Optimization And Arrangement Of The Inner UHF Sensors For Partiai Discharge Measurement In Transformers

UHF sensors are one of the key components of partial discharge detection system in transformers. Unoptimized structural parameters and unreasonable arrangement of UHF sensors are deficiencies that severely decrease the detection sensitivity of partial discharge and restrict the development of ultra-high-frequency detection technology. Therefore, it has great significance to study on optimization and arrangement of the inner UHF sensors for partial discharge measurement in transformers. In view of this, this paper carried out the following tasks:The influence of dielectric constants of dielectric plate for sealing flange hole on the disc sensor’s detection sensitivity was simulated by using finite-difference-time-domain (FDTD) method. The simulation results show that, when the dielectric constants of the dielectric plate and transformer oil were the same w, the effects of dielectric plate is negligible.The influence of installation depth on the disc sensor’s detection sensitivity was simulated by using FDTD method. The simulation results show that, the detection sensitivity of sensor increased along with the installation depth; the installation depth reduction of 40mm, the attenuation of the signal which frequency lower than 600MHz is 2dB. Therefore, the PTFE dielectric plate was choosed to seal the flange hole in transformer’s inner wall,the sensor was recommended to be installed flushing with the inner wall of the tank.The influence of disc UHF sensor structure parameters on the detection performance was simulated by using FDTD method. The simulation results show that, the first valley frequency of the VSWR curve decreases with the increase of flange-hole’s diameter; the second valley frequency decreases with the increase of of the disc’s diameter; the two valley frequency decrease with the increase of the medium plate’s dielectric constant; the VSWR increases with the increase of the thickness of the medium plate. According to the simulation results obtained the optimum sensor dimensions, namely:the diameter of the flange hole was 200mm, the diameter of the sensor was 120mm, the relative dielectric constant of medium plate was 4.5, the thickness of the medium plate was 20mm. The simulation results show that, the equivalent height greater than 10mm in the frequency range of 0.3GHz～1.5GHz was 80%.The influence of the arrangement of disc sensor on detection sensitivity was simulated by using FDTD method. The simulation results show that, the coverage is higher when the disc sensor was installed at the center of the long side or at the corner in side and top. Test in 110kV transformer verifies the correctness of simulation results.According to the above conclusions, the arrangement of disc sensor was put forward:(1) To measure partial discharge that discharge capacity greater than 500pC in 110kV transformer, one disc sensor was recommended to be installed in the coner of the side or the top in transformers. (2) To achieve higher sensitivity, two disc sensors were recommended to be installed at the corner of two sides of the transformer.