Centralized photovoltaic (PV) systems have different fault characteristics from distributed PV systems due to the different system structures and controls. This makes the fault analysis and protection methods used in distribution networks with distributed PV not suitable for a centralized PV power plant. Therefore, a consolidated expression for the fault current within a PV power plant under different controls was calculated considering the fault response of the PV array. Then, supported by the fault current analysis and the field-testing data, the overcurrent relay (OCR) performance was evaluated in the collection system of an 850 MW PV power plant. It reveals that the OCRs at PV side on overhead lines may malfunction. In this case, a new relay scheme was proposed using directional distance elements. In PSCAD/EMTDC, a detailed PV system model was built and verified using the field-testing data. Simulation results indicate that the proposed relay scheme could effectively solve the problems under variant fault scenarios and PV plant output levels.