JPH01206836A - Superconducting current limiter - Google Patents

Abstract

PURPOSE:To improve insulation to the ground and interpole insulation, and to enable the miniaturization of the device by housing a current limiting element into a cryostat composed of an insulator and storing the whole into an insulating vessel filled with an insulating medium. CONSTITUTION:A plural layer of stacks 1 in which oxide superconducting wires are arranged zigzag are laminated, and these stacks 1 are connected in series, thus constituting a current limiting element 2. The current limiting element 2 is housed into a cryostat 3, into which liquid nitrogen 4 is sealed and which is made of an insulator. Those current limiting element and cryostat are stored into a cylindrical ribbed bushing 8, and both ends of the bushing 8 are fixed to spacers 10, through which leads 9 led out of the current limiting element 2 are penetrated. A section between the cryostat 3 and the bushing 8 is filled with SF6 gas or insulating oil, and the whole current limiting element is installed onto an insulating rest 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) This invention relates to a superconducting current limiting device using an oxide superconducting material.

(Conventional technology) The application of superconductors to power equipment has been studied for a relatively long time, and recently, along with the development of AC superconducting wires, research into the application of superconductors to AC electrical equipment such as transformers has also begun. It's progressing. However, there are various technical problems in putting it into practical use.

This is due to the fact that devices using superconducting materials, such as conventional NbTi and Nb5S ports, which are designed to be cooled with liquid helium, require the ultimate technology of freezing at extremely low temperatures, which is an issue in terms of economy and reliability. One of the major factors was that it had been an obstacle to practical application.

However, recently, the development of oxide-based high-temperature superconductors has progressed rapidly, and the discovery of materials such as YBa2Cu, O, and -X, which exhibit the characteristics of superconductors such as zero electrical resistance and complete diamagnetism above liquid nitrogen temperature, has been reported in various places. ing.

When such high-temperature superconducting materials are used, liquid nitrogen can be used as a refrigerant, which not only reduces the cost of the refrigerant itself, but also makes refrigeration technology much easier, making it not only economical but also highly reliable equipment. As a result, it is expected that in addition to superconducting generators, applications in power equipment such as superconducting transformers and superconducting power transmission lines will rapidly advance.

In particular, current limiting devices can take advantage of the properties of high-temperature superconductivity, and research is currently underway in a variety of fields.

However, current limiting devices using such high-temperature superconductors have the following problems.

(Problem to be Solved by the Invention) The principle of a current limiting device using a superconducting wire will be briefly explained. A superconducting wire is in a superconducting state below a critical temperature, critical current, and critical magnetic field, and has zero resistance.

Therefore, if the constant load current is set below the critical current of the superconducting wire, the superconducting wire will maintain zero resistance during normal operation.

Next, when a ground fault or the like occurs in the system, a short circuit current that is ten times or more of the load current generally flows. If the critical current of the superconducting wire is less than this short-circuit current value, when a short-circuit current flows through the superconducting wire, a transition from the superconducting state to the normal conducting state, so-called quenching occurs, and the superconducting wire has a resistance value of the normal conducting state. It becomes a resistor with Generally, the short circuit current is determined by the impedance of the power supply in the system, but if a superconducting current limiting device is used, the impedance of the short circuit is given by the sum of the resistance when the superconducting current limiting element is quenched and the impedance of the power supply, so the current limiting If the resistance value of the element is made high, the short circuit current will be greatly limited.

Since the impedance is always zero and becomes high resistance when quenched, the superconducting wire used in the current limiting element must be non-inductively wound and must be longer than a certain length. To achieve this, for example, as shown in Figure 2, a stack of superconducting wires arranged in a zigzag pattern on an insulating substrate is laminated in multiple layers, and these are connected in series to create a desired length of superconducting wire. A current-limiting element 2 consisting of a wire is constructed, and this is housed in a taliostat filled with liquid nitrogen, and these are further housed in a grounded tank base, with terminals connected from both sides of the current-limiting element. A structure in which the bushing is pulled out using a bushing 6 was considered.

In this case, the current limiting element -2- has the line voltage of the system during normal operation, so it is necessary to provide insulation that can withstand the line voltage between the main current limiting element and the tank housing it. Ta. Therefore, it is conceivable to fill the space between the cryostat and the tank with an insulating medium -7- such as SF, gas, or insulating oil.

Furthermore, when the current limiting element quenches, a voltage shared by the resistance of the current limiting element is applied between the terminals of the current limiting element, so insulation in the creeping direction of the element is also required. In particular, in order to pass the lead from the terminal of the current limiting element or terminal through the tank and lead it out to the outside, a bushing similar to that of a general transformer or circuit breaker is required.

When trying to use a current limiting device in a high voltage system like this, the ground insulation and interpole insulation of the current limiting element become complicated.
The drawback was that the tank size was larger than necessary.

The object of the present invention is to improve the drawbacks of such a superconducting current limiting device and to obtain a highly reliable and economical superconducting current limiting device with good insulation properties.

[Structure of the invention]

(Means to solve the ill! problem) The present invention aims to solve the above problems.

A current limiting element made of superconducting wire is housed in an insulating cryostat filled with liquid nitrogen, etc., and this is placed in an insulating container filled with an insulating medium, leads are pulled out from both ends, and the entire device is Install on an insulated stand.

(Function) When configured as above, the current limiting element usually acts as a superconductor, and when a current exceeding the critical current at short circuit current flows, it quenches and becomes a high resistance element, exerting the current limiting effect. .

In this case, during normal operation, the entire current-limiting element has the line voltage and is at the same voltage, so there is no need to insulate the container or the lead-out portion. Furthermore, insulation from the ground can be maintained using an external insulating frame. Furthermore, when a short-circuit current flows and a potential difference occurs between the electrodes, insulation is maintained by the insulation strength in the creeping direction of the insulating container, but the insulation strength in the creeping direction of the container is limited by the longitudinal insulation strength of the current limiting element. It must be sufficiently long and, if necessary, can be made sufficiently tall by providing pleats on the outside of the container in the air. Therefore, earth insulation,
Insulation between electrodes can be made extremely easy and highly reliable, and the entire device can be downsized.

(Example) An embodiment of the present invention will be described below with reference to FIG.

A stack of oxide superconducting wires having a critical temperature higher than the boiling point of liquid nitrogen is arranged in a zigzag pattern on a disc-shaped insulating substrate, and these are stacked in multiple layers and then connected in series to create a superconducting wire of a desired length. The current limiting element is mainly housed in an FRP cryostat filled with liquid nitrogen. Furthermore, these are mainly housed in a cylindrical pleated insulator tube, and both ends of the insulator tube are equipped with current limiting elements. Fix the spacer river that penetrates the lead main body pulled out from Yu. Cryostat-β
Fill the space between the unit and the insulator with SFG gas or insulating oil.

The entire current limiting device is installed on an insulating frame.

If the current limiting device is configured in this way, the current limiting element -? Since the entire current limiting device has the same potential and there is no conductor with a potential other than the insulation voltage, there is no need for insulation within the device, and there is no risk of dielectric breakdown. Insulation to the ground is maintained by the insulating mount that supports the entire device, so as long as the insulation distance between the insulating mount and the ground is ensured, the reliability is sufficiently high.

Next, when a short-circuit current flows and the main current-limiting element quenches, a voltage determined by the distribution of the impedance of the power supply and the resistance value of the element is applied between the poles of the element.

With respect to this voltage between the electrodes, insulation between the unit units of the element is originally maintained by an insulating substrate and liquid nitrogen. Also, Taliostat? The outer peripheral surface of - is guaranteed to be insulated by the insulating pipe and the SFG gas or insulating oil filled inside.

Therefore, the weakest point is the voltage between electrodes.

The insulator tube and its surface are exposed to the air, but the surface of the insulator tube 1 is pleated to increase dielectric strength in the creeping direction, making it possible to obtain highly reliable insulation over a relatively short distance. .

In addition, although the above explanation took as an example the case where the current limiting element is placed horizontally, the configuration of the present invention is not limited to this. It is also possible to have a structure in which the lower part of the insulator is supported by, for example, a tank of another device to which the current limiting device is connected.

Further, the material of the outer container is not limited to porcelain pipe, and the same effects as in the above embodiments can be obtained even if other insulating materials such as FRP are used.

〔Effect of the invention〕

As explained above, this invention has high reliability of ground insulation and inter-electrode insulation by housing the current limiting element in an insulating cryostat and further housing the whole in an insulating material container filled with an insulating medium. A current limiting device that can be downsized can be provided.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a current limiting device according to an embodiment of the present invention;
FIG. 2 is a longitudinal sectional view of a conventional current limiting device. 1... Current limiting element unit stack, 2... Current limiting element,
3... Cryostat, 4... Liquid nitrogen, 5... Ground tank, 6... Bushing, 7... SFG gas, 8... Insulator tube, 9... Lead, 10... Spacer , 11... Insulating frame. Figure 1 Figure 2

Claims (1)

[Claims] A current limiting element formed by non-inductively wound oxide superconducting material having a critical temperature of liquid nitrogen temperature is housed in a cryostat made of an insulator filled with liquid nitrogen, and the whole is housed in a container made of an insulator, A superconducting current limiting device characterized in that an insulating medium such as an insulating gas or an insulating oil is filled between a cryostat and an outer container.