Study on Monitoring System of On-Line PowerTransmission Lines Based on ZigBee Technology*ZHONG Yun-ping1, CHENG Xiao-hua1, DAI Dong1, ZHANG Jian-wei2, ZHAI Shao-lei2(1.South China University of Technology, Guangzhou 510640，China.2. Electric Power Research Institute of Yunnan Electric Power Test & ResearchInstitute Group Corporation Limited, Kunming 650217, China）Received July 2012; accepted November 2012 Abstract：Combining the need of monitoring high voltage in power systemwith the technical advantages of ZigBee，this paper proposes a set of high-voltage wireless monitoring system with the characteristics of ZigBeewireless sensor networks, the basic principles and its composition, and itpresents the use of the emerging ZigBee wireless networking technology inthe on-line monitoring system. ZigBee communication module, theinducing power design on high -voltage transmission lines, solar moduledesign, and the structure design of software system are also described indetail. The system has advantages of high reliability, simple arrangement,good expandability, low running cost. The laboratory test results are stableand reliable.Key words:ZigBee technology, wireless communication technology,transmission line monitoring, CC2530, wireless sensor network1. IntroductionIn recent years, with the development of social economy, the national power consumption has skyrocketed, ultra-high voltage power grid construction and scale expands rapidly.Because of the high voltage transmission line has a long distance, wide distribution, patrol and maintenance difficulty etc[1]. In remote areas, the terrain complex work in harsh environment network of transmission lines of transmission line and its environment, meteorological parameters, the real-time remote monitoring become an urgent work, based on the transmission line running status real-time monitoring, establish corresponding natural disaster warning mechanism, can reduce the power outage caused economic losses, improve the stability of the safety of power grid operation efficiency[2]. Therefore, to establish the stable operation of the transmission line on-line monitoring system for power grid plays an important role,* Fund project: the project is supported by the national 863 plan (2011 aa05a120)and the establishment of a transmission line on-line monitoring system is an important part of the smart grid[3].Traditional monitoring network is given priority to with cable, wiring complexity, low reliability, safety, high cost, low extension and maintenance difficulties and other issues. The common wireless communication technology, such as GPRS, Wi-Fi, that exist such problems as high cost, large power consumption. Designed a kind of wireless sensor network based on ZigBee technology, it has low power consumption, low cost, safe, reliable and network advantages of large capacity and high efficiency of the collection. At the same time because of it’s no wiring, easy extension, high flexibility, etc. it has been applied gradually in the transmission line monitoring system[4]. Transmission distance of each network node can from the standard 80 meters, after add power amplifier can be extended to a few hundred meters, even several kilometers; In addition the ZigBee network can also communicate with other existing communication network..Considering the high voltage transmission line monitoring equipment working environment and conditions, this paper designs a wireless transmission line on-line monitoring system based on ZigBee technology, combining induction way to fundamentally solve the problem of the high voltage insulation, has a large capacity of the network at the same time, small volume, light weight, low power consumption, and the advantages of convenient installation, is an ideal solution for high voltage transmission line monitoring.2. The overall frame structure of the systemWireless Sensor networks is composed of a large number of micro Sensor nodes deployed in monitoring area, through Wireless communication mode to form a multiple hops self-organizing network system, collaborative perception, and collection and processing network coverage area by monitoring object information, and sent to the coordinator. Sensors, monitoring objects, and the coordinator constitute the three elements of the wireless sensor network.Wireless sensor network monitoring system based on ZigBee technology structure[5] is shown in figure 1.GPRSReceiverwireless sensor nodewireless sensor nodeThe background data monitoring centerFig.1 Monitoring system’s structure of wireless sensor networkSensor network system includes sensor nodes (sensor node), routing node, the coordinator node and monitoring host. Within the scope of sensor nodes deployed in monitoring area, can constitute a sensor network by way of self-organization. Sensor nodes monitoring data can be transmitted along the other sensor nodes, jumping by, monitoring data in the process of transmission is likely to be more than one node processing, through multiple hops posterior to the coordinator node. Wireless sensor monitoring system consists of sensors, wireless router nodes, the coordinator node, the data collection center, monitoring host, sensor acquisition node is installed on the high voltage transmission line and tower, can be used for the collection, transmission line conductor temperature tension, lightning current data, through the wireless network, such as temperature, tension, lightning current data through wireless router nodes is passed to the coordinator, the coordinator of the RS232 serial port to monitor host, monitoring host through the GPRS data transmission to the background.3. The design of system hardware3.1 based on CC2530 ZigBee module designSensor nodes, wireless routing node, the coordinator node adopt CC2530 chip of TI Company newly, CC2530 is based on a 2.4 GHz IEEE 802.15.4 on a real piece of ZigBee (SoC) solution. It can build strong at very low cost network nodes. CC2530 combines the leading the good performance of RF transceiver, the industry standard of enhanced 8051 CPU, the system programmable flash memory, 8 KB of RAM and many other powerful features CC2530 with different operation mode, makes it especially adapted to ultra low power requirements of the system. Sensor is responsible for the monitoring area information acquisition and data transfer; Processor module is responsible for the control of the operation of sensor nodes, data storage and processing itself and data from other nodes; Wireless communication module is responsible for the wireless communication with other sensor nodes, exchange control information and to send and receive data; Running mode conversion between short time further ensures that the low energy consumption; Power supply module for sensor nodes provide the energy needed to run.In this system, according to the different functions in the network, the wireless modules can be divided into wireless sensor module (that is, the terminal nodes of the sensor data acquisition and communication module) and the coordinator module, as shown in figure 2.Fig.2 Block diagram of monitoring deviceWireless sensor nodes usually consist of four main modules: sensor (signal adjusting, transmitter), a processor module (microprocessors, memory), a wireless transceiver module, wireless network, MAC, transceiver) and a power supply module, power supply, AC-DC). Sensor module and data acquisition node (CC2530) communication using RS-485, when send sensors read data acquisition node command, if the sensor received reply read data command, the corresponding data as a response, read sensor serial data acquisition node, and the serial port read packets package check generates a message, send packets processed task, the final data to the frequency of 2.4 GHz is sent to the coordinator (or router nodes).Coordinator module and terminal node module is different is the coordinator with the wireless sensor in the form of wireless data communication, and each terminal node receives data via a serial port RS-232 transmission to the ARM9 data collection platform.3.2 The power supply designAt present, the electronic devices at high pressure side can take way mainly include solar battery and battery laser power and electronic current induction can (i.e., induction can). Considering the high voltage power electronic device on the transmission line maintenance and working environment, etc factors, unfavorable use battery and solar battery power supply. As a result, the design of the power system is divided into two kinds of situations: the first kind of circumstance, has greater advantages for monitoring equipment on the transmission line, adopt induction way to sensor and ZigBee module power supply. Sensor module voltage grade for DC12V, ZigBee module power supply voltage is DC2.5 ~ 3.6 V, so the induction can should have two different way, and the output voltage; The second case, the tower for the monitoring equipment includes monitoring host, use of solar battery power supply.According to the law of electromagnetic induction, When alternating current flows through the set of high voltage side of the ring core bus (the equivalent of a winding), on the annular core coil (secondary winding) induction of induction electromotive force, called high voltage induction. V oltage induction power supply guarantee for high voltage side of electronic equipment and reliable power at the same time, and can ensure the reliability of the insulation. The change of the high voltage side bus current situation is very complicated, when resources used current minimum may be only A few A, and when happen transmission line fault transient current may reach tens of kA[6].Considering the change of the transmission line current unpredictability,electronic device for transmission line power supply increased the compensation loop, two with different magnetic ring core material, which can take core using the initial permeability significantly higher than the initial compensation core permeability of soft magnetic materials, and can take reverse series winding and compensation winding connection[7], as shown in figure 3.highvoltagebusFig.3 Device of inducing powerInduction power supply can by taking quad, compensating winding, impact protection unit, the whole bridge rectifier, regulator, filter unit drop of subsection pressure units. When the high voltage bus bar through the electric current is small, due to large initial magnetic permeability of the compensation winding, the compensation winding induced voltage is negligible, under the condition of high current can compensation winding induction electromotive force and winding induction electromotive force partially offset each other, to reduce the heat loss, so that can take the power supply in the high voltage bus a relatively wide range change can work normally. When impact current is too large, due to the limited compensation winding, to protect can take power from damage under impulse current, between the whole bridge rectifier and induction winding to join impact protection unit. When current flows through too much impact on a bus, impact protection unit, the winding current flow only impact protection unit and the protection of the whole bridge rectifier circuit level and after, during normal working condition impact protection unit does not work. By voltage filtering unit of after full bridge rectifier voltage ripple voltage regulator and filter out noise, make its have the pulsating multiplexed output dc small, little harmonic, safe and stable operation to ensure electronic devices[8].For tower on electronic device adopt solar battery power supply mode, selects the conversion efficiency of monocrystalline silicon solar panels, the standard for the power to choose: first to calculate the consumption of hours a day, when the outputpower for 1P (W), if every day use 1T (h), the power consumptionfor 11T PP ⋅=(Wh). Calculate the solar panels: according to the daily sunshine time is T hour’s calculation effectively, and the loss in the process of considering the charging efficiency and charging, the output power of solar panels should be )η⋅=T P P O (W). Where η is the charging process, the actual use of power of solar panels? Battery with small volume, long life, good environmental compatibility, high temperature resistant, suitable for fast charging, high safety coefficient of lithium iron phosphate batteries, battery capacity calculation formula:C T N P A B O L C ⋅⋅⋅= (Ah)Type A is the safety factor;P for daily average power consumption, as the working current multiplied by the first day working hours;L N for the longest continuous rainy days; TheO T for temperature correction coefficient; C for batterydischarge depth.4. The design of system softwareSystem software design is divided into the coordinator routing node software design, software design and software design of wireless sensor nodes [9,10][10], in addition to the three required different functionality, its design method and process are the same. After the system is powered on, performing ZMain file. The c of the main () function realization of the hardware initialization, including customs always interrupt osal_int_disable, initialization of board hardware setup HAL_BOARD_INIT initialization (), I/O port InitBoard (), initialize the HAL layer driver HalDriverInit (), initialize the nonvolatile memory osal_nv_init (), initialize the MAC layer ZMacInit (), distribution, a 64-bit address zmain_ext_addr osal_init_system (), initialize the operating system (), etc.When the smooth completion of initialization, execution osal_start_system () function starts running OSAL (Operating system abstraction layer) Operating system. The task scheduling function polling each task is ready or not, according to the priority of the task event. If there is a high priority task ready call the tasksArr [] processing function corresponding to the task in place to handle events, until all ready tasks. If there is no ready task the task list, you can make the processor into sleep mode to achieve low power osal_start_system () once executed, is no longer return tothe Main () function.OSAL is the core of the protocol Stack, Z - any a subsystem of the Stack as a task of OSAL and therefore in the development of the application layer, must through the creation of OSAL task to run the application, in osalInitTasks () function creates OSAL tasks, including TaskID unique identification number for each task. Any OSAL task must be divided into two steps: one is to task initialization; second is processing tasks event task initialization as shown in figure 4.Fig.4 Workflow of initializingIs the application run at the bottom of the ZigBee protocol stack, the application first carries on the system initialization process, function call osal_init system (), including hardware initialization and protocol stack initialization, hardware initialization including serial port initialization, the I/O initialization; Initialization protocol stack is mainly set protocol stack the layers of the initial state. ZigBee protocol stack by adopting the idea of OSAL operating system to build, rotary circulation mechanism, namely task events after the initialization of each layer, the system to enter low power mode, if any task, system will be awakened, and began to enter the interrupt handling events, after the treatment will continue to enter low power mode, if there are several events occur at the same time, the system will determine the priority among events, successive processing events, this kind of system architecture, can greatly reduce the power consumption of the system.Because of the limitation of wireless sensors work environment and conditions for wireless sensors initialized in electricity after operation, can automatically to the coordinator (or routing nodes) automatically for the net, according to the properties ofself-organization network ZigBee agreement completed network registration, distribution of assigned tasks such as operation, the node flow chart shown in figure 5.Fig.5 Workflow of nodeEntered the stage of normal work, according to the actual need real-time sensor data, CC2530 according to the set time interval to the sensor through RS485 sends a request to read data command When CC2530 detected a serial port operation, according to the serial port operation taskID serial processing function calls a corresponding task events and sensor after receiving command corresponding to the detected information via RS485 to CC2530 response, CC2530 collected sensor data carries on the preliminary processing of backwardness to the coordinator node of ZigBee network coordinator reply received after a successful close sensor node power supply, system again into dormancy stage. According to the serial port operation taskID serial processing function calls a corresponding task events and sensor after receiving command corresponding to the detected information via RS485 to CC2530 response, CC2530 collected sensor data carries on the preliminary processing ofbackwardness to the coordinator node of ZigBee network coordinator reply received after a successful close sensor node power supply, system again into dormancy stage.5. Application examplesUse for inspection monitoring system, with wire tension sensor as an example to test in the laboratory, node CC2530 every 10 s send a read to pull sensor measurement information command, tension sensor strain data after a successful receipt, once every 50 s read voltage information. Using serial debugging assistants, according to the pull data and the power supply voltage as shown in figure 6, the right to left to the corresponding hexadecimal display, 796 f for the coordinator for the 16-bit network address of the sensor distribution.Fig.6 Data displayed on UART assist6. ConclusionsIn this paper, based on the ZigBee wireless communication technology, developed a transmission line conductor tension wireless monitoring system. The system is composed of ZigBee nodes that measure the wire tension and transmission to the coordinator, and then the pull data will be sent to the monitoring host via RS232, which can effectively solve the problem of measuring the insulation of wire tension, formed a set of high reliability, lower cost, easy to install, easy to manage, close to the free maintenance solutions, easy to expand (such as it can easy to join wire temperature sensor , weather sensor, lightning current sensor node etc.),provides the powerful guarantee for the safe and reliable operation of power system.V ol.50 No.569Electrical Measurement & Instrumentation May. 2013 AcknowledgmentThe authors also gratefully acknowledge the helpful comments and suggestions of the reviewers, which have improved the presentation.REFERENCES[1] LIANG Ming, MA Helou, CHEN Haibin, etal. The development of the high voltage induction can take communication power supply [J]. 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Xi 'an: Northwestern Polytechnical University, 2007.Author introduction:Zhong Yunping (1986), male, han nationality, ganzhou in jiangxi province, graduate student, research directions for the new type of intelligent electrical equipmentEmail:******************Cheng Xiaohua (1963), male, han ethnic group, Dr, jiangxi jiujiang, professor, engaged in the study of new type of intelligentelectricalequipmentatEmail:**************.cnDai Dong (1976), male, han ethnic group, Dr, jiangsu province, associate professor, engaged in gas discharge nonlinear circuit and key technology of intelligent power transmission and transformation system atEmail:*************.cnZhang (1978), male, yunnan is crucified, master's degree, engineer, work in the electric energy metering at Email:*****************Zhai Shaolei (1984), male, xi 'an, master graduate student, research directions of transmission line on-line monitoringatEmail:*************Abstract date: 2012-07-23; Take back date: 2012-11-07(Chang Huimin Compiled and distributed)。
