Modeling and simulation of metal bellows in vacuum interrupters

2000

In the past years the vacuum switching principle has gained wide acceptance in medium voltage systems. While vacuum circuit breakers, where high short-circuit currents have to be mastered, nearly exclusively utilize CuCr 25 wt.-% to 50 wt.-% as contact material, the choice in vacuum interrupters for switching lower load currents (e.g. contactors) is less definite. The material must meet the requirements of low erosion losses on a high number of switching operations, low chopping currents, low tendency to generate HF transients and a satisfying quenching capability as well. Often materials based on refractory components are used, such as WCu, MoCu, WCAg, but also CuCr seems applicable. The aim of this work has been to investigate such contact materials with respect to their interrupting behavior on load and overload conditions. The experiments were carried out with a vacuum test chamber in a synthetic test circuit. The contacts were stressed by arc currents up to 7 kA RMS and a transient recovery voltage of 23 kV PEAK. Different contact materials have been compared with respect to their breaking capability and the state of their contact surfaces after arcing by means of scanning electron microscopy.

1999

Bouncing is a phenomenon often experienced during vacuum circuit-breaker (VCB) no-load operations. The effect occurs at the moment the interrupter contacts touch each other during closing. It is anticipated that the bouncing duration is somehow correlated with the oscillatory frequencies of the moving parts of the vacuum interrupter and of the kinematic chain of support and mechanical parts. The influence of bouncing on the capability for short-circuit making and capacitive switching is discussed. It is shown that the no-load bouncing time is not a relevant parameter to predict the performance of a VCB. Therefore it is not useful to set arbitrary limitations on the value of this parameter.

2016

The resistance of vacuum interrupters can be calculated from the geometry and resistivity of current carrying parts and the additional resistance of the contact points between movable and fixed contacts. Since vacuum interrupter contacts are designed as flat contacts facing each other, the resistance is mainly determined by contact force, hardness and resistivity of the contact material. It is known that the contact material changes consistency and structure during short-circuit interruptions within melting depth. Indeed, the overall resistance of a vacuum interrupter has been observed to increase by up to 60% after short-circuit making and breaking tests. Since the resistance increase across the switching device is considered by IEC and IEEE standards as one of the acceptance criteria for the integrity of the interrupter after tests, it is essential to understand the origin of this increase. Different causes are discussed, among them the change of grain structure, resistivity and h...

IEEE Transactions on Dielectrics and Electrical Insulation, 2000

According to the relevant IEC standards vacuum circuit-breakers have to meet various needs, e.g. the interruption capability, making operations, and dielectric strength. Besides the interruption of short-circuit currents, switching of capacitive currents causes high stress of the circuit-breaker. Switching of capacitor banks, overhead lines, or cables leads to very small currents in comparison with short circuit currents. After current interruption the circuit-breaker must withstand twice the peak value of the system voltage. Furthermore, restrikes can lead to voltage multiplication. This conjunction of relatively small breaking currents with high voltage stress must be considered in detail. This work introduces a test arrangement for combined tests of making operation, current interruption, and dielectric stress of a vacuum gap under capacitive switching condition. A test vessel permits investigations of various contact materials and designs. It is connected to a synthetic test circuit which provides the appropriate test currents and capacitive voltage. During the test sequence the contacts are stressed by inrush-currents up to 4.5 kA peak, followed by a breaking operation at 500 A peak and a subsequent capacitive voltage up to 50 kV peak. Both the appearance of pre-ignitions at contact closing and the behavior under capacitive voltage stress after breaking are indications of the contact surface conditions.

IET Electric Power Applications, 2018

The SWASTIK type radial magnetic field (RMF) contact design is widely used in vacuum interrupters. The mutually perpendicular petal limbs are a unique feature of this contact design. The focus of this work is to relate the Lorentz force acting on the arc with petal dimensions through closed-form expressions. Considering the petal limbs as equivalent to finite current carrying conductors, analytical equations are derived to compute the magnetic flux density at any point in space. The results are verified by using finite-element method (FEM) simulations of rail electrodes. The expressions are then used to compute the Lorentz force on the arc in SWASTIK contacts. The analytical predictions are compared with three-dimensional FEM simulations of a CAD model of the contacts. Applicability of the analytical results is investigated in the context of parametric variation of the radius, length and position of the arc and temporal variation of the contact current. The present work can be used in the first iteration of contact petal design. It is also applicable for the design of rail gun geometries.

IEEE Transactions on Magnetics, 2000

We present a model of a rotating arc by coupling a finite element method (FEM) and an arc model. A FEM is used to calculate magnetic field between electrodes taking into account the real current distribution in the contacts and in the arc; moreover, ferromagnetic effects and induced currents can be taken into account. A phenomenological arc model is used to predict the arc voltage, which depends on the local magnetic field and the arc length. This arc voltage is updated as the arc displaces itself across the contact surface. The information about arc voltage and local circuit equations is sufficient to find the velocity of the moving arc; hence this model seems more effective than models using Lorentz-forces to describe arc movement which need a priori knowledge about viscosity. This presented method seems to be a promising tool to describe the behavior of rotating arcs in vacuum circuit breakers.

2014 International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2014

In the vacuum interrupters employing the radial magnetic field (RMF) type of contacts, the constricted arc column is made to move on the surface of the contacts. The motion of the arc ensures that no particular area of the contact surface is overheated thus minimizing the emission of metal vapor and temperature rise of the contact surface and hence enhancing the current interruption performance. The arc motion is the result of the interaction of the arc current and the magnetic field produced by the flow of the current through the contacts. The velocity of the arc motion would thus be governed by the magnitude of arc current and the design of the contact. Higher the velocity of motion of the arc, higher would be the probability of a successful interruption. A wide range of the values of this velocity and the empirical formulae for the velocity have been reported in the literature. This paper reports the results of a research work which aims to arrive at the value of the arc velocity through experimentation and also through a modeling-simulation approach. The research also aims to establish a correlation between the arc velocity, magnitude of current and the contact design. This correlation is also presented in this paper.

International Journal of Advance Research and Innovative Ideas in Education, 2016

In an electric power system, switchgear is the combination of electrical disconnector switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply. The high-voltage circuit breaker was invented at the end of the 19th century for operating motors and other electric machines. The technology has been improved over time & there has been substantial growth in design & requirements of circuit breakers for various applications. There are merits & demerits of different types of breakers over each other. Vacuum Circuit breakers are generally operated with the help of mechanical mechanism. Circuit breakers operated with mechanical mechanisms are having limited life because of wear & tear of mechanical linkages. Replacement & maintenance lead to larger down time and become very costlier affair. To overcome these applications based demerits of circuit breaker, contactors came into the pictures. Vacuum contactors are widely used in medium voltage switchgear. In this project work, primary aim is to understand the different requi rements of vacuum contactors and different ways to achieve it. Also, we are going to cover design & simulation analysis of key components & features of medium voltage vacuum contactors like electromagnetic coils, vacuum interrupter, HT fuses, touch proof h ousing.