Simulation Of Multi-physical Fields In Self-resettable Current Breaker Employing Magnetic Fluid And Liquid Metal

The research on limiting and breaking short-circuit current plays an important role in ensuring the steady operation of the power system. For the traditional current breakers which consist of mechanical parts and contacts, attrition and corrosion are likely to occur on the surfaces of the contacts in the presence of load and repeated relative surface motion, which may lead to the failure of the current breakers. Compared with the traditional ones(solid-solid contact), the current breakers which employ liquid metal as their electrical contact elements(solid-liquid contact) have much better performance such as less wear, lower contact resistance and self-recovery, etc., which has attracted a lot of researchers’attention.First of all, a review of the research on the traditional circuit breakers and Liquid Metal Current Limiters (LMCL) was made in the paper. The Finite Element Method (FEM) and the ANSYS software were also introduced in order to establish the accurate mathematical model for the simulation. Then the electric field and temperature field of the self-resettable circuit breaker which employs the immiscible magnetic fluid and liquid metal were studied through FEM, together with the distribution of the magnetic field and electromagnetic forces which includes the Lorentz force and magnetization force. Moreover, some experiments were conducted with the circuit breaker in order to examine the interfacial deformation of the magnetic fluid and the liquid metal when the short circuit or overload exists. Then the experimental results were contrasted with the simulated data.The coupled numerical simulation of the multi-physical fields was conducted and the distributions of the temperature, the thermal gradient, the magnetic fields and the electromagnetic forces were obtained when changing the variables such as the current values, electrode materials and the volume ratio of the magnetic fluid and the liquid metal. The results indicate that the influence on the external magnetic field gets larger with the increasing current. The external field generated by the permanent magnet could also have a significant change when the non-magnetic electrodes were replaced by the ferromagnetic ones, in which a redistribution of the magnetic field would occur. The magnetic flux density and the distribution area of the magnetic fields, especially the magnetization force, would increase when the volume ratio of the magnetic fluid and liquid metal gets larger. It has also shown that the distribution of these variables can be optimized with adjusting the placement of the permanent magnets. Moreover, an extremal distribution of the electromagnetic forces was found when the circuit breaker employs an electromagnet as its magnetic field generator. The experiments were conducted with the circuit breaker and an abnormal deformation was observed in the breaking process of the circuit. The experimental results are consistent with the numerical analysis.