JPH02157672A - Searching device for ground fault point of cable - Google Patents

Abstract

PURPOSE:To search the ground fault point of a shield wire by adjusting a balance in the manner of short-circuiting optional two conductors and the shield wire at one end of a cable and forming a bridge at another end, and performing the balance adjustment again by means of changing over to other bridge constitution. CONSTITUTION:The bridge is composed of the conductors 100, 102, shield wire 104, variable resistor 106, galvanometer 108, fixed resistor 110, voltage divider 112 with movable contact, and power supply 114. First of all, the balance adjustment is made between vertexes C1-C3 by the galvanometer 108 in the manner of adjusting the variable resistor 106. Next, one terminal of the galvanometer 108 is detached from the conductor 102 for grounding and another terminal is detached from the vertex C3 for connecting to the movable contact 112b of the voltage divider 112, then the balance adjustment is again performed by the galvanometer 108. Thus, the distance from the vertex C4 side to the ground fault point 104b of the shield wire 104 can be searched by means of reading out a position of the movable contact 112b of the voltage divider 112.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention detects ground faults in shielded wires of shielded multi-core wires installed underground, on conductors, or in metal piping, tanks, etc. It is related to the device.

[Prior art] As an exploration device of this type, Fig. 1 of Japanese Patent Application Laid-Open No. 60-85374 shows a short-circuit (midway short circuit) between the cable cores.
A search for a point P is disclosed. This can be done by short-circuiting the non-straight core wire L1 and one of the mixed core wires 1 and 3 at one end of the cable, and forming a bridge at the other end to prevent crosstalk over the entire length of the cable. The ratio of distances to point P is determined and the 7-line point is searched.

Furthermore, Japanese Patent Application Laid-Open No. 61-201171 discloses a method for detecting ground fault points in shielded wires of cables. This method makes it possible to detect ground faults in the shield wires or conductors of multiple cables in one go, but in principle, the ground faults in the shield wires of one cable can be detected as follows. explore. First, a pulse signal is sent to the shielded wire to be inspected, and this pulse signal, which leaks into the ground from the ground fault point and returns to the pulse transmitter, is captured as a potential difference using two electrodes inserted into the ground and a galvanometer. By moving the two electrodes along the cable,
The ground fault point is detected from the change in this potential difference.

[Problems to be Solved by the Invention] In the former prior art (Japanese Unexamined Patent Publication No. 60-85374), it is possible to detect cross-wire points between core wires of the same type, but it is not possible to detect ground fault points in shielded wires. This is because the bridge is constructed on the assumption that the resistance value of the core wire is almost the same, whereas the shield wire usually has a resistance value several to several tens of times higher than that of the core wire. This is to have.

In addition, according to the conventional technique of the latter (Japanese Patent Publication No. 6L-2Q11?1), it is necessary to move two electrodes along the laid cable, which is time-consuming and impedes the speed of exploration. It has the disadvantage of being lacking.

[Means for Solving the Problems] A cable ground fault detection device according to the present invention searches for a ground fault in a shield layer wire of a multi-core cable having a plurality of core wires and a shield layer wire (shield wire). This solves the problems of the prior art (g) and allows the ground fault point of the shielded wire of the cable to be detected quickly and without moving along the cable.

This cable ground fault detection device consists of a conductor, a variable resistor,
It comprises a galvanometer, a fixed resistance, a movable contact 11 voltage divider having a total resistance equal to the fixed resistance, and a power source,
Furthermore, it is characterized by having the following configuration.

First, form the following bridge.

(a) At one end of the cable, any two of the plurality of core wires
The first core wire, the second core wire, and the shielding layer wire are short-circuited with a conductor to form the first vertex, and (b) a variable resistor is connected in series with the first core wire at the other end of the cable. to form a second vertex, connect a galvanometer in series with the second core wire to form a third vertex, set the other end of the shielding layer wire as the fourth vertex, and connect the second vertex and the third vertex. Connect a fixed resistor between
A voltage divider is connected between the third apex and the fourth apex, and a power source is connected between the second apex and the fourth apex.

Then, from the above bridge configuration to a bridge configuration in which one end of the galvanometer is grounded and the other end is connected to the movable contact of the voltage divider,
Provide a changeover switch.

[Operation] The principle of operation will be explained with reference to FIG. FIG. 3(A) shows the bridge configuration according to the above (a) and (b). In this figure, the first, second, third, and fourth vertices are CLC2 and CLC2, respectively.
3, C4, the first core wire is ioo, the second core wire is 102
, shielded wire is 104, variable resistor is 106, galvanometer is 1
08, Fixed resistance is 110, Voltage divider with movable contact is 112,
A power source is indicated at 114.

With this bridge, balance adjustment is first performed by adjusting the resistance value of the variable resistor 106 while looking at the galvanometer 108 so that the current between the first vertex C1 and the third vertex C3 becomes zero. At this time, if the resistance (direction) of each element is represented by a symbol R with the number of the element attached, then R110=R112, so R104=R100+R10G.

Next, use the changeover switch to switch one end of the galvanometer 108 to the second
Separate it from the core wire 102 and ground it, and connect the other end to the third vertex C3.
It is separated from the voltage divider 112 and connected to the movable contact 1i2b of the voltage divider 112. This state is shown in FIG. 3(B). By grounding one end of the cross current meter 108, the ground fault point 104b of the shield layer wire 104 and that one end of the galvanometer 108 are short-circuited, resulting in a configuration as shown in FIG. 3 (El). In this state, adjust the position of the movable contact 112b of the voltage divider 112, and
Balance is made so that the current value of 08 becomes O.

At this time, the first
The resistance value on the vertex C1 side is R104a, the resistance value on the fourth vertex C/l side is R104c, the resistance value on the third vertex 63 side of voltage divider 1i2 is R112a, and the resistance value on the fourth vertex C4 side is R11.
2c, R104c/R104=R112c
/ R112. Thereby, the distance Lx from the other end of the cable, that is, the side where the fourth vertex is formed, to the ground fault point 104b of the shielding layer wire 104 can be determined by reading the position of the movable contact 112b of the voltage divider 112, LX: It is determined as L◆ (R112c/R112). Here, L is the total length of the cable.

[Example 1] A cable ground fault detection device which is an example of the present invention is described in the first example.
This will be explained based on Figure 2. This exploration device consists of a main body 2 and a conductor 4, where the conductor 4 has two core wires 8, 1O and a shield wire 12 at one end of a shielded multi-core cable 6 to be investigated.
Used to short circuit. The short-circuit point at this one end corresponds to the first vertex C1 in the configuration of the present invention. The body 2 is used at the other end of the cable 6. It is assumed that the shield wire 12 of the cable 6 has a ground fault at a point 14.

As shown in FIG. 2, on the front panel 20 of the exploration device body 2, there are three terminals 22, 24, 2 for connecting the two-core wire 8.10 of the cable to be investigated and the shield wire 12, respectively.
6 and a ground terminal 28.

This ground terminal 28 is connected to the object that the shield wire 12 of the cable 6 to be probed is in contact with.

For example, if the cable 6 is buried underground, the terminal 2B should be connected to the terminal buried underground, and if the cable 6 is installed inside piping or on the chassis, it should be connected to those conductors. do.

The internal circuit of the main body 2 will be explained with reference to FIG.

A variable resistor 30 is connected to the terminal 22 connected to the first core wire 8, and is connected to a second connection point 32 corresponding to the second vertex C2. The resistance value of the variable resistor 30 can be changed using a knob 54 on the front panel 20. A galvanometer unit 36 is connected to the terminal 24 connected to the second core wire 10 via a changeover switch 34a, and a changeover switch 34
It is connected to the third connection point 38 corresponding to the third vertex C3 via b. These two changeover switches 34a and 34b are interlocked and can be switched simultaneously by a knob 34 on the front panel 20 of the main body 2. A fourth connection point 40 corresponding to the fourth vertex C4 is immediately connected to the terminal 26 connected to the shield wire 12. Second connection point 32 and third connection point 38
A fixed resistor 42 is connected between the third connection point 3B and the fourth connection point 40, and a voltage divider 44 is connected between the third connection point 3B and the fourth connection point 40. The overall resistance value R44 of the voltage divider 44 is the resistance (a
Equal to R42. Further, the voltage divider 44 has a movable contact 44a, and the ten positions of this movable contact 44a can be changed using a knob 46 on the front panel 20.

The second connection point 32 and the fourth connection point 40 are the opening/closing switch 4.
8 and a DC power supply 50. This opening/closing switch 48 can be operated from the front panel 20.

In this embodiment, the galvanometer unit 36 has the following internal configuration. A resistor 36a is connected between the two changeover switches 34a and 34b, and an amplifier 36b is connected in parallel with this resistor 36a. A galvanometer meter 36d is connected to the amplifier 36b via a low-pass filter 36C that cuts 182 or more fluctuation components.

Galvanometer 36 of switch switch 34a closer to terminal 24
The above-mentioned grounding terminal 28 is connected to the contact point that is not on the side via the earth current canceling circuit 56. The earth current canceling circuit 56 is a circuit consisting of two dry batteries and a variable resistor, and by adjusting this variable resistor with the knob 52 on the front panel 20, the stray current flowing to the ground is canceled.

Next, how to use this exploration device will be explained. First, by setting the knob 34 on the front panel 20 to position A, the switch 34a and the switch 34b are interlocked and placed in the position shown in FIG. 3
Connection point 38 is connected. As a result, a bridge is formed whose vertices are the short-circuit point 4 at one end of the cable 6 and the second to fourth connection points 32°38.40. In this state, electricity is 15
0 switch 48 is turned on, the needle of galvanometer meter 36d is 0.
Adjust the resistance value R30 of the variable resistor 30 by turning the knob 54 on the front panel 20 so that When the bridge is balanced in this way, the resistance value of the core wire 8 is set to R8.
, if the resistance value of the shield wire 12 is R12, then R
42=R44, R8+R30=R12.

Next, switch the knob 34 to position B. Then, the switch 34a and the switch 34b are switched in conjunction with each other, and one end of the galvanometer unit 36 is grounded via the earth current canceling circuit 56 and the terminal 28. Further, the other end is connected to a movable contact 44a of a voltage divider 44. This allows the above-mentioned third
A bridge circuit corresponding to that shown in Figure (B) is constructed. In this state, first, the power switch 48 is turned off, and the earth current canceling circuit 56 is adjusted using the knob 52 so that the value of the galvanometer meter 36d becomes 0.

Then, turn on the power switch 48, and turn on the galvanometer meter 36d.
While looking at the knob 46, move the movable contact 4 of the voltage divider/14.
Adjust the position of 4a to balance this bridge.

When this balance is achieved, the distance from the cable end to which this exploration device 2 is connected to the shield wire ground fault point 14 can be determined from the position of the movable contact 44a based on the above principle. In this embodiment, a percentage of the movable contact position is printed around the knob 46 of the front panel 20, and the ground fault point can be immediately determined by reading the scale.

The above has only shown one embodiment of the present invention, and it goes without saying that the present invention can be implemented in various other embodiments. In particular, in the above embodiment, in order to eliminate the influence of current induced into the exploration cable from other cables, the galvanometer 36 is provided with a low-pass filter 38c,
Earth current cancellation circuit 5G to eliminate errors due to earth current
However, these were used in the embodiments to particularly enhance the effectiveness of the exploration device, and the essence of the present invention is not dependent on these.

[Effects of the Invention] In the cable ground fault detection device according to the present invention, any two core wires and the shielding layer wire are short-circuited at one end of the cable, and a bridge is formed at the other end to perform balance adjustment. A ground fault point in the shielding layer wire can be detected with a simple configuration and operation of changing to another bridge/solid configuration using a changeover switch and re-balancing.

Moreover, there is no need to move along the cable, and the operation can be performed while staying at one end of the cable, significantly reducing exploration time.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a cable ground fault detection device which is an embodiment of the present invention, and Fig. 2 is an external view of the front panel of the same detection device.
FIGS. 3(A) and 3(B) are circuit diagrams for explaining the operating principle of the exploration device of the present invention. 4...Conductor, 6...Cable, 8.10, too
, 102... Core wire 12.104... Shield wire,
30.106...Variable resistance, 36.108...
Galvanometer, 42.110...Fixed resistance, 44
．． 112... Voltage divider with movable contact, 50.1148
．．・Power supply 34...Switch switch Sochi, C1...
・1st vertex, C2... 2nd vertex, C3... 3rd vertex, C4... 4th vertex, Agent: Patent attorney Tsutomu Sadate (2 others) Figure 1

Claims (1)

[Claims] A device for detecting a ground fault point in a shield layer wire of a multi-core cable having a plurality of core wires and a shield layer wire, the device comprising a conductor, a variable resistor, a galvanometer, and a fixed resistor. , a voltage divider with a movable contact having an overall resistance equal to this fixed resistance, and a power supply, and at one end of the cable, any two of the plurality of core wires, a first core wire and a second core wire, are connected to each other. and the shielding layer wire to form a first vertex, and at the other end of the cable, connect a variable resistor in series with the first core wire to form a second vertex, and connect the variable resistor in series with the second core wire to form the second vertex. connect the current meter to form a third apex, and the other end of the shielding layer line to be a fourth apex;
A fixed resistor is connected between the second apex and the third apex, a voltage divider is connected between the third apex and the fourth apex, and a voltage divider is connected between the second apex and the fourth apex.
A bridge is formed by connecting a power supply between the apex and a switch is provided to switch from this bridge configuration to a bridge configuration in which one end of the galvanometer is grounded and the other end is connected to the movable contact of the voltage divider. A cable ground fault detection device characterized by: