Xiamen Cai Mao Communication Technology Co., Ltd.
Distribution Monitoring System Based on CDMA Communication
application solution
This paper presents a design principle and implementation scheme of CDMA based power distribution monitoring system. It briefly introduces the basic knowledge of CDMA technology and describes the implementation method of CDMA wireless transmission applied to remote data monitoring. Through practical application, achieved the desired effect.
I. INTRODUCTION With the development of science and technology, the realization of automation of low-voltage distribution networks has become a trend in the development of power systems. The low-voltage distribution network is the last link of the transmission and distribution system, and its degree of automation is closely related to the quality and reliability of the power supply. For this reason, this article discusses the necessity of the automation of the low-voltage distribution network and its implementation.
Distribution transformers are power devices that distribute electrical energy directly to low-voltage users. Their operational data are an important part of the basic data of the entire distribution network. Therefore, it is necessary to monitor its operating parameters and status. This article discusses the use of CDMA as a means of communication to establish distribution transformer monitoring systems.
In the communication of the distribution transformer monitoring system, digital radio stations, GSM short messages, and optical fiber access can be used. The advantage of digital radio stations is that in addition to the annual frequency fees, there is no extra cost for normal operation; the disadvantage is that it is affected by the terrain and climate, resulting in poor system reliability and real-time performance, and it cannot be reported actively. GSM short message way can realize initiative reporting; The disadvantage is to charge according to the bar, the operation cost is high, and the time delay is very long while the holiday short message center server is busy. Fiber-optic communication is stable and reliable, but it is inconvenient for construction costs, poor scalability, and maintenance of equipment. CDMA communication avoids these problems.
CDMA is a new wireless data transmission service that aims to provide users with high-speed wireless IP or X.25 services. CDMA theoretical bandwidth up to 171.2Kbit/s, practical application bandwidth is about 40~100Kbit/s, providing TCP/IP connection on this channel, can be used for INTERNET connection, data transmission and other applications. CDMA uses packet switching technology. Each user can occupy multiple wireless channels at the same time. The same wireless channel can be shared by multiple users, and resources can be used effectively. CDMA allows users to send and receive data in end-to-end packet transfer mode without the need to utilize circuit switched mode network resources. CDMA is always online, according to traffic accounting, thus providing an efficient, low-cost wireless packet data service. Especially suitable for intermittent, sudden and frequent, multi-disperse, small and medium-sized data transmission, but also for occasional large data transmission.
Second, the system structure distribution transformer integrated management system development goal is to establish a safe and reliable, can provide a variety of advanced services, and there is an open platform for the implementation of the application and implementation of stronger features and run on the platform A system consisting of relatively independent application subsystems has become a distributed, open, modular, and scalable distribution transformer integrated management system that meets the requirements of modern distribution system management. In addition to providing basic hardware technologies and operating system kernels, basic platforms also provide basic services such as database systems, information transfer, human-machine interfaces, and real-time environment applications. Each application subsystem based on the basic platform includes: distribution transformer management, line loss management, automatic meter reading, VQC function, harmonic data, purchasing power management, data query, automatic reporting, charts and interfaces with other systems, etc. . These subsystems realize organic horizontal and vertical integration on the basis of open system architecture (OSA) to form a complete distribution transformer integrated management information system.
The network architecture of the CDMA distribution transformer monitoring system is shown in the figure below. The system is divided into four parts: the monitoring center master station, network proxy server, CDMA data transmission terminal, and monitoring terminal equipment. The main station mainly completes the human-computer interaction; the network proxy server is mainly responsible for the establishment of the network data link and the transparent transfer of data transmission and reception; the CDMA data transmission terminal completes the sending and the issuance of information; and the monitoring terminal equipment mainly completes the digital and analog quantities. collection.
In this system, the network proxy server can use the INTELNET public network such as ADSL, LAN, etc., and use the public IP or public network dynamic IP+DNS resolution service. For security reasons, the monitoring center master station is not directly connected to the LAN. On the Internet, the network proxy server is responsible for the establishment of transparent data links and the transparent transfer of data.
After the CDMA data transmission terminal is powered on, it will actively access the network proxy server according to the IP address or the domain name set in advance in it, and establish a TCP/IP link through the proxy server and the monitoring center. The monitoring center master station maintains the IP address and ID number of each terminal that it accesses. When the master station requests data from a monitoring terminal, it will find the corresponding terminal based on the IP address and ID number. Send to this terminal, the terminal responds to send the data through the GRPS data transmission terminal to the network proxy server port, through the port mapping and relaying to the monitoring center master station, namely completing a responding communication flow.
The above method is implemented through the Internet, so that the user's implementation cost is relatively low. If you need high reliability data transmission. China Unicom provides direct access to CDMA networks for this application. The monitoring center master station directly accesses the CDMA Unicom 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. The monitoring point DTU also uses a SIM card with a fixed IP address. The point-to-multipoint network constructed in this way has the characteristics of good real-time performance and high security, but the access cost is relatively high.
Third, the monitoring terminal The monitoring system used in the distribution of integrated monitoring instrument is based on the power demand side management technical requirements and distribution transformer load monitoring standards designed and manufactured a high-tech products. It adopts high-precision digital sampling processing technology, integrates data acquisition, display, storage, communication and other functions into one, and can use background software to display, print, and analyze the stored data in the form of charts or reports. Its technology is leading, powerful and reliable, and can be widely used in the monitoring of distribution automation systems. Its main functions are:
Basic measurement parameters:
There are nine types and more than thirty parameters for three-phase voltage, current, frequency, active power, reactive power, power factor, four-quadrant electric energy, and ambient temperature.
Technical parameters • Rated technical parameters Rated voltage Un: 100V
Rated current In: 5A
Rated frequency Fn: 50Hz
• Measurement Accuracy Voltage/Current/Frequency: Class 0.2 Power Factor/Active Power/Reactive Power: Class 0.5 Active/Reactive Power: Class 1.0 • Built-in flash capacity Storage capacity: 1024k bytes for continuous 84 days Electrical data records (recorded every 15 minutes)
Accuracy Voltage/Current/Frequency: Class 0.2 Power Factor/Active Power/Reactive Power: Class 0.5 Active/Reactive Power: 1.0-level system parameter setting device CT, PT ratio ratio data storage interval system clock LCD contrast overvoltage Parameters Undervoltage Parameters Overcurrent Parameters IV. Data Transmission Terminal - Adopted by Xiamen Cai Mao Communication Technology Co., Ltd. CM 6550P CDMA DTU
CM 6550P CDMA DTU uses ARM9 high-performance industrial-grade embedded processor, real-time operating system as a software support platform, built-in proprietary intellectual property rights TCP / IP protocol stack. To provide users with high-speed, stable and reliable, data terminal is always online, a variety of protocol conversion virtual private network. For users of network traffic control, the product supports the functions of voice, SMS, data on-line triggering and automatic timeout disconnection. It also supports dual data center backups, as well as multiple data centers that receive data synchronously. The company's products have been widely used in finance, water conservancy, environmental protection, electricity, postal services, weather and other industries.
First, wireless parameters
1. Supports IS-95 A/B and CDMA2000 1xRTT wireless networks
2, support 13K QCELP audio codec
3, support data, voice, SMS and fax
Second, the hardware system
1. CPU: Industrial-grade high-performance ARM9 embedded processor, 200MPS, MMU, 16KB Dcache, 16KB Icache
2, FLASH: 8MB, can be expanded to 32MB
3, SDRAM: 64MB, can be expanded to 256MB
4, interface:
1 RS232 serial port. (Supports RS422/RS485 as required), serial port speed 110~230400 bits/s
Indicator: Power, communication, and online indicator.
Antenna Interface: Standard SMA female antenna interface, characteristic impedance 50 ohms.
UIM card interface: 3V/5V standard push-type user card interface.
Power Interface: Standard 3-pin locomotive power socket.
Voice interface: standard headphone microphone interface.
5, power supply:
External power supply: DC 9V 500mA
Wide voltage supply: DC 5-35V
Communication current: 350mA
Standby current: 35mA
6, size
Dimensions: 92.7x61.3x23 mm (not including antenna and fixture)
7, other parameters:
Working environment temperature -25~+65oC
Storage temperature -40~+85oC
Relative humidity 95% (non-condensing)
Third, software function
1. Smart anti-drop, support for online detection, online maintenance, dropped automatic redial, to ensure that the device is always online.
2. Support RSA, RC4 encryption algorithm
3. Support virtual value watch (VWM) function to ensure stable and reliable system
4. Support virtual data private network (APN)
5. Transparent data transmission and protocol conversion, support multiple working modes
6. Support data center dynamic domain name and IP address access
7. Support dual data center backup
8. Support multiple data centers
9. Supports wake-up methods such as SMS, voice, data, and timeouts to disconnect the network.
10. Support short message backup and alarm.
11. Multiple hardware and software watchdogs
12. Packet transmission status report.
13. Standard AT Command Interface
14. Can be used as a normal dial MODEM
15. Support telnet function.
16. Support remote configuration, remote control
17. Through the serial port software upgrade
18. Supports both LINUX and WINDOWS operating systems
19. There are dual hardware and software watchdogs, which can automatically reset the power supply when the DTU fails to work.
IV. Monitoring Center Master Station The innermost layer of the main station system is the operating system and system software. The second layer is the system support software layer, including the database system, power system model, data acquisition and transmission. The power system model mainly refers to the power system equipment objectification and network topology; the database system is divided into four parts: running base, basic library, standard library, and historical library; data collection and transmission is to collect various data from different terminals according to various communication protocols. Come, but do not deal with it, and then distribute it through the network to systems that need this data. The third layer is the basic application layer. The collected data is processed through various processes and displayed to the user through the GUI interface. The fourth layer is the advanced application layer. The data it generates is mainly for the further management and decision-making of the power supply system.
The upper software mainly completes the following functions:
(1) Transformer operation monitoring of distribution transformer SCADA system, abnormal condition monitoring of transformer, analysis, processing and storage of data, parameter setting and status display of RTU. It can not only obtain the basic information of distribution network operation, but also provide a good foundation for function expansion.
(2) The automatic meter reading system automatically records the distribution transformer and the user's electrical power according to the set time. It also has alarms for meter abnormality, and tracking functions such as meter reading records and operation records.
(3) User purchase power management For users with poor reputation, power is supplied to the system after it is purchased first, and a warning is issued when the power usage reaches a certain percentage.
(4) Line loss management is mainly line loss management and line loss management in Taiwan.
(5) The management of distribution equipment is mainly the management of equipment such as distribution lines and distribution transformers.
(6) Terminal error The intelligent identification terminal error is divided into communication recovery, communication interruption (a terminal cannot be detected three times in a row), wireless error of the terminal (never ten times in a row), wireless interruption (30 consecutive times The terminal could not test it.
(7) Load forecasting Calculate the load of the next stage by calculating the total added value of the total active power of all stations in the main station and substations.
(8) Capacitor switching is adjusted on-the-fly according to voltage and power factor. Time factor and switching times are taken into account when adjusting. Local monitoring and remote control can be achieved in the event of local adjustment failure. If the terminal does not have adjustment and switching function, the system can control the capacitor switching after the calculation.
(9) The terminal operation can read or set the parameters of the terminal, such as the setting parameters of the transformer. Can set the switch closing, switch opening. The VQC parameters can be read or set.
(10) The interface with the marketing system database can easily provide data sources for the marketing system.
(11) Collect harmonic data The system can collect the user's various harmonic content.
(12) The user's power steal management increases the comparison between the user's power and the conversion of the power to the power, and a warning is generated by setting the proportional coefficient, for example, when the active power is generated and the power does not move, a warning is generated.
V. Conclusions Realizing the automation of China's low-voltage distribution network is the need to improve the quality of power supply, reliability of power use and the level of power companies themselves. As a new means of communication, CDMA has many advantages in the application of power distribution automation. The distribution transformer integrated management system of CDMA communication is a relatively promising implementation scheme.