Optimum acoustic sensor placement for partial discharge allocation in transformers

Partial discharges (PDs) are a cause of degradation of insulation system and its permanent activity monitoring is used as a tool for insulation condition assessment in power transformers. Information on PD position can be used by plant monitors to diagnose the cause of PD and can help to identify type and severity of an insulation fault for maintenance strategies. The acoustic PD detection system, with great advantages relative to other methods, contains inaccuracies in PD localisation, such as the multipath interferences due to reflections within transformer tank, improper acoustic coupling between sensor and tank surface, mechanical vibrations and inherent sensor inaccuracies, which can severely limit the accuracy of the positioning system and make locating the exact positions of PD difficult. In this study, a method has been proposed for calculation of position measurement sensitivity for different PD origins within transformer tank. Different possible cases have been considered for placement of acoustic emission (AE) sensors. For each case, sensitivity of PD location to the time measurement errors has been calculated. The optimum arrangement of AE sensors has been chosen as the configuration yielding lowest error in the PD localisation. A test setup has been organised and the experimental results have justified the theoretical analysis.