A new method for the evaluation and recognition of corona under direct voltage stress

A new method for the analysis of partial discharges (PD), which are used as an indicator for insulation quality in electrical apparatuses, is evaluated for corona discharges at DC voltage. This method targets pattern generation for DC PD similar to the well-known AC PD diagnostic method called phase-resolved partial discharge (PRPD) representation. For DC voltage the important phase relation is missing. Therefore, the missing phase relation for DC PD is made by superimposing a repeating sequence onto the DC voltage. In this paper the DC voltage is obtained via half wave rectification of a 50 Hz AC voltage. Thus, if the circuit is not being properly smoothed or is resistively loaded a voltage ripple repeating at 50 Hz will be present on the DC voltage which is then used to obtain phase relation. Several tests with different amounts of ripple are presented. The results show that a pattern generation for DC corona via the superimposing of a repeating sequence in that case a 50 Hz voltage ripple is possible. Furthermore, the patterns can be and are explained in terms of the physical discharge behavior. Finally, it is shown that a small enough ripple does not change the general discharge behavior of the corona source.