# Non-Real-Time Wireless System for Lightning Effect Measurements
## 2 Theory  
The study of the impact of lightning discharges is of great importance for the everyday life of people, the operation of facilities and their technical equipment. The frequency of storms depends on the region of the world and on topography. The lightning discharge takes place in the thin core of the channel, formed during the stepped leader stage before the first return-stroke and during the dart leader stages before the next subsequent return-strokes. Therefore, this process can be compared to the flow in a conductor of a fast-varying surge current with a very high peak value in the order of tens of kiloamperes. The effect of this is the propagation of an electromagnetic field in the form of the so-called LEMP (Lightning ElectroMagnetic imPulse) [5]. The LEMP couples with the conductive transmission lines and induces dangerous overvoltage (Figure 1). Among others, sensitive electronic systems such as avionics, power grid supervision systems, or various types of measuring and monitoring devices located on telecommunications masts are at risk. The measurement systems of surge waveforms (naturally and artificially generated) are specialized systems. They enable the recording of fast-changing waveforms with a voltage up to megavolts and a current in the order of a hundred kiloamperes. They must perform measurements with a high sampling frequency due to the nature of lightning phenomena [6;7]. Surge waveforms are defined in different standards and they represent discharges in clouds and between cloud and earth. For example, in lightning protection of aircraft, a pulse numbered as WF4 with the waveshape 6.4/69 us (rise time/time to half-peak on the falling slope), representing the lightning impact, is defined in the DO-160 standard, which is dedicated to immunity tests of avionics [8;9]. Therefore, what is needed is a system capable of recording the surge waveforms with the time resolution in the order of hundreds of nanoseconds [2]. The method of determining the time parameters of the impulse time parameters is shown in Figure 2. One can find the same definition of rising time and time to half-peak on the falling slope in the lightning protection standard PN-EN 62305-1 [10] for buildings and the standard for electromagnetic compatibility PN-EN 61000-4-5: 2014-10 [11]. Figure 1: Scheme of propagating the LEMP [1;2;5]. As mentioned, lightning discharge measurements are recorded using various types of devices [12; 13; 14]. They are determined by the place, working time and type of the tested signal. Monitoring systems use dedicated solutions [15; 16; 17]. In laboratories, oscilloscopes are used [18; 19]. The parameters of these devices allow for the accurate recording of the tested waveform, but they do not always provide protection against interference and over-voltage. Each system uses security measures to ensure the safety of people and equipment, and one must be aware that conducting high-voltage tests is a risk. For lightning resistance tests, standardized waveforms are used as discussed (e.g., avionics). Their measurement is primarily the protection of measuring cables against LEMP [20]. Another method is computer simulation [21; 22]. It enables 3D modeling and examination of the same object many times without changing the parameters [23; 24; 25]. It is a very good solution for protection design. However, a mathematical model is necessary. It can be created in a laboratory by measuring the values tested. [26] It is also very important to compare the results of experiments and simulations. This allows to determine whether the designed model corresponds to the real object [26; 27]. Current shunts, Rogowski coils and high-voltage measurement probes are most often used to measure different surge waveforms [28; 29]. They are used both for recording the lightning current (mainly at stations located at high facilities), as well as during laboratory and field tests using impulse current/voltage generators [30].