4. THOUGHTS ABOUT THE LIGHTNING PROTECTION OF
4.5 P OSSIBLE SOLUTION FOR NON - METAL FRAMED VEHICLES
Technically, the aim is to capture the lightning and conduct it towards the ground. To find the position of the lightning arrestors, we should use the rolling sphere method. This is a procedure in designing the lightning arrestors, according to which protection is appropriate, if a rolling sphere of given radius cannot come in contact from the outside of the protected surface without touching the lightning arrestor. In practice, this means that we are moving a sphere of given radius in the space around the protected object (building, vehicle, etc.) and where the sphere touches an object that will be the touchpoint of the bolt. With this design method the given object can be protected, because the protected surface will be part of the protected space, since the sphere reaches the end point of the protective conductor (better known as lightning arrestor) first. For this design method there are different kinds of 3D software available on the market. As a result, we get a blanket-like surface around the examined object, behind which the protected space is located (Figure 37).
Figure 37: Types of 3D diagram of the rolling sphere design [74][75]
Nowadays, the technology (Figure 38) is available for a device to laser scan an object in 3D and design its rolling spherical editing in 3D to make the protected areas. Its great advantage is that it’s not necessary to draw the examined object separately in advance.
Figure 38: 3D rolling sphere design for buildings in real life with 3D scan [76] [77]
According to the above-mentioned method, the lightning is most easily “captured” by a well placed metal body which therefore is protecting the surfaces. In the case of electric vehicles, for this purpose, a mechanically fixed radio antenna (mast) is partially suitable.
It is important that the any strong wind should not bend the antenna in any direction, because this is protecting part of the body. For this, adequate mechanical placement is a must. Moreover, the vehicle must be provided with arrestors on several other points as well.
Figure 39: Rolling sphere design for a commercially available car
(Edited by author)
The Figure 39 shows us an electric vehicle available on the commercial market, currently manufactured with a metal body. On the left side, the actual, original condition of the vehicle is visible, on the right side the rolling sphere design with the planned arrestors (red markings) is detailed. We should notice that thanks to the arrestors, the sphere is not contacting the vehicle surfaces, therefore, they are protecting not only the automobile, but the passengers inside the car. The Figure 39 shows us one variation of the theoretical design and placement of arrestors. Of course, in the case of the vehicle’s complete design, the full three-dimensional protection of the body should be compiled and completed. For the implementation of lightning protection, not only capturing, but conducting the lightning current is also a problem to solve. When we can speak about designing, the largest stress must be considered as engineering idea, in this case this means a situation when only one arrestor and one conductor would conduct the lightning current. The system should be designed to be capable of conducting even 200 kA of current impulse without any damage and warming. For this, a 50 mm2 cross-section conductor is perfect. The lightning current must be conducted to the ground from the body. A solution to this might be a movable conductor that automatically reaches the
ground in different intervals when the car is stopped/parked. To avoid excessive and unnecessary requisition (opening of this device at every stop, then closing at start), in practice the movement of this device should be controlled by an electric field strength gauge or by storm warning system (TWS). This means that the mobile conductor would be automatically activated when clouds start to develop in the sky and therefore the electric field strength changes measurably. A further task is the protection of electric appliances against the induced overvoltage that may appear in such cases. Electric devices in different automobiles are very sensitive to overvoltage. Protection of such appliances can be solved by installing them into metal housings, and electric cables may be threaded through protective tubes or provided with electric shielding.
4.6 Chapter summary
Technology is continuously developing. Our tools are becoming faster and smarter.
Some tools and vehicles etc. may be connected to a common system in the future, forming a kind of community. If the above activities are implemented in practice, we can usually speak of a smart city, which, regardless of its size, has the same public tasks that can be clearly identified and grouped. As technology advances, different types of electric vehicles are becoming more common on the roads. To achieve lighter weight for the vehicles, the frame will be produced from some kind of non-metal material. The frame is not protecting the passengers and also the electric parts of the vehicle during the lightning.
In this chapter this kind of problem and my recommended solution were introduced.
I made a theoretical engineering opinion and recommendation on the specific lightning protection requirements of non-metal (e.g.: composite) body electric cars as a possible area of theoretical research and practical implementation in the future [P4]107 [P12]108[P13]108
Nowadays, it is not in the standardization process at the moment, the performance of sensitivity tests based on model experimentation may be an area of engineering and standardization field of research in the future.
107 See: p.153
108 See: p.154