JP3231837B2 - Superconducting current limiting device - Google Patents

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 device for suppressing an overcurrent such as an accident current generated in an alternating current circuit, and more particularly to a superconductor in which a superconductor suddenly undergoes a phase transition to a normal conductor due to a critical current. The present invention relates to a superconducting current limiting device that can increase the current density of a superconducting trigger coil, which is an AC superconducting switch utilizing the quench phenomenon, and reduce Joule loss during current limiting.

[0002]

2. Description of the Related Art When a three-phase short circuit or a ground fault occurs in an AC line such as a distribution line, a fault current of several tens of kA flows, causing serious damage to systems and equipment. Recently, superconductivity has been devised as one of current limiting techniques for instantaneously detecting and suppressing such fault currents.

FIG. 4 shows a circuit example of a typical conventional superconducting current limiter, which has already been disclosed in Japanese Patent Application Laid-Open No. 2-168525. In this example, 1 is a power supply, 2 is a circuit breaker, 3 is a current limiter, 3a is a superconducting current limiting coil (hereinafter, referred to as a current limiting coil), 3b and 3c are trigger coils, 3d is a switch, and 3g is a quench sensor. 4, a load; 11, a current transformer for detecting the total current of the circuit;
Is a current transformer for detecting the loop current of the trigger coils 3b and 3c, 13 is a control power supply, 14 is a loop current phase detector, 15 is a switch for connecting and disconnecting the loop current phase detection circuit to and from the main circuit, 16 Denotes a trigger coil voltage phase detector for detecting the phase of the voltage across the trigger coil, and 17 denotes a phase comparator for comparing and detecting the phase difference between the current and the voltage of the trigger coil.

The operation of the superconducting current limiter will be briefly described. In the normal state, the circuit current flows through the superconducting (zero resistance) trigger coils 3b and 3c without induction and the load 4
Power continues to be supplied. Next, the load 4 is short-circuited, etc.
Excessive fault current flows through the circuit and the value is
When the critical current value of the superconducting wires constituting b and 3c is reached, the trigger coils 3b and 3c are quenched and transit to a high resistance body. As a result, the fault current is suppressed, and the current limiting coil 3a having a lower impedance than the trigger coils 3b and 3c.
Commutation to the side. During this time, since the trigger coils 3b and 3c are normal conductors, the temperature of the superconducting wire rises at the same time as it continues to generate heat and consume the refrigerant.
The switch 3d is opened immediately after the current flowing in the trigger coils 3b and 3c is diverted to the current limiting coil 3a, thereby suppressing the evaporation of the refrigerant, and at the same time, the trigger coils 3b and 3c.
To help the trigger coils 3b and 3c return to the superconducting state so that the next cooling event can be dealt with by increasing the cooling rate of the trigger coil. The superconducting return of the trigger coils 3b and 3c is performed by the phase detectors 14 and 16 respectively.
The switch 3d is closed and the state can be returned to the steady state when the two conditions of the recovery of the system fault and the return of the superconductivity of the trigger coils 3b and 3c are met.

The above-described conventional superconducting current limiter has an excellent feature that the operation speed is extremely high and the current can be limited from the first wave even for an overcurrent having a steep rise such as a short-circuit current. Because of the method to quench the superconductor,
A considerable Joule loss Pj occurs during the current limiting operation (quench). If the power supply voltage V is constant, the value is inversely proportional to the quench resistance value Rq of the trigger coil as shown in the following equation.

Pj = (V ² / Rq) · t (J) t: energization time after occurrence of quench (sec) Therefore, the larger the quench resistance value Rq, the more the refrigerant cooling the superconductor is consumed (vaporization). Can be reduced and the apparatus can be made more economical. As a method of increasing the quench resistance Rq, a method of increasing the resistance of the matrix (stabilizing material) of the superconducting wire can be considered.

FIG. 5 shows a superconducting wire having a matrix of copper (Cu) generally used for a superconducting magnet and a Cu-Ni (30) used for a trigger coil of this type.
FIG. 5 is a diagram illustrating a temperature characteristic comparison of the specific resistance value of the matrix superconducting wire. As can be seen from the figure, Cu-Ni (30%)
The specific resistance of the matrix superconducting wire is about 25 times that of the Cu matrix superconducting wire at room temperature,
At 10K, it reaches 1000 times or more.

Accordingly, the trigger coil is made of Cu-Ni (30
%) By using a matrix superconducting wire, a large quench resistance can be obtained, and the consumption of the refrigerant at the time of current limiting can be remarkably suppressed. However, on the other hand, it has also been found that increasing the resistance of the matrix lowers the stability and makes the matrix less susceptible to disturbances, thereby lowering the current density.

Generally, in order to increase the current-carrying capacity of the superconducting conductor, a twisted wire method is used in the same manner as a normal electric wire. However, as described above, when a stranded wire configuration is adopted in a superconducting wire with relatively low stability in a high resistance matrix,
Due to the electromagnetic force at the time of the alternating current, a minute movement of the strand occurs inside the stranded wire, and in some cases, quench occurs due to frictional heat at that time.

FIG. 6 shows an Nb-T for AC having a diameter of 0.2 mm.
The decreasing tendency of the AC quench current value Iq per strand when the i ultra-fine multi-core wire (Cu-Ni (30%) matrix) is stranded (primary and secondary) is plotted against the current time change di / dt. FIG. As can be seen from the figure, the quench current value of the superconducting conductor slightly changes depending on the time change (di / dt) value of the current, but becomes substantially constant in a high di / dt region. Comparing the quench current value due to the stranded wire in the saturation region, the quench current value per one wire constituting the superconducting conductor decreases as the twist order increases. In other words, in the case of a strand having a current carrying capacity of about 100 A, the primary stranded wire is reduced to 67 to 75 A and the secondary stranded wire is further reduced to 23 to 30 A. The reason why the quench current value is reduced or irregularly varied with the stranded wire is considered to be due to mechanical movement of the superconducting wire.

Therefore, in order to improve the current density of the trigger coil, the coil is made of a conductor having a low twist order.
It seems more effective to configure these coils in parallel.

FIG. 7 and FIG. 8 are diagrams showing the configuration of the trigger coil manufactured based on such a concept and its internal connection. In both figures, the trigger coil is composed of two sets of inner non-inductive coils 3b and 3c and outer non-inductive coils 3d and 3e, and the above-described secondary stranded wire is used as a conductor of each coil. . Even when attempting to quench all coils simultaneously using the same type of superconducting conductor, the quench current value is the same due to the instability of the superconducting conductor itself, the magnetic field distribution inside the coil, and the degree of matching with the coil winding frame, etc. Often not. When a short-circuit test was performed using such a coil, deterioration occurred in which the operating current decreased in several tests.

FIG. 9 shows the result of a short-circuit test after the characteristic deterioration of the coil, and shows the complicated exchange of current (commutation / return) between the current I31 flowing through the coils 3b and 3c and the current I32 on the coils 3d and 3e. (E in the figure is a voltage across the trigger coil). This complicated current change is caused by paralleling non-inductive coils, and it is considered that such coil characteristics have caused deterioration.

That is, there is no mutual induction between the non-inductive coils, and there are independent impedance elements.
The impedance component after quenching is almost resistive.
Therefore, when the short-circuit current starts to flow, first, the coil having the smaller quench current value, for example, the coils 3b and 3c quench (point "A") first, but the quench at this time may remain in a very narrow range. . The reason is that the circuit current on the quenched side, even if the generated resistance is extremely small, is suppressed if the impedance of the partner coil is smaller (point "B"), and the partner coil 3 which has not been quenched yet
This is because the current commutates to the d and 3e sides.

On the other hand, coils 3d and 3e
Since the commutation current from b and 3c and the current flowing through itself are superimposed, a current having a larger di / dt value than the above-described current I31 flows. In this kind of coil,
The larger the di / dt value of the applied current, the wider the quench region tends to be.

When the quench region occurs in a wide range, the quench resistance of the coils 3d and 3e also becomes large, and the coil 3d in which the sudden recommutation current partially quench.
It flows to the b, 3c side ("C" point). Due to this recommutation current, a large Joule loss occurs in the normal conducting portions of the coils 3b and 3c that have already been quenched, the temperature rises, and thermal deterioration and burnout occur.

[0017]

As described above, in the prior art, when the current density and current capacity of the trigger coil are to be increased, the method of increasing the twist order of the superconducting conductor to be used is difficult. The energization efficiency is reduced by the movement of the wire, and the method of simply parallelizing the coils using low-order stranded wires has a problem that multiple quench occurs in the trigger coil and the coil characteristics are deteriorated.

The present invention has been made in view of the above,
The purpose is to obtain a large-capacity superconducting trigger coil with a high current density using a low-order stranded wire as much as possible, and a superconducting current limit that can prevent multiple quench due to short-circuit current to prevent deterioration of characteristics. It is to provide a device.

[0019]

In order to achieve the above object, a superconducting current limiting device according to the present invention uses a quench phenomenon caused by a critical current value of a superconductor to suppress an overcurrent generated in an alternating current circuit. Wherein the superconducting trigger coil comprises a plurality of
Number of conditions, having a predetermined winding direction and a predetermined number of turns, with provided coaxially so as to have a negative mutual inductance each other and which are connected in parallel or in series connected in a non-inductive mutually parallel The gist consists of a plurality of connected superconducting coils.

[0020]

In the superconducting current limiting device according to the present invention, the plurality of superconducting coils constituting the superconducting trigger coil have a mutual mutual inductance and are connected in parallel or in series so as to be non-inductive with each other and are connected in parallel. <br/>

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing a configuration of a superconducting trigger coil applied to a superconducting current limiting device according to one embodiment of the present invention. The superconducting trigger coil shown in FIG.
, And an outer coil 32 as a second superconducting coil wound coaxially outside the inner coil 31.

FIG. 2 is a circuit diagram showing the internal connection of the superconducting trigger coil shown in FIG. 1. As shown in FIGS. 1 and 2, the inner coil 31 has right-handed superconducting coils 31a, 3a.
1b and 31c are wound in three turns, and the outer coil 32 is similarly wound left-handed superconducting coils 32a, 32b and 32c in three turns. Also, both terminals 3 of the inner coil 31
1d, 31e and both terminals 32d of the outer coil 32,
32e, as shown in FIG. 2, three coils are connected so as to be two in parallel.

Therefore, the superconducting trigger coil applied to the superconducting current limiting device of the present embodiment does not have a single-layer, single-layer winding structure as in the conventional superconducting trigger coil, but includes a plurality of single-layer coil windings. (3 threads in this embodiment)
It is characterized by winding three superconducting coils.
That is, a superconducting coil in which a primary stranded wire having a high current-carrying efficiency and a relatively small diameter is wound around three layers in one layer and both ends of the three-layer coil are connected to each other to form three primary stranded wires in parallel. Have gained.

Further, at least two (one set) of these three-coil coils are formed coaxially close to each other, and these coils are wound in reverse winding so that the supermagnetic forces cancel each other out in the winding direction.
By short-circuiting both ends of the two coils to each other,
The six superconducting coils constitute a superconducting trigger coil which is closely coupled in parallel and electromagnetically non-inductive.

In the superconducting current limiting device using the superconducting trigger coil configured as described above, since the superconducting trigger coil is a three-row, two-parallel coil, it is equivalent to six times the current carrying capacity of the primary stranded wire. Continuous power capacity can be obtained.

FIG. 3A is an electrical equivalent circuit diagram of the operation state of the above-described superconducting trigger coil. In the superconducting trigger coil shown in the figure, an inner coil 31 and an outer coil 32 are shown to have self-inductances L31 and L32, respectively, and both coils 31, 32 maintain a superconducting state with respect to a steady current, and each other. Self inductance L3
1 and L32 are negatively magnetically coupled to cancel each other (−
M), the impedance of the superconducting trigger coil is almost zero as shown in FIG.

FIG. 3C shows a state in which an overcurrent such as a short-circuit current flows and one of the superconducting coils 31, 32, for example, the inner coil 31 is quenched. Then, a quench resistor R31 is generated in the quenched inner coil 31, and the coil current I31 is attenuated (current-limited). When the current of the inner coil 31 is reduced in this manner, the magnetic flux generated by the inner coil 31 is also reduced, so that the non-inductive state between the coils 31 and 32 is broken, and the outer coil 32 that has not been quenched has a reactor action. Occurs.

Since the current limiting operation by mutual induction between the coils is an electromagnetic phenomenon, it responds to a steep rising current such as a short-circuit current without delay. Also, since this action always acts to eliminate the shunt imbalance between the inner coil 31 and the outer coil 32, when only one of the coils is quenched, or as shown in FIG. Are quenched together, and even if the quench resistance values are significantly different, short-circuit current is exchanged between the coils as in the conventional coils, and the coils are not deteriorated or burnt out.

As described above, the present superconducting trigger coil
Since the inner coil 31 and the outer coil 32 are magnetically tightly coupled with each other, even if quench occurs in one of the coils even under various circuit conditions, the short-circuit current is shared almost simultaneously and uniformly to limit the current. Actions can be taken.

Next, as an example of a specific configuration of the superconducting trigger coil shown in FIG. 1, the primary stranded wire shown in FIG.
A case where a wire of 7A to 75A / wire is used will be described.

The primary stranded wire is as thin as 1/3 or less of the secondary stranded wire, and the electromagnetic force generated between turns (proportional to the square of the conducting current) is also reduced to 1/4. The winding pitch can be reduced. Therefore, if the outer shape of the coil is the same as that of the conventional coil, the length of the conductor per strip can be made equal to that of the conventional single-wound coil.

In the conventional coil, a parallel non-inductive coil is formed by using a secondary stranded wire composed of 36 strands.
This means that the superconducting wires are used in parallel.

The continuous current carrying capacity of the conventional coil is 72 times the wire capacity of the secondary stranded wire, that is, 23 A × 72 =
1656A.

On the other hand, in the superconducting trigger coil of the present embodiment, the number of superconducting wires is 36 since six primary wires in which six wires are twisted are connected in parallel. The conductor cross-sectional area is 1/2 of the coil. However, the continuous current carrying capacity is 36 times the wire current carrying capacity in the primary twist, that is, 67 A × 36 = 2412 A, and a current carrying capacity approximately 1.5 times that of the conventional coil can be obtained.

As described above, the superconducting trigger coil of the present embodiment has a current carrying capacity of about 1.5 times as large as that of the conventional coil with a current carrying sectional area of ２ and a circuit current up to about 2400 A. On the other hand, the superconducting state is maintained in a state where the impedance is almost zero, and when a current exceeding this level flows, it is quenched to perform a current limiting action.

Next, such trigger coils 31, 32
Will be described in the case where is applied to the circuit shown in FIG. 4 instead of the trigger coils 3b and 3c.

First, when the circuit breaker 2 is closed and energization to the load 4 is started, the circuit current passes through the superconducting and almost non-inductive trigger coils 31 and 32 as shown in FIG. Power is normally supplied to the load 4. Next, for example, when a short-circuit accident occurs in the load 4 and a short-circuit current flows, the peak value of the short-circuit current exceeds 2400 A, and a quench occurs in the trigger coil 31, a resistor R31 is generated in the trigger coil 31. To limit the circuit current of the trigger coil 31. When the circuit current of the trigger coil 31 decreases, the impedance action described above occurs in the coil 32, and the trigger coil 3
The circuit current on the second side is also limited almost simultaneously (see FIG. 3).
(C)).

In this case, the short-circuit current is limited by the resistance of the trigger coil 31 and the reactance of the coil 32. However, if the short-circuit current increases significantly, the circuit current increases even after the trigger coil 31 is quenched. Subsequently, when the value exceeds the quench current value of the coil 32, the coil 32
Also quench. As a result, the short-circuit current is limited to a predetermined value by the quench resistance values of the two coils 31 and 32 and the reactance generated according to the degree of imbalance of the coil currents (FIG. 3D).

In the above embodiment, a coil wound three turns with a primary stranded wire has been described. However, the present invention is not limited to this, and the number of turns of the superconducting conductor applied to such a coil and The number of windings may be arbitrary. Also, combinations of coils are not limited to those described in a set of second parallel non-inductive coil as in this embodiment, effects similarly to the plurality of sets of coils constituting those multiple parallel or series connected in parallel The effect can be obtained.

[0041]

As described above, according to the present invention,
The plurality of superconducting coils constituting the superconducting trigger coil have negative mutual inductance with each other, and are connected in parallel or in series so as to be non-inductive with each other , and
Since they are connected in parallel , a large-capacity superconducting trigger coil can be constructed with a low-order stranded wire, the length of the winding per wire can be made equal to that of the conventional coil, and the current-carrying cross-sectional area becomes smaller. The quench resistance can be increased accordingly. Further, even under various short-circuit conditions and variations in the quench current of the trigger coil, it is possible to prevent the deterioration of the trigger coil characteristics due to multiple quench due to the mutual induction between the superconducting coils. Furthermore, the loss of the superconducting wire of the superconducting trigger coil is proportional to the conductor volume, and the volume of the superconducting conductor used decreases as the current carrying density increases,
The AC loss is also reduced, and the refrigerator for cooling the superconducting trigger coil can be made compact and power saving.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of a superconducting trigger coil applied to a superconducting current limiting device according to one embodiment of the present invention.

FIG. 2 is a circuit diagram showing an internal connection of the superconducting trigger coil shown in FIG.

FIG. 3 is an electrical equivalent circuit diagram of an operation state of the superconducting trigger coil shown in FIG.

FIG. 4 is a circuit diagram of a conventional superconducting current limiting device.

FIG. 5 is a diagram showing temperature characteristics of electric resistance of copper and copper nickel serving as a matrix of a superconductor.

FIG. 6 is a diagram showing a decrease characteristic of a quench current of an Nb-Ti ultrafine multi-core wire having a matrix of copper nickel depending on a twisted wire order.

FIG. 7 is a diagram showing a conventional general coil configuration for increasing a current carrying capacity.

8 is a diagram showing the internal connection of the coil of FIG. 7 and the relationship between the current and the direction of the magnetomotive force of the coil.

9 is a diagram showing a voltage-current waveform in a short-circuit test of the coil shown in FIG. 7, in which the horizontal axis represents a time change and the vertical axis represents E;
Is the voltage waveform across the trigger coil, I31 is the inner layer coil 3.
b, 3c, the change of the combined current, I32 is the outer layer coil 3d,
3e shows a change in the combined current.

[Explanation of symbols]

 31 inner coil 32 outer coil 31a, 31b, 31c inner coil superconducting coil 32a, 32b, 32c outer coil superconducting coil

Continuing on the front page (72) Inventor ▲ Tsuru ▼ Kazuyuki Naga Toshiba, Fuchu-shi, Tokyo 1 Toshiba Corporation Fuchu Factory (72) Inventor Osamu Ito 1 Komukai Toshiba-cho, Kochi-ku, Kawasaki-shi, Kanagawa Prefecture Co., Ltd. In the Toshiba Research Institute (72) Inventor Eriko Yoneda 1 in Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture In the Toshiba Research Institute (56) References JP-A-2-202320 (JP, A) JP-A-1-214223 (JP, A) JP-A-2-26224 (JP, A) JP-A-3-145922 (JP, A) JP-A-3-503945 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ H01L 39/16-39/20 H01L 39/00 H02H 9/02 H01F 5/08 H01F 7/22

Claims (1)

(57) [Claims] 1. A superconducting current limiting device having a suppressing superconducting trigger coil overcurrent occurring in the superconductor utilized to AC circuit quenching phenomenon by the critical current value of the superconducting trigger coil, each predetermined plurality number of conditions, having a predetermined winding direction and a predetermined number of turns, with provided coaxially so as to have a negative mutual inductance each other, or connected in series which are connected in parallel so as to be non-inductive with each other
And a superconducting current limiting device comprising a plurality of superconducting coils connected in parallel .