JPH01286737A - Current limiting device - Google Patents

Abstract

PURPOSE:To reduce in size and cost a current limiting device by employing, in addition to a superconducting wire made of a ceramic superconducting material, a resistor and a disconnecting mechanism. CONSTITUTION:A current limiting device has a current limiting wire G made of a ceramic superconducting material, a variable resistor R connected to the upstream side of the wire, and a disconnecting mechanism provided at the downstream side of the wire for disconnecting a line when the wire G performs a current limiting operation. The mechanism is composed of a branch variable resistor (r), a coil 1, an iron rod 2, a coil spring 3 and a switch 4. Further, the resistor R is connected to the resistor (r) of the mechanism by a cooperating machine 6. In order to maintain its superconducting state, the wire G is contained in a cooling tank 8. Thus, when a large current flows to the wire G through a master line 10 due to a short-circuit or the like, it is shifted to a nonsuperconductor to reduce the large current. As a result, the energizing force of the coil 1 is weakened, the switch 4 is opened to disconnect the line 10.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a current limiting device installed on the main line of a power system line, and in particular, a current limiting device that is directly connected to a consumer in the power system to supply power. Connect to the main line of the distribution system that is part of the
This relates to a current limiting device that cuts off the flow of excessive current when it flows through the main line in excess of its rating.

[Conventional technology]

In a nutshell, an electric power system is a system that integrates everything from electricity generation to consumption, that is, it generates electricity at power plants, transmits it through transmission lines, and then distributes it to factories and homes using distribution lines. This is a system that includes everything up to the load equipment. Electric power transported by transmission lines cannot be suddenly supplied to consumers at the same transmission voltage, so it is necessary to change the voltage to a voltage that is convenient for the demand load. must descend to.

In a power system connected in the form of a cable, if an accident occurs somewhere along the line, the effects will immediately spread to the entire region. Therefore, even if an accident occurs, it is extremely important to suppress its effects locally and prevent it from spreading to other areas, from the standpoint of maintenance and safety, as well as from the standpoint of ensuring a constant supply of power.

There are many types of accidents that occur on power transmission lines, but they include abnormal voltage generation due to lightning strikes, and excessive current flowing due to line short circuits and ground faults. For this reason, to protect against abnormal voltages, overhead ground wires or buried ground wires are installed on power transmission lines to protect the lines, and various types of lightning arresters are installed near the entrances or exits of the lines at power plants and substations. , when abnormal voltage waves attack, they are temporarily grounded and guided to the earth in an effort to prevent insulation breakdown in electrical facilities. In addition, if a power line is short-circuited or grounded due to disconnection or contact, a strong current will flow to the fault location and burn out the electrical equipment in the circuit, so as a measure to prepare for such an unexpected situation, certain sections of the line A current limiting line may be provided for each area. This is to prevent the effects of an accident from spreading by cutting off the faulty section and cutting off the current by the current-limiting action of the current-limiting wire at the same time that a large current flows through the line.

As such current limiting wires, those constructed as an IT wire by covering a conductor having a current limiting function with an insulating coating, or those made of a metallic superconductor are mainly used.

The former type of current limiting wire is made of a material that is a good conductor and has a large resistance temperature and whose resistance increases as the temperature rises, such as metals such as iron, iron-cobalt alloy, tungsten, iron-nickel alloy, copper-coated steel wire, etc. . However, temperature rise is a requirement for current-limiting action, and even though the temperature rises rapidly, the process is a gradual increase, so it takes a certain amount of time to reach a resistance that provides sufficient current-limiting action. . Because of the slowness of this current limiting effect, if a large current flows during a fault such as a short circuit, a considerable amount of current will flow through the line before the current limiting effect fully appears, completely preventing the flow of large current. It is impossible to do so. This is extremely undesirable from the standpoint of preventing the spread of accidents.

In a current-limiting wire made of a metallic superconductor, current flows without loss due to its superconducting state during normal times, but due to the large current during a fault, the current-limiting wire shifts from a superconductor to a non-superconductor in a short period of time and performs a current-limiting action. However, niobium, titanium, zirconium, vanadium, and
Metals such as tantalum exhibit a certain degree of conductivity, so even if they become non-superconducting, they cannot completely stop the flow of large currents; on the contrary, the temperature of the conductor may rise excessively due to fault current. Eventually, it may melt. Naturally, the current limiting wire cannot be reused after it is fused, and there is even a risk of fire due to the heat generated when it is fused.

[What the invention tries to solve! Title]

In order to overcome the above-mentioned drawbacks of the current-limiting wire, the present inventor provided a current-limiting wire made of ceramic-based electromotive conductive material (Japanese patent application No. 6
2-248935), this current limiting line utilizes both the superconducting and non-superconducting properties of a superconducting wire made of ceramic-based superconducting materials. Since it is a superconductor, it can effectively block overcurrent.

By the way, the current limiting line disclosed in the specification of Japanese Patent Application No. 62-248935 is based on the premise that when the superconducting phase is destroyed and the superconductor transitions from a superconductor to a non-superconductor, it becomes a complete non-superconductor. . In other words, the gist is an ideal current-limiting line where the resistance becomes infinite when it transitions to a non-superconductor.

However, at present, current limiting wires do not have infinite resistance when they become a non-superconductor, and do not completely block excessive current due to their low resistance. will flow to the load side.

From this point of view, in a current limiting device using a current limiting wire made of a ceramic superconducting material, it is preferable to take measures so that the load side is not affected by the current when cutting off an excessive current.

Furthermore, as the demand load increases with the development of industry, the power system will gradually expand in scale and become more complex due to the development of power sources and the reinforcement of facilities. Electricity companies provide an abundance of high-quality electricity,
In order to be able to supply electricity at low levels, this entire power system must always be operated rationally and economically, and it is essential to minimize the total cost of electricity supplied to the loads.

Therefore, in view of the above points, it is an object of the present invention to provide a current limiting device that suppresses the current flowing to the load side due to its low resistance when a current limiting wire made of a ceramic superconducting material exhibits a current limiting effect. It is about providing.

Another object of the present invention is to miniaturize a current limiting device using current limiting wires made of ceramic superconducting material and to make it inexpensive.

[Means to solve the problem]

The purpose is to provide a current limiting line made of ceramic superconducting material, connect a resistor on the upstream side of the current limiting line, and disconnect the line when the current limiting line exerts a current limiting action on the downstream side of the current limiting line. This is achieved by a current limiting device characterized by being provided with a disconnection mechanism.

Since the current limiting device of the present invention is equipped with a resistor and a disconnection mechanism for the low resistance characteristics of the current limiting wire made of ceramic superconducting material, there is no transmission loss in the superconducting state of the current limiting wire during normal times. When a large current flows due to an accident, the current-limiting wire becomes unable to maintain its superconducting state due to the excessive current, so it changes from a superconductor to a non-superconductor in a short time, and due to the combined resistance of the current-limiting wire and the resistor, To suppress excessive current to a level that does not cause negative effects such as burning out load equipment.

There are no particular restrictions on the ceramic superconducting material used in the present invention. For example, oxide ceramic materials containing rare earth elements include barium, yttrium, copper,
Ceramics containing oxygen, barium, lanthanum, lanthanum, copper, and oxygen, and oxide ceramic materials that do not contain rare earth elements include bismuth, strontium,
An example is ceramics whose composition is calcium, copper, and oxygen.

The current limiting wire can be manufactured using conventional methods using the ceramic superconducting materials mentioned above, but when the superconducting phase of the current limiting wire is destroyed and the current limiting wire transitions from a superconductor to a non-superconductor, It is necessary to set the critical current appropriately. For example, in the main line of the power distribution system, which is the part of the power system that is directly connected to supply electricity to consumers, the rated current of the main line is 600 A and the breaking current is 20,000 A. In other words, for the main line, a current limiting line is used that has a cross-sectional area such that a critical current occurs at 20,000 A, and a current limiting effect occurs by transitioning from a superconductor to a non-superconductor.

Also, although the current limiting wire varies depending on the superconducting material, if it is cooled with a refrigerant (such as liquid nitrogen) to maintain the superconducting state, the current limiting wire is immersed in the refrigerant, so it is protected from water. Although there is no particular need to provide a waterproof layer on the current limiting line, it is preferable to provide a waterproof layer when used in a normal temperature environment without cooling with a refrigerant.

〔Example〕

EMBODIMENT OF THE INVENTION Hereinafter, the current limiting device of this invention is demonstrated based on an Example.

The current limiting device shown in FIG. 1 includes a current limiting line G made of ceramic superconducting material, a variable resistor R is connected to the upstream side of the current limiting line G, and a current limiting line G is connected to the downstream side of the current limiting line G. A disconnection mechanism is provided that disconnects the line when G exerts a current limiting effect.

As is clear from the figure, the disconnection mechanism is a shunt variable resistor r
, a coil 1 connected in series to a shunt variable resistor r, and an iron rod 2 inserted into the coil 1 and displaced as the coil is energized and demagnetized.
, a coil spring 3 attached to the end of the iron rod 2, and a switch 4 that opens and closes the line according to the displacement of the iron rod 2. Further, the variable resistor R and the shunt variable resistor r of the disconnection mechanism are connected by an interlocking mechanism 6. In order to maintain its superconducting state, the current limiting line G is housed in a cooling tank 8 containing a refrigerant and is constantly cooled.

Such a current limiting device is installed, for example, in the zero line 10 of the power distribution system. Here, in the current limiting device, in normal times, the current limiting line G is a superconductor, and the electrical resistance is O, so there is no generation of Joule heat, and therefore there is no transmission loss. When the current shunted from the zero wire 10 flows through the coil l, the coil l is excited, and the iron bar 2 overcomes the biasing force of the coil spring 3 and is displaced in the direction of the arrow, and the switch 4 is in a closed state. .

If an abnormality such as a short circuit or ground fault occurs in the line for some reason and a large current flows through the wooden wire 10 to the current-limiting line G, the current-limiting line G changes from the superconductor to the original characteristics of the ceramic material in a short time. transitions to a high electrical resistance material, that is, a non-superconductor.

Therefore, if the large current is narrowed down by the combined resistance of the high electrical resistance element and the variable resistor R due to the transition of the current limiting line G from a superconductor to a non-superconductor due to an excessive current, the shunt variable resistor r
The shunt current also becomes smaller, the excitation force of the coil 1 becomes weaker, the iron rod 2 is displaced in the direction of arrow A by the restoring force of the coil spring 3, and the switch 4 opens to disconnect the zero wire 10.

In order to resume power supply from the main line 1O after the accident has been restored, the switch 4 is closed and power supply is started.

Here, the specific resistance value of the variable resistor R depends on the resistance value of the current-limiting line G at the time of quenching and the allowable current of the zero wire 10, and the shunt current flowing through the shunt resistor changes accordingly, so the shunt current is variable. It is also necessary to change the resistor r in conjunction with the variable resistor R, but for example, if the allowable current of the main line of the power distribution system is 20,000 A, a maximum resistance of about 0.04 Ω is sufficient. The resistance value of the shunt variable resistor r of the disconnection mechanism is also linked to the above value.

Furthermore, it is preferable that the above-mentioned current limiting device is provided with an additional mechanism that can easily visually confirm that the zero wire 10 is in a disconnected state.This protects people who operate electrical facilities such as restoration work from the risk of electric shock. It is a treatment.

Furthermore, the disconnection mechanism of the current limiting device is not limited to that shown in the embodiments, and may be a completely different mechanism.

〔Effect of the invention〕

Since the current limiting device of the present invention is configured as described above, it produces the effects described below.

In addition to the current-limiting wire made of ceramic-based superconducting material, it is equipped with a resistor and a disconnection mechanism, so when the current-limiting wire transitions from a superconductor to a non-superconductor in a short period of time due to an abnormal overcurrent, the resistor Overcurrent can be effectively narrowed down by the combined resistance with the current limiter, which is not only an effective treatment for ceramic current limiting wires that develop low resistance, but also makes the current limiting device smaller and cheaper. be able to.

Therefore, the current limiting device of the present invention makes it possible to operate the power system rationally and economically.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the current limiting device of the present invention. G: Current-limiting line R: Variable resistor r: Shunt variable resistor 1: Coil 2: Iron bar 3: Coil spring 4: Switch 6: Interlocking mechanism 8: Cooling tank Figure 1

Claims (1)

[Claims] Equipped with a current-limiting wire made of ceramic superconducting material, a resistor is connected to the upstream side of the current-limiting wire, and a disconnection mechanism is installed downstream of the current-limiting wire to disconnect the line when the current-limiting wire exerts a current-limiting action. A current limiting device characterized by: