第二章 短路电流的计算2013B - 图文

Friday, March 07, 2014无限大功率电源供电网络的波形曲线91、无限大功率电源容量无限大，内阻抗为零。端电压保持恒定。短路计算中，当电源内阻抗不超过短路回路总阻抗的5%~10%时，就可以近似认为此电源为无限大功率电源。2、短路暂态过程分析（三相短路）1）短路前u?Umsin(?t??)i?Imsin(?t????[0])Im?Um(R?R?)??(L?L?)222?(L?L?)?[0]?arctgR?R?返回下一页Friday, March 07, 2014无限大功率电源供电网络的波形曲线diaL?Ria?Umsin(?t??)dt102）设在t = 0秒发生三相短路时的微分方程其解为：?周期分量ip：Umip?sin(?t????)?Ipmsin(?t????)ZIpm?Um/R2?(?L)2??arctg??LR?tTa非周期分量inp：inp?AeTa＝L/R?短路全电流表达式ia?ip?inp?Ipmsin(?t????)?Ae?t/Ta上一页返回Friday, March 07, 201411?短路前后瞬间电感中电流不能突变，故有Imsin(???[0])?Ipmsin(???)?AA?inp0?Imsin(???[0])?Ipmsin(???)?a相短路电流?t/Taia?Ipmsin(?t????)?[Imsin(???[0])?Ipmsin(???)]eFriday, March 07, 201412无限大功率电源供电网络的波形曲线图