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1 John Dalsgaard Sørensen 1,2, Jens Nørkær Sørensen 2 & Jørgen Lemming 2 1) Aalborg University, Denmark 2) DTU Wind Energy, Denmark Introduction Risk assessment.

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Presentation on theme: "1 John Dalsgaard Sørensen 1,2, Jens Nørkær Sørensen 2 & Jørgen Lemming 2 1) Aalborg University, Denmark 2) DTU Wind Energy, Denmark Introduction Risk assessment."— Presentation transcript:

1 1 John Dalsgaard Sørensen 1,2, Jens Nørkær Sørensen 2 & Jørgen Lemming 2 1) Aalborg University, Denmark 2) DTU Wind Energy, Denmark Introduction Risk assessment - wind turbine parts Risk assessment - ice throw Acceptable risk level Conclusions Risk assessment of wind turbines close to highways

2 2 Introduction Lystrup (Jutland, Denmark), February 2012

3 3 Scope: Assessment of the minimum distance from wind turbines to highways (in Denmark) based on risk assessments of the consequences due to –total or partial failure of a wind turbine –ice throw in case of over-icing Introduction Laakso et al. IEA 2009

4 4 Methodology: Data collected from a large number of modern wind turbines from Denmark and abroad –same basic technology as new large wind turbines –information on events where parts of the turbine is thrown / dropped at a distance from the turbine Risk estimated that persons in a car are killed because of –wind turbine parts 'thrown away' from a wind turbine in events with total or partial failure –ice pieces 'thrown away' from a wind turbine in events with over-icing Introduction

5 5 Data from representative large databases with information on parts ’thrown’ in case of failure (from nacelle and blades): –Distance from wind turbine –Size of with turbine part Estimation of probability per year per m 2 that a wind turbine part hits in radius R from the wind turbine Estimation of probability per km that a vehicle is hit by a wind turbine part thrown from a wind turbine placed in a distance d from a road – depending on –Vehicle velocity V (80 km/h) –Distance D between wind turbines Assumption: If a wind turbine part hits a vehicle then in average 1.5 persons are killed (conservative) Risk assessment – wind turbine parts

6 6 General statistical risk to be killed when driving on a highway in Denmark: per km driven (2009) ALARP (As Low As Reasonably Practicable) principle: An additional / extra risk contribution can be assumed unimportant if the risk contribution is less than 1/100, i.e per km driven Additionally it can be expected that the number of killed persons at highways in Denmark is reduced by a factor 2 each 10 years.  risk accept limit for new wind turbines close to highways in Denmark becomes per km driven Risk assessment – acceptable risk level

7 7 Probability per km driven that a person in a vehicle is killed Risk assessment – wind turbine parts - result D = 500m D = 400m

8 8 Estimation of probability per km that a vehicle is hit by an ice piece thrown from a wind turbine placed in a distance d from a road depends on –Vehicle velocity V (80 km/h) –Distance D between wind turbines –Distribution of mean wind speeds at hub height –P z (s,v): Probability per year and per m that ice pieces lands in a distance s from the wind turbine given mean wind speed v Risk assessment – ice throw

9 9 Over-icing in Denmark: (approximate estimates) –ice pieces larger than 3 mm: 0,175 times per year –one over-icing: 10 ice pieces with a weight > 1 kg –probability distribution of wind speed in case of over-icing: - assumption: if ice piece hits a vehicle then in average 1.5 persons are killed with a probability equal to 10% Risk assessment – ice throw

10 10 Throwing distances are computed using the 6 DOF trajectory code by J.N. Sørensen (Wind Engineering, vol. 8(3), 1984) Risk assessment – ice throw

11 11 Throwing distances during operation Risk assessment – ice throw Tower height Wind speed 40 m50 m70m100 m120 m 5 m/s m/s m/s m/s m/s Assumptions: Tip speed = 70 m/s Blade position = -45 degrees to horizontal Thickness of ice fragments = 2cm Rotor diameter = tower height

12 12 Throwing distances at stand still Risk assessment – ice throw Total height Wind speed 50 m75 m100 m150 m200 m 5 m/s m/s m/s m/s m/s Assumptions: Total height corresponds to tip position Thickness of ice fragments = 2cm

13 13 Probability per km driven that a person in a vehicle is killed Tower height = 120m / Total height = 200m Risk assessment – ice throw - results Stand-still Operation

14 14 Increase (in %) of probability that a person in a vehicle is killed due to thrown wind turbine parts or ice pieces Increase in risk level is low for distances above 150m Risk assessment

15 15 Risk assessment of wind turbines close to highways taking into account –total or partial failure of a wind turbine –to ice throw in case of over-icing Data collected from a large number of modern wind turbines from Denmark and abroad The studies show that the probability per kilometer that a person in a vehicle is killed due to total or partial failure / collapse (damage) of a wind turbine can be assumed to be of minor importance. Summary

16 16 Assessment of risks due to ice throw in case of over-icing is associated with many uncertainties The generally accepted risk on highways in increased with less than 0.1% in wind turbines are installed more than 150 meters from the highway The risk due to ice throw from a wind turbine in operation is seen to be slightly greater than the risk if the wind turbine is parked It is recommended that for practical projects a proper risk assessment is performed, which also include the location in relation to the road and the prevailing wind direction Summary

17 17 John Dalsgaard Jens Nørkær Jørgen Sponsorship: Danish Energy Agency Reference: Sørensen, J.D., J. Lemming & J.N. Sørensen: risk assessment of siting wind turbines close to highways Risø report: Risø-R-1788, 2011 (in Danish). Risk assessment of wind turbines close to highways Thank You For Your Attention


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