JPH11204845A - Superconducting current limiter element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase current limiter element capacity by providing a substrate comprising a first substrate with a superconductor thin film and second substrate with a conductive thin film. SOLUTION: On a support substrate 15 are disposed a first substrate 11 using a polycrystalline substrate having an intermediate layer of such as SrTiO3 , MgO, NdGaO3 or LaAlO3 and, second substrate 12, a superconductor thin film 13 is formed on the first substrate 11 to suppress the temp. rise, a first conductive thin film 14a is formed on the superconductor thin film 13, and a second conductive thin film 14b is formed on the second substrate 12 and electrically connected to the first conductive thin film 14a. Thus it is possible to dissipate the heat produced at the time of current limiting to a wide area and improve the current limiter element capacity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting current limiting element using a superconductor that limits an excessive current such as a short-circuit current flowing in an electric circuit.

[0002]

2. Description of the Related Art A superconductor can pass a current with almost zero resistance. However, any large current cannot flow at zero resistance, but when a certain current value (critical current value) is exceeded, resistance starts to be generated. The temperature rises rapidly to a temperature above the superconducting transition temperature, resulting in a so-called quenched state. As described above, when an excessive current flows through the superconductor, the superconductor quenches, and instantaneously changes from a superconducting state to a normal conducting state. Therefore, an element that generates resistance when an overcurrent flows can be made by inserting a conductor made of a superconductor in series into an electric circuit.

However, if a metal-based superconductor is used as the superconductor, it must be cooled using liquid helium which is expensive and has a low withstand voltage, which is an obstacle to producing a practical device. . Therefore, recently, research on a current limiting element using an oxide superconductor that can use liquid nitrogen having a low cooling cost and a high withstand voltage has been advanced. Among them, a current limiting device using a Y-based oxide superconductor thin film formed on a substrate has a critical current density at liquid nitrogen temperature of B
It is larger than an i-type oxide superconductor or the like, and has been studied by many research institutions in order to reduce the size of the device.

[0004] As a result, the problem of fabricating a current limiting device using a Y-based oxide superconductor has been gradually clarified. The most fundamental problem is to protect a superconducting thin film from a sudden rise in temperature due to heat generation at the time of current limiting, and to produce an element that can be used repeatedly. Generally, a metal thin film is provided as a protective layer on a superconducting thin film. Therefore, as a method for reducing the temperature rise, by increasing the thickness of the metal film and lowering the normal conduction resistance of the line,
Attempts have been made to reduce the amount of heat generated at the beginning of the current limit.

[0005] However, the above-described method causes a new problem that the resistance value at the time of current limiting is reduced and a sufficient current suppressing effect cannot be obtained. Therefore, as a method of generating sufficient resistance to suppress overcurrent and preventing an excessive rise in temperature at the time of current limiting, for example, a conductive thin film is provided so as to cover the entire substrate on which a superconducting thin film is partially formed. It has been proposed to increase the surface area of a region where heat is dissipated at the time of quench (see Japanese Patent Application Laid-Open No. 5-226706).

[0006]

In the conventional superconducting current limiting device, the conductive thin film is formed on the same substrate as the superconducting thin film. A large-area substrate on which a thin film can be formed is required.
However, the types of substrates on which high-performance superconducting thin films can be formed are limited, and the size of the obtained substrates is also limited. Therefore, there is a demand for a structure that increases the capacity of the superconducting current limiting element without increasing the size of the substrate on which the superconducting thin film having excellent characteristics is produced.

For example, Applied Physics Letter 59 (1991) 2034-20
From the research results published on page 36, the magnitude of the thermal contact resistance between the Y-based oxide superconductor thin film fabricated on a single crystal substrate and the substrate is about 10 ^-3 Kcm ² / W. You can see that there is. Considering this value and the value of the thermal conductivity of liquid nitrogen, if the current limiting element placed in liquid nitrogen causes quench due to overcurrent and the temperature rises by more than 100K within several tens of ms, It is found that most of the generated heat is transmitted to the substrate, and that the temperature of the superconducting thin film is almost the same as the temperature of the substrate surface in contact with the superconducting thin film.

That is, in the conductive thin film portion of the prior art, when a current is limited, a part of the overcurrent is diverted to the conductive thin film portion, and the heat generated by increasing the area of the heat generating portion is spread over a wide area of the substrate. It works to suppress the temperature rise of the current limiting element. Therefore, if a substrate with a small amount of temperature rise can be used even if the amount of heat transmitted is the same, the temperature rise can be kept within an allowable range even with a larger amount of heat generation. In other words, the current limiting capacity of the current limiting element can be increased, and the size of the element can be reduced. However, the conventional method cannot be applied to a superconducting current limiting element even if there is a substrate excellent in temperature rise, unless a superconducting thin film having good characteristics can be formed on the substrate.

Further, when the surface area of the conductive thin film is increased, if all the superconductor lines are in a normal conduction state, the current certainly flows over a larger area than the superconducting thin film portion, so that the calorific value per unit area decreases. This has the effect of suppressing the temperature rise. However, an actual superconducting thin film always has a local variation in a critical current value, and when the current increases, quench does not occur uniformly but locally.

FIG. 33 is an example of a plan view of a current-limiting conductor disclosed in Japanese Patent Application Laid-Open No. 5-226706. However, in this figure, the conductive thin film provided on the superconducting thin film is omitted. When a portion X of the superconducting thin film 1 is locally quenched, the current shunts to the conductive thin film 2. 3A is a shunt current flowing near the superconducting thin film 1 and 3B is a shunt current flowing near the end of the conductive film 2. When a local quench occurs in a region where the length in the longitudinal direction is very short compared to the line width, the resistance of the path along the shunt current 3B is larger than the resistance of the path along the shunt current 3A. It increases by the ratio of the height. Therefore, the magnitude of the shunt current 3A and the shunt current 3B is much larger for the shunt current 3A. That is, in this conventional device structure, the current concentrates on a part of the conductive thin film 2 for the quench generated locally,
The entire conductive thin film 2 provided cannot be used effectively.

The present invention has been made to address such a problem, and an object of the present invention is to provide a superconducting current limiting element which can increase the current limiting element capacity. More specifically, a superconducting current-limiting element that enables the current-limiting element capacity to be increased without increasing the size of the substrate for producing a superconducting thin film, and a conductive conducting element that shunts a part of the overcurrent during quench. It is an object of the present invention to provide a superconducting current-limiting element capable of increasing the use efficiency of a film and increasing the current-limiting element capacity.

[0012]

A first superconducting current limiting element according to the present invention comprises a superconducting thin film and a conductive thin film formed on a substrate, and the first superconducting current limiting element is formed by an overcurrent. In a superconducting current limiting element having a structure in which a part of an overcurrent is shunted to the conductive thin film when the superconducting thin film is quenched, the substrate is formed by the first substrate on which the superconducting thin film is formed and the conductive thin film. And a second substrate that is provided.

In the first superconducting current limiting element, the second substrate may be formed by calculating a square root of a product of a thermal conductivity and a heat capacity per unit volume as a normal operating temperature of the element. The average value over the temperature reached by the element at the time of current limiting is larger than that of the first substrate.

Further, in the first superconducting current limiting element, for example, the first substrate is embedded in a concave portion provided in the second substrate. Alternatively, as described in claim 4, the first substrate on which the superconducting thin film is formed is joined to the second substrate on which the conductive thin film is formed, and the conductive thin film is formed. And the superconducting thin film are electrically connected via a conductive member.

The second superconducting current limiting element according to the present invention comprises:
6. A superconducting thin film and a conductive thin film formed on a substrate, and a bridge portion for electrically connecting the superconducting thin film and the conductive thin film, wherein the superconducting thin film and the conductive thin film are formed by an overcurrent. When the thin film is quenched, a part of the overcurrent is diverted to the conductive thin film through the bridge portion.

In the first superconducting current limiting element of the present invention, the conductive thin film is formed on a second substrate different from the first substrate on which the superconducting thin film is formed. Therefore, without being limited to the first substrate on which the superconducting thin film is formed, the conductive thin film can be formed on various substrates capable of suppressing a temperature rise. That is, the current limiting capacity of the current limiting element can be increased.

Further, in the second superconducting current limiting element of the present invention, since a bridge portion for electrically connecting the superconducting thin film and the conductive thin film is provided in addition to the current introducing portion, the superconducting thin film is locally formed. Even when quenching occurs, the overcurrent shunts over a wide portion of the conductive thin film. As a result, an excessive rise in temperature can be effectively prevented. That is, the current limiting capacity of the current limiting element can be increased.

[0018]

Embodiments of the present invention will be described below.

FIG. 1 is a sectional view showing a schematic structure of an embodiment of the first superconducting current limiting element of the present invention. In the figure, 11 is a first substrate on which a superconducting thin film is formed,
Reference numeral 12 denotes a second substrate on which a conductive thin film is formed. First
Is a substrate on which a superconducting thin film having excellent characteristics can be formed, specifically, SrTiO ₃ , Mg
O, NdGaO ₃ , LaAlO ₃ , Y having high in-plane orientation
It is preferable to use a polycrystalline YSZ substrate provided with an intermediate layer such as stabilized ZrO ₂ (YSZ). On the other hand, as the second substrate 12 on which the conductive thin film is formed, a substrate capable of suppressing a rise in temperature is used.

A superconducting thin film 13 is formed on a first substrate 11, and a first conductive thin film 14a is formed on the superconducting thin film 13. In addition, a second conductive thin film 14b is formed on the second substrate 12, and the second conductive thin film 14b is electrically connected to the first conductive thin film 14a. The first on which the superconducting thin film 13 is formed
Substrate 11 and the second conductive thin film 14b formed on the second
The substrates 12 are arranged on a support substrate 15 and are respectively joined to the support substrate 15 with an epoxy-based adhesive or the like. Note that the first substrate 11 and the second substrate 12 may be directly bonded and used.

The superconducting thin film 13 is made of Y 2a ₂ Cu ₃
RE-Δa-Cu—O such as O ₇ (YBCO) (RE is a Y and lanthanide element (except when RE is all Pr)), Δi-Sr—Ca—Cu—O, T
l-Ba-Ca-Cu-O system, (Βa, K) -Βi-O
Various oxide superconductors, such as systems, can be used. Ag, Au, Pt, I
Various metal thin films such as n, Cu, Al, Ni, Cr, Fe and alloys thereof can be used.

Here, when a conductive thin film for overcurrent shunt is formed on the substrate on which the superconducting thin film is formed, the area for dispersing the amount of heat generated at the time of current limiting is limited by the size of the substrate on which the superconducting thin film is formed. You. On the other hand, by using the first substrate 11 on which the superconducting thin film is formed and the second substrate 12 on which the conductive thin film is formed as different substrates, it is possible to disperse the generated heat over a wider area. It is possible to increase the capacity of the flow element.

Consider a rise in the temperature of a substrate provided with a thin-film heating element on the surface and transmitting heat of Q watts per unit area. In general, the distance over which heat is transmitted during Δt seconds is given by the so-called thermal diffusion length. This is expressed as follows: where Cσ is the heat capacity per unit volume of the substrate and κ is the thermal conductivity.

(Equation 1) It is expressed as When the thickness of the substrate is larger than this value, the heat capacity of the portion where the heat spreads is represented by S, where S is the surface area of the substrate.

(Equation 2) It is expressed as

On the other hand, the amount of heat transmitted to the substrate during Δt seconds is Q
Since S · Δt, the temperature rise ΔT after Δt seconds from the start of heat generation is

(Equation 3) For the same calorific value, the larger the thermal conductivity or the heat capacity per unit volume, the smaller the temperature rise during current limiting.

Therefore, the first substrate 11 on which the superconducting thin film 13 is formed and the second substrate on which the conductive thin film 14b is formed, rather than making the substrate on which the conductive thin film is formed the same as the substrate on which the superconducting thin film is formed. The substrate 12 is another substrate, and the second
By using a substrate material having a large thermal conductivity and a large heat capacity per unit volume for the substrate 12, it is possible to more effectively suppress the temperature rise at the time of current limiting.

Further, the SrTiO ₃ substrate (11) and the like capable of forming the superconducting thin film 13 having excellent characteristics are limited in the size of the obtained substrate. Without being limited to the size of the first substrate 11), it is possible to suppress a temperature rise due to heat generation at the time of current limiting. In other words, it is possible to increase the current limiting element capacity.

As the second substrate 12, for example, a YSZ substrate, Al ₂ O ₃ substrate, AlN substrate, SiC substrate, Si ₃
An N ₄ substrate or the like is used, and these may be either a single crystal substrate or a polycrystalline substrate. In particular, if the second substrate 12 has a larger square root of the product of the thermal conductivity and the heat capacity per unit volume than that of the first substrate 11, it is more effective to suppress the temperature rise. .

The square root of the product of the above thermal conductivity and the heat capacity per unit volume was averaged between the normal operating temperature (T ₁ ) of the device and the temperature (T ₂ ) reached by the device at the time of current limiting. The value (Cκ _av ) is calculated based on, for example, the following equation.

[0029]

(Equation 4) For example, as shown in FIG. 2, the first substrate 11 may be embedded in a concave portion 16 provided in the second substrate 12 for use.
In this case, after the first substrate 11 is embedded in the concave portion 16 provided in the second substrate 12, the surfaces are polished so that their surfaces become flat, and the superconducting thin film 13 and the conductive thin film are formed on such surfaces. 14 are preferably formed in order.

As described above, the superconducting current limiting device according to this embodiment includes the substrate 12 for forming the conductive thin film 14b.
Is a substrate different from the substrate 11 for forming the superconducting thin film 13, and the superconducting thin film 13 and the conductive thin film 14
b is electrically connected. To shunt overcurrent, there is a method of connecting a resistor in parallel to the superconducting thin film,
In this case, the current does not shunt at high speed due to the inductance of the electric wire used for the connection. In the superconducting current limiting element of the present invention, since the conductive thin film 14 is used as a member for shunting the overcurrent, and this is disposed near the superconducting thin film 13,
Overcurrent can be divided at high speed. In addition, when a conductive thin film that is insulated from the front surface is provided on the back surface of the second substrate 12 on which the conductive thin film 13 that shunts the overcurrent is formed, the overcurrent can be shunted at a higher speed. .

Here, the substrate 11 for forming the superconducting thin film 13 is replaced with the substrate 1 for forming the conductive thin film 14b.
When embedding in the concave portion 16 provided in the
If there is a difference between the coefficients of thermal expansion 1 and 12, thermal distortion occurs in the process of increasing the temperature at the time of current limiting, which degrades the characteristics of the superconducting thin film 13 and disconnects the connection between the superconducting thin film 13 and the conductive thin film 14. There is a possibility that.

In order to avoid these problems, the substrate on which the conductive thin film and the superconducting thin film are formed is preferably made of the same material. However, when a polycrystalline substrate is used, an intermediate layer (YS) for promoting the orientation of the superconducting thin film is formed on the substrate on which the superconducting thin film is formed.
Z, MgO, CeO ₂ , SrTiO ₃ ). However, it is not necessary to provide such an intermediate layer on the substrate on which the conductive thin film is formed. Thus, even if the same material is used, it is possible to improve production efficiency by separately manufacturing the two substrates.

On the other hand, as shown in FIGS. 3 and 4, the superconducting thin film 13 is formed on the second substrate 12 on which the conductive thin film 14b is formed.
It is also preferable to form a structure in which the first substrate 11 on which is formed is bonded, and the conductive thin film 14b and the superconducting thin film 13 are electrically connected via a conductive member.

In FIG. 3, a current bypass conductive thin film 17 is further provided on the conductive thin film 14b on the second substrate 12 side, and the current bypass conductive thin film 17 and the superconducting thin film 1 are provided.
3 and is electrically connected to the conductive thin film 14a formed thereon. In this connection, it is preferable that a conductive bump (not shown) such as an In bump is interposed, and electrical and mechanical bonding is performed with the conductive bump. According to such an element structure, thermal strain can be reduced by the conductive bumps.

In FIG. 4, after bonding the first substrate 11 on which the superconducting thin film 13 is formed on the second substrate 12 on which the conductive thin film 14b is formed, the conductive thin film 18 such as an In wire is used. 14b and the superconducting thin film 13 are electrically connected. Even with such an element structure, thermal distortion can be reduced.

Here, a superconducting thin film 13 (for example, a YBCO thin film) which is a design parameter of the superconducting current limiting element of the present invention.
Width Ws, thickness ds, length Ls and width Wm, thickness dm, length Lm of the conductive thin film 14b for shunting overcurrent.
Is preferably designed as shown below, for example.

Firstly, the width Ws of the superconducting thin film 13 is the critical current density J _c in the normal energization peak current I and the superconducting thin film 13 of the current limiting element, than the thickness ds, determined as I / (J _c ds). If the thickness of the superconducting thin film 13 is increased, the crystallinity deteriorates. Therefore, the thickness ds is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 10 μm or less. Also, in order to transfer heat to the substrate efficiently,
Width Ws is preferably set to 10 times or more the thickness ds, and it is more desirable that the 10 ² times or more. Further, in order to efficiently shunt the current to the conductive thin film 14b, it is preferable that the length Ls of the superconducting thin film 13 is equal to the length Lm of the conductive thin film.

By the way, the distance at which the current rapidly diffuses within 1 ms from the superconducting thin film 13 to the conductive thin film 14b during the current limiting operation is about 100 mm. Therefore, in order to respond at a practically necessary speed, the width Wm of the conductive thin film is preferably 200 mm or less, and more preferably 100 mm or less. Further, in order to enhance the handleability of the substrate 12, the width Wm of the conductive thin film 14b is preferably 2 mm or more.

The length Lm of the conductive thin film 14b is preferably at least VαI / QWm (1) in order to prevent the substrate from being damaged by thermal shock during the current limiting operation. Here, V is the voltage of the system to which the current limiting element is connected, Q is the amount of heat generated per unit area that can be allowed during current limiting operation, and α is the ratio between the current limiting current and the normal energizing current, which differs depending on the system. Usually takes a value of 2 to 4. The calorific value of the oxide substrate without destroying the substrate is 3
Because it is ~10kW / cm ^2, Q is preferably set to 10 kW / cm ² or less, more preferably 5 kW / cm ² or less,
Further, it is desirable to set it to 1 kW / cm ² or less. The upper limit of the length Lm of the conductive thin film 14b is determined by the size of the substrate 12, and is preferably 10 m or less.

The thickness dm of the conductive thin film 14b is determined by the resistance V / (αI) required at the time of current limiting. Conductive thin film 1
Assuming that the resistivity of 4b is ρm, V / (αI) = (ρm L
m) / (dm Wm), and (αI) = (QWm Lm)
/ V, dm = (Qρm Lm ² ) / V ² (2)

In order to sufficiently conduct the conductive thin film 14b, the thickness dm is preferably 50 nm or more, more preferably 100 nm or more. The conductive thin film 14b
If the length Lm is increased, the thickness dm can be increased. However, since the length Lm is limited by the size of the substrate 12, the thickness dm is preferably 100 μm or less, more preferably. It is desirable that the thickness be 10 μm or less, and more preferably 1 μm or less.

A 6.6 kV / 400 A class current limiting device is designed by the above procedure. The ratio α of the current limiting current of this current limiting element to the normal energizing current
Is 2. First, when using a YBCO thin film (13) having a thickness of 1 μm and J _c = 10 ⁶ A / cm ² formed on a SrTiO ₃ substrate (11), the YBCO The width Ws of the thin film (13) needs to be 40 mm. When a silver thin film formed on a YSZ polycrystalline substrate (12) is used as the conductive thin film 14b, the current is sufficiently diffused into the silver thin film (14b) during operation.
Is set to 80 mm, and from the thermal shock resistance of the substrate 12, Q = 1k
Assuming W / cm ² , Lm = 6.6 m from equation (1). YBC
The length Ls of the O thin film (13) is the same as Lm. Silver ρ
Since m is 2 × 10 ^-6 Ωcm, dm is 200 nm from the equation (2).
Becomes

The second substrate 12 on which the conductive thin film 14b is formed does not need to be one, and may have a structure in which a plurality of substrates are connected. When a plurality of substrates are connected, the amount of liquid nitrogen decreases due to the heat generated at the electrode connection portions.Therefore, the number of electrode connection portions is preferably small, and the number of substrates connected in series is preferably 50 or less. , And more preferably 25 or less. In addition, the number of the first substrates 11 (substrate on which the superconducting thin film 13 is formed) to be bonded on the second substrate 12 on which the conductive thin film 14b is formed is not limited to one, and a large number of substrates 1
1 may be bonded on the second substrate 12. Furthermore, the first
As the shapes of the second substrates 11 and 12, various shapes can be adopted as shown in the embodiments described later.

Next, an embodiment of the second superconducting current limiting element of the present invention will be described. FIG. 5 is a plan view showing a schematic structure of one embodiment of the second superconducting current limiting element of the present invention.
The superconducting current limiting element shown in FIG. 5 has a superconducting thin film 22 formed on a substrate 21, and a conductive thin film 23 is formed on the superconducting thin film 22. The conductive thin film 23 is also formed on the surface of the substrate 21 that is not covered with the superconducting thin film 22. In FIG. 5, the conductive thin film 23 on the superconducting thin film 22 is omitted.

On the conductive thin film 23, a bridge portion 24 for electrically connecting the superconducting thin film 22 and the conductive thin film 23 is provided at a portion other than the current introducing portion. The bridge portion 24 shunts a part of the overcurrent from the superconducting thin film 22 to the conductive thin film 23 at the time of quenching.
For example, the cross-sectional area of a conductive film such as a metal film is increased, and the normal conduction resistance of the line is reduced. If such a low-resistance film is formed over the entire surface, the resistance value at the time of current limiting is reduced as described above, and a sufficient current suppressing effect cannot be obtained.

In such a superconducting current limiting element, when a portion X of the superconducting thin film 22 is locally quenched, the shunt current 25A flowing near the superconducting thin film 22 and the shunt current 25B flowing near the end of the conductive thin film 23 are reduced. Along the line resistance, the presence of the bridge portion 24 made of a conductive material reduces the line resistance in the direction in which the current crosses the conductive thin film 23. The difference between the values of the current 25B becomes smaller.

In other words, even when the superconducting thin film 22 is locally quenched due to the presence of the bridge portion 24, the overcurrent is diverted over a wide portion of the conductive thin film 23. When the conductive thin film 23 is not in direct contact with the superconducting thin film (superconducting line) 22, the conductive thin film 23 is not shunted without the bridge portion 24. By providing, even if quenching occurs locally, the conductive thin film 2
3, an overcurrent can be diverted to prevent an excessive rise in temperature. That is, it is possible to increase the current limiting element capacity.

The substrate used for the second superconducting current limiting element of the present invention may be a normal single plate-shaped substrate, but in particular, the same substrate as that of the first superconducting current limiting element of the present invention, ie, It is preferable to use a first substrate on which a superconducting thin film is formed and a second substrate on which a conductive thin film is formed.

[0049]

Next, specific examples of the present invention and evaluation results thereof will be described.

Example 1 In this example, a superconducting current limiting element having the element structure shown in FIG. 1 was manufactured. The first substrate 11 has a width of 5 mm and a length of 5 mm.
Using a 40 mm SrTiO ₃ substrate, a 1.1 μm thick YBC thin film 13 was formed on the SrTiO ₃ substrate 11 by laser evaporation.
Was formed. On the YBC thin film 13, a silver thin film 14a having a thickness of 100 nm was formed as a stabilizing film. As the second substrate 12, a polycrystalline YSZ substrate having a width of 5 mm and a length of 40 mm was used, and an 80 nm thick silver thin film 14b having a function of shunting overcurrent was formed on the polycrystalline YSZ substrate 12.

Each of the first and second substrates 11 and 12 has a thickness of 2 mm, and has a substrate 11 on which a YBC thin film 13 is formed and a substrate 12 on which a silver thin film 14b is not yet formed.
Is fixed on a supporting substrate 15 with an epoxy-based adhesive,
Thereafter, a silver thin film 14b was formed using a metal mask.
At this time, one end of the silver thin film 14b slightly protrudes above the YBC thin film 13 to make electrical contact. The critical current value of the device thus fabricated was 53 A, and the line resistance at room temperature was about 0.7Ω.

This device was cooled with liquid nitrogen and subjected to a 50 Hz half-wave current limiting test. FIG. 6 shows the result. This element starts current limiting at a current value of about 115A, and succeeds in suppressing an overcurrent of about 300A without a current limiting element. At this time, the maximum power applied to the device was 4.5 kW (50 V, 90 A).

For comparison with the present invention, a width of 5 mm and a length of 40
The line resistance is approximately equal to the liquid nitrogen temperature on the SrTiO ₃
When a silver thin film was vapor-deposited so as to have a current of 0.7 Ω and a current of 50 Hz and a half-wave was applied, the element was burned at a current and voltage value of about 52 A and 40 V. In other words, SrTiΟ ₃ having a width of 5 mm and a length of 40 mm
Substrates can only withstand up to about 2kW of heat. Actually, when a current limiting element having various patterns including the presence of the conductive thin film was formed on this substrate and a test was performed, none of the elements could achieve the current limiting capacity of Example 1. .

[0054] As a second substrate for forming a conductive thin film for diverting Example 2 overcurrent, but using Al ₂ Omicron ₃ substrate, produce current-limiting device having the same structure as in Example 1 Then, it was cooled with liquid nitrogen and subjected to a 50 Hz half-wave current limiting test.

As a result, although the current-limiting start current value hardly changed, the power supply voltage could be further increased, and no damage was caused even when the maximum load reached 6 kW (60 V, 100 A). The resistance generated during the current limit reached its maximum after about 9 ms, and was 0.66Ω. Considering that the resistance of this element increases with increasing temperature and that the resistance at room temperature is 0.7Ω, it can be seen that the temperature of the element has not increased to room temperature.

Therefore, the square root of the product of the heat capacity and the heat conductivity per unit volume from 60 K to 300 K is shown in FIG. 7 as a function of temperature. As can be seen from FIG. 7, the square root of the product of the heat capacity and the thermal conductivity per unit volume is always larger in the Al ₂ O ₃ substrate than in the SrTiO ₃ substrate at the operating temperature of the current limiting element. That is, it can be said that the reason why the current limiting capacity could be increased is that a conductive thin film was formed using a substrate having a small temperature rise.

Example 3 In this example, a superconducting current limiting element having the element structure shown in FIG. 2 was manufactured. First, a groove 6 having a size of 5 mm × 40 mm × 2 mm in depth is previously formed in a polycrystalline YSZ substrate 12, and an SrTiO ₃ substrate 11 is buried in the groove 6.
After surface polishing was performed so that the surfaces of the Z substrate 12 and the SrTiO ₃ substrate 11 were flat, a YBC thin film 13 was formed, and a current limiting element was manufactured in the same manner as in Example 1.
The current limiting characteristic of this element is the same as that of the first embodiment.
The current limiting capacity is increased as compared with the case where only the SrTiO ₃ substrate is used.

Example 4 In this example, a superconducting current limiting element having the element structure shown in FIG. 3 was manufactured. First, as shown in FIGS. 8 and 9, a YBCO thin film 13 and a silver thin film 14 a were formed on an SrTiO ₃ substrate 11, and a current bypass conductive thin film 17 was further formed. 8 shows a case where the areas of the YBCO thin film 13 and the silver thin film 14a are the same, and FIG. 9 shows a case where the silver thin film 14a is formed to have a larger area than the YBCO thin film 13. On the other hand, a YSZ substrate 12 having a silver thin film 14b on the surface was prepared. FIG. 10 shows a method of manufacturing the device of this embodiment.
It will be described in detail with reference to FIG.

In FIG. 10, the member indicated by A has a width of 15 mm,
A silver thin film is formed on the entire surface of a YSZ substrate 12 having a length of 50 mm and a thickness of 2 mm.
Sputtered 100nm, then 2μm thick for current bypass
m A silver thin film 17 is partially formed, and an In bump 31 having a diameter of 1 mm and a thickness of 1 mm is adhered to the bonded portion. The member indicated by B in the figure is formed by forming a YBCO thin film 13 on a SrTiO ₃ substrate 11 having a width of 5 mm, a length of 50 mm, and a thickness of 2 mm, then sputtering a silver thin film 14 a to a thickness of 100 nm, and forming a 2 mm wide current bypass on the silver thin film 14 a. A silver thin film 17 having a thickness of 2 μm is formed, and an In bump 31 is further adhered to the bonded portion. The members A and B thus produced were bonded together, and annealed in an electric furnace at 100 ° C. for 10 minutes to join the In bumps 31 together.

As shown in FIG. 9, 1.5 mm of both ends of the YBCO thin film 13 on the 8 mm wide SrTiO ₃ substrate 11 are wetted in order to prevent the diffusion of In into the YBCO thin film 13 to deteriorate the superconducting characteristics. After the etching, it is preferable to use the silver thin film 14a. FIGS. 11 and 12 show cross-sectional views of the element after bonding when both ends are not etched (FIG. 8) and when both ends are etched (FIG. 9).

When a current of 50 Hz was applied to these elements, current limiting was started at 120 A, and the device did not burn even at a maximum applied voltage of 50 V and a maximum heat load of 7.5 kW, and a current limiting function was obtained.
Further, the current limiting test was repeated 10 times, but the device characteristics did not deteriorate. This is because thermal distortion during current-limiting operation, which is a cause of element deterioration, is alleviated by the In bump, thereby improving the stability of repeated operation.

Embodiment 5 The superconducting current limiting element of this embodiment is, as shown in FIG.
It has a structure in which silver thin films 14b and 14c are formed on both surfaces of a YSZ substrate 11 having a width of 15 mm, a length of 50 mm and a thickness of 2 mm. 1 in the figure
4b is a silver thin film having a thickness of 100 nm, and an overcurrent flows through this layer. On the other hand, 14c in the figure is a silver thick film having a thickness of 100 μm, and is not electrically connected to the silver thin film 14b.

Since the thick silver film 14c is formed on the back side of the YSZ substrate 11 as described above, the inductance of the silver thin film 14b can be reduced.
Overcurrent can be shunted from the CO thin film 13 to the silver thin film 14b faster than in the fourth embodiment, and the withstand voltage of the element can be increased. This element starts current limiting at 120A,
It was able to operate up to the maximum applied voltage of 80V.

Embodiment 6 As shown in FIG. 14, the superconducting current limiting element of this embodiment
On a polycrystalline YSZ substrate 12 having a width of 300 mm, a length of 800 mm, and a thickness of 2 mm on which a silver thin film 14 b is disposed on the surface, a member 32 having a width of 10 mm, a length of 100 mm, and a thickness of 2 mm as shown in FIG. It has a structure in which a plurality of substrates are laminated in series via In bumps. A current limiting test was performed by flowing a half-wave current of 50 Hz to this device. As a result, current limiting was started at 240 A, and the device was able to operate repeatedly without burning out up to the maximum applied voltage of 2.4 kV.
Further, a current limiting element having the same structure as that shown in FIG. 14 on the back side of the YSZ substrate 12 was manufactured, and a current limiting test was performed.
Current limiting was started at 0A, and operation was repeated up to the maximum applied voltage of 2.4kV.

FIG. 15 shows a structure in which six members 32 having the structure shown in FIG. 8 are connected in series and four sets are connected in parallel. The device started current limiting at 960A and operated without burning up to a maximum applied voltage of 600V.

Embodiment 7 As shown in FIG. 16, the superconducting current limiting element of this embodiment
A member formed by spirally depositing a silver thin film 14b on a cylindrical YSZ substrate 12 having an outer diameter of 200 mm, a thickness of 5 mm, and a length of 300 mm is formed on the substrate 1 in the same configuration as in FIG.
m, a member 32 using a YSZ tape having a length of 4 m is helically bonded by In bumps. This device started current limiting at 240 A and was able to operate repeatedly up to the maximum applied voltage of 2 kV.

Further, as shown in FIG.
When current limiting elements wound on 200 mm, 220 mm and 240 mm cylinders are superposed and connected in series,
Operable up to 240A and maximum applied voltage of 6.2kV.

Embodiment 8 The superconducting current limiting device of this embodiment has a width as shown in FIG.
Silver thin film 1 on YSZ substrate 12 of 20 mm, length 50 mm and thickness 2 mm
YBC with a thickness of 1 μm is placed on a member on which 4b is deposited to a thickness of 100 nm.
O thin film 13 formed on the surface, width 10 mm, length 50 mm, thickness
It has a structure in which a 0.5 mm SrTiO ₃ substrate 11 is arranged. The YBCO thin film 13 and the silver thin film 14b are electrically connected by an In wire 18 having a diameter of 1 mm.

According to the superconducting current limiting element of this embodiment, the YSZ substrate 12 and the SrTiO ₃ substrate 11
Can be mitigated by the In line 18. The device starts current limiting at 240A and the maximum applied voltage is 5
It could be operated up to 0V and could be operated repeatedly.

As shown in FIG. 18, a member formed by forming a YBCO thin film 13 on a tapered SrTiO ₃ substrate 1 is joined to a YSZ substrate 12 having a silver thin film 14b disposed on the surface, and furthermore, an electrical connection is made. A silver thick film 33 having a thickness of 20 μm was formed in order to obtain a film. In this case, the SrTiO ₃ substrate 11 is provided with a 50 ° taper in order to establish conduction between the YBCO thin film 13 and the silver thin film 14b. The angle of the taper is preferably 80 ° or less, and more preferably 60 ° or less in order to facilitate conduction. In addition, 30 mm or more is preferable so that the substrate can be easily handled.

Embodiment 9 The superconducting current limiting element of this embodiment is, as shown in FIG.
A member formed by forming a YBCO thin film 13 on both sides of an SrTiO ₃ substrate 11 having a width of 5 mm, a length of 50 mm, and a thickness of 1 mm is provided with a silver thin film 14 b having a thickness of 100 nm via an In bump 31.
It has a structure in which two YSZ substrates 12 of 50 mm in length, 50 mm in length and 2 mm in thickness are connected. With such a structure, the current capacity could be increased, and the current limiting onset current of this device was 240A.

Embodiment 10 The superconducting current limiting element of this embodiment has a structure as shown in FIG.
A 10 mm width, 10 mm width is formed on both sides of a member formed by forming a YBCO thin film 13 on an SrTiO ₃ substrate 11 having a width of 5 mm, a length of 50 mm, and a thickness of 2 mm.
It has a structure in which members in which a silver thin film 14b having a thickness of 100 nm is formed on a YSZ substrate 12 having a length of 50 mm and a thickness of 2 mm are respectively connected by In. With such a structure,
The width of the silver thin film 14b through which the current is diffused can be doubled as compared with the fourth embodiment, and the heat load of the element can be reduced. This element starts current limiting at 120A and the maximum applied voltage is 8
It was able to operate up to 0V.

As shown in FIG. 21, the SrTiO ₃ substrate 11 on which the YBCO thin film 13 was formed was laminated and connected in parallel.

Example 11 In this example, a superconducting current limiting element having the element structure shown in FIGS. 22 to 24 was manufactured. FIG. 23 corresponds to FIG.
FIG. 24 is a sectional view taken along line AA ′ of FIG.
It is sectional drawing which followed the B 'line.

The substrate 21 for forming the YBCO thin film has a width of 5
A SrTiO ₃ substrate having a thickness of 50 mm, a length of 50 mm and a thickness of 2 mm was used.
Reference numeral 22 denotes a YB having a thickness of about 1 μm formed by a laser evaporation method.
The CO thin film 26 is a silver thin film having a thickness of 100 nm as a protective film. Reference numeral 23 denotes a silver thin film having a thickness of 80 nm for overcurrent shunting.

In order to process a Y-based superconducting thin film into a desired shape, first, a YBCO
A thin film 22 is formed, and a silver thin film 26 is formed on the surface thereof by vapor deposition.
Was formed, wet etching was performed using a photoresist. The width of the line at both ends is 5 mm to allow current to flow in and out from the outside, while the width of the superconducting line at the other portions is 2 mm. Further, a silver thin film 23 is formed on both sides with a width of 1.5 mm using a metal mask and a vapor deposition method. Finally, a silver layer having a width of 5 mm, a length of 1 mm, and a thickness of 2 μm is formed as a bridge portion 24 by a metal mask and a vapor deposition method. 7mm
Formed at intervals. The critical current value of this line at liquid nitrogen temperature was 24A.

On this device, three voltage terminals (terminal 1, terminal 2, terminal 3: not shown) are provided at intervals of 10 mm.
While measuring the voltage V ₂₃ between the voltage V ₁₂ and the terminals 2 3 between the terminal 2 of current 50Hz sink 1 cycle, we examined the current limiting characteristics gradually even increasing the peak current value. Figure 2 shows the result.
It is shown in FIG. FIG. 26 is an enlarged view of the initial stage of the voltage generation. As can be seen from FIG.
Current limiting has started at 5A. Appears to almost the same behavior with FIG 25, two voltages, looking at Figure 26 an enlarged this voltage quickly approximately 50μs than towards the V ₁₂ is V ₂₃ occurs, quenched locally You can see that it started. When the current limiting characteristics were measured by further increasing the voltage, the current limiting element did not burn even at an applied voltage of 45 V and a maximum current of 50 A.

For comparison with the present invention, the bridge 24
An element having the same structure as in Example 11 was prepared except that no current was provided, and a current limiting test was performed. As a result, although the current limiting onset current value did not change, the element burned out when the power supply voltage was increased to 35V. From this, it can be seen that according to the superconducting current limiting device of the present invention provided with the bridge portion 24, the overcurrent is diverted to a wider area of the conductive thin film.

Example 12 In this example, a superconducting current limiting element having the element structure shown in FIGS. 27 to 29 was manufactured. 28 is the same as FIG.
FIG. 29 is a sectional view taken along line AA ′ of FIG.
It is sectional drawing which followed the B 'line.

In these figures, 21a is a 5 mm wide, 50 mm long, 2 mm thick SrTiO ₃ substrate, on which a 1 μm thick YBCO thin film 22 is formed by laser evaporation. This substrate 21a is fitted into a polycrystalline YSZ substrate 21b having a groove of 5 mm in width and 2 mm in depth,
After bonding, silver having a thickness of 100 nm was deposited on the entire surface of the substrate to form a silver thin film 26 as a protective film and a silver thin film 23 for overcurrent shunt at the same time. The width of the polycrystalline YSZ substrate 21b is 15
mm.

As the bridge portion 24, a silver layer having a width of 15 mm, a length of 2 mm and a thickness of 2 μm was formed at intervals of 10 mm by a metal mask and an evaporation method. Further, the substrate 21a and the substrate 21
The top of the seam b was reinforced with silver paste 27. The device has a resistance of 0.4Ω at room temperature and a critical current of 53A at liquid nitrogen temperature. The current limiting characteristics in liquid nitrogen are the same as in FIG. 26, and although the quench start time varies in the superconducting line, the element does not burn out, but generates resistance against overcurrent and has a current limiting function. Demonstrated. This current limiting element started current limiting at about 120A, and was able to suppress overcurrent without burning out even with a maximum applied voltage of 50V and a maximum thermal load of 7.5kW.

For comparison with the present invention, the bridge 24
An element with the same structure was fabricated except that no current was formed, and the current limiting characteristics were examined.When the power supply voltage was low, overcurrent was suppressed without burnout, but the maximum voltage was 30 V and the maximum thermal load was low.
Burnout at 4.5kW.

Example 13 In this example, a superconducting current limiting element having the element structure shown in FIGS. 30 to 32 was manufactured. FIG. 31 is the same as FIG.
FIG. 32 is a cross-sectional view taken along the line AA 'in FIG. 30.

The superconducting current limiting element of this embodiment is the same as the eleventh embodiment in plan view, but as shown in FIG. 32, the YBCO thin film 22 is disposed under the silver thin film 23 for overcurrent shunting. Remains. In order to manufacture an element having such a structure, first, a YBCO thin film 22 is formed on a substrate 21,
After depositing a silver thin film 26 thereon by 100 nm, patterning as shown in FIG. 31 is performed by photoresist and wet etching. After that, a silver thin film 23 is deposited by 80 nm,
Finally, a silver layer having a thickness of 2 μm is formed as a bridge portion 24.

As a result of the current limiting test of this device, the applied voltage 50
Even at V and the maximum current of 55 A, the current limiting element did not burn out, and the characteristics were improved as compared with Example 11. This is because when a local quench occurs, a part of the overcurrent flows not only in the bridge portion 24 but also in the superconducting thin film (YBCO thin film 22) itself and shunts to the silver thin film 23. It is thought that it was possible to wake up.

[0086]

As described above, according to the first superconducting current limiting element of the present invention, since the substrate on which the superconducting thin film is formed and the substrate on which the conductive thin film is formed are different, the superconducting thin film is formed. The amount of heat generated at the time of current limiting can be diffused to a wider area without increasing the size of the substrate to be formed. Therefore, it is possible to improve the capacity of the current limiting element. Further, according to the second superconducting current limiting element of the present invention, since the superconducting thin film and the conductive thin film are bridged with a conductive material, a part of the overcurrent flowing through the conductive thin film is made more uniform, The current limiting capacity can be increased by using a conductive thin film having the same area. By combining these two configurations, the current limiting capacity can be further increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of an embodiment of a first superconducting current limiting element of the present invention.

FIG. 2 is a sectional view showing a modification of the superconducting current limiting element shown in FIG.

FIG. 3 is a perspective view showing a schematic structure of another embodiment of the first superconducting current limiting element of the present invention.

FIG. 4 is a diagram showing a modification of the superconducting current limiting element shown in FIG.

FIG. 5 is a plan view showing a schematic structure of an embodiment of the second superconducting current limiting element of the present invention.

FIG. 6 is a diagram showing a current limiting characteristic of the superconducting current limiting element according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a temperature change of Al ₂ O ₃ and SrTiO ₃ at a value of (thermal conductivity × heat capacity per unit volume) ^0.5 .

FIG. 8 is a perspective view showing an example of a superconducting thin film-side constituent member of a superconducting current limiting element according to Embodiment 4 of the present invention.

FIG. 9 is a perspective view showing another example of the superconducting thin film-side constituent member of the superconducting current limiting element according to Embodiment 4 of the present invention.

FIG. 10 is a diagram for explaining a method of manufacturing a superconducting current limiting device according to Example 4 of the present invention.

FIG. 11 is a cross-sectional view illustrating a configuration example of a superconducting current limiting element according to Embodiment 4 of the present invention.

FIG. 12 is a cross-sectional view showing another configuration example of the superconducting current limiting element according to Embodiment 4 of the present invention.

FIG. 13 is a sectional view showing a configuration of a superconducting current limiting element according to Embodiment 5 of the present invention.

FIG. 14 is a plan view showing a configuration example of a superconducting current limiting element according to Embodiment 6 of the present invention.

FIG. 15 is a plan view showing another configuration example of the superconducting current limiting element according to Embodiment 6 of the present invention.

FIG. 16 is a perspective view showing a configuration example of a superconducting current limiting element according to Embodiment 7 of the present invention.

FIG. 17 is a perspective view showing another configuration example of the superconducting current limiting element according to Embodiment 7 of the present invention.

FIG. 18 is a diagram showing another configuration example of the superconducting current limiting element according to Embodiment 8 of the present invention.

FIG. 19 is a sectional view showing a configuration of a superconducting current limiting element according to Embodiment 9 of the present invention.

FIG. 20 is a diagram showing a configuration example of a superconducting current limiting element according to Embodiment 10 of the present invention.

FIG. 21 is a diagram showing another configuration example of the superconducting current limiting element according to Embodiment 10 of the present invention.

FIG. 22 is a plan view showing a configuration of a superconducting current limiting element according to Embodiment 11 of the present invention.

FIG. 23 is a sectional view taken along the line AA ′ of FIG. 22;

24 is a sectional view taken along the line BB 'of FIG.

FIG. 25 is a diagram illustrating current limiting characteristics of a superconducting current limiting element according to Embodiment 11 of the present invention.

FIG. 26 is an enlarged view of the initial stage of voltage generation of the current limiting characteristic of FIG. 25;

FIG. 27 is a plan view showing a configuration of a superconducting current limiting element according to Embodiment 12 of the present invention.

FIG. 28 is a sectional view taken along the line AA ′ in FIG. 27.

FIG. 29 is a sectional view taken along line BB ′ of FIG.

FIG. 30 is a plan view showing a configuration of a superconducting current limiting element according to Embodiment 13 of the present invention.

FIG. 31 is a plan view showing a patterning state of a YBCO thin film in Example 13.

FIG. 32 is a sectional view taken along the line AA ′ of FIG. 30.

FIG. 33 is a plan view schematically showing a configuration example of a conventional superconducting current limiting element.

[Explanation of symbols]

 11 First substrate 12 Second substrate 23, 22 Superconducting thin film 14, 23 Conductive thin film 24 Bridge part

[Procedure amendment]

[Submission date] March 5, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

The second superconducting current limiting element according to the present invention comprises:
As described in claim 5, the superconducting thin film formed on the substrate and the superconducting thin film on the surface of the substrate are not covered with the superconducting thin film.
A conductive thin film formed on a portion thereof, and a bridge portion for electrically connecting the superconducting thin film and the conductive thin film, and when the superconducting thin film is quenched by an overcurrent, an overcurrent flows through the bridge portion. Is characterized in that it has a structure in which a part of the shunt flows into the conductive thin film.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hisashi Yoshino 1 Tokoba Toshiba-cho, Koyuki-ku, Kawasaki-shi, Kanagawa Inside Toshiba R & D Center Co., Ltd.

Claims (5)

[Claims] 1. A superconducting limit comprising a superconducting thin film and a conductive thin film formed on a substrate, and having a structure in which a part of the overcurrent is shunted to the conductive thin film when the superconducting thin film is quenched by an overcurrent. In the flow element, the substrate includes a first substrate on which the superconducting thin film is formed and a second substrate on which the conductive thin film is formed. 2. The superconducting current limiting element according to claim 1, wherein the second substrate reaches a square root of a product of a thermal conductivity and a heat capacity per unit volume at a normal operating temperature of the element and at the time of current limiting. A superconducting current limiting element, wherein a value averaged over the temperature of the first substrate is larger than that of the first substrate. 3. The superconducting current limiting device according to claim 1, wherein the first substrate is embedded in a concave portion provided in the second substrate. 4. The superconducting current limiting element according to claim 1, wherein the first substrate on which the superconducting thin film is formed is joined to the second substrate on which the conductive thin film is formed, A superconducting current limiting element, wherein the conductive thin film and the superconducting thin film are electrically connected via a conductive member. 5. A superconducting thin film and a conductive thin film formed on a substrate, and a bridge portion for electrically connecting the superconducting thin film and the conductive thin film, wherein the superconducting thin film is quenched by an overcurrent. A superconducting current limiting element having a structure in which a part of the overcurrent is diverted to the conductive thin film through the bridge portion.