Kerr Electro-Optic Sensor for Electric Field in Large-Scale Oil–Pressboard Insulation Structure

The design of the oil–pressboard/paper insulation structure is the key to maintain the safe and reliable operation of power transformers, which mainly relies on simulation and verification test undertaken with simple or equivalent models, falling short of the physical entity verification undertaken in the large-scale structure. Based on the Kerr electro-optic effect and the optical fiber technology, a novel electric field measuring sensor was developed in this paper for the application test in the large-scale oil–pressboard structure. The sensor is contained of collimator, total reflection prism, coupler, and customized optical elements, whose appearance is a miniature capsule-shaped configuration. The key technical performance parameters of sensor were obtained, for instance, and the effect of imported sensor on the electric field under measurement is an average 1.17% reduction in intensity; the sensitivity of designed system is 162.84 V/mm under ac voltage and 40.43 V/mm under dc voltage. Under dc voltage, the measuring accuracy of the designed system is greater than 97.42%, while in the context of ac voltage, it could reach 97.14%. The application test was conducted to capture the dynamic process of the electric field in oil in the large-scale outlet device model, which has three uniformly spaced oil spacings divided by pressboards, under ac voltage, dc voltage, and polarity reversal voltage. The experimental results verify that the developed electric field sensor could be effectively and reliably applied in the large-scale oil–pressboard insulation, and it could be confidently inferred that the larger the scale of insulation structure, the better is the performance of sensor.