Acoustic emission techniques for transformers during lightning impulse voltage excitation

Abstract

Location of partial discharge (PD) is essential for transformer manufacturer to assess the dielectric integrity of the winding insulation during lightning impulse (LI) test in order to reduce the time and manpower utilization for diagnostics purpose at manufacturing place. As per international standards, there is a requirement of PD free behavior during impulse voltage excitation. Though, electrical methods are more sensitive for identification of PD, it is difficult to locate the location of the PD source accurately. Hence, with the increasing the use of Acoustic Emission (AE) techniques for acquisition of PD signal through acoustic sensor during power frequency voltage excitation, it would be instructive to provide the location of PD during impulse voltage excitation. Hence, the usefulness of AE technique is effectively adopted in this paper for location of the PD source during impulse voltage excitation. To study the impulse PD responses through AE techniques at different locations within the transformer, a PD source model is used to create the PD. The single and multi layer winding arrangements are also considered over the PD source model to analyze the AE signal propagation from PD source location to surface of the tank wall during impulse voltage excitations. The maximum cumulative energy criterion and variable S method are compared to estimate the relative time arrival of sensors responses. To avoid the convergence issues, non-iterative method is adopted for location of PD source accurately and it is compared with iterative method. 315 MVA, 400/220 kV auto transformer is utilized for validation of AE technique in order to declare whether the transformer has withstood the impulse test voltage or not. AE technique is verified with electrical method for detection purpose.