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.

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Safety and Function Test Report 

for the Viryd CS8 Wind Turbine

J. Roadman, M. Murphy, and J. van Dam

National Renewable Energy Laboratory

Technical Report

NREL/TP-5000-60060

October 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.

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Safety and Function Test 

Report for the Viryd CS8 Wind 

Turbine

J. Roadman, M. Murphy, and J. van Dam

National Renewable Energy Laboratory

Prepared under Task No. WE11.0206

Technical Report

NREL/TP-5000-60060

October 2013
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of 

any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately 

owned rights. Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, 

or favoring by the United States government or any agency thereof. The views and opinions of authors

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

This report is available at no cost from the National Renewable Energy Laboratory (NREL) 

at www.nrel.gov/publications.

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Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

16560, photo by Dennis Schroeder, NREL 17613, photo by Dean Armstrong, NREL 17436, photo by Pat Corkery, NREL 17721.

Printed on paper containing at least 50% wastepaper, including 10% post consumer waste.
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Safety and Function Test Report

for the

Viryd CS8 Wind Turbine

at the

National Wind Technology Center in

Boulder, Colorado

Conducted for

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, Colorado 80401

Conducted by

National Wind Technology Center

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, Colorado 80401

Jason Roadman

Mark Murphy

Jeroen van Dam

June 2013
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Table of Contents

List of Figures ............................................................................................................................................. 3

List of Tables ............................................................................................................................................... 4

1 Background........................................................................................................................................... 5

2 Test Objective ....................................................................................................................................... 5

3 Description of Test Turbine and Setup .............................................................................................. 5

4 Test Site Description............................................................................................................................ 8

5 Description of Instrumentation ......................................................................................................... 10

6 Procedure............................................................................................................................................ 12

6.1 Control and Protection System Functions...................................................................................... 12

6.2 Personnel Safety Provisions........................................................................................................... 13

6.3 Dynamic Behavior......................................................................................................................... 13

7 Results................................................................................................................................................. 13

7.1 Control and Protection System Functions...................................................................................... 13

7.2 Personnel Safety Provisions........................................................................................................... 21

7.3 Dynamic Behavior......................................................................................................................... 25

8 Deviations and Exceptions................................................................................................................ 25

8.1 Deviations from the Standard ........................................................................................................ 25

8.2 Deviations from Quality Assurance............................................................................................... 25

Appendix A. Instrument Calibration Certificates................................................................................... 26

References................................................................................................................................................. 47

List of Figures

Figure 1. Viryd CS8 test turbine at the NWTC.......................................................................................... 6

Figure 2. Electrical schematic of turbine installation.............................................................................. 8

Figure 3. Map of the test site...................................................................................................................... 9

Figure 4. Close up of test site around the test turbine ........................................................................... 9

Figure 5. View of instruments on the met tower.................................................................................... 11

Figure 6. Power response to wind speed, 1-minute data...................................................................... 14

Figure 7. Power response to wind speed (close-up), 1-minute data ................................................... 15

Figure 8. Rotor-speed response3 to wind speed, 1-minute data.......................................................... 15

Figure 9. Normal operation including startup and shutdown, 1-Hz data ............................................ 17

Figure 10. Normal shutdown (controller-initiated), 1-Hz data .............................................................. 17

Figure 11. High wind shutdown and startup .......................................................................................... 18

Figure 12. High wind shutdown (controller-initiated)............................................................................ 19

Figure 13. Manual stop (grid disconnect) and normal restart with winds between 10 and 15 m/s .. 20

Figure 14. Manual stop (grid disconnect)............................................................................................... 20

Figure 15. Viryd CS8 lockable disconnect switch and power meter ................................................... 23

Figure 16. Viryd CS8 controller enclosure, showing a voltage warning and additional voltage 

labeling added by NREL .................................................................................................................... 24

Figure A1. Calibration sheet for the primary anemometer used through 12 September 2012 ......... 26

Figure A2. Calibration sheet for the primary anemometer used from 17 September 2012 onward. 27

Figure A3. Calibration sheet for the wind vane used through 12 September 2012 ........................... 28

Figure A4. Calibration sheet for the wind vane used from 17 September 2012 onward ................... 29

Figure A5. Page 1 of the power transducer calibration sheet used through 12 September 2012.... 30

Figure A6. Page 2 of the power transducer calibration sheet used through 12 September 2012.... 31

Figure A7. Page 1 of the power transducer calibration sheet used from 17 September 2012 

onward................................................................................................................................................. 32

Figure A8. Calibration sheet for the pressure transducer used 15 May 2012 .................................... 33

Figure A9. Post-calibration sheet for the pressure transducer used through 15 May 2012 ............. 34

Figure A10. Calibration sheet for the pressure transducer used 16 May 2012 onward .................... 35
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Figure A11. Calibration sheet for the temperature sensor used through 12 September 2012 ......... 36

Figure A12. Calibration sheet for the temperature sensor used 17 September 2012 onward.......... 37

Figure A13. Calibration sheet for the signal conditioning module 13DEC38 used through 26 July 

2012...................................................................................................................................................... 38

Figure A14. Post-calibration sheet for the signal conditioning module 13DEC38 used through 26 

July 2012.............................................................................................................................................. 39

Figure A15. Calibration sheet for the signal conditioning module 12A2037 used from 26 July 2012 

onward................................................................................................................................................. 40

Figure A16. Calibration sheet for the signal conditioning module 13FAE1C used through 26 July 

2012...................................................................................................................................................... 41

Figure A17. Post-calibration sheet for the signal conditioning module 13FAE1C used through 26 

July 2012.............................................................................................................................................. 42

Figure A18. Calibration sheet for the signal conditioning module 12BFEE2 used from 26 July 2012 

onward................................................................................................................................................. 43

Figure A19. Calibration sheet for the signal conditioning module 13E3D05 used through 26 July 

2012...................................................................................................................................................... 44

Figure A20. Post-calibration sheet for the signal conditioning module 13E3D05 used through 26 

July 2012.............................................................................................................................................. 45

Figure A21. Calibration sheet for the signal conditioning module 14DA726 used from 26 July 2012 

onward................................................................................................................................................. 46

List of Tables

Table 1. Test Turbine Configuration and Operational Data.................................................................... 7

Table 2. Measured Blade Pitch Angle Relative to the Hub Plate............................................................ 7

Table 3. List of Channels and Measurement Instruments .................................................................... 10
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1 Background

This test was conducted as part of the U.S. Department of Energy’s (DOE) Independent Testing 

project. This project was established to help reduce the barriers of wind energy expansion by 

providing independent testing results for small turbines. Several turbines were selected for 

testing at the National Wind Technology Center (NWTC) at the National Renewable Energy 

Laboratory (NREL) as a part of the Small Wind Turbine Independent Testing project. Safety and 

function testing is one of up to five tests that may be performed on the turbines. Other tests 

include duration, power performance, acoustic noise, and power quality. Viryd Technologies, 

Inc. of Austin, Texas, was the recipient of the DOE grant and provided the turbine for testing.

The NWTC conducted this test in accordance with its quality system procedures to ensure that 

this final test report meets the full accreditation requirements by A2LA. NREL’s quality system 

requires that the test meet all applicable requirements specified by A2LA and ISO/IEC 17025 or 

to note any exceptions in the test report.

2 Test Objective

The objective of this test is to:

• Verify that the test turbine displays the behavior predicted in the design

• Determine if provisions relating to personnel safety are properly implemented

• Characterize the dynamic behavior of the wind turbine at rated wind speed and above.

NREL does not limit the safety and function test to features described in the wind turbine 

documentation. NREL also inspects, possibly tests, and reports on features that are required by 

IEC 61400-2 that may not be described in the wind turbine documentation. 

NREL conducted this test in accordance with Section 9.6 of the International Electrotechnical 

Commission (IEC) standard, Wind Turbines – Part 2: Design requirements for small wind 

turbines, IEC 61400-2, second edition, 2006-03.

3 Description of Test Turbine and Setup

The test turbine, shown in Figure 1, is a three-bladed, upwind, passive yaw turbine with a rated 

power of 8 kW. It was commissioned on 12 October 2011 and decommissioned on 7 May 2013. 

Safety and function testing was conducted from 12 October 2011 through 13 February 2013.

Table 1 lists the basic turbine configuration and operational data provided by the manufacturer. 

As part of Viryd’s standard commissioning procedure, small shims were inserted between the 

hub plate and the blade root, thereby pitching the leading edge of the blades into the wind. The 

pitch angle of each blade with respect to the hub plate is fixed. The angle was measured and is 

provided in Table 2. Figure 2 shows the one-line diagram for the test turbine installation.
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The following components were considered part of the test turbine system:

• A tower and foundation that were designed for installation at the NWTC test site 3.3a 

• The wiring and components on the turbine side of the test shed’s electrical panel, 

connecting the turbine to the electrical grid 

• All control components including wiring between the up-tower components and the 

down-tower control panel.

Figure 1. Viryd CS8 test turbine at the NWTC 

(Photo by Mark Murphy, NREL 22258)
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Table 1. Test Turbine Configuration and Operational Data

Turbine Manufacturer and Address

Viryd Technologies, Inc.

9701 Metric Blvd. Suite 200

Austin, TX 78758

Model Viryd CS8

Serial number CS008100X

Rotor diameter (m) 8.5

Hub height (m) 25

Tower type U.S. Tower, guyed, tilt-up lattice

Rated electrical power (kW) 8

Rated wind speed (m/s) 10

Small wind turbine class II

Rotor speed range (rpm) 115−125

Fixed or variable pitch Fixed

Power regulation (active or 

passive)

Passive

Number of blades 3

Blade pitch angle (deg) See Table 2

Blade make, type, serial number Viryd proprietary design, serial numbers 

not provided

Direction of rotation Clockwise viewed from upwind

Description of control system 

(device and software version)

Proprietary – PCB

Tower make, type, height U.S. Tower, tilt-up, guyed lattice, 24.4 m

Electrical output 240 VAC single phase

Table 2. Measured Blade Pitch Angle Relative to the Hub Plate

Blade Pitch Angle

1 1.4°

2 1.1°

3 1.4°

The test configuration consisted of the turbine mounted on a lattice tower, the controller, the 

meteorological tower, associated wiring and junction boxes, and a data shed containing the data 

acquisition instrumentation. The turbine was installed on a guyed, tilt-up, 24.4-m lattice tower. 

The wire run from the base of the tower to the data shed is approximately 98 meters of #6

American Wire Gauge (AWG) wire. Inside the test shed, the turbine was connected to a 240-volt 

(V) panel, where 240/480-V and 0.480/13.2 kilovolt (kV) transformers allowed the turbine to 

connect to the site’s 13.2-kV grid. Grid tolerances were 1% for frequency and 5% for voltage.

This general electrical arrangement is shown in Figure 2.
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Viryd Control

Panel

Supplemental

Junction Box

Uptower 

J-box

Met tower jbox

Power 

measurement box

60A 600V 

disconnect

kWh 

meter

Power panel 3-3L 

120/240V

L1

datashed

3*6AWG

>8*20AWG

4* 8AWG

Ground (8AWG)

Ground (6AWG)

Ground rod on the north 

side of datashed

2 pole 60A 

breaker 

no.27&29

Everything between power 

box and panel 3-3 L 

6AWG

N

L2

60A 600V 

disconnect

LO/TO 

Disconnect

3* 4AWG

Viryd control wires

Viryd DAS 

Box

>8*20AWG

3* 6AWG

Figure 2. Electrical schematic of turbine installation

(Source: NREL 2012)

4 Test Site Description

The Viryd CS8 wind turbine was located at test site 3.3a of the NWTC, approximately 8 km 

south of Boulder, Colorado. The site consists of mostly flat terrain with short vegetation and 

prevailing winds bearing 292° relative to true north. Figure 3 and Figure 4 show the turbine and 

meteorological (met) tower locations, as well as nearby turbines. For measurements requiring 

accurate wind speed data, NREL personnel used data that was obtained when the wind direction 

was between 211° and 38° true. In this measurement sector, the influence of terrain and 

obstructions on the anemometer is small and meets the requirements in accordance with IEC 

61400-12-1 without having to conduct a site calibration test.
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Figure 3. Map of the test site 

(Source: NREL 2012)

Figure 4. Close up of test site around the test turbine 

(Source: Map data ©2012 Google earth)

Skystream

Test turbine

Met tower

50 m
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5 Description of Instrumentation

In this test, the following parameters were measured: wind speed, electrical power, rotor speed, 

grid voltage, and turbine status. Additional parameters were logged for other tests. 

For turbine status, NREL added voltage signals to monitor the status LEDs on the controller. The 

green LED indicates when the turbine is producing power; the blue LED indicates when the 

turbine is in standby, “waiting for wind” (solid), or experiencing a cut-out wind condition 

(blinking); and the red LED indicates when the turbine has faulted. This LED blinks various 

times at various duty cycles, based on whether the turbine is experiencing a recoverable fault, 

unrecoverable fault, or startup/shutdown sequences. However, Viryd informed NREL that the 

number of blinks alone was not sufficient to determine the cause of a fault. A computer running 

proprietary Viryd software was required to log into the controller and determine the exact cause; 

however, NREL personnel did not have the appropriate level of access to the turbine, therefore 

these diagnostics were beyond the scope of the test.

Rotor speed was measured by tapping into the Viryd CS8’s RPM signal being sent to the 

controller. NREL personnel used an optically isolated frequency to voltage converter for this 

purpose, which is detailed in Table 3.

Table 3. List of Channels and Measurement Instruments

Signal Location Sensor Make Model Serial Number Cal Due Date

Primary Wind 

Speed

24.9 m Thies First Class 0707884

0609006

12 Sept. 2012

17 Sept. 2013

Reference Wind 

Speed

23 m Met One, 010C U2643 NA

Wind_Direction 23 m Met One, 020 U1475

W5515

13 Sept. 2012

17 Sept. 2013

Air_Pressure 22.1 m Vaisala, PTB101B T0740016

C1040014

5 April 2012

13 Feb. 2013

Air_Temperature 22.4 m Met One, T-200 0566229

0603-1

15 Sept. 2012

17 Sept. 2013

Precipitation Data Shed Campbell Scientific 237 NA NA

Active_Power Data Shed Secondwind Phaser 5-4A20

with OSI pn. 12973 CT’s

01091

01091

15 Sept. 2012

15 Sept. 2013

Turbine Status Turbine 

Controller

Turbine Controller Lights/ 

Brake Solenoid

NA NA

Rotor Speed Turbine 

Controller

Phoenix Contact MCR-f-UIDC67472901 3 Oct. 2012

Data Acquisition 

Modules

Data Shed National Instruments NI 9229

National Instruments NI 9217

National Instruments NI 9205

13DEC38

12A2037

13FAE1C

12BFEE2

13E3D05

14DA726

24 June 2012

27 June 2013

24 June 2012

27 June 2013

24 June 2012

27 June 2013
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Table 3 provides an equipment list that includes the specifications of the instruments used and 

Figure 5 provides the location of the met tower instruments. The first set of data acquisition 

modules were used beyond their calibration due date from 25 June 2012 through 26 July 2012. 

They were post-calibrated and found to be within tolerance. The pressure transducer was out of 

calibration from 6 Apr 2012 through 15 May 2012 and was post-calibrated. Residuals between 

the two calibrations were found to be at most 0.006 kPa, a negligible amount in the context of 

this test.

Calibration and post-calibration sheets are included in Appendix A.

Figure 5. View of instruments on the met tower 

(Source: NREL 2012)

Reference Wind Speed

Air Pressure

Wind Direction

Primary Wind Speed

Air Temperature
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6 Procedure

Safety and function testing can involve some risk to personnel and equipment. By incorporating 

appropriate controls into testing procedures, NREL staff worked to accomplish the tasks with 

minimal risk. This test report documents these controls in areas where they might have influenced the 

results. After installing the Viryd CS8 at NREL, Viryd’s ability to directly support the turbine 

was significantly limited. As a result, not all of the required testing steps could be performed by 

NREL and are detailed throughout this report.

6.1 Control and Protection System Functions

Major turbine response categories for this type of testing include the following:

• Power control

• Rotor speed control

• Yaw orientation

• Startup, which was tested:

o During normal operation (winds rising above cut-in)

o After maintenance or fault clearance at the design wind speed or above

o During maintenance of fault conditions at design wind speed or above

• Normal shutdown, which was tested:

o During normal operation (wind speed decreasing to less than cut-in) 

o During normal operation (wind speed increasing to greater than cut-out) 

• Emergency shutdown, which was tested during operation, and included:

o Behavior upon excessive vibration1

o Behavior upon loss of load

o Turbine-specific checks1

NREL personnel observed the turbine response for each major response category: startup, 

normal shutdown, and emergency shutdown. In a normal test, faults or other actions that cause

one of these major responses are simulated using the appropriate input and turbine response, and 

then verified by sensing the condition and indicating an appropriate response. For example, this 

procedure enables all of the emergency-stop functions to be checked without exposing the 

turbine to multiple, potentially damaging stops. These checks are designated by the term 

“behavior” in the list below. However, because NREL personnel did not have sufficient access to 

the turbine to change any controller parameters or simulate these conditions, the results presented 

are limited to those observed over the course of normal turbine testing.

 

1 NREL was unable to simulate some of these conditions.
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6.2 Personnel Safety Provisions

The second part of the test procedure was to evaluate provisions for personnel safety. For this 

turbine, the following list of NWTC-standardized safety and function issues were reviewed:

• Safety instructions

• Climbing

• Standing place, platforms, and floors

• Electrical and grounding system

• Fire resistance and control

• Fire extinguisher

• Emergency stop buttons

• Lock-out/tag-out provisions

• Interlock on electrical cabinets

• Safety signs

• Unauthorized changing of control settings

• Lightning protection

• Presence and functioning of rotor and yaw lock.

6.3 Dynamic Behavior

NREL staff observed the turbine at all operating wind speeds to evaluate the dynamic behavior 

of the turbine, including (but not limited to) vibration, yaw behavior, and noise.

7 Results

Test results reported here are based on tests conducted from 12 October 2011, when the turbine 

was commissioned, through 13 February 2013.

7.1 Control and Protection System Functions

The turbine controller appeared to operate as designed by Viryd. Cut-in appeared to miss some 

of the dynamic winds available on the NWTC’s site. Viryd explained that the turbine controller 

utilizes a wind-speed-weighted algorithm to determine when to initiate a normal startup 

operation. Thus, a quick transition from low to strong winds will initiate a startup sooner than 

winds that are slowly increasing past cut-in. Cut-out appears to work well and as designed. 

Additionally, the turbine controller was able to sense downwind operation by monitoring wind 

speed measured by its tower-mounted anemometer and power.

Faults were observed throughout the test, but there was little to no indication of the causes of 

those faults. In all cases, the turbine shut down appropriately. Furthermore, NREL was limited in 

its ability to actively test single-fault failures and did not complete an exhaustive investigation or 

examine failures of “safe life” components. If a second fault were to occur during a critical 
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event, severe results can be expected. NREL staff do not make judgments on whether such 

failures are likely or whether additional features in the control and protection system are needed 

to protect against such consequences.

NREL staff conducted the following tests and observations on the Viryd CS8.

Power Control

Figure 6 and Figure 7 show that the power output of the turbine system was limited. Power 

limiting was achieved through stall control. Furthermore, the turbine draws a large inrush current 

during the motoring portion of the startup sequence. However, the power transducer rails at -24 

kW during these events, so NREL analysts cannot comment on the magnitude of the inrush 

current.

Figure 6. Power response to wind speed, 1-minute data2

(Green: maxima, Red: minima, Blue: average)

 

2 The first power transducer installed during the test railed at -12 kW. Its range was adjusted, but the turbine railed 

it again at -24 kW. The power transducer was not adjusted further, as this would have represented an 

unacceptable loss of resolution. As such, no comment can be made about the magnitude of the minimum power 

during startup events.
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Figure 7. Power response to wind speed (close-up), 1-minute data2

Rotor Speed Control

During the test, the synchronous generator limited rotor RPM, as expected. Figure 8 shows both 

1-minute average rotor speed data and maximum and minimum values in each 1-minute period,

based on 40-Hz data. The increase of the RPM with wind speed was due to the generator slip.

Figure 8. Rotor-speed response to wind speed, 1-minute data 

(Red: maxima, Green: minima, Blue: average)

115

116

117

118

119

120

121

122

123

124

125

4 5 6 7 8 9 10 11 12 13 14

Rotor Speed, rpm

Wind Speed, m/s
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Yaw Orientation

NREL staff observed yaw behavior frequently during the test period and compared yaw position 

with the nearby wind-vane indication of wind direction. Normal behavior was observed under all 

wind conditions. At all wind speeds, the rotor operates roughly aligned with the prevailing wind 

direction. Any yaw error decreases as the wind speed increases.

Occasionally, the turbine was observed to run in a downwind condition. However, in all of these 

cases, the turbine controller sensed the condition, shut down the turbine, allowed the nacelle to 

passively yaw into the wind, and initiated a normal start procedure.

The Viryd turbine uses slip rings to transmit power to and from the nacelle to the tower cable. 

Therefore, droop cable over-twist is not an issue.

Startup

NREL staff observed large variations in the wind speed at which the turbine rotor initiates 

startup, ranging from 4 m/s to 8 m/s. As described above, Viryd’s cut-in algorithm and the 

dynamic nature of the winds at the NWTC are thought to contribute to this variation. Once the 

winds are high enough for a long enough time period to satisfy the counter, the turbine controller 

responds by opening the brakes and motoring the turbine. Once wind speed and rotor speed are 

sufficiently high, the turbine begins to produce positive power. NREL staff observed the turbine 

starting up in a wide range of conditions, and did not notice any abnormal behavior during any of 

the startups. The staff also observed similar smooth cut-ins when the turbine was returned to 

service after a manual shutdown.

Normal Shutdown

The turbine manual identifies two types of shutdowns initiated by the controller: a normal, or 

controlled stop shutdown, and an emergency stop. When winds drop below cut-in, the rotor will 

motor for a period of time (again depending on the wind-speed-weighted counter). If winds 

remain low, the turbine will initiate a normal stop: engaging its brakes, disconnecting the 

generator, and bringing the rotor to a stop in approximately two rotations. Figure 9 shows a short 

time series of turbine operations including normal startup and shutdown. Figure 10 is a close-up 

of part of this time series and shows a normal shutdown initiated by the controller.
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Figure 9. Normal operation including startup and shutdown, 1-Hz data 

Figure 10. Normal shutdown (controller-initiated), 1-Hz data

0

50

100

150

200

250

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

5000 7000 9000 11000 13000 15000 17000

Turbine Voltage, [VAC]

Power, [kW] & Wind Speed, [m/s]

Time, [sec]

Power

Primary Wind Speed

Turbine Voltage

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

10080 10085 10090 10095 10100 10105

Rotor Speed [rpm]

Power [kW], Wind Speed [m/s] & Brake Signal [volts]

Time, [sec]

Power

Primary Wind Speed

Brake Solenoid Voltage

Rotor Speed
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If the turbine senses an instantaneous wind speed greater than 25 m/s, it engages the brake and 

stops the rotor. This will send the turbine into a recoverable fault state for 5 minutes. If, after this 

time period, the winds have dropped below 25 m/s, the turbine will motor and start up again. 

NREL personnel observed high-wind cut-out several times over the course of the test. An 

example is shown in Figure 11 and Figure 12.

3

Figure 11. High wind shutdown and startup

 

3 The turbine monitors wind speed with an anemometer mounted on the turbine tower below hub height. This 

signal was not recorded by NREL’s data acquisition system. However, the primary wind speed signal is shown on 

the plot.

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

-4

-3

-2

-1

0

1

2

3

4

5

6

7

8

3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000

Wind Speed, [m/s]

Power, [kW] & LED Signal, [volts]

Time, [sec]

Blue LED

Power

Primary Wind Speed
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Figure 12. High wind shutdown (controller-initiated)

Emergency Shutdown during Operation from Any Operating Condition

As NREL staff did not have access to the controller software interface, the only means of 

stopping the turbine during the test was by using the grid disconnect (recommended by Viryd). 

As such, normal and emergency stops initiated by the end user were identical.

According to the manual, emergency stops will be initiated by the controller when the following 

conditions are sensed:

• A transmission speed ratio error4

• Rotor over-speed

• Delayed controlled shutdown

• Excessive start-up power draw.

To NREL’s knowledge, the turbine never initiated an emergency stop for these conditions. 

A user-initiated emergency stop is the same as a normal stop: disconnecting the grid. During the 

test, shutdown behavior was consistent with the manual: the turbine applied the brakes and 

 

4 The constant speed (CS) model is instrumented with a single RPM sensor on the low-speed shaft. Therefore , it 

cannot sense a transmission speed ratio error.

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

14

16

18

20

3335 3340 3345 3350

Wind Speed [m/s] & Rotor Speed [rpm]

Power [kW], LED Signal [volts] & Brake Signal [volts]

Time, [sec]

Power

Brake Solenoid Voltage

Primary Wind Speed

Rotor Speed
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brought the rotor to a stop. NREL staff performed these types of shutdowns in addition to the 

automatic shutdowns observed. An example time series is shown in Figure 13 and Figure 14. 

The turbine safely brought the rotor to a stop any time this test was performed.

Figure 13. Manual stop (grid disconnect) and normal restart with winds between 10 and 15 m/s

Figure 14. Manual stop (grid disconnect)

-50

0

50

100

150

200

250

300

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2

4

6

8

10

12

14

16

18

20

22

9000 9100 9200 9300 9400 9500 9600 9700 9800 9900 10000

Turbine Voltage, [VAC]

Power, [kW] & Wind Speed, [m/s]

Time, [sec]

Power

Primary Wind Speed

Turbine Voltage

-50

0

50

100

150

200

250

300

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-2

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6

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9380 9385 9390 9395

Turbine Voltage [VAC] & Rotor Speed [rpm]

Power [kW], Brake Signal [volts] & Wind Speed [m/s]

Time, [sec]

Power

Primary Wind Speed

Brake Solenoid Voltage

Turbine Voltage

Rotor Speed
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Behavior upon Excessive Vibration

To NREL’s knowledge, the turbine has no means of sensing excessive vibration. The IEC 

turbine design standards require such sensors on large turbines, but not on turbines smaller than 

200 m2

.

Behavior upon Loss of Load

For the Viryd CS8 turbine, loss of load is identical to a normal shutdown. The brakes are applied 

and the rotor is brought to a stop. To assess this capability, NREL personnel conducted manual 

grid outages several times during the test. Additionally, the turbine experienced several grid 

outages when NREL lost power over the course of the test. In all cases, the rotor was brought to 

a stop and the turbine returned to normal operation after power was restored. In one case, the 

turbine entered a faulted state after power was restored, but the exact cause could not be 

determined because the controller does not convey the nature of certain types of faults to the end 

user. However, a manual fault reset performed by NREL at Viryd’s request brought the turbine 

back to normal operation. Figure 13 and Figure 14 show plots of the rotor coming to a stop 

during a manual stop (disconnecting grid power) and restarting after grid power is restored and 

the wind speed counter is satisfied.

Turbine-Specific Checks

There were several tests that did not occur during the testing campaign, as they would have 

required a temporary change of controller setpoints, and Viryd was unable to support this level of 

testing. These turbine-specific checks include:

• Grid under- and over-frequency

• Grid under- and over-voltage

• Over-speed condition

• Temperature fault

• Pressure fault

• Generator over power

• Transmission ratio error (may not apply to the constant speed (CS) model).

There may be more cases that the controller is designed to sense and act upon but Viryd was not 

available to help perform a complete inventory of those cases.

7.2 Personnel Safety Provisions

Safety Instructions

The turbine operator’s manual (first edition) provides safety instructions for installation, 

operation, and maintenance. The owner’s manual encourages a licensed contractor to review 

plans and participate in the installation, but does not list this requirement on the manual’s cover,

as required by the IEC standard. Use of a forklift or telehandler is required to attach the nacelle 

to the tower. The maintenance is split into maintenance that must be done by the owner and 

maintenance that must be performed by the installer. The owner-completed maintenance includes 

only simple tasks with minimal safety implications. The annual maintenance must be conducted 
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by an installer or trained service technician only. NREL personnel checked the manual to 

determine if the safety instructions addressed requirements in the IEC small turbine design 

standard and found one additional issue: the turbine has no provisions for securing the yaw 

mechanism.

Climbing

Although the tower is a lattice-type that can be climbed, opening the nacelle covers could present 

a potentially dangerous situation while climbing. The manual recommends tilting the tower 

down whenever work must be performed on the turbine or using a man-lift to access the turbine 

without tilting the tower down. During the test, NREL staff used man-lifts to access the turbine. 

Standing Places, Platforms, and Floors

There are no standing places, platforms, or floors on the turbine.

Electrical Grounding System

The owner’s manual shows a schematic of the electrical system and provides information on how 

to size, wire, and properly ground the electrical system. The manual recommends that a licensed 

electrician be part of the installation crew.

Fire Resistance and Control/Fire Extinguisher

The turbine generator has a cooling fan and is rated for normal operating temperatures of up to 

40 ̊C. NREL provided a fire extinguisher in the test shed near the turbine. The manufacturer does 

not provide fire extinguishers or recommend that they be installed. However, for a turbine of this 

size, this is what can be reasonably expected.

Lock-Out/Tag-Out Provisions

Viryd provided a lockable disconnect switch between the grid and the turbine (shown in Figure 

15).
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Figure 15. Viryd CS8 lockable disconnect switch and power meter 

(Photo by Mark Murphy, NREL)

Emergency Stop Button

The turbine does not have an emergency stop button, only a disconnect switch. The turbine 

manual recommends only engaging the disconnect switch in dangerous situations. However, 

during installation, Viryd personnel instructed NREL staff to use the disconnect switch for 

stopping the turbine. The disconnect switch was the only provided means of stopping the turbine.

Interlock on Electrical Cabinets

There is no interlock on the controller enclosure.

Safety Signs

There is one safety sign on the turbine that states: “Hazardous voltages, disconnect power before 

opening. Contact causes severe electrical shock.” See Figure 16.

NREL staff added labels indicating the voltage levels on all enclosures, electrical panels, and 

disconnect switches (see Figure 15 and Figure 16).
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Figure 16. Viryd CS8 controller enclosure, showing a voltage warning and additional voltage 

labeling added by NREL 

(Photo by Jason Roadman, NREL)

Unauthorized Changing of Control Settings

There is no easy way for an unauthorized user to change any of the control settings, as this would 

require intimate knowledge of the controller communication protocol. 

Lightning Protection

The turbine does not have a dedicated lightning protection system, but the tower was grounded 

(as indicated by the owner’s manual).

During the test period, no direct or nearby lightning strikes were observed. 

Presence of Rotor and Yaw Lock

The brake system serves as the rotor lock on this turbine. The brake calipers are pneumatically 

actuated against an internal mechanical spring and are of the fail-closed type. The brake will 

prevent the rotor from spinning in windy conditions, and was found to lock the rotor so it was 

completely stationary for any maintenance performed over the course of the test.

There is no yaw lock present on this turbine, nor is disabling the yaw motion described as part of 

the maintenance procedures. During the course of the test, NREL staff would approach the 

turbine in the man-lift, grab the tail, and position the man-lift basket to limit the yaw motion.

Documentation

NREL personnel checked the manual to determine if the turbine met the documentation

requirements in the IEC small turbine design standard and found the following issues:
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• The manual cover does not display the statement : “Maintenance and repairs to be 

performed by trained personnel only” 

• The manual was not updated from the continuously variable transmission to the constant 

speed model installed

• The manual is of a generic type and does not provide specific serial numbers of major 

components for the turbine installation

• There is no turbine nameplate, as referred to in the standards. Individual components 

such as the generator, gearbox, and blades have individual nameplates, but they did not 

cover the range of information required by the standard for the turbine nameplate.

7.3 Dynamic Behavior

Turbine operation was observed by NWTC personnel for several minutes on a weekly basis over 

the course of the test. Observed wind speeds ranged from less than 5 m/s (below cut-in) to more 

than 26 m/s. Total observation time was well in excess of 1 hour. The turbine was observed to 

cut-in between 4 and 8 m/s, smoothly motoring up and switching to producing power. The exact 

wind speed for cut-in varied based on the wind-speed-weighted counter mentioned earlier. The 

turbine was observed to passively track the wind well, both when running and parked with only 

minor vibration of the tail. Occasionally, the turbine was observed to run downwind (detailed 

above). Running downwind was always detected by the controller and initiated a shutdown 

algorithm, followed by the tail passively turning the turbine back into the wind, thereby allowing 

the turbine to start back up. No excessive vibration of any components was observed throughout 

the test.

8 Deviations and Exceptions

8.1 Deviations from the Standard

The initial power transducer used during the test railed at -12 kW and was re-configured and recalibrated, but railed at -24 kW when the turbine motored the rotor upon start up. High-speed 

data showed no significant impact on the 1-minute averages, but no statement can be made about 

the absolute magnitude of the inrush current during turbine startup.

Not all tests could be performed because of the lack of support from the manufacturer.

8.2 Deviations from Quality Assurance

The first set of data acquisition modules were used beyond their calibration due date; they were 

post-calibrated and found to be within tolerance. Appendix A includes post-calibration sheets. 

The pressure transducer was out of calibration from 6 Apr 2012 through 15 May 2012. Residuals 

between the calibration and post-test calibration were found to be 0.006 kPa at most, a negligible 

amount in the context of this test.
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Appendix A. Instrument Calibration Certificates

Figures A1 through A21 show the calibration sheets for the instruments used during the Viryd 

CS8 safety and function tests. 

Figure A1. Calibration sheet for the primary anemometer used through 12 September 2012
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Figure A2. Calibration sheet for the primary anemometer used from 17 September 2012 onward
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Figure A3. Calibration sheet for the wind vane used through 12 September 2012
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Figure A4. Calibration sheet for the wind vane used from 17 September 2012 onward
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Figure A5. Page 1 of the power transducer calibration sheet used through 12 September 2012
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Figure A6. Page 2 of the power transducer calibration sheet used through 12 September 2012
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Figure A7. Page 1 of the power transducer calibration sheet used from 

17 September 2012 onward
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Figure A8. Calibration sheet for the pressure transducer used 15 May 2012
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Figure A9. Post-calibration sheet for the pressure transducer used through 15 May 2012
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Figure A10. Calibration sheet for the pressure transducer used 16 May 2012 onward
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Figure A11. Calibration sheet for the temperature sensor used through 12 September 2012
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Figure A12. Calibration sheet for the temperature sensor used 17 September 2012 onward
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Figure A13. Calibration sheet for the signal conditioning module 13DEC38 used through 

26 July 2012
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Figure A14. Post-calibration sheet for the signal conditioning module 13DEC38 used through 

26 July 2012
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Figure A15. Calibration sheet for the signal conditioning module 12A2037 used from 

26 July 2012 onward
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Figure A16. Calibration sheet for the signal conditioning module 13FAE1C used through 

26 July 2012
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Figure A17. Post-calibration sheet for the signal conditioning module 13FAE1C used through 

26 July 2012
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Figure A18. Calibration sheet for the signal conditioning module 12BFEE2 used from 

26 July 2012 onward
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Figure A19. Calibration sheet for the signal conditioning module 13E3D05 used through 

26 July 2012
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Figure A20. Post-calibration sheet for the signal conditioning module 13E3D05 used through 

26 July 2012
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Figure A21. Calibration sheet for the signal conditioning module 14DA726 used from 

26 July 2012 onward
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References

International Electrotechnical Commission (IEC). (2006). Wind Turbines – Part 2: Design 

requirements for small wind turbines, IEC 61400-2, Ed 2.0, Clause 9.6, 2006-03, Geneva, 

Switzerland.