................. 86

Figure B-43. Radial motion of generator input shaft............................................................................. 87

Figure B-44. Deflection of nacelle frame aft of gearbox ....................................................................... 88

Figure B-45. Generator shaft speed and azimuth.................................................................................. 89

Figure B-46. Generator shaft encoder .................................................................................................... 90

Figure B-47. Gearbox oil sump temperature.......................................................................................... 91

Figure C-1. Normal operation, Vwind = 5 m/s (file: NO-05 2009-10-07-08-01-43.xlsx) .......................... 92

Figure C-2. Normal operation, Vwind = 10 m/s (file: NO-10 2009-09-26-00-09-16.xlsx) ........................ 92

Figure C-3. Normal operation, Vwind = 15 m/s (file: NO-15 2009-09-22-13-41-21.xlsx) ........................ 93

Figure C-4. Normal operation, Vwind = 20 m/s (file: NO-20 2009-09-21-11-30-49.xlsx) ........................ 93

Figure C-5. Normal operation, Vwind = 25 m/s (file: NO-25 2009-10-01-08-41-19.xlsx) ........................ 94

Figure C-6. Startup to low-speed generator (file: Startup2 2009-09-21-19-50-59.xlsx)...................... 94

Figure C-7. Startup to high-speed generator (file: Startup1 2009-09-21-07-40-45.xlsx) .................... 95

Figure C-8. Shutdown from high-speed generator (file: Shutdown1 2009-09-21-19-40-59.xlsx) ..... 95

Figure C-9. Upshift (file: Upshift 2009-09-26-00-19-17.xlsx) ................................................................. 96

Figure C-10. Downshift (file: Downshift 2009-09-22-21-31-30.xlsx) ..................................................... 96

List of Tables

Table 1. Gear Dimensions and Details...................................................................................................... 6

Table 2. Bearing Types............................................................................................................................... 7

Table 3. Field Conditions to be Simulated in the Dynamometer.......................................................... 35

Table 4. List of Accelerometers for Vibration Testing .......................................................................... 38
1 

1 Introduction and Background

Gearboxes in wind turbines have not been achieving their expected design life; however, they 

commonly meet and exceed the design criteria specified in current standards in the gear, bearing, 

and wind turbine industry as well as third-party certification criteria. The failures are widespread 

across manufacturers and turbine sizes, and the majority of these failures are not due to 

manufacturing issues. One of the basic premises put forth by the National Renewable Energy 

Laboratory (NREL) Gearbox Reliability Collaborative (GRC) is that this gap between designestimated and actual gearbox reliability results from the absence of critical elements in the design 

process or insufficient design tools. 

Key goals of the GRC are to improve design approaches and analysis tools, and to recommend

practices and test methods resulting in improved design standards for wind turbine gearboxes 

that lower the cost of energy (COE) through improved reliability. The GRC uses a combined 

gearbox testing, modeling, and analysis approach, along with a database of information from 

gearbox failures collected from overhauls and investigation of gearbox condition monitoring 

(CM) techniques to improve wind turbine operations and maintenance practices. 

Full-scale dynamometer testing builds an understanding of how selected loads and events 

translate into gear and bearing response, including reactions, load distributions, displacements, 

temperatures, stresses, and slip. Ideally, the knowledge gained from the GRC will result in any 

necessary improvements to gearbox design standards and associated modeling tools.

There are four main objectives of the GRC gearbox testing program. Testing to be conducted 

under this plan addresses some, but not all of these objectives. 

1. Verify the gearbox operates within the basic design standards and assumptions, such as: 

o Load distribution and sharing for the gears and bearings 

o Structural deflections

o Bearing race temperature gradients 

o Cooling capacity. 

2. Assess the effect of real-world operating conditions on the as-built gearbox and potentially 

extend the current design standards and assumptions to consider these effects, such as: 

o Static and dynamic non-torque loading

o High-speed shaft misalignment

o Bearing rolling element skidding. 

3. Validate key portions of drivetrain, gear, and bearing analysis tools, such as: 

o Dynamic response 

o Generator coupling stiffness 

o Bearing rolling element skidding. 

4. Develop a standard dynamometer testing and acceptance process, including tests such as: 

o Non-torque loading

o Dynamic (field representative) loading

o Length of testing 

o Modal testing. 
2 

Testing in the GRC project has included eleven test series to date, including tests that have been 

grouped under the nomenclature of Phase 1 and Phase 2 tests [1]. This test plan describes the 

first of two test series under Phase 3. Phase 3 tests are currently planned in the National Wind 

Technology Center (NWTC) dynamometer as described below.

• Phase 3a. Test of gearbox 2 (GB2) using the two-speed turbine controller that has been 

used in prior testing. This test series will investigate non-torque loads, high-speed shaft

misalignment, and reproduction of field conditions in the dynamometer. This test series 

also includes vibration testing using an eddy-current brake on the gearbox’s high-speed 

shaft. This will permit operation at any generator speed between 100 rpm and 2,000 rpm 

at torque levels of about 5% of rated—sufficient to load bearings and gear mesh. 

Vibration testing enables the investigation of gearbox modal behavior and enhances the 

ability to duplicate high-frequency torque events observed in Phase 1 field testing. 

• Phase 3b. Test of the newly designed gearbox 3 (GB3) in the NWTC dynamometer using 

the variable frequency drive. GB3 is a redesigned and rebuilt version of the GB1. It is 

expected to demonstrate a significantly better capability to withstand non-torque loads.

Other non-dynamometer tests also are planned for completion in 2013. Each of these tests is 

described in a separate test plan. 

• High-speed flexible coupling stiffness measurement. The coupling is removed from the 

GRC drivetrain and installed in a test rig, which simulates radial (also known as parallel) 

misalignment conditions. A range of lateral forces is applied and the resulting deflections 

are measured, yielding a force-deflection curve that will most likely be non-linear. 

Determining the coupling stiffness enables a greater understanding of axial and bending 

loads induced in the high-speed shaft when the coupling is subjected to the radial

misalignment. This information can be of direct use in simulating the radial misalignment 

tests described herein.

• High-speed bearing stiffness measurement. Both the cylindrical and tapered roller 

bearings used on the high-speed shaft are installed in a test rig, which determines the 

5 x 5 stiffness matrix for each bearing. A range of radial forces is applied under different 

preload conditions and the resulting small deflections are measured, yielding a forcedeflection curve. Once completed, the experimentally determined stiffness matrix is

compared to theoretical predictions, likely resulting in a modification of GRC gearbox 

models. 

• Static modal test. Accelerometers are attached to shafts inside the GRC gearbox and 

torsional vibration modes are excited with a hammer. Shafting is locked to prevent 

rotation and various torque settings are applied. This test is similar to a test previously 

conducted by Purdue University, but this test provides vibration data from internal 

components of the gearbox. 

• Lubrication flow check. Delivery of lubrication oil to the gears and bearings has been 

predicted but not yet measured. This test uses several non-intrusive flow meters to 

measure flow through several of the branches of the lubrication system distribution tree. 

The flow meters are calibrated relative to a positive displacement flow meter currently 

used to measure total flow to the gearbox. 
3 

2 Test Article

2.1 Test Turbine

The GRC drivetrain originally was designed for a stall-controlled, three-bladed upwind turbine 

with a rated power of 750 kW. Figure 1 shows a field of these turbines at Xcel Energy’s 

Ponnequin Wind Farm in northern Colorado. The turbine generates electricity at two rotor 

speeds, 14.7 rpm and 22.1 rpm. The gearbox ratio of 81.491 converts these mainshaft speeds to 

generator speeds of 1,200 rpm and 1,800 rpm. 

The generator has two sets of windings that permit generation of 200 kW at 1,206 rpm and 

750 kW at 1,809 rpm. The generator has 0.5% slip, which accounts for operation at speeds 

slightly greater than synchronous, 1,200 rpm and 1,800 rpm. Thus, online speed variation is 

limited to only 9 rpm when the high-speed windings are engaged. During startup, the generators 

are connected to the utility grid using custom soft-start electronics that soften torque spikes 

associated with electrical contactor closure. After the soft start establishes stable operation at 

synchronous speed, a bypass contact is engaged. 

Figure 1. Ponnequin wind farm in northern Colorado (NREL PIX/19258) 

The GRC turbine follows a conventional, modular configuration. In this configuration, all 

individual components of the drivetrain are mounted onto the bed plate or main frame. These 

components include the hub, main bearing, mainshaft, gearbox, brake, generator shaft, and 

generator as shown in Figure 2. Everything but the hub is included in the dynamometer tests. 
4 

Figure 2. Gearbox Reliability Collaborative drivetrain configuration

The GRC lubrication system used in dynamometer testing consists of two circuits, the inline 

filter loop featuring an 8 gallon per minute (gpm) pump and two stage filters of 50 μm and 

10 μm, the offline filter loop featuring a 0.65-gpm pump and a filter of 3 μm.

The GRC cooling system used in dynamometer testing features a custom glycol cooling and 

pumping unit. This unit provides a cool glycol/water mixture to the generator and to the 

lubrication system heat exchanger. 

Several condition monitoring instruments will be employed in Phase 3 testing, including a Hydac 

CSM2000 particle counter that samples unfiltered oil from the gearbox sump. Other sensors 

include an inline filter loop wear debris sensor, and several offline filter loop wear debris and oilcondition sensors [2]. 

2.2 Test Drivetrain

2.2.1 External Gearbox Configuration

The configuration of the GRC gearbox follows the typical configuration of the megawatt-scale 

turbines used in the industry today. The gearbox is mounted with a three-point configuration in 

which torsional loads are transferred to the main frame through two torque arms, and non-torque 

moments and forces are reacted mostly at the main bearing. Each torque arm transfers loads by 

means of an elastomeric bearing supported by mounts that help isolate and reduce noise. Figure 3 

shows the torque arm configuration and a cutaway view of the elastomeric mount [1]. 

Generator

Main 

Bearing Main Shaft

Brake

Generator Shaft

Gearbox

Bed Plate

Hub

Torque Arms
5 

Figure 3. Torque arm and rubber mount detail

2.2.2 Internal Gearbox Configuration

The gearbox used in the GRC project has been modified from the original gearbox configuration 

used in the commercial versions of this wind turbine [1]. The gearbox has an overall ratio of 

81.491. It is composed of one low-speed (LS) planetary stage and two parallel shaft stages. The 

planetary stage accommodates three planet gears. The annulus gear of this stage also serves as 

part of the gearbox housing. The sun gear is set in a floating configuration to equalize the load 

distribution among the planets. To accommodate the floating sun arrangement, the low-speed 

shaft (LSS) is hollow and has an internal spline that transfers the torsional loads to the parallelshaft stages.

2.2.2.1 Gear Arrangements

The LS planetary gears have a helix angle of 7.5°, and the intermediate speed (IS) and highspeed (HS) gear sets have a helix angle of 14°. Figure 4 and Figure 5 show the internal 

components and their nomenclature [1]. Table 1 gives the dimensions and details of the gearing.

Figure 4. Gearbox Reliability Collaborative gearbox internal component view
6 

Figure 5. Gearbox Reliability Collaborative gearbox internal nomenclature and abbreviations

Table 1. Gear Dimensions and Details

Gear Element Teeth

Mate

Teeth

Root Diameter

(mm)

Helix

Angle

Facewidth

(mm)

Speed 

Ratio

Planet gear 39 99 372 7.5°L 227.5

Ring gear 99 39 1047 7.5°L 230 5.71

Sun pinion 21 39 186 7.5°R 220

Intermediate gear 82 23 678 14°R 170 3.57 Intermediate pinion 23 82 174 14°L 186

High-speed gear 88 22 440 14°L 110 4.00 HSS pinion 22 88 100 14°R 120

Overall speed ratio 81.49

2.2.2.2 Bearing Arrangements

Several roller-bearing types are employed in the gearbox according to the loading conditions and 

gearbox-life requirements. The planet carrier is supported by two full-complement cylindrical 

roller bearings (fcCRBs), and each planet gear assembly is supported by two identical cylindrical 

Annulus

Planet

Sun

Gear

Gear Pinion

Pinion

Planet 

Carrier

Low-Speed Stage

LS-ST

High-Speed Stage

HS-ST

Intermediate-Speed Stage

IMS-ST

Low-Speed Shaft

LSS 

Intermediate-Speed 

Shaft

ISS

High-Speed Shaft 

HSS
7 

roller bearings (CRBs). Each parallel shaft in the gearbox is supported by a CRB on the upwind 

side of the assembly, and by two back-to-back mounted, duplex, tapered roller bearings (TRBs) 

on the downwind side.

Table 2 gives the location and bearing type for all bearings in the gearbox. The letter following 

the location abbreviation indicates the position of the bearing according to the component from 

upwind (A) to downwind (B, C). 

Table 2. Bearing Types

Location Type

PLC-A fcCRB

PLC-B fcCRB

PL-A CRB

PL-B CRB

LSS-A fcCRB

LSS-B TRB

LSS-C TRB

ISS-A CRB

ISS-B TRB

ISS-C TRB

HSS-A CRB

HSS-B TRB

HSS-C TRB

Conduit DGBB

2.3 Coordinate System

The coordinate system used in GRC testing is consistent with common wind turbine drivetrain 

practice as described below. 

• X-axis: Aligned with the input low-speed shaft with the downwind direction being 

positive. In the GRC drivetrain, this axis is inclined at 5° to the horizontal. Thrust (Fx) is 

force acting along the positive X-axis and torque is a moment about the X-axis.

• Z-axis: Orthogonal to the X-axis with upward being positive. Vertical force acts along the 

Z-axis and yaw moment (Mzz) acts about the Z-axis. Rotor weight causes negative 

vertical force acting at the main bearing.

• Y-axis: Orthogonal to the X-axis and Z-axis with leftward being positive when viewing 

the drivetrain from upwind. Lateral force acts along the Y-axis and rotor weight causes a 

negative pitch moment (Myy) about the Y-axis.

• Rotor azimuth angle: Increases clockwise when viewed from upwind with 0° being 

upward. Normal rotor rotation in the GRC drivetrain, as for most wind turbines, is 

positive.
8 

Figure 6. Gearbox coordinate system 

3 Test Environment

3.1 Dynamometer Configuration

The National Wind Technology Center 2.5-MW dynamometer test facility [3] will be used for 

Phase 3 testing, as shown in Figure 7 and Figure 8 [1]. All references to “dynamometer” in this 

document mean the 2.5-MW facility, not the 225-kW or 5-MW dynamometers that also are 

available for drivetrain testing at the NWTC. The 2.5-MW dynamometer is essential for this 

project because it enables loads to be applied to the drivetrain under controlled conditions, in 

contrast to field testing where wind loads are not controllable. These test conditions can be 

steady-state conditions that are useful for simple model validation, but also can be dynamic and 

compare the response in the dynamometer versus the field test turbine and even more complex 

models. Furthermore, it is much easier to modify instrumentation, service the drivetrain, and 

modify the configuration in the dynamometer than it is to perform these tasks on a drivetrain 

installed in a turbine in the field.
9 

Figure 7. The NWTC 2.5-MW dynamometer test facility (NREL PIX/17398) 

Figure 8. Schematic of NWTC 2.5-MW dynamometer test facility and control block diagram

3.2 Dynamometer Control

The dynamometer can be operated in either torque or speed control. In torque control, the 

operator commands a torque level that the dynamometer motor applies. The test drivetrain—in 

this case the GRC drivetrain—regulates speed. In speed control, the dynamometer operator 

commands the dynamometer motor’s speed, and torque is regulated by the test drivetrain. The

GRC drivetrain uses a generator that operates at two speeds. At each of those speeds, however, 

the generator allows only a 0.5% change from nominal, synchronous speed. It therefore is 

preferable to operate the dynamometer in torque-control mode. All Phase 1 and Phase 2 testing 

was conducted in this mode. Unfortunately, acceleration during start-up is difficult to control 

using torque control. 
10 

During Phase 2 testing, the dynamometer control was enhanced to provide more precise control 

of the start-up ramp rate and dynamometer behavior during grid connection. In this configuration, the dynamometer was started in speed-control mode at a preprogrammed rate of change 

(ramp rate). At generator synchronous speed, the torque set point was set to the current torque 

demand and the dynamometer is switched to torque control mode. Once in torque control mode, 

the dynamometer ramps at a specified rate to a predetermined torque value. Details of the 

asynchronous generator control mode are shown in Figure 9 [1]. 

Figure 9. Asynchronous generator control mode

3.3 Non-Torque Loading System

In addition to torque and thrust, a wind turbine rotor applies loads to the drivetrain in four other 

degrees of freedom perpendicular to the main shaft axis: lateral force, vertical force, pitch 

moment, and yaw moment. These four off-axis loads are interrelated and can be simulated for 

testing purposes with just two actuators. During early GRC testing, the dynamometer was 

enhanced to provide control of these off-axis loads as well as thrust. The system used to apply 

these loads is called a non-torque loading (NTL) system. The NTL system used in the NWTC 

2.5-MW dynamometer is shown in Figure 10 and Figure 11 [1]. 

The current NTL system uses three servo-hydraulic cylinders to apply thrust and the other four 

off-axis loads. This system can apply loads statically or dynamically over a limited frequency 

range. 

Speed, Torque

Speed Control Torque Control Speed Control

Disconnect on 

negative power

(sub synchronous)

Switch to torque control 

at synchronous speed 

Speed at rated 

torque

Torque

Speed
11 

Figure 10. Upwind view of test article and NTL system components (thrust frame hidden) 

Figure 11. Side view of system showing thrust components

Given the fixed distance between the NTL bearing housing and the GRC main bearing, the 

relationship between the radial force and pitch or yaw moment for the system is fixed. Further, 

the geometry of the radial hydraulic actuators limits radial force in all directions to the maximum 
12 

vertical force. The following maximum loads are defined at the main bearing of the GRC 

drivetrain. 

• Maximum pitch or yaw moment +/- 1,337 kNm

• Maximum radial force +/- 685 kN 

• Maximum thrust force +/- 311 kN 

These are “NTL-applied” loads and should not be confused with the loads applied to the 

drivetrain during testing. Overhanging weight of shafting and NTL components add the 

following loads. 

• Pitch moment from overhanging weight - 14 kNm 

• Vertical force from overhanging weight - 83 kN 

• Thrust force from overhanging weight 7 kN 

Additionally, flexible couplings between the NTL and the dynamometer gearbox impart 

moments during testing. These are functions of torque loads and coupling misalignment. Thus, 

tare loads (i.e., loads applied to the drivetrain when NTL-applied loads are zero) must be 

measured as part of each test condition.

In comparison to the shaft overhanging loads in the dynamometer, the turbine rotor’s weight of 

12,500 kg centered at 1.291 m upwind of the main bearing applies the following loads to the 

mainshaft at the main bearing. 

• Pitch moment from rotor weight - 158 kNm 

• Vertical force from rotor weight - 122 kN 

• Thrust force from rotor weight 11 kN 

3.4 Data-Acquisition System

The data-acquisition system (DAS) is based on National Instruments (NI) deterministic Ethernet 

platform [4]. One system consisting of two backplanes is mounted to the mainshaft. The output 

of that system is converted to fiber optic and sent across a fiber optic rotary joint to the nonrotating frame. On top of the gearbox, a second system is mounted with two more deterministic 

Ethernet backplanes. The deterministic Ethernet synchronizes the different modules. Figure 12 

shows a general layout of the DAS and Figure 13 shows the physical layout of the dataacquisition boxes. The two boxes mounted on top of the gearbox process fixed-frame signals.

The box mounted on the mainshaft, attached with the blue safety strap, processes signals 

generated on the mainshaft and carrier assembly. 
13 

Figure 12. Schematic of GRC data acquisition system during Phase 2 testing

Figure 13. Data acquisition boxes for the GRC drivetrain (NREL PIX/24914) 

For Phase 3 testing, the gearbox-mounted DAS and signal conditioning will be expanded to 

acquire additional data pertaining to dynamic high-speed shaft alignment and external ring gear 

stress and strain. To accommodate additional channels and signal conditioning hardware, a new 

enclosure will be added in the stationary frame.

For most of the testing a 100-Hz sample rate is used, unless otherwise specified in the test 

description. Snapshot data also can be collected in so-called burst mode at 2,000 Hz.

Gearbox mounted 

Power supply box

Low Speed Shaft 

mounted DAS box

Gearbox mounted 

Signal 

conditioning

Gearbox mounted 

DAS box

PXI chassis DAS Computer

FO Fiber 

Optic

28VDC

24VDC 24VDC FO

Rotating frame
14 

4 Instrumentation

Instrumentation for Phase 3 testing can be categorized by location of the sensor. General 

descriptions of the sensors in these areas are provided in this section. Appendix A contains a 

listing of all sensors and resulting signals, and Appendix B provides details on sensor installation 

and wiring. 

• Non-torque loading system

• Mainshaft/gearbox low-speed shaft

• Gearbox housing 

• Gearbox ring gear 

• Low-speed stage planet carrier

• Low-speed stage planet

• Low-speed stage sun

• Intermediate stage

• High-speed stage and shaft

• Generator

• Controller 

• Lubrication system

4.1 Non-Torque Loading System

The non-torque loading system has three actuators, each of which has a load cell and a 

displacement sensor. The thrust actuator is offset from the center of the shaft, therefore its load is 

balanced by a linkage which also features a load cell. Strain gages on the stabilizer link provide 

measurements of axial and lateral loads transmitted by that component. Hydraulic pressure to the 

actuators is monitored using a pressure transducer. During Phase 2 testing, the flexible couplings 

between the non-torque loading system and the dynamometer gearbox were determined to impart 

significant bending loads on the mainshaft. These loads are greatly affected by coupling 

misalignment. Therefore, in Phase 3 these loads will be measured using two sets of strain gages 

to measure bending loads at each end of the jackshaft that connects the dynamometer gearbox to 

the non-torque loading system. Additionally, two proximity sensors on each of the two flexible 

couplings indicate the magnitude and direction of coupling misalignment. 

4.2 Mainshaft and Gearbox Low-Speed Shaft

The mainshaft is rigidly connected to the gearbox low-speed shaft and planet carrier and 

measurement of this assembly provides the critical input loads to the drivetrain. Torque is 

measured on the mainshaft with a full strain gage bridge, as shown in Figure B-1 in Appendix B. 

Mainshaft torque is also measured with a custom torque spool located upwind of the non-torque 

loading equipment. This measurement device is more accurately calibrated than the torque gages 
15 

on the GRC mainshaft, but it does not account for friction in the NTL bearing or the GRC main

bearing. 

A shaft encoder on the aft end of the signal conduit tube measures the speed and azimuth of the 

gearbox LSS, as shown in Figure B-2. A pulse counter/timer circuit derives the speed, giving a 

0- to 5-volt DC (VDC) output proportional to speed. The azimuth angle is from a separate 

counter circuit using the same encoder input, generating a 0 to 4.095 VDC sawtooth output 

proportional to shaft position. The sawtooth is reset to 0 by the index pulse once per revolution. 

Resolution is about 1/4°. Zero azimuth angle is defined when Planet C is upward at “top dead 

center” (TDC).

Main shaft bending is measured in both directions, as shown in Figure B-3 and Figure B-4. The 

measured shaft azimuth is used to convert these rotating shaft-bending moments into pitch and 

yaw moments in the fixed frame. Additionally, a proximity sensor quantifies axial displacement

of the mainshaft relative to the mainframe close to the mainshaft flange, as shown in Figure B-5. 

4.3 Gearbox

4.3.1 Housing

Gearbox housing measurements provide information on the displacement of the gearbox relative 

to the mainframe. Motion of the gearbox relative to the mainframe in six degrees of freedom is 

measured using six proximity sensors, as shown in Figure B-6 to Figure B-9. These are located 

on the trunnion arms and on the bottom of the gearbox. A three-element strain gage set is used to 

validate finite element models of the gearbox, as shown in Figure B-10. 

Motion of the gearbox relative to the ground is measured using low-frequency (DC – 100 Hz) 

accelerometers, as shown in Figure B-11. Two of these are triaxial accelerometers mounted close 

to the trunnion mounts. A single-axis accelerometer measures motion about the trunnion axis. 

Additionally, high-frequency vibration is measured, focusing on gear mesh frequencies, bearing 

ball pass frequencies, and higher order drivetrain natural frequencies. This is done using CM 

systems with accelerometers, and stress wave microphones with analysis of notch frequencies of 

interest.

4.3.2 Ring Gear

Strain gages on both the inside and the outside of the gearbox ring gear indicate contact patterns 

between the ring gear teeth and planet teeth. Other gages quantify ring gear deformation, which 

occurs primarily because of loads induced by meshing with the planets. 

On its inner surface, the ring gear has strain gages mounted in the root area of the internal teeth

arranged to sense tooth bending strain. Experience suggests that gages in this orientation are 

relatively insensitive to alignment errors. These gages are distributed axially at eight locations 

along the root apex to measure the tooth–face width load distribution. The gages are arranged in 

two separate Wheatstone bridges of four gages each. This approach has several advantages, 

including increasing the signal-to-noise ratio and temperature compensation. It requires spacing 

the gages over several teeth, however, such that the gages on adjacent bridge arms are not in the 

contact area at the same time. If they are, the signal could be attenuated erroneously. The ring 

gear has a 7.5° helix angle and the contact ratio is moderately high. For these reasons, adjacent 
16 

gages were installed four teeth apart. This arrangement is repeated at three circumferential 

locations on the ring gear at TDC and spaced 120° apart (as shown in Figure B-12, Figure B-13, 

and Figure B-14), for a total of 24 internal gages. 

On its external surface, the ring gear has one set of eight strain gages in an arrangement similar 

to the internal gages (see Figure B-15), to measure the tooth–face width load distribution from 

the exterior of the ring gear. These gages are located at approximately 65° from TDC.

Also on its external surface the ring gear has four sets of two gages, each arranged in Poisson 

bridges gages oriented to measure ring gear hoop strain. These gages are located 45° from TDC 

and are spaced 90° apart, as shown in Figure B-16. These gages help to define positions of 

internal components relative to the mainshaft.

The primary function of the internal gages is to determine load share between planets and 

characterize changes in the face width load distribution. Additionally, the external gages enable 

comparison to be made to investigate the accuracy of measuring face width load distribution 

from the exterior of the gearbox—which is significantly easier than using gages that are inside 

the gearbox. The external gages also can be used to investigate the effect of the stiffness of the 

ring gear. 

4.3.3 Planet Carrier

Proximity sensors indicate the radial and axial motion of the planet carrier relative to the 

housing, as shown in Figure B-17 and Figure B-18. This motion is a combination of rigid body 

and deformation. These sensors are mounted on the upwind face and sides of the gearbox 

housing, using a custom fitting that bolts to the housing. 

4.3.4 Planetary Gears

Planetary gear sensors include six proximity sensors which are mounted on the carrier. These 

measure the position of two of the planets (B and C) relative to the carrier. Each set of three is 

mounted identically, as shown in Figure B-19 and Figure B-20. These indicate both axial and 

tilting motion of the planetary gears.

4.3.5 Planetary Bearings

Thirty-six strain gages are mounted in axial grooves in the inner races of the planet bearings to 

provide information on planet loads and roller contact pressure distribution. Three grooves were 

machined into each bearing. Each groove has two strain gages—one at 25% and one at 75% of 

the inner ring width as shown in Figure B-21. All six bearings have a groove at top dead center 

which is in the direction of motion of the planet pin and close to the center of pressure between 

the pin and the planet. The remaining grooves on each planet are located at different azimuthal

locations, as shown in Figure B-22 to Figure B-24. 

This instrumentation allows measurement of the following: 

• The axial and circumferential distribution of load through the load zone 

• Change of load distribution during shaft and gear load fluctuations and motions 

• Load sharing between planet bearings. 
17 

Thermocouples are also mounted in the axial midpoint of the each groove to measure planet 

bearing inner race temperatures, as shown in Figure B-25. Of the eighteen installed 

thermocouples, the twelve were judged to be sufficient to characterize bearing temperatures and 

therefore were connected to the data-acquisition system. This includes all thermocouples from 

planet A, as well as selected ones from the other two planets. One radiant-type non-contact

temperature sensor is used to measure temperature on the outer race of Planet A to identify the 

temperature gradient across the bearing, as shown in Figure B-26. 

An inductive proximity sensor is used to sense passage of the eighteen rivets in the roller cage of 

one of the planet bearings, as shown in Figure B-27. This provides a measure of the rotational 

speed of one of the rollers about the planet pin, and is used to detect slippage of the rollers 

relative to the planet bearing races. Bearing slip is suspected to play a significant role in contact 

damage. Slip is expected to be less than 1% of race speed at high bearing loads, but could be 

more than 25% in lightly loaded and transient situations. 

4.3.6 Sun Gear

Two proximity sensors indicate the radial position of the sun gear relative to the planet carrier, as 

shown in Figure B-28. They sense the upwind end of the sun shaft in the area of the shaft that 

extends about 50 mm beyond the end of the sun pinion. These sensors record this motion relative 

to carrier in two orthogonal directions. These rotating frame internal gearbox measurements exit 

the gearbox through a slip ring assembly (Figure B-29). 

4.3.7 Intermediate Stage

The two measurements in the intermediate stage are axial position of the intermediate shaft 

relative to the housing using a proximity sensor, as shown in Figure B-30, and the temperature of 

the rear bearing, as shown in Figure B-31. 

4.3.8 High-Speed Shaft

In Phase 2, the only sensors on the high speed shaft section were two resistance temperature 

detectors (RTDs) measuring the outer ring temperatures of the CRB and the upwind TRB. In 

Phase 3, the high-speed shaft instrumentation is significantly enhanced to assess high-speed 

shaft, pinion, and bearing loads. Three sets of bending gages define shaft bending loads on either 

side of the high-speed gear mesh and downwind of the pair of TRBs as shown in Figure B-32 to 

Figure B-34. An additional set of gages also downwind of the pair of TRBs measures torque 

transmitted by the high-speed shaft. Eight gages are installed in the root of the teeth of the highspeed pinion to measure the face width load distribution as shown in Figure B-35. The shaft 

bending gages are not capable of distinguishing loads between the two TRBs, so additional gages 

are mounted in axial grooves in the outer races to measure bearing loads on the TRBs as shown 

in Figure B-36 and Figure B-37. Each bearing has 4 axial grooves with 2 gages per groove for a 

total of 16 strain gages to measure these TRB loads. Two RTDs will also measure the 

temperature of the outer races of the two TRBs as shown in Figure B-38. 

4.4 Brake Disk

An encoder measures shaft speed and position as shown in Figure B-39. Five proximity 

sensors—three axial, one vertical, and one lateral—measure the brake disk position relative to 

the dynamometer floor, as shown in Figure B-40 and Figure B-41. These, in combination with 
18 

similar proximity sensors on the generator shaft, provide the data required to calculate alignment 

of the two flexible couplings in the high-speed shaft assembly. 

4.5 Generator

Five proximity sensors—three axial, one vertical and one lateral—measure generator position 

and rotation relative to the dynamometer floor in five degrees of freedom, as shown in Figure 

B-42 and Figure B-43. A robust framework is needed to measure generator displacement, 

because the downwind portion of the mainframe is very flexible. This mainframe displacement 

measurement is shown in Figure B-44. In combination with measurements of gearbox housing 

motion, these generator measurements yield information on alignment of the high-speed shaft 

assembly during applications of torque and non-torque load to the main shaft. 

An encoder on the aft end of the generator measures the generator shaft speed and azimuth as 

shown in Figure B-45 and Figure B-46. An RTD measures the temperature of the downwind 

bearing, which previously has run hotter than the upwind bearing. 

4.6 Additional Measurements

Relays indicate the status of the generator’s electrical connection to the grid; one relay for the 

high-power generator windings, one for the low-power generator windings, and one to indicate 

when the soft-start components are bypassed. A power meter indicates real and reactive power at 

the connection of the generator to the grid. 

The gearbox lubrication system is monitored using a temperature and pressure sensor at the 

distribution manifold, a temperature sensor at the outlet of the sump (Figure B-47), and a 

displacement-type flow meter to measure total oil flow to the gearbox. An optical particle sensor 

measures metallic and non-metallic particles in the sump oil. The entire drivetrain (i.e., main 

bearing, gearbox, and generator) is instrumented with various condition monitoring systems 

(e.g., vibration and oil debris analysis packages). 

5 Test Sequence

5.1 Test Overview

Testing in Phase 3a consists of the following major activities:

• Drivetrain recommissioning

• Effect of non-torque loads 

• Radial misalignment of high-speed shaft

• Reproduction of field conditions 

• Campbell diagram measurement. 

The first test sequence in the dynamometer verifies that the drivetrain operates normally and that 

all controls and data systems perform as desired. The GRC drivetrain has not been operated for 

several years and a number of sensors have been added to the instrumentation suite since Phase 2 

testing concluded. Recommissioning tests are used to gradually increase speed, torque, and non-
19 

torque loads, with frequent checks to ensure acceptable control and data-acquisition 

performance.

Non-torque loading effects were investigated in Phase 2 tests. Analysis of test data after testing 

was completed, however, indicated that the test series was not as comprehensive as desired. In 

Phase 3 tests the range of non-torque loads is expanded, simple dynamic non-torque load events 

are applied, and the response of the gearbox and other drivetrain components are measured more 

completely. 

In Phase 2 tests the high-speed shaft was purposefully misaligned. The high-speed shaft, pinion, 

and bearing were not instrumented, however, so it was not possible to measure misalignment 

effects. By outfitting the high-speed shaft with improved instrumentation, Phase 3 tests will 

clarify what conditions, if any, impart excessive loads onto the HSS bearings. Phase 3 tests 

investigate radial misalignment of the generator, non-torque loading of the mainshaft, and brake 

application as possible contributors to HSS bearing loads. 

Reproduction of field conditions in the dynamometer was attempted in Phase 2 testing. A key 

shortfall in the NWTC 2.5-MW dynamometer is the limited control bandwidth of the variable 

frequency drive. The bandwidth of the 15-year-old drive limits the frequency with which torque 

can be applied to the test drivetrain. NREL is in the process of replacing the drive with a more 

modern and more reliable drive which will be available in time for GRC Phase 3 testing. This 

new drive should permit more accurate reproduction of field loading in the dynamometer. 

Several tests have been conducted on the GRC gearbox to determine vibration characteristics.

However, NREL has not been able to conduct a test that would describe both excitation and 

resonant frequency characteristics under torque and over a broad speed range. This is because the 

only method of resisting torque applied by the dynamometer is the two-speed GRC generator and 

generator controller. In Phase 3, NREL plans to procure either a variable frequency drive (VFD) 

or an eddy-current brake. Either device will permit operation over a range of speeds and torques. 

The VFD is the preferred device that would permit operation at torque ranging from zero to rated

and at speeds from 50 rpm to 2,000 rpm. An eddy-current brake would enable operation over a 

similar speed range. But torque would be limited to approximately 5% of rated. This plan will 

describe the full range of testing desired. The test will be conducted over as broad a range as 

possible depending upon the equipment obtained. 

5.2 General Dynamometer Test Procedures

In Phase 3 testing, NREL will verify operation of data acquisition signals before each 

dynamometer run. This allows the test operator to fix signals critical to the test before the test 

begins. In general each run should be preceded with the slow roll checks described in step 4 of 

the recommissioning test in section 5.3. Because some signals only show a response under load, 

it is essential to look at data sets shortly after they are collected to judge whether critical signals 

are still functioning. Automatic indicators should be in place to alert the user to issues such as 

signal railing.

Building on knowledge from Phase 1 testing, it has become clear that to maximize the 

effectiveness of individual data sets, it is necessary to implement data standards. Because the 
20 

GRC is focused on elucidating response to static and dynamic loading conditions, finding the 

response against background noise can be vastly improved by following a few simple steps.

1. Acquire data while stopped, before operation. In doing this, it ensures that the data 

will capture movement from rest for solid body motion. This is very useful for seeing 

gearbox response to non-torque loads. At least 60 seconds of data are necessary to 

complete this section. 

2. If possible, perform unloaded (torque and non-torque) slow rolls before 

accelerating. These provide response to rotation and might contain misalignment caused 

by rotation. Around 60 seconds of data will be sufficient. 

3. Take a snapshot of desired data when the generator comes online. Transient events, 

which frequently occur at start-up, are aliased by the standard data sampling rate.

4. Take a snapshot of data when the test article goes offline. This helps characterize the 

generator response. 

5. Acquire data while stopped, after operation. It has been found that the gearbox does 

not settle in the same position after each run.

5.3 Recommissioning Test

Prior to the first start of the dynamometer NREL will verify control and instrumentation as much 

as possible.

1. Prior to connection of the dynamometer low-speed shaft to the GRC drivetrain. 

A. With the dynamometer drive off, check Emergency Power Off (EPO) buttons to 

ensure that the EPO relay in the Vista Switch operates properly.

B. Exercise each fault sensor to ensure that the fault is detected at the dynamometer 

control panel and that the dynamometer drive shuts down.

i. Dynamometer motor overspeed 

ii. Dynamometer lube oil pressure

iii. GRC controller fault

C. Verify dynamometer motor and drive controls are operating properly. 

D. Get zero position on proximity sensor by hand rotation of brake in both directions 

and unloading. 

E. For each proximity sensor the signal will be calibrated by moving the proximity 

sensor closer or further from its actual target by either turning the proximity 

sensor in the threaded hole it is mounted in or by turning the locking nuts holding 

the sensor in an unthreaded hole. The thread pitch is known, therefore the increase 

or decrease in distance will be known. The initial distance is measured with feeler 

gages or gage block depending on the gap size. 

F. For all strain gage channels, shunt calibrations are performed. 
21 

G. For each Linear Variable Displacement Transformer (LVDT), gage blocks or 

feeler gages are used to calibrate the sensor. The LVDT’s are used only in 

locations where the change in distance is important.

H. Check other data-acquisition channel to ensure that nominal values are reported. 

2. Check GRC mainshaft bending moments. 

A. Check other data acquisition channel to ensure that nominal values are reported. 

B. With no shaft adapters attached, slow roll the GRC main shaft. Bending moments 

should be less than 1 kNm. 

C. With the 5,100-lb white coupling (cylinder and upwind flange) attached to the 

GRC mainshaft, slow roll. Bending moments should be about 8 kNm. 

3. Connect the dynamometer shaft to the GRC drivetrain.

A. Verify that the NTL actuator tuning parameters are set up properly; that load cell 

and LVDT signals are nominal; and that the mechanical system is set up, torqued, 

and adjusted. Refer to the document used to commission the NTL equipment and 

to the readiness verification checklist for these verifications. 

B. Place the NTL radial actuators in force feedback and command oscillations at a 

force value of +/- 5 kN and a frequency of less than 0.3 Hz. Using the force 

feedback signal, adjust the swivel ends so the there is no backlash in the system 

and low friction in the swivels.

4. Conduct a slow roll with no GRC-generator connection to the grid. 

A. Listen for unusual sounds or vibrations in the dynamometer and GRC drivetrain. 

B. Check each data acquisition channel to ensure that nominal values are reported. 

C. Verify that data are recorded in both slow and fast recording modes. 

D. Check GRC main shaft bending. With shaft overhanging weight, it should be 

about 65 kNm.

E. Check NTL vertical load required to zero mainshaft bending. This should be 

approximately 65 kN. 

5. Accelerate to synchronous speed and connect the high-power generator windings.

Command 5% rated torque. 

A. Listen for unusual sounds or vibrations in the dynamometer and GRC drivetrain. 

B. Check each data acquisition channel to ensure that nominal values are reported. 

6. Gradually increase torque to 100% of rated.

A. Listen for unusual sounds or vibrations in the dynamometer and GRC drivetrain. 

B. Check each data-acquisition channel to ensure that reasonable responses are 

reported. 

7. Reduce torque to 5% of rated and gradually apply Fx to 50 kN. 

A. Listen for unusual sounds or vibrations in the dynamometer and GRC drivetrain. 
22 

B. Check each data-acquisition channel to ensure that reasonable responses are 

reported. 

8. At 5% of rated torque and 0 kN Fx, gradually apply Myy to -50 kNm and then from 

-50 kNm to +50 kNm. 

A. Listen for unusual sounds or vibrations in the dynamometer and GRC drivetrain. 

B. Check each data-acquisition channel to ensure that reasonable responses are 

reported. 

9. At 5% of rated torque, with 0 kN Fx, and 0 kNm applied Myy, gradually apply Mzz to -

50 kNm and then from -50 kNm to +50 kNm. 

A. Listen for unusual sounds or vibrations in the dynamometer and GRC drivetrain. 

B. Check each data-acquisition channel to ensure that reasonable responses are 

reported. 

5.4 Non-Torque Load Test

The primary objective of the non-torque load test is to quantify the effects of non-torque loads 

(thrust, pitch, and yaw) on both internal and external features of the gearbox. This test also will 

help define how flexible couplings—typically used in dynamometer drivetrains—add to the 

loads applied by non-torque loading devices. Primary measurements include gearbox solid body 

motion, main shaft to gearbox alignment, and planet to ring tooth contact changes. Secondary 

measurements include HSS alignment, HSS bearing loads, dynamometer flexible coupling 

alignment, and loads. NREL staff also will monitor planet bearing roller behavior to determine 

whether skidding occurs when the roller moves into the load zone. Although non-torque loads 

might not affect the intermediate- and high-speed stages, data will be obtained to assess this 

possibility. 

5.4.1 Static Bending Moment Test

The static bending moment test is a continued test from Phase 2. A major finding from Phase 2 

testing is that pitch and yaw moments affect tooth contact in the planetary gear stage, as shown 

in Figure 14 [5]. These effects were seen when moments were varied from zero to approximately 

170 kNm. In this test, moments are increased to 300 kNm, a level approached during limited 

field testing, as shown in Figure 15. 

Tests also are conducted over a range of torques. It is possible that torque will change the effect 

of non-torque loads on bearing loads and tooth-contact patterns. This phenomenon is

investigated by applying bending moments at essentially zero torque (when the generator is offline) as well as at greater torque levels.
23 

 a. Ring gear load distribution at 120° b. Ring gear load distribution at 240° 

Figure 14. Effect of pitching moment (Myy) on ring gear load distributions 

Figure 15. Torque and bending moment distribution measured during the GRC field test

As non-torque loads are introduced, changes in critical measurements for the gearbox and turbine 

nacelle are expected. The following parameters should be observed carefully to assure that the 

system is behaving as expected. 

• Shaft Bending: Calculate the bending measured by the gages on the LSS in terms of 

magnitude and direction to verify that they are within limits. 

• Misalignment: Use the information from proximity sensors to verify that displacements 

of the high-speed shaft and generator are logical. 

• Load Share: Verify that loads in the actuator load cells, dead-link, and torque reaction 

arm are within limits. 

• Temperature: Look for any adverse or unusual temperature increases of the bearings. 
24 

5.4.1.1 Test Procedure

Apply torque and non-torque bending moments as follows. At each test condition, record 

1 minute of 100 Hz data. At all test conditions where torque is applied, record 10 seconds of 

5 kHz data to capture HSS measurements.

5.4.1.2 Torque and Non-Torque Bending Moments

1. Off-line, 100 rpm, normal direction 

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Mzz -100 kNm, Myy -200 to +200 in 100 kNm steps

C. Applied Mzz -200 kNm, Myy -200 to +300 in 100 kNm steps

D. Applied Mzz +100 kNm, Myy -300 to +300 in 100 kNm steps 

E. Applied Mzz +200 kNm, Myy +200 to +300 in 100 kNm steps 

F. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

G. Applied Myy -100 kNm, Mzz -200 to +200 in 100 kNm steps 

H. Applied Myy -200 kNm, Mzz -200 to +300 in 100 kNm steps 

I. Applied Myy +100 kNm, Mzz -300 to +300 in 100 kNm steps 

J. Applied Myy +200 kNm, Mzz +200 to +300 in 100 kNm steps 

2. Off-line, 100 rpm, reverse direction 

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

3. Off-line, 1,800 rpm 

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

4. Online, 25% rated torque 

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Mzz -100 kNm, Myy -200 to +200 in 100 kNm steps 

C. Applied Mzz -200 kNm, Myy -200 to +300 in 100 kNm steps 

D. Applied Mzz +100 kNm, Myy -300 to +300 in 100 kNm steps 

E. Applied Mzz +200 kNm, Myy +200 to +300 in 100 kNm steps 

F. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

G. Applied Myy -100 kNm, Mzz -200 to +200 in 100 kNm steps 

H. Applied Myy -200 kNm, Mzz -200 to +300 in 100 kNm steps 

I. Applied Myy +100 kNm, Mzz -300 to +300 in 100 kNm steps 

J. Applied Myy +200 kNm, Mzz +200 to +300 in 100 kNm steps. 
25 

5. Online, 50% rated torque

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Mzz -100 kNm, Myy -200 to +200 in 100 kNm steps 

C. Applied Mzz -200 kNm, Myy -200 to +300 in 100 kNm steps 

D. Applied Mzz +100 kNm, Myy -300 to +300 in 100 kNm steps 

E. Applied Mzz +200 kNm, Myy +200 to +300 in 100 kNm steps 

F. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

G. Applied Myy -100 kNm, Mzz -200 to +200 in 100 kNm steps 

H. Applied Myy -200 kNm, Mzz -200 to +300 in 100 kNm steps 

I. Applied Myy +100 kNm, Mzz -300 to +300 in 100 kNm steps 

J. Applied Myy +200 kNm, Mzz +200 to +300 in 100 kNm steps 

6. Online, 75% rated torque 

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Mzz -100 kNm, Myy -200 to +200 in 100 kNm steps 

C. Applied Mzz -200 kNm, Myy -200 to +300 in 100 kNm steps 

D. Applied Mzz +100 kNm, Myy -300 to +300 in 100 kNm steps 

E. Applied Mzz +200 kNm, Myy +200 to +300 in 100 kNm steps 

F. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

G. Applied Myy -100 kNm, Mzz -200 to +200 in 100 kNm steps 

H. Applied Myy -200 kNm, Mzz -200 to +300 in 100 kNm steps 

I. Applied Myy +100 kNm, Mzz -300 to +300 in 100 kNm steps 

J. Applied Myy +200 kNm, Mzz +200 to +300 in 100 kNm steps 

7. Online, 100% rated torque 

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Mzz -100 kNm, Myy -200 to +200 in 100 kNm steps 

C. Applied Mzz -200 kNm, Myy -200 to +300 in 100 kNm steps 

D. Applied Mzz +100 kNm, Myy -300 to +300 in 100 kNm steps 

E. Applied Mzz +200 kNm, Myy +200 to +300 in 100 kNm steps 

F. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

G. Applied Myy -100 kNm, Mzz -200 to +200 in 100 kNm steps 

H. Applied Myy -200 kNm, Mzz -200 to +300 in 100 kNm steps 

I. Applied Myy +100 kNm, Mzz -300 to +300 in 100 kNm steps 

J. Applied Myy +200 kNm, Mzz +200 to +300 in 100 kNm steps 
26 

8. Off-line, 100 rpm 

A. Applied Mzz zero, Myy -300 to +300 in 50 kNm steps 

B. Applied Myy zero, Mzz -300 to +300 in 50 kNm steps 

5.4.2 Dynamic Bending Moment Test

Some GRC participants have suggested that quickly changing bending moments might affect 

bearings and teeth mesh in ways not seen under steady-state conditions. This test explores that 

possibility by using the NTL device to apply sinusoidal pitch and yaw moments of varying 

magnitude and frequency. 

5.4.2.1 Test Procedure

Apply torque and non-torque bending moments as follows. At each test condition, record 

1 minute of 100 Hz data. During each frequency sweep every 30 seconds, record 10 seconds of 

5 kHz data to capture HSS measurements.

5.4.2.2 Torque and Non-Torque Bending Moments

1. Off-line, 1,800 rpm, normal direction 

A. Applied Mzz 0, vary Myy from 0 to -50 kNm at 0.30 Hz 

B. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

C. Stop cycling Myy and set Myy to equal 0 

D. Begin another frequency sweep by varying Myy from 0 to -200 kNm at 0.3 Hz 

E. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

F. Stop cycling Myy and set Myy to equal 0 

G. Applied Myy 0, vary Mzz from 0 kNm to 50 kNm at 0.30 Hz 

H. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

I. Stop cycling Mzz and set Mzz to equal 0 

J. Begin another frequency sweep by varying Mzz from 0 kNm to 200 kNm at 0.3 Hz 

K. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

L. Stop cycling Mzz and set Mzz to equal 0 

M. Begin another frequency sweep by varying Mzz from -200 kNm to 200 kNm at 

0.3 Hz

N. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

O. Stop cycling Mzz and set Mzz to equal 0 

2. Online, 25% rated torque 

A. Applied Mzz 0, vary Myy from 0 kNm to -50 kNm at 0.30 Hz 

B. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

C. Stop cycling Myy and set Myy to equal 0 
27 

D. Begin another frequency sweep by varying Myy from 0 kNm to -200 kNm at 

0.3 Hz

E. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

F. Stop cycling Myy and set Myy to equal 0 

G. Applied Myy 0, vary Mzz from 0 kNm to 50 kNm at 0.30 Hz 

H. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

I. Stop cycling Mzz and set Mzz to equal 0 

J. Begin another frequency sweep by varying Mzz from 0 kNm to 200 kNm at 0.3 Hz 

K. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

L. Stop cycling Mzz and set Mzz to equal 0 

M. Begin another frequency sweep by varying Mzz from -200 kNm to 200 kNm at 

0.3 Hz

N. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

O. Stop cycling Mzz and set Mzz to equal 0 

3. Online, 100% rated torque 

A. Applied Mzz 0, vary Myy from 0 kNm to -50 kNm at 0.30 Hz 

B. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

C. Stop cycling Myy moment and set Myy to equal 0 

D. Begin another frequency sweep by varying Myy from 0 kNm to -200 kNm at 

0.3 Hz

E. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

F. Stop cycling Myy moment and set Myy to equal 0 

G. Applied Myy 0, vary Mzz from 0 kNm to 50 kNm at 0.30 Hz 

H. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

I. Stop cycling Mzz and set Mzz to equal 0 

J. Begin another frequency sweep by varying Mzz from 0 kNm to 200 kNm at 0.3 Hz 

K. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

L. Stop cycling Mzz and set Mzz to equal 0 

M. Begin another frequency sweep by varying Mzz from -200 to 200 kNm at 0.3 Hz 

N. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

O. Stop cycling Mzz and set Mzz to equal 0 

5.4.3 Static Thrust Test

Phase 2 GRC tests explored the response of the drivetrain to thrust loads over a range of -20 kN 

to 100 kN. This range is reasonably representative of thrust loads during normal operating 
28 

conditions in the field. There is some potential for larger negative thrust loads in the field, 

however, which could have deleterious effects on the gearbox. Figure 16 shows that, under a 

sufficiently large negative thrust load, the mainshaft is expected to move upwind. If the gearbox 

motion does not follow the mainshaft exactly, the relative motion will change mesh patterns in 

the planetary stage. In Phase 3 tests, thrust is varied between -100 kN and +100 kN. 

Figure 16. Response of GRC mainshaft and gearbox to thrust load 

5.4.3.1 Test Procedure

Apply torque, bending moments, and thrust as follows. At each test condition, record 1 minute of 

100 Hz data. At all test conditions where torque is applied, record 10 seconds of 5 kHz data to 

capture HSS measurements.

5.4.3.2 Torque, Bending Moments, and Thrust

1. Off-line, 100 rpm, normal direction, with zero applied moment

A. Apply Fx from 0 to +100 in 20 kN steps 

B. Apply Fx from +100 to -100 in 20 kN steps 

C. Apply Fx from -100 to +100 in 20 kN steps 

D. Apply Fx from +100 to -100 in 20 kN steps 

E. Apply Fx from -100 to 0 in 20 kN steps 

2. Off-line, 100 rpm, normal direction, with applied moments to zero mainshaft bending 

A. Apply Fx from 0 to -100 in 20 kN steps 

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-100 -80 -60 -40 -20 -10 0 25 50 75 100

Displacement wrt Mainframe (mm)

Thrust (kN)

Gearbox, Phase 2

Mainshaft, Phase

2
29 

B. Apply Fx from -100 to +100 in 20 kN steps 

C. Apply Fx from +100 to 0 in 20 kN steps 

3. Online, 25% rated torque, with Myy zero

A. Apply Fx from 0 to -100 in 20 kN steps 

B. Apply Fx from -100 to +100 in 20 kN steps 

C. Apply Fx from +100 to 0 in 20 kN steps 

4. Online, 50% rated torque, with Myy zero

A. Apply Fx from 0 to -100 in 20 kN steps 

B. Apply Fx from -100 to +100 in 20 kN steps 

C. Apply Fx from +100 to 0 in 20 kN steps 

5. Online, 75% rated torque, with Myy zero

A. Apply Fx from 0 to -100 in 20 kN steps 

B. Apply Fx from -100 to +100 in 20 kN steps 

C. Apply Fx from +100 to 0 in 20 kN steps 

6. Online, 100% rated torque, with Myy zero

A. Apply Fx from 0 to -100 in 20 kN steps 

B. Apply Fx from -100 to +100 in 20 kN steps 

C. Apply Fx from +100 to 0 in 20 kN steps 

7. Online, 100% rated torque, with applied moments to zero mainshaft bending 

A. Apply Fx from 0 to -100 in 20 kN steps 

B. Apply Fx from -100 to +100 in 20 kN steps 

C. Apply Fx from +100 to 0 in 20 kN steps 

5.4.4 Trunnion Mount Axial Locking Test

Figure 16 shows that the gearbox moved in response to thrust loading, but not as much as the 

mainshaft moved. This is expected because the gearbox position relative to the mainshaft is 

constrained by friction in the planetary stage mesh when torque is applied and by shoulders on 

the carrier cylindrical roller bearings when no torque is present. For the gearbox to move, these 

internal forces must overcome the friction between the trunnion pins and the trunnion blocks, 

which resists gearbox motion. The extent of gearbox motion, however, can be limited by 

eventual contact between a steel sleeve on the trunnion pin and the inner surfaces of the trunnion 

blocks or can be constrained entirely by the trunnion pins if they become corroded and 

effectively “lock” the gearbox in place. Should either of these conditions occur, thrust loads will 

likely cause greater displacements of the mainshaft relative to the gearbox housing and greater 

displacements of the carrier relative to the ring gear.

This test explores the effects of this “locked” condition. Specifically, the loads in the ring gear 

teeth could increase or the load distribution might shift to an edge-loading condition. Similarly, 
30 

the loads in the planet bearings could increase or become more unevenly distributed among the 

planets or between the upwind and downwind bearings. 

In the first part of this test, the gearbox housing is pulled upwind with moderate force to load the 

carrier bearing and main bearing. Shims then are installed between the trunnion sleeves and the 

downwind trunnion blocks. Then the NTL applies positive (downwind) thrust to measure the 

effects when the gearbox is prevented from following the mainshaft as it moves downwind. 

Next the constraint is reversed. After removal of the shims, the housing is pushed downwind. 

Shims then are installed between the trunnion sleeves and the upwind trunnion blocks. Then 

negative (upwind) thrust is applied. Torque is limited to 50% of rated and test duration is limited 

to minimize damage in case the carrier bearings are adversely loaded. 

5.4.4.1 Test Procedure

Apply torque, bending moments, and thrust as follows. At each test condition, record 1 minute of 

100 Hz data. At all test conditions where torque is applied, record 10 seconds of 5 kHz data to 

capture HSS measurements.

5.4.4.2 Torque, Bending Moments, and Thrust

1. Off-line, 1,800 rpm, normal direction, with Myy and Mzz zero

A. Apply -100 kN Fx

B. Stop rotation and lock out drive 

C. Install shims between the trunnion pin sleeves and the downwind trunnion blocks 

D. Resume rotation at 1,800 rpm 

E. Apply Fx from -100 to +100 in 20 kN steps 

F. Apply Fx from +100 to -100 in 20 kN steps 

2. Online, 50% rated torque, with Myy and Mzz zero

A. Apply Fx from -100 to +100 in 20 kN steps 

B. Apply Fx from +100 to -100 in 20 kN steps 

C. Stop rotation and lock out drive 

D. Remove shims 

3. Off-line, 1,800 rpm, normal direction, with Myy and Mzz zero

A. Apply +100 kN Fx

B. Stop rotation and lock out drive 

C. Install shims between the trunnion pin sleeves and the upwind trunnion blocks 

D. Resume rotation at 1,800 rpm 

E. Apply Fx from +100 to -100 in 20 kN steps 

F. Apply Fx from -100 to +100 in 20 kN steps 
31 

4. Online, 50% rated torque, with Myy and Mzz zero

A. Apply Fx from +100 to -100 in 20 kN steps 

B. Apply Fx from -100 to +100 in 20 kN steps 

C. Stop rotation and lock out drive 

D. Remove shims 

5.4.5 Dynamic Thrust Test

Some GRC participants have suggested that quickly changing thrust forces could affect bearings 

and teeth mesh in ways not seen under steady-state conditions. This test explores that possibility 

by using the NTL device to apply sinusoidal thrust forces of varying magnitude and frequency. 

5.4.5.1 Test Procedure

Apply torque and non-torque bending moments as follows. At each test condition, record 

1 minute of 100 Hz data. During each frequency sweep every 30 seconds, record 10 seconds of 

5 kHz data to capture HSS measurements.

5.4.5.2 Torque and Non-Torque Bending Moments

1. Off-line, 1,800 rpm, normal direction 

A. Applied Myy and Mzz 0, vary Fx from 0 kN to +50 kN at 0.30 Hz 

B. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

C. Stop cycling Fx

D. Begin another frequency sweep by varying Fx from -50 kN to +50 kN at 0.3 Hz 

E. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

F. Stop cycling Fx

2. Online, 25% rated torque 

A. Applied Myy and Mzz 0, vary Fx from 0 kN to +50 kN at 0.30 Hz 

B. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

C. Stop cycling Fx

D. Begin another frequency sweep by varying Fx from -50 kN to +50 kN at 0.3 Hz 

E. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

F. Stop cycling Fx

3. On-line, 100% rated torque 

A. Applied Myy and Mzz 0, vary Fx from 0 kN to +50 kN at 0.30 Hz 

B. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

C. Stop cycling Fx

D. Begin another frequency sweep by varying Fx from -50 kN to +50 kN at 0.3 Hz 
32 

E. Increase frequency from 0.30 Hz to 2 Hz over a period of 5 minutes 

F. Stop cycling Fx

5.5 HSS Radial Misalignment Test

A significant number of failures of wind turbine gearboxes occur in the high-speed shaft 

bearings. Overload of these bearings is a possible cause of bearing-life reduction, and additional 

studies have examined the potential for gearbox-generator misalignment as a potential 

contributor [6] [7]. This test series investigates the potential for radial (also called parallel) 

misalignment of the generator relative to the gearbox to contribute to the high frequency of these 

failures by measuring the loads on the HSS TRBs in both aligned and radial misalignment 

conditions. 

Figure 17 shows the commonly used arrangement on the GRC drivetrain. The low-speed stage, 

with a planet carrier (red), is partially visible on the right side of the semitransparent gearbox. 

The high-speed gear mesh is visible at the top of the gearbox, with the large-diameter gear on the 

intermediate shaft closest to the front and the smaller-diameter pinion on the high-speed shaft 

immediately behind it. The high-speed shaft extends to the left out of the gearbox and ends with 

a flange that supports the brake disk. In this picture, the generator (blue) is located to the left.

The high-speed coupling is mounted between the brake disk and the generator. The high-speed 

coupling uses flexible, “dog-bone”–style links to allow axial, angular, and radial misalignment of 

the gearbox high-speed shaft relative to the generator shaft. 

Three factors might contribute increased bearing loads leading to these bearing failures. The 

three factors are: 

• An excessive misalignment of the gearbox high-speed and generator shafts, which would 

impart additional loads due to the coupling link stiffness 

• A mass imbalance of the brake disk, which would impart additional radial loads 

• The nature of the current brake disk, which is located on only one side of the brake disk 

rather than both sides imparting additional radial loads. 

In Phase 2, tests were conducted in which the generator was purposely misaligned with the 

gearbox. The instrumentation that was installed to measure reaction on the gearbox HSS did not 

perform as planned, however, so new sensors and new components of the data-acquisition 

system are being installed for Phase 3 testing.

Figure 17. High-speed coupling with flexible “dog bone” links
33 

The test matrix for this study includes the baseline and misaligned conditions listed below. These 

cases exercise the flexible links in the high-speed coupling to their intermittent load limit and to 

increase the loads on the HSS TRBs. The allowable angular misalignment conditions listed 

below are from published values for the CENTALINK CL-60 series coupling [8]. 

• Generator aligned at no-load conditions 

• Generator vertically offset by 5 mm (coupling misalignment = 1⁄2°) 

• Generator vertically offset by 11 mm (coupling misalignment = 1°) 

• Generator vertically offset by 33 mm (coupling misalignment = 3°) 

Note that each case is a radial misalignment condition. Additionally, 1° angular misalignment is 

the maximum allowed for continuous operation by the coupling manufacturer, and 3° angular 

misalignment is the maximum allowed for transient operation. These load cases should apply 

24% and 73%, respectively, of the combined radial load from the HSS-ISS gear mesh on the 

HSS TRBs.

Prior to the start of this test series, all applied loads to the gearbox are removed and the HSS 

brake is rotated to unload the GRC mainshaft. Then the generator is carefully aligned with the

HSS. A newly purchased laser alignment tool will be used for this purpose. After alignment, all 

proximity sensors on the generator and high-speed shaft are set to midrange, and their offsets are 

set to zero. All generator and HSS motion is relative to this position. After placing shims for 

each test case, the generator alignment is checked and recorded with the laser alignment tool.

5.5.1.1 Test Procedure

Apply torque and non-torque bending moments as follows. At each test condition, record 

1 minute of 100 Hz data and record 10 seconds of 5 kHz data to capture HSS measurements.

5.5.1.2 Torque and Non-Torque Bending Moments

1. Generator aligned

A. At 100 rpm, off-line, take one data set

B. At 1,800 rpm and no applied NTL, step torque from 25% to 100% rated torque in 

25% rated torque steps

C. At 100% rated torque, apply Myy of -200 and +200 kNm 

D. At 100% rated torque, apply Mzz of -200 and +200 kNm 

E. Take generator off-line and slow to 100 rpm for a second, slow-roll data set

2. Generator vertically offset by 5 mm (coupling misalignment = 1⁄2°) 

A. At 100 rpm, off-line, take one data set

B. At 1,800 rpm and no applied NTL, step torque from 25% to 100% rated torque in 

25% rated torque steps 

C. At 100% rated torque, apply Myy of -200 and +200 kNm 

D. At 100% rated torque, apply Mzz of -200 and +200 kNm 
34 

3. Generator vertically offset by 11 mm (coupling misalignment = 1°) 

A. At 100 rpm, offline, take one data set 

B. At 1,800 rpm and no applied NTL, step torque from 25% to 100% rated torque in 

25% rated torque steps 

C. At 100% rated torque, apply Myy of -200 and +200 kNm 

D. At 100% rated torque, apply Mzz of -200 and +200 kNm 

4. Generator vertically offset by 33 mm (coupling misalignment = 3°) 

A. At 100 rpm, offline, take one data set 

B. At 1,800 rpm and no applied NTL, step torque from 25% to 100% rated torque in 

25% rated torque steps 

C. At 100% rated torque, apply Myy of -200 and +200 kNm 

D. At 100% rated torque, apply Mzz of -200 and +200 kNm 

5.6 Field Representative Test: Dynamic Torque and 

Non-Torque Loads

Wind turbine drivetrain loads vary in response to turbulent winds passing through the rotor and 

as a function of the operating state of the wind turbine. It is possible that, within these variations, 

some events cause damage to the drivetrain beyond that predicted by standard models. It would 

be beneficial if these events could be identified in dynamometer testing, assuming that the 

dynamometer can be operated in a manner that truly duplicates conditions in the field. In this test 

series, the ability of the dynamometer to accurately duplicate field loads on the GRC drivetrain is

examined. Importantly, during testing some events can cause unexpected responses within the 

gearbox. 

It is expected that the dynamometer’s capability to duplicate dynamic oscillations in torque 

loading will be enhanced by a new variable frequency drive for the dynamometer motor. The 

new VFD is capable of accepting torque commands at frequencies as high as 400 Hz. The old 

VFD was limited to frequencies below about 2 Hz. During this test, this new capability should be 

sufficient to reproduce all the frequencies of interest and to counteract test-specific driveline 

resonances.

Common wind turbine design methods investigate many design load cases (DLCs). These 

represent the variety of wind and turbine state conditions likely to be encountered during the 

turbine’s lifetime. The International Electrotechnical Commission (IEC) wind turbine design 

standard (61400-1) lists a variety of DLCs that should be analyzed during the design of a wind 

turbine. Field loads tests are used to verify that the turbine operates as designed for some of the 

load cases [9]. Similarly, dynamometer tests can be conducted to verify the design. In GRC 

Phase 3 testing, we have selected a subset of the DLCs for investigation, as shown in Table 3. 

NREL plans to determine how well the dynamometer can reproduce the input speed, torque, and 

non-torque load inputs to the drivetrain. Example time series are provided in Appendix C. 
35 

Table 3. Field Conditions to be Simulated in the Dynamometer

Situation Load Case Condition

Dynamometer

Tests

Power production DLC 1.1 NTW, Vwind,average = 5 m/s 2

DLC 1.1 NTW, Vwind,average = 10 m/s 2

DLC 1.1 NTW, Vwind,average = 15 m/s 2

DLC 1.1 NTW, Vwind,average = 20 m/s 2

DLC 1.1 NTW, Vwind,average = 25 m/s 2

Start up DLC 3.1 NWP, Rotor acceleration = 2.5 

rpm/min

2

DLC 3.1 NWP, Rotor acceleration = 5 

rpm/min

2

DLC 3.1 NWP, Rotor acceleration = 10 

rpm/min

2

Normal shut down, 

tip brakes only

DLC 4.1 NWP 2

Emergency shutdown, 

tip brakes and HSS 

brake

DLC 5.1 NTW 2

DLC 5.1 NTW 2

Generator shift up Non DLC NWP, Rotor acceleration = 2.5 

rpm/min

2

Generator shift down Non DLC NWP, Rotor acceleration = 2.5 

rpm/min

2

For each test condition identify a field-test dataset. Extract a time-series file of speed, torque, 

pitch, and yaw. Use this time-series file as input to the VFD and NTL controller. Program 

transitions between VFD torque control and speed control as required. Program an “apply-brake” 

signal as required for emergency-stop simulations.

Apply torque and non-torque bending moments per the time-series input file. For each powerproduction test, record 1 minute of 100 Hz data and record 10 seconds of 5 kHz data to capture 

HSS measurements. For startup and generator shift tests, record 100 Hz data for the duration of 

the test and record 5 kHz data starting just prior to cut-in of the generator. For normal shutdown 

tests, record 5 kHz data starting just before issuing the shutdown command and ending after 

disconnect oscillations dissipate. For emergency shutdown tests, record 5 kHz data starting just 

before issuing the shutdown command and ending after stopping oscillations dissipate. 

5.7 Campbell Diagram Measurement Test

This test series is intended to build upon the results obtained to date by collecting vibration data 

while operating at various speeds and torque levels. Vibration data are often shown as a spectrum 

which presents the energy as a function of frequency, as seen in Figure 18. In these plots, peaks 

are of special interest and can be the result of a resonance or forced excitation.
36 

Figure 18. Sample time series and vibration spectrum

(Reproduced from http://en.wikipedia.org/wiki/File:Voice_waveform_and_spectrum.png) 

In rotating equipment such as the GRC drivetrain, the excitations change with rotational 

speed [10]. This relationship can be shown in waterfall plots or in Campbell diagrams, such as 

that in Figure 19. A Campbell diagram plots frequency peaks against rotational frequency. In a 

Campbell diagram, excitation frequencies such as gear meshing orders can be identified as 

diagonal lines intersecting the origin and resonances generally are horizontal lines at a fixed 

frequency. Intersections of excitation lines with resonance lines typically indicate speeds to be 

avoided during normal operation. In this test, however, they represent an opportunity to identify 

phenomena which otherwise might be lost in the spectrum plot acquired at a given speed. 
37 

Figure 19. Example of a Campbell diagram; BW and FW represent resonances that are slightly 

dependent upon spin speed and the origin-intersecting line represents frequencies at 1P. 

(Reproduced from http://en.wikipedia.org/wiki/File:Campbelldiagram.png) 

In this test, excitations are expected at 1P (1 times rotational frequency of LSS) and higher due to 

rotational frequencies of the planets, sun, intermediate- , and high-speed shafts. Higher frequency 

excitations are expected due to transmission error in tooth meshing and other phenomena. 

Inasmuch as torque should affect resonance frequencies, this test is preferably conducted at 

several torque levels. Because of equipment limitations, however, the test currently is planned 

for only low-torque (~5% rated) using an eddy-current brake on the high-speed shaft.

Tests conducted in Phase 2 showed significant energy peaks up to 2,800 Hz. Therefore 

accelerometers must have a frequency range of 6 kHz or higher. Six accelerometers are used, as 

indicated in Table 4. They are positioned as shown in Figure 20. 

A1

A2

A3

A7

A5

A6 A4

A8

Figure 20. Accelerometer locations for Phase 3 vibration testing
38 

Table 4. List of Accelerometers for Vibration Testing

Sensor 

Notation Description

A3 Planet gear radial 

A4 LSS radial

A5 ISS radial

A6 HSS radial 

A7 Generator DE radial

A8 Generator NDE radial

No non-torque loads are applied in this test series. The dynamometer is operated in speed-control 

mode with torque controlled by setting the eddy-current brake. 

1. Install and verify operation of accelerometers

2. Install and verify operation of eddy-current brake

3. Set dynamometer speed ramp to 360 rpm per minute on HSS

4. Set DAS to sample and record drivetrain operating conditions at 100 Hz

5. Set accelerometer DAS to sample and record at 40 kHz

6. Conduct the test as follows:

A. Start DAS

B. Start dynamometer motor and ramp to 2,000 rpm 

C. Shut down 

D. Repeat test once
39 

6 References

1. Link, H.; LaCava, W.; van Dam, J.; McNiff, B.; Sheng, S.; Wallen, R.; McDade, M.; Lambert, 

S.; Butterfield, S.; Oyague, F. Gearbox Reliability Collaborative Project Report: Findings from 

Phase 1 and Phase 2 Testing. NREL/TP-5000-51885. Golden, CO: National Renewable Energy 

Laboratory, 2011. 

2. Sheng, S.; Link, H.; LaCava, W.; van Dam, J.; McNiff, B.; Veers, P.; Keller, J. Wind Turbine 

Drivetrain Condition Monitoring During GRC Phase 1 and Phase 2 Testing. NREL/TP-5000-

52748. Golden, CO: National Renewable Energy Laboratory, 2011. 

3. “Dynamometer Testing (Fact Sheet), National Wind Technology Center (NWTC).” National 

Renewable Energy Laboratory, 2010. Accessed Nov. 20, 2012: http://www.nrel.gov/docs/

fy11osti/45649.pdf. 

4. McNiff, B.; van Dam, J.; Oyague, F.; Wallen, R.; Sheng, S.; Lambert, S.; Link, H. Gearbox 

Reliability Collaborative Phase 2 Test Plan. National Renewable Energy Laboratory, 2010. 

(internal only).

5. Keller, J.; Guo, Y.; McNiff, B.; LaCava, W.; Link, H. “Gearbox Reliability Collaborative 

Phase 1 and 2: Testing and Modeling Results.” International Conference on Noise and Vibration 

Engineering; September 17–19, 2012, Leuven, Belgium. 

6. Malkin, M.; Byme, A. “Torque-Induced Shaft Misalignment as a Potential Source of Gearbox 

High-Speed Bearing Failure.” American Wind Energy Conference & Exhibition; June 3–6, 2012, 

Atlanta, Georgia. 

7. Whittle, M.; Shin, W.; Trevelyan, J.; Wu, J. “A Parametric Study of the Effect of Generator 

Misalignment on Bearing Fatigue Life in Wind Turbines.” European Wind Energy Conference & 

Exhibition; March 14–17, 2011, Brussels, Belgium. 

8. “Product Catalog CL-07-08.” CENTA. Accessed Feb. 21, 2013: http://www.centa.info/data/

products/43/int/cl-07-08_01.pdf. 

9. International Electrotechnical Commission. 61400-4:2012(E) Wind Turbines—Part 4: Design 

Requirements for Wind Turbine Gearboxes. Geneva, Switzerland : International Organization for 

Standardization, 2012. 

10. Helsen, J. The Dynamics of High Power Density Gear Units with Focus on the Wind Turbine 

Application. Leuven, Belgium: Katholieke Universiteit Leuven, 2012. 
40 

Appendix A. Signal List

Location Nomenclature Expanded Nomenclature Sensor

Mainshaft LSS_TQ Torque Strain gage

Mainshaft MSBM_YY Bending Z-axis Strain gage

Mainshaft MSBM_ZZ Bending Y-axis Strain gage

Mainshaft LSS_Az Azimuth Encoder

Mainshaft LSS_Speed Speed Encoder

Mainshaft LSS_AZ_synch Azimuth synch Encoder

Mainshaft Main_Shaft_Axial Displacement X Proximity

Housing Trunion_Z_stbd Displacement Z starboard Proximity

Housing Trunion_Z_port Displacement Z port Proximity

Housing Trunion_My_bottom Displacement X bottom Proximity

Housing Trunion_Y_port Displacement Y port Proximity

Housing Trunion_X_stbd Displacement X starboard Proximity

Housing Trunion_X_port Displacement X port Proximity

Housing Case_A_XX Strain X, A Strain gage

Housing Case_A_YY Strain Y, A Strain gage

Housing Case_A_45 Strain 45°, A Strain gage

Housing ACC_TopX Acceleration, X top Accelerometer

Housing ACC_PortX Acceleration, X port Accelerometer

Housing ACC_PortY Acceleration, Y port Accelerometer

Housing ACC_PortZ Acceleration, Z port Accelerometer

Housing ACC_StbdX Acceleration, X starboard Accelerometer

Housing ACC_StbdY Acceleration, Y starboard Accelerometer

Housing ACC_StbdZ Acceleration, Z starboard Accelerometer

Ring Ring_0 Strain, ring gear teeth, 0°, 1st set Strain gage

Ring Ring_0a Strain, ring gear teeth, 0°, 2nd set Strain gage

Ring Ring_120 Strain, ring gear teeth, 120°, 1st set Strain gage

Ring Ring_120a Strain, ring gear teeth, 120°, 2nd set Strain gage

Ring Ring_240 Strain, ring gear teeth, 240°, 1st set Strain gage

Ring Ring_240a Strain, ring gear teeth, 240° 2nd set Strain gage

Ring EXT_KHB_23 Strain, external, 23° Strain gage

Ring EXT_KHB_46 Strain, external, 46° Strain gage

Ring EXT_KHB_69 Strain, external, 69° Strain gage

Ring EXT_KHB_92 Strain, external, 92° Strain gage

Ring EXT_KHB_115 Strain, external, 115° Strain gage

Ring EXT_KHB_149 Strain, external, 149° Strain gage

Ring EXT_KHB_184 Strain, external,184° Strain gage

Ring EXT_KHB_207 Strain, external, 207° Strain gage

Ring Ring_Local_45 Strain, circumferential, 45° Strain gage
41 

Location Nomenclature Expanded Nomenclature Sensor

Ring Ring_Local_135 Strain, circumferential, 135° Strain gage

Ring Ring_Local_225 Strain, circumferential, 225° Strain gage

Ring Ring_Local_315 Strain, circumferential, 315° Strain gage

Carrier Carrier_317 Displacement X 317° Proximity

Carrier Carrier_047 Displacement X 047° Proximity

Carrier Radial_310 Displacement Radial 310° Proximity

Carrier Radial_040 Displacement Radial 40° Proximity

Carrier Carrier_137 Displacement, X 137° Proximity

Carrier Carrier_227 Displacement, X 227° Proximity

Planet PlanetB_RIM_0 Displacement, X, B, 0° Proximity

Planet PlanetB_RIM_90 Displacement, X, B, 90° Proximity

Planet PlanetB_RIM_180 Displacement, X, B, 180° Proximity

Planet PlanetC_RIM_0 Displacement, X, C, 0° Proximity

Planet PlanetC_RIM_90 Displacement, X, C, 90° Proximity

Planet PlanetC_RIM_180 Displacement, X, C, 180° Proximity

Planet PlanetA_Bearing_slip Slip, Planet A, cage Proximity

Planet AU_Kb00_25 Strain, Planet A, upwind, 0°, 25% Strain gage

Planet AU_Kb00_75 Strain, Planet A, upwind, 0°, 75% Strain gage

Planet AD_Kb00_25 Strain, Planet A, downwind, 0°, 25% Strain gage

Planet AD_Kb00_75 Strain, Planet A, downwind, 0°, 75% Strain gage

Planet AU_Kb86_25 Strain, Planet A, upwind, 86°, 25% Strain gage

Planet AU_Kb86_75 Strain, Planet A, upwind, 86°, 75% Strain gage

Planet AD_Kb86_25 Strain, Planet A, downwind, 86°, 25% Strain gage

Planet AD_Kb86_75 Strain, Planet A, downwind, 86°, 75% Strain gage

Planet AU_Kb274_25 Strain, Planet A, upwind, 274°, 25% Strain gage

Planet AU_Kb274_75 Strain, Planet A, upwind, 274°, 75% Strain gage

Planet AD_Kb274_25 Strain, Planet A, downwind, 274°, 25% Strain gage

Planet AD_Kb274_75 Strain, Planet A, downwind, 274°, 75% Strain gage

Planet BU_Kb00_25 Strain, Planet B, upwind, 0°, 25% Strain gage

Planet BU_Kb00_75 Strain, Planet B, upwind, 0°, 75% Strain gage

Planet BD_Kb00_25 Strain, Planet B, downwind, 0°, 25% Strain gage

Planet BD_Kb00_75 Strain, Planet B, downwind, 0°, 75% Strain gage

Planet BU_Kb256_25 Strain, Planet B, upwind, 256°, 25% Strain gage

Planet BU_Kb256_75 Strain, Planet B, upwind, 256°, 75% Strain gage

Planet BD_Kb256_25 Strain, Planet B, downwind, 256°, 25% Strain gage

Planet BD_Kb256_75 Strain, Planet B, downwind, 256°, 75% Strain gage

Planet BU_Kb308_25 Strain, Planet B, upwind, 308°, 25% Strain gage

Planet BU_Kb308_75 Strain, Planet B, upwind, 308°, 75% Strain gage

Planet BD_Kb308_25 Strain, Planet B, downwind, 308°, 25% Strain gage

Planet BD_Kb308_75 Strain, Planet B, downwind, 308°, 75% Strain gage
42 

Location Nomenclature Expanded Nomenclature Sensor

Planet CU_Kb00_25 Strain, Planet C, upwind, 0°, 25% Strain gage

Planet CU_Kb00_75 Strain, Planet C, upwind, 0°, 75% Strain gage

Planet CD_Kb00_25 Strain, Planet C, downwind, 0°, 25% Strain gage

Planet CD_Kb00_75 Strain, Planet C, downwind, 0°, 75% Strain gage

Planet CU_Kb290_25 Strain, Planet C, upwind, 290°, 25% Strain gage

Planet CU_Kb290_75 Strain, Planet C, upwind, 290°, 75% Strain gage

Planet CD_Kb290_25 Strain, Planet C, downwind, 290°, 25% Strain gage

Planet CD_Kb290_75 Strain, Planet C, downwind, 290°, 75% Strain gage

Planet CU_Kb334_25 Strain, Planet C, upwind, 334°, 25% Strain gage

Planet CU_Kb334_75 Strain, Planet C, upwind, 334°, 75% Strain gage

Planet CD_Kb334_25 Strain, Planet C, downwind, 334°, 25% Strain gage

Planet CD_Kb334_75 Strain, Planet C, downwind, 334°, 75% Strain gage

Planet AU_temp0 Temperature, Planet A, upwind, 0° Thermocouple

Planet AD_temp86 Temperature, Planet A, downwind, 86° Thermocouple

Planet AU_temp86 Temperature, Planet A, upwind, 86° Thermocouple

Planet AD_temp274 Temperature, Planet A, downwind, 

274° Thermocouple

Planet BU_temp0 Temperature, Planet B, upwind, 0° Thermocouple

Planet BD_temp0 Temperature, Planet B, downwind, 0° Thermocouple

Planet BU_temp256 Temperature, Planet B, upwind, 256° Thermocouple

Planet BD_temp256 Temperature, Planet B, downwind, 

256° Thermocouple

Planet CU_temp0 Temperature, Planet C, upwind, 0° Thermocouple

Planet CD_temp0 Temperature, Planet C, downwind, 0° Thermocouple

Planet CU_temp290 Temperature, Planet C, upwind, 290° Thermocouple

Planet CD_temp290 Temperature, Planet C, downwind, 

290° Thermocouple

Planet PlanetA_OR_temp Temperature, Planet A, outer race Thermocouple

Sun SUN_radial_ZZ Displacement, radial, Z Proximity

Sun SUN_radial_YY Displacement, radial, Y Proximity

ISS ISS_Axial Displacement, X Proximity

ISS ISS_aft_roller_temp Temperature IR sensor

HSS HSS_UY_BM Bending, upwind, YY Strain gage

HSS HSS_UZ_BM Bending, upwind, ZZ Strain gage

HSS HSS_DY_BM Bending, downwind, YY Strain gage

HSS HSS_DZ_BM Bending, downwind, ZZ Strain gage

HSS HSS_exY_BM Bending, External, YY Strain gage

HSS HSS_exZ_BM Bending, External, ZZ Strain gage

HSS HSS_TQ Torque Strain gage

HSS TRB_Up_00_A Strain, upwind TRB, 0°, thin end Strain gage

HSS TRB_Up_00_B Strain, upwind TRB, 0°, thick end Strain gage
43 

Location Nomenclature Expanded Nomenclature Sensor

HSS TRB_Up_90_A Strain, upwind TRB, 90°, thin end Strain gage

HSS TRB_Up_90_B Strain, upwind TRB, 90°, thick end Strain gage

HSS TRB_Up_180_A Strain, upwind TRB, 180°, thin end Strain gage

HSS TRB_Up_180_B Strain, upwind TRB, 180°, thick end Strain gage

HSS TRB_Up_270_A Strain, upwind TRB, 270°, thin end Strain gage

HSS TRB_Up_270_B Strain, upwind TRB, 270°, thick end Strain gage

HSS TRB_Dwn_00_D Strain, downwind TRB, 0°, thin end Strain gage

HSS TRB_Dwn_00_C Strain, downwind TRB, 0°, thick end Strain gage

HSS TRB_Dwn_90_D Strain, downwind TRB, 90°, thin end Strain gage

HSS TRB_Dwn_90_C Strain, downwind TRB, 90°, thick end Strain gage

HSS TRB_Dwn_180_D Strain, downwind TRB, 180°, thin end Strain gage

HSS TRB_Dwn_180_C Strain, downwind TRB, 180°, thick end Strain gage

HSS TRB_Dwn_270_D Strain, downwind TRB, 270°, thin end Strain gage

HSS TRB_Dwn_270_C Strain, downwind TRB, 270°, thick end Strain gage

HSS TEMP_TRB_Up Temperature, upwind TRB RTD 

HSS TEMP_TRB_Dwn Temperature, downwind TRB RTD 

HSS HSP_K1234 Strain, HSS pinion teeth, 1st set Strain gage

HSS HSP_Kabcd Strain, HSS pinion teeth, 2nd set Strain gage

Brake BRK_azimuth Azimuth Encoder

Brake BRK_speed Speed Encoder

Brake BRK_X_225 Displacement, X, 225° Proximity

Brake BRK_X_315 Displacement, X, 315° Proximity

Brake BRK_X_45 Displacement, X, 45° Proximity

Brake BRK_YY Displacement, Y Proximity

Brake BRK_ZZ Displacement, Z Proximity

Generator GEN_X_45 Displacement, X, 45° Proximity

Generator GEN_X_225 Displacement, X, 225° Proximity

Generator GEN_X_315 Displacement, X, 315° Proximity

Generator GEN_YY Displacement, Y Proximity

Generator GEN_ZZ Displacement, Z Proximity

Generator Gen_Temp Temperature, generator downwind 

bearing RTD 

Generator HSS_Speed Speed Encoder

Generator HSS_Az Azimuth Encoder

Mainframe Frame_Z_stbd Displacement, Z, starboard, in-line with 

generator flange Proximity

Mainframe Frame_Z_port Displacement, Z, port, in-line with 

generator flange Proximity

Controller G_Contactor Closed, large generator contactor Relay

Controller gg_Contactor Closed, small generator contactor Relay

Controller Bypass_Contactor Closed, soft-start bypass contactor Relay
44 

Location Nomenclature Expanded Nomenclature Sensor

Controller KW_electrical Power, real

Potential 

Transformer / 

Current 

Transformer

Controller KVAR_electrical Power, reactive

Potential 

Transformer / 

Current 

Transformer

Lube system Lube_Manifold_Temp Temperature, distribution manifold RTD 

Lube system Lube_Manifold_Pressure Pressure, distribution manifold Pressure

Lube system Sump_Temp Temperature, sump RTD 

Lube system Lube_Flow_Dist Flow rate, to distribution manifold Flow

Lube system Lube_Flow_Br_1 Flow rate, branch 1 Flow

Lube system Lube_Flow_Br_2 Flow rate, branch 2 Flow

Lube system Lube_Flow_Br_3 Flow rate, branch 3 Flow

Lube system Lube_Particles Particle counts Particle 

counter

Dyno TQ_Applied_Force Force, torque arm 1 Load cell

Dyno TQ_Applied_Force2 Force, torque arm 2 Load cell

Dyno Dyno_Torque Torque, torque spool Strain gage

NTL NTL_Port_displ Displacement, port cylinder Proximity

NTL NTL_Port_force Force, port cylinder Load cell

NTL NTL_Star_displ Displacement, starboard cylinder Proximity

NTL NTL_Star_force Force, starboard cylinder Load cell

NTL NTL_thrust_displ Displacement, thrust Proximity

NTL NTL_thrust_star_force Force, thrust starboard Load cell

NTL NTL_thrust_port_force Force, thrust, port Load cell

NTL NTL_stab_link_eX Strain, stabilizer link, X Strain gage

NTL NTL_stab_link_eY Strain, stabilizer link, Y Strain gage

NTL Static_Loading_System_Force Pressure, hydraulic Pressure

NTL NTL_DW_BM_Y Mainshaft bending, downwind, Y Strain gage

NTL NTL_DW_BM_Z Mainshaft bending, downwind, Z Strain gage

NTL NTL_UW_BM_Y Mainshaft bending, upwind, Y Strain gage

NTL NTL_UW_BM_Z Mainshaft bending, upwind, Z Strain gage

NTL NTL_DW_BM_X_Y Flex coupling displacement, 

downwind, Y Proximity

NTL NTL_DW_BM_X_Z Flex coupling displacement, 

downwind, Z Proximity

NTL NTL_UW_BM_X_Y Flex coupling displacement, upwind, Y Proximity

NTL NTL_UW_BM_X_Z Flex coupling displacement, upwind, Z Proximity
45 

Appendix B. Instrumentation Details

Figure B-1. Mainshaft torque 
46 

Figure B-2. Mainshaft speed and azimuth
47 

Figure B-3. Mainshaft Bending Z-axis
48 

Figure B-4. Mainshaft Bending Y-axis
49 

Figure B-5. Mainshaft axial motion
50 

Figure B-6. Gearbox motion, XX at trunnion 
51 

Figure B-7. Gearbox motion, YY at trunnion 
52 

Figure B-8. Gearbox motion, ZZ, at trunnion
53 

Figure B-9. Gearbox motion, YY bottom rotation
54 

Figure B-10. Gearbox case triaxial strain, AA location
55 

Figure B-11. Gearbox accelerometers
56 

Figure B-12. Ring gear 0° face width load distribution
57 

Figure B-13. Ring gear 120° face width load distribution
58 

Figure B-14. Ring gear 240° face width load distribution
59 

Figure B-15. Ring gear external face width load distribution 
60 

Figure B-16. Ring gear local distortion strain
61 

Figure B-17. Carrier-rim radial displacement
62 

Figure B-18. Carrier-rim axial displacement
63 

Figure B-19. Planet gear B rim deflection
64 

Figure B-20. Planet gear C rim deflection
65 

Figure B-21. Planet bearing radial load sensor arrangement
66 

Figure B-22. Planet bearing A radial load 
67 

Figure B-23. Planet bearing B radial load 
68 

Figure B-24. Planet bearing C radial load 
69 

Figure B-25. Planet bearing inner ring temperature
70 

Figure B-26. Planet bearing outer ring temperature 
71 

Figure B-27. Planet bearing slip
72 

Figure B-28. Sun pinion radial motion 
73 

Figure B-29. Mainshaft aft-end slip ring assembly
74 

Figure B-30. Intermediate-shaft axial motion 
75 

Figure B-31. Intermediate-shaft aft bearing temperature 
76 

Figure B-32. High-speed shaft bending and torque at location A
77 

Figure B-33. High-speed shaft bending and torque at location B
78 

Figure B-34. High-speed shaft bending and torque at location C
79 

Figure B-35. High-speed shaft pinion face width load distribution
80 

Figure B-36. High-speed shaft downwind tapered roller bearing strain
81 

Figure B-37. High-speed shaft upwind tapered roller bearing strain
82 

Figure B-38. High speed shaft tapered roller bearing outer ring temperature
83 

Figure B-39. Brake disk speed and azimuth
84 

Figure B-40. Brake disk axial motion 
85 

Figure B-41. Brake disk radial motion 
86 

Figure B-42. Axial motion of generator upwind face
87 

Figure B-43. Radial motion of generator input shaft
88 

Figure B-44. Deflection of nacelle frame aft of gearbox 
89 

Figure B-45. Generator shaft speed and azimuth
90 

Figure B-46. Generator shaft encoder
91 

Figure B-47. Gearbox oil sump temperature
92 

Appendix C. Sample Design Load Cases

Figure C-1. Normal operation, Vwind = 5 m/s

(file: NO-05 2009-10-07-08-01-43.xlsx) 

Figure C-2. Normal operation, Vwind = 10 m/s

(file: NO-10 2009-09-26-00-09-16.xlsx) 
93 

Figure C-3. Normal operation, Vwind = 15 m/s

(file: NO-15 2009-09-22-13-41-21.xlsx) 

Figure C-4. Normal operation, Vwind = 20 m/s

(file: NO-20 2009-09-21-11-30-49.xlsx) 
94 

Figure C-5. Normal operation, Vwind = 25 m/s

(file: NO-25 2009-10-01-08-41-19.xlsx) 

Figure C-6. Startup to low-speed generator

(file: Startup2 2009-09-21-19-50-59.xlsx) 
95 

Figure C-7. Startup to high-speed generator

(file: Startup1 2009-09-21-07-40-45.xlsx) 

Figure C-8. Shutdown from high-speed generator 

(file: Shutdown1 2009-09-21-19-40-59.xlsx) 
96 

Figure C-9. Upshift

(file: Upshift 2009-09-26-00-19-17.xlsx) 

Figure C-10. Downshift

(file: Downshift 2009-09-22-21-31-30.xlsx)