The cathodic erosion of Cu, Cr and Cd has been measured at DC currents below 2000 A, and was found to be, to a first approximation, dependent on the total charge passed through the arc only. The observed erosion rates were 76, 22 and 400 μg C−1 for Cu, Cr and Cd respectively.Measurements on different kinds of copper indicate that the crystal grain size is of influence on the erosion rate.Of the total energy dissipated in the arc, about 25% is transferred to the cathode and 75% is divided between the losses to the surroundings and input to the anode. An attempt is made to correlate the erosion rate to one or more of the material properties of the metal.

The IEC TR 60890 provides an empirically based method for calculating the air temperature inside LV switchgear. One might assume that the method could be applied for estimating the temperature rise of the air inside MV equipment too. However, the IEC method assumes the uniform distribution of the power input, which is not normally the case for MV equipment. This paper explores what happens when the IEC TR 60890 requirement of uniform heat input is violated.The presented experiments and simulations show that changing the height of the heat source significantly affects the cooling conditions of the enclosure and therefore the air temperature distribution. The temperature distribution factor should be adjusted to apply the IEC method if the heat source is located in the upper part of the enclosure.

An experimental and theoretical study of the behaviour of a vacuum arc on Cu and Mo electrodes in an axial magnetic field at currents between 150 A and 16 kA has been carried out. The maximum magnetic field strength was 0.25 T. It was found that the influence of the magnetic field on both the high- and low-current arc was determined by the ratio between the cyclotron frequency and collision frequency of the electrons. The relatively small difference in behaviour of the Mo and Cu arcs was explained by the presence of neutrals in the Cu arc, while in the Mo arc these particles were practically absent. Some conclusions have been made about the electron temperature and the energy losses of the individual arc columns observed at high magnetic field strengths.

Electrical equipment will experience a rise in temperature during normal operation. During a development process, prototypes and laboratory tests will be required to make sure the temperature rises are within acceptable limits as defined by standards. The aim of having a tool to predict the temperature rise, is to reduce the number of prototypes and test loops needed in the laboratory during a development period. Advanced simulation tools such as CFD can give valuable results, however, they require expertise user and extensive compute and manpower allocation. This paper presents a practical design approach developed for providing a first, quick and rough estimate of the temperature rise of the most critical parts in an air insulated switchgear. The main idea behind the method is to first use the method described in IEC 60890 to estimate the temperature rise of the gas inside the switchgear. Then, simplified heat transfer calculations are used to estimate the over-temperature of critical parts relative to the surrounding gas. The accuracy of the temperature estimates will depend on how well the power input is known, especially the contact resistances. Further, it may be challenging to predict the influence of large metallic construction elements that may function as heat sinks.

MV switchgear experiences a rise in temperature during normal operation due to ohmic losses in conductors and contacts. If the temperature rise is too high, the switching device may be degraded. The focus of this paper is to find a value for the total heat transfer coefficient that may be applied to estimate the temperature of critical parts (open/close contact) of the load break switch in an enclosed MV switchgear, relative to the surrounding air (inside the enclosure) for future design. The values for the total heat transfer coefficient (including all transfer mechanisms) showed a relatively strong dependence on the surface emissivity and the actual design of the switch, but was less dependent on temperature changes within the relevant temperature range. Based on our findings, it is reasonable to assume that the total heat transfer coefficients may be applied in a first approximation of the temperature rise of a load break switch contacts relative to the surrounding air inside an enclosure. Further refinement could be obtained by taking the actual design of the switch into consideration, especially details influencing the emissivity and design elements influencing the heat conduction to adjacent conductor parts.

An arc fault inside metal enclosed switchgear will cause the pressure to rise and vaporization of electrode material may contribute to the pressure rise. An experimental study of high current arc erosion on copper electrodes in air has been performed, with an evaluation of fraction lost by gross melting and vaporization. All experiments were performed at NEFI High Voltage Laboratory in Skien, Norway. The measured mass loss from vaporization in our experiments seems to be negligible compared to erosion by gross melting.

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An arc fault inside metal enclosed switchgear causes a rise in gas temperature and pressure and may endanger the safety of personnel. Passive devices that effectively cool down the gas with limited extra cost are of special interest to investigate. An energy based evaluation of different gas cooling installations and materials related to internal arc faults in medium voltage switchgear has been carried out. Temperature measurement in inhomogeneous gas flows constitutes a central part of this study. A thermal efficiency of 79 % (∆T of 540 K) is observed with an aluminium mesh as absorption material. The energy distribution in the system is visualized in a Sankey diagram showing that 2/3 of the energy is absorbed in the arc compartment. The remaining energy enters a buffer room, from which about 50 % escapes through an energy absorber. Depending on design, between 5 and 10 % of the total energy input from the electric arc escapes to the surroundings. By introducing boric acid in the absorber, cooling by ablation seemed to take place. Depending on buffer and absorber design, the observed pressure rises in the arc compartment indicate that some precautions may have to be taken to avoid excessive stress on the switchgear compartment (arc compartment). Based on the experimental setup presented in this paper, 5 of 6 tests with different designs passed the standard safety test.