JP2831823B2 - Superconducting current limiter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting current limiter that suppresses an excessive short-circuit current from flowing in a power system at the time of a ground fault or the like.

(Prior art)

FIGS. 4 and 5 show a conventional superconducting current limiter. The superconducting current limiting device shown in FIG. 4 has a superconducting current limiting element 2 formed in a meandering shape in a form embedded in an electrically insulating substrate 1. The superconducting current limiting device shown in FIG. The superconducting current limiting element 2 is formed in a meandering shape. The superconducting current limiting element 2 is made of a material exhibiting superconductivity at a liquid nitrogen temperature (77 K), for example.

These superconducting current limiters are used by being connected in series to an electric power system while being cooled to extremely low temperature by, for example, liquid nitrogen. The critical current of the superconducting current limiting element 2 is designed to be larger than the rated current of the power system and smaller than the short-circuit current at the time of an accident. Therefore, the superconducting current limiting element 2 is in a superconducting state when the steady current that is equal to or less than the rated current flows in the power system, and the electric resistance is zero, but when an accident occurs and a large short-circuit current flows, the superconducting current limiting element 2 2 changes from a superconducting state to a normal conducting state, and an electric resistance is generated. Therefore, the impedance of the power system increases, and the short circuit current is suppressed to a low value, so that the power system is protected from an excessive short circuit current.

〔Task〕

In a conventional superconducting current limiting device, the superconducting current limiting element is integrated with an electrically insulating substrate by means such as sintering or bonding in order to protect the superconducting current limiting element from vibration or external force.

However, since the superconducting current limiting element and the electrically insulating substrate have different thermal expansion coefficients, when the superconducting current limiting device is cooled from room temperature to extremely low temperature such as liquid nitrogen temperature, or after a long-term temperature history, There is a problem that a difference in the amount of expansion and contraction occurs in the superconducting current limiting element having a relatively low mechanical strength and a crack is generated in the superconducting current limiting element.

If such a crack occurs even at one point, the critical current of the superconducting current limiter decreases, so that the current-limiting element transitions from the superconducting state to the normal conducting state even in a steady state below the rated current, and the electric resistance is reduced. There is a risk of occurring. In the worst case, the above-described failure of the current limiter necessitates stopping the power transmission of the power system and replacing the current limiter with a normal product, which seriously hinders stable power supply.

[Solutions to solve the problem]

The present invention has been made in view of the above-described problems of the prior art, and does not cause cracks in the superconducting current limiting element even for long-term use, and does not cause performance degradation as a current limiter, and thus has high reliability. It is an object to provide a superconducting current limiter.

In order to achieve this object, the present invention is connected in series to a power system, is in a superconducting state when a steady current flows, and enters a normal conducting state when a short circuit current flows due to a power system accident to reduce the electric resistance. In a superconducting current limiting device provided with a superconducting current limiting element for limiting the occurrence of an excessive short-circuit current in a power system, the superconducting current limiting element is provided in a groove or a hole formed in an electrically insulating support. It is characterized in that it is housed so that a gap is formed between the groove and the inner surface of the hole, and is not fixed to the electrically insulating support.

Also, if necessary, a liquid-permeable buffer material is interposed between the peripheral surface of the superconducting current limiting element and the inner surface of the groove or hole of the electrically insulating support.

[Action]

In the superconducting current limiting device of the above configuration, since the superconducting current limiting element is not fixed to the electrically insulating support, the thermal expansion and contraction of the superconducting current limiting element and the thermal expansion and contraction of the electrically insulating support show behavior independent of each other, The superconducting current limiting element does not receive stress from the electrically insulating support. Therefore, the superconducting current limiting element does not exert an excessive force, and there is no risk of cracking.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 and 2 show an embodiment of the present invention. The superconducting current limiter includes an electrically insulating support 3 including an electrically insulating substrate 4 and a cover plate 5. A plurality of grooves 6 are formed in the substrate 4 in parallel, and the rod-shaped superconducting current limiting element 2 is housed in each groove 6. Adjacent superconducting current limiting elements 2 are connected in series by a flexible conductor 7 such as a stranded wire. The cross-sectional shape of the superconducting current limiting element 2 is a quadrangle in the illustrated example, but may be another shape.

The superconducting current limiting element 2 is made of, for example, an oxide superconducting material composed of yttrium-barium-oxygen or an oxide superconducting material composed of bismuth-lead-strontium-calcium-copper-oxygen. The substrate 4 and the cover plate 5 are made of, for example, glass fiber reinforced plastic, epoxy resin,
It consists of bakelite and the like.

FIG. 4 shows a state in which the superconducting current limiting element 2 is accommodated in the groove 6 and the cover plate 5 is covered as shown in FIG.
Are integrated by bonding or the like. Thereby, superconducting current limiting element 2 is housed in hole 8 of electrically insulating support 3. There is a gap between the peripheral surface of the superconducting current limiting element 2 and the inner surface of the hole 8, and this gap is filled with a cryogenic refrigerant such as liquid nitrogen to directly cool the superconducting current limiting element 2. . Further, the superconducting current limiting element 2 is only mounted on the bottom surface of the hole 8 and is not fixed to the substrate 4. Therefore, the superconducting current limiting element 2 and the electrically insulating support 3 can thermally expand and contract independently of each other.

When the superconducting current limiting element 2 enters a normal conducting state, it generates heat,
Since the cryogenic refrigerant is gasified, the cover plate 5 is formed with a discharge hole 9 for releasing the gas.

Although not shown, it is preferable that stoppers are provided at both ends of the substrate 4 or the cover plate 5 to limit the longitudinal movement of the superconducting current limiting element 2 within a certain limit.

FIG. 3 shows another embodiment of the present invention. In this superconducting current limiting device, a liquid-permeable buffer material 10 is interposed between the peripheral surface of the superconducting current limiting element 2 and the inner surface of the hole 8 of the electrically insulating support 3. Other configurations are the same as those of the above-described embodiment, and the same parts as those in FIG. 1 are denoted by the same reference numerals.

As the liquid-permeable buffer material 10, for example, open-cell foamed polyurethane, open-cell foamed polyethylene, fiber, or the like can be used. Since these materials have the property of passing a cryogenic refrigerant such as liquid nitrogen, they do not hinder the cooling of the superconducting current limiting element 2. By providing such a buffer material 10, the position of the superconducting current limiting element 2 in the hole 8 is stabilized, and the superconducting current limiting element 2 and the electrically insulating support 3 do not collide with each other due to vibration or the like.

In the above embodiment, the case where the electrically insulating support is composed of the substrate having the groove and the cover plate has been described.
When an electrically insulating string is horizontally wound around the substrate 4 in the state 2
If the superconducting current limiting element 2 does not escape from the groove 6 of the substrate 4 by providing an overhanging piece at the edge of the groove 6, the cover plate can be omitted.

〔The invention's effect〕

As described above, according to the present invention, since the superconducting current limiting element is supported without being fixed to the electrically insulating support, stress is generated in the superconducting current limiting element due to the difference in the amount of thermal expansion and contraction between the two. And the generation of cracks in the superconducting current limiting element can be prevented. Therefore, the performance of the superconducting current limiter can be prevented from deteriorating, and a highly reliable superconducting current limiter can be obtained.

[Brief description of the drawings]

FIG. 1 is a front view showing a superconducting current limiting device according to an embodiment of the present invention, FIG. 2 is a perspective view of the superconducting current limiting device of FIG. 1 with a cover plate removed, and FIG. FIG. 4 is a front view showing a superconducting current limiting device according to another embodiment, and FIGS. 4 and 5 are perspective views showing conventional superconducting current limiting devices. 2: Superconducting current limiting element, 3: Electrically insulating support 4: Electrically insulating substrate, 5: Electrically insulating lid plate 6: Groove, 7: Flexible conductor, 8: Hole 9: Gas exhaust hole, 10: Liquid-permeable buffer material

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-3477 (JP, A) JP-A-2-27615 (JP, A) JP-A-1-151169 (JP, A) 48603 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02H 9/02 H01B 12/02 H01L 39/00

Claims (2)

(57) [Claims] 1. A superconducting state is connected when a steady current is flowing in a power system, and a superconducting state is established when a short circuit current flows due to an accident in the power system. In a superconducting current limiting device provided with a superconducting current limiting element for limiting the flow of an excessive short-circuit current, the superconducting current limiting element is provided inside a groove or a hole formed in an electrically insulating support, and an inner surface of the groove or the hole. A superconducting current limiter, wherein the superconducting current limiter is housed so that a gap is formed between the superconducting current limiter and the superconducting current limiter. 2. The superconducting current limiting device according to claim 1, wherein a liquid-permeable buffer material is interposed between the peripheral surface of the superconducting current limiting element and the inner surface of the groove or hole of the electrically insulating support. Characterized by that.