Research Of Real-time Ethernet To Enhance Communication Of Digital Substation Process Layer

With the development of information technology, computer technology and network technology, building a digital substation becomes available as a result of these necessary conditions. According to the IEC61850standard, the digital substation can be divided into three parts:the substation layer, the spacer layer and the process layer corresponding to substation’s structure and logic. As the interface of primary equipments and secondary equipments, process layer should provide the following functions:uploading real-time sampling values; exchanging some detection and statistical information such as circuit breaker’s and switches’working conditions and so on. Compared with spacer layer, messages of process layer have a larger quantity and own more variable types. Therefore under different working conditions, the claim of the response and priority requirement for these messages is different as well. To ensure the normal communication, process layer select switched Ethernet to work in process layer instead of parallel cable. We call this communication means process bus technology.This paper studies the principle of multiple real-time Ethernet technology and explores how to apply real-time Ethernet technology in the process layer of digital substation expecting to improve the communication performance of the process layer bus. Generally, reliability, synchronization and time-liness consist of the three aspects of communication evaluation. For the first two aspects, the solution is relatively uniform:IEC62439standard is used to achieve redundancy so as to solve reliability problem; Then, it’s widely accepted that using IEEE1588protocol to solve synchronization problem of sampling values. But for the third point, the main solutions rely on message priority, network structure and streaming technology of ethernet switch. However, these methods cost too much and can’t solve problems fundamentally. Above all, the subject of this paper focus on the third problem.The root cause of that Ethernet can’t guarante real-time transmission is its physical layer adopts Collision Detection and Carrier Sense Multiple Access (CSMA/CD) technology. Thus, each node in the communication network uses a competitive mechanism to possess bandwidth. When several nodes detect the communication bus is idle, they send packets at the same time, conflict happens. Conflict nodes stop sending packets immediately, after a short period, they send again. This mechanism is simple and reliable, but also cause uncertain delay. Under heavy network load, some nodes even can’t send packets. So, Ethernet can’t meet the requirement of real-time transmission.Combined with the topic content of this paper, we start from the structure of digital substation. This paper points out the primary problems and present research status in process layer communication. Real-time Ethernet is introduced in this paper, we analyse the technical characteristics of different real-time Ethernet and their principle to achieve timeliness. With the principle and the characteristics of data transmission in process layer, a scheme that how to apply real-time Ethernet in process layer of digital substaion is discussed. To evaluate the performance of this scheme, an experimental platform is created. Finally, the scheme is tested under the help of this platform and the result is analysed as well.