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一、d-1点短路电流1、基准电流Ij=Sr∑/SQRT(3)/10.5=5.499kASr∑=100MVA2、电力系统阻抗标么值X*s=Sj/Ss=0.33310.5KV3、电缆埋地阻抗标么值查表4-7得电缆电抗X1=0.080Ω/km估计电业电缆长度L=0.010kmX*1=X1xL1xSj/Uj2=0.0014、d-1点总电抗标么值d-1X*∑d-1=X*s+X*1=0.3341)计算d-1点三相短路电流L1=10mI*k=S*k=I*k=1/X*∑d-1=2.993Ik=IkxIj=I*xIj=Ij/X*∑d-1=16.460kASk=S*kxSj=I*kxSj=I*xSj=Sj/X*∑d-1=299.348MVA变压器:2MVAI0.2=I=I∞=Id=16.46kAuk%=6%2)短路冲击电路ichip=2.55I=41.97kA3)第一周期短路全电流有效值IchL2=40mIp=1.51I=25.02kA4)短路电流热效应Qt=Qz+Qf=tf×Ik2=54.19kA2·s5)变压器进线电缆最小截面积d-2Ur2=6.3KVSmin=103×SQRT(Qt)/c53.73mm2二、d-2点短路电流5、基准电流Ij=Sr∑/SQRT(3)/0.63=9.164kA6.36、变压器阻抗标么值X*T=uk%×Sj/100×Sr=0.03Ω7、电缆埋地阻抗标么值查表4-7得电缆电抗X2=0.070Ω/km估计电业电缆长度L=0.040kmX*2=X2xL2xSj/Uj2=0.0078、d-2点总阻抗X*∑d-2=X*s+X*1+X*T+X*2=0.371Ω9、计算d-2点三相短路电流I*k=S*k=I*k=1/X*∑d-2=2.695Ik=IkxIj=I*xIj=Ij/X*∑d-2=24.694kASk=S*kxSj=I*kxSj=I*xSj=Sj/X*∑d-2=269.459MVAip=2.55I=62.970kAIp=1.51I=37.288kA电力系统Ur1=系统短路容量取300MVA三相短路全电流峰值系数取1.8高压短路电流计算表远离发电机端(无限大电源容量的)网络发生短路时,即以电源容量为基准的计算电抗X*c≧3时,短路电流分量在整个短路过程中不发生衰减,即Ik=I0.2=Ik(0.2s的短路电流I0.2,稳态电流I∞,三相次暂态短路电流I);三相短路全电流峰值系数取1.8,ip=KpxSQRT(2)xIk;Ip=IkxSQRT(1+2(Kp-1)2)M三相短路电流(KA)两相短路电流(KA)单相接地故障电流(KA)单相短路电流(KA)短路电流冲击系数短路冲击电流(KA)短路全电流最大有效值(KA)R(mΩ)X(mΩ)Rphp(mΩ)Xphp(mΩ)Zk=SQRT(Rk2+Xk2)Zphp=SQRT(Rphp2+Xphp2)Zph。N=SQRT(Rph。N2+Xph。N2)=2xZkIk3=cxUn/SQRT(3)xZkIk2=0.866Ik3Id=cxUn/SQRT(3)xZphpIk1=cxUn/SQRT(3)xZph。NKp查图4-14ip=SQRT(2)xKpxIk3Ip=Ik3xSQRT(1+2(Kp-1)2)1系统S300查表4-210.0500.5300.0300.3502变压器T2000查表4-230.5304.7700.5304.7703母线m3×[2(125×10)+1(125×10)]10查表4-240.0140.1700.0420.34441+2+3k10.7207.0000.9808.5607.0378.61614.07432.7428.3525.4615.599.721.7279.6346.725线路L13510查表4-250.5010.0802.3970.19161+2+3+5k25.7307.80024.95010.4709.67827.05819.35723.8020.618.1111.337母线m'40x45查表4-240.0140.1700.0420.34481+2+3+5+7k35.8008.65025.16012.19010.41527.95720.82922.1219.167.8510.531.491.0532.8522.189线路L23510查表4-250.5010.0802.3970.191101+2+3+5+7+9k410.8109.45049.13014.10014.35851.11328.71616.0413.894.297.6411母线m40x44查表4-240.0140.1700.0420.344121+2+3+5+7+9+11k510.86610.13049.29815.47614.85651.67029.71115.5113.434.257.380.931.0222.3715.5113线路L3410查表4-254.3000.09712.9000.028141+2+3+5+7+9+13k653.86611.100178.29815.75654.998178.993109.9964.193.631.231.99PHPR(1)=R(0).S+R(0).T+R(0).m+R(0).L+R(0).L'X(1)=X(1).S+X(1).T+X(1).m+X(1).L+X(1).L'X(2)=X(2).S+X(2).T+X(2).m+X(2).L+X(2).L'X(1)=X(0).S+X(0).T+X(0).m+X(0).L+X(0).L'Z(1)、Z(2)、Z(0)—短路电路正序、负序、零序阻抗,(mΩ)Rphp、Xphp、Zphp—短路电路相线—保护线回路电阻,电抗,阻抗,简称相保电阻,相保电抗,相保阻抗,(mΩ)Un—网络标称电压(线电压),V,220/380V网络为380V,Un/1.732=220;c—电压系数,计算单相接地故障电流时取1.0;二、单相短路(包括单相接地故障)短路电流的计算一、三相和两相(不接地)短路电流的计算Ik3=cxUn/SQRT(3)xZk=1.05Un/SQRT(3)xSQRT(Rk2+Xk2)=230/SQRT(3)xSQRT(Rk2+Xk2)(KA)Un—网络标称电压(线电压),V,220/380V网络为380V;Xk=XS+XT+Xm+XL+XL'Rk=RS+RT+Rm+RL+RL'c—电压系数,计算三相短路电流时取1.05;(3)两相短路稳态电流Ik2与三相短路电流Tk3的比值也和高压系统相同。远离发电机短路时Ik2=0.866Ik3;在发电机出口处短路时Ik2=1.5Ik3;RT、XT—变压器的电阻,电抗,(mΩ)RS、XS—变压器高压侧系统的总电阻,总电抗(归算到400V侧),(mΩ)TN系统的低压网络单相接地故障电流按下式计算:Ik1=cxUn/SQRT(3)xZphp=1.0xUn/SQRT(3)xSQRT[(R(1)+R(2)+R(0))2/9+(X(1)+X(2)+X(0))2/9]=220/Zphp(KA)R(1)、R(2)、R(0)—短路电路正序、负序、零序电阻,(mΩ)X(1)、X(2)、X(0)—短路电路正序、负序、零序电抗,(mΩ)Rm、Xm—变压器低压侧母线段的电阻,电抗,(mΩ)RL、XL—配电线路干线段的电阻,电抗,(mΩ)R'L、X'L—配电线路支线段的电阻,电抗,(mΩ)(1)只要SQRT(Rk2+Xk2)/SQRT(Rk2+Xk2)≧2,变压器低压侧短路时电流交流分量不衰减,即三相短路电流稳态值Ik3=Ik3(2)低压网络两相短路电流Ik2与三相短路电流Ik3的关系和高压系统相同,即Ik2=0.866Ik3Zk、Rk、Xk—短路电路总阻抗,总电阻,总电抗,(mΩ)Rphp=[R(1)+R(2)+R(0)]/3=Rphp.s+Rphp.T+Rphp.m+Rphp.L+Rphp.L'在220/380网络中以三相短路电流为最大。一台变压器供电的低压网络三相起始短路电流分量有效值按下式计算:一、220/380V低压网络参数分项统计表二、220/380V低压网络短路电流计算线路参数线路长度(m)Xphp=[X(1)+X(2)+X(0)]/3=Xphp.s+Xphp.T+Xphp.m+Xphp.L+Xphp.L'R(1)=R(1).S+R(1).T+R(1).m+R(1).L+R(1).L'R(2)=R(2).S+R(2).T+R(2).m+R(2).L+R(2).L'序号电路元件短路点元件阻抗(mΩ)短路点阻抗(mΩ)参数选择Xk/Rk电气设备选择:短路容量相保电阻相保电抗电阻电抗阻抗S(MVA)Rphp.s(mΩ)Xphp.s(mΩ)Rs(mΩ)Xs(mΩ)Zs(mΩ)101.0610.611.5915.9216.00200.535.310.807.968.00300.353.530.535.305.33500.212.120.323.183.20750.141.410.212.122.131000.111.060.161.591.602000.050.530.080.800.803000.030.350.050.530.53∞1.220.000.000.000.00当前选择#REF!#REF!#REF!#REF!#REF!0.5310(6)、0.4KV变压器高压侧系统短路容量与高压侧阻抗、相保阻抗(归算到400V)的数值关系查表4-21正、负序零序相保正、负序零序相保RT.(1)、RT.(2)、RT.(0)RT.(0)RT.phpXT.(1)、XT.(2)、XT.(0)XT.(0)XT.php16041.9812.3812.3812.3838.0438.0438.0420042.248.968.968.9629.9329.9329.9325042.416.176.176.1724.8524.8524.8531543.105.005.005.0019.7019.7019.7040043.603.603.603.6015.5915.5915.5950044.302.752.752.7512.5012.5012.5063045.402.182.182.189.929.929.9263065.602.262.262.2615.0715.0715.0780066.601.651.651.6511.8911.8911.89100067.601.221.221.229.529.529.52125069.100.930.930.937.627.627.621600611.000.690.690.695.965.965.962000613.300.530.530.534.774.774.772500615.800.400.400.403.823.823.82当前选择#REF!0.530.534.774.77负载损耗(KW)D,yn11联结的SC(B)9系列10(6)/0.4kV变压器的阻抗平均值(归算到400V侧)查表4-2310/0.4SC9SCB9RT电阻(mΩ)XT电抗(mΩ)型号电压(KV)容量(KVA)阻抗电压(%)2503502503503[2(125x10)]+125x100.0140.0420.1470.1700.3170.3443[2(125x10)]+80x100.0140.0540.1470.1700.3400.3674(125x10)0.0280.0560.1470.1700.3170.3443(125x10)+80x80.0280.0780.1470.1700.3410.3693(125x10)+80x6.30.0280.0880.1470.1700.3430.3704[2(100x10)]0.0160.0320.1560.1810.3360.3663[2(100x10)]+100x100.0160.0480.1560.1810.3360.3663[2(100x10)]+80x80.0160.0660.1560.1810.3500.3804(100x10)0.0330.
本文标题:短路电流计算
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