JP2010045267A - Method and apparatus for regulating current-limiting operation starting current value of superconducting current limiter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To regulate variations of starting current value in a current-limiting operation, that occurs as individual difference in a manufactured SN-transition type superconducting current limiter so that they lie within a range from a non-actuation duty required from a system to actuation duty. <P>SOLUTION: In an SN-transition type superconducting current limiter which houses a superconducting current-limiting element 1 inside a low-temperature container 3 and holds the element in a superconducting state, a freezer 4 is provided in the low-temperature container 3, and while defining as a current-limiting operation starting current value a current value when the resistance is generated, at a fixed ratio with respect to resistance of the SN-transition type superconducting current limiter, just above the critical temperature and defining as a reference a previously measured current-limiting operation starting current value of the current limiter; the temperature of a cooling fluid 9 inside the low-temperature container 3 is controlled by the freezer 4 so as that it makes the current-limiting operation initiation current value lie within a range of actuation duty and non-actuation duty, at a point where the current limiter is introduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for adjusting a current limiting operation start current value of a superconducting fault current limiter using a superconducting conductor.

  By applying the superconducting technology to the current limiter, it is possible to reduce the normal loss and to detect the fault occurring in the system by itself and to limit the current from the first wave. In particular, the SN transition type superconducting fault current limiter utilizing the superconducting-normal conducting transition has a simple principle and structure and a simple configuration, and is considered to be a realizable device.

As the SN transition type superconducting fault current limiter, various materials such as metallic superconducting wires, high temperature superconducting bulk materials, high temperature superconducting wires and high temperature superconducting thin films have been studied so far. Among them, the SN transition type superconducting fault current limiter using a YBa ₂ CuO _7-y (hereinafter referred to as YBCO) thin film can be applied due to the high critical current density of the thin film and the realization of high resistance at the normal conducting transition. Expectation is high. However, in order to construct an actual-scale current limiting device, the current YBCO thin film fabrication technology has a small current capacity and voltage withstand capability per element, so a large number of YBCO thin films must be connected in series and parallel. Moreover, since no manufacturing technology has been established that can control the superconducting characteristics such as the critical current value, the current-limiting operation varies from element to element, and the characteristics of the current-limiting device that is configured by combining these elements vary. It is difficult to produce multiple current limiters that operate on values.

  In addition, current limiters using superconductors use Cu-Ni alloys with high electrical resistance as the matrix of superconducting conductors, so they are not stable and can be quenched even when there is a small amount of conductor movement (from superconducting state to normal conducting state). (Sudden transition phenomenon to the state), and there is a problem that the operation becomes uneasy.

  Therefore, a part for applying heat to the superconducting conductor used for the current limiter is provided so that it is in close contact with or adjacent to the superconducting conductor. Some attempt to set a predetermined current-limiting operation start current value (Patent Document 1). By providing a part that applies heat to the superconductor in the current limiter, the quench current of the superconductor used in the current limiter is reduced due to the influence of the applied heat, and the quench current is set as set by changing the amount of heat applied. Trying to.

JP-A-8-335525

  However, since the heater is embedded around the superconducting conductor and the quench current is adjusted by heating, the adjustment of the quench current value is only in one direction, and the optimum value is not always obtained. In other words, the critical current of the entire YBCO thin film is adjusted only in the direction of lowering the current limiting start current value of the superconductor current limiting element, although the distribution of the critical current density in each part of the thin film also varies. Therefore, there is a possibility that the current limiting operation start start current value cannot be set within the range from the non-operation duty required by the system to the operation duty.

  In addition, in this current limiting operation start current value adjusting method, since the amount of heat is always supplied to the current limiting device, liquid helium used as a refrigerant is vaporized as Joule loss and generated as a loss. Therefore, when applied to the whole superconducting current limiting element, the loss cannot be ignored. On the other hand, even if the current limiting element is heated locally by the heater in order to reduce the loss, the entire YBCO thin film is not adjusted to a constant current limiting operation start current value. At the same time, current-limiting operation does not occur, and since all the voltage is shared only by the current-limiting part and the current-limiting effect is small, a large current continues to flow in the current-limiting part, and the current-limiting part may burn out There is. Moreover, if there are variations in the length direction, it is difficult to transfer from superconductivity to normal conductivity all at once, and the current limiting operation becomes unstable.

  Further, the high-temperature superconductor belongs to the type 2 superconductor, and has a mixed state in which the magnetic field and the superconductivity coexist (between the lower critical magnetic field Hc1 and the upper critical magnetic field Hc2). Quench at a current of 150% to 200% of the critical current without quenching. For this reason, even if the quench current value, that is, the critical current value is assumed to be the current limiting operation start current value, it is actually difficult to cause the current limiting operation stably. For this reason, various current limiters have been proposed so far, and a principle verification test and the like have been carried out, but few have been introduced into actual systems.

  The actual power system is composed of a load system and a relay system to protect them in addition to the load and power equipment, so it may operate depending on the duty and event of the current limiter that reliably performs the current limiting operation. Non-operational obligations that must not be made need to be finely designed or adjusted according to the demands of the power system. In other words, it is important to maintain not only the operation responsibility for failure and the like, but also non-operation such as during transformer inrush current and overload operation. If the current limiter operates for a non-operational duty or becomes non-operational for an operation duty, there is no point in introducing the current limiter into the system. Moreover, this requirement depends on where the current limiter is installed. In addition, the operational responsibility of the current limiter must be easily adjustable according to changes in the protection relay system. Therefore, it is desired to establish a technique for adjusting the operation start current value according to the place where the current limiter is introduced and setting it within the range from the non-operation duty to the operation duty required by the system.

  The present invention responds to such a demand, and the variation of the current limiting operation start current value generated as a solid difference of the produced SN transition type superconducting fault current limiter, from the non-operation duty required by the system to the operation duty. It is an object of the present invention to provide a method and an apparatus for adjusting to be within a range.

  In order to achieve this object, the present inventors conducted various experiments on the influence of the current-limiting operation starting current value when the temperature and frequency (current increase rate) at the time of AC energization of the current-limiting element using the YBCO thin film were changed. As a result of research, the current value when a certain ratio of resistance (a% R: resistance that can be separated from noise) occurs with respect to the resistance value (R) of the current limiting element immediately above the critical temperature Tc of the high-temperature superconductor. When it is defined as a current limiting operation start current value and the temperature dependency of the current limiting operation start current value is obtained, it changes almost linearly as well as the temperature change of the critical current value (Ic), and the temperature dependency is It was clarified that it was high (temperature dependence of the current limiting operation starting current value). By using this characteristic, it was found that the operation start current value of the SN transition type superconducting current limiter can be controlled by changing the temperature.

  It was also clarified that the current limiting operation start current value immediately before the transition to the normal conducting state does not depend on the current increase rate (current increase rate dependency of the current limiting operation start current value). This is presumably because the main factor for transition to normal conduction is dominated by current. This suggests that the current at which the current limiting operation is started is not affected even if the rate of increase in current varies depending on the phase and magnitude at the time of failure.

  Therefore, from the current-voltage characteristics in the current-limiting operation start current value measurement, the temperature rise due to heat generation is triggered in the low magnetic flux resistance region at the initial stage of the superconducting-normal conducting transition, but in the vicinity of the high magnetic flux flow resistance region leading to the quench, Therefore, it is considered that the fault current is limited by the normal conduction transition due to the magnitude of the current. In other words, if the current value in the non-operation duty area is smaller than the current value of the operation duty, the current at which the current limiting operation starts is not affected even if the rate of increase of the current changes depending on the phase or magnitude at the time of failure. This is considered to be influenced by the magnitude of the current value in the area of the operation duty which is strongly influenced by the temperature change and becomes a current value larger than the current value of the non-operation duty.

  That is, by setting the current limiting operation starting current value in the low flux flux resistance region in a mixed state (between the lower critical magnetic field Hc1 and the upper critical magnetic field Hc2) in which the magnetic field and the superconductivity coexist, It was found that it was possible to adjust the operation start current value uniquely determined by the critical current of the thin film.

  The adjustment method of the current limiting operation start current value of the superconducting fault current limiter of the present invention is based on such knowledge, and generates a certain ratio of resistance to the resistance just above the critical temperature of the SN transition type superconducting current limiter. The current value of the current limiter as a current limiting operation start current value, the current limiting operation start current value of the current limiter is measured, and the cooling fluid that cools the superconducting current limiting element in a cryogenic vessel based on the measured value By controlling the temperature, the current limiting operation start current value is adjusted to be within the range of the operation duty and the non-operation responsibility at the place where the current limiter is introduced.

  According to a second aspect of the present invention, there is provided a current limiting adjustment device for current limiting operation of a superconducting fault current limiter, wherein the superconducting current limiting element is housed in a cryogenic container and held in a superconducting state. In the flow device, the cryogenic vessel is equipped with a refrigerator, and the current value when a certain percentage of resistance is generated with respect to the resistance just above the critical temperature of the SN transition type superconducting current limiter is defined as a current limiting operation start current value, The current limiting operation start current value is within the range of the operation duty and the non-operation responsibility at the place where the current limiter is introduced with reference to the current limit operation start current value of the current limiter measured in advance. Thus, the temperature of the cooling fluid in the cryogenic container is controlled by the refrigerator.

  Furthermore, the current limiting operation start current value adjusting device for a superconducting fault current limiter according to the invention of claim 3 is an SN transition type superconducting limit in which a superconducting current limiting element is accommodated in a cryogenic container and held in a superconducting state. In a fluidizer, the cryogenic vessel is provided with a vacuum pump for pressurizing or depressurizing the refrigerant gas, and a current when a certain ratio of resistance is generated with respect to the resistance just above the critical temperature of the SN transition type superconducting fault current limiter Within the range of operational responsibility and non-operational responsibility at the location where the current limiter is introduced with reference to the current limit operation start current value of the current limiter measured in advance as a current limiting operation start current value The temperature of the cooling fluid in the cryogenic vessel is controlled by the vacuum pump so as to contain the current limiting operation start current value.

  According to the method and apparatus for adjusting the current limiting operation start current value of the superconducting fault current limiter of the present invention, the temperature of the cooling medium that cools the superconducting conductor is changed even after the current limiting unit is manufactured, thereby limiting the superconducting current limiter. Adjust the current-limiting operation start current value so that it falls within the range of operating responsibility and non-operating responsibility of the current limiter by arbitrarily increasing or decreasing the current value at which the current-limiting element starts current-limiting operation. Can do.

  Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.

  FIG. 1 shows an embodiment of a current limiting operation starting current value adjusting device for a superconducting fault current limiter according to the present invention. This current limiting operation start current value adjusting device for a superconducting current limiting device is of a type that cools a refrigerant using a refrigerator, and includes a current limiting element 1 and a cold head portion 2 that cools the current limiting element 1. A cryogenic container 3 comprising a vacuum container that contains the current limiting element 1 and the cold head part 2 and is filled with the cooling fluid 9 and held in a superconducting state, and a GM refrigerator 4 that cools the cold head part 2 Is provided. When the current limiting operation start current value of the manufactured current limiting element 1 is measured, the current limiting operation start of the current limiting element 1 manufactured with the shunt resistor 5, the power amplifier 6, and the arbitrary waveform generator 7 is started. Prepare as a measuring instrument to measure the current value. Of course, before introducing the current limiter into the system, when liquid nitrogen is used as a reference, for example, when the liquid nitrogen is used, the resistance (R) immediately above the critical temperature with saturated liquid nitrogen (77.3 K) is obtained, When the current value at the time of resistance (a% R) is measured in advance as the current-limiting operation start current value, for example, when measured at the time of manufacture and clearly indicated as an eigenvalue, the arbitrary waveform generator 7 or the like No measuring equipment is required. In the present invention, since the current limiting operation start current value is to be adjusted by controlling the temperature of the refrigerant, the low temperature container 3 containing the current limiting element and the refrigerant is used to prevent the refrigerant temperature from changing. It is desired that the sealed container is excellent in heat insulating properties and easy in temperature control.

  Here, the cold head unit 2 is made of a material having good thermal conductivity, such as copper, and is connected to the GM refrigerator so as to cool the cooling fluid 9 such as liquid nitrogen. At the same time, although not shown, a monitoring temperature sensor and a heater are embedded in the inside, and not only cooling the liquid nitrogen but also heating to control the temperature to 77.3 K or higher. The structure is made possible. Then, by combining the cooling by the refrigerator 4 and the heating by the heater, the temperature of the cold head unit 2 can be adjusted to the designated temperature and maintained at that temperature. On the current limiting element 1, a temperature sensor for measuring the temperature of the current limiting element 1, for example, a Cellnox temperature element, is fixed to the current limiting element 1 by bonding or the like. Moreover, the code | symbol 10 in a figure is a voltage tap.

  As the cooling fluid (refrigerant) 9, in the case of a current limiting element of a high-temperature superconductor, for example, liquid nitrogen is generally used, but in some cases, liquid hydrogen, liquid neon, or the like can be used. A device suitable for the composition of the current limiting element 1 is used.

According to the current limiting operation start current value adjusting device of the SN transition type superconducting fault current limiter configured as described above, first, the shunt resistor 5, the power amplifier 6, and the optional current limiting element 1 in the cryogenic vessel 3. The waveform generator 7 is connected and the resistance value immediately above the critical temperature is obtained. Then, a current value when a certain ratio of resistance (a% R) is generated with respect to the resistance (R) immediately above the critical temperature is defined as a current limiting operation start current value Ils. Here, in the present embodiment, the current limiting operation start current value of the SN transition type superconducting current limiting element using the YBCO thin film is calculated by calculating the generated resistance from the current-voltage characteristics, and the critical temperature Tc as the level of resistance that can be separated from noise. It was defined as the current value when a resistance of 10% of the resistance value of the current limiting element directly above was generated. The numerical value of 10% itself has no absolute significance. For example, it may be smaller or larger. However, if a value that is excessively smaller than 10% of the resistance value immediately above Tc is taken, it may be possible that the current returns to superconductivity if the current becomes small like an alternating current even if the normal conduction transition is made. According to the experiments by the inventors, when a small value of about 0.3% of the resistance value immediately above Tc is taken, it is considered that the return to superconductivity occurs along with the change of the alternating current. According to the experiment, changes such as a slight increase in current were observed in the upper and lower regions where the current increase rate was 10 ⁴ A / sec. Further, at about 1%, the temperature dependency of the current limiting operation start current value is lower than that in the case of 10%. Therefore, it can be determined that if about 10% of the total undergoes normal conduction transition, the size is such that it does not return to the superconducting state in the current limiting state. In other words, it means that a certain progress of the current limiting operation can be expected by continuing the accident. In the present specification, the duty that the current limiter must not operate in response to an event such as an inrush current is regarded as a non-operation duty, and the current limiter is required to be inoperative below the current value. On the other hand, the duty that the current limiter must operate against a fault current or the like is called an operation duty. The current value of the operation duty is larger than the non-operation duty. Further, in the present embodiment, the frequency, that is, the rate of current increase when the current limiting element using the YBCO thin film is energized, is defined by the slope of the tangent of the rising sine wave current as shown in FIG.

Next, the current limiting operation start current value is set within the range of the operation responsibility and the non-operation responsibility at the location where the current limiter is introduced with reference to the current limit operation start current value of the current limiter measured in advance. The temperature of the cooling fluid in the cryogenic container is determined so as to be accommodated, and the refrigerator 4 is controlled so that the inside of the cryogenic container 3 is maintained at that temperature. Here, since the current dependence between the current limiting operation start current value and the refrigerant temperature (in other words, the current limiting element temperature) has the temperature dependence shown in FIG. 8, a current limiting device is introduced. The operation start current value is determined so that the current limiting operation start current value falls within the range of the operation responsibility and the non-operation responsibility at the location, and the temperature corresponding to the operation start current value is obtained. For example, in the case of the current limiting element using the YBCO thin film used in the experiment, it is possible to easily obtain how much temperature change should be given using FIG. 8 or the following approximate expression obtained from this figure. In the approximate expression, T is temperature and the unit is K.
Ils = −15T + 1350 (1)
According to this approximate expression, it can be seen that the current limiting operation start current value of 15 A changes with a temperature change of 1K. From the results showing the temperature dependence of the current limiting operation start current value at a current increase rate of 31 kA / sec (FIG. 8), the current limiting operation start current value at 85.9K is 70A, and at 89.2K. The current limit operation start current value is 20A, and the current limit operation start current value can be adjusted within a range of about 20% for temperature adjustment of 1K, and it can be used in most places where current limiters are installed. Is considered possible. Therefore, the refrigerator is set so that the temperature of the cooling fluid 9 is set and maintained so that the current limiting operation start current value is within the range of the operation duty and the non-operation responsibility at the place where the current limiter is introduced. 4 or a heater (not shown) is operated. As a result, the current limiting operation start current value of the current limiter can be adjusted within the range according to the actual use environment after manufacture, that is, within the range of operation responsibility and non-operation responsibility at the place where it is introduced. it can.

  Further, the temperature control of the cooling fluid 9 can be performed not only by the combination of the refrigerator and the heater using the above-described cold head 2 but also by other appropriate means. For example, although not shown in the drawing, a vacuum pump for pressurizing or depressurizing the refrigerant gas (for example, nitrogen gas) is provided in the hermetic cryogenic container 3, and the temperature can be adjusted only by heating or depressurizing the refrigerant gas. . In this case, the cold head unit 2 is not necessary.

  Experiments were conducted on the temperature dependence of the current limiting operation start current value of the current limiting element using the YBCO thin film, and it was examined whether the adjustment of the current limiting operation start current value could be controlled by the temperature control of the refrigerant.

(Current limiting element and experimental device)
A YBCO thin film having a width of 1 cm, a length of 10 cm and a thickness of 0.3 μm deposited on a sapphire substrate was used as a sample of the current limiting element used for the measurement.
The temperature dependence of the critical current of the YBCO thin film of the current limiting element 1 was measured using the apparatus shown in FIG. The current limiting element 1 is placed on the copper cold head part 2 in the vacuum chamber 3 of the superconducting cooling device, the temperature of the cold head part 2 is controlled in vacuum, and the temperature of the sample is changed by conduction cooling. And measured. A block diagram of the measurement is shown in FIG. The temperature was measured by attaching a Cellnox temperature element to the sample. The critical temperature measured was 95K. The voltage of the YBCO thin film was measured by the four probe method. A current waveform was generated by the arbitrary waveform generator 7, and a current of 0 to 100 A was passed through the power amplifier 6 using a DC power source. In the measurement of critical current, current was applied at a constant sweep rate. In AC energization, a half-wave current was applied only on the positive side of the AC. As the frequency, an alternating current of 10 to 100 Hz was applied, and the current increase rate dI / dt at the tangent line of the rising current was evaluated. FIG. 2 shows the definition of dI / dt. This time, dI / dt up to 60 kA / sec was applied. The temperature of the YBCO thin film was varied in the range of 86 to 90K using a Cellnox resistance temperature sensor.

(Measurement results of basic characteristics of superconducting current limiting element)
First, the temperature characteristic of the resistance when a current of 1 mA was passed through the current limiting element 1 used in this experiment was obtained. The result is shown in FIG. From this result, it can be seen that the critical temperature Tc of this current limiting element is about 95K. The resistance value at room temperature was about 1.1Ω, and the resistance just above Tc was about 0.3Ω.

(Experimental result)
(1) Measurement of critical current First, the temperature dependence of the critical current of the YBCO thin film was measured. The critical current value was measured by using an arbitrary waveform generator 7, controlling a 12 V, 100 A DC power supply at a constant current, and increasing the current from 0 to 100 A in a fixed time. The rise in current reached a maximum value over about 4 seconds as a sufficiently slow time in which the influence of the temperature rise accompanying the change in current was negligible. The electric field characteristics were measured in the range of about 86K to 90K. As shown in FIG. 3, the measured current-voltage characteristics were in the range of 86.1 K to 91.3 K, and 1 μV / cm was used to define the critical current.
From the current-voltage characteristics obtained in FIG. 3, the critical current at each temperature is shown in FIG. FIG. 4 shows that the critical current increases linearly with decreasing temperature. A current change of about 8 A is observed for a temperature change of 1 K.

(2) Characteristics of the operation start current value Next, in order to grasp the transient characteristics under actual operating conditions of the current limiter, the voltage setting of the DC power supply is set to the maximum voltage of 12 V for the purpose of changing the current increase rate. Then, using the arbitrary waveform generator 7, the voltage was measured by changing the frequency between 10 to 50 Hz of the current limiting operation when an AC half-wave current of up to 100 A was applied. The measured temperature is 87K. The current voltage waveform at each frequency is shown in FIG.
In general, the voltage drop in the YBCO thin film above the critical current value is proportional to the power of the current. Although such a characteristic is seen also from FIG. 5, the difference by the difference in frequency is not seen. Further, in FIG. 5, the entire YBCO thin film is not in the normal conducting transition, and a part remains in the superconducting state. Therefore, the current limiting operation start current value Ils is defined as a current value when the value reaches 10% of the resistance value immediately above the critical temperature of the YBCO thin film. FIG. 6 shows a plot when the current increase rate is calculated by converting 10% of the total resistance as the current limiting operation starting current value into the current increase rate when the maximum current value is divided by the time until the current zero-peak. Show.

  From FIG. 6, it can be seen that there is no difference in the current limiting operation start current value at a current increase rate in the range of 10 to 60 kA / sec. This indicates that the operation of the current limiter is dominated by the absolute value of the current.

Next, the current limiting operation at 31 kA / sec was measured while changing the temperature. The measurement was performed by using the arbitrary waveform generator 7, controlling the DC power supply at a constant current, and increasing the current to 0 to 100 A in a certain time. The rise in current reached a maximum value over about 4 seconds as a sufficiently slow time in which the influence of the temperature rise accompanying the change in current was negligible. Current electric field characteristics were measured in the range of about 89.2K to 85.9K.
FIG. 7 and FIG. 8 show the temperature dependence of the current-voltage characteristics and the current-limiting operation start current value at each temperature. From FIG. 7, it can be seen that how the voltage rises during current limiting operation changes greatly even if the temperature is slightly changed. This indicates the possibility that the current limiting start current value can be largely controlled by changing the temperature of the current limiting element. Also from FIG. 8, it is clear that the current limiting start current value shows a strong temperature dependence, and it can be seen that the same tendency as in FIG. 4 is shown. The current limiting operation start current value decreased almost linearly as the temperature increased, and changed by about 15 A with respect to a 1 K temperature change. Further, it can be seen from FIG. 8 that the current-limiting operation start current value can be greatly changed by a small temperature change.

  From the above experimental results, the following was found. From the current-voltage characteristics shown in FIG. 6, the current-limiting operation start current value does not have a current increase rate dependency. This indicates that the current limiting operation start current is determined only by the absolute value of the current magnitude, and does not change with respect to the change in the current increase rate that changes depending on the phase at the time of failure. Further, it can be seen that the current-voltage characteristics continuously change from the low electric field region at the time of critical current measurement to the high voltage region just before quenching until the current limiter transitions from the superconducting state to the normal conducting state. As a result, useful information was obtained for the construction of a detailed current-limiting motion analysis model up to just before quenching.

FIG. 8 shows the strong temperature dependence of the current limiting operation start current value. The temperature dependence of the critical current has been measured so far, but the temperature dependence of the current limiting operation starting current value has not been clarified. This is probably because most current limiting tests have been performed only with saturated liquid nitrogen (77.3 K). As shown in FIG. 8, the possibility of adjusting the current limiting operation start current value by changing the temperature of liquid nitrogen was shown. From FIG. 8, for example, the following approximate expression is obtained. T is temperature and the unit is K. It should be noted that the approximate expression illustrated may vary depending on the characteristics of the YBCO thin film.
Ils = −15T + 1350 (1)
From this equation, it can be seen that the current limiting operation start current value of 15A changes with a temperature change of 1K. The current-limiting operation start current value at 85.9K is 70A, and it is considered that it can be supported in most places where a current limiter is installed for temperature adjustment of 1K. The operation start current value can be adjusted.

(Conclusion)
As described above, as a result of measuring the current limiting operation start current value at various temperatures and current increasing rates, it was found that the current limiting operation starting current value does not particularly depend on the current increasing rate. The current-voltage characteristic changes almost continuously from the low electric field region, which is the critical current measurement range, to the high voltage region immediately before quenching. As a result, it was shown that it is possible to create a detailed current-limiting motion analysis model until just before the quench.

  It was also shown that the critical current and the current limiting current value of the YBCO thin film have a strong temperature dependence. In particular, as the current rise rate increases, the ratio of critical current / current limiting operation start current value increases slightly, suggesting that the current limiting operation start current value is easily affected by heat in the low flux flow resistance generation region. it seems to do. On the other hand, in the vicinity of the high flux flow resistance region leading to quenching, it is expected that the fault current will be limited due to the normal conduction transition due to the magnitude of the current. It was shown that by adjusting the liquid nitrogen temperature by 1K, the current limiting operation start current value can be adjusted within a range of 15A. This is considered to be almost appropriate as the adjustment range in the system where the current limiter is introduced.

  Therefore, by adjusting the current limit operation start current value by temperature control, the current limit operation start current value can be adjusted quickly and easily within the range of the current limiter operation responsibility and non-operation responsibility required for each installed location. Is possible. As a result, we were able to demonstrate the possibility of controlling the operation of the SN transition type superconducting fault current limiter even after the current limiter was manufactured.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, the current limiting element using a YBCO thin film has been mainly described in the present embodiment, but the present invention is not particularly limited to this, and a current limiting device using a coil current limiting element of YBCO or a current limiting element other than YBCO. The present invention can also be applied to a current limiting device using two types of superconductors.

It is a block diagram which shows one Embodiment of the current limiting operation start electric current value adjustment apparatus of the superconducting fault current limiter of this invention. It is a figure showing the definition of an electric current increase rate (dI / dt). It is a current-voltage waveform diagram at each temperature. It is a graph which shows the relationship (temperature dependence of a critical current) with a critical current value and temperature. It is a current voltage waveform figure in each frequency in 87K. It is a graph which shows the electric current increase rate dependence of the current limiting operation start electric current value in 87K. It is a current-voltage characteristic figure in each temperature in 31 kA / sec. It is a graph which shows the relationship between the current limiting operation start current value and temperature (temperature dependence of the current limiting operation start current value) at 31 kA / sec. It is a graph which shows the temperature dependence of resistance.

Explanation of symbols

1 Current limiting element (sample)
2 Cold Head 3 Cryogenic Container 4 Refrigerator 5 Shunt Resistance 6 Power Amplifier 7 Arbitrary Waveform Generator 8 Temperature Sensor 9 Cooling Fluid (Refrigerant: Liquid Nitrogen)
10 Voltage tap

Claims (3)

Measure the current-limiting operation start current value of the current limiter with the current value when a certain percentage of resistance is generated relative to the resistance just above the critical temperature of the SN transition type superconducting current limiter as the current-limiting operation start current value Then, by controlling the temperature of the cooling fluid that cools the superconducting current limiting element in the cryogenic vessel on the basis of the measured value, the range of operational responsibility and non-operational responsibility at the location where the current limiter is introduced The adjustment method of the current limiting operation start current value of the superconducting current limiter which adjusts so that the said current limiting operation start current value may be accommodated in the inside. In the SN transition type superconducting fault current limiter in which the superconducting current limiting element is housed in a cryogenic container and kept in a superconducting state, the cryogenic container is equipped with a refrigerator, and immediately above the critical temperature of the SN transition type superconducting fault current limiter. The current value when a certain percentage of resistance is generated with respect to the resistance of the current limit is set as the current limiting operation start current value, and the current limiter is based on the current limiting operation start current value of the current limiter measured in advance. A superconducting fault current limiter that controls the temperature of the cooling fluid in the cryogenic vessel with the refrigerator so that the current-limiting operation start current value falls within the range of operating duty and non-operating duty at the place of introduction. Current-limiting operation start current value adjustment device. In the SN transition type superconducting fault current limiter, in which the superconducting current limiting element is housed in a cryogenic container and maintained in a superconducting state, the SN container is equipped with a vacuum pump for pressurizing or depressurizing refrigerant gas, and the SN The current value when a constant ratio of resistance is generated with respect to the resistance just above the critical temperature of the transition type superconducting current limiter is defined as the current limiting operation starting current value, and the current limiting operation starting current of the current limiting device measured in advance The temperature of the cooling fluid in the cryogenic vessel is set to the vacuum pump so that the current limiting operation start current value is within the range of the operation duty and the non-operation responsibility at the place where the current limiter is introduced on the basis of the value. The device for adjusting the current limiting operation start current of the superconducting fault current limiter which is controlled by

Images