三段爱惜和四段爱惜(国外英文资料).docVIP

三段保护和四段保护(国外英文资料) 3 protection of low voltage circuit breaker: Overload long delay protection, short circuit short delay protection, instantaneous action protection; In the case of A distribution breaker, it has A class A and B: class A is non-selective, and class B is selective. The so-called choice type refers to the three protection features of the circuit breaker, which have overload length delay, short circuit short delay and short circuit. Universal type (also called A frame type) of the circuit breaker DW15 series, DW17 (ME) series, AH series and DW40, most of DW45 series is B type, while DZ5, DZ15, DZ20, TO, TG, CM1, TM30 and HSM1 series and some specifications of the universal type DW15, DW17 for only overload long time delay, short circuit instantaneous secondary protection, they are belong TO wide choices of class A circuit breaker. Selective protection, as shown in figure 1. When F point short circuit, only near the point F QF2 circuit breaker action, and the azimuth QF1 circuit breaker is not action, this is the selective protection (due to QF1 not action, it is to keep not QF3, QF4 branch of the failure of power supply). If QF2 and QF1 is A kind of circuit breaker, the F point short circuit, short circuit current value reaches A certain value, the QF1, QF2 action at the same time, QF1 circuit breaker under the loop and its branch power outages, all this is not the selective protection. Can realize the reason of the selective protection, QF1 for B type circuit breaker, it has a short circuit, short time delay performance when F point short circuit, short circuit current to flow through QF2 branch, also flows through QF1 loop, the instantaneous QF2 action trip action (usually it all breaking time not more than 0.02 s), because QF1 short time delay, QF1 within 0.02 s not action (its short time delay acuity 0.1 s or 0.2, 0.3, 0.4 s). When the QF2 action cut off the fault line, the whole system returned to normal. Visible, if the requirement for selective