JPH03145922A - Current limiter - Google Patents

Abstract

PURPOSE:To reduce power loss at the time of limiting a current by connecting a normally closed contact in series with a plurality of series first superconducting coils wound noninductively, and connecting a second conductive superconducting coil having a higher critical current value than that of the first coil in parallel. CONSTITUTION:A normally closed contact switch 2, a current limiter 3 and a load 9 are connected in series with an AC power source 1. In the limiter 3, a current limiting coil 5 made of an inductive superconducting coil having a predetermined critical current (IC2) is wound inside a common spool 4. A heat insulating plate 7 is held at the outside, a plurality of noninductively wound coils 6a-6c are connected in series in a multilayer state to form a trigger coil. The coils 6a-6c are formed by winding superconducting materials set lower in critical current (IC1) than the IC2 and connecting a switch 8 in series. When the critical current IC1 exceeds by the overcurrent of the load 9, the trigger coil is quenched to show a high resistance, the current is commutated to the coil 5, thereby rapidly opening the switch 2 by the voltage of both ends. Thus, the power loss at the time of limiting the current is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a current limiting device that electromagnetically suppresses overcurrent in an AC power line.

(Prior Art) In order to protect electrical equipment from overcurrent, it is necessary to limit the overcurrent instantaneously when it flows through the electrical equipment. Among current limiting devices for limiting such overcurrent,
For example, in the restoration using superconducting coils,
The one disclosed in Japanese Patent No. 8-2038 is known.

FIG. 5 shows its configuration. Coils 11 and 12 made of superconducting material are wound around a common spool in a low-temperature container 13 that provides a flow path 14 for a cooling medium such as helium. A normal conduction reactor 15 and a switch 19 are connected in series to the electric path that supplies power to the coil. Here, the coils 11 and 12 are configured such that their magnetomotive force directions are opposite to each other, and the coil 11 and 12 are arranged in opposite directions.
The critical current value of is set lower than the critical current value of the coil 12.

Next, the operation of this device will be explained.

For steady current, both coils 11 and 12
Since it is in a superconducting state, its impedance is only the leakage magnetic flux φs1 between the coils, that is, the leakage reactance, and the vehicle power is supplied to compensate for the loss. On the other hand, when an overcurrent occurs in the circuit 8, the coil 11 is first quenched due to the critical current value. As a result, the coil 11 becomes a normal conductor and becomes a high resistance element.
The current flowing through coil 1 is limited by its resistance, and most of the current is commutated to coil 12, which is in a superconducting state. As a result, a magnetic flux is generated passing through the coil 12, and an inductance proportional to the value of the magnetic flux is generated. Overcurrent is suppressed by this inductance. Thereafter, the operator opens the switch 19 to completely cut off the electrical circuit. This electrical circuit is cut off in order to suppress an increase in the amount of vaporized expensive cooling medium (for example, helium) due to the heat generated by the quenched coil 11.

By the way, this type of current limiting device is commonly used for suppressing short circuit current in high voltage and large current circuits, for example, 6.6KV-6.
Applies to each feeder in a 00A rated distribution unit. In this case, the characteristics required of this device are a current-limiting operating current of 120 OA.

The current limiting peak value is about 3KA when the electric current dynamic impedance is 2Ω. In order to meet this demand, the coil 12
The inductance of approximately 6.5 mH is required in a 50 Hz system. In addition, since the coil must be constructed of superconducting wire with a critical current value of 3 KA or more,
G-structure inevitably has to be multi-layered.

Therefore, in the current technology, the width of the coil 2 or, for example, an inner diameter of 100+a+aφ and an outer diameter of 200 mm.
φ, coil length 400+111, number of turns 400 is 10
It will be composed of layers. The coil 11, which is configured to generate a magnetomotive force in the opposite direction, is also configured to generate a magnetomotive force of the same magnitude and is placed inside the coil 12 in order to minimize its leakage reactance (steady impedance). Ru.

[The problem that the invention attempts to solve]

However, the cancellation rate of the magnetic flux between the coils 11 and 12 increases as the difference in cross-sectional area of each coil increases, and in the above-mentioned element, a leakage inductance of about 1 mH occurs.

This leakage inductance acts as a steady impedance in the current limiting device and therefore contributes several orders of magnitude to the supply voltage.

For example, in the 6.6KV-60OA current limiting device mentioned above, 60
A voltage drop of about 190V will occur at 0A current I+, 17.

As described above, in conventional superconducting current limiting devices, the higher the applied circuit voltage, the greater the operating impedance (
Since the inductance of the fill 2 is required, the leakage inductance increases and the steady-state voltage drop increases.

The present invention was made to solve these problems, and it maintains the steady impedance to a minimum regardless of the size of the current limiting impedance, and also reduces the supply voltage of the coil that is quenched during operation, that is, when overcurrent is applied. The purpose is to provide a current limiting device that can reduce losses due to descent.

[Structure of the invention]

(Means for Solving the Problems) According to the present invention, in a current limiting device for suppressing overcurrent in an electric circuit, substantially the same first critical current value is set to 6°, and a plurality of first A superconducting coil (trigger coil), a current-limiting element that produces a second critical current value higher than that of the first superconducting coil (1'L), and a current-limiting element that reduces the inductance, and the first superconducting coil. It is characterized by comprising a switch connected in series, normally closed, and opened by quenching the superconducting coil, and a series circuit of the first superconducting coil and the switch is connected in parallel with the current limiting element.

(Function) During steady state when the circuit current is below the critical current value of the trigger coil, most of the current flows through the current non-inductively wound trigger coils connected in series.

Therefore, the element impedance at this time is only the series component of the leakage reactance of each trigger coil, and this value is extremely small. Therefore, the current limiting device according to the present invention has almost no induction during normal operation and acts as a zero resistance (superconducting) element.

On the other hand, when an overcurrent flows in the electrical circuit and its value exceeds the critical current value of the trigger coil, the quench generated in one of the multiple trigger coils will cause the short-leafed current to flow through the other trigger coils. It propagates internally, and the entire trigger coil becomes a high-resistance element.

Therefore, most of the circuit current is diverted to the current limiting coil, and overcurrent is suppressed by the inductance of the current limiting coil. At this time, a voltage proportional to the product of current-limiting coil impedance and current is generated between the terminals of the current-limiting coil, so
By using this voltage as a current-limiting operation signal and opening a switch inserted in series with the trigger coil, it is possible to eliminate the loss generated in the trigger coil, and at the same time start cooling the trigger coil to increase the superconducting return speed. You can hasten it.

(Example) FIG. 1 is a schematic diagram showing an example of the current limiting device according to the present invention.

The AC power supply 1 includes a switch 2 and a current limiting device 3 according to the present invention.
and a load 9 are connected in series. This current limiting device 3 has a predetermined critical current value (I cl
) A superconducting current-limiting coil 5 is disposed, and a plurality of trigger coils 6a, 6 are connected to the outer periphery of the coil 5 via a heat insulating shield 7.
b, 6c are wound in a multilayered manner, and a switch 8 is provided. Here, the heat insulating shield 7 is for thermally shielding between the current limiting coil 5 and the trigger coils 6a, 6b, and 6c. Each trigger coil 6a~
6c and the switch 8 are connected in series, and both ends thereof are connected in parallel to the current limiting coil 5. This switch 8 is of a normally closed type, and is controlled by a control circuit (not shown) so that when a predetermined voltage is generated between both ends of the current limiting coil 5, the switch 8 instantaneously opens.

FIG. 2 is an explanatory diagram showing the winding direction and internal connections of each coil constituting the water chamber device, and includes trigger coils 6a, 6b,
As an example of non-inductive winding, 6c has AP winding (Ayr ton -- Per
ry) volume) is used.

Further, as the superconducting wire constituting the trigger coil, for example, an Nb-Ti based AC wire is used. A feature of this superconducting wire is that the apparent propagation speed of current quench is extremely fast.

FIG. 3 is a graph showing an example of measuring the quench propagation velocity of an AC Nb-Ti superconducting wire with a diameter of 0.1 mm. The apparent quench propagation velocity at this time is 6 kII/see, but from this measurement result, the quench does not propagate thermally sequentially from a certain point, but rather through the superconducting conductors that make up the coil. It was found that a large number of quench buds already exist in the wire, and the number of quench generation points increases in proportion to the di/dt of the alternating current, and the apparent quench propagation speed in the coil increases. . That is, it is actually difficult to observe the critical current value in any direction over the entire length of this type of superconducting wire, and the critical current value usually varies somewhat depending on the position. Therefore, the portion where the critical current value is low becomes the bud of quenching. In addition, one of the reasons for the above-mentioned phenomenon in which the quench propagation speed increases is that the di/dt (current increase rate per hour) is extremely large as a condition of h° at AC short circuit current. . That is, in general, when a quench occurs in a part of the coil, the current is suppressed due to the increase in resistance, and the quench region then propagates only thermally. However, the short circuit current is
Since the di/dt value is 50 to 1.00 times the steady current, there is no current attenuation even if the first quench occurs.
As a result, quenching occurs almost simultaneously at many points ("A"). Due to the combination of the above phenomena, the entire coil instantaneously becomes a resistor, and almost all of the current is instantaneously commutated to the current limiting coil.

In this way, if superconducting wires are used for multiple trigger coils and a di/dt value larger than the critical current value is obtained, all of the multiple trigger coils connected in series can be
1! Making y quench becomes oral performance.

Next, the operation of the current limiting device according to one embodiment of the present invention will be explained.

Figure 4 shows the steady state of the current limiting device shown in Figures 1 and 2.
2 is a graph showing changes in current values and changes in element impedance for current limiting operations p, , and current-limiting operation p. In FIG. 4(a), the total current io1 trigger coil 6a, 6b, 6cmt-
Current flowing 11% Current flowing through the current limiting coil 12, trigger coils 6a, 6b.

6c, critical current 1 of current limiting coil 5, critical current 1 of current limiting coil 5, and short circuit 2 total current if (estimated short circuit current) when the current limiting device is not connected. Further, FIG. 4(b) shows the steady-state impedance Z of the current limiting device, the current limiting operation n3C impedance Z'1, and the line impedance Cz1+.

In Figure 1, if the circuit is operating normally,
The total current 10 is the trigger coil 6a, 6b.

The critical current 1c1 of 6c is suppressed to below, and most of the current flows through the non-inductive trigger coils 6a, 6b, and 6c. Therefore, only an extremely low voltage corresponding to the product of the leakage reactance of the trigger coils 6a, 6b, 6c and the total current is generated across the current limiting coil, and the switch 8 remains open and the negative ρj9 is generated. Supply voltage and current.

Assume that a zero short circuit accident occurs here. As a result, a short circuit current flows in the circuit, and when the value exceeds the instantaneous current value (I cl ) of the trigger coil, the trigger coils 6a, 6b, 6
All of c quench almost simultaneously and turn into a high resistance material at an extremely rapid rate as shown in FIG. Therefore, most of the current that had previously flowed through the trigger coils 6a, 6b, and 6c is commutated to the current-limiting coil 5 at instants n and r. As a result, the short circuit current is limited by the action of the current limiting coil 5 as shown in FIG. At the same time, a predetermined voltage is generated across the current-limiting coil 5, and after that level is established, the switch 8 is opened by a switch control circuit (not shown), triggering coils 6a, 6b, 6c.
cut off the current flowing to the In addition, the current limiting coil 5 is
Since the critical current value Ic2 is designed to exceed the current limiting peak value, it is in a superconducting state. Therefore, after the switch 8 is opened, no loss occurs in this device.

In addition, the trigger coils 6a, 6b, and □c return to the superconducting state after a predetermined period of time after the switch 8 is opened, so the switch 8 is closed after the field lightning state is eliminated. The water chamber device can be returned to a steady state simply by

In this way, according to the present example, by increasing the number of trigger coils, the trigger coil 6a.

The quench resistance values of the trigger coils 6a, 6b, 6c can be increased arbitrarily while minimizing the deflection reactance of the trigger coils 6b, 6c. The loss (Psc) generated in the trigger coil during current limiting is as shown in the following equation.

2 P sc cp knee-N Here, E: circuit voltage (V) R: quench resistance of the trigger coil (Ω>>N: number of series connections of the trigger coil.

Therefore, the generated loss can be suppressed to a value inversely proportional to the number of trigger coils connected in series.

In the above embodiments, the current limiting coil is arranged on the inner circumferential side of the trigger coil, but the same effect can be obtained even if the current limiting coil is arranged on the outer circumferential side of the trigger coil.

Further, although the trigger coil and the current limiting coil are arranged coaxially, the same effect can be obtained even if they are arranged separately. Historically, a normally conducting impedance element may be used instead of the current limiting coil.

Further, in the embodiment, three sets of trigger coils are shown, but the number of trigger coils can be selected arbitrarily.

In addition, in the embodiment, the switch is located outside the cryogenic container.
Although it is provided in a 9-temperature range, it may also be stored in a low-temperature container.

〔Effect of the invention〕

As described above, according to the current limiting device of the present invention, by using a plurality of series-connected trigger coils, the resistance of the trigger coil during current limiting operation can be increased and the steady state impedance can be reduced by nJ. , operating losses can be significantly reduced.

Therefore, it is possible to reduce the amount of vaporized cooling medium and downsize the refrigerator.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a current limiting device according to the present invention;
Figure 2 is a wiring diagram showing the connection state of the current limiting coil and trigger coil in Figure 1, Figure 3 is a graph showing an example of measuring the quench propagation velocity of a superconducting wire, and Figure 4 is a diagram showing the connection state of the current limiting coil and trigger coil in Figure 1.
A graph showing changes in each current value and element impedance during steady state and current limiting operation of the current limiting device shown in the figure. Figure 5 shows the configuration of a current limiting device using a conventionally proposed superconducting coil. FIG. 1...Power supply, 2...Switch, 3...Current limiter, 4
...Spool, 5...Current limiting coil, 6a, 6b, 6
c...Trigger coil, 7...Insulation shield, 8...
・Switch, 9...Load.

Claims (1)

[Claims] 1. In a current limiting device for suppressing overcurrent in an electric circuit, a plurality of first superconducting coils (trigger coils) each having substantially the same first critical current value and each non-inductively wound. and a current limiting element having a second critical current value higher than that of the first superconducting coil and having an arbitrary inductance, connected in series with the first superconducting coil, normally closed, and What is claimed is: 1. A current limiting device comprising: a switch that opens a circuit by quenching a superconducting coil; and a series circuit of the first superconducting coil and the switch is connected in parallel with the current limiting element. 2. The current limiting device according to claim 1, wherein the current limiting element constitutes a second superconducting coil (current limiting coil). 3. The current limiting device according to claim 1, wherein the current limiting element is a normally conductive impedance element. 4. The current limiting device according to claim 2, wherein the first superconducting coil and the second superconducting coil are coaxially arranged.