Power Frequency High Voltage Digital Measurement System

Our country is vast, the development of electric power resource and power consumption is extremely unbalanced. The distance between electric power and power load centre is gradually increasing. And highly efficient energy-saving, safe and reliable ultra-high voltage (UHV) transmission technology has been put to the agenda. China Electric Power Research Institute (Beijing) constructed the country's ultra-high voltage DC test base in Changping, the test base will provide a strong technical support for the construction and operation of China's UHV DC projects.This paper presents a power frequency high voltage digital measurement system based on the virtual instrument technology. This measurement system has been successfully applied to±1200kV bipolar DC high voltage generator measurement system in Beijing China Electric Power Research Institute. In this measurement system, the input voltage and current signal of rectifier transformer, as well as the output voltage and current signal of DC generator have been measured using the mainstream Data Acquisition (DAQ) card. This digital measurement system can calculate the peak and Root Mean Square (RMS) of voltage and current signals, analyze the spectrum of the voltage and current signals and calculate harmonic components. This measurement system can display the dynamic waveform and record the historical data. Meanwhile, the measurement system can also transmit the results to the terminals through Internet, and realize the sharing of data.In this paper, the concept and composition of virtual instrument, as well as the hardware foundation of this digital measurement system were discussed. The performance and use of PCI-6250 DAQ card were also discussed in detail. In the hardware design of measuring circuit, this paper elaborated the design of the measuring circuit for voltage and current signals, and the selection of voltage and current transformer, as well as the design of low-pass filter circuit. In the software segment, the paper presents the structure of the software system, and the calculating method of the peak, RMS, as well as the algorithm design of Fast Fourier Transform (FFT).Finally, the author established test circuit in the laboratory, and compared the results of digital measurement system with the results of TDS3012B digital oscilloscope. After the error analysis, the algorithm of peak, RMS and FFT was confirmed. At the test site, the author focused on the interference and the coupling problem of the DAQ card, the hardware and software filtering technology had been developed to suppress the high-frequency interference signals in the measurement system. The accuracy and anti-interference capability of the measurement system were highly improved. The author analyzed the input voltage signal spectrum of the rectifier transformer using MATLAB digital signal analysis tools, and compared the results with the digital measurement system. After filtering, the harmonic content of the electric power met the requirements of the project. Meanwhile, the output voltage of±1200kV DC high voltage generator was measured. The comparison with approved measurement system (AMS) proved that the power frequency high voltage digital measurement system met the requirements of the project.