TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to contacts for switching devices used in the protection
of electrical equipment against high current discharges and/or overload events, such
as electromagnetic contactors and relays, and more specifically, to a system of contacts
that compensates for the repulsive Holm forces generated between contacts and to switching
devices comprising the contact system.
BACKGROUND OF THE INVENTION
[0002] Electromagnetic switching devices, such as relays and contactors, are commonly used
in association with power equipment and circuits of industrial plants for protecting
such equipment from overloads and/or high current discharges. In particular, recent
developments towards more powerful power equipment, such as batteries for electrical
vehicles, led to a demand for relays and/or contactors capable of providing reliable
protection against high current discharges, for e.g. in the order of 15000 Ampere
(15 kA) or higher.
[0003] Conventional relays and contactors are commonly switched between closed and open
states via contact systems that are operated to connect/disconnect a load to/from
a power source. Therefore, the switching reliability of such relays and contactors
is closely related with the underlying system of switching contacts. In general, common
contact systems include a stationary contact, which is fixed to the relay or contactor
body, and a movable contact which can be moved with respect to the stationary contact
for switching the contact system (and the relay or contactor) between open and closed
states. Under normal operating conditions (i.e. in the absence of overloads and/or
high discharge currents) the stationary and movable contacts are maintained in mechanical
contact by the contact forces generated with an internal magnet or electromagnetic
coil of a magnetic driving system included in the relay or contactor. In case of an
overcurrent event, the internal magnet or electromagnetic coil is de-energized and
the contact system opens.
[0004] However, it is a well-known phenomenon that the current across the stationary and
movable contacts generates repulsive forces, often referred to as Holm forces, which
tend to pull the contacts apart. At currents above a certain level, the repulsive
Holm forces become stronger than the total contact force that keeps the contact system
closed and will force the contact system to open. Thus, the current level above which
the contact system opens depends on the interplay between the total attractive contact
force, which includes the force applied by the internal magnetic coil, and the intensity
of the repulsive forces generated by the intensity of the discharge current across
the contacts.
[0005] In addition, as the generated repulsive forces increase with the intensity of the
current flowing across the closed contacts, the speed with which the moving and stationary
contacts are pulled apart also increases with the discharge current. This effect increases
the contact system responsivity but may result in the moving and stationary contacts
being so strongly pulled apart at high discharge currents that the contact system
will be partially or totally destroyed. As a result, the relay or contactor will become
inoperable for interrupting future overload events and require replacement. In particular,
the Holms force can be very strong at high current discharges of 15 kA or higher.
This problem requires that contact forces need to be increased to prevent that the
contact system and respective relay or contact collapses under high overcurrent conditions.
[0006] The negative effect of the repulsive Holm forces on the contact system reliability
could be counteracted by increasing the coil of the internal magnetic driving system
so as to generate contact forces sufficiently strong to compensate the repulsive Holm
forces at high currents. However, stronger coil motors are expensive and occupy a
large volume. Furthermore, the power consumed by the internal coil would increase
significantly in order to produce a contact force capable of compensating the repulsive
forces generated at discharge currents of 15 kA or higher. Thus, the compensation
of repulsive forces via an increase of the contact force generated by the internal
coil is not an adequate solution for many applications which require contactors and/or
relays of compact size and reduced energy consumption.
[0007] Consequently, there is a need for contact systems and switching devices capable of
providing protection against high current discharges, in particular at currents of
the order of 15 kA or higher, in a reliable manner and without compromising the compactness
of the switching devices.
SUMMARY OF THE INVENTION
[0008] The present invention has been made in view of the shortcomings and disadvantages
of the prior art, and an object thereof is to provide contact systems, and switching
devices comprising the same, that are capable of withstanding high current discharges
and having a compact size.
[0009] This object is solved by the subject matter of the independent claims. Particular
embodiments of the present invention are subject matter of the dependent claims.
[0010] The present invention follows from recognizing that, in order for an electromagnetic
contactor and/or relay to survive the pulling effect of the repulsive Holm forces
generated at high current discharge events, e.g. of 15 kA or higher, additional attractive
forces between contacts needs to be generated, i.e. aside from the attractive contact
force generated by the internal magnetic driving system for maintaining the contacts
closed under normal operating conditions.
[0011] The concept underlying the solution provided by the present invention lies in counteracting
the repulsive Holm forces generated with an attractive Lorenz force which is produced
between the stationary and movable contacts using the overcurrent itself. More specifically,
the contact system provided by the present invention is so configured that the current
received by one of the contacts is made to recirculate in the other contact along
a specific path that makes the circulated current to be transported in a final section,
at close proximity and in the same direction, as in the receiving contact. As a result,
an attractive Lorentz force can be generated between contacts using the overcurrent
itself and which is proportional to the intensity of the recirculated current. This
attractive force supplements the contact force produced by the internal magnetic coil
and allows to achieve an effective balance between the Holm repulsive force and the
total attractive forces applied to the contacts.
[0012] As a result, the present invention allows producing smaller relays that can withstand
a very high current discharge without collapsing. Namely, the present invention allows
to fulfil the technical requirement of relays capable of providing a reliable overcurrent
protection for current discharges of 15kA and able to meet future increases in overcurrent
specifications.
[0013] Furthermore, the present invention also allows to counter-act the repulsive Holm
forces based on a self-compensating effect that is produced by an unbalance of the
currents that flow across the contact points between the stationary and movable contacts
when the contact system is closed and which becomes particularly important for stationary
and movable contacts having a compact size and a three-contact points geometry.
[0014] According to the present invention, it is provided a contact system for a switching
device, comprising: a first contact adapted to receive an input current supplied to
an input terminal of the contact system; and a second contact adapted to receive the
input current from the first contact; wherein the first contact comprises an input
conductive section configured to provide an incoming current path for transporting
the input current, wherein the second contact comprises a plurality of second conductive
sections configured to provide an outgoing current path for transporting the current
received from the first contact towards an output terminal when the contact system
is in a closed state, and wherein one of the plurality of second conductive sections
is arranged adjacent to the input conductive section to provide an output conductive
section in which current received by the second contact from the first contact is
transported in the same direction as the current direction along the incoming current
path in the input conductive section.
[0015] According to a further development, the output conductive section is substantially
parallel to the input conductive section, and/or the plurality of second conductive
sections are arranged in a same plane which is substantially parallel to the input
conductive section.
[0016] According to a further development, the output conductive section is disposed adjacent
the input conductive section in a direction of a relative linear movement between
the first and second contacts.
[0017] According to a further development, the input conductive section and the output conductive
section are configured such that a section of the incoming current path defined by
the input conductive section and a section of the outgoing current path defined by
the output conductive section are substantially orthogonal or non-parallel to a direction
of a relative linear movement between the first and second contacts.
[0018] According to a further development, the input conductive section and the output conductive
section have respective shapes that extend in a longitudinal direction of the incoming
current path by at least a predetermined length at which an attractive Lorentz force
between the input and output conductive sections compensates the repulsive Holm's
force generated between the first and second contacts at a given intensity of input
current, and preferably for an input current density of 15 kA or higher, wherein said
longitudinal direction is substantially orthogonal or at least non-parallel to a direction
of a relative linear movement between the first and second contacts.
[0019] According to a further development, the first contact further includes one or more
interconnection branches which extend away from the input conductive section by a
predetermined length so as to pass at least part of the input current from the input
conductive section to one of the second conductive sections of the second contact
other than the output conductive section, and wherein said second conductive section
other than the output conductive section forms a recirculation conductive section
configured to define a portion of the outgoing current path along which the current
received from the one or more interconnection branches of the first contact is recirculated
towards the output conductive section.
[0020] According to a further development, the recirculation conductive section is shaped
with an extended section that is arranged substantially parallel to and opposed to
the output conductive section.
[0021] According to a further development, the second contact includes a plurality of second
contact islands arranged thereon in number and positions corresponding to a plurality
of first contact islands arranged on the first contact the first and second contact
islands providing a plurality of contact pairs via which electrical contact between
the first and second contacts is established when the contact assembly is in the closed
state; wherein at least one of the second contact islands is provided on said recirculation
conductive section of the second contact at a respective position for electrically
contacting to a corresponding first contact island provided in the interconnection
branch of the first contact when the contact system is in the closed state; and/or
wherein at least one of the second contact islands is provided on said output conductive
section at a respective position for electrically contacting a corresponding first
contact island provided on a central region of the input conductive section of the
first contact when the contact system is in the closed state.
[0022] According to a further development, the second contact islands are provided in a
number of three and each arranged in a position corresponding a position of a respective
one of three first contact islands provided in the first contact,
wherein a single second contact island is arranged on said output conductive section
at a respective position for electrically contacting to a first contact island provided
in the input conductive section of the first contact, and
wherein a pair of the second contact islands is arranged at a central area of said
recirculation conductive section of the second contact, a corresponding first contact
island being arranged at an end portion of said one or more interconnection branches
of the first contact so that the outgoing current paths for currents received by the
recirculation conductive section of the second contact via said pair of second contact
islands includes two half-loops that direct the received current towards the output
conductive section.
[0023] According to a further development, the single first contact island is arranged on
said input conductive section and positioned with its center at a first predetermined
distance (d) from a center axis (C) of the first contact, the pair of first contact
islands is arranged on an end portion of the interconnection branch, each first contact
island of the pair being positioned in a symmetric manner with respect to a mirror
plane, which contains the center axis (C) and the center of the first contact island
arranged on said input conductive section, and such that a projection of their respective
centers onto said mirror plane is distant by a second predetermined distance (d
B) from the center axis (C), and wherein the first and second predetermined distances
(d
A, d
B) are the same and/or selected based on a width of the input conductive section and
a width of the interconnection branch in a direction transverse to the center axis
(C) so as to achieve an asymmetry on the distribution of currents paths along the
first contact that results in a current imbalance of up to a predetermined imbalance
threshold between the current passing from the first contact to the second contact
across the single first contact island on the input conductive section and the currents
passing from the first contact to the second contact across each of the first contact
islands arranged on the interconnection branch, respectively.
[0024] According to a further development, the plurality of second conductive sections are
configured to form the second contact with a closed loop geometry. The geometries
of the first and second contacts are configured such that the interconnection branch
of the first contact extends from a central region of the input conductive section
along a direction transverse to a longitudinal length of the input conductive section
and the center axis (C) to overlap said recirculation conductive section of the second
contact, wherein the geometry of the first contact further includes two input end
sections at respective end portions of the input conductive section to feed the input
current to said input conductive section and which extend in a direction transverse
to the longitudinal length of the input conductive section and the center axis (C),
and wherein the input conductive section further includes two intermediate sections,
one at each side of said central region and through which the current received from
the input end section at the respective side is passed to the central region and/or
the interconnection branch of the first contact, wherein the width and the position
of each of said intermediate sections in the direction transverse to the longitudinal
length of the input conductive section and the center axis is selected in combination
with the position of the first contact islands arranged on the first contact so as
to achieve an asymmetry on the distribution of currents paths along the first contact
that results in said current imbalance of up to the predetermined imbalance threshold
between the current passing from the first contact to the second contact across the
first contact island on the input conductive section and the currents passing from
the first contact to the second contact across each of the first contact islands arranged
on the interconnection branch, respectively.
[0025] According to a further development, the predetermined imbalance threshold is 80%
or below.
[0026] According to a further development, the plurality of second conductive sections is
configured to form the second contact with a closed loop geometry, the geometries
of the first and the second contacts being configured such that said interconnection
branch of the first contact is provided as a pair of protrusions that respectively
extend from a central region of the input conductive section in a direction transverse
to a longitudinal length of the input conductive section to make electrical contact
with the intermediate section of the second contact (220) and split the outgoing current
paths in two half-loops between the intermediate section and the output terminal of
the second contact.
[0027] According to a further development, the plurality of second conductive sections are
configured to form the second contact with an open loop shape, the first and second
contacts being configured such that the interconnection branch of the first contact
is provided at an end section of the input conductive section to make electrical contact
with said second conductive section other than the output conductive section at an
end section of the open loop shape by a gap.
[0028] The present invention also provides a switching device for high current discharges,
comprising the contact system and a magnetic driving system adapted to operate switching
of the contact system between a closed state, at which the first and second contacts
contact each other, and an open state at which the second contact is separated from
the first contact.
[0029] According to a further development, the switching device is one of a electromagnetic
relay and an electromagnetic contactor.
[0030] Thus, the present invention lies makes possible dealing with overcurrent protection
without increasing the power consumed by the magnetic driving system. Further, as
the additional attractive Lorentz forces are produced proportionally to the overcurrent
intensity, an effective compensation of the repulsive forces can be reached at all
times.
[0031] Further technical advantages of the present invention are an increase of shock resistance
due to the additional attraction between contacts. This also results in an increased
contact force and consequently, reduced contact resistance.
[0032] The accompanying drawings are incorporated into and form a part of the specification
for the purpose of explaining the principles of the invention. The drawings are not
to be construed as limiting the invention to only the illustrated and described examples
of how the invention can be made and used.
BRIEF DESCRIPTION OF THE FIGURES
[0033] Further features and advantages will become apparent from the following and more
detailed description of the invention as illustrated in the accompanying drawings,
in which:
Fig. 1 is a schematic view of a switching device with a contact system according to the
first embodiment of the present invention;
Fig. 2 is a schematic view of the contact system according to the first embodiment;
Fig. 3 is a further schematic view of the contact system shown in Fig. 2;
Fig. 4 is a schematic view showing first and second contacts of the contact system shown
in Fig. 2, in an open state;
Fig. 5 is a schematic view of the first and second contacts of the contact system shown
in Fig. 2, in a closed state, and showing the direction of current circulation in
the first and second contacts as indicated by the arrows, in which the solid arrows
and the dashed arrows illustrate the direction of the current circulation in the first
contact and in the second contact, respectively;
Fig. 6 is a schematic view of a contact system according to a second embodiment of the present
invention and where the direction of the current circulation in the first and second
contacts of the contact system are illustrated by solid and dashed arrows, respectively;
Fig. 7 is a perspective view of a switching device having a contact system according to
the third embodiment of the present invention (viewed from a top side which is the
side of the input and output terminals of the contact system);
Fig. 8 is another perspective view of the switching device shown in Fig. 8 (viewed from
a bottom side which the side of the terminals of an actuation coil of the contact
system);
Fig. 9 is a perspective view (partially see-through) of the contact system according the
third embodiment (viewed from a side of a driving shaft coupled to the contact system);
Fig. 10 is a simplified perspective view of the contact system shown in Fig. 9 in an open
state;
Fig. 11 is a simplified side view of the contact system shown in Fig. 10 in the open state;
Fig. 12 is a simplified side view of the contact system shown in Fig. 10 in the closed state;
Fig. 13 is a perspective view of the contact system having a stationary contact and a movable
contact according to the third embodiment (showing a top side of the contact system);
Fig. 14 is a bottom view of the movable contact and stationary contact shown in Fig. 13;
Fig. 15 is a top view of the stationary contact and movable contact shown in Fig. 13;
Fig. 16 is a perspective (see-through) view of the contact system shown in Fig. 13 that depicts
the arrangement of contact islands on the stationary and movable contacts;
Fig. 17 is a perspective view of the movable contact shown in Fig. 16 (viewed from a side
that faces the stationary contact in Fig. 16) and depicts in a simplified manner the
direction of current flow in the movable contact;
Fig. 18 is a perspective view of the stationary contact shown in Fig. 16 (viewed from a side
that faces the movable contact in Fig. 16) and depicts in a simplified manner the
direction of current flow in the stationary contact;
Fig. 19 is a simplified side view of the contact system shown in Fig. 13 in the closed state
and showing schematically the forces applied to the movable contact at a first stage
where the contact island at side A is crossed by a higher current than each of the
contact islands at side B, thereby causing an imbalance of the repulsive Holm's forces
generated at sides A and B which is responsible for a stronger levitating effect at
side A than at side B (without opening the contact system), and consequently, leads
to a decrease of the contacts resistance at side B and an increase of the contact
resistance of the contact island at side A; and
Fig. 20 shows the contact system at a second stage, subsequent to the first stage shown in
Fig. 19, and in which the currents crossing each contact island at side B having increased
due to the decrease of the contacts resistance at side B during the first stage, thereby
causing an imbalance of the repulsive Holm's forces generated at sides A and B which
is responsible for a stronger levitating effect at side B than at side A (without
opening the contact system).
DETAILED DESCRIPTION OF THE INVENTION
[0034] The present invention will now be more fully described hereinafter with reference
to the accompanying drawings, in which exemplary embodiments of the invention are
shown. The present invention may, however, be embodied in many different forms and
should not be construed as limited to the embodiments set forth herein. Rather, these
embodiments are provided so that the disclosure will be thorough and complete, and
will fully convey the scope of the invention to those skilled in the art. Like numbers
refer to like elements throughout.
[0035] Fig. 1 shows a switching device 100 having a contact system 200 according to a first
embodiment and a magnetic driving system 300 for driving the contact system 200.
[0036] The contact system 200 comprises first and second contacts 210, 220 which function
as power contacts for connecting to a load (not shown), such as an electrical equipment
(e.g. an automobile battery) or industrial equipment to be protected from high current
discharges. The first and second contacts 210, 220 have a configuration that makes
possible to generate an add-on Lorentz force between contacts by making the current
input to the first contact 210 to flow over a circulating current path in the second
contact 220, as it will be described below. The magnetic system 300 carries energizing
terminals and an electromagnetic coil 320 which provides a contact force for maintaining
the first and second contacts 210, 220 closed under normal operating conditions. In
the present configuration, the contacts 210, 220 are of a normally-open contact type,
so that they supply power to the load when the electromagnetic coil 320 is energized
(closed state) and shut off the power supply to the load when the electromagnetic
coil 320 is de-energized (open state).
[0037] The switching between open and closed states of the contact system 220 is associated
with the first and second contacts 210, 220 being moved away from and towards each
other, respectively, along a linear movement direction, for e.g. parallel to the Y-axis
indicated in Fig. 2. In particular, the contact system 200 is so designed that, in
operation, the second contact 220 remains fixed to an output terminal of the load
(not shown) via a conductive protrusion 221 provided for this effect in the second
contact 220 (stationary contact). On the other hand, the first contact 210 is configured
to move towards to and away from the stationary contact 220 in the direction parallel
to the Y-axis to close and open the contact system 200. For this purpose, the first
contact 210 (hereinafter referred to as movable contact 210) is mounted on a support
structure 230 which allows the linear displacement of the movable contact 210 along
the Y-axis direction. More specifically, the support structure 230 includes a rigid
shell 232 configured to accommodate both the stationary and the movable contacts 220,
210 inside. The rigid shell 232 is preferably made of an electrically conductive material
and may be provided with a through-hole 234, for e.g. on a top side 236, for connecting
a screw or plug of an input terminal of a load (not shown). The rigid shell 232 may
also serve the function of protecting the stationary and the movable contacts 220,
210 from the external environment and of preventing obstructions to the displacement
of the movable contact 210. The rigid shell 232 is preferably provided with appropriate
openings for connecting the terminal protrusion 221 of the stationary contact 220
to an output terminal of the load. Additional openings may also be provided on the
rigid shell, e.g. for facilitating heat dissipation from all sides, such as shown
in Fig. 2.
[0038] In the configuration shown in Figs. 1 - 4, the support structure 230 is designed
to be mounted with a bottom side 237 (opposed to the top side 236) onto the magnetic
coil system 300. The electrical connection of the movable contact 220 to the support
structure 230 is also preferably provided on the bottom side 237. For instance, a
pair of flexible terminals 238, 239, such as conductive braids, may be arranged on
opposed locations of the structure bottom side 237 for electrically connecting the
two opposite end sections 212, 214 of the movable contact 210 to the support structure
230. The current entry points at opposed locations of the movable contact 210 helps
to reduce the current resistance and the sectional size. Further, the flexibility
of the conductive braids 238, 239 allows a vertical displacement of the movable contact
210 within the shell 232 for switching the contact system 200 between closed and open
states, while maintaining electrical contact of the movable contact 210 with the support
structure 230 and consequently, with the input terminal of the load.
[0039] The contact system 200 is configured to recirculate the overcurrent received from
one of the contacts, e.g. the movable contact 210, along an outgoing current path
in the other contact, e.g. the stationary contact 220, that becomes sufficiently close
and parallel to the incoming current path at a final section (close to the output
terminal) such that current is transported in the same direction as in the incoming
current path, and consequently, an additional attractive Lorenz forces is produced.
Thus, the contact force produced by the electromagnetic coil 320 to maintain the contact
system 200 closed is automatically supplemented with an additional attractive force
produced by the overcurrent itself and which is proportional to the intensity of the
recirculated overcurrent. Moreover, as the attractive Lorentz force arises only when
current flows along nearby paths and in the same direction, the distance between the
stationary and movable contacts 210, 220 and relative sizes are selected or adjusted
according to the particular application for the contactor or relay so as to produce
an attractive force of a suitable intensity for compensating the repulsive Holm forces
generated at the overcurrent of interest. For instance, the additional Lorentz force
can be increased by increasing the length of the contacts 210, 220 in the direction
X. i.e. the overlapping length of the parallel current paths in the contacts 210,
220.
[0040] Thus, the contact system 200 is designed so as to achieved such a compensation of
the repulsive Holm forces. More specifically, the movable and stationary contacts
210, 220 have shapes and are placed in an arrangement that allow for an effective
force balance between the Holms repulsive force generated by the flow of current through
the contacts, the contact force generated by the electromagnetic coil 320 and the
additional Lorentz force at high discharge currents, such as 15 kA or higher.
[0041] Figs. 4-5 shows the movable and stationary contacts 210, 220 of the contact system
200 shown in Figs. 2 - 3 without the support structure 230 and viewed from a lower
side, which is the side facing the magnetic driving system 300. As described above,
the movable contact 210 receives the input current from the braids 238, 230 at the
end sections 211, 212 and comprises an input conductive section 213 (between end sections
211, 212) that defines an incoming current path for transporting the input current
along the movable contact 210. The input conductive section 213 is preferably designed
with the shape of a bar that extends in a longitudinal direction.
[0042] The stationary contact 220 includes a plurality of second conductive sections 222,
224, which are disposed with respect to one another such as to define an outgoing
current path along the stationary contact 220, in which the current received from
the movable contact 210 is recirculated towards the output terminal 226, i.e. the
received current is firstly transported in a section away from the input conductive
section 213 of the movable contact 210 and then directed towards a section close to
the input conductive section 213. More specifically, the stationary contact 220 is
shaped such that one of the plurality of second conductive sections, i.e. the conductive
section 222 (output conductive section) close to the output terminal 226, is arranged
adjacent to the input conductive section 213 of the movable contact 210 to transport
the current received from the other second conductive sections of the stationary contact
in substantially the same direction as the current direction in the incoming current
path defined by the input conductive section 213. As a result, any current passing
across the closed contact system 200 generates an additional attractive Lorenz between
the output and input conductive sections 222, 213.
[0043] In particular, the output conductive section 222 is preferably shaped and oriented
with respect to the input conductive section 213 of the movable contact 210 so that
the incoming current path in the input conductive section 213 and/or the section of
the outgoing current path defined by the output conductive section 222 are substantially
orthogonal, or at least non-parallel, to the direction of movement of the movable
contact 210 (as indicated in upward arrow in Fig. 4). This geometry and arrangement
allows to achieve maximum compensation of the repulsive Holm effect for a given current
intensity, since Lorenz forces are maximized for currents flowing in the same direction
along parallel paths.
[0044] In addition, the output conductive section 222 is preferably disposed adjacent to
the input conductive section 213 in the direction of the relative linear movement
between the movable and the stationary contacts 210, 220, i.e. at a certain separation
distance along the Y-direction and overlapping the input conductive section 213 so
that the attractive Lorentz force generated by the currents flowing in the adjacent
parallel paths (which is maximum in the direction orthogonal to the parallel paths)
is predominantly oriented in the direction of the relative movement between the movable
and the stationary contacts 210, 220. The stationary contact 220 is preferably shaped
with a planar structure and oriented so that the remaining second conductive sections
are arranged in substantially the same plane as the output conductive section 222.
This planar structure and arrangement simplifies the overall geometry and increases
mechanical stability of the contact system 200.
[0045] As shown in Figs. 4-5, the input and output conductive sections 213, 222 have respective
shapes that extend in a longitudinal direction of the incoming current path by at
least a predetermined length L.
[0046] The movable contact 210 may include an interconnection branch 216 through which the
input current is transferred from the input conductive section 213 to the stationary
contact 220. In this case, the interconnection branch 216 is provided with a length
suitable to contact a conductive sections of the stationary contact 220 other than
the output conductive section 222, preferably to an opposite conductive section 224,
to ensure the desired recirculation of current along the stationary contact 220. As
shown in Figs. 4-5, this opposed conductive section is shaped so as to define a recirculation
conductive section 224 along which the current received from the interconnection branch
216 of the movable contact 210 is directed along a semi-loop section of the outgoing
current path towards the output conductive section 222 and output terminal 226 of
the stationary contact 220. The recirculation conductive section 224 is preferably
shaped with an extended section substantially parallel to the output conductive section
222 and arranged at a predetermined separation therefrom.
[0047] In the configuration of the contact assembly 200 shown in Figs. 4-5, the plurality
of second conductive sections forming the stationary contact 220, which include the
output conductive section 222 and the recirculation conductive section 224, are shaped
and arranged such that the stationary contact 220 has the shape of a closed loop.
In this configuration, the interconnection branch 216 of the movable contact 210 is
preferably provided at an intermediate section of the input conductive section 213
and makes electrical contact with the recirculation conductive section 224 at a respective
intermediate section of the closed loop shape. In particular, the interconnection
branch 216 of the movable contact 210 may be provided as a pair of parallel protrusions
or branches extending from the input conductive section 213, in a direction perpendicular
to the longitudinal direction, which make electrical contact with the intermediate
section 227 of the stationary contact 220 at adjacent positions for splitting the
outgoing current path in the stationary contact 220 into two half-loops between the
intermediate section 227 and the output terminal 226.
[0048] As mentioned above, the additional Lorentz force can be increased by increasing the
length of the contacts 210, 220 in the longitudinal direction (X-axis in Fig. 4),
and therefore, increase the overlapping length of the parallel current paths in the
input and output conductive sections 213, 222. In order to generate an attractive
Lorentz force capable of compensating the repulsive Holm force between the contacts
210, 220 at a given intensity of discharge current, the shape and dimensions of the
contacts 210, 220, including the dimensions of input and output conductive sections
213, 222, may be determined by experimentation and/or using simulation methods known
in the technical field and based on parameters required for an intended application
of the contact system 200 and switching device 100, such as discharge current to be
withstand by the contacts 210, 220, contact force generated by the internal coil 320,
materials and overall dimensions of the contact system 200 and switching device 100,
including the geometry and cross-section of the contacts 210, 220 which has impact
in the contact resistance. For instance, the magnetic flux density generated between
input and output conductive sections 213, 222 may be calculated for different values
of arm length, cross-section and air gap between input and output conductive sections
213, 222. As a specific example of implementation of the contact system 200 for withstanding
overcurrent of 15 KA, the stationary contact 220 may have a rectangular loop shape
dimensioned with a predetermined length L of 15 mm by a width W of 19 mm, and with
a separation gap between movable and stationary contacts of 3.9 mm. At these dimensions,
the movable contact 210 may be dimensioned with a width W2 for the input conductive
section 213 of 7 mm and an overall width W1 of 16 mm (which includes W2 and the length
of the intermediate branches 216). The length of the movable contact 210 is preferably
the same or close to the overall length of the stationary contact 220 in order to
maximize the attractive Lorentz force. For instance, the attractive force generated
with such a dimensioned contact system 200 can reach up to 40 N when a discharge current
of 15kA passes contacts 210, 220.
[0049] As shown in Fig. 4, the electrical contact between the stationary 220 and the movable
contact 210 is preferably established via one or more second contact islands 228,
which are provided in number and positions corresponding to one or more first contact
islands provided in the movable contact 210 (not shown). The first and second contact
islands 218, 228 provide the single electrical contact points between the movable
and stationary contacts 210, 220, and consequently, define the locations at which
current can entry from the movable contact 210 into the stationary contact 220. This
ensures that the current received from the movable contact 210 is transported along
the recirculation conductive section 224 and the output conductive section 222 before
exiting the output terminal 226. The second contact islands 228 may be provided as
islands of electrical conductive material which is deposited on facing sides of the
movable and stationary contacts 210, 220. The contact islands may be provided on either
the movable or stationary contacts 210, 220, which then establish direct electrical
contact with the opposed contact of the contact assembly 220. An additional contact
island may be provided to establish electrical contact between the input and output
conductive sections 213, 222, as illustrated in Fig. 4, to improve stability.
[0050] In illustrated configuration, the contact system 200 is provided with two contact
islands 228 disposed on an intermediate section 227 of the stationary contact 220,
respectively, and a contact island 219 an intermediate position of the output conductive
section 222. The contact resistance of the island 219 may be higher than offered by
the contact islands 218 for avoiding the input current to exit directly through the
contact island 219 and the output terminal 226. Thus, the current flow across the
contact system 200 is divided in three branches that pass through each of the contact
islands 218, 219. The solution can yield low resistance due to the double sided current
path in the stationary contact 220 and produce very high attractive forces to counter
the repulsive Holm force. Furthermore, the contact system 200 allows a symmetrical
force effect and is extendable to low proportional force generation or high proportional
force generation.
[0051] Fig. 6 shows a contact system 400 according to a second embodiment. The contact system
400 comprises first and second contacts 410, 420 for connecting to a load (not shown).
Similarly to the contact system 200 described above, the first and second contacts
410, 420 can be moved relative to each other along the Y-direction indicated in Fig.
6 so as to switch between closed and open states, for e.g. under operation of the
magnetic driving system 300 shown in Fig. 1. For instance, the first contact 410 can
function as the movable contact which moves with respect to a stationary, second contact
420.
[0052] In the present configuration, the first and second contacts 410, 420 have a configuration
in which the current input to the first contact 410 is transported along an input
conductive section 413 and recirculated along an outgoing current path in the second
contact 420 towards the output terminal 426.
[0053] More specifically, the second contact 420 has a plurality of second conductive sections
arranged in the form of a single, open loop shape, such as to achieve a recirculating
outgoing current path in the second contact 420. One of the second conductive sections.
The output conductive section 422, is arranged adjacent and in parallel to the input
conductive section 413 so that an attractive Lorentz force is generated by the currents
transported in the same direction in the input and output conductive sections 413,
422. In the present configuration, the first contact 410 also includes an interconnection
branch 416 to make electrical contact with an end section of an recirculation conductive
section 424 of the second contact 420. The current received from the stationary contact
420 is then recirculated along the recirculation conductive section 424 so as to enter
in the output conductive section 422 with the same direction as the current direction
in the input conductive section 413 before exiting through the output terminal 426.
Thus, the contact system 400 also allows to achieve a compensation of repulsion Holm
forces based on the same principle of recirculation of the overcurrent of the present
invention to produce additional attractive forces between the stationary and movable
contacts 420, 410.
[0054] As explained above with reference to Fig. 4, the additional Lorentz force self-generated
by the recirculation of current on the stationary contact 220 allows to counter-act
the levitation effect produced by the Holm's force at high current discharges and
may be increased by increasing the length of the movable and stationary contacts 210,
220 in the longitudinal direction (X-axis in Fig. 4) as well as the distance between
the input conductive section 213 and the recirculation conductive section 224. However,
such an increase of the counter-acting effect is upper-limited by the size constraints
imposed on contactors and relay for certain real-life applications. In particular,
a reduction of the length L and width of the stationary contact 220 for accommodating
into a contactor of smaller size will reduce the attractive Lorenz force self-produced
by current recirculation.
[0055] A switching device and a contact system according to a third embodiment of the present
invention allows to effectively counter-act the levitating effect caused by repulsive
Holm's forces generated at discharge currents of the order of 15kA or more while meeting
the requirements of compactness desired for several applications, such as batteries
for electrical vehicles, as it will be described with reference to figures 7 to 19.
[0056] Figs. 7 and 8 show perspective views of a switching device 100' having a contact
system 500 according to the third embodiment. The contact system 500 comprises a first
contact 510 and a second contact 520 for connecting the switching device 100' between
terminals of a load (not shown), such as an external electrical equipment, an electrical
circuit, an automobile battery and the like. Similarly to the first embodiment, the
contact system 500 is configured to switch between a closed circuit configuration
and an open circuit configuration under the actuation of a magnetic driving system,
such as the magnetic driving system 300 described with reference to Fig. 1. For instance,
as shown in Fig. 9, the movable contact 510 may be coupled to a driving shaft 540
which can be moved back and forth along the central axis C under the electromagnetically
actuation produced by the coil 320 of the magnetic driving system 300, as it will
be described later.
[0057] Fig. 10 shows a simplified perspective view of the contact system 500 in an open
circuit configuration ("open state"), in which the movable contact 510 and the stationary
contact 520 are separated by a gap that interrupts the flow of electric current through
the contact system 500. The movable contact 510 ("first contact") is intended to receive
a current (I
in) input to the contact system 500 and can move towards to and away from the stationary
contact 520 ("second contact") in a direction of relative movement, which is parallel
to the central axis C of the contact system 500 shown in Fig. 7. The stationary contact
520 is intended to remain fixed with respect to the switching device 100' when the
contact system 500 is coupled to the magnetic driving system 300 and is generally
used to output the current (lout) that passes through the contact system 500 to another
load terminal via an output terminal 525.
[0058] The contact system 500 also includes a support structure or frame 530 within which
both the stationary and movable contacts 510 and 520 are arranged. An input terminal
535 is provided on a top side 536 of the frame 530 for connecting the contact system
500 to the load terminal (not shown) that supplies the input current I
in to the contact system 500. The electrical contact between the movable contact 510
and the frame 530 is made via flexible stripes or braids 534 arranged on support frame
legs at the lower side 537. The support frame 530, including the flexible stripes
534, comprise good electrical conductor material(s) so that the support frame 530
transports the electrical current received from the input terminal 535 towards the
flexible stripes 534, which feed the input current I
in into the movable contact 510. The flexible stripes 534 are made of a resilient material
designed to exert a suitable pressure against the movable contact 510 and to allow
the displacement of the movable contact 510 between the open and closed states. The
flexible stripes 534 are preferably soldered or welded to input end sections 511,
512 of the movable contact 510 to ensure good electrical contact in the closed state.
The connection of the contact system 500 to the other load terminal (not shown) is
made via an output branch or output terminal 525 directly connected to the stationary
contact 520 and that protrudes to outside the frame 530. The stationary and movable
contacts 520 and 510 comprise good electrically conductive materials that can support
the current transport function of the contact system 500 at currents of the order
of 15 kA and higher, such as copper or any good electrical conductive material known
in the art. The stationary contact 520 may be mounted/fixed to the support frame 530,
for e.g. on a bar (not shown) passing transversally across the support frame 530,
and is electrically insulated from the support frame 530 by insulating elements arranged
between the support frame 530 and the stationary contact 520 as needed to ensure that
the stationary contact 520 receives the input current I
in fed to the contact system 500 from the movable contact 510 only.
[0059] As mentioned above, the movement of the movable contact 510 towards the stationary
contact 520 to close the contact system 500 may be operated by the magnetic driving
system 300, which also generates the contact force that holds the movable contact
510 in the closed position against the stationary contact 520. Specifically, the magnetic
driving system 300 inductively actuates the driving shaft 540 which is coupled/attached
to the movable contact 510 via an over-travel spring 550 arranged on a central region
555 of a bottom side surface of the movable contact 510 (which is the side facing
the magnetic driving system 300 in the switching device 100'). The driving shaft 540
extends at a right angle from the bottom side surface of the movable contact 510 and
is configured to plunge in the inner core of the coil 320 (i.e. along the central
axis C) when the contact system 500 is mounted onto the magnetic driving system 300.
Thus, when the coil 320 of the magnetic driving system 300 is energized with a suitable
current, the driving shaft 540 moves linearly along the central axis C towards the
top side 536 of the contact system 500, pressing the movable contact 510 against the
stationary contact 520. In the closed state, the electric current I
in supplied to the input terminal 535 of the contact system 500 flows from the movable
contact 510 to the stationary contact 520 to be output at the output terminal 525
(output current lout), as depicted by the direction of the arrows in Fig. 12.
[0060] When the actuation coil 320 of the magnetic driving system 300 is de-energized, the
driving shaft 540 plunges back to the coil 320, thereby separating the movable contact
510 from the stationary contact 520, as shown in Fig. 11. Further, the over-travel
spring 550 allows to bias the movable contact 510 towards the open position when the
coil 320 of the magnetic driving system 300 is not actuating on the driving shaft
540. The resultant of these forces (F
coil+spring) should be sufficient to maintain the contact system 500 closed during normal operation
and until the contact system 500 is crossed by a high discharge current at which the
repulsive Holm's forces generated between the movable and stationary contacts 510,
520 begin to play a major role in the closed state of the contact system 500.
[0061] As discussed above, the repulsive Holm's force generated between the movable and
stationary contacts at high-intensity currents, such as 15 kA and above, can cause
negative effects to the operation and reliability of the contact system and switching
device. In particular, the reduced size of the contact system 500 in comparison to
the contact system 200 of the first embodiment leads to the counter-effect achieved
by the self-generated Lorentz forces having less impact in keeping the contact system
500 closed. Thus, the generated repulsive Holm's forces may cause an abrupt separation
of the movable and stationary contacts 510 and 520 against the contact force generated
by the magnetic driving system 300 and therefore, lead to an undesired interruption
of the electrical path connected to the switching device 100'. The abrupt separation
of the movable and stationary contacts 510 and 520 at high currents may also result
in welding of contacts due to the heat generated by arc currents. Due to their relative
larger dimensions, the contact systems 200 and 400 described above can counter-act
the negative effects caused by the repulsive Holm's force by mainly relying on the
self-generated Lorenz forces to attract the stationary and movable contacts to each
other under high current discharges.
[0062] The contact system 500 of the present embodiment is specifically designed to create
an additional self-compensation effect of the repulsive Holm's forces generated between
the movable and stationary contacts 510 and 520 and that helps to maintain the contact
system 500 closed at current discharges higher than usually expected at typical contact
forces (for e.g. at currents above 15 kA and contact forces between 40 N and 60 N),
although the size of the stationary and movable contacts 520 and 510 has been decreased
to be accommodated in a more compact contactor or relay.
[0063] Similarly to the first embodiment, the electrical contact between the movable and
stationary contacts 510 and 520 is established via pairs of contact islands which
are arranged on the side surfaces of the movable and stationary contacts 510 and 520
that face each other, i.e. an upper side surface 519 of the movable contact 510 shown
in Fig. 17 and a bottom side surface 529 of the stationary contact 520 shown in Fig.
18. For instance, as shown in Fig. 16, three contact pairs are provided, where each
of the contact pairs has one contact island arranged onto the upper side surface 519
of the movable contact 510 (i.e. the first contact islands 518a, 518b, 518c shown
in Fig. 17) and another contact island arranged onto the bottom side surface 529 of
the stationary contact 520 (i.e. the second contact islands 528a, 528b, 528c shown
in Fig. 18). Each contact island of a contact pair is relatively positioned so as
to contact with the corresponding contact island of the same contact pair when the
contact system 500 is in the closed state. Preferably, three contact pairs are provided
to establish the electrical contact between the movable and stationary contacts 510
and 520 at three distinct contact points which are positioned relative to each other
so as to achieve an asymmetry in the current paths generated in the movable contact
510 and the stationary contact 520, respectively. Further, they also ensure that the
input current received by the movable contact 510 is passed to the stationary contact
520 only at the specific contact regions and that it is transported along determined
current paths in the stationary contact 520 before exiting via the output terminal
525. Thus, the three contact pairs (518a, 528a), (518b, 528b) and (518c, 528c) define
the sole points (or regions) of electrical contact between the stationary and movable
contacts 520 and 510, and consequently, influence the current paths along which electric
current passes from the movable contact 510 into the stationary contact 220. The contact
system 500 in the present embodiment is provided with a single contact pair (518a,
528a) on side A and two contact pairs (518b, 528c) and (518b, 528c) on side B, opposed
to side A, of the contact system 500. However, other configurations in which only
one contact is provided on side B may be envisaged.
[0064] In addition, the shape of the movable and stationary contacts 510 and 520 and relative
position of the contact pairs leads to a specific current distribution along the movable
and stationary contacts 510 and 520, which is responsible for producing an imbalance
between the current that passes across the contact pair (518a, 528a) at a side A of
the contact assembly 500 and the currents that pass across each of the contact pairs
(518b, 528b) and (518c, 528c) at a side B of the contact assembly 500, as it will
be described in the following.
[0065] Similarly to the previous embodiments, the movable and stationary contacts 510 and
520 of the contact system 500 have respective geometries which impose specific current
paths for passing the current across the movable contact 510 (incoming current paths)
and across the stationary contact 520 (outgoing current paths) and which result in
a re-circulation of the current along the stationary contact 520, so that parallel
currents flow in the same direction over respective, parallel sections of the stationary
and movable contacts 520 and 510 to produce Lorenz forces that counteract (at least
partially) the repulsive effect generated by the Holm's force. As shown in Fig. 14,
the movable contact 510 is designed with a planar geometry that includes two end sections
511, 512, each configured to receive current from the frame 530 via the flexible stripes
534, and a main, input conductive section 513 (or branch) configured to transport
the current received via the input end sections 511, 512 towards a center region 515
of the movable contact 510. The input conductive section 513 extends longitudinally
(i.e. along the direction of the X axis which is transverse to the central axis C
as shown in Fig. 13) over a length L', preferably having a symmetric length to the
left and right sides of the central axis C and the central region 515. The end sections
511, 512 are disposed at respective ends of the input conductive section 513, on left
and right sides of the central region 515, and both extend in a direction transverse
to the longitudinal direction X of the input conductive section 513 and the central
axis C (for e.g. parallel to the Z axis shown in Fig. 14). The end sections 511 and
512 are dimensioned with a size suitable for establishing a good electrical contact
with the underlying flexible stripes 534.
[0066] The geometry of the movable contact 510 further includes an interconnection branch
516 that extends away from the central region 515 of input conductive section 513
in a direction transverse to the longitudinal axis X of the input conductive section
513. The interconnection branch 516 is disposed substantially in parallel with and
between both the input end sections 511 and 512.
[0067] As shown in Fig. 17, one of the contact islands 518a is arranged at the central region
515 of the input conductive section 513, more specifically, at an intermediate position
of the longitudinal length L' and width W' of the input conductive section 513, such
that the current distribution paths established between the end sections 511 and 512
and the contact island 518a are substantially symmetric. Further, the contact island
528a is positioned in alignment with the center axis C of the movable contact 510
and with its the center being located at a predetermined distance d
A from the center axis C. The interconnection branch 516 serves the purpose of partially
deviating the current paths established along the input conductive section 513, between
the input end sections 511, 512 and the contact island 518a, towards the contact islands
518b and 518c. The contact islands 518b and 518c are disposed at an end portion of
the interconnection branch 516 for contacting with the conducting islands 528b and
528c disposed on the opposed stationary contact 520, as shown in Fig. 17. In particular,
the contact islands 518b and 518c are disposed on the right and left sides of the
interconnection branch 516 in a symmetric manner with respect to a mirror plane containing
the center axis C and the center of the contact island 518a and are positioned such
that the projection of their respective centers on the mirror plane are at a same
predetermined distance d
B from the center axis C. The interconnection branch 516 and the adjacent contact islands
518b and 518c allow to split the current paths established on the interconnection
branch 516 and provide additional current paths for passing the incoming current from
the input conductive section 513 towards the stationary contact 520, which results
in an unbalanced distribution of the currents between the contact pair at side A and
the two contact pairs at side B of the contact system 500.
[0068] The first and second predetermined distances (d
A, d
B) are preferably the same and/or selected based on parameters of the movable contact
510, such as the width W' of the input conductive section 513 and a width of the interconnection
branch 516 in a direction transverse to the center axis (C) (i.e. along the direction
of the Z axis in Fig. 14) so as to achieve an asymmetry on the distribution of currents
paths along the movable contact 510 that results in a current imbalance of up to a
predetermined imbalance threshold (preferably up to 80% current imbalance) between
the current passing from the movable contact 510 to the stationary contact 520 across
the single first contact island 518a arranged on the input conductive section 513
and the currents passing from the movable contact 510 to the stationary contact 520
across each of the first contact islands 518b and 518c arranged on the interconnection
branch 516, respectively.
[0069] In addition, as shown in Fig. 14, the input conductive section 513 further includes
two intermediate sections 517, 518, one at each side of the central region 515 and
through which the current received from the input end section 511, 512 at the respective
side left and right sides is passed to the central region 515 and/or to the interconnection
branch 516 of the movable contact 510. The width and the position of each of intermediate
section 517 and 518 along the direction transverse to the longitudinal length of the
input conductive section 513 and the center axis (C) (i.e. along the direction of
the Z axis in Fig. 14) also play a major role in the distribution of the current paths
along the movable contact 510. Therefore, these parameters can be selected (for e.g.
based on simulation analysis) in combination with the position of the first contact
islands 518a, 518b and 518c arranged on the movable contact 510 so as to achieve an
asymmetry on the distribution of currents paths along the movable contact 510 that
results in a current imbalance of up to a predetermined imbalance threshold being
reached between the current Ia passing from the movable contact 510 to the stationary
contact 520 across the contact island 518a on the input conductive section 513 and
the currents Ia and Ib, which pass from the movable contact 510 to the stationary
contact 520 across each of the first contact islands 518b and 518c arranged on the
interconnection branch, respectively. In the configuration of Fig. 14, the intermediate
sections 517 and 518 have the same width has the width W' of the input conductive
section 513. However, a geometry may be envisaged in which the intermediate sections
517 and 518 have a smaller width than the width W' of the input conductive section
513 and/or which are displaced towards the end portion of the interconnection branch
516, thereby significantly modifying the current distribution along the movable contact
510 and the currents Ia, Ib and Ic across the contact pairs (518a, 528a), (518b, 528b)
and (518c, 528c). In particular, the current imbalance between the currents across
the contact pair (518a, 528a) at side A and the contact pairs (518b, 528b) and (518c,
528c) at side B of the movable contact 510 is expected to decrease with a displacement
of the intermediate sections 517, 518 closer to the center axis C and/or with an increase
of the width of the intermediate sections 517, 518. Fig. 16 depicts the relative positioning
of the movable and stationary contacts 510 and 520 when arranged in the support frame
530 and the relative positioning of the respective contact islands (518a, 528a), (518b,
528b) and (518c, 528c). Fig. 17 illustrates in a simplified manner the directions
of current flow (current paths) through the movable contact 510 (dashed arrows) as
well as the direction of the currents Ia, Ib and Ic (solid arrows) that pass across
the contact islands of the contact pairs (518a, 528a), (518b, 528b) and (518c, 528c),
respectively, when the contact system 500 is closed.
[0070] The stationary contact 520 has a planar geometry comprising a plurality of conductive
sections 522 - 527 which are disposed and electrically connected with respect to each
other so as to form a closed-loop geometry, as shown in Fig. 15. The plurality of
conductive sections 522 - 527 may form a single body or may be separate conductive
sections electrically connected to the immediately adjacent conductive sections to
form the closed-loop shape.
[0071] The geometry of the stationary contact 520 includes an output conductive section
522 that extends longitudinally (for e.g. parallel to the X axis shown in Fig. 15)
to the left and right sides of the output terminal 525 over a length L", and a recirculation
conductive section 524, arranged opposite to the output conductive section 522 and
across the central hole of the closed-loop geometry. The output conductive section
522 is intended to be placed adjacent to the input conductive section 513 of the movable
contact 510 such that the current paths in the input conductive section 513 and the
output conductive section 522 respectively lie in parallel planes that are orthogonal,
or at least non-parallel, to the direction of relative movement of the movable contact
510 (i.e. the direction of the C axis), as shown in Fig. 13. This allows to maximize
the Lorenz forces self-generated by the recirculation of current in the stationary
contact 520.
[0072] A contact island 528a is arranged at an intermediate position of the output conductive
section 525 in correspondence with the contact island 518a of the movable contact
510. Additional contact islands 528b and 528c are positioned adjacent to each other
on an central area of the recirculation conductive section 524 and in correspondence
with the contact islands 518b and 518c on the movable contact 510. The narrow width
of the recirculation conductive section 524 on this area ensures that the current
received via each the contact islands 518b, 518c is re-circulated along the semi-looped
current paths established on the right and left sides of the loop shape shown in Fig.
18, respectively, towards the output conductive section 522 and the output terminal
525. The closed-loop shape of the stationary contact 520 is completed by the second
conductive sections 526, 527, adjacent recirculation conductive section 524.
[0073] The closed-looped shape of the stationary contact 520 determines the outgoing current
path(s) between the output terminal 525 and each point of contact established with
the movable contact 510 via the contact pairs and ensures that part of the current
received by the recirculation conductive branch 524 is redirected towards the output
conductive section 522 to flow in the same direction as the flow direction in the
input conductive section 513 of the movable contact 510. As a result, an additional
attractive Lorenz between the output and input conductive sections 522 and 513 is
generated by an overcurrent passing across the closed contact system 500.
[0074] Fig. 18 shows a simplified representation of the currents Ia, Ib and Ic (solid arrows)
that are received by the contact islands 528a, 528b and 528c, respectively, when the
contact system 500 is closed and the directions of current flow (outgoing current
paths) established along the closed loop of the stationary contact 520 (dashed arrows)
towards the output terminal 525.
[0075] The contact islands 528a - 528c on the stationary contact 520 and the contact islands
518a - 518c on the movable contact 510 preferably have the same shape, size as well
as surface roughness and hardness properties so as to have a similar contact resistance
across the contact pairs. However, due to the asymmetry of the current paths imposed
by the specific geometries of the stationary and movable contacts 520 and 510 and
the three-point contacts, the intensities of the currents across each of the contact
pairs (518a, 528a), (518b, 528b), and (518c, 528c) will not be the same. Specifically,
the current across the contact pair (518a, 528a) on side A of the movable contact
510 (which is the side of the input conductive section 513) will be significantly
higher than across each of the opposed contact pairs (518b, 528b) and (518c, 528c)
on the opposed side B.
[0076] Experimental observation and simulation analysis have shown that the unbalanced currents
across the contact pairs disposed on sides A and B play an important role in the effective
Holm's force generated between the movable and stationary contacts 510 and 520, namely,
it may increase the threshold value of discharge current above which the contact system
500 will open against the contact force created by the underlying magnetic driving
system 300. This effect may also be present in the contact systems 200 and 400 described
above, but becomes particularly important for a three-point contact geometry and asymmetric
load paths, such as achieved with the geometry of the contact system 500, since it
is then very difficult to obtain asymmetric load paths with the same resistance between
the input and output terminals of the contact system 500.
[0077] The contact system 500 of the present embodiment exploits the effect produced by
unbalanced currents on the overall repulsive Holm's force felt by the movable contact
510 and which is caused by the asymmetric load paths available for the flow of current
through the contact system 500. In particular, simulation of the current distribution
and current densities achieved for the specific geometry of the movable and stationary
contacts 510 and 520 with three-point contact show that the current Ia across the
contact island 518a is significantly higher than the intensity of the currents Ib
and Ic across the contact islands 518b and 518c on the intermediate connection branch
512 at the opposed side B. Namely, the current distribution along the stationary contact
520 and the movable contact 510 is such that different current intensities across
the contact pairs are achieved depending on the side A or B on which the contact pairs
are located. For instance, at a contact force of 13.3N per contact pair and an input
current load of 15kA, it is estimated that the current Ia across the intermediate
contact pair (218a, 228a) at side A of the contact assembly 500 may reach 10560 A
against current intensities Ib and Ic of 2220 A across the contact pairs (218a, 228a)
and (218c, 228c) located at the opposite side B, which corresponds to a current imbalance
of about 78%. In this case, a repulsive Holm's force of about 60N may be generated
at side A against a repulsive Holm's force of 2.7N per contact pair on side B of the
movable contact 510. Thus, even under similar roughness and hardness conditions of
the contact islands, the sides A and B of the movable contact 510 initially feel an
imbalance of the repulsive Holm's forces caused by the unbalanced currents across
the contact pairs.
[0078] This current unbalance may be sufficient for counter-acting the Holm's force generated
on sides A and B of the movable contact 510, depending on the contact force generated
by the actuating coil 320 to maintain the contacts closed, the surface condition and
hardness of the contact islands. For instance, it is known that the electrical contact
between contact islands may be accomplished over discrete areas or spots of a much
smaller size than the area of the contact islands themselves depending on the roughness
and hardness of the contact island surface. The number and size of contact spots influences
the current distribution close to the contact islands and may lead to the generation
of Holm's forces sufficiently strong to cause levitation of the movable contact at
high currents, for e.g. at 15kA and above. This effect is already visible in low voltage
drop measurements of the contact resistance and is expected to increase at very high
current flow and low contact forces. In case of poor contact surface conditions, the
number or size of spot contacts is further reduced, leading to a significant increase
of the repulsive effect and eventually total failure of the contact system and respective
switching device. Calculation results performed for the geometry of the contact system
500 with an arrangement of three contact pairs at a discharge current of 15 KA and
a total contact force of 41.5 N assumed to be equally distributed per contact pair
(i.e. 5 kA and 13.8 N per contact pair) and a contact spot of 0.1 mm size show that
the theoretical Holm's force estimated for medium hardness and surface finishing of
contact islands may achieve 13.4 N against 6.3 N obtained for contacts in perfect
conditions. In real conditions, a higher Holm's force of 17.5 N has been measured.
Nonetheless, experimental and simulation results show that an imbalance of up to 80%
between the current Ia across the intermediate contact pair (518a, 528a) at side A
and the currents Ib and Ic across each of the contact pairs (518b, 528b) and (518b,
528b) at the opposed side B of the movable contact 510 may lead to a sufficient self-compensating
effect of the repulsive Holm's forces for maintaining the contact system 500 closed
at a total load current of 15 kA and above.
[0079] Specifically, the unbalance between the current Ia across the contact pair (518a,
528a) at side A and the currents Ib and Ic across each of the contact pairs (518b,
528b) and (518b, 528b) on side B results in a higher repulsive Holm's force being
initially generated on side A, due to a higher current passing across the contact
pair (518a, 528a) when the contact assembly 500 is in the closed state and receives
a high current discharge, as illustrated in Fig. 19.
[0080] Fig. 19 shows a simplified side view of the movable and stationary contacts 510 and
520 of the contact system 500 at a first stage in which the contact system 500 is
in the closed state, i.e. the movable contact 510 is pressed against the stationary
contact 520 by the force F
coil + spring applied at the center of the movable contact 510, and the current Ia passing through
the contact island 518a at side A is significantly higher than the currents Ib and
Ic that pass through each of the contact islands 518b and 518c at side B.
[0081] The force F
coil + spring applied onto the movable contact 510 results from the bias exerted by the over-travel
spring 550 and the actuation force generated by the actuation coil 320 to move the
driving shaft 540 towards the stationary contact 520 so as to maintain the contact
system 500 closed for currents within a desired operation range (for e.g. at currents
below 15 kA). The resilience of the over-travel spring 550 allows not only slight
displacements of the movable contact 510 along the center axis C but also slight oscillations
of the movable contact 510 about an axis R that passes longitudinally through the
movable contact 510 at a direction transverse the central axis C (see Fig. 13). The
axis R define an axis of oscillation of the movable contact 510 (real or virtual rotation)
with respect to the contact assembly 500. The force F
coil + spring causes reaction forces to be applied onto each of the contact islands 518a, 518b,
and 518c by the opposed contact islands 528a, 528b and 528c of the stationary contact
520 (for e.g. see the downward reaction forces R
a and R
b onto the movable contact 510 depicted in Fig. 19 and correspondent to the contact
islands 518a and 518b, respectively). Under normal operation conditions, the resultant
force and resultant torque applied on the movable contact 510 should be negligible,
so that the movable contact 510 is in a stable equilibrium state, i.e. with no translation
and/or rotation movement with respect to the stationary contact 520. However, a discharge
current lin of the order of 15 kA and above may lead to the appearance of significant
Holm's forces at each of the sides A and B of the movable contact 510.
[0082] However, due to the shape and three-point contact geometry of the movable and stationary
contacts 510 and 520, at high overload currents the current I
in input to the contact system 500 is distributed along asymmetric current paths on
the movable contact 510, leading to an initial imbalance between the current Ia across
the single contact island 518a at side A and the currents Ib and Ic across the pair
of contact islands 518b and 518c at side B, respectively. The current Ia can be up
to a 80% higher value than each of the currents Ib and Ic (which have substantially
the same intensity in the configuration of the present embodiment). As a result, the
higher Holm's force generated at side A of the movable contact 510 will produce a
levitation effect (repulsive force) at side A much stronger than the levitation effect
produced by the lower Holm's forces on side B, mechanically unbalancing the movable
contact 510 and increasing the overall contact force on side B while reducing the
overall contact force on side A, thereby decreasing the contact resistance at side
B and increasing the contact resistance at side A (without opening the contact system
500).. Thus, the effect of the imbalanced Holm's forces is equivalent to that of an
effective torque that attempts to rotate the movable contact 510 about the axis R
towards the side B (without opening the contact system 500), leading to a decrease
of the contact resistance across the contact pairs (518b, 528b) and (518c, 528c) at
side B and an increase of the contact resistance across the contact pair (518a, 528a)
at side A.
[0083] Meanwhile, the increase of the contact pressure on side B and the associated reduction
of the contact resistance across the contact pairs (518b, 528b) and (518c, 528c) is
reflected in a consequent increase of the current density across these contact pairs
(518b, 528b) and (518c, 528c). At the same time, the current density across the contact
pair (518a, 528a) at side A becomes to decrease due to the increase of the contact
resistance caused by the levitating effect produced by the Holm's force generated
at this side. The repulsive Holm's force will then progressively decrease at side
A, while the Holm's force at side B is increased, until a stage in time where the
imbalance of the Holm's forces generated at sides A and B is equivalent to an effective
torque about the axis R that attempts to rotate the movable contact 510 about axis
R in the opposite direction, i.e. towards side A, thereby increasing the pressure
of the contact island 518a on side A against the contact island 528a of the stationary
contact 520. The oscillating variation of the contact pressure on side A and side
B of the movable contact 510 against the stationary contact 520 created by the unbalanced
Holm's forces is equivalent to an additional attractive force that attracts one of
the respective sides A and B towards the stationary contact 520. At the same time,
the oscillating contact pressure decreases the repulsive Holm's force being generated
at the side of the movable contact 510 that tends to levitate, and therefore, allows
to maintain the contact system 500 closed at higher discharge currents than normally
expected.
[0084] Fig. 20 shows a simplified side view of the movable and the stationary contacts 510
and 520 of the contact system 500 in a closed state and at a second stage, i.e. at
a time subsequent to the first stage shown in Fig. 19.
[0085] In this second stage, the currents Ib and Ic crossing each contact island 518b and
518c at side B of the movable contact 510 have increased due to the decrease of the
respective contacts resistance at side B during the first stage, while the current
Ia has decreased as a consequence of the contact resistance decrease caused by the
higher levitating effect produced by the Holm's force at this side during the first
stage. As a result, the higher Holm's forces associated with the higher currents at
side B will have a stronger levitation effect on side B than on the lower Holm's force
produced at side A, resulting in a reduction of the contact pressure and increase
of the contact resistance at side B. The imbalance of the repulsive Holm's forces
between sides A and B at the second stage is equivalent to an effective torque that
attempts to rotate the movable contact 510 about the axis R towards side A (without
opening the contact system 500), leading to a new increase of the contact pressure
exerted by the stationary contact 520 onto the contact islands 518a at side A and
a decrease of the contact pressure exerted onto the contact islands 518b and 518c
at side B. The repulsive Holm's forces generated by the unbalanced currents will continue
to increase/decrease in an oscillatory manner at each of sides A and B, at least for
a given time interval, although the contact system 500 remains closed. The attractive
Lorentz forces self-generated by the recirculation of current on the stationary contact
520 are still present (particularly on side A of the movable and stationary contacts
510, 520) but may not have sufficient intensity to fully counter-act the Holm's force
due to the size of the contact system 500 (length L" and width W") being reduced in
comparison with the contact systems 200 and 400 described above. However, due to the
self-compensating effect of the repulsive Holm's force achieved by the geometry of
the contact system 500, it is possible to achieve a contact system 500 of compact
size that is capable of remaining close at currents of the order of 15 kA (or higher)
while using typical contact forces (n the range between 40 N and 60 N) generated by
the actuation coil 320 and over-travel spring 540. For instance, the self-compensating
effect can be achieved at such operating parameters with a movable contact 510 dimensioned
with a length L' of about 40 mm, a width W' of about 7 mm for the input conductive
section 513 and a comparable width of about 7 mm of the interconnection branch 516
(i.e. in the direction of the axis Z shown in Fig. 14), combined with a stationary
contact 520 dimensioned with a length L" of about 41 mm, a lateral width W" of 19
mm and loop hole of about 5 mm (in the direction of the Z axis shown in Fig. 15).
[0086] The movable contact 510 may continue such a virtual oscillation movement for a given
time duration which is sufficient for a fuse or other disconnecting mechanism safely
disconnecting the load from the path of current discharge before the contact system
500 is forced to open. Thus, this combined self-compensating effect of the unbalanced
Holm's forces allows to maintain the contact system 500 and the switching device 100'
closed at discharge currents well above 15kA and/or during a longer time period than
usually observed for this order of discharge currents in conventional contacts systems.
[0087] An important parameter of the self-compensating Holm's effect lies in the distances
d
A and d
B at which the contact pairs (518a, 528a), (518b, 528b), and (518c, 528c) are positioned
with respect to the center axis C (d
A and d
B corresponding to a same distance d in the exemplary configuration illustrated in
Figs. 19 and 20), since the torque generated by the unbalance Holm's force tends to
increase with the distance d. On the other hand, an increase of the distance d implies
a change in the geometries of the movable and stationary contacts 510 and 520 and
therefore, will also affect the current distribution on the contacts 510 and 520 and
the currents across the individual contact pairs (518a, 528a), (518b, 528b), and (518c,
528c). Other parameters that play a major role in the contact resistance of the individual
contact pairs (518a, 528a), (518b, 528b), and (518c, 528c), and therefore, on the
self-compensating Holm's effect, include the contact force generated by the actuation
coil 320 and the bias pressure generated by the over-travel spring 550. In order to
maximize the self-compensating Holm's effect produced by the unbalanced currents,
the shape and dimensions of the contacts 510 and 520, including the dimensions of
the input and output conductive sections 513 and 522, may be determined using simulation
methods known in the art for the parameters required for an intended application,
such as discharge current to be withstand by contact system without opening, the contact
force generated by the actuating coil 320, materials and overall dimensions of the
contact system 500 and switching device 100', including the geometry and cross-section
of the contacts 510 and 520 as well as the condition and hardness of the contact islands.
[0088] Thus, the contact system 500 allows to effectively counter-act the negative effects
produced by the repulsive Holm's force at high discharge currents, such as 15 kA or
above, via a combination of the contact force generated by the actuating coil 320,
the attractive Lorentz force which is self-generated by the re-circulation of current
in the stationary contact 520 and, most importantly, the self-compensating effect
of the Holm's force produced by the unbalance of currents across the contact pairs
disposed at opposite sides of the movable contact 510 with respect to the central
axis C.
[0089] The first and second contacts of the contact systems described above are preferably
made of an electrical conducting material capable of withstand erosion and mechanical
stress. The contact material should also provide high welding resistance and stable
arc resistance so that the contacts may withstand high current discharges.
[0090] In conclusion, the present invention provides reliable contact systems and switching
devices for protecting electrical equipment used in high voltage applications by using
a design of the underlying contact system that allows to generate additional attractive
Lorentz forces between the stationary and movable contacts using recirculation of
the overcurrent itself and therefore, capable of self-compensating the repulsion caused
by Holm forces generated at high discharge currents, such as in the order of 15 kA
or higher. Moreover, as the attractive Lorentz force is proportional to the discharge
current flowing across the contact system, a collapse of the contact system and resultant
destruction of the respective switching devices can be avoided for a large range of
discharge currents with the same contact system design. In addition, the contact systems
of present invention also allow to counter-act the repulsion effects caused by Holm's
forces at high discharge current by exploiting a mechanism of self-compensation of
the effective Holm's force which is associated with unbalanced currents being produced
across the contact points between the stationary and movable contacts due to the asymmetrical
load paths achieved by the specific geometries of the stationary and movable contacts.
[0091] It should be noted that in the description above assumed that, in Figs. 2 - 3 and
6, the horizontal direction is a direction along the X-axis and the vertical direction
is a direction parallel to the Y - axis. Further, although certain features of the
above exemplary embodiments were described using terms such as "top", "bottom", "upward"
or "downward", "vertical", "left" and "right", these terms were used for the purpose
of facilitating the description of the respective features and their relative orientation
only and should not be construed as limiting the use of the claimed invention or any
of its components to a particular spatial orientation. Moreover, although the present
invention has been described above with reference to switching devices for high current
applications and/or high overloads, the principles of the present invention can also
be advantageously applied to switching devices intended for low voltage applications.
Reference Signs
[0092]
- 100
- switching device
- 200
- contact system of first embodiment
- 210
- first contact (movable contact)
- 211, 212
- end sections of the first contact member
- 213
- input conductive section
- 216
- intermediate branch
- 220
- second contact (stationary contact)
- 221
- protrusion of stationary contact
- 222
- output conductive section
- 224
- recirculation conductive section
- 226
- output terminal
- 227
- intermediate section
- 228
- second contact island
- 230
- support structure
- 232
- rigid shell
- 234
- through-hole on support shell
- 236
- top side of shell
- 237
- bottom side
- 238, 239
- pair of braids
- 300
- magnetic driving system
- 320
- electromagnetic coil
- 332, 334
- terminals of electromagnetic coil
- 400
- contact system of second embodiment
- 410
- first contact (movable contact)
- 413
- input conductive section
- 416
- intermediate branch
- 420
- second contact (stationary contact)
- 422
- output conductive section
- 424
- recirculation conductive section
- 426
- output terminal
- 100'
- switching device of third embodiment
- 500
- contact system of third embodiment
- 510
- first contact (movable contact)
- 511, 512
- end sections of the first contact
- 513
- input conductive section
- 515
- central section
- 516
- interconnection branch
- 517, 518
- intermediate sections
- 518a - 518c
- first contact islands (on movable contact)
- 519
- upper side surface
- 520
- second contact (stationary contact)
- 521
- intermediate section of stationary contact
- 522
- output conductive section
- 524
- recirculation conductive section
- 526, 527
- adjacent conductive section of second contact
- 525
- output terminal
- 528a - 528c
- second contact islands (on stationary contact)
- 529
- bottom side surface of the second contact
- 530
- support frame
- 534
- pair of braids
- 535
- input terminal
- 536
- top side of support frame
- 537
- bottom side of support frame
- 540
- driving shaft
- 550
- over-travel spring
- 555
- central region
- C
- central axis of contact system, direction of relative movement
1. Contact system for a switching device, comprising:
a first contact (210; 410; 510) adapted to receive an input current supplied to an
input terminal (234; 535) of the contact system; and
a second contact (220; 420; 520) adapted to receive the input current from the first
contact (210; 410; 510);
wherein the first contact (210; 410; 510) comprises an input conductive section (213;
513) configured to provide an incoming current path for transporting the input current,
wherein the second contact (220; 420; 520) comprises a plurality of second conductive
sections (222, 224; 521 - 527) configured to provide an outgoing current path for
transporting the current received from the first contact (210; 410; 510) towards an
output terminal (226; 525) when the contact system is in a closed state, and
wherein one of the plurality of second conductive sections is arranged adjacent to
the input conductive section and provides an output conductive section (222; 422;
522) in which current received by the second contact (220; 420; 520) from the first
contact (210; 410; 510) is transported in the same direction as the current direction
along the incoming current path in the input conductive section.
2. A contact system according to claim 1, wherein
the output conductive section (222; 422; 522) is substantially parallel to the input
conductive section (213; 413; 513), and/or
the plurality of second conductive sections are arranged in a same plane which is
substantially parallel to the input conductive section.
3. A contact system according to claim 1 or 2, wherein
the output conductive section (222; 422; 522) is disposed adjacent the input conductive
section in a direction of a relative linear movement between the first (210; 410;
510) and second contacts (220; 420; 520).
4. A contact system according to any one of claims 1 to 3, wherein
the input conductive section (213; 413; 513) and the output conductive section (222;
422; 522) are configured such that a section of the incoming current path defined
by the input conductive section (213; 413; 513) and a section of the outgoing current
path defined by the output conductive section (222; 422; 522) are substantially orthogonal
or non-parallel to a direction of a relative linear movement between the first (210;
410; 510) and second contacts (220; 420; 520).
5. A contact system according to any one of claims 1 to 4, wherein
the input conductive section (213; 413; 513) and the output conductive section (222;
422; 522) have respective shapes that extend in a longitudinal direction of the incoming
current path by at least a predetermined length at which an attractive Lorentz force
between the input and output conductive sections compensates the repulsive Holm's
force generated between the first (210; 410; 510) and second contacts (220; 420; 520)
at a given intensity of input current, and preferably for an input current of 15 kA
or higher; wherein
said longitudinal direction is substantially orthogonal or at least non-parallel to
a direction of a relative linear movement between the first (210; 410; 510) and second
contacts (220; 420; 520).
6. A contact system according to any one of claims 1 to 5, wherein
the first contact (210; 410; 510) further includes one or more interconnection branches
(216; 416; 516) which extend away from the input conductive section by a predetermined
length so as to pass at least a part of the input current from the input conductive
section (213; 413; 513) to one of the second conductive sections of the second contact
(220; 420; 520) other than the output conductive section (222; 422; 522), and
wherein said second conductive section other than the output conductive section (222;
422; 522) forms a recirculation conductive section (224; 424; 524) configured to define
a portion of the outgoing current path along which the current received from the one
or more interconnection branches (216; 416; 516) of the first contact (210; 410; 510)
is recirculated towards the output conductive section (222; 422; 522).
7. A contact system according to claim 6, wherein
the recirculation conductive section (224; 524) is shaped with an extended section
that is arranged substantially parallel to and opposed to the output conductive section
(222; 422; 522).
8. A contact system according to claim 6 or 7, wherein
the second contact (220; 420; 520) includes a plurality of second contact islands
(528a - 528c) arranged thereon in number and positions corresponding to a plurality
of first contact islands (518a - 518c) arranged on the first contact (210; 410; 510),
the first and second contact islands providing a plurality of contact pairs via which
electrical contact between the first and second contacts is established when the contact
assembly is in the closed state;
wherein at least one of the second contact islands is provided on said recirculation
conductive section (224; 414; 524) of the second contact (220; 420, 520) at a respective
position for electrically contacting to a corresponding first contact island provided
in the interconnection branch (216; 516) of the first contact (210; 410; 510) when
the contact system is in the closed state; and/or
wherein at least one of the second contact islands is provided on said output conductive
section (213; 413; 513) at a respective position for electrically contacting to a
corresponding first contact island provided on a central region of the input conductive
section (213; 413; 513) of the first contact (210; 410; 510) when the contact system
is in the closed state.
9. A contact system according to claim 8, wherein
the second contact islands (528a - 528c) are provided in a number of three and each
arranged in a position corresponding a position of a respective one of three first
contact islands (518a - 518c) provided in the first contact (210; 510),
wherein a single second contact island (528a) is arranged on said output conductive
section (213; 513) and at a respective position for electrically contacting to a single
first contact island (518a) arranged on the central region of the input conductive
section (213; 513) of the first contact (210; 510), and
wherein a pair of the second contact islands (528b, 528c) is arranged at a central
area of said recirculation conductive section (224; 524) of the second contact (220;
520), a corresponding first contact island (518b, 518c) being arranged at an end portion
of said one or more interconnection branches (216; 516) of the first contact (210;
510) so that the outgoing current paths for currents received by the recirculation
conductive section of the second contact (220; 520) via said pair of second contact
islands (528b, 528c) includes two half-loops that direct the received current towards
the output conductive section (222; 522).
10. A contact system according to claim 8 or 9, wherein
the single first contact island (518a) is arranged on said input conductive section
(213; 513) and positioned with its center at a first predetermined distance (dA) from a center axis (C) of the first contact (210; 510);
the pair of first contact islands (518b, 518c) is arranged on an end portion of the
interconnection branch (216; 516), each first contact island of the pair (518b, 518c)
being positioned in a symmetric manner with respect to a mirror plane, which contains
the center axis (C) and the center of the first contact island (518a) arranged on
said input conductive section (213; 513), and such that a projection of their respective
centers onto said mirror plane is distant by a second predetermined distance (dB) from the center axis (C); and
wherein the first and second predetermined distances (dA, dB) are the same and/or selected based on a width of the input conductive section and
a width of the interconnection branch (516) in a direction transverse to the center
axis (C) so as to achieve an asymmetry on the distribution of currents paths along
the first contact (510) that results in a current imbalance of up to a predetermined
imbalance threshold between the current passing from the first contact to the second
contact across the single first contact island on the input conductive section and
the currents passing from the first contact to the second contact across each of the
first contact islands arranged on the interconnection branch, respectively.
11. A contact system according to any one of claims 6 to 10, wherein
the plurality of second conductive sections are configured to form the second contact
(520) with a closed loop geometry; and
wherein the geometries of the first (510) and the second contacts (520) are configured
such that the interconnection branch (516) of the first contact (510) extends from
a central region of the input conductive section (513) along a direction transverse
to a longitudinal length of the input conductive section (513) and the center axis
(C) to overlap an intermediate section of said recirculation conductive section (524)
of the second contact at ,
wherein the geometry of the first contact (510) further includes two input end sections
(511, 512) at respective end portions of the input conductive section (513) to feed
the input current to said input conductive section (513) and which extend in a direction
transverse to the longitudinal length of the input conductive section (513) and the
center axis (C), and
wherein the input conductive section (513) further includes two intermediate sections
(517, 518), one at each side of said central region and through which the current
received from the input end section at the respective side is passed to the central
region and/or the interconnection branch of the first contact,
wherein the width and the position of each of said intermediate sections in the direction
transverse to the longitudinal length of the input conductive section and the center
axis (C) is selected in combination with the position of the first contact islands
arranged on the first contact so as to achieve an asymmetry on the distribution of
currents paths along the first contact (510) that results in said current imbalance
of up to the predetermined imbalance threshold between the current passing from the
first contact to the second contact across the first contact island on the input conductive
section and the currents passing from the first contact to the second contact across
each of the first contact islands arranged on the interconnection branch, respectively.
12. A contact system according to claim 10 or 11, wherein
the predetermined imbalance threshold is 80% or below.
13. A contact system according to any one of claims 6 to 10, wherein
the plurality of second conductive sections is configured to form the second contact
(520) with a closed loop geometry,
the geometries of the first (210) and the second contacts (220) being configured such
that said interconnection branch (216) of the first contact (210) is provided as a
pair of protrusions that respectively extend from a central region of the input conductive
section (213) in a direction transverse to a longitudinal length of the input conductive
section (213) to make electrical contact with the intermediate section (227) of the
second contact (220) and split the outgoing current paths in two half-loops between
the intermediate section and the output terminal of the second contact (220); or
wherein the plurality of second conductive sections (424; 424) are configured to form
the second contact (420) with an open loop shape,
the first (410) and second contacts (420) being configured such that the interconnection
branch (416) of the first contact (410) is provided at an end section of the input
conductive section (413) to make electrical contact with said second conductive section
(424) other than the output conductive section at an end section of the open loop
shape.
14. A switching device for high current discharges, comprising:
a contact system (200; 400; 500) according to any one of claims 1 to 13; and
a magnetic driving system (300) adapted to operate switching of the contact system
(200; 400; 500) between a closed state, at which the first (210; 410; 510) and second
contacts (220; 420; 520) contact each other, and an open state at which the second
contact (220; 420; 520) is separated from the first contact (210; 410; 510) by a gap.
15. A switching device according to claim 14, wherein
the switching device is one of a electromagnetic relay and an electromagnetic contactor.