U.S. patent application number 13/904080 was filed with the patent office on 2014-03-06 for superconductive device without an external shunt system, in particular with a ring shape.
The applicant listed for this patent is Bruker HTS GmbH. Invention is credited to Alexander Usoskin.
Application Number | 20140066315 13/904080 |
Document ID | / |
Family ID | 46516521 |
Filed Date | 2014-03-06 |
United States Patent
Application |
20140066315 |
Kind Code |
A1 |
Usoskin; Alexander |
March 6, 2014 |
Superconductive device without an external shunt system, in
particular with a ring shape
Abstract
A superconducting device (1; 1a, 1b), having a coated conductor
(2) with a substrate (3) and a quenchable superconducting film (4),
wherein the coated conductor (2) has a width W and a length L, is
characterized in that 0.5.ltoreq.L/W.ltoreq.10, in particular
0.5.ltoreq.L/W.ltoreq.8, and that the coated conductor (2) has an
engineering resistivity .rho..sub.eng shunting the superconducting
film (4) in a quenched state, with .rho..sub.eng>2.5.OMEGA.,
wherein R.sub.IntShunt=.rho..sub.eng*L/W, with R.sub.IntShunt:
internal shunt resistance of the coated conductor (2). The risk of
a burnout of a superconducting device in case of a quench in its
superconducting film is thereby further reduced.
Inventors: |
Usoskin; Alexander; (Hanau,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bruker HTS GmbH |
Hanau |
|
DE |
|
|
Family ID: |
46516521 |
Appl. No.: |
13/904080 |
Filed: |
May 29, 2013 |
Current U.S.
Class: |
505/230 ;
174/125.1; 361/93.9 |
Current CPC
Class: |
H01L 39/16 20130101;
H02H 9/023 20130101; H01B 12/06 20130101 |
Class at
Publication: |
505/230 ;
174/125.1; 361/93.9 |
International
Class: |
H01B 12/06 20060101
H01B012/06; H02H 9/02 20060101 H02H009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2012 |
EP |
12 171 087.5 |
Claims
1. A superconducting device having a coated conductor, the coated
conductor comprising: a substrate; and a quenchable superconducting
film, wherein said coated conductor has a width W and a length L,
with 0.5.ltoreq.L/W.ltoreq.10 or 0.5.ltoreq.L/W.ltoreq.8, the
coated conductor having an engineering resistivity .rho..sub.eng
shunting said superconducting film in a quenched state thereof,
wherein .rho..sub.eng>2.5.OMEGA., with
R.sub.IntShunt=.rho..sub.eng*L/W and R.sub.IntShunt: an internal
shunt resistance of the coated conductor.
2. The superconducting device of claim 1, wherein the substrate is
a metallic substrate electrically insulated from said
superconducting film, a dielectric substrate, a thin metallic
substrate or a thin metallic substrate having a thickness
T.ltoreq.100 .mu.m.
3. The superconducting device of claim 1, wherein W.gtoreq.12 mm or
W.gtoreq.40 mm.
4. The superconducting device of claim 1, wherein W.gtoreq.50 mm or
W.gtoreq.100 mm.
5. The superconducting device of claim 1, wherein L.gtoreq.10 cm or
L.gtoreq.36 cm.
6. The superconducting device of claim 1, wherein L.gtoreq.50 cm or
L.gtoreq.100 cm.
7. The superconducting device of claim 1, wherein said
superconducting film comprises YBCO material.
8. A superconducting device having a coated conductor, the coated
conductor comprising: a substrate; and a quenchable superconducting
film, the coated conductor having a width W and a length L, wherein
a length of a primary normal zone generated by a quench in said
quenchable superconducting film corresponds to said length L of the
coated conductor or to a substantial part of said length L.
9. The superconductive device of claim 8, wherein said coated
conductor has a width W and a length L, with
0.5.ltoreq.L/W.ltoreq.10 or 0.5.ltoreq.L/W.ltoreq.8, the coated
conductor having an engineering resistivity .rho..sub.eng shunting
said superconducting film in a quenched state thereof, wherein
.rho..sub.eng>2.5.OMEGA., with R.sub.IntShunt=.rho..sub.eng*L/W
and R.sub.IntShunt: an internal shunt resistance of the coated
conductor.
10. The superconducting device of claim 1, wherein the coated
conductor forms a closed loop.
11. The superconducting device of claim 8, wherein the coated
conductor forms a closed loop.
12. The superconducting device of claim 10, wherein, in an end
region of the coated conductor, a part of said substrate is removed
and superconducting film parts at said end region and at a further
end region of the coated conductor are jointed with each other or a
mechanical support structure is provided on top of said
superconducting film at said end region near said removed part.
13. The superconducting device of claim 10, wherein said substrate
of the coated conductor is of a ring type or circular ring
type.
14. The superconducting device of claim 10, wherein two end regions
of the coated conductor are bent inward or outward and
superconductor film parts are jointed with each other at end
regions thereof.
15. A superconducting assembly comprising a plurality of coaxially
arranged superconducting devices of claim 10, placed one within an
other.
16. A fault current limiter comprising the superconducting device
of claim 1.
17. A fault current limiter comprising the superconducting device
of claim 8.
18. The fault current limiter of claim 16, wherein the fault
current limiter is of an AC type with a primary coil for carrying a
current to be limited and a secondary coil to be coupled to said
primary coil via a common magnetic flux, wherein the
superconducting device is included in said secondary coil.
19. The fault current limiter of claim 18, wherein said secondary
coil comprises a plurality of sub-coils which are realized as
superconducting devices, wherein said coated conductor forms a
closed loop, the superconducting devices being placed next to each
other and within said primary coil.
Description
[0001] This application claims Paris convention priority of EP 12
171 087.5 filed Jun. 6, 2012 the entire disclosure of which is
hereby incorporated by reference
BACKGROUND OF THE INVENTION
[0002] The invention relates to a superconducting device,
comprising a coated conductor with a substrate and a quenchable
superconducting film, wherein the coated conductor has a width W
and a length L.
[0003] Such a superconducting device is known for example from EP 2
192 629 A1.
[0004] Superconducting devices are used in different ways, in
particular to transport electric currents, for current conditioning
such as in fault current limiters, or for generating high strength
magnetic fields.
[0005] Superconducting devices comprise a conductor which may, at a
temperature below the so called critical temperature Tc, carry an
electric current at practically no ohmic losses. In order to
achieve said low temperature, the conductor is typically cooled
with liquefied gases such as liquid helium. Further, to have a
superconducting state, it is also necessary to stay below a
critical current density and below a critical magnetic field with
the conductor.
[0006] When using high temperature superconductor (HTS) materials,
e.g. yttrium barium copper oxide (YBCO) material, higher
temperatures, current densities and magnetic fields become
accessible. HTS material is typically used as a film (or coating)
on a normally-conducting or insulating substrate.
[0007] A difficulty when employing superconducting devices is the
risk of a sudden loss of the superconducting state, also called a
quench. If a region of a superconducting film quenches, a high
electric current has to pass through the region now normally
conducting, what causes a considerable heating of said region. The
high current and heating may damage the superconducting material,
what is also called a burnout.
[0008] Generally, it is desired that a superconducting device can
survive a quench, so it can be used again e.g. after recooling of
the device. In order to avoid a burnout of the superconducting
material, it is known to protect superconducting films with shunt
resistance.
[0009] EP 2 117 056 B1 discloses an elongated coated conductor,
comprising a superconducting film on a substrate, covered by a
first metallic member, and electrically connected to a resistive
member running in parallel to the elongated conductor via regularly
spaced bridge contacts. The resistive member is spaced apart from
the elongated conductor, so the resistive member is thermally
decoupled from the elongated coated conductor. The resistive member
provides an external shunt protection.
[0010] In case of a quench in the superconducting film, the major
part of the electric current is rerouted around the quenched region
through the resistive member, so the current strength through the
elongated conductor in the quenched region is reduced. The major
heating occurs in the resistive member then, and not in the
elongated conductor.
[0011] It is also known to cover or encapsulate superconducting
films with a normally conducting stabilization layer, e.g. made of
copper, compare U.S. Pat. No. 7,774,035 B2. Again, in case of a
quench, the electric current is to be rerouted through the
stabilization layer in order to preserve the superconducting films.
The stabilization layer provides an internal shunt system for a
coated conductor. Coated conductors with external shunt protection
are difficult to manufacture. Internal shunt protection may reroute
a major part of the electric current away from the superconducting
film, but heating may still damage the superconducting film.
Therefore, even when using known external and internal shunt
protection, a burnout of the superconductor film may still
occur.
[0012] It is the object of the invention to further reduce the risk
of a burnout of a superconducting device in case of a quench in its
superconducting film.
SUMMARY OF THE INVENTION
[0013] This object is achieved, in accordance with the invention,
by a superconducting device as mentioned in the beginning,
characterized in
that 0.5.ltoreq.L/W.ltoreq.10, in particular
0.5.ltoreq.L/W.ltoreq.8, and that the coated conductor has an
engineering resistivity .rho..sub.eng shunting the superconducting
film in a quenched state, with .rho..sub.eng>2.5.OMEGA., wherein
R.sub.IntShunt=.rho..sub.eng*L/W, with R.sub.IntShunt: internal
shunt resistance of the coated conductor.
[0014] The inventors have found that surprisingly, when the length
L of the coated conductor (or its superconducting film,
respectively) is chosen sufficiently small as compared to the width
W of the coated conductor (or its superconducting film,
respectively), namely up to about ten times the width W, and the
engineering resistivity .rho..sub.eng is chosen sufficiently large,
namely above 2.5 Ohms, the risk of a burnout of the superconducting
film in case of its quench becomes very low. Accordingly, a
superconducting device meeting the above criteria is very likely to
survive a quench event, so expensive replacements after a quench
may be avoided. An external shunt protection (which is thermally
decoupled from the coated conductor or its superconducting film,
respectively, such as bridge contacts linking a spaced apart
resistive member) is not necessary and typically dispensed with, in
accordance with the invention.
[0015] In use, the superconducting film carries a current in
the
direction of the extension of the length L of the coated conductor.
The internal shunt resistance is the (ohmic) resistance of the
coated conductor in the quenched state, available to the electric
current that would flow through the superconducting film in the
superconducting state, excluding any external shunt protection. The
current paths providing the internal shunt resistance are thermally
coupled to the coated conductor or its superconducting film,
respectively (such as the substrate or cap layers on the
superconducting film).
[0016] Note that the thickness of the superconducting film (on top
of the substrate, perpendicular to the substrate plane) and the
height of the coated conductor (perpendicular to the substrate
plane) seem to be irrelevant for the inventive protective effect
against burnout, at least as long as said height is in a reasonable
range, such as below 400 .mu.m.
[0017] The engineering (internal shunt) resistivity .rho..sub.eng
according to the invention is comparably high, typically available
only with a dielectric (electrically insulating) substrate, or with
a metallic substrate electrically insulated from the
superconducting film, or with a rather thin metallic substrate. In
particular, the engineering (internal shunt) resistivity
.rho..sub.eng, in accordance with the invention is lower than with
a non-insulated metal substrate of typical thickness (which is
about 100 .mu.m).
[0018] A particularly reliable protection against burnout of the
superconducting film can be achieved when choosing
.rho..sub.eng>5.0.OMEGA..
[0019] In a preferred embodiment of the inventive superconducting
device, the substrate is [0020] a metallic substrate electrically
insulated from the superconducting film, [0021] a dielectric
substrate, or [0022] a thin metallic substrate, in particular with
a thickness T.ltoreq.100 .mu.m. When choosing a substrate according
to one of the above types, the engineering resistivity can easily
be set in accordance with the invention.
[0023] Further preferred is an embodiment wherein W.gtoreq.12 mm,
in particular W.gtoreq.40 mm. Moreover, it is preferred when
W.gtoreq.50 mm, in particular W.gtoreq.100 mm. These dimensions
have shown good results in practice. A large width W allows a
comparably large length L.
[0024] Also preferred is an embodiment wherein L.gtoreq.10 cm, in
particular L.gtoreq.36 cm. Moreover, it is preferred when
L.gtoreq.50 cm, in particular L.gtoreq.100 cm. With such large
lengths, closed loops with a comparably large cross-sectional area
can be formed.
[0025] In another preferred embodiment, the superconducting film
comprises YBCO material. YBCO films have shown a high immunity
against damage upon quench (burnout) in an inventive
superconducting device.
[0026] Also within the scope of the present invention is a
superconducting device, comprising a coated conductor with a
substrate and a quenchable superconducting film, wherein the coated
conductor has a width W and a length L, characterized in that the
length of a primary normal zone generated by a quench in the
quenchable superconducting film corresponds to the length L of the
coated conductor or to a substantial part of the length L of the
coated conductor. This reduces the risk of a burnout of a
superconducting device in case of a quench in its superconducting
film. A "primary normal zone" is a first minimal-area zone which
crosses the width W of the quenchable superconducting film at the
first stage of quench. This zone exhibits a normal (in particular
metallic) conductivity which forms as a result of a full or a
partial (local) quench of the quenchable superconducting film. The
formation of the primary normal zone is very short in time: for
tape widths of 40-100 mm this process takes 10-40 microseconds.
Further development of the normal zone leads to its propagation
along the length of the quenchable superconducting film. Within the
first 100-200 microseconds the normal zone may spread across a
distance that corresponds to from 2 to 20 widths W (if the coated
conductor is long enough). A substantial part of the length L of
the coated conductor is, in particular, 25% or more of the length
L, preferably 50% or more of the length L.
[0027] In a preferred embodiment of this superconducting device,
the superconducting device is designed as an inventive
superconducting device as described above.
[0028] In an advantageous embodiment of an above mentioned
superconducting device, the coated conductor forms a closed loop.
Accordingly, a circular superconducting current may run through the
superconducting film with a minimum of jointing; such a closed loop
may in particular be used in an AC fault current limiter. The width
W becomes a height of a basically ring-shaped structure here. Note
that the in accordance with this embodiment, a superconducting
bridge element may be employed to electrically close the loop
between the two ends parts of the superconducting film
(corresponding to two joints); note that the bridge element
typically bridges a gap GP much shorter than the length L here,
typically with L.gtoreq.10*GP, preferably L.gtoreq.30*GP.
Alternatively, it may be preferred to do without a bridge element
and realize the closed loop structure with direct jointing of the
superconducting film parts at the end regions of the coated
conductor (i.e. with only one joint), or even without joints at all
(see below).
[0029] In an advantageous further development of said embodiment,
in an end region of the coated conductor, a part of the substrate
is removed, and superconducting film parts at said end region and
at a further end region of the coated conductor are jointed with
each other, in particular wherein a mechanical support structure is
provided on top of the superconducting film at the end region near
the removed part. The part of the substrate may be removed by
etching, for example.
[0030] In another advantageous further development, the substrate
of the coated conductor is of a ring type, in particular circular
ring type. Here a closed loop substrate (typically of metal type)
is prepared first (e.g. by cutting away a piece of a seamless metal
tube) and then the superconducting film is deposited, typically on
the outer side of the cut substrate ring. Jointing is completely
unnecessary in this further development.
[0031] Yet another further development provides that two end
regions of the coated conductor are bent inward or outward, and the
superconductor film parts at said end regions are jointed with each
other. This jointing is particularly simple. The end regions
typically show a v-shaped jointing region here.
[0032] Also within the scope of the present invention is a
superconducting assembly, comprising a plurality of coaxially
arranged superconducting devices of closed loop structure, placed
one within the other. Thus a particularly high current carrying
capacity for circular currents can be achieved in a compact
design.
[0033] Further within the scope of the present invention is a fault
current limiter, comprising an inventive superconducting device or
an inventive superconducting assembly. In a fault current limiter,
a high tolerance against burnout is particularly valued. The fault
current limiter may be of resistive (DC) or inductive (AC)
type.
[0034] In a preferred embodiment of the inventive fault current
limiter, the fault current limiter is of AC type with a primary
coil for carrying a current to be limited and a secondary coil to
be coupled to the primary coil via a common magnetic flux, and the
superconducting device or superconducting assembly is included in
the secondary coil. Within the secondary coil, superconducting
devices in a closed loop arrangement are particularly useful.
[0035] A further development of said embodiment provides that the
secondary coil comprises a plurality of sub-coils which are
realized as superconducting devices with a closed loop structure,
wherein said superconducting devices are placed next to each other
and within the primary coil. These sub-coils can be built with a
high aspect ratio, what makes it easier to adhere to the inventive
geometry.
[0036] Further advantages can be extracted from the description and
the enclosed drawing. The features mentioned above and below can be
used in accordance with the invention either individually or
collectively in any combination. The embodiments mentioned are not
to be understood as exhaustive enumeration but rather have
exemplary character for the description of the invention.
[0037] The invention is shown in the drawing.
BRIEF DESCRIPTION OF THE DRAWING
[0038] FIG. 1 an embodiment of an inventive superconducting device,
with a flat coated conductor, in a schematic perspective view;
[0039] FIG. 2a an embodiment of an inventive superconductive device
in schematic cross-section, with a metallic substrate and a
dielectric intermediate layer;
[0040] FIG. 2b an embodiment of an inventive superconductive device
in schematic cross-section, with a dielectric substrate;
[0041] FIG. 2c an embodiment of an inventive superconductive device
in schematic cross-section, with a thin metallic substrate;
[0042] FIG. 3a an embodiment of an inventive superconducting
device, with a closed loop structure, with outwardly bent ends of
the coated conductor, in a schematic top view;
[0043] FIG. 3b the embodiment of FIG. 3a in a schematic side
view;
[0044] FIG. 4a an embodiment of an inventive superconducting
device, with a closed loop structure, with substrate material
removed at an end of the coated conductor, in a schematic top
view;
[0045] FIG. 4b the embodiment of FIG. 4a, in an uncoiled state, in
a schematic illustration;
[0046] FIG. 5 an embodiment of an inventive superconducting device,
with a closed loop structure, with a bridge element; in a schematic
top view;
[0047] FIG. 6 an embodiment of an inventive superconductive
assembly comprising two superconducting devices with a closed loop
structure, placed one within the other, in a schematic top
view;
[0048] FIG. 7a an embodiment of an inventive fault current limiter
of AC type, in a schematic cross-sectional view, with one secondary
coil surrounding a primary coil;
[0049] FIG. 7b an embodiment of an inventive fault current limiter
of AC type, in a of closed loop structure arranged next to each
other and placed within a primary coil.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0050] FIG. 1 shows an embodiment of a superconducting device 1 in
accordance with the present invention. In FIG. 1, the general
geometry is particularly obvious.
[0051] The superconducting device 1 here consists a coated
conductor 2, with a substrate 3 and a superconducting film 4
deposited on top of it. Note that there may be additional layers,
such as one or more buffer layers between the substrate 3 and the
superconducting film 4, and protection and/or shunting layers
(capping layers) on top of the superconducting film 4 (not shown
for simplification).
[0052] The coated conductor 2 has a length L, in the direction of
which flows, in use, a superconducting current I (or normally
conducting current, in case of a quench). The coated conductor 2
has a width W and a height H. Typical lengths L are about 10 cm and
above. Typical widths are at about 12 mm and above. The height H is
typically 400 .mu.m or less.
[0053] In the example shown, the ratio of L/W is about 4. In
accordance with the invention, said ratio is between 0.5 and 10,
preferably between 0.5 and 8.
[0054] The coated conductor 2 has, between its ends E1 and E2 in
the non-superconducting state, an internal shunt resistance
R.sub.IntShunt of about 12 Ohms here; said resistance can be
measured, e.g., by contacting the opposing side faces SF (only one
of which is visible in FIG. 1) of the superconducting film 4 with
metallic electrodes and measuring the voltage at a known electric
current. An engineering resistivity .rho..sub.eng with
.rho..sub.eng=R.sub.IntShunt*W/L results here to 3.0 Ohms then. In
accordance with the invention, .rho..sub.eng is above 2.5 Ohms,
preferably above 5 Ohms.
[0055] An inventive superconducting device 1 shows a very low
probability of a damage upon a quench of the superconducting film
4.
[0056] The inventive engineering resistivity .rho..sub.eng is
significantly higher than typical engineering resistivities known
form conventional coated conductors, e.g. of YBCO type.
[0057] The large engineering resistivity, in accordance with the
invention, may be achieved for example by providing a dielectric
(electrically insulating) intermediate layer 21 between a metal
substrate 3 and the superconducting film 4, compare FIG. 2a showing
an inventive superconducting device 1 in cross-section. In
addition, a buffer layer 22 between the substrate 3 and the
superconducting film 4 may be used in order to increase the crystal
quality of the superconducting film 4 (typically, the
superconducting film is epitaxial). In the example shown, there is
also a protection layer 23 of a precious metal (such as gold) on
top of the superconducting film 4. If desired, a shunt layer
(typically of copper) may further be deposited (not shown); however
this shunt layer should be relatively thin in order to keep the
internal shunt resisitivity large enough. It should be noted that
the protection layer 23 as well as a possible shunt layer should
not be enveloping and therefore not electrically connect the
superconducting film 4 with the metallic substrate 3, in order to
exclude the metal substrate 3 from affecting the internal shunt
resistance.
[0058] Alternatively, the substrate 3 may be of dielectric type,
compare FIG. 2b. In this case, no insulation of the superconducting
film 4 and the substrate 3 is necessary. In the example shown, a
buffer layer 22 and a protection layer 23 are also used. If
desired, a sufficiently thin shunt layer may be employed (not
shown).
[0059] If the substrate 3 is sufficiently thin, compare FIG. 2c,
the substrate 3, even if of metal type, need not be insulated from
the superconducting film 4 in order to achieve a sufficiently large
engineering resisitivity. In the example shown, there is again a
buffer layer 22 and a protection layer 23. A sufficiently thin
shunt layer may also be used, if desired (not shown).
[0060] FIG. 3a in a top view and FIG. 3b in a side view show an
inventive superconducting device 1, wherein the coated conductor 2
forms a closed loop. The superconducting film 4 (shown as a thick
black line, also in the following figures) is deposited on the
inward side of the substrate 3. In order to establish a
superconducting connection between the two ends of the
superconducting film 4, the end regions E1, E2 of the coated
conductor 2 are outwardly bent and the superconducting film 4 at
the two end regions E1, E2 is directly jointed together, typically
using a silver solder, compare joint region 31. Note that
alternatively, the end regions 31, 32 may be inwardly bent if the
superconducting film 4 was deposited on the radially outer side of
the substrate 3. This jointing is particularly simple.
[0061] If bending the end regions of a coated conductor 2 is not
possible (e.g. if the radius of curvature would be so small that
the superconducting film 4 would be damaged), it is also possible
to have a direct jointing of the superconducting film 4 at the end
regions E1, E2 when removing (e.g. etching away) some part 41 of
the substrate 3 at one end region, here E2, compare FIG. 4a in a
top view and FIG. 4b in a decoiled view. In the area of the removed
part 41, the coated conductor 2 of the other end region E1 may
access with its superconducting film part 4a the remaining
superconducting film part 4b of end region E2 directly (typically,
a solder is used for this jointing, such as a silver solder). If
needed, end region E2 may be mechanically stabilized by means of a
stabilizing structure 42 (e.g. a thin metal film) so the remaining
superconducting film part 4b, which is not supported by the
substrate 3 any more, does not break off.
[0062] In another embodiment of a coated conductor 2 with a closed
loop structure, shown in FIG. 5 in a top view, a bridge element 51
is used to provide a superconducting electric connection between
the superconducting film parts 4a, 4b at end regions E1, E2. The
bridge element 51 comprised a superconducting layer 52 on a bridge
substrate 53, with the superconducting layer 52 being directly
jointed (typically by means of a solder, such as a silver solder)
to both superconducting film parts 4a, 4b. The bridge element t 51
thus crosses a gap GP between the two end regions E1, E2 of the
coated conductor 2, wherein said gap GP corresponds to about
1/20.sup.th of the total length L of the coated conductor here. By
use of a bridge element 51, bending of the coated conductor 2 is
avoided.
[0063] FIG. 6 shows in a top view an inventive superconducting
assembly 61, comprising (here) two superconducting devices 1a, 1b,
which have both coated conductors in a closed loop structure, and
with the superconducting devices 1a, 1b placed (here
concentrically) one in another. In this arrangement, both
superconducting devices 1a, 1b may affect the center region CR of
the superconducting assembly 61, in particular by generating or
interacting with a magnetic flux in the center region CR.
[0064] In the example shown, the two superconducting devices 1a, 1b
are jointless, what may lead to particularly stable circular
superconducting currents. In order to achieve this, closed ring
shaped substrates 3 were produced first (for example by welding two
ends of a tape type substrate, or by cutting a ring from a seamless
tube produced by extrusion molding). Subsequently, the
superconducting films 4 (and other layers, if need may be) were
deposited on the substrates 3 (typically wherein a substrate ring
is rotated under a deposition apparatus).
[0065] FIG. 7a shows in a vertical, cross-.sectional view an
inventive fault current limiter 71 of AC type, in which an
inventive superconducting device 1 (or alternatively an inventive
superconducting assembly) is used.
[0066] The fault current limiter 71 comprises a normally conducting
primary coil 72 and a coaxially arranged secondary coil 73, which
is realized with an inventive superconducting device 1 as shown in
FIG. 4a here; support structure of the secondary coil 73 is not
shown, for simplification.
[0067] Inside the primary coil 72, a ferromagnetic core 74 is
positioned, providing a good coupling of the primary and secondary
coil 72, 73. During normal operation, the primary coil 72 carries
an electric current to be limited against fault current, and in the
secondary coil 73, a superconducting current is induced which
largely counter-balances the magnetic field of the primary coil 72,
so the primary coil 72 experiences no significant inductive
resistance.
[0068] The secondary coil 73 is located within a cryostat 75,
inside of which a cryogenic temperature (such as at or below 90K,
preferably at or below 4.2K) has been established, so the
superconducting device 1 or its superconducting film 4,
respectively can assume the superconducting state.
[0069] In case of a rise of the current in the primary coil 72
("fault current"), the current in the secondary coil 73 also rises,
namely above the critical current Ic of the secondary coil 73, and
the superconductivity collapses in the secondary coil 73
("quench"). As a consequence, the primary coil 72 now experiences a
considerable inductive resistance, what limits the current in the
primary coil 72.
[0070] In order to be able to bear the quench, in accordance with
the invention, the secondary coil 73 or the superconducting device
1, respectively, has a geometry with a ratio of length L (here
corresponding to the circumference 2*R*.pi. of the secondary coil
73) and width W of about L/W=6, and is realized with a dielectric
substrate 3 carrying the superconducting film 4 so that the
engineering resistivity .rho..sub.eng of the coated conductor is
relatively high at about 3 Ohms.
[0071] Since the secondary coil 73 can stand a quench, the fault
current limiter can easily be reused after a quench, in particular
after having sufficiently recooled of the secondary coil 73.
[0072] FIG. 7b shows a further embodiment of an inventive fault
current limiter 71, comprising a primary coil 72, here wound upon a
cylinder shaped support 76, and a secondary coil 73 comprising a
plurality of sub-coils, which are realized as inventive
superconducting devices 1 with a coated conductor of closed loop
structure ("one winding sub-coil"). Said superconducting devices 1
are arranged next to each other within the primary coil 72, so each
sub-coil may interact with a part of the magnetic flux of the
primary coil 72. For simplification, the cryostat for the
superconducting devices 1 is not shown in FIG. 7b.
* * * * *