JP2562910B2 - Cable accident point measurement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cable fault point measuring method for digitally detecting the position of a fault point on a cable line.

[Prior Art] Conventionally, the Murray loop method has been known as a method for detecting an accident point of a cable line, for example, a ground fault accident point or a wire break accident point. FIG. 2 is an explanatory view of the measurement principle, in which the accidental phase cable line 3 having the ground fault accident points at the near ends A and the points P of the sound phase cable line 2 at both ends of the variable resistor 1.
, And the far end C of the sound phase cable line 2 and the far end D of the accident phase cable line 3 are short-circuited. A galvanometer 4 is connected between the near end A and the near end B, and a DC power supply 5 is connected to the variable contact 1a of the variable resistor 1. In addition,
The cable lines 2 and 3 each have a length L with the same distribution constant.
The resistance is proportional to the length of the cable lines 2 and 3, and the total resistance of each is R3.

The fault point P of the fault phase cable line 3 is grounded via the resistor Rf, but the resistance between the line BP at this time is R
4, the resistance between the lines DP is R5, the length between the lines BP is 1, and the position F of the variable contact 1a of the variable resistor 1, that is, the total resistance of the variable resistor 1 is divided into resistors R1 and R2. DC power supply 5 to F
Assuming that the voltage Eh is ignited from, the equilibrium condition for the current not to flow in the galvanometer 4 is R1 / R2 = (R3 + R5) / R4 (1). Since the resistance of the cable lines 2 and 3 is proportional to the length of the cable, (R3 + R5) / R4 = (2L-1) / l (2), and from equations (1) and (2), l = 2L ・R2 / (R1 + R2) (3) is derived. Since the length l is the distance from the near end B to the accident point P, the length L of the cable lines 2 and 3 and the resistance R1,
The position of the accident point P can be obtained by measuring the value of R2.

By the way, when measuring the resistances R1 and R2, the variable resistor 1 is adjusted so that no current flows in the galvanometer 4, and the variable contact at that time is adjusted.
It is done by reading the scale of 1a in analog. For this reason, not only the scale of the variable resistor 1 needs to be very precisely scaled, but also a reading error is introduced. In addition, there is a drawback that the mechanical moving part is liable to fail.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional example and provide a cable fault point measuring method capable of obtaining an accurate measurement result by digital measurement.

[Summary of the Invention] The gist of the present invention for achieving the above-mentioned object is to short-circuit the far-end comrades of a sound phase cable line having the same total length and total resistance and a fault phase cable line having a ground fault point, The near ends of the two cable lines are connected to both ends of a parallel circuit of a first variable resistor and a galvanometer, and a variable contact of the first variable resistor is connected to a first power source, In the cable fault point measuring method for detecting the position of the ground fault point from the resistance division ratio of the first variable resistor by the variable contact in a state where no current flows in the galvanometer by adjusting the contacts,
A second power source is connected to both ends of the second variable resistor, and the variable contact of the first variable resistor and the variable contact of the second variable resistor are interlocked with each other so that a current flows in the galvanometer. The resistance division ratio of the second variable resistor by the variable contact of the second variable resistor in a non-flowing state is determined by the voltage value of the second power source applied to the variable contact of the second variable resistor. And the voltage value is converted into a digital value, and the position of the ground fault accident point is obtained from the displayed value.

[Embodiment of the Invention] A cable accident point measuring method according to the present invention will be described in detail based on an embodiment of FIG. The same reference numerals as in FIG. 2 indicate the same members.

FIG. 1 is a circuit diagram to which the method according to the present invention is applied,
A circuit for digital display is added to the circuit of FIG. 2, and a variable resistor 6 in which the variable resistor 1 and the variable contacts are interlocked is provided. The variable resistor 6 is configured so that the total resistance is divided into resistors R6 and R7 by a variable contact 6a, a DC power supply 7 is connected to both ends of the variable resistor 6a, and the variable contact 6a of the variable resistor 6 is A /
The A / D converter 8 is connected to a D converter 8, and a memory and a digital display 10 are connected to the A / D converter 8. The DC power supply 7 applies a voltage Es across the variable resistor 6, and the memory 9 is a ROM (Read
Only Memory). In addition, the galvanometer 4 is a filter 4a,
It consists of an amplifier 4b and an indicator lamp 4c such as an LED.
By the indication of c, the rotation directions R and L of the rotary knob 11 for interlocking the variable contacts 1a and 6a are designated as the directions satisfying the expression (1).

Here, the variable contact 1a and the variable resistor 6 of the variable resistor 1
When the position of the variable contact 6a of is adjusted by the rotary knob 11 so that the current does not flow to the galvanometer 4, that is, the indicator lamp 4c is turned on at the neutral position, the dividing resistor R1 of the variable resistor 1, R2 satisfies the equilibrium condition of equation (1).
At this time, the voltage Ei is applied to the variable contact 6a of the variable resistor 6, that is,
Ei = EsR7 / (R6 + R7) is applied, and this voltage Ei is input to the A / D converter 8. At this time, according to the equation (3), l = 2L · R7 / (R6 + R7) = 2L · Ei / Es (4) is obtained, and the values of the length L and the voltage Es are constant. The distance l from B to the accident point P is proportional to the obtained voltage Ei.

Therefore, if the digital display value for the voltage Ei as shown in Table 1 is stored in the memory 9 in advance, the A / D converter 8 outputs the digital data for the voltage value Ei input from the variable contact 6a from the memory 9. Read out and display on digital display 10.

Table 1 Ei (V) L / R display Digital display value (%) 0.0000Es R 0.0 0.0005Es R 0.1 0.0010Es R 0.2 ::: 0.4995Es R 99.0 0.5000Es −100.0 0.5005Es L 99.9 ::: 0.9990Es L 0.2 0.9995Es L 0.1 1.0000Es L 0.0 Here, the L / R display shows the position of the rotary knob 11. If R, the accident point P is on the near end B side, and if L, it is on the far end D side. It means that. Also, for the digital display value, 1/2 of the cable length L is 100% and the minimum resolution is 0.1%,
The distances from the near end B and the far end D to the accident point P are shown. Note that the digital display value 100.0% is the division resistance R6 and R
7 corresponds to each other, that is, R6 = R7, and the digital display value of 0.0% corresponds to the dividing resistance R6 = 0 or R7 = 0.

Furthermore, if errors such as non-linearity error and resistance value error of the variable resistors 1 and 6 are previously corrected when data is stored in the memory 9, the measurement error theoretically becomes zero.

[Effects of the Invention] As described above, in the cable fault point measuring method according to the present invention, two variable resistors are interlocked with each other, and errors are less likely to intervene by measuring digitally, which is precise and accurate. It becomes possible to make measurements.

[Brief description of drawings]

FIG. 1 is a circuit diagram for carrying out the cable fault point measuring method according to the present invention, and FIG. 2 is a circuit diagram of a conventional example. Reference numerals 1 and 6 are variable resistors, 2 and 3 are cable lines, 4 is a galvanometer, 5 and 7 are DC power supplies, 8 is an A / D converter, 9 is a memory, 10 is a digital display, and 11 is a rotation. It is a knob.

Claims (2)

(57) [Claims] 1. Short-circuiting the far ends of a sound phase cable line having the same total length and total resistance and a fault phase cable line having a ground fault point, and connecting the near ends of the two cable lines to a first variable resistor. Connected to both ends of a parallel circuit of a detector and a galvanometer, the variable contact of the first variable resistor is connected to a first power source, and the variable contact is adjusted so that no current flows in the galvanometer. In the cable fault point measuring method for detecting the position of the ground fault point from the resistance division ratio of the first variable resistor by the variable contact in the state, a second power source is connected to both ends of the second variable resistor. The variable contact of the first variable resistor and the variable contact of the second variable resistor are interlocked with each other, and the variable contact of the second variable resistor is used in a state where no current flows in the galvanometer. The resistance division ratio of the second variable resistor is set to the second variable resistor. Measuring the cable fault point by converting the voltage value by the second power source applied to the variable contact of the above, converting the voltage value into a digital value, and obtaining the position of the ground fault point from the display. Law. 2. The cable fault point measuring method according to claim 1, wherein the current state of the galvanometer is indicated by a lamp.