Aiming at the difficulties of load transfer without power interruption between two distribution lines with 30° phase angle difference which are existed in a fair amount in present power system in China

a scheme of fast closing and opening loop is proposed to shorten the duration of loop current

and the sequence control of pro-assigned circuit breaker group is proposed to copy with the possible refusing action of circuit breaker. Taking the real network as case study

firstly

the loop current characteristics under the fault and normal condition are analyzed. The electrodynamic force can be ignored if the corresponding power system is not working in its maximum operation mode. Secondly

the allowable loop current time duration of main electrical equipment to bear the thermal effect is estimated as well as the maximum duration of over limit loop current considering fault scenarios without affecting relay protection. And the minimum loop current time duration will be selected as the maximum operation time window for sequence control of pre-assigned circuit breaker group. Thirdly

it is revealed that the minimum loop current can be obtained under the coordinated selection between angle of voltage on two sides of the closing circuit breaker and the time interval of closing-opening of pre-assigned circuit breaker group. Finally

the overvoltage effect due to the loop closing-opening operation has been studied. The whole studies provide a calculation support for the proposed scheme of high-speed and sequence control automatic loop closing-opening to finish the load transfer without interruption operation

and it is proved by the pilot real applications.