The protection system is an integral part of an electrical transmission system. Previously, various protection methods have been proposed for AC systems and have been hammered for years to achieve better performance. In recent decades, HVDC transmission has been introduced as a solution for long-distance transmissions and offshore transmission, thanks to technological developments in power electronics. Fast and flexible control, high transmission capacity, economical justification for distances greater than 500 km (depends on power electronic technology) and less occupied footprint (RoW) compared to CVC transmission for a certain capacity of power[1], are some of the advantages of using HVDC transmission. Statistical analysis on an HVDC transmission system in China shows that 36.8% of 114 valve group failures were caused by line protection zone faults[2]. Thus, a reliable protection method can prevent erroneous fault detection and thus reduce total power outages. Differential protection is one of the traditional solutions used for AC transmission. In [3], a typical SIEMENS HVDC line protection configuration was studied, introducing differential protection as a backup protection. An improved differential protection of Current Source Converter (CSC)-HVDC transmission lines was proposed in [4] in which a composite of a blocking unit and a newly defined differential current criterion was used for the fault detection. [5] Defined a signal distance between rectifier side and inverter side currents to distinguish external and internal faults. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get Original Essay The effect of capacitive current and the problematic requirements of communication channels have been alleviated in [6], [7]. Transient power and other combinations of bilateral voltage and current measurements have been studied in [8]–[10]. The presence of smoothing reactors and DC-side filters at both ends of a CSC-HVDC link makes it possible to implement certain non-unitary selective protection methods[11], such as the use of the impedance characteristic of the reactors smoothing and DC side filters in faulty conditions. which was carried out in [2], [12], [13]. Traveling wave protection (TWP), which is used as primary protection [14], can benefit from some methods such as principal component analysis (PCA), wavelet transform (WT), etc. [15]–[17], but the attenuation and distortion of the traveling wave caused by fault resistance and fault location must be considered. Although some protections have been suggested for VSC-HVDC systems, they can also be applied to CSC-HVDC transmission lines. (methods based on current and voltage derivatives can also be mentioned, which in case the references in the introductory part reach more than 23). It should be noted that almost all of the research mentioned has used the concept of threshold as a criterion which is usually obtained non-analytically (worst case based). There is usually a trade-off between security and reliability in protection systems, leading to inaccuracy in threshold-based methods. On March 21, 2005, the primary protection of Tian-Gaung HVDC system failed to detect a high impedance fault because.