IEEE Electrification Magazine - December 2013 - 70

Rear View

30-MW Superconductor
6-MW Superconductor
Power Transmission
Electrical Motor Turbo Fans

superconductors due to their cooling
advantages. the first Hts-based prototype shown in Figure 4 was tested
in Japan and successfully exceeded
500 km/h the very first day of testing.
the Japan railway company is planning to finalize the railway to provide
passenger service by 2025, connecting
the cities of tokyo and nagoya.

cryogenic cooling Systems

cryogenic refrigeration is a key technology for superconducting genera30-MW Superconductor
tors and cryogenic power electronics.
Electrical Generator
the choice of the cryogenic plant is
Superconductor
Power
determined by several factors such
Power
Power
Applications
Generators
Motors
Transmission
as availability of cryogenic media,
Inverters
Electronics
Needed
Cables
temperature, response to dynamic
Power Levels 30-40 MW
4-6 MW
5-70 MW
1-30 MW 30-40 MW
loads, power requirements in steady
state and recovery, and the control
Figure 3. The hybrid electric distributed propulsion (HEDP) Aircraft, 45 MW. (Photos used with persystem. the power requirements of
mission from Luongo et al. and Haugan.)
refrigeration are very dependent on
the unit power losses and the
alternative frictionless mass transportation systems that
required cooling temperature. For example, 1 W of power
can exceed the maximum speed (350 km/h) of conventionloss in the unit to be cooled may require about 8-10 W of
al railway systems. For this purpose, research teams in
refrigeration power (cryogenic plant) at liquid nitrogen
Japan and the United states have been working on supertemperature (63-77 K), whereas to cool at 4 K may require
conducting maglev trains using linear synchronous motor
about 800-1,000 W of refrigeration power. the cooling
superconducting magnets and armature coil on the ground.
requirements at low temperatures incur significantly
the superconducting maglev train is one of the most promhigher cryogenic costs. although the refrigeration cost
ising high-speed mass transportation systems in the world,
may have a small impact on the overall cost, it does affect
offering a fast, reliable, and environmentally friendly systhe selection of a cryogenic plant.
tem that will encourage people to use train transportation
cryocoolers are generally divided into three types:
over aircraft and automobiles. it is also known as one of the
recuperative (steady flow), regenerative (oscillating flow),
safest transportation alternatives with an accident-free
and a hybrid of the two. there are two major types of
safety record so far. the co2 emissions are about one-third
recuperative cycles: Joule-thomson and Brayton cycleof traditional transportation systems. the recent trend for
based systems in which there is a steady flow of gas in
superconducting maglev trains is to replace the low-temone direction with steady low and high pressures in the
perature superconducting element with high-temperature
appropriate locations. they primarily use heat exchangers
to transfer heat between a working fluid and a transportation fluid. there are three main regenerative cycle cryocoolers: stirling cycle, Gifford-McMahon (GM), and pulse
tube refrigerators. all three use a transport fluid that passes cyclically through a regenerator and a displacer. the
flow of the gas is controlled such that one end of the displacement tube forms a cold head and the other end
forms a hot end. the frequencies vary from about 1 Hz for
the GM cycle and some pulse tube cryocoolers to about
60 Hz for stirling cycle coolers. in these regenerative cryocoolers, heating occurs as the pressure increases, and
cooling occurs as the pressure decreases. Depending on
the required power and the cryogenic temperature, a particular cooling system needs to be selected. in general, the
liquefaction plants are relatively more efficient than
regenerative systems. However, they are expensive and
Figure 4. The ultra-high-speed superconducting maglev train tested
in Japan. (Photo used with permission from Sawada.)
suitable mainly for large-scale systems.

I E E E E l e c t r i f i c ati o n M agaz ine / december 2013

Table of Contents for the Digital Edition of IEEE Electrification Magazine - December 2013