Abstract: detailed analysis of the requirement for communication system, power distribution automation system and combined with wireless communication terminal in the practical application experience in power distribution automation system and equipment research and development experience, put forward the suitable integrated wireless communication solution for application of power distribution automation system, and the characteristics and the design technology of the scheme are summarized and expounded.
Key words: power distribution automation; intelligent area; 3G/4G; LoRa; APP
According to the national grid company distribution network construction reform action plan (2015-2020)”, in 2020 will completely build intelligent power distribution network with the guideline of reliably and secure, efficient and economic, flexible and advanced, green low carbon, environmentally friendly, distribution automation will achieve coverage of 90%. Communication systems is the information center of the distribution network, its performance to a large extent determine the performance of the whole distribution network, in the role of distribution automation. Visibly, the design of suitable for the application of distribution automation communication scheme to realize the goal of action plan in the state grid has the very vital significance.
Distribution network especially the wide coverage of rural power grids are with condition of complex and rugged environment, the construction and maintenance work is not convenient, unattended on the scene and complex business. So the main requirements of distribution automation on communication system is safe and reliable, convenient maintenance, meet the needs of all kinds of mixed business communication bandwidth.
Proposed in this paper, the fusion of 2.5G/3G/4G wireless public network communication technology and LoRa/Zigbee/433 MHz wireless Internet collection technology integrated wireless communication solution, with characteristics of communication and reliable, easy to use, easy maintenance, high bandwidth, very suitable for distribution automation of various mixed business demand, especially the coverage is needs of rural electric automation with very broad coverage. This article will be discussed at length in combination with the practical cases of distribution automation, integrated wireless communication solutions in the application of distribution automation and its design technology.
1. Integrated wireless communication scheme design
1.1 Solution overview
The scheme is a blend of 2.5G/3G/4G wireless public network communication technology and LoRa/Zigbee/433 MHz wireless Internet collection technology, provide WiFi hotspots, Ethernet and RS232/RS485 and I/O interface, realize the wireless data transmission, wireless data collection, image/video monitoring, APP on-site operations, comprehensive functions such as wired sensors. In power distribution automation, intelligent power distribution area, electric line monitoring, overhead line fault location, and other fields are widely used.
1.2 2.5G/3G/4G wireless public network communication design
1.2.1 Wireless public network characteristics and the application case of wireless public network has wide coverage, use convenient maintenance, low investment, high bandwidth, etc. And distribution network, especially in rural power grid coverage is wide, the environment is complex, if using wire communication construction cost is high, maintenance inconvenience, so distribution automation used wireless public network communication will be a trend. At present, in the column on the switch monitoring, overhead line fault location has been extensively used in applications such as wireless public network communication.
Switch monitoring network diagram on the pillars:
Overhead line fault location system network diagram:
1.2.2 Wireless communication module selection: wireless communication module is the core component of the wireless communication terminal, it completes the air interface and the link between the terminal and base station building, most adopt industrial low power consumption modules. At the same time, in order to be compatible with all operators network, it is suggested that using the multi-band multi-mode netcom module.
1.2.3 Prevent drop mechanism design: wireless communication link is information transmission channel, must ensure that the real-time online wireless link. The drop mechanism includes two aspects of link detection and link back. Link detection include wireless module status detection and on-line detection. Inspection found that the problem, if the link is to link recovery, including wireless module state recovery process, to initiate connections and redial.
1.2.4 Protocol compatibility design: around 2.5G/3G/4G network condition is with very big different, if the TCP/IP protocol compatibility is no good, can appear the point works well, and the other a point don’t work properly. To solve this problem, only according to the different modified network protocol stack. So requires that designers have the ability to modify the TCP/IP protocol, rather than simply call the wireless module embedded TCP/IP protocol stack.
1.2.5 Communication backup design: distribution network especially for rural power grid in remote, mountainous, complex terrain, the wireless signal is not stable, the single communication mode cannot meet the requirements of distribution automation. Can use wired and wireless link backup, wireless double card double link backup, wired and wireless card three link backup methods such as improving the stability of the link.
1.2.6 Communication security encryption design: safety is an important index of power distribution automation. Can through the PPTP/L2TP/IPSEC VPN encryption algorithm and APN/VPDN private network, etc. To ensure the security of the data.
1.3 Wireless Internet of acquisition design
1.3.1 Wireless Internet to collect technical characteristics and application case of LoRa/Zigbee/433 Mhz wireless acquisition technology with low power consumption, such as ad-hoc network, without wiring etc., especially suitable for wireless sensor acquisition. Such as wireless temperature and humidity sensor, displacement sensor, wireless switches etc. Through wireless Internet collection technology, can quickly realize monitoring in the system, improve the level of intelligent shipment inspection.
1.3.2 LoRa wireless technology characteristics and application case. LoRa is a kind of low power wireless wan (LPWAN) technology, has the characteristics such as low power consumption, long distance transmission, the transmission distance up to 10 km, which is especially suitable for the intelligent power distribution area on the user side of monitoring equipment, such as user secondary leakage protection switch, charging pile and distributed monitoring of power equipment. Through the technology, can realize monitoring scope covers the whole area, but is not limited to the electrical equipment around the distribution transformer to monitor no dead angle. As shown in the figure below:
1.4 On-site operations APP design
1.4.1 Technology implementation: embedded WIFI hotspot in wireless communication terminals, smart phones to access the hotspot, you can access data in site terminal.
1.4.2 Operations APP features: on-site check the equipment running status, modify the equipment operation parameters, receive the alarm information and control field equipment, etc.
1.5 Image/video monitoring design
1.5.1 By external web camera or a serial port camera, image/video monitoring, distribution automation monitor more intuitive, improve the level of intelligent operations.
1.5.2 Through the integrated design of video telemetry terminal implementation. The scheme is to realize wireless video, images, video capture, data acquisition, data transmission function four unity, products more stable and most cost-effective.
1.6 Multi- interface design
Wireless communication terminal support RS232/RS485, DIO, A/D, RELAY interface, conveniently docking with the various sensors, achieve more abundant data acquisition and control functions. Parameters such as environment monitoring, entrance guard monitoring, etc.
1.7 The remote device management platform design
Equipment management platform to realize the remote centralized management and maintenance of the equipment, including equipment condition monitoring, the function such as remote configuration, remote upgrade, further improve the management level, reduce the operational cost.
2. Industrial application design
2.1 The key device selection
Distribution automation applications are no duty occasions, temperature difference is big, complex environment, bad and changeable, required equipment satisfies the requirement of high temperature, low temperature, damp and hot work. Design, selection of the key devices to meet the requirements of industrial application. CPU system is the core of the wireless communication terminal processing system, its stability and frequency properties determine the performance of the entire device. Recommended industrial-grade 32-bit CPU system, low power consumption can not only satisfy the stability requirement, also can meet the performance requirements of high-speed data processing.
2.2 Low power consumption design
A lot of power distribution automation applications take electricity is not convenient, should also consider a power outage cases equipment can continue to work normally, so require equipment used battery as backup power supply. This requires that the equipment must be meet the requirements of low power consumption.
2.2.1 The key device selection. CUP system and wireless communication module must choose low power consumption, with multi-stage sleep/wake mode.
2.2.2 Low power consumption mode design. On the software design, when the device does not need normal working equipment will be placed in a suspended state, and cut off all don’t need the outside of the work function module of the power supply, to ensure that the power consumption to a minimum. On the hardware design, use the external interrupt of the CPU system to awaken the equipment, to meet the requirements of deep dormancy.
2.3 The stable reliability design
The application of distribution automation field scattered, remote, not easy to maintain, and complex, rugged and changeable environment. How to implement equipment to ensure that the equipment is stable and reliable, “maintenance”, is the problem that designers must first consider.
2.3.1 The stability of the system design. Hardware and software watchdog is a useful method of stability design, but in harsh industrial applications, and can not completely solve the problem. To ensure that equipment normal work, under any circumstances also need on the system protection measures, such as systems, such as power control, truly “free maintenance”.
2.3.2 Over voltage/over current protection
2.3.3 EMC design, including the ESD protection, surge protection, etc.
Distribution automation is more and more high requirement to wireless communication system, the designer only in combination with the actual application requirements, follow the basic principles of combining practicality and advanced nature, the Internet technology, Internet technology, wireless communication technology, comprehensive measures such as reliability design technology, that can better meet the application requirements.
The state grid corporation of distribution network constructio