1756L55M14 1756L55M14

　电力变压器纵差保护是所有电气元件差动保护中最复杂的一种。在运行过程中,保护误动作的现象也时有发生,在1997年华北电网220kV及以上变压器不正确动作统计中,共不正确动作18次,其中变压器纵差保护不正确动作5次,约占不正确动作的1/3。分析造成纵差保护误动和拒动的原因,有运行维护和管理上的问题,也有制造、安装和设计上的问题。电工之家就运行工作中容易出现的问题进行分析并介绍处理方法。
　　1. 由变压器励磁涌流所产生的不平衡的电流
　　变压器在正常运行时,励磁电流只流过电源侧,在纵差保护中将产生不平衡电流。一般情况下励磁电流为额定电流的3%～8%,大型变压器的励磁电流相对较小,一般小于1%。在外部故障时,由于电压降低,励磁电流也相应减少,其影响就小。但是,在变压器空载投入和外部故障切除后电压恢复时,则可能产生数值很大的励磁涌流,其数值可达变压器额定电流的6～8倍。励磁涌流中含有大量的非周期分量和高次谐波分量,其中以二次谐波为主,在波形中还会出现间断角。
　　变压器纵差保护中减小励磁涌流影响的方法:(1)采用BCH型具有速饱和变流器的继电器,当外部故障时,所含非周期分量的最大不平衡电流能使速饱和变流器的铁芯很快饱和,致使不平衡电流难以传变到差动继电器的线圈上,保证差动保护不会误动。内部故障时,速饱和变流器的一次线圈中虽然也有非周期分量,但它的衰减速度很快,一般2个周期衰减完毕,以后变流器中通过的全是周期性的短路电流,所以继电器能灵敏动作。(2)微机型变压器纵差保护多采用二次谐波制动原理,如在外部故障切除时差动保护误动作,保护为分相制动方式时可设为最大相制动方式,即或门制动方式,并在或门制动方式的基础上,减小二次谐波制动系数,可取10%～12%。考虑到系统容量大、外部短路故障切除时五次谐波也较大的因素可增设五次谐波制动措施。如一个变压器有两套差动保护,可采用波形对称原理来识别励磁涌流。因为波形对称原理比二次谐波制动识别励磁涌流要灵敏、可靠。

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ROCKWELL ICS Triplex Trusted TMR ESD SIS

T8403 Trusted TMR 24Vdc Digital Input Module

T8431 Trusted TMR Analogue Input Module

T8480 Trusted TMR Analogue Output Module

T8451 Trusted TMR 24Vdc Digital Output Module

T8433 Trusted TMR Isolated Analogue Input Module

T8461 Trusted TMR 24 48Vdc Digital Output Module

T8423 Trusted TMR 35 - 120Vdc Digital Input Module

T8402 Trusted Dual 24Vdc Digital Input Module

T8424 Trusted TMR 120Vac Digital Input Module

T8473 Trusted TMR 120Vac Isolated Digital Output Module

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T8110B Trusted TMR Processor

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T813X Trusted TMR Processor Interface Adapter

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T8153 Trusted Communication Interface Adapter

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T8310 Trusted Expander Processor

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T8270 24Vdc Fan Assembly, Rack Mounting

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T8231 Power Pack

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T8173 Trusted Gateway Adaptor

T8170 Trusted Gateway Module

T8160 Trusted TMR Regent Interface

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T8805 Trusted 60 Channel 24 Vdc Digital Input FTA

T8821 Trusted 40 Channel 120Vdc Digital Input FTA

T8824 Trusted 40 Channel 120Vac Digital Input FTA

T8831 Trusted 40 Channel Analogue Input FTA

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T8834 Trusted 20 Channel AI_DI FTA external power

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T8873 Trusted 16 Channel 120Vac Isolated Digital Output FTA

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TC600 Trusted Dual IO SmartSlot Cables

TC800 Trusted Special IO Cables

TC700 Trusted Dual IO Companion Slot Cables

TC300 Trusted Communications Cables

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TC500 Trusted TMR IO SmartSlot Cables

TC-301-02-4M5 Local Expansion Cable

TC-001-02-2M5 Chassis Power Cable

TC-201-02-4M5 IO Companion Slot