Determination of sparking voltage and residual voltage of a void included in an electrical insulation system

An approach is developed which can be used to calculate the sparking and residual voltages V/sub s/ and V/sub r/, or the ratio between them, from the corner values V/sub p/ and V/sub q/ in a parallelogram. From a theoretical analysis of the parallelogram method, which is used for partial-discharge measurement, the width of the parallelogram is equal to the sum of the partial discharge inception voltage plus the voltage that equals the residual voltage of a void multiplied by a factor of 1+C/sub c//C/sub b/. If the sparking voltage is approximately equal to the residual voltage, the width of the parallelogram is approximately equal to the partial-discharge inception voltage multiplied by 2 square root 2. V/sub s/ and V/sub r/, or V/sub r//V/sub s/, can also be calculated from the corner parameters of parallelograms.<>