Online Detection Method of Open Circuit Fault of Rotating Diode in Multi-phase Brushless Exciter

Aiming at the open-circuit detecting difficulty of the rotating diode of polyphase brushless exciter, the 39-phase-11-pole brushless exciter is taken as the example in this paper, the armature current characteristics of the brushless exciter during normal operation and single-tube open-circuit fault are analyzed. Firstly, the change law of armature magnetic field in two states is analyzed, a magnetic field detection coil is proposed to be installed on any pole of the stator in the exciter according to the structural characteristics of the exciter and electromagnetic coupling relationship. Then, combining with the harmonic characteristics of the spatial magnetic field of the brushless exciter, the flux expression of the detection coil is derived, and the induced voltage of the detection coil could be obtained. Specifically, it is found that an open diode fault causes a change in the amplitude of a specific frequency harmonic in the induced voltage. Finally, the finite element simulation proves that the detection coil method can effectively identify the rotating diode open circuit fault without affecting the normal operation of the brushless exciter.