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A mechanical arcless dc circuit breaker for a superconducting magnet system
Fusion Engineering and Design 20 (1993) 415-419 North-Holland
415
A mechanical arcless dc circuit breaker for a superconducting magnet system S. Yamaguchi, H. Sasao, Y. M a t u m u r a a n d T. T u k a m o t o Department of Nuclear Energy Deuelopment, Mitsubishi Electric Corporation, 2-2-3 Marunouchi, Tokyo 100, Japan
Next fusion research experiments plan to use many superconducting magnets. When a quench phenomenon is observed, the current should be interrupted to protect the magnet. Therefore, a dc circuit breaker is necessary. There are four technical situations to be considered for the dc circuit breaker system; (1) high rated current, (2) smaller size breaker, (3) high reliability and (4) no surge voltage during the interruption. The size of the breaker is limited by the arc current density of the contacts, and the low current density is better in the circuit breakers. A high rated current also needs the large contacts of the breaker. Here, we introduce a new type of dc circuit breaker system which does not generate an arc plasma between the contacts, equip the high rated current disconnecting switch and a fuse for the failure of the interruption, and use the conventional ac breaker. The switch size of the breaker is almost one hundred times smaller than that of the previous switch.
1. Introduction High magnetic field and low energy loss systems are needed to construct the fusion experimental devices and fusion reactor, and therefore, the superconducting magnet is the key component. The quench phenomenon is known as the destruction of the superconducting state, and after it is observed, the coil current should be interrupted for safety reasons. The dc cicuit breaker is used to interrupt the current. A dc cicuit breaker is used to generate the plasma in tokamaks [1,2]. One or two breakers are applied because they are used only for the primary winding copper coil. It is not necessary to use a high rated current breaker because the current duration time is not long in the above case, and the usual small breaker can be used. If it is failed to interrupt, the plasma is not generated, and this is not a serious problem because the tokamak device is not destroyed. However, the characteristics of the dc circuit breaker system for the superconducting magnet is quite different from that of other breakers, and the requirements are listed below: (1) high rated current is needed, (2) smaller size is better,
Correspondence to: Dr. S. Yamaguchi, National Institute for Fusion Science, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan. 0920-3796/93/$06.00
(3) high reliability is needed, (4) no surge voltage is induced. The current of the superconducting magnet is high and its duration time is long. These parameters depend on the design and are planned to be 10-100 kA over one hour [3]. This magnitude is almost ten to twenty times higher than the rated current of the conventional breaker for long time operation. After the quench is occurred, the magnitude of current is almost constant. Because of these, if the breaker is connected in the main circuit, we must use many conventional breakers in parallel or a very large breaker. Moreover, many dc circuit breaker systems will be needed because the next fusion experiment needs many toroidal and poloidal superconducting magnets. A wide area and large buildings are necessary to set up the breaker systems. If the current interruption is failed, the superconducting magnet will burn out, and therefore, high reliability is needed. Surge voltage sometimes is observed just after the interruption in the conventional circuit breaker, and it should be avoided for the safety of the magnet. Here, we propose a new dc circuit breaker system for the superconducting magnet, and discuss the above situations. The main circuit and its operation are mentioned and the technical situations are discussed in section 2, the arcless dc circuit breaker experiment [4] in section 3, and the discussion and conclusion in section 4.
© 1993 - E l s e v i e r S c i e n c e P u b l i s h e r s B.V. A l l rights r e s e r v e d
416
S. Yarnaguchi et al. / A mechanical artless dc circuit breaker
2. Proposed circuit and operation Figure 1 shows the proposed main circuit. Since the circuit breaker (CB) is not connected to the circuit of the main power supply (PSO) and the superconducting magnet (SCM), high current does not flow in long time. The disconnecting switch DS1 is used and its rated current is high. Thc disconnecting switch, DS2, CB and the saturable reactor (SR) are connected in series, and SR is used as a rectifying device which is necessary to rcalize thc arcless interruption. The principle of the arclcss interruption is mentioned in section 3. The capacitor C1, the inductor LI and the switch SWI are called the commutation circuit to make a current zero phase of the circuit breaker. The circuit of the switch SW2 and the power supply PS is called the reset circuit for the saturable reactor and can be omitted if the output voltage of the power supply PSO is high enough. The circuit, which is constituted with the switch DS3 and the fuse F, is connected to the breaker CB in parallel. This is a backup system if the breaker fails to interrupt the current. The operation is indicated in tablc 1. Before the experiments starts, SW2 is closed and the power supply PS is operated to make a high residual magnetism of the iron core in SR. If the residual magnetism of the iron core is high, the commutation time from the main
circuit current to the breaker current is short and the whole interruption time is shortened. After the experiment starts, the main circuit current will be increased and the C1 capacitor voltage is controlled to be proportional to the magnitude of current because if the voltage is low, the breaker current cannot be zero and it is impossible to interrupt, and if the voltage is high, the iron core is saturated and the current zero phase cannot be realized for arcless operation. However, this control is not so difficult because the energy of C I capacitor bank is low. During this time period, DS2 and SW2 open, so the rated current CB and DS2 arc low. After the quench is observed, the output voltage of PSO is reversed and DS2 and CB are closed. The main current flows into the circuit of DS2, CB and SR, and this commutation time is limited by the circuit resistance, inductance and the residual magnetism of iron core in SR. After the current of DS1 is zero, it is opened, and the operation of interruption starts. As PSO is disconnected to SCM and the circuit breaker system, high interruption voltage affects on PSO. The current from the commmutation circuit to CB makes the current zero period, and CB open during this period. This is an arcless interruption, and the magnetic energy of SCM dissipates by the break resistor Rx.
/o DSI
PS0
rf
C !!
DC Circuit Breaker System Fig. 1. A proposed circuit.
M!
417
S. Yamaguchi et al. / A mechanical arcless dc circuit breaker
Table 1 A proposed operation for a proposed circuit Time a
to
tl
t2
t3
t4
f5
t6
Status Iscm Icb DS 1 DS2 DS3 SWl SW2 PS0 PS C
Pre-operation zero zero OFF OFF OFF OFF ON no-operation Operation Charged
Startup Finite Value zero ON OFF OFF OFF OFF Opeartion( + ) no-operation Hold
Quench Finite Value zero ON ON OFF OFF OFF Operation( - ) no-operation Hold
Idsl = 0 Finite Value Finite Value OFF ON OFF OFF OFF Operation( - ) no-operation Hold
Comm. start Finite Value Same Value OFF ON OFF ON OFF no-operation no-operation Discharge
Inter. start Finite Value Same Value OFF ON OFF ONN or OFF OFF no-operation no-operation Neg. voltage
Interruption zero zero OFF ON OFF OFF OFF no-operation no-operation Neg. voltage
a t o _ t 1 > l 0 S, t l - t 2 > 1.0 s, t 2 - t 3 > 0.1 s, t 3 - t 4 > 0.05 s, t 4 - t 5 > 0 . 0 l s, t 5 t 6 > 0.005 s.
The proposed circuit and operation answers the technical requirements for the dc circuit breaker. As the disconnecting switch is used and the breaker is not connected in the main circuit, it is not necessary to use a large and expensive breaker. The arcless operation also allows a small breaker to interrupt a high dc current. The arcless interruption is ideal to interrupt a current because an arc plasma is the current carrier, and is not induced between the contacts, so this operation has basically a high reliability. The backup fuse also improves the reliability. The arcless operation and the saturable reactor reduces the surge voltage because of the arcless plasma and high impedance of the saturable reactor.
Rx
~
SWI
CI
L1
Load Inductor Lx
Supply
CB
3. Arcless interruption
CB
Current S.W. ON
The principle of the arcless operation is indicated in fig. 2. The commutation circuit is composed by the capacitor C1, the inductor L1 and the switch SW1. Here, the break resistor Rx is connected in parallel to the commutation circuit. The rectifying device is connected to the circuit breaker CB in series. At first the load inductor Lx is magnetized by the power supply, and the current flows through the rectifying device and CB. C2 is charged before the interruption starts. In order to interrupt the dc current, SW1 is closed and the current zero phase is realized by the rectifying device. Since GB opens during this period, no arc plasma is induced between the contacts of the breaker. Since the leak current is observed in every rectifying device, the perfect arcless operation is impossible. However, the characteristics of a low current arc is quite different from a high current arc, and it is easy to
CB
J tl)
time
t3 Current
/ /.~.... Zero
Phase
Fig. 2. Principle circuit for arcless interruption.
interrupt. The magnitude of the leak current depends on the characteristics of the rectifying device and the commutation circuit parameters, and is of the order of 10 A for the saturable reactor. Figure 3 shows the experimental waveforms of the CB current, the commutation current, the load current,
418
S. Yamaguchi et aL / A mechanical arcless dc circuit breaker $635.KE
150
lnlerrupti0n 100
" ~-~
~
~ CB Current m
5o
.
.',:,
,
, ......
~OPeq
~., CB Voltag~l ~ ~ " "',,'~. . . . . . . . ,,J •,. . . .
.~.
0
,
.
.
:
.
,
.
i .';
• C ....
_,a-'~
. . . . . . .
........ Currefit : j... ...... i '
SR ,
150 0
I
[
0.0005
0.001
0.0015
.
, _
0.002
Time
Fig. 3. Experimental waveforms of current and voltage for 15 kA, 5 kV interruption. the CB voltage and the SR voltage. This operation interrupts 15 kA, 5 kV by a 20 kJ capacitor bank. The design of the saturable reactor is different from the other dc circuit breaker [5], and the magnitude of the leak current is about one hundred times smaller than that of the previous system [5]. The gas circuit breaker (GCB) is used here. The contact open time during the saturable reactor works to rectify, however, since the magnitude of leak current is about 30 A, the current cannot be interrupted immediately and it is interrupted at the real current zero time. The arc voltage is about 10 V. The contact open time and the interruption time are indicated in the figure. In order to measure the low magnitude of the CB current and voltage, a special technique is used [6], and when the magnitudes are high, the signals are saturated. When the current is interrupted, the low surge voltage of CB is observed and its magnitude is about 100 volt because of the low current arc. Moreover, this can be canceled by the opposite surge voltage of SR. Because of this, no surge voltage is induced to the load inductor. Since the damage of the contact can be observed hardly after the experiment, the life time of the breaker is long and the small contact breaker can be used to interrupt a high current.
4. Discussion and conclusion
The arcless operation is mentioned in the previous section, and this is one of the key technologies to realize the proposed idea. However, we should continue to study the backup fuse and the current commutation experiments.
Since the arc voltage of GCB is several times higher than that of vacuum circuit breaker (VCB), the short commutation time is realized by use of GCB. However, VCB is better if the large current arc is induced by the failure of current interruption because the VCB contact is strong for the arc plasma. The fuse and air circuit breaker system is developed to interrupt the dc current [7], the similar system is studied by use of VCB [8]. If the commutation and the interruption experiment is succeeded in VCB, it is easy to expand to use GCB and the fuse backup system to improve the reliability. The contact resistance of the disconnecting switch is low, however, the magnitude of current is over 50 kA and the output voltage of the power supply is around 10 V, the whole resistance of the breakers circuit must be below 500 p~[~. The interruption time depends on the design of superconducting magnet, and therefore, a short interruption time is better because it gives a wide margin to design the superconducting magnets. When the inductance of the breaker circuit is high, the commutation time is elongated. Because of this, the inductance and resistance should be low enough. If the residual magnetism of iron core is low, the output voltage of the power supply is consumed by the iron core and the commutation time is elongated. This time depends on the iron core material and the design of SR. The reset circuit is used to shorten this time length. The iron core hysteresis should be studied experimentally and theoretically because the minor loop characteristics can not be estimated adequately by a computer simulation.
Acknowledgment
The authors are grateful to Drs. T. Morikawa, K. Ibuki and T. Yamada of the Mitsubishi Electric Corporation for their interest and encouragement through this study. Useful discussions were made by Drs. S. Tanahashi and S. Kitagawa of the National Institute for Fusion Science, and T. Isono and K. Yoshida of the Japan Atomic Energy Research Institute. The authors acknowledge the members of the Nuclear Fusion Development Division in the Head Office of Mitsubishi Electric Corporation.
References
[1] R. Shimada, K. Tani, K. Kishimoto, S. Tamura, S. Yanabu, T. Tamagawa, N. Takahashi and Y. Kanai, Analysis and
S. Yamaguchi et al. / A mechanical arcless dc circuit breaker
full scale test of dc circuit breaker for tokamak device JT-60, J. Inst. Electr. Eng. Jpn. B 99 (1979) 773. [2] T. Eriksson, P.L. Mondino C. Raymond and A. Stella, Fabrication, installation and testing of the JET ohmic heating circuit, Proc. 10th Symp. Fusion Eng. Vol. 2 (1983) p.2070. [3] S. Tamura and FER Design Team, Design study of fusion experimental reactor at JAERI, Fusion Engrg. Des. 8 (1989) 29. [4] S. Yamaguchi, H. Sasao, H. Hasegawa, K. Ikeda and T. Tukamoto, A mechanical arcless dc circuit breaker by current zero operation, Rev. Sci. Instrum. 63 (1992) 3993.
419
[5] T. Eriksson, A. Stella, K. Papp and P. Tiez, Design, manufacture and testing of the saturable inductor for JET ohmic heating sub-system, J. de Phys. 45 (1984) C1-675. [6] V. Vokurka, U. Ackermann and E. Schade, New device for measuring post-arc currents in circuit breakers, Rev. Sci. Instrum. 58 (1987) 1087. [7] U. Braunsberger, E. van Mark and G.A. Muelle, A circuit breaker fuse system for the wendelstein VII A, Proc. 9th Symp. on Fusion Technol. (1976) p.723. [8] S. Tanahashi and T. Sato, National Institute of Fusion Science, private communication.
415
A mechanical arcless dc circuit breaker for a superconducting magnet system S. Yamaguchi, H. Sasao, Y. M a t u m u r a a n d T. T u k a m o t o Department of Nuclear Energy Deuelopment, Mitsubishi Electric Corporation, 2-2-3 Marunouchi, Tokyo 100, Japan
Next fusion research experiments plan to use many superconducting magnets. When a quench phenomenon is observed, the current should be interrupted to protect the magnet. Therefore, a dc circuit breaker is necessary. There are four technical situations to be considered for the dc circuit breaker system; (1) high rated current, (2) smaller size breaker, (3) high reliability and (4) no surge voltage during the interruption. The size of the breaker is limited by the arc current density of the contacts, and the low current density is better in the circuit breakers. A high rated current also needs the large contacts of the breaker. Here, we introduce a new type of dc circuit breaker system which does not generate an arc plasma between the contacts, equip the high rated current disconnecting switch and a fuse for the failure of the interruption, and use the conventional ac breaker. The switch size of the breaker is almost one hundred times smaller than that of the previous switch.
1. Introduction High magnetic field and low energy loss systems are needed to construct the fusion experimental devices and fusion reactor, and therefore, the superconducting magnet is the key component. The quench phenomenon is known as the destruction of the superconducting state, and after it is observed, the coil current should be interrupted for safety reasons. The dc cicuit breaker is used to interrupt the current. A dc cicuit breaker is used to generate the plasma in tokamaks [1,2]. One or two breakers are applied because they are used only for the primary winding copper coil. It is not necessary to use a high rated current breaker because the current duration time is not long in the above case, and the usual small breaker can be used. If it is failed to interrupt, the plasma is not generated, and this is not a serious problem because the tokamak device is not destroyed. However, the characteristics of the dc circuit breaker system for the superconducting magnet is quite different from that of other breakers, and the requirements are listed below: (1) high rated current is needed, (2) smaller size is better,
Correspondence to: Dr. S. Yamaguchi, National Institute for Fusion Science, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan. 0920-3796/93/$06.00
(3) high reliability is needed, (4) no surge voltage is induced. The current of the superconducting magnet is high and its duration time is long. These parameters depend on the design and are planned to be 10-100 kA over one hour [3]. This magnitude is almost ten to twenty times higher than the rated current of the conventional breaker for long time operation. After the quench is occurred, the magnitude of current is almost constant. Because of these, if the breaker is connected in the main circuit, we must use many conventional breakers in parallel or a very large breaker. Moreover, many dc circuit breaker systems will be needed because the next fusion experiment needs many toroidal and poloidal superconducting magnets. A wide area and large buildings are necessary to set up the breaker systems. If the current interruption is failed, the superconducting magnet will burn out, and therefore, high reliability is needed. Surge voltage sometimes is observed just after the interruption in the conventional circuit breaker, and it should be avoided for the safety of the magnet. Here, we propose a new dc circuit breaker system for the superconducting magnet, and discuss the above situations. The main circuit and its operation are mentioned and the technical situations are discussed in section 2, the arcless dc circuit breaker experiment [4] in section 3, and the discussion and conclusion in section 4.
© 1993 - E l s e v i e r S c i e n c e P u b l i s h e r s B.V. A l l rights r e s e r v e d
416
S. Yarnaguchi et al. / A mechanical artless dc circuit breaker
2. Proposed circuit and operation Figure 1 shows the proposed main circuit. Since the circuit breaker (CB) is not connected to the circuit of the main power supply (PSO) and the superconducting magnet (SCM), high current does not flow in long time. The disconnecting switch DS1 is used and its rated current is high. Thc disconnecting switch, DS2, CB and the saturable reactor (SR) are connected in series, and SR is used as a rectifying device which is necessary to rcalize thc arcless interruption. The principle of the arclcss interruption is mentioned in section 3. The capacitor C1, the inductor LI and the switch SWI are called the commutation circuit to make a current zero phase of the circuit breaker. The circuit of the switch SW2 and the power supply PS is called the reset circuit for the saturable reactor and can be omitted if the output voltage of the power supply PSO is high enough. The circuit, which is constituted with the switch DS3 and the fuse F, is connected to the breaker CB in parallel. This is a backup system if the breaker fails to interrupt the current. The operation is indicated in tablc 1. Before the experiments starts, SW2 is closed and the power supply PS is operated to make a high residual magnetism of the iron core in SR. If the residual magnetism of the iron core is high, the commutation time from the main
circuit current to the breaker current is short and the whole interruption time is shortened. After the experiment starts, the main circuit current will be increased and the C1 capacitor voltage is controlled to be proportional to the magnitude of current because if the voltage is low, the breaker current cannot be zero and it is impossible to interrupt, and if the voltage is high, the iron core is saturated and the current zero phase cannot be realized for arcless operation. However, this control is not so difficult because the energy of C I capacitor bank is low. During this time period, DS2 and SW2 open, so the rated current CB and DS2 arc low. After the quench is observed, the output voltage of PSO is reversed and DS2 and CB are closed. The main current flows into the circuit of DS2, CB and SR, and this commutation time is limited by the circuit resistance, inductance and the residual magnetism of iron core in SR. After the current of DS1 is zero, it is opened, and the operation of interruption starts. As PSO is disconnected to SCM and the circuit breaker system, high interruption voltage affects on PSO. The current from the commmutation circuit to CB makes the current zero period, and CB open during this period. This is an arcless interruption, and the magnetic energy of SCM dissipates by the break resistor Rx.
/o DSI
PS0
rf
C !!
DC Circuit Breaker System Fig. 1. A proposed circuit.
M!
417
S. Yamaguchi et al. / A mechanical arcless dc circuit breaker
Table 1 A proposed operation for a proposed circuit Time a
to
tl
t2
t3
t4
f5
t6
Status Iscm Icb DS 1 DS2 DS3 SWl SW2 PS0 PS C
Pre-operation zero zero OFF OFF OFF OFF ON no-operation Operation Charged
Startup Finite Value zero ON OFF OFF OFF OFF Opeartion( + ) no-operation Hold
Quench Finite Value zero ON ON OFF OFF OFF Operation( - ) no-operation Hold
Idsl = 0 Finite Value Finite Value OFF ON OFF OFF OFF Operation( - ) no-operation Hold
Comm. start Finite Value Same Value OFF ON OFF ON OFF no-operation no-operation Discharge
Inter. start Finite Value Same Value OFF ON OFF ONN or OFF OFF no-operation no-operation Neg. voltage
Interruption zero zero OFF ON OFF OFF OFF no-operation no-operation Neg. voltage
a t o _ t 1 > l 0 S, t l - t 2 > 1.0 s, t 2 - t 3 > 0.1 s, t 3 - t 4 > 0.05 s, t 4 - t 5 > 0 . 0 l s, t 5 t 6 > 0.005 s.
The proposed circuit and operation answers the technical requirements for the dc circuit breaker. As the disconnecting switch is used and the breaker is not connected in the main circuit, it is not necessary to use a large and expensive breaker. The arcless operation also allows a small breaker to interrupt a high dc current. The arcless interruption is ideal to interrupt a current because an arc plasma is the current carrier, and is not induced between the contacts, so this operation has basically a high reliability. The backup fuse also improves the reliability. The arcless operation and the saturable reactor reduces the surge voltage because of the arcless plasma and high impedance of the saturable reactor.
Rx
~
SWI
CI
L1
Load Inductor Lx
Supply
CB
3. Arcless interruption
CB
Current S.W. ON
The principle of the arcless operation is indicated in fig. 2. The commutation circuit is composed by the capacitor C1, the inductor L1 and the switch SW1. Here, the break resistor Rx is connected in parallel to the commutation circuit. The rectifying device is connected to the circuit breaker CB in series. At first the load inductor Lx is magnetized by the power supply, and the current flows through the rectifying device and CB. C2 is charged before the interruption starts. In order to interrupt the dc current, SW1 is closed and the current zero phase is realized by the rectifying device. Since GB opens during this period, no arc plasma is induced between the contacts of the breaker. Since the leak current is observed in every rectifying device, the perfect arcless operation is impossible. However, the characteristics of a low current arc is quite different from a high current arc, and it is easy to
CB
J tl)
time
t3 Current
/ /.~.... Zero
Phase
Fig. 2. Principle circuit for arcless interruption.
interrupt. The magnitude of the leak current depends on the characteristics of the rectifying device and the commutation circuit parameters, and is of the order of 10 A for the saturable reactor. Figure 3 shows the experimental waveforms of the CB current, the commutation current, the load current,
418
S. Yamaguchi et aL / A mechanical arcless dc circuit breaker $635.KE
150
lnlerrupti0n 100
" ~-~
~
~ CB Current m
5o
.
.',:,
,
, ......
~OPeq
~., CB Voltag~l ~ ~ " "',,'~. . . . . . . . ,,J •,. . . .
.~.
0
,
.
.
:
.
,
.
i .';
• C ....
_,a-'~
. . . . . . .
........ Currefit : j... ...... i '
SR ,
150 0
I
[
0.0005
0.001
0.0015
.
, _
0.002
Time
Fig. 3. Experimental waveforms of current and voltage for 15 kA, 5 kV interruption. the CB voltage and the SR voltage. This operation interrupts 15 kA, 5 kV by a 20 kJ capacitor bank. The design of the saturable reactor is different from the other dc circuit breaker [5], and the magnitude of the leak current is about one hundred times smaller than that of the previous system [5]. The gas circuit breaker (GCB) is used here. The contact open time during the saturable reactor works to rectify, however, since the magnitude of leak current is about 30 A, the current cannot be interrupted immediately and it is interrupted at the real current zero time. The arc voltage is about 10 V. The contact open time and the interruption time are indicated in the figure. In order to measure the low magnitude of the CB current and voltage, a special technique is used [6], and when the magnitudes are high, the signals are saturated. When the current is interrupted, the low surge voltage of CB is observed and its magnitude is about 100 volt because of the low current arc. Moreover, this can be canceled by the opposite surge voltage of SR. Because of this, no surge voltage is induced to the load inductor. Since the damage of the contact can be observed hardly after the experiment, the life time of the breaker is long and the small contact breaker can be used to interrupt a high current.
4. Discussion and conclusion
The arcless operation is mentioned in the previous section, and this is one of the key technologies to realize the proposed idea. However, we should continue to study the backup fuse and the current commutation experiments.
Since the arc voltage of GCB is several times higher than that of vacuum circuit breaker (VCB), the short commutation time is realized by use of GCB. However, VCB is better if the large current arc is induced by the failure of current interruption because the VCB contact is strong for the arc plasma. The fuse and air circuit breaker system is developed to interrupt the dc current [7], the similar system is studied by use of VCB [8]. If the commutation and the interruption experiment is succeeded in VCB, it is easy to expand to use GCB and the fuse backup system to improve the reliability. The contact resistance of the disconnecting switch is low, however, the magnitude of current is over 50 kA and the output voltage of the power supply is around 10 V, the whole resistance of the breakers circuit must be below 500 p~[~. The interruption time depends on the design of superconducting magnet, and therefore, a short interruption time is better because it gives a wide margin to design the superconducting magnets. When the inductance of the breaker circuit is high, the commutation time is elongated. Because of this, the inductance and resistance should be low enough. If the residual magnetism of iron core is low, the output voltage of the power supply is consumed by the iron core and the commutation time is elongated. This time depends on the iron core material and the design of SR. The reset circuit is used to shorten this time length. The iron core hysteresis should be studied experimentally and theoretically because the minor loop characteristics can not be estimated adequately by a computer simulation.
Acknowledgment
The authors are grateful to Drs. T. Morikawa, K. Ibuki and T. Yamada of the Mitsubishi Electric Corporation for their interest and encouragement through this study. Useful discussions were made by Drs. S. Tanahashi and S. Kitagawa of the National Institute for Fusion Science, and T. Isono and K. Yoshida of the Japan Atomic Energy Research Institute. The authors acknowledge the members of the Nuclear Fusion Development Division in the Head Office of Mitsubishi Electric Corporation.
References
[1] R. Shimada, K. Tani, K. Kishimoto, S. Tamura, S. Yanabu, T. Tamagawa, N. Takahashi and Y. Kanai, Analysis and
S. Yamaguchi et al. / A mechanical arcless dc circuit breaker
full scale test of dc circuit breaker for tokamak device JT-60, J. Inst. Electr. Eng. Jpn. B 99 (1979) 773. [2] T. Eriksson, P.L. Mondino C. Raymond and A. Stella, Fabrication, installation and testing of the JET ohmic heating circuit, Proc. 10th Symp. Fusion Eng. Vol. 2 (1983) p.2070. [3] S. Tamura and FER Design Team, Design study of fusion experimental reactor at JAERI, Fusion Engrg. Des. 8 (1989) 29. [4] S. Yamaguchi, H. Sasao, H. Hasegawa, K. Ikeda and T. Tukamoto, A mechanical arcless dc circuit breaker by current zero operation, Rev. Sci. Instrum. 63 (1992) 3993.
419
[5] T. Eriksson, A. Stella, K. Papp and P. Tiez, Design, manufacture and testing of the saturable inductor for JET ohmic heating sub-system, J. de Phys. 45 (1984) C1-675. [6] V. Vokurka, U. Ackermann and E. Schade, New device for measuring post-arc currents in circuit breakers, Rev. Sci. Instrum. 58 (1987) 1087. [7] U. Braunsberger, E. van Mark and G.A. Muelle, A circuit breaker fuse system for the wendelstein VII A, Proc. 9th Symp. on Fusion Technol. (1976) p.723. [8] S. Tanahashi and T. Sato, National Institute of Fusion Science, private communication.