Physical Simulation of the Spectrum of Possible Electromagnetic Effects of Upward Streamer Discharges on Model Elements of Transmission Line Monitoring Systems Using Artificial Thunderstorm Cell

The results of a physical simulation using negatively charged artificial thunderstorm cells to test the spectrum of possible electromagnetic effects of upward streamer discharges on the model elements of transmission line monitoring systems (sensor or antennas) are presented. Rod and elongated model elements with different electric field amplification coefficients are investigated. A generalization is made about the parameters of upward streamer current impulse and its electromagnetic effect on both kinds of model elements. A wavelet analysis of the upward streamer corona current impulse and of the signal simultaneously induced in the neighboring model element is conducted. A generalization of the spectral characteristics of the upward streamer current and of the signals induced by the electromagnetic radiation of the nearby impulse streamer corona on model elements is made. The reasons for super-high and ultra-high frequency ranges in the wavelet spectrum of the induced electromagnetic effect are discussed. The characteristic spectral ranges of the possible electromagnetic effect of upward streamer flash on the elements of transmission line monitoring systems are considered.

CORRECTION OF THE METHOD FOR MEASURING THE AMPLITUDES OF THE CURRENT OF THE IMPULSE ALONG THE LONG EARTH ELECTRODE

An improved method for measuring the amplitude reduction of the lightning current impulse as it flows from the beginning to the end of long horizontal earthing arrangement using ferromagnetic recorders has been substantiated. Two existing methods of pulse amplitude measurements at high voltages, the magnetic recording method and the method using a shunt, are used in justification. It is noted that in a number of cases it becomes necessary to determine the decrease in the pulse amplitude as it flows on a long object. This leads to the need to develop a method for performing such measurements. As an example, a long horizontal earth electrode was investigated when a lightning current pulse moves on it. Based on experimental studies in natural conditions, an improved method for measuring the decrease in the amplitude of the lightning current impulse along a long earth electrode is proposed. The proposed method has a measurement error not exceeding 10 %, and allows simultaneous measurements of the amplitude of the current strength at given points of the object, which can amount to tens or even hundreds. This method is implemented in a simple design and has an affordable manufacturing cost. The results of the experiments performed make it possible to recommend the corrected measurement method for practical use on existing electrical installations. The use of ferromagnetic recorders for recording and measuring the lightning current in areas of complex earthing arrangements is relevant for practical reasons, which include the possibility of measuring during a long wait and long-term storage of measurement results, does not require additional power sources and provides the possibility of synchronous measurements at various points of the grounding device. An important feature of the method is safety for technical equipment and personnel.

Estimation of voltage waveform at top of transmission line tower struck by lightning of negative and positive polarity

The object of research is a circuit that simulates a lightning strike to a tower of 220 kV power transmission line, taking into consideration the reflection of a current wave from 10 nearest towers. Computation of the voltage arising at the top of the struck tower is necessary further to determine the lightning performance of transmission line by various methods. The lightning current has several maxima, in the case of a positive impulse polarity and, accordingly, several minima, in the case of a negative polarity, which are generally being called peaks. In addition, the lightning current impulse has a non-constant steepness in the entire area of current rise up to the first peak. The approximation of the real lightning current by simplified mathematical expressions cannot take into account all its real features. For a more detailed study of transient processes caused by thunderstorm activity, there is a need to use oscillograms of real lightning currents when modeling. The problem of determining the voltage at the top of the stricken transmission line tower was solved using circuit simulation. For an in-depth study of how the shape of the lightning current impulse affects the shape of the voltage at the top of the tower struck, digitized oscillograms of real lightning currents were used. The simulation was carried out for 7 negative lightning impulses with the first peak varying from –33.380 kA to –74.188 kA. In the case of positive lightning, 3 oscillograms were used with the first peak varying from +38.461 kA to +41.012 kA. The article shows that the shape of the front of the lightning current impulse and the amplitude of the first peak of the lightning current have a decisive effect on the maximum voltage value at the top of a power transmission line tower struck by lightning. The maximum voltage occurs precisely at the front of the current wave before the first peak of the lightning current. Therefore, the back flashover of the insulation from the tower to the phase conductor is most likely at a moment in time at the front of the current wave. By the time the maximum current is reached, the voltage at the top of the tower will be reduced by several tens of percent, compared to the maximum voltage at the tower, which occurs much earlier at the front of the current wave. The conducted research contributes to the development of methods for calculating the lightning performance of power lines and extends the scope of application of circuit simulation programs.

On the Characterisations of the Impulse Breakdown in High Resistivity Soils by Field Testing

This paper presents experimental results of high-current impulse tests on six ground electrode configurations. A high impulse current generator is employed to inject different magnitudes of current into these rod electrodes, under both positive and negative impulse polarities. The effect of increasing the number of rod electrodes, hence the resistance at DC or steady-state (RDC), on the impulse response of ground electrodes is analysed. From the analysis of the results, it was found that the larger the size of rod electrodes, the less current-dependent Zimpulse becomes. The percentage of reduction of impulse impedance, Zimpulse from its steady state, and RDC values are found to be independent of impulse polarity. However, as the voltage magnitudes were increased, an occurrence of breakdown was seen, with higher breakdown voltage seen in negative impulse polarity in comparison to positive impulse polarity. Relatively, the higher the breakdown voltage is, seen in the ground electrodes subjected to negative polarity, the faster the time to breakdown is.

Thermal Simulation of a Conductive Fabric Sheet Subjected to a Lightning-like Current

A sample of electroconductive fabric subjected to a lightning-like current impulse is analyzed in this contribution. A multiphysics simulation is used to calculate the temperature distribution produced by a lightning-like current flowing through the material sample. A decoupled, electromagnetic (EM) and thermal, simulation was conducted for the analysis and is explained in the paper. The scaling factor calculation to represent the energy presented during current impulse tests is also detailed. Numerical results present patterns that agree with experimental tests reported in the literature and represent an additional tool for the phenomena insight.

Nutritional Quantification and Shelf Life Analysis of Non-thermal Processed Coconut Juice

Nonthermal processing methods are attracted by many food and beverage industry because it can kill the microbial contamination under mild temperatures used in thermal processing; They can sustain flavours, essential nutrients, and vitamins undergo minimal changes. The objective of this research was to evaluate nonthermal processing as the high current impulse generator (HCIG) and investigate the reduction the contaminated microorganism in coconut juice under the batch and continuous treatment of HCIG. The physical, biochemical and nutritional changes of treated coconut juice were also investigated. The application of the direct electricity through cathode of high current impulse generator (HCIG) in 1,170 chambers contained the contaminated coconut juice. Significantly reduction both Saccharomyces cerevisiae and Escherichia coli as 5-log were found when treatments were applied with impulses at 5.17 kA. Comparison of nutritional value of non-thermal processes before and after high current impulse was showed no significant differences between main nutritional values and free amino acid. For the continuous HCIG treatment under the treatment of 5.17 kA current with 9, 15 and 30 pulses with 5 L coconut juice at the flow rate of 1 L/min, results from initial concentration at 1.41 × 105 CFU/mL showed that S. cerevisiae reductions were found 78%, 66% and 96% as increasing number of pulses as 9, 15 and 30 pulses, respectively. The increment of microbial reduction with the increasing number of pulses was also detected as 78 %, 82 % and 96 % from 1.11 × 105 CFU/ml E. coli. Results revealed that the microbial reduction with HCIG under batch treatment were successful preserved the nutritional components of the coconut juice without significant physicochemical changes.