IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 28, NO. 4, JUNE 2018
3700305
Design and Fabrication of a 1-MW High-Temperature
Superconductor DC Induction Heater
Ping Yang
, Yawei Wang
, Derong Qiu
, Tongxu Chang, Huatao Ma, Jiamin Zhu, Zhijian Jin, and Zhiyong Hong
Abstract—The high-temperature superconductor (HTS) dc induction heater shows great potential in the efficiency increase and
heating quality improvement, which has been validated by previous
prototypes. Now, Shanghai Jiao Tong University has been developing and fabricating an industrial scale 1-MW HTS dc induction
heater in China. The heater is utilized to preheat aluminum billets
446 mm in diameter × 800–1500 mm in length. Two cryocoolers
are applied for coil cooling with pluggable sleeve and providing
an additional safety margin whose normal operating temperature
is 30 K. The magnet consists of a double pancake coils wound
by REBa2 Cu3 O7 −δ -coated conductors, which are produced by
Shanghai Superconductor Technology Company. More than
12-km HTS tapes are used and the inductance of coil with iron
is 98 H. The HTS magnet’s critical current is 213 A. The 0.5-T dc
magnetic field is set up in the two air gaps of HTS magnet with
an iron core. The adjustable iron yoke distribution along the axial
direction of billets can meet the 100 °C adjustable temperature
gradient design requirement. The results will be helpful to design
for the commercialization of the HTS dc induction heater.
Index Terms—Aluminum billet, HTS DC induction heater,
FEM, adjustable iron yoke, temperature distribution.
I. INTRODUCTION
HE high critical current density and economical cost of
a REBa2 Cu3 O7−δ (REBCO) tape make it a research focus for various applications [1]–[7]. The novel high temperature
superconductor (HTS) DC induction heater is designed to heat
aluminum billets in extrusion press [8]–[10]. The energy efficiency of conventional induction technology is just around 50%
for aluminum materials because a large proportion of energy is
dissipated as heat in the copper wires. The energy efficiency of
HTS induction heater is up to nearly 80–90%, due to the high
T
Manuscript received September 19, 2017; accepted February 21, 2018. Date
of publication February 28, 2018; date of current version April 2, 2018. (Corresponding author: Yawei Wang.)
P. Yang is with the Scientific Research Academy, Shanghai Maritime University, Shanghai 200135, China (e-mail: yangpingchinese@gmail.com).
Y. Wang was with Shanghai Jiao Tong University, Shanghai 200240 China.
He is now with the University of Bath, Bath BA2 7AY, U.K. (e-mail: y.wang2
@bath.ac.uk).
D. Qiu and Z. Jin are with Shanghai Jiao Tong University, Shanghai 200240,
China (e-mail: eddiechiu@sjtu.edu.cn).
T. Chang, H. Ma, and J. Zhu are with Shanghai Superconductor Technology
Company Ltd., Shanghai 201210, China (e-mail: tongxu.chang@shsctec.com;
huatao.ma@shsctec.com; jiamin.zhu@shsctec.com).
Z. Hong is with JIANGXI Lianchuang Opto-eletronic Science and Technology Company Ltd., Jiangxi 330096, China (e-mail: zjjin@sjtu.edu.cn; zhiyong.hong@sjtu.edu.cn).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TASC.2018.2810498
efficiency of the motor (above 95%) and the low power of coil
cooling system [9]–[14].
In 2008, Germany developed a commercial 360 kW HTS DC
induction heater, which was built in using 1st HTS tapes for
aluminum billets 200 mm in diameter and 1000 mm in length
[10]. In 2013, a 10 kW prototype for an HTS DC induction
furnace was developed for aluminum billets Φ 80 mm × 300 mm
[15], [16]. In 2014, Korea proposed a HTS DC induction heater
with 300 kW to achieve 90% efficiency within 3 years [17].
In 2013, SJTU had started the 1 MW HTS induction apparatus
development in China. The heater was designed for aluminum
billets 466 mm in diameter and 800–1500 mm in length. The
0.5 T DC magnetic flux density was obtained in the two air
gaps of HTS magnet with iron core. It was designed to preheat
aluminum billets to 520 °C within 7–10 minutes [18]–[20].
After four years, this project is going to be finished by the end
of this year. This paper is to describe economic feasibility and
design principles of this MW-scale HTS apparatus. The subsystems are analyzed including HTS magnet, conduction-cooling,
quench protection and driving system. Two cryocoolers are applied for coil cooling with pluggable sleeve and providing an
additional safety margin. A hybrid driving system based on flywheel energy storage (FES) is designed to solve the problem of
peak torque. An adjustable iron yoke of HTS magnet is proposed
to achieve a gradient temperature along the axial direction.
II. DESIGN OF INDUCTION HEATER
A. Introduction of 1 MW HTS Induction Heater
The major parts consist of HTS coils, iron yoke, driving system, conduction-cooling system, power supply system and control system. As shown in Fig. 1, The around 0.5 T DC magnetic
flux density is obtained in the two air gaps by HTS coils coupled
with iron core. The iron yoke is designed to set up the DC magnetic field. Two billets are rotated in the DC magnetic field by
motors and they are preheated by the induced eddy current. The
adjustable iron yoke are used for aluminum billets with different
diameter and length. The magnetic flux density and distribution
of magnet are modifiable by changing the locations of the iron
yoke, and then the temperature distribution of aluminum billet
along axial direction can be adjusted to meet the temperature
requirement. Table I shows the specifications of 1 MW HTS
induction heater. The iron yoke and motors have been already
finished, and the HTS coils are still in the test stage, as shown
in Fig. 2.
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Fig. 1.
IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 28, NO. 4, JUNE 2018
Schematic drawing of the HTS magnet.
TABLE I
DESIGN SPECIFICATIONS OF 1 MW HTS INDUCTION HEATER
Parameters
System capacity
Billet radius
Billet length
Efficiency
Rotational frequency
Target temperature
Period of heating
Target magnetic field
Quantity
1.2 MW
446 mm
800–1, 500 mm
ࣙ85%
4–12 Hz (240–720 r/min)
520 °C
7–10 min
0.5 T
Fig. 3.
Net present value of 1 MW HTS induction heater.
TABLE II
DESIGN SPECIFICATIONS OF HTS MAGNET FOR 1 MW INDUCTION HEATER
Parameters
Inner diameter
Quantity of turns
Quantity of DPC
Total length of tape
Width and thickness of tape
Operation current
Operating temperature
Induction value
Quantity
2.1 m
180 turns × 2 layers
5
12 km
4.74/0.25 mm
213 A
30 K
98 H
The initial capital cost (ICC) for HTS DC induction heater
is much higher than AC induction heaters. The economic feasibility depends on whether the energy cost saved in the future
can pay the extra capital cost of HTS induction heater. The
economic indexes to evaluate the economic performance of the
HTS induction heater includes the net present value (NPV) and
payback period (PBP). The PBP refers to the period of time
required for the return of the ICC. Shorter payback periods are
always preferred. The NPV of this 1 MW HTS induction heater
is shown in Fig. 3, which illustrates the PBP of this device is
2.25 years.
B. HTS Magnet
Fig. 1 shows the schematic drawing of the HTS DC magnet.
Technical specifications of magnet are listed in Table II. The 5
identical double pancake coils (DPC) compose HTS DC magnet.
The total length of REBCO tapes is approximate 12 km. The
critical current (Ic ) was 213 A at 77 K in self-field. The copperlaminated layers consist of two 100 μm thick copper strips and
5 μm thick copper layer. Kapton tape is considered for insulation
material of insulated coil. The metallic insulation coil technique
is studied on the coil to enhance its thermal stability during
quench for next version apparatus in future [21]–[26].
C. Conduction Cooling
Fig. 2.
Photos of 1 MW HTS induction heater in fabrication.
Fig. 4 shows the cooling system of the HTS magnet. A twostaged G-M cryocoolers is applied to the magnet. Cu current
leads are designed between ambient temperature and the warm
YANG et al.: DESIGN AND FABRICATION OF A 1-MW HIGH-TEMPERATURE SUPERCONDUCTOR DC INDUCTION HEATER
Fig. 4.
Schematic of the 1 MW HTS magnet with conduction cooling system.
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Fig. 6. Dependence of electromagnetic torque and heating power with respect
on the rotational speed, aluminum billet Φ 446 mm × 1500 mm, B = 0.5 T [32].
Three parallel dump resisters are designed for the 1-MW HTS
induction heater. Three parallel dump resisters are designed.
The resistance/power of single dump resister is 3.6 Ω/667 kW.
E. Driving System
Fig. 5.
Active protection for magnet with iron core.
head of the HTS current lead. The 1st stage of the refrigerator is designed to cool thermal shield, current lead and accessories. The 2nd stage of the refrigerator is designed to cool the
HTS magnet. The operating temperature of the HTS magnet is
30 K. Two cold heads are applied for coil cooling with pluggable sleeve and providing an additional safety margin. The
cryocooler is RDK-415D with CSA-71, which is installed in
spare space between two sets of driving system. The refrigeration capacity of RDK-415D is 1.5 W@4.2 K, 35 W@50 K.
The temperature distributions are evaluated by sensors located
at different positions of the magnet. The time for the 2nd stage
temperature to reach 30 K is approximately 25 hours.
D. Quench Protection
The quench protection has always been a critical issue for
HTS magnets [27]–[30]. The inductance value of magnet is
approximately 98 H, which is much higher than that of conventional magnets. Because of the considerable amount of energy
stored, the quench protection system becomes very important.
Fig. 5 shows a passive protection system is developed for the
HTS magnet [31].
Leq is the inductance value of HTS magnet; Rd is the resistance value of parallel dump resistors. Rd can be modified by
changing the status of the switch. Rd is designed to modify the
discharging time duration and voltage of coil terminal Vcoil . D1
is the Schottky barrier diode, which serves as the function of
fly-wheel diode. The IGBT serves as control switch for charging
and discharging. Nanovoltmeter V is used to detect the coil voltage, and the shunt resistor Rs is used to detect the instantaneous
current in the coil. Rw is the equivalent circuit wire resistor.
Based the simulation result of the 1-MW HTS induction
heater, during the startup of the aluminum billet with dimensions Φ 446 mm × 1500 mm, a high peak load torque appears
at a low rotational speed [32]. One of the challenges in the design of the driving system is how to drive the billets with low
cost. As shown in Fig. 6 [32], the load torque increases with the
increase in the rotational speed when the range of the rotational
speed is low, and reaches the peak value of 24701 N·m at a
rotational speed of 20 r/min. The peak load torque is 3.6 times
of the rated load torque at 250–750 r/min, while the load power
at peak torque point (20 r/min) is less than half of the rated load
(250–750 r/min). Generally, the torque output and power output
of electrical motors show a similar trend with rotation speed.
The motor meeting the requirements of both maximum torque
output and power output will lead to a huge waste of torque and
power capacity, which significantly reduces the capability/price
ratio of the driving system.
A FES strategy is applied to solve the startup problem of
the peak overload torque [32]. The FES apparatus provides
additional torque for the original driving during the startup.
The side clutch of the aluminum billet is disengaged until the
main motor is capable of driving the aluminum billet independently. Thereafter, the aluminum billet is driven using the
main motor independently and is accelerated to a rated speed of
500 r/min [32].
III. NUMERICAL MODEL AND PERFORMANCE EVALUATION
A. Numerical Model
While the aluminum billets are heated in the HTS DC induction heater, the billet are rotated in a static transverse magnetic
field to induce an eddy current and are heated by Joule loss.
In theory, this model is equivalent to a standstill billet being
immersed in a rotational magnetic field with the same rotational frequency. A multi-physics model has been developed to
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IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 28, NO. 4, JUNE 2018
Fig. 7. The FEM model of 1 MW HTS induction heater. (a) Overall Mesh of
3D model. (b) Quarter mesh of 3D model. (c) Enlarged view of the coil mesh.
Fig. 10.
Different gap shape of magnet to obtain gradient magnet density.
Fig. 11.
gap.
Gradient temperature varies with the total distance of gradient air
Fig. 8. Illustrations of the gradient aluminum alloy hot extrusion. (a) The
outlet temperature. (b) Gradient heating temperature for aluminum billets.
Fig. 9. (a) Iron yoke with parallel air gap structure. (b) Irion yoke with gradient
air gap shape. (c) Magnetic field in the aluminum billet with the uniform air gap
shape. (d) Magnetic field with the gradient air gap shape.
analyze the DC inducting heating process, as shown in Fig. 7.
It is solved in Comsol Multiphysics [33].
B. Adjustable Temperature Profile
As shown in Fig. 8, more than 100 °C temperature gradient is
required along the axial direction of the billets in the aluminum
extrusion industry. For this heater, this is achieved by adjusting the magnetic field distribution along the axial direction, as
shown in Fig. 9 [34], [35].
Fig. 10 shows the magnetic flux density along the length of
the aluminum billet with five different gradient air gaps: 0 cm,
4 cm, 10 cm, 16 cm, and 20 cm. The magnetic flux density of the
air gap in the center of the aluminum billet decreases linearly
as the increase of gradient air gap. When the gradient distance
is 0 cm and 20 cm, the difference of magnetic flux density is
about 0.14 T, reduced by 28.6%.
Fig. 11 shows the gradient temperature variation with the
total distance of gradient air gap. The maximum gradient temperature ΔT = 168–201 ◦ C is at gradient air gap Δd = 16 cm.
The Δd = 16 cm is optimal gradient air gap value for gradient
temperature design.
IV. CONCLUSION
The paper presents a 1 MW HTS DC induction heater apparatus for heating of aluminum billets. The HTS DC magnet is
designed to set up 0.5 T DC magnetic flux density in the two air
gaps of iron core. An active quench protection system for the
HTS magnet is designed. A startup strategy of FES for 1 MW
HTS DC induction heater is proposed to overcome the peak
load torque at startup. To achieve 100 °C adjustable temperature gradient in the axial direction of billet, an adjustable air gap
structure is designed and fabricated. When the air gap distance
is 20 cm, the different of the magnetic field is 0.14 T, reduced
by 28.6%. Though the initial investment of HTS DC induction
apparatus is much higher than AC induction heaters, the extra
capital cost can be covered by power saving in 3 years.
YANG et al.: DESIGN AND FABRICATION OF A 1-MW HIGH-TEMPERATURE SUPERCONDUCTOR DC INDUCTION HEATER
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