JPH10275711A - Ptc current limiter provided with backup function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a PTC current limiter using a PTC element of superior backup function. SOLUTION: A PTC current limiter is constituted with a composite PTC element body 10a, a first metal electrode plate 15 connected with a 15a in between and a second metal electrode plate 16 connected with a fix-bonding metal foil 16a in between. The composite PTC element body 10a is constituted with a first PTC element plate 11, a low heat quantity fusing point metal foil 12 fix-bonded to the top of the first PTC element plate 11, a thermal accumulator 13 fix-bonded to the top of the low heat quantity fusing point metal foil 12, and a plate-like second PTC element plate 14, fix-bonded to the top of the thermal accumulator 13, in which a temperature at which a resistance value increases is higher and amounts of energy and current for increase of resistance are larger than the first PTC element plate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to protection of power equipment disposed in a power transmission line such as a transmission / distribution system or a power transmission / distribution system from an overcurrent such as a short-circuit current or an overload current flowing in a power supply line such as a power transmission / distribution system. More particularly, the present invention relates to a PTC current limiter having a backup function and configured using a plurality of PTC elements having different temperatures at which resistance values increase.

[0002]

2. Description of the Related Art In recent years, in order to protect power equipment disposed in an electric circuit such as a power transmission / distribution system or a power transmission / distribution system from an overcurrent such as a short-circuit current flowing in the power transmission / distribution system, a resistance value increases due to an increase in temperature. It has been proposed to use a current limiter including an element having a positive temperature coefficient of resistance (PTC (Positive Temperature Coefficient) thermistor, hereinafter referred to as a PTC element) for an electric circuit of a transmission and distribution system.
When a current limiter equipped with this PTC element is used in conjunction with a circuit breaker on the electric circuit of the power transmission and distribution system, for example, if an overcurrent such as a short-circuit current flows through this electric circuit, Joule heat is generated in the PTC element. As a result, the temperature of the PTC element rises. Then, since the PTC element has a positive temperature coefficient of resistance, when the temperature of the PTC element rises and becomes equal to or higher than a predetermined resistance transition temperature (or phase transition temperature), the resistance value sharply increases,
The overcurrent flowing in the electric circuit is suppressed (current-limited), and the circuit is cut off by operating the circuit breaker thereafter. Meanwhile, after the accident recovered, PT
When the temperature of the C element returns to normal temperature, the resistance value returns to the original low resistance value, so that the PTC element automatically returns. After that, when the circuit breaker is turned on again, a normal predetermined current flows through this circuit. It will flow.

[0003]

However, if the PTC element used for the current limiter is a single PTC element, if the rate of increase of the overcurrent flowing through the electric circuit is higher than the rate of temperature rise of the PTC element, The PTC element has a problem that a predetermined increase in resistance cannot be obtained and a current limiting operation cannot be performed. Further, if an abnormal short-circuit current flows and an abnormal surge voltage is generated at the same time, an excessive stress is applied to the PTC element, so that the PTC element penetrates or flashes over, and the PTC element is destroyed. The problem also arises.

Therefore, the present invention has been made in view of the above-mentioned problems, and a PTC element which operates at an overcurrent at different temperatures at which the resistance value increases, and a PTC element which constantly operates in response to an overcurrent.
Based on the knowledge that if a PTC element that operates when a TC element fails is used in combination, an overcurrent prevention function can be exerted if the other PTC element operates even if the constantly operating PTC element is destroyed. An object of the present invention is to provide a PTC current limiter having an excellent backup function.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a PTC current limiter having a backup function and configured using a plurality of PTC elements having different temperatures at which the resistance value increases. In order to solve the problem, according to the first aspect of the present invention, the first PTC element plate and the first PTC element plate whose resistance value rapidly increases at a predetermined temperature are increased.
A plate-like second P having a higher temperature at which the resistance value increases than the C element plate and a large amount of energy and current leading to an increase in resistance.
A composite PTC element formed by electrically connecting at least two PTC element plates with a TC element plate in series, and metal electrode plates electrically connected to both surfaces of the composite PTC element, respectively. I have to.

With such a composite PTC element body, the first PTC element plate and the second
Since the resistance value of the PTC element plate at room temperature is small, the current supplied to the electric circuit flows through the first PTC element plate and the second PTC element plate. On the other hand, when an overcurrent such as a short-circuit current flows through this electric circuit due to an accident such as a short circuit, the resistance value of the first PTC element plate having a lower temperature at which the resistance value increases than the second PTC element plate increases, and current limiting operation is performed. .

When the accident is resolved and the power supply to the electric circuit is resumed, the first PTC element plate and the second PTC
As the current flows through the TC element plate,
When the temperatures of the first PTC element plate and the second PTC element plate gradually decrease, and the temperatures of the first PTC element plate and the second PTC element plate reach normal temperature, a normal load current flows through the electric circuit.

Further, when the first PTC element plate is damaged and does not function as a PTC element for some reason, the resistance value of the second PTC element plate increases to perform a current limiting operation. For this reason, a composite PT with a backup function
It is possible to operate as a C element body, and the reliability of this type of current limiter is improved, and the reliability of a power transmission and distribution system including this PTC current limiter is improved.

A PT having such a backup function
An important point of the C current limiter is that if the first PTC element plate is damaged, the damage can be easily known. Therefore, in the invention described in claim 2, when the first PTC element plate is damaged, that is, arc heat generated thereafter due to dielectric breakdown of the first PTC element plate itself,
Alternatively, a low-calorie melting point metal foil that melts and evaporates due to the amount of heat such as partial heat generated by partial current concentration or the like may be used as the first PT.
The first PTC element plate is disposed on the surface of the C element so that the first PTC element plate is damaged by the evaporated metal and the damage of the first PTC element plate can be displayed.

By providing such a low-calorie metal foil, when a large amount of heat is generated when the first PTC element plate is damaged and destroyed for some reason, the low-calorie metal foil melts and evaporates. . Due to the evaporation of the low-calorie melting point metal foil, the surroundings of the PTC current limiter may be discolored or an abnormal odor may be generated due to soot or the like generated when the metal foil is re-solidified. Thus, when the circuit breaker is turned on, it is possible to easily detect that the first PTC element plate has failed.

According to the third aspect of the present invention, the low-calorie metal foil may be a metal that melts, evaporates and solidifies to become soot, a metal that melts and evaporates to blow out a gas, or a metal that melts and evaporates to discolor. Metal.

As described above, when the low-calorie metal foil is formed of a metal that melts, evaporates, and solidifies with heat generated at the time of failure due to destruction of the first PTC element plate or the like, the surroundings of the PTC current limiter during solidification are formed. Since the soot adheres to the first PTC element plate, it is possible to easily detect that the first PTC element plate has failed. In addition, if a low-calorie metal foil is formed from a metal that melts and evaporates and a gas is blown out, an abnormal smell is generated around the PTC current limiter, so that it is easy to detect that the first PTC element plate has failed. Becomes possible. further,
When a low-calorie melting point metal foil is formed from a metal that discolors by melting and evaporating, the surroundings of the PTC current limiter change color, so that the failure of the first PTC element plate can be easily detected.

[0013] In the invention described in claim 4, the first P
Between the TC element plate and the second PTC element plate, a heat accumulator for absorbing heat generated by the first PTC element plate or the second PTC element plate and storing the heat is interposed. By providing such a heat accumulator, when the first PTC element plate or the second PTC element plate generates heat, the generated heat is conducted to the heat accumulator. Then, even if an overload current flows through the first PTC element plate or the second PTC element plate for a long time, and the first PTC element plate generates heat, the heat is successively absorbed by the regenerator, so that the first PTC element plate or the second PTC element plate is heated.
The TC element plate can be prevented from reaching the resistance transition temperature (or the phase transition temperature).

According to the present invention, the surface area of the metal electrode plate is increased by the first PTC on both surfaces of the composite PTC element body.
The metal plate is formed so as to be smaller than the surface area of the element plate and the second PTC element plate, and the metal electrode plate is arranged so that the surfaces of the peripheral portions of the first PTC element plate and the second PTC element plate are exposed. Thus, the first PTC element plate and the second PT
When the peripheral portions of the respective surfaces of the C element plate are formed so as to be exposed, it is possible to maintain a sufficient dielectric strength between the end faces of the two electrode plates, so that the first PTC element plate and the second PTC element plate can be maintained. Even if either of them reaches the resistance transition temperature (or the phase transition temperature), the resistance value increases rapidly and an overvoltage occurs between the end faces of both electrode plates due to the resistance drop voltage, but the flashover occurs between the end faces of both electrode plates. Can be prevented from occurring.

In the invention described in claim 6, the metal electrode plate is chamfered at its corner to form a plate having a substantially square planar shape with rounded corners.
If the corners of the two electrode plates are rounded in this manner, the electric field at the corners becomes equal to the electric field at the other portions and the current density becomes uniform, so that the electric current density becomes uniform. Current is concentrated in the first PTC element plate or the second PTC element plate.
It is possible to prevent the TC element plate from locally reaching the resistance transition temperature (or the phase transition temperature), and prevent the first PTC element plate and the second PTC element plate from locally deteriorating.

In the invention according to claim 7, the composite P
The corner of the side wall of the TC element body is chamfered so that the corner of the side wall is rounded. As described above, when the corner portion of the side wall of the composite PTC element body is chamfered so that the corner portion is rounded, the electric field at the corner portion of the side wall of the composite PTC element body becomes equal to the electric field of the other portion.
Since the current density is also uniform, local deterioration of the composite PTC element body can be prevented.

In the invention described in claim 8, the first P
The first PTC element plate, the second PTC element plate, the second PTC element plate, the metal electrode plate, and the first PTC element plate, the second PTC element plate, the metal electrode plate, Are fixed to each other. When each electrode plate and each PTC element plate are fixed in this manner, the contact area of these fixing surfaces increases, so that the contact resistance decreases and a composite PTC element body with low internal resistance can be obtained.

According to the ninth aspect of the present invention, the fixing metal foil is made of a metal having a lower hardness than the first PTC element plate, the second PTC element plate and the metal electrode plate, or the first PTC element plate.
It is made of a metal having a smaller surface roughness than the element plate, the second PTC element plate and the metal electrode plate. A metal foil formed of a metal having such a relationship of hardness or surface roughness is arranged between the first PTC element plate and the electrode plate and between the second PTC element plate and the electrode plate, and both surfaces of these two electrode plates are made of metal foil. When pressed by applying compressive stress that deforms
The metal foil is deformed and tightly bonded and fixed via each PTC element plate, electrode plate and metal foil. As a result,
It is possible to reduce the contact resistance of the respective joints between the first PTC element plate and the electrode plate and between the second PTC element plate and the electrode plate.

According to the tenth aspect of the present invention, the fixing metal foil is made of a metal having a higher hardness than the first PTC element plate and the second PTC element plate and a lower hardness than the metal electrode plate, or a first PTC element plate and the second PTC element plate. It is formed from a metal having a larger surface roughness than the element plate and a smaller surface roughness than the metal electrode plate. A metal foil formed of a metal having such a relationship of hardness or surface roughness is used as a first metal foil.
Even when disposed between the PTC element plate and the electrode plate and between the second PTC element plate and the electrode plate, when both surfaces of these two electrode plates are pressed by applying compressive stress such that the metal foil is deformed, the metal foil is deformed and The PTC element plate and the electrode plate are tightly bonded and fixed via the metal foil. As a result, it is possible to reduce the contact resistance of each joint between the first PTC element plate and the electrode plate and between the second PTC element plate and the electrode plate.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a PTC current limiter having a backup function according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a schematic configuration of a PTC current limiter 10 according to the present embodiment. The PTC current limiter 10 includes a composite PTC element body 10a, a first metal electrode plate 15 connected to a lower surface of the composite PTC element body 10a via a fixing metal foil 15a, and an upper surface of the composite PTC element body 10a. And a second metal electrode plate 16 connected via a fixing metal foil 16a.

The composite PTC element body 10a includes a first PTC element plate 11, a low-calorie metal foil 12 fixed on the first PTC element plate 11, and a heat storage element fixed on the low-calorie metal foil 12. A heat exchanger 13 and a plate-shaped second PTC element plate 14 having a higher temperature at which the resistance value increases than the first PTC element plate 11 fixed to the upper part of the heat storage unit 13 and a large energy amount and current amount leading to an increase in resistance. doing.

As the first PTC element plate 11 and the second PTC element plate 14, an element (PTC (Posi
tiveTemperature Coefficient) thermistor, P
That TC element), for _{example, V 2 O 3 -Cr 2 V} 2 of O _3,
O ₃ ceramics, bismuth titanate (BiTiO ₃ )
The temperature at which the specific resistance of ceramics or a solid solution thereof or a composite ceramic material such as cristobalite-carbon system rapidly increases (hereinafter referred to as resistance transition temperature or phase transition temperature) is 200 ° C. to 2 ° C.
A PTC element having a resistance of about 80 ° C. and having a small resistance at room temperature and rapidly increasing in resistance at a resistance transition temperature is used.

A PTC element selected from these is formed into a rectangular plate shape in plan view. Among them, as the first PTC element plate 11, a PTC element having a resistance transition temperature of about 230 ° C. is used.
It is preferable to use a PTC element having a resistance transition temperature of about 280 ° C. and a large amount of energy and a large amount of current for increasing the resistance.

The low-calorie melting point metal foil 12 is formed of a metal that melts, evaporates, and solidifies into soot when it is melted by the amount of heat generated when the first PTC element plate 11 breaks down or the like. Are arranged on the upper surface of the first PTC element plate 11 and fixed by pressure bonding, bonding with a conductive adhesive, brazing or welding. This low calorie melting point metal foil 12
For example, a low melting point metal whose main melting point is tin whose melting point is about 350 ° C. is used.

Here, as the first PTC element plate 11, for example, a PTC element having a resistance transition temperature of about 230 ° C. is used. The plate 11 rises to a temperature of about 300 ° C. Then, penetration breakdown due to a resistance drop voltage based on the increased resistance, or thermal stress breakdown that causes a current to concentrate on a specific portion to form a heat spot occurs. Therefore, when the low-calorie metal foil 12 is formed using a low-melting-point metal having a melting point of about 350 ° C., when the first PTC element plate 11 is broken, the low-calorie melting point metal foil 12 melts and evaporates. When solidified, it becomes soot. Since the low-calorie melting point metal foil 12 becomes soot, soot adheres around the PTC current limiter 10, so that the first PTC element plate 11
Can easily be detected as having failed.

The metal constituting the low-calorie melting point metal foil 12 is mainly composed of tin which melts, evaporates, and solidifies to become soot when it is melted, evaporated and solidified by the heat generated at the time of failure due to destruction of the first PTC element plate 11 or the like. In addition to low-melting-point metals, metals that melt and evaporate to blow out gas, or metals that dissolve and evaporate and change color, and metals such as aluminum and gold, whose melting points are higher than tin, are made into extremely thin films. One that dissolves and evaporates with a small amount of heat can be used.

When the metal foil 12 having a low calorific value is formed of a metal from which a gas is blown by melting and evaporating, the PTC current limiting device 10
The first PTC is easily generated because an abnormal smell is generated around the
It becomes possible to detect that the element plate 11 has failed. Furthermore, when the low-calorie melting point metal foil 12 is formed of a metal that dissolves and evaporates and changes color, the periphery of the PTC current limiter 10 changes color, so that it is possible to easily detect that the first PTC element plate 11 has failed. become.

The regenerator 13 is placed in a metal container made of a metal having good thermal conductivity such as copper, aluminum, stainless steel, etc.
For example, the melting point of a lead-tin alloy, solder, or the like is 130 to 150.
It is filled with a low-melting-point metal at ℃ and is sealed. The heat accumulator 13 is disposed on the upper surface of the low-calorie melting point metal foil 12 of the first PTC element plate 11 to which the low-calorie melting point metal foil 12 is fixed, and the heat accumulator 13 and the low-calorie melting point metal foil 12 are electrically conductively bonded. It is fixed by bonding with an agent, brazing or welding. The second PTC element plate 14 is arranged on the upper surface of the heat accumulator 13, and the heat accumulator 13 and the second PTC element plate 14 are fixed to each other by bonding, brazing, welding, or the like using a conductive adhesive.

By providing such a heat storage device 13, when the first PTC element plate 11 generates heat, the generated heat is conducted to the heat storage device 13. Then, the regenerator 13
When the low melting point metal sealed and filled in the metal container absorbs this heat and reaches its melting point, the low melting point metal is melted and converted into heat of fusion. Thereby, the first PTC element plate 11
Even if an overload current flows for a long time and the first PTC element plate 11 generates heat, this heat is sequentially converted into heat of fusion of the low melting point metal, so that the first PTC element plate 11 reaches the resistance transition temperature. Can be prevented.

As described above, the low-calorie melting point metal foil 12 is fixed to the upper surface of the first PTC element plate 11, the regenerator 13 is fixed to the upper surface of the low-calorie melting point metal foil 12, and the second PTC A composite PTC element body 10a is formed by laminating the element plate 14 to form a laminate.

The electrode plates 15 and 16 are made of a metal such as copper, aluminum, stainless steel or the like in the form of a metal plate having a square planar shape. The electrode plates 15 and 16 are arranged on both surfaces of the composite PTC element body 10a as described above, that is, the electrode plate 15 is connected to the first PTC element plate 1.
1, an electrode plate 16 is arranged on the upper surface of the second PTC element plate 14, and fixing metal foils 15a, 16a, which will be described later, are arranged between them.
By pressing the surface of 6, the two electrode plates 15, 16 are fixed to both surfaces of the composite PTC element body 10a via the fixing metal foils 15a, 16a.

The fixing metal foils 15a and 16a are made of both PTCs.
The hardness of the element plates 11 and 14 is defined as Ha, and the electrode plates 15 and 1 are hardened.
6 is Hc and the hardness of the fixing metal foils 15a and 16a is Hb, the hardness H has a relationship of Ha>Hc> Hb or a hardness H having a relationship of Hc>Ha> Hb.
The metal b, for example, a metal such as tin, copper, aluminum, or gold is formed of a metal foil whose plane shape is formed into a square.

The fixing metal foils 15a and 16a made of a metal having a hardness of Hb having a relationship of Ha>Hc> Hb or a relationship of Hc>Ha> Hb are provided between the first PTC element plate 11 and the electrode plate 15. And between the second PTC element plate 14 and the electrode plate 16, and these two electrode plates 1
A compressive stress is applied to both sides of the fixing metal foils 15 and 16 so that the fixing metal foils 15a and 16a are deformed. Thereby, the first
The PTC element plate 11, the fixing metal foil 15a, and the electrode plate 15 are tightly bonded and fixed, respectively, and the second P
The TC element plate 14, the metal foil 16a, and the electrode plate 16 are tightly coupled and fixed. As a result, it is possible to reduce the contact resistance of each joint between the first PTC element plate 11 and the electrode plate 15 and between the second PTC element plate 14 and the electrode plate 16.

The fixing metal foils 15a and 16a are made to have the surface roughness A of both PTC element plates 11 and 14,
The surface roughness of each of the metal foils 15 and 15 is defined as C.
Assuming that the surface roughness of 6a is B, a metal having a surface roughness B having a relationship of A = C> B, for example, a metal such as tin, copper, aluminum, or gold is formed into a quadrangular planar shape. Even if it is formed of metal foil, it becomes possible to reduce the contact resistance of the respective joints between the first PTC element plate 11 and the electrode plate 15 and between the second PTC element plate 14 and the electrode plate 16.

Further, the hardness of both PTC element plates 11 and 14 is minimized, and the hardness of fixing metal foils 15a and 16a is made larger than the hardness of both PTC element plates 11 and 14 so that both electrode plates 15 and 16 are hardened. Even if the hardness is further increased, or
Even if the surface roughness of the fixing metal foils 15a, 16a is maximized, and the surface roughness of both PTC element plates 11, 14 and both electrode plates 15, 16 is smaller than this, the first PTC element plate 11 and the electrode It is possible to reduce the contact resistance of each joint between the plate 15 and the second PTC element plate 14 and the electrode plate 16.

First PTC element plate 1 constructed as described above
A current limiter 10 (hereinafter, referred to as a PTC current limiter 10) including the first and second PTC element plates 14 is connected in series to an electric circuit L of a power transmission and distribution system to limit an overcurrent flowing through the electric circuit L (current limiting). This will be described with reference to FIG. In FIG. 2, the PTC current limiter 10 is
0 and a load 40 and an AC power supply 30 and a load 40 on an electric circuit L.
Are connected in series via a circuit breaker 20.

(1) Normal State First, the operation in the normal state will be described. When the load current I ₀ in the normal state is supplied to the electric circuit L from the AC power supply 30 when the circuit breaker 20 is closed (operating state). , The load 40, the electrode plate 15, the fixing metal foil 15a, the composite PT
The load current I ₀ flows through the C element body 10a (the first PTC element plate 11, the low-calorie melting point metal foil 12, the heat storage unit 13, the second PTC element plate 14), the metal foil 16a, and the electrode plate 16. At this time, the first PTC element plate 11 and the second PTC
Since the resistance value of the element plate 14 is small, the first PTC element plate 1
Even if the first and second PTC element plates 14 are connected to the electric circuit L, the power loss is small.

[0038] (2) overload condition where the load 40 is overloaded for some reason, so that an overload current I ₁ flows through the path L. Then, the resistance transition temperature of the first PTC element plate 11 becomes the second PT
Lower than the resistance transition temperature of the C element plate 14 and the second P
Since the TC element plate 14 has a larger amount of energy and current to increase the resistance than the first PTC element plate 11, the first PT
The C element plate 11 generates heat due to Joule heat and the temperature rises. As a result, the generated heat is conducted to the heat accumulator 13, but when the low melting metal sealed and filled in the metal container of the heat accumulator 13 absorbs this heat and reaches the melting point, the low melting metal melts. And converted to heat of fusion. As a result, the first PT
Even if the overload current flows through the C element plate 11 for a long time and the first PTC element plate 11 generates heat, this heat is sequentially converted into the heat of fusion of the low melting point metal.
No. 1 can prevent reaching the resistance transition temperature.

(3) First Short-Circuit State If, for some reason, an accident occurs in which the load disposed at the point X of the electric circuit L downstream of the PTC current limiter 10 is short-circuited, the short-circuit current Is ₁ is reduced. It flows to the electric circuit L. First PTC element plate 11 and second PTC element plate 12
If to flow rated current or overcurrent I _S is the resistance transition temperature of the 1PTC element plate 11 is smaller than the resistance transition temperature of the 2PTC element plate 14, and the 2PTC element plate 14 energy leading to increased resistance Since the amount and the current amount are larger than the first PTC element plate 11,
The element plate 11 generates heat due to Joule heat and the temperature rises, and the temperature reaches the resistance transition temperature. The specific resistance of the first PTC element plate 11 rapidly increases, and the resistance value rapidly increases. The current limiting operation is performed immediately. Therefore, the second P
The temperature of the TC element plate 14 does not rise so much.

When the short-circuit current Is ₁ flows through the electric circuit L, a sensor (not shown) detects this over-current Is ₁ and shuts off the circuit breaker 40. Thus, a short-circuit current Is ₁ stops flowing to the 1PTC element plate 11 and the 2PTC element plate 14.

On the other hand, when the short-circuit fault is recovered and the circuit breaker 40 returns, the normal load current I ₀
Supplied from 0. In this case, if the temperatures of the first PTC element plate 11 and the second PTC element plate 14 have not decreased to room temperature, the resistance values of the first PTC element plate 11 and the second PTC element plate 14 will be high, but eventually The first PTC element plate 11 and the second PTC element plate 14 are cooled.
Temperature gradually decreases to a low resistance value at normal temperature.

(4) Second Short-Circuit State Further, for some reason, a load short-circuited at the point X of the electric circuit L downstream of the PTC current limiter 10 occurs. The current Is ₁ is the electric circuit L
And the first PTC element plate 11 and the second
Overcurrent I _{S that} is equal to or greater than the rated current flows through the PTC element plate 12, and as described above, the first PTC element plate 11
Although the generate heat, corresponding to the long-term the 1PTC or element plate 11 has been deteriorated or current increase rate conventional short-circuit current Is ₁ or more short-circuit current Is ₂ flows, through the use resistors but by Joule heat Not gaining,
Furthermore, when the abnormal surge voltage to the short-circuit current Is ₁ is added, and abnormal stress is applied to the 1PTC element plate 11, or the 1PTC element plate 11 through, or flashover occurs. In such a case,
In any case, arc discharge eventually occurs.

Then, the amount of energy and the amount of current leading to an increase in the resistance of the second PTC element plate 14 are reduced.
Since it is larger than 1, the temperature of the second PTC element plate 14 reaches the resistance transition temperature without being destroyed, the specific resistance of the second PTC element plate 14 rapidly increases, and the resistance value rapidly increases. Perform current limiting operation. At this time, the metal constituting the low calorific value melting point metal foil 12 is melted by the first PTC element plate 11 penetrating or by the arc heat generated by flashover or the localization of current due to local concentration of current, and the like.
Evaporate. The metal constituting the low-calorie melting point metal foil 12 is soot when solidified, melts and evaporates to emit a gas, or dissolves and evaporates to discolor, so that the first PTC element plate 11 is broken. You can easily know what was done.

After a predetermined time (0.5 to 2.5 cycles) has elapsed after the second PTC element plate 14 has performed the current limiting operation, a sensor (not shown) detects such an abnormal short-circuit current, and 40 is turned off. As a result, an abnormal short-circuit current does not flow through the first PTC element plate 11 and the second PTC element plate 14. When the circuit breaker 20 is turned on after the recovery from the short-circuit accident, the metal constituting the low-calorie melting point metal foil 12 melts and evaporates to become soot, and the PTC current limiter 1
0, the PTC current limiter 10 has an abnormal smell around it, or the periphery of the PTC current limiter 10 is discolored.
Can be easily known that the circuit breaker has been destroyed.
By exchanging the PTC current limiter 10 in which the first PTC element plate 11 has been destroyed before the power supply, the normal load current I ₀ can be supplied to the electric circuit L from the AC power supply 30.

In the above-described embodiment, the low-calorie melting point metal foil 12 is connected to the first PTC element plate 11 and the regenerator 13.
Although the example in which the low-calorie melting point metal foil 12 is interposed between the first PTC element plate 11 and the fixing metal foil 15a
May be interposed between.

Further, in the above-described embodiment, when forming the composite PTC element body 10a, an example in which the composite PTC element body 10a has a two-stage configuration including two PTC element plates, that is, a first PTC element plate 11 and a second PTC element plate 14. I explained, PT
A multi-stage configuration such as a three-stage configuration using three C element plates or a four-stage configuration using four PTC element plates, etc.
You may make it comprise a C element body.

Modification 1 In the embodiment described above, the composite PTC element body 10a
And the case where the surface areas of the two electrode plates 15 and 16 are the same, but if the surface areas are the same, one of the first and second PTC element plates 11 and 14 reaches the resistance transition temperature and suddenly increases. When the resistance value increases, the two electrode plates 15 and 1 are moved by a resistance drop voltage based on the increased resistance.
6, an overvoltage occurs between the end faces.

The outside of the periphery of the composite PTC element body 10a is in contact with the outside air, and the outside air of the periphery rises as the temperature of the first PTC element plate 11 or the second PTC element plate 14 rises. Since the dielectric strength of the atmosphere whose temperature has risen is lower than that at normal temperature, the overvoltage generated between the end faces of the electrode plates 15 and 16 causes a problem that flashover occurs between the end faces of the electrode plates 15 and 16. . Then, in order to prevent such a problem, the first modified example was considered.

Here, FIG. 3 shows a PTC current limiter of the first modification, FIG. 3 (a) is a bottom view, and FIG. 3 (b) is a sectional view taken along line AA of FIG. 3 (a). It is. In the first modified example, as shown in FIG. 3, a composite PTC element in which the surface area of both electrode plates 15 and 16 in which the planar shape is formed in a square shape as in the above embodiment is formed in a rectangular shape in plan view. Body 10
a, the two electrode plates 15 and 16 are arranged at the center of both surfaces of the composite PTC element body 10a, and the peripheral edges of both surfaces of the composite PTC element body 10a are , 16 so as to be exposed.
That is, the first PTC element plate 11 and the second PTC element plate 1
4 are both electrode plates 1
It is formed so as to be exposed from 5,16.

According to an experiment, if the composite PTC element body 10a has an edge surface distance of 0.5 mm or more, a sufficient dielectric strength can be maintained. And second PTC element plate 14
The width of the exposed portion may be 0.25 mm.

As described above, when the first PTC element plate 11 and the second PTC element plate 14 are formed so as to expose the peripheral edges of the respective surfaces, both electrode plates 15, 1 are formed.
6, it is possible to maintain a sufficient dielectric strength between the end faces, so that one of the first PTC element plate 11 and the second PTC element plate 14 reaches the resistance transition temperature, and the resistance value increases rapidly, and Even if an overvoltage occurs between the end faces of the two electrode plates 15 and 16 due to the voltage drop, it is possible to prevent a problem that flashover occurs between the end faces of the two electrode plates 15 and 16.

When the first modified example is applied, in addition to using both the electrode plates 15 and 16 as metal electrode plates,
This modification can also be applied to the case where the TC element plates 11 and 14 are directly plated or the electrodes are formed by irradiating the metallicon.

Modified Example 2 In the first modified example described above, the two electrode plates 15 and 16 each having a rectangular planar shape are provided at the center of both surfaces of a composite PTC element body 10a having a rectangular planar shape. They are arranged so that their peripheral edges are exposed. When the two electrode plates 15 and 16 are arranged in this manner, the electric field is concentrated on the corners of the two electrode plates 15 and 16 and the current density in this portion increases. When the current density at the corner increases, the first PTC element plate 11 or the second
There is a problem that the PTC element plate 14 locally reaches the resistance transition temperature.

Specifically, when a voltage is applied between the two electrode plates 15 and 16, a potential distribution as shown by the curve in FIG. 4 is generated. As is clear from this potential distribution curve, both electrode plates 1
The electric field at the corners of 5 and 16 becomes denser than the electric field at the other portions, and the potential gradient increases. An increase in the potential gradient means that a distance at which a voltage is shared at a certain point is shortened, so that a resistance value between them is relatively small. Therefore, as shown by the arrows in FIG.
The current densities at the corners 5 and 16 are higher than the current densities at other portions.

Therefore, in the second modified example, the first PTC element plate 1
This was conceived to prevent the first or second PTC element plate 14 from locally reaching the resistance transition temperature. here,
FIG. 5 shows a PTC current limiter of the second modified example, and FIG.
FIG. 5B is a bottom view, and FIG. 5B is a BB view of FIG.
It is sectional drawing. In the second modification, as shown in FIG. 5, the corners of both electrode plates 15 and 16 are chamfered into an arc shape (for example, 0.5r) so that the corners are rounded. .

If the corners of the two electrode plates 15 and 16 are rounded as described above, a potential distribution curve along the roundness can be obtained. Since it becomes equal to the electric field and the current density becomes uniform, the first PTC element plate 11 or the second PTC element plate 1
4 can be prevented from locally reaching the resistance transition temperature, and the first PTC element plate 11 or the second PTC element plate 14 can be prevented from being locally deteriorated.

Modification 3 In the above embodiment, the composite PTC element body 10a
Because the plane shape of the square is a quadrangle, the electric field at the corner of the side wall of the square becomes denser than the electric field of the other side wall, and the current density at the corner of the side wall increases,
The problem that stress concentrates on this part occurred.

Therefore, in the third modified example, an attempt was made to prevent such stress concentration. Here, FIG. 6 shows a PTC current limiter of the third modified example, FIG. 6 (a) is a bottom view thereof, and FIG. 6 (b) is a cross-sectional view taken along line CC of FIG. 6 (a). . In the third modified example, as shown in FIG. 6, the corner of the side wall of the composite PTC element body 10a is chamfered, and the side wall is also chamfered, so that the corner is rounded.

As described above, when the corner of the side wall of the composite PTC element body 10a is chamfered and the side wall is also chamfered so that the corner is rounded, a potential distribution curve along the rounded corner is obtained. , So composite PTC
The electric fields at the corners and the side walls of the element body 10a become equal to the electric fields at the other parts and the current density becomes uniform, so that local deterioration of the composite PTC element body 10a can be prevented.

The first PTC element 10a of the composite PTC element body 10a having the chamfered side wall corners and side walls as described above.
In the exposed portion of the element plate 11 or the second PTC element plate 14,
As shown in FIG. 7, by coating the insulating resin 17 or applying or baking the insulating resin 17, a composite PTC element body 10a having excellent dielectric strength can be obtained.

The PTC current limiter of the present invention is not limited to the above-described embodiment and its modifications. For example, the PTC current limiter may be built in a circuit breaker for low-voltage wiring, a circuit breaker for high-voltage and extra-high-voltage or higher, or may be separately connected in series. Can also be used. It can also be used to protect thyristor devices, or can be used in place of current limiting fuses for low voltage network distribution.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic configuration of an embodiment of a PTC current limiter of the present invention.

FIG. 2 is a diagram showing an example of connecting a PTC current limiter of the present invention to an electric circuit of a power transmission and distribution system.

FIG. 3 shows a PTC current limiter according to a first modification;
FIG. 3A is a bottom view, and FIG. 3B is a sectional view taken along line AA of FIG.

FIG. 4 is a diagram showing a part of a potential distribution curve obtained by applying a voltage between electrode plates.

5 shows a PTC current limiter according to a second modified example, and FIG.
5A is a bottom view, and FIG. 5B is a cross-sectional view taken along the line BB of FIG. 5A.

6 shows a PTC current limiter according to a third modification, and FIG.
6A is a bottom view, and FIG. 6B is a cross-sectional view taken along the line CC of FIG. 6A.

FIG. 7 is a view showing a state in which an exposed portion of the PTC current limiter of FIG. 6 is covered with an insulating resin.

[Explanation of symbols]

10: PTC current limiter, 10a: Composite PTC element body, 11
... 1st PTC element plate, 12 ... low calorie melting point metal foil, 13 ...
Heat storage device, 14: first PTC element plate, 15, 16: electrode plate, 15a, 16a: fixing metal foil, 20: circuit breaker, 3
0: AC power supply, 40: Load

Claims (10)

[Claims] A plurality of Ps having different resistance increasing temperatures.
P with backup function configured using TC element
A TC current limiter, wherein a plate-shaped first PTC element plate whose resistance value rapidly increases when a predetermined temperature is reached, and an energy amount at which the resistance value increases at a higher temperature than the first PTC element plate and which leads to an increase in resistance And a composite PTC element configured by electrically connecting at least two PTC element plates with a plate-shaped second PTC element plate having a large amount of current, and electrically connected to both surfaces of the composite PTC element body, respectively. A PTC current limiter having a backup function, comprising: 2. The method according to claim 1, wherein the first PTC element plate is melted and evaporated by a heat amount at the time of damage to the first PTC element plate.
2. The backup function according to claim 1, wherein the backup function is provided on a surface of the C element plate so that the damage of the first PTC element plate can be displayed by the metal evaporated and damaged by the first PTC element plate. Equipped with PTC current limiter. 3. The low-calorie metal foil is formed of a metal that melts and evaporates to form a soot when solidified, a metal that melts and evaporates to blow out a gas, or a metal that melts and evaporates and changes color. The PTC current limiter having a backup function according to claim 2. 4. The first PTC element plate and the second PTC
The first PTC element plate or the second
The PTC current limiter having a backup function according to any one of claims 1 to 3, wherein a heat storage unit that absorbs heat generated by the PTC element plate and stores the heat is interposed. 5. The composite PT having a surface area of
The first PTC element plate and the second PTC element plate are formed to be smaller than the surface areas of the first PTC element plate and the second PTC element plate on both surfaces of the C element body.
The PTC current limiter having a backup function according to any one of claims 1 to 4, wherein the PTC current limiter is provided with a connection so that a surface of a peripheral portion of the PTC element plate is exposed. 6. The metal electrode plate according to claim 5, wherein a corner of the metal electrode plate is chamfered to form a plate having a substantially square planar shape with a rounded corner. PTC current limiter with backup function. 7. The composite PTC element body according to claim 1, wherein the corner of the side wall of the composite PTC element body is chamfered to form a round corner. PTC current limiter with backup function. 8. The first PTC element plate and the metal electrode plate, and the first PTC element plate and the metal electrode plate are each bonded to each other with a fixing metal foil interposed between the first PTC element plate and the metal electrode plate.
The PTC current limiting device having a backup function according to any one of claims 1 to 7, wherein the C element plate and the metal electrode plate and the second PTC element plate and the metal electrode plate are fixed to each other. vessel. 9. The fixing metal foil is a metal having a lower hardness than the first PTC element plate, the second PTC element plate, and the metal electrode plate, or the first PTC element plate, the second PTC element plate, and the metal electrode. 9. The PTC current limiter having a backup function according to claim 8, wherein the PTC current limiter is formed of a metal having a smaller surface roughness than a plate. 10. The fixing metal foil has a hardness higher than the first PTC element plate and the second PTC element plate and a lower hardness than the metal electrode plate, or the first PTC element plate and the second PTC element plate. 9. The PTC current limiter having a backup function according to claim 8, wherein the PTC current limiter is formed from a metal having a larger surface roughness and a smaller surface roughness than the metal electrode plate.