JPH09233686A - Protector of power system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a quick return operation possible without the abnormal increase in temperature of an element which has a positive temperature coefficient. SOLUTION: A protective element 20 wherein a PTC(positive temperature coefficient) element 21 which has a positive temperature coefficient and an NTC(negative temperature coefficient) element 22 which has a negative temperature coefficient are integrally joined to each other and phase transition temperatures of these two elements are the same is directly connected to a line L of a power system. In a steady state, the current supplied to the line L is caused to flow through the PTC element 21. When overcurrent which is the same or above the rated current flows in the line L and the temperature of the PTC element 21 becomes the temperature the same as or higher than the phase transition one, the current in the PTC element 21 is suppressed and the suppressed current is caused to commutate through the NTC element 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power system protection device, and more particularly to protecting a power transmission / distribution system from an overcurrent such as a short-circuit current or an overload current flowing in an electric line of the power transmission / distribution system, or to a power transmission / distribution system. The present invention relates to a power system protection device for protecting a power device arranged in a power line such as a power system.

[0002]

2. Description of the Related Art In recent years, in order to protect a power transmission / distribution system from an overcurrent such as a short-circuit current or an overload current flowing in the power transmission / distribution system, a positive temperature coefficient of resistance, which increases with increasing temperature, is provided. Element (PTC (Positive Tempera
(ture coefficient) 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 an electric line of a power transmission and distribution system, for example, when an overcurrent exceeding the rated current flows in this electric line, Joule heat is generated and the temperature of the PTC element rises. Then, since this PTC 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 the overcurrent flowing in this electric path is suppressed (current limiting). Like On the other hand, when the accident recovers and the temperature of the PTC element returns to room temperature, the resistance value returns to the original low value, so that the power is automatically restored and power supply to this electric path is restarted.

[0003]

[Problems to be Solved by the Invention] However, PTC
NTC element has a resistance value that decreases when the temperature rises above a certain level.
Since there is a (Negative Temperature Coefficient) region, there is a problem that when the temperature of the PTC element rises abnormally, the resistance value decreases and a large current flows, and the PTC element is destroyed. Further, in order to reduce the power loss in the PTC element in the steady state, it is necessary to increase the cross-sectional area of the PTC element in order to reduce the resistance value at room temperature. However, when the cross-sectional area of the PTC element is increased, Even if an overcurrent more than the rated current flows, the temperature rise rate of the PTC element decreases, so that the current limiting operation becomes slow and the responsiveness deteriorates.

When the accident recovers after the current limiting operation, it is necessary to allow a predetermined current to flow in the electric line. However, if the temperature of the PTC element remains high, the resistance value remains large. There is also a problem that the current limiting operation continues until the temperature of the PTC element returns to room temperature and the recovery operation is delayed. Further, if the overcurrent flows for a long time at the accident point, there is a problem that damage such as melting of the line at the accident point increases. Therefore, in order to solve the above-mentioned problems, the present invention enables quick recovery operation without causing an abnormal temperature rise of an element having a positive temperature coefficient of resistance, and commutates an accident current to protect a PTC element. It is also to prevent the spread of damage at the accident point.

[0005]

SUMMARY OF THE INVENTION The present invention is a power system protection device for protecting a power system, and in order to solve the above-mentioned problems, in the invention described in claim 1, a power line of the power system is A first element (PTC element) having a positive temperature coefficient of resistance whose resistance value rapidly increases at a predetermined temperature of 1, and a negative element whose resistance value sharply decreases at a second predetermined temperature. Second element (NTC) having a temperature coefficient of resistance
Element) and a protection element in which the second predetermined temperature is made equal to or higher than the first predetermined temperature, and the current supplied to the electric line in the steady state is PT.
When the temperature of the PTC element reaches the first predetermined temperature due to an overcurrent exceeding the rated current flowing through the C element, the resistance value of the PTC element rapidly increases to suppress the current flowing through the PTC element. The suppressed current is commutated through the NTC element.

With this configuration, the resistance value of the PTC element at room 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
When an abnormality occurs in 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 the first predetermined temperature, the resistance value of this element rapidly increases, The current flowing through the device is suppressed (current limit). At the same time, as the temperature of the PTC element rises, P
When the temperature of the NTC element integrally joined with the TC element also rises and the temperature of the NTC element reaches the second predetermined temperature, the resistance value of this element sharply decreases and the current limited by the PTC element Will be commutated through the NTC element.

Further, in the invention according to claim 2,
Connect one end of the above-mentioned PTC element to the load side of the electric circuit,
Since the junction between the C element and the NTC element is connected to the power source side of the electric path and one end of the NTC element is grounded via a grounding resistance, for example, a short circuit accident occurs at the downstream side of the protective element of this electric path. When an arc current occurs at this accident point, a large current flows through the PTC element, causing a current limiting operation, and this limited current is grounded through the NTC element and the grounding resistor. The current will stop flowing and the arc will be extinguished in a short time.

Further, in the invention described in claim 3,
A power device directly connected to an electric path of the electric power system is provided, and a PTC element and a second predetermined electric resistor that are thermally coupled to the electric power device and whose resistance value rapidly increases when the electric circuit reaches a first predetermined temperature. It is equipped with a protective element that is thermally coupled to the NTC element whose resistance value suddenly decreases when the temperature rises, and that makes the second predetermined temperature equal to or higher than the first predetermined temperature. A current to be supplied is caused to flow through the PTC element and the power equipment, and when the power equipment abnormally heats up and the temperature of the PTC element and the NTC element reaches a first predetermined temperature, the current flowing through the PTC element and the power equipment is suppressed. This suppressed current is commutated through the NTC element.

With this configuration, the resistance value of the PTC element at room temperature is small in a steady state,
The electric current supplied to the electric circuit flows through the PTC element and the electric power equipment. On the other hand, when the electric power device generates heat for some reason, P of the protection element thermally coupled to the electric power device is generated.
The temperature of the TC element and the NTC element will rise. PT
When the temperature of the C element reaches the first predetermined temperature, the resistance value of the PTC element rapidly increases, and the current flowing through the PTC element and the power device is limited. At the same time, the resistance value of the NTC element sharply decreases, and the current limited by the PTC element is commutated through the NTC element.

Further, in the invention described in claim 4,
Connect one end of the above-mentioned PTC element to the power source side of the electric circuit,
Since the joint between the C element and the NTC element is connected to one end of the electric power device and one end of the NTC element is connected to the load side of the electric line, for example, harmonics flow in this electric line and the electric power device is abnormal. When heat is generated, the temperatures of the PTC element and the NTC element rise and the PTC element operates in a current limiting manner. On the other hand, this limited current flows through the NTC element, bypassing the power equipment.

Further, in the invention according to claim 5,
Connect one end of the above-mentioned PTC element to the power source side of the electric circuit,
Since the junction between the C element and the NTC element is connected to one end of the electric power device and one end of the NTC element and the other end of the electric power device are connected to the ground, for example, a short circuit current, In case of abnormal heat generation of electric power equipment due to current flow, PTC
The temperature of the element and the NTC element rises and the PTC element operates in a current limiting manner. On the other hand, this limited current flows through the NTC element and bypasses the power equipment, so that the power equipment is protected from overcurrent.

According to the invention of claim 6,
Since the above PTC element made of V ₂ O ₃ ceramics formed in a honeycomb structure is used, even if an overcurrent flows through this element or the temperature of this element rises due to heat generation of electric power equipment, the honeycomb structure radiates heat. Due to its large area, it quickly radiates heat and quickly returns to room temperature.

According to the invention of claim 7,
As the above-mentioned V ₂ O ₃ -based ceramic, a V ₂ O ₃ —Cr ₂ O ₃ ceramic having a honeycomb structure in which the resistance increase with respect to room temperature resistivity is 2 to 3 digits is used. Even if an overcurrent flows, the temperature does not rise before reaching the NTC region, and the resistance value suddenly increases.

Further, in the invention described in claim 8, as the above NTC element, a VO ₂ thin film, La _{1 -X} Sr _{X is used.}
These NTC elements have a large resistance decrease with respect to the room temperature resistivity because they are selected and used from MnO ₃ series ceramics and VO ₂ series ceramics. Therefore, when the temperature of this NTC element rises, its resistance value suddenly decreases. become.

[0015]

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. Also, PT
When the C element starts the current limiting operation, it is commutated to the NTC element, so that the abnormal temperature rise of the PTC element can be prevented and the destruction of the PTC element can be prevented. improves.

Further, in the invention according to claim 2,
Even if a short-circuit accident or the like occurs, the arc can be extinguished and automatically restored in a short time, so that maintenance of the power system becomes easy and maintainability is improved. In addition, one end of the PTC element is connected to the load side of the electric path, the joint between the PTC element and the NTC element is connected to the power supply side of the electric path, and one end of the NTC element is simply grounded via a ground resistance. Therefore, the circuit configuration is simplified, and this type of protection device can be manufactured in a small size and at low cost. Further, in the invention according to claim 3, even if the electric power device abnormally generates heat, the PTC element starts to conduct the current limiting operation, and at the same time, the PTC element is commutated to the NTC element, so that the electric current from the electric line does not flow to the electric power apparatus. It becomes possible to prevent the electric power equipment from being abnormally heated and destroyed, and the reliability of the electric power system is improved.

Further, in the invention described in claim 4,
One end of the PTC element is connected to the power supply side of the electric path, the joint of the PTC element and the NTC element is connected to one end of the power device, and N
Since the construction is such that only one end of the TC element is connected to the load side of the electric path, in the invention described in claim 5, P
One end of the TC element is connected to the power source side of the electric circuit, and the joint between the PTC element and the NTC element is connected to one end of the power device.
Since only one end of the C element and the other end of the electric power device are grounded, the circuit configuration is simple, and this type of protection device can be manufactured in a small size and at low cost.

Further, in the invention described in claim 6,
The use of V ₂ O ₃ based ceramic honeycomb structure, V ₂
Since the O ₃ -based ceramic has a smaller resistance than the BaTiO ₃ -based ceramic, it is possible to reduce the cross-sectional area, use a small element, and downsize this type of protection device. . Also, because of the honeycomb structure, the cooling efficiency is improved, and even if a large current flows through this element and the temperature rises, it is cooled early and the recovery operation becomes faster,
The recoverability of this type of protection device is improved.

According to the invention of claim 7,
V ₂ O ₃ whose resistance increase rate with respect to room temperature resistivity is 2 to 3 digits
By using -Cr ₂ O ₃ ceramics, even if an overcurrent exceeding the rated current flows through this element, the temperature does not rise until it reaches the NTC (negative temperature coefficient of resistance) region. Will be able to prevent the destruction of. Further, when the 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 protection device is improved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 Hereinafter, an embodiment of a power system protection device of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a case in which the power system protection device of the present invention is directly connected to an electric line of a power transmission and distribution system to limit an overcurrent flowing through the electric line. As shown in FIG. 1, the protective device in this case includes a protective element 20 and a ground resistance R, and the protective element 20 is connected between the AC power source 10 and the load 40 via an electric path L.

The protective element 20 is an element (P having a positive resistance temperature coefficient whose resistance value increases as the temperature rises).
A TC (Positive Temperature Coefficient) thermistor (hereinafter referred to as PTC element) 21 and an element having a negative temperature coefficient of resistance (NTC (Negative Temperatutu) which is integrally formed with the PTC element 21 via the electrode C ₁ ).
re Coefficient) thermistor, hereinafter referred to as NTC element) 22. The electrode C _{1 at} the joint between the PTC element 21 and the NTC element 22 is connected to the power source 10 side of the electric path L, and P
The electrode C ₂ on the opposite side of the electrode C ₁ at the joint between the TC element 21 and the NTC element 22 is connected to the load 40 side of the electric line L, and NT
Through the opposite electrode C3 Ha grounding resistance R of the electrode C ₁ of the joint between the PTC element 21 of the C element 22 is grounded.

In the above description, the PTC element 2
Although the example in which the 1 and the NTC element 22 are thermally coupled by interposing the electrode C ₁ has been described, other than this, for example, they may be thermally coupled by a heat pipe or the like.

The PTC element 21 has a temperature at which its specific resistance rapidly increases (generally called a phase transition temperature) of 8
It is preferable to use a material having a resistance value of about 0 ° C. to 200 ° C. and having a small resistance value at room temperature and a sharp increase in resistance value at the phase transition temperature. Here, as the PTC element,
Generally, it is known to use barium titanate (BaTiO ₃ ) ceramics, but as shown in Table 1, V ₂ O ₃ ceramics have higher room temperature resistivity and higher resistance than BaTiO ₃ ceramics. Since it has been revealed that the PTC element has excellent characteristics in terms of mechanical strength and the like, V ₂ O ₃ is used as the PTC element in the present invention.
Based ceramics, especially V ₂ O ₃ —Cr ₂ O ₃ ceramics are used.

[0024]

[Table 1]

As shown in FIG. 2, the PTC element 21 made of the V ₂ O ₃ --Cr ₂ O ₃ system ceramics has a honeycomb structure having a large number of voids 21a like a honeycomb therein. To do. A PTC made of V ₂ O ₃ -Cr ₂ O ₃ ceramics formed in a honeycomb structure in this way
As shown in the temperature-specific resistance characteristic of FIG.
A PTC element that undergoes a phase transition at about 30 ° C. is obtained.

On the other hand, the NTC element 22 has a temperature (generally referred to as a phase transition temperature) at which its specific resistance sharply decreases at about 80 ° C. to 200 ° C., and has a large resistance value at room temperature and a phase difference. It is preferable to use a material whose resistance value sharply decreases at the transition temperature. In the present invention, V
O ₂ thin film, La _1-X Sr _X MnO ₃ ceramics, VO ₂
Use ceramics. These NTC elements 22
As shown in the temperature-specific resistance characteristic of FIG. 4, a material having a large specific resistance at room temperature and undergoing a phase transition at about 130 ° C. is used.

Next, the operation of the protective device constructed as described above will be explained. In a steady state in which a current equal to or lower than the rated current flows in the electric path L, the resistance value of the PTC element 21 at room temperature is small, and therefore the current supplied from the power source 10 is
An electrode C _{1 at} the joint between the TC element 21 and the NTC element 22,
A current is supplied to the load 40 from the electrode C ₂ through the PTC element 21. At this time, since the resistance value of the PTC element 21 is small, the power loss caused by the current flowing through the PTC element 21 is small.

If, for some reason, the insulator 30 on the downstream side electric line L of the protective device is flashed over, an overcurrent I _S above the rated current flows into the electric line, and P
The TC element 21 generates heat due to Joule heat and its temperature rises. The temperature of the PTC element 21 rises and the temperature rises to 13
When the temperature exceeds 0 ° C., the specific resistance of the PTC element 21 increases as shown in FIG. 3 and the resistance value sharply increases, so that the current flowing in the PTC element 21 is limited. On the other hand, PTC
When the temperature of the element 21 rises, the temperature of the NTC element 22 integrally joined to the PTC element 21 also rises, and when the temperature exceeds 130 ° C., the specific resistance of the NTC element 22 decreases.
As shown in, the resistance value decreases sharply.
Then, the current flowing in the PTC element 21 is commutated to the NTC element 22 side and is grounded via the ground resistance R, so that the arc generated in the insulator 30 is extinguished.

At this time, as shown in Table 1 above, the PTC element 21 has a resistance increase of 2 to 3 digits with respect to the room temperature resistivity, so that its specific resistance increases rapidly and its resistance value increases rapidly. Therefore, the PTC element 21 has a negative resistance temperature coefficient (NTC (Negative Temperature Coeff).
icient)) temperature will rise up to the area,
The PTC element 21 will not be destroyed due to overcurrent exceeding the rated current. In this way, the PT of the protection element 20
After the C element 21 performs the current limiting operation and the NTC element 22 performs the commutation operation, the PTC element 21 has a honeycomb structure having the voids 21a as shown in FIG. The element 21 is cooled and rapidly radiates heat to return to the resistance value at room temperature. Therefore, the recovery after the current limiting operation becomes faster.

FIG. 5 is a diagram showing an example of a case where the protective device configured as described above is directly connected to the electric path between the connection points in the parallel operation of the transformer to limit the overcurrent flowing at the accident point. . In this case, as shown in FIG. 5, from the first path L ₁ connecting the transformer T _1, from the second path L ₂ connecting the transformer T _2, the secondary side of the transformer T ₁ A The point and the point B on the secondary side of the transformer T ₂ are connected to a protective device including a protective element 20 and a ground resistance R. By connecting the protection device in this manner, the loads 41, 4 and 4 are connected from the first electric line L ₁ through the transformer T _1.
2 is supplied with electric power, the electric power is supplied to the loads 41, 42 from the second electric line L ₂ through the transformer T ₂ , and the loads 41, 4 are supplied.
The electric power is exchanged to the transformer 2, and the transformer T ₁ ,
Efficient operation of T ₂ will be performed.

Here, when a short circuit accident occurs at a point C between the point A and the load 41, I ₁ + I _{2 at the} accident point C unless a protective device is provided on the electric path between the points A and B. However, by providing the protection device 10 of the present invention in the electric path between the points A and B, the current I ₂ is current-limited and commutated as described above to the ground resistance R. Since it is grounded through, only the current I ₁ flows at the accident point C, and the overcurrent flowing at the accident point C can be prevented.

In the first embodiment configured as described above, since the V ₂ O ₃ --Cr ₂ O ₃ ceramics having a small resistance value at room temperature is used as the PTC element 21, this PTC element 21 is electrically connected. Even if it is directly connected to L, the resistance loss becomes small. For this reason, power loss in a steady state can be minimized, and overcurrent can be prevented without power loss. Further, when the PTC element 21 starts the current limiting operation, it is commutated to the NTC element 22, so that the abnormal temperature rise of the PTC element 21 can be prevented, and P
Since the destruction of the TC element 21 can be prevented, the reliability of this type of protection device is improved.

Further, even if a short-circuit accident or the like occurs, the arc can be extinguished and automatically restored in a short time, so that maintenance of the electric power system becomes easy and maintainability is improved. In addition, the PTC element 2
1 is the load on the electric path on the side opposite to the junction with the NTC element 22.
0 side, the junction of the PTC element 21 and the NTC element 22 is connected to the power source 10 side of the electric circuit, and the P of the NTC element 22 is connected.
Since the opposite side of the junction with the TC element 21 is simply grounded via the grounding resistor R, the circuit configuration is simplified, and this type of protection device can be manufactured in a small size and at low cost.

The V ₂ O ₃ system ceramic is BaTiO _3.
Since the resistance is smaller than that of ₃ series ceramics, it is possible to reduce the cross-sectional area and the small PTC element 21.
Can be used, and this type of protection device can be downsized. Further, since it has a honeycomb structure, the cooling efficiency is improved, and a large current flows through the PTC element 21 and
Even if the temperature of 1 rises, it is cooled early and returns to room temperature, so the recoverability of this type of protection device is improved.

Further, in V ₂ O ₃ -Cr ₂ O ₃ ceramics, the resistance increase with respect to the room temperature resistivity is two to three orders of magnitude, so that even if an overcurrent exceeding the rated current flows through the PTC element 21, it will be in the NTC region. Since the temperature does not rise by the time the temperature rises, it becomes possible to prevent the PTC element 21 from being destroyed due to the temperature rise. Further, when the 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 protection device is improved.

Embodiment 2 FIG. 6 shows a protective element 2 constructed in the same manner as in Embodiment 1 described above.
It is a figure which shows an example in case 0 is thermally connected with the series reactor used as a power equipment, and is directly connected to an electric circuit, and protects a series reactor from abnormal heat generation. As shown in FIG. 6, the AC power source 10 is connected to the electrode C ₂ of the PTC element 21 of the protection element 20 through the electric path L, and one end of the reactor 50 is connected in series with the electrode C _{1 at} the joint between the PTC element 21 and the NTC element 22. And the other end of the reactor 50 is connected to the load side of the electric path L. The electrode C ₃ of the NTC element 22 is connected to the other end of the reactor 50. And NTC element 2
CT60 between the second electrode C ₃ and the other end of the reactor 50.
, And the lamp 70 is connected in series to the CT 60. The PTC element 21 and the NTC of the protection element 20
The element 22 and the reactor 50 are arranged close to each other or thermally coupled by a heat pipe or the like.

With the above-described structure, in a steady state in which a current equal to or less than the rated current flows in the electric path L, as described above, the resistance value of the PTC element 21 at room temperature is small, so that the current supplied from the power supply 10 is small. Is the circuit L, electrode C ₂ , PTC
The reactor 50 passes through the element 21 and the electrode C _{1 at the} junction.
A current is supplied to a load (not shown) via the. At this time, since the resistance value of the PTC element 21 is small, the power loss caused by the current flowing through the PTC element 21 is small.

If harmonics are generated in the electric path L for some reason and the reactor 50 heats up abnormally, the temperature of the PTC element 21 and the NTC element 22 of the protection element 20 thermally coupled to the reactor 50 rises. When the temperature of the PTC element 21 and the NTC element 22 rises and exceeds 130 ° C., the specific resistance of the PTC element 21 increases as shown in FIG. The current that was flowing inside was limited and the reactor 50
A current stops flowing through the NTC element 22, while the specific resistance of the NTC element 22 decreases as shown in FIG. 4, and the resistance value decreases sharply. Then, the current flowing through the PTC element 21 becomes N
It is commutated to the side of the TC element 22 and the lamp 7 passes through CT60.
The current flows to 0, and the lamp 70 is turned on. As a result, it becomes possible to inform that an abnormal accident has occurred.

When a short circuit accident or the like occurs at the point D of the electric line L and an overcurrent exceeding the rated current flows in the electric line L, the PTC element 21 generates heat due to Joule heat and its resistance value increases, so that the fault current is increased. Since the current is limited, the overcurrent does not flow in the reactor 50. On the other hand, when the PTC element 21 generates heat, the temperature of the NTC element 22 also rises as described above, and the NTC element 2
The resistance value of No. 2 decreases and the current flowing in the PTC element 21 commutates to the NTC element 22 side. As a result, the lamp 70 is turned on and it becomes possible to notify that an abnormal accident has occurred.

FIG. 7 shows a parallel device (electric power device) connected in parallel to an electric circuit and a protection element 20 configured in the same manner as in the above-described first embodiment, which is thermally coupled and connected in parallel to prevent the parallel device from overcurrent. It is a figure which shows an example at the time of protecting from abnormal heat generation based on. As shown in FIG. 7, the AC power source 10 is connected to the electrode C ₂ of the PTC element 21 of the protection element 20 through the electric path L,
The electrode C ₃ of the NTC element 22 is grounded. Also, PT
One end of the parallel device 80 is connected in series with the electrode C _{1 at} the joint between the C element 21 and the NTC element 22, and the other end of the parallel device 80 is grounded. PTC element 21 and N of protection element 20
The TC element 22 and the parallel device 80 are arranged close to each other or thermally coupled by a heat pipe or the like.

Here, for some reason, the parallel device 80
When an overcurrent flows through the parallel device 80 and the parallel device 80 abnormally generates heat, the temperature of the PTC element 21 and the NTC element 22 of the protection device 20 thermally coupled to the parallel device 80 rises. When the temperature of the PTC element 21 and the NTC element 22 rises and exceeds 130 ° C., the specific resistance of the PTC element 21 increases as shown in FIG.
The current flowing through the element 21 is limited and the parallel device 80
A current stops flowing through the NTC element 22, while the specific resistance of the NTC element 22 decreases as shown in FIG. 4 and its resistance value sharply decreases. Then, the current flowing in the PTC element 21 is NT
It is commutated to the C element 22 side.

In the second embodiment configured as described above, even if the reactor 50 or the parallel device 80 abnormally generates heat, the PTC element 21 is commutated to the NTC element 22 at the same time when the current limiting operation starts. Since the current from the electric path L does not flow to the reactor 50 or the parallel device 80, it is possible to prevent the reactor 50 or the parallel device 80 from being abnormally heated and destroyed, and the reliability of the power system is improved. In addition, in the above-described first and second embodiments, the PTC element 21 and the NTC element 22 are used one by one, and they are integrally joined to each other to protect the protection element 20.
However, the protective element 20 may be configured by using two PTC elements and two NTC elements each and integrally joining them. In this case, as shown in FIG. 8, the PTC elements 23 and 24 are arranged outside and the NTC elements 25 and 26 are arranged inside. Further, the first electrodes C ₁ and C ₁ are provided between the PTC element 23 and the NTC element 25 and between the PTC element 24 and the NTC element 26, and the NTC element 25
A second electrode C ₂ is provided between and 26. Then, the first electrodes C ₁ and C ₁ are connected to the power source side of the electric path, and the electrodes C ₂ and C _{2 of} the PTC elements 23 and 24 are connected to the load side of the electric path.
Further, the second electrode C ₂ is grounded via the ground resistance R, for example.

With this configuration, when an overcurrent exceeding the rated current flows in the electric path and the PTC elements 23 and 24 generate heat and the temperature rises, these PTC elements 23 and 24 are generated.
The NTC elements 25 and 26 arranged inside of the NTC elements are efficiently heated, and the temperature rising rate of the NTC elements 25 and 26 can be improved. Further, the protection element 20 of the present invention is not limited to the above-mentioned embodiment, but can be used, for example, for protection of a thyristor device, or can be used as a fuse for low-voltage network power distribution.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a PTC element of the present invention formed in a honeycomb structure.

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

FIG. 4 is a diagram showing temperature-specific resistance characteristics of the NTC element of the present invention.

FIG. 5 is a diagram showing an example in which the protection device of the present invention is directly connected to an electric circuit of a connection point in parallel operation of a transformer.

FIG. 6 is a diagram showing an example of protecting a power device by connecting the protection device of the present invention and the power device in series to an electric path of a power transmission and distribution system.

FIG. 7 is a diagram showing an example of connecting the protection device of the present invention and a power device in parallel to an electric path of a power transmission and distribution system to protect the power device.

FIG. 8 is a diagram showing another example of the configuration of the protection element of the present invention.

[Explanation of symbols]

10 ... AC power supply, 20 ... Protecting element, 21 ... PTC element (element having positive temperature coefficient of resistance), 22 ... NTC element (element having negative temperature coefficient of resistance), R ... Ground resistance, 4
0 ... load

Claims (8)

[Claims] 1. A power system protection device for protecting a power system, which has a positive temperature coefficient of resistance whose resistance value rapidly increases when a first predetermined temperature is reached in an electric path of the power system. Is thermally coupled to a second element having a negative temperature coefficient of resistance, the resistance value of which rapidly decreases when the second predetermined temperature is reached, and the second predetermined temperature is set to the second predetermined temperature. 1
A protective element that is equal to or higher than the predetermined temperature of, and in a steady state, a current supplied to the electric path is caused to flow through the first element, and an overcurrent of a rated current or more flows in the electric path, and When the temperature of the first element reaches the first predetermined temperature, its resistance value suddenly increases and the current flowing through the first element is suppressed, and the suppressed current is commutated through the second element. A power system protection device characterized in that 2. The one end of the first element of the protection element is connected to the load side of the electric path, and the joint portion of the first element and the second element of the protection element is connected to the power supply side of the electric path. The power system protection device according to claim 1, wherein one end of the second element of the protection element is grounded via a grounding resistance. 3. A power system protection device for protecting a power system, comprising: a power device directly connected to the power line of the power system; and a first power line connected to the power device by being thermally coupled to the power device. A first element having a positive resistance temperature coefficient whose resistance value rapidly increases at a predetermined temperature, and a first element having a negative resistance temperature coefficient whose resistance value rapidly decreases at a second predetermined temperature. The second element is thermally coupled to the second element, and the second predetermined temperature is equal to or higher than the first predetermined temperature. Flow through the first element and the power device, and when the power device abnormally generates heat and reaches the first predetermined temperature, its resistance value rapidly increases and flows to the first element and the power device. To suppress the current An electric power system protection device, characterized in that the suppressed current is commutated through the second element. 4. One end of a first element of the protection element is connected to a power source side of the electric circuit, and a joint portion of the first element and a second element of the protection element is connected to one end of the power device. 4. The power system protection device according to claim 3, wherein one end of the second element of the protection element is connected to the load side of the electric path. 5. The one end of the first element of the protection element is connected to the power source side of the electric circuit, and the joint between the first element and the second element of the protection element is connected to one end of the power device. The power system protection device according to claim 3, wherein one end of the second element of the protection element and the other end of the power device are connected so as to be grounded. 6. The power system according to claim 1, wherein the first element of the protective element is formed of V ₂ O ₃ -based ceramics in a honeycomb structure. Protective device. 7. The V ₂ O ₃ -based ceramics having a resistance increase rate with respect to room temperature resistivity of 2 to 3 digits is V ₂ O ₃ —Cr ₂ O ₃
The protective device according to claim 6, wherein the ceramic is formed into a honeycomb structure. 8. The second element of the protective element is selected from any one of VO ₂ thin film, La _{1 -X} Sr _X MnO ₃ based ceramics, and VO ₂ based ceramics. 5. The power system protection device according to any one of 5.