Impacts of digital and networked technologies used in smart substation on relay protection

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.

I. Introduction

Smart substation, which serves as the physical basis and important parts of smart grid, adopts a lot of advanced, integrative and intelligent equipments, to achieve the functions such as information acquisition, measurement, metering, control and protection [1]. Smart substation has two basic characteristics, namely primary equipment intelligentization and secondary equipment networking. With regard to the first characteristic, it means that a number of intelligent equipments are used in the primary side. For instance, electronic voltage and current instrument transformers with digital outputs are selected, and smart switches (or traditional switches equipped with smart terminals) are installed to implement the accuracy control and local motion of switch. For the other characteristic, it means that the secondary equipments of smart substation, such as the protection, control, and metering, can exchange information according to communication networks. Further, between the primary and secondary equipments, the optical fiber transmission digital coding information is used to transmit sampling values, switch information, control commands, etc., and conventional hard-wiring control cables are cancelled.