Lightning protection

Below is an evaluation of risks for airborne systems (pdf available on request):


A variety of innovative airborne concepts are being developed to capture the wind energy available at higher altitudes, facilitate wireless communication and provide heavy lift capability. These airborne systems will be in close proximity to cloud cover and exposed to increased risk of lightning strikes. A two-dimensional physics based formulation that was recently developed to investigate the potential field behavior about circular sections was used to develop uniform and tapered cylindrical elements. These elements were then combined to approximate the total charge and lightning behavior about an airborne wind turbine and a heavy lift airship. Surface electrical charge and lightning collection area are developed as a function of elevation, body shape, cloud cover and leader properties. The surface charge density is utilized to compute the degree of field intensification on the body periphery in order to determine the level of susceptibility of the airborne system to lightning strikes. It was observed that as airborne bodies move closer to the thundercloud the ambient potential field becomes more highly perturbed and leads to greater risk of lightning strikes. The lightning collection area was shown to increase with elevation of the airborne body and decrease with increase in the leader propagation angle. Keywords: Lightning strikes, physics based formulation, electric potential field, composite shapes, surface electrical charge, lightning collection area, strike frequency

See also AI tech predicts time and place of lightning-strikes .

Several possibilities to protect airborne systems has been achieved or envisaged:

Some of them concern the tether (see below, in bold):

Tether Cable Design Attributes:
Electrical Conductors - ETP stranded copper, high-strength copper alloys, copper aluminum, with bare tinned or
silver plating constructions
• Optical Fiber Components - SMF-28E incased in SS steel tube or simplex designs cabled within power cable cores
• Data Pairs - Meeting Ethernet, RS-232, RS-485 and Bus-data rates can be offered
• Strength Layers - High modulus synthetic strength layer designs using Kevlar®, Twaron®, and Vectran®, for high fatigue life
• Insulations - Lightweight copolymers and fluoropolymers are chosen specific to voltage requirements from 300v to 4.5kv
Shields - Lightweight shield designs are available for EMI/RFI, static dissipation, as well as lightning strike grounding considerations
• Jackets - Materials such as TPE, Polyurethane, Hytrel®, HDPE and others, considering outdoor environment, cycle duties and handling system are carefully designed into each aerostat tether Falmat® produces
• Aerial jacket profile extrusion designs can be offered for reduced strum and drag, high visibility colors, reflective coatings, and external lighting features can be added

Other means are also envisaged.

Below is Wind Farm Lightning Protection System With a Kite publication (pdf on request):


Height of tips of the high power wind turbine blades reaches over 200m. The objects of this height, either offshore or onshore, are often targets of direct atmospheric discharges. The existing concept of protection is not capable of providing a complete protection of all wind turbine elements against lightning currents and induced over-voltages, thus lightning strikes constitute a very frequent cause of wind turbine failures and outages. A novel concept of wind turbine protection against direct lightning strikes is presented. The idea is to place a protective system, in the form of grounded conductive wires, in close vicinity and within the area of a wind farm, the tips of the wires being kept by kites at a desired height. Height of a protective wire has to be significantly above the topmost point of any wind turbine. Stormy clouds, carried by the wind, approach first the very high tips of the protective wires, which usually results in an upward discharge, relieving charge from the clouds, thus making the probability of lightning strikes at the wind turbines considerably smaller.

If an airborne system is envisaged to protect a farm of regular wind turbines, it could also protect a farm of AWES?

Great idea to fly kites with metal tethers over a windfarm when a storm is coming. What could possibly go wrong?