Partial discharge detection during electrical aging of generator bar using acoustic technique

Partial discharge is of the most powerful and important means to diagnose insulation health in generator bar. There are many methods available to detect the PD activity in generator bar. Acoustic detection as a partial discharge detection method has wide range of applications. Acoustic method versus electrical detection methods has several advantages such as immunity against electromagnetic fields. In this paper, an air-cooled generator bar (15.75 kV nominal voltage) is aged under electrical stress. Electrical aging test is carried out according to IEEE 1553-2002. Acoustic signals due to partial discharge during electrical aging of generator bar within 500 hours are recorded using acoustic technique every day. In this method, two points of the bar as test points are considered. The first point is located on one of the lateral side of generator bar while the other point is located on the bar centre. Acoustic sensor output is sent to an 80MHz PC-based A/D card and is filtered at the maximum frequency band-width of the sensor. Acoustic signal variations are investigated during aging process. The variations show that acoustic signal amplitude due to partial discharge increases at the first days, then collapses and remain constant during the aging.