JPH11308763A - Current limiter with ptc element and circuit breaker with the current limiter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a current limiter that is capable of suppressing the break down of a positive temperature coefficient(PTC) element by preventing the temperature gradient from being generated, even if the PTC element reaches its resistance transition temperature. SOLUTION: A current limiter 10 is provided with a PTC element plate 11, consisting of first and second PTC elements 11a and 11b that are electrically connected in parallel. The second PTC element 11b is constituted by a PTC element that has a lower resistance and lower resistance change temperature than those of the first PTC element 11a at normal temperatures and a larger resistance change rate, after the resistance change. When a short-circuiting current flows in the current limiter 10, it first flows through the second PTC element 11b, but Joule heat is generated at the second PTC element 11b from self heating, and at the same time the first PTC element 11a is preheated due to this heat. When the second PTC element 11b reaches a resistance change temperature and the resistance is increased, though a short-circuiting current is commutated to the first PTC element 11a, it immediately reaches a resistance change temperature for limited flow since it has been preheated.

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 transmission / distribution system or power equipment disposed in the power transmission / distribution system from an overcurrent such as a short circuit current or an overload current flowing in the power transmission / distribution system. More particularly, the present invention relates to a current limiter using a PTC element and a circuit breaker using the current limiter.

[0002]

2. Description of the Related Art In recent years, in order to protect a power transmission / distribution system or power equipment disposed in the power transmission / distribution system from an overcurrent such as a short-circuit current or an overload current flowing through the power transmission / distribution system, the resistance value increases due to an increase in temperature. Having a positive temperature coefficient of resistance (PTC (Positive Temperature Coefficien)
t) A thermistor, hereinafter referred to as a PTC element) has been proposed to be used for an electric circuit of a power transmission and distribution system.

[0003] When this PTC element is used in conjunction with a circuit breaker in a power transmission and distribution system, for example, if an overcurrent exceeding the rated current flows through this system for some reason, Joule heat is generated in the PTC element. The temperature of the PTC element increases.
Then, since this PTC element has a positive temperature coefficient of resistance, when the temperature of the PTC element becomes higher than a predetermined resistance transition temperature (or phase transition temperature: hereinafter, referred to as a resistance transition temperature), the resistance value sharply increases. The overcurrent flowing through the lever system is suppressed (current limit). Thereafter, the circuit breaker operates to cut off the circuit. On the other hand, after the accident has recovered,
When the temperature of the TC element returns to normal temperature, the resistance value returns to the original low resistance value, so that the PTC element automatically recovers, and when the circuit breaker is turned on again, a normal predetermined load current is applied to this system. It will flow.

A PTC element of this type is manufactured by mixing a conductive material into a ceramic as a base material and sintering the mixed material. When mixing the conductive material, it is mixed so as to be uniformly dispersed in the ceramic as the base material. However, when manufacturing a PTC element having a large cross-sectional area, it is necessary to obtain an element in which the conductive material is uniformly dispersed. It is difficult, and PTC elements having different resistance values are formed at respective portions of the cross section. As described above, when a current flows through a PTC element having a different resistance value at each portion of the cross section, the current density at each portion of the cross section varies due to the different resistance value.

[0005] If the current density varies, the self-heating based on the Joule heat naturally differs in each part of the cross section. For this reason, a steep temperature gradient is formed inside the PTC element, and a difference in thermal expansion occurs in each part, and there is a problem that the PTC element is eventually broken by thermal stress.

Therefore, a PTC element capable of preventing the element from being broken has been proposed in Japanese Patent Application Laid-Open No. 8-236303. The PTC element proposed in Japanese Patent Application Laid-Open No. H8-236303 subdivides the PTC element, and separates the subdivided PTC elements by honeycomb-shaped partition walls. As described above, if each PTC element is separated by a partition, even if one PTC element is destroyed, this destruction is interrupted by the partition, so that the PTC element as a whole is not destroyed. Become.

[0007]

However, the PTC proposed in the above-mentioned Japanese Patent Application Laid-Open No. 8-236303 has been proposed.
In the element, since the resistivity or shape (for example, cross-sectional area, length) of each subdivided PTC element is not taken into account, the resistance value of each subdivided PTC element by the partition wall varies. There is a variation. For this reason, when an overcurrent such as a short-circuit current flows through a current limiting device constituted by each PTC element subdivided by such a partition, the temperature rise of each PTC element varies, and as a current limiting device, It will have a temperature distribution.

In the case where the resistance value of each PTC element has a large variation, if an overcurrent such as a short-circuit current flows through the current limiting device, a sharp temperature gradient is generated in the current limiting device, and this is caused by thermal stress. The current limiter is destroyed. In addition, when the resistance value of each PTC element has a large variation, the current concentrates on the PTC element having a low resistance value. Therefore, the PTC element with the concentrated current generates Joule heat due to the concentrated current. To the resistance transition temperature.

As a result, the PTC element in which the current is concentrated has a sudden increase in resistance and exhibits a current limiting effect. However, other PTC elements having a high resistance value do not reach the resistance transition temperature and have a current limiting effect. Cannot be exhibited. As a result, since only a part of the PTC elements exerts the current limiting effect as the current limiting device, there is a problem that the predetermined current limiting effect cannot be exerted as the entire current limiting device.

[0010]

Means for Solving the Problems and Action / Effect of the Invention The present invention provides a method of heating a PTC element uniformly to a vicinity of a predetermined resistance transition temperature by external heating or internal heating in advance to obtain a predetermined resistance transition caused by an overcurrent. Self-heating required to reach the temperature can be reduced. Therefore, PTC
It is based on the knowledge that the PTC element can reach the resistance transition temperature without a temperature gradient even if the resistance value inside the element varies,
It is an object of the present invention to prevent a temperature gradient from occurring even when the PTC element reaches its resistance transition temperature and to obtain a current limiter capable of suppressing the destruction of the PTC element.

Therefore, the current limiter of the present invention comprises a first PTC element having a PTC element electrically connected in parallel with a second PTC element.
The second PTC element is constituted by a PTC element having a lower resistance value at normal temperature and a lower resistance transition temperature than the first PTC element and a higher rate of change in resistance after the resistance transition. When the second PTC element is configured as described above,
In a state where a current equal to or lower than the normal rating flows, the current flows through the second PTC element having a low resistance value at normal temperature. At this time, since Joule heat is generated based on the resistance value of the second PTC element, the second PTC element is self-heated, and the first PTC element is heated by the heat based on the heat generated by the second PTC element.

As a result, the first and second PTC elements are heated to a temperature near the resistance transition temperature of the second PTC element. In such a state, when an overcurrent such as a short-circuit current flows in the electric circuit to which the current limiter is connected, the second P due to Joule heat based on the overcurrent.
The TC element shifts to a resistance transition temperature and its resistance value increases. Thus, the overcurrent based on the short-circuit current is reduced to the first PTC
The first PTC element reaches the resistance transition temperature by Joule heat based on the overcurrent. At this time, the second
Since the rate of resistance change after the resistance transition of the PTC element is large, this overcurrent is suppressed (current-limited) by the first PTC element.

When the second PTC element is disposed directly around the side wall of the first PTC element, the second PTC element
When Joule heat is generated based on the resistance value of the element, the first
Since the PTC element is directly heated from around the side wall by the self-heating of the second PTC element, the first PTC element is
The element is efficiently heated to a temperature near the resistance transition temperature of the TC element. For this reason, when the overcurrent based on the short-circuit current is commutated to the first PTC element, the first PTC element can immediately reach the resistance transition temperature.

Further, if a heat storage material is provided on at least the outer surface where the second PTC element is exposed, and a heat radiator having good thermal conductivity is provided on the outer surface of the heat storage material, the heat is immediately generated when the second PTC element generates heat. The heat is transferred to the first PTC element and stored in the heat storage material, and the heat stored in the heat storage material is radiated from the radiator. As a result, the second P
The TC element is always maintained at a temperature near the resistance transition temperature of the second PTC element.

Further, the PTC element made of cristobalite-based ceramics has a lower resistance value and a lower resistance transition temperature at room temperature and a larger rate of resistance change after the resistance transition than the PTC element made of titanium-based ceramics.
Since it is an element, the first PTC element is preferably made of a titanium-based ceramic, and the second PTC element is preferably made of a cristobalite-based ceramic.

On the other hand, according to the present invention, one terminal of the above-described current limiter is connected to the power supply side of the electric circuit, the other terminal of the current limiter is connected to one terminal of the circuit breaker, and the other terminal of the circuit breaker is connected to the other terminal. Circuit breaker is connected to the load side of the circuit, and if an overload current exceeding the rated current flows in the circuit,
The C element should not reach the resistance transition temperature,
When an overcurrent such as a short-circuit current flows in the circuit, each PTC element of the current limiter reaches a resistance transition temperature to suppress the overcurrent, and the overcurrent or overload current is set in the circuit for a predetermined time. Only when the current flows continuously, the overcurrent or overload current is cut off.

By configuring the circuit breaker in this way,
When a short circuit occurs in the circuit and a short-circuit current flows through this breaker, the current limiter suppresses (limits) the short-circuit current, so the breaking capacity of this type of breaker can be greatly improved. Becomes If the current limiter having the PTC element described above is connected to this circuit breaker and used, the current limiter having the PTC element has a large current limiting effect, so that a circuit breaker excellent in breaking capacity can be obtained. become.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of a current limiter including a PTC element according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a schematic configuration of a current limiter including the PTC element of the present embodiment, and FIG. 1A is a perspective view of the current limiter.
FIG. 2B is a perspective view schematically showing a schematic configuration of a PTC element used in the current limiting device of FIG.

As shown in FIG. 1, a current limiting device 10 according to the present invention has an upper terminal plate 12 and a lower terminal plate 13 connected to upper and lower surfaces of a PTC element plate 11 formed in a thin plate shape.
A heat accumulator 14 for absorbing heat generated when the PTC element plate 11 generates heat is connected to the terminal plate 12 in close contact with the upper portion of the heat sink 2, and a radiator 16 is disposed on the heat accumulator 14 via an insulating plate 15. The structure to be installed is adopted.

Here, the PTC element plate 11 has a structure in which a first PTC element 11a is provided therein, and a second PTC element 11b is provided on an outer peripheral portion of the first PTC element 11a.
The first 1PTC element 11a, room temperature resistivity [rho ₀₁ (e.g., ρ ₀₁ = 1Ω · cm) with a small, rate of increase in resistance against cold resistivity [rho ₀₁ (e.g., 1 normal temperature resistivity [rho ₀₁
000 times) and its resistance transition temperature (Tc1)
Of lead titanate (PbTiO ₃ ) with a temperature of about 260 to 300 ° C.
It is preferable to use ceramics, bismuth titanate (BiTiO ₃ ) ceramics, or titanium-based ceramics composed of a solid solution of these. The first PTC element 11a made of this titanium-based ceramic is represented by a curve A in FIG.
Has a temperature (° C.)-Resistivity (ρ) characteristic as shown in FIG.
1), the resistivity (ρ) becomes maximum (ρmax1).

The second PTC element 11b has a small room temperature resistivity ρ ₀₂ (for example, ρ ₀₂ = 0.1 Ω · cm), and has a resistance increasing ratio with respect to the room temperature resistivity ρ ₀₂ (for example, the room temperature resistivity ρ _02). It is preferable to use cristobalite-based ceramics whose resistance transition temperature (Tc2) is about 200 to 240 ° C. A second cristobalite-based ceramic
The PTC element 11b has a temperature (° C.)-Resistivity (ρ) characteristic as shown by a curve B in FIG.
When the resistance transition temperature (Tc2) reaches 00 to 240 ° C., the resistivity (ρ) becomes the maximum (ρmax2).

In this embodiment, the first PTC element 11a made of the titanium-based ceramic is formed in a thin plate shape, and the first PTC element 11a formed in the thin plate shape is formed.
A second PTC element 11b made of cristobalite-based ceramics is formed in a frame shape and fixedly in contact with the outer peripheral portion of the C element plate.

The terminal plates 12 and 13 are formed of a metal having good conductivity and good heat conductivity, such as copper, aluminum and stainless steel, in a strip shape. Then, these two terminal plates 12 and 13 are sandwiched in the thickness direction of the PTC element plate 11 so that a current flows in the thickness direction of the PTC element plate 11, and are bonded, brazed or welded with a conductive adhesive. And is integrated with the PTC element plate 11. In this way, the terminal plates 12, 13 are PT
When connected to the C element plate 11, the thin PTC element plate 11
Since the direction of conduction of each of the PTC elements 11a and 11b is in the direction of its thickness, each of the PTC elements 1
Even if a current flows in 1a and 11b, the conduction resistance is reduced and the power loss is reduced. In addition, these two terminal boards 1
Mounting holes 12a and 13a are provided at the respective ends of the members 2 and 13.

The regenerator 14 includes a metal container made of a metal having good thermal conductivity such as copper, aluminum, and stainless steel, and a low melting point metal (for example, a lead-tin alloy, Low melting point of solder etc. (for example, 130-1
50 ° C.). The heat storage unit 14 is fixed to at least one of the terminal plates 12 and 13 by bonding with an adhesive, brazing, welding, or the like (FIG. 1 shows an example in which the heat storage unit 14 is disposed on the terminal plate 12 side). ) To be integrated with both terminal boards 12 and 13. Therefore, the PTC element plate 11, the two terminal plates 12, 13 and the regenerator 14 are integrated. The regenerator 14 is made of copper,
It may be made of a metal body having a large heat capacity such as tin or lead. In this case, the configuration of the heat storage unit 14 is simplified, and the heat storage unit 14 can be manufactured at low cost.

As a result, when an overload current flows through the PTC element plate 11 and the first PTC element 11a of the PTC element plate 11 generates heat due to the Joule heat, the generated heat is conducted to the regenerator 14. Then, the low melting point metal sealed and filled in the metal container absorbs this heat and melts when reaching the melting point. Thereby, the first P of the PTC element plate 11
Even if an overload current flows through the TC element 11a for a long time and the first PTC element 11a of the PTC element plate 11 generates heat, this heat is sequentially converted into heat of fusion of the low melting point metal. The first first PTC element 11a can be prevented from reaching the resistance transition temperature (Tc1 = 260 to 300 ° C.), and does not affect the operation of an MCCB (circuit breaker) described later.

The radiator 16 is composed of a radiator fin in which a plurality of fins 16a are integrally formed on a plate made of aluminum alloy having good thermal conductivity. In order to electrically insulate the heat radiator 16 from the heat accumulator 14, it is integrally fixed to the upper portion of the heat accumulator 14 via an insulating plate 15 having good heat resistance. Thereby, the heat generated by the first PTC element 11a of the PTC element plate 11 stored in the heat storage unit 14 is released from the radiator 16 to the outside air.

As described above, the current limiting device 10 of the present invention is configured, and the terminal plate 12 having the mounting hole 12a connected to the electric circuit on the power supply side is fixed to one surface of the PTC element plate 11,
Since the terminal plate 13 having the mounting hole 13a connected to the electric circuit on the load side is fixed to the other surface of the PTC element plate 11, the direction of conduction of the thin PTC element plate 11 is in the thickness direction. in the state where the flowing rated current during steady, low room temperature resistivity [rho ₀₂ of the PTC element plate 11 first 2P
Although flowing through the TC element 11b, the second PTC element 11
In the case of b, since the normal temperature resistivity ρ ₀₂ is low, the conduction resistance decreases and the power loss decreases. At this time, when the second PTC element 11b generates heat by Joule heat, the generated heat is converted to the first PTC element 11b.
The first PTC element 11a is also heated by conducting heat to the TC element 11a.

When an overload current exceeding the rated current flows, the Joule heat causes the second PT of the PTC element plate 11 to move.
When the C element 11b generates heat, the generated heat is transferred to the first PT.
It conducts heat to the C element 11a and also to the regenerator 14. As a result, the first PTC element 11a is also heated, but even if an overload current flows through the second PTC element 11b for a long time and the second PTC element 11b generates heat, this heat is successively absorbed by the heat accumulator 14 and Heat storage 14
Is absorbed by the heat radiator 16 and the second P
The TC element 11b can be prevented from reaching the resistance transition temperature (Tc1), and the first PTC element 11a
The temperature is maintained near the resistance transition temperature (Tc2) of the TC element 11b.

On the other hand, when a short circuit current flows in the electric circuit, P
The second PTC element 11b of the TC element plate 11 generates heat due to Joule heat caused by the short-circuit current, and the PTC element plate 1
When the resistance value of the second PTC element 11b reaches the resistance transition temperature (Tc1) and increases rapidly, the short-circuit current commutates to the first PTC element 11a of the PTC element plate 11.
At this time, if the second PTC element 11b generates heat due to Joule heat, the generated heat is conducted to the first PTC element 11a and the first PTC element 11a is also heated.
The PTC element 11a immediately reaches the resistance transition temperature (Tc2) due to the short-circuit current, and its resistance value rapidly increases, so that the short-circuit current is suppressed (current limit).

The current limiting device 20 of the modified example and the present modified example is shown in FIG.
As shown in the perspective view of (a), a PTC element formed in a columnar shape and used as a cylindrical PTC element body 21 is used, and the outer surface of the cylindrical PTC element body 21 has a cylindrical shape made of a heat storage material. The heat storage unit 22 is fixed by bonding with an adhesive, brazing or welding. The cylindrical regenerator 22 made of this heat storage material uses the same low melting point alloy as in the above-described embodiment, and is made of a metal having good heat conductivity and good conductivity such as copper, aluminum, and stainless steel. The container is filled and sealed. The cylindrical heat storage 22 made of a heat storage material may be made of a metal body having a large heat capacity, such as copper, tin, and lead. In this case, the manufacture of the cylindrical regenerator 22 becomes easy, and it becomes possible to manufacture it cheaply.

A cylindrical heat radiator 25 made of a material having good heat conductivity is fixed to the outer surface of the cylindrical heat accumulator 22 by bonding with an adhesive, brazing or welding. Note that a large number of radiating fins 25 a are formed on the outer surface of the cylindrical radiator 25. A first terminal body 23 and a second terminal body 24 are welded to both ends of the cylindrical PTC element body 21, respectively. The first terminal body 23 is a cylindrical PTC element body 2
1 and a main body 2 connected to the right end of the main body 1
A rising portion 23b that rises vertically from 3a is provided, and a mounting hole 23c is provided in the rising portion 23b. The second terminal body 24 is a cylindrical PTC element body 21.
A main body 24a (not shown) connected to the left end of the main body 24 and a rising portion 24b rising vertically from the main body 24a are provided, and a mounting hole 24c is provided in the rising portion 24b. These terminals 23 and 24 are formed of an aluminum alloy having good conductivity.

This cylindrical PTC element body 21 is shown in FIG.
As shown in the sectional view of (b), a first PTC element 21a is provided therein, and a second PTC element 21a is provided on the outer surface of the first PTC element 21a.
The structure includes the PTC element 21b. 1st PTC
The elements 21a, similar to the embodiments described above, room temperature resistivity [rho ₀₁ (e.g., ρ ₀₁ = 1Ω · cm) with a small, rate of increase in resistance against cold resistivity [rho ₀₁ (e.g., room temperature resistivity [rho ₀₁ of Lead titanate (PbTiO ₃ ) ceramics and bismuth titanate (B) having a large resistance transition temperature (Tc1) of about 260 to 300 ° C.
It is preferable to use iTiO ₃ ) ceramics or titanium-based ceramics made of these solid solutions. First PTC element 11a made of this titanium-based ceramic
Has a temperature (° C.)-Resistivity (ρ) characteristic as shown by a curve A in FIG.
When the resistance transition temperature (Tc1) is reached, the resistivity (ρ) becomes the maximum (ρmax1).

As the second PTC element 21b, a normal temperature resistivity ρ ₀₂ (for example, ρ
₀₂ = 0.1Ω · cm) and the room temperature resistivity ρ
₀₂ (for example, 10 at room temperature resistivity ρ ₀₂
000 times) and its resistance transition temperature (Tc2)
However, it is preferable to use cristobalite-based ceramics having a temperature of about 200 to 240 ° C. The second PTC element 11b made of cristobalite-based ceramic has a temperature (° C.)-Resistivity (ρ) characteristic as shown by a curve B in FIG. 2, and has a resistance transition temperature (200 ° C. to 240 ° C.). Tc2), the resistivity (ρ) becomes maximum (ρmax)
2)

In the present modification, the first PTC element 21a made of the titanium-based ceramic is formed in a cylindrical shape, and the first PTC element 21a formed in the cylindrical shape is formed.
A second PTC element 21b made of cristobalite-based ceramic is formed in a cylindrical shape and fixedly in contact with the outer peripheral portion of the element 21a.

The current limiting device 20 of the present modified example configured as described above
In the state where the rated current in the steady state flows, the second PT in which the room temperature resistivity ρ ₀₂ of the PTC element body 21 is low is low.
Although flowing through the C element 21b, the second PTC element 21b
Since the room temperature resistivity ρ ₀₂ is low, the conduction resistance is reduced and the power loss is reduced. At this time, when the second PTC element 21b generates heat by Joule heat, the generated heat is converted to the first PTC element 21b.
The first PTC element 21a is also heated by conducting heat to the C element 21a.

When an overload current exceeding the rated current flows, Joule heat causes the second PT of the PTC element body 21 to move.
When the C element 21b generates heat, the generated heat is transferred to the first PT.
It conducts heat to the C element 21a and also to the regenerator 22. As a result, the first PTC element 21a is also heated, but even if an overload current flows through the second PTC element 21b for a long time and the second PTC element 21b generates heat, this heat is successively absorbed by the heat accumulator 22 and Heat storage 22
Is absorbed by the heat dissipating body 25,
The PTC element 21b can be prevented from reaching the resistance transition temperature (Tc2), and the first PTC element 21a
The temperature is maintained near the resistance transition temperature (Tc2) of the PTC element 21b.

On the other hand, when a short-circuit current flows in the electric circuit, P
The second PTC element 21b of the TC element 21 generates heat due to Joule heat caused by the short-circuit current, and the PTC element 2
When the first second PTC element 21b reaches the resistance transition temperature (Tc1) and its resistance value sharply increases, this short-circuit current is commutated to the first PTC element 21a of the PTC element body 21.
At this time, when the second PTC element 21b generates heat by Joule heat, the generated heat is conducted to the first PTC element 21a and the first PTC element 21a is also heated.
The PTC element 21a immediately reaches the resistance transition temperature (Tc2) due to the short-circuit current and rapidly increases its resistance value, so that the short-circuit current is suppressed (current limit).

2. Circuit Breaker with Current Limiter An embodiment of the circuit breaker with the current limiters 10 and 20 described above will be described below with reference to FIGS. 4 and 5. As shown in FIG. 4, the circuit breaker 100 includes a current limiter 10 (20) including the above-described PTC element, and a switch 100a connected in series to the current limiter 10 (20). The circuit breaker 100 is connected in series between the AC power supply 110 and the load 120 on the electric circuit L including the AC power supply 110 and the load 120.

FIG. 5 is a front view showing the outer shape of a circuit breaker (MCCB) 100. The circuit breaker 100 includes a main contact 100a connected in series to a current limiter 10 (20) on an electric circuit, and a main contact 100a (not shown). An opening / closing mechanism (not shown) for opening and closing the main contact 100a, an arc-extinguishing chamber (not shown) for extinguishing an arc generated when the main contact 100a is opened, and an overload current or a short-circuit current Release the opening and closing mechanism to release the main contact 100
a switch for tripping the main contact 100a into the electric circuit L by operating the opening / closing mechanism, and a power supply side for connecting the circuit breaker 100 to the electric circuit L on the power supply side. Terminals 102 </ b> X, 102 </ b> Y, 102 </ b> Z and a load-side terminal (not shown) for connecting the circuit breaker 100 to the load-side electric circuit L are provided.

The current limiting devices 10 (20), 10
Terminals 13 (24), 13 of (20), 10 (20)
(24), 13 (24) mounting holes 13a (24)
c), 13a (24c), 13a (24c)
00 and attached to the power supply side terminals 102X, 102Y, 102Z, respectively, and screwed down.
0 (20), 10 (20) terminals 12 (23), 12
(23), mounting holes 12a (23) of 12 (23)
c), 12a (23c), and 12a (23c) are respectively attached to the electric wires X, Y, and Z on the power supply side and screwed, so that the electric wires X, Y, and Z on the power supply side and the circuit breaker 100 are each current-limited. They are connected via devices 10 (20), 10 (20), 10 (20). On the other hand, a load-side electric wire is connected to a load-side terminal (not shown) for each phase. As a result, the circuit breaker 100 including the current limiter 10 (20) for each phase is connected to the electric circuit L.

Next, the operation of the circuit breaker 100 provided with the current limiter 10 for each phase connected as described above will be described. First, the normal operation will be described.
When the main contact 100a is inserted into the electric circuit L by operating the opening / closing mechanism by operating the power supply 110, the power of the power supply 110 is reduced.
The power is supplied to the load 120 (not shown) through (20) and the main contact 100a, and the rated current flows through the electric circuit L. At this time, the room temperature resistivity of the second PTC element 11b (21b) of the current limiter 10 (20) is
a (21a), the load current is smaller than the second PTC element 1
Although flowing through the first PTC element 11b (21b), since the normal temperature resistivity of the second PTC element 11b (21b) is small, power is supplied to the load 120 without power loss.

Here, an overload current (a current of 1.25 to 10 times the rated current) is applied to the load side of the electric circuit L for some reason.
When the flow is abnormal, the second P of the current limiter 10 (20)
The TC element 11b (21b) has a rated current of 1.25 to 1
0 times overload current flows and the Joule heat causes the second P
The TC element 11b (21b) generates heat. Then, the generated heat is thermally conducted to the first PTC element 11a (21a) and is thermally conducted to the heat accumulator 14 (22) to be stored. Then, the low melting point metal sealed and filled in the regenerator 14 (22) absorbs this heat and melts when reaching the melting point. Further, the heat stored in the heat storage device 14 (22) is conducted to the radiator 16 (25) and the fins 16a (25).
a) It is released to the outside.

Thus, the second PTC element 11b (21
b) the overload current flows for a long time and the second PTC
Even if the element 11b (21b) generates heat, this heat is successively converted into the heat of fusion of the low melting point metal in the regenerator 14 (22), so that the second PTC element 11b (21b) has a resistance transition temperature (Tc2 = (200 to 240 ° C.), and the first PTC element 11a (21a) is heated and maintained at a temperature near the resistance transition temperature of the second PTC element 11b (21b). At this time, if an overload current of 1.25 to 10 times the rated current (In) continues to flow through circuit breaker 100 for a long time, a predetermined time (10 seconds to 120 seconds) corresponding to the overload current is set. After elapse of (minutes), the tripping device of the circuit breaker 100 operates to release the switching mechanism and trip the main contact 100a, so that the load 120 is cut off from the power supply 110 and the overload current does not flow through the electric circuit L.

On the other hand, when a short-circuit accident occurs at the point X on the load side of the electric circuit L and a short-circuit current flows through the electric circuit L,
Second PTC element 11b (21b) of current limiter 10 (20)
Since an excessive short-circuit current flows through the first PTC element 11b (21b), the second PTC element 11b (21b) generates heat by the Joule heat, and this heat is conducted to the first PTC element 11a (21a) to heat the first PTC element 11a (21a). Is done.
Then, the generated heat causes the second PTC element 11b (21
When b) reaches the resistance transition temperature (Tc2 = 200 to 240 ° C.), the resistivity (ρ) of the second PTC element 11b (21b) reaches the maximum value (ρmax2).

The maximum value (ρmax2) of the resistivity (ρ) of the second PTC element 11b (21b) is equal to the first PTC element 11a.
(21a) is higher than the maximum value (ρmax1) of the resistivity (ρ), and the resistance transition temperature (Tc1 = 260 to 300 ° C.) of the first PTC element 11a (21a) is the resistance transition temperature of the second PTC element 11b (21b). (Tc2 = 200-
240 ° C.), the short-circuit current is higher than the first PTC element 1
Commutated to 1a (21a). At this time, since the first PTC element 11a (21a) has been heated in advance by the heat generated by the second PTC element 11b (21b), the first PTC element 11a (21a) immediately reaches the resistance transition temperature (Tc1 = 260 to 300 ° C.). Maximum value (ρmax) of the resistivity (ρ)
Therefore, the operation for suppressing (current limiting) the short-circuit current is started.

As a result, the short-circuit current is suppressed (current limit) and 0.02 seconds (5 seconds) after the start of the suppression operation.
Within one cycle at 0 Hz), the opening operation of the main contact 100a of the circuit breaker 100 ends, and the load 120
The short circuit current flowing to the point X is interrupted because the short circuit current does not flow through the electric circuit L due to the interruption at 10. Thereby, the temperature rise of the first PTC element 11a is suppressed, and the first PTC element 11a has a negative temperature coefficient of resistance (NTC (Nega
tive Temperature Coefficient)) The temperature does not rise before reaching the area, and the first PTC
The element 11a is not destroyed.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a schematic configuration of a current limiter provided with a PTC element of the present invention, FIG. 1 (a) is a perspective view of the current limiter, and FIG. P used for the current limiter of 1 (a)
It is a perspective view which shows typically the schematic structure of a TC element.

FIG. 2 shows a first PTC element and a second PTC element used in the current limiter of FIG.
FIG. 4 is a diagram illustrating a relationship between the temperature and the resistivity of the PTC element.

FIG. 3 is a diagram schematically showing a schematic configuration of a current limiter including a PTC element according to a modification of the present invention, and FIG. 3 (a) is a perspective view of the current limiter, and FIG. 3) is a sectional view showing a vertical section of FIG.

FIG. 4 is an electric circuit diagram showing a state where the current limiting device of FIGS. 1 and 2 is connected to an electric circuit L such as a distribution system together with a circuit breaker.

FIG. 5 is a diagram showing an appearance of the circuit breaker and a state where a current limiter is connected to the circuit breaker.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Current limiter provided with PTC element, 11 ... PTC element board, 11a ... First PTC element, 11b ... Second PTC element, 12 ... Upper terminal board, 13 ... Lower terminal board, 14 ... Regenerator, 15 ... Insulating board , 16 radiator, 20 current limiter provided with PTC element, 21 cylindrical PTC element, 21a first PTC element, 21b second PTC element, 22 cylindrical heat storage, 23, 24 terminal , 25 ... Cylindrical radiator, 1
00: Circuit breaker (MCCB), 100a: Main contact, 110
... power supply, 120 ... load, L ... electric circuit

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Naogo Okada 2-56 Suda-cho, Mizuho-ku, Nagoya-shi, Aichi Japan Inside Nihon Insulator Co., Ltd.

Claims (5)

[Claims] 1. A PT having a positive temperature coefficient of resistance that suppresses the overcurrent by rapidly increasing its resistance value when a predetermined resistance transition temperature is reached by a rise in temperature due to the flow of an overcurrent.
A current limiter including a C element, wherein the PTC element is composed of a first PTC element and a second PTC element electrically connected in parallel, and the second PTC element has a resistance at room temperature higher than that of the first PTC element. And a current limiter comprising a PTC element having a low resistance transition temperature and a large resistance change rate after the resistance transition. 2. The current limiter according to claim 1, wherein the second PTC element is arranged directly around a side wall of the first PTC element. 3. A heat storage material is provided on at least the outer surface where the second PTC element is exposed, and a heat radiator having good thermal conductivity is provided on the outer surface of the heat storage material. 3. A current limiter comprising the PTC element according to 2. 4. The current limiting device having a PTC element according to claim 1, wherein the first PTC element is made of a titanium-based ceramic, and the second PTC element is made of a cristobalite-based ceramic. vessel. 5. A current limiter according to claim 1, wherein one terminal of the current limiter is connected to a power supply side of an electric circuit, and the other terminal of the current limiter is connected to one terminal of a circuit breaker. Connected, the other terminal of the circuit breaker is connected to the load side of the circuit, when the overload current of the rated current or more flows in the circuit, each PTC element of the current limiter is When an overcurrent such as a short-circuit current flows in the electric circuit, each PTC element of the current limiter reaches the resistance transition temperature to suppress the overcurrent so that the electric circuit does not reach the resistance transition temperature. Wherein the overcurrent or the overload current is interrupted when the overcurrent or the overload current continuously flows for a preset time.