Research and Development on Frequency Domain Dielectric Response Test Device for Transformer Oil-Paper Insulation

The frequency domain dielectric response method has garnered significant attention due to its ability to provide abundant information for non-destructive testing of transformers. However, in the response current of oil paper insulated dielectric reaches picoampere level. Due to the influence of on-site electromagnetic interference, the sampling accuracy is difficult to guarantee. Therefore, the errors will be generated in the obtained frequency-domain dielectric spectra. To resolve these problems, this paper designs a cascaded amplifier topology based on parallel optocoupler isolation drive technology, achieving high-voltage sinusoidal output in the 0.001 Hz to 10 kHz range. The anti-interference capability of the testing system is enhanced through the increasing of the excitation source voltage amplitude. To achieve high-precision and phase-shift-free acquisition of dielectric response micro-currents, an adaptive differential current voltage conversion circuit is constructed for accurate acquisition within the 0.01 pA to 1 mA range. The dielectric response testing system developed in this paper is used to conduct frequency domain spectroscopy tests on in-service transformers. The experiment results demonstrated the accuracy and anti-interference capabilities of the proposed system.