Development of 3 kV Low-Frequency Induction Voltage Divider Using Two-Stage Excitation

To address the lack of voltage ratio standards for accuracy testing of low-frequency voltage transformers, it is necessary to develop a 3 kV low-frequency induction voltage divider. Firstly, based on the analysis of the error sources of the induction voltage divider, a method was proposed to calculate the excitation impedance of the induction voltage divider using complex magnetic permeability. A measurement circuit based on the lock-in principle was set up to measure the complex magnetic permeability of grained-oriented silicon steel 30P100 and permalloy 1J85 at different frequencies. Secondly, a 3 kV low-frequency induction voltage divider with a two-stage excitation and a series-wound ratio winding in 10 sections was designed. The errors of the two stages of the instrument transformers were calculated at 20 and 50 Hz, respectively. Finally, the divider's errors were calibrated at 20 and 50 Hz using the reference potential method. The results showed that, compared to 50 Hz, the excitation impedance of the two stages decreased and the errors increased at 20 Hz, with the overall error of the induction voltage divider being better at 50 Hz than at 20 Hz. Experimental measurements indicated that at 20 Hz, the ratio error and phase error of the 3 kV two-stage excitation induction voltage divider were better than 1 × 10⁻⁵, whereas at 50 Hz, the errors were better than 1 × 10⁻⁶. This study provides support for the accuracy testing of voltage transformers used in low-frequency flexible AC transmission projects.