Optical Fiber Imported Electric Field Measurement In Transformer Oil For Oil-paper Insulation

The insulation design of converter transformer has been one of the key problems in UHVDC transmission field.With regard to the design of oil-paper insulation structure of converter transformer,the current research focuses on the numerical calculation under different operating conditions.However,the validity and accuracy of the results are not verified by the measured data.The measurement of electric field in oil in confined space has always been a difficult problem.At present,there is no equipment or sensors that can be introduced into oil-filled sealed equipment to carry out electric field measurement.In this paper,the research of optical fiber imported electric field measurement in oil-paper insulation based on Kerr effect is carried out,which is helpful for the optimization design of oil-paper insulation structure of converter transformer,the verification of simulation method and the analysis of insulation fault.In this paper,the measurement system of the electric field in the oil-paper insulation structure is studied by means of the optical fiber imported method and Kerr electro-optic effect principle.Based on the scheme,a measuring device for the electric field in transformer oil of the oil-paper insulation structure is developed.The measuring device mainly comprises a 637 nm semiconductor laser,a polarization maintaining fiber,a collimator,a polarizer,a quarter wave plate,an analyzer,a coupler,a multimode optical fiber,a photodetector and etc.Using the polarization maintaining fiber and multimode optical fiber,the electric field measurement system can be imported into a sealed oil-filled equipment for AC-DC composite electric field measurement.The electric field measurement device has a small size and uses non-metallic material.The sensing device of the electric field measuring device has a totally enclosed structure,so that the transformer oil can be prevented from penetrating inside the sensing device,and the sensing element is prevented from being corroded by the transformer oil.Through the test and measurement error analysis,the electric field measurement sensitivity of the electric field measurement device in the transformer oil reaches 0.6kV / mm for DC electric field,and 0.2kV / mm for AC electric field.The maximum relative measurement error of the DC electric field is 4.08% and the maximum relative measurement error of the AC electric field is 0.28% after the correction of the electric field formula.Based on the first-generation electric field measuring device,the second-generation electric field measurement device is proposed.