Long-term operational experience with first Siemens 400 kW HTS machine in diverse configurations

Siemens has built a synchronous machine consisting of an HTS rotor and an air-cored stator. Rotor cooling is provided by a Gifford-McMahon (GM) "off the shelf" cryocooler, the typical requirement being about 30 W @ 25 K. The machine was designed for a rated power of 380 kW (rated voltage 3 phases 400 V Y), but achieved a maximum continuous power of 450 kW and a short term maximum power of 590 kW at 1500 rpm. In all cases, output power was limited by stator cooling. Characteristic parameters such as reactances, inductances, and time constants were determined to obtain a consistent overview of the machine properties. The machine was tested under different operational modes, including motor mode as well as generator mode. In the generator mode, it was operated on water cooled resistors or connected to the grid. The properties of motor mode have been determined synchronized to the grid as well as via an inverter. Special attention was taken to investigate the influences of asymmetric loads, grid and inverter harmonics on rotor cooling requirements. Numerical calculations were performed and compared to the experimental data showing good correlation.