BENTLYNEVADA330100-90-00在主变差动保护所用电流互感器选择时，除应选带有气隙的D级铁芯互感器外，还应适当地增大电流互感器变比，以降低短路电流倍数，这样可以有效削弱励磁涌流，减少差动回路中产生的不平衡电流，提高差动保护的灵敏度。这对避免保护区外故障，尤其是***严重的三相金属性短路而导致的主变差动保护误动作尤为有效。下面将通过实例进行分析：实例：一台三相三绕组***变压器，容量Se=40.5MVA，电压110&plu***n;2×2.5%kV/385&plu***n;2×2.5%kV/11kV，接线方式：Ydd11-11，变压器额定电流：213A/608A/2130A。主变差动保护采用BCH-2型差动继电器。基本计算如表1所示，已确定110kV侧为基本侧。主变差动保护部分整定值如下(计算过程略)：差动线圈的计算匝数：Wcd.js=6.3匝，实际匝数向下取整，取Wcd.js=6匝;继电器的实际动作电流：Idz=10A;灵敏度K1m=2.1。该变电所曾发生10kV线路出线处因外力***导致三相金属性短路，10kV线路电流速断动作，相继引起主变差动保护误动作。我们初步分析因短路点离保护太近，又是***严重的三相金属性短路，短路电流极大，当外部故障切除，电压***时，出现数值很大的励磁涌流，从而使差动回路产生的不平衡电流大于整定电流值而导致主变差动保护误动作。但如果提高保护定值，如保护定值增大为11A，则灵敏度变小K1m=1.91<2，不能满足灵敏度的要求。后经综合分析，认为采用BCH-2型具有速饱和变流差动继电器来避免励磁涌流存在一定缺陷。从励磁涌流的特性看，对三相变压器，电压***时，至少有两相出现程度不同的励磁涌流，即三相励磁涌流中可能有一相没有非周期分量，这时速饱和变流器将失去作用。分析保护定值，差动保护电流互感器变比选得有些偏低，且趋于饱和。这样当发生***严重的三相金属性短路时，电流互感器因饱和其误差增大，不但增大不平衡电流，而且使电流互感器严重过载。而增大电流互感器变比，可降低短路电流倍数，减少差动回路中的不平衡电流，因而能有效地削弱励磁涌流和区外故障产生的不平衡电流。根据以上分析，采用增大电流互感器变比的方法，其数据如表2所示(与表1相同部分略)。主变差动保护部分整定值如下(计算过程略)：差动线圈的计算匝数：Wcd.js=8.1匝，实际匝数向下取整，取Wcd.js=8匝;继电器的实际动作电流：Idz=9A;灵敏度K1m=2.44。由表1、2及部分整定数据可知：电流互感器变比增加后，其二次电流110kV侧由4.6A减为3.69A，35kV侧由4.05A减为3.38A，10kV侧由3.55A减为2.66A;差动回路中的不平衡电流：35kV侧由0.55A减为0.31A，10kV侧由1.05A减为1.03A;灵敏度由2.1增为2.44。即减少了电流互感器二次回路电流和差动回路中的不平衡电流，提高了保护装置的灵敏度，使主变差动保护区外发生***严重的三相金属性短路时，电流互感器不致于严重过载而使误差增大，有效地削弱励磁涌流和区外故障产生的不平衡电流。该所自增大电流互感器变比后，10kV线路再发生类似短路故障时，主变差动保护再未误动过。为防止主变差动保护因不平衡电流的影响造成的保护误动作，在选择保护用电流互感器时，除应选带有气隙的D级铁芯互感器外，适当增大电流互感器变比，这样可以降低短路电流倍数，减少差动回路中产生的不平衡电流，有效削弱励磁涌流，提高差动保护的灵敏度。这对避免保护区外故障，尤其是***严重的三相金属性短路而导致的主变差动保护误动作不失为有效的方法之一。NEWSquareDI-LineRG1200AmpPowerPactBreakerLSIGRGA36120CU44AAA?SAYP1200ASquareDI-LineRG1200AmpPowerPactBreakerLSIRGA36120CU33AYPRGA361201200ANEWSquareDI-LinePG1200AmpPowerPactBreakerLSIGPGA36120U44AAAS?AYPPGASquareDI-LineNX361200G1200AmpCircuitBreaker1200ASensorTypeNXS3BLSIGSquareDI-LinePJ800PJA36080CU33A800AmpPowerPactBreakerPJA36080800ALSISquareDI-LineLE36600LS600AmpBreakerARP100Trip600VLE36600ALAM600ALSISquareDI-LineLE36600LS600AmpBreakerARP075450ATripLE36600ALAMLELSINIBSquareDI-LineJL250JLA36200200AmpPowerPactBreaker200A600VAL250JDSquareDI-LineLE36400LS400AmpBreakerARP100400ATripLE36400ALAMLSISquareDI-LineLE36400LS400AmpBreakerARP090360ATripLE36400ALAMLELSISquareDI-LineLE36400LS400AmpBreakerARP050200ATripLE36400400AALAMLSISquareDI-LineLE36400LS400AmpBreakerARP088350ATripLE36400ALAM400AdmgSquareDI-LineLE36400LS400AmpBreakerARP088350TripLE36400ALAMLSISquareDI-LinePGA36080U44AYKPG800AmpPowerPactBreakerLSIG800APGA36080SquareDI-LineLE36250LS250AmpBreakerARP090225ATripALAMLE36250250ALSISquareDI-LineLE36225LS250AmpCircuitBreakerLEARP090600V225APlugLSISquareDI-LineBreaker500AmpMGA36500MG500AMGA36500600V3PHSquareDI-Line400AmpCircuitBreakerME36400LIG400APlug600VMEME36400LIGSquareDI-LineME36400LI400AmpCircuitBreaker400ASensorRP100ME36400LISquareDI-LineME36400LI400AmpCircuitBreakerRP100TripLIME36400400AdmgSquareDI-LineME36600LIG600AmpCircuitBreaker800ASensorS5MEME36600LIGSquareDI-LineMX36250G250AmpCircuitBreaker200w/CurrentTransformerLSIGSquareDI-LineJL250JLA36225225AmpPowerPactBreaker600VJLAAL250JD225ASquareDI-LineJL250JLA36200200AmpPowerPactBreaker600VJLAAL250JD200ASquareDI-LineLE36350LS400AmpBreakerARP088350TripLE36350350ALSISquareDI-LineLE36300LS400AmpCircuitBreaker300APlugLE36350400ALSISquareDI-LineME36800LI800AmpCircuitBreaker800ASensorRP100ME36800LINEWSquareDI-LineBreakerKHB36225225AmpBreaker225AKHB-36225TypeKABNIBSquareDI-LineHL150HLA36100100AmpPowerPactBreakerHJ150AL150HDSqD100ASquareDI-LineME836LIG500AmpCircuitBreaker600VS3TypeMEGround500ALIGSquareDI-LineKC24150BC150AmpCircuitBreaker480VKCS22PoleKC24150150ASquareDI-LineMEC236LSIG225AmpCircuitBreaker175ATrip600VMEC236LSIGSquareDI-LineKH26000MAC250AmpMoldedCaseSwitch600VKAKAALKH26000250ASquareDI-LineMH36800800AmpCircuitBreaker240/480/600VS2MAMH-36800800ASquareDI-LineKA36200200AmpCircuitBreaker600VS2IADILineKA-36200200ASquareDI-LineKCB34125125AmpCircuitBreaker480VS2KC34125KCBILine125ASquareDI-LineKC24150AC150AmpCircuitBreaker480VS22PoleKCKC24150150ASquareDI-LineKC24150AB150AmpCircuitBreaker480VKCKC24150ILineS2150ASquareDI-LineQ4B32400400AmpCircuitBreakerLABS4Q4B-32400ILine400ASquareDI-LineKA362251021225AmpCircuitBreaker600VKAKA36225Shunt225ASquareDI-LineKAB362251021225AmpCircuitBreaker600VKAB36225Shunt225ASquareDI-LineKAB36200200AmpCircuitBreaker600VILineKABKAB-36200200ASquareDI-LineLI36400400AmpCircuitBreakerI-LimiterS3IADLI-36400400ASquareDI-LineQ432400400AmpCircuitBreaker240VLAS4ILineQ4-32400400ASquareDI-LineKAB36225225AmpCircuitBreaker600VILineKABKAB-36225225ASquareDI-LineLI36400400AmpI-LimiterCircuitBreaker600VLI-36400SqD400ASquareDI-LineIK34200200AmpCircuitBreakerBlack480VILineIK-34200200ASquareDI-LineJG250JGA36175175AmpPowerPactBreaker600VILineJGA175ASquareDI-LineKA26250AB250AmpCircuitBreaker600VKAKAAS2KA26250250ASquareDI-LineKH36125125AmpCircuitBreaker600VS2IADILineKH-36125125ASquareDI-LineKA361501021150AmpCircuitBreaker600VKAKA36150Shunt150ASquareDI-LineKA26250BC250AmpCircuitBreaker600VKAKAAS2KA26250250ASquareDI-LineQ432300300AmpCircuitBreaker240VILineLAS4Q4-323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