Online Diagnostics of Brushless Synchronous Machine Exciter Field Winding Through Temperature and Resistance Measurement

Excitation power provision is crucial for the operation of wound-field synchronous machines. Modern excitation systems are predominantly brushless, comprising an additional machine called exciter. The field winding of exciters can suffer from various faults, such as interturn faults due to insulation failures, or electrical continuity losses due to poor connections or deficient welding. Despite the criticality of exciters to the operation of brushless synchronous machines, there is a lack of protection in the state-of-the-art. To address the gap, this paper presents a novel condition monitoring method for exciter field windings. The proposed method involves monitoring the winding resistance, as well as the winding temperature. The healthy winding resistance is estimated from the measured temperature. This estimation is based on a healthy characteristic obtained during machine commissioning. By comparing the measured and estimated winding resistances at any operating point, electrical faults in the winding can be detected. The applicability of the method is experimentally verified through tests under both healthy and faulty winding on a 4900-kVA brushless synchronous machine. Additionally, finite element analysis and thermal imaging are employed to describe the experimental approach. The results are consistent and promising.