A cable fault location device and method for a bipolar auxiliary and bipolar power supply

Abstract

The present invention relates to a cable fault location device and method with bipolar assistance and bipolar power supply, belonging to the field of electrical detection. The present invention includes a current sampling resistor, a current sampling unit, a negative power supply, and a voltage sampling unit. Its structural characteristics are as follows: It further includes a positive power supply and an FPGA main control unit. One end of the current sampling resistor is connected to the common end of the positive power supply and the negative power supply, and the other end of the current sampling resistor is grounded. Both the current sampling unit and the voltage sampling unit are connected to the FPGA main control unit, and the FPGA main control unit is respectively connected to the positive power supply and the negative power supply. By adopting the test method of bipolar assistance and bipolar power supply, it can not only eliminate the errors caused by the change of ground potential, thermal electromotive force, etc., but also eliminate the errors introduced by short connection wires, and at the same time can offset the zero error of the sampling circuit itself.

Description

Technical Field

[0001] The present invention relates to a cable fault location device and method with bipolar assistance and bipolar power supply, belonging to the field of electrical detection. Background Art

[0002] After an insulation breakdown fault occurs in a power cable, a professional cable fault tester is required to find and locate the fault in order to repair the faulty cable faster. Currently, there are mainly two categories of cable fault ranging techniques: the bridge method and the wave reflection method, and the Murray bridge is the most commonly used bridge location method. However, the Murray bridge method also has some drawbacks, mainly because: there are operating cables around the faulty cable, and the operating cables will generate power frequency magnetic fields. The faulty cable will generate induced voltages due to these power frequency magnetic fields, and these induced voltages may be up to hundreds of volts. The maximum voltage that the galvanometer can withstand does not exceed the mV level. Therefore, the galvanometer cannot be used normally or even be damaged, and the fault distance cannot be measured. To improve the drawbacks of the Murray bridge, the voltage ratio method and the resistance ratio method have emerged. The key to these two methods lies in accurately collecting the voltage drop of the cable core. Since the internal resistance of high-voltage cables is mostly in the mΩ level and the leakage current flowing through the fault point is also very small, the voltage drop generated by the test current on the cable is only a few mV, or even less than 1 mV.

[0003] Existing intelligent bridge devices use a unipolar power supply and a single-phase assistance method for testing. The testing method is as Figure 1 shown: BF is the auxiliary phase, CG is the faulty phase, FG is the short connection wire, and point D is the fault point. Its testing steps are divided into two steps. In the first step, K1 is disconnected and K2 is closed. The test current flows through the cable CD section. Since no current flows through the cable BF section and the cable DG section, the voltage U CB collected between points CB is the voltage U CD between points CD. U CD divided by the test current I gives the resistance R CD of the CD section; in the second step, K2 is disconnected and K1 is closed. The same current as in the first step flows through the cable BF and DG sections. Since no current flows through the cable CD section, the voltage U BC collected between points BC is the voltage U BD between points BD. U BD divided by the test current I gives the resistance R BF +R DG of the BF and DG sections. The fault point distance can be deduced from the resistance values obtained through the two measurements:

[0004] However, in practical applications, the resistance of the connection wire FG at the opposite end and the contact resistance of the short connection wire must be considered. The sum of these two resistances is R FG, after adding the resistance of the opposite-end connection cable, the fault distance is: When the length of the faulty cable is short or the resistance value is small, due to the influence of the opposite-end short connection wire R FG the measured value will be smaller than the true value.

[0005] Existing single-pole power supplies and single-phase auxiliary intelligent bridges cannot locate faults in the outer sheath of multi-core cables. Since multi-core cables have only one layer of armor, the resistance values of the cable cores and the armor are not equal, so it is impossible to find an auxiliary phase that matches the armor resistance for reference, and thus it is impossible to measure the fault distance. Generally, the wave reflection method cannot be used to measure the distance of cable outer sheath faults either.

[0006] There are often multiple operating cables in underground cable galleries. When measuring the fault distance of a faulty cable, the operating cables will interfere with the faulty cable; at the same time, the impedance at the cable fault point is unstable, resulting in unstable leakage current at the fault point. This requires the entire system to achieve fast constant current, fast sampling, and fast operation; traditional signal filtering schemes use RC low-pass filtering methods, and the filtering circuit consists of a capacitor and a resistor; however, the power frequency interference in DC signals belongs to low-frequency signal interference, so the cut-off frequency of RC low-pass filtering must be set very low; but too low a cut-off frequency will make the entire sampling system respond slowly; due to the unstable impedance at the cable fault point, the magnitude of the leakage current will also change, and a sampling system with a low response speed will affect the accuracy of measuring the fault point distance.

[0007] The entire test system needs to form a loop through the ground, and there are stray currents distributed in the ground. Therefore, the ground potential is constantly changing, and the change in the ground potential affects the accuracy of system testing; the cable laying distance is generally long. If there is a temperature difference at both ends of the cable, a thermal electromotive force will be generated in the cable, bringing a fixed DC bias to the sampling system; traditional cable fault testing equipment uses a single-phase auxiliary and single-pole power supply method for testing, and a short connection wire is required to short-circuit the far end of the faulty cable. The short connection wire itself has resistance, and there is also an uncertain contact resistance at the connection point between the short connection wire and the cable head, which will bring certain errors to the test results.

[0008] In view of this, for the "DC signal intelligent acquisition device for high-voltage cable fault location" [Patent No. CN201510609209.2], the signal sampling scheme of this invention device uses a multi-stage RC low-pass filtering method. Using a passive filter will result in energy loss, slow system response, and a long signal stabilization period; especially when the impedance at the fault point is unstable, it is impossible to accurately collect the voltage drop signal of the faulty cable, resulting in inaccurate test results. The test method uses a single-pole power supply and single-phase auxiliary scheme, and there are errors introduced by the resistance of the opposite-end short connection wire itself, the contact resistance of the short connection wire, the change in ground potential, and the thermal electromotive force.

[0009] In view of this, the method of "locating the insulation fault point of a submersible cable by the double Wheatstone bridge method" [Patent No. CN201610221333.6] has a testing method based on the Murray bridge. When there are operating cables around the faulty cable, the operating cables will generate power frequency magnetic fields, and the faulty cable will generate induced voltages due to these power frequency magnetic fields, resulting in unstable values displayed on its digital voltmeter and making it impossible to measure the fault distance. Moreover, its testing method requires the known resistivity and cross-sectional area of the cable core. The resistivity of the cable core is related to the impurities it contains and the temperature it is at, and it is difficult to accurately measure the cross-sectional area of the cable without professional equipment, thus affecting the measurement accuracy.

[0010] In view of this, for the "DC bipolar cable fault point location testing device" [Patent No. CN201820319674.1], although the testing method of this invention device uses the bipolar testing method, it only uses single-phase assistance. At the opposite end, a short wire is needed to short-circuit the far end of the faulty cable. The resistance of the short wire itself and the contact resistance of the short wire will also bring certain errors to the test results. And its testing method is based on the Murray bridge method. When there are operating cables around the faulty cable, the operating cables will generate power frequency magnetic fields, and the faulty cable will generate induced voltages due to these power frequency magnetic fields. When the external interference of the faulty cable is severe, the bridge arm cannot be balanced. Summary of the Invention

[0011] The purpose of the present invention is to overcome the above-mentioned deficiencies existing in the prior art, and to provide a cable fault location device and method with a reasonable structural design, which can achieve fast constant current output, fast sampling, and fast operation under the condition of unstable impedance at the cable fault point, improve the real-time performance of the entire testing system and the accuracy of the test results. By using this cable fault location device and method with dual-phase assistance and bipolar power supply, the errors introduced by the resistance of the short wire itself, the contact resistance of the short wire, the change of ground potential, the thermoelectromotive force, etc. can be eliminated, and the accuracy of fault point location can be further improved.

[0012] The technical solution adopted by the present invention to solve the above problems is: This cable fault location device with dual-phase assistance and bipolar power supply includes a current sampling resistor, a current sampling unit, a negative power supply, and a voltage sampling unit. Its structural feature is that it further includes a positive power supply and an FPGA main control unit. One end of the current sampling resistor is connected to the common end of the positive power supply and the negative power supply, the other end of the current sampling resistor is grounded, both the current sampling unit and the voltage sampling unit are connected to the FPGA main control unit, and the FPGA main control unit is respectively connected to the positive power supply and the negative power supply.

[0013] Furthermore, the current sampling unit is connected to the current sampling resistor.

[0014] Furthermore, the FPGA main control unit adjusts the voltage and current magnitudes output by the positive power supply and the negative power supply through PID.

[0015] Furthermore, it also includes relay K1, relay K2, relay K3, and relay K4. The positive power supply and the negative power supply are connected to the cable fault phase CG and the auxiliary phase AE through relay K1, relay K2, relay K3, and relay K4, and there is a fault point D on the cable fault phase CG.

[0016] Furthermore, the voltage sampling unit is connected to the cable fault phase CG and the auxiliary phase BF, and there is a fault point D on the cable fault phase CG.

[0017] Furthermore, the voltage sampling unit includes an input protection circuit, a programmable gain amplifier circuit, a fifth-order active filter circuit, a voltage follower circuit, an A / D analog-to-digital conversion circuit, and a single-chip microcomputer sampling control circuit, and the input protection circuit, the programmable gain amplifier circuit, the fifth-order active filter circuit, the voltage follower circuit, the A / D analog-to-digital conversion circuit, and the single-chip microcomputer sampling control circuit are connected in sequence.

[0018] Furthermore, the input protection circuit is connected to the C end of the cable fault phase CG and the B end of the auxiliary phase BF through a signal input interface, and the single-chip microcomputer sampling control circuit is connected to the FPGA main control circuit of the FPGA main control unit.

[0019] Furthermore, the positive power supply includes a phase-shifted full-bridge controller, a full-bridge power device, a positive voltage multiplier circuit, and a high-voltage output sampling unit. The FPGA main control unit, the phase-shifted full-bridge controller, the full-bridge power device, the positive voltage multiplier circuit, the high-voltage output sampling unit, and the FPGA main control unit are connected in sequence, and the positive voltage multiplier circuit is connected to relay K1.

[0020] Another technical object of the present invention is to provide a cable fault location method for a two-phase auxiliary and bipolar power supply.

[0021] The above technical object of the present invention is achieved through the following technical solutions.

[0022] Furthermore, a cable fault location method for a two-phase auxiliary and bipolar power supply, the cable fault location method includes the following steps:

[0023] The first step: Close relay K1 and relay K4, the positive power supply works, and outputs positive-polarity high-voltage electricity.

[0024] The second step: Close relay K2 and relay K4, the negative power supply works, and outputs negative-polarity high-voltage electricity.

[0025] Step 3: Close relay K1 and relay K3, the positive power supply works, and positive-polarity high-voltage electricity is output.

[0026] Step 4: Close relay K2 and relay K3, the negative power supply works, and negative-polarity high-voltage electricity is output.

[0027] Further, in the first step, the current flows into the cable from point C and leaks to the ground through the fault point D. Since there is no current flowing through the section from the fault point D to point G, the voltage between point C and point B collected by the voltage sampling unit at this time is the voltage difference U1 between point C and the fault point D. At the same time, the current sampling unit collects the current I1 flowing through the fault point D, and the resistance value R1 from point C to the fault point D is obtained by calculating U1 / I1.

[0028] Further, in the second step, the current flows into the cable from the fault point D and flows out of the cable from point C. Since there is no current flowing through the section from the fault point D to point G, the voltage between point C and point B collected by the voltage sampling unit at this time is the voltage difference U2 between point C and the fault point D. At the same time, the current sampling unit collects the current I2 flowing through the fault point D, and the resistance value R2 from point C to the fault point D is obtained by calculating U2 / I2.

[0029] Further, in the third step, the current flows into the cable from point A and leaks to the ground through the fault point D. Since there is no current flowing through the section from the fault point D to point C, the voltage between point C and point B collected by the voltage sampling unit at this time is the voltage difference U3 between point G and the fault point D. At the same time, the current sampling unit collects the current I3 flowing through the fault point D, and the resistance value R3 from point G to the fault point D is obtained by calculating U3 / I3.

[0030] Further, in the fourth step, the current flows into the cable from the fault point D and flows out of the cable at point A. Since there is no current flowing through the section from the fault point D to point C, the voltage between point C and point B collected by the voltage sampling unit at this time is the voltage difference U4 between point G and the fault point D. At the same time, the current sampling unit collects the current I4 flowing through the fault point D, and the resistance value R4 from point G to the fault point D is obtained by calculating U4 / I4.

[0031] Further, the cable fault distance is: where L is the set full length of the cable.

[0032] Further, assuming that U is the true voltage drop signal from the near end of the faulty cable to the fault point, and Ux is the fixed voltage difference such as the change of the ground potential in the cable and the thermal electromotive force, then:

[0033] During the test of the positive power supply output: U1 = U + Ux collected by the voltage sampling unit, and the current collected by the current sampling unit is I;

[0034] During the negative power supply output test: U2 collected by the voltage sampling unit is -U + Ux, and the current collected by the current sampling unit is -I;

[0035] The sum of the positive power supply test resistance value and the negative power supply test resistance value is:

[0036] Compared with the prior art, the present invention has the following advantages: By adopting a fifth-order active filter circuit and an A / D analog-to-digital conversion circuit, the DC voltage drop signal on the faulty cable can be collected more quickly and accurately. The active filter has no energy loss for the signals in the passband, the load effect is not obvious, and the mutual influence is very small when cascaded. It is very easy to form a high-order filter by using the simple method of cascading, and the filter has a small volume and light weight; The A / D analog-to-digital conversion circuit can quickly convert the analog signal into a digital signal, and the processor performs digital filtering on the collected digital signal, which is convenient for obtaining an accurate cable voltage drop signal.

[0037] By adopting the test method of dual-phase assistance and bipolar power supply, it can not only eliminate the errors caused by the change of ground potential, thermal electromotive force, etc., but also eliminate the errors introduced by the short connection wire, and at the same time can offset the zero-point error of the sampling circuit itself. Brief Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the test principle of the intelligent bridge test method in the prior art.

[0039] Figure 2 It is a schematic diagram of the structure of the cable fault location device with dual-phase assistance and bipolar power supply according to the embodiment of the present invention.

[0040] Figure 3 It is a schematic diagram of the structure of the voltage sampling unit according to the embodiment of the present invention.

[0041] Figure 4 It is a schematic diagram of the principle of the fifth-order active filter circuit according to the embodiment of the present invention.

[0042] Figure 5 It is a schematic diagram of the principle of the voltage follower circuit according to the embodiment of the present invention.

[0043] Figure 6 It is a schematic diagram of the principle of the A / D analog-to-digital conversion circuit according to the embodiment of the present invention.

[0044] Figure 7 It is a schematic diagram of the principle of the FPGA main control unit to achieve fast constant current by PID controlling the positive power supply according to the embodiment of the present invention.

[0045] In the figure: current sampling resistor 1, current sampling unit 2, positive power supply 3, negative power supply 4, voltage sampling unit 5, FPGA main control unit 6,

[0046] Phase-shifted full-bridge controller 31, full-bridge power device 32, positive voltage multiplier circuit 33, high-voltage output sampling unit 34,

[0047] Input protection circuit 51, programmable gain amplifier circuit 52, fifth-order active filter circuit 53, voltage follower circuit 54, A / D analog-to-digital conversion circuit 55, single-chip microcomputer sampling control circuit 56,

[0048] Relays K1, K2, K3, K4,

[0049] Cable fault phase CG, auxiliary phase AE, auxiliary phase BF, fault point D. Specific implementation mode

[0050] The present invention will be further described in detail below in conjunction with the accompanying drawings and through embodiments. The following embodiments are explanations of the present invention, and the present invention is not limited to the following embodiments.

[0051] Embodiment

[0052] See Figures 2 to 7 As shown, it should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have technical essence. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention. At the same time, if terms such as "upper", "lower", "left", "right", "middle", and "one" are used in this specification, they are only for the convenience of clear narration and are not used to limit the scope under which the present invention can be implemented. The change or adjustment of their relative relationships, without substantial change in technical content, should also be regarded as the scope under which the present invention can be implemented.

[0053] The cable fault location device with two-phase auxiliary and bipolar power supply in this embodiment includes current sampling resistor 1, current sampling unit 2, positive power supply 3, negative power supply 4, voltage sampling unit 5, FPGA main control unit 6, relays K1, K2, K3, and K4.

[0054] One end of the current sampling resistor 1 in this embodiment is connected to the common terminal of the positive power supply 3 and the negative power supply 4, the other end of the current sampling resistor 1 is grounded, both the current sampling unit 2 and the voltage sampling unit 5 are connected to the FPGA main control unit 6, and the FPGA main control unit 6 is respectively connected to the positive power supply 3 and the negative power supply 4; the current sampling unit 2 is connected to the current sampling resistor 1.

[0055] In this embodiment, the positive power supply 3 and the negative power supply 4 are connected to the cable fault phase CG and the auxiliary phase AE through the relays K1, K2, K3, and K4. There is a fault point D on the cable fault phase CG. The voltage sampling unit 5 is connected to the cable fault phase CG and the auxiliary phase BF, and there is a fault point D on the cable fault phase CG.

[0056] Under normal circumstances, the voltage sampling unit 5 is connected to the cable fault phase CG and the auxiliary phase BF through the test connection line. The voltage sampling unit 5 transmits the collected data to the FPGA main control unit 6 through the optical fiber; at the same time, the data collected by the current sampling unit 2 is transmitted to the FPGA main control unit 6. The FPGA main control unit 6 adjusts the output voltage and current of the positive power supply 3 and the negative power supply 4 through PID.

[0057] The voltage sampling unit 5 in this embodiment includes an input protection circuit 51, a programmable gain amplifier circuit 52, a fifth-order active filter circuit 53, a voltage follower circuit 54, an A / D analog-to-digital conversion circuit 55, and a single-chip microcomputer sampling control circuit 56. The input protection circuit 51, the programmable gain amplifier circuit 52, the fifth-order active filter circuit 53, the voltage follower circuit 54, the A / D analog-to-digital conversion circuit 55, and the single-chip microcomputer sampling control circuit 56 are connected in sequence; the input protection circuit 51 is connected to the C end of the cable fault phase CG and the B end of the auxiliary phase BF through the signal input interface, and the single-chip microcomputer sampling control circuit 56 is connected to the FPGA main control circuit of the FPGA main control unit 6.

[0058] Under normal circumstances, the input protection circuit 51 of the voltage sampling unit 5 is connected to the B and C ends of the cable, and then connected to the input port of the programmable gain amplifier circuit 52. Its output is connected to the input port of the fifth-order active filter circuit 53, and then the filtered signal is transmitted to the voltage follower circuit 54. The low-impedance signal after voltage following is transmitted to the A / D analog-to-digital conversion circuit 55. The A / D analog-to-digital conversion circuit 55 converts the analog signal into a digital signal and then transmits it to the single-chip microcomputer sampling control circuit 56. The specific implementation method of the voltage sampling unit 5 is as Figure 3 shown.

[0059] The fifth-order active filter circuit 53 uses LTC1062CSW, and its filtering effect is faster than that of the RC passive filter and has a better filtering effect. It can completely filter out the power frequency signal and high-frequency interference signal, as Figure 4 shown.

[0060] The voltage follower circuit 54 has the characteristics of high input impedance and low output impedance. The signal after the fifth-order active filter enters the A / D analog-to-digital conversion circuit 55 through the voltage follower circuit 54. The model of the voltage follower circuit 54 is the operational amplifier ADA4898-1, as Figure 5 shown.

[0061] The A / D analog-to-digital conversion circuit 55 uses the AD7610 chip. The AD7610 is a high-speed ADC chip with a data throughput rate of up to 250 kSPS. It can be configured for parallel or SPI serial output. It is a 16-bit charge redistribution successive approximation register (SAR) architecture analog-to-digital converter. The single-chip microcomputer sampling control circuit 56 can read the digital signal converted by the AD7610 through the SPI method, such as Figure 6 shown.

[0062] The single-chip microcomputer sampling control circuit 56 uses an 8-bit single-chip microcomputer of microchip. This processor has extremely strong anti-interference ability and is the core control device of the voltage sampling unit 5. It controls the amplification ratio of the programmable amplification circuit 52 and reads the conversion result of the A / D analog-to-digital conversion circuit 55 respectively, and transmits the data to the FPGA main control unit 6 through optical fiber communication. The FPGA main control unit 6 performs digital filtering processing on the collected voltage and current signals and calculates the resistance value of the cable.

[0063] The FPGA main control unit 6 includes a PID control and adjustment module. The positive power supply 3 includes a phase-shifted full-bridge controller 31, a full-bridge power device 32, a positive voltage multiplier circuit 33, and a high-voltage output sampling unit 34. The FPGA main control unit 6, the phase-shifted full-bridge controller 31, the full-bridge power device 32, the positive voltage multiplier circuit 33, the high-voltage output sampling unit 34, and the FPGA main control unit 6 are connected in sequence. The positive voltage multiplier circuit 33 is connected to the relay K1.

[0064] The FPGA main control unit 6 controls the bipolar power supply through the PID control and adjustment module to achieve fast constant current. Taking the positive power supply 3 as an example: a PWM module is built inside the FPGA main control unit 6, and the PWM signal is transmitted to the positive power supply 3. The phase-shifted full-bridge controller 31 inside the positive power supply 3 converts the given PWM signal into a full-bridge drive signal with a phase angle difference. The full-bridge drive signal drives the full-bridge power device 32 to complete power conversion; the positive voltage multiplier circuit 33 converts the low-voltage AC signal output by the phase-shifted full-bridge controller 31 into a positive-polarity high voltage, and the output of the positive voltage multiplier circuit 33 is connected to the relay K1.

[0065] Meanwhile, the high-voltage output sampling unit 34 samples and converts the output positive-polarity high-voltage electricity, and sends the converted voltage value to the FPGA main control unit 6. The FPGA main control unit 6 transmits the voltage value, current value of the high-voltage output, and the set voltage and current parameters to the PID control and adjustment module. After calculation through the formula, the PID control and adjustment module transmits the result to the PWM control and adjustment module built inside the FPGA main control unit 6. When the output current of the positive power supply 3 is less than the set value, the PID control and adjustment module increases the PWM parameter transmitted, the PWM output duty cycle increases. After the phase-shifted full-bridge controller 31 detects the increase in the duty cycle, it adjusts the output phase angle difference, the full-bridge power device 32 increases the output, and at the same time the output current after positive voltage multiplication also increases; conversely, when the output current is greater than the set value, the PWM output duty cycle is decreased, thereby reducing the output current. Through the adjustment and control of a complete closed-loop PID control and adjustment module, the size of the output current is quickly adjusted and fast constant current is achieved, as Figure 7 shown.

[0066] The implementation scheme of the negative power supply 4 is similar to that of the positive power supply 3. By changing the positive voltage multiplication circuit to a negative voltage multiplication circuit, the output of negative-polarity high-voltage electricity can be achieved, and the output of the negative voltage multiplication circuit is connected to the relay K2.

[0067] The cable fault location method for the bipolar auxiliary and bipolar power supply in this embodiment includes the following steps:

[0068] The first step: Close the relay K1 and the relay K4, disconnect the relay K2 and the relay K3. The positive power supply 3 works and outputs positive-polarity high-voltage electricity. The current flows into the cable from point C and leaks to the ground through the fault point D. Since there is no current flowing through the fault point D to point G, the voltage between point C and point B collected by the voltage sampling unit 5 at this time is the voltage difference U1 between point C and the fault point D. At the same time, the current sampling unit 2 collects the current I1 flowing through the fault point D, and the resistance value R1 from point C to the fault point D is obtained by calculating U1 / I1.

[0069] The second step: Close the relay K2 and the relay K4, disconnect the relay K1 and the relay K3. The negative power supply 4 works and outputs negative-polarity high-voltage electricity. The current flows into the cable from the fault point D and flows out of the cable from point C. Since there is no current flowing through the fault point D to point G, the voltage between point C and point B collected by the voltage sampling unit 5 at this time is the voltage difference U2 between point C and the fault point D. At the same time, the current sampling unit 2 collects the current I2 flowing through the fault point D, and the resistance value R2 from point C to the fault point D is obtained by calculating U2 / I2.

[0070] Step 3: Close relay K1 and relay K3, and open relay K2 and relay K4. The positive power supply 3 operates to output positive high-voltage electricity. The current flows into the cable from point A and leaks to the ground through the fault point D. Since no current flows through the section from the fault point D to point C, the voltage between point C and point B collected by the voltage sampling unit 5 at this time is the voltage difference U3 between point G and the fault point D. At the same time, the current sampling unit 2 collects the current I3 flowing through the fault point D, and the resistance value R3 from point G to the fault point D is obtained by calculating U3 / I3.

[0071] Step 4: Close relay K2 and relay K3, and open relay K1 and relay K4. The negative power supply 4 operates to output negative high-voltage electricity. The current flows into the cable from the fault point D and flows out of the cable at point A. Since no current flows through the section from the fault point D to point C, the voltage between point C and point B collected by the voltage sampling unit 5 at this time is the voltage difference U4 between point G and the fault point D. At the same time, the current sampling unit 2 collects the current I4 flowing through the fault point D, and the resistance value R4 from point G to the fault point D is obtained by calculating U4 / I4.

[0072] The cable fault distance is: where L is the set full length of the cable.

[0073] The resistance values from two proximities (point A and point C) to the fault point D and the resistance values from two distals (point E and point G) to the fault point D are collected in the four steps. The two auxiliary phases (auxiliary phase AE and auxiliary phase BF) are responsible for transmitting current and collecting voltage respectively. Since the potential of point G is collected at the distal, the resistance value and contact resistance of the distal short connection wire will not affect the accuracy of the sampling calculation.

[0074] The resistance values collected by the single-phase auxiliary method twice are the resistance value from the proximity (point C) to the fault point D, the resistance value from the distal (point G) to the fault point D, the resistance of the auxiliary phase, the resistance of the opposite-end short connection wire, and the contact resistance of the opposite-end short connection wire. However, the resistance of the opposite-end short connection wire and the contact resistance of the opposite-end short connection wire are not definite values, and the resistance of the opposite-end short connection wire and the contact resistance of the opposite-end short connection wire are not reflected in the calculation formula.

[0075] The double-phase auxiliary and bipolar power supply test methods can also eliminate the fixed voltage differences such as the ground potential change and thermal electromotive force in the cable; since the magnitude of the current output in the four steps is the same, the true voltage drop value of the cable is also a fixed value. The bipolar power supply measurement only has different current directions flowing through the faulty cable, and the polarity of the cable voltage drop is opposite.

[0076] Assume that U is the true voltage drop signal from the proximity of the faulty cable to the fault point, and Ux is the fixed voltage differences such as the ground potential change and thermal electromotive force in the cable, then:

[0077] When testing the output of the positive power supply 3: the voltage U1 collected by the voltage sampling unit is U1 = U + Ux, and the current collected by the current sampling unit 2 is I;

[0078] When testing the output of the negative power supply 4: the voltage U2 collected by the voltage sampling unit is U2 = -U + Ux, and the current collected by the current sampling unit 2 is -I;

[0079] Adding the test resistance value of the positive power supply and the test resistance value of the negative power supply gives:

[0080] It can be seen from the formula that by using the bipolar test method, fixed voltage differences such as the change of ground potential and thermal electromotive force in the cable can be cancelled, thereby improving the test accuracy.

[0081] In addition, it should be noted that for the specific embodiments described in this specification, the shapes, names of the components, etc. can be different. The above content described in this specification is only an example of the structure of the present invention. Any equivalent changes or simple changes made according to the structure, features and principles described in the inventive concept of the present invention are included in the protection scope of the present invention. Those skilled in the art of the present invention can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they should fall within the protection scope of the present invention.

Claims

1. A cable fault location device with bipolar auxiliary and bipolar power supply, comprising a current sampling resistor (1), a current sampling unit (2), a negative power supply (4), and a voltage sampling unit (5). It is characterized in that: It further includes a positive power supply (3), an FPGA main control unit (6), a relay K1, a relay K2, a relay K3, and a relay K4. One end of the current sampling resistor (1) is connected to the common end of the positive power supply (3) and the negative power supply (4), and the other end of the current sampling resistor (1) is grounded. Both the current sampling unit (2) and the voltage sampling unit (5) are connected to the FPGA main control unit (6). The FPGA main control unit (6) is respectively connected to the positive power supply (3) and the negative power supply (4). The current sampling unit (2) is connected to the current sampling resistor (1). One end of the relay K1 is connected to the positive power supply (3), one end of the relay K2 is connected to the negative power supply (4), one end of the relay K3 is connected to the auxiliary phase AE, one end of the relay K4 is connected to the cable fault phase CG. The other ends of the relay K1, the relay K2, the relay K3, and the relay K4 are connected to each other. There is a fault point D on the cable fault phase CG. The voltage sampling unit (5) is connected to the cable fault phase CG and the auxiliary phase BF. There is a fault point D on the cable fault phase CG.

2. The cable fault location device with bipolar auxiliary and bipolar power supply according to claim 1, It is characterized in that: The voltage sampling unit (5) includes an input protection circuit (51), a programmable gain amplifier circuit (52), a fifth-order active filter circuit (53), a voltage follower circuit (54), an A / D analog-to-digital conversion circuit (55), and a single-chip microcomputer sampling control circuit (56). The input protection circuit (51), the programmable gain amplifier circuit (52), the fifth-order active filter circuit (53), the voltage follower circuit (54), the A / D analog-to-digital conversion circuit (55), and the single-chip microcomputer sampling control circuit (56) are connected in sequence.

3. The cable fault location device with bipolar auxiliary and bipolar power supply according to claim 2, It is characterized in that: The input protection circuit (51) is connected to the C end of the cable fault phase CG and the B end of the auxiliary phase BF through a signal input interface. The single-chip microcomputer sampling control circuit (56) is connected to the FPGA main control circuit of the FPGA main control unit (6).

4. The cable fault location device with bipolar auxiliary and bipolar power supply according to claim 1, It is characterized in that: The positive power supply (3) includes a phase-shifted full-bridge controller (31), a full-bridge power device (32), a positive voltage multiplier circuit (33), and a high-voltage output sampling unit (34). The FPGA main control unit (6), the phase-shifted full-bridge controller (31), the full-bridge power device (32), the positive voltage multiplier circuit (33), the high-voltage output sampling unit (34), and the FPGA main control unit (6) are connected in sequence. The positive voltage multiplier circuit (33) is connected to the relay K1.

5. A cable fault location method for a bipolar auxiliary and bipolar power supply, which is implemented by using the cable fault location device described in any one of claims 1-4. Characterized in that: The cable fault location method includes the following steps: The first step: Close relay K1 and relay K4, the positive power supply (3) works, and outputs a positive high voltage. The specific content of the first step is: Close relay K1 and relay K4, open relay K2 and relay K3, the positive power supply (3) works, and outputs a positive high voltage. The current flows into the cable from point C and leaks to the ground through the fault point D. Since there is no current flowing through the section from the fault point D to point G, the voltage between point C and point B collected by the voltage sampling unit (5) at this time is the voltage difference U1 between point C and the fault point D. At the same time, the current sampling unit (2) collects the current I1 flowing through the fault point D, and the resistance value R1 from point C to the fault point D is obtained by calculating U1 / I1. The second step: Close relay K2 and relay K4, the negative power supply (4) works, and outputs a negative high voltage. The specific content of the second step is: Close relay K2 and relay K4, open relay K1 and relay K3, the negative power supply (4) works, and outputs a negative high voltage. The current flows into the cable from the fault point D and flows out of the cable from point C. Since there is no current flowing through the section from the fault point D to point G, the voltage between point C and point B collected by the voltage sampling unit (5) at this time is the voltage difference U2 between point C and the fault point D. At the same time, the current sampling unit (2) collects the current I2 flowing through the fault point D, and the resistance value R2 from point C to the fault point D is obtained by calculating U2 / I2. The third step: Close relay K1 and relay K3, the positive power supply (3) works, and outputs a positive high voltage. The specific content of the third step is: Close relay K1 and relay K3, open relay K2 and relay K4, the positive power supply (3) works, and outputs a positive high voltage. The current flows into the cable from point A and leaks to the ground through the fault point D. Since there is no current flowing through the section from the fault point D to point C, the voltage between point C and point B collected by the voltage sampling unit (5) at this time is the voltage difference U3 between point G and the fault point D. At the same time, the current sampling unit (2) collects the current I3 flowing through the fault point D, and the resistance value R3 from point G to the fault point D is obtained by calculating U3 / I3. The fourth step: Close relay K2 and relay K3, the negative power supply (4) works, and outputs a negative high voltage. The specific content of the fourth step is: Close relay K2 and relay K3, open relay K1 and relay K4, the negative power supply (4) works, and outputs a negative high voltage. The current flows into the cable from the fault point D and flows out of the cable from point A. Since there is no current flowing through the section from the fault point D to point C, the voltage between point C and point B collected by the voltage sampling unit (5) at this time is the voltage difference U4 between point G and the fault point D. At the same time, the current sampling unit (2) collects the current I4 flowing through the fault point D, and the resistance value R4 from point G to the fault point D is obtained by calculating U4 / I4. The cable fault distance is: where L is the set total length of the cable.

6. The cable fault location method for a bipolar auxiliary and bipolar power supply according to claim 5, characterized in that: assuming that U is the true voltage drop signal from the proximal end of the faulty cable to the fault point, and Ux is the change in ground potential and the fixed voltage difference of the thermal electromotive force in the cable, then: When the positive power supply (3) outputs a test: U1 collected by the voltage sampling unit = U + Ux, and the current collected by the current sampling unit (2) is I; When the negative power supply (4) outputs a test: U2 collected by the voltage sampling unit = -U + Ux, and the current collected by the current sampling unit (2) is -I; The sum of the positive power supply test resistance value and the negative power supply test resistance value can be obtained as follows:

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