Researches On The Opening Velocity Detection Of VCB Based On Zernike Moments

In the vacuum circuit breakers(VCBs),arc is produced by the opening of moving contact and static contact.Changes in the electrical,thermal and magnetic processes and their interactions during the contact opening process will have significant effect on the success of the extinguishment of the arc after the zero crossing of the current.However,the motion of the contact is driven by the operating mechanism.It is necessary to study on the influence of operating parameters to the arc characteristics.The principle of opening velocity detection is to locate the accurate contact position in its images,tracking the moving contact movement and calculating the opening velocity curve.By means of overlap feature and testing relative bright arc edges,contacts location can be traced.So,the moving contact trace can be hold,while the lower edge of arc is preciously located.The appearance variations of arc which were generated by the separation of contacts is relatively close to the VCBs' actual working way.The main experimental synthesis loop of the contacts separation and the control loop of the permanent magnet actuator were designed in this work.The combustion process sequence images of vacuum arc were collected by CMOS,and 434 frames were obtained.Combined with the acquired arc images,the qualitative analysis of arc shape evolution at different stages of arc combustion is carried out,the reason for the arc shape and the change of the arc column brightness is explained in detail.Before the precise positioning of the arc edges,the contact image should be pretreated.The median filter has an excellent noise effect on the filtered contact images.The visual effect of the contact image can be enhanced and improved by pseudo-color and false color processing;the details of the arc image are enhanced.In the detection of arc edges detection,the Canny operator detects arc edges effect better than other operators.In order to ensure the accuracy and efficiency of arc edge detection,prior to precise positioning of the arc edge,detection position range is narrowed by locating all possible edges of arc in pixel level by Canny operator,then all possible edges of arc is redetected by Zernike moments,finally the detection of opening velocity is realized in sub-pixel level.The experimental result shows that edges located by the Zernike moments can be reached to two bits after the decimal point,especially for the initial opening of contacts when the velocity changes dramatically.Compared with the pixel precision algorithm,the proposed method increased operation rate by 35% in the premise of accuracy.The stability of the algorithm is more excellent than before,and the measurement result is not affected by the choice of operating mechanisms.