Abstract: In order to accurately analyze the impact of system frequency on the error characteristics of standard voltage transformers and obtain the low-frequency applicability of standard voltage transformers, this paper establishes an equivalent circuit model of standard voltage transformers, proposes a method for analyzing the low-frequency excitation characteristics of ferromagnetic materials using complex permeability, and constructs a measurement circuit based on phase-locked principle to obtain the complex permeability of oriented silicon steel sheet 30P100 at different frequencies. Secondly, the no-load error and load error function of standard voltage transformer are obtained analytically. A 35 kV standard voltage transformer is taken as a model, the parameters of primary and secondary leakage impedance are obtained through error increment backstepping and short circuit method, respectively, and the parameters of low-frequency excitation impedance are obtained through complex permeability. Finally, through simulation calculations, the no-load error and load error curves were obtained at 20 Hz and 50 Hz, and compared and verified with the measured results. Research has shown that the real and imaginary parts of the complex permeability of oriented silicon steel sheets increase with the decrease of frequency. In the frequency range of 20 Hz to 50 Hz, the no-load ratio error and no-load phase displacement of standard voltage transformers both shift forward with the decrease of frequency, the load ratio error is less affected by frequency, and the load phase displacement shifts forward as the frequency decreases. The lower the frequency is, the smaller the impact of load changes on their error will be. The designed 35 kV standard voltage transformer is taken as an example, and it is found that the impact of frequency change on the no-load ratio error of the standard voltage transformer is 2×10⁻⁵, the impact on the no-load phase displacement is within 0.4′, and its no-load error can at least meet the error limit requirements of level 0.01 at both 20 Hz and 50 Hz. At a 15 VA load, the impact of frequency variation on phase displacement reaches about 3′. At 20 Hz and 50 Hz, it can only simultaneously meet the error limit requirement of level 0.5. In conclusion, the low-frequency error characteristics of standard voltage transformers are obtained, providing supports for the experimental verification of voltage transformers used in low-frequency flexible AC transmission engineering.