JPH0454820A - Protective unit for superconducting coil - Google Patents

Abstract

PURPOSE:To simplify the constitution and to improve the reliability by inserting a circuit breaker and a current limit fuse between the terminals of a protective resistor and thereby commutating coil current in the order of the circuit breaker the current limit fuse the protective resistor upon occurrence of quenching. CONSTITUTION:Upon occurrence of quenching, a throw-in unit 10 is thrown in to open a disconnector 7. Upon subsequent opening of a vacuum circuit breaker 8, coil current is commutated to a current limiting fuse 9 by an arc voltage. Consequently, the current limit fuse 9 is blown out and a high arc voltage is produced through the current limit effect thereof. The coil current is then commutated to a protective resistor 4 by the arc voltage of the current limit fuse 9 thus interrupting the current of the current limit fuse 9. Furthermore, coil current flowing through the protective resistor 4 damps and the energy stored in a superconducting coil l is entirely consumed through the protective resistor 4. Consequently, reliability of DC interruption can be improved through a simplified constitution resulting in reduction of size and cost.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a protection device for a superconducting coil used in a strong magnetic field generator.

<Prior art> In recent years, superconducting coils used in strong magnetic field generators such as power storage and nuclear fusion have become larger, and the coil current has also increased, reaching several to tens of kA, which is accumulated in the superconducting coil. Energy is also becoming huge, ranging from tens to hundreds of MJ.

A superconducting coil maintains its superconducting state by being cooled by liquid helium, or if a part of the coil undergoes a normal conduction transition (hereinafter referred to as quench) for some reason, that part generates heat, and the surrounding area further heats up. It is well known that there is a problem in which quenches occur one after another, eventually destroying the superconducting coil.

For this reason, superconducting wires are made by coating the thin superconducting wire with a thick layer of copper, and when a quench occurs, current is passed through the copper part to prevent the superconducting wire from breaking and to minimize heat generation. I have to.

Is it possible to prevent short-term quenching in a small area like this, or if the quenching time is long or the cooling capacity of the coil is insufficient, the current can be reduced immediately. Is it necessary to protect the superconducting coil by releasing the stored energy to the outside?

An example of such a protection device is shown in FIG. 5. To explain this, 1 is a superconducting coil as a load, 2 is a thyristor converter connected to a converter transformer 3 connected to an AC power source (not shown), and supplies DC current obtained by rectifying AC power to the superconducting coil l. It is. A protective resistor 4 is connected in parallel to the superconducting coil 1 via a diode 5, and is used to absorb energy accumulated in the superconducting coil 1 when a quench occurs in the superconducting coil 1. Reference numeral 6 denotes a DC cutoff circuit inserted on the DC output side of the thyristor converter 2. this is,
A DC breaker VCB consisting of a vacuum breaker etc. connected in series to the thyristor converter 2, and a gap switch G consisting of a capacitor C, commutation reactor L, ignitron, trigger gap etc. to this DC breaker VCB.
and a DC power source DC is connected between the terminals of the capacitor C via a resistor R.

Then, during normal operation, the thyristor converter 2
A DC breaker V of the DC breaker circuit 6 is connected to the superconducting coil L.
Direct current is supplied via CB.

In this state, if a quench occurs in the superconducting coil l, the direct current is cut off by the DC breaker VCB, and the energy stored in the superconducting coil l is rapidly consumed by the protective resistor 4 to protect the coil 1. There is.

At this time, the DC breaker circuit 6 opens the DC breaker VCB, causes the gap switch G to be discharged and conductive by the charge of the pre-charged capacitor C by the DC power supply DC, and resonates via the commutation reactor L. A large current is injected into the DC breaker VCB to forcibly create a current zero point and cut off the DC current. The coil current of the DC breaker is l → 4
The energy flows through the path 5 → 1, and the energy stored in the superconducting coil 1 is consumed by the protective resistor 4.

<Invention or problem to be solved> However, when configured as described above, it is possible to protect the superconducting coil l, but a current of several tens of kA or more must be continuously passed through the DC breaker VCB. Therefore, a fairly large DC breaker is required, and since a general-purpose DC breaker has a diameter of several kA, it cannot be realized with a single pulp, and a special configuration such as parallel use is required. I'm growing up.

Moreover, the capacitor that discharges to create a current zero point when the DC breaker is opened has a large capacity, and a charging device is also required, which complicates the configuration, making the device larger and more expensive. have.

In addition, the capacitor must be constantly charged, and if the gap switch discharges incorrectly, there is a risk of losing the breaker function, and if the timing of the opening of the DC breaker and the discharge conduction of the gap switch is misaligned, the breaker cannot be disconnected. As a result, the accuracy of timing adjustment has become higher (for example, 1 ms).
(below), the adjustment of the combination of the two becomes complicated and time-consuming, and there is a problem that reliability is reduced.

The present invention has been made in consideration of the above-mentioned points, and its purpose is to provide a device that has a simplified configuration, is small and inexpensive, and can improve reliability.

<Means for Solving the Problems> In order to achieve the above object, the present invention inserts a disconnector between a thyristor converter as a power source and a superconducting coil as a load, and connects the superconducting coil to the superconducting coil via an energizer. A protective resistor is inserted in parallel, and a breaker and a current limiting fuse are inserted in parallel between the terminals of this protective resistor, and when a quench occurs, the coil current is commutated in the order of breaker → current limiting fuse → protective resistor. It is characterized in that the superconducting coil is protected by

When a quench occurs in the superconducting coil, the thyristor converter is delayed in control delay angle from 900 to output a negative voltage, then the closing device is turned on, the coil current is transferred to the breaker, and the power supply side The current is reduced to zero, the disconnector is opened, and then the breaker is opened.The arc voltage generated by this opening causes the coil current to be diverted to the current limiting fuse, and the arc voltage generated when the current limiting fuse blows changes the coil current. is commutated to a protective resistor, the coil current is attenuated by L/R,
The accumulated energy is consumed by the protective resistor and the superconducting coil 1 is protected.

<Example> Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 4. Note that the same parts as in FIG. 5 are given the same reference numerals, and redundant explanation will be omitted. In Fig. 1, 7 is a disconnector inserted between the DC output side of the thyristor converter 2 and the superconducting coil 1, and is equipped with an electric, hydraulic, etc. driving means, and can be remotely operated by opening/closing commands. It has become. lO
Similar to the above-mentioned disconnector 7, the disconnector 7 is a closing device that can be remotely operated by an opening/closing command. Then, a protective resistor 4 is connected in parallel to the superconducting coil l via the input device IO, and a vacuum breaker 8 and a current limiting fuse 9 are inserted in parallel between the terminals of the protective resistor 4. After the input device 1O is turned on, the vacuum breaker 8 is opened, so that the coil current of the superconducting coil 1 is sequentially commutated from the current limiting fuse 9 to the protective resistor 4.

Then, the disconnector 7, the input device IO and the vacuum breaker 8
Opening/closing commands for the thyristor converter 2 and gate signals for the thyristor converter 2 are sent from a control device (not shown).

Next, its operation will be explained with reference to FIGS. 2 to 4. During normal operation, the disconnector 7 is closed, the input device 10 is open, the vacuum breaker 8 is closed, and the DC low voltage obtained by rectifying the AC power by a gate signal from a control device (not shown) is generated. A current (for example, 50 V, 32 kA) is supplied to the superconducting coil 1 as a load.

If a quench occurs in this state (at time tO in Figure 2)
A detection signal is sent by a quench detection means (not shown) to a control device (not shown), and upon receiving this, the control device sends a gate signal delayed by a control delay angle of 90° to the thyristor converter, thereby controlling the thyristor converter 2. The inverse conversion operation is performed and a negative voltage (for example, -50V) is output (FIG. 2).

Next, the input device 10 is loaded according to a command from the control device (time point 1 in FIG. 2). As a result, the superconducting coil l
The coil current flows along the path l→10→8→l, and the current from the power supply side becomes zero.

Next, the disconnector 7 is opened according to a command from the control device (time t7 in FIG. 2). At this time, since the current on the power supply side is zero, no arc is generated even if the disconnector 7 is opened, and the superconducting coil 1 and the thyristor converter 2 are disconnected. Next, the vacuum breaker 8 is opened according to a command from the control device (second
Figure t2).

At this time, an arc is generated between the poles, and the resulting arc voltage causes the coil current to be commutated to the current limiting fuse 9.

To explain this commutation using the equivalent circuit diagram in FIG. 3 and the waveform diagram in FIG. 4, the arc voltage of the vacuum breaker 8 is Vvc
The voltage drop of the ms current limiting fuse 9 is expressed as V (i.e., i, XR,
However, the inductance of the circuit wiring of the vacuum breaker 8 and the current limiting fuse 9 is L+L, the disconnection current is Ic, and V. Assuming that IIVF is constant, the commutation time T1 is roughly shown, and as understood from equation (1), the commutation time T1 increases from the vacuum breaker 8 to the current limiting fuse 9 as the arc voltage increases. The inductance L1 of the circuit wiring of
The lower the value, the more quickly the commutation will occur. Now, for example, in the above equation, = 2μH, V, c, -V, = 50V,
Assuming Ic=32 kA, the commutation time T is 1.3 ms from equation (1).

This means that in a normal configuration, commutation is completed in about 1 to 3 ms.

In general, the vacuum breaker 8 sustains an arc for 1/2 cycle (8 to 10 m5) of the commercial frequency, and is formed to withstand this, so as can be understood from the above example, the arc time is short, There is no possibility of damaging the vacuum breaker 8.

Next, due to the opening of the vacuum breaker 8, the coil current is transferred to the current limiting fuse 9, the current limiting fuse 9 is blown, and a high arc voltage is generated due to the current limiting effect (Fig. 2, t4).
time). If the melting start time and arc voltage generation time of the current-limiting fuse 9 is selected to be longer than the recovery time of the vacuum breaker 8 or the insulation that does not re-ignite (Fig. 4, Fig. 3, for example, 1 to 3 ms or more), the current-limiting fuse 9 The point at which the arc voltage occurs (Fig. 4 t)
At time point 4), the vacuum breaker 8 recovers without being re-ignited, and recovers to about several tens of kV after, for example, 3 to Bms.

However, at the time of the above commutation, 1'l! T, and fusing start time T
, (T + 172) or 3 ms or more using the above-mentioned example value, the coil current will be reliably commutated.

Then, due to the arc voltage of the current limiting fuse 9, the coil current is commutated to the protective resistor 4, and the current of the current limiting fuse 9 is cut off. The current limiting fuse 9 is a high voltage (for example, if a 6kl current limiting fuse is used, an arc voltage of about 10 kV or more will be generated, and if (rated current) x (protective resistance) is set to several kV or less, the coil current will flow to the protective resistor 4. The commutation of the arc voltage of the current limiting fuse 9 is VF, and the voltage drop of the protective resistor 4 is V.

, the inductance of the circuit wiring is L2, and ■.

If (2) is constant, the commutation time T is approximately shown, for example, L 2 = 20 u HlVr VR = 50V
, Ic=32kA, T2 is 1 from equation (2).
．． It will be 3ms.

The coil current flowing through the protective resistor 4 is attenuated by L/R,
The energy stored in the superconducting coil 1 is consumed and protected by the protective resistor 4.

The above L/R time constant is selected so that the terminal voltage of the superconducting coil does not become so large that it becomes difficult to insulate the coil. It may be selected to be about seconds.

When returning to normal operation, the vacuum breaker 8 is closed, the current limiting fuse 9 is replaced, the closing device 10 is opened,
The disconnector 7 is turned on to prepare for the next quench.

As can be understood from the above description, only the disconnector 7 continuously passes a large current, and no current is cut off, so a general-purpose disconnector can be used. Also, the injector l
O is the energization time or the discharge time constant (L/R
(time constant) (for example, several seconds), it can be applied with a short-time rated type, and it is only necessary to apply the rated current of the superconducting coil l, so it is possible to apply it with a short-time rated type. Never. Furthermore, the vacuum breaker 8 only needs to have current carrying capacity for a short period of time (for example, 1 second or less) from when the input device 10 is turned on until it opens and commutates the coil current to the current limiting fuse 9. A general-purpose type (for example, 120OA class, capable of shutting off 32kA for a short time) can be applied. Furthermore, the current limiting fuse 9 can be selected to have a rated current as small as possible on the condition that the vacuum breaker 8 is opened, insulation of the vacuum breaker 8 is ensured, and it does not melt. For example, if a current limiting fuse for high voltage (6kV) is in the 300 to 400A class, the blowout time is 5
Since the size can be selected from ms to about 10m5, a general-purpose type can be used. Moreover, since the fuse holder of this class can be easily attached and comes with an operation indicator, it can be easily replaced after operation without requiring much effort. In addition, quenching only occurs once a year, so if you prepare a few as spare parts, they can be used for several years, and general-purpose high-pressure current-limiting fuses can be used, reducing running costs. It does not increase the

In addition, as can be understood from the rated current example above, since a current of several tens of kA flows through a current limiting fuse of several hundred, the fuse current is reliably cut off. Moreover, the breaking capacity of a general-purpose current-limiting fuse is several tens of kA or more, and if the voltage after commutation to the protective resistor is set to several kV or less, there will be no restriking or failure of breaking.

In the above embodiment, 8 is described as a vacuum breaker, but is not limited to this, and is a breaker that has a speed that allows the insulation of the opened breaker to be recovered by the time when the current limiting fuse 9 starts blowing. Of course, it can be applied.

<Effects of the Invention> According to the present invention, when a quench occurs, the coil current is sequentially commutated to the protective resistor via the current-limiting fuse by simply sending a breaker command to the breaker, so timing deviation is avoided. It is possible to cut off direct current accurately without causing any damage, and protect the superconducting coil.

Moreover, pre-charging of the capacitor for DC cutoff and highly accurate timing control are no longer necessary, making it possible to further improve the reliability of DC cutoff with a simplified configuration.

Furthermore, since DC is cut off after disconnecting the power supply side, the superconducting coil can be protected without damaging the power supply side due to DC cutoff, so there is no need to make the converter as a power supply high withstand voltage. Instead, it can be formed using a thyristor or the like with low withstand voltage.

Furthermore, since the constituent members can be formed using highly versatile materials, the device can be manufactured in a small size and at low cost.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of Fig. 1, Fig. 3 is an equivalent circuit diagram explaining commutation, and Fig. 4 is a waveform of each part during commutation. FIG. 5 is a block diagram showing a conventional example. 1. Superconducting coil 2. Thyristor converter 4: Protective resistor 7 Disconnector 8, vacuum breaker 9: Current-limiting fuse lO2 input device

Claims (1)

[Claims] (1) A thyristor converter that rectifies the output of an AC power source and supplies DC low voltage and large current to a superconducting coil as a load, and a disconnector inserted between the DC output side of this converter and the superconducting coil. , a protective resistor inserted in parallel to the superconducting coil via a energizer, and a breaker and current-limiting fuse connected in parallel to this protective resistor, and when a quench occurs, the breaker, current-limiting fuse, and protection A protection device for a superconducting coil, characterized in that the coil current is commutated in the order of resistance to protect the coil.