JPH05164804A - Fault section detecting method for power cable line - Google Patents

Abstract

PURPOSE:To correctly detect a fault section of a power cable line by presuming a fault section from combination of the intensity and direction of a fault current flowing through the earthing conductor of each ordinary junction box and intensity of a cable conductor current, and, thereafter, by measuring the degree of the correlated phase- difference between the earth current in the fault phase and the one in another phase. CONSTITUTION:A current sensor 30 is set up in the earthing line 20 of each of ordinary junction boxes N1-N3 and the intensity and direction of a current flowing through the earthing line 20 are continually measured with the said sensor 30. And a current sensor 32 is set up into a terminal 18 of each phase of a power load and the current flowing through each of cable conductors is continually measured. When the fault of earthing takes place, the records of the current sensors 30 and 32 are examined and it is assumed from the combined pattern that there is the fault in, for instance, D section. But, when the earthing fault occurs at a close position of the ordinary junction box N2, it is difficult to decide which of A or D is in fault. Hence, by using a phase difference measuring device 40 connected to the junction box N1 one step nearer to the power supply side, the degree of correlated phase difference of an earth current between the faulty phase and another phase is measured and fault section is confirmed based on these results.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting a ground fault accident section in a power cable line.

[0002]

2. Description of the Related Art The following method shown in FIG. 3 is known (see Japanese Patent Laid-Open No. 62-265578). In the figure,
Reference numeral 10 is a cable, 16 is a power supply side end portion, and 18 is a load side end portion. N1, N2, ----- indicate ordinary junction boxes. In order to avoid complication, the ordinary connection boxes N1, N2, etc. will be simply written as N1, N2, etc. N is N of NJ. Ordinary junction boxes are collectively referred to as NJ. 20 is a ground wire. Also, I1, I
2, ----- indicates an insulated junction box. Also in this case, what should be written as the insulated junction boxes I1, I2, etc. will be simply written as I1, I2, etc. I is I of IJ. IJ is used as a general term for insulated junction boxes. 22 is a bond line.

A current sensor 30 is attached to the ground wire 20 of each NJ. Further, a current sensor 32 for measuring the cable conductor current is provided at each of the terminal ends 18 of the respective phases on the load side.

For example, as shown in FIG. 3, it is assumed that a ground fault accident occurs in the R-phase A section (between N2 and I5).
First, the fault current I flowing on the power supply side (left side) is shunted by the ground wire 20 of N2. The magnitude of the fault current detected by the R-phase current sensor 30 is, for example, approximately 2 / 3I (depending on the line impedance), and the direction is rightward. The left and right refer to the drawings. The magnitude of the fault current detected by the S-phase and T-phase current sensors 30 is, for example, approximately 1 / 3I, and the direction is leftward.

On the other hand, the fault current I ′ flowing to the load side passes through the bond wire 22, the S-phase B section, the T-phase C section, and the N3.
It is shunted at the ground wire 20 of. And the T-phase current sensor 30
The current detected by is, for example, approximately 2 / 3I ',
The direction is to the right. In addition, the S-phase and R-phase current sensors 3
The current detected by 0 has a magnitude of, for example, about 1 / 3I '.
And the direction is left.

Even if a ground fault occurs in each of the S-phase B section and the T-phase C section, the same fault current as above is detected in N2 and N3.

Therefore, when a ground fault occurs, each NJ
By checking the record of the current sensor 30 of No. 3, and finding the one in which the current value is large and the direction is opposite in only one of the three phases as described above, the section in which the fault current flows is known. If you know the accident phase, you can know the accident section.

[0008]

However, when a ground fault occurs in the vicinity of NJ (a few meters to a few tens of meters, depending on the section length) when the above method is carried out, the section is mistaken as follows. I was afraid.

For example, as shown in FIG. 4, the D section (R phase I
It is assumed that a ground fault occurs just to the left of N2 (between 4 and N2).
Then, a very large current I ′ flows toward the load side. About 2/3 of that, for example, flows to the ground line 20 of N2, but the other, for example about 1/3, flows through the sections A, B, and C, and is detected by the T-phase current sensor 30 of N3. .. The fault current flowing through the ground wire 20 of N2 is shunted to N
The R-phase and S-phase current sensors 30 of 3 are detected. However, part of the shunt current also flows to the ground, so the R phase, S
The current detected by each phase current sensor 30 is smaller than the current detected by the T phase current sensor 30. Since the pattern of this accident current is the same as the case of FIG. 3 described above, it may be mistaken for an accident to occur in the section A. Or section A or D
You may not know the section.

[0010]

As described above, after estimating the fault section from the combination pattern of the magnitude and direction of the fault current flowing through each ground wire of each NJ and the magnitude of the cable conductor current, the fault phase and other The magnitude of the phase difference between the ground wire current and the phase of the ground wire is measured.

The phase difference between phases is measured by the phase difference measuring device 40 as shown in FIG. 1 from the recording of the current sensor 30 of each NJ. The phase difference measuring device 40 is also attached to another NJ, but is not shown. By the above method, for example, when the accident is estimated to be the section A, or when it is unclear whether the section is the section A or the section D, the phase difference between phases is measured at N1 (NJ close to the power supply side by one).

[0012]

[Operation] The phase difference between phases of the fault current in N1 changes depending on the ground fault position in sections D and A. This is because when the ground fault position changes, the sheath return path impedance changes accordingly.

The relationship between the ground fault position in the D and A sections and the phase difference between the fault currents at N1 can be calculated in advance for an actual cable line. As an example, the relationship between the distance from N2 to the fault point and the fault current phase difference between the R and S phases in N1 (unit: degree) in the case of a ground fault in the A (load side) or D (power source side) section Is shown in Table 1, and the relationship of Table 1 is shown in a graph in FIG.

[0014]

[Table 1] However, in this case, N1 to I3 are 557 m, I3 to I4 are 639 m, I4 to N2 are 621 m, N2 to I5 are 683 m, I5 to I6 are 647 m, and I6 to N3 are 577 m.

From Table 1, when the phase difference is about 3 degrees or more, the accident point can be judged to be the section D on the left side (power supply side) from N2. If it is less than about 3 degrees, it can be judged to be the section A on the right side from N2.

The same operation as described above can be performed for NJs other than N2.

[0017]

EFFECTS OF THE INVENTION After estimating the fault section from the combination pattern of the magnitude and direction of the fault current flowing through each ground wire of each NJ and the magnitude of the cable conductor current, the ground line currents of the fault phase and other phases are further estimated. Since the magnitude of the phase difference between the phases is measured, even if a ground fault occurs in the vicinity of NJ (within several meters to several tens of meters), the accident section can be correctly detected as described above.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for explaining a method according to an embodiment of the present invention.

FIG. 2 is a chart showing an example of phase difference between ground wire fault currents.

FIG. 3 is an explanatory diagram of a conventional technique.

FIG. 4 is an explanatory diagram of a problem to be solved by the present invention.

[Explanation of symbols]

 10 Cables 12 Cable Conductors 14 Cable Sheaths 16 Power Supply Terminals 18 Load Terminals 20 Ground Wires 22 Bond Wires 30, 32 Current Sensors 40 Phase Difference Measuring Instruments

Claims (1)

[Claims] 1. The magnitude and direction of the current flowing through the ground wire of each ordinary junction box is constantly measured for each phase, and the magnitude of the cable conductor current is always measured for each phase. When a ground fault occurs, the fault section is estimated from the combination pattern of the magnitude and direction of the fault current flowing through each ground wire of each of the ordinary junction boxes and the magnitude of the cable conductor current, and the fault phase and other phases A method for detecting a faulty section of a power cable line, in which the faulty section is determined by measuring the phase difference between the fault currents.