In the case of circuit-breakers breaking the short-circuit current the mechanism and formulas of distortioncurrent in high-current interval are discussed in appendix A of IEC 62271—101:2017 high-voltage switchgear andcontrolgear-Part 101:Synthetic testing. By applying the superposition principle of linear current

this paper theoreti-cally deduced the distortion current formulas in high-current interval with constant arc voltage and linearly rising arcvoltage

and compares it with the formulas given in the IEC standard. The results show that the distortion current for-mulas of this paper is the same as the IEC standard when the arc voltage is constant

but the distortion current formu-las of the IEC standard are in problem and need to be amended when the arc voltage is linearly rising. The researchcontents of this paper provide reference and basis for the evaluation and calculation current distortion of synthetictest in high power station.