Optical Sensor with Wide Range and High Sensitivity for Internal Magnetic Field Detection of Transformer

The deterioration of winding defects is one of the important causes of power transformer fires and even explosion failures. The change of leakage magnetic field distribution is the most direct response to winding defects. Currently there are few sensors suitable for online measurement of the internal magnetic field of transformers. Based on the Faraday magneto-optical effect, a magnetic field sensor with wide range and high sensitivity is proposed in this paper, which is suitable for the interior use of transformers. The straight-through optical structure with interior polarizer is adopted, and the sensor has a measurement range of 1.5 T and a sensitivity of 1 mT. It also possesses a small size, with a length of about 30 mm after encapsulation. The influence mechanism of vibration and temperature is revealed through theoretical analysis and numerical simulation. It is proposed to filter out the interference of vibration by characteristic frequency analysis and to compensate for temperature by a two-probe structure. An anti-interference test verifies the effectiveness of this method, and it can reduce the error from 80.56% to 2.63% under the combined interference of vibration and temperature.