Lin Guoying

An edge-detection method based on adaptive canny algorithm and iterative segmentation threshold

In the technology of crack detection, the traditional Canny algorithm uses fixed spatial scale coefficient of Gauss filter and empirical values of the high and low thresholds, and it has defective in self-adaptability because it is unable to correct parameters according to the actual image. This paper proposes a method based on adaptive Canny algorithm and iterative threshold segmentation algorithm to detect surface crack. Firstly, in the process of image smoothing, the adaptive Canny algorithm automatically calculates difference between the gray value of present pixel and the average gray value of image in the filter window, and the difference is set as the spatial scale coefficient for Gauss filter of the current pixel. Secondly, the Otsu method is applied to calculate image gradient histogram so as to get high and low thresholds and those new values are applied to detect the edge of the crack. Finally, based on the iterative threshold segmentation algorithm, the image with crack is binarized, and the breakpoints in the crack and the cavities inside the crack are eliminated by morphological dilation. Experimental results show that the new crack detection method can well retain crack edge and get better effect on noise cancellation. It can also reduce the false and missed detections. Better results can be achieved on crack detection.

Analysis of the influencing factors for the 500 kV DC voltage reference divider used for on-site calibration

High-voltage dc (HVDC) reference divider is essential for on-site calibration of HVDC measuring systems. In this paper the effect of the change of temperature, electromagnetic environment of converter station and other factors on the ratio accuracy of reference divider is analyzed. The influence of high voltage connection cables, which apply high voltage to the reference divider and calibrated divider, on the uncertainty of the reference divider is also analyzed, with the application of ANSYS software. The simulation results show that the influence of high-voltage connection cables on the ratio error of the designed 500kV reference divider is less than 1×10-5. In addition, a kind of anti-interference method is proposed for the output signal of reference divider. That is, single-grounded twin shielding cable can effectively reduce common mode interference.