JPH1153954A - Current limited power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability of operation without increasing the cost of an electric power system by a method, wherein a good electrical conductor whose electrical resistance increases sharply by a temperature rise is used as an inner conductor, an electrical insulation layer is provided outside the inner conductor, and furthermore an outer shielding conductor is provided outside the electrical insulation layer, and a value of a relation expressing a resistance change characteristic of the good electrical conductor is set equal to or larger than a specific value. SOLUTION: A semiconductor heat-insulating material layer 2, a highly heat-resistant semiconductor layer 3, a highly heat-resistant electrical insulation layer 4 and a highly heat- resistant semiconductor layer 5 are provided in this order outside an inner conductor 1 made up of a good electrical conductor whose electrical resistance increases sharply by a temperature rise, and further an outer shield conductor 6 made of metal is provided thereoutside. A good electrical conductor of the inner conductor 1 is adapted such that a value of an expression which expresses its resistance change characteristic is equal to or larger than 4×10<5> , [where, α: a temperature coefficient of resistance (-), ρ: resistivity (Ωcm), T: melting point ( deg.C), Q: heat capacity (cal/cm<3> deg.C)]. An allowable load current and a range of temperature rise under normal conditions can be set up arbitrarily by changing the size of the inner conductor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current-limiting power cable for suppressing a fault current in a power system, and more particularly to a current-limiting power cable having high operation reliability without increasing the cost of the power system. .

[0002]

2. Description of the Related Art A current limiter provided in an electric power system is a device having a function of suppressing a fault current in the grid, and flows a current with almost no loss in normal times, and an excessive current such as a fault current. When current flows, current is suppressed.

[0003] Conventional current limiters include a semiconductor-based type, an arc-based type, and a superconducting-type. These current limiters mainly have a function of suppressing current, and do not have a function of power transmission. These current limiters are additionally installed at important points in the power system, but the cost of the power system is increased by the amount of installation. Further, since the device is provided in addition to the power system, it is necessary to configure the device as compact as possible so as to fit in the space of the power system.

[0004]

The performance required of the current limiter is that it does not perform any special action in steady operation and rapidly suppresses the fault current when a fault occurs. By providing the current limiter, a circuit breaker having a low fault current interrupting capability can be used, and the cost of the circuit breaker can be reduced. Also,
Damage to equipment provided in the power system and reduction in power supply voltage can be suppressed. However, the conventional current limiter has a problem that the cost of the power system is relatively high. And the conventional current limiter was uneasy about the reliability of operation.

An object of the present invention is to solve the above-mentioned problems and to provide a current-limiting power cable having high operation reliability without increasing the cost of a power system.

[0006]

In order to achieve the above-mentioned object, the present invention provides an electric conductor whose electric resistance sharply increases due to a rise in temperature as an internal conductor, and an electric insulating layer provided outside the internal conductor. Further, an external shielding conductor is provided outside the electric insulating layer, and a characteristic expression showing a resistance change characteristic of the above-mentioned electrically good conductor.

[0007]

(Equation 1)

Is set to 4 × 10 ⁵ or more.

[0009] A semiconductive electrostatic shielding layer may be provided inside and outside the electric insulating layer.

[0010] The internal conductor may be constituted by combining a plurality of materials.

[0011] A cooling member for cooling the internal conductor may be provided.

[0012]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIG. 1, a current-limiting power cable 10 according to the present invention is provided with an inner conductor 1 made of an electrically good conductor whose electric resistance rapidly rises due to a rise in temperature, and in order outside the inner conductor. Providing a semiconductive heat insulating material layer 2, a high heat resistant semiconductive layer 3, a high heat resistant electrical insulating layer 4, and a high heat resistant semiconductive layer 5,
Further, an external shielding conductor 6 made of metal is provided on the outside. A good electrical conductor of the inner conductor 1 has a characteristic expression showing its resistance change characteristic.

[0014]

(Equation 1)

Is configured to be 4 × 10 ⁵ or more.

The current-limiting power cable 10 of the present invention is provided by being inserted into a power system as a cable for transmitting and distributing power.
The electrical resistance suddenly rises due to the accident current, and operates as a power cable in normal times. The current limiting power cable 10 has flexibility and can be laid in the same manner as a normal cable. The current-limiting power cable 10 is laid instead of a normal power cable at a point in a power system.

Now, it is assumed that the voltage of the power system is 22 kVrms and the load current is 30 A, and a pure iron wire is used as a good electrical conductor constituting the inner conductor 1 of the current limiting power cable. When the temperature of the inner conductor 1 of the current limiting power cable 10 becomes 600 ° C. due to an accident current such as a short circuit accident,
The resistance value of the internal conductor 1 increases seven times as compared with the resistance value at 20 ° C. In order to obtain the performance of suppressing the flowing fault current to 200 A by the internal conductor 1 having this high-temperature resistance value, the resistance value must be 22 kV / 200 A = 11Ω. From the requirement of a resistance value of 11Ω at a temperature of 600 ° C, the resistance value at 20 ° C is 1.57Ω. That is,
The current limiting power cable 10 is set so as to exhibit a resistance value of 1.57Ω in normal times.

Here, assuming that a pure iron wire having a cross-sectional area of 8 mm ² (1.2φ7 strands) is used for the inner conductor 1, the pure iron wire has a resistance value per unit length of 1 at 20 ° C.
Since the resistance is 6.3 Ω / km, the length of the inner conductor 1 is 1.57 Ω / 16.3 Ω ×
1000 = about 100 m. That is, the current-limiting power cable 1 having the above configuration that satisfies the performance in the power system.
The cable length of 0 is about 100 m. Therefore, it is only necessary to insert the current-limiting power cable 10 into the power system for a section of about 100 m. The current limiting power cable 10
Since it is not provided in addition to the electric power system unlike the current limiter, no extra space is required and the cost does not increase.

In order to cope with a short-circuit between phases of a three-phase power system, it is sufficient to insert the current-limiting power cable 10 into each phase by about 50 m.

Next, the outer layer of the current limiting power cable 10 will be described. The semiconductive heat insulating material layer 2 is made of carbon fiber, chrome fine wire (ρ = 40 μΩcm), mesh conductor,
Conductive mica is preferred. The high heat-resistant semiconductive layer 3 is preferably made of a high heat-resistant polyimide resin mixed with carbon particles to impart conductivity. As the high heat-resistant electric insulating layer 4, a polyimide film, a Teflon film, or another high heat-resistant electric insulating material is suitable. The high heat resistant semiconductive layer 5 is suitably made of a polyfluoroethylene resin or a polyimide resin mixed with carbon particles. The outer shielding conductor 6 is suitably made of copper, aluminum, or an uncast steel wire.

In the above embodiment, a pure iron wire is used for the inner conductor 1.
However, for the internal conductor 1, a material having a large value of a characteristic expression indicating a resistance change characteristic is suitable. Table 1 shows the values of the characteristic formulas for typical metals.

[0022]

[Table 1]

The characteristic equation showing the resistance change characteristic shows a measure of the rate of change of the resistance value in the process of rising to the melting point which is a measure of the allowable temperature of the conductor when a constant current flows through the conductor. The larger the value of this characteristic equation, the more the resistance value changes in a shorter time, and thus the better the current limiting conductor.

Now, among the four metals shown in Table 1,
Aluminum has the largest characteristic value and its melting point is 6
Since it is the lowest at 60 ° C., the conductor allowable temperature is low, that is, the temperature rise of the entire current-limiting power cable 10 is small. Therefore, aluminum is most suitable for the internal conductor 1.

Here, it is assumed that the temperature coefficient of resistance α, the resistivity ρ, and the heat capacity Q have no temperature dependence. When these factors have temperature dependence, it can be said that the one having the largest integral value up to the melting point is good. In addition, the conductor cannot be used up to its melting point, and its performance may be degraded at high temperatures. In such a case, it is necessary to evaluate in consideration of the deterioration.

Next, an embodiment provided with a cooling member will be described. A liquid passage is provided in the internal conductor 1, and the cooling liquid is caused to flow through this passage. By forcibly cooling the internal conductor 1, it is possible to suppress a rise in temperature in normal times.
In addition, cooling can also be performed from the outside of the current limiting power cable 10. When an accident occurs, the inner conductor 1 rises sharply,
Since there is a time delay in the cooling effect, a temperature rise equivalent to that without cooling is observed, so that the same current limiting effect can be obtained.

[0027]

The present invention exhibits the following excellent effects.

(1) The use of a current-limiting power cable greatly reduces the cost of the power system.

(2) By changing the thickness of the insulating phase and the length of the cable, the present invention can be applied to a power system of an arbitrary voltage class.

(3) By changing the size of the internal conductor, the allowable load current and the normal temperature rise range can be arbitrarily set.

[Brief description of the drawings]

FIG. 1 is a sectional view of a current limiting power cable showing one embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 inner conductor 2 semiconductive heat insulating material layer 3 high heat resistant semiconductive layer 4 high heat resistant electric insulating layer 5 high heat resistant semiconductive layer 6 outer shielding conductor

Claims (4)

[Claims] An internal conductor is a good electrical conductor whose electrical resistance rises rapidly due to a rise in temperature, an electrical insulating layer is provided outside the internal conductor, and an external shielding conductor is provided outside the electrical insulating layer. Characteristic expression showing the resistance change characteristic of a good electrical conductor A current-limiting power cable characterized in that the value of the current-limiting power is 4 × 10 ⁵ or more. 2. The current-limiting power cable according to claim 1, wherein a semiconductive electrostatic shielding layer is provided inside and outside the electric insulating layer. 3. The current-limiting power cable according to claim 1, wherein the inner conductor is formed by combining a plurality of materials. 4. The current-limiting power cable according to claim 1, further comprising a cooling member for cooling the internal conductor.