JPH05260648A - Superconducting current limiter - Google Patents

Abstract

PURPOSE:To make it possible to return a superconducting current limiter to the low impedance state immediately after releasing the ground fault point by connecting a switch in series to a non-inductively wound superconducting coil, detecting a current flowing through a current-limiting main coil and providing a detect/control portion for switching and controlling the switch based on the current value detected. CONSTITUTION:If a detection control portion 5 detects a current Ib which commutated to the side of a main coil 3 for current limiting due to a ground fault overcurrent, the detection control portion 5 controls a switch 4 to open state, releases the overcurrent state at a non-inductively wound superconducting coil 2, and resets the superconducting coil 2 from normal conducting state to superconducting state. If the electrical system resets to normal state by the separation of the ground fault point and the current Ib flowing through a current-limiting main coil 3 decreases, then the detection control portion 5 detects it, controls the switch 4 to closed state, and returns the superconducting current limiter 1 to low impedance state. By doing this, a sound system can be immediately operated continuously after the release of the ground fault point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting fault current limiter used for suppressing accidental overcurrent of electric equipment.

[0002]

2. Description of the Related Art Conventionally, a circuit breaker having a breaking capacity equal to or larger than the maximum fault current has been used for breaking an accident current in an electric system. However, the capacity of the electric system is increased in response to an increase in power demand. If this happens, the short-circuit fault current will also increase and exceed the rated breaking capacity of the existing circuit breaker. In this case, it is necessary to replace the circuit breakers that have already been installed in large quantities, and there is a limit to increasing the capacity of the electric system from the economical point of view. Therefore, as a countermeasure for this, a superconducting fault current limiter is connected to suppress the fault current by changing to a high impedance state at the time of an accident without affecting the electric system in a low impedance state when the electric system is normal. The method of doing is proposed.

FIG. 3 shows the structure of a conventionally proposed superconducting fault current limiter. In FIG. 3, 2 is a non-induction wound superconducting coil.
Reference numeral 3 is a main coil for current limiting. The non-induction winding superconducting coil 2 and the current limiting main coil 3 are connected in parallel, and when the electric system is normal, the non-induction winding superconducting coil 2 is in the superconducting state and the current limiting main coil 3 is short-circuited. The vessel is in a low impedance state. At the time of an electric system accident, an excessive current flows in the non-induction winding superconducting coil 2, which changes the non-induction winding superconducting coil 2 from the superconducting state to the high resistance state of the normal conducting state, so that the current is commutated to the current limiting main coil 3 side. The superconducting fault current limiter 1 is brought into a high impedance state.

[0004]

In the conventional superconducting fault current limiter, it is difficult to spontaneously return to the low impedance state once it is in the high impedance state, and the high impedance state continues even after the accident point is separated. This will impede continuous operation to the healthy system after release. Therefore, the present invention enables the superconducting fault current limiter to return to the low impedance state immediately after the accident point is released.

[0005]

According to the present invention, a non-inductively wound superconducting coil and a switch connected in series with each other, a current limiting main coil connected in parallel thereto, and a current flowing through the current limiting main coil. And a detection control unit for controlling the opening of the switch when the current exceeds a predetermined value, and then closing the switch when the current falls below a predetermined value different from the predetermined value. Equipped with.

[0006]

In the superconducting fault current limiter of the present invention, the detection controller detects the current commutated to the main coil for current limiting due to an accidental overcurrent, and immediately opens the switch connected to the non-induction winding superconducting coil side. Control is performed to release the non-induction winding superconducting coil from the charged state, and the non-induction winding superconducting coil is returned from the normal conducting state to the superconducting state. Next, when the electric system returns to normal due to disconnection of the accident point and the current flowing through the main coil for current limiting decreases, this is detected by the detection control unit and the switch connected to the non-induction winding superconducting coil side is detected. Control to closed state. This returns the superconducting fault current limiter to the low impedance state.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a superconducting fault current limiter of the present invention. FIG. 2 shows current waveforms for explaining the operation.

In FIG. 1, 1 is a superconducting fault current limiter, 2 is a non-induction winding superconducting coil, 3 is a main coil for current limiting, 4 is a switch, and 5 is a detection control section. Ia is the total current flowing in the superconducting fault current limiter 1, Ib is the current flowing in the current limiting main coil 3 side, and Ic is the current flowing in the non-induction winding superconducting coil 2 side.

In FIG. 2, the waveform portions a and e are the rated current flowing through the superconducting fault current limiter 1 when the electric system is normal, and the point P.
Is the short-circuit accident occurrence point, the waveform part b is the estimated short-circuit current when the superconducting fault current limiter 1 is not connected, the point Pa is the normal conduction transition point of the non-induction winding superconducting coil 2, and the point Pb is the opening of the switch 4. The control point, the waveform part c is the short-circuit current suppressed by the main coil 3 for current limiting, the point Pc is the point where the accident location is cut off,
The waveform portion d is the current when the electric system is normal when the switch 4 is still in the open state and is suppressed by the current limiting main coil 3 after the accident point is separated, and the point Pd is the closing control point of the switch 4.

When the electric system is normal, the non-induction winding superconducting coil 2 is in a superconducting state and the switch 4 is closed, so that the current limiting main coil 3 is short-circuited by the non-induction winding superconducting coil 2. The superconducting fault current limiter 1 is in a low impedance state. At this time, the superconducting fault current limiter 1 is energized up to the rated current of the waveform portion a.

When a short-circuit accident occurs at the point P, the excessive current shown in the waveform portion b tends to flow in the superconducting fault current limiter 1. However, at point Pa, the critical current value of the non-induction winding superconducting coil 2 is exceeded, and the non-induction winding superconducting coil 2 changes to normal conduction and suddenly changes to a high resistance coil. From the time when the electric system is normal to this point Pa, the superconducting fault current limiter 1 is in a low impedance state and Ia = Ic. After the point Pa, the current is commutated to the current limiting main coil 3 side, and the superconducting fault current limiter 1 is in a high impedance state, and the current is rapidly attenuated.

The detection control unit 4 detects that the current commutated to the side of the current-limiting main coil 3 exceeds a predetermined value, and controls the opening of the switch 4 at the point Pb. After the point Pb, the fault current is limited by the current limiting main coil 3 to the value shown in the waveform portion c.

A point Pc indicates a point where the short-circuited portion is cut off, and the current is a waveform portion c at the time of short-circuiting as shown by a waveform portion d.
It gets smaller. The detection control unit 4 detects that the value has become equal to or less than a predetermined value different from the above value, and the switch 4 is controlled to be closed at the point Pd. I is between the point Pb and the point Pd.
a = Ib and Ic = 0. Non-induction winding superconducting coil 2
Is restored to the superconducting state during the non-energized state from the point Pb to the point Pd, and at the same time as the switch 5 is closed, the current limiting main coil 3 is short-circuited and the superconducting fault current limiter 1 is returned to the low impedance state. Therefore, the electric system returns to normal and can be energized up to the rated current shown in the waveform portion e.

[0014]

As described above, according to the structure of the present invention, the superconducting fault current limiter is returned to the low impedance state immediately after the accident point is released, so that the healthy system can be continuously operated.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a superconducting fault current limiter of the present invention.

FIG. 2 is a diagram showing a current waveform during operation of the superconducting fault current limiter of the present invention.

FIG. 3 is a diagram showing a configuration of a conventionally proposed superconducting fault current limiter.

[Explanation of symbols]

 1 superconducting fault current limiter 2 non-induction winding superconducting coil 3 main coil for limiting current 4 switch 5 detection control unit

Claims (1)

[Claims] 1. A non-inductively wound superconducting coil and a switch connected in series with each other, a current limiting main coil connected in parallel to the coil and a current limiting main coil, and a current flowing through the current limiting main coil is detected. A superconducting fault current limiter, comprising: a detection control unit for controlling the opening of the switch when the current exceeds a value and thereafter controlling the switch to close when the current thereof falls below a predetermined value different from the predetermined value.