Tonghua Wu 1,2,3, Yuping Zheng 1,2,3, Yutao Qiu4, Xiaoping Zhang5, Gang Yao1,2, Jimin Chai3, Xiaofan Hou1
1. NARI Group Corporation/State Grid Electric Power Research Institute，Nanjing 211106, China
2. State Key Laboratory of Smart Grid Protection and Control，Nanjing 211106, China
3. College of Energy and Electrical Engineering Hehai University, Nanjing 210098, China
4. State Grid Zhejiang Electric Power Corporation, Hangzhou 310007, China
5. Electrical and System Engineering, University of Birmingham, Birmingham, B15 2TT, UK
By focusing on the problems of speed, reliability, operation and maintenance in the practical application of line protection in conventional and smart substations, we propose system architecture and a technical scheme for in-site (similar in meaning to on-site or near-process)line protection based on vertical integration and outdoor installation. The functions of the single-bay merging unit, relay protection, and intelligent terminal are vertically integrated to reduce the number and types of devices, simplify the configuration, reduce signal transmission, and shorten the protection action time. In addition, this vertically integrated device is applied to provide data acquisition and control execution support for substation-area protection, security and stability of devices, and other substation-area devices. The vital performance outputs are tested and compared. Finally, the experimental results verify that the proposed scheme is feasible and the technology is advanced.
Line protection, In-site relay protection, Merging unit, Vertical integration.
The protection devices of a conventional substation are usually installed in a control or protection room and use direct sampling and tripping via electrical cables. The distance between the primary and secondary equipment results in longer cables, which present some problems such as current transformer (CT) saturation, multi-point grounding, crosstalk, distributed capacitance discharge, and failure in data sharing .
Smart substations make data sharing possible by adding intelligent electronic devices, which include a merging unit and an intelligent terminal. These process-level devices can solve the problem of long cables through near-process installation in the control cubicle. However, new devices and installation methods present new problems such as the following.
1) A 5–10-ms actuation time delay is added because the installation of intermediate devices (transmission, sampling, and tripping), which also reduces the reliability and quick action of the main protection and makes the grid operate at the boundary condition.
2) The malfunction rate of the process-level devices is relatively high because they are installed in control cubicles of the primary equipment; thus, they operate under poor environmental condition, which affects the system reliability [2-5].
Reference  proposed a strategy of a smart substation with vertically integrated device design and system integration based on discrete components. This strategy integrates the functions of merging units, protection devices, and intelligent terminals in different plugins but uses the same equipment to solve the problem of complicated configuration and redundant devices. However, the integrated equipment still needs to be installed in local control cubicles because its protection grade and anti-interference ability are not better than those of conventional secondary equipment. The problems of high malfunction rate and difficulty in inspection/ debugging still exist. On the other hand, although this method reduces the intermediate transmission devices, different functions are realized in different plug-ins, which causes transmission time delay and provides little response improvement.
In recent years, the development of system on chip (SoC), highly reliable protection techniques, and highly reliable connector techniques have made integrated and local design of protection devices possible [6-8]. A vertical function- integrated in-site line-protection scheme based on SoC is presented in the present paper. The functions of the merging units, intelligent terminal, and line protection are integrated in a single plug-in to shorten the response time, minimize the device types, and simplify the configuration. The miniaturization design supports outdoor installation. The standard connector interface realizes plug and play (PnP). The performance test and comparison analysis are discussed in the last section.