Experiments on the multi-functional current sensor for condition detection of transformer bushings

In recent years, time based maintenance of electrical of power equipment is gradually replaced by condition based maintenance. In China, smart grid acts as the great goal of the electric power industry, in which smart equipment such as smart transformer play important roles. As one part of the smart transformer, a smart multi-functional current sensor was designed to replace the leakage current sensor and the partial discharge sensor, the latter are usually installed on the grounding line of the bushing tap. This sensor has small volume, convenient interface and can measure the leakage current and partial discharge and overvoltage signals at the same time. In this paper the construction design of the sensor is displayed. And experiments were carried out in the laboratory to prove the feature of the sensor to measure the signals and the protection circuit under lightning overvoltage. Finally, the sensor was used on a 220kV transformer to prove its effectiveness.