The public’s concern over the cost and reliability of small wind 

turbines continues to be a barrier to the deployment of wind 

energy in the marketplace. A marketing advantage exists for 

manufacturers who can provide test results that prove the 

reliability of their turbine designs. This capability exists at the 

National Renewable Energy Laboratory’s (NREL’s) National Wind 

Technology Center (NWTC) near Boulder, Colorado . 

NREL’s 225-kW dynamometer tests a variety of components and 

subsystems, including generators, gearboxes, mechanical or 

electro-dynamic brakes, power electronics, control systems, and 

software. 

Manufacturer’s test objectives might include performance, system 

integration (generator, power electronics, and grid), software 

development, or accelerated life testing. NREL is actively seeking 

industry partners to utilize this facility and advance the 

technology for small, distributed wind turbines. 

Test Capabilities 

The 225-kW dynamometer can be used in a wide range of 

technology testing and development activities focusing on drive 

train components, power electronics, and controls used in small 

wind turbines. These include: 

Generator/Alternator Testing 

 • Efficiency 

 • Cogging torque 

 • Equivalent circuit parameters 

 • Thermal characteristics 

 • Vibration 

 • Defect testing (infant mortality) 

 • Insulation life testing 

Gearbox Testing 

 • Efficiency 

 • Thermal characteristics 

 • Lubrication flow 

 • Tooth contact patterns 

 • Vibration 

 • Endurance or fatigue 

Power Electronics Testing 

 • Efficiency 

 • Thermal characteristics 

 • Control and stability 

 • Power quality 

 • Defect testing (infant mortality) 

 • Control systems and software testing 

 • System integration (generator/power electronics/grid) 

 • Software development and testing 

Operating Envelope 

The NWTC 225-kW dynamometer tests small wind turbine 

components from the smallest turbines to turbines with nearly 

200-kW ratings. Some headroom between the component rating 

and the dynamometer rating is typically needed to adequately 

cover over-speed and over-torque conditions that turbine 

components encounter in real applications. Maximum available 

shaft speed is 4,140 revolutions per minute (rpm) and the 

maximum available shaft torque is 37,000 foot-pounds (ft-lb) or 

51,000 Newton meters (Nm). The operating envelope depicted in 

the figure also shows the range of expected values of power vs. 

rpm for typical small wind turbines.

225-kW Dynamometer for Testing 

Small Wind Turbine Components

National Wind Technolo gy Center

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Operating Envelope for the NWTC 225-kW Dynamometer
The dynamometer drive motor is a 

225-kW (300-horsepower [hp]) rated, 

variable-speed, induction motor, with a 

matched variable-speed drive and 

harmonic filter. The motor reaches rated 

power at 1,800 rpm and has a top speed 

of 3,600 rpm.

Three speed-reducing gearboxes are 

available for the dynamometer. The first, 

coupled to the drive motor, is a 13-speed 

transmission with gear ratios ranging 

from 12.5:1 up to an overdrive gear at 

0.87:1. This transmission will be coupled 

directly to the unit under test or to one of 

two fixed speed gear boxes to reduce 

shaft speed and increase torque. These 

gear boxes have ratios of 9:1 and 26:1. 

Gearbox specifications are shown in 

Table 1. 

Electric Loads 

Three types of electric loads are available for units under test on 

the dynamometer. The first is single-phase service at 120/240 volts 

alternating current (VAC), 60 Hertz (Hz), with up to 50 kilovoltampere (kVA) capacity. This load simulates the typical 100- or 

200-ampere (A) utility service available to most homes, small 

farms, and small businesses. The second load is three-phase 

service at 480 VAC, 60 Hz, with up to 250 kVA capacity. This 

simulates utility service for farms and businesses that have larger 

power requirements, up to 250 kW. Other service voltages as well 

as 50 Hz operation are possible but will require enhancements 

to the facility. For testing off-grid systems designed to charge 

batteries, the dynamometer includes battery bank simulation via 

a voltage-controlled direct current (DC) bus with capacity up to 

20 kVA and voltages up to 216 volts DC. 

Dyno Components 

The drive system for the dynamometer consists of a drive motor 

coupled to one or more speed-reducing gear boxes selected to 

deliver the requisite torque and shaft speed for a given test 

program. These components are installed on concrete and steel 

pedestals with a drive shaft extending over a rigid steel table as 

shown in the photo above. This table is on jack screws such that its 

height can be changed to allow alignment of various test article 

input shafts with the dynamometer drive shaft. At its lowest 

available height, the table is about 5 ft or 1.5 meters (m) below the 

dynamometer drive shaft, providing room for installation of test 

articles with diameters up to about 8-10 ft (2.4-3.0 m).

225-kW Dynamometer. PIX #14739.

National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401 • 303-275-3000 • www.nrel.gov

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

Office of Energy Efficiency and Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

NREL/FS-500-48536 • June 2010

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% post consumer waste.

Photo credits for page 1 masthead: PIX15758, PIX15005, PIX12415, and PIX14691.

Table 1. NWTC 225-kW Dynamometer Gearbox Specifications

Device Brand Gear Ratios Torque Limit

Transmission Fuller 13 ratios 12.5:1-

 0.87:1

1,250 ft-lb 

1,700 Nm

Fixed-Ratio Gearbox Byrne 9:1 8,750 ft-lb 

(11,900 Nm)

Fixed-Ratio Gearbox Flender 26:1 37,600 ft-lb 

(51,000 Nm)

Partnerships with NREL 

The NWTC is seeking opportunities to collaborate with industry 

partners in the use of the 225-kW dynamometer for small wind 

turbine technology development. For more information, contact: 

Jim Johnson

National Wind Technology Center 

National Renewable Energy Laboratory 

1617 Cole Blvd., MS 3811 

Golden, CO 80401 

Jim.johnson@nrel.gov 

303-384-6989