This paper presents a distributed multiagent scheme to detect and identify cyber threats on the protection systems of power grids. The integration of information and communication technologies into existing power grids builds critical cyber-physical energy systems, in which digital relays are networked cyber-physical components subject to various cyber threats. Cyber attacks on protection systems may mimic real faults, cause component failure, and disable the communication links. Agents utilize both cyber and physical properties to reinforce the detection technique and further distinguish cyber attacks from physical faults. This paper also introduces the problem of secure communication protocols and highlights the comparative studies for enhancing the security of the protection systems. The proposed scheme is validated using a benchmark power system under various fault and cyber attack scenarios.