CN114236305A - Single-core cable online fault positioning device and method - Google Patents

Abstract

The invention provides a single-core cable online fault positioning device and a single-core cable online fault positioning method, wherein the single-core cable online fault positioning device comprises a first end current transformer, a second end current transformer, a first end current signal outgoing line, a second end current signal outgoing line and a distance meter; after the single-core cable outer sheaths of all phases pass through the cable terminal, the first end and the second end are respectively led to the grounding box through the cable outgoing lines; the first end current transformers of all the phases are correspondingly connected in series in the first end cable sheath outgoing lines of all the phases, and the second end current transformers of all the phases are correspondingly connected in series in the second end cable sheath outgoing lines of all the phases; the secondary side of the first-end current transformer of each phase is connected to a distance meter through a first-end current signal outgoing line; the secondary side of the second section of current transformer of each phase is connected to a distance meter through a second end current signal outgoing line; the distance measuring instrument leads out a signal wire to an upper computer. The invention has accurate positioning, almost no time delay, high reliability and capability of positioning the fault point within 0.67 m.

Description

Single-core cable online fault positioning device and method

Technical Field

The invention relates to a single-core cable online fault positioning device and a cable online fault positioning method thereof, and belongs to the field of electrical equipment diagnosis.

Background

The high-voltage cable has the advantages of small occupied area and flexible connection with electrical equipment, so that the commissioning amount of the high-voltage cable is gradually increased, but the generated cable faults are increased day by day. Due to the concealment of the cable line and the limitation of the testing equipment, the fault point is not easy to directly find. Therefore, attention is paid to how to quickly find the accurate position of the cable fault, and reduce the fault repairing time and repairing cost.

The invention patent CN202010896345.5 discloses a cable fault point positioning system, which needs to set multiple monitoring points and multiple sensing devices on a cable, and is not suitable for buried cabling. The invention patent CN202010692477.6 discloses a positioning device and method for fault point of extra-high voltage cable sheath, but because of the dependence on capacitance, the capacitance value of the capacitor in the current market has low precision, which greatly affects the positioning precision. The invention patent CN201810789101.X discloses a method, a device and a system for positioning a short-circuit fault of a high-voltage single-core cable.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, provides the single-core cable online fault positioning device and method, and improves the positioning precision.

According to a first aspect of the object of the invention, the invention adopts the following technical scheme:

the utility model provides an online fault locating device of single core cable which characterized in that: the distance measuring device comprises a first end current transformer, a second end current transformer, a first end current signal outgoing line, a second end current signal outgoing line and a distance measuring instrument; the single-core cable is provided with two end heads which are respectively a first end and a second end; after the single-core cable outer sheaths of all phases pass through the cable terminal, the first end and the second end are respectively led to the grounding box through the cable outgoing lines; the first end current transformers of all the phases are correspondingly connected in series in the first end cable sheath outgoing lines of all the phases, and the second end current transformers of all the phases are correspondingly connected in series in the second end cable sheath outgoing lines of all the phases; the secondary side of the first-end current transformer of each phase is connected to a distance meter through a first-end current signal outgoing line; the secondary side of the second section of current transformer of each phase is connected to a distance meter through a second end current signal outgoing line; and a signal wire is led out of the range finder to an upper computer.

Furthermore, the secondary side of the current transformer CT-A1 of the first end phase A is led to a distance meter port A1 through a first end current signal outgoing line and then divided into two paths, one path is connected with the anode of a first operational amplifier through a resistor R4_ A1+, the cathode of the first operational amplifier is led out and connected with the ground potential through a resistor R2_ A1+, and is connected with the output end INA1+ of the first operational amplifier through a resistor R3_ A1 +; the other path is connected with the anode of a second operational amplifier through a resistor R2_ A1-, the cathode lead-out of the second operational amplifier is connected with the ground potential through a resistor R4_ A1-, and is connected with the output end INA 1-of the second operational amplifier through a resistor R3_ A1-; the output ends of the first operational amplifier and the second operational amplifier are connected with the input port of the editable logic device of the distance meter;

the secondary side of the current transformer CT-A2 of the phase A at the second end is led to a port A2 of the distance measuring instrument through a current signal outgoing line at the second end and then divided into two paths, one path is connected with the positive electrode of a third operational amplifier through a resistor R4_ A2+, the negative electrode of the third operational amplifier is led out and connected with the ground potential through a resistor R2_ A2+, and the other path is connected with the output end INA2+ of the third operational amplifier through a resistor R3_ A2 +; the other path is connected with the anode of a fourth operational amplifier through a resistor R2_ A2-, the cathode lead-out of the fourth operational amplifier is connected with the ground potential through a resistor R4_ A2-, and is connected with the output end INA 2-of the fourth operational amplifier through a resistor R3_ A2-; the output ends of the third operational amplifier and the fourth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-B1 of the phase B at the first end is led to a B1 port of the distance meter through a first end current signal outgoing line and then divided into two paths, one path is connected with the positive electrode of a fifth operational amplifier through a resistor R4_ B1+, the negative electrode of the fifth operational amplifier is led out and connected with the ground potential through a resistor R2_ B1+, and is connected with the output end INB1+ of the fifth operational amplifier through a resistor R3_ B1 +; the other path is connected with the positive electrode of a sixth operational amplifier through a resistor R2_ B1-, the negative electrode of the sixth operational amplifier is led out and connected with the ground potential through a resistor R4_ B1-, and is connected with the output end INB 1-of the sixth operational amplifier through a resistor R3_ B1-; the output ends of the fifth operational amplifier and the sixth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-B2 of the phase B at the second end is led to a B2 port of the distance meter through a second end current signal outgoing line and then divided into two paths, one path is connected with the anode of a seventh operational amplifier through a resistor R4_ B2+, the cathode of the seventh operational amplifier is led out and connected with the ground potential through a resistor R2_ B2+, and the other path is connected with the output end INB2+ of the seventh operational amplifier through a resistor R3_ B2 +; the other path is connected with the anode of an eighth operational amplifier through a resistor R2_ B2-, the cathode lead-out of the eighth operational amplifier is connected with the ground potential through a resistor R4_ B2-, and is connected with the output end INB 2-of the eighth operational amplifier through a resistor R3_ B2-; the output ends of the seventh operational amplifier and the eighth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-C1 of the first end C phase is led to a C1 port of the distance meter through a first end current signal outgoing line and then divided into two paths, one path is connected with the anode of a ninth operational amplifier through a resistor R4_ C1+, the cathode of the ninth operational amplifier is led out to be connected with the ground potential through a resistor R2_ C1+, and is connected with the output end INC1+ of the ninth operational amplifier through a resistor R3_ C1 +; the other path is connected with the anode of a tenth operational amplifier through a resistor R2_ C1-, the cathode lead-out of the tenth operational amplifier is connected with the ground potential through a resistor R4_ C1-, and is connected with the output end INC 1-of the tenth operational amplifier through a resistor R3_ C1-; the output ends of the ninth operational amplifier and the tenth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-C2 of the second end C phase is led to a distance meter C2 port through a second end current signal outgoing line and then divided into two paths, one path is connected with the anode of an eleventh operational amplifier through a resistor R4_ C2+, the cathode of the eleventh operational amplifier is led out and connected with the ground potential through a resistor R2_ C2+, and is connected with the output end INC2+ of the eleventh operational amplifier through a resistor R3_ C2 +; the other path is connected with the anode of a twelfth operational amplifier through a resistor R2_ C2-, the cathode lead-out of the twelfth operational amplifier is connected with the ground potential through a resistor R4_ C2-; the anode lead-out of the twelfth operational amplifier is connected with the output end INC2 of the twelfth operational amplifier through a resistor R3_ C2-; the output ends of the eleventh operational amplifier and the twelfth operational amplifier are connected with the input port of the editable logic device;

and the programmable logic device is connected with an upper computer through a signal wire.

And the lengths of the phase current signal outgoing line at the first end and the phase current signal outgoing line at the second end are preferably equal.

According to a second aspect of the object of the invention, the invention adopts the following technical scheme:

a cable fault locating method of a single-core cable on-line fault locating device is characterized in that any one single-core cable on-line fault locating device is adopted;

when the single-phase grounding short-circuit fault occurs in the ith phase (any phase I is applicable to A, B, C) of the single-core cable, the short-circuit current I1 flows to the sheath at the end of the cable 1 from the short-circuit point, and the short-circuit current I2 flows to the sheath at the end of the cable 2; the current flows to the cable sheath outgoing line after passing through the cable terminal along the sheath, and after passing through the current transformer CT-i1 and the current transformer CT-i2, the current is induced on the secondary side of the current transformer and is led to the i1 port and the i2 port of the distance meter through the signal outgoing line.

When the current signal reaches the i1 port, according to the operational principle of the operational amplifier, there will be:

U_INi1+＝(1+Z_{R3_i1+}/Z_{R2_i1+})*U_i1and U is_INi1+≤3.3V

U_INi1-＝-(Z_{R3_i1-}/Z_{R2_i1-})*U_i1And U is_INi1-≤3.3V (1)

In the formula of U_INi1+Middle is the voltage of the INi1+ port; z_{R3_i1+}The same holds true for the resistance value of R3_ i1 +.

According to the formula (1), when the single-phase grounding short circuit does not occur to the single-core cable, the current transformer CT-i1 has no current output, and Ui1 voltage U_i1Because the resistor R1_ i1 is zero, the output voltages of the ports INi1+ and INi 1-are both 0. Selection of Z_{R3_i1+}Is far greater than Z_{R2_i1+}，Z_{R3_i1-}Is far greater than Z_{R2_i1-}When the i-phase is short-circuited, if the short-circuit moment is in a positive half cycle, Ui1 is positive, and the INi1+ output voltage is 3.3V; when the i-phase is short-circuited, if the short-circuit moment is in a negative half period, Ui1 is negative, and the INi 1-output voltage is 3.3V.

When the current signal reaches the i2 port, according to the operational principle of the operational amplifier, there will be:

U_INi2+＝(1+Z_{R3_i2+}/Z_{R2_i2+})*U_i2and U is_INi2+≤3.3V

U_INi2-＝-(Z_{R3_i2-}/Z_{R2_i2-})*U_i2And U is_INi2-≤3.3V (2)

In the formula of U_INi2+Middle is the voltage of the INi2+ port; z_{R3_i2+}A resistance value of R3 — i2 +; u shape_INi2-Middle is the voltage of the INi 2-port; z_{R3_i2-}Is the resistance value of R3_ i 2-.

According to the formula (1), when the single-phase grounding short circuit does not occur to the single-core cable, the current transformer CT-i2 has no current output, and Ui2 voltage U_i2Because the resistor R1_ i2 is zero, the output voltages of the ports INi2+ and INi 2-are both 0. Selection of Z_{R3_i2+}Is far greater than Z_{R2_i2+}，Z_{R3_i2-}Is far greater than Z_{R2_i2-}When the i-phase is short-circuited, if the short-circuit moment is in a positive half cycle, Ui2 is positive, and the INi2+ output voltage is 3.3V; when the i-phase is short-circuited, if the short-circuit moment is in a negative half period, Ui2 is negative, and the INi 2-output voltage is 3.3V.

If the short occurs in the positive half cycle, the programmable logic device inputs INi1+ and INi2+ both transition from 0 to 3.3V. Since the lengths of the first terminal current signal outgoing line and the second terminal current signal outgoing line are equal, the position of the short circuit occurrence point can be determined according to the time difference of the level jump of the INi1+ and the INi2 +. If the length of the single-core cable is L, the signal propagation speed is v, and the short-circuit point is deviated from the center of the cable to the end h of i1, the time when INi1+ occurs is as follows: t1 ═ 0.5L-h)/v, the time at which INi 1-occurred was: t2 ═ 0.5L + h)/v; therefore, h is (t2-t1) v/2, and t2-t1 is equal to the time difference of the jump of the levels INi1+ and INi2+, so that the distance of the fault point can be positioned.

If the short occurs in the negative half cycle, the programmable logic device inputs INi 1-and INi 2-will both transition from 0 to 3.3V. Since the first terminal current signal lead wire and the second terminal current signal lead wire are equal in length, the position of the short circuit occurrence point can be determined according to the time difference of the voltage level transition of the INi 1-and the INi 2-. If the length of the single-core cable is L, the signal propagation speed is v, and the short-circuit point is deviated from the center of the cable to the end h of i1, the moment when INi 1-occurs is as follows: t1 ═ 0.5L + h)/v, the time at which INi 1-occurred was: t2 ═ 0.5L-h)/v; therefore, h is (t2-t1) v/2, and t2-t1 is equal to the time difference of the level jump of the INi1 and INi2, so that the distance of the fault point can be positioned.

And after the distance of the fault point is obtained, the data are uploaded to an upper computer, and the position can be displayed.

By adopting the fault positioning device, the fault positioning can be realized by measuring the time difference of the fault point signal reaching the two ends of the cable, and the crystal oscillator frequency of the programmable logic device adopted by the distance meter can be as high as 3x10⁸Hz, and the propagation speed of the charge in the cable is 2x10⁸m/s, the device does not need a logic device to perform complex function transformation operation, only performs simple comparison and addition and subtraction operation, has almost no time delay, can position the fault point within 0.67m, and has high reliability.

Drawings

FIG. 1 is a schematic diagram of the present invention.

Fig. 2 is a basic schematic diagram of the rangefinder of fig. 1.

Detailed Description

The present invention will be described in further detail below by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting the present invention.

Referring to fig. 1, a single core cable online fault locating device which characterized in that: the device comprises a first end current transformer 1, a second end current transformer 2, a first end current signal outgoing line 3, a second end current signal outgoing line 4 and a distance meter 5; the single-core cable is provided with two end heads which are respectively a first end and a second end; after the single-core cable outer sheaths of all phases pass through the cable terminal, the first end and the second end are respectively led to the grounding box through the cable outgoing lines; the first end current transformers of all the phases are correspondingly connected in series in the first end cable sheath outgoing lines of all the phases, and the second end current transformers of all the phases are correspondingly connected in series in the second end cable sheath outgoing lines of all the phases; the secondary side of the first-end current transformer of each phase is connected to a distance meter 5 through a first-end current signal outgoing line; the secondary side of the second section of current transformer of each phase is connected to a distance meter through a second end current signal outgoing line; and a signal wire is led out of the range finder to an upper computer.

The secondary side of the current transformer CT-A1 of the first end phase A is led to a distance meter port A1 through a first end current signal outgoing line and then divided into two paths, one path is connected with the anode of a first operational amplifier through a resistor R4_ A1+, the cathode of the first operational amplifier is led out and connected with the ground potential through a resistor R2_ A1+, and is connected with the output end INA1+ of the first operational amplifier through a resistor R3_ A1 +; the other path is connected with the anode of a second operational amplifier through a resistor R2_ A1-, the cathode lead-out of the second operational amplifier is connected with the ground potential through a resistor R4_ A1-, and is connected with the output end INA 1-of the second operational amplifier through a resistor R3_ A1-; the output ends of the first operational amplifier and the second operational amplifier are connected with the input port of the editable logic device of the distance meter;

the secondary side of the current transformer CT-A2 of the phase A at the second end is led to a port A2 of the distance measuring instrument through a current signal outgoing line at the second end and then divided into two paths, one path is connected with the positive electrode of a third operational amplifier through a resistor R4_ A2+, the negative electrode of the third operational amplifier is led out and connected with the ground potential through a resistor R2_ A2+, and the other path is connected with the output end INA2+ of the third operational amplifier through a resistor R3_ A2 +; the other path is connected with the anode of a fourth operational amplifier through a resistor R2_ A2-, the cathode lead-out of the fourth operational amplifier is connected with the ground potential through a resistor R4_ A2-, and is connected with the output end INA 2-of the fourth operational amplifier through a resistor R3_ A2-; the output ends of the third operational amplifier and the fourth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-B1 of the phase B at the first end is led to a B1 port of the distance meter through a first end current signal outgoing line and then divided into two paths, one path is connected with the positive electrode of a fifth operational amplifier through a resistor R4_ B1+, the negative electrode of the fifth operational amplifier is led out and connected with the ground potential through a resistor R2_ B1+, and is connected with the output end INB1+ of the fifth operational amplifier through a resistor R3_ B1 +; the other path is connected with the positive electrode of a sixth operational amplifier through a resistor R2_ B1-, the negative electrode of the sixth operational amplifier is led out and connected with the ground potential through a resistor R4_ B1-, and is connected with the output end INB 1-of the sixth operational amplifier through a resistor R3_ B1-; the output ends of the fifth operational amplifier and the sixth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-B2 of the phase B at the second end is led to a B2 port of the distance meter through a second end current signal outgoing line and then divided into two paths, one path is connected with the anode of a seventh operational amplifier through a resistor R4_ B2+, the cathode of the seventh operational amplifier is led out and connected with the ground potential through a resistor R2_ B2+, and the other path is connected with the output end INB2+ of the seventh operational amplifier through a resistor R3_ B2 +; the other path is connected with the anode of an eighth operational amplifier through a resistor R2_ B2-, the cathode lead-out of the eighth operational amplifier is connected with the ground potential through a resistor R4_ B2-, and is connected with the output end INB 2-of the eighth operational amplifier through a resistor R3_ B2-; the output ends of the seventh operational amplifier and the eighth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-C1 of the first end C phase is led to a C1 port of the distance meter through a first end current signal outgoing line and then divided into two paths, one path is connected with the anode of a ninth operational amplifier through a resistor R4_ C1+, the cathode of the ninth operational amplifier is led out to be connected with the ground potential through a resistor R2_ C1+, and is connected with the output end INC1+ of the ninth operational amplifier through a resistor R3_ C1 +; the other path is connected with the anode of a tenth operational amplifier through a resistor R2_ C1-, the cathode lead-out of the tenth operational amplifier is connected with the ground potential through a resistor R4_ C1-, and is connected with the output end INC 1-of the tenth operational amplifier through a resistor R3_ C1-; the output ends of the ninth operational amplifier and the tenth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-C2 of the second end C phase is led to a distance meter C2 port through a second end current signal outgoing line and then divided into two paths, one path is connected with the anode of an eleventh operational amplifier through a resistor R4_ C2+, the cathode of the eleventh operational amplifier is led out and connected with the ground potential through a resistor R2_ C2+, and is connected with the output end INC2+ of the eleventh operational amplifier through a resistor R3_ C2 +; the other path is connected with the anode of a twelfth operational amplifier through a resistor R2_ C2-, the cathode lead-out of the twelfth operational amplifier is connected with the ground potential through a resistor R4_ C2-; the anode lead-out of the twelfth operational amplifier is connected with the output end INC2 of the twelfth operational amplifier through a resistor R3_ C2-; the output ends of the eleventh operational amplifier and the twelfth operational amplifier are connected with the input port of the editable logic device;

and the programmable logic device is connected with an upper computer through a signal wire.

The lengths of the phase current signal outgoing line at the first end and the phase current signal outgoing line at the second end are preferably equal, paths from the two ends of the cable to the distance meter are completely symmetrical and consistent, and fault location can be realized more conveniently by measuring the time difference of a fault point signal reaching the two ends of the cable.

When a single-phase grounding short-circuit fault occurs in the single-core cable (taking A-phase K-point short circuit as an example), starting from a short-circuit point, a short-circuit current I1 flows to the outer sheath of the single-core cable at the first end, and a short-circuit current I2 flows to the outer sheath of the single-core cable at the second end; the current flows to the cable sheath leading-out wire after passing through the cable terminal along the single-core cable outer sheath, and after passing through the current transformer CT-A1 and the current transformer CT-A2, the current is induced from the secondary side of the current transformer and is led to the A1 port and the A2 port of the distance meter through the signal leading-out wire.

When the current signal reaches the port a1, according to the operational principle of the operational amplifier, there will be:

U_INA1+＝(1+Z_{R3_A1+}/Z_{R2_A1+})*U_A1and U is_INA1+≤3.3V

U_INA1-＝-(Z_{R3_A1-}/Z_{R2_A1-})*U_A1And U is_INA1-≤3.3V (1)

In the formula of U_INA1+Medium is the voltage of the INA1+ port; z_{R3_A1+}The resistance value is R3_ A1+, the same holds true.

According to the formula (1), when the single-phase grounding short circuit does not occur to the single-core cable, the current transformer CT-A1 has no current output, and the voltage U of UA1_A1Because the resistor R1_ A1 is zero, the output voltages at the ports INA1+ and INA 1-are both 0. Selection of Z_{R3_A1+}Is far greater than Z_{R2_A1+}，Z_{R3_A1-}Is far greater than Z_{R2_A1-}When the phase A is short-circuited, if the short-circuit moment is in a positive half cycle, the phase UA1 is positive, and the INA1+ output voltage is 3.3V; when the short circuit occurs in the A phase, if the short circuit moment occurs in a negative half period, UA1 is negative, and the INA 1-output voltage is 3.3V.

When the current signal reaches the port a2, according to the operational principle of the operational amplifier, there will be:

U_INA2+＝(1+Z_{R3_A2+}/Z_{R2_A2+})*U_A2and U is_INA2+≤3.3V

U_INA2-＝-(Z_{R3_A2-}/Z_{R2_A2-})*U_A2And U is_INA2-≤3.3V (2)

In the formula of U_INA2+Medium is the voltage of the INA2+ port; z_{R3_A2+}The resistance value is R3_ A2+, the same holds true.

According to the formula (2), when the single-phase grounding short circuit does not occur to the single-core cable, the current transformer CT-A2 has no current output, and the voltage U of UA2_A2Because the resistor R1_ A2 is zero, the output voltages at the ports INA2+ and INA 2-are both 0. Selection of Z_{R3_A2+}＝100Z_{R2_A2+}，Z_{R3_A2-}＝100Z_{R2_A2-}When the phase A is short-circuited, if the short-circuit moment is in a positive half cycle, the phase UA2 is positive, and the INA2+ output voltage is 3.3V; when the short circuit occurs in the A phase, if the short circuit moment occurs in a negative half period, UA2 is negative, and the INA 2-output voltage is 3.3V.

If the short occurs in the positive half cycle, the inputs INA1+ and INA2+ of the programmable logic device will both transition from 0 to 3.3V. Since the first terminal current signal lead wire and the second terminal current signal lead wire have the same length, the position of the short circuit occurrence point can be determined according to the time difference of the voltage level transition of INA1+ and INA2 +. If the length of the single-core cable is 2000m, the signal propagation speed is 2.5 multiplied by 10⁸m/s, the short circuit point is 500m away from the cable center to the A1 end, and the time when INA1+ occurs is as follows: t1 ═ 1000-⁸2000ns, the moment at which INA 1-occurs is: t2 ═ 1000+ 500)/2.5X 10⁸6000 ns; and t2-t1 is 4000ns, if the programmable logic device adopts a crystal oscillator frequency of 100MHz, the time identification precision is 10ns, and the positioning error is 10 multiplied by 500/4000 which is 1.25m, so that the positioning requirement is completely met.

And after the distance of the fault point is obtained, the data are uploaded to an upper computer, and the position can be displayed.

It should be noted that the above describes exemplifying embodiments of the invention. It will be understood by those skilled in the art, however, that the present invention is not limited to the embodiments described above, which are given by way of illustration of the principles of the present invention, but that various changes and modifications may be made without departing from the scope of the invention as defined by the appended claims.

Claims (3)

1. The utility model provides an online fault locating device of single core cable which characterized in that: the device comprises a first end current transformer (1), a second end current transformer (2), a first end current signal outgoing line (3), a second end current signal outgoing line (4) and a distance meter (5); the single-core cable is provided with two end heads which are respectively a first end and a second end; after the single-core cable outer sheaths of all phases pass through the cable terminal, the first end and the second end are respectively led to the grounding box through the cable outgoing lines; the first end current transformers of all the phases are correspondingly connected in series in the first end cable sheath outgoing lines of all the phases, and the second end current transformers of all the phases are correspondingly connected in series in the second end cable sheath outgoing lines of all the phases; the secondary side of the first-end current transformer of each phase is connected to a distance meter (5) through a first-end current signal outgoing line; the secondary side of the second section of current transformer of each phase is connected to a distance meter through a second end current signal outgoing line; and a signal wire is led out of the range finder to an upper computer.

2. A single core cable on-line fault location device as claimed in claim 1, wherein:

the secondary side of the current transformer CT-A1 of the first end phase A is led to a distance meter port A1 through a first end current signal outgoing line and then divided into two paths, one path is connected with the anode of a first operational amplifier through a resistor R4_ A1+, the cathode of the first operational amplifier is led out and connected with the ground potential through a resistor R2_ A1+, and is connected with the output end INA1+ of the first operational amplifier through a resistor R3_ A1 +; the other path is connected with the anode of a second operational amplifier through a resistor R2_ A1-, the cathode lead-out of the second operational amplifier is connected with the ground potential through a resistor R4_ A1-, and is connected with the output end INA 1-of the second operational amplifier through a resistor R3_ A1-; the output ends of the first operational amplifier and the second operational amplifier are connected with the input port of the editable logic device of the distance meter;

the secondary side of the current transformer CT-A2 of the phase A at the second end is led to a port A2 of the distance measuring instrument through a current signal outgoing line at the second end and then divided into two paths, one path is connected with the positive electrode of a third operational amplifier through a resistor R4_ A2+, the negative electrode of the third operational amplifier is led out and connected with the ground potential through a resistor R2_ A2+, and the other path is connected with the output end INA2+ of the third operational amplifier through a resistor R3_ A2 +; the other path is connected with the anode of a fourth operational amplifier through a resistor R2_ A2-, the cathode lead-out of the fourth operational amplifier is connected with the ground potential through a resistor R4_ A2-, and is connected with the output end INA 2-of the fourth operational amplifier through a resistor R3_ A2-; the output ends of the third operational amplifier and the fourth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-B1 of the phase B at the first end is led to a B1 port of the distance meter through a first end current signal outgoing line and then divided into two paths, one path is connected with the positive electrode of a fifth operational amplifier through a resistor R4_ B1+, the negative electrode of the fifth operational amplifier is led out and connected with the ground potential through a resistor R2_ B1+, and is connected with the output end INB1+ of the fifth operational amplifier through a resistor R3_ B1 +; the other path is connected with the positive electrode of a sixth operational amplifier through a resistor R2_ B1-, the negative electrode of the sixth operational amplifier is led out and connected with the ground potential through a resistor R4_ B1-, and is connected with the output end INB 1-of the sixth operational amplifier through a resistor R3_ B1-; the output ends of the fifth operational amplifier and the sixth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-B2 of the phase B at the second end is led to a B2 port of the distance meter through a second end current signal outgoing line and then divided into two paths, one path is connected with the anode of a seventh operational amplifier through a resistor R4_ B2+, the cathode of the seventh operational amplifier is led out and connected with the ground potential through a resistor R2_ B2+, and the other path is connected with the output end INB2+ of the seventh operational amplifier through a resistor R3_ B2 +; the other path is connected with the anode of an eighth operational amplifier through a resistor R2_ B2-, the cathode lead-out of the eighth operational amplifier is connected with the ground potential through a resistor R4_ B2-, and is connected with the output end INB 2-of the eighth operational amplifier through a resistor R3_ B2-; the output ends of the seventh operational amplifier and the eighth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-C1 of the first end C phase is led to a C1 port of the distance meter through a first end current signal outgoing line and then divided into two paths, one path is connected with the anode of a ninth operational amplifier through a resistor R4_ C1+, the cathode of the ninth operational amplifier is led out to be connected with the ground potential through a resistor R2_ C1+, and is connected with the output end INC1+ of the ninth operational amplifier through a resistor R3_ C1 +; the other path is connected with the anode of a tenth operational amplifier through a resistor R2_ C1-, the cathode lead-out of the tenth operational amplifier is connected with the ground potential through a resistor R4_ C1-, and is connected with the output end INC 1-of the tenth operational amplifier through a resistor R3_ C1-; the output ends of the ninth operational amplifier and the tenth operational amplifier are connected with the input port of the editable logic device;

the secondary side of the current transformer CT-C2 of the second end C phase is led to a distance meter C2 port through a second end current signal outgoing line and then divided into two paths, one path is connected with the anode of an eleventh operational amplifier through a resistor R4_ C2+, the cathode of the eleventh operational amplifier is led out and connected with the ground potential through a resistor R2_ C2+, and is connected with the output end INC2+ of the eleventh operational amplifier through a resistor R3_ C2 +; the other path is connected with the anode of a twelfth operational amplifier through a resistor R2_ C2-, the cathode lead-out of the twelfth operational amplifier is connected with the ground potential through a resistor R4_ C2-; the anode lead-out of the twelfth operational amplifier is connected with the output end INC2 of the twelfth operational amplifier through a resistor R3_ C2-; the output ends of the eleventh operational amplifier and the twelfth operational amplifier are connected with the input port of the editable logic device;

and the programmable logic device is connected with an upper computer through a signal wire.

3. A cable fault locating method of a single-core cable on-line fault locating device is characterized in that the single-core cable on-line fault locating device of claim 1 or 2 is adopted;

when the single-phase grounding short-circuit fault occurs to the single-core cable, the short-circuit current I1 positioned on the first end side in two sides from the short-circuit point flows to the first end single-core cable outer sheath, and the short-circuit current I2 positioned on the second end side flows to the second end single-core cable outer sheath; the current flows to the cable sheath outgoing line after passing through the cable terminal along the single-core cable outer sheath, and after passing through the first end current transformer and the second end current transformer, the current is induced from the secondary side of the current transformer and is led to two interfaces of the same phase of the distance meter through the signal outgoing line; when the current signal reaches the interface of the corresponding first end of the distance meter, according to the working principle of the operational amplifier, the following steps are carried out:

U_INi1+＝(1+Z_{R3_i1+}/Z_{R2_i1+})*U_i1and U is_INi1+≤3.3V

U_INi1-＝-(Z_{R3_i1-}/Z_{R2_i1-})*U_i1And U is_INi1-≤3.3V (1)

In the formula of U_INi1+Middle is the voltage of the INi1+ port; z_{R3_i1+}A resistance value of R3 — i1 +; i is any one of A, B, C;

according to the formula (1), when the single-phase grounding short circuit does not occur to the single-core cable, the current transformer CT-i1 has no current output, and Ui1 voltage U_i1Because the existence of the resistor R1_ i1 is zero, the output voltages of the ports INi1+ and INi 1-are both 0; selection of Z_{R3_i1+}Is far greater than Z_{R2_i1+}，Z_{R3_i1-}Is far greater than Z_{R2_i1-}When the i-phase is short-circuited, if the short-circuit moment is in a positive half cycle, Ui1 is positive, and the INi1+ output voltage is 3.3V; when the i-phase is short-circuited, if the short-circuit moment is in a negative half period, Ui1 is negative, and the INi 1-output voltage is 3.3V;

when the current signal reaches the i2 port, according to the operational principle of the operational amplifier, there will be:

U_INi2+＝(1+Z_{R3_i2+}/Z_{R2_i2+})*U_i2and U is_INi2+≤3.3V

U_INi2-＝-(Z_{R3_i2-}/Z_{R2_i2-})*U_i2And U is_INi2-≤3.3V (2)

In the formula of U_INi2+Middle is the voltage of the INi2+ port; z_{R3_i2+}Resistance value R3 — i2+, the same holds true;

according to the formula (1), when the single-phase grounding short circuit does not occur to the single-core cable, the current transformer CT-i2 has no current output, and Ui2 voltage U_i2Because the existence of the resistor R1_ i2 is zero, the output voltages of the ports INi2+ and INi 2-are both 0; selection of Z_{R3_i2+}Is far greater than Z_{R2_i2+}，Z_{R3_i2-}Is far greater than Z_{R2_i2-}When i-phase short circuit occurs, if the short circuit moment occurs in the positive half periodIf so, Ui2 is positive, and the INi2+ output voltage is 3.3V; when the i-phase is short-circuited, if the short-circuit moment is in a negative half period, Ui2 is negative, and the INi 2-output voltage is 3.3V;

if the short circuit moment occurs in the positive half cycle, the input ends INi1+ and INi2+ of the programmable logic device jump from 0 to 3.3V; because the lengths of the first end current signal outgoing line and the second end current signal outgoing line are equal, the position of a short circuit generating point can be determined according to the time difference of the level jump of the INi1+ and the INi2 +; if the length of the single-core cable is L, the signal propagation speed is v, and the short-circuit point is deviated from the center of the cable to the end h of i1, the time when INi1+ occurs is as follows: t1 ═ 0.5L-h)/v, the time at which INi 1-occurred was: t2 ═ 0.5L + h)/v; therefore, h is (t2-t1) v/2, and t2-t1 are equal to the time difference of the jump of the levels of INi1+ and INi2+, so that the distance of a fault point can be positioned;

if the short circuit moment occurs in the negative half cycle, the input ends INi 1-and INi 2-of the programmable logic device jump from 0 to 3.3V; since the first terminal current signal lead wire and the second terminal current signal lead wire are equal in length, the position of the short circuit occurrence point can be determined according to the time difference of the voltage level transition of the INi 1-and the INi 2-. If the length of the single-core cable is L, the signal propagation speed is v, and the short-circuit point is deviated from the center of the cable to the end h of i1, the moment when INi 1-occurs is as follows: t1 ═ 0.5L + h)/v, the time at which INi 1-occurred was: t2 ═ 0.5L-h)/v; therefore, h is (t2-t1) v/2, and t2-t1 is equal to the time difference of the level jump of the INi1 and the level jump of the INi2, so that the distance of a fault point can be positioned;

and after the distance of the fault point is obtained, the data are uploaded to an upper computer, and the position can be displayed.

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