The Application Of Main Board In New Digital Protection Device

It is unavoidable that all sorts of faults happen in the running of power systems, so the installation of protection devices in electric equipments is a powerful measure for the safety of power systems. The developmental requirement of power systems and the continuous appearance of new technology are the source of the evolution of the theory and technology in relay protection of power systems. With the development of computer technology, relay protection has entered into digital age.In recent years, there have been abundant experiences in the applying and development of digital protection. Current devices have high performance in reliability, economy and speed, However, there are still many disadvantages in the existing microprocessor-based protection with the increasing maturation of power systems, the growing development of computer technology and the higher requirement for protection devices. So this paper presents a new scheme of using double CPU: CPUs in main board and managing board are linked via CAN buses. The managing board realizes the person-computer dialogs. This paper will introduce MCU chip, SPI, data sampling and its algorithms digital output circuit in mainboard and anti-jamming method in the device.MCU is the core of protection devices, MCUs in both managing and main boards are both MC9S12DG256 chips. The applying of SPI improves the reliability, simplifies the circuit and expands the external devices. The paper will introduce SPI separately.According to the designing requirement of relay protection, the paper analyses the bad handling ability of single A/D converters, the conflict between high speed and high precision of VFC, low precision in inside A/D of MC9S12DG256, then brings forward the AD7890 which include multi-path switches, track/hold and A/D circuits. In addition ,the traditional digital output circuit consists of parallel interfaces. photo-electricity segregation and middle relays, which are complex and low reliable. The use of MC33291 chip improves the performance of the device. Moreover, for data disposal, we select the algorithm of the combination of Fourier and difference algorithm. In the end, we present the interference-free methods in software and hardware of devices.The developing direction of new relay protection is high speed. intelligence and integrity. MC9S12DG256,SPI,the DATA sampling and its algorithm, the digital output circuit presented in this paper greatly enhance the speed, precision, reliability and anti-jamming. Those improvements are powerful technology supports in running more safely and more reliably of power systems.