Compared to the AC microgrids, the advantages of DC microgrids are notable. However, the development of DC microgrids is being constrained by the lack of mature protection schemes. For the foundation of designing protection schemes, the existing fault analysis focused on the fault characteristics of voltage source converters and ignored other generators. However, in DC microgrids with high permeability of photovoltaic (PV) powers, the effects of PV powers should be paid considerable attention. In this paper, the cable fault characteristics of the PV powers are analyzed in detail, and both the pole-to-ground fault and the pole-to-pole fault are considered. The fault processes are divided into several stages, and the fault circuits and main equations are described for each stage. All of the analyses are verified by the simulation model based on the PSCAD/EMTDC, and with the help of simulation results, the two main challenges the protection system confronted with are emphasized and the impacts of fault distance are analyzed. Finally, this paper proposes to employ a more reasonable converter structure and a transverse differential protection to overcome the main challenges; the effectiveness of the methods is verified by the simulation.