Zi-Gang Deng, Qun-Xu Lin, Wei Liu, Jia-Su Wang, and Su-Yu Wang
9 HTS Maglev bearing and flywheel energy storage
system
9.1 Introduction
A bearing is a machine element which offers the desired movement or rotation
with low friction, and constrains other relative motions [1]. Generally, the bearing is
typically classified as mechanical, permanent magnet (PM), gas suspension, electro-
magnetic, and high-temperature superconducting bearing (HTSB).
The mechanical bearing is one of the most important machine elements, which
is widely applied in industry, agriculture, traffic, military, and so on. There are many
kinds for particular applications. For example, a high-speed precision ball bearing
enables a high rotational speed of 150,000 rpm [2]. A large-load thrust bearing with
elastic metal-plastic pads can support the magnitude of 6000 tons [3], a huge-size
turnplate bearing for wind power generators has an outer diameter of more than
7.3 m [4]. However, due to the inherent solid-solid or solid-liquid contact between
moving parts (rotor and stator), the mechanical bearing has some unavoidable dra-
wbacks, like vibration and noise. Furthermore, mechanical abrasion and related
temperature rise also limit the ultimate rotational speed and the service life. At the
same time, special lubricants have to be used in almost all applications of mechanical
bearings, even including the food processing and pharmaceutical industries which
do not welcome any lubricants [5]. At low temperature, lubricants cannot be used
in the cryogenic pump system since they will freeze. Thus, the service life of the
mechanical bearing is greatly reduced. For the flywheel energy storage system (FESS),
rotational loss from mechanical bearings is the main technological obstacle for long
time high-efficient energy storage.
To solve the above problems, PM bearings [6], gas suspension Bearings [7], elec-
tromagnetic bearings [8], and HTSBs have been developed based on the consideration
of physically separating the moving parts. Strong points of these bearings are non-
contact, no abrasion, low rotational loss and long service life. PM bearings have the
advantages of low cost, simple structure, and low rotational loss. Yet, they cannot
achieve complete free and stable levitation in both axial and radial directions, so other
auxiliary bearings are combined to use. Gas suspension bearings support the load by
a thin layer of gas [9]. They operate at very high speed (of 8× 105 rpm [10]), have a
large working temperature range, and are non-polluted [7], but their load capacity
and suspension gap are small and rotational loss is higher than that of PM and elec-
tromagnetic bearings. Moreover, gas suspension bearings cannot be used in a vacuum
environment. Electromagnetic bearings work under the principle of controlling the
position of the rotor with an electromagnet assembly [11]. The rotational loss is small