Distribution monitoring system based on GPRS communication

　　With the development of science and technology, realizing the automation of low-voltage distribution network has become the development trend of power system. As the last link of power transmission and distribution system, the degree of automation of low-voltage distribution network is closely related to the quality and reliability of power supply and consumption. Distribution transformer is a kind of power equipment that directly distributes electric energy to low-voltage users. Its operation data is an important part of the basic data of the whole distribution network. Therefore, it is necessary to monitor its operating parameters and status. This paper introduces the distribution transformer monitoring system established by using GRPS as a means of communication.

　　1、 Communication mode of distribution transformer monitoring system

　　1.1 data transmission station

　　The advantage of data transmission radio station is that there is no additional cost for normal operation in addition to the annual frequency point fee; The disadvantage is that it is greatly affected by terrain and climate, resulting in poor reliability and real-time performance of the system, and it is unable to report actively.

　　1.2 GSM mode

　　GSM mode can realize active reporting; The disadvantage is that it charges according to the rule, the operation cost is high, and the delay is quite long when the server of the short message center is busy on holidays.

　　1.3 optical fiber access

　　Optical fiber communication is stable and reliable, but it has large construction cost, poor expansibility and inconvenient equipment maintenance.

　　1.4 GPRS communication

　　General packet radio service GPRS is a new wireless data transmission service developed from the existing GSM system. Its purpose is to provide mobile users with high-speed wireless IP or X.25 services. The theoretical bandwidth of GPRS can reach 128kbit / s, and the actual application bandwidth is about 40 ~ 100kbit / s. TCP and IP connections are provided on this channel, which can be used for In-ternet connection, data transmission and other applications. GPRS adopts packet switching technology. Each user can occupy multiple wireless channels at the same time, and the same wireless channel can be shared by multiple users. Resources are effectively used. GPRS allows users to send and receive data in end-to-end packet transfer mode without using the network resources of circuit switching mode. GPRS is always online and billed by traffic, which provides an efficient and low-cost wireless packet data service. It is especially suitable for intermittent, sudden and frequent data transmission with multiple points and small and medium flow, as well as occasional large amount of data transmission.

　　2、 GPRS distribution transformer monitoring system

　　The development goal of distribution transformer integrated management system is to establish an open platform that is safe and reliable, can provide various advanced services, and has strong functions for the implementation and implementation of application programs, and a system composed of multiple relatively independent application subsystems running on the platform, so as to become a distributed, open Modular and expandable distribution transformer integrated management system. In addition to providing basic hardware technology and operating system kernel, the basic platform also provides basic services such as database system, information transmission, man-machine interface, real-time environment application and so on. The application subsystems based on the basic platform include distribution transformer management, line loss management, automatic meter reading, VQC function, harmonic data, power purchase management, data query, automatic report, chart and scanning with other systems. These subsystems realize organic horizontal and vertical integration on the basis of open system architecture (OSA), forming a complete distribution transformer integrated management information system.

　　2.1 composition

　　The network architecture of GPRS distribution transformer monitoring system is shown in Figure 1. The system is divided into four parts: monitoring center master station, network proxy server, GPRS data transmission terminal and monitoring terminal equipment. The master station mainly completes human-computer interaction; The network proxy server is mainly responsible for the establishment of network data link and transparent transfer of data sending and receiving; GPRS data transmission terminal completes the transmission and distribution of information; The monitoring terminal equipment mainly completes the collection of digital quantity and analog quantity.

　　Figure 1 GRPS distribution transformer monitoring network architecture

　　2.2 network connection

　　The network proxy server in the system can be connected with internet public networks such as ADSL and LAN, and use public network fixed IP or public network dynamic IP + DNS resolution services. For security reasons, the master station of the monitoring center is in the local area network and is not directly connected to the Internet. It is responsible for the establishment of network data link and transparent transfer of data sending and receiving through the network proxy server. After the GPRS data transmission terminal is powered on, it will actively access the network proxy server according to the preset IP address or domain name, and establish the TCMP link through the proxy server and the monitoring center. The master station of the monitoring center maintains the IP address and ID number of each terminal accessed. When the master station wants to make a data request to a monitoring terminal, it will find the corresponding terminal according to the IP address and ID number and send the command to the terminal. After the terminal responds, it will send the data to the network proxy server port through the GRPS data transmission terminal and forward it to the master station of the monitoring center through the port mapping, That is, a response communication process is completed.

　　The above methods are implemented through Internet (cmnet), so the implementation cost of users is relatively low. If high reliability data transmission is required. China Mobile (Unicom) provides a direct connection to GPRS network for this application. The master station of the monitoring center directly accesses the GPRS mobile base station through a dedicated line and obtains a fixed IP address. The monitoring point data does not need to be routed to the Internet network, and the monitoring point DTU also adopts the SIM card with fixed IP address. The point to multipoint network formed in this way has the characteristics of good real-time and high security, but the access cost is relatively high.

　　3、 Monitoring terminal

　　The power distribution integrated monitor used in the monitoring system is a high-tech product designed and manufactured according to the technical requirements of power demand side management and relevant standards for distribution transformer load monitoring. It adopts high-precision digital sampling and processing technology, integrates data acquisition, display, storage, communication and other functions, and can display, print and analyze the stored data in the form of chart or report through background software. With leading technology, powerful function and high reliability, it can be widely used in the monitoring of distribution automation system. The main functions are as follows:

　　3.1 multiple meter interfaces

　　RS-485 interface, RS232 interface, pulse interface.

　　3.2 electric quantity data acquisition function

　　It has a variety of electric quantity data that can collect a variety of electric meters: forward / reverse

　　Active power, forward / reverse reactive power, maximum demand, three-way voltage, current, load curve, reverse and voltage loss alarm.

　　3.3 support multiple meter reading protocols

　　The system can support various meter reading protocols such as ministerial standard 645, Weisheng and iec-61107 at the same time;

　　3.4 support multiple data transmission platforms

　　The data collector has a variety of communication modes, which can transmit data to the main control center of the Bureau through PSTN wired telephone network or Ethernet; When the above conditions are not met, it can also be realized by wireless GSM dial-up mode or GPRS packet switching network.

　　3.5 various communication modes

　　The system can not only upload data automatically at fixed points, but also access the data of the collector at any time in the Bureau Center. In addition, the system has the function of one sending and two receiving, and can send the collected data to the main and auxiliary control centers; And realize local data reading through local communication interface. During data transmission, the collector has the function of automatically identifying whether it is an incoming call or transmitting data, so the telephone does not ring during communication.

　　3.6 meter reading bus switching function the ps485 interface of the collector can switch the data bus of the watt hour meter when it does not read the meter, so as to facilitate other equipment (such as negative control, local monitoring, etc.) to read the watt hour meter data, and solve the problem that the watt hour meter has only one RS485 interface for the communication of two meter reading equipment.

　　4、 GPRS data transmission terminal

　　The characteristics of GPRS data transmission terminal are as follows:

　　(1) The built-in communication rate is 2400bit and the theoretical mode is 2400m;

　　(2) With automatic real-time routing function module, multi-level relay can be realized;

　　(3) Power supply, 50Hz, 220 V;

　　(4) Power, P ≤ 5W (static), P ≤ 10W (transmitting);

　　(5) Temperature, 40 ~ + 85 ℃;

　　(6) Support infrared PDA handheld meter reader;

　　(7) Provide RS232 and RS485 interfaces;

　　(8) Upgrade program through serial port;

　　(9) Using low-power and high-performance CPU as processor, 16 bit internal data bus, 128kbi "SRAM, 512kbi" SRAM, which can process protocol and a large amount of data at high speed.

　　5、 Monitoring center master station

　　5.1 communication control software

　　5.1.1 functions of communication software

　　(1) Remotely receive the data sent back by the data collector;

　　(2) Remotely modify the working parameters (clock parameters) of the data collector;

　　(3) Query the system operation status;

　　(4) Bidding and measurement of on-site electricity data;

　　(5) Support local and network multi-path data backup and storage;

　　(6) Support the secondary stations in the bureau to share the data of the primary station.

　　5.1.2 multiple communication modes

　　(1) Access and collect various data at the main control center of the bureau at any time;

　　(2) The system has the function of one transmitter and two receivers, which can send the collected data to the main and auxiliary control centers;

　　(3) Realize local data reading through local communication interface;

　　(4) Automatic fixed-point data upload system.

　　5.1.3 multiple transmission modes

　　(1) PSTN wired telephone network;

　　(2) Optical fiber Ethernet;

　　(3) GSM dialing mode;

　　(4) GPRS packet switching network mode.

　　5.1.4 communication startup mode

　　(1) Both the office and the station can start communication;

　　(2) During data communication, the station telephone does not ring.

　　5.2 power management analysis software

　　5.2.1 system characteristics

　　(1) Adopt advanced client / server architecture to meet the requirements of users' distributed application, large capacity and fast real-time;

　　(2) Modular and parametric design is adopted, which has good expansibility and maintainability;

　　(3) The system adopts the current popular large-scale database system (or acle), which ensures the reliability, security and portability of the system;

　　(4) The flexible structure of user application allows users to better combine the system with practical work;

　　(5) Provide web page dynamic query function to facilitate data information sharing within the power company system;

　　(6) The user application can be flexibly constructed according to the operation relationship of various electric quantity data;

　　5.2.2 system functions

　　(1) User's password, parameter setting and operation parameter maintenance of the system.

　　(2) Data maintenance: carry out data correctness inspection and data compression and storage for the originally collected electricity meter data through the system, and provide the data planting function module to manually copy and supplement the incomplete data caused by various conditions, so as to ensure the integrity, correctness and safety of electricity calculation.

　　(3) Application structure: construct various types of electricity statistical analysis users. According to the classification and purpose of application, various query schemes are flexibly constructed. It is convenient to describe the incoming and outgoing line relationship of various line loss analysis according to the file parameters of the electricity meter, and the assessment value of each line loss analysis can be defined.

　　(4) Basic file maintenance: complete the file maintenance and query of station terminal, electricity meter, bypass and other related equipment, as well as the function modules such as table replacement file maintenance and table replacement status query. So as to realize the factuality and accuracy of relevant equipment archives.

　　(5) Power query statistics.

　　(6) Assessment and analysis of power consumption.

　　6、 Conclusion

　　Realizing the automation of low-voltage distribution network is the need to improve the quality of power supply, the reliability of power consumption and the level of power enterprises. As a new means of communication, GPRS has many advantages in distribution automation. Therefore, the integrated management system of distribution transformer based on GPRS communication is a promising scheme, and will eventually bring tangible benefits to users.