Molecular Dynamics Simulation Studies of Graphene Reinforced Cu-W Circuit Breaker Contacts

Abstract

High-voltage circuit breakers (HVCB) are critical components of power systems. They are designed to interrupt fault currents when a short circuit fault occurs on an item of plant that is controlled by the breakers, and also to change network topology during normal operating conditions. In the interruption process, the electric arcs cause erosion of contact materials, resulting in mass loss and surface morphology changes. Conventionally Cu-W materials are employed as arc contacts in HVCB. Graphene is becoming a potential additive to mitigate contact erosion of Cu-W materials, but enhancement mechanisms of graphene remain unclear. This work aims to study the effects of graphene additives on anti-erosion properties of Cu-W composites by using MD simulations.

Material characterisation tests were conducted on the Cu-W and G-Cu-W (graphene-reinforced Cu-W) contacts following a series of arc tests. The quantitative analysis revealed that G-Cu-W contact surfaces were smoother, characterised by fewer cracks, holes and less Cu deposition compared to Cu-W contacts. Additionally, various graphene flakes were detected from G-Cu-W contacts. Subsequently, the anti-erosion properties of G-Cu-W composites were investigated, through MD modelling, by varying arcing-related (the types and energies of incident ions) and graphene-related parameters (sizes, positions and orientations of graphene). Extents of contact erosion were estimated by analysing erosion craters and lost atoms in simulations.

Results demonstrated that the graphene layers can enhance the anti-erosion properties of metal substrates, particularly those located on the substrate surface. The surface graphene layers can protect the substrate from ion bombardment due to their excellent mechanical properties and high melting point, especially at incident energies below 50 eV. Graphene layers embedded within the substrates exhibited a delayed enhancement effect compared to those on the surface. Additionally, graphene layers smaller than ion bombardment area can improve anti-erosion properties of the Cu-W substrate by dissipating heat from the contact when they were sputtered away, and they are feasible to incorporate into practical contact materials. Finally, through tensile simulations and nanoindentation simulations, results indicated that graphene can improve Young’s modulus and hardness of Cu and W matrices in certain scenarios.