The stochastic power fluctuation with a large amplitude has frequently emerged on the ultra-high voltage (UHV) tie-line during normal operation of the interconnected power system in North and Central China

which may result in an adverse impact on the power transmission capability of tie-lines. Based on an analysis of such characteristics of stochastic tie-line power fluctuation as the waveform

the cycle and the amplitude

this paper proposes a quasi-steady-state method for quantitatively analyzing the impact of stochastic power fluctuation on the power transmission capability. The method simulates UHV tie-line power fluctuation by superposing the power fluctuation on the load

then the quantitative relationship between the stochastic UHV tie-line power fluctuation and the power transmission capability can be calculated. The impact of the UHV tie-line power fluctuation on the power transmission capability by considering the transient stability restriction is analyzed with this method. The results can provide theoretical reference to the operation of the UHV synchronous power grid.