Design of field sampling unit of an on-line monitoring system of dielectric loss in capacitive high-voltage apparatus

To assess the insulation condition of capacitive high-voltage apparatus, on-line monitoring of dielectric loss angle (delta) is an effective measure. A type of field sampling unit (monitoring terminal) based on a new-style on-line monitoring system of dielectric loss in capacitive high-voltage apparatus is designed, with which the safety, reliability and information-based standard of monitoring high-voltage apparatus in power systems can be improved greatly. An approach using GPS to implement high-accuracy synchronization sampling in different places, and using GPRS to implement remote control and communication is presented in order to achieve relative comparison method. The accurate acquisition and control of ADS8505 is realized by EP1C6Q240C8 that includes Nios II embedded soft-core processors. The logic sequential control of frequency measurement and a logic sampling module are designed by using hardware description language VHDL as well as Verilog, and the extraction and storage of digital signal is completed in the period during which the logic design is realized by Quartus II. Then the digital information is packed and transmitted through the GPRS wireless network, Internet, the server to the client by monitoring terminal. Finally, the expert software assesses the insulation condition of the apparatus according to the relevant insulation diagnosis strategies. Testing results show that the monitoring system can improve the measurement of dielectric loss angle greatly with regard to confidence, accuracy and stability compared with conventional equipment.