Digital substation is different with the traditional substation in structure, communication mode and communication content. The signal received by the relay protection device and protection of traditional relay device are also different, therefore, the new requirements on relay protection tester has been put out. The definition and function of optical digital relay protection tester is introduced in this paper, which follow the standard IEC61850, and an implementation method of ARM based on Cotex-M3 processor is proposed. The tester complete the Ethernet communication with the host computer, which uses Ethernet controller built-in ARM Cotex-M3 processor, also implement the test data package ,transmission and receiving of the protection signal. The test instrument based ARM Cotex-M3 processor has high operation ability and interrupt response ability, which uses the C/OS-II real-time high as the operating system software, and it can meet the test requirements of real-time systems.
