Date post: | 30-Dec-2015 |
Category: |
Documents |
Upload: | octavius-roberts |
View: | 27 times |
Download: | 0 times |
1
John Dalsgaard Sørensen1,2, Jens Nørkær Sørensen2 & Jørgen Lemming2
1) Aalborg University, Denmark2) 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
Introduction
Lystrup (Jutland, Denmark), February 2012
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
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
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 m2 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
General statistical risk to be killed when driving on a highway in Denmark: 2 10-9 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.
2 10-11 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 5 10-12 per km driven
Risk assessment – acceptable risk level
7
Probability per km driven that a person in a vehicle is killed
Risk assessment – wind turbine parts - result
D = 500m
D = 400m
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
– Pz(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
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
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
Throwing distances during operation
Risk assessment – ice throw
Tower heightWind speed
40 m 50 m 70m 100 m 120 m
5 m/s 69 69 67 70 6810 m/s 88 91 98 111 12115 m/s 112 119 134 159 17820 m/s 138 149 172 209 23425 m/s 166 181 212 259 292
Assumptions: Tip speed = 70 m/sBlade position = -45 degrees to horizontal Thickness of ice fragments = 2cmRotor diameter = tower height
12
Throwing distances at stand still
Risk assessment – ice throw
Total heightWind speed
50 m 75 m 100 m 150 m 200 m
5 m/s 7 12 18 30 4210 m/s 16 27 38 62 8715 m/s 28 45 62 98 13520 m/s 42 64 88 136 18525 m/s 57 85 115 176 238
Assumptions: Total height corresponds to tip position Thickness of ice fragments = 2cm
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
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
• 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
• 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
John Dalsgaard Sørensen [email protected]
Jens Nørkær Sørensen [email protected]
Jørgen Lemming [email protected]
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