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 (GRC) 

Description and Loading 

F. Oyague

Technical Report

NREL/TP-5000-47773

November 2011
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

1617 Cole Boulevard

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

Gearbox Reliability 

Collaborative (GRC) 

Description and Loading 

F. Oyague

Prepared under Task No. WE10.1131

Technical Report

NREL/TP-5000-47773

November 2011
NOTICE

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iii

Table of Contents

Executive Summary ........................................................................................................... 1

Introduction ........................................................................................................................ 1

Turbine Technical Description .......................................................................................... 2

General Description of the Wind Turbine ............................................................................... 2

General Design Operation......................................................................................................... 2

Blades .......................................................................................................................................... 2

Drive Train ................................................................................................................................. 2

Drivetrain Description ....................................................................................................... 4

Detailed Gearbox Description ........................................................................................... 5

External Configuration.............................................................................................................. 5

Internal Configuration............................................................................................................... 5

Bearing Configuration............................................................................................................... 7

GRC Analysis Round Robin .............................................................................................. 8

Load Generation and Load Cases ..................................................................................... 9

Simulated Load Cases ...................................................................................................... 10

FAST Model Input Parameter and Validation......................................................................10

Tower.........................................................................................................................................10

Blades ........................................................................................................................................10

Drivetrain..................................................................................................................................10

Generator..................................................................................................................................10

Nacelle .......................................................................................................................................11

Dynamometer Load Cases ............................................................................................... 11

Field Load Cases .............................................................................................................. 11

Load Spectrum ................................................................................................................. 12

Fatigue Load Spectrum ...........................................................................................................12

Ultimate Strength Load Spectrum .........................................................................................14

Final Remarks .................................................................................................................. 16

References ........................................................................................................................ 17

Appendix A-1: Basic Gear Tables ................................................................................... 18

Appendix A-2: Extreme Events Tables ........................................................................... 19
iv

List of Figures 

Figure 1: GRC drivetrain configuration. ............................................................................. 4

Figure 2: Torque arms and rubber mounts detail ................................................................ 5

Figure 3: GRC gearbox internal components view ............................................................. 6

Figure 4: GRC gearbox internal nomenclature and abbreviations ...................................... 6

Figure 5: Bearing nomenclature and location ..................................................................... 8

Figure 6: Torque distribution per wind speed ................................................................... 13

Figure 7: Torque at level hours/year ................................................................................. 13

Figure 8: Torque at level cycles/year ................................................................................ 14

List of Tables 

Table 1: Bearing number and location ................................................................................ 7

Table 2: Load spectrum ...................................................................................................... 9

Table 3: GRC generator characteristics ............................................................................ 11

Table 4: Turbine class II characteristics ........................................................................... 12

Table 5: Fatigue load cases ............................................................................................... 12

Table 6: Accounted ultimate stregth load cases ................................................................ 14

Table 7: Extreme events table ........................................................................................... 15

Table 8: Planetary gear data .............................................................................................. 18

Table 9: IMS helical gear data .......................................................................................... 18

Table 10: HSS helical gear data ........................................................................................ 18

Table 11: Extreme events table for DLC 1.2 .................................................................... 19

Table 12: Extreme events table for DLC 1.3 .................................................................... 19

Table 13: Extreme events table for DLC 1.4 .................................................................... 20

Table 14: Extreme events table for DLC 1.5 .................................................................... 20

Table 15: Extreme events table for DLC 6.1 .................................................................... 21

Table 16: Extreme events table for DLC 6.3 .................................................................... 21

Table 17: Extreme events table for DLC 7.1 .................................................................... 22
v 

List of Abbreviations and Symbols

CLC Calibration load case 

CRB Cylindrical roller bearing 

DGBB Deep groove ball bearing 

DLC Design load case

ECD Extreme coherent gust 

ETM Extreme turbulent model 

EWM Extreme wind speed model 

EWS Extreme wind sheer 

fcCRB Full Complement Cylindrical roller bearing

GPa Gigapascal

HS High Speed 

HS-SH High Speed Shaft 

IMS Intermediate Speed 

IMS-SH Intermediate Speed Shaft 

INP-SH Rotor shaft or main shaft 

LS Low Speed

LS-SH Low Speed Shaft 

NTM Normal turbulence model 

NWP Normal wind profile model 

PL Planet 

PLC Planet carrier

SRB Spherical roller bearing 

ST Stage

TRB Tapered roller bearing

Vave Annual average wind speed at hub height 

Vhub wind speed at hub height averaged over ten minutes 

Vin cut–in wind speed 

Vout cut–out wind speed 

Vr Rated wind speed

Vref Reference wind speed averaged over ten minutes 
1 

Executive Summary

This document describes simulated turbine load cases in accordance with the IEC 61400-

1 Ed.3 standard, which is representative of the typical wind turbine design process. The 

information presented herein is intended to provide a broad understanding of the Gearbox 

Reliability Collaborative 750kW drivetrain and turbine configuration. In addition, fatigue 

and ultimate strength drivetrain loads resulting from simulations are presented. This

information provides the basis for the analytical work of the Gearbox Reliability 

Collaborative effort. 

Introduction

The National Wind Technology Center (NWTC), at the National Renewable Energy 

Laboratory (NREL), has embarked on the task of revealing the causes and loading 

conditions that result in the premature failure of wind turbine gearboxes. 

The NWTC approaches the problem by bringing together the different parties involved in 

the gearbox design process, with the common goal of the improvement of the lifetime of 

gearboxes. It achieves this with the Gearbox Reliability Collaborative (GRC). 

The GRC seeks to achieve its goal by exploring three avenues of research. These include 

drivetrain numerical analysis and modeling, full-scale dynamometer testing, and field 

testing. These different branches will be iteratively correlated to arrive at a

comprehensive understating of the loading conditions and internal behavior that 

potentially could be the culprit of the premature failures. 

Numerical analysis plays a key role in the design process of the gearboxes. To better 

understand the implementation and capabilities of the analytical tools currently available 

in the industry, the GRC has initiated an Analysis Round Robin. The round robin explores 

various analytical approaches to gain insight into the validity and level of fidelity in the 

design practice. The analysis is based on modeling techniques that range from simple 

torsional models to models that account for gear tooth contact and gear tooth load 

distribution, as well as bearing compliances and roller load distribution. 

The gearbox description and loading conditions presented here serve as the basis for the 

previously mentioned analytical evaluation. In addition, this report gives the reader a 

broad understanding of the drivetrain and gearbox operation. Detailed information of the 

gearing and other components is not in the public domain at this point. However, it will 

be released to the public as the project proceeds. 
2 

Turbine Technical Description 

General Description of the Wind Turbine

Type 3 Blade upwind

Power rating 750 kW 

Rotor diameter 48.2 m

Rated generator speed 22/15 rpm 

Power regulation Stall

Aerodynamic Brake Pitchable tips 

Nacelle Lay out Three point suspension drivetrain with a low speed 

shaft, external main bearing, separate gearbox, high 

speed shaft with spring applied, hydraulic pressure 

release disc brake. 

Tower Welded tubular Steel

Nominal hub height 55m 

General Design Operation

Cut-in wind speed vin 3 m/s (nominal) 

Rated wind speed vr 16 m/s

Cut-out wind speed vout 25 m/s

Design wind class IEC Class II

Design life 20 years 

Blades 

Blade length 23.5 m 

Material Glass fiber-polyester/wood-epoxy 

Type of rotor brake Pivotal blade tip

Twist 18.66 o

Tip angle -3.5 o 

Largest cord 2.25 m

Tip length 3.5 m

Blade area (projected) 38.6 m2

Drive Train

Main shaft

Type Description Forged shaft and flange 

Material 34 CrNiMo6V 

Main bearing 

Type description Spherical roller bearing 

Main bearing housing Flange bearing 
3 

Gearbox

Type description LS planetary, IMS, and HS parallel shaft

Gearbox housing material Cast iron

Ratio 1:81.491 

Mechanical power 800 kW 

Oil filling 100 l 

Generator

Type description 2 speed generator, water cooled 

Rated power 750 kW 200 kW 

Apparent power 825 kVA 238 kVA 

Synchronous rotation speed 1800 rpm 1200 rpm 

Rotation speed at rated power 1809 rpm 1208 rpm 

Slip at rated power 0.5 % 0.67 % 

Voltage 3x600 V 

Frequency 60 Hz 
4 

Drivetrain Description 

The GRC test turbine has a modular configuration. In this configuration, all individual 

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

components include the main bearing, main shaft, gearbox, brake, high speed shaft, and 

generator. This configuration is very common within the industry because it allows the 

outsourcing of independent drivetrain components. The figure below shows the GRC 

drivetrain configuration [9]. 

Figure 1: GRC drivetrain configuration. 

Generator

Hub

Main 

Bearing

Main 

Shaft

Brake High Speed 

Shaft

Gearbox

Bed Plate
5 

Detailed Gearbox Description 

External Configuration

The configuration of the GRC gearbox is typical of the MW class turbines used today. 

The gearbox is mounted in a three-point configuration, which transfers loads to the main 

frame through the main bearing and two torque arms. The torque arms contain two rubber 

mounts that help to reduce noise. The figure below depicts a front view of the gearbox 

showing the torque arm configuration and a side view of the rubber mount in the torque 

arm of the gearbox. 

Figure 2: Torque arms and rubber mounts detail

Internal Configuration

The gearbox has an overall ratio of 1:81.491. It is composed of one low speed (LS) 

planetary stage and two parallel shaft stages. The LS planetary stage accommodates 

three planet gears, an annulus gear, and a sun gear. As depicted in Figure 4, the annulus 

gear of this stage is part of the gearbox housing. The sun gear is set in a floating 

configuration to better equalize the load distribution among the planets. To accommodate 

the floating sun arrangement, the low speed shaft is hollow and has an internal spline that 

transfers the torsional loads to the parallel shaft stages. The LS planetary gears have a 

helix angle of approximately 7.5 degrees, and the IMS and HS gear sets have a helix 

angle of 14 degrees. The figures below show the internal components as well as the 

nomenclature used to describe them. Additional gearing information can be found in

Appendix A-1. 

Torque Arms

Rubber Mount
6 

Figure 3: GRC gearbox internal components view

Figure 4: GRC gearbox internal nomenclature and abbreviations 

Annulus

Planet

Sun

Gear

Gear Pinion

Pinion

PLC

Low Speed Stage

LS-ST 

High Speed Stage

HS-ST 

Intermediate Speed Stage

IMS-ST 

Low speed Shaft

LS-SH 

Intermediate Speed 

Shaft

IMS-SH

High Speed 

Shaft 

HS-SH
7 

Bearing Configuration

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 fullcomplement cylindrical roller bearings (fcCRB); each planet gear assembly is supported 

by two identical cylindrical roller bearings (CRB). Each parallel shaft stage in the 

gearbox is supported by a CRB on the upwind side of the assembly, and by two back-toback mounted, duplex tapered roller bearings on the downwind side. Table 1 lists the 

location and bearing number of all bearings in the gearbox. The letter following the 

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

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

Table 1: Bearing number and location 

Location Type Number Provider 

INP-A SRB 24076 CC W33 SKF/INA 

PLC-A fcCRB NCF 1892 V SKF

PLC-B fcCRB SL 18 1880 E FAG

PL-A CRB NJ2232E.M1.C3 FAG

PL-B CRB NJ2232E.M1.C3 FAG

LS-SH-A fcCRB SL181856E FAG

LS-SH-B TRB 32948 SKF

LS-SH-C TRB 32948 SKF

IMS-SH-A CRB NU 2220 ECM SKF

IMS-SH-B TRB 32032 X/DF SKF

IMS-SH-C TRB 32032 X/DF SKF

HS-SH-A CRB NU 2220 ECM SKF

HS-SH-B TRB 32222 A FAG

HS-SH-C TRB 32222 A FAG

CONDUIT DGBB 6016 Z SKF
8 

The figure below shows the nomenclature used to describe the locations of the bearings 

Figure 5: Bearing nomenclature and location

GRC Analysis Round Robin

The GRC Analysis Round Robin seeks to evaluate the different analytical tools and 

approaches utilized in the development and design of horizontal axis wind turbine 

drivetrains. The round robin utilizes the GRC drivetrain to provide its participants with a 

comprehensive characterization of the gearbox and other components. From there, the

participants can develop models with different levels of complexity and fidelity. 

A series of loading conditions, such as the calibration load case (CLC), are specific to this 

effort, though they are not a guideline according to the IEC standard. As the round robin 

progresses, the loading conditions will increase in complexity ranging from fully static to 

dynamic and transient events. This progressive approach assures that the discrepancies in 

the analysis results are due to the different tools employed and not the result of an 

analyst’s assumptions. 

PLC-A PLC-B

LS-SH-A LS-SH-B LS-SH-C

PL-A PL-B

IMS-SH-A IMS-SH-B IMS-SH-C

HS-SH-A HS-SH-B HS-SH-C Annulus

Planet

Sun

Gear

Gear Pinion

Pinion
9 

Load Generation and Load Cases 

The loads presented in this document can be classified into calibration load cases (CLC)

and design load cases (DLC). The calibration load cases are simplified load cases; some 

of them are static. These load cases are intended for the initial phase of the code-to-code 

comparison as described above. The design load cases follow the guidance of the IEC 

61400-1 ed.3 standard. These loading conditions reflect the loads experienced by turbines 

under normal as well as extreme wind conditions. 

The intent of these load cases is to provide a global understanding of the loads generated 

by the turbine under most operational conditions. The load cases can be translated into 

drivetrain loading conditions, which are implemented in the design process. Table 2 

shows a summary of all the simulated load cases. 

Table 2: Load spectrum 

Design Situation Load Case Wind Model Wind Speed Range Decryption 

Static CLC 1.1 N/A N/A 25% rated power

 CLC 1.2 N/A N/A 100% rated power 

Dynamic CLC 2.1 N/A N/A 25% rated power 

 CLC 2.2 N/A N/A 39.5% rated torque

 CLC 2.3 N/A N/A 100% rated power 

Power Production DLC 1.1 NTM Vin < Vhub < Vout N/A

 DLC 1.2 NTM Vin < Vhub < Vout N/A

 DLC 1.3 ETM Vin < Vhub < Vout N/A

 DLC 1.4 ECD Vhub = Vr-2m/s, Vr, 

Vr+2m/s N/A

 DLC 1.5 EWS Vin < Vhub < Vout N/A

Emergency shut 

down DLC 5.1 NTM Vhub = Vr-2m/s,Vout, Vr+2m/s N/A

Parked (Idling) DLC 6.1a Turbulent EWM Vhub = 0.95*Vref N/A

 DLC 6.3a Turbulent EWM Vhub = 0.95*V1 N/A

 DLC 6.4 NTM Vhub < 0.7*Vref N/A

Parked (Idling) and 

Fault DLC 7.1a Turbulent EWM Vhub = 0.95*V1 N/A
10 

Simulated Load Cases 

FAST Model Input Parameter and Validation 

Simulated load cases are generated with FAST (Fatigue, Aerodynamic Structures and 

Turbulence) and AeroDyn, which is a medium complexity code for aerodynamic analysis 

of horizontal axis turbines. FAST allows the simulation of turbines with two or three 

blades, as well as those with a teetering or rigid rotor [1]. FAST models a wind turbine 

by combining rigid and flexible bodies. The flexible bodies include the blade tower and 

drivetrain shaft. The code uses Kane’s method to solve the equations of motion that 

describe the behaviour of all independent components. The model employs generalized 

coordinates that result in the elimination of constraint equations, thus reducing the 

computational time [2]. The analysis allows for 14 degrees of freedom including 

multiple tower bending modes. [1] 

The aero-elastic model uses parameters specific to the GRC turbine. The parameters that 

were not available were taken from similar turbines and tuned with experimental data. 

The parameters that integrate the model can be classified into the following subdivisions: 

tower, blades, drivetrain and nacelle. 

Tower

Stiffness and mass distribution were calculated from the geometrical characteristics of the 

tower. These parameters were used to calculate the modal behaviour of the structure. To 

assure the correlation between the calculated mode shapes and the physical structure, 

frequencies were experimentally collected and the modal characteristics were then tuned

[7]. 

Blades 

Geometrical characteristics such as chord and twist were measured from an existing 

blade. Parameters such as mass and stiffness distribution were obtained by means of 

modifying the parameters from similar blades and adjusting them to match the overall 

mass and center of mass of the GRC blade. The modal behaviour was adjusted to match 

natural frequencies experimentally collected. Airfoil characteristics were obtained by 

modifying standard airfoils and matching the power curve and Cp curve of the turbine 

[7]. 

Drivetrain 

The bulk stiffness characteristics of the drivetrain were calculated from natural 

frequencies recorded in the field. The damping characteristics were obtained from the 

torque characteristics exhibited in several braking events. 

Generator 

The generator is normally considered part of the drivetrain; however, it is a separate item 

in the FAST simulation. The generator is a dual speed induction generator that changes 

speed by changing the number of poles in operation. The FAST model included a linear 

model of the induction generator following the characteristics provided by the generator 

manufacturer.
11 

Table 3: GRC generator characteristics

GRC 60 Hz Generator 

Rated power 750 kW 200 kW

Apparent power 825.00 kVA 238 kVA

Rated current 820.00 A 230 A 

Max power at class F 825.00 kW 220 kW

Max current at class F 902.00 A 253 A

No load current 230.00 A 71 A

Reactive power consumption at rated 

power (acc. To IEC 60034-1) 405.00 kvar 130 kvar

Reactive power consumption at no load 

(acc. To IEC 60034-1) 240.00 kvar 74 kvar

number of poles 4 - 6 -

synchronous rotation speed 1800.00 RPM 1200 RPM

Rotation speed at rated power 1809.00 RPM 1208 RPM

voltage 0.50 % 0.67 %

Frequency 6X600 V 6X600 V

Coupling 60.00 - 60 -

Enclosure IP54 - IP54 -

Insulation class F/B - F/B - 

Nacelle 

The most relevant parameters for the nacelle, from a modeling standpoint, are mass and 

inertia. The inertial characteristics of the nacelle were estimated by correlating the 

overall manufacturer published weight of the nacelle and estimated bulk geometry. 

Dynamometer Load Cases 

In addition to the simulated load cases presented in this document, a series of 

dynamometer load cases have been applied to the test subject at the National Wind 

Technology Center dynamometer facility. The facility is capable of producing up to 2.5 

megawatts of power, with a velocity range of 0-146 rpm [3]. This allows for flexibility in 

the load cases that can be generated. The empirical loading conditions will be correlated 

to the simulated loading conditions, as well as the field test loading conditions, thus tying 

the loads together in a global load matrix to better understand their effects. The GRC 

dynamometer loading conditions, as well as information regarding the channels 

characteristics, can be found in the GRC test plan [8]. 

Field Load Cases 

The field load cases have been generated with a nearly identical test subject in the 

dynamometer. The only difference between the model and the test subject is that a small 

number of channels have been eliminated due to size constraints that exist in the field. A 

series of transient events and regular operations have been recorded in the field. These

events occur in operational conditions that may not be created in the dynamometer [8]. 
12 

Load Spectrum 

The fatigue and ultimate strength load spectrum was generated from the simulated load 

results. The simulations followed the guidelines provided by the IEC 61400-1 Ed 3 

standard for fatigue and ultimate strength. The load spectrum follows the characteristics 

for a class II turbine specification. Table 3 shows the characteristics for class II turbines. 

Table 4: Turbine class II characteristics

GRC Turbine Characteristics 

Wind Turbine Class II

Vref (m/s) 42.5

Vave (m/s) 8.5

Turbulence Class B

Turbulence intensity 

@15m/s 0.14

Fatigue Load Spectrum 

The design load cases specified by the IEC 61400-1 Ed.3 standard as fatigue load cases 

were used to generate the torque at level load spectrum. Because control algorithms are 

unknown for the GRC turbine, the load cases that depend on the control system are 

excluded from the load spectrum. These cases include DLC 2.4, 3.1 and 4.1. Therefore, 

the effects of the load cases 3.1 and 4.1 in the load spectrum are used throughout the

experimental data. The table below shows the fatigue load cases as specified by the IEC 

standard. 

Table 5: Fatigue load cases 

Design Situation Load Case Wind Model Wind Speed 

Range

# Wind

Speeds 

Power Production DLC 1.2 NTM Vin < Vhub < Vout 23

Power Production plus 

occurrence of fault DLC 2.4 NTM Vin < Vhub < Vout 23 

Start up DLC 3.1 NTM Vin < Vhub < Vout 23

Normal shut down DLC 4.1 NWP Vin < Vhub < Vout 23

Parked (Idling) DLC 6.4 NTM Vhub < 0.7*Vref 1

The load spectrum was generated using the previously described FAST model. Each 

individual simulation’s duration was 10 minutes, 30 seconds. The first 30 seconds of 

generated data were truncated to eliminate the influence of the initial conditions. The 

wind files stipulated by the IEC standard were generated using 25 random numbers. This 

resulted in 25 simulations for each individual wind speed. In addition to the FAST model 

characteristics previously mentioned, rotor imbalance was introduced to the model. This 
13 

was achieved by making one blade 0.5% heavier, another blade 0.5% lighter, and leaving 

one as reference [6]. 

Probability density functions were generated from the obtained files and then scaled to a 

Rayleigh distribution as specified by the standard. The figure below shows the scaled 

probability function of each wind speed. 

Figure 6: Torque distribution per wind speed 

The scaled probability functions were added to obtain the torque at level curve. This was 

done by subdividing the torque values into 100 bins and linearly interpolating the time 

that each wind speed would be at that torque level. Finally, the interpolated values were 

added to obtain the cumulative torque at level. The figure below shows the torque at level 

for one year of operation. 

Figure 7: Torque at level hours/year
14 

For gear and bearing calculations it is also relevant to evaluate the number of cycles at 

which the drivetrain operates. Figure 8 shows the number of cycles for each generator, 

which can be correlated to the operational speed of the drivetrain. The aggregate or total 

number of cycles can also be seen in the figure. 

Figure 8: Torque at level cycles/year

Ultimate Strength Load Spectrum 

The ultimate strength load spectrum follows the load cases specified by the IEC standard. 

As mentioned in the fatigue load spectrum, the lack of knowledge of the control 

algorithm prevented the simulation of load cases that are highly dependent on the control 

system. The design load cases considered for the ultimate strength events are presented 

in the table below.

Table 6: Accounted ultimate stregth load cases

Design Situation Load Case Wind Model Wind Speed Range

Power Production DLC 1.1 NTM Vin < Vhub < Vout

 DLC 1.3 ETM Vin < Vhub < Vout

 DLC 1.4 ECD Vhub = Vr-2m/s, Vr, 

Vr+2m/s

 DLC 1.5 EWS Vin < Vhub < Vout

Parked (Idling) DLC 6.1a Turbulent EWM Vhub = 0.95*Vref

 DLC 6.3a Turbulent EWM Vhub = 0.95*V1

Parked (Idling) and Fault DLC '7.1a Turbulent EWM Vhub = 0.95*V1

-50 0 50 100 150 200 250 300 350 400 0

1

2

3

4

5

6

7

8

9

10 x 104

Torque [kN.m]

Cycles/year

Agreagate

4 Pole Gen

6 Pole Gen
15 

The loading conditions are described in the FAST coordinate system [3]. Parameters such 

as torque and thrust follow the FAST sign convention and are aligned with the main shaft 

axis. Parameters such as shear are described at the location of the main bearing. The 

bending moments are calculated at the center of the hub, 1.293 m upwind from the main 

bearing. The table below shows the values for the maximum loading condition as well as 

the file and the design load case associated with the load value. The extreme event for 

each individual design load case can be found in Appendix A-2. 

Table 7: Extreme events table

DLC File Name Load Units 

RotThrust

DLC6.1 DLC6.1a_0044_40.4V0_000ny_S15.out 2.57E+02 kN Max 

DLC1.3 DLC1.3_0011_03.0V0_S11.out -2.16E+01 kN Min 

LSShftTq

DLC1.3 DLC1.3_0327_20.0V0_S02.out 4.01E+02 kN·m Max 

DLC1.3 DLC1.3_0025_07.0V0_S25.out -1.92E+01 kN·m Min 

LSSGagFzs

DLC1.3 DLC1.3_0172_13.0V0_S22.out -1.15E+02 kN Max 

DLC1.3 DLC1.3_0160_13.0V0_S10.out -1.42E+02 kN Min 

LSSGagFys

DLC1.3 DLC1.3_0376_22.0V0_S01.out 1.08E+01 kN Max 

DLC1.3 DLC1.3_0328_20.0V0_S03.out -1.26E+01 kN Min 

LSSTipMys

DLC6.1 DLC6.1a_0009_40.4V0_008ny_S03.out 467.5 kN·m Max 

DLC1.3 DLC1.3_0172_13.0V0_S22.out -399.8 kN·m Min 

LSSTipMzs 

DLC1.3 DLC1.3_0189_14.0V0_S14.out 397.7 kN·m Max 

DLC1.3 DLC1.3_0106_11.0V0_S06.out -443 kN·m Min 
16 

Final Remarks

This document describes the GRC drivetrain in a general manner by providing an 

overview of the drivetrain configuration, gearbox configuration, as well as fatigue and 

ultimate strength load spectrum. This information provides the necessary information to 

assist universities and other interested parties in the development of basic initial 

drivetrain models. The GRC drivetrain has been heavily studied and there is a large 

amount of information that was not included in this document. At this point, further 

information is available only to the participants of the gearbox reliability collaborative. 

Additional information will be publically released later. This includes drivetrain solid 

models, material properties, bearing and gear micro geometry, experimental datasets for 

model validation, time series from the simulated load spectrum, and manufacturing 

drawings. To gain access to this information, the GRC requires partnership through a 

substantial contribution. 
17 

References 

[1] J.F. Manwell J., G. Mc Gowan, A.L. Rogers. Wind Energy Explained: Theory, 

Design and Application. 

[2] Jonkman, Jason. NWTC Design Codes Fast.

http://wind.nrel.gov/designcodes/simulators/fast/ 

[3] Jonkman, Jason. NWTC Design Codes Fast Users Guide.

http://wind.nrel.gov/designcodes/simulators/fast/FAST.pdf 

[4] http://www.nrel.gov/wind/facilities_dynamometer.html

[5] International Electrotechnical Commission Wind Turbines Part 1: Design 

requirements IEC 61400-1 Ed. 3, 3 December 2003 

[6] Jonkman, Jason.. Dynamics Modeling and Loads Analysis of an Offshore Floating 

Wind Turbine. http://www.nrel.gov/docs/fy08osti/41958.pdf 

NREL/TP-500-41958 November 2007 

[7] G.S. Bir, F. Oyague, Estimation of Blade and Tower Properties for the Gearbox 

Reliability Collaborative Wind Turbine http://www.nrel.gov/docs/fy08osti/42250.pdf

NREL/TP-500-42250, November 2007 

[8] McNiff B., Van Dam J, Gorman D. Gearbox Reliability Collaborative Phase 1 Test 

Plan , NREL/TP-500-47842, National Renewable Energy Laboratory, Golden, 

Colorado (Forthcoming). 

[9] F. Oyague, Gearbox Modeling and Load Simulation of a Baseline 750-kW Wind 

Turbine Using State-of-the-Art Simulation Codes, NREL/TP-500-41160 February 

2009
18 

Appendix A-1: Basic Gear Tables

Table 8: Planetary gear data

Parameter Annulus 

Gear

Planet 

Gear

Sun 

Gear

Drawing Number 251240 251242 251246

Number of Teeth 99 39 21

Normal Module (nm) 10.00 10.00 10.00

Normal Pressure Angle (deg) 20.00 20.00 20.00

Table 9: IMS helical gear data 

Parameter IMS-ST 

Gear

IMS-ST 

Pinion

Drawing Number 251341 251243

Number of Teeth 82 23

Normal Module (nm) 8.25 8.25

Normal Pressure Angle (deg) 20.00 20.00

Table 10: HSS helical gear data

Parameter HS-ST 

Gear

HS-ST 

Pinion

Drawing Number 251241 251244

Number of Teeth 88 22

Normal Module (nm) 5.00 5.00

Normal Pressure Angle (deg) 20.00 20.00
19 

Appendix A-2: Extreme Events Tables

Table 11: Extreme events table for DLC 1.2

DLC File Name Load Units

DLC1.2

RotThrust

DLC1.1_0451_25.0V0_S01.out 1.30E+02 kN Max 

DLC1.1_0024_03.0V0_S24.out -8.44E+00 kN Min 

LSShftTq

DLC1.1_0355_21.0V0_S05.out 4.00E+02 kN·m Max 

DLC1.1_0006_07.0V0_S06.out -1.57E+01 kN·m Min 

LSSGagFzs

DLC1.1_0194_14.0V0_S19.out -1.16E+02 kN Max 

DLC1.1_0204_15.0V0_S04.out -1.40E+02 kN Min 

LSSGagFys

DLC1.1_0376_22.0V0_S01.out 9.30E+00 kN Max 

DLC1.1_0390_22.0V0_S15.out -9.91E+00 kN Min 

LSSTipMys

DLC1.1_0294_18.0V0_S19.out 3.90E+02 kN·m Max 

DLC1.1_0272_17.0V0_S22.out -3.70E+02 kN·m Min 

LSSTipMzs

DLC1.1_0209_15.0V0_S09.out 3.52E+02 kN·m Max 

DLC1.1_0294_18.0V0_S19.out -4.28E+02 kN·m Min 

Table 12: Extreme events table for DLC 1.3

DLC File Name Load Units

DLC1.3

RotThrust

DLC1.3_0451_25.0V0_S01.out 1.43E+02 kN Max 

DLC1.3_0011_03.0V0_S11.out -2.16E+01 kN Min 

LSShftTq

DLC1.3_0327_20.0V0_S02.out 4.01E+02 kN·m Max 

DLC1.3_0025_07.0V0_S25.out -1.92E+01 kN·m Min 

LSSGagFzs

DLC1.3_0172_13.0V0_S22.out -1.15E+02 kN Max 

DLC1.3_0160_13.0V0_S10.out -1.42E+02 kN Min 

LSSGagFys

DLC1.3_0376_22.0V0_S01.out 1.08E+01 kN Max 

DLC1.3_0328_20.0V0_S03.out -1.26E+01 kN Min 

LSSTipMys

DLC1.3_0195_14.0V0_S20.out 459.6 kN Max 

DLC1.3_0172_13.0V0_S22.out -399.8 kN Min 

LSSTipMzs

DLC1.3_0189_14.0V0_S14.out 397.7 kN Max 

DLC1.3_0106_11.0V0_S06.out -443 kN Min 
20 

Table 13: Extreme events table for DLC 1.4

DLC File Name Load Units

DLC1.4

RotThrust

DLC1.4_0001_ECD+R-20.out 63.56 kN Max 

DLC1.4_0001_ECD+R-20.out 23.31 kN Min 

LSShftTq

DLC1.4_0003_ECD+R+20.out 346.3 kN·m Max 

DLC1.4_0002_ECD+R.out 132.9 kN·m Min 

LSSGagFzs

DLC1.4_0002_ECD+R.out -121.3 kN Max 

DLC1.4_0002_ECD+R.out -134.3 kN Min 

LSSGagFys

DLC1.4_0002_ECD+R.out 3.342 kN Max 

DLC1.4_0002_ECD+R.out -4.295 kN Min 

LSSTipMys

DLC1.4_0002_ECD+R.out 234.6 kN Max 

DLC1.4_0002_ECD+R.out -240.4 kN Min 

LSSTipMzs

DLC1.4_0002_ECD+R.out 195.3 kN Max 

DLC1.4_0002_ECD+R.out -276 kN Min 

Table 14: Extreme events table for DLC 1.5

DLC File Name Load Units

DLC1.5

RotThrust

DLC1.5_0074_EWSH-25.0.out 7.84E+01 kN Max 

DLC1.5_0001_EWSH+03.0.out -3.18E-01 kN Min 

LSShftTq

DLC1.5_0042_EWSH-17.0.out 3.48E+02 kN·m Max 

DLC1.5_0002_EWSH-03.0.out 1.29E+00 kN·m Min 

LSSGagFzs

DLC1.5_0034_EWSH-15.0.out -1.21E+02 kN Max 

DLC1.5_0034_EWSH-15.0.out -1.35E+02 kN Min 

LSSGagFys

DLC1.5_0038_EWSH-16.0.out 3.34E+00 kN Max 

DLC1.5_0038_EWSH-16.0.out -4.30E+00 kN Min 

LSSTipMys

DLC1.5_0038_EWSH-16.0.out 234.6 kN Max 

DLC1.5_0033_EWSH+15.0.out -244.2 kN Min 

LSSTipMzs

DLC1.5_0033_EWSH+15.0.out 205.2 kN Max 

DLC1.5_0033_EWSH+15.0.out -288.1 kN Min 
21 

Table 15: Extreme events table for DLC 6.1

DLC File Name Load Units

DLC6.1

RotThrust

DLC6.1a_0044_40.4V0_000ny_S15.out 2.57E+02 kN Max 

DLC6.1a_0001_40.4V0_352ny_S01.out 3.85E+01 kN Min 

LSShftTq

DLC6.1a_0007_40.4V0_352ny_S03.out 2.70E+02 kN·m Max 

DLC6.1a_0025_40.4V0_352ny_S09.out -2.70E+00 kN·m Min 

LSSGagFzs

DLC6.1a_0030_40.4V0_008ny_S10.out -1.23E+02 kN Max 

DLC6.1a_0001_40.4V0_352ny_S01.out -1.37E+02 kN Min 

LSSGagFys

DLC6.1a_0055_40.4V0_352ny_S19.out 6.82E+00 kN Max 

DLC6.1a_0051_40.4V0_008ny_S17.out -8.41E+00 kN Min 

LSSTipMys

DLC6.1a_0009_40.4V0_008ny_S03.out 467.5 kN Max 

DLC6.1a_0007_40.4V0_352ny_S03.out -291.9 kN Min 

LSSTipMzs

DLC6.1a_0017_40.4V0_000ny_S06.out 382.9 kN Max 

DLC6.1a_0053_40.4V0_000ny_S18.out -378.3 kN Min 

Table 16: Extreme events table for DLC 6.3

DLC File Name Load Units

DLC6.3

RotThrust

DLC6.3a_0044_32.3V0_000ny_S15.out 1.57E+02 kN Max 

DLC6.3a_0003_32.3V0_020ny_S01.out 2.09E+01 kN Min 

LSShftTq

DLC6.3a_0009_32.3V0_020ny_S03.out 2.05E+02 kN·m Max 

DLC6.3a_0051_32.3V0_020ny_S17.out 4.28E+00 kN·m Min 

LSSGagFzs

DLC6.3a_0030_32.3V0_020ny_S10.out -1.25E+02 kN Max 

DLC6.3a_0037_32.3V0_340ny_S13.out -1.34E+02 kN Min 

LSSGagFys

DLC6.3a_0019_32.3V0_340ny_S07.out 4.64E+00 kN Max 

DLC6.3a_0051_32.3V0_020ny_S17.out -7.73E+00 kN Min 

LSSTipMys

DLC6.3a_0011_32.3V0_000ny_S04.out 287.2 kN Max 

DLC6.3a_0041_32.3V0_000ny_S14.out -197.1 kN Min 

LSSTipMzs

DLC6.3a_0017_32.3V0_000ny_S06.out 229.9 kN Max 

DLC6.3a_0053_32.3V0_000ny_S18.out -244 kN Min 
22 

Table 17: Extreme events table for DLC 7.1

DLC File Name Load Units

DLC7.1

RotThrust

DLC7.1a_0044_32.3V0_000ny_S15.out 1.56E+02 kN Max 

DLC7.1a_0001_32.3V0_352ny_S01.out 2.28E+01 kN Min 

LSShftTq

DLC7.1a_0007_32.3V0_352ny_S03.out 2.20E+02 kN·m Max 

DLC7.1a_0025_32.3V0_352ny_S09.out 5.06E+00 kN·m Min 

LSSGagFzs

DLC7.1a_0030_32.3V0_008ny_S10.out -1.26E+02 kN Max 

DLC7.1a_0001_32.3V0_352ny_S01.out -1.34E+02 kN Min 

LSSGagFys

DLC7.1a_0019_32.3V0_352ny_S07.out 3.22E+00 kN Max 

DLC7.1a_0051_32.3V0_008ny_S17.out -7.84E+00 kN Min 

LSSTipMys

DLC7.1a_0012_32.3V0_008ny_S04.out 290 kN Max 

DLC7.1a_0042_32.3V0_008ny_S14.out -206.2 kN Min 

LSSTipMzs

DLC7.1a_0017_32.3V0_000ny_S06.out 230.2 kN Max 

DLC7.1a_0053_32.3V0_000ny_S18.out -244.6 kN Min