Based on Comsol, this paper establishes a transient multi-physical field coupling computational model for the temperature distribution of transformer OLTC vacuum tube contacts under harmonic current disturbance and a field-circuit coupling simulation model for the unbalanced breakdown process after the arc under harmonic voltage disturbance by using transient electromagnetic field computational theory with arc power loss, inter-contact recovery voltage calculation as the target and external circuit port characteristics as the constraints and coupling temperature and flow fields to study the energy dissipation characteristics, contact temperature distribution, re-breakdown probability and opening reliability of the breaking process under harmonic action.

Under the effect of different harmonic current and voltage, the physical parameters of the arc plasma and the post-arc space have different change processes, including the particle composition of the plasma, thermodynamic properties and transport coefficients (including electrical conductivity, thermal conductivity and viscosity coefficient), which in turn lead to different energy dissipation characteristics, contact temperature distribution and post-arc voltage rise rate.

Harmonic current and voltage have a great influence on the breaking behavior of the OLTC vacuum tube of the UHV converter transformer, which is clearly different from the breaking characteristics under the action of the fundamental wave, and the subsequent parameter design should focus on the influence of harmonics.