JPS6229748B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting fault points in cables.

Conventionally, the Murray loop method is a typical method for detecting fault points in cables. This method uses the cable conductor to be measured as a piece of a bridge, and detects the fault point by balancing the bridge. The one shown in Figure 1 is the high voltage Murray loop method, where R ₁ R ₂ is the resistance of the cable conductor, VR is the variable resistance, Rx is the grounding resistance at the fault point, E is the high voltage source, and galvanometer A is VR to reduce vibration to zero
This method detects the accident point by adjusting the The method shown in Fig. 2 is a low-pressure Murray loop method, and the difference from the method shown in Fig. 1 above is that the galvanometer A
This is the point where the current part E is replaced with the current part E, and Ex in the figure indicates the potential difference at the fault point.

However, the one in Figure 1 above uses a high voltage, so the device is large-scale and poses a risk of measurement, and the one in Figure 2 uses a variable voltage source EA for the galvanometer and DC, causing an accident. The problem is that the operation is troublesome because it is necessary to balance the bridge after canceling out the slight potential difference that exists between the points and the ground, and the potential difference at the accident point changes while balancing the bridge, causing measurement errors. It was hot.

The present invention has been made in view of the above problems, and
The object of the present invention is to provide a method for detecting a fault point in a cable, which has a simple device, is easy to handle, and does not cause measurement errors.

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 3 to 5. FIG. 3 is a schematic configuration diagram of the present invention, and two cable conductors 1 and 2 to be measured are connected at one end. It is electrically connected with a conductive wire 3, and a DC power source E is inserted into the other end via a switch S.
A current is allowed to flow through the cable conductors 1 and 2 to be measured. A voltmeter Vo is inserted between the terminals of the cable conductors 1 and 2 to be measured, so that the potential difference Vo between the terminals of the cable conductors 1 and 2 to be measured can be measured. Further, a voltmeter Vx is inserted between the terminal of one of the cable conductors 2 to be measured and the cable shielding layer, so that the potential difference between the two can be measured. Note that Rx indicates the grounding resistance at the fault point, and Ex indicates the potential difference at the fault point.

Figure 4 is an equivalent circuit diagram of Figure 3, with R ₁ , R ₂
indicates the resistance of the cable conductor. In this circuit diagram, when the switch S is closed, the value V ₂ of the voltmeter Vx becomes V ₂ =I ₀ R ₂ −Ex (1). However, I ₀ =V ₀ /R ₁ +R ₂ .

Next, when the polarity of the power source E is changed while the switch S is closed, the value V ₃ of the voltmeter Vx becomes V ₃ =-I ₀ R ₂ -Ex (2). Here, |V ₂ −V ₃ | is found as |V ₂ −V ₃ |=2IoR ₂ (3). Substituting Io=Vo/R ₁ +R ₂ into this equation (3), |V ₂ −V ₃ |/2Vo=R ₂ /R ₁ +R
₂ (4). Therefore, when the polarity of the DC power source E is changed, the voltage between each conductor and the shielding layer V ₂ and
By measuring the potential difference V ₃ and the potential difference Vo between the cables to be measured, it is possible to know the ratio of the resistance of the cable conductor to the fault point, that is, the ratio of the distance from the terminal to the fault point.

The polarity of the DC power source can be changed very easily by using interlocking switches _S1 and _S2 as shown in FIG. Furthermore, if a circuit is provided that automatically calculates the ratio between the potential difference |V ₂ −V ₃ | and the measured voltage Vo, direct reading of the distance becomes possible.

As described above, the cable fault point detection method according to the present invention applies a DC voltage to two cable conductors to be measured whose ends are electrically connected by a conductive wire, and changes the polarity of the DC power source. Measure the voltage between the conductor and the cable shielding layer to find the potential difference between the two, measure the potential difference between the cable conductors to be measured, and locate the cable fault point from the potential difference when the polarity is changed and the potential difference between the cable conductors. This is a method for detecting a fault point in a cable. Therefore, there is no need to balance the bridge as in conventional devices, so the operator is easy and does not require any skill, the device is simple, and measurement errors are less likely to occur.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams of a conventional cable fault point detection method, FIG. 3 is a schematic configuration diagram of a cable fault point detection method according to the present invention, and FIG. 4 is an equivalent circuit diagram of FIG. FIG. 5 is a configuration diagram of the switch section. 1 and 2 are the cables to be measured, 3 is the conductive wire, E is the DC power supply, R ₁ and R ₂ are the resistances of the cable conductors, Vo, Vx
is a voltmeter.

Claims (1)

[Claims] 1 Apply a DC voltage to two cable conductors to be measured whose ends are electrically connected with a conductive wire, and measure the voltage between the cable conductor and the cable shielding layer when the polarity of the DC power source is changed. A method for detecting a fault point in a cable, characterized by determining a potential difference, measuring a potential difference between cable conductors to be measured, and detecting a cable fault point from the potential difference when the polarity is changed and the potential difference between the cable conductors.