JPS63160201A - Current limiting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a current limiting element that limits the current flow during a short circuit in an overcurrent circuit breaker, etc., and more specifically relates to a current limiting element using a shape memory alloy. It is related to the element.

(Background Art) Conventionally, current-limiting wires have been used as current-limiting elements that limit the current flowing during short circuits in overcurrent circuit breakers and the like.

The current-limiting wire generates heat due to the current flowing during a short circuit, and the rise in specific resistance of the current-limiting wire due to the temperature rise at this time is utilized to limit the current during the short circuit. Generally, the current limiting wire material is Fe alloy type, for example, FeMn or FeN.
iCo etc. are used.

However, when using this current-limiting wire, the rate of change in electrical resistance is about 1O times, so the current-limiting effect is small, and the temperature of the current-limiting element rises to about 1000°C, so it has poor heat resistance and acid resistance. The disadvantage of a hat is that it has a short lifespan and is slow to develop.

(Object of the invention) The present invention has been made in view of the above points, and
The purpose of this is to use shape memory or gold to have a large rate of change in electrical resistance, and to repeat ff If;
To provide a long current limiting element.

(Disclosure of the Invention) As shown in FIG. 1, the current limiting element according to the present invention is formed from a shape memory alloy 1 whose shape reversibly expands and contracts with temperature changes that sandwich the martensite two-state temperature. In this current limiting element, the shape memory alloy 1 is coated with a precious metal 2, and the surface of the shape memory alloy 1 is coated with a noble metal 2.

FIG. 1 is a diagram showing the configuration of the present invention. A linear shape memory alloy 1 is wound into a coil, and an upper electrode 3 and a lower electrode 4 are attached to both ends thereof. Each t[! 3.4 is connected to an external circuit via leads i15 and i6. Figure 1(a) shows the same [] (1,
) indicates the state of the element when an overcurrent flows between the electrodes,
Figure 1(c) shows the cross-sectional structure of the linear shape memory alloy 1 wound into a coil.As shown in Figure 1(e), the surface of the shape memory alloy 1 is made of noble metal. 2 is coated.

The current limiting element of the present invention is inserted in series in a load power circuit,
When a short-circuit current or an abnormal current, that is, an overcurrent flows, the current increases its own resistance value to limit the overcurrent. First, under normal conditions, that is, when no overcurrent is flowing, the linear shape memory alloy 1 is in a low-temperature phase (martensite phase) and is folded into a coil shape, as shown in FIG. 1(a). The lines are close to each other. However, 31! When the S current flows, transformation begins due to temperature rise, resulting in a high-temperature summation (austenite phase), and as shown in the figure (1,), the shape Irp! Alloy 1 is in an elongated state. The electrode 3 undergoes a shape change from the state shown in FIG. 1(a) to the state shown in FIG. 1(b).
．． The current is limited by the resistance change between the two.

The amount of change in electrical resistance is determined by the following equation: When a linear shape memory alloy 1 having a cross-sectional shape as shown in Figure 2 is wound into a coil, the resistance when it is in close contact is R1, and the resistance when it is stretched is R2. Ba,
It can be calculated using the following formula.

RI= p nb/a D yr =-■R2
=ρπD n, /ab −・■R之/R1=(
πD/b)2...■Here, ρ is the shape description +1
is the specific resistance of gold 1, n is the number of turns, a, b are the second [2I
As shown, the cross-sectional dimension of the shape memory 6 gold wire (a is the contact surface dimension), and D is the coil diameter. R, /R, is shown by the formula 0, and if b = 1 m + s and D = 10 mm, then R2
/R,=987, which is a very large resistance ratio.

However, in the case of i\i without surface coating as shown in Fig. 2, there is contact resistance between the lines in the state shown in Fig. 1 (a), and this contact resistance is expressed by the formula Since it is an order of magnitude larger than the resistance R1, it has a large effect on the rate of change in electrical resistance.

Shape memory alloys are practical materials such as CuZn-based, Ni
Although Ti-based metals are base metals, their contact resistance is quite high. Therefore, in the present invention, as shown in FIG. 1(c), the surface of shaped metal alloy 1 is coated with noble metal 2
The contact resistance between the wires is reduced. Precious metals are suitable for use in reducing contact resistance between wires because they are resistant to @<< and also have excellent atmospheric resistance.

AuJ'd or the like can be used as the noble metal, and plating, cladding, or the like can be used as the coating method.

Note that there are no particular limitations on the shape that causes a resistance change by utilizing the fact that the shape reversibly expands and contracts with temperature changes that sandwich the martensitic transformation point temperature.
As shown in the figure, a linear shape memory alloy 1 may be wound into a coil, or as shown in FIG. 3, a plate shape memory alloy 1 may be folded in a zigzag manner.

In addition, as shown in FIG. 4, in order to reduce and stabilize the contact resistance, a shape memory alloy is applied in the opposite direction to the pll direction of the shape memory alloy 1 (in combination with a bias spring 7 that biases the shape memory alloy 1). The bias spring 7 is interposed between the spring fixing part 8 and the upper electrode 3, and by pulling the upper electrode 1f+3 in the direction shown by the arrow P, compressive force is applied to the shape memory alloy 1, thereby reducing the contact resistance. This is intended to stabilize the lower electrode 3.
is vertically movable within the insulating bot 9. Also,
Since the lead wire 5 moves together with the lower electrode 3, a highly flexible material is used, and its end is connected to the lead tall via a relay terminal plate 10. It goes without saying that when an overcurrent occurs, the shape memory alloy 1 overcomes the biasing force of the bias spring 7 and expands, resulting in a state as shown in FIG. 1(b).

E1: Shape description of NiTi and CuZn series f! ! ! Uses alloy.

We made coil springs made of linear shape memory alloys with two types of cross-sectional shapes: round and square. A to this coil spring
It was plated with U or Pd to make a current limiting element. Characteristics of this current limiting element were compared with and without plating and with and without a bias spring. Table 1 shows the details of the prototype current-limiting element and the electrical resistance measurement results. Note that the operating temperature of the prototype current-limiting element was 45 to 55°C. The electrical resistance was determined by measuring the resistance R1 when the current limiting element was in close contact with the current limiting element and the resistance R2 when the current limiting element was stretched, and evaluating the resistance change R3/R1. Note that the tensile force of the bias spring was 80 g.

(Left below) In the upper table of Table 1, * 1: 1. O×0.6 (1 and 01 surfaces are contact surfaces)
*2: 0.6×0.4 (0, hm surface is the contact surface) (Effects of the invention) As described above, the present invention provides a current limiting element by forming a shape memory alloy coated with a noble metal. The electrical resistance when the shape memory alloy is in close contact can be lowered, and therefore the rate of increase in electrical resistance at high temperatures increases, resulting in a greater current limiting effect when an overcurrent flows.
Furthermore, since it operates at low temperatures, it has the advantage of having an excellent repeat life.

As mentioned in the explanation of the examples, by using a bias spring that biases the shape memory alloy in the shape change direction where the resistance value becomes smaller, the electrical resistance of the shape memory alloy when it is in close contact can be further lowered. This makes it possible to obtain a current limiting element with good current limiting characteristics.

[Brief explanation of the drawing]

FIG. 1(a) is a front view of a current-limiting element according to an embodiment of the present invention, with a main part broken away during normal operation, and FIG. e) is the same as above. Figure 2 is a cross-sectional view of the shape memory alloy used in the conventional example. Figure 3 (a) is a normal current limiting element according to another embodiment of the present invention. FIG. 4 is a front view of the current limiting element according to another embodiment of the present invention. FIG. 1 is a shape memory alloy, and 2 is a noble metal.

Claims (2)

[Claims] (1) In a current limiting element that is formed from a shape memory alloy that reversibly expands and contracts its shape with temperature changes around the martensitic transformation temperature, and has a shape memory that changes its resistance value due to expansion and contraction, the shape memory alloy A current limiting element characterized by having a surface coated with a precious metal. (2) The current-limiting element according to claim 1, wherein the shape memory alloy is biased by a bias spring in a direction of shape change in which the resistance value thereof becomes smaller.