The Research Of The On-Line Power Quality Monitoring

In the recent years, the quality and reliability of the electrical power supply in energy grids are worsened due to the persistent growth of non-linear, asymmetrical and frequently variable loads. At the same time, industrial and residential consumers require higher quality electrical power because of increasing applications of power-sensitive receivers. Some customers are suffering severe consequences of poor power quality, e.g. malfunction of machines and instruments and consequently economic losses. Solving this problem requires monitoring and measuring the power quality in energy grids. This can be realized by characterizing variations of the supply voltage at a given location over a period. Measurement results can be used to identify and describe electromagnetic phenomena which may cause problems in supplying consumers.In this dissertation, characteristics and parameters related to the power quality are introduced firstly. Then a special DSP-based system for power quality measurement was presented. The system was designed firstly for evaluating the supply characteristics according to the Natianal Standard, i.e. long-term changes of the voltage and current RMS values, total harmonic distortion(THD) factor, harmonics contents, asymmetry factor for 3 phase voltages. In addition, the system was extended and equipped with the software for measuring disturbances in the power system, such as transient oscillations and short-term voltage variations.The system hardware architecture consists 3 blocks, i.e. the A/D front-end signal processing circuit, the A/D sampling circuit and the processing system based on a DSP processor. The CPLD (max II EPM240C100) is used to glue A/D and DSP. External memory SRAM, FLASH and CF card are also used to enlarge memory. This system provides the RS-232/RS-485 serial interface, and 10/100 M Ethernet interface.The designed power quality monitoring has passed the test of the GB/T19862-2005 standard.