Rapid voltage change (RVC), as an important power quality disturbance, frequently occurs in distribution systems with impulsive loads and high penetration of renewable energy sources. This paper compares the RVC detection methods specified in IEC 61000-4-15 and IEC 61000-4-30, and analyzes the influence of different steady-state threshold settings on RVC event detection results based on measured voltage data from electric arc furnaces. Existing RVC assessment systems mainly reflect overall disturbance control requirements by constraining the amplitude and occurrence frequency of voltage changes within a specified time period; however they have difficulty characterizing the differences among various RVC events in terms of time-domain characteristics and actual disturbance in intensity. In response to this problem, and in combination with RVC limit requirements, a severity assessment index and corresponding assessment methods are proposed that simultaneously consider the instantaneous impact and cumulative time effect of disturbances. The results demonstrate that the proposed index can effectively distinguish the severity differences among various RVC events, providing an effective basis for RVC disturbance analysis and mitigation strategy formulation in typical impulsive load scenarios such as electric arc furnaces.