AC/DC line touching fault protection scheme based on AC single-ended fault information

For hybrid parallel HVAC/HVDC overhead transmission lines (HPOTLs), the probability of AC/DC line touching faults (LTFs) between conductors of different systems are greatly increased. It is more conducive to the safety and stability of the system to deal with the fault by the AC circuit breaker tripping after the LTFs, but there is currently a lack of AC/DC LTF protection schemes specifically designed to match AC circuit breakers. Therefore, this paper proposes a new AC/DC LTF protection scheme, which only requires obtaining single-ended fault information from the AC transmission line and can complete the LTF discrimination without interacting with other devices. Firstly, the expression of DC component when only AC line fault and when AC/DC LTF are derived, which reveals that there is an essential difference in the composition of DC component under the two fault conditions. Then, the main criterion based on the ratio of DC component to the root mean square (RMS) of transient current is constructed. Finally, considering the blind area of the main criterion in individual working conditions, two auxiliary criteria are designed to form a new protection scheme. Experimental results show that the proposed new protection scheme can quickly and reliably identify various different types of AC/DC LTFs.