JPH03145923A - Current limiter - Google Patents

Abstract

PURPOSE:To shorten current limiting time by connecting two sets of noninductively wound superconducting coils having the same critical current value in series with normally closed and open contacts, and connecting inductive superconducting coils having higher critical current value than the previous coil in parallel. CONSTITUTION:A normally closed contact 10 to be opened by the output of a quench signal detector 9 is connected to a trigger coil in which noninductively wound superconducting coils 6a, 6b having the same critical current value (IC1) are connected in series. Noninductively wound superconducting coils 7 having the same critical current value IC1 are connected to a normally open contact 11. Further, a current limiting coil 5 made of inductive superconducting coil having higher critical current value (IC2) than the IC1 is connected in parallel with the trigger coil. If a load 12 is short-circuited so that the overcurrent exceeds the IC1, the trigger coil is quenched to show a high resistance, the current is commutated to the coil 6 to detect the voltage at both ends by the detector 9, thereby opening the contact 10. If an accident is vanished, the contact 11 is closed to commutate the current from the coil 6 to the coil 7. Thus, its current limiting time is shortened.

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, when an overcurrent flows through the electrical equipment, it must be instantaneously 11. Must be limited to +1. Among current limiting devices for limiting such overcurrent, examples of current limiting devices using superconducting coils include:
One disclosed in Japanese Unexamined Patent Publication No. 63-253315 is known.

FIG. 6 shows the structure of the first hollow bobbin 2.
1 and a superconducting reactor wound around the outer surface of a second hollow bobbin 23 located on the outer periphery of the superconducting coils 22 and a second hollow bobbin 23 located on the outer periphery of these coils It is equipped with 24. These coils are adapted to be drawn out by terminals 25,26. In this current limiting device, the critical current value of the coil 22 is set lower than the critical current value of the coil 24.

Next, the operation of this device will be explained.

For steady current, both coils 22 and 24'' (
Since they are in a superconducting state, their impedance is only the stray magnetic flux φS1 between the coils, that is, the stray reactance, and power is supplied with low loss. When χ=t, the coil 22 first quenches the current value at n and r when an overcurrent occurs in the electric circuit. As a result, the coil 22 becomes a normal conductor and becomes a high-resistance element, so the current flowing through the coil 22 is limited by its resistance, and most of the current is commutated to the coil 24, which is in a superconducting state. As a result, a magnetic flux is generated passing through the coil 24, and an inductance proportional to the value of the magnetic flux is generated. This inductance suppresses overcurrent (
Current limiting) is performed.

[Problem to be solved by the invention]

However, when the grid electrification increases, depending on the value of the quench resistance of the non-inductive superconducting coil 22, the quench-specific loss of the trigger coil becomes large, and the superconducting wire is heated and deteriorated, and may even burn out or melt down.

Therefore, the quench resistance value of the trigger coil needs to be higher as the system voltage increases, but with conventional technology, it is necessary to increase the size to increase the resistance value.
Demand for downsizing is increasing.

Furthermore, after an accident occurs in the grid and current limiting operation occurs,
After the cause of the accident is removed, it is desirable for the current limiting device to quickly return to a steady state, but with conventional technology,
Once the trigger coil is quenched, even if the circuit is cut off, it will not be able to return to the superconducting state until a cooling period of at least 1 second has passed, and during that time, the current limiting device as a whole will not be able to return to a steady state. There was a problem.

The present invention was made in order to solve these problems, and provides a current limiting device that can cope with increases in system voltage without increasing the size of the system, and can quickly return to normal operation if necessary. The purpose is to provide.

[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, a first critical current value is set to zero, and a plurality of non-inductively wound series connected 1 superconducting coil (trigger coil)
, a second superconducting coil (return coil) having the same critical current value as the first superconducting coil and non-inductively wound;
a current limiting element having a second critical current value higher than that of the superconducting coil and having an arbitrary inductance; and quench detection means for detecting quenching of the first superconducting coil;
A first switch means connected in series to the first superconducting coil, normally closed and opened by the quench detection output of the quench detection means, and a first switch means connected in series to the second superconducting coil, normally open and current limiting. and a second switch means that is closed after operation, and current-limits a series circuit between the first superconducting coil and the first switch means and a series circuit between the second superconducting coil and the second switch means. Features (effects) characterized by parallel connection with the element: During steady state when the circuit current is below the critical current value of the trigger coil, most of the current flows through the non-inductively wound coil side. Therefore, the element impedance at 0 and H is only the series component of the leakage reactance of each trigger coil, and this value is extremely small. For this reason, the current limiting device according to the present invention has almost no conduction during the constant voltage χ and acts as an element with zero resistance (superelectricity 4).

On the other hand, when an overcurrent flows in the circuit and its value exceeds the critical current value of the trigger coil, the trigger coil quenches and becomes a high-resistance element, so most of the negative circuit current is diverted to the current-limiting coil. Overcurrent is suppressed by current limiting coil actance. A voltage proportional to the product of current-limiting coil impedance and current is generated between the terminals of the current-limiting coil, so this voltage is used as a current-limiting operation signal to trigger a suppressed switch in series with the trigger coil. By opening the pole, it is possible to eliminate the loss generated in the trigger coil.

Immediately after this current limiting, when the cause of the accident has been removed and it is necessary to return to normal operation, if the switch connected in series with the recovery coil is closed, the current flowing through the current limiting coil becomes superconducting and non-inductively coiled. The current is recommutated to the restored coil side, the voltage drop due to the current limiting coil disappears, and the normal load power supply status is restored. When the coil cools down and returns to the superconducting state, the current limiting device returns to its steady state. In this way, quick recovery becomes possible.

(Example of Thick Weave) Hereinafter, one embodiment of the current limiting device according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of a system using the current limiting device according to the present invention, FIG. 2 is an explanatory diagram showing the winding direction and internal connections of each coil portion constituting the current limiting device, FIG. 3 is a circuit diagram of the configuration shown in FIG. 1.

The AC power supply 1 includes a switch 2 and a current limiting device 3 according to the present invention.
and load 12 are connected in series.

This current limiting device 3 operates on the inner peripheral side of the spool 4 at a predetermined critical current value (Ic
A superconducting current limiting coil 5 with A return coil 7 is wound coaxially. The critical current value (Ic2) of these trigger coils 6a, 6b and the return coil 7 is the critical current value (Ic2) of the current limiting coil 5.
) is a smaller value. In addition, the heat insulation shield 8
is for thermally shielding between the current limiting coil 5, trigger coils 6a, 6b, and return coil 7. A normally closed type trigger switch 10 is connected in series to the series connected trigger coils 6a and 6b, and a normally open type return switch 11 is connected in series to the return coil 7, and each of these series circuits has a current limiting current. It is connected in parallel to the coil 5.

Referring to FIG. 2 showing the winding direction and internal connections of each coil, the current limiting coil 5 is wound as a mere reactor to have a predetermined inductance, and the trigger coil 6
a, 6b and the return coil 7 are AP14 (
Ayrton-Perry (at Ayrton-Perry)
It is wound as a non-inductive winding.

A quench detector 9 is connected between both terminals of the current-limiting coil 5 to detect that the trigger coil is quenched and the current-limiting coil is performing current-limiting action, and its detection output is sent to the switch 10 by the trigger. The trigger switch 10 is placed in a current-limiting operating state.

That is, this detector 9 detects that the current limiting device is in a steady state of superconductivity when the voltage across the current limiting coil is significantly lower than the power supply voltage, and conversely, a voltage drop of more than a predetermined value is occurring. At times, the trigger coils 6a and 6b are quenched to detect that they are in a current-limiting operating state.

Here, an example of the specifications of these circuit elements is as follows.

Current limiting coil 5L-0,75mH Ic-40OA Trigger coil 6a, 6b L=50μHIc-120
A Return coil 7 L-25μH IC-120A Load resistance 12 R-10Ω Power supply voltage E-10(')V In addition to these, 0, 1Ω as a simulated line resistance
, 3Ω is expected for the current limiting resistance device as a whole.

Further, as the superconducting wire whose birds constitute the coil, for example, an Nb-Ti based AC wire is used.

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

FIG. 4 is a graph showing the current change during each operation of the device according to the thick weave example shown in FIGS. 1 to 3, and FIG. 5 is a graph showing the relationship between the switch operation and the impedance change.

Assume that the circuit breaker 2 is set and power is being supplied, the total current is 10, the current flowing through the current limiting coil is iL, the current flowing through the trigger coils 6a and 6b is iLI, and the current flowing through the recovery coil 7 is Let's call it IL2.

When the circuit is operating normally, the trigger switch 10 is in an open state, the return switch 11 is in an open state, and most of the main current 10 flows through the trigger coil, which is formed without induction. Therefore, the residual inductance of the trigger coils 6a, 6b and the trigger coil 6a,
There is only a slight voltage drop corresponding to the product of current ill flowing through 6b. For this reason, the load 12 has χ・l
power can be supplied without any problems.

Next, when a short-circuit accident occurs in the load 12, a short-circuit commutation occurs in the circuit and the current tries to rise to its peak value, I. When the value exceeds 1c2, the trigger coils 6a and 6b are quenched, become normal conductors, and have one false resistance. Therefore, the current flowing through the trigger coils 6a, 6b rapidly decreases, and all the 7T5 currents are gradually commutated to the current limiting coil 5 side.

As a result, in this current limiting device, an impedance obtained by multiplying the inductance of the current limiting coil by ω (2πf) is generated, thereby limiting the short circuit current. Note that this impedance effect is due to an induction phenomenon caused by the superconducting conductor, so there is no resistance component and no heat generation occurs. Current-limiting coil during current-limiting operation 5. The combined impedance of the trigger coils 6a, 6b and restoration coil 7 is shown in FIG. 4, and it can be seen that the impedance becomes large at the time of current limitation.

On the other hand, when the trigger coils 6a and 6b are quenched, a large current flows through the current limiting coil 5, and the voltage across the current limiting coil 5 increases rapidly, and this voltage increase is detected in quench detection S9. The detection output of the quench detector 9 is applied to a trigger switch 10 to open it. this is,
Even when commutation occurs on the current limiting coil side, the trigger coil 6
a.

6b has the problem that an extremely small current flows through it and generates Joule heat, which causes the refrigerant that cools the superconducting coils, such as extremely expensive liquid helium, to vaporize. This is to do so.

By the way, some fault currents occur accidentally and are instantaneous.
In some cases, the system may self-recover at J or remove the self-portion as a system and restore normality. When such a restoration occurs, it is desirable for the current limiting device to quickly return to a steady state. Therefore, when performing restoration, the restoration switch 11 is closed and the restoration coil 7 is connected in parallel to the current limiting coil 5. This switch may be turned on directly by the operator, or may be carried out based on a command from a control device monitoring accident recovery.

Since the return coil 5 is non-inductive and in a superconducting state as described above, most of the current flowing through the current limiting coil is re-commutated to the return coil side, resulting in a low impedance as a whole of the current limiting device.

The time it takes for the trigger coil 5 to return to the superconducting state is approximately several seconds, so after confirming that the trigger coil has returned to superconducting state after this time has elapsed, the bird closes the switch 10 and presses the return switch 1 again. When opened, this current limiting device returns to a steady state.

Further, in the current limiting device according to the present invention, a plurality of tri-coils connected in series is used as the trigger coil.

In such a configuration, by changing the number of trigger coils connected in series, the resistance values of quench (1) and +1 can be arbitrarily increased while minimizing the residual inductance. The loss (Psc) generated in the trigger coil during current limiting is as shown in the following equation.

2 5CcC -N Here, E: circuit voltage (V) R: quench n of the trigger coil, 1 resistance (Ω).

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

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. Furthermore, a normally conducting impedance element may be used instead of the current limiting coil.

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

Further, in the embodiment, the switch is provided in the normal temperature region outside the low temperature container, but it may be stored outside the 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, it is possible to increase the resistance of the trigger coil during current limiting operation and reduce the steady state impedance. Therefore, operating loss can be significantly reduced.

Therefore, it is possible to reduce the amount of vaporization of the cooling medium and downsize the refrigerator, and the overall downsizing can be achieved.

Further, since a tji conduction coil for return is provided, and the trigger coil can be quickly brought to normal conductivity, the normal state can be restored quickly.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing an embodiment of a system using the current limiting device according to the present invention, Fig. 2 is a wiring diagram of the coil portion of the current limiting device, and Fig. 3 is a circuit having the configuration shown in Fig. 1. 4 is a graph showing current changes during each operation of the device according to the embodiment shown in FIGS. 1 to 3, FIG. 5 is a graph showing the relationship between switch operation and impedance change, and FIG.
The figure is a circuit diagram showing the configuration of a current limiting device using a conventionally proposed superconducting coil.

Claims (1)

[Claims] 1. In a current limiting device for suppressing overcurrent in an electric circuit, a plurality of first superconducting coils (trigger coils) having a first critical current value and non-inductively wound are connected in series. ), a non-inductively wound second superconducting coil (return coil) having the same critical current value as the first superconducting coil, and a second critical current value higher than the first superconducting coil. quench detection means for detecting quenching of the first superconducting coil; and quench detection means connected in series to the first superconducting coil and normally closed to detect quenching of the quench detection means. a first switch means that is opened by a quench detection output; and a second switch means that is connected in series to the second superconducting coil, is normally open, and is closed after a current limiting operation; A current limiting device characterized in that a series circuit of the first superconducting coil and the first switch means, and a series circuit of the second superconducting coil and the second switch means are connected in parallel with the current limiting element. Device. 2. The current limiting device according to claim 1, wherein the current limiting element constitutes a third 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, a first superconducting coil and a second superconducting coil,
3. The current limiting device according to claim 2, wherein the third superconducting coil is disposed coaxially with the third superconducting coil.