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Compared with the relay protection devices located in traditional substation, the protection devices used in smart substation based on IEC61850 are different under hardware structure and signal processing. Electromagnetic instrument transformers are replaced by electronic transformers with digital outputs, and hard-wiring control cables are displaced by optical fibers to transmit switch information and control commands. Besides, some communication networks are built for information sharing Adopting the digital acquisition equipment, fiber communication and information network will undoubtedly affect the relay protection's action performance and may expand the functions to a certain extent. In this paper, the structure scheme of a smart substation was introduced firstly. Then, the technical characteristics of the electronic transformer and communication network technologies were analyzed, and their impacts on the operation performance and functional expansion of the relay protection installed in the substation's bay level were studied. According to the analysis results, it is founded that, applying the electronic instrument transformer can help to enhance the relay protection's reliability and simplify its hardware configuration, and constructing the communication network can contribute to achieve the integrated protection and substation area protection. In addition, a few application problems existed in the electronic transformer and communication network were briefly discussed.