Studies On Internet Technology Based Communication System In Power System Wide Area Protection

The power industry of China is in the transition from the stage of "interconnection of nationwide power grid, west-east electricity transmission, extra-high voltage power transmission and large power generation units" to the stage of "ultra-high voltage power transmission, smart grid and green energy generation". The reliability of power supply is increased as well as the operation and control for power grids are going harder and harder. Once the grid has a serious failure which can lead to wide spread break out. it will cause huge losses on the national economic and severe negative impacts on the community. The sphere of influence of interconnected power grid blackouts and socio-economic losses caused by blackouts can be controlled by the reliable and rapid relay protection and the emergency control scheme. But the experience of several large area blackouts indicated that problems of traditional protection may cause threats to the safe and stable operation for the interconnected power grid.The wide area protection system (WAPS) provides the important means of control for ensuring the safe and stable operation for the interconnected power grid. The real-time and reliable communication is the key for WAPS. WAPS has the characteristics include diversified system structure, covering a wide geographical field, lots of monitoring points and complex communication process et al. The traditional point-to-point or the dedicated channel communication in power systems can not meet WAPS’s demand for communication. To meet the demand for transmitting various information for power system operation and control on the power information network platform, a Utility Intranet based on Internet technologies will be used widely under the trend of rapid developing of smart grid. Communication technologies based on Internet protocols will be new technology means for the implementation of the WAPS communication. In the thesis Internet protocols based communication technologies will be researched for WAPS’s demand for the real-time capability and reliability of the information transmission in power grids. It has theoretical and practical significance for the implementation of WAPS. The main contents of the thesis are about the Internet communication technology and its application in the information transmission for WAPS in power systems. It focus on the Internet quality of service guarantee technology and the network transport layer stream control transport protocol to ensure real-time capability and reliability of information transmission for WAPS and the method for designing the WAPS simulation model based on the standard benchmark system on EPOCHS. It is of great significance for the Internet communication technology can be applied to the information transmission for the operation and control for power systems as well as WAPS is applied into the actual system.The thesis introduces the definition and the system architecture for wide area protection (WAP) firstly, analyzes WAPS’s demand for communication, takes an overview about applications of Internet technologies in power systems and research status for WAPS communication, and illustrates the main works in the thesis.To guarantee the quality of service of various wide area communication services for integrated information transmission in power systems, an improved worst-case fair weighted fair queueing plus (IWF Q+) scheduling algorithm was proposed. IWF-Q+scheduling algorithm was obtained by introducing virtual delay time in the formulas of virtual start time and virtual finish time of WF2Q+scheduling algorithm. The problem that the packets of high-priority communication services were delayed by WF2Q+scheduling algorithm was solved by IWF2Q+scheduling algorithm. The integrated information transmission network model on IEEE14bus test system was constructed in NS2based on the Differentiated Services (Diffserv) architectural model which was implemented by IWF2Q+scheduling algorithm. Real-time performance and fairness of the communication services in integrated information transmission had been verified by a network simulation. The simulation result shows that IWF2Q+scheduling algorithm is validity and feasibility as the packet delay of high-priority communication services is reduced and the fairness of the traffics is considered.Electric power wide area control systems (WACS) need reliable real-time information transmission. An Internet Protocol (IP) based private Utility Intranet can form a medium for protection and control system communication. This article discuss differentiated services (DiffServ) for quality of service guarantees in Utility Intranet communication. As a case study, the simulation models of the wide area frequency stability predictive control system (WAFSPCS) and the communication system are created on the electric power and communication synchronizing simulator (EPOCHS). WAFSPCS is implemented on a modified IEEE50-generator test system. It is used to research the quality of service guarantee problem for the WACS information transmission implemented by the Internet protocol. The agent control system for WAFSPC is constructed. It has the centralized master-slave structure. A hierarchical star-ring communication network simulation model is designed. PSS/E is combined the Network Simulator2(NS2) in the EPOCHS simulation environment. The simulation results show the effectiveness of the advocated QoS guarantee scheme. The optional communication recovery technologies for the IntelliGrid architecture are analyzed and compared. It is known that SCTP is a transport layer protocol which can provide the communications recovery service. SCTP has a good applying prospect in power communication system. The characteristics of SCTP and TCP are compared and analyzed. In the case of network link failure, network-level fault tolerance mechanism based on SCTP multi-homing path switch is simulated. In order to find a way to overcome the drawback of the original SCTP path switching method based on multi-homing, an improved method is proposed. The simulation verifies the validity of the method in the single-router network model and the multi-router network model.When a communication link and a transmission line fail simultaneously, with consideration of the problem that how to ensure that the faulty transmission line is located and removed quickly and accurately by the wide area backup protection (WABP) through improving real-time capability and reliability for information transmission, the SCTP based communication mode is introduced in the thesis. The measure to improve real-time capability is taken. It is applied to the information transmission for WABP with the improved multi-homing path switching method of SCTP. The simulation model is constructed for the WABP communication mode research. The communication network and protocols, WABP agent system and the power grid are modeled on EPOCHS. The effectiveness of the proposed communication mode, which is used in WABP information transmission, is verified by simulating experiments.