Research on Noncontact Voltage Measurement Method for Three-Phase Busbar of Low-Voltage Distribution Cabinets

The important role of the distribution cabinets in the power system makes voltage monitoring of them of great significance. However, traditional voltage measurement methods (e.g., electromagnetic voltage transformers) have defects such as galvanic contact and magnetic saturation. Under this background, this article proposes a noncontact (NC) voltage measurement method for three-phase busbar of low-voltage distribution cabinets. Injecting a high-frequency calibrating signal into the capacitive-coupling network of the capacitive-coupled voltage sensor to achieve the self-calibration of the voltage sensor. Additionally, a detailed analysis is conducted on the frequency selection of the calibrating signal. Furthermore, a dc component filtering method based on least squares curve fitting is proposed to achieve accurate voltage measurement. An NC voltage measurement system, dedicated to three-phase busbar in low-voltage distribution cabinets, is designed, and the system includes three-phase capacitively coupled voltage sensor, a measuring circuit, an analog-to-digital converter (ADC), and a microcontroller. A test platform is built to evaluate the system. The test results show that for measuring the three-phase voltage of 220 V/50 Hz, the relative amplitude error of the instantaneous voltage waveform is less than 1%, the phase error is less than 0.5 degrees, and the relative error of the voltage root-mean-square (rms) measurement is less than 0.35%. High linearity is observed with a maximum nonlinearity error of only 0.04%. Frequency response characterization shows the system has an almost constant gain factor and phase errors of less than 1 degrees and 3 degrees at 250 Hz and 1 kHz, respectively. The temperature characteristic of the system is evaluated and the results show as the busbar temperature rises from 28 degrees C to 42 degrees C, the rms error increases from 0.07% to 0.4%.