Investigation on the performance of DI-BSCCO superconducting electric motor

doi:10.4236/ns.2011.31004

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Vol.3, No.1, 36-41 (2011) Natural Science

http://dx.doi.org/10.4236/ns.2011.31004

Investigation on the performance of DI-BSCCO

superconducting electric motor

Chin Kat Meng, Nasri A. Hamid*, Mohd. Yusri Abd. Rahman

Department of Engineering Sciences & Mathematics, College of Engineering, Universiti Tenaga Nasional, Kajang, Selangor, Malay-

sia; *Corresponding author：[email protected]

Received 3 November 2010; revised 5 December 2010; accepted 8 December 2010.

ABSTRACT

Superconducting electrical devices have been

developed in various fields especially in indus-

trial energy over a decade. Superconducting

motor is one of the electrical devices that at-

tracted the attention of engineers and re-

searchers from the universities and industries

due to its distinctive energy efficiency. This

paper describes the performance of supercon-

ducting electric motor and its performance was

compared with conventional copper electric

motor. Direct current (DC) synchronous single-

phase series motor has been chosen as the

base for development of both motors. Two pro-

totypes of electric motor fabricated using con-

ventional copper coil and superconducting coil

were developed with similar motor type, design,

dimension, and features. The superconducting

motor coil was wound using Bi-2223 (DI-BSCCO)

Type H wires developed by Sumitomo Electric

Industries Limited, Japan. A finite element

analysis was performed to get a clear view on

flux plots of the magnetic induction. Features of

the superconducting motor and the special coil

frame designed to protect the superconducting

wire was also presented in this paper. In addi-

tion, the torque performances for both types of

motor were measured. The superconducting

electric motor was found to consume lower

power to produce the same output compared

with the conventional copper-wound motor.

Keywords: Superconductor; Magnetic flux; Finite

Element Analysis; Electric Motor

1. INTRODUCTION

Since the discovery of superconductivity in 1911 by

Kamerlingh Onnes, the dream of creating highly effi-

cient electric machine is getting closer to a reality. Su-

perconducting materials are able to carry current with

zero resistance and reduce power loss during the process

of transmitting electricity [1]. This distinctive property

of superconductor has seized the attention of many re-

searches and a lot of studies have been carried out to

produce superconducting wire with high stability. Fi-

nally, long length superconducting wire has been suc-

cessfully produced with a very reliable performance

[2,3]. Superconducting devices such as magnetic reso-

nance imaging (MRI) and superconducting quantum

interference devices (SQUID) have been used in medi-

cine and industry extensively. Several others electrical

power devices such as motor, generator, fault current

limiter and magnetic storage system have been devel-

oped [4-6]. Superconductor required cooling process

below the critical temperature, Tc which is also called as

transition temperature to become zero resistance. The

conventional low temperature superconductor operates

at below 20 K, where cooling by liquid helium is re-

quired. In 1986, researchers discovered high temperature

superconductor where the critical temperature is higher

than 77 K. Therefore, the use of cheaper refrigerant such

as liquid nitrogen is sufficient to cool the superconduct-

ing material and become superconductivity [7].

The distinctive properties of superconductor enable

the development of high efficiency energy devices. It is

believed that superconducting motor is able to reduce in

size and minimize energy loss compared to the conven-

tional copper-base motor [7,8]. In this work, a low

power superconducting electric motor is fabricated and

its performance was compared with a conventional elec-

tric motor. All the specifications for both types of motor

are similar except for the coils. The intended applica-

tions of the motor are for driving industry devices such

as pump and fan that can operate continuously at a con-

stant speed. The features and performance of both types

of motor were investigated. The simulation of the flux

plot was also presented.

K. M. Chin et al. / Natural Science 3 (2011) 36-41

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2. EXPERIMENTAL

2.1. Motor Design Description

The new architecture for designing of electric motors

was first introduced about a decade ago [9]. In our work,

similar approach was adopted at the designing stage of

the motor. Figure 1 shows the model of motor prototype

that was designed. It has three main structures, namely,

coil, stator and rotor. Two different coils were fabricated;

the first type was wound with high-temperature super-

conductor (HTS) DI-BSCCO wire and the second type

was wound with normal cooper wire. The design of the

motor was made flexible where the coils can be inter-

changed easily. The stator was laminated by a metal

sheet with 5 mm thick. In addition, to reduce the effect

of eddy current loss during the motor operation, each

layer of lamination was insulated with varnish. The fab-

ricated coil was directly mounted to the two-leg of the

stator and cooled by liquid nitrogen. In addition, the ro-

tor was installed to the stator with the support of the ro-

tor housing. The stator is designed with a deep “U”

shape; where the rotor will be mounted at the opening of

the “U” with rotor housing and coils will be directly

assembled to one of the stator legs. With this design,

various tests can be conducted, each with different

number of coil [10]. Table 1 shows the summary of the

design of the motor.

2.2. Coil Structure

For the superconducting wire, its critical current is

strongly influenced by the bending diameter of the wire

at 77 K [2]. A frame was designed to protect the super-

conducting wire from any external impact or damage.

Figure 2 shows the dimensional sketch of the coil layout,

where the coil was wound around the frame with a dou-

ble pancake style. Each coil structure has a total of 100

turns. Figure 3 shows the final product of the supercon-

ducting coil. Similar design was used to fabricate the

Figure 1. Model of the prototype.

Table 1. Summary of the design of the conventional and su-

perconducting motors.

Motor Type: DC Synchronous Machine

Details of Field Winding

Field winding wire type: Copper

Operating current: < 2 A

Details of Superconducting Coils Winding Stator

Stator winding wire type: HTS

Cooling type: Immersion

Coolant: Liquid Nitrogen (LN

Operating Temperature: 77 K

Operating current: < 65 A

Details of Copper Coils Winding Stator

Stator winding wire type: Copper

Operating current: < 16 A

Stator Lamination Sheet

Metal sheet type: Cooled-roll metal sheet

Thickness: 0.5 mm

Figure 2. Dimensional sketch of the coil.

Figure 3. Superconducting coil structure.

K. M. Chin et al. / Natural Science 3 (2011) 36-41

conventional copper coil as shown in Figure 4. The

conventional coil structure has exactly the same design

and dimensions with the superconducting coil.

Table 2 shows the materials and specifications for the

superconducting coil and its components. Selection of

the materials for the coil unit is important to ensure the

effective distribution of magnetic flux. Ferromagnetic

material must be avoided in the coil components to

eliminate the suppression of magnetic flux [11]. In this

design, brass which is a non-magnetic material was used

in the construction of the frame and edge plate.

3. THEORY

3.1. Electromagnetic Theory

Rotating machinery working principles are based on

electromagnetic laws. One of the main laws is Ampere’s

law which is defined as “the line integral of the magnetic

field strength taken around any closed path is propor-

tional to the total current flowing across any area,

bounded by the path” [12]. Mathematically, the law is

expressed by:

dlJ ds

 (1)

where J is conduction current density, H is magnetic

field intensity, dl is the differential length, ds is differen-

tial surface enclosed by the closed path of length, and

 is integral over a closed loop or closed path.

3.2. Field Strength of Magnetic Circuit

A magnetic field system comprises of N-turns coil

wound on the ferromagnetic core. The coil carries a con-

stant current, i through a uniform cross-sectional area, Ac

of the core. When the current flows inside the conductor,

magnetic field is generated inside the core and a mag-

netic flux is confined to the ferromagnetic core. In the

actual practice, a small portion of the flux will leak to

the environment but this can be neglected due to its

small percentage compared to the total flux. Therefore,

the current through the enclosed path is expressed by:

ds Ni

 (2)

where N is number of turn wound on the core and i is

current inside conductor. From (1) and (2), the following

relationship is obtained and is expressed by:

dl Ni

 (3)

Figure 5 shows the equivalent magnetic circuit of the

motor. Subscripts r, a, y, and c indicate “rotor”, “air-

gap”, “york” and “cor e”, respectively.



represents

magnetic flux. Symbols c



and r



denote magnetic

fluxes that are generated by the coil and the rotor, re-

spectively. “R” indicates the reluctance inside the circuit.

In this case, circuital law can be applied to this flux path,

and thus from (3), the total current in the circuit shown

in Figure 5 is expressed as:

Figure 4. Conventional copper coil structure.

Table 2. Specification of the superconducting coil and compo-

nents.

No.Item Material Specification

1 HTS coil Type H Double Pancake 100 turns

2 Frame Brass -

3 Edge Plate Brass -

4 Terminal Copper -

5 Separator GFRP Thickness 0.2 mm

6 Edge SeparatorGFRP Thickness 0.2 mm

7 Insulation PlateGFRP Thickness 0.2 mm

8 Screw Blot - M3

9 Screw - M3

*GFRP = Glass Fiber Reinforced Polymer



Figure 5. Equivalent magnetic circuit of the system.

K. M. Chin et al. / Natural Science 3 (2011) 36-41

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Ni HL

 (4)

ccrryya ar r

NiNiHLHLH L (5)

4. RESULTS AND DISCUSSIONS

4.1. Finite Element Analysis

A finite element analysis was applied to investigate

the behavior of the magnetic flux inside the motor. The

analysis is very useful to verify an ideal magnetic circuit

and to detect any error in the electrical connection, espe-

cially for the DC machine. Another advantage of apply-

ing finite element analysis before the actual testing is to

avoid any short-circuit current between the motor com-

ponents. Figure 6 shows the model of the motor which

was constructed from the finite element analysis. The

model was built with a full scale dimension.

Figure 7 shows the magnetic flux path in the circuit.

From the flux plot, it indicates that the flux loss was in

the form of flux leakage and fringe effect. The simulated

result shown in Figure 8 indicates that the flux density

was inside the body of the motor. In the figure, it is ob-

vious that a high flux density is in the area around the

air-gap and the rotor. In contrast, the other parts of the

motor do not show high flux density, indicating a low

distribution of flux. The high flux density in the rotor

and air-gap area is needed to establish a high force that

enables the rotor to rotate.

4.2. Motor Assembly and Testing

The lamination of metal sheet on the motor formed

the stator. The superconducting coil was mounted on one

leg of a stator. A rotor was then mounted on the rotor

housing and the housing was attached to the stator. Thus,

a complete superconducting electric motor was assem-

bled. The procedure was repeated to assemble a copper

electric motor. Photograph of the completed assembly of

Figure 6. Model generated from the finite element analysis.

superconducting coil motor and copper coil motor are

shown in Figure 9 and Figure 10, respectively.

Flux lossFringe

Figure 7. Simulation of the magnetic flux path.

Figure 8. Simulation of the magnetic field density.

Figure 9. Superconducting coil motor assembly.

K. M. Chin et al. / Natural Science 3 (2011) 36-41

Figure 10. Conventional copper coil motor assembly.

Figure 11. The performance of motor with superconducting

coil.

Figure 12. The performance of motor with copper coil.

Motor torque measurement is used to gauge the per-

formance of the fabricated motor. Motor torque is one of

the motor ratings that is normally used to rate the motor

rotary force produced on its output shaft [13]. In the

measurement of motor torque, lever length is referred to

the radius of the shaft, and the force applied to the lever

is generated by the weight attached to the motor shaft.

DC current is used to provide the input current to both

the field coil and the rotor. In testing both types of mo-

tors, a constant current was supplied to the rotor, while

the current applied to the coil was varied at a fixed in-

terval with a load mounted on a shaft.

The data was taken once the rotor started to rotate. In

testing the motor with the superconducting coil, a rapid

cooling of the coil affected its performance. As such, the

coil was cooled gradually by pumping a small amount of

liquid nitrogen into the reservoir at a time until equilib-

rium temperature was reached. Testing conventional

copper coil was repeated with the same conditions but

without any cooling process. From the testing results, the

input power against the horizontal torque generated by

the shaft for each type of motor were plotted and are

shown in Figure 11 and Figure 12. The figures show

that the input power to establish a certain level of torque

for the superconducting coil motor is much lower than

the conventional copper coils motor. This shows that for

the same volume of conductor used in the construction

of the motor, the motor with superconducting coil per-

formed better performance in term of higher efficiency

than the motor with copper coil. One of the possible

factors in the enhancement of the efficiency of the motor

system is due to lower hysteresis loss inside the super-

conductor coils [14].

5. CONCLUSIONS

The design and feature of the motor components have

been presented in this paper. The results of finite ele-

ment analysis on the motors design have also been pre-

sented. Successful preliminary testing of the prototypes

of the bench-top motor proved that the performance and

energy efficiency of motor with superconductor coils is

superior. In addition, the superconducting motor is

lighter and compact with almost zero flux and noise

leakages. The encouraging results indicate the potential

of superconductor applications in machine devices and

the possibility of commercialization in the near future.

6. ACKNOWLEDGEMENTS

This project is supported by the Ministry of Science, Technology

and Innovation (MOSTI), Malaysia under the eScience Grant project

no. 03-02-03-SF0132.

K. M. Chin et al. / Natural Science 3 (2011) 36-41

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