박상용
(Sang-Yong Park)
1iD
최효상
(Hyo-Sang Choi)
†iD
-
(Dept. of Electrical Engineering, Chosun University, Korea)
Copyright © The Korean Institute of Electrical Engineers(KIEE)
Key words
Lorentz force, Superconducting bulk-type magnet, Arc-induction type, Superconducting wire-type electromagnet
1. Introduction
The interest in the direct current (DC) power distribution systems are growing worldwide
with the development of renewable energy sources because the overall system efficiency
will be improved compared to the existing alternating current (AC) systems if the
generation and consumption of DC electricity will be realized in the DC system(1-2). Building a grid infrastructure for the DC system, however, requires the development
of CB (circuit breaker) that can increase the grid reliability(3-4). DCCB applicable to the current distribution system include mechanical CB that utilize
mechanical contacts. These consist of a main switch with a mechanical break contact,
a magnet, an LC oscillator, and a reverse current supply, as necessary. Devices other
than mechanical break contacts are used to increase the breaking capacity, thereby
contributing to the advancement of LV(low voltage) DC to MV(middle voltage) DC. The
development of HV(high voltage) DCCB, which are currently in the commercialization
stage, is currently actively being undertaken(5-7). The aforementioned issue, however, cannot be addressed with passive devices or a
magnet because the isolation must be done at high voltage levels. Therefore, the development
and commercialization of related devices with fast breaking is under way, utilizing
power semiconductors. On the normal operation mode in the system, when heat is generated
for the power semiconductors in the system, and the resulting efficiency lossed. In
addition, the system should be composed of over 100 expensive power semiconductors
to increase the breaking operation reliability. If any problem occurs in one of those
semiconductors, it will be difficult to perform a normal break operation. Therefore,
there are potentially more sensitive and worrying issues in the operation of HVDCCB
than in other types of breakers.
This study was conducted to develop an HVDCCB by combining a mechanical switch with
a superconducting magnet. This mechanical switch is AI (arc induction) type DCCB consists
the mechanical contacts and the induction needle, a very simple structure. For superconducting
magnets, two types were considered for application: a superconducting bulk-type magnets
and a superconducting wire-type electromagnet. Based on previous studies, the operating
characteristics of an arc induction type DC circuit breaker using an induction needle
were confirmed. Based on this, a superconductor was applied to increase the induction
efficiency of the induction needle(8). Simulation was performed using the Maxwell program, an electromagnetic field analysis
program.
그림 1 기계식 DC 차단기의 원리 및 메커니즘
Fig. 1 The principle and mechanism of the mechanical DC circuit breaker
그림 2 플래밍의 왼손 법칙
Fig. 2 Fleming’s left-hand law
2. Body
2.1 Principles and mechanism of DC circuit breaker
Figure 1 shows the principle and mechanism of the AI type DCCB, where ⓐ is a positive anode,
ⓑ is a negative cathode, ⓒ is an induction needle, ⓓ is a ground wire, ⓔ is the spacing
between the mechanical contacts and the induction needle, and ⓕ is the gap between
the anode and the cathode in the interval between the poles. Figure 1-(a) shows the position of the AI type DCCB when the system is in a normal state. Normal
current flows through the anode and cathode. The induction needles set apart at a
certain distance by the induction interval of ⓔ do not affect the normal current.
Figure 1-(b) shows the point where the contact starts to open. System transients cause an arc
between the electric contacts. Figure 1-(c) shows that the anode and cathode are fully open, thereby ensuring a sufficient gap
between them. In this case, the arc flows between the induction needle and the anode
rather than between the poles. This arc is absorbed and induced by an induction needle
before being extinguished along the ground line to the ground. The flow of the arc
in this moment was analysed using Coulomb’s law (1) (8).
Equation (1) is Coulomb’s law, which represents the relationship between the stimulus distance
and the stimulus intensity, where $m_{1}$ and $m_{2}$ represent the pole strengths
and $r$ represents the distance between the poles. $F$ is the force acting between
the poles. As the distance between the poles increases, as shown in Equation (1), the force generated between the two poles decreases. This is because when the arc
occurs between two poles due to the increase in pole distance, the force generated
by the arc decreases, thereby facilitating easy induction of the force to another
pole.
2.2 Lorentz force for the superonducting magnet
Figure 2 shows force F [N] generated by current I [A] and magnetic field B [H] in the arc
blow method (The Lorentz force based on Fleming’s left-hand law). Equation (2) is a force that affects the direction of motion under the influence of the magnetic
flux density of the magnets, which are generated from the electric field triggered
by the opening of the mechanical contacts by the Lorentz force. A represents the charged
particle, B is the electric field, C is the magnetic field, and D is the movement
speed of the charged particles(9).
In the AI type DCCB, the arc is blown in the direction of the induction needle by
the fault current I [A] occurring between the anode and the mechanical breaking contact
of the cathode and the magnetic flux density B [H] of the magnet located near the
contacts. The cone-shaped induction needle has a high electric-field concentration,
thereby facilitating the easy induction of blown arcs.
2.3 Design of the simulation model
Figure 3 shows an AI type DCCB simulation model by superconducting types: ⓐ superconducting
bulk-type magnets and ⓑ superconducting wire-type electromagnet. The AI type DCCB
contact consists of an anode and a cathode. It measures 12 mm in diameter and 150
mm in height, with its main consisting material being copper. The cone-shaped induction
needle measures 4 mm in base diameter, with its round sphere at the top measuring
0.2 mm in diameter. This unique design increases the concentration of the electric
field and aids in arc absorption. Figure 3-(a) shows a DCCB with a superconducting bulk magnet while Figure 3-(b) shows a DCCB with a superconducting wire-type electromagnet. In addition, Figure 3-(a) shows a superconducting bulk magnet on both sides of the mechanical breaker perpendicular
to the contact while Figure 3-(b) shows that the superconducting wire was designed with an AI type DCCB and a wire-type
electromagnet with the bulk-type magnet position. The distance between the break contacts
and the magnets of the two models is approximately 42.5 mm.
그림 3 각 타입에 따른 AI 타입의 DC 차단기 모델 (a) 벌크형 자석, (b) 선재형 전자석
Fig. 3 AI type DCCB model by superconducting types: (a) The bulk-type magnets, (b)
THe wire-type electromagnet
2.4 The design of the model by superconducting bulk-type magnet and wire-type electromagnet
Figure 3-(a) shows a superconducting bulk-type magnet measuring 40 mm in diameter and 15 mm in
height, with its material reflecting the YBaCuO superconductivity. It is a high temperature
oxide superconductor with a high critical temperature of 92 K. It also has strong
magnetic-field characteristics, with a maximum magnetic force of about 63.89 N(10).
Figure 3-(b), on the other hand, shows a wire-type electromagnet using the superconducting wire.
Measuring 42 mm in diameter and 40 mm in height, its main material is 8602 of AMSC,
and the stabilization layer is made of stainless steel with about 1.00 × 〖10〗^(-7)
[Ωm, 20℃] $\rho$ (resistivity). The critical current flows through the superconductor,
which causes the phase conduction to change, and the heat generated in the process
can be represented by the energy relation Equation (3). Equation (4) lists Equation (3) as the applied voltage per unit length of superconducting wire. $v$ is the voltage
across the superconductor, $R$ is the superconductor generating resistance, $C_{V}$
is the heat capacity of the stabilizing layer constituent material, $\triangle t$
is the temperature change of the superconductor, $E$ is the applied voltage per unit
length (V/m) of the superconducting wire, $\rho$ is the resistivity of the stabilization
layer material, and $\triangle t$ is the superconductor operating time.
그림 4 초전도 벌크형 자석의 자속밀도 분포도
Fig. 4 Magnetic flux density distribution of superconducting bulk-type magnets
그림 5 초전도 선재형 전자석의 자속밀도 분포도
Fig. 5 Magnetic flux density distribution of superconducting wire-type electromagnet
2.5 Simulation results
Figure 4 shows the magnetic flux density distribution of the superconducting bulk magnet,
and Figure 5 shows the magnetic flux density distribution of the wire-type electromagnet. Figure 4 shows that the superconducting bulk magnet has a high residual magnetic field. An
about 269.3 [A/m] magnetic field was generated at the center of the bulk magnet while
a high magnetic field of about 512 [A/m] was generated outside.
Figure 5 shows a model designed with a superconducting wire-type electromagnet. The magnetic
force is generated by the turn ratio of 5. The magnetic field was generated by superconducting
wire. The highest magnetic field of 610 [A/m] was recorded in the center of the superconducting
wire.
3. Conclusions
The AI type superconducting DCCB extinguishes arcs using the magnetic field of the
superconducting magnet based on the AI characteristic of the induction needle. In
order to compare the strength of the magnetic field generated by the superconducting
bulk-type magnet and the superconducting wire-type electromagnet, simulation modeling
was performed under the same size conditions. In this paper, the magnetic flux density
distributions generated when the superconducting bulk magnets and superconducting
wire magnets are applied, respectively, to the AI type DCCB were compared. As a result,
the magnetic field of the bulk-type magnet showed a difference of about 98 [A/m] from
that of the wire-type electromagnet under the same diameter condition, however both
types of magnet generated a magnetic field of about 500 [A/m] or more. AI type DCCB
requires the superconducting magnet that can generate a high magnetic field through
a minimum space, therefore the bulk-type magnet is more advantageous than the wire-type
electromagnet. The reason is that the circuit becomes relatively complicated due to
the auxiliary power of the wire-type electromagnet, which increases the volume of
the superconducting magnet. We will continue our research to perform simple configuration
and reliable cutting-off operation of AI-type DCCB using the superconducting bulk-type
magnets.
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저자소개
Graduated from Chosun University Graduate School in 2018 (Master of Engineering).
Currently completing the PhD program at the same graduate school.
Regular member of the Korean Electrical Society
Major Research Areas of Interest : Applications of superconducting Power system, Applications
of DC circuit breaker
Tel: 062-230-7054
E-mail : sangyong4400@gmail.com
Currently Professor, Department of Electrical Engineering, Chosun University, 2021~
Vice President of the Korean Electrical Society.
Major Research Areas of Interest : Applications of superconducting Power system, Applications
of DC circuit breaker, wireless power transmission
Tel: 062-230-7025
E-mail : hyosang@chosun.ac.kr