We develop an on-line monitoring method for partial discharge of high-voltage electrical cable. The optical fiber current sensor construction that combines the magneto-optic material with the ferromagnetic ring concentrator. We carry on the simulation and analysis to air gap magnetic field of the ferromagnetic ring concentrator using the COMSOL Multiphysics finite element analysis software, find the method to solve the air gap size of ferromagnetic ring concentrator and the placement of the magnetic field crystal according to the magnetic field distribution rule. We have studied distinctive features of the response of a fibre-optic current sensor with a magneto-optic crystal sensing to short current pulses. The response of the current sensor to the pin-to-plate discharge model of electrical cable at different voltage levels has a linear relationship and its duration is determined by the relationship between the current pulse duration.
Measuring equipment is very important in smart grid, for example, the real-time accurate current measurement is necessary for over-current protection, leakage detection. Faraday Effect causes light polarization to rotate when the fiber is exposed to a magnetic field in the direction of light propagation. Thus, the magnetic field strength can be determined from the light polarization change. By applying Ampere’s law, we can get the current by measuring the light rotation. In this paper, optical current sensor (OCS) based on magneto-optic crystal has been developed. The sensing principles, optical and electronic design, as well as its characterization have been described. The weak current signal detection technique is further discussed by means of spectral analysis and lock-in amplifier methods. The performance of the prototype was tested experimentally, the sensor has a high sensitivity for currents and is capable of achieving weak electric current detection with accuracy of 1mArms (50 Hz). A linear response is obtained for current amplitude as low as several mArms at an AC frequency of 50 Hz. For the direct current (DC) current measurement, a lock-in amplifier is used in our scheme; the detection limit of the magneto-optic crystal current sensor is less than 1 mA. There is a wide range of applications for the magneto-optic crystal current sensor, which will be mainly used to monitor currents both on photovoltaic grid-connected system and insulator operating state.
For the first time, we experimentally study the transversal-stress (T-stress) induced polarization crosstalk behaviors in polarization maintaining fibers (PMFs) including the linearity, sensitivity, response time and recovery time, using a distributed polarization crosstalk analysis (DPXA) system. Using two Panda PMFs with or without polyacrylate buffer coating and one Bow-tie PMF with golden polyimide coating as experimental samples, we find that: I) the polarization crosstalk can be highly linear with the T-stress for PMFs no matter with or without coating; II) the polyacrylate coating can reduce the crosstalk sensitivity of naked PMFs by more than hundreds of times, while replacing the polyacrylate coating with polyimide coating can increase the sensitivity by tens or even hundreds of times; III) the polyacrylate coating can induce a significant recovery time of crosstalk when a T-stress is removed after a long loading time compared with that in naked PMFs or golden PMF with polyimide coating, however the crosstalk response speed is too fast to be measured by the DPXA system. Additionally, we also find that the current polyimide coating technique still needs to be improved further to reduce the crosstalk base level. This work will be very useful for PMF-based distributed sensing applications and sensing PMF manufacturing.
The coded aperture spectrometer can achieve high throughput and high spectral resolution by replacing the traditional single slit with two-dimensional array slits manufactured by MEMS technology. However, the sampling accuracy of coding spectrum image will be distorted due to the existence of system aberrations, machining error, fixing errors and so on, resulting in the declined spectral resolution. The influence factor of the spectral resolution come from the decode error, the spectral resolution of each column, and the column spectrum offset correction. For the Czerny-Turner spectrometer, the spectral resolution of each column most depend on the astigmatism, in this coded aperture spectroscopy, the uncorrected astigmatism does result in degraded performance. Some methods must be used to reduce or remove the limiting astigmatism. The curvature of field and the spectral curvature can be result in the spectrum revision errors.
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