This paper presents measurement results for the random variable "vacuum breakdown voltage", obtained by the application of pulse, dc, and ac voltage. Parameters varied during the measurements were: 1) vacuum pressure and 2) inter-electrode gap width. The measurements were performed under strictly controlled laboratory conditions. Conclusions about the influence that the variable parameters in the experiment exert on the parameters of theoretical statistical distributions have been drawn, based on the statistical analysis of the obtained experimental results. The obtained results have been explained by the mechanisms constituting the process of electrical breakdown in vacuum.

Generalized lightning traveling-current-source return-stroke model (GTCSM) has been used to calculate the conductivity of the channel corona sheath and to examine the radiated lightning electromagnetic pulse (LEMP) during the return stroke. By using a two-layer cylindrical model of the lightning channel, the connection between the channel sheath conductivity and the channel discharge function is derived. The conductivities of the corona sheath for different channel line charge density distributions are calculated and compared with the predictions of transmission-line type of models. It is concluded that the GTCSM and the transmission line model (TLM) predict similar values of the corona sheath conductivity during the return-stroke process along the bottom portion of the channel on the order of 10 muS/m. However, the time for achieving more or less constant value of the corona sheath conductivity is about 200 ns for the GTCSM, about two orders of magnitude smaller than that for the TLM. Different line charge distributions along the bottom portion of the channel are analyzed, and corresponding waveforms of the radiated LEMP are calculated. The GTCSM eliminates completely all shortcomings of the ldquoengineeringrdquo traveling-current-source type of return-stroke models concerning the current discontinuities and the discontinuities of the current derivative at the place of the return-stroke wave front. Obtained results show good matching with the measured data for far distances (bipolar structure of the field derivative) as well as for very close distances from the strike point (monopolar structure of the field derivative). The presence of the upward connecting leaders from the elevated object and their influence on the line charge distribution along the bottom portion of the channel is considered. Given results provide better understanding of the channel corona sheath dynamics based on the remote measurements of the radiated LEMP as well as on the measured electric and magnetic field waveforms in the immediate vicinity of the lightning channel.

The principles that represent the basics of the work of the high voltage and high frequency generator with oscillating circuits will be discussed. Until 1891, Tesla made and used mechanical generators with a large number of extruded poles for the frequencies up to about 20 kHz. The first electric generators based on a new principle of a weakly coupled oscillatory circuits he used for the wireless signal transmission, for the study of the discharges in vacuum tubes, the wireless energy transmission, for the production of the cathode rays, that is x-rays and other experiments. Aiming to transfer the signals and the energy to any point of the surface of the Earth, in the late of 19th century, he had discovered and later patented a new type of high frequency generator called a magnifying transmitter. He used it to examine the propagation of electromagnetic waves over the surface of the Earth in experiments in Colorado Springs in the period 1899-1900. Tesla observed the formation of standing electromagnetic waves on the surface of the Earth by measuring radiated electric field from distant lightning thunderstorm. He got the idea to generate the similar radiation to produce the standing waves. On the one hand, signal transmission, i.e. communication at great distances would be possible and on the other hand, with more powerful and with at least three magnifying transmitters the wireless transmission of energy without conductors at any point of the Earth surface could also be achieved. The discovery of the standing waves on the surface of the Earth and the invention of the magnifying transmitter he claimed his greatest inventions. Less than two years later, at the end of 1901, he designed and started to build a much stronger magnifying transmitter on Long Island near New York City (the Wardenclyffe tower) wishing to become a world telecommunication center. During the tower construction, he elaborated the plans for an even stronger transmitter based on new principles. Due to lack of the funds Tesla was forced to sell or to return the devices and apparatus, he gathered in the Wardenclyffe tower facility, which intended to use to operate the tower. He left the tower in 1907 and since then he was mainly engaged in inventions that were not directly related to the electrical engineering. The unfinished magnifying transmitter on Long Island was demolished in June 1917 by the American government.