Abstract The breaking capacity of a medium voltage (MV) rotary SF6 load break switch (LBS) can be improved by incorporating permanent magnets into the stationary contacts. The magnetic field is intended to blow the switching arc root towards a recessed space at the stationary contacts thereby preventing reignition of the arc after current zero. Making and breaking tests of load current 630 A were performed comparing the switching performance of load break switches equipped without a permanent magnet, with a ferrite and with a neodymium magnet. The impact of different polarity arrangements of the magnets in the three phases is also considered and analysed. In order to understand the arc behaviour caused by the effect of permanent magnet, arcing times and arc voltage were measured and evaluated. The results show that the arc voltage depends on the direction of the electromagnetic force, which is determined by the phase current direction but also by the polarity of the magnets. When the force is directed towards the recessed space at the stationary contacts, the arc voltage is notably higher than in the case where the arc is blown in the opposite direction. The higher arc voltage is a reliable indication that the length of the arc is increased, which significantly reduces the risk of both thermal and dielectric breakdowns after the first current zero. The consequences are noticed first in the reduction of the number of missed current zeroes and second in shorter minimum arcing times. An adverse arrangement of the magnet polarity in the three phases increases the number of missed current zeroes.

Abstract This paper presents the study of deformations and Von-Misses stresses of the main shaft system during opening and closing operations of a rotary SF6 load break switch (LBS). The shaft consists of three axially connected parts made of steel where components are on ground potential and of plastic material, which is on high potential. The insulating shaft carries three rotating knife-blade contacts for the three phases. Static deformation of the insulating shaft is calculated by applying a defined torque between the two ends of the shaft. The results allow deducing the dynamic deformation. Maximum values of Von-Misses stresses are located at the geared connection between the plastic and the steel shaft. The rotation of the shaft system is measured synchronously by two optical rotary encoders in the front and rear sides of the LBS. The results confirm the twisting of the shaft system and provide its elastic deformation values. Travel curves obtained on both side of the LBS show different courses with respect to overtravel and rebound. Discrepancies can be explained by the deformation of the main shaft due to the acting forces, whereas manufacturing tolerances resulting in loose have a certain contribution.

The breakdown voltage during interruption of capacitive currents is defined by two physical quantities: the electric field and the gas density field, which are calculated in different calculation domains and using different mashes. In order to calculate the breakdown voltage, it is necessary to map these two mashes and calculate the ratio density/electric field in every calculation point. The straightforward solution is to pair each density cell with the nearest cell from the electric field mesh, based on their coordinates. Although this solution gives good results, it is very time consuming. Therefore, this paper presents a new approach for mapping of two meshes based on the algebra of fractal vector, so called Bosnian algebra. This approach does not search the meshes for the closest pair based on the coordinates of each point, but instead uses only the assigned cell indexes and simple fractal operations to determine the neighboring cells. This way, the search for the nearest pair is much more efficient and faster.

High reliability of HV SF6 switchgear makes an internal arc fault an extremely rare event. However, its occurrence cannot be completely avoided, and therefore must be considered in the design process. Internal arc testing in SF6 is not recommended due to its harmful environmental impact, but if necessary, tests should be performed only inside special containers, that will prevent the release of SF6 into the atmosphere. Having in mind that tests in SF6 and air are not yet fully comparable, accurate modeling of pressure rise due to internal arc faults is still the main means to evaluate required design parameters of SF6 switchgear in respect of safety from internal arc faults. A simulation tool, which calculates the pressure rise due to an internal arc inside a metal-enclosed SF6 compartment, was developed and used in the design of a new HV GIS. The calculation procedure and obtained results were described and discussed. Validation of the tool was performed using experimental data from SF6 internal arc tests, dating back several decades ago, when internal arc tests in SF6 were not questionable as today.

Partial discharges, as their name states, only partially bridge a small portion of electrical insulation in the form of a tiny electrical arcs, which burn inside the defects that could appear in insulation system. Because of the fact that extruded cable system insulation is very sensitive on partial discharge activities detection vise, partial discharge measurements could be used as a powerful diagnostic tool in evaluating the actual condition of cable system through measuring procedures during after laying tests. If such procedures would be included in standards, they would provide an effective way to identify and detect the defects that might appear during the cable system installation and to forestall their appearance during exploitation, ultimately reducing the probability of failure. Very first aim of this paper is to address some shortcomings of current IEC standards related to analyses of cable systems with polymer insulation (IEC 60840 and IEC 62067). In order to justify these statements, a review of a recent alignment between IEC 60840 and IEC 62067, simulation support, using the contemporary software tool (COMSOL Mph), backed up with experimental results for two artificially induced defects in cable accessories, are provided in this paper.

In this paper, the impact of several 145 kV 40 kA GIS (Gas Insulated Switchgear) circuit breaker design parameters, such as length of the main nozzle throat, contact travel and average opening speed, on the estimated breakdown voltage of the contact gap of an interrupter during capacitive current breaking is analyzed. A new approach for breakdown voltage estimation, which provides full correlation between all circuit breaker design parameters and dielectric characteristics of the contact gap and the criterion for breakdown occurrence, was used for this purpose. The estimated capacitive current breaking capability of the circuit breaker was verified by type testing in KEMA High Power Laboratory, the Netherlands.