With the rapid development of the electricity market, users have put forward higher requirements for electricity consumption. The reliability of power supply and power quality are the two main evaluation indexes of power system. Distribution system automation is the use of modern electronic technology, communication technology, computer technology and network technology to integrate information on the distribution network online and offline data, distribution network data and user data, power grid structure and geographic graphics to form a complete automation The system realizes the modernization of the normal operation and accident monitoring, protection, control, power consumption and distribution management of the power distribution system. The purpose of implementing power distribution system automation is to improve the reliability of power supply, improve the quality of power supply, improve the quality of service, improve the economic efficiency of enterprises, and improve the management level, so as to benefit both power supply enterprises and users. This paper will focus on the implementation of the county-level distribution network automation system, using GPRS technology to realize the distribution network automation system design, so as to share with peers.
1 Design of distribution network automation system based on GPRS
1. 1 System Hierarchy
The distribution network automation system is easy to adopt hierarchical distribution, the general situation is: distribution main station layer, distribution terminal layer, if there is a power supply switch, you can set up a distribution electronic station between the main station and the terminal for data forwarding . Using this layered structure effectively reduces the load of the distribution main station and improves the system efficiency, so that we can reasonably construct the communication topology of the system, thereby saving communication resources and improving the utilization rate. Figure 1 is a schematic diagram of the hierarchy of the system.
Figure 1 Schematic diagram of the hierarchical architecture of the distribution network automation system
1. 2 system networking
The communication network of this system is GPRS network and Inter net network, so there are two ways of data transmission between the monitoring center and the GPRS module on the FTU of the remote monitoring device. One is that the monitoring center connects to the GPRS network through the mobile company's dedicated line or GPRS Modem wireless mode to achieve GPRS network data transmission between the monitoring center and the remote monitoring device FTU; the other is that the monitoring center uses a fixed IP Or access to the Internet network through dynamic IP. Since the GPRS network of China Mobile is interconnected with the Inter net network through the CMNet gateway, the GPRS module on the remote monitoring device FTU can also be connected to the Internet network to realize data communication between the two parties.
This system adopts the way that the monitoring center accesses the Internet network with a fixed IP address. Each communication is established by connecting a remote GPRS data terminal to the base station, connecting to the GPRS network, gathered by the GGSN gateway, passing through the mobile company's internal firewall, router and The Internet network initiates a connection to a fixed IP address, that is to say, a remote GPRS data terminal logs into the monitoring center with a fixed IP address to establish communication with it to realize data transmission. The system's networking scheme is shown in Figure 2. The GPRS network and the Internet are connected to each other. The data transmission between the FTU terminal and the monitoring center is a transparent transmission, and the underlying protocol between the data transmission is blocked. Once the data terminal is connected to the monitoring center, it will always be online! It uses a virtual connection technology between the GPRS network and the Internet, so only when there is data transmission between the two parties, it is charged according to the flow rate, which is economical and affordable.
Figure 2 Schematic diagram of the network structure of the distribution network automation system
2 Analysis of specific problems based on GPRS-based distribution network automation system
2. 1 GPRS communication protocol analysis
When the GPRS module on the FTU is powered on, it is connected to the Internet through the mobile company's network, which can be regarded as a client on the Internet. After the IP address and terminal * on the server are determined, the FTU terminal can be Connect to the server. The end-to-end connection on the Internet using Socket socket communication is a relatively mature method.
So cket essentially provides an endpoint for process communication. Before the process communicates, the two parties must first create an endpoint, otherwise there is no way to establish contact and communicate with each other. Just as before making a call, both parties must own a telephone. Within the Internet, each Socket uses a semi-relevant description: A complete Socket has a locally unique Socket number, which is allocated by the operating system. Most importantly, Socket is designed for the client / server model and provides different So cket system calls for client and server programs. Customers randomly apply for a Socket, the system assigns a Socket number; the server has a globally recognized So cket, any customer can send connection requests and information requests to it. Socket uses the client / server model to skillfully solve the problem of establishing a communication connection between processes. It is very important that the server So cket semi-correlation is recognized globally.
In the GPRS communication of the distribution network automation system, the network communication of the application program ultimately uses the same communication protocol to complete the transmission of information. Both the application and Winso ck work in the user mode of Window s. The operating system cannot complete the communication between networks only through Winsock. It also requires low-level support. The socket emulator (Socket Core Mode Driver) and The transmission driver interface is responsible for network communication in the core state of the operating system, and serves as a communication bridge between Winsock and the transmission protocol. Since most of the objects we transmit are data files of the power distribution system, it is necessary to set the send buffer and the receive buffer of the system accordingly to ensure the transmission and reception of large amounts of file data, so as to achieve narrowband Under the environment, GPRS transmission and communication of relevant data of the distribution network automation system are still realized.
2. 2 Implementation of distribution network automation system
(1) Overhead line
The feeder is connected by two load switches, three sections, and one contact switch, so that the two power points become the hand-in-hand ring network power supply method. Generally two or two contacts are used, and special important users (municipalities, TV stations, and hospitals) use three contacts or Four contacts, but only for two-way automatic, one way can be remotely opened and closed. This not only ensures that each section of each feeder can obtain power from different substations, but also makes the grid and operation mode simple and safe.
The number of sections of each feeder is generally controlled in three sections, with an average of 1.5 ~ 1.8 km / section. For load-intensive areas, according to the load section, each section has a load of <2 500 kv a; for light loads In regions, according to the number of users, each high-voltage user is less than 10 users.
The branch line is connected to the main line through the load switch. When a permanent fault occurs on the branch line, the load switch is used to isolate the faulty branch line through fault location and restore the main line power supply. The 10 kV overhead main line uses 185 conductors, and the branch line uses 95 conductors.
(2) Cable ring network
The main loop is segmented through the ring network cabinet, and the branch circuit is connected with the outgoing load switch. Users access the branch loop through the cable branch box; each branch loop is connected to the adjacent main loop. Different ends of the main ring network are connected to different substations. All loops operate in open loop. When a permanent fault occurs in any section of the loop, through fault location, disconnect the switch or cable plug at both ends of the fault to isolate the fault and at the same time make the fault at the point where the loop is disconnected. Failure of any segment of the main ring network or branch ring network will not affect the power supply.
The redistribution load capacity of each ring network switchgear is "5 000 kVA. The 10kV main line uses 240 or above copper core cable, and the branch line uses 120 or above copper core cable.
(3) Switch equipment
Vacuum load switches are used for the section of overhead lines. When a short circuit fault occurs on the line, the circuit breaker of the substation performs the protection action. The switch on the column is controlled by the distribution automation control system to perform fault isolation and load transfer and ground fault isolation operations. The inlet and outlet switch of the cable ring network cabinet and the load switch on the column achieve the same function. The fully sealed insulation and arc extinguishing gas isolation FS6 load switch device is used.
3 Conclusion
The development of distribution automation has not yet been able to be carried out on a large scale. The main reasons are: on the one hand, due to excessive project investment and doubts about the implementation efficiency; on the other hand, due to the lagging of related supporting reform measures such as electricity price reform. This paper designs and analyzes the implementation of distribution network automation system based on GPRS technology, which is a beneficial attempt to implement distribution network automation. With the deepening of power market reforms, only by improving the reliability of distribution networks and strengthening distribution management through distribution automation can both power supply companies and users benefit. Therefore, the implementation of distribution automation is an inevitable trend.
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