Real-Time Rotor Ground Fault Protection Based on the Convolution Integral for Synchronous Motors With Static Excitation

The detection of motor failures is a very active research topic within the literature. In particular, ground faults in wound rotors of synchronous motors have a relatively high failure rate since the rotor winding is exposed concomitantly to electrical, mechanical, and thermal stress cycles. Its detection depends on the grounding type of the electrical power system, and, in its early stages, it may present significant resistance. This article provides a new rotor ground fault protection method based on the convolution integral of the neutral voltage that is measured by a single extra sensor. In addition, it is able to fill out the gaps of the current state-of-the-art, such as: provides a larger detection frontier for incipient faults; has low sensitivity for dynamic variances of the firing angle, allowing its utilization in cyclical applications; and can be implemented in power electronic controller systems with limited bandwidth. In this sense, mathematical modeling, simulations and experimental data are presented to support to the proposed method. Furthermore, it was implemented in the controller of static excitation converters for real-time protection and successfully tested with synchronous motors (2.4MW/3.3kV) of a cold rolling mill plant owned by ArcelorMittal Group.