An imaging system permits the study of motion of the electric arc formed during the breaking operation of a miniature circuit breaker under short circuit conditions. The imaging system employs an array of up to 45 optical fibres to detect the light emitted by the arc in the arc chamber of the miniature circuit breaker. The light from the fibres is detected electronically and stored digitally then transferred to a computer. Over 4000 images can be captured at a rate of 1 image per (my)s. A computer program uses the optical information to display an image of the arc on the screen. The imaging process includes steps of: (a) identifying a group of event locations at which the event parameter sample value exceeds a predetermined threshold value; (b) identifying event locations at the boundary of an area encompassing the group; (c) responding to the identified boundary event locations to plot a line representing a contour of constant event parameter value corresponding to the threshold value; and (d) increasing the predetermined threshold and repeating steps (a), (b) and (c) for the increased threshold until a desired number of contours lines for respective event parameter threshold values have been generated.
