Point-on-Wave Analysis of Three-Phase Induction Motor Drive under Fault External to the Power Plant

Adjustable speed drives are widely used in industrial facilities and power plants to power single-phase and three-phase induction motors. The behavior of ASDs and motor assemblies has been explored at the component level but little investigation has been completed of transient behaviors of ASDs. Point-on-wave analysis is used here to evaluate motor drive behavior with respect to single-phase to ground and three-phase to ground faults external to the power plant with simulations completed in MATLAB Simulink. Results provide motor speed, positive sequence terminal voltage and real power, DC bus voltage, instantaneous real and reactive power, terminal current, and other metrics for comparison under various fault conditions. Findings indicate that power consumption stays constant at a value lower than the steady state value for a single-phase fault that occurs below a threshold voltage of 85%. For a three-phase fault, the ASD works as a constant power load above a specific threshold terminal voltage of 86%. Below that value, however, the power drops to zero but not linearly as assumed in the dynamic model of an ASD. Results also show that the positive sequence real power absorption profile differs between a single-phase and three-phase fault for the same amount of voltage dip which dictates the importance of including the fault type while deriving a positive sequence model of the drive for dynamic simulation.