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第十章不对称故障的分析计算用对称分量法分析计算电力系统的不对称故障的步骤为:1、计算系统中各元件的各序电抗。2、制订电力系统的各序网络。3、形成复合序网4、对复合序网进行分析计算,可求出短路点特殊相的电流和电压的对称分量。5、根据短路点特殊相的电流和电压的对称分量,求出短路点的各相电流、电压。第一节各种不对称短路故障时故障处的电流和电压计算一、单相短路接地f(1)以a相为特殊相(a相发生单相接地短路)0aUa相短路点的对地电压abcaUbUcUaIbIcIf1、边界条件:b、c相没有接地,其接地电流0,0cbII2、用对称分量表示的边界条件0aU0021aaaaUUUU3/021aaaaIIII相当于各序网络相串联3、复合序网——根据用对称分量表示的边界条件,将三个序网络连接起来的等值电路单相接地短路的复合序网=正、负、零序网络相串联E1jX1aI1aU1f1n2jX2aI2aU2f2n0jX0aI0aU0f0n由复合序网可求出短路点处的a相的电流和电压的各序对称分量:)(021021XXXjEIIIaaaE1jX1aI1aU1f1n2jX2aI2aU2f2n0jX0aI0aU0f0n则a相短路电流为:)(3021021XXXjEIIIIaaaa根据复合序网可得故障处三序电压分量分别为:)(0211XXIjEUaa222XIjUaa000XIjUaa4、短路点各相的电流和电压0221021210003aaacaaabacbaaUUaUaUUUaUaUUIIII5.相量图:以为参考相量画电流、电压相量图1aI1aI2aI0aIaI2bI1cI1bI2cIE1aU2aU0aU1bU2CU0CUCU2bU0bUbU)(0aUE)0(0KUc)0(0KUb0cU10K0bU10K)(0KUc)(0KUc6、结论:(1)短路点故障相电流中的正序、负序、零序分量相等;短路点非故障相的电流等于零。(2)短路点故障相电压等于零,两个非故障相电压幅值相等,其值取决于与之比,当在零到无穷大范围内变化时,非故障相电压的相位在之间变化。(3)单相接地短路的正序电流值相当于在三相短路电流计算的等值电路中的短路点处串联一个附加电抗后发生三相短路的短路电流0X1X)(11XXjEIa60~18002XXX10/XX二、两相短路f(2)以a相为特殊相(b、c相短路)1、边界条件:a相没有短路,其短路点的短路电流0aIabcaUbUcUaIbIcIcbIIcbUU2、用对称分量表示的边界条件0011111312222021bbbbaaaIaaIaaIIaaaaIII)()(0:021aaaIII即0)()(3111111312222021bababbaaaaUaaUUaaUUUUaaaaUUU0:021aaaUUU即表明:正序网与负序网相并联,零序网络开路,没有零序电流分量。由各序分量电压关系可得:0:021aaaIII又3、复合序网两相短路的复合序网=正序网与负序网络相并联由复合序网可求出短路点处的a相的电流和电压的对称分量:)(2121XXjEIIaa901211221aaaaaaIUUIjXUU超前、即E1jX1aI1aU1f1n2jX2aI2aU2f2n4、故障处各相的电流为:1122123)(aaaabIjIaaIaIaI1122213)(aaaacIjIaaIaIaI故障处各相的电压为:EXXjEjXIjUUUUaaaaa2221121222221212aaaabUUUaUaU21221aaaacUUUaUaU5.相量图:以为参考相量画电流、电压相量图1faI1aU1aU2aUaU1cU1bU2bU2cUbUcU2aIcI2bI1cI1bI1aIbI2cIE6、结论:1)短路电流、电压中无零序分量。2)两相短路电流中的正、负序分量大小相等,方向相反;两故障相的电流大小相等(幅值=),方向相反。3)短路点处两故障相的电压大小相等、相位相同,幅值为非故障相的电压的一半,相位与非故障相电压相反。4)与三相短路的情况相比,两相短路的正序分量与在短路点串接一个附加电抗时的三相短路电流相等aI3X)(11XXjEIa2XX三、两相接地短路f(1,1)以a相为特殊相(b、c相接地短路)1、边界条件:a相短路电流0aIb、c相接地短路,其短路点的短路电压0cbUUabcaUbUcUaIbIcI2、用对称分量表示的边界条件0021aaaaIIIIaaaaaaaaaaaUUUUUUUUaaaaUUU313100111113102122021即表明:正序网、负序网、零序网相并联0021aaaaIIII又E1jX1aI1aU1f1n2jX2aI2aU2f2n0jX0aI0aU0f0n3、复合序网两相接地短路的复合序网=正、负、零序网络相并联由复合序网可求出短路点处a相的电流和电压的对称分量:02210020120211)//(XXXIIXXXIIXXXjEIaaaaa反向与、即102aaaIII90)//(1021102021aaaaaaaaIUUUIXXjUUU超前、、即4、短路点处各相的电流和电压022102121003aaacaaabacbaaIIaIaIIIaIaIIUUUU120202)(13acbIXXXXII两相短路接地时,流入地中的电流为:0201033XXXIIIIIacbg5.相量图:以为参考相量画电流、电压相量图1aI反向与、102aaaIII901021021aaaaaaaIUUUUUU超前、、1aU0aU1aUaU1cU1bU2bU2cU2aU2aI0aI1cIcI2cI0cI0bI2bIbI1aI1bI6、结论:两相接地短路时:(1)短路点处两故障相的电流幅值相等。(2)短路点处非故障相电压中的正序、负序、零序分量相等。(3)两相短路接地时,流入地中的电流为(4)短路点处的正序电流分量与故障处串接一个附加电抗后产生的三相短路电流相等,即0201033XXXIIIIIacbg)(11XXjEIa02//XXXX总结:1、单相接地短路时:复合序网为正、负、零序网相串联;短路点电流的正序分量)(/0211XXXjEIa故障相电流13aaII2、两相短路时:复合序网为正序网与负序网相并联;短路点电流的正序分量)(/211XXjEIa13acbIjII故障相电流3、两相接地短路时:复合序网为正、负、零序网相并联;短路点电流的正序分量)//(0211XXXjEIa故障相电流120202)(13acbIXXXXII例:7-4例10-1~fLGT12.0,01.1,85.0cos200,5.10:1dXEMWkVG,功率为电压为发电机VuMWTkk5.10/242,5.10%250:电压为,容量为变压器解:(1)计算参数,做各序网络等值电路,取基准容量基准电压,则各元件参数为:的电压的短路电流和非故障相点发生单相直接接地时计算,长度为线路fxxkmxL,5.3,/4.0km60:101MVASB100avBUU051.085.0/20010012.0:21GGXXG发电机042.0250100105.0:TXT变压器0454.02301004.06.0:221LLXXL线路159.00454.05.35.310LLXX2aU2f051.0j042.0j0454.0j2n0aU0f042.0j159.0j0n~fLGT051.085.0/20010012.0:21GGXXG发电机042.0250100105.0:TXT变压器0454.02301004.06.0:221LLXXL线路159.00454.05.35.310LLXX1aU1f051.0j042.0j0454.0j1n01.1(2)做各序网络图201.0,138.0021jXjXX(3)根据单相短路特点,作复合序网图01.1138.0j1aI1aU1f1n138.0j2aI2aU2f2n201.0j0aI0aU0f0n(4)计算正序电流,再算故障相电流31.2)201.02138.0(1.1)(0211jjXXXjEIa93.631.2331jjIIaa)(74.1230310093.6)1(kAIIaf(5)计算非故障相电压01.1138.0j1aI1aU1f1n138.0j2aI2aU2f2n201.0j0aI0aU0f0n783.0)201.0138.0()31.2()(0211jjXXIjUaa319.0138.0)31.2(222jjXIjUaa464.0201.0)31.2(000jjXIjUaa11.12618.10212aaabUUaUaU11.12618.10221aaacUUaUaU)(70.156323018.1kVUUcb
本文标题:20不对称短路分析(新).
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