Measurement and Analysis of Induced Voltage in a Rotating Coordinate System of a 1 kW-Class High Temperature Superconducting Squirrel-Cage Rotor Winding

Abstract

This work presents a simple and direct measurement method for rotor bar voltages in the rotating coordinate system of a high temperature superconducting induction/synchronous motor (HTS-ISM). The arrangement consists of soldering copper wires to the opposing ends of the rotor bars and routing them through a spinning reel to avoid entanglement, thereby providing a continuous electrical connection between the rotating quantities of the rotor and the stationary measurement instruments. Experiments with both ramped and stepped stator voltage inputs under no-load conditions revealed markedly different dynamic behaviors, including rapid acceleration, hunting torque, and current distortion. A recurring component at $ \approx $1.05 Hz was consistently identified on the rotor bar voltages across independent tests, including at different input frequencies, suggesting the presence of an intrinsic oscillation under low excitation. The proposed measurement approach provides new experimental access to the flux-flow and synchronous regimes of HTS machines and establishes a foundation for future studies under load and with varied rotor designs.