JPH10145964A - Self-cooled current limiter employing pct element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the temperature of a PTC element down to a normal level immediately after current limit operation by increasing the cooling rate of the PTC element through a simple structure. SOLUTION: The current limiter 10 is connected between an AC power supply and a load in line comprising the AC power supply and the load through a circuit breaker. The current limiter 10 comprises PTC elements 11, 12 having resistance increasing with the temperature, and electrode plates 13, 14, 15 arranged across and between the PTC elements 11, 12. A terminal extending from the electrode plate 14 arranged between the PTC elements 11, 12 is connected with one input side terminal of a motor drive circuit 50. A terminal extending from the electrode plate 15 is connected with the other input side terminal of the motor drive circuit 50. The motor drive circuit 50 is connected, on the output side thereof, with a motor 60 having a rotary shaft fixed with a fan 61.

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 self-cooling type current limiting device using a PTC element.

[0002]

2. Description of the Related Art In recent years, in order to protect power equipment disposed on an electric circuit such as a transmission / distribution system or a transmission / distribution system from an overcurrent such as a short-circuit current or an overload current flowing through the transmission / distribution system,
An element having a positive temperature coefficient of resistance (PTC: Positive Temperature C
oefficient) thermistor (hereinafter referred to as PTC element) has been proposed for use in the electric circuit of the power transmission and distribution system.

When this PTC element is used in conjunction with a circuit breaker in an electric circuit of a power transmission and distribution system, for example, when an overcurrent exceeding a rated current flows through this electric circuit, Joule heat is generated in the PTC element to cause a PTC element. Temperature rises. Then this P
Since the TC element has a positive temperature coefficient of resistance, when the temperature of the PTC element becomes equal to or higher than a predetermined phase transition temperature, the resistance value sharply increases, and an overcurrent flowing through this electric circuit is suppressed (current limit).
I will be. Thereafter, the circuit breaker operates to cut off the circuit.

On the other hand, when the temperature of the PTC element returns to normal temperature after the recovery from the accident, the resistance value returns to the original low resistance value, so that the PTC element automatically recovers. , A normal predetermined current flows.

[0005]

SUMMARY OF THE INVENTION However, PTC
If the temperature of the element continues to rise, its resistance value remains large, so even if the circuit breaker is turned on again, the state of current limiting operation will continue until the temperature of the PTC element returns to normal temperature. This causes a problem that the recovery operation of the electric circuit becomes slow. Therefore, it is proposed that the PTC element be cooled by rotating a cooling fan or the like in conjunction with the breaking operation of the breaker, since the breaker operates when an overcurrent flows in the electric circuit. When the cooling fan or the like is driven to rotate in conjunction with the operation, the circuit configuration becomes complicated, and an expensive relay or the like must be used. Therefore, there is a problem that this type of current limiting device becomes expensive. Therefore, the present invention solves the above-mentioned problems by using a simple configuration of PTC.
It is an object of the present invention to increase the cooling rate of the element and to immediately lower the temperature of the PTC element after the current limiting operation to room temperature.

[0006]

According to the present invention, a PTC element having a positive temperature coefficient of resistance, whose resistance value rapidly increases when a predetermined temperature is reached, is provided on an electric circuit to suppress overcurrent flowing through the electric circuit. A self-cooling type current limiting device using a PTC element for cooling the PTC element whose temperature has risen. In order to solve the above problem, in the invention according to claim 1, a flow path of a cooling medium flows through the PTC element. And a cooling means for forming a pair of branch terminals on the PTC element for branching and extracting a current flowing through the PTC element from the PTC element, and for sending a cooling medium toward the flow passage, and between the pair of branch terminals. And a drive circuit for driving the cooling means when a voltage drop based on a resistance voltage drop caused by the flow of the current becomes a predetermined voltage or more.

With this configuration, the resistance value of the PTC element at normal temperature is small in a steady state,
The current supplied to the electric circuit flows through the PTC element. On the other hand, if the overcurrent exceeding the rated current is
In the event of an abnormality flowing through the element, the temperature of the PTC element rises due to Joule heat generated when an overcurrent flows, and when the temperature of the PTC element reaches a predetermined temperature, the resistance value of this element rapidly increases, and the PTC element The flowing current is suppressed (current-limited). When the resistance value of the PTC element increases, the voltage drop generated between the branch terminals increases, and when the voltage drop exceeds a predetermined voltage, the drive circuit drives the cooling means, so that the temperature of the PTC element decreases. become.

When the overcurrent state is resolved, the power is supplied to the electric circuit and the current flows through the PTC element. In this case, the temperature of the PTC element is still high, so The drive circuit drives the cooling means. For this reason, the cooling medium flows through the cooling medium flow passage formed in the PTC element, and the temperature of the PTC element immediately decreases to room temperature. Thus, after the return, the current supplied to this electric circuit flows through the PTC element.

According to the second aspect of the invention, the normal load current flowing through the electric circuit is defined as I _S , the resistance value between the branch terminals at this time is defined as r, and the abnormal overcurrent flowing through the electric circuit is defined as I _MAX. When the resistance value between the branch terminals at this time is R, the above-mentioned predetermined voltage V is R × I _MAX >> R × I _S ≧ V
>> It is set so as to satisfy the relational expression of r × I _S.
Therefore, immediately cooling means when the overcurrent I _MAX flows path is driven, temperature rise of the PTC element is prevented.
In addition, the load current I when the overcurrent state is resolved and the circuit
_{When S} starts to flow, the resistance value between the branch terminals at this time is R, so that the cooling means is driven again, and the temperature of the PTC element immediately drops to room temperature.

In the third aspect of the present invention, the flow holes formed in the PTC element are through holes formed in the honeycomb structure of the PTC element. As described above, when the through-hole is formed in a honeycomb structure, the honeycomb structure has a large surface area, so that the heat radiation effect is large and the heat in the PTC element is radiated through the through-hole. It immediately drops to room temperature.

[0011] In the invention described in claim 4, to use the V ₂ O ₃ -Cr ₂ O ₃ ceramic resistance rise room temperature resistivity against small and room temperature resistivity is 2 to 3 orders of magnitude as the above PTC element I have to. This V ₂ O ₃ -Cr ₂
O ₃ ceramics have a low room temperature resistivity, and the current supplied to the electric circuit under normal conditions is PT
It flows through the C element. V ₂ O ₃ -Cr
₂ O ₃ ceramics have a resistance rise of 2 to room temperature resistivity.
Since there are three digits, in the event of an overcurrent exceeding the rated current flowing through this element, its resistance value rapidly increases, so that the overcurrent flowing through this circuit can be reliably limited. Become.

[0012]

According to the first aspect of the present invention, the PT
Since the resistance value of the C element at room temperature is small, even if this element is directly connected to the electric circuit, the resistance loss is small, and the power loss during the steady state can be minimized. You will be able to protect. Further, when the overcurrent state is resolved, the cooling medium flows through the flow passage, and P
Since the temperature of the TC element immediately drops to room temperature, the reliability of this type of current limiting device is improved.

According to the second aspect of the present invention, when the overcurrent state is eliminated and the normal load current I _S flows through the electric circuit, the resistance value between the branch terminals at this time is R. The cooling means is driven again, and the temperature of the PTC element immediately drops to room temperature. Therefore, the reliability of this type of current limiting device is improved.

According to the third aspect of the present invention, the PTC
Since the elements are formed in a honeycomb structure, the PTC element can be cooled in a short time due to the heat dissipation based on the honeycomb structure, and the PTC element whose temperature has risen immediately drops to room temperature. As a result, the return operation becomes faster, and the return property of this type of current limiting device is improved.

According to the fourth aspect of the present invention, the room temperature resistivity is small and the rate of resistance increase with respect to the room temperature resistivity is 2 to 2.
When three-digit V ₂ O ₃ —Cr ₂ O ₃ ceramics are used,
The resistance loss is small, the power loss in a steady state can be minimized, and the power system can be protected without power loss. In addition, since the resistance is smaller than that of BaTiO ₃ ceramics, the cross-sectional area can be reduced, a small PTC element can be used, and the size of this type of current limiting device can be reduced. . Furthermore, even if an overcurrent exceeding the rated current flows through this element, the element can be prevented from being destroyed due to a rise in temperature. Further, when an overcurrent flows, the resistance value surely increases, so that the responsiveness of the current limiting operation is improved, and the responsiveness of this type of current limiting device is improved.

[0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of a self-cooling type current limiting device using a TC element will be described. FIG. 1 is a diagram showing an example of a case where a self-cooling type current limiting device using a PTC element of the present invention is connected in series to an electric circuit of a power transmission and distribution system to limit (current limit) an overcurrent flowing through this electric circuit. is there. As shown in FIG. 1, this current limiting device 10 is
0 and a load 30 and an AC power supply 20 and a load 30 on an electric circuit L.
Are connected in series via a circuit breaker 40.

FIG. 2 is a diagram showing a schematic configuration for cooling the current limiting device 10 by itself. As shown in FIG.
0 denotes an element having a positive temperature coefficient of resistance (PTC (Positive Temperatu
a first PTC element 11 and a second PTC element 12, and a first PTC element 11 and a second PTC element.
The first electrode plate 13, the second electrode plate 15, and the third electrode plate 14 are disposed between the first PTC element 11 and the second PTC element 12. Note that the first electrode plate 13 and the second electrode plate 15 have terminals (not shown)
5 and are arranged so as to extend outward, respectively, so that these terminals are connected to the electric circuit L.

A terminal (not shown) extending from the third electrode plate 14 provided between the first PTC element 11 and the second PTC element 12 is provided. Side is connected to one terminal.
Further, the terminal extending from the second electrode plate 15 and the other terminal on the input side of the motor drive circuit 50 are connected. The output side of the motor drive circuit 50 is connected to the motor 60, and a fan 61 is mounted on the rotating shaft of the motor 60.

The motor drive circuit 50 comprises a transformer and a voltage-sensitive element connected to the secondary side of the transformer, for example, a semiconductor element such as a zinc oxide varistor ceramic element or a silicon Zener diode. Here, when a load current flows through the electric circuit L, the third electrode plate 14 and the second
When voltage drop based on the resistor voltage drop caused between the electrode plate 15 becomes a voltage V ₂ induced in the secondary side of the transformer when a predetermined voltage V _1, the zinc oxide varistor ceramic element or silicon Zener The voltage-sensitive element made of a semiconductor element such as a diode is turned on, the motor 60 is driven, and the fan 61 mounted on the rotating shaft is rotated.

The normal load current flowing through the electric circuit L is defined as I _S, and the third electrode plate 14 and the second electrode plate 15
When the resistance value between the third electrode plate 14 and the second electrode plate 15 at this time is R, the resistance between the third electrode plate 14 and the second electrode plate 15 at this time is I _MAX , The above-mentioned predetermined voltage V ₁ is set so as to satisfy the relational expression of R × I _MAX >> R × I _s ≧ V ₁ >> r × I _S.

Each of the first PTC element 11 and the second PTC element 12 has a temperature at which its specific resistance sharply increases (generally called a phase transition temperature) of about 80 ° C. to 200 ° C., and has a resistance value at room temperature. It is preferable to use a material having a small value and a sharp increase in the resistance value when the phase transition temperature is reached.
Here, the first PTC element 11 and the second PTC element 12
Generally, barium titanate (BaTiO
₃ ) It is known to use ceramics. As shown in Table 1, V ₂ O ₃ ceramics are made of BaTiO _3.
It has been found that the PTC element has excellent characteristics in terms of room temperature resistivity, voltage dependency, mechanical strength, and the like from the system ceramics. Therefore, in the present invention, the first PTC element 11 and the second PTC element 12 are: V ₂ O ₃ based ceramics, in particular using a V ₂ O ₃ -Cr ₂ O ₃ ceramic.

[0022]

[Table 1]

The first PTC element 11 and the second PTC element 12 made of V ₂ O ₃ —Cr ₂ O ₃ ceramics
As shown in FIG. 2, one integrally formed in a honeycomb structure having many through holes like a beehive inside is used. As a method for forming a honeycomb structure having a number of through-holes, the V ₂ O ₃ -Cr ₂ O ₃ based ceramics in addition to integrally formed into a honeycomb structure, V ₂ O ₃ -
Cr ₂ O ₃ -based ceramics formed into a cylindrical shape, a rectangular tube shape, a round bar shape, a square bar shape, or the like can be assembled to form an aggregate having a large number of through holes or through voids formed therein. . V ₂ formed in the honeycomb structure as described above
First PTC element 1 made of O ₃ —Cr ₂ O ₃ ceramics
As the first and second PTC elements 12, as shown in the temperature-resistivity characteristics of FIG. 3, PTC elements that undergo a phase transition at about 130 ° C. are obtained.

It should be noted, in addition to the above-mentioned V ₂ O ₃ -Cr ₂ O ₃ ceramics as V ₂ O ₃ based ceramics may be used V ₂ O ₃ based ceramics obtained by solid solution Al ₂ O _3. Alternatively, lead titanate (PbTiO ₃ ) ceramics, bismuth titanate (BiTiO ₃ ) ceramics, or a solid solution thereof may be used.

The first PTC element 11 and the second PT
The C element 12 can also be formed of a synthetic resin made of a polyethylene-carbon composite material, a polyolefin-carbon composite material, or the like.

The electrode plates 13, 14, and 15 are formed of a metal such as copper, aluminum, and stainless steel in a honeycomb structure. Then, the through holes of the honeycomb structure formed in the first PTC element 11 and the second PTC element 12 and the electrode plates 13, 1
The honeycomb structure is formed so that the through-holes of the honeycomb structure formed at the holes 4 and 15 coincide with each other. In addition, the first electrode plate 13 is provided on one end face of the first PTC element 11 having the through-hole, and the other end face having the through-hole of the first PTC element 11 and the second PTC element 12 are provided such that the respective through-holes coincide with each other. The third electrode plate 14 is disposed between the one end surface having a hole and the second electrode plate 15 is disposed on the other end surface having a through hole of the second PTC element 12, and tin / lead solder, silver brazing, conductive adhesive It is fixed and integrated by the like. Alternatively, the first PTC element 11 and the second PTC element 11
The same effect can be obtained by forming metallikons on both end surfaces of the TC element 12 having through holes and pressing the respective electrode plates 13, 14, 15 on the metallikons.

Next, the operation of the self-cooling type current limiting device using the PTC element configured as described above will be described. First, when the operation of the normal, state breaker 40 is closed when the load current I _S during normal from the AC power supply 20 to the path L in the (operating condition) is supplied to the load 30 is first 1PTC element Load current I _S flows through 11 and second PTC element 12. At this time, the third electrode plate 14 and the second
Since the resistance value between the second electrode plate 15 and the third electrode plate 15 is r, the voltage drop between the third electrode plate 14 and the second electrode plate 15 is r × I _S.

Here, as described above, the voltage V ₂ at which the voltage sensing element of the motor drive circuit 50 is turned on and the motor 60 is driven to rotate is set when the drop voltage becomes V ₁ . because they are set so as to satisfy the relation of _{R × I MAX >> R × I} S ≧ V 1 >> r × I S, the voltage sensitive element is a motor 60 without conducting a stopped state. Since the resistance value r of the 1PTC element 11 and the 2PTC element 12 at this time it is small, so that the load current I _S from the AC power source 20 without the power loss is supplied to the load 30.

Here, for some reason, the current limiting device 1
When the load arranged in the X point downstream of the path L (see FIG. 1) of the zero accident for short-circuiting occurs, the rated current or overcurrent I _MAX is to flow through the path L. First PTC element 1
The overcurrent I exceeding the rated current is supplied to the first and second PTC elements 12.
_{When MAX} flows, the first PTC element 11 and the second PTC element 11
The element 12 generates heat due to Joule heat and its temperature rises.
When the temperature of the first PTC element 11 and the second PTC element 12 rises and the temperature exceeds 130 ° C., the specific resistances of the first PTC element 11 and the second PTC element increase as shown in FIG. The first PTC
The current flowing through the element 11 and the second PTC element 12 is limited.

At this time, the first PTC element 11 and the second
As shown in Table 1 above, the PTC element 12 has a two- to three-digit increase in resistance with respect to the normal-temperature resistivity, so that its specific resistance rapidly increases, and its resistance value sharply increases. The first PTC element 11 and the second PTC element 1
2 is a negative resistance temperature coefficient (NTC (Negative Temperature
(Coefficient)), the temperature rises to reach the region, and the PTC element 11 is not destroyed by an overcurrent exceeding the rated current.

When Joule heat is generated in the first PTC element 11 and the second PTC element 12 and the resistance between the third electrode plate 14 and the second electrode plate 15 becomes R, the third electrode plate 14 and the second electrode The voltage drop to the plate 15 is R × I _MAX .
In this case, since it is set so as to satisfy the relation of _{R × I MAX >> R × I} S ≧ V 1 >> r × I S, the voltage sensitive element of the motor drive circuit 50 is turned, the motor 60 Is driven to rotate, and the fan 61 rotates. Therefore, air serving as a cooling medium is supplied to the first PTC element 11 and the second PTC element 12.
Into the through-hole of the honeycomb structure of the first PTC element 11
And the temperature rise of the second PTC element 12 stops.

[0032] rated current or overcurrent I _MAX is to flow path L, not shown sensors overcurrent I
Detect _MAX and shut off circuit breaker 40. This allows
Since no current flows through the first PTC element 11 and the second PTC element 12, the motor 60 stops.

On the other hand, when the circuit breaker 40 to recover a short circuit accident is restored, the path L normal load current I _S AC power supply 2
Supplied from 0. In this case, if the temperatures of the first PTC element 11 and the second PTC element 12 remain elevated,
The resistance values of the first PTC element 11 and the second PTC element 12 remain at R, and the voltage drop between the third electrode plate 14 and the second electrode plate 15 becomes R × I _S. And R × I _MAX >
> R × I _s ≧ V ₁ >> r × I _S , the voltage-sensitive element of the motor drive circuit 50 is turned on, and the motor 60 is again driven to rotate. The fan 61 rotates. Therefore, the air serving as the cooling medium is
It flows into the through-holes of the honeycomb structure of the PTC element 11 and the second PTC element 12, and the first PTC element 11 and the second PTC element
When the temperature of the TC element 12 gradually decreases, and when the temperature of the TC element 12 becomes room temperature, the driving of the motor 60 is stopped.

In this embodiment constructed as described above, since the first PTC element 11 and the second PTC element 12 are made of V ₂ O ₃ —Cr ₂ O ₃ ceramics having a small resistance at room temperature, these elements are used. Even if the first PTC element 11 and the second PTC element 12 are directly connected to the electric circuit L, the resistance loss is reduced. For this reason, power loss in a steady state can be minimized, and overcurrent can be prevented without power loss.

The first PTC element 11 and the second PT
Since the C element 12 is formed in a honeycomb structure having a large number of through-holes, the cooling efficiency is improved, and even if a short circuit accident or the like occurs, the element is cooled early and returns to normal temperature. Of the power system is improved, and the system can be automatically restored in a short time.
Maintainability is improved.

Further, V ₂ O ₃ —Cr ₂ O ₃ ceramics have a smaller resistance than BaTiO ₃ ceramics, so that the cross-sectional area can be reduced, and the small first PTC element 11 and second PTC element 12 can be used, and this type of current limiting device can be downsized. Further, since the resistance rise with respect to the normal temperature resistivity is two to three digits, the first PTC element 11 and the second PTC element 12
Even if an overcurrent flows over the rated current, the temperature does not rise before reaching the NTC region, so that the destruction of the first PTC element 11 and the second PTC element 12 due to the temperature rise can be prevented. Become. Further, when an overcurrent flows, the resistance value surely increases, so that the responsiveness of the current limiting operation is improved, and the responsiveness of this kind of current limiting device is improved.

In the above-described embodiment, the rotation of the fan 18 using air as the cooling medium causes the PTC to rotate.
Although an example in which a cooling medium made of air flows into the element 11 has been described, a liquid (for example, insulating oil or the like) or a gas other than air (for example, CO ₂ or N ₂ gas) is used as the cooling medium. Is also good. In this case, the cooling medium is circulated by a driving device such as a pump so that the cooling medium flows into and out of the through holes of the first PTC element 11 and the second PTC element 12 formed in the honeycomb structure during the circulation cycle of the cooling medium. do it.

In the above-described embodiment, an example has been described in which the through-holes of the honeycomb structure are provided in the direction in which the current flows. However, the through-holes in the honeycomb structure may be provided in the direction perpendicular to the direction in which the current flows. Good. In this case, since there is no need to provide a through-hole having a honeycomb structure in each electrode plate, this type of current limiting device can be manufactured at a lower cost. Further, when the heat radiation fins are provided on the outer peripheral surfaces of the first PTC element 11 and the second PTC element 12, the heat radiation effect is further improved.

The first terminal is connected between a terminal extending from the third electrode plate 14 and one terminal on the input side of the motor drive circuit 50.
A bimetal switch may be added in contact with the PTC element 11 or the second PTC element 12. In this case, a bimetal switch that turns on when the first PTC element 11 or the second PTC element 12 reaches a temperature higher than the normal temperature and turns off when the temperature drops to the normal temperature may be used. When such a bimetal switch is used, the motor 60 is driven to rotate until the first PTC element 11 and the second PTC element 12 reach the normal temperature, so that the temperature of the first PTC element 11 and the second PTC element 12 whose temperature has increased can be reduced to the normal temperature in a short time. It is possible to lower it.

The current limiting device 10 of the present invention is not limited to the above-described embodiment. For example, the current limiting device can be used for protecting a thyristor device, or a current limiting fuse for power distribution in a low-voltage network. Can be used instead of

[Brief description of the drawings]

FIG. 1 is a diagram showing an example in which a current limiting device of the present invention is directly connected to an electric circuit of a power transmission and distribution system.

FIG. 2 is a diagram showing a schematic configuration for self-cooling the current limiting device of the present invention.

FIG. 3 is a diagram showing a temperature-resistivity characteristic of the PTC element of the present invention.

[Explanation of symbols]

Reference numeral 10: current-limiting device, 11, 12: PTC element (element having a positive temperature coefficient of resistance), 13, 14, 15: electrode plate, 2
0: AC power supply, 30: Load, 40: Circuit breaker, 50: Motor drive circuit (drive circuit), 60: Motor, 61: Fan (cooling means)

Claims (4)

[Claims] 1. A PTC element having a positive temperature coefficient of resistance, whose resistance value rapidly increases when a predetermined temperature is reached, is provided on an electric circuit to suppress overcurrent flowing through the electric circuit and cool the PTC element whose temperature has increased. A self-cooling type current limiting device using a PTC element, wherein a pair of branch terminals are formed, wherein a flow path of a cooling medium is formed in the PTC element, and a current flowing through the PTC element is branched out from the PTC element. A cooling unit that sends the cooling medium toward the flow passage; and a cooling unit that is driven when a voltage drop based on a resistance voltage drop caused by a current flowing between the pair of branch terminals is equal to or higher than a predetermined voltage. A self-cooling type current limiting device using a PTC element, comprising a drive circuit. 2. The normal load current flowing through the electric circuit is represented by I
_S, and the resistance between the branch terminals at this time is r,
The overcurrent abnormality flowing through said path and I _MAX, the resistance value between the branch terminal of the time when the R, the predetermined voltage V is _{R × I MAX >> R × I} S ≧ V >> The self-cooling type current limiting device using a PTC element according to claim 1, wherein a relational expression of r × I _S is set to be satisfied. 3. A flow passage formed in the PTC element has the same shape as that of the PTC element.
The self-cooling type current limiting device using a PTC element according to claim 1 or 2, wherein the TC element is a through hole formed in a honeycomb structure. Wherein said V ₂ PTC element is a rate of increase in resistance against cold resistivity is small and cold resistivity 2-3 digits
O ₃ -Cr ₂ O ₃ self cooling current limiting device using a PTC element according to claim 3, characterized in that the ceramic.