Development Of Space Electric Field Measuremen Sensor For Transformaer Oil

In recent years,HVDC project has developed rapidly in our country.As one of the key apparatus,the safe and stable operation of converter transformers is very important.The design of the insulation structure of converter transformers is still mainly based on the numerical simulation of electric field.The accuracy and validity of the results are not verified by the measured data.Therefore,there is an urgent need of a method and devices to measure electric field directly.The Kerr effect method has the advantages of high sensitivity,little influence on the electric field to be measured and it can be applied to on-line measurement.The application prospect is quite broad.However,the method of electric field measurement based on Kerr effect is generally only for open space and related optical components are usually discrete.For transformers and other apparatus,there is oil-filled and confined space and the current method cannot be applied directly.With Kerr effect and optical fiber sensing technology,a research on electric field measurement for oil in transformers is carried out in this thesis,which is helpful for the electric field measurement in oil in transformers.In this thesis,an electric field sensor is developed and it can be applied into transformer.For existing measurement technology and devices,the measurement sensors are large.Aiming at this problem,a circularly polarized laser,spun fibers and polarized fibers are adopted to simplify optical path and reduce size.Aiming at the problem of low sensitivity,a total reflection prism is introduced to increase the Kerr integral path and improve the sensitivity of the sensor.The influence of the reflection on the measurement of the electric field is analyzed.The relationship between the reflection times and the sensitivity of the electric field sensor is studied.According to the sensor material requested under actual working conditions,polysulfone is selected as the sensor material.Polysulfone has high mechanical strength and can be used in high temperature environment.The dielectric constant of polysulfone is close to oil,which can minimize the influence on the electric field to be measured.The sensor can be imported into oil-filled and confined space and connected with the laser and the photodetector outside by fibers.Through the test,the sensitivity of AC electric field is 140V/mm and the sensitivity of DC electric field is 35.16V/mm.The average measurement error of electric field sensor under AC electric field is 3.52%,and the average measurement error under DC electric field is 6.21%.