Research on Power Quality Monitoring and Analyzing System Based on Embedded Technology

2010 China International Conference on Electricity Distribution 1 Research on Power Quality Monitoring and Analyzing System Based on Embedded Technology Zhang Hong-tao, Ye Ying, An Qing China Zhoukou Power Supply Company, Zhoukou City, Henan Province 466000 E-MAIL: yeying7306@163.com Abstract: Based on actual problems in power industry, a power quality on-line monitoring system was set up by comprehensively adopting embedded technology of software and hardware platform, GIS (Geographic Information System) information technology and Internet technology. Meanwhile analyzing methods of time domain, frequency domain and mixed domain were used in this system to monitor, evaluate and analyze all monitoring data, which realizes the evaluation of power system reliability index and thereby continuously improves power system reliability and then plays an active role on enhancing the power quality level of power system in Henan province. Keywords: Power Quality; Monitoring and Analyzing System; Embedded; Harmonic; GIS 1. Introduction With the large increase in new types of load and nonlinear load of power system, serious distortion would happen among voltage and current waveforms of power system and thus cause mass power system pollution to power system. Serious power pollution has occurred as both users internal short and short supply interruption during the operation of switches and the switching of transformers and capacitors would lead to lots of power quality disturbance, consisting of temporary overvoltage, transient overvoltage, voltage sag, voltage swell or short interruption of power supply etc. The pollution has already been a great threat to certain industries (such as precise instruments and microcomputer system of hospitals and microprocessors in smart electron and industrial process control and so on) and triggered a waterfall chain reaction, thus raising the event of the collapse of power system. Problems arising from power quality may not only affect the running safety and stability of power system but also cause great economic losses to users. Therefore, effective and reasonable monitoring and analyzing to power quality of power system and the enhancing of power quality have become the focus of correct operation of power system. 2. Demand Analysis on Power Quality Monitoring System Generally power quality monitoring system shall own a three-layer framework, consisting of client terminal of power substation field monitoring, central server of power quality monitoring in district power system and communication network. System functions shall meet following demands [ 1] : a) The terminal can monitor at the same time five power quality indexes relative to voltage deviation, frequency deviation, harmonic, voltage fluctuation and flicker and three-phase unbalance etc; it can show the result on display interface and save partial data. b) Software platform in monitoring center can complete the management of several terminals and add or delete monitoring stations according the demand. c) The software platform can analyze and calculate data or information uploaded from client terminals. It can also achieve many functions such as curve shown, passing statistic and report print etc. d) Via Ethernet, client terminal can upload data at monitoring center. Software platform at monitoring center can initialize hardware of client terminal and then read data and transmit command. 3. Overall Implementation of System 3.1 System Configuration Power quality monitoring and analyzing system is

2 2010 China International Conference on Electricity Distribution comprised of client terminal of field monitoring at power substation, central server of power quality monitoring in district power system and communication network. The sketch is shown in Fig.1. Client terminals can monitor power quality index in real-time via power substations and upload relevant data. Those client terminals would be installed at power substations or user sides. The specific installation number shall depend on the actual demand of power quality supervision and management in power system. Client terminal equipment, made up of collector and computer, is constitutive of signal panel (incl. sensor and connection terminal), backlight and keyboard interface board, signal adjusting board, flicker measuring board and IPC (Industrial Personal Computer) system. On basis of our state s five standards of power quality, collectors can complete the acquisition and processing of relevant data on power quality such as voltage, current and frequency etc; communication network shall adopt Internet network. Multi-client terminal can be monitored and managed by one server at power quality monitoring center in district power system. By Web server it will publish power quality status and release operation and control commands to client terminals, thus completing the real-time supervision and management of power quality index of each power system points (power substations). corresponding parameters. For example, harmonic wave and voltage variation will separately be described by effective value and THD (Total Harmonic Distortion). These data would be useful for finding out the reason of disturbance and locating the source. During the monitoring, power quality monitoring instrument (front-end equipment) will detect and catch disturbance and transmit it to central servers where the disturbance data will be done with further processing and saved. All of this has to be realized under intercommunication through Ethernet. Fig. 2 Function sketch of power quality monitoring system 4. Design Implementation of Client Terminal Fig. 1 Sketch of power quality monitoring system 3.2 Implementation of System Functions Functions of power quality monitoring system are illustrated in Fig.2. The monitoring is comprised of three sections: data acquisition, data processing and analyzing, and result releasing. Essentially, power quality monitoring is the collection and processing of information. Firstly it shall catch disturbance. List them in categorizing and then judge disturbance degree in terms of their characteristics and A client terminal of power quality monitoring and analyzing system is realized by adopting embedded technology of software and hardware platform. The function structure of the whole client terminal concludes of two parts. The first part is composed of data acquisition, data processing, data display and data storage. The other part concludes of data analyzing and statistic and report generation. Its function block diagram is shown in Fig.3. The procedure at the first part keeps in running status during the whole monitoring. Data acquisition card will not stop collecting data. And data processing module will process at a regular time all data acquired from buffer cache at once, which then will be analyzed and calculated so as to get every index value. Then data display module will judge whether the index value is over proof and display relevant information on the interface while the index data will be saved into database. Finally client terminal realizes the real-time monitoring to monitoring place in this process.

2010 China International Conference on Electricity Distribution 3 Fig. 3 The client system block diagram 4.1 Data acquisition module Data acquisition module would make programming by cycling cache technology, which owns an advantage to make a non-stop data acquisition of acquisition card in a setting sampling rate. Each time using cycling cache technology, data shall be saved into part of buffer cache only. When reaching the bottom of buffer cache, it returns to the top. This could be done again in the same buffer ache. For further ensuring real-time monitoring of power quality, the suggested algorithm of power quality monitoring shall be loaded into a high-speed operational DSP (digital signal processor). 4.2 Data processing module The main function of data processing module is to perform corresponding mathematic operation to acquisition data of acquisition card, which is comprised of two submodules, separately monitoring and calculating both steady state index of power quality and transient state index of power quality. Fig. 5 Data Processing Module 4.3 Modules of data storage, analyzing and statistics, and report generation Data storage module is mainly to perform functions of list generation, write data, read data and delete records in database. It is programmed in SQL language, by which lots of data manipulation statements can be generated. So users can operate data flexibly according to their own requirements and complete different data management or operational functions as requested. In programs, data storage module will write data separately into data tables of steady state of power quality and transient state of power quality. The function of data analyzing and statistic module is to collect and analyze data in database so that operator would have a better understanding about power quality status, from a statistical point of view. Report generation module is able to generate reports in the Word or HTML format. The report may show in data, tables or diagrams to display power quality status. The module can set the display of statistic data that users want to see in the report. It is convenient for printing and saving in records. 5. Design Implementation of Server Firstly, a server shall be able to receive data from client terminals, write the data to corresponding data tables in database of server in terms of their sources and then display them in main interface. Secondly, the server shall be capable of general collecting and analyzing data in the whole district s power system, realizing effective management to each client terminal and releasing various commands so that client terminals would execute corresponding performances. As a result, its task is mainly composed of two sections. The first includes of data receiving and the storage and display of categorized data; the other is the function of collecting and querying various kinds of data, and it shall be able to publish overall information of the whole district s power quality in Web format and provide to users the download of various kinds of data about power quality. All these functions are realized by adopting dynamic allocation technology, which makes the system more flexible and convenient for extending. The design of the server s main interface in power quality monitoring and analyzing system can also adopt a human-computer interactive mode similar to Windows interface. On basis of the human-computer interactive mode of client terminal s interface, it is more emphasized about the monitoring, evaluation and management of general power quality index for the district power system.

4 2010 China International Conference on Electricity Distribution 6. Communication Network and Implementation of WebGIS Technology By adopting the microcontroller technology of embedded TCP/IP protocol, the system is responsible for the communication between the acquisition and the remote management, and transmitting acquisition data and statistical result to main management computer promptly, realizing centralized monitoring to different power supply systems. Major technologies of WebGIS includes of CGI (Common Gateway Interface), ActiveX and Java etc. The WebGIS system is set up based on these technologies. It provides more clear function layers and more normative module connectors, easier to extend and more appropriate for distributed processing. The system is a typical three-layer framework, comprised of data presentation, application service and data service. 6.1 Implementation of data service Data service is set in a special data server where there are initial data for storage in data base, mid-processing data, result data returned to terminals and all data for operation and maintenance of systems, providing all necessary services to data storage for the operation of the whole system. It adopts large scale of rational database Oracle9i, mainly used for saving map property data, parameters of power system electric components and parameters of operation status of power system, real-time data of power quality index, historical data and necessary initial data etc. It also provides initial data required by application service and data presentation and save data that have been submitted and processed by other two layers. All initial data will be provided by a data acquisition system. 6.2 Implementation of application service Application service is mainly composed of Web service module, GIS application service module and data service module. GIS application service module uses MAPXTREME map application server manufactured by MapInfo to present lots of information and resource on a map in multifarious visualizing manners. After users perform relevant map operations at client terminal, the browser at client terminal will send a HTTP request to Web service module, Submit forms and the Javascript of Javascript VB/Script and then set a request sting according to information of current tool number and users mouse operation etc. Javascript applications would judge request types of users map operation through information of submit forms and visit MAPXTREME Map engine. If necessary, the Map engine will acquire required data from data service module and perform corresponding spatial analysis and processing and then transmit processing result to Web service module in format of vector diagram. Then Web service module will transmit the information to browsers at client terminals in data flow and the received data flow will be converted into required JPG or GIF images. 6.3 Principle and Implementation of Data Presentation Data presentation is mainly used for users data query and map presentation. Client terminal will visit front-end agent server through Web Browser. It will send a HTTP request to Web service module. Then with the service supplied by RMI (Remote Method Invocation) application server, users at home can perform basic business operations such as enlarging, narrowing, roaming and query etc. For thematic map and the like of complex business operations, users at client terminal will establish a session with map application server (MapInfo MAPXTREME), which will provide required parameters for server to process. It is ensured by this way that common users could use WebGIS and front-end plugins would be simplified. Thus the front-end software will be updated and managed so that it could be very appropriate to publish and query information. 7. Conclusions This system has already been successfully applied in Zhoukou Power Supply Company, subsidiary company of Electric Power of Henan. The system has improved both power quality and reliability of power system and played an active role on enhancing the power quality level of power system in Henan province. References [1] Xu Xia-ling, Zha Xiao-ming. Study on Power Quality Monitoring and Evaluating System. High Voltage Engineering, 2008,34(1):158~162. [2] Yao Jian-gang, Li Ji-guang, Li Tang-bing, etal. Design and Application of Novel Power Quality Monitoring and Evaluation System. Proceedings of the Chinese Society of

2010 China International Conference on Electricity Distribution 5 Universities for Electric Power System and Automation, 2009,21(2):76~80. [3] Cheng Peng-bo, Liu Can-ping, Liang Xiao-jian. Research of WebGIS power quality monitoring system based on MapXtreme[J]. Telecommunications for Electric Power System, 2006,27(167):63~65. [4] Duan Cheng-gang, Ou yang-sen, Song Zheng-xiang,etal. Desing of a New Online and Real-time Power Quality Monitor [J]. Power System Technology,2003, 28 (2):60-63. [5] Sun cai-xin, Sun zhou-yuan, Liu li-feng, etal. Power Geographic Information System and Its Application in Distribution Power System[M]. Beijing: Science in China Press, 2003, 5-1 Author :Zhang Hong-tao, Male, Born in 1967, Master Degree, Senior Engineer, Chief Engineer of Zhoukou Power Supply Company, Subsidiary Company of Electric Power of Henan. Ye Ying, Female, Born in 1973, Bachelor Degree, she is an Engineer of Zhoukou Power Supply Company, Subsidiary Company of Electric Power of Henan. An Qing, Female, Born in 1975, Master Degree, she is an Engineer of Zhoukou Power Supply Company, Subsidiary Company of Electric Power of Henan.