Condition Monitoring of Rotating Diodes in Synchronous Machines Through the Exciter Stray Flux Analysis

Brushless excitation systems have many advantages mainly related to the low maintenance. A failure in the rotating diodes leads to an increase in the exciter field current and an unbalance in the currents supplied by the exciter armature. This produces additional losses in the exciter and, in some cases, severe damage in the machine if operated for a long time under fault conditions. The supervision of the condition of the rotating diodes is, therefore, essential for the protection of the exciter and the machine. In this paper, monitoring of the diodes is carried out via the analysis of the exciter's stray flux. Numerous experimental tests have been performed on a synchronous machine with axial and radial flux measurements under healthy condition, under one open diode fault and finally under a shorted diode. The experimental results prove that a failure in the diodes can be reliably detected due to the axial and radial stray flux signatures which significantly increase in comparison to the healthy condition.