Application Of Communication Technology To Digital Protection Devices

Relay protection is very important to guarantee the security of electric power system, so the reliability, rapidness, economy and sensitivity of relay protection devices have large effects to the development of power system. With the improvement of computers, the studies of digital protection devices based on MCU have given them better solution.In recent years, with the development of communication technologies, digital protection devices are also improved. In this paper, the communications that are used in digital protection device and the protocol they followed are studied. As a kind of field bus technology, CAN (control area network) is applied to the communications of double MCU, which has higher reliability and strong transmission ability. Because the transmission data are given in digital protection device, we need to establish the adapted transmission regulation based on the standard CAN protocol, which is very important to guarantee the consecution and veracity of data. In our protection device, CAN is used for the communication of double MCU, one is the main protection MCU, which gathers the analog data, drives the switch-out and switch-in circuit, the other is managing MCU, which takes charge the person-computerdialogue and the communication with the outside devices. CAN is the ligament of them, so its protocol is very important to the protection device.The Inter-IC Bus (IIC or I2C) is a two-wire, bi-directional serial bus that provides a simple, efficient method of data exchange between devices. Being a two-wire device, the IIC Bus minimizes the need for large numbers of connections between devices, and eliminates the need for an address decoder. IIC is used to communicate with clock chip PCF8583, which can directly attain and revise the clock in PCF8583 and revise the software clock. In addition, we simulate the IIC bus using the general I/O interfaces, which greatly extend the applying range of IIC bus. Those devices that have not IIC bus are able to communicate with some chips that are very needed.SPI and SCI are serial communication interfaces that are extensively applied. In this paper, the communication of MCU and MC33884 is introduced. As a switch monitor interface, MC33884 can provide the switch-on circuit for the protection equipment. Compared with the old switch-on circuit, it has many excellent features. Using the SPI interface, the area of PCB and the interfaces of MCU are both saved. Moreover, MC33884 has the advantages in temperature and disturbance resisting. The reliability and economy of the new switch-on circuit also have great improvement. SCI is used to communicate with MC908GP32, which has the special function to communicate with Internet network. This is an important research, if it is succeeded, many remote communication problems of protection equipment will be solved.So with the research of MCU with high-performance, multi-functional and strong integration, digital protection devices will be reformed gradually, which will follow the international advanced technologies and promote the improvement of electric power system.