Experimenters are well aware of the kind of energy that is necessary for the leader's breakthrough channel. To obtain the necessary information, they carried out numerous measurements of the current in the channel. Economical mode meant getting not more than 1A. Similar values were obtained in the previously calculated model. The height of the sprouting channel from the lightning rod is 50 m. The same speed of its movement is approximately 2 cm/μs. At the beginning of the path, the length of which is about 10 m, the channel consumes about 0.5 A (iL). It was in this place that the viability of the channel was assessed. The charge rate for 600 μs (Δt) was 0.3 mCal. To calculate it, we used the formula Δq = iLΔt = 0.5×6×10-4.
Taking a drop in the control voltage by 0,5 from the magnitude of the amplitude as the base, it can be predicted that the accumulated charge (Q) of the output capacity of the forming device will be 0.6 mCal. It is calculated as 2Δq. The required output capacity (C) at the voltage of 500 kV of the control pulse (ΔU) is 1000 pF. For its calculation, the following formula is used: Q/ΔU=6×10-4/5 × 105 ≈10-9 F.
Figure 1. The dynamics of growth of the current and of the counter leader from a lightning rod 50 m high at a control action of 500 kW in a thundercloud 50 kV/m
The author of the source of control actions for active lightning rods should understand that there is a certain technical problem for the solution of which a small technological volume is provided. In practice, the situation becomes even more complicated when the reference is to a source that can be used for devices of active lightning protection of medium height (approximately 15-20 m). At this level, the electric field of the charged cloud will be seriously weakened by the space charge of the corona from the inhomogeneous system on the ground surface. The approximate field height is about 10-20 kV/m. The potential of a vertex in such a weak field U0 = E0H can never be more than 150-400 kV. Consequently, it is not possible to charge the storage capacity with a crown current to the required voltage. It is necessary to consider the scheme of voltage multiplication. As an example, we can mention the familiar Marx scheme used to construct standard pulse voltage generators.
At a voltage below the set level, it is possible to save energy intensity by increasing the capacity of the capacitor bank. As a result, the storage capacitor of the control device becomes more capacious.
It is also necessary to increase the value of C2 Up to 0.1 μF in determining the step in the multiplication scheme U2 = 50 kV. And in this case, the large size of the capacitors to store electricity will not cause any problems. The charge coming to the devices will not disturb it.
In the figure below you can see the built-in dependence of the corona charge on time for a twenty-meter lightning rod with an active lightning rod. And after 20 seconds the created charge will still be 7 times less than the planned value calculated by experts.
Figure 2. Charge growth dynamics, supplied by the corona from the top of the lightning rod 20 m high in the electric field of a thunderstorm cloud, rising up to 20 kV/m in 10 seconds and not changing later*
Заряд, мКл – charge, mCal
Время, с – time, s
It should be noted that the electric field of a storm cell can be recovered even faster and a charge in such a case will be smaller. You can try not to use crown current, but use an inpedendent source to fill the energy storing capacitor. However, this method will be more expensive and would entail additional costs. Introduction of several coronary nodules to construct a more complex coronary system is a tempting offer. This is an alternative approach to the rapid aggravation of the corona apex, which is not capable of having a significant effect on the current of the developed corona. This fact was fully proved in the analysis carried out by the results of the constructed computer model.
* - illustrations are taken from the article of prof. E.M. Bazelyan "Are active lightning rods active?"
See also:
- What is offered by companies manufacturing active lightning protection
- Album of standard solutions on grounding and lightning protection
- Video recording of the lecture "Answers to the questions of designers"
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