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1. Introduction
    With the development of science and technology to realize the automation of low voltage distribution network has become the development trend of power system. In low voltage distribution network as the transmission and distribution system, the last link, the degree of automation for power quality and reliability are closely related. Therefore, this article takes a simple discussion of on the need for low voltage distribution network automation and the implementation scheme.
    Distribution transformer is directly assigned to the low voltage power users of electrical equipment, its operation the whole distribution network data is an important part of the basic data. Therefore, it’s operating parameters and status monitoring is necessary. This article discusses the use GRPS as a means of communication, the establishment of distribution transformer monitoring system.
    In distribution transformer monitoring system of communication, you can use data radio, GSM short message, optical access, etc. Data Radio’s advantage is the annual frequency fee in addition to other, usually run at no additional cost; defects is affected by terrain, climate, greater impact, resulting in system reliability, real-time poor and can not take the initiative to report. GSM Short Message ways to achieve active reporting; drawback is that according to article charges are expensive, but also in the busy holidays when the short message center server for a long delay. Stable and reliable optical fiber communication, but the construction cost into large, extended, poor equipment maintenance convenient.  The GPRS communication is to avoid the above problems.
    General Packet Radio Service GPRS in the existing GSM system, developed a number of new wireless data transmission services, the purpose is to give mobile users high-speed wireless IP or GPRS 1X services. GPRS theoretical bandwidth of up to 171.2Kbit / s, the practical application of the bandwidth about 40 ~ 100Kbit / s, in this channel to provide TCP / IP connection, can be used for INTERNET connection, data transmission applications. GPRS uses packet switching technology, each user can simultaneously occupy multiple wireless channels, the same radio channel can also shared by multiple users, resource are used effectively. GPRS allows the user end to end packet transfer mode to send and receive data without the need to use the circuit-switched mode of network resources. GPRS always online, according to traffic accounting, thus it provide an efficient, low-cost wireless packet data services.  Especially suitable for intermittent, sudden and frequent, point more dispersive, small and medium flow of data transmission, but also to the occasional large data transfers.
2. System Structure
    Distribution Transformer Management System development objective is to create a safe and reliable, can provide a variety of advanced services, and promising applications in the implementation and enforcement of strong features providing an open platform and run on the platform of several independent application subsystems of the system, into a modern distribution system comply with regulatory requirements, distributed, open, modular, scalable, integrated management system for distribution transformer. In addition to the basic platform to provide basic hardware and operating system kernel, but also information such as database systems, information transmission, human-machine interface, real-time environment, applications and other basic services.
    Based platform based on the various application subsystems include: management of distribution transformer, line loss management, automatic meter reading, VQC function, harmonic data, purchase power management, data query, automatic reports, graphs and interfaces with other systems. Between these subsystems in the open system architecture (OSA) based on the horizontal and vertical integration of organic, to form a complete integrated management information system of distribution transformer.
    Distribution Transformer Monitoring System GPRS network architecture as shown below, the system is divided into four parts, namely, the master control center, the network proxy server, GPRS data transmission terminals, monitoring devices. Master key to complete the work of human-computer interaction; network proxy server is mainly responsible for the network data link establishment and transparent transfer of data sent and received; GPRS data transmission terminal to complete the information on the delivery and issued; monitoring device was completed for the amount of digital and analog collection.
    The system can use a proxy server network ADSL, LAN and other INTELNET public network connection, using the fixed public network or public network IP Dynamic IP + DNS resolution service, for security considerations, local area network control center in the main stand, not directly connected to the INTERNET-line, through the network proxy server for network data link establishment and transparent transfer of data transceivers.
    GPRS data transmission terminal after power-up, it will be a pre-set in its internal IP address or a domain name initiatives visit the Web proxy server, proxy server and the monitoring center through the establishment of TCP / IP link. Master control center to maintain their access to each terminal’s IP address and ID, while the main station to request a presentation of data monitoring terminal When it will be under the IP address and ID number to find the corresponding terminals, the command issued to the terminal, the terminal after responding to the terminal via GRPS data transfer data to the network proxy server port, port mapping through the main points forwarded to the monitoring center, which completed a response style of communication processes.
    Above way is through the Internet (CMNET) to achieve, so the user’s implementation costs are lower. If need high reliable data transmission. China Mobile to provide direct access to this application, the way GPRS network. Master control center directly through dedicated access GPRS mobile base station, and get a fixed IP address. Monitoring data without routing to the Internet network, monitoring DTU has a fixed IP address SIM card. Formed this way of one point to multi-points network with real time, high security, but the relatively high access costs.
3. Monitoring Terminal
    The monitoring system used by integrated monitor distribution is based on DSM technical requirements and standards for distribution transformer load monitoring related to the design, manufacture of a high-tech products.  It uses high-precision digital sampling processing, data acquisition, display, storage, communications and other functions into one, and through the background the software will be stored record data to the chart or report in the form of display, printing and analysis.  Its advanced technology, powerful, high reliability, can be widely used in power distribution automation system monitoring.  Its main features are:
    Basic measurement parameters: three-phase voltage, current, frequency, active power, reactive power, power factor, power four-quadrant, nine categories of environmental temperature, more than 30 parameters.
4. GPRS Data Transfer Terminal
    GPRS data transmission terminal achieve the main station and the control monitoring center communication. The system uses KB3000 GRPS DTU. The DTU functions and features are as follows:

  • A. Features:
    Standard AT command interface for program design;
    TCP / IP Internet protocol stack embedded, easy interconnection;
    RS232 interface mode, a more convenient means of communication;
    Can upgrade via the serial port.
  • B. Performance:
    The use of low-power high-performance CPU to do processor, 16-bit internal data bus, 128KBSRAM, 512KBFLASH, high-speed processing agreements and large amounts of data;
    Support full transparency and data transmission frame format;
    Support the TCP, IP, PPP, ICMP, UDP, TELNET, HTTP protocol stack;
    A consistent standard of ISO7816-3IC SIM card slot, support line GSM11.11 and GSM11.10, standard SIM card;
    Simplify the interface design, use of 232 common and simple AT command interface;
    For a more convenient power connector, you can use the external power supply. Can take power directly from the serial port;
    Machine power consumption less than 3W;
    Perfected the GPRS network, dial-up arising from false, dropped automatically restart, remote wake-up functions.