The density and SF6 gas pressure distribution along the nozzle of a HV circuit breaker plays an important role in the process of current interruption. Therefore, the analysis of the pressure distribution is essential for researchers and designers of HV SF6 circuit breakers. In this paper, simulation software for HV SF6 circuit breakers, which is based on an integral-physical enthalpy flow arc model, and CFD simulation software were used for determination of the pressures inside the interrupter chambers and pressure distribution along the nozzle. The calculated results are verified by comparison with the experimentally measured transient gas pressures for several positions inside the puffer cylinder, nozzle throat, upstream and downstream of the nozzle in a 252 kV puffer type SF6 circuit breaker during no-load operations and breaking of short-circuit currents. Comparison of the calculation results with the measurements revealed very good matching. In addition, the same simulation method is applied to some other types of HV circuit breakers and the obtained results are analyzed and discussed.

A considerable part of the energy released by electric arc during breaking of a short-circuit current is being absorbed in the moving and stationary arcing contacts. The rest of the energy is being released as thermal stresses of the nozzle and of other parts of the arcing chamber, as well as heating, dissociation and ionization of the arc extinction medium, and in losses to the nearby environment. The absorption of the energy causes heating, melting and finally the vaporization of contact material and it is the main cause of contact erosion. It is obvious that the process of arcing contact erosion has a considerable influence on the state of SF6 gas in the contact gap, but also in the adjacent interrupting chambers. A contact erosion model is incorporated into a computer program for high voltage circuit breaker interruption simulation. The calculated contact erosion intensity is verified by comparing the calculated change in the contact shape and mass losses with experimentally obtained data. The influence of vaporized contact material on the state of SF6 gas in the interrupter chambers and the dielectric performance of the contact gap is also analyzed and discussed.

This paper focuses on the optimization of the design of high voltage transmission lines in order to reduce the negative impact of electric and magnetic fields. Within this paper the results of measurements of electric and magnetic fields near 400 kV transmission line were presented. Measurements were performed in the middle of the range between two towers, because at this point transmission lines are closest to the ground. In order to make better validation of the used calculation models of electric and magnetic fields, measurement of temperature, pressure, humidity and height of particular transmission lines in the middle range, were performed simultaneously. The values of current and voltage on the transmission line, at the time of measurement of the fields, are also given. Based on the measured values of electric and magnetic fields, validation of calculation was performed. This paper also contains a brief comparative analysis of regulations on non-ionizing radiation of power facilities that are in use in some European countries, as well as recommendations of the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Calculation of electric and magnetic fields of different configurations of 400 kV transmission line, were performed in order to find optimal solution in terms of reducing the negative impact of electric and magnetic fields of high voltage transmission

The biggest drawback in modelling the reliability of high voltage circuit breakers is the lack of access to data on failures in service, due to the very long lifetime of circuit breakers. This paper presents the application of reliability calculation based on Bayesian statistics to a 245 kV SF6 circuit breaker and its operating mechanism. By using the Bayesian theorem, the prior probability density function of failures in circuit breaker components, which is calculated based on data on the circuit breaker and the operating mechanism failures in service, is combined with data on the failures registered during an extensive mechanical development tests. During the tests more than 32000 "CO" (close-open) operations were performed. Based on the posterior probability density function, the reliability of circuit breaker components and the overall reliability of the breaker is estimated. The paper also presents some analysis of the impact of circuit breaker maintenance on its reliability.

Energy released by electric arc during short circuit switching is mostly absorbed by the surrounding cold SF6 gas. However, a considerable part of this energy is also transferred and absorbed by other elements of the circuit breaker interrupter which are located near the electric arc. The most important parts are the transfer of energy to the arcing contacts and to the nozzles, absorption of the energy by these elements and the resulting effects. The absorption of the energy causes heating, melting and finally the vaporization of structural material and it is the main cause of wearing of arcing contacts and nozzles, where the latter is commonly referred to as the nozzle ablation. The nozzle ablation causes an increase in the nozzle throat diameter which generally has a negative effect on the circuit breakers breaking performance. The other significant effect is the mixing of SF6 gas and the nozzle vaporized material in the nozzle space and in the surrounding chambers. It is obvious that the ablation process has a considerable influence on the state of SF6 gas in the contact gap but also in the adjacent interrupting chambers, in particular on the state of gas in the thermal chamber in case of self-blast interrupting units. In this paper, a method of calculation of intensity of nozzle ablation is presented as well as a variety of calculation results. The calculated nozzle ablation intensity is verified by comparing the calculated results of the nozzle diameter increase and mass losses, with experimentally obtained data. In addition to the nozzle ablation intensity, the influence of the ablated nozzle material on the state of SF6 gas in the thermal chamber is also analyzed and discussed. The model is incorporated into a computer application for high voltage circuit breaker interruption simulation.