Theoretical Analysis and Calculation Model of the Electromagnetic Torque of Nonsalient-Pole Synchronous Machines With Interturn Short Circuit in Field Windings

This paper studies the electromagnetic torque (EMT) of a nonsalient-pole synchronous generator with the interturn short circuit of field windings (ISCFW). First, the virtual displacement method serves as a basis for analyzing the postfault steady-state harmonic characteristic of EMT. The interactions among various space magnetic fields with different orders, speeds, and rotation directions generated by the stator and rotor are considered. A general conclusion on the EMT characteristics under the fault is then derived. Second, based on the connection conditions of the rotor and stator windings under the fault, the voltage and flux relationships among each circuit are analyzed and the calculation model of the EMT under the fault is built. Through comparisons among the simulations, experiments, and theoretical analyses, the correctness of the calculation model is verified. In addition, a three-pole-pair nonsalient-pole synchronous generator after transformation is used for the case study. The calculation and analysis results indicate that ISCFW generates ac pulsation components with their harmonics closely linked to the stator winding configuration. This paper deepens the fault mechanism of ISCFW and lays a foundation for fault monitoring based on mechanical characteristics.