REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS

1 / 9C. Heilmann, EWEA 2013 Annual Event, Vienna,4 – 7 February 2013

REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS

REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON

BUILDINGSDr. Christoph Heilmann1 (Presenter), Anke Grunwald1, Michael Melsheimer1, Prof. Dr. Jochen Twele2, 3 , Norman Pieniak2, Jonathan Amme3

1: BerlinWind GmbH ([email protected]) 2: Reiner Lemoine Institut gGmbH ([email protected])3: Hochschule für Technik und Wirtschaft – University of Applied Sciences ([email protected])

4

6

3

1 2

5

7

8

n



Content

Investigated vertical-axis small wind turbine (SWT) and vibration measuring system

Potential vibrations systems at SWT and excitation Campbell-diagram of excitation and natural frequencies Measured vibration signals during operation Evaluation of amplitudes produced by rotor speed and harmonics Conclusions



Investigated vertical-axis small wind turbine (SWT)

Gravity foundations

Minimast

Rotor blades

Generator, tower connection with dampers

Blade holders

Speed sensor

Accelerometers

Wind vane & cup anemometer

Accelerometers

Long braces

Clamp

BalustradeShort braces

Foot braces

Steel tower

Strain gauges

Elevator house

End disk

AccelerometersWEST

NORTH

Measuring system box

Power: 600 W Rotor: 1.9 x 1.9 m Hub height: 6 m Tower support by long and

short braces Gravity foundation: 660 kg each Gap between tower bottom and roof Steel framework roof, 7 floor building Mobile vibration measuring system

with up to 17 sensors



Vibration systems… 1. Blades + holders2. Rotor + dampers3. Top mass + minimast (MM) + tower 4. Long braces (LB)5. Short braces (SB)6. Foot bars7. Gravity foundations8. Building

Blade-mast interaction producing harmonic excitation by 1*n, 3*n and 6*n

…and excitation

Wind vMast

Blade

n Wake

uw

v

4

6

3

1 2

5

7

8

n

4

6

3

1 2

5

7

8

n



SWT-Campbell-Diagram: Harmonic excitations and natural frequencies

15 Critical intersection points from harmonics with potential resonance hazard

0

5

10

15

20

25

30

35

40

45

50

0 50 100 150 200 250Rotor speed

in rpm

Ex

cit

ati

on

an

d n

atu

ral

fre

qu

en

cy

in

H

z

0,0

1,5

3,0

4,5

6,0

7,5

9,0

10,5

12,0

13,5

15,0

Win

d s

pe

ed

in

m/s

OperationLow wind idling

Bdg high: 12.0 HzTower 1st: 10.5 HzBdg low 1st: 7.9 Hz

SB 1st soft: 42 Hz LB 2nd, SB 1st: 47 Hz

Tower 2nd: 22 Hz

Natural frequency (NF) from standstill tests

Win

d sp

eed

in m

/s

Nat

ura

l or

exci

tatio

n fr

eque

ncy

in H

z Wind60 n 20 n

6 n

3 n1 n

Rotor speed in rpm

Blades+Holders: 7.5 Hz

• 20 n and 60 n from generator pole pair number



Measured accelerations at SWT minimast and long brace

Sensor color code:

• Horizontal at minimast: blue and red (at rectangles)

• Middle of long brace: green

• SWT with long braces and removed top dampers

• Measurement time: 40 min

• Wind speed: 3.5 to 5.0 m/s

• Rotor speed: 80 to 220 rpm

• If resonance occurs amplitudes exceed gravitational constant: 1000 mg = 1.0 g = 9.81 m/s²

• At long brace short-time ampli-tudes above 1500 mg = 1.5 g

*) Unit: 1 mg = milli g = 9.81 * 10-3 m/s²

Detail Time in s

Time in s

1500

1000

500

0

-500

-1000

-1650

Acc

eler

atio

n

ampl

itude

in m

g *)

1500

1000

500

0

-500

-1000

-1500

Acc

eler

atio

n

ampl

itude

in m

g *) Minimast 1

Long brace Minimast 2

Minimast 1 Long brace Minimast 2



Sliding window vibration evaluation reveals resonances during SWT-operation

*) Unit: 1 mg = 9.81 * 10-3 m/s²NF = Natural frequency

*)

Tower: 1st NF by 3 n

LB: 1st NF by 3 n

SB: 1st NF soft by 20 n

Tower, 3rd

NF by 20 n

Even more resonance issues from harmonics visible than expected!

LB: 2ndNF, SB: 1st NF by 20 n

Blades +holders, 1st NF by 3 n Tower, 2nd

NF by 6 n

MM1, 1 nLB, 1 nMM2, 1 nMM1, 3 nLB, 3 nMM2, 3 nMM1, 6 nLB, 6 nMM2, 6 nMM1, 20 nLB, 20 nMM2, 20 nMM1, 60 nLB, 60 nMM2, 60 n

Sensor color code:

• Horizontal atminimast (MM): blue and red

• Middle of long brace (LB): green

Rotor speed: 30 to 220 rpm

Evaluation: Order analysis of sliding window ( 8 revolutions)

Excitation frequency from rotor speed 1 nand harmonics 3 n, 6 n, 20 n, 60 n in Hz



Conclusions

Dynamics of variable-speed vertical-axis SWT very complex

Harmonics produce resonance issues, despite sub-critical rotor speed

Additional vibration systems formed by SWT components may amplify vibration by their resonance

Total system of SWT and building relevant for resonance issues

SWT design including dynamic analysis imperative, professional manufacture, siting (including dynamics) and installation as well

Recommendations for the investigated SWT:- Fixing gravity foundations - Two-plane rotor balancing due to mass imbalance above limit - Removal of top dampers- Pre-tensioned guy wires instead of long braces

Development of compact load measuring system and sophisticated evaluation software for SWT vibration analysis in process



Thank you for your attention!

say…BerlinWind GmbH ([email protected]) Reiner Lemoine Institut gGmbH ([email protected])Hochschule für Technik und Wirtschaft – University of Applied Sciences ([email protected])

Documents

REDUCING VIBRATION ISSUES AT SMALL VERTICAL-AXIS WIND TURBINES ON BUILDINGS