变电站短路电流及主变保护整定计算书

A)Р2)35kV电压等级的基准电流为:РIB= =1.560(kA)Р罗村变对d2短路点的转移电抗为:РX*=0.306×0.108×(1/0.495+1/0.306+1/0.108)=0.481Р所以当d2点三相短路时,由罗村变提供的短路电流为:Р次暂态短路电流有效值==3.243(kA)Р稳态短路电流有效值I∞==3.243(kA)Р短路冲击电流ich=2.55=2.55×3.243=8.270(kA)Р短路全电流最大有效值Ich=1.52=1.52×3.243=4.929(kA)Р短路容量=Uav=×3.243×37=207.8(MVA)Р3)当d2点三相短路时,由高岭变提供的短路电流为:Р次暂态短路电流有效值==1.962(kA)Р稳态短路电流有效值I∞==1.962(kA)Р短路冲击电流ich=2.55=2.55×1.962=5.003(kA)Р短路全电流最大有效值Ich=1.52=1.52×1.962=2.982(kA)Р短路容量=Uav=×1.962×37=125.7(MVA)Р1.5 10kV侧发生三相短路Р当火电厂和罗村变同时供电,且永和变两台主变高、中、低压侧并列运行时,10kV侧母线发生三相短路最严重,故按此情况进行计算短路电流。简化电路如图5。Р图5Р其中X23*=0.215/2=0.108Р X24*=0/2+0.795=0.795РX25*=0.135/2=0.068Р1)昌河火电厂对短路点d3的转移电抗为:РX*=0.495×(0.108+0.068)×[1/0.495+1/0.306+1/(0.108+0.068)]=0.956Р计算电抗为:РXj*=0.956×=0.598Р火电厂应查汽轮机运算曲线求短路电流周期分量标么值,分别查0S、4S的运算曲线,得=1.752,=1.887。相应的有名值分别为:Р×=1.752×=6.021(kA)