| With the rapid increase of electric power load, especially the increase of unbalanced, impact and nonlinear loads, the power quality problems have been more and more serious. On the other hand, more sensitive loads need higher power quality with the development of information technology.On the basis of consulting literatures, the definition, categories and influence to sensitive loads of power quality are summarized. According to the national standards about power quality, the measurement principles and computing methods are induced. The work is the theory base of developing online power quality analyzer.The online power quality analyzer is designed and implemented in this paper. It is a new type of virtual instrument based on the advanced the DSP and computer technology. The analyzer has the abilities of long-term online operating, real-time measuring and analyzing, managing of history data, etc. Compared with the traditional analyzer, it has many advantages, such as easy controlling, strong processing and graphics output, etc. It is able to record the abundant and integrated data for the Electric Department, and provide the reference for selecting correct compensation technology.In this paper, some key technologies are discussed and analyzed. The software function modules, such as data acquisition, data processing, human-machine interface and data management, are introduced. The crucial software design concepts of using multithread and double buffers for exchanging data are emphasized. The data transmission between the data collecting site and supervision center is implemented for constructing a distribute supervision system based on the network. The result of survey indicates that the design of online power quality is correct.Using this online power quality analyzer, the author measured and recorded the indicators of power quality when electric arc furnace (EAF) operating, provided the persuasive reference data for metallurgical industry improving the power quality.
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