Research on Communication Systems under Wide Area Network Protection
Ai Hongjie, Qi Xiangdong, Wang Xing
(School of Electronic and Information Engineering, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030024, China) Tel: 13643450973
Abstract: This article discusses the concept of wide area protection (WAN), the functions and structural components of a WAN protection system, and the configuration of its communication network. A simulation of the WAN communication system was conducted using OPNET software. The results demonstrate that the IP over SDH communication mode based on MPLS technology, relying on the low latency and reliability of the SDH self-healing ring, can achieve coordinated operation of the entire power system's protection devices and provides a certain degree of immunity against cascading tripping. This system is of great significance for the safe and stable operation of the power network.
Abstract: Article discussed the wide-area protection concept, function and structure, and the configuration of communication network. OPNET software application to the wan communication system is simulated, the practice has proved, based on MPLS technology IP OVER SDH, relying on SDH self-healing ring low delay and reliability, can realize the whole power system protection device between data quickly transmission and coordinated action of cascade trip will play a certain role, the system of immunity to the safe and stable operation of power network has an important significance.
0 Introduction
For abnormal operation and fault conditions in power systems, the control criteria currently used for relay protection and automatic devices are mostly based on local quantities, reflecting only the operating status of a single point in the system. This fails to reflect the operating status of a larger regional power grid, and the lack of coordination and cooperation between devices makes it difficult to optimize system control. Thus, when a fault occurs at a point in the system, it causes the directly related relay protection and safety automatic devices to activate without considering the impact of this single-point activation on the power flow distribution and network topology of the entire power system. This could further expand the scope of the fault's impact and cause serious accidents such as cascading trips. To ensure coordinated operation among devices distributed throughout the system, it is essential to obtain information from multiple points, including electrical quantities at each test point, operational information of each local device, and network topology information. Therefore, the key to realizing a new generation of protection and control systems lies in how to quickly and reliably transmit this information. This paper proposes to establish a wide area network communication system based on a fiber optic self-healing ring and utilizing IP over SDH based on MPLS technology. This system can quickly determine local fault information and take corresponding protective actions based on the overall network operating status. It can, to a certain extent, avoid cascading tripping and achieve a smooth transition and normal operation of the power grid.
1. Concept and structural composition of wide area systems
Wide-area protection can be defined as: relying on information from multiple points in the power system to quickly, reliably, and accurately isolate faults, while analyzing the impact of fault isolation on the safe and stable operation of the system and taking corresponding control measures, which can improve the available capacity of transmission lines or the reliability of the system. Such a system that simultaneously realizes relay protection and automatic control functions is called a wide-area protection system.
As today's power grids become increasingly large and complex, the requirements for real-time data processing are becoming higher and higher. In line with the development trends of computer and communication technologies, in order to meet the needs of power system protection, wide area network systems must be able to quickly detect local fault information using the information provided by the network, take swift action, and analyze the network topology and power flow before and after the action. They should selectively trip generators, disconnect loads, and reconfigure the power grid to avoid cascading trips or even system collapse.
To ensure the rapid and accurate operation of protection equipment, the data processing and action commands of the wide area network system must meet the following requirements:
First, the real-time performance of data transmission must be guaranteed. Wide-area protection systems are designed for the protection and stability of power systems. Excessive latency in the communication system will result in low real-time performance for the entire system, preventing the decision-making center from responding before the system becomes unstable.
Secondly, the reliability of data transmission must be ensured. Reliability is the foundation for accurate scheduling and optimization by the decision-making center. If data transmission is faulty or fails to transmit at all, it will have a severe impact on the normal operation of the power system.
Based on the definition of a wide area network (WAN), this paper designs a WAN logical structure as shown in Figure 1.
Data from each substation is accessed through the CE (Customer Network Edge) and PE (Carrier Edge Router) to the SDH ring network. The PE of the entire ring network is connected by several (as needed) P (Core Layer Equipment) devices, enabling communication between the substations. The dispatch center accesses the SDH ring network through the core router, allowing the dispatch center to monitor and control the operation of the entire power grid.
The protection system, composed of a dispatch center, monitoring substations, and a high-speed fiber optic network, is similar to a multi-agent system (MAS). Each monitoring substation acts as a hardware agent, and all agents communicate and coordinate their actions. The entire network is adaptive. If a fault occurs at a monitoring substation or a protection device fails to operate, the system can select the optimal path for this fault information. Commands are sent from nearby monitoring substations via the high-speed SDH network to take measures such as load shedding, generator switching, valve control, and system disconnection. Simultaneously, fault information is transmitted to the dispatch center, where fault recording equipment records the fault information.
2 Communication Protocol
According to the requirements of the "Regulations on Security Protection of Secondary Power Systems" (Order No. 5 of the State Electricity Regulatory Commission), various types of data are divided into different security zones. Among them, the data in Security Zone 1 is real-time business data, and the data in Security Zone 2 is non-real-time business data. Regarding the delay performance of the wide-area protection communication system, the literature [3] points out that in order to ensure the acquisition of complete transient information of the system and to issue anti-accident emergency control measures before instability or collapse, in order to control the power system in real time, the system must complete the measurement, transmission and processing of state data within 30"--50ms to ensure that the system obtains complete transient state information and takes anti-accident measures before instability. For a provincial power grid with 50 nodes and substations within a range of 1000km from the central dispatch, the dispatch center master station must obtain the measurement information of all substations within 20ms, and the control command of the master station can also be issued to each substation within 20ms. Therefore, the delay of the entire communication network should be less than 20ms to meet the communication requirements of wide-area protection.
The delay of a wide-area protection communication system can be expressed by the following formula:
In traditional IP transmission, IP packets calculate and compare routing tables at routing crossroads to select the next-hop address. MPLS, however, packages IP packets together for transmission. MPLS technology can be considered a combination of IP and ATM. It only requires hardware switching at the OSI data link layer, integrating IP routing and Layer 2 label switching into a single system. This reduces addressing time overhead, thus effectively solving routing problems, shortening data transmission latency, and enhancing network real-time performance. Furthermore, MPLS features traffic engineering and Quality of Service (QoS) capabilities. Traffic engineering means that MPLS can control the path IP packets take in the network. Unlike traditional networks where a path is selected for an IP packet and transmitted regardless of link congestion, MPLS balances traffic load, preventing traffic from flowing to congested nodes. This avoids blind behavior of IP packets in the network and ensures the rational utilization of network resources.
As for quality of service, it means ensuring speed while reducing the error rate of data transmission and improving transmission quality.
3 Simulation Results
This paper uses OPNET software to simulate the wide area network power communication system described above. A random fault occurs in the system between 100 and 200 seconds. The simulation results are shown in Figure 3.
The simulation results show that the IP over SDH system based on MPLS technology has a latency of only about 16ms, which fully meets the real-time requirements of power system data transmission. It can quickly and accurately process the real-time data of each monitoring substation, transmit control commands, quickly isolate fault points, protect electrical equipment, and ensure the stable operation of the power system.
4. Conclusion
This paper proposes a novel wide-area protection system based on fiber optic networks. This system meets the requirements for safe and stable operation of power systems in terms of both speed and accuracy, supplements and enhances the operational capabilities of the original primary and backup protection equipment, significantly optimizes the operation modes of primary and backup protection, improves the speed and reliability of protection, and to a certain extent ensures the stable operation of the power system. Simulation results demonstrate the feasibility and theoretical advancement of the proposed solution. With the development of computer and communication technologies, the integration of protection and control is becoming increasingly close. Based on this system, further research can be conducted on an integrated protection and control system for power systems based on fiber optic networks, further expanding and improving the application of fiber optic networks in the field of power system protection and control.
References
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