JP2787624B2 - Fault detection method for power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the position of a ground fault on a power cable line.

[0002]

2. Description of the Related Art A current flowing in a cross-bond line of an insulated junction box of a power cable line or a ground wire of a normal junction box is constantly measured. When a ground fault occurs, the difference in the magnitude of the current causes an accident section. Many methods have been conventionally proposed for detecting. However, these methods detect an accident section having a junction box as a boundary and do not detect an accident point.
As a method for detecting an accident point, a pulse radar method, a Murray loop method, and the like have been proposed.

[0003]

The above-described pulse radar method, Murray loop method, and the like require operations such as line separation. It takes a considerable amount of time before exploration, and no real-time detection is possible.

[0004]

Means for Solving the Problems As shown in FIG. 1, (1) the setting of each of the normal connection boxes NJ1, NJ2, --- of the one-sided power supply type three-phase power cable line connected by the normal connection box;
The three-phase combined current of the current flowing through the ground wire 16 at each location and the current of the cable conductor 13 are measured by the sensor 18 and the
Leave constantly measured by the sensor 20, (2) at least one Tsugasho of the ground wire composite current
When the threshold value is exceeded, the magnitude of each ground line combined current at each installation point is compared, and the maximum value is determined. (3) The maximum ground line combined current and the conductor current are calculated. obtains a phase difference between the largest of the, (4) the flow of the maximum of the ground wire combined current based on the phase difference
The distance from the installed location of the normal connection box to the accident point
By doing so, the ground fault point is detected.

[0005]

[Operation] (1) When a ground fault occurs, set so that the combined current of the ground line exceeds the threshold. (2) Although a large amount of fault current flows to the power supply side, it also flows to the load side. Since the current is shunted to the ground at each NJ (normal junction box, hereinafter simply referred to as NJ), the fault current decreases as the distance from the fault point increases. When the threshold line is exceeded, when comparing the ground line combined currents, the ground line combined current of the NJ on the power supply side closest to the fault point is the largest (first place), and the NJ on the load side is next ( Second place). Conversely, if the NJ with the first largest ground line combined current is known, the fault point A
It can be seen that it is between J and the next (closer to the load) NJ. (3) The largest phase of the cable conductor current is the phase in which the accident occurred.

(4) As illustrated in FIG. 2 (a), a ground fault current flowing through a ground side conductor 15 such as a cable sheath receives induction from a cable conductor current I in an accident phase (for example, R phase). The distance to the power supply side NJ changes depending on the position of the accident point A. Accordingly, the distance to receive the guidance changes (the value of the induction reactance changes). As a result, the phase of the ground line combined current changes. FIG. 2B shows the state. What changes depending on the position of the fault point A is the phase φr (with respect to the conductor current I) of the ground line current Ir in the fault phase R. However, since the combined ground line current Ia is a combination of the other ground line currents Is and It, the phase of the combined ground line current with respect to I is φa. For an actual cable line, for example, a known calculation method program EMT
P (US Bonneville Power Admi
Electro Mag released by Nistration
netic Transient Program)
The relationship between the phase φa of the combined ground line current and the distance from the fault point A is calculated in advance . Then, the position of the fault point A can be determined by comparing the phases of the maximum combined ground line current and the largest one of the conductor currents (conductor current in the fault phase).

[0007]

First Embodiment [Configuration] In FIG. 1, reference numeral 12 denotes a terminal end on the power supply side, 13 denotes a cable conductor, 14 denotes a terminal end on the load side, and NJ1 and NJ2.
Is a normal connection portion, and is simply expressed as NJ1, NJ2, and the like. When there is no need to distinguish between 1 and 2, this is indicated as NJ. Reference numeral 16 is a ground line of the NJ. A current sensor 18 is provided on each of the ground lines 16. Also, a current sensor 18 is provided on each ground line 17 of the terminal section 12. A current sensor 20 for detecting a cable conductor current is provided in the terminal portion 12 or the insulated connection box IJ.

Reference numeral 22 denotes a combined current measuring device, which combines the currents detected by the current sensors 18 of the R, S, and T phases. Further, the synthesized current waveform is always and continuously stored in the memory for a fixed time (for several cycles), and when a trigger is activated as described later in the event of an accident, the memory at that time is fixed and transmitted. Reference numeral 24 denotes a comparison circuit 24 which compares a preset threshold value with a ground line composite current detected by the composite current measuring device 22. The threshold value is set to a level slightly higher than the ground line combined current in the normal state. 26 is a conductor current measuring device,
The waveforms of the currents detected by the current sensors 20 of the R, S, and T phases are always and continuously stored in the memory for a certain period of time (several cycles). In the event of an accident or a trigger as described later, The memory at that time is fixed and transmitted.

[Operation] 1) For example, it is assumed that a ground fault has occurred at point A of the R phase. 2) The combined current of the ground line detected by the combined current measuring device 22 of NJ1 and NJ2 increases and exceeds the threshold, and the comparison circuit 24 sends a signal to the trigger circuit 28. 3) The trigger circuit 28 operates to read from the current waveform recorded in each synthesized current measuring device 22 several cycles before and after the trigger in each memory device 30 and store them. FIG.
The model of the read waveform is shown in FIG. The second and subsequent waves are the waveforms of the fault current. In the case of FIG. 1, the accident point A is NJ1.
And NJ2, the combined ground line current of NJ1 (closest to the power supply side when viewed from the fault point A) is maximized. In addition, the ground line combined current of NJ2 (closest to the load side when viewed from the fault point A) is the second highest. 4) The current level after the second wave of the current waveform in each memory device 30 is compared by the section determination circuit 32, thereby determining an accident section based on the above reason.

5) Based on the above determination, the maximum (first
Then, the current waveform of the memory device 30 (in this case, NJ1) which has detected the current waveform of the current position is sent to the fault point determination circuit 34. 6) The trigger signal of the trigger circuit 28 is also sent to the conductor current measuring device 26, and the number of the maximum level (accident phase, in this example, R phase) of the recorded current waveform before and after the trigger is detected. The number of cycles is read out and stored in the memory device 36 and sent to the fault point determination circuit 34. 7) In the fault point determination circuit 34, the cable conductor current waveform and
The phases of the combined current waveforms of the ground lines are compared. Figure 4 shows the situation.
Is shown in model form. By calculating the phase difference φa between the two waveforms, the distance from NJ1 to accident point A can be determined as described above.

[0011]

[Embodiment 2] As shown in FIG. 5, only one current sensor 18 is provided for each of the common ground lines 19 and 21 of each of the NJs and the termination portion 12. These current sensors 18 can detect a combined current of the currents flowing through the ground lines 16 and 17. Except for this point, the configuration is the same as that of the first embodiment. In this case, the number of current sensors 18 may be smaller than in the first embodiment. However, the sensitivity is slightly reduced, and the accuracy of the accident point rating is slightly reduced.

[0012]

A procedure for constantly measuring the combined current of the current flowing through the grounding wire of each ordinary junction box of the power cable line and the cable conductor current; and Compare the magnitude of the combined wire current,
A procedure for obtaining the maximum current and a procedure for comparing the phase of the maximum combined ground line current with the maximum of the conductor currents are provided, so that the following effects can be obtained. (1) As described above, the ground fault point can be detected. (2) Since the section discrimination is performed based on the combined current of the NJ ground lines, the boundary discrimination in the NJ is possible. (3) It can be detected in real time.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing that the phase of a ground line combined current changes depending on the position of an accident point.

FIG. 3 is an explanatory diagram of a waveform of a ground line combined current read into a memory device.

FIG. 4 is an explanatory diagram showing a phase shift between a cable conductor current and a ground line combined current.

FIG. 5 is an explanatory diagram of a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Power supply side terminal part 13 Cable conductor 14 Load side terminal part 16,17 Grounding wire 19,21 Common grounding wire 18,20 Current sensor 22 Synthetic current measuring device 24 Comparison circuit 26 Conductor current measuring device 28 Trigger circuit 30,36 Memory device 32 Section judgment circuit 34 Accident point judgment circuit

Claims (1)

(57) [Claims] 1. A common connected by a junction box the side-powered 3-phase <br/> power cable line, three-phase case <br/> forming current of the current flowing through the ground line of each installation location of ordinary connection box, And a procedure for constantly measuring the cable conductor current, and when at least one of the ground line combined currents exceeds a predetermined threshold, compares the magnitude of the ground line combined current for each installation point , A step of obtaining a maximum one; a step of obtaining a phase difference between the maximum combined ground line current and the largest one of the conductor currents; and a step of determining a maximum ground line combined current based on the phase difference.
To determine the distance from the connection box installation point to the accident point
And order, consisting of, fault point detection method of the power cable.