There exists complicated electromagnetic coupling between different polar lines for double-circuit high-voltage direct current(HVDC)transmission lines on the same tower. In an actual project

the control and protection of each circuit is still based on the single-circuit electrical quantities. Inevitably

it is unable to achieve its complete decoupling

which increases the difficulty in accurate fault location. Firstly

the characteristics of the modulus based on single-circuit quantities are analyzed using the transformation matrix. Based on this

the new differential-mode component

which has eliminated the influence of the earth-mode

is constructed. The characteristics and parameter selection of the new differential-mode component are also given. Then

given the characteristic that the voltage distributions of the non-fault point calculated by the voltage and current measured in both terminals have the largest difference around the fault time

the maximum voltage difference zone of the non-fault point is defined. Further

a fault location method based on single-circuit quantities is proposed. The PSCAD/EMTDC simulation model of real double-circuit HVDC transmission lines on the same tower is constructed with extensive simulation results showing that the proposed method is not only highly accurate

but also unaffected by fault polar lines

fault position and the resistance. This work is supported by National Natural Science Foundation of China(No. 51577072)and Fundamental Research Funds for the Central Universities(No. 2013ZZ028).