Short-circuit currents of renewable energy sources exhibit different characteristics from the conventional power grid

such as controlled phase and limited amplitude. These factors can significantly impact the sensitivity and reliability of the pilot current differential protection on AC transmission lines

which relies on the fixed restraint coefficient. Additionally

the decreased precision of Fourier algorithm calculations further worsens the adaptability of the protection. In this paper

a novel line protection based on sampled values is proposed

which is not affected by the control strategies of renewable energy sources. The analysis initially examines the disparities and correlations between the sampled current and voltage under internal and external faults. Building upon this analysis

the cumulative-current differential protection utilizing the differential sampled current for operation and the differential sampled voltage for restraint is proposed. To further enhance the sensitivity during internal faults and maintain reliability during external faults

a sampling plane is constructed to extract sampled value features

which are unaffected by the control strategies of renewable energy sources. Leveraging these findings

a self-adaptive restraint coefficient is incorporated as an additional parameter to supplement the existing restraint value. During internal faults

the operating and restraining values reflect the amplitude characteristics of the fault current and line capacitance current

respectively

making fault identification results reliable. Moreover

the self-adaptive restraint coefficient can also distinguish between internal and external faults

reducing the restraining value and enhancing the sensitivity of protection

especially in scenarios involving high impedance short circuits and weakly coupled systems. The proposed methodology utilizes sampled values

eliminating the need for Fourier calculations and effectively mitigating the influences of controlled phase and amplitude limitations of fault currents in renewable energy sources. The PSCAD/EMTDC platform is used to build models of power systems with renewable energy integration

and the effectiveness and operational speed of the proposed principle are demonstrated via a large number of simulations.