I???11??11.3940 X90.0877I??有名值?11.3940?0.5020?5.7198kA
0.0897?4.0850
0.0897?0.16050.1605?7.3091 发电机电流标么值?11.3940?0.2502S系统电流标么值?11.3940?
3．试计算图3-14所示系统中流过断路器A的最大可能电流I??。
115kV10.5kV100km0.4?/kmA2?20MVAUS%?10.610kV，0.5kAXR%?82?25MVAcos??0.8???0.13Xd300MVA???0.5Xd图3-14 习题3图
解：取SB?100MVA。则
IB(110kV)?1003?115?0.5020kA
IB(10kV)?1003?10.5?5.4986kA
等值电路及其化简
21
X2X1X4AX71X4AX71X6X3X5X82X9X5X6X82X12AX71X12X71X9X10X13X11X82X112X15X12X7X16X711
X1?0.5?100300?0.1667 X1002?X3?0.4?100?1152?0.3025 X4?X5?10.6100?10020?0.5300 X8105.49866?100?10.5?0.3?1.3965
X7?X8?0.13?100250.8?0.4160 XX2X30.3025?0.9?X1?X?0.1667?30250.3025?0.3179
2?X30.3025?X?X4X510XX?0.5300?0.53001.3965?0.1144 4?X5?60.5300?0.5300?XX5X611?X12?X?0.5300?1.3965?0.1597
4?X5?X60.5300?0.5300?1.3965X13?X9?X10?0.3179?0.1144?0.4323 X14?X8?X11?0.4160?0.1597?0.5757 X15?X13X140.4323?0X?X?.5757?0.2469
13140.4323?0.5757
22
X16?X12?X15?0.1597?0.2469?0.4066
则： 断路器A的右侧短路时，流过A的电流If1?11??2.4594 X160.406611??2.4038 X70.4160断路器A的左侧短路时，流过A的电流If2?流过A的可能最大短路电流为2.4594。其有名值?2.4594?5.4986?13.5233kA 4．系统接线如图3-15所示。求f点三相短路的短路电流。 （1）次暂态电流初始值的有效值I??；
（2）t?0.2s时电流有效值（按同一变比法和个别变比法两种方法计算）。 取基准功率SB?100MVA。
6.3kV115kV2?15MVA???0.125Xd6kV，0.6kAXR%?1050km0.4?/km无穷大系统汽轮发电机f2?7.5MVAUS%?10.6
图3-15 习题4图
解：（1）IB(6kV)?1003?6.3?9.1643
一台发电机额定电流IN?153?6.3?1.3746kA
两台发电机额定电流IN?2?1.3746?2.7492kA
等值电路及其化简
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X1X3X6X1X7X2fX5X2fX9X6X4X8X2X10X11X8X12fX2fX8100?0.8333 1510.6100X3?X4???1.4133
1007.51069.1643X5????1.4547
1006.30.6X2fX13X14f X1?X2?0.125?X6?1100?0.4?50??0.0756 22115X7?X8?X3X51.4133?1.4547??0.4802
X3?X4?X51.4133?1.4133?1.4547X9?X3X41.4133?1.4133??0.4666
X3?X4?X51.4133?1.4133?1.4547X10?X1?X7?0.8333?0.4802?1.3135 X11?X6?X9?0.0756?0.4666?0.5422 X12?X10X111.3135?0.5422??0.3838
X10?X111.3135?0.5422X13?X8?X12?0.4802?0.3838?0.8640 X14X2X130.8333?0.8640???0.4242 X2?X130.8333?0.864011??2.3576 X140.4242次暂态电流I??? 24
I??有名值?2.3576?9.1643?21.6052kA
（2）运算曲线法 1）按个别变比
1X10X111X17X15s2sf2X2fX8X2X16
X10、X8、X11组成的星形变换为三角形
X15?X8?X10?X8X100.4802?1.3125?0.4802?1.3135??2.9572 X110.5422X16X8X110.4802?0.5422?X8?X11??0.4802?0.5422??1.2206
X101.3135发电机G1的计算电抗 Xjs1?2.9572?15?0.443 6100查运算曲线得：I1(0\)?2.4，I1(0.2\)?2.0。
I1(0\)有名值?2.4?1.3746?3.2990kA
I1(0.2\)有名值?2.0?1.3746?2.7492kA
发电机G2的计算电抗 Xjs2?0.8333?15?0.125 0100查运算曲线得：I2(0\)?8.6，I2(0.2\)?5.05。
I2(0\)有名值?8.6?1.3746?11.8219kA I2(0.2\)有名值?5.05?1.3746?6.9419kA
无限大电源S向短路点f输送的电流
25