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.
Modeling of pressure rise in SF6 GIS (Gas Insulated Switchgear) due to internal arc faults is a complex and challenging task, due to a large number of highly variable factors, which influence the whole process. This is especially the case in GIS with high rated short circuit currents, where the effects, such as material evaporation and erratic arc behavior, and consequently the pressure build-up rate, are much more pronounced. These severe conditions ultimately determine the design limits and must therefore be carefully investigated. The enhanced internal arc simulation model, presented in this paper, considers the impact of evaporation of different materials on gas properties and the pressure rise, as well as the dependence of released arc energy, thermal transfer and evaporation intensity on the state of gas. The experimental set-up and the test configuration, used to validate the calculation results, are evaluated and discussed. An evident finding, which is supported by measurements, is that the implemented improvements of the basic simulation model (introduced in the Technical Brochure 602 by the CIGRÉ working group A3.24) increase the prediction accuracy of GIS withstand performance during internal arc faults.
Nowadays, high voltage circuit breaker (CB) simulations are mostly based on Computational Fluid Dynamics (CFD) models. Such simulations require significant computer resources. An alternative approach is to use enthalpy flow models, which do not use space discretization of the interrupter unit chambers and valves. Gas flow is calculated based on state of gas in adjacent chambers and valve settings. However, the valve shape has significant influence on the effective flow cross section between chambers. Therefore, in order to ensure correct simulation results, it is necessary to determine the correct values of discharge coefficients for all valves in the interrupter unit of a circuit breaker. In this paper, the discharge coefficients were determined by combining a series of CFD and enthalpy flow simulations for each valve in the interrupter unit. After that, discharge coefficients are used as input for further simulations based on the enthalpy flow model. This way, benefits from both models are combined: more precise gas flow calculation and faster simulations. The proposed novel approach is validated in a high-power laboratory by pressure measurements on a 420 kV 63 kA self-blast circuit breaker.
The self-blast type circuit breaker has been developed to reduce mechanical operation energy by building up the pressure of arc extinguishing gas flow from the heat of the arc itself. Unlike a puffer type, breaking performance for self-blast type are influenced and sensitive by various factors inside interrupter parts, such as the nozzle structure, chamber shape as well as amplitude of short circuit current. These days, particularly, it has been difficult to secure a low current breaking performance as the circuit breaker has been compacted. The currents for breaking test duties belong to from 10% to 30% of the rated breaking current in accordance with IEC standard. Although the arc energy for interruption is lower than the rated breaking current test duties, the breaking performance could be lower than the tests because the transient recovery voltage (TRV) after the current zero is relatively high. The capability of interruption is related to dielectric recovery after the arc quenching. Therefore, a complex analytical method is needed to secure the breaking performance for the current and to improve the performance by using the limited gas flow inside the interrupter parts. In this paper, it described the techniques to verify breaking performance such as hot gas flow analysis and dielectric analysis. And it has studied a method for improving the performance with various design parameters using computational fluid dynamics (CFD) programs and high power laboratory test. Finally, this paper shows us the improvement of dielectric recovery performance for the self-blast type circuit breaker.
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.
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