核电站配电系统暂态过电压与过电流特性研究

Study on the Transient Overvoltage and Current Characteristics of Distribution System in Nuclear Power Plant

电缆线路中的操作过电压与过电流会加剧电缆本体与附件缺陷的发展,核电站低压配电系统进行重新规划以及设备更新后,往往缺乏必要的过电压计算校核。本文以EMTP平台为基础,搭建了常规岛低压配电系统的仿真模型,分别研究了不同运行工况下6.6kV电缆线路的暂态合闸过电压、分闸过电压的幅值与频率特性,以及380V线路送电端单相短路故障下的过电流与工频过电压。计算结果表明,6.6kV电缆线路的合闸过电压可高达2.59p.u.,暂态过程包含30kHz以及83.74kHz的高频电压分量。分闸过程中电弧重燃产生的过电压可高达2.66p.u.,且过电压主导频率与合闸过电压主导频率具有一致性。380V线路送电端短路时,故障相过电流可达到1.3kA,健全相会产生450.4V的工频过电压,进一步导致母线处健全相过电流达到0.88kA。计算结果为电力设备的状态评估与继电保护的整定配合,提供了重要的参考价值。

The incipient defect in cable body or accessory can be further developed under the pressure of switching overvoltage and overcurrent.Usually,the overvoltage calculation is not performed in the distribution system of nuclear power plant after the reconfiguration or equipment replacement.The simulation model of the distribution system in conventional island is established in EMTP to study the transient closing overvoltage and breaking overvoltage along 6.6kV cable line.Besides,the short-circuit current and power-frequency overvoltage in 380V system are calculated.The calculation results indicate that the closing overvoltage with 30kHz and 83.74kHz high-frequency component in 6.6kV cable can be 2.59 p.u..During the line de-energization,the overvoltage caused by re-striking can be 2.66p.u.,and the dominant frequency is consistent with that of closing overvoltage.The short-circuit current in 380V can be 1.3kA,and the power-frequency overvoltage can be 450.4V.Thus,the current in busbar increases to 0.88kA.The calculation results have significance reference values for state assessment of power equipment and coordination of relay settings.