Research On Lightning Disaster Mechanism And Its Protection Methods For Wind Turbine

By the end of 2017,the global total wind power capacity reaches 5.39×108kW and it reaches 1.88×10kW in China,which keeps the first place in the world.Lightning is one of the most serious natural disasters which will destroy wind turbines.This paper analyzes the law of wind turbine struck by lightning through the statistics of wind turbine lightning disaster cases.In this paper,lightning protection technique development of wind turbine is introduced in detail.Statistical analysis is made on the characteristics of wind turbine damage caused by lightning.The connection process between lightning channel and wind turbine is simulated using pilot 2D random model.The distribution of lightning electromagnetic field inside the wind turbine tower is studied based on the cutoff waveguide theory.The transmission of lightning current in wind farms is studied based on transmission-line theory.Energy coupling from lightning to wind turbines is studied based on artificial triggered lightning.The main contents and conclusions of this paper are as follows:1?In all cases of wind turbine damage caused by lightning,blade damage comprises about 20%-28%of the total and the electrical and electronic system is about 70.5%-71%.The connection process between lightning channel and wind turbine is simulated 1600 times using pilot 2D random model.The simulation results show that:With the increase of the horizontal distance between starting position of the downward pilot and the wind turbine,the number of connections between the downward pilot and the wind turbine decreases significantly.In the simulation output of the 10m×10m space grid,the length of the final jump is in the range of 70m-280m.and it is in the range of 30m-160m in the simulation output of the 4m×4m space grid.The position of the connecting point between the lightning channel and the wind turbine blade is related to the rotating angle of the blade.The lightning connection points is mainly located in the 0-1 zone of the blade,accounting for 80%of the simulation times.2?The amplitudes of the vertical electric field and horizontal magnetic field are lowest in the center of the tower bottom and increase from the center to tower wall along horizontal radial.The field intensity is exponential decay along the height direction inside the wind turbine tower.Take the pulse current excitation source of ?1=0.5?S,?2=63?S,I0=9.5kA for example,the peak values of the vertical electric field and the horizontal magnetic field at the tower bottom are 4.1kV/m and 6.36kA/m respectively.The amplitudes are close to 0 in the distance of 10m along the height direction.The peak value of the induced voltage in the metal wire inside the tower caused by vertical electric field is 3.82kV.The peak value of the induced voltage in the electronic and electrical circuit caused by horizontal magnetic field is 44.76kV.Induced voltage and current in electronic and electrical circuits inside the wind turbine towers may exceed insulation level of terminal equipments and cause damage when lightning occurs.The research results of this paper can provide the technical basis for optimizing routing scheme inside the tower.3?Current amplitude frequency characteristic curves in wind farm transmission lines are oscillatory decay distribution in the first return stroke current and the subsequent return stroke current.The energy of the first return stroke current and the subsequent return stroke current are distributed in the 80 kHz and 160 kHz range respectively.The high frequency component of lightning current on power line is attenuated.The amplitude of lightning current decreases with the increase of distance.Take the lightning current wave of ?1=10?S,?2=350?S,I0=40kA for example,the current amplitudes are attenuated to 16.44kA,14.39kA,11.24kA respectively when x=3000m,6000m,9000m.The lightning current can spread along the power line in the wind farms and the current magnitude along the power line may cause the damage to the device,which will result in a large increase of the damage probability of the wind farm equipment.It is necessary to take some measures to protect equipments.The research results of this paper can provide the technical basis for lightning protection design in wind farms.4?Energy coupling testing from lightning to wind turbines is designed and carried out in Guangzhou Field Experiment Site for Lightning Research and Testing of China Meteorological Administration.The trigger lightning current measured in the experiment are precursor pulse current with damped oscillation waves.Through the analysis,pulse amplitude of the precursor pulse current can reach 850?1162.5 A;the spectrum is a single peak curve;the amplitude monotonically rises rapidly and reaches the peak value at the point of 351.875 kHz;then,the amplitude attenuates monotonically and rapidly;the energy of precursor pulse current is mainly concentrated among the low frequency range of 0?800 kHz.The peak value of induced voltage in phase line L2 of generator inside the wind turbine tower reaches-8.876 kV;the peak value of induced voltage in controlling line reaches 2.39 kV;the peak value of induced current in generator's phase L1—L3 circuit is 1.118 kA;the peak value of induced current in twisted pair laying circuit is only-60.55 A.5?On the basis of the research on the mechanism of lightning disaster of wind turbines,the paper presents main measures of lightning protection technology for wind turbines.Lightning protection device should be strengthened in the 0-1 zone,1-2 zone,2-3 zone of the blade in the design of direct lightning protection.High-permeability material can be used to shield the low frequency magnetic field caused by lightning.Energy coupling from lightning to signal lines can be reduced to the lowest level through the twisted pair wiring mode.The amplitudes of the induced voltage are related to the position of the lines inside wind tower.Electrical and electronic circuits should be laid in the weakest area of lightning electromagnetic field inside the wind tower.The damage caused by induced voltage can be reduced by methods such as earthing system,equipotential connection,the installation of SPD,shielding,proper routing,and so on.