Sensoring partial discharge signals in MV switchgears

Outages of high voltage apparatuses at the generation or transmission level involve large economic losses that justify using technologies of relatively-high cost to prevent failures. At the distribution level, on the contrary, individual outages may not cause severe economic losses. Redundant circuits with automatic switching systems are often a viable solution to further alleviate the impact of failures. For condition assessment of distribution circuit apparatus, therefore, fast, effective and economic solutions are needed. The focus of this paper is on partial discharge (PD) measurements of switchgears. In order to be successful, any tool devised to assess the condition of these equipment should be able to (a) pick up PD signal with large sensitivity, (b) identify the nature of PD, (c) localize the compartment where PD occur. Requirement (b), i.e., the capability of performing PD source identification, is of major importance since different defect types have different degradation rates (as an example, internal PD in bushings or cable terminations are far more harmful than corona discharges). Thus, identification it is the key to schedule in the most effective way maintenance operations, focusing primarily on harmful defects. This paper describes a methodology devised to achieve condition assessment of medium voltage switchgears through PD analysis. Case studies are reported to show the effectiveness of these tools.