Introduction 7-MVA CGI Configuration CGI Facility Status

Wind Turbine Generators

Mark McDade, Vahan Gevorgian, Robb Wallen • National Renewable Energy Laboratory • Golden, CO

William Erdman • DNV • San Ramon, CA

NWTC’s New Test Grid Concept

WINDPOWER 2013, Chicago, IL May 5 – 8, 2013 • NREL/PO-5000-58229

Main Specifications 

References

In order to understand the behavior of wind turbines experiencing grid disturbances,

it is necessary to perform a series of tests and accurate transient simulation studies.

The latest edition of the IEC 61400-21 standard describes methods for such tests

that include low voltage ride-through (LVRT), active power set-point control, ramp

rate limitations, and reactive power capability tests. The IEC methods are being

widely adopted on both national and international levels by wind turbine

manufacturers, certification authorities, and utilities. On-site testing of wind turbines

might be expensive and time consuming since it requires both test equipment

transportation and personnel presence in sometimes remote locations for significant

periods of time because such tests need to be conducted at certain wind speeds

and grid conditions. Changes in turbine control software or design modifications

may require repeating of all tests. Significant cost and test-time reduction can be

achieved if these tests are conducted in controlled laboratory environments that

replicate grid disturbances and simulation of wind turbine interactions with power

systems. Such testing capability does not exist in the United States today.

An initiative by NREL to design and construct a 7-MVA grid simulator to operate

with the 2.5-MW and 5.8-MW dynamometer facilities will fulfill this role and bring

many benefits to the U.S. wind industry with the ultimate goal of reducing wind

energy integration costs.

The proposed grid simulator is a combination of hardware and real-time

control software for simulating grid disturbances on wind turbine terminals

and estimating impacts of turbine response on the grid. Also, the

performance of wind turbine drivetrain components (both mechanical and

electric) can be tested and quantified under such conditions.

Output loads:

• Type 1 wind turbines

• Type 2 wind turbines

• Type 3 wind turbines

• Type 4 wind turbines

• PV inverters

• Energy storage inverters

Power rating: 

7 MVA continuous

39 MVA up to 2 sec

Other specifications:

Output Frequency: 50/60 Hz (±3 Hz)

Programmable impedance

Symmetrical voltage variations (±10%)

IEC–LVRT tests, NERC–LVRT/HVRT tests

Voltage magnitude modulations: 0-10 Hz 

1. J. Niiranen, S. Seman, J-P Matsinen, R. Virtaanen, A. Vilhunen. “Low 

voltage ride through testing of wind turbine drives”. 

2. C. Wessels, T. Wehrend, F.W. Fuchs. “Transformer based voltage sag 

generator to test renewable energy systems during grid faults in 

laboratory.”

3. M. Harica-Gracia, M. Paz Comech, J. Sallan, D. Lopez-Andia, O. 

Alonso. “ Voltage dip generator for wind energy systems up to 5 MW”. 

Applied Energy 86 (2009), pp 565-574.

4. IEC 61400-21 Standard. “Measurement and assessment of power 

quality characteristics of grid connected wind turbines”. Edition 2.0, 

2008.

FERC−LVRT Requirement NERC−PRC-024 LVRT/HVRT Requirement

Fault Type Voltage drop (fraction of 

nominal L-to-L voltage)

Fault Duration (ms)

Three-phase, balanced 0.9 500

Three-phase, balanced 0.5 500

Three-phase, balanced 0.2 200

Two Line-to-Line (L-L), unbalanced 0.9 500

Two Line-to-Line, unbalanced 0.5 500

Two Line-to-Line, unbalanced 0.2 200

IEC−LVRT Test Requirement for Wind Turbines

NWTC Grid and Fault Simulator will allow testing of many grid integration 

aspects for multi-MW utility-scale variable renewable generation (wind and 

solar) and storage technologies. 

The NWTC Controllable Grid Interface as a New Unique Testing Capability

The authors wish to acknowledge the support of the U.S. 

Department of Energy for this research.

•Installed at NWTC test site in Nov 2012

•Commissioning and initial testing is scheduled during May-Dec 2013

5 MW dynamometer,

CGI arrival

New 5MW dynamometer facility

CGI installed on foundation

Photo credit: Vahan Gevorgian, NREL

Photo credit: Mark McDade, NREL