FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
SWITCHING DEVICE
MITSUBISHI ELECTRIC CORPORATION, A CORPORATION
ORGANISED AND EXISTING UNDER THE LAWS OF JAPAN, WHOSE
ADDRESS IS 7-3, MARUNOUCHI 2-CHOME, CHIYODA-KU, TOKYO 1008310,
JAPAN
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

2
DESCRIPTION
TECHNICAL FIELD
[0001] The present disclosure relates to a switching device such as a switch, a circuit
5 breaker, an electromagnetic contactor or a relay that opens/closes an electric circuit.
BACKGROUND ART
[0002] Conventionally, in addition to closing or opening an electric circuit by means of
an electric contact or the like, a switching device safely opens the electric circuit upon
occurrence of an abnormality such as a short circuit or overcurrent. As an example,
10 the switching device includes: a first contact for preventing a current increase upon
occurrence of an abnormality; a second contact provided in parallel with the first
contact; a PTC element provided in series with the second contact; and a currentlimiting element provided in parallel with the first contact and the second contact.
The switching device sequentially opens the first contact and the second contact upon
15 occurrence of an abnormality. In normal state, the switching device conducts current
with low resistance loss through the first contact, and when an abnormality occurs, the
switching device transfers the current to a circuit having the second contact and the
PTC element as a stage prior to transferring the current to the current-limiting element.
This can stabilize the current transfer to the current-limiting element while preventing
20 damage to the first contact due to arc discharge, to thereby prevent a current increase
(see PTL 1, for example).
CITATION LIST
PATENT LITERATURE
[0003] PTL 1: Japanese National Patent Publication No. 2001-515337
25 SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0004] On the other hand, when connecting an electric circuit using the conventional
switching device, a large current of from several kA to several tens of kA or even

3
higher may flow upon occurrence of an abnormality such as a short circuit condition in
the circuit to be connected.
[0005] In the conventional switching device, in this respect, when the large current
passes through the second contact provided in series with the PTC element, an
5 electromagnetic force generated near an interface between contact surfaces of a pair of
contacts included in the second contact may open the contact before the current is
transferred to the current-limiting element, resulting in damage to the contact due to arc
discharge.
[0006] The present disclosure has been made to solve the above problem, and an object
10 of the present disclosure is to provide a switching device that can prevent damage to a
contact in a simple manner.
SOLUTION TO PROBLEM
[0007] According to an embodiment, a switching device includes: a first contact; a
second contact provided in parallel with the first contact; a discharge switch provided
15 in parallel with the second contact and energized only when discharge occurs; and a
fault detection unit to perform an operation of opening the first contact when a fault is
detected. The discharge switch has a function of increasing resistance. The second
contact is opened when energized, and discharge that occurs when the second contact is
opened is driven to the discharge switch, whereby a current-carrying path is switched
20 from the second contact to a circuit having the discharge switch.
ADVANTAGEOUS EFFECTS OF INVENTION
[0008] The switching device according to the present disclosure can prevent damage to
a contact in a simple manner.
BRIEF DESCRIPTION OF DRAWINGS
25 [0009] Fig. 1 illustrates an appearance configuration of a switching device 1 according
to a first embodiment.
Fig. 2 is a circuit configuration diagram of switching device 1 according to the
first embodiment.

4
Fig. 3 illustrates a main part of a commutation unit 10 according to the first
embodiment.
Fig. 4 illustrates a main part of a commutation unit 10A according to a second
embodiment.
5 Fig. 5 illustrates a main part of a commutation unit 10B according to a third
embodiment.
Fig. 6 illustrates a main part of a second contact 18#A according to a fourth
embodiment.
Fig. 7 illustrates a main part of a commutation unit 10C according to a
10 modification of the fourth embodiment.
Fig. 8 is a circuit configuration diagram of a switching device 1A according to a
fifth embodiment.
Fig. 9 is a circuit configuration diagram of a switching device 1B according to a
modification of the fifth embodiment.
15 DESCRIPTION OF EMBODIMENTS
[0010] Embodiments will be described hereinafter with reference to the drawings. In
the following description, the same components are denoted by the same reference
characters. Their names and functions are also the same. Therefore, a detailed
description thereof will not be repeated.
20 [0011] First Embodiment
Fig. 1 illustrates an appearance configuration of a switching device 1 according
to a first embodiment. Referring to Fig. 1, switching device 1 includes, within an
enclosure 7, a fault detection unit 4, a first contact 6, a commutation unit 10 including a
second contact, a current-limiting resistor 2 (2A and 2B), and a contact pressure spring
25 5B.
[0012] Current-limiting resistor 2 includes current-limiting resistors 2A and 2B.
Current-limiting resistors 2A and 2B are connected in series by a resistor connection
conductor 3.

5
[0013] First contact 6 has one side connected to commutation unit 10, and the other
side connected to commutation unit 10 through a flexible conductor 5A. First contact
6 is pressed into a closed state by contact pressure spring 5B in normal operation.
Fault detection unit 4 is disposed on a common conductor where a parallel circuit joins.
5 [0014] Fault detection unit 4 detects a magnetic flux density produced from a current
within the conductor, and is formed of a movable core that is driven when a current
equal to or higher than a certain level flows, and a fixed core, where the movable core
is coupled to first contact 6. First contact 6 is driven along with the movable core.
[0015] When an abnormality occurs in the parallel circuit and the current flowing
10 through the conductor increases, fault detection unit 4 drives the movable core.
Accordingly, the first contact is opened, and the current is transferred to commutation
unit 10.
[0016] Fig. 2 is a circuit configuration diagram of switching device 1 according to the
first embodiment. Referring to Fig. 2, switching device 1 includes first contact 6, and
15 fault detection unit 4 for controlling an operation of opening/closing first contact 6.
Commutation unit 10 is connected in parallel with first contact 6. Current-limiting
resistor 2 is connected in parallel with first contact 6 and commutation unit 10.
[0017] Commutation unit 10 includes a discharge switch 12, a discharge resistor 14, an
opening operation unit 16, and a second contact 18.
20 [0018] Second contact 18 is connected in parallel with first contact 6. Opening
operation unit 16 maintains second contact 18 in an opened state.
[0019] Discharge switch 12 is provided in parallel with second contact 18, is energized
only when discharge occurs, and has the function of increasing resistance.
Specifically, discharge switch 12 is connected in series with discharge resistor 14, and
25 is connected in parallel with second contact 18. Discharge switch 12 is energized only
when arc discharge occurs.
[0020] Second contact 18 is opened when energized, and arc discharge that occurs
when second contact 18 is opened is driven to discharge switch 12, whereby a current-

6
carrying path is switched from second contact 18 to a circuit having discharge switch
12.
[0021] Fig. 3 illustrates a main part of commutation unit 10 according to the first
embodiment. Referring to Fig. 3 (A), commutation unit 10 includes an enclosure 22,
5 terminals TA, TB and TC, opening operation unit 16, second contact 18, a contact
pressure spring 20, arc runners 24 and 28, and an arc-extinguishing member 26.
[0022] Second contact 18 is formed of a pair of elongate current-carrying electrodes
facing each other, and includes a fixed contactor 30 having a fixed contact, and a
movable contactor 32 having a movable contact that is brought into and out of contact
10 with the fixed contact. Second contact 18 is connected to a connection node between
fault detection unit 4 and first contact 6 through terminal TA.
[0023] Movable contactor 32 is coupled to contact pressure spring 20, and is pressed
into contact with fixed contactor 30 and is conducting in normal operation.
[0024] Opening operation unit 16 is coupled to movable contactor 32, and performs an
15 operation of opening the second contact.
Opening operation unit 16 is connected to the connection node between fault
detection unit 4 and first contact 6 through terminal TB.
[0025] Arc runners 24 and 28 are disposed at an upper portion and a lower portion of
enclosure 22. Arc runner 24 is coupled to movable contactor 32. Arc runner 28 is
20 coupled to fixed contactor 30. Arc-extinguishing member 26 is provided between arc
runner 24 and arc runner 28.
[0026] When second contact 18 is energized due to an operation of opening first
contact 6, currents in opposite directions flow through the pair of elongate currentcarrying electrodes facing each other. A resulting electromagnetic force separates the
25 movable contact from the fixed contact.
[0027] Specifically, second contact 18 is closed by contact pressure spring 20 in
normal operation, and when first contact 6 is opened and the current is transferred to a
circuit having second contact 18, a current path is formed from terminal TA through

7
fixed contactor 30 and movable contactor 32 to terminal TB.
[0028] Each of fixed contactor 30 and movable contactor 32 is formed of a pair of
elongate current-carrying electrodes facing each other. When second contact 18 is
energized, currents in opposite directions flow through this pair of current-carrying
5 electrodes, to thereby generate a repelling force between the current-carrying electrodes.
That is, when second contact 18 is energized, second contact 18 is automatically and
rapidly opened by the repelling force.
[0029] When second contact 18 is opened, a gap is formed between the fixed contact
and the movable contact, and arc discharge occurs between these contacts. The
10 discharge switch is also formed between the fixed contact and the movable contact.
[0030] An electromagnetic force is generated within the arc discharge due to a
contribution of a magnetic field produced between fixed contactor 30 and movable
contactor 32, and the arc discharge is driven toward discharge switch 12.
[0031] Discharge switch 12 is connected to arc runner 24 and arc runner 28. The
15 driven arc discharge is commutated to arc runner 24 and arc runner 28, and driven and
extended toward the tips of arc runner 24 and arc runner 28.
[0032] The arc discharge that occurs between arc runner 24 and arc runner 28 increases
in discharge resistance with the extension of the arc discharge, and the current is
suppressed.
20 [0033] Arc-extinguishing member 26 is provided between arc runner 24 and arc runner
28. It is possible to increase the discharge resistance by arc-extinguishing member 26
such as an arc-extinguishing plate provided at the extending end of the arc discharge.
[0034] The configuration of commutation unit 10 according to the first embodiment
allows electrical resistance in the circuit to increase without using a resistor element
25 such as a PTC element. It is possible to achieve the function of suppressing the
current even for a large current of from several kA to several tens of kA or even higher,
without constraints imposed by the current used by the PTC element.
[0035] In a conventional configuration, when a large current passes through the second

8
contact provided in series with the PTC element, an electromagnetic force generated
near an interface between contact surfaces of a pair of contacts included in the second
contact may open the contact before the current is transferred to the current-limiting
element, resulting in damage to the contact due to arc discharge. Preventing the
5 opening of the contact by the electromagnetic force to avoid the damage to the contact
requires a robust switching mechanism to retain the closing of the contact until after the
current transfer to the current-limiting element has been completed, which may cause
an increase in size of the switching device.
[0036] The configuration of commutation unit 10 according to the first embodiment
10 allows the contacts to be promptly separated from each other immediately after second
contact 18 is energized, and allows the current to be instantly limited before the current
increases by providing the arc runners. Therefore, the robust mechanism to retain the
closing of the second contact is not required, and switching device 1 can be
implemented with a simple configuration without an increase in size.
15 [0037] The arc discharge that occurs at second contact 18 is driven to discharge switch
12 and retained. It is thus possible to suppress wear and tear of second contact 18, to
provide longer life through use.
[0038] Switching device 1 according to the first embodiment is configured such that
current-limiting resistor 2 is provided in parallel with first contact 6. Providing
20 current-limiting resistor 2 in parallel allows a part of the current to be commutated to
current-limiting resistor 2 with increase in the electrical resistance of discharge switch
12, thereby further suppressing the wear and tear due to the arc discharge of discharge
switch 12.
[0039] When interrupting the circuit by switching device 1 according to the first
25 embodiment in coordination with another circuit breaker or switch, it is possible to
maintain the effect of limiting the circuit current by current-limiting resistor 2 for a
long time until an operation of opening the another circuit breaker or switch is
performed.

9
[0040] Commutation unit 10 according to the first embodiment includes opening
operation unit 16 that performs an operation of opening second contact 18.
[0041] Referring to Fig. 3 (B), opening operation unit 16 includes a connection
component 160 that is connected to movable contactor 32, a movable core 162, a fixed
5 core 164, and a current-carrying conductor 166.
[0042] Opening operation unit 16 retains the opening of second contact 18. The
contacts are promptly separated from each other immediately after second contact 18 is
energized, and even when the electromagnetic force acting on movable contactor 32
decreases, opening operation unit 16 can retain second contact 18 in the opened state by
10 driving movable contactor 32.
[0043] In this respect, opening operation unit 16 may be formed of an electromagnet
including a plurality of cores.
Movable core 164 is coupled to movable contactor 32 through connection
component 160.
15 [0044] When a current flows through current-carrying conductor 166 disposed between
the cores, an attraction force is generated between the cores. Movable core 162 is
driven by this attraction force, which is then converted into a force for opening
movable contactor 32.
[0045] Current also branches off and flows in opening operation unit 16 through
20 current-limiting resistor 2, when second contact 18 is energized. It is thus possible to
increase the speed of opening second contact 18, by using the attraction force of the
cores before the opening of movable contactor 32 is completed.
[0046] Since opening operation unit 16 is provided, second contact 18 can be
continuously retained in the opened state even when the current path is shifted from the
25 circuit having discharge switch 12 to current-limiting resistor 2. Accordingly, it is
possible to suppress a reduction in the interval between openings of second contact 18,
to help ensure the insulated state between the contacts.
[0047] Further, opening operation unit 16 or fault detection unit 4 may receive a power

10
signal from a system different from the system to be opened/closed. Opening
operation unit 16 or fault detection unit 4 performs, upon receiving another power
signal, an operation of opening second contact 18 or first contact 6. Specifically, a
separate control power supply may be provided and connected to opening operation
5 unit 16 or fault detection unit 4, and an operation of opening second contact 18 or first
contact 6 may be performed using power from this control power supply. The
presence or absence of an abnormality may be determined based on sensor information
from a current sensor (not shown) or the like, and when the presence of an abnormality
is determined, power may be supplied from the control power supply to thereby start
10 the operation of the switching device based on various types of information. The
current sensor is not restrictive, and other sensors may be used.
[0048] For example, in this configuration, when connecting a load circuit such as a
motor and switching device 1 which involves the generation of an inrush current upon
connection of the circuit, an operation of opening first contact 6 or second contact 18 is
15 performed in advance by the power signal described above. It is possible to form a
circuit through current-limiting resistor 2 included in switching device 1. Accordingly,
it is possible to connect the load circuit while suppressing the inrush current to a low
level by current-limiting resistor 2.
[0049] Further, since second contact 18 can be opened/closed by the power signal from
20 the different system described above, a command indicating fault clearing can be
received from other than the switching device of the present disclosure. This
eliminates the need to determine whether the fault has been cleared at fault detection
unit 4. Accordingly, even in the case where a current limiting resistor that is set to a
large electrical resistance value is provided and the limited current is extremely small,
25 it is possible to stably control the retention of the opening of second contact 18.
[0050] Second Embodiment
Fig. 4 illustrates a main part of a commutation unit 10A according to a second
embodiment. Referring to Fig. 4 (A), the difference from commutation unit 10 is that

11
opening operation unit 16 is replaced by an opening operation unit 16A. The
configuration is otherwise the same as that described in Fig. 3, and the detailed
description thereof is not repeated.
[0051] Opening operation unit 16A is formed of a single coil or a plurality of coils.
5 An operation of opening second contact 18 is performed using a magnetic flux
generated by the coil or coils.
[0052] Since opening operation unit 16A is formed of a coil, a reactance is generated in
the circuit when a current passes through the coil, and the current can thereby be
limited to a low level.
10 [0053] A high magnetic flux density is produced around the coil depending on the
number of turns in the coil and the passing current. It is possible to generate an
electromagnetic force and the like by using the magnetic flux density, to thereby retain
the opening of movable contactor 32. By using this electromagnetic force before the
circuit having discharge switch 12 is energized, opening operation unit 16A can
15 increase the speed of opening second contact 18.
[0054] When the coil is formed of a plurality of coils, movable contactor 32 and arc
runner 24 may be electrically connected to each other for one of the coils used, while
the other coil may be connected to a power supply of another system, and an operation
of opening movable contactor 32 may be performed by a power signal from the another
20 system.
[0055] It is not necessarily required to electrically connect one of the coils to movable
contactor 32 or arc runner 24, and movable contactor 32 may be opened/closed upon
receiving a power signal from a system different from the system that is entirely
opened/closed.
25 [0056] When a plurality of coils are provided, it is also possible to perform control
involving complex commands by adjusting the timings and conditions for receiving
power signals.
[0057] Opening operation unit 16A can also perform an operation of opening second

12
contact 18 or retain the opening of second contact 18, by employing a core, winding a
coil 168 around fixed core 164, and operating movable core 162 using a magnetic flux
generated from coil 168, as in the first embodiment with reference to Fig. 4 (B).
[0058] Third Embodiment
5 Fig. 5 illustrates a main part of a commutation unit 10B according to a third
embodiment. Referring to Fig. 5, the difference from commutation unit 10 is that
further components are added to contact pressure spring 20. The configuration is
otherwise the same as that described in Fig. 3, and the detailed description thereof is
not repeated.
10 [0059] Commutation unit 10B further includes a spring force accumulation component
21 and a contact pressure adjustment mechanism 23.
Specifically, contact pressure spring 20 is provided with spring force
accumulation component 21 and contact pressure adjustment mechanism 23.
[0060] Contact pressure adjustment mechanism 23 is provided, on the side of contact
15 pressure spring 20 opposite to the side where movable contactor 32 is disposed, with
spring force accumulation component 21 that can adjust the amount of force
accumulated in contact pressure spring 20. It is possible to adjust the magnitude of
contact pressure to push movable contactor 32 by adjusting the position of spring force
accumulation component 21.
20 [0061] Accordingly, a difference in time from the opening of first contact 6 to the
opening of second contact 18 can be adjusted by the magnitude of contact pressure,
which allows second contact 18 to be opened after the current has been completely
transferred from first contact 6 to the circuit having second contact 18. If second
contact 18 is opened before the current is transferred from first contact 6 to the circuit
25 having second contact 18, first contact 6 is more susceptible to wear and tear because it
takes an extended time for arc discharge that occurs when first contact 6 is opened to
extinguish. According to the third embodiment, it is possible to prevent the extension
of the duration of the arc discharge that occurs when first contact 6 is opened.

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[0062] Fourth Embodiment
Fig. 6 illustrates a main part of a second contact 18#A according to a fourth
embodiment. Referring to Fig. 6, the difference is that second contact 18 is replaced
by second contact 18#A. The configuration is otherwise the same as those of the
5 other embodiments.
[0063] Second contact 18#A is formed in a U-shape.
Specifically, second contact 18#A includes a plurality of fixed contactors, and a
plurality of movable contactors provided to correspond to the plurality of fixed
contactors, respectively.
10 [0064] As an example, second contact 18#A includes fixed contactors 30A, 30B and
movable contactors 32A, 32B. Second contact 18#A is formed of pairs of fixed
contacts and movable contacts, where the plurality of fixed contacts and movable
contacts are connected in series.
[0065] When the circuit having second contact 18#A is energized, second contact
15 18#A is almost simultaneously opened. The pairs of contacts included in second
contact 18#A may be more than two pairs in series.
[0066] Arc runners 28A and 28B are also provided to correspond to fixed contactors
30A and 30B, respectively. Arc runners 24A and 24B are also provided to correspond
to movable contactors 32A and 32B, respectively.
20 [0067] With the configuration according to the fourth embodiment, when second
contact 18#A having the plurality of pairs of contacts is opened, a plurality of arc
discharges occur from the respective pairs of contacts.
[0068] The plurality of arc discharges are driven toward discharge switch 12 by an
electromagnetic force.
25 Discharge switch 12 is connected to arc runners 24A, 24B and arc runners 28A,
28B, and the driven arc discharges are driven and extended toward the tips of arc
runners 24A, 24B and arc runners 28A, 28B.
[0069] The arc discharges that occur between arc runners 24A, 24B and arc runners

14
28A, 28B increase in discharge resistance with the extension of the arc discharges, and
the current is suppressed.
[0070] In this case, an electrode drop voltage also increases with the number of arc
discharges that occur. Thus, the effect of limiting the circuit current can be enhanced.
5 [0071] An arc-extinguishing member may be provided between arc runner 24A and arc
runner 28A, and an arc-extinguishing member may be provided between arc runner
24B and arc runner 28B.
[0072] Fig. 7 illustrates a main part of a commutation unit 10C according to a
modification of the fourth embodiment. Referring to Fig. 7, the difference from
10 commutation unit 10 is that second contact 18 is replaced by a second contact 18#B.
Second contact 18#B is linearly formed instead of in a U-shape.
[0073] Specifically, second contact 18#B includes a plurality of fixed contactors, and a
plurality of movable contactors provided to correspond to the plurality of fixed
contactors, respectively.
15 [0074] As an example, second contact 18#B includes fixed contactors 30A, 30B and
movable contactors 32A, 32B. Second contact 18#B is formed of pairs of fixed
contacts and movable contacts, where the plurality of fixed contacts and movable
contacts are connected in series. Movable contactors 32A and 32B are pressed against
fixed contactors 30A and 30B, respectively, by contact pressure springs 20A and 20B.
20 [0075] When the circuit having second contact 18#B is energized, second contact 18#B
is almost simultaneously opened. The pairs of contacts included in second contact
18#B may be more than two pairs in series.
[0076] As an example, fixed contactor 30A is disposed on the right side, and fixed
contactor 30B is disposed on the left side.
25 Arc runners 28A and 28B are provided to correspond to fixed contactors 30A
and 30B, respectively. Arc runners 24A and 24B are also provided to correspond to
movable contactors 32A and 32B, respectively.
[0077] An arc-extinguishing member 26A is provided between arc runner 24A and arc

15
runner 28A. An arc-extinguishing member 26B is provided between arc runner 24B
and arc runner 28B.
[0078] With the configuration according to the modification of the fourth embodiment,
when second contact 18#B having the plurality of pairs of contacts is opened, a
5 plurality of arc discharges occur from the respective pairs of contacts. The plurality of
arc discharges are driven toward discharge switch 12 by an electromagnetic force.
Discharge switch 12 is connected to arc runners 24A, 24B and arc runners 28A, 28B,
and the driven arc discharges are driven and extended toward the tips of arc runners
24A, 24B and arc runners 28A, 28B. The arc discharges that occur between arc
10 runners 24A, 24B and arc runners 28A, 28B increase in discharge resistance with the
extension of the arc discharges, and the current is suppressed. In this case, an
electrode drop voltage also increases with the number of arc discharges that occur.
Thus, the effect of limiting the circuit current can be enhanced.
[0079] Fifth Embodiment
15 A method for stabilizing the control of current commutation from first contact 6
to commutation unit 10 is described in a fifth embodiment.
[0080] Fig. 8 is a circuit configuration diagram of a switching device 1A according to
the fifth embodiment. Referring to Fig. 8, switching device 1A is different from
switching device 1 in that first contact 6 is replaced by a first contact 6A.
20 [0081] First contact 6A has two pairs of contacts arranged in series. The pairs of
contacts are not limited to two pairs in series, and first contact 6A may include any
number of pairs of contacts in series greater than the number of pairs of contacts in
series of second contact 18.
[0082] With the configuration according to the fifth embodiment, even in the case
25 where second contact 18 is opened before the current transfer from first contact 6A
having the plurality of pairs of contacts to commutation unit 10 is completed, an
electrode drop voltage generated on first contact 6A having the plurality of pairs of
contacts is always higher than an electrode drop voltage generated on second contact 18.

16
It is thus possible to suppress a reduction in speed of the current commutation from first
contact 6A having the plurality of pairs of contacts to commutation unit 10, to perform
stable commutation control. Therefore, the duration of arc discharge that occurs when
first contact 6A is opened can be shortened, and wear and tear of first contact 6A can be
5 suppressed.
[0083] Further, it is possible to reduce a difference in time from the opening of first
contact 6A having the plurality of pairs of contacts and the opening of second contact
18, to stably perform the commutation control due to the difference between the
electrode drop voltages even when both of the contacts are almost simultaneously
10 opened. It is thus possible to more quickly transfer the current from second contact 18
to discharge switch 12, and quickly increase the discharge resistance to thereby
promptly limit the circuit current immediately after the occurrence of an abnormality.
[0084] Fig. 9 is a circuit configuration diagram of a switching device 1B according to a
modification of the fifth embodiment. Referring to Fig. 9, switching device 1B is
15 different from switching device 1 in that first contact 6 is replaced by a first contact 6B.
[0085] First contact 6B has a plurality of pairs of contacts provided in parallel. The
pairs of contacts are not limited to two pairs in parallel, and more contacts may be
provided in parallel.
[0086] Note that a plurality of movable electrodes each having a contact may be
20 provided so that a plurality of contact points can be opened/closed, or a single movable
electrode may be provided with a contact in a shape having a plurality of contact points.
[0087] In the configuration according to the modification of the fifth embodiment, the
contact resistance at a contact point is inversely proportional to the square root of a
contact pressure load according to the Holm method. It is thus possible to provide a
25 plurality of contact points to distribute and arrange the load for each contact point, to
thereby suppressing the contact resistance to a low level.
[0088] It is also possible to open the plurality of contact points at different timings, to
thereby limit the locations where arc discharges occur upon the opening.

17
[0089] Therefore, it is also possible to provide the following features by devising the
material, shape and the like of the last contact to be opened. For example, by
employing a high-melting-point material for the last contact to be opened, melting
damage upon occurrence of arc discharge can be reduced, and deterioration upon
5 opening/closing of first contact 6B can be prevented. By limiting the facing area of
the pair of contacts to a small area at the last contact to be opened, the cross-sectional
area of arc discharge can be reduced to a small area, and the drop voltage generated on
first contact 6B can thereby further increased upon opening of the contact. The
control of current commutation from first contact 6B to commutation unit 10 can also
10 be stabilized.
[0090] In the present disclosure, the embodiments can be partially or wholly combined
in any way, or the embodiments can be modified or omitted as appropriate, within the
scope of the disclosure.
[0091] The configurations illustrated as the embodiments described above are
15 exemplary configurations of the present disclosure, and the configurations can be
combined with other known techniques, or can be modified by being omitted partially,
for example, without going beyond the scope of the present disclosure. Moreover,
each embodiment described above may be implemented by appropriately introducing,
into the embodiment, processes and configurations described in other embodiments.
20 [0092] It should be understood that the embodiments disclosed herein are illustrative
and non-restrictive in every respect. The scope of the present disclosure is defined by
the terms of the claims rather than the description above, and is intended to include any
modifications within the scope and meaning equivalent to the terms of the claims.
REFERENCE SIGNS LIST
25 [0093] 1, 1A, 1B switching device; 2, 2A, 2B current-limiting resistor; 3 resistor
connection conductor; 4 fault detection unit; 5A conductor; 5B, 20, 20A, 20B contact
pressure spring; 6, 6A, 6B first contact; 7, 22 enclosure; 10, 10A, 10B, 10C
commutation unit; 12 discharge switch; 14 discharge resistor; 16, 16A opening

18
operation unit; 18 second contact; 21 spring force accumulation component; 23 contact
pressure adjustment mechanism; 24, 24A, 24B, 28, 28A, 28B arc runner; 26, 26A, 26B
arc-extinguishing member; 30, 30A, 30B fixed contactor; 32, 32A, 32B movable
contactor.

We Claim:
[Claim 1] A switching device comprising:
a first contact;
5 a second contact provided in parallel with the first contact;
a discharge switch provided in parallel with the second contact and energized
only when discharge occurs; and
a fault detection unit to perform an operation of opening the first contact when a
fault is detected, wherein
10 the discharge switch has a function of increasing resistance, and
the second contact is opened when energized, and discharge that occurs when
the second contact is opened is driven to the discharge switch, whereby a currentcarrying path is switched from the second contact to a circuit having the discharge
switch.
15
[Claim 2] The switching device according to claim 1, wherein
the second contact is formed of a pair of elongate current-carrying electrodes
facing each other, and includes a fixed contactor having a fixed contact, and a movable
contactor having a movable contact that is brought into and out of contact with the
20 fixed contact,
when the second contact is energized due to an operation of opening the first
contact, the movable contact is separated from the fixed contact by an electromagnetic
force generated by a flow of currents in opposite directions through the pair of currentcarrying electrodes, and
25 the discharge switch is formed between the movable contact and the fixed
contact that are separated,
the switching device further comprising:
a first arc runner electrically connected to the fixed contactor for driving, by an

20
electromagnetic force, arc discharge that occurs when the second contact is opened; and
a second arc runner electrically connected to the movable contactor.
[Claim 3] The switching device according to claim 2, further comprising an
5 arc-extinguishing member between the first arc runner and the second arc runner.
[Claim 4] The switching device according to claim 1 or 2, further comprising:
a current-limiting resistor provided in parallel with the first contact and the
second contact; and
10 an opening operation unit connected in series with the current-limiting resistor
for maintaining opening of the second contact while the second contact is energized
after being opened.
[Claim 5] The switching device according to claim 4, wherein
15 the opening operation unit is formed of a single coil or a plurality of coils, and
performs an operation of opening the second contact by using a magnetic flux
generated by the coil or coils.
[Claim 6] The switching device according to claim 4, wherein
20 the opening operation unit is formed of an electromagnet including a plurality
of cores, and performs an operation of opening the second contact by using an
attraction force generated between the cores.
[Claim 7] The switching device according to claim 4, wherein
25 the opening operation unit is provided to be able to receive an externally
supplied current command, and
the opening operation unit performs an operation of opening the second contact
in accordance with the external current command.

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[Claim 8] The switching device according to any one of claims 1 to 7, further
comprising:
a pressing spring for pressing the movable contactor against the fixed contactor;
5 and
a contact pressure adjustment mechanism to adjust a contact pressure of the
pressing spring.
[Claim 9] The switching device according to any one of claims 1 to 8,
10 wherein
the second contact includes
a plurality of fixed contactors, and
a plurality of movable contactors provided to correspond to the plurality
of fixed contactors, respectively.
15
[Claim 10] The switching device according to claim 9, wherein
the plurality of fixed contactors and the plurality of movable contactors are
provided in series.
20 [Claim 11] The switching device according to any one of claims 1 to 10,
wherein
the first contact has a plurality of contact points, and
the first contact has more contact points than the second contact.
25

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[Claim 12] The switching device according to claim 11, wherein
the plurality of contact points of the first contact are provided in parallel