The alternating current flowing in the busbars of gas insulated switchgears (GIS) or substations generates Jouleheat both in the busbars and -due to eddy currents -in the metal enclosure. Besides heat conduction, the steady-state temperature of the conducting parts highly depends on the heat transfer between them and the encompassing gas insulation. The flow of the gas inside and outside the equipment that is, natural convection together with radiation determines the transferred heat. Such conjugate heat transfer problems can be treated numerically by finite element simulations. This paper compares the results of uni-and bidirectional coupling of electromagnetic and flow field simulations of a high voltage, gas insulated, threephase busbar. It also discusses the influence of radiation on the results.

Abstract. In order to reduce electric potential difference between the sheathings of single core three-phase cables, the sheathing is grounded and bonded at one or both ends of the cables. If the cable is long, double bonding has to be carried out which leads to circulating currents and increased power loss. Based on finite element (FE) calculations, this paper shows, that raising the sheath's resistance, by decreasing its cross section and increasing its resistivity, can significantly reduce this loss. The magnetic field close to the ground surface and the behaviour of the cable during fault conditions are also investigated.

A fast acting, all-metal valve has been developed for injecting pulses of neutral gases into a high vacuum. The theoretical motion of the piston is analyzed and compared with its actual dynamic and electrical operating characteristics. The design of the valve makes it possible to change the length of time the valve is open and thus vary the number of atoms admitted. Preliminary measurements of the pressure in the gas pulses have been made with fast stabilized ionization gauges. Reproducibility of measurement of the operating times of valve and gas pressure pulses was better than 95%. The gases used were hydrogen, helium, argon, and nitrogen.

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