Exciter Axial and Radial Stray Flux Analysis for Rotating Diodes Supervision

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 unbalance produces additional losses in the exciter and, in some cases, severe damages if the machine is long time under operation with faulty diodes. The supervision of the rotating diodes is essential for the protection of the exciter. In this paper, monitoring of the diodes condition is carried out through the analysis of the exciter stray flux. Numerous tests have been performed in a laboratory synchronous machine measuring the axial and radial flux both in healthy conditions and with one open diode. The results prove that a failure in the diodes can be easily detected as the stray flux component corresponding to the exciter frequency significantly increases in comparison to the healthy conditions. Moreover, the use of any axial, radial or both stray fluxes are suitable for the supervision.

I. Introduction

Synchronous machines are key elements of power systems as medium and large size generators. The protection systems of synchronous machines are very important for the reliability not only of the machine but also of the power system. There are some minimum requirements for the protection [1].