An adaptive reclosing scheme for flexible DC grid based on residual voltage S-transformation.

When a fault occurs on a line, it is necessary to quickly isolate the fault to improve the safety and reliability of the transmission system. Due to the lack of effective ability to identify the nature of faults, the traditional automatic reclosing scheme is highly likely to cause the circuit breaker to reclose onto a permanent fault in practical applications. This will then cause a secondary impact on the power transmission system, seriously threatening the stable operation of the system. Furthermore, existing methods lack sufficient accuracy in determining fault arc extinction moments, making it difficult to meet the urgent need for rapid power supply restoration. In view of the above problems, this paper innovatively proposes an adaptive reclosing scheme based on the S-transform of the residual voltage. This scheme cleverly applies the principle of electrostatic induction to accurately calculate the induced voltage generated by the healthy pole line on the faulty pole line before and after the fault arc extinction, and then discovers the key characteristic that after the fault arc extinction, the voltage of the faulty pole will deviate from the zero axis due to the effect of the induced voltage. Based on this important discovery, this paper conducts an S-transform processing on the residual voltage of the faulty pole, and further enhances the abrupt change characteristics of the residual voltage by calculating the sum of the amplitude squares and the mean value, thus achieving the accurate identification of the fault nature and the precise determination of the arc extinction moment. It is particularly worth mentioning that this method does not require the addition of extra control measures during the implementation process, and has high convenience and practicality. Through simulation experiments for verification, the results clearly show that compared with the traditional automatic reclosing scheme, when facing transient faults, the scheme proposed in this paper can shorten the reclosing time, and thus effectively accelerate the speed of the system's power supply restoration. At the same time, this scheme can also effectively prevent the secondary fault impact on the system caused by the DC circuit breaker reclosing onto a permanent fault, providing a more reliable guarantee for the safe and stable operation of the power transmission system.