9.5 Development of a 5-kWh HTS FESS prototype Ë 353Fig. 9.19:Design concept of a 5-kWh HTS FESS. (1) PM
assistant bearing. (2) Stator of motor. (3) Rotor of motor.
(4) Carbon fiber composite flywheel. (5) Wheel hub.
(6) HTS bearing.400 kW on one subway station. When the SC units are used in series, the HTS FESS
array can supply more than 11 kWh with 75% DOD and average I/O power more than
1.2 MW, which satisfies most energy and power demands of a subway regenerative
braking system. The conceptual design of a 5-kWh HTS FESS is shown in Fig. 9.19.
9.5.2HTS Maglev bearing
The stator of HTS Maglev bearing with inner diameter of 151 mm is composed by
YBCO bulk. The length, width, and height of the YBCO bulk are 64, 32, and 12 mm,
respectively. The rotor of HTS Maglev bearing is composed of PM rings and iron hoops
just like the typical axial assembly mode (RSB) as shown in Refs. 11 and 17. The
diameter of the PM rotor is 147 mm. All of the PM rings have a magnetic energy product
of 50 MGOe (398 kJ/m^3 ). The total length of the PM rotor of the HTS bearing is about
240 mm in order to supply enough axial forces to suspend the flywheel. A cryogenic
refrigerator is introduced to supply the 40–50-K working temperature for the YBCO
bulks. It can supply a cooling capacity of 100 W at 40 K. The designed load capacity of
this HTS Maglev bearing is 600 kg. The assembled PM rotor of the HTS Maglev bearing
is shown in Fig. 9.20. The assembled PM rotor has been tested for its dynamic balance
characteristic which is adjusted by the de-weighting method with the drilled holes on
the flange shown in Fig. 9.20. After this adjustment, the dynamic balance performance
index of the PM rotor is about 0.1 g.
9.5.3Flywheel rotor
The composite material of flywheel rotor was chosen as T-700 carbon fiber, which had a
high tensile strength, more than 1600 MPa. For safety considerations, the upper limit
of strength was set to 800 MPa in the analog calculation and design, only the half