Abstract: As the first defense line for power grid, the longterm reliable operation of relay protection device is very important for power grid. With the rapid development of smart grid and distributed energy system in recent years, the integration and complexity of the device is increasing as its comprehensive performance is more demanding. In addition, the requirement on primary and secondary equipment fusion and local installation of relay protection device leads to a harsher operation environment for the relay protection device and a higher demand on its reliability. The reliability designs for sampling systems, trip control systems, input and output circuits are introduced from the perspective of hardware reliability, and the design of electromagnetic compatibility(EMC), thermal design and online fault detection design are presented as well.The verification methods of the reliability design are proposed as the final step for a closedloop development process including requirements, design and verification,which offers a reference for improving the reliability of relay protection devices.

Key words: smart grid, relay protection device, hardware reliability design, hardware reliability test, distributed energy, intelligent power plant