JPH08251811A - Spot network - Google Patents

Abstract

PURPOSE: To obtain a spot network in which a fault generation position can be cut off from a power-supply passage by a method wherein a fuse, for reverse- current prevention, whose cutoff characteristic is close to that of a protective fuse is interposed and inserted in a position near a network bus. CONSTITUTION: When a short circuit or a ground fault is generated in a point B between a protect circuit breaker 10a in a supply line 4a and a fuse 14a for reverse-current prevention, a forward current I which is supplied from the side of a power-supply cable 1a exceeds a rated current IR so as to be increased to a fault current IS, and a protective fuse 8a or the protective circuit breaker 10a is cut off. In addition, a reverse current via a network bus 5 from other normal supply lines 4b, 4c flows to a fault generation point A via the fuse 14a for reverse-current prevention. In this case, since a reverse fault current which flows to the fault generation point B becomes 21S, the fuse 14a for reverse-current prevention is cut off after the time required for its cutoff has elapsed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot network for supplying electric power from a power supply source to a common network bus via three or more circuit power supply paths, and particularly when a fault current flows in one line. Spot network with improved circuit disconnection characteristics.

[0002]

2. Description of the Related Art For example, in a power supply system for supplying power to each device in a production facility of a factory where a long power failure is not allowed, power is supplied from a power supply source to a common network bus via a plurality of power supply paths. And a load composed of each of the above-mentioned devices is connected to the common network bus.

By supplying power from a power supply source to a common network bus via a plurality of power supply paths in this way, it is possible to avoid a load from concentrating on a specific power supply path and to use one power supply path. Even when the supply path cannot be used, power can be supplied to each load through another power supply path.

Such a spot network is constructed, for example, as shown in FIG. Cable heads 2a, 2b, 2c and a primary circuit breaker 3 for power cables 1a, 1b, 1c connected to a power supply source (not shown)
Supply line 4 as a power supply path via a, 3b, 3c
One ends of a, 4b, and 4c are connected. One common network bus 5 is connected to the other ends of the supply lines 4a, 4b, 4c. This common network bus 5
To the trunk protection device 6a. 6b. 6c. A plurality of loads (not shown) are connected via 6d and 6e.

Each of the supply lines 4a, 4b, 4c has a primary circuit breaker 3a, 3b. From the 3c side, voltage step-down transformers 7a, 7b, 7c, protective fuses 8a, 8b, 8c, power detecting current transformers 9a, 9b, 9c, protective breaker 10
a, 10b, 10c are directly inserted.

Protective relays 11a, 11b and 11c are connected in parallel to the protective circuit breakers 10a, 10b and 10c. The protective relays 11a, 11b, 11c are current transformers 12a, 12b, which are inserted in the supply lines 4a, 4b, 4c.
When the current I detected via 12c exceeds the rated current I _R and becomes the fault current (short circuit current) I _S , the protective circuit breaker 10
a, 10b, 10c are cut off.

Also, in each of the protective fuses 8a, 8b, 8c, the current I flowing through the supply lines 4a, 4b, 4c is the rated current I.
_If it exceeds _R and becomes the fault current (short circuit current) I _S, it will melt down. In addition, the landslide relay 13 is a transformer 7a, 7b, 7c.
Detect that a landfall accident has occurred.

In the spot network having such a configuration, when the supply lines 4a, 4b, 4c are in a normal state, the power supplied from the power cables 1a, 1b, 1c is passed through the supply lines 4a, 4b, 4c. And is supplied to the common network bus 5. Then, the electric power is supplied to each load connected to the common network bus 5.
The currents I flowing through the supply lines 4a, 4b, 4c are the same.

In such a spot network, for example, the protective fuse 8 in one supply line 4a
When a short circuit or ground faults accident point A between a and the protective circuit breaker 10a is generated, forward current I supplied from the power supply cable 1a side is increased to fault current I _S exceeds the rated current I _R Therefore, the protective fuse 8a is blown.

When a short circuit or a landfall accident occurs at the point A, a reverse current flows from the other normal supply lines 4b and 4c via the common network bus 5 to the protective circuit breaker 10.
It flows to the accident occurrence point A through a. Since this current also becomes the fault current I _S exceeding the rated current I _R , the protective circuit breaker 1
0a shuts off.

As a result, the accident occurrence point A is completely protected by the protective fuse 8a and the protective circuit breaker 10a.
Separated from a, this spot network operates normally on each of the remaining normal supply lines 4b, 4c.

[0012]

However, the spot network shown in FIG. 3 still has the following problems to be solved. For example, if a short circuit or a landfall accident occurs at a point B between the protective circuit breaker 10a and the network bus 5 in one supply circuit 4a, the forward current I supplied from the power cable 1a side is the rated current. I
_The fault current I _S exceeds _R, and either the protective fuse 8a or the protective circuit breaker 10a is cut off, and the forward current I supplied from the power cable 1a side is cut off.

However, from the other normal supply lines 4b, 4c via the common network bus 5, this supply circuit 4a
The electric current flowing into the accident occurrence point B of is not cut off. As a result, the quasi-directional current I of the other normal supply lines 4b, 4c
There exceeding the rated current I _R, the fault current I _S, and the normal supply line 4b, 4c of the protection fuse 8b, 8c or protective breakers 10b, 10c is cut off.

As a result, not only the power supply line 4a in which an accident has occurred but also all the power supply lines 4a to 4c including the normal power supply lines 4b and 4c are cut off, which causes a problem that power supply by the spot network is stopped.

Even if a short circuit or a landfall accident occurs at the point A, there are still the following problems. That is, other normal supply lines 4b, 4c to the accident occurrence point A
A reverse current flows from the same through the common network bus 5, and this current I exceeds the rated current I _R. Fault current I _S
Then, the protective circuit breaker 10a is cut off.

However, in general, the protective circuit breaker 10a and the protective fuse 8a are not instantaneously interrupted when an accident current I _S exceeding the rated current I _R flows, but the protective circuit breaker 10a is not instantaneously interrupted.
It is cut off based on the cut-off characteristics of a and the protective fuse 8a. FIG. 4 shows the breaking characteristic F ₀ of the general protective fuses 8a to 8c and the breaking characteristic B ₀ of the protective breakers 10a to 10c.

Breaking characteristics F _{0 of the} protective fuses 8a to 8c
Is the protective fuses 8a to 8a when the fault current I _S and the corresponding fault current I _S flow when the current I of the supply circuits 4a to 4c becomes the fault current I _S that exceeds the rated current I _R.
The time T _F required for shutting off (melting) of c is shown. When the fault current I _S is small, the required breaking time T _F is long (long), and when the fault current I _S is large, the required breaking time T _F is short (short).

On the other hand, the breaking characteristic B ₀ of the protective circuit breakers 10a to 10c is such that the current I of the supply circuits 4a to 4c is the rated current I _R.
When the fault current I _S exceeds the fault current I _S and the fault current I _S and the relevant fault current I _S flow, the protective circuit breaker 10
cutoff time required a~10c shows the T _B. Generally, in the protective circuit breakers 10a to 10c, the required breaking time T _B has a substantially constant value when the fault current I _S is in a certain range.

Consider a case in which a fault current flows from each of the cutoff characteristics F ₀ and B ₀ to the fault occurrence point A in FIG. 3 from the other normal supply lines 4b and 4c. Other normal supply line 4
When the fault current I _S flows through the protective fuses 8b and 8c of the b and 4c, the fault current 2I _S that is the total of these flows through the protective breaker 10a of the supply line 4a.

For example, if the fault current I _S is the breaking characteristic F ₀ . B
_{If 0} has the relationship shown in FIG.
The required time T _B for breaking the protective circuit breaker 10a at I _S is
Since the protective fuses 8b, 8c of the supply lines 4b, 4c are shorter than the required breaking time T _{F at} the fault current I _S , the protective breaker 10a is cut off, but the protective fuses 8b, 8c are not blown. In this case, when the cause of the accident is eliminated, the protection circuit breaker 10a may be restored (reset) based on the original condition.

However, if the required time T _F for shutting off the protective fuses 8b and 8c and the required time T _B for shutting off the protective circuit breaker 10a are close to each other, the protective fuses 8b and 8c are also closed until just before the occurrence of fusing. The accident current I _S will flow. When a fault current I _S that exceeds the rated current I _R is applied to the protective fuses 8b and 8c, deterioration of the protective fuses 8b and 8c begins immediately before the interruption required time T _F after the start of the flow, and the interruption required time T _{The F} reaches the limit of deterioration and melts.

Once deteriorated, this deterioration history is not restored. Therefore, when the same fault current value I _S occurs next time, the deterioration history due to this fault current I _S is added to the previous deterioration history. To be done. Thus, even if the protective fuses 8a and 8b are not blown, the deterioration history is accumulated. As a result, the current I of the supply circuits 4b and 4c
Even if does not reach the rated current value I _R , the protective fuses 8a and 8b may be blown.

Therefore, the reliability of power supply to the spot network is reduced. The present invention has been made in view of such circumstances, even if a short circuit or a landfall accident occurs at any point in the power supply path, the accident occurrence position can be separated from the corresponding power supply path, It is an object of the present invention to provide a spot network that can reliably supply power to a load and improve the reliability of the entire network.

[0024]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a common power supply source through three or more circuits each of which has a protective fuse and a protective circuit breaker connected in series. Power is supplied to the network bus, multiple loads are connected to this network bus, and when a fault current exceeding the rated current flows in each power supply line, the protective fuse or protective breaker of the power supply line is blown. Alternatively, in a spot network to be interrupted, a backflow preventing fuse having an interrupting characteristic similar to that of a protective fuse is inserted at a position near a network bus in each power supply path.

[0025]

In the spot network configured as described above, the backflow preventing fuse is inserted in the vicinity of the network bus in each power supply path. And
If a fault current exceeding the rated current flows due to a short circuit or ground break between the protective fuse and the protective circuit breaker in one power supply path, the protective fuse will melt and the power supply source will supply this power. The forward current supplied to the path is cut off.

When a fault current exceeding the rated current flows due to a short circuit or a ground drop between the protective circuit breaker and the backflow prevention fuse, the protective fuse or protective circuit breaker cuts off the power. The forward current supplied from the supply source to this power supply path is cut off.

In any case, a reverse fault current exceeding the rated current flowing from another normal power supply line to the fault occurrence point of this power supply line via the network bus is fed to the backflow prevention fuse. Flowing. Since there are two or more normal power supply paths, the fault current flowing through the backflow prevention fuse has a current value that is at least twice the fault current flowing through each power supply channel.

Therefore, if the backflow prevention fuse has a breaking characteristic similar to that of the protective fuse, the time at which the fault current flowing through the protective fuse in the normal power supply path starts fuse deterioration immediately before the required interruption time. The backflow prevention fuse is always blown by the time the temperature reaches. Similarly,
The backflow prevention fuse is blown before the protective circuit breaker of the normal power supply path is cut off.

Therefore, even if a short circuit or a landfall accident occurs at any point in the power supply path, the accident occurrence point can be separated from the corresponding power supply path. Further, the protective fuses and protective circuit breakers of other normal power supply paths are not cut off, and the protective fuses are not deteriorated.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a power system diagram showing a schematic configuration of the spot network of the embodiment. The same parts as those of the conventional spot network shown in FIG. 3 are designated by the same reference numerals. Therefore, detailed description of the overlapping portions will be omitted.

In the spot network of this embodiment, the network buses within the respective supply lines 4a, 4b, 4c as the respective power supply paths connected between the respective power cables 1a, 1b, 1c and the common network bus 5. Backflow prevention fuses 14a, 14b, 1 at positions near 5 respectively.
4c is inserted. Other configurations are almost the same as those of the conventional spot network shown in FIG.

Each of the backflow preventing fuses 14a, 14
b and 14c have a breaking characteristic similar to that of the protective fuses 8a, 8b and 8c provided in the supply lines 4a, 4b and 4c.

In FIG. 2, the breaking characteristic F ₀ of the protective fuses 8a to 8c, the breaking characteristic H ₀ of the backflow preventing fuses 14a to 14c, the breaking characteristic B ₀ of the protective breakers 10a to 10c, and the deterioration of the protective fuses 8a to 8c. The characteristic G ₀ is shown.

Since the breaking characteristic F ₀ of the protective fuses 8a to 8c and the breaking characteristic B ₀ of the protective circuit breakers 10a to 10c have been described with reference to FIG. 4, detailed description thereof will be omitted. The cutoff characteristic H ₀ of the backflow prevention fuse has a characteristic similar to the cutoff characteristic F ₀ of the protection fuse, as shown in the figure. The breaking characteristic H ₀ of the backflow preventing fuse is the breaking characteristic F _{0 of the} protective fuse.
Compared with, the interruption required time is set to be slightly shorter for the same fault current I _S.

Further, the deterioration characteristic G ₀ of the protective fuses is that the protective fuses 8a to 8c correspond to the protective fuses 8a to 8c after the fault current I _S exceeding the rated current I _R starts flowing.
The deterioration start time T _G until the deterioration of c starts is shown.

Next, such cutoff characteristics F ₀ , B ₀ , H
₀ and the protective fuses 8a to 8c having the deterioration characteristic G ₀ ,
Protective circuit breakers 10a to 10c and backflow certain use fuse 14
The operation of the spot network incorporating the supply circuits 4a to 4c in which a to 14c are connected in series will be described.

For example, if a short circuit or a landfall occurs at a point A between the protective fuse 8a and the protective circuit breaker 10a in one supply line 4a, the forward current I supplied from the power cable 1a side is the rated current. Since the fault current I _S increases beyond I _R , the protective fuse 8a is blown.

In this embodiment, the rating of the transformer 7a is 1500 kVA, the internal impedance of the transformer 7a is 7.5%, the secondary side voltage of the transformer 7a is 415 V, and the line impedance is neglected. Supply line 4
The maximum current that can be supplied by a is about 27.8 kA. Therefore, when an accident occurs, the accident current I _S flowing from the power supply side is 2
It becomes 7.8 kA (I _S = 27.8 kA).

When a short circuit or a landfall accident occurs at the point A, a reverse current flows from the other normal supply lines 4b and 4c via the common network bus 5 to the backflow preventing fuse 14a and the protective circuit breaker. It flows to the accident occurrence point A through 10a. In this case, the maximum supplyable current of the normal supply lines 4b and 4c is about 27.8 kA, and the reverse fault current flowing to the fault occurrence point A is 2I _S (= 2 × 27.8).
kA), the backflow prevention fuse 14a or the protective relay 10a is cut off.

In this case, which of the backflow prevention fuse 14a and the protective relay 10a is to be cut off is determined by the breaking characteristics H ₀ and B ₀ and the fault current 2I _S (= 55.6) shown in FIG.
It depends on the value of kA). In the spot network of this embodiment, as shown in FIG. 2, when the interruption required times T _H and T _B at the fault current 2I _S are compared, the interruption required time T _H of the backflow prevention fuse 14a is shorter.
Backflow prevention fuse 1 with cutoff time T _H = 9.5 ms
4a is melted and shielded, and the protective relay 10a is not cut off.

Therefore, the accident occurrence point A is separated from the supply circuit 4a. Next, the protective fuses 8b and 8c and the backflow prevention fuse 14 in the normal supply circuits 4b and 4c at the time when the backflow prevention fuse 14a is fused and shielded.
b. Verify 14c.

In each of the protective fuses 8b and 8c and the flow prevention fuses 14b and 14c, the maximum current that can be supplied to the supply circuit 4a in which an accident has occurred is 27.
A quasi-direction fault current I _S of 8 kA flows. As shown in FIG. 2, the breaking time T _F of each protective fuse 8b, 8c and the breaking time T _H1 of the flow preventing fuses 14b, 14c at the fault current I _S = 27.8 kA are determined by the supply circuit 4a in which the fault has occurred. Fault current 2I _S of the flow prevention fuse 14a
Breaking time required at (= 55.6 kA) T _H = 9.5
It is much longer than ms, so it will not be blown out.

The fault current I _S = 27.8 kA interruption time T _H = 9.5 m in the normal supply circuits 4b and 4c.
s is the protective fuse 8b, 8 at the relevant fault current I _S
Since the deterioration start time T _G of the deterioration characteristic G ₀ of c is shorter than 43 ms, the protection fuses 8b and 8c are not affected by the deterioration history.

Similarly, although not shown in FIG. 3, the deterioration characteristics of the flow prevention fuses 14b and 14c are also shown in FIG.
b. Since it is close to the deterioration characteristic G _{0 of} 8c, the flow prevention fuses 14b and 14c are not affected by the deterioration history.

Further, the fault current I _{S of the} protective circuit breakers 10b and 10c in the normal supply circuits 4b and 4c is I _S = 27.8.
Since the required interruption time T _B (= 90 ms) at kA is much longer than the required interruption time T _H = 9.5 ms of the flow prevention fuse 14a of the supply circuit 4a in which the accident has occurred, the interruption is not interrupted.

In this way, each of the normal supply circuits 4b,
4c, each protection fuse 8b, 8c, each backflow prevention fuse 14b, 14c, and each protection circuit breaker 10b, 10
c is not cut off, and each protection fuse 8
b, 8c and the respective backflow preventing fuses 14b, 14c are not subject to deterioration history.

Next, a point B between the protective circuit breaker 10a and the backflow prevention fuse 14a in one supply line 4a.
If a short circuit or a landfall accident occurs in the power supply cable 1a, the forward current I supplied from the power cable 1a side exceeds the rated current I _R and increases to the accident current I _S , so the protective fuse 8a or the protective circuit breaker 10a is cut off. To be done. Which is to be cut off is determined from the comparison of the respective breaking times T _F and T _{B at} the fault current I _S = 27.8 kA shown in FIG.
Is cut off.

When a short circuit or a landfall accident occurs at the point B, a reverse current flows from the other normal supply lines 4b and 4c through the common network bus 5 and the backflow prevention fuse 14a. Flow to point A. in this case,
The maximum current that can be supplied by the normal supply lines 4b and 4c is about 2
Since it is 7.8 kA, the reverse fault current flowing to the accident occurrence point B is 2I _S (= 2 × 27.8 kA), and therefore the backflow prevention fuse 14a requires the interruption time T _H =
It is cut off after 9.5 ms.

Therefore, the accident occurrence point B is separated from the supply circuit 4a. In this case, the normal supply circuits 4b and 4c
Of the protection fuses 8b and 8c, the backflow prevention fuse 14b. The operation of 14c and each of the protective circuit breakers 10b and 10c is not interrupted and does not receive a deterioration history as in the case where a short circuit or a landfall accident occurs at the point A described above.

In the spot network having such a structure, a point A between the protective fuse 8a and the protective breaker 10a or a point between the protective breaker 10a and the backflow preventing fuse 14a in one supply circuit 4a. B
In the above, even if a short circuit or a landfall accident occurs, the accident occurrence points A and B can be reliably separated from the corresponding supply circuit 4a without adversely affecting the other normal supply circuits 4b and 4c. it can. Therefore, power can be continuously supplied to each load via the common network bus 5, and the reliability of the entire spot network can be significantly improved.

Furthermore, even if a short circuit or a landfall accident occurs in one supply circuit 4a, the other normal supply circuits 4b, 4
Even if the fault current I _S flows in c, this fault current I _S
Each fuse 8b. 8c, 14b, 14
Not to mention that c is not blown, it does not receive a deterioration history. Therefore, due to the performance deterioration, the current I
Is less than or equal to the rated current I _R , but the fuse 8b.
It is possible to prevent the fusing of 8c, 14b, and 14c, and it is possible to further improve the reliability of the entire spot network.

The present invention is not limited to the above embodiment. In the embodiment spot network shown in FIG. 1, three supply circuits 4a, 4b and 4c are used, but it is also possible to use four or more supply circuits, for example.

[0053]

As described above, in the spot network of the present invention, the backflow preventing fuse is inserted near the common network bus of each power supply path. Therefore, no matter where in the power supply path a short circuit or a landfall accident occurs, this accident location can be reliably separated from the power supply path without affecting other normal power supply paths. In addition, the power can be supplied to each load connected to the network bus without giving a history of deterioration to the protective fuse in the normal power supply path, and the reliability of the entire system can be improved.

[Brief description of drawings]

FIG. 1 is a power system diagram showing a schematic configuration of a spot network according to an embodiment of the present invention.

FIG. 2 is a breaking characteristic diagram of each fuse and each protective breaker incorporated in each supply circuit of the network of the embodiment.

FIG. 3 is a power system diagram showing a schematic configuration of a conventional spot network.

FIG. 4 A breaking characteristic diagram of a general fuse and a circuit breaker

[Explanation of symbols]

1a, 1b, 1c ... Power cable, 4a, 4b, 4c ...
Supply circuit, 5 ... Network bus, 7a, 7b, 7c ...
Transformers, 8a, 8b, 8c ... Protective fuses, 10a, 1
0b, 10c ... Protective circuit breaker, 14a, 14b, 14c ...
Backflow prevention fuse, F ₀ , H ₀ , B ₀ ... Breaking characteristic, G
₀ ... Degradation characteristics, T _F , T _B. T _H ... interruption time, T _G
… Deterioration start time

Claims (1)

[Claims] 1. Power is supplied from a power supply source to a common network bus through three or more power supply paths in which a protective fuse and a protective circuit breaker are respectively connected in series, and a plurality of power is supplied to the network bus. In the spot network in which the protective fuse or the protective circuit breaker of the corresponding power supply path is melted or cut off when an accident current exceeding the rated current flows in each of the power supply paths, A spot network in which a backflow preventing fuse having a breaking characteristic similar to that of the protective fuse is inserted near the network bus.