JPS6229749B2 - - 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, V _R is the variable resistance, Rx is the grounding resistance at the fault point, E is the high voltage source, and the galvanometer A V _R so that the runout becomes zero
This method detects the accident point by adjusting the The one shown in Figure 2 is a low-pressure Murray loop method, and the difference from the one shown in Figure 1 above is that the galvanometer A
This is the point where the power supply section E was replaced, 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 to measurement.The one in Figure 2 has a variable voltage source E _A connected in series with the galvanometer. The operation is cumbersome because it is necessary to balance the bridge after canceling out the slight potential difference that exists at the fault point and the ground, and the potential difference at the fault point changes while the bridge is balanced, causing measurement errors. There was a problem.

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

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 3 and 4. 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. They are electrically connected by a conductive wire 3, and a power source E is inserted into the other end via a switch S so that current can flow through the cable conductors 1 and 2 to be measured. A voltmeter V ₀ is inserted between the terminals of the cable conductors 1 and 2 to be measured.
It is possible to measure the potential difference V ₀ between the terminals. In addition, a voltmeter is connected between the terminal of one cable conductor 2 to be measured and the earth (cable shielding layer or earth).
Vx is inserted so that the potential difference between them can be measured. Note that Rx indicates the grounding resistance at the fault point, and Ex indicates the potential difference at the fault point.

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

Next, when the switch S is open, the value V ₃ of the voltmeter Vx becomes V ₃ =-Ex (2). Here, |V ₂ −V ₃ | is found as |V ₂ −V ₃ |=I ₀ R ₂ (3). Substituting I ₀ =V ₀ /R ₁ +R ₂ into this equation (3) gives |V ₂ −V ₃ |/Vo=R ₂ /R ₁ +R ₂
......(4) becomes. Therefore, if we measure the potential difference due to the opening and closing of switch S, that is, the potential difference between the terminal of one cable conductor to be measured and the ground |V ₂ −V ₃ |, and the potential difference V ₀ between the cable conductors 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. Note｜
If a circuit is provided that automatically calculates the ratio of V ₂ −V ₃ | and V ₀ , direct reading of the distance becomes possible.

In the above embodiment, the switch is opened and closed,
A time-varying current was passed through the cable conductor to be measured, and the associated |V ₂ −V ₃ | was determined. However, instead of opening and closing a switch, the polarity of the power supply was switched and the time-varying current was applied. |V ₂ −V ₃ | may be determined through the measurement cable conductor, or |V ₂ −V ₃ | may be determined using two separate power supplies. In addition to the DC power source, an AC power source can also be used as the power source.

As described above, the method for detecting a fault point in a cable according to the present invention is to
A time-varying current is passed through the cable conductors 1 and 2 to be measured, and the potential difference |V ₂ −V ₃ | between the terminal of one cable conductor to be measured and the ground is measured. Potential difference between side terminals V ₀
This is a method to detect fault points on cables by measuring Therefore, there is no need to balance the bridge as in the conventional method, so the operation is easy and does not require 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. 3. . 1 and 2 are cable conductors to be measured, 3 is a conductive wire,
R ₁ and R ₂ are the resistances of the cable conductors, and V ₀ and Vx are the voltmeters.

Claims (1)

[Claims] 1 A time-varying current is passed through two cable conductors to be measured whose ends are electrically connected by a conductive wire, and the potential difference between the terminal of one of the cable conductors to be measured and the ground is measured. A method for detecting a fault point in a cable, characterized by detecting a cable fault point by measuring a potential difference between terminals of the cable.