After the Auto Reclosing Circuit Breaker is switched off for some fault reason, it is automatically reclosed by mechanical device or relay automatic device. If the fault of power system is temporary, after the LV circuit breaker is tripped and cut off by relay protection device, it will automatically reclose after a predetermined time. If the fault has been automatically eliminated, the line will restore power supply; if the fault is persistent, the circuit breaker will be tripped again and will not reclose. According to the number of reclosures, it can be divided into one reclosure and multiple reclosures; according to the number of phases, it can be divided into three phases and single phase automatic reclosure; and according to the use situation, it can be divided into one-side power supply and two-side power supply automatic reclosure.

The Auto Reclosing Circuit Breaker is an automatic device that automatically puts the circuit breaker into operation according to the need after the breakdown. Power system operation experience shows that most of the overhead line faults are "instantaneous" and permanent faults are generally less than 10%. Therefore, after the short circuit fault is removed by relay protection, the arc will be extinguished automatically. In most cases, the insulation at the short circuit can be restored automatically. Therefore, automatic overlapping of circuit breakers not only improves the safety and reliability of power supply, reduces the loss of power outage, but also improves the transient level of power system, increases the capacity of high voltage lines, and also corrects the wrong trips caused by circuit breakers or relay protection devices. Therefore, overhead lines should be reclosed automatically.

Main functions of Auto Reclosing Circuit Breaker:

(1) It greatly improves the reliability of power supply and reduces the number of power outages, especially for single-circuit lines with one-side power supply.
(2) The use of Reclosure on high voltage transmission lines can also improve the stability of parallel operation of power systems.
(3) In the process of design and construction of power grid, in some cases, double-circuit lines can be postponed to save investment due to the consideration of reclosure.
(4) It can also correct the wrong tripping of LV circuit breaker itself caused by bad mechanism or misoperation of relay protection.

The economic benefit of reclosure should be measured by the national economic loss caused by power outage when there is no reclosure. Because the reclosing device itself has low investment and reliable operation, it has been widely used in power system.

But things are divided into two parts. After reclosing, when reclosing to permanent fault, it will also bring some adverse effects, such as:

(1) Make the power system suffer the impact of faults once again;
(2) Make the working condition of LV circuit breaker more serious, because it needs to cut off two short-circuit currents in a very short time. This situation must be considered for oil circuit breakers, because the insulation strength of oil has been reduced due to the effect of arc during the first trip, and the second trip after reclosure is carried out under the unfavorable condition that the insulation has been reduced. Therefore, after reclosure, the interruption capacity of oil circuit breakers will also be reduced to varying degrees (generally reduced to about 80%). ) Therefore, in power systems with large short-circuit capacity, the above disadvantages often limit the use of reclosure.