Temperature Distributed Measurement Of GIS Spacer Based On OFDR

One of the main reasons for limiting the large-scale development of DC-GIL is that the surface charge accumulation on spacers is severe,and the distortion of the electric field reduces the flashover voltage of the spacers.However,the temperature distribution has great influence on the charge accumulation,and the temperature distribution of the entire spacer surface has not been obtained in the current measurement research.In order to master the accumulation characteristics of the surface charge more accurately,it is necessary to achieve a distributed measurement of the spacer temperature.The existing temperature sensors can only realize the measurement at a single point,the system wiring is complicated,and the ability of anti-electromagnetic interference is poor,so it is difficult to obtain the temperature distribution of the spacer surface.In order to solve the problem,a new distributed optical fiber temperature sensor based on optical frequency domain reflectometry(OFDR)is proposed in this paper,which can realize the distributed measurement of spacer surface temperature simply and reliably.Firstly,the signal model of optical frequency domain reflection was analyzed.The system used coherent heterodyne detection technology to realize the acquisition of measurement signals.The spectrogram of the beat signal could be used to locate the measurement points accurately.The nonlinear sweeping effect of the light source was analyzed,and a method to solve the nonlinear frequency sweeping effect of the light source was proposed.The polarization fading effect in optical fiber was analyzed and the polarization diversity receiver was selected to suppress the polarization fading.On this basis,the OFDR distributed measurement system was built and the effectiveness of the proposed nonlinear compensation method for the light source was verified by experiments.In addition,according to the principle of OFDR distributed measurement,the method of realizing distributed temperature measurement was given theoretically.Secondly,different experimental platforms were designed for the two different fibers of the All Grating Fiber(AGF)and the ordinary single-mode fiber.The external temperature measurement was realized by reasonable signal processing methods.Through experiments,it was found that the measurement distance of 11.2m can be achieved by using AGF as the sensing fiber,the spatial resolution was 1cm,and the temperature sensitivity coefficient of this fiber is 10.16pm/0C.When the single-mode fiber was used as the sensing fiber,the Rayleigh scattering signal in the fiber was used to realize distributed temperature sensing.The experimental results show that the detection distance of the distributed optical fiber sensing system can reach 50m with a spatial resolution of 3 cm,and the temperature sensitivity coefficient of this fiber is 10.5pm/℃.Finally,a test platform for distributed measurement of surface temperature of 126 kV GIS spacer was built in the laboratory.The temperature changes of 212 measuring points were obtained by the all grating fiber placed on the spacer.The temperature changes obtained by the OFDR system were consistent with those measured by the traditional electronic temperature sensor,and the average temperature deviation was only 1.4℃.The distributed temperature measurement with spatial resolution of 1cm was achieved.In the experiment,the temperature distribution of the spacer surface at different time during the heating process were obtained,which provided a reference for studying the accumulation effect of space charge.