JPH02237413A - Cryogenic current lead - Google Patents

Abstract

PURPOSE:To suppress the occurrence of partial discharge by putting the part where the electric field concentrates in the atmosphere or in liquid helium and by putting only the low electric field part in the cold gas helium. CONSTITUTION:Since a flange 2 and a shield member 12 of an angle section 9 are both earthed, the electric field of the angle section 9 becomes zero. Likewise, as a supporting body 3 of a clearance section 10 and the shield member 12 are both earthed, the electric field of the clearance section 10 becomes zero. No partial discharge will thereby occur at the angle section 9 and clearance section 10. The electric field of shield ends 12a and 12b becomes high, but it is hard to discharge the current partially since their location is in atmosphere 6 and liquid helium 8 high in dielectric strength.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is applicable to ultra-low temperature applications such as current leads and quench detection lead wires of superconducting equipment using liquefied inert gas such as liquid helium as a refrigerant. Regarding current leads. (Prior Art) Regarding cryogenic current leads for superconducting equipment, for example, Japanese Utility Model Application Laid-open No. 63-49265 is known. This type of current lead will be explained with reference to FIG. Fourth
In the figure, ■ is a current lead, and the upper part of the current lead ■ is strongly fixed to a metal flange ■. Also, there is an airtight seal between the current lead and the flange (not shown).
has been applied. The central part of the current lead (2) is supported by a metal support (2), and these flanges (2) and support (2) are electrically grounded. The current lead (2) is a conductor (A) covered with an insulating member 0, leaving the end portion intact.

The location of the current lead (■) is in the atmosphere from the flange (■), the vicinity of the bottom of the flange (■) is in room-temperature gas helium (2), and the lower end of the current lead (■) is in liquid helium (2). In an atmosphere of room temperature gas helium ■, 0 is the corner where the flange ■ and the insulating member ■ contact, and (10)
is the gap between the support ■ and the insulating member ■. (Problem to be solved by the invention) In the current lead ■ configured as described above, the conductor ←
), or when a high voltage is generated, the electric field concentrates at the corner 0 or the gap (10). Moreover, the atmosphere in the corners (9) and gaps (10) is room temperature gas helium, and its dielectric strength is low, less than 1/6 of the value in the atmosphere (0) and less than 1/40 of the value in liquid helium (0). ．． Corner ■)
and the gap (10) are places where partial discharge is likely to occur.

When a partial discharge occurs, the insulating material ■ gradually deteriorates,
ultimately destroy it.

An object of the present invention is to provide a current lead for cryogenic temperatures that eliminates deterioration of the insulating member (2) at the corners (1) and gaps (10), and improves insulation reliability by preventing dielectric breakdown.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the first means of the present invention is as follows. It is equipped with a conductor drawn out from a cryogenic refrigerant such as liquid helium to the atmosphere, an insulating member covering the conductor with the ends of the conductor remaining, and a shielding member tightly attached to the surface with the ends of the insulating member remaining. , one end of the shield is exposed to the atmosphere,
The other end is placed in a cryogenic refrigerant and a grounding member is provided to ground the shield member. As a second means,
A hollow conductor drawn out from a cryogenic refrigerant such as liquid helium into the atmosphere, an insulating member covering the hollow conductor leaving the ends of the hollow conductor intact, a conductive layer that adheres to the surface of the insulating member, and a conductive layer attached to the conductive layer. The present invention is characterized by providing a conductive tape layer in which the conductive tape is easily wound and covered with the conductive tape, leaving the ends intact, a metal pipe covered with the conductive tape layer, and a grounding member for grounding the metal pipe.

(Function) By configuring as in the first means, the electric field becomes zero at the corner (2) and the gap (10), so no partial discharge occurs. Also, the shield end (1
In cases 2a) and (12b), the locations are the atmosphere (2), a liquid helium (2), and a cryogenic refrigerant such as aluminum (2), respectively, so the partial discharge is less likely to occur than when the atmosphere is room-temperature gas helium (3), which has low dielectric strength. Occurrence can be suppressed.

In addition, by configuring as in the second means, the conductive tape layer between the conductive layer and the metal pipe shifts when the conductive layer and the metal pipe undergo relative displacement due to temperature changes, thereby preventing wear and peeling of the conductive layer. Prevented. (Examples) Example 1 A first example of the present invention will be described below with reference to FIG. 1. Figure 1, like Figure 4, shows a longitudinal cross-sectional view of the current lead. 2 is a current lead, which differs from the conventional current lead (1) shown in FIG. 4 in that a shield member (12) is closely attached to the surface of the insulating member 2 and is grounded. The shield member (12) is made of non-magnetic metal braided wire, plating, or conductive paint. Upper shield end (12
The atmosphere in a) is set to 0, and the lower shield end (
12b) is filled with liquid helium (c), which is a cryogenic liquid refrigerant.

That is, the upper shield end (12a) is provided outside the superconducting device, and the lower shield end (12b) is provided inside. Next, we will explain the effect of the above configuration. Since the flange (2) of the corner (2) and the shield member (l2) are both grounded, the electric field at the corner (2) becomes zero. Similarly, the gap (1
Since the support body 0) and the shield member (12) are both grounded, the electric field in the gap (10) becomes zero. As a result, partial discharges at the corner ■ and the gap (10) no longer occur. Note that the shield ends (12a) and (12b
), but since the electric field is located in the atmosphere ■ and liquid helium ■, which have high dielectric strength, respectively, the shield ends (12a) and (12b) are similar to the corners ■ and the conventional example shown in Fig. 4. Occurrence of partial discharge can be suppressed compared to the gap (IO).

As explained above, the current lead ■ shown in FIG. The shield end (12a), (1
2b) is located in the atmosphere and in liquid helium, respectively, so that the occurrence of partial discharge can be suppressed.

Embodiment 2 Next, a second embodiment of the present invention will be described with reference to FIG. Figure 2 shows a cross-sectional diagram of the current lead, similar to Figures 1 and 3. (1) is a current lead, which differs from the current lead (I1) shown in FIG. 1 in that a semiconducting layer (14) is applied to the upper shield end (12a). The semiconductive layer (14) is formed of paint or tape containing silicon carbide.

Next, the operation of this second embodiment will be explained. Semiconducting layer (
14) has an electric field relaxation effect that gradually changes the surface potential of the insulating member ① near the shield @(12a). This effect can suppress the occurrence of partial discharge at the shield end (12a). The rest is as in Example 1.6 Furthermore, as a modification of FIGS. 1 and 2, the semiconducting layer (l4) shown in FIG.
It can be applied to both. In addition, when the shield member (12) shown in Figs. 1 and 2 is made of braided wire, the adhesion between the insulating member ■ and the shield member (12) can be improved by coating the outside of the shield member (l2). can be increased.

Example 3 A third example is shown in FIG. Current lead for cryogenic temperatures■
One end is the room temperature side (L6a), and the other end is the low temperature side (L6a).
b). The normal temperature side (16a) is attached to the outside of a superconducting device (not shown), and the low temperature side (16b) is attached to the inside.

The center of the cryogenic current lead (2) is a conductor (d) made of a hollow copper pipe, and the hollow hole (17) is for guiding the evaporated gas of the cryogenic refrigerant. The conductor (A) is covered with an insulating member 0, and the material of the insulating member 0 is fiber-reinforced plastic. A conductive layer (
18), the conductive layer (18) is formed by electroless plating, and the conductive layer (18) is provided with a conductive tape layer (18).
9) is coated, and the conductive tape layer (19) is made of aluminum tape wound multiple times, and is wound loosely so that adjacent tapes can be easily shifted. The conductive tape layer (19) is covered with a stainless steel metal pipe (20). It is grounded with the grounding member (E). Next, we will explain the effect of the above configuration. current lead ω
On the low temperature side (lb), the temperature changes greatly as the superconducting equipment operates and stops. With this temperature change, the conductor (A),
The insulating member (1) and the conductive layer (18) expand and contract together, but the conductive layer (18) and the metal pipe (20) are displaced relative to each other. With this relative displacement, adjacent tapes in the conductive tape layer (19) between the conductive layer (18) and the metal vibrator (20) are easily displaced. In addition, since the conductive tape layer (l9) provides electrical continuity between the conductive layer (18) and the metal pipe (20), no electric field is generated between the surface of the insulating member ■ and the metal pipe (20), so no partial discharge occurs. .

As explained above, the conductive layer (18) and the golden shoulder pipe (20)
) does not rub directly, and the conductive tape layer (19) absorbs the relative displacement between the conductive layer (18) and the metal pipe (20), so the conductive layer (18) is less likely to be rubbed. Furthermore, as a modification of Example 3. A copper introduction wire may be used as the conductive layer (18), and twenty braided wires may be bonded to the surface of the insulating member (1). Furthermore, a conductive paint may be used as the conductive layer (18). The conductive tape layer (19) may be formed by winding the tapes in an overlapping manner, or may be formed by winding the tapes without overlapping them. Further, by using an embossed tape, adjacent tapes may be easily displaced. The metal pipe (20) may be a combination of previously divided pieces. By fixing the conductive layer (18) and the metal scrap pipe (2o) in one place so that they do not displace relative to each other, and hardening the fixed part of the conductive tape layer (19) with adhesive, the evaporated gas of the cryogenic refrigerant becomes conductive. Tape layer (19)
It may be arranged so that it does not pass through the layer.

〔Effect of the invention〕

As explained above, by configuring as in the first means shown in claim 1, the electric field becomes zero at corners and ltjl gaps, so partial discharge does not occur, and the shield where the electric field becomes high The ends are connected to the atmosphere and cryogenic refrigerant, respectively, so the occurrence of partial discharge can be suppressed. Further, by configuring as in the second means shown in claim 2, when the conductive layer and the metal pipe undergo relative displacement due to a temperature change, the conductive tape layer between the conductive layer and the metal pipe is shifted, so that the conductive tape layer is displaced. Abrasion and peeling of the layer can be prevented.

Therefore, according to the present invention, damage to the insulating member can be prevented and a highly reliable current lead for cryogenic temperatures can be provided.

[Brief explanation of drawings]

1 to 3 are longitudinal sectional views showing first to third embodiments of the present invention, and FIG. 4 is a longitudinal sectional view showing a conventional example. 1... Current lead 4... Conductor 5... Insulating member 6... Atmosphere 8... Liquid helium l2
... Shield member l8... Conductive layer l9.
...Conductive tape layer 20...Metal pipe E...
Grounding component representative Patent attorney Norio Ogo

Claims (2)

[Claims] (1) A conductor drawn out from a cryogenic refrigerant such as liquid helium to the atmosphere, an insulating member covering the conductor with the ends of the conductor remaining, and a shielding member tightly attached to the surface with the ends of the insulating member remaining. A current lead for cryogenic use, characterized in that one end of the shield is exposed to the atmosphere, the other end is placed in a cryogenic refrigerant, and a grounding member is provided for grounding the shield member. (2) A hollow conductor drawn out from a cryogenic refrigerant such as liquid helium into the atmosphere, an insulating member covering the hollow conductor with the ends of the hollow conductor remaining, and a conductive layer in close contact with the surface of the insulating member; The present invention is characterized by the following: a conductive tape layer in which a conductive tape is wound to easily cover the conductive tape so as to leave an end on the conductive layer; a metal pipe covered with the conductive tape layer; and a grounding member for grounding the metal pipe. Current lead for cryogenic temperatures.