JPH0210561B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides a method for when an excessive current flows through a current-carrying body.
The present invention relates to an electrical device that prevents the adverse effects of temperature rise on the surrounding area.

Generally, in a high-voltage power converter using a thyristor, the number of elements connected in series is determined in consideration of the normal operating voltage. Sporadically applied lightning impulses, switching surges, etc. are limited to a predetermined voltage by arresters.

In the conventional type, as shown in Fig. 1, arresters A ₁ , A ₂ , A ₃ and snapper circuits S ₁ , S ₂ , S ₃ are connected in parallel to each thyristor element T ₁ , T ₂ , T ₃ . There is.
In this case, even if an overvoltage such as a lightning impulse is applied from the outside to each thyristor element T ₁ , T ₂ , T ₃ , the arresters A ₁ , A ₂ , A ₃ and the snapper circuit S ₁ , which are connected in parallel, Voltage limited by S ₂ and S ₃
Since only V _M is applied, each thyristor element T ₁ ,
T ₂ and T ₃ are protected.

However, when a conduction command is issued to each thyristor T ₁ , T ₂ , T ₃ , if only thyristor element T ₁ fails to conduct due to a failure in the ignition circuit, all but thyristor element T ₁ and the other The thyristor conducts,
A load current determined by external circuit conditions is forced to flow through the arrester A ₁ connected in parallel with the thyristor element T ₁ , and its terminal voltage has a value determined by the voltage-current characteristics of the arrester A ₁ .

Usually, arresters do not have the ability to carry an excessive current such as the load current for a long period of time, so they overheat and have an adverse thermal effect on the surrounding area. Furthermore, if overheating causes mechanical destruction, flying debris may damage the surrounding area, so as shown in Figure 2, if excessive current flows through the arrester,
Arresters configured to electrically connect both ends of the arrester have been proposed.

That is, in FIG. 2, a low melting point metal 3 such as solder is connected to an overvoltage limiting element 1 such as a zinc oxide type arrester.
The overvoltage limiting element 1 and the low melting point metal 3 are electrically connected in series between the pair of electrodes 5 and 6, and the spring 8 presses one electrode 5 and the other electrode 6 is connected to the shunt 9. so that both current-carrying parts 5a and 6a are electrically connected by the molten low-melting point metal 3.
Both opposing current-carrying parts 5a and 6a are arranged below the low melting point metal 3.

In the above configuration, when an excessive current flows through the overvoltage limiting element 1, the electrode 5→overvoltage limiting element 1→
It passes through a circuit of low melting point metal 3 → shunt 9 → electrode 6. As a result, the temperature of the overvoltage limiting element 1 rises, so that the low melting point metal 3 melts and both current-carrying parts 5
It falls between electrodes 5 and 6a, and both electrodes 5 and 6 are electrically connected. Therefore, the current flowing through the overvoltage limiting element 1 flows through the low melting point metal 3 that has fallen between the current carrying parts 5a and 6a, so that overheating of the overvoltage limiting element 1 can be suppressed.

However, if a part of the overvoltage limiting element electrically breaks down and excessive current concentrates there, the low melting point metal in the vicinity will instantly melt and fall.
Since the amount of melting of the low-melting point metal differs depending on the location where the current is concentrated, there is a drawback that the connection between the two current-carrying parts is unstable.

This invention was made in order to eliminate the above-mentioned drawbacks, by providing a heat transfer body with low thermal conductivity and good electrical conductivity between a current-carrying body such as an overvoltage limiting element and a low-melting point metal. Accordingly, an electric device is provided in which a large amount of low-melting point metal is melted.

The figures will be explained below. Figures 3 and 4
In the figure, 1 is a current carrying body made of an overvoltage limiting element such as a zinc oxide element, and 2 is a heat transfer body closely attached to one end of the current carrying body 1, which is a plate-shaped ceramic 2a surrounded by a conductive member 2b such as aluminum. It is. Note that the heat conductivity of the heat transfer body 2 is lower than that of solder (0.1 cal/cm ² /cm/°Csec), for example.
It is made of a material with a resistivity smaller than that of solder (10μΩcm), for example. 3 is a low-melting point metal such as solder that is in close contact with the heat transfer body 2; 4 is a conductive plate that is in close contact with the low-melting point metal 3; and 5 is a conductive plate that is in close contact with the other end of the current-carrying body 1 to connect the first current-carrying portion 5a. a first electrode having a 6
is a second electrode having a second current-carrying portion 6a facing the first current-carrying portion 5a with a predetermined distance therebetween.
Note that both current-carrying parts 5a and 6a are arranged below the low-melting point metal 3 so that the molten low-melting point metal 3 can fall and establish an electrical connection. Reference numeral 7 denotes an insulating cylinder in which the current-carrying body 1 is housed and both electrodes 5 and 6 are held, and a reservoir portion 7 is in contact with the lower part of both the current-carrying parts 5a and 6a.
It constitutes a. A spring 8 is arranged between the plate 4 and the second electrode 6 and presses the overvoltage limiting element 1 against the first electrode 5. A shunt 9 electrically connects the plate 4 and the second electrode 6.

Next, the operation will be explained. In FIG. 3, even if an excessive current flows locally through the current carrying body 1, the heat transfer body 2 is gradually heated, so that the low melting point metal 3 is heated on average as a whole. Therefore, since the low melting point metal 3 melts and falls almost simultaneously, the reservoir 7a is filled with a large amount of the low melting point metal 2, so that the current carrying capacity between the two current carrying parts 5a, 6a can be secured.

In the above embodiments, an overvoltage limiting element such as a zinc oxide arrester has been described, but similar effects can be expected if the overvoltage limiting element is one in which an excessive current flows during an accident and causes overheating.

According to this invention, by providing a heat transfer body with low thermal conductivity and low specific resistance between the current carrying body and the low melting point metal, the low melting point metal is heated evenly as a whole, so that a large amount of heat is generated. The low melting point metals melt almost simultaneously, ensuring a sufficient amount of current melting between both electrodes.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a power conversion device, Fig. 2 is a sectional view showing a conventional electrical device, Fig. 3 is a sectional view showing an embodiment of the present invention, and Fig. 4 shows the main parts of Fig. 3. FIG. In the figure, 1 is a current carrying body, 2 is a heat exchanger plate, 3 is a low melting point metal, 5 is a first electrode, and 6 is a second electrode. Note that the same reference numerals in each figure indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1 A pair of electrodes are connected to both ends of a current carrying body, and a low melting point metal is melted by a temperature rise when a current of a predetermined value or more flows through the current carrying body, and the low melting point metal is melted. In the device for electrically connecting the two electrodes, the low melting point metal is disposed between at least one of the electrodes and the current carrying body, and the heat transfer body having low thermal conductivity and low specific resistance is connected to the low melting point metal. An electric device characterized in that it is interposed between a current carrying body and the low melting point metal. 2. The electrical device according to claim 1, wherein the heat transfer body is a plate-shaped ceramic surrounded by aluminum.