AMASIS: Getting electric arc simulation right
Shortcircuit current breaking inside a circuitbreaker chamber involves phenomena ranging from plasma fluid dynamics to mechanical destruction. A multiphysics macroscopic simulation tool can be used to model what is happening to improve circuitbreaker design.
Modelling is very important for circuitbreaker development since it makes it possible to study different configurations before tests and investigate specific behaviour. A modern high voltage circuit breaker is a lot easier to describe than to model: separate two contacts in a gas with good dielectric properties; an arc forms and carries the current; blast this arc with the gas to cool it and quickly extinguish the arc. The difficulties come from the fact that we are dealing here with a complex system where multiple nonlinear physical processes are occurring and interacting simultaneously, including phase changes, convection, conduction and radiation. And all that in a small module with moving parts where arc temperatures can reach 20,000 °C and pressure can be over 100 atmospheres (10 MPa).
Fiveminute simulations
Despite improvements in computing power and software, simulating precisely what is happening inside the circuit breaker is usually very time consuming. A new modelling approach from Alstom is changing that. AMASIS (Arc Model for AMESim Interrupting Simulation) is a macroscopic model of the core of the circuitbreaker chamber that can perform a simulation in only five minutes.
On the left : Microscopic modeling ; On the right : Macroscopic modeling
The AMESim part refers to the commercial software for modelling multidomain systems from LMS Imagine.Lab on which the Alstom application is based. In AMESim, models are described using nonlinear timedependent analytical equations that represent the system’s hydraulic, pneumatic, thermal, electric or mechanical behaviour. Standard AMESim modules are used to model the different parts of the circuit breaker other than the core, with AMASIS concentrating on the zone of influence of the electric arc itself.
Modelling the joule effect
Measuring up

MC3: Getting down to detailAMASIS has the great advantage of allowing parametric studies to be done quickly, but as its “macroscopic” label suggests, it gives a broad picture. This is useful for predimensioning a device, but the results then have to be refined, which is where MC3 comes in. This is a finite elementsmethod design and analysis software suite based on a physical model of the operation of interrupters and fuses on high voltage electric networks. The challenge is to model the highly complex plasma phenomena occurring in the interaction of a highvelocity dielectric gas jet with an electrical current. MC3 assumes local thermodynamic equilibrium in the device and deduces mass, momentum and energy. The viscous effects of the gas in the presence of an arc are negligible at high temperature and high velocity and do not need to be taken into account. An energy equation includes radiation and heating effects and another set of equations is used to calculate the electromagnetic fields. Gas ionisation, which has nonlinear behaviour, is deduced depending on the temperature and pressure.
MC3 integrates the geometric representation of the configuration, and numerical solution of the flow, energy and electromagnetic field equations. A series of distinct modules allows the designer to create models for devices, specify their operating characteristics, and simulate the transient phenomena to extract the pertinent parameters.MC3 accuracy and productivity are far superior to more traditional approaches involving multiple tests.