JPH1023660A - Current limiting device - Google Patents

Abstract

An object of the present invention is to ensure a current limiting function of a current limiting device for protecting a semiconductor device or the like from an overcurrent, and to enable a device having a slow shutoff speed to shut off. SOLUTION: (V _{1-X AX} ) ₂ O (0.001 ≦ x ≦ 0.02,
A is a PTC of a vanadium oxide-based ceramic having a composition of at least one element selected from Al, Cr and Sc).
A branch A in which a resistor 1 and a diode 2 are connected in series;
A similar branch B in which the PTC resistor 3 and the diode 4 are connected in series is connected in parallel so that the diodes 2 and 4 are in opposite directions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current limiting device for limiting an overcurrent flowing in an electric device to protect the electric device.

[0002]

2. Description of the Related Art In recent years, with the increase in capacity of electric equipment, an overcurrent generated due to a short circuit accident or the like tends to increase. In such a case, preparing a large circuit breaker that sufficiently satisfies the short-circuit capacity is economically burdensome. By connecting a resistor having a positive temperature characteristic (hereinafter referred to as a PTC resistor) in series and limiting the current,
Ensuring a large breaking capacity is being performed.

[0003] such as certain additives vanadium oxide plus (V ₂ O ₃₎ based ceramics, the resistivity at a given temperature rapidly increases - is one with the (metal insulator transition) characteristic. A resistor having such a property (hereinafter referred to as a “transitional resistor”) can limit the overcurrent by utilizing the fact that the temperature rises due to Joule heat when an overcurrent flows and the resistance value rises. Because it is possible, it is suitable for a current limiting element. The temperature at which the resistivity changes abruptly is called the transition temperature.

FIG. 2 is a sectional view of an example of a conventional current limiting element. 5 is obtained, for example, by adding chromium (Cr) to vanadium sesquioxide (V ₂ O ₃ ) and having a composition of (V _{1 -X} Cr _X ) ₂ O ₃ (0.001 ≦
x ≦ 0.02) is a columnar transitional resistor of a V ₂ O ₃ ceramic resistor, 6 is a silver-copper solder, and 7 is an electrode made of Mo. The shape varies depending on the rating.
mm and a length of about 30 mm.

FIG. 3 is a temperature characteristic diagram of the resistivity of the current limiting element of FIG. The resistivity gradually increases from room temperature to 100 ° C., rapidly increases by about two digits around 100 ° C. to 150 ° C., and peaks at 150 ° C. to 200 ° C.
It drops at higher temperatures.

[0006]

However, due to the characteristics of such a PTC resistor, in a device such as an earth leakage breaker, which has a slow shut-off speed and requires a period of one cycle of a short-circuit current to complete the shut-down, Since the temperature of the resistor increases and the temperature coefficient of the resistor is applied to the negative region, the overcurrent once limited increases again, and there is a problem that a sufficient current limiting effect cannot be obtained.

FIG. 5 shows a current waveform when a short circuit of 50 Hz is interrupted. The horizontal axis is time. The condition of short-circuit current is 100V /
4 kA. In FIG. 5, a dotted line indicates a short-circuit current when no load is connected to the system, and a solid line indicates a current limit when a current limiting element of a PTC resistor is connected. The resistance value of the P ₂ O ₃ ceramic PTC resistor increases up to 160 ° C. due to a rise in temperature, and the current is limited. However, in a device having a slow shutoff speed, such as an earth leakage circuit breaker, the current cannot be shut off during this period, and the current increases again because the device enters a region where the resistance value exceeding the transition temperature decreases. When the temperature rise is excessive, the resistivity becomes almost the same as before the increase. As a result, as shown by the solid line in FIG.
With the C resistor alone, the current is limited for up to a half cycle, but thereafter, the current limiting effect is almost eliminated due to temperature rise, and a current about the same as a short-circuit current when no load is connected flows.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a current limiting device in which a current limiting operation is reliably performed.

[0009]

In order to solve the above-mentioned problems, a current limiting device according to the present invention comprises a series connection of a diode and a PTC resistor which has a positive temperature coefficient of resistance and whose temperature coefficient of resistivity changes rapidly. The plurality of branches are connected in parallel so that the diodes are in opposite directions. In this case, currents of a half cycle respectively flow through the PTC resistors arranged in parallel by the diodes connected in reverse. PTC with half-cycle currents arranged in parallel
By alternately flowing the resistors, both resistors
To limit the current every half cycle, once the current is limited,
The current limiting effect can be maintained for a long time without increasing the current due to the temperature rise.

In particular, when the PTC resistor is (V _{1 -X} A _X ) ₂ O ₃
(0.001 ≦ x ≦ 0.02, where A is at least one element selected from Al, Cr and Sc) is a vanadium oxide-based ceramic. Al, Cr, and Sc are all additives that rapidly change the temperature coefficient of the resistivity of the main resistor made of a vanadium oxide-based ceramic. When x <0.001, the temperature coefficient of the resistivity is not rapidly changed. When x> 0.02, the transition temperature becomes too low to use as a current limiting element.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a configuration of a current limiting device according to the present invention. That is, the current limiting device of the present invention is a PTC
Branch A and PTC in which a resistor 1 and a diode 2 are connected in series
The branch B in which the resistor 3 and the diode 4 are connected in series is connected in parallel. However, the diode 2 and the diode 4 are connected in the opposite directions.

The PTC resistors 1 and 3 are, for example, columnar transition resistors 5 made of vanadium oxide ceramics.
And molybdenum electrodes 7 brazed with brazing foils 6 at both ends. A method for manufacturing the PTC resistors 1 and 3 as the embodiment of FIG. 1 will be described. Powders of vanadium oxide (V ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), and iron oxide (Fe ₂ O ₃ ) were used as raw materials.
_0.9965 Cr _0.0035 ) ₂ O ₃ +5 mass% Fe was weighed and blended, and then mixed and pulverized in a wet ball mill for 12 hours. The resulting powder was molded under pressure, baked in hydrogen at 1700 ° C. for 1 hour, and then cut and polished to a diameter of 10 mm.
A columnar transitional resistor having a length of 30 mm and a room temperature resistance of 15 mΩ is used. The temperature dependency of the resistivity of the V ₂ O ₃ ceramic resistor is almost the same as that of the conventional example shown in FIG.

[0013] Subsequently, silver-
A copper (Ag-Cu) eutectic brazing foil is placed, sandwiched between molybdenum (Mo) electrodes, baked at 900 ° C. for 10 minutes in a hydrogen stream under a pressure of 1 × 10 ⁴ Pa, and the electrodes are attached. As the diode, a diode having a required withstand voltage and current capacity may be selected and connected in series with the PTC resistor. Each of the diodes 1 and 3 of this embodiment is a general rectifying diode having a rated reverse voltage of 1000 V.

The characteristics of the current limiting device thus obtained will be described below. FIG. 4 shows a current waveform in a case where the current limiting device of the present invention is connected in series with a breaker rated at 20 A, and a short-circuit break is performed. The horizontal axis is time. The condition of the short-circuit current is 100 V / 4 kA. The dotted line in FIG.
The short-circuit current when there is no load in the system, and the solid line is the current when a current limiting device is connected.

When the PTC resistor 1 is heated to a high temperature by Joule heat due to the initial half-wave of the short-circuit current, the PTC resistor 1 enters a high resistance state,
The current flowing through the C resistor 1 is reduced. However, because of the diodes 2 and 4 connected in the reverse direction, the next half-wave must be P
It flows to the TC resistor 3. Then, due to the action of the PTC resistor 3, the current is also limited as shown by the solid line. During this period, the current does not flow through the PTC resistor 1, and the PTC resistor 1 is cooled. As shown in FIG. 5, in the conventional PTC resistor alone, the current is limited for up to half a cycle, but thereafter the temperature rises, so On the other hand, in the current limiting device of the present invention, the first half cycle of the overcurrent is divided by the branch A in FIG.
Since the following half cycle is flow-limited by the branch B, the current-limiting action can be maintained for one cycle. Therefore, even a device having a low shutoff speed, such as an earth leakage breaker, can be shut off during this time.

[0016]

As described above, according to the present invention, a plurality of branches in which a PTC resistor such as a vanadium oxide ceramic is connected in series with a diode are connected in parallel so that the diodes are in opposite directions. By using the current limiting device described above, the current limiting effect can be ensured, and can be maintained more than twice as long as the conventional one. For this reason, it is possible to sufficiently apply even a device having a low breaking speed such as an earth leakage breaker.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a current limiting device of the present invention.

FIG. 2 is a sectional view of a conventional current limiting element.

FIG. 3 is a diagram showing a temperature characteristic of resistivity of a V ₂ O ₃ ceramic resistor.

FIG. 4 is a current waveform diagram showing a current limiting action of a short-circuit current by the current limiting circuit of the present invention.

FIG. 5 is a current waveform diagram showing a current limiting effect of a short-circuit current by only a PTC resistor.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 PTC resistor 2 diode 3 PTC resistor 4 diode 5 transitional resistor 6 brazing foil 7 electrode

Claims (2)

[Claims] 1. A plurality of branches in which a PTC resistor having a positive temperature coefficient of resistance and a temperature coefficient of resistivity changes rapidly and a diode are connected in series so that the diodes are in opposite directions. Current limiting device characterized by the following. 2. The method according to claim 1, wherein the PTC resistor is (V _{1 -X} A _X ) ₂ O (0.
2. The current limiting device according to claim 1, wherein 001.ltoreq.x.ltoreq.0.02, and A is a vanadium oxide-based ceramic having a composition of (A, at least one element selected from Al, Cr, Sc).