Technical Field
[0001] The invention relates to a high or medium voltage switch, particularly a DC switch,
comprising a first and a second set of contact elements that are mutually displaceable.
The invention also relates to a current breaker comprising such a switch.
Background Art
[0002] A switch of this type is disclosed for example in the co-owned United States patents
and published patent application
US7235751,
US2012/0256711, and
US2013/0098874. It has a first and a second set of contact elements and a drive adapted to mutually
displace the contact elements along a displacement direction. Each contact element
carries at least one conducting element. In a first mutual position of the contact
elements, their conducting elements combine to form at least one conducting path between
the first and second terminals of the switch, in a direction transversally to the
displacement direction. In a second position of the contact elements, the conducting
elements are mutually displaced into staggered positions and therefore the above conducting
path is interrupted.
[0003] The switches described in
US2012/0256711, and
US2013/0098874 have contact elements with an insulating carrier carrying conducting elements. In
the closed state of the switch, the conducting elements align to form one or more
current paths between the terminals of the switch along an axial direction. For opening
the switch, the contact elements are mutually displaced by means of two drives along
a direction perpendicular to the axial direction. The switching arrangement is arranged
in a fluid-tight housing in a gas of elevated pressure or in a liquid. The switch
has a high voltage withstand capability and fast switching times. The conducting element
project over the two opposite surfaces of the carrier that carries it and are slightly
movable in axial direction in respect to the carrier that carries it and/or it is
slightly tiltable around a tilt axis, wherein said tilt axis is perpendicular to the
axial direction and to the direction of displacement. Each terminal forms a contact
surface for contacting the conducting elements, wherein at least one of the terminals
comprises a spring member that elastically urges the contact surface of the terminal
against the conducting elements. This ensures a proper contacting force between the
conducting elements themselves and between the conducting elements and the contact
surfaces and, with conducting elements being movable in axial direction the forces
between all the conducting elements in a current path are substantially equal.
[0004] While generally satisfactory it is seen as an object of the present invention to
simplify the assembly of conducting elements onto their respective carriers and to
improve the carrier itself.
Summary of the Invention
[0005] Hence, according to a first aspect of the invention, the switch has at least a first
terminal and a second terminal for applying the current to be switched and at least
a first set of contact elements and a second set of contact elements and a drive adapted
to mutually displace the sets of contact elements relatively to each other along a
displacement direction with each contact element including an insulating carrier part
that carries at least one conducting element with the positions of the conducting
elements being such that in a first mutual position of the contact elements the conducting
elements form at least one conducting path between the first terminal and the second
terminal, i.e. the switch is in the closed, conducting position; and in a second mutual
position of the contact elements the conducting elements are mutually displaced such
that there is no conducting path formed by the conducting elements between the first
terminal and the second terminal, i.e. the switch is in its opened, non-conducting
position, with the conducting elements mounted onto the carrier part are locked into
their operating position by one or more spring-loaded pins.
[0006] The pin or pins are best rounded to allow for a small limited rotation movement of
a main body of the conducting element around the central axis of the pin. Thus the
main body of the conducting element is slightly tiltable around a tilting axis, wherein
said tilt axis is perpendicular to the axial direction and to the direction of displacement.
This allows the conducting element to axially position itself accurately when the
switch is in its first, closed position, thereby improving current conduction.
[0007] The invention allows for a connection between the carrier and the conducting elements
which is essentially free of hetero-material, in particular gluefree (free from glue).
[0008] The main body is preferably an elongated rectangular cuboid with two long flattened
contact faces oriented parallel to the plane of the contact element or its carrier
part for contacting in operation the flattened contact face of a conducting element
of an adjacent contact element. The cuboid main body has two further long faces and
two small faces with such faces oriented in position perpendicular to the plane of
the contact element. The small faces can have blind holes to mount the pins. Preferably
an elastic element such as a spring is mounted behind the pins in the blind hole to
facilitate the assembly and offer a latching action to lock the conducting element
in its place on the contact element or carrier part. In a preferred embodiment the
conducting elements are mounted within openings of the carrier part with the pin or
pins having a forked tip to latch onto a side wall of the opening. The openings are
made preferably slightly wider than the distance between the second long faces or
sides of the main body of the conducting elements, thus providing a small gap for
a limited movement of the main body of the conducting elements within the opening
of the carrier part in its mounted position.
[0009] The pins are best made of a harder material than the main body, which in turn are
typically manufactured using a material of high electrical conductivity such as silver,
copper or aluminium. The pins themselves can be made of steel, preferably hardened
steel or plastic material with a comparable hardness to steel. The term 'harder' is
understood as a comparison of the hardness degree of different materials.
[0010] Further, the conducting element should advantageously project over the two opposite
surfaces of the carrier that carries it. When a conducting element projects above
the surface of the surrounding carrier, it can be shown that the electrical field
at the intersection between the surface and the conducting element is smaller than
for a device where the surface of the conducting element is substantially flush with
the surface of the carrier.
[0011] While having a cuboid main body it is preferred to have all contour lines or edges
which are visible after mounting in the carrier rounded, including the exposed contour
lines of the pins.
[0012] Another aspect of the invention relates to the material used to manufacture the carrier
part and/or a frame structure for the contact elements onto which frame the conducting
elements can be mounted. It has been found that manufacturing the frame of the contact
elements from an epoxy material reinforced by aramid fibers offers a superior performance
in a DC switch as described above compared for example to the same structure manufactured
from an epoxy material reinforced by glass fibers.
[0013] The switch is advantageously used in high voltage applications (i.e. for voltages
above 72 kV), but it can also be used for medium voltage applications (between some
kV and 72 kV), particularly DC voltages.
[0014] Other advantageous embodiments are listed in the dependent claims as well as in the
description below.
Brief Description of the Drawings
[0015] The invention will be better understood and objects other than those set forth above
will become apparent from the following detailed description thereof. Such description
makes reference to the annexed drawings, wherein:
FIG. 1 shows a cross-sectional view of a known switch;
FIG. 2 shows an enlarged cross-sectional view of the contact elements of FIG. 1;
FIG. 3A shows a schematic perspective view of a contact element with carrier part
and acceleration rod but without conducting elements;
FIGs. 3B and 3C show an enlarged section of FIG. 3A with a conducting element inserted
into the carrier part;
FIGs. 4A and 4B shows a schematic view of a main body of a conducting element at two
different stages in the manufacturing process, respectively, in accordance with an
example of the invention; and
FIG. 4C shows a schematic view of a pin of a conducting element in accordance with
an example of the invention.
Modes of Carrying Out the Invention
[0016] An example of the present invention is now described in further detail using the
switch design as described in the above cited applications
US2012/0256711, and
US2013/0098874. Accordingly, the switch of Fig. 1 includes a fluid-tight housing 1 enclosing a space
2 filled with an insulating fluid, in particular SF
6 or air at elevated pressure or an oil.
[0017] Housing 1 forms a GIS-type metallic enclosure of manifold type and comprises two
tube sections. A first tube section 3 extends along an axial direction A, and a second
tube section 4 extends along a direction D, which is called the displacement direction
for reasons that will become apparent below. Axial direction A is perpendicular or
nearly perpendicular to displacement direction D. The tube sections are formed by
a substantially cross-shaped housing section 5.
[0018] First tube section 3 ends in first and second support insulators 6 and 7, respectively.
First support insulator 6 carries a first terminal 8 and second support insulator
7 carries a second terminal 9 of the switch. The two terminals 8, 9 extending through
the support insulators 6, 7 carry the current through the switch, substantially along
axial direction A.
[0019] Second tube section 4 ends in a first and a second cap 10 and 11, respectively.
[0020] First terminal 8 and second terminal 9 extend towards a center of space 2 and end
at a distance from each other, with a switching arrangement 12 located between them,
at the intersection region of first tube section 3 with second tube section 4.
[0021] As can best be seen from Fig. 2, switching arrangement 12 comprises a first set of
contact elements 13a, 13b, 13c and a second set of contact elements 14a, 14b, 14c.
In the embodiment shown here, each set comprises three contact elements, but that
number may vary, and, for example, be two or more than three. The first and second
set may also have different numbers of contact elements, e.g. two and three, respectively.
Advantageously, the number is at least two contact elements per set. The contact elements
of the two sets are stacked alternatingly, i.e. each contact element of one set is
adjacent to two contact elements of the other set unless it is located at the end
of switching arrangement 12, in which case it is located between one contact element
of the other set and one of the terminals 8, 9.
[0022] Each contact element comprises a plate-shaped insulating carrier 15, one or more
conducting elements 16 and an actuator rod 17. In the embodiment shown here, each
carrier 15 carries two conducting elements 16.
[0023] Figs. 1 and 2 show the switch in the closed state with the contact elements 13a,
13b, 13c, 14a, 14b, 14c in a first mutual position, where the conducting elements
16 align to form two conducting paths 34 along axial direction A between the first
and the second terminals 8, 9. The conducting paths 34 carry the current between the
terminals 8, 9. Their number can be greater than one in order to increase continuous
current carrying capability.
[0024] For example an arrangement with three conducting elements 16 in each insulating carrier
15 leads to three conducting paths 34 when the switch is closed. A non-inline arrangement
with four contact elements 16 in each insulating carrier 15 results in four conducting
paths 34 when the switch is closed and so forth.
[0025] The contact elements 13a, 13b, 13c, 14a, 14b, 14c are moved in operation along the
displacement direction D into a second position, where the conducting elements 16
are staggered in respect to each other and do not form a conducting path. In Fig.
2, the position of the conducting elements in this second position is shown in dotted
lines under reference number 16'. As can be seen, the conducting elements 16' are
now separated from each other along direction D, thereby creating several contact
gaps, thereby quickly providing a high dielectric withstand level.
[0026] To achieve such a displacement, and as best can be seen in Fig. 1, the actuator rods
17 are connected to two drives 18, 19. A first drive 18 is connected to the actuator
rods 17 of the first set of contact elements 13a, 13b, 13c, and a second drive 19
is connected to the actuator rods 17 of the second set of contact elements 14a, 14b,
14c.
[0027] In the embodiment shown in Figs. 1 and 2, the switch is opened by pulling the actuator
rods 17 away from the center of the switch, thereby bringing the conducting elements
into their second, staggered position. Alternatively, the rods 17 can be pushed towards
the center of the switch, which also allows to bring the conducting elements into
a staggered position.
[0028] The drives 18, 19 can e.g. operate on the repulsive Lorentz-force principle and be
of the type disclosed in
US 7 235 751, and they are therefore not described in detail herein. Each drive is able to displace
one set of contact elements along the displacement direction D. They are adapted and
controlled to move the first and second sets in opposite directions at the same time
in order to increase the travelling length as well as acceleration and speed of displacement.
[0029] The drives 18, 19 are arranged in opposite end regions of second tube section 4.
[0030] It should be noted that the full stroke (e.g. 20 mm per drive) of the drives may
not be necessary to travel in order for the contact system to provide the dielectric
strength required, but a distance much shorter (e.g. 10 mm per drive), which can be
reached in an even shorter time, suffices. This also provides certain safety in case
of backtravel upon reaching the end-of-stroke position and damping phase of the actuators.
A sufficient separation of the conducting elements 16 can be reached within 1 or 2
ms (milliseconds).
[0031] As shown in Fig. 2, each terminal 8, 9 carries a contact plate 32 forming a contact
surface 33 contacting the conducting elements 16 when the switch is in its first position.
The contact plates 32 are mounted to the terminals 8, 9 in axially displaceable manner,
with springs 20 elastically urging the contact surface 33 against the conducting elements,
thereby compressing the conducting elements 16 in their aligned state for better conduction.
In the embodiment of Fig. 2, helical compression springs 20 are used for this purpose,
but other types of spring members can be used as well. Also, even though it is advantageous,
if there is at least one spring member 20 in each terminal 8, 9, a compression force
for the aligned conducting elements 16 can also be generated by means of a spring
member (s) in only one of the terminals 8, 9 to reduce the contact resistance between
the elements 16 in the closed position of the switch.
[0032] A perspective schematic view of a single contact element 13a prior to its full assembly
is shown in FIG. 3A. The contact element includes a carrier part 15 and the actuator
rod 17. In the example shown both parts are made together as a single part from the
same material. The carrier part 15 has a frame structure with cut-out sections or
holes 151, 152 to mount further conducting elements 16 and/or other elements. The
carrier part 15has a central opening 153 and further cut-out sections at one end to
reduce the mass which has to be accelerated at each operation of the switch without
reducing the mechanical stability unduly.
[0033] The material used to make the frame structure of the contact element 13a of FIG.
3A is an epoxy resin reinforced with aramid fibers. Glass fiber reinforced epoxy materials
have been found to be prone to electrically induced erosion processes and to lower
insulation breakdown strength, which can be avoided with the epoxy resin reinforced
with aramid fibers. The later material is still capable of withstanding the high acceleration
forces during switching.
[0034] An enlarged section of the carrier part 15 is referred to below in figures 3B and
3C. This section includes a hole or opening 151 for the insertion of a conducting
element 16 as described in the following.
[0035] FIG. 4A is a cross-section of a main body 160 for use to manufacture a conducting
element 16 for insertion into the carrier part 15 of a contact element such as the
frame shown in FIG. 3A above. The main body 160 of conducting element 16 has essentially
a rectangular cuboid shape with an aspect ratio of approximately 5:1. It is made of
aluminium coated with a silver layer. Both ends or small faces of the main body 160
are machined into semi-spherical shape. All edges of the main body 160 are rounded.
[0036] The shape of the main body 160 is chosen such that the width in direction of the
displacement is small to ensure that conducting elements 16 can be separated with
a correspondingly small displacement of the contact elements 13a -14c. The length
in a direction perpendicular to both, the direction of displacement and the axial
direction of the switch, i.e. in direction of the tilting axis as defined above, however
is chosen to ensure a large contact area between two neighbouring conducting elements
(16) in the closed state.
[0037] In Fig. 4B a cross-section of the main body 160 of a conducting element 16 is shown
with a blind bore or hole 163 drilled into each of the rounded ends or small faces.
The bore 163is used to accommodate a spring 161 and a pin 162.
[0038] A cross-section of such a pin 162 is shown in FIG. 4C. It has an essentially cylindrical
shape with one rounded end. A central cut 164 is machined into the rounded end rendering
this end of the pin into a two pronged fork. The in radial direction outer corners
of each prong are again all rounded.
[0039] A fully mounted conducting element 16 within the frame structure of a contact element
13a (as shown in FIG. 3A) is illustrated in figures 3B and 3C, with FIG. 3B showing
a perspective view on an enlarged section of FIG. 3A with a conducting element 16
inserted into the pre-cut hole 151 of the carrier 15 of the contact element 13a. Due
the manufacturing steps as described above, all external exposed edges and corners
are rounded, thus providing a better protection against discharges and/or arc-forming
in a medium and high voltage environment.
[0040] The cross-section along the dash-dotted line X-X in FIG. 3B and perpendicular to
the plane of the opening 151 within the frame structure of the contact element 13a
(as shown in FIG. 3A) and with an conducting element 16 inserted is shown in FIG.
3C.
[0041] The conducting element 16 is shown in its assembled and mounted state. The conducting
element 16 includes the main body 160 and two pins each inserted into one of the blind
holes 163 at either end of the main body. Also located within the blind hole 163 is
a springy or an elastic element 161. In the absence of forces the springy element
161 pushes the upper, forked part of the pin 162 in direction out of its blind hole.
[0042] A conducting element 16 as described can be mounted into an opening 151 and thus
onto the carrier 15 of a contact element by exerting a force on the pin or pins 162
and by releasing this force, after the conducting element is in its desired position.
After the release of the force, the pins loch against the walls of the opening 151.
The width of the cut 164 in each pin is matched by the thickness of carrier wall at
this location. Thus a secure fastening is achieved without any further fastening means
such as screws or glues. At the same time, each contact element can be easily assembled
and conducting elements can be easily mounted or replaced.
[0043] Instead of or in addition to the two-pronged fork, the pin can be designed, for example
with a smaller pin at the top, to be inserted into holes within the side wall of the
openings 151. However this alternative is considered inferior to the example presented
above as it further weakens the structural integrity of the carrier part 15 or requires
at least a local increase in its thickness.
[0044] It is also possible, for example with a further cut perpendicular to the first cut
164 to structure the tip of the pin as four-pronged fork with each prong at the corner
of a rectangular. Again, this alternative is considered inferior as it weakens the
prongs and generates more edges and small features on the surfaces of the carrier.
The latter can again be the location of discharges and/or arc-forming in a medium
and high voltage environment.
[0045] It should be noted that the springy element 161 together with the cylindrical shape
of each pin 162 enable small tilting movements of the main body 161 out of the plane
of the carrier part 15. This aspect becomes important when the conducting elements
16 of two adjacent contact elements, e.g. contact element 13a and 14a of FIG. 1 come
into contact during the closing or opening of the switch. The tilting ensures that
in the final closed position the flattened long sides of the main body 160 are fully
in contact with each other and thus reduce the contact resistance and limit the heat
generated at the interface between the neighbouring conducting elements (16).
[0046] A switch with spacer elements as described above has applications for example in
a high voltage circuit breaker as illustrated in the FIG. 5 and described in the accompanying
text of
US 2013/0098874. In such arrangement the switch is connected in series with solid state breakers
and in parallel with a second set of solid state breakers.
[0047] While in the present description preferred embodiments of the invention are described,
it should be noted that the invention is not limited to those and can be implemented
in other ways within the scope of the following claims.
Reference numerals
[0048]
1: housing
2: space
3, 4: tube sections
5: housing section
6, 7: support insulators
8, 9: terminals
10, 11: caps
12: switching arrangement
13a, 13b, 13c: first set of contact elements
14a, 14b, 14c: second set of contact elements
15: insulating carrier part
151,152,153: recesses, openings of the carrier
16, 16': conducting elements
160: main body of conducting element
161: springy element
162: pin
163: blind hole
164: cut through pin
17: actuator rods
18: drive
19: drive
20: springs
32: contact plate
33: contact surface
34: conducting path
1. A high or medium voltage switch comprising
a first and a second terminal (8, 9),
a first and a second set of contact elements (13a, 13b, 13c; 14a, 14b, 14c) arranged
between the first and the second terminal (8, 9),
at least a first drive (18) for mutually displacing the sets of contact elements (13a,
13b, 13c; 14a, 14b, 14c) along a displacement direction (D),
wherein each contact element (13a, 13b, 13c; 14a, 14b, 14c) comprises an insulating
carrier part (15) carrying at least one conducting element (16), and
wherein in a first mutual position of said contact elements (13a, 13b, 13c; 14a, 14b,
14c) the conducting elements (16) of said contact elements (13a, 13b, 13c; 14a, 14b,
14c) form at least one conducting path (34) in an axial direction (A) between said
first and said second terminals (8, 9) in a direction transversally to said displacement
direction (D), and wherein in a second mutual position of said contact elements (13a,
13b, 13c; 14a, 14b, 14c) the conducting elements (16) are mutually displaced and do
not form said conducting path,
characterized in that the conducting elements (16) are fastened to the contact elements (13a, 13b, 13c;
14a, 14b, 14c) with at least one spring-loaded pin (161,162) allowing for a limited
amount of rotation or tilting of each conducting element (16) around its respective
at least one pin (161,162).
2. The switch of claim 1, wherein the conducting element (16) comprises an elongated
rectangular cuboid as main body (160) with two flattened long contact faces for contacting
in operation the flattened contact side of the conducting element (16) of an adjacent
contact element (13a, 13b, 13c; 14a, 14b, 14c) and further comprises at least one
spring-loaded pin (161,162) partially inserted into a blind hole (163) at at least
one of the small faces of the main body (160).
3. The switch of claim 2 with the conducting element (16) having spring-loaded pins (161,162)
partially inserted into blind holes (163) at both small faces of the main body (160).
4. The switch of claim 2 or 3, wherein the main body (160) of the conducting element
(16) is located within a hole (151) in the carrier part (15) such that the flattened
contact faces of the main body are parallel to the plane of the carrier and the one
or more pins (161,162) lock with the side walls of the hole (151).
5. The switch of claim 4, wherein the tip of the one or more pins (161,162) includes
a recess (164) with a width matching the thickness of the carrier part (15) such that
the pin can latch onto the carrier (15).
6. The switch of claim 4 or 5, wherein the width of the hole (151) is slightly larger
than the width of the main body (160) of the contacting element (16) such that a rotational
movement around the at least one pin (161,162) is limited to less than 5° in each
rotational direction about a tilt axis defined by the at least one pin (161,162).
7. The switch of any of the preceding claims, wherein the at least one pin (161,162)
is made of a harder material than the main body (160).
8. The switch of any of the preceding claims, wherein all exposed contours of the conducting
element (16) including all exposed contours of the at least one pin (161,162) are
rounded.
9. The switch of any of the preceding claims, wherein the connection between the carrier
(15) and the conducting element (16) mounted on it is free of hetero-material, in
particular gluefree.
10. A DC switch, particularly in accordance with any of the preceding claims, wherein
at least a carrier part (15) for mounting conducting elements (16) is made of a material
comprising a composite of epoxy resin reinforced with aramid fibers.
11. The switch of claim 10, wherein at least the carrier part (15) and an actuator rod
(17) connecting the carrier part (15) with a drive (18,18) for opening and closing
the switch are essentially made of a single sheet of material comprising a composite
of epoxy resin reinforced with aramid fibers providing a frame with recesses and/or
holes (151) for mounting conducting elements (16).
12. A current breaker comprising the switch of any of the preceding claims, said current
breaker further comprising
a primary branch and a secondary branch in parallel,
at least one solid state breaker arranged in the primary branch,
a plurality of solid state breakers (arranged in series in the secondary branch,
wherein a number of solid state breakers in the secondary branch is larger than a
number of solid state breakers in the primary branch, and wherein said switch is arranged
in said primary branch in series to said solid state breaker of said primary branch.