An overview of Superconducting Magnetic Energy Storage (SMES) and Its Applications

Abstract

Superconducting magnetic energy storage (SMES) is a promising, highly efficient energy storing device. It’s very interesting for high power and short-time applications. In 1970, the first study on SMES appeared and since then it’s a topic of interest for many scientists and the people working on energy sectors. A SMES device possesses excellent efficiency of energy transfer conversion which is greater than 96%. A superconducting magnet is the heart of this device. High capital cost is still the obstacle for widespread utilization of SMES devices. In this paper, we have focused on the organization of the SMES device, discussed its history, opportunities and limitations and after that, we have talked about some of the applications of this technology. We think that in future this technology may replace many other devices that we use today.

Full text

International Conference on Nanotechnology and Condensed Matter Physics 2018 (ICNCMP 2018)
January 11–12, 2018, BUET –Dhaka, Bangladesh
An Overview of Superconducting Magnetic Energy Storage (SMES) and Its
Applications
Md. Abdullah Al Zaman1, Sabbir Ahmed2, Nusrath Jahan Monira3
1,2,3Department of Physics
University of Chittagong
Chittagong-4331, Bangladesh
01627041786
E-mail: Proyashzaman@gmail.com
ABSTRACT
Superconducting magnetic energy storage (SMES) is a promising, highly efficient energy storing
device. It’s very interesting for high power and short-time applications. In 1970, first study on
SMES appeared and since then it’s a topic of interest for many scientists and the people working
on energy sectors. A SMES device possesses excellent efficiency of energy transfer conversion
which is greater than 96%. A superconducting magnet is the heart of this device. High capital
cost is still the obstacle for widespread utilization of SMES devices. In this paper we have
focused on the organization of the SMES device, discussed about its history, opportunities and
limitations and after that we have talked about some of the applications of this technology. We
think that in future this technology may replace many other devices that we use today.
I. INTRODUCTION
SMES is an energy storage system that was first proposed in 1979, capable of storing electric
energy in the magnetic field generated by DC current flowing through it. Superconductivity is
a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring
in certain materials when cooled below a characteristic critical temperature. The metals
following the character are called superconductors. In SMES, conductors for carrying the
current operate at cryogenic temperatures where it becomes superconductor and thus has
virtually no resistive losses as it produces the magnetic field. In this state the current in a coil
can flow for infinite time. This can also be seen from the time constant of a coil τ = L/R,
where R goes to zero and τ then goes to infinity. The energy stored is inductive.
The energy stored in such circuit can be written in the form,
E = 
 LI2

International Conference on Nanotechnology and Condensed Matter Physics 2018 (ICNCMP 2018)
January 11–12, 2018, BUET –Dhaka, Bangladesh
II. COMPONENTS OF A SMES SYSTEM
A SMES system consists of four components and they are
1. Superconducting magnet with its supporting structure
2. Cryogenic refrigerator or cryogenic system
3. Power conditioning system (PCS)
4. Control system.
Figure 1 illustrates the organization of a typical SMES system.
A. Superconducting magnet and supporting structure includes a superconducting coil,
magnet and coil protection. The superconducting coil is the heart of a SMES system,
stores energy in the magnetic field generated by a circulating current. The maximum
stored energy can be determined by two factors [15]
i. Size and geometry of the coil, larger the coil, the greater the energy.
ii. Characteristics of the conductor, which determines the maximum current.
There are two main magnet topologies; Solenoid and Toroid [7][14]. Because of relatively lower
conductor amount and supporting structure requirement with low cost, Solenoids are more used
than toroid arrangement.
Superconducting materials used as magnet in SMES system are of two types
i. Low-temperature superconductor magnet (LTS)
ii. High-temperature superconductor magnet (HTS)
At present a superconducting alloy of Niobium and Titanium (Nb-Ti) is utilized in the SMES
systems. But this alloy requires being operated at 4.2 k. Though it’s good at work but remains
pretty expensive in terms of investment and operational cost. [14] Due to this researchers are
more interested to utilize the HTS where the temperature requirement is relatively easier to
attain. Some research-based SMES systems use HTS. The protection system can vary with the
size and power requirement of the SMES system. Its main function is to dissipate energy in any
kind of failure in the system and also making the arrangement stable. [13]
B. The cryogenic refrigerator or cryogenic system includes cryostat, compressor, vacuum
enclosures, coolant, etc. In order to maintain superconducting state extremely low
temperature (4.2k) is required, so helium is used as the coolant because it is the only
material that is not solid at those temperatures. There are one or more compressors for
Figure 1: Schematic diagram of a SMES system.

International Conference on Nanotechnology and Condensed Matter Physics 2018 (ICNCMP 2018)
January 11–12, 2018, BUET –Dhaka, Bangladesh
gaseous helium. The vacuum enclosure receives the compressed helium and produces
liquid helium for the coil [7][14][15].
C. Inverters, rectifiers, electronic circuits, etc. are typically the parts of the power
conditioning system (PCS). It can also be referred as power conversion system. In
general, this portion of a SMES system contains converters that convert DC currents to
AC and vice versa. According to the utilization of the various converters and other
circuits, a SMES system can be classified into 3 major categories [3][7][14],
i. Thyristor based SMES,
ii. Voltage source converter (VSC) based SMES,
iii. Current source converter (CSC) based SMES.
D. Control system develops a link between the power demand from the grid and power
flow to and from the SMES coil. It also measures the condition of the SMES coil in order
to maintain safety by controlling other equipment like the refrigerator. The control
system usually composed of controlling devices or circuits like Microcontroller, DSP etc.
[7][11][13].
Besides these, the mechanical design of a SMES system is firmly important. The magnet
conductor must be designed in such a way that it can withstand high stresses and deformations
without limiting or changing the superconducting properties. If the bedrock can support the
SMES structure then the SMES system can be installed anywhere useful to the power system
[11].
III. CHARACTERISTICS OF A SMES SYSTEM
The main characteristics of a SMES system are [4][7][11][13][14][15]
 A SMES system provides high power density but relatively lower energy density.
 The response time of a SMES system is pretty fast.
 The number of charge-discharge cycle is very high i.e. the cycle efficiency is more than
appreciable. For that reason fast recharge is possible.
 There are no moving parts in a SMES system which ensures that the maintenance cost is
comparatively lower than the other cotemporary storage systems.
 The energy conversion efficiency is very high (>95%) which is comparatively higher
than batteries (60 to 90%) or Pumped hydro (up to 70%).
 Life time of a SMES system is very high, more than 30 years.
 Environmentally sound.

International Conference on Nanotechnology and Condensed Matter Physics 2018 (ICNCMP 2018)
January 11–12, 2018, BUET –Dhaka, Bangladesh
IV. APPLICATIONS OF SMES
A. FACTS (FLEXIBLE AC TRANSMISSION SYSTEM)
SMES systems are utilized in the FACTS devices. It is a static device which can be installed
in the electric grid in order to enhance the controllability and power transfer capability of the
grid. A SMES system operating as FACTS was the first superconducting application
operating in a grid. In 1980 Bonneville power authority in U.S. A. utilized a SMES system in
the grid condition to damp the low frequency [13] [14]. They were successful in that and
continued it for about one year. In other words, a SMES system as a FACTS device acts as a
system stabilizer. In 2000 American superconducting company installed six SMES units at
key points in the grid in Northern Winston (USA) to enhance the stability of the grid. FACTS
is also useful in renewable energy technologies like wind generator [14][15].
B. ELECTROMAGNETIC LAUNCHERS
The Electromagnetic launcher is an electric weapon that can launch a projectile at a very high
velocity. Some electromagnetic launchers require high power pulse sources. Due to high
power density and quick release of the stored energy [14], SMES is a potential energy
storage device for an electromagnetic launcher [7][14].
C. LOAD LEVELING
Electric power demands vary with predictable magnitude. Both commercial and residential
demands are greater during the day and less at night. The demands also vary with seasons. A
SMES unit has the ability to follow system load changes almost instantaneously which
provides for conventional generating units to operate at a constant output. It can store energy
at fewer demand situations and deliver it back to the grid during high demands [2] [7] [15].
D. UPS (UNINTERRUPTIBLE POWER SUPPLIES)
It has been used to sustain a continuous power supply to certain critical loads protecting them
against unexpected power outages as well as over and under voltage conditions. Fast
response, compensation and instant availability of electrical power are the basic requirements
of UPS. In recent years, due to the dynamic capabilities and long-term lifecycle of SMES, it
has received a great attraction as an energy storage unit instead of conventional batteries.
Because of its storage capacity, SMES is a potential option for the industrial customers in
case of loss of the utility main power supply [2] [7] [9].
E. CIRCUIT BREAKER RECLOSING
A conventional circuit breaker attempts to reclose and return the affected transmission line to
service by following the clearance of a fault. This is done routinely whenever the power
angle difference across the circuit breaker is within a certain limit. However, if the angle
difference is too large, protective relays prevent the circuit breaker from reclosing. SMES
can reduce the power angle difference across a circuit breaker and allow reclosure of the
circuit breaker by briefly supplying some fraction of the power normally transmitted by the

International Conference on Nanotechnology and Condensed Matter Physics 2018 (ICNCMP 2018)
January 11–12, 2018, BUET –Dhaka, Bangladesh
transmission line. This allows restoration of the system power transfers quickly following
outages of major transmission lines [2] [7].
F. SPINNING RESERVE
Due to the fast recharge time and fast AC-DC conversion process, SMES can be utilized as a
spinning reserve when a major grid or transmission line is out of service [2][7][11].
V. CHALLENGES OF SMES
A. HIGH COST
The SMES system utilizing LTS has to be operated at a very low temperature (4.2k).
Though the energy conversion and related issues are satisfactory but maintaining the
refrigeration system at that temperature requires huge investments. In order to
increase the refrigeration temperature HTS superconducting materials have been
developed. HTS magnets offer the possibility to operate at relatively higher
temperatures (50-70K) which would reduce the operating cost of the cryogenic
refrigerator. Higher operating temperatures also make the system stable and viable. For
coolant, liquid nitrogen is using these days which are also less expensive than liquid
Helium. But as we can see that refrigeration process is only a part of the whole
arrangement and in the case of large systems, the cost does not reduce significantly
[5][6][9][7][11][12][14][15].
B. REQUIREMENT OF ADDITIONAL PROTECTION
The energy stored in the superconducting magnet can be released in a very short time. The
power per unit mass does not have a theoretical limit and can be extremely high (100
MW/kg) so the system must be contained in an excellent electric isolation [14].
Again, in case of coil failure, the energy has to be released otherwise; the coil will be
damaged [11]. Due to the release, the conversion system and the whole arrangement may
undergo system failure also. Some conceptual designs of SMES system propose the
absorption of energy by the superconducting cable and the support structure in case of system
failure. [11][14]
C. LONG PRECOOLING TIME
As the operating temperature of a SMES system is very low, it takes about four months to
cool the superconducting magnet from room temperature to operating temperature. In case of
coil failure or emergency energy release, it requires the same amount of time to recover [11].

International Conference on Nanotechnology and Condensed Matter Physics 2018 (ICNCMP 2018)
January 11–12, 2018, BUET –Dhaka, Bangladesh
VI. CONCLUSION
So we have presented an overview of the SMES system. We have talked about its principle,
organization, and applications. We have also discussed its major limitations. SMES is an
excellent technology in today’s world even it is a good option for the people who are concerned
about the environment. SMES can also reduce the cost of oil and gas by a good amount. The
high capital cost is still an obstacle to the widespread availability of the SMES system but still
many projects have been utilizing SMES successfully. Research works are going on and in the
future it will surely come within the range of commercial usages.
REFERENCE
1. Luo, X., Wang, J., Dooner, M., & Clarke, J. (2015). Overview of current development in
electrical energy storage technologies and the application potential in power system
operation. Applied Energy, 137, 511-536.
2. Ali, M. H., Wu, B., & Dougal, R. A. (2010). An overview of SMES applications in
power and energy systems. IEEE Transactions on Sustainable Energy, 1(1), 38-47.
3. Heydari, H., & Mohammadpour, G. (2010, March). Application of a SMES to protect a
sensitive load in distribution networks from two consecutive voltage sags. In Advanced
Computer Control (ICACC), 2010 2nd International Conference on (Vol. 1, pp. 344-347).
IEEE.
4. Chen, H., Cong, T. N., Yang, W., Tan, C., Li, Y., & Ding, Y. (2009). Progress in
electrical energy storage system: A critical review. Progress in Natural Science, 19(3),
291-312.
5. Rong, C. C., & Barnes, P. N. (2017, December). Developmental Challenges of SMES
Technology for Applications. In IOP Conference Series: Materials Science and
Engineering (Vol. 279, No. 1, p. 012013). IOP Publishing.
6. Hassenzahl, W. (1989). A comparison of the conductor requirements for energy storage
devices made with ideal coil geometries. IEEE Transactions on Magnetics, 25(2), 1799-
1802.
7. M. R. Islam, “Study of SMES technology for electric power supply and investigation of
its utility and possible implementation in Bangladesh.” A project report, University of
Chittagong. (July, 2014).
8. V.G. Welsby, The theory and design of inductance coils. (Macdonald, London, 1960).
9. Kwon, C. S., & Kang, F. S. Superconducting Magnet Energy Storage Unit.
10. Vulusala G, V. S., & Madichetty, S. (2018). Application of superconducting magnetic
energy storage in electrical power and energy systems: a review. International Journal of
Energy Research, 42(2), 358-368.
11. Hsu, C. S., & Lee, W. J. (1993). Superconducting magnetic energy storage for power
system applications. IEEE Transactions on industry applications, 29(5), 990-996.

International Conference on Nanotechnology and Condensed Matter Physics 2018 (ICNCMP 2018)
January 11–12, 2018, BUET –Dhaka, Bangladesh
12. Xu, Y., Tang, Y., Ren, L., Jiao, F., Song, M., Cao, K., ... & Dong, H. (2013). Distribution
of AC loss in a HTS magnet for SMES with different operating conditions. Physica C:
Superconductivity, 494, 213-216.
13. Yuan, W., & Zhang, M. Superconducting Magnetic Energy Storage (SMES) Systems.
Handbook of Clean Energy Systems.
14. Tixador, P. (2012). Superconducting magnetic energy storage (SMES) systems. In High
temperature superconductors (HTS) for energy applications (pp. 294-319).
15. http://www.climatetechwiki.org/technology/jiqweb-ee