PSI - Issue 17

Takanori Hasegawa et al. / Procedia Structural Integrity 17 (2019) 487–494 Takanori Hasegawa et al./ Structural Integrity Procedia 00 (2019) 000 – 000

489

3

There is a known fault state in that a pivot bearing loses the levitation pressure, and the bearing wear out in this device. In the normal state, the pivot is levitated and the case is filled with helium, there is no attrition of the pivot bearing and few windage. However, when it loses helium for some reasons such as a problem in the case, the windage loss increases and the air temperature inside the case is raised. As the temperature rises, the viscosity of the oil decreased causing the levitation pressure decreases. Finally, the pivot shaft comes in contact with the bearing, causing it to be scraped and worn, and oil is deteriorated. To avoid this fault state, it is important to detect the state when helium has decreased before oil is deteriorated.

Specifications of flywheel. Energy Capacity

900kJ (30kW*30sec or 15kW*60sec)

Rotation Speed

200Hz (6000rpm)

Rated Input Power Bearing System Flywheel Size, Wight

AC200V (three-phase three-wire)

Pivot

620W×741D×326H, 130kg

Internal Gas

Helium

Material of Housing Overall Size, Weight

Aluminium

820W×950D×400H, 285kg

Manufacturer

SANKEN ELECTRIC CO., LTD.

Fig. 1. Overview and specifications of flywheel. From https://www.products.sanken-ele.co.jp/prod/powersp/emu/what_emu/emu_w00.html

Fig. 2. Left figure illustrates internal structure of flywheel. Pivot bearing is mounted at center of rotor. Rotor and heavy weight rotates around bearing during energy storage. Right figure illustrates pivot bearing diagram. Concave of bearing is suffused with oil. Pivot bearing generates levitation pressure owing to spiral groove on conical axial end catches up oil when conical axial end is rotated at high speed. (Reprinted from Figs. 3 and 4 in Kato et al. (2015))

2.2. Vibration materials

Three operational conditions listed in Table 1 were simulated. A triaxial acceleration sensor was mounted on the top of a device to pick up vibration signals of a FESD in the XYZ directions (i.e., three-channel signals). Four sequences of three-channel vibration signals were recorded under the aforementioned three conditions. Durations of