JPH02101926A - Current limiting apparatus - Google Patents

Abstract

PURPOSE:To miniaturize an apparatus by connecting a superconducting coil having a critical current value more than the current-limiting value of a circuit and a non-inductive superconducting switch having a critical current value lower than said current-limiting value and higher than a normal current in parallel with each other. CONSTITUTION:Between a power supply 1 and a load 5, a breaker 2 and a current-limiting device 3 are connected in series together with a line impedance 4. To form said current limiter 3, a reactor 3a of superconducting material having a critical current value more than a current value allowable for a line and a non-inductive switch 3b composed of superconducting material having a critical current value higher than a normal current value and lower than said allowable current are connected in parallel with each other. A normal current flows through said switch 3b, but, in case of an overload, the switch 3b opens to commutate a load current to said reactor 3a to limit said current. When the electric current further increases, however, the reactor 3a is also quenched and becomes higher in resistance to limit said current. Thus, an overload current is suppressed by a simple circuit.

Description

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

(Prior Art) As a conventional device of this type, for example, Japanese Patent Laid-Open No. 60-74
There is one disclosed in Publication No. 932.

FIG. 12 is a circuit diagram showing the configuration of this current limiting device. In the figure, a coil 34 and a coil 35 are wound around the iron core 33 so that the magnetomotive force is approximately equal, and one end of each of the coil 34 and the coil 35 is placed on the power supply side so that the direction of the magnetic flux is reversed. The coil 34 is connected to the electric circuit 31 of
The other end of the coil 35 is connected to the load-side electric path 32 via the switch 38, and the other end of the coil 35 is also connected to the load-side electric path 32. Further, a surge absorber 36 is connected in parallel to the coil 34, and a current limiting resistor 37 is connected in parallel to the switch 38.

On the other hand, a current transformer 39 is provided in the electric line 32, and is configured to trip the switch 38 when an overcurrent is detected.

Here, when a normal level current (hereinafter referred to as normal current) flows through the electric circuits 31 and 32 with the switch 38 closed, this current is divided into the coils 34 and 35, but the magnetic flux generated in these coils are canceled out, so
The current will not be affected by the inductances L t , L 2 . Therefore, electric power can be supplied to the load with high efficiency, excluding a slight loss due to leakage magnetic flux.

On the other hand, when an excessive current flows through the electrical circuits 31 and 32 due to a load short circuit or the like, the current transformer 39 detects this, opens the switch 38, and inserts the resistor 37 into the circuit of the coil 34. As a result, the current in the coil 34 decreases and at the same time the current in the coil 35 increases, and the magnetic flux of the iron core 33 becomes dominated by the coil 35. Therefore, the inductance of the coil 35 acts, that is, the reactor acts to limit the fault current.

(Problem to be Solved by the Invention) Since a current of several hundred to several thousand amperes flows through the above-mentioned current limiting device during steady state, the cross-sectional area of the coils 34 and 35 must be made large, and the current limiting device Since the number of turns must be increased in order to increase the impedance, there is a problem in that the device becomes larger and a large amount of power loss due to heat cannot be avoided.

In addition, in the above-mentioned current limiting device, a mechanical switch is often used as the switch 38, and from the time an overcurrent is detected to the time when the switch 38 is opened to perform the current limiting operation,
Another problem is that it requires 1 to 3 cycles, making it difficult to protect the line during this time.

As a countermeasure against this, a semiconductor switch such as a thyristor can be used as the switch 38, but in this case, a power loss occurs due to the voltage drop in the forward direction of the thyrisk, and the device becomes larger and more complicated. Recruitment was difficult.

This invention was made in order to solve the above problems, and aims to provide a current limiting device that can miniaturize the device, ensure line protection, and keep power loss due to heat extremely low. purpose.

[Structure of the invention]

(Means for Solving the Problem) In order to achieve this object, a first invention provides a superconducting material having an inductance that suppresses the current in an electric circuit to a limit value or less, and having a critical current value greater than or equal to the limit value. It is characterized by comprising a coil and a superconducting switch formed without induction and having a critical current value smaller than the limit value and larger than the normal current, and the superconducting coil and the superconducting switch are connected in parallel.

Further, a second invention provides a first superconducting coil having an inductance that suppresses a current in an electric circuit to a limit value or less and having a critical current value greater than or equal to the limit value, and a first superconducting coil for the first superconducting coil. a second superconducting coil that is wound around a common magnetic core and can obtain substantially the same magnetomotive force for the same terminal voltage; the first and second superconducting coils are connected in parallel so that the directions of magnetic flux are opposite to each other, and the superconducting switch is inserted in series with the second superconducting coil. This is a characteristic feature.

(Function) In the first invention, if only a normal current flows in the electric circuit, both the superconducting coil and the superconducting switch are maintained in a superconducting state, and moreover, the superconducting coil inserted in parallel to the electric circuit is relatively Although it has a large impedance, the impedance of a superconducting switch is essentially zero, and most of the current in the electrical path flows through the superconducting switch. Then, when the current in the circuit becomes excessive, the superconducting switch quenches, and the current that has been flowing until now is diverted to the superconducting coil. Therefore, the current in the electric circuit can be suppressed to a limited value by using a superconducting coil.

Further, in the second invention, if only a normal current is flowing through the electric path, both the first and second superconducting coils and the superconducting switch are maintained in a superconducting state, and the impedance of the current in the electric path is substantially zero. The current is divided into a first superconducting coil and a second superconducting coil that are wound so that Then, when an excessive current flows in the electrical circuit, the superconducting switch quenches, so the current that had been flowing in the second superconducting coil is commutated to the first superconducting coil, and the electrical current flows only in this first superconducting coil. will flow. Therefore, the inductance of the first superconducting coil acts to suppress the current in the electric path to the limit value.

(Embodiment) FIG. 1 is a circuit diagram showing the configuration of an embodiment corresponding to the first invention of this application, together with an object to which it is applied. In the figure, a circuit breaker 2, a current limiting device 3, and a line impedance 4 are shown inserted into one side of a line serving as an electric path connecting an AC power source 1 and a load 5. Here, the current limiting device 3 includes a superconducting coil 3a that is wound so as to have an inductance that suppresses the current in the line below a limiting value, and has a critical current value larger than the current limiting value.
Non-inductive (AP) so that the inductance is virtually zero
) and is connected in parallel with a superconducting switch 3b having a critical current value larger than the normal current of the electric circuit and smaller than the current limit value.

FIG. 2 is a diagram showing a specific configuration of the superconducting coil 3a and the superconducting switch 3b. The superconducting coil 3a is wound around a bobbin 3C, and the superconducting switch 3b is wound around a bobbin 3d. 3a, and the coil end is connected to terminal 3e.
, 3f are commonly connected.

The operation of this embodiment configured as described above will be explained below.

First, when both the superconducting coil 3a and the superconducting switch 3b are in a superconducting state, the superconducting coil 3a exhibits a relatively large impedance to the current flowing through the line, but the superconducting switch 3b exhibits a relatively large impedance because it is non-inductive. becomes essentially zero. FIG. 3 is a diagram for explaining this, in which a current i is applied to the superconducting coil 3a and the superconducting switch 3b in the direction of the arrow. If , a magnetic flux φ0 is generated by the superconducting coil 3a and has an impedance according to the inductance, but the magnetic fluxes φ1 and φ2 of the AP-wound superconducting switch 3b are canceled out and the impedance becomes substantially zero.

And there was no accident on the load 5 side, and the current was normal! . When , the current flowing through the superconducting coil 3a is iLl, and the current flowing through the superconducting switch 3b is 'L2, the following relationship holds true.

L −i +i ... (1) OLI
L2'Ll(iL2...(2) Therefore,
Most of the line current 10 flows through the superconducting switch 3b, and the resulting voltage drop is substantially zero.

Next, when an overcurrent flows through the line due to a short-circuit accident in the load 5, and its value exceeds the critical current value Jcl of the superconducting switch 3b, the superconducting switch 3b instantly quenches and becomes an extremely large resistor. As a result, superconducting switch 3b
Most of the current flowing in the superconducting coil 3a is diverted to the superconducting coil 3a,
The relationship between both currents is shown in the equation below.

'Ll>iL2°-(3) Therefore, the line current is limited to the limit value by the inductance of the superconducting coil 3a. In this case, the current 'L2 flowing through the superconducting switch 3b is extremely small, so power loss consumed as heat can be suppressed to an extremely small amount.

FIGS. 4(a) and 4(b) show how the current i and the impedance 2 of the current limiting device C change during normal operation and during current limiting operation. That is,
During steady operation, the impedance 2 of the current limiting device 3
is extremely small, and the line current i.

SC is maintained normally mainly by the load impedance zl. On the other hand, when a load short circuit occurs, an estimated short circuit current if tends to flow through the line. However, the moment the line current exceeds the critical current value 'cl' of the superconducting switch 3b, the impedance of the current limiting device increases to 2' as described above, and the short circuit current e is limited to below the limiting value.

In this case, the critical current value J of the superconducting coil 3a. 2 is set larger than the current limit value of the line.

Further, the current limiting device 3 is cooled by interrupting the line with the circuit breaker 2, and easily returns to a steady state.

In the above embodiment, the two superconducting coils are placed together, making it significantly more compact and making it easier to maintain the superconducting state. However, even if these superconducting coils are placed apart, the above-mentioned current limiting It can be made to perform an action.

According to this embodiment, by employing superconducting coils and arranging these superconducting coils together, it is possible to simplify the configuration and miniaturize the device, and at the same time achieve fast response and reliability. line protection is possible.

FIG. 5 is a circuit diagram showing the configuration of an embodiment corresponding to the second invention of this application, together with the object to which it is applied. In the figure, a circuit breaker 2 and a current limiting device consisting of a superconducting reactor 6 and a superconducting switch 7 are inserted into one of the lines connecting an AC power source 1 and a load 5, and a line impedance 4 is inserted. It is shown as follows. Here, the superconducting reactor 6 has an inductance that suppresses the current in the line below the limit value, and this is because the superconducting coil 6a, which has a critical current value larger than the current limit value, and the same iron core as this superconducting coil are connected to each other. A superconducting coil 6 whose magnetomotive force is the same and the magnetic flux cancels out when it is wound and inserted in parallel to a railway line.
b, and when currents iLl and iL2 flow into them, the impedance becomes substantially zero. On the other hand, the superconducting switch 7 is a non-inductively wound superconducting coil, which is connected in series to the superconducting coil 6b.

FIG. 6 is a diagram showing a specific configuration of the superconducting reactor 6, in which the superconducting coil 6a is wound around a bobbin 6C, the superconducting coil 6b is wound around a bobbin 6d, and the superconducting coil 6b is wound inside the superconducting coil 6a. The two coils are arranged one after the other, and one end of each coil is commonly connected to the terminal 6e.
The other end of the superconducting coil 6a is connected to the terminal 6f, and the superconducting coil 6
The other ends of the terminals b are respectively connected to the terminals 6g. In addition,
6h is a spacer that maintains insulation between terminals 6f and 6g of these superconducting coils.

FIG. 7 is a diagram showing the internal connections and magnetic flux of this superconducting reactor 6, and shows the superconducting coil 6a.

6b is connected in parallel to the line, the magnetic flux φ1 generated in the superconducting coil 6a and the magnetic flux φ generated in the superconducting coil 6b
The structure is such that the two cancel each other out.

FIG. 8 is a diagram showing a concrete configuration of the superconducting switch 7, which is composed of superconducting coils 7a and 7b, of which the superconducting coil 7a is mounted on the bobbin 7c and the superconducting film 7 is mounted on the bobbin 7c.
b are respectively wound around a bobbin 7d, and the superconducting coils 7b are arranged together inside the superconducting coil 7a, one end of each coil is commonly connected to the terminal 7e, and the other end is commonly connected to the terminal 7f. There is.

FIG. 9 is a diagram showing the internal wiring and magnetic flux of this superconducting switch 7. When a current is passed between the terminals 7es and 7f, this current is divided into each coil and the magnetic flux φ1 generated in the superconducting coil 7a and the superconducting coil The configuration is such that the magnetic flux φ2 generated in 7b is canceled out.

Note that the superconducting coil 6a constituting the superconducting reactor,
The critical current value of the superconducting coil 6b is made to be larger than the current limit value of the line, and the superconducting switch 7 has a value proportional to the overcurrent of the line, for example, the current of the superconducting coil 6b is set to a value proportional to the overcurrent of the line. It is designed to quench when it increases.

The operation of this embodiment configured as described above will be explained below with reference to FIG. 10.

First, the current i flowing through the line. If the superconducting reactor 6 and the superconducting switch 7 are normal, both the superconducting reactor 6 and the superconducting switch 7 are maintained in a superconducting state. Thereby, the superconducting coil 7a that constitutes the superconducting switch 7.

The resistance of 7b is zero, and moreover, it is a non-inductive element. Therefore, the current io is divided into the superconducting coils 5a and 6b forming the superconducting reactor 6, and the magnetic flux is canceled by the current lLl''L2 flowing through these coils, and although the current io has a mutual inductance -M, a self-inductance L
1 and L2 are in a state where they do not affect the current.

FIG. 10(a) is an equivalent circuit thereof, in which the superconducting switch 7 acts as an element having only a minute leakage inductance L3, and the superconducting reactor 6 also acts as an element having only a mutual inductance -M.

Next, when an accident such as a load short circuit occurs and an estimated short circuit current 1f determined by the power supply voltage E and line impedance Z1 begins to flow, the current in the superconducting switch 7 also increases in accordance with the increase in current.

Superconducting coils 6a, 6 constituting this superconducting switch 7
b is the current value in the middle of its increase, and the corresponding critical current value Jc
current 'L2 flowing through the superconducting coil 6a.
is this current value J. The current iL2 that was flowing through the superconducting coil 6b is quenched as soon as it exceeds 1, and the current iL2 that was flowing through the superconducting coil 6b is
Commutation to a. As a result, most of the current flowing through the line flows through the superconducting coil 6a. Therefore, superconducting reactor 6
has a large inductance due to the magnetic flux φ1 generated by the superconducting coil 6a. FIG. 10(b) is an equivalent circuit in this case, in which the superconducting switch 7 changes to an element having an extremely large resistance value R, and the line current i. is limited by the self-inductance L1 of the superconducting coil 6a.

According to this embodiment, the impedance becomes substantially zero for normal line currents, and instantaneously acts as a reactor to limit the line currents for overcurrents.

Figures 10(a) and 10(b) show the current i. and how the impedance Z of the current limiting device changes between normal operation and current limiting operation.

That is, during steady operation, the impedance Z of the current limiting device 3 is extremely small, and the line current C 1o is maintained normally mainly by the load impedance z1. On the other hand, when a load short circuit occurs, an estimated short circuit current l tends to flow through the line. However, when the line current increases to J, the current in the superconducting switch 7 reaches the critical current value J. 1, the impedance of the superconducting reactor 6 increases to Z' at that moment, and the short circuit current is limited to below the limit value e.

Thus, in this embodiment as well, by employing superconducting coils and arranging these superconducting coils in the same manner, it is possible to simplify the configuration and downsize the device, and at the same time achieve fast response and reliability. Line protection becomes possible.

〔Effect of the invention〕

As is clear from the above description, according to the present invention,
It is possible to downsize the device and ensure reliable line protection, and
This has the effect of significantly reducing power loss due to heat.

[BRIEF DESCRIPTION OF THE DRAWINGS] Figure 1 is a circuit diagram showing the configuration of an embodiment corresponding to the first invention of this application, together with its application target, and Figure 2 is a circuit diagram showing the specific configuration of the embodiment. , a partially cross-sectional view, FIG. 3 is a magnetic flux generation state diagram for explaining the operation of the same embodiment, and FIG.
Figures (a) and (b) show temporal changes in current and impedance to explain the operation of the embodiment, and Figure 5 shows the configuration of the embodiment corresponding to the second invention of this application. , FIG. 6 and FIG. 8 are partial cross-sectional diagrams showing the specific configuration of the main elements of the same embodiment, and FIGS. 7 and 9 are circuit diagrams shown together with the applicable target. FIG. 10(a) is a magnetic flux generation state diagram of these main elements. (b) is an equivalent circuit diagram for explaining the operation of the same embodiment,
11(a) and 11(b) are diagrams showing temporal changes in current and impedance to explain the operation of the same embodiment, and FIG. 12 is a circuit diagram showing the configuration of a conventional current limiting device. be. 3... Current limiting device, 3a, 6a, 6b... Superconducting coil, 3b, 7... Superconducting switch, 6... Superconducting reactor.

Claims (1)

[Scope of Claims] 1. A superconducting coil having an inductance that suppresses the current in the electric circuit to a limit value or less, and having a critical current value greater than or equal to the limit value, and a superconducting coil that is formed non-inductively and is smaller than the limit value; 1. A current limiting device comprising: a superconducting switch having a critical current value larger than a normal current; and the superconducting coil and the superconducting switch being connected in parallel. 2. A first superconducting coil having an inductance that suppresses the current in the electric circuit below a limit value and having a critical current value greater than the limit value, and a coil wound around a common magnetic core for the first superconducting coil. a second superconducting coil which is equipped with a second superconducting coil and can obtain substantially equal magnetomotive force for the same terminal voltage; and a superconducting switch which is formed without induction and has a critical current value proportional to the excessive current in the electric circuit. , a current limiting device characterized in that the first and second superconducting coils are connected in parallel so that the directions of magnetic fluxes are opposite to each other, and the superconducting switch is inserted in series with the second superconducting coil. .