采区低压电网短路电流的计算

采区低压电网短路电流的计算短路电流是选择电气设备和载流导体、选择和整定继电保护的依据。短路电流可以由公式计算法或查表计算法得到。一、短路的基本知识1、短路的概念所谓短路是指供电系统中不等电位的导体在电气上被短接。在煤矿井下的两种短路形式见表3-2-4。表3-2-4短路种类示意图代表符号性质三相短路)3(d三相同时在一点短接，属于对称短路两相短路)2(d两相同时在一点短接，属于不对称短路2、短路的危害发生短路时，由于系统中总阻抗大大减小，因而短路电流可能达到很大的值。强大的短路电流所产生的热和电动力效应会使电气设备受到破坏；短路点的电弧可能烧毁电气设备；短路点附近的电压显著ABCABC降低使供电受到严重影响或被迫中断；在井下，短路产生的电弧还可能点燃瓦斯、煤尘，引起严重的安全事故。3、短路的原因产生短路的主要原因是由于电气设备载流部分绝缘损坏。绝缘损坏是由于绝缘老化、过电压、机械损伤等造成。二、短路电流的计算方法1、公式计算法（1）两相短路电流I)2(d的计算两相短路电流可用下式计算：)2(Id=22)()(2XRUN3-2-4221/XRKRRbb221/XXKXXXbbX式中)2(Id------两相短路电流，A；R、X-----短路回路内一相电阻、电抗值的总和，Ω；XX------根据三相短路容量计算的系统电抗值，见附录一表1，Ω；R1、X1------高压电缆的电阻、电抗值，见附录一表2，Ω；Kb-----矿用变压器的变压比，若一次电压为6000V，二次电压为400V、690V、1200V时，变压比为依次为15、8.7、5；当一次电压为3000V，二次电压为400V时，变压比为7.5；Rb、Xb----矿用变压器的电阻、电抗值，见附录四，Ω；R2、X2-----低压电缆的电阻、电抗值，见附录二表1，Ω；UN----变压器二次侧的额定电压，对于380V网络，UN以400V计算；对于660V网络，UN以690V计算；对于1140V网络，UN以1200V计算；对于127V网络，UN以133V计算。利用式（3-2-4）计算两相短路电流时，不考虑短路电流周期分量的衰减、短路回路的接电阻和电弧电阻忽略不计。（2）三相短路电流的计算若需计算三相短路电流值，可按下式计算：)3(dI1.15)2(dI(3-2-7)2、查表计算法两相短路电流还可以利用计算表查出。此时可根据变压器的容量、短路点至变压器的电缆换算长度、高压电缆的折算长度，从附录三表2中查出。电缆的换算长度可根据电缆的截面、实际长度，用下式计算得出。LH=K1L1+K2L2+…+KnLn+Lx+KgLg（3-2-8）式中LH---电缆总的换算长度，m；K1、K2、…、Kn-----换算系数，各种截面电缆的换算系数可以从附录二表2中查得；Lx----系统电抗的换算长度，m；Kg----6KV电缆折算至低压侧的换算系数，见附录一表4；Lg----6KV电缆的实际长度。电缆的换算长度，是根据阻抗相等的原则将不同截面和长度的高、低压电缆换算到标准截面长度，在380V、660V、1140V系统中，以50mm2为标准截面；在127V系统中，以4mm2为标准截面。电缆的芯线电阻值选用芯线允许温度65oC时的电阻值；电缆芯线的电抗值按0.081Ω/km计算；线路的接触电阻和电弧电阻均忽略不计。附录一高压系统参数表表1根据三相短路容量计算的系统电抗值(Ω)三相短路容量SK(3)(MVA)额定电压(V)1015202530405010040069012000.0160.04760.14400.01070.03070.09600.0080.02330.07200.00640.0150.05760.00930.01530.04800.0040.01190.03600.00320.00950.08880.00160.00480.0144表2高压电缆的电阻、电抗值（1）高压铠装电缆的电阻、电抗值（Ω/km）截面（mm2）电压（KV）1625355070铜铝铜铝铜铝铜铝铜铝6R11.342.2570.8571.4450.6121.030.4290.7220.3060.516X10.0680.0680.0660.0660.0640.0640.0630.0630.0610.06110R11.3132.2120.841.4140.60.0110.420.7080.30.506X10.080.080.080.080.080.080.080.080.080.08截面（mm2）电压（KV）95120150185240铜铝铜铝铜铝铜铝铜铝6R10.220.880.1790.3010.1430.2410.1160.1950.0890.15X10.060.050.060.050.060.060.060.060.060.0610R10.2210.3720.1570.2950.140.2360.1140.1910.0880.147X10.080.080.080.080.080.080.080.080.080.08注：电缆线芯温度，对于6kV为65oC，对于10kV为60oC。（2）6kV铜芯电缆的电阻、电抗值（Ω/km）截面（mm2）162535507095120150185R21.2870.8240.5880.4120.2940.2170.1920.1370.111X20.0940.0850.0780.0750.0720.0690.0680.0660.066表3系统电抗的换算长度(m)三相短路容量SK(3)(MVA)额定电压(V)10152025304050100400600120035.1164.6316.323.469.7210.917.552.3158.214.141.8126.511.734.9105.48.826.179.17.020.963.33.5110.4631.63注:表中数据为折算至低压50mm2时电缆的折算长度。表46KV电缆折算至以下电压的换算系数表电缆截面（mm2）铜芯铝芯400V690V120V400V690V1200V100.0190.0580.1710.0320.0970.286160.0120.0360.1080.0200.0610.183250.0060.0230.0720.0130.0390.115350.0060.0170.0640.0090.0230.034500.0040.0120.0360.0060.0200.051700.0030.0080.0270.0050.0140.045950.0020.0060.0180.0040.0110.036注:表中数椐为折算至低压50mm2时电缆的折算系数。附录二低压电缆参数表表1电缆的电阻值与电抗值(Ω/km)（1）矿用橡套电缆的电阻、电抗值(Ω/km)阻抗电缆型号电缆芯线截面（mm2）2.54610162535507095UZ10.426.36UUP5.53.692.161.370.8640.6160.4480.315UCUCP2.181.480.9370.6830.491UPQ2.161.370.3640.6160.4480.3150.230UCPQUCPJQ0.6830.4910.3460.247电抗0.1010.0950.0920.0900.0880.0840.0810.0780.075（2）铠装电缆的电阻、电抗值(Ω/km)阻抗电缆类型电缆芯线截面（mm2）2.5461016电阻铜芯8.5595.3483.5562.1391.337铝芯14.429.0136.0093.6052.253电抗铜芯0.1020.0950.0900.0730.0675铝芯0.1020.0950.0900.0730.0675阻抗电缆类型电缆芯线截面（mm2）2535507095电阻铜芯0.8560.6100.4280.3040.225铝芯1.4411.0390.7210.5140.616电抗铜芯0.06620.06370.06250.06120.0602铝芯0.06620.06370.06250.06120.0602注:表中所列电阻为45oC时的数值。表2电缆换算长度表（1）电网电压为1140V、660V和380V时电缆不同芯线截面的换算长度表电缆截面（mm2）4610162535507095换算系数电缆实际长度（m）11.978.114.753.011.911.371.000.730.53101208148301914107520239162956038272015113035924314390574130221640479324190120765540292150599405238151966950372660718487285181115826044327083856833321113496705137809586493802411531108058429010777304282711721239066481001197811475301191137100735311013178925233312101511108058....(2)电网电压为127V时电缆不同芯线截面的换算长度表(m)电缆截面（mm2）2.54610换算系数电缆实际长度（m）1.641.000.580.3410161063203320127304930171040664023145082502917609860352070115704124801318046279014890523110016410058341101801106437注:表(1)和表(2)根据电缆实际长度、截面和换算系数以此类推计算。附录三变压器低压侧两相短路电流计算表(1)KBGS型变压器二次侧电压400V时的两相短路电流计算表电缆的换算长度(m)变压器容量(KVA)5010020040050+50100+100100+200015613123625112490312362479333201509292655289564290954397631401454272047667142269246566084601400251814015553248539974938801346232835564499229434664111100129421553119376521213043350112012421998276632301966270230441401194185824792825182824252687160114717332242250917052196240218011031621204422551596200521712001061152118772048149818441979220102114321734187514101705181824098313511611172813311586168126094812781504160312601481156328091412131409149511961390146030088211531326140011371308137032085310981252131610841236129034082410481185124210351171121936079810031126117699011121155380773961107111169491059109840074992210221062911101110464207268869771014876967998440705853936969843927955460685822898928813889916480666793863891785855879500647766831856758823845520630741800824734794814电缆的换算长度(m)变压器容量(KVA)5010020040050+50100+100100+20054061471777279471075678556059869574676668874075858058367472274