9.5 Development of a 5-kWh HTS FESS prototype Ë 357Fig. 9.24:PLC modules of customized machining equipment for
HTS bulk.Fig. 9.25:Processed bulk YBCO with an arc surface.process, the grinding wheel is set to descend vertically in multiple cycles. After every
machining cycle, the grinding wheel will hold in a non-contact position and stay for a
short time. It lets the revolving grinding wheel cool in the air. Thus, there is no need of
any cooling fluid that may have a bad effect on the material properties of the HTS bulk.
The minimum displacement of the servo motor is about 0.01 mm so that the machining
precision of the HTS bulk is about 0.1 mm. Figure 9.25 shows a YBCO bulk processed
with the customized equipment.
9.5.7Complete HTS FESS test system
The complete HTS FESS system is shown in Fig. 9.26. The refrigerator (1) and the
vacuum pump (4) are used to supply the cryogenic operation conditions of the HTS
bulks. Furthermore, the vacuum environment could reduce the air friction loss of the
flywheel rotor under high rotation speed. The designed vacuum is 0.1 Pa.
The power cabinet (2) transmits the electrical energy from the power grid to the
HTS FESS unit and the accessory equipment, which can supply a maximum power of
140 kW. Between the power cabinet and the HTS FESS unit, the frequency converter (6)
is necessary regulate the speed of the PM synchronous motor. This frequency converter
has a power level of 110 kW with the maximum current modulation frequency of
300 Hz, which is equivalent to 20,000 rpm rotation speed for the PM synchronous