JPH06290940A - Protective system for superconducting coil - Google Patents

Abstract

PURPOSE:To increase the flash-over voltage between contacts by a method wherein an air blasting means which blows air of high pressure between the contact electrodes of the disconnecting switch when the disconnecting switch is opened, wherein the disconnecting switch possessing no direct current breaking capacity but possessing of a large current continuously carrying capacity is connected in parallel with a direct current breaker. CONSTITUTION:A superconducting coil 5 is normally excited by an ac-dc converter through the intermediary of a disconnecting switch 4 connected in parallel with a direct current breaker 11, and the disconnecting switch 4 is opened at quenching to divert a current to the direct current breaker 11. Thereafter, a current is cut off by the direct current breaker 1 and diverted to a quenching protective resistor 2, whereby an energy stored in the superconducting coil 5 is absorbed to protect the superconducting coil 5. An air blowing means composed of an air nozzle 6 which blows air of high pressure between the contact electrodes of the disconnecting switch 4 when the disconnecting switch 4 is opened, a solenoid valve 7, and an air tank 8 is provided. By this setup, a current can be quickly diverted to a direct current breaker to enable quenching protection to be effectively carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting coil protection system, and more particularly to a superconducting coil protection system suitable for a system provided with a quench protection device for dumping energy stored in the superconducting coil at a high speed during quenching. .

[0002]

2. Description of the Related Art Generally, a disconnecting switch does not have a current interrupting ability, and the arc voltage becomes low at a large current of several kA or more.
Only about 0 to 20V is generated.

On the other hand, in a capacitor commutation type DC circuit breaker, a saturable reactor is usually inserted in series with a DC circuit breaker (for example, a vacuum circuit breaker). This saturable reactor does not have an inductance of zero even when saturated, and has some residual inductance.
It is difficult to make it below μH. In addition, there is circuit inductance, and as the device becomes larger as the circuit becomes larger, the circuit inductance also increases. Due to the presence of this inductance, the commutation of the current from the disconnector to the DC circuit breaker does not occur instantaneously, and the time shown in the following equation is required.

[0004]

[Equation 1]

Here, Va is the arc voltage generated by the disconnector, and L is the commutation inductance from the disconnector to the DC circuit breaker (circuit inductance + residual inductance of saturable reactor).

The protection of the superconducting coil is disclosed in Japanese Patent Laid-Open No. 3-40409.

[0007]

As is well known, the arc voltage does not become so high in a large current region because it exhibits a negative characteristic with respect to the current, and most of the arc voltage exceeds a few kA. It is occupied by the cathode drop voltage required to emit electrons from. Therefore, the arc voltage hardly increases even if the distance between the contact electrodes is increased.

[0008] Normally used contact materials (Cu, Ag-based alloys) show similar values for the cathode drop voltage.
It is about V. Further, the arc resistance is a plasma resistance in the air, but as the current becomes larger, the plasma density increases and the resistance becomes lower and becomes almost zero. Due to the above reasons, it is very difficult to increase the arc voltage with a normal disconnector.

On the other hand, an air circuit breaker (AC
It is possible to apply a circuit breaker with a high arc voltage such as B) or a gas circuit breaker (GCB). But in reality,
A circuit breaker capable of continuously passing a superconducting coil current of several tens of kA does not exist on the market, and even if manufactured, it will be very large and expensive.

Now, Va = 20 V, L = 50 μH, I =
Considering the case of 50 kA, T = 125 msec,
During this time, the contact electrodes of the disconnector will continue to generate arcs and the contacts will be severely damaged.

For this reason, the contacts of the disconnector can withstand only a few uses, and it is very difficult to use them repeatedly. Further, the protection time of the superconducting coil is delayed by that time, which is a serious problem from the viewpoint of quench protection.

The present invention has been made in view of the above points,
The purpose is to increase the arc voltage rapidly,
Another object of the present invention is to provide a superconducting coil protection system capable of suppressing damage to a contact electrode of a disconnecting switch, accelerating current commutation to a DC circuit breaker, and effectively performing quench protection.

[0013]

DISCLOSURE OF THE INVENTION The present invention relates to a high voltage between contact electrodes of a disconnecting switch which is connected in parallel with a direct current circuit breaker and has no direct current blocking capability but has a large current continuous energizing capability. It is characterized in that it is provided with air blowing means for blowing air.

[0014]

The air blowing means comprising the air tank, the solenoid valve and the air nozzle according to the present invention opens the solenoid valve in conjunction with the opening of the contact electrode of the disconnecting switch, and the arc plasma generated between the contacts is discharged from the air nozzle. The high-pressure air is blown to cool the plasma and the high-pressure air is diffused to reduce the plasma density and increase the arc voltage between the contacts.
As a result, the arc voltage can be increased 10 times or more, and the commutation time can be shortened 10 times or more, as can be seen from the equation (1).

For this reason, the disconnecting switch, which has conventionally reached the life of several times, can be used several tens of times or more. In addition, the holding time (commutation time) until the DC cutoff is shortened to 1/10 or less, and effective quench protection becomes possible.

[0016]

The present invention will be described in detail below with reference to the illustrated embodiments.

FIG. 1 shows an embodiment of the superconducting coil protection system of the present invention.

As shown in the figure, an AC / DC converter 1 and a superconducting coil 5 to be protected are connected in parallel, and a disconnecting switch 4 having no direct current interruption ability but having a large current continuous conduction ability is connected in series in the middle thereof. It is connected. The disconnector 4 is connected in parallel with a direct current circuit breaker 11 composed of a vacuum circuit breaker 3 and a saturable reactor, which does not have a large-current continuous current-carrying capability but has a circuit breaking capability. Further, a quench circuit is connected in parallel with the direct current circuit breaker 11. A quench protection resistor 2 which absorbs energy stored in the superconducting coil 5 is sometimes connected to form a basic circuit.

During normal operation, the superconducting coil 5 is excited from the AC / DC converter 1 through the disconnecting switch 4 connected in parallel with the DC circuit breaker 11, while at the time of quenching, the disconnecting switch 4 is opened to direct the current. The superconducting coil 5 is protected by commutating it to the circuit breaker 11, then interrupting the current by the DC circuit breaker 11 and transferring the current to the quench protection resistor 11 so as to absorb the stored energy of the superconducting coil 5. ing.

In the circuit configuration as described above, in the present embodiment, when the disconnector 4 is opened, the air nozzle 6 for blowing high pressure air between the contact electrodes of the disconnector 4, the solenoid valve 7 and the air tank 8 are used. A structured air blowing means is provided.

FIG. 2 shows a specific structure of the disconnecting switch 4 provided with this air blowing means.

As shown in the figure, the disconnector 4 comprises a large number of current-carrying contacts 9 through which a normal current flows, and a small number of arc contacts 10 for interrupting the current and having an air nozzle 6. Each contact is interlocked and driven by the air cylinder 13. The energizing contacts 9 are opened all at once and a little later than that (several ms
ec) Since the arc contact 10 is configured to open, when the disconnecting switch 4 is opened during energization of current, the current flowing through the constantly energizing contact 9 is transferred to the arc contact 10 which has not been opened yet. Shed. Since the energizing contact 9 and the arc contact 10 are arranged very close to each other, the commutation time is 1 msec.
Below, and since the energizing contact 9 is divided by a large number of energizing contacts 9, it is about a fraction of the main current, so there is almost no damage to the contact.

After the commutation, all the current flows through the arc contact 10, and then the arc contact 10 is opened to generate an arc. On the other hand, just before the arc contact 10 opens (several msec)
First, the solenoid valve 7 is opened, and high pressure (several kgf / cm ² ) is sprayed from the air nozzle 6 in advance. The arc between contacts will be generated in a high-speed air flow, and the arc voltage will rise significantly, reaching from 100V to several 100V.

Using this arc voltage as commutation electromotive force, the contact current quickly commutates to the DC circuit breaker 11. The commutation time can be calculated by the equation (1), and is 8.3 msec when the arc voltage Va is 300 V using the constant of the above example. In this way, the commutation time can be significantly reduced.

According to the structure of this embodiment, the quench protection time can be greatly shortened, and the repeated life of the disconnector can be greatly increased. In addition, the disconnector is composed of a large number of energizing contacts and a few arc contacts, and by providing an air blowing mechanism only on the arc contacts, it can be manufactured at low cost, and expensive contact materials (arc resistant metal) can be used only on the arc contacts. Since it can be used, the disconnector itself can be manufactured inexpensively,
Since maintenance (contact replacement) only requires arc contacts,
Maintenance costs are also low. In addition, expensive and large ACB, GCB
There is an effect that the superconducting coil protection system can be configured with an inexpensive and small disconnector without using the.

[0026]

According to the above-described superconducting coil protection system of the present invention, when a disconnecting switch which is connected in parallel with a DC circuit breaker and has a DC current blocking capability but a large current continuous current-carrying capability is opened, the disconnection is performed. Since it is equipped with air blowing means for blowing high-pressure air between the contact electrodes of the vessel, the high-pressure air can be blown to the arc plasma generated between the contacts by the air blowing means, so the arc voltage rises sharply. Therefore, it is possible to suppress damage to the contact electrodes of the disconnecting switch, accelerate the current commutation to the DC circuit breaker, and effectively perform quench protection.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a superconducting coil protection system of the present invention.

FIG. 2 is a specific configuration diagram of a disconnector constituting the superconducting coil protection system of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC / DC converter, 2 ... Quench protection resistor, 3 ... Vacuum circuit breaker, 4 ... Disconnector, 5 ... Superconducting coil, 6 ... Air nozzle, 7 ... Solenoid valve, 8 ... Air tank, 9 ... Energizing contact, 10
... arc contact, 11 ... DC circuit breaker, 13 ... air cylinder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoji Tanaka 3-1-1, Saiwaicho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi factory (72) Inventor Morihiro Kubo 3-2, Saiwaicho, Hitachi-shi, Ibaraki No. 2 In Hitachi Engineering Service Co., Ltd. (72) Inventor Toru Sato 1 Aichi-cho, Kasugai-shi, Aichi Aichi Electric Co., Ltd.

Claims (3)

[Claims] 1. An AC / DC converter, a quench protection resistor, and a DC circuit breaker that does not have a large-current continuous energizing ability but has a breaking ability, and is connected in parallel with the DC circuit breaker and does not have a DC breaking ability, but has a large-current continuous state. With a disconnecting switch having an energizing capacity, normally, the superconducting coil is excited from the AC / DC converter via a quench protection resistor and a disconnecting switch connected in parallel with a DC circuit breaker, while at the time of quenching the disconnecting switch. After opening the current to divert the current to the DC circuit breaker, the current is cut off by the DC circuit breaker to transfer the current to the quench protection resistor so that the energy stored in the superconducting coil is absorbed. In the superconducting coil protection system described above, the superconducting coil is provided with air blowing means for blowing high-pressure air between contact electrodes of the disconnector when the disconnector is opened. Protection system. 2. The superconducting coil protection system according to claim 1, wherein the air blowing means comprises an air nozzle, a solenoid valve and an air tank. 3. A saturable reactor is connected in series to a parallel circuit of the quench protection resistor and the DC breaker, and the series-parallel circuit is connected in parallel to the disconnector. Superconducting coil protection system.