JPH10271667A - Current limiter and breaker for wiring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the surge voltage generated in the case where the resistance value goes up suddenly, and prevent the dielectric breakdown of a PTC element or the burn by sudden temperature rise, by connecting a capacitor and/or a varistor in parallel to the PTC element. SOLUTION: A capacitor 34 is connected in parallel as a surge bypass element to a PTC element 31. This capacitor 34 scarcely lets a current flow to with commercial frequency, but it has a property of letting a current flow to the sudden voltage change in case that the generation of the surge voltage along with the current limitation of the PTC element 31 occurs. Accordingly, the capacitor 34 shows the same function as a resistor, and one part of the surge voltage falls on the capacitor 34, so the surge voltage falling on the PTC element 31 itself is reduced, and the dielectric breakdown of the PTC element 34 or the sudden heat generation caused by the surge voltage can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current limiter for protecting a power supply device installed in a premises wiring system or a premises wiring system from an excessive current such as a short-circuit current flowing in an electric circuit such as a premises wiring system. More specifically, a PTC element and a capacitor and / or a varistor connected in parallel to the PTC element provide a PTC element.
The present invention relates to a current limiter and a circuit breaker for wiring which suppress generation of a surge voltage due to a rapid rise in resistance value at a phase transition temperature of an element to avoid burn-in of a current limiter and insulation breakdown of a PTC element due to rapid heat generation of a PTC element. .

[0002]

2. Description of the Related Art When a large number of devices are connected to one power source (outlet) and operated simultaneously, or when an electric appliance such as a heating device that consumes a large amount of current is operated at the same time, a "breaker falls". Toss is something that you experience everyday. The interruption of the current by such a breaker
This is to protect the premises wiring system from an overload current exceeding the rated capacity or an overcurrent due to a short circuit accident or a short circuit. Such breakers are formally known as circuit breakers (M
old Case Circuit Break
r: hereinafter abbreviated as MCCB), which is inserted and connected between the on-premises wiring systems on the power supply side and the load side.

The structure of the MCCB generally includes an opening and closing mechanism for opening and closing an electric circuit, and a trip device for automatically opening and closing the electric circuit according to a current value for a current larger than a rated current. The power supply side terminal and the load connection side terminal which are incorporated in the insulating container and which communicate with these current interrupt mechanisms are provided outside the insulating container. Here, the electric circuit refers to a wiring path between the power supply side terminal and the load connection side terminal in the MCCB.

In order to increase the current interrupting capacity of the MCCB, a device for limiting an overcurrent flowing in an electric circuit is provided by an MCC while leaving a tripping mechanism of the MCCB itself.
Attempts have been made to increase the substantial current blocking capacity of the MCCB by attaching it to B. Such current limiting devices include an electromagnetic repulsion mechanism, a current limiting fuse, a PT
C resistance elements and the like are being studied.

For example, Japanese Patent Application Laid-Open No. 4-351825 proposes a current limiter using a PTC element.
When the PTC element is heated to a temperature higher than a predetermined temperature (phase transition temperature) determined by a material constituting the PTC element, the resistance value sharply increases, and the current is limited. Therefore, according to the current limiter using the PTC element, Joule heat due to the resistance component of the PTC element is generated in the PTC element due to the overload current or the overcurrent,
The generated heat activates the opening / closing mechanism in the MCCB to cut off the overcurrent. Therefore, since the short-circuit current is limited by the high resistance of the PTC element, there is an advantage that the cut-off current capacity can be increased in practical use with an MCCB having a small cut-off current capacity.

[0006]

However, when a PTC element is used as described above, as shown in FIG. 4, the PTC element reaches a phase transition temperature due to an overcurrent, and the resistance value rapidly increases. At the moment of increasing and limiting the current limit,
It can be seen that the voltage applied to the PTC element also increases rapidly, and its magnitude reaches 5 to 10 times the power supply voltage. The occurrence of such a sudden large voltage is called a surge,
This surge voltage causes damage such as dielectric breakdown of the PTC element, thereby making it impossible to cut off the electric current in the electric circuit, and causing an accident such as a sudden increase in the temperature of the PTC element causing burning of the current limiter.

The wiring from the power supply to the load has an impedance corresponding to the thickness and length of the wiring, and the current at the time of a short circuit accident is determined from the wiring impedance and the power supply voltage. JIS-C8370 stipulates the wiring impedance to be applied in accordance with the breaking capacity as a short circuit breaking test circuit constant of MCCB.

In general, the impedance of a wiring having a small short-circuit current is resistive, whereas the impedance of a wiring having a large short-circuit current is inductive. For this reason, when using the PTC element to increase the breaking capacity of the MCCB, the wiring impedance is inductive, and when the PTC element rapidly increases the resistance and tries to limit the overcurrent, the inductance of the inductance increases. A surge voltage is generated such that the action prevents the current from decreasing.

[0009]

Therefore, the present inventor has studied to suppress the generation of a surge voltage due to the current limiting action of the PTC element, and to provide a more reliable current limiting device and wiring breaker. And arrived at the present invention. That is, according to the present invention, a PTC element having a positive temperature coefficient of resistance, whose resistance value rapidly increases when a predetermined phase transition temperature is reached, is provided in an electric circuit, and an overcurrent flows through the electric circuit, so that the PTC element is provided. A current limiter using a PTC element that suppresses an overcurrent by rapidly increasing the resistance value when the temperature of the element rises and the temperature reaches the predetermined phase transition temperature.
A current limiter is provided in which a capacitor and / or a varistor are connected in parallel to the C element.

Here, when the short-circuit inductance of the wiring is L and the current-limiting resistance of the PTC element is R, the capacitance C of the capacitor is:
Those in the range of 0.1 L / R ² <C <10 L / R ² are preferably used. Further, the varistor generates a substantially constant varistor voltage below a predetermined varistor current, and the varistor voltage is 1 to 2 times the rated voltage of the circuit breaker to which the current limiter is mounted, and Is more than the breaking capacity of the circuit breaker.

Further, according to the present invention, when an overcurrent such as a short-circuit current flows through the electric circuit, the temperature rises, and when the temperature reaches a predetermined phase transition temperature, the resistance value sharply increases, and the overcurrent increases. A circuit breaker for wiring, comprising: a PTC element that limits a current; and a current limiter in which a capacitor and / or a varistor are connected in parallel to the PTC element.
Is provided.

Here, as the current limiter provided in the circuit breaker for wiring, it is preferable to use the current limiter provided with the above-mentioned capacitor or varistor.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the current limiter and the MCCB using the current limiter according to the present invention, the surge voltage generated when the PTC element reaches the phase transition temperature and starts the current limit is described. And therefore P
Failure of the current limiter due to insulation breakdown or seizure of the TC element can be avoided. Also, due to the current limiting effect of such a PTC element, the capacity of the low-capacity MCCB can be increased without increasing the size,
That is, the maximum current breaking capacity can be increased. Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

FIG. 1 is a perspective view showing an embodiment of a basic structure of a current limiter 30 according to the present invention. The current limiter 30 is connected such that the flat surfaces of the PTC element 31 formed in a flat shape are sandwiched between the long flat plate-shaped terminal plates 32 and 33 to form a conductive path.

In general, the resistance value of the PTC element 31 decreases in proportion to its cross-sectional area and decreases in inverse proportion to its length. It is preferable to increase the cross-sectional area through which the air flows, and shorten the length thereof. Further, in order to increase the temperature rising speed from the temperature in a normal use state of the PTC element 31 to the phase transition temperature, it is preferable that the volume of the PTC element 31 is small. Therefore, the PTC element 31
Is preferably formed in a thin plate shape. Conversely, when the volume of the PTC element 31 is small, the resistance value is also small.
To increase the current limiting effect, it is preferable that the rate of increase in resistance at the phase transition temperature is large. Further, the PTC element 31
Is the resistivity at normal operating conditions (ρ)
Is small, and the resistance rise rate at the phase transition temperature (Tc) is preferably large.

In the present invention, such a PTC element has a room temperature resistivity of about 10 to 100 mΩ · cm, a phase transition temperature of 200 ° C. to 260 ° C., and a resistance rise rate at the phase transition temperature of about 1000. Cristobalite-based composite ceramics that are twice or more
Vanadium oxide (V ₂ O ₃ ) -chromium oxide (Cr ₂ O ₃ ) having a characteristic of 10 mΩ · cm, a phase transition temperature of about 60 ° C. to 150 ° C., and a resistance rise rate at the phase transition temperature of about 1000 times or more. ) -Based ceramics are preferably used.

Other PTC elements include lead titanate (PbTiO ₃ ) ceramics, barium titanate (BaTiO ₃ ) ceramics, and bismuth titanate (B
iTiO ₃ ) ceramics or solid solutions thereof may be used. Further, a PT made of a polyethylene-carbon composite material or a polyolefin-carbon composite material
It is also possible to use a C element.

Next, the terminal plate 3 formed in a long plate shape
For 2, 33, a metal material having good conductivity, such as copper, aluminum, and stainless steel, is used. These terminal plates 32 and 33 are connected to the PTC element 31 with a conductive adhesive or the like so as to overlap the flat surface of the PTC element 31 formed in a thin plate shape, or
1 is metallized and fixed by metal brazing or welding to be electrically connected. Therefore, since the cross-sectional area of the PTC element 31 through which current flows is large and the distance is short, the resistance value of the PTC element 31 is reduced, and a reduction in power loss can be prevented. Furthermore, since the good conductive metal used for the terminal plates 32 and 33 is generally excellent in heat conductivity, it also plays a role of radiating heat generated in the PTC element 31 by a steady current. In addition, the terminal plate 3
2, 33 are provided with mounting holes 32A, 33A used for connection with MCCB and wiring.

The PTC element 31 of such a current limiter 30
On the other hand, as shown in the circuit diagram of FIG. 3, a capacitor 34 is connected in parallel as a surge bypass element. Although little current flows at the commercial frequency, the capacitor 34 has a property of flowing electricity in response to the sudden voltage change when a surge voltage occurs due to the current limit of the PTC element 31. Therefore, the capacitor 34
It exhibits the same function as the resistor, and a part of the surge voltage is applied to the capacitor 34. Therefore, the surge voltage applied to the PTC element 31 itself is reduced, and the dielectric breakdown of the PTC element 34 and the rapid heat generation due to the surge voltage are suppressed. be able to.

As the capacitor 34, the PTC element 3
In order to obtain an electrical circuit matching with the capacitor 1, when the short-circuit inductance of the wiring is L and the current limiting resistance of the PTC element 31 is R, the capacitance C of the capacitor is 0.1 L / R ²
Those in the range of <C <10 L / R ² are preferably used. Specifically, the capacitance of the capacitor 34 is 0.0
Those having a size of 1 to 100 μF are preferably used. The shape and material of the capacitor 34 are not particularly limited.

In the present invention, the capacitor 3
A varistor can be used as a surge bypass element instead of 4. The varistor has a high resistance in a normal state and is an insulator that hardly allows a current to flow. However, since the varistor has a property of allowing a current to flow at a certain critical voltage or higher, the surge voltage caused by the current limit by the PTC element 31 is reduced. Functions in the same manner as the capacitor 34 described above. In the case of the present invention, the varistor generates a substantially constant varistor voltage when the varistor current is equal to or less than a predetermined varistor current, and the varistor voltage is 1 to 2 times the rated voltage of the wiring breaker to which the current limiter is mounted. In addition, a varistor current that is equal to or greater than the breaking capacity of the wiring breaker is preferably used.

FIG. 2 shows a current limiting device 30 in which a capacitor 34 is attached as a surge bypass element, which is a three-phase MC.
It is a top view which shows the external shape in the state connected to CB50. M
The CCB 50 has a main contact connected to an electric circuit, an opening / closing mechanism for opening and closing the main contact, an arc-extinguishing chamber for extinguishing an arc generated when the main contact is opened, and an overcurrent such as an overload current or a short-circuit current. A built-in release device for releasing the opening / closing mechanism and tripping the main contact, an operation switch 51 for operating the opening / closing mechanism to connect the main contact to the electric circuit, and a power supply side terminal 52X for connecting the MCCB 50 to the electric circuit on the power supply side , 52Y, 52Z
And load-side terminals 53X, 53Y, 53Z for connecting the MCCB 50 to the load-side electric circuit. Note that 54
X, 54Y and 54Z are power supply cables;
X, 55Y and 55Z are load distribution cables.

For connection of the current limiter 30 to the MCCB, for example, in the case of the power supply cable 54Z, the mounting hole 33A of the terminal plate 33 of the current limiter 30 is attached to the power supply side terminal 52Z of the MCCB 50 and screwed. And then the current limiter 3
This is performed by screwing the power supply cable 54Z on the power supply side into the mounting hole 32A of each of the terminal boards 32. Similar connections are made to the power supply cables 54X, 54Y and the MCCB 50.
The power supply cables 54X, 54Y, 54Z are connected to the MCCB 50 via the respective current limiters 30 by performing the operations for the power supply side terminals 52X, 52Y. On the other hand, load wiring cables are connected to the load-side terminals 53X, 53Y, and 53Z for each phase. Thereby, the current limiting device 30 is provided for each phase.
Will be connected to the wiring.

Then, terminals 35 and 36 of the capacitor 34 are connected to terminal plates 33 and 32 of the current limiter, respectively, so that the capacitor 34 is connected in parallel with the PTC element 31. At this time, the PTC element 31 and the capacitor 34
3 is shown in the circuit diagram of FIG. When a varistor is used instead of the capacitor 34, the circuit configuration is the same as that of FIG.

Next, as described above, the current limiting device 30
The operation of the MCCB 50 to which is attached will be described. First, in the normal state, that is, when the rated current flows, the operation switch 51 is operated to operate the opening / closing mechanism and the main contact is turned on to the electric circuit.
0 and the MCCB 50 are supplied to the load, and the rated current flows through this electric circuit. At this time, the current limiter 3
Since the resistance value of the PTC element plate 31 of 0 is small, power is supplied to the load with almost no power loss. The Joule heat generated in the PTC element 31 at this time is very small, and is radiated through the terminal plates 32 and 33.

On the other hand, when an overcurrent such as a short-circuit current flows in the electric circuit, the PTC element 31 is designed to generate heat instantaneously and start current limiting. When the current limit of the overcurrent by the PTC element 31 occurs, even if the resistance of the PTC element rapidly increases, the current does not decrease instantaneously due to the inductance of the wiring, but the overcurrent is connected in parallel to the PTC element 31. By flowing by bypassing the capacitor 34 or the varistor, generation of a surge voltage to the PTC element 31 is suppressed,
Dielectric breakdown and sudden heat generation of the PTC element 31 are prevented. Since the current maintaining action by the inductance is completed in a short time, the overcurrent is gradually limited. Then, within 0.02 seconds, the instantaneous tripping mechanism of the MCCB 50 operates to cut off the electric circuit and stop the overcurrent. Therefore, when the current limiter 30 is operated, the current value after the current limit is reduced by the MCCB 50.
By designing the characteristics of the PTC element 31 so as to be at least about 10 times the rated current value and not more than the maximum breaking capacity, the current breaking capacity of the MCCB 50 can be increased.

The embodiments of the current limiter of the present invention and the MCCB using the current limiter have been described above.
It should be understood that the present invention is not limited to such embodiments, and that various changes can be made without departing from the spirit of the present invention. For example, the shape of the PTC element in the present invention may be a circular or polygonal plate, or may be an elliptical cylinder or a polygonal cylinder.
It goes without saying that the shapes of the terminal plate and the heat radiator can be appropriately changed according to the shape of the PTC element and the like. In addition, a block-shaped PTC element having a low resistance can be used. Further, a plurality of capacitors and / or varistors connected in parallel with the PTC element may be used at the same time, and when attaching them to the MCCB, the capacitors and the like are fixed to an insulating ceramic body and the lead wires of the capacitors and the like are insulated. By using a capacitor component or the like connected to the electrode terminal provided on the ceramic body, it is possible to improve the workability of the mounting work.

[0028]

Hereinafter, the present invention will be described in more detail with reference to examples. Table 1 shows the surge bypass element and PT used in each of the current limiting devices of Examples 1 and 2 and Comparative Example.
The characteristics, shape, and the like of the C element were shown. In the first embodiment, a capacitor is used as a surge bypass element, and in the second embodiment, a varistor is electrically connected so as to be in parallel with the PTC element to constitute a current limiter, and a current limiter not using a surge bypass element is used. This was a comparative example. These current limiters were connected to the MCCB shown in Table 1 and a short circuit current cutoff test based on JIS-8370 was performed in the test circuit shown in Table 1.

[0029]

[Table 1]

Table 2 shows the test results. In the first and second embodiments of the present invention using the surge bypass element, the MCC
The maximum passing current passing through B is from 125 kA to 48 kA.
And was well blocked by MCCB. In the first embodiment using a capacitor as a surge bypass element, no surge voltage is generated, and the PTC at the time of current interruption is not generated.
The device temperature was 340 ° C. Furthermore, the PTC after the test
The state of the device was observed, but no abnormality was observed. Similarly, in the second embodiment using a varistor as a surge bypass element, the surge voltage is as small as the power supply voltage, and the generation of such a voltage does not cause a problem in the circuit. Temperature and condition after test
It was equivalent to Example 1.

On the other hand, in the comparative example not using the surge bypass element, the maximum passing current passing through the MCCB is limited from 125 kA to 48 kA,
Although cut off by the CB, a surge voltage of about six times the power supply voltage was generated, and the temperature of the PTC element also rose to 600 ° C., and the PTC element after the current cut off had a crack between the PTC element and the electrode. Occurrence was observed.

As described above, by connecting a surge bypass element such as a capacitor or a varistor in parallel to the PTC element, generation of a surge voltage and rapid heating of the PTC element due to the surge voltage are prevented, and the current limiter itself is protected. Was done.

[0033]

[Table 2]

[0034]

As described above, according to the current limiter and the circuit breaker of the present invention, the capacitor and / or the varistor are connected in parallel with the PTC element. , And a surge voltage generated when the resistance value rises sharply is suppressed, so that it is possible to prevent insulation breakdown of the PTC element and burn-in due to a rapid temperature rise. In addition, when an overcurrent such as a short-circuit current flows through an electric circuit by using a PTC element, the PTC element instantaneously reaches a phase transition temperature and is current-limited, so that the breaking current capacity of the MCCB increases. Therefore, even if a small-capacity MCCB is used, the same current interruption effect as when a large-capacity MCCB is used can be obtained, so that the installation cost of the MCCB can be significantly reduced, and replacement of parts, etc. Since there is almost no necessity, there is an advantage that the maintainability is excellent.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a current limiting device of the present invention.

FIG. 2 shows a circuit breaker (MCCB) for a current limiting device according to the present invention.
It is a top view which shows the example attached to.

FIG. 3 is a circuit breaker (MCCB) for a current limiting device according to the present invention.
FIG. 4 is a wiring circuit diagram when the device is attached to the device.

FIG. 4 is an explanatory diagram showing operating characteristics of a current limiting device using a conventional PTC element.

[Explanation of symbols]

Reference numeral 30: current limiter, 31: PTC element, 32: terminal plate, 32
A: mounting hole, 33: terminal plate, 33A: mounting hole, 34: capacitor, 35: terminal, 36: terminal, 50: MCCB,
51: operation switch, 52X / 52Y / 52Z: power supply side terminal, 53X / 53Y / 53Z: load side terminal, 54X /
54Y / 54Z ... Three-phase power supply cable, 55X / 55
Y / 55Z: Load wiring cable.

Claims (5)

[Claims] A PTC element having a positive temperature coefficient of resistance whose resistance value rapidly increases when a predetermined phase transition temperature is reached is provided in an electric circuit, and an overcurrent flows through the electric circuit, whereby the temperature of the PTC element is increased. A current limiter using a PTC element that suppresses an overcurrent by rapidly increasing its resistance when the temperature reaches the predetermined phase transition temperature, wherein a capacitor is provided for the PTC element. And / or a varistor is connected in parallel. 2. The circuit according to claim 1, wherein the short-circuit inductance of the wiring is L,
The current limiting resistor TC element when the R, the electrostatic capacitance C of the capacitor, 0.1L / R ² <C <limited according to claim 1, wherein a is in the range of 10L / R ² Sink. 3. The varistor generates a substantially constant varistor voltage below a predetermined varistor current, and the varistor voltage is 1 to 2 times a rated voltage of a wiring breaker to which the current limiting device is attached. 2. The current limiter according to claim 1, wherein the varistor current is equal to or greater than the breaking capacity of the circuit breaker. 4. When an overcurrent such as a short-circuit current flows in an electric circuit,
When the temperature rises and the temperature reaches a predetermined phase transition temperature, the resistance value sharply increases, and a PT that limits the overcurrent.
C element and a capacitor and / or
Or a circuit breaker for wiring, comprising a current limiter connected in parallel with a varistor. 5. The circuit breaker according to claim 4, wherein the current limiter provided in the circuit breaker is the current limiter according to any one of claims 1 to 3.