JPH01146222A - Fuse - Google Patents

Abstract

PURPOSE:To protect a circuit such as a winding of a motor, as well as to let flow securely a current necessary for a motor circuit and an incandescent lamp circuit to which a large current flows instantly when the circuit is turned on, by applying a magnetic field to a straight line part of a coil wound to surround the straight line part of a lead wire to try to convert the critical current value. CONSTITUTION:Inside an insulating tube 2, is filled an arc extinguish sand 4 to function to cut off the current flow between electrodes 3 and 3' perfectly by absorbing the molten substance when a lead wire 5 made of a superconductive material is molten. When a current flows through the lead wire 5 of a fuse 1, a magnetic field is generated around the coil 5b of the lead wire 5. The influence of the magnetic field is received by a straight line part 5a surrounded by the coil 5b of the lead wire 5, and the critical current density is reduced. When the density of the current flow through the lead wire 5 is reduced and reaches the critical current density, the lead wire 5 is converted from a superconductive condition to a normal conductive condition, an electric resistance is generated in the lead wire 5, and the current is reduced. When the current is reduced and the density of the current flow through the lead wire 5 comes to be less than the critical current density, the lead wife 5 is converted from the normal conductive condition to the superconductive condition, and the electric resistance of the lead wire 5 is turned to zero.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a fuse, which is particularly useful for protecting wiring in motor circuits, incandescent lamp circuits, etc., through which a large current flows instantly when the circuit is turned on. Regarding the fuse used.

(Prior Art) A fuse conventionally used to protect a motor circuit will be explained with reference to FIG.

A curve 21 shows changes in the starting current flowing through the motor over time (hereinafter referred to as motor starting current characteristics).

As described above, when starting the motor, a starting current approximately 10 times as large as the rated load current flows for a short period of about several hundred milliseconds. A curve 22 shows a change over time in the maximum current value that can be passed through the motor windings (hereinafter referred to as motor winding allowable current time characteristics).

In this case, the curve representing the change over time in the maximum value of current that can be reliably passed through the fuse without blowing out (hereinafter referred to as allowable current-time characteristics of the fuse) always exceeds the curve 21 representing the motor starting current characteristics. In this case, the change over time in the limit current value at which the fuse blows (hereinafter referred to as the limit current-time characteristic of the fuse) becomes like a curve 24, which exceeds the curve 22 representing the permissible current-time characteristic of the motor windings. This allows currents to flow in excess of what the motor windings will allow, and the motor windings are not protected by such fuses. Conversely, if the curve 23 representing the fuse's limit current-time characteristics is always lower than the curve 22 representing the motor's winding allowable current-time characteristics, the fuse's allowable current-time characteristics will be curve 2.
6, which is below the curve 21 representing the motor starting current characteristic. Therefore, when an attempt is made to start the motor, the fuse blows even if the starting current is normal, and the motor starting current cannot be passed without any problem.

Therefore, in order for the fuse to be able to protect the motor windings and at the same time allow the motor starting current to pass without any trouble, the curve representing the limit current-time characteristics of the fuse must always be the same as the curve representing the allowable current-time characteristics of the motor windings. 22, and the curve representing the permissible current-time characteristic of the fuse must at any moment exceed the curve 21 representing the motor starting current characteristic.

(Problem to be Solved by the Invention) However, it is extremely difficult to provide a fuse with such characteristics. For this reason, in order to pass the motor starting current without any problems, it is practically impossible to protect the motor windings with a fuse, and it is necessary to use a fuse whose sole purpose is to interrupt the short-circuit current. Therefore, if the insulation of the motor windings deteriorates due to overloading, or if a short circuit occurs due to this insulation deterioration, the motor burns out and the motor itself has to be replaced.

In order to protect the motor windings using such a fuse, it is necessary to use thick winding diameter windings with a large allowable current in the motor, which increases the size and weight of the motor and increases its cost. There was a problem.

In view of the above circumstances, the present invention allows the starting current to flow in a motor circuit, etc., in which a large current flows instantaneously when the circuit is turned on, without any hindrance.
Moreover, it is an object of the present invention to provide a fuse that can protect the windings of a motor, etc., and at the same time, reduce the size and weight of the circuit and reduce costs.

(Means for Solving the Problems) The above object is to connect an insulating cylinder having insulation properties, an electrode attached to both ends of the insulating cylinder, and a straight portion between the electrodes inside the insulating cylinder. A conductive wire made of a superconducting material and having a coil portion wound around a straight portion of the conductive wire; This is achieved by a fuse characterized by having arc sand.

(Operation) When current flows through the fuse conductor, a magnetic field is generated around the coil portion of the conductor. The linear portion of the conducting wire surrounded by the coil portion is affected by this magnetic field, and the critical current density decreases. When the density of the current flowing through the conducting wire reaches this critical current density, the conducting wire changes from a superconducting state to a normal conducting state, electrical resistance is generated in the conducting wire, and the current decreases. When the current decreases and the density of the current flowing through the conductor falls below the critical current density,
The conductor changes from a normal conducting state to a superconducting state, and the electrical resistance of the conducting wire becomes zero.

(Example) Hereinafter, the present invention will be described in detail based on illustrated embodiments.

First, regarding the fuse according to one embodiment of the present invention, the first
This will be explained with reference to the figures. Electrodes 3 and 3' are attached to both ends of the insulating cylinder 2, and a conductor of, for example, Ba is attached between the electrodes 3 and 3'.
YCu3069 and B a 2E u 9 Y t Cu
A conductive wire 5 made of superconducting material such as A069 is connected. The conductive wire 5 has a straight portion 5a and a coil portion 5b wound around the straight portion 5a. Inside the insulating tube 2, there is a fire extinguisher made of insulating granular material, which has the function of completely cutting off the current flow between the electrodes 3 and 3' by exposing the conductor to the melted material. It is filled with arc sand 4. Here, it is assumed that the fuse of the present invention is used at an ambient temperature below the critical temperature of the superconducting material used for the conductor 4.

Generally, as shown in FIG. 2, when the density per cross-sectional area of a flowing current exceeds the critical current density Jc, a superconductor loses its superconducting properties and develops resistance. As shown in FIG. 3, the critical current density Jc changes depending on the strength of the magnetic field applied to the superconductor. The stronger the magnetic field, the lower the critical current density Jc.

Next, the current-time characteristics of a fuse made from a superconducting material will be explained below. FIG. 4 shows the current-time characteristics when no magnetic field is applied, and FIG. 5 shows the current-time characteristics when a magnetic field is applied. In Figures 4 and 5, the curve 27 represents the allowable current-time characteristics of the motor windings, and the limit current of the fuse in the normal conduction state where a current exceeding the critical current density of the superconductor flows and resistance is generated. A curve representing the time characteristics is a curve 28, and a curve representing the allowable current time characteristics of the fuse is a curve 29.

A critical current value Jc·a obtained by multiplying the critical current density Jc by the cross-sectional area a when no magnetic field is applied to the superconductor is shown as a straight line 31 in FIG. During the period from when the current starts flowing until time T1, a curve 28 showing the limit current-time characteristics of the fuse
When a current exceeding the current flows, the superconductor becomes a normal conductor and the generated resistance generates heat and blows the fuse. This protects the motor windings. However, after time T1, as long as the current does not exceed Jc-a, the superconducting state occurs and there is no resistance and no heat is generated, so even if a current exceeding curve 28 flows, the fuse will not blow out. Therefore, in this case, a current exceeding the curve 27 representing the allowable current-time characteristics of the motor windings continues to flow, so that the motor windings are not protected.

When a magnetic field is applied to the superconductor, the critical current density Jc becomes a reduced value Jc', and the critical current value Jc'·a multiplied by the cross section faa in this case is shown as a straight line 31' in FIG. The value of J c I ·a can be freely changed by changing the number of turns of the coil portion 5b of the conducting wire 5 and changing the strength of the magnetic field applied to the straight portion 5b.

Therefore, the value of J c / ・a is set as shown in Figure 5, J c
/・a is set to be slightly below the curve 29 representing the allowable current-time characteristics of the fuse in the normal conduction state. As a result, if a current larger than the curve 28 representing the limit current-time characteristics of the fuse flows, the fuse will melt at any instant, so a current larger than the curve 27 representing the motor winding allowable current-time characteristics will not flow. , the motor windings will be protected.

Next, the relationship between the limit current time characteristics of such a fuse and the starting current characteristics of the motor will be explained with reference to FIG.

Similarly to FIGS. 4 and 5, curve 27 represents the allowable current-time characteristics of the motor windings, curve 28 represents the limit current-time characteristics of the fuse in the normal conduction state, and curve 28 represents the allowable current-time characteristics of the fuse. Assume that there are two curves representing the characteristics. Furthermore, by changing the number of turns of the coil portion 5b of the conductor 5, the strength of the magnetic field applied to the straight portion 5a is adjusted, and the critical current value J c / · a is slightly lower than the curve 29 indicating the allowable current-time characteristics of the fuse. Set it as follows. When the starting current 32 flows through the motor, if the fuse conductor 5 is always in a superconducting state, the starting current 32' flows as shown by the - dotted chain line, and therefore the fuse exceeds the curve 28 representing the limit current-time characteristic of the fuse. melts. However, when a magnetic field is applied, the critical current value decreases to a value of J c /·a. As a result, the starting current 32 of the motor becomes this J
When the value of c/・a is exceeded, resistance is generated in the conductor 5, so the current is limited and flows as the starting current 32'' shown by the solid line.For this reason, the starting current 32 of the motor depends on the allowable current-time characteristics of the fuse. The curve 29 shown is not exceeded and the fuse does not blow out.The fuse therefore carries the motor starting current without any problem and protects the motor windings.

If the motor uses windings in which the allowable motor winding current is lower than the motor starting current, the motor can be made smaller and lighter, but if a conventional fuse is used, the starting current will be lower than the starting current. If the current flows, the windings will short out and become unusable.

However, as shown in FIG. 7, the motor starting current 33
When the conventional fuse is used, the starting current flows as shown by the dashed line 33', but when the fuse of this embodiment is used, the starting current flows as a solid line as explained with reference to FIG. A limited current flows, such as the starting current 33'' shown.As a result, only a current that is lower than the curve 27 showing the allowable current-time characteristics of the motor windings as well as the curve 29 showing the allowable current-time characteristics of the fuse flows. No flow will occur and the motor windings will be protected.

In this way, the fuse of this embodiment can pass the starting current of the motor without any trouble, and can also roughly protect the windings of the motor. Moreover, since the windings of the motor can be used with the smallest diameter within the range that allows the rated load current to be passed while ignoring the starting current, the motor can be made smaller and lighter.

The conductor 5 according to this embodiment has the shape shown in FIG. 1 from the straight part 5a to the coil part 5b, but it may have a different shape as long as the straight part 5a is surrounded by the coil part 5b. You can. Any material may be used as the arc-extinguishing sand 4 as long as it can be used as an insulator to cut off current flow between the electrodes 3 and 3' when the conducting wire 5 is fused.

〔Effect of the invention〕

As explained above, in the fuse of the present invention, the conducting wire is made from a superconducting material, and the coil part wound around the straight part of the conducting wire applies a magnetic field to the straight part, changing from a superconducting state to a normal conducting state. By changing the critical current value at the point where the circuit is turned on, it is possible to flow the necessary current in motor circuits and incandescent lamp circuits, where large currents flow instantly when the circuit is turned on, without any hindrance, and at the same time, it is possible to It is also possible to protect circuits, and it is also possible to reduce the size and weight of circuits such as motors.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a fuse according to an embodiment of the present invention, Figure 2 is a diagram showing the relationship between current density and resistivity of a superconducting material, and Figure 3 is a diagram showing the change in critical current density of a superconducting material with respect to a magnetic field. Figure 4 shows the current-time characteristics of a fuse made of superconducting material when no magnetic field is applied, and Figure 5 shows the current-time characteristics of a fuse made of superconducting material when a magnetic field is applied. Diagram showing current time characteristics,
FIG. 6 is a diagram showing current-time characteristics of a fuse according to an embodiment of the present invention, FIG. 7 is a diagram showing current-time characteristics of a fuse according to an embodiment of the present invention, and FIG. 8 is a diagram showing current-time characteristics of a conventional fuse. FIG. 3 is a diagram showing characteristics. 1... Fuse, 2... Insulating tube, 3.3'...
Electrode, 4... Arc-extinguishing sand, 5... Conductor, 5a... Straight portion, 5b... Coil portion, 21... Motor starting current characteristics, 22... Motor winding allowable current time Characteristics, 2
3.24...Fuse limit current time characteristics, 25.2
6... Allowable current time characteristics of fuse, 27... Allowable current time characteristics of motor winding, 28... Limit current time characteristics of fuse, 2... Allowable current time characteristics of fuse, 31° 31 '...Critical current value, 32.32', 3
2'...Motor starting current characteristics, 33.33', 33
'...Motor starting current characteristics. Applicant's agent Sato - Rooster 1 figure and figure 2 figures Horse 3 figure Horse 4 figure and figure 5 figure and figure 6 figure and parturition 7 figure

Claims (1)

[Claims] An insulating cylinder having insulation properties, electrodes attached to both ends of the insulating cylinder, a straight part connecting the electrodes inside the insulating cylinder, and a coil part wound around the straight part. 1. A fuse comprising: a conductive wire made of a superconducting material; and arc-extinguishing sand that is filled inside the insulating cylinder and cuts off current flow between the electrodes when the conductive wire is fused.