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Description
This paper studies, experimentally and analytically, on the characteristics of fly-wheel type uninterruptible power supply (FW-UPS) using high-temperature superconducting (HTS) induction machine (HTS-SIM). This study assumed that the SIM is iron-cored and composed of Cu wire stator windings and HTS rotor windings. The rotor windings consist of HTS wires embedded in iron rotor core and connected to HTS end-rings. The entire assemble of the rotor windings are placed in a rotor cryostat and cooled at cryogenic temperature, with no electric connections to the rotor. The stator is at room temperature. When AC currents are applied to the stator windings by an AC power supply to start the SIM, the HTS rotor windings are subject to AC magnetic field. Initially, no rotating torque is produced as the rotor windings are superconductive. However, when subjected to AC magnetic field, the AC losses are generated in the rotor windings raising the winding temperature. Simultaneously, the AC shielding currents is induced to expel the magnetic flux. When the shielding currents exceed the critical currents of the HTS rotor wires which are lowered by the temperature rise, the HTS rotor becomes resistive. As a result, the magnetic fluxes penetrate in the rotor windings, generating the rotating torque. When the revolution speed of the rotor becomes close to the synchronous speed, the shielding currents and the temperature of HTS wires of the rotor decrease due to the reduction of resistive and AC losses, and the rotor wires regain the superconductive state. Then, the rotor is pulled into the synchronous speed by the trapped magnetic fluxes. The back electromotive voltages induced by the trapped magnetic flux are maintained even when the SIM is disconnected from the power supply. Therefore, by inserting an SIM combined with a fly-wheel between a power line and electric loads, electric power to the load is sustained even when the power from the line is lost. When the power from the line is recovered, the SIM-FW-UPS recovers idling state automatically. There is no need for a device to synchronize the SIM-FW-UPS to the power line frequency.
The authors made 3kW class SIM to study fundamental characteristics of HTS-SIM and investigate feasibility of application to FW-UPS. The authors also conducted numerical simulation to study dynamic characteristics of 3MVA class SIM-FW-UPS for industrial use.
Acknowledgements
This work was based on results obtained from Grant-in-Aid for Scientific Research (C) [19K04356] from the Ministry of Education, Science and Technology, Japan
| Submitters Country | Japan |
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