CN110244192B - Electric power overhead line ground fault distance measurement method - Google Patents
Electric power overhead line ground fault distance measurement method Download PDFInfo
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- CN110244192B CN110244192B CN201910677475.7A CN201910677475A CN110244192B CN 110244192 B CN110244192 B CN 110244192B CN 201910677475 A CN201910677475 A CN 201910677475A CN 110244192 B CN110244192 B CN 110244192B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
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Abstract
The invention discloses a power overhead line ground fault distance measurement method, which belongs to the field of relay protection in power engineering and comprises the following steps: a. carrying out short circuit on the fault phase of the ground fault line and the head end of any non-fault phase through a sampling circuit to form a head end short circuit point A, and carrying out short circuit on the fault phase and the tail end of the non-fault phase; b. injecting a high-voltage low-frequency alternating current power supply signal between the head end short contact A and the earth grounding system, and collecting electrical parameters of the sampling circuit; c. changing parameters of the sampling circuit, injecting a high-voltage low-frequency alternating current power supply signal again, and collecting electrical parameters of the sampling circuit; d. and (c) listing an equation set by using the electrical parameters collected in the step (b) and the step (c) to calculate the resistance of the power transmission line before and after the ground fault point, and calculating the position of the fault point according to the total length of the power transmission line.
Description
Technical Field
The invention relates to the technical field of fault location in a power system, in particular to a power overhead line ground fault location method.
Background
A neutral point non-effective grounding mode, also called a small current grounding system, is widely adopted in a 6 kV-35 kV power distribution network in China, and the system has the advantages that when a single-phase grounding fault occurs, a fault loop does not need to be disconnected immediately, and operation with the fault is allowed for one to two hours. The disadvantage is that when single-phase earth fault occurs, it is impossible to determine which loop the problem is on and find the fault point quickly. Since the rise in the phase voltage caused by such a fault poses a great threat to the insulation performance of the system, the fault loop must be quickly detected and eliminated. Although the market already has a mature line selection device and a positioning device, the positioning operation needs to segment a fault loop, climb a rod and hook a detection sensor, the operation process is relatively complex, and the fault positioning efficiency is low. Because the distribution network has multi-stage branches and a large number of distribution transformers are installed on the loop, the resistance method, the traveling wave method and other technologies which are widely used for the transmission loop are difficult to apply to the distribution loop. Therefore, it is an urgent need to design an overhead line ground fault distance measurement method.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the electric overhead line ground fault distance measuring method is used for rapidly obtaining the position of the overhead line grounding point.
The technical scheme of the technical problem to be solved by the invention is as follows:
a. the method comprises the steps that the head end of a fault phase of a line with a ground fault and the head end of any non-fault phase in the fault line are in short circuit through a sampling circuit, the sampling circuit comprises a first sampling resistor and a second sampling resistor which are connected in series, the connection point of the first sampling resistor and the second sampling resistor is formed into a head end short circuit point A, the fault phase of the line with the ground fault and the tail end of the non-fault phase in the fault line are in short circuit to form a tail end short circuit point B, and the fault phase and the non-fault phase after short circuit form a fault distance measuring loop;
b. injecting a high-voltage low-frequency alternating current power supply signal between the head end short contact A and the earth grounding system to the fault distance measuring loop, and collecting the electrical quantity parameters of the fault distance measuring loop and the electrical parameters of the high-voltage low-frequency alternating current power supply signal;
c. changing the resistance values of the first sampling resistor and the second sampling resistor, injecting a high-voltage low-frequency alternating-current power supply signal between the head-end short contact A and the earth grounding system to the fault distance measuring loop again, and collecting the electrical quantity parameters of the fault distance measuring loop and the electrical parameters of the high-voltage low-frequency alternating-current power supply signal;
d. and c, calculating the resistance of the power transmission line before and after the ground fault point by using the electrical parameters acquired in the steps b and c and according to an impedance method, and calculating the length of the fault point at one end of the high-voltage low-frequency alternating current power supply signal injected into the power transmission line according to the total length of the power transmission line.
Preferably, the maximum output voltage of the signal source is 80% -110% of the rated voltage of the overhead loop.
Preferably, the maximum output voltage of the signal source is 85% -100% of the rated voltage of the overhead loop.
Preferably, the frequency of the signal source is 0.5-15 Hz.
Preferably, the frequency of the signal source is 1-5 Hz.
Preferably, the resistance from the ground fault point of the ground fault phase to the head-end short contact a is a front-stage resistance, and the resistance from the ground fault point of the ground fault phase to the tail-end short contact B is a rear-stage resistance.
The step b is operated as follows: measuring voltage values of the first sampling resistor, the second sampling resistor and the high-voltage low-frequency alternating-current power supply signal, and listing a first equation of the fault distance measuring loop according to ohm law and kirchhoff voltage law;
the step c is operated as follows: adjusting the resistance value of the first sampling resistor and/or the second sampling resistor to make the adjusted resistance value of the first sampling resistor and/or the second sampling resistor different from the resistance value before adjustment,
then, measuring the voltage values of the first sampling resistor and the second sampling resistor and the voltage value of the high-voltage low-frequency alternating-current power supply signal, and listing a second equation of the fault distance measuring loop according to ohm law and kirchhoff voltage law;
the step d is operated as follows: the method comprises the steps of solving the resistance values of a front-section resistor and a rear-section resistor according to a linear equation of two-dimensional system composed of a first equation and a second equation, calculating the length of one end of a fault point at a distance from a high-voltage low-frequency alternating-current power supply signal according to the principle that the resistance value of a wire is in direct proportion to the length and the total length of a power transmission line, and enabling a first sampling resistor and a second sampling resistor to be precise resistors.
Preferably, in the step b, when the voltage values of the first and second sampling resistors are measured and recorded, the first sampling resistor is connected with the fault. In step c, when measuring and recording, the second sampling resistor is connected with the fault.
Preferably, two sampling circuits are provided, the resistance values of the first sampling resistor and/or the second sampling resistor in the two sampling circuits are different,
in the step b, a first sampling circuit is used for short circuit during measurement and recording;
in step c, a second sampling circuit is used for short circuit during measurement and recording.
Preferably, in step b and step c: and the voltage between the connection point of the sampling circuit and the fault phase and the head end short contact A is also collected, and the voltage between the connection point of the sampling circuit and the non-fault phase and the head end short contact A is also collected, so that the influence of the contact resistance is avoided.
The invention has the beneficial effects that: the general position of the fault point can be quickly positioned, the time for finding the fault of the loop is shortened, and the power supply quality is improved.
Drawings
Figure 1 is a schematic diagram of a first embodiment of the invention,
FIG. 2 is an equivalent circuit diagram of the first measurement in one embodiment of the present invention,
figure 3 is an equivalent circuit diagram for re-measurement in one embodiment of the invention,
FIG. 4 is a schematic diagram of two voltage acquisitions according to an embodiment of the present invention.
In the figure:
rkb, back end resistance; rak, front section resistance; r02 and a second sampling resistor; r01, a first sampling resistor;
Detailed Description
In order to make the technical solution and the advantages of the present invention clearer, the following explains embodiments of the present invention in further detail.
The first embodiment is as follows:
when an overhead line has a ground fault, a microcomputer relay protection device in the prior art can judge which phase of A, B, C three phases is a fault phase, but the position or the approximate position of a ground fault point cannot be positioned.
The invention discloses an overhead line ground fault distance measuring method, which comprises the following steps:
a. and short-circuiting the fault phase of the line with the ground fault and the head end of any non-fault phase in the fault line through a sampling circuit. The sampling circuit is a first sampling resistor R01 and a second sampling resistor R02 which are connected in series. The junction between the first and second sampling resistors R01 and R02 is a head end short contact a.
Because the current signal detection needs a current sensor or a current transformer to reuse an instrument for detection, the current signal detection is more complicated when the current is measured. The voltage detection is direct, and can be measured by directly utilizing a relay protection device or an intelligent instrument, so that the collection of electrical parameters is realized by adopting a voltage collection mode in order to facilitate measurement and operation, wherein the electrical parameters refer to parameters such as voltage, current and phase angle. When the measurement is carried out, the voltages at two ends of the first sampling resistor R01 and the second sampling resistor R02 and the voltage of a high-voltage low-frequency alternating current power supply signal output by a signal source are collected, and then the currents flowing through the first sampling resistor R01 and the second sampling resistor R02 are deduced and calculated.
It is assumed that the head end of the overhead line is located at a first substation or distribution substation and the tail end is located at a second substation or at a customer load site. Meanwhile, it is assumed that a ground fault occurs at point k and the ground fault phase is the C phase. And if the detection is carried out in the first substation, the non-fault phase A and the fault phase C of the fault line of the first substation are short-circuited. The short-circuit non-fault phase B and fault phase C are the same and can be measured, and in this embodiment, the short-circuit non-fault phase a and fault phase C are taken as examples. The first transformer substation is the head end, and the second transformer substation is the tail end. The resistance from the ground fault point k of the ground fault phase to the head end is the front stage resistance Rak, and the resistance from the ground fault point of the ground fault phase to the tail end is the rear stage resistance Rkb. The impedance from the earth fault point k of the earth fault phase to the head end short contact point A is the front section impedance
Ground faultThe impedance from the earth fault point of the phase to the end short-circuit point B is the back-end impedance
The fault phase of the line with the ground fault and the end of the non-fault phase of the fault line are short-circuited to form an end short-circuit point B. Based on the assumption of the above steps, the failed phase C phase and the non-failed phase A phase are shorted at the end short-circuit point B, namely the substation B. Or in order to simplify the operation and reduce misoperation, the A, B, C three phases of the fault line of the substation B can be directly short-circuited.
And the short-circuited fault phase, the non-fault phase and the sampling circuit form a fault distance measuring loop. Since both ends of the two phases of A, C are short-circuited, the fault-finding circuit is a loop.
b. And injecting a high-voltage low-frequency alternating current power supply signal to the fault distance measuring loop between the head end short contact A and the earth grounding system. And collecting the electrical quantity parameters of the fault distance measuring loop and the electrical parameters of the high-voltage low-frequency alternating current power supply signal.
In an electrical distribution system, a grounding grid or grounding system is a necessary electrical installation. The grounding point of the fault line is equivalent to connecting one point of the fault distance measuring loop with a grounding grid, namely the ground. And the first transformer substation is also provided with a grounding system, so that a grounding grid or the ground is used as a virtual lead to be connected to a grounding point of the fault distance measuring loop, and a leading-out point of the grounding grid or the grounding system of the first transformer substation can be used as a signal input node of the fault distance measuring loop. The head end short contact A of the fault distance measuring loop is used as a node of another signal input of the fault distance measuring loop. And then a high-voltage low-frequency alternating current power supply signal is loaded to the fault distance measuring loop between the two signal input nodes.
The voltage of the high-voltage low-frequency alternating current power supply signal is 80% -110% of the rated voltage of the overhead line, and the frequency of the signal source is 0.5-15 Hz. Preferably, the voltage of the high-voltage low-frequency alternating current power supply signal is 85% -100% of the rated voltage of the overhead line, and the frequency of the signal source is 1-5 Hz. In the embodiment, the voltage is the rated voltage of the overhead line, and the frequency is 1 Hz.
The voltage of the high-voltage low-frequency alternating current power supply signal is based on the condition that the insulation requirement of the existing overhead transmission line is not destroyed when the grounding point is broken down, so that 85% -100% of the rated voltage of the overhead transmission line is adopted.
In the prior art, a person skilled in the art considers that due to the effect of a hanging transformer and a line conductor on the ground capacitance on an overhead line, whether a direct current signal source or an alternating current signal source is adopted, the position of a ground fault is measured by adopting an impedance method, and the position has a large error. The invention has the innovation point that the conventional understanding and the technical prejudice of the technicians in the field on the overhead line distance measurement are overcome, the low-frequency alternating-current power supply signal is loaded into the fault line, and the position of the fault point can be obtained by using an impedance method. Research and practice of developers of the company shows that when a high-voltage low-frequency alternating current signal is loaded between a fault phase and a non-fault phase and the ground, a signal injection mode is that two phase lines are injected to the ground, and at the moment:
first, the primary side inductance Zl of the transformer is 2 pi fL, and the higher the frequency and the larger the inductance, the larger the inductance value, and when the inductance value is much larger than the loop impedance, it is equivalent to an open circuit, and when the frequency is 0, it is a direct current, which is equivalent to a short circuit. In the prior art, the inductance of the transformer often reaches hundreds of henries, and even if the frequency is very low, the inductive reactance value is in the range of hundreds of henries and is far greater than the resistance of the overhead transmission line, so that the transformer can be considered to be in an open circuit state. In actual operation, due to the influence of the material and environment of the transmission line of the line, the voltage difference between the two phase lines is small, and meanwhile, because the injected current is below 100mA, the maximum resistance of the cable is less than 10 Ω, the voltage difference between the two phase lines loaded with the high-voltage low-frequency alternating-current power supply signal is 1V or less than 1V. The current generated by the voltage difference of 1V to the transformer and the transformer load is very small and can be ignored, so that the influence of the transformer and the load on the distance measurement is avoided. When direct current is adopted, the transformer is equivalent to short circuit and also influences the measurement result, so that direct current is unavailable, namely 0Hz is unavailable. The ground current generated by the distributed capacitance of the overhead transmission line after the alternating current signal is loaded cannot be avoided, wherein the total capacitance reactance Zc of the loop is 1/(2 pi fC), and the higher the frequency is, the larger the generated capacitive current is, and the measurement result is influenced. Therefore, a signal source with lower frequency is selected, so that the capacitive reactance of the signal source is higher, and the influence of capacitive current on a measurement result is reduced. In the process of practical application, a low-frequency alternating-current power supply signal is utilized, the influence of a transformer hung on a line can be ignored, but the influence on the ground capacitance cannot be eliminated, and the influence of the capacitive current on the ground capacitance on the resistive current can only be infinitely reduced. In order to make the calculation more accurate, a phasor method is adopted for calculation in the calculation process. Or separating the collected voltages into capacitive current and capacitive voltage through orthogonal operation, then calculating and processing by using the resistive current, and collecting signal source voltage signals based on the calculation and processing.
And the first and second lines are integrated, when a low-frequency alternating current signal is adopted, the total capacitive reactance of the line is large, the capacitive current is small, the influence on the resistive current is small, and the resistive component can be separated through phasor calculation. Meanwhile, the inductance of the transformer in the hundred-henry level is equivalent to an open circuit, so that the low-frequency alternating current power supply signal can be adopted, and the calculation and measurement can be carried out by adopting an impedance method. The frequency range is selected from 1Hz to 5Hz through the comprehensive measurement and calculation of the company. In order to reproduce the ground fault, the ground fault point is grounded again under the state of loading a high-voltage low-frequency alternating current electric signal, and the output voltage is 80-100% of the rated voltage of the overhead line. Wherein the preferred output voltage is the rated voltage of the overhead line.
c. And changing the resistance values of the first sampling resistor R01 and the second sampling resistor R02, injecting a high-voltage low-frequency alternating current power supply signal between the head-end short contact A and the earth grounding system to the fault distance measuring circuit again, and collecting the electrical quantity parameters of the fault distance measuring circuit and the electrical parameters of the high-voltage low-frequency alternating current power supply signal.
The resistance value adjusting modes of the first sampling resistor and the second sampling resistor comprise the following steps:
in the first measurement, as shown in fig. 2, the first sampling resistor and the second sampling resistor have different resistance values, the first sampling resistor R01 is connected with a non-fault, and the second sampling resistor R02 is connected with a fault.
For the second measurement, as shown in FIG. 3, the first sampling resistor R01 is connected to the failed connection and the second sampling resistor R02 is connected to the non-failed connection.
Finally, collecting voltage parameters and listing a equation set to solve the resistance values of the front-section resistor Rak and the rear-section resistor Rkb. Further, the distances of the grounding point from the head-end short contact A and the tail-end short contact B are calculated.
The two sampling circuits are provided, the resistance values of a first sampling resistor R01 and/or a second sampling resistor R02 in the two sampling circuits are different, and the first sampling circuit is used for short circuit when the first measurement record is carried out; and the second measurement is recorded by using a second sampling circuit for short circuit.
d. And c, calculating the resistance of the power transmission line before and after the ground fault point by using the electrical parameters acquired in the steps b and c and according to an impedance method, and calculating the length of the fault point at one end of the high-voltage low-frequency alternating current power supply signal injected into the power transmission line according to the total length of the power transmission line.
Taking the first method as an example, for the steps b, c, d, specifically:
because the front-stage resistance Rak and the rear-stage resistance Rkb are two unknowns, at least two equations are required to form an equation set, and therefore, the electrical parameters of the fault location loop in two states need to be collected for calculation. In this embodiment, the resistances of the front-stage resistor Rak and the rear-stage resistor Rkb are obtained by using the principle of an unbalanced bridge.
The operation of step b is as follows:
and measuring the voltage values of the first sampling resistor R01 and the second sampling resistor R02 and the voltage value of the high-voltage low-frequency alternating current power supply signal output by the signal source. At this time, the resistance values of the first and second sampling resistors R01 and R02 are R11、R12. As shown in fig. 2, the first sampling resistor R01 is connected to the non-fault phase and the second sampling resistor R02 is connected to the fault phase. According to voltage waveform
Wherein
Is the initial phase. Function(s)
Is a periodic function. In this embodiment, the initial phase of the output voltage of the signal source is defined as 0 degree, and the initial phase is converted into phasor
The voltage output by the signal source is taken as a reference signal, and the phasor value of the voltage of the first sampling resistor R01 is obtained by comparing the collected voltages of the first sampling resistor R01 and the second sampling resistor R02 with the voltage of the signal source
Phasor value of voltage of second sampling resistor R02
The capacitance to ground is equivalent to capacitive reactance, so the fault distance measuring loop as a load is a capacitive load, and an included angle is generated. And a first equation of the fault location loop is listed according to ohm's law and kirchhoff's voltage law. And calculating the current flowing through the loop of the first and second resistors according to the acquired voltage value and the resistance values of the first and second sampling resistors R01 and R02.
And obtaining the resistive component of the voltage of the first sampling resistor through orthogonal calculation according to the included angle between the voltage U12 of the first sampling resistor and the voltage of the signal source.
As shown in FIG. 2, the resistive current flowing through the non-faulted phase is
I11＝U11cosα1/R11(1)
Current flowing through fault phase
I12＝U12cosβ1/R12(2)
The voltage flowing through the front-stage resistor Rak and the rear-stage resistor Rkb can be obtained by multiplying the current by the front-stage resistor Rak and the rear-stage resistor Rkb, and the voltage is obtained according to kirchhoff's voltage law: in either closed loop, the principle that the algebraic sum of the voltage drops across the elements is zero can be formulated as,
U11cosα1+I11(Rak+2Rkb)＝U12cosβ1+I12Rak(3)
substituting into the formula (1) and the formula (2),
U11cosα1+(U11cosα1/R11)(Rak+2Rkb)＝U12cosβ1+(U12cosβ1/R12)Rak(4)
and c, adjusting the resistance values of the first sampling resistor R01 and/or the second sampling resistor R02, so that the adjusted resistance values of the first sampling resistor R01 and the second sampling resistor R02 are different from the resistance values before adjustment. In this embodiment, for example, the connection mode of the sampling circuit is changed, the first sampling resistor R01 is connected to the fault, and the second sampling resistor R02 is connected to the non-fault. This adjustment is made because the parameters of the faulty measurement loop need to be changed to once again list the different equations.
The voltage values of the first and second sampling resistors R01, R02 are measured and the second equation of the fault-finding circuit is formulated according to ohm's law and kirchhoff's voltage law. Setting the initial phase of the output voltage of the collected signal source to 0 degree, and converting the initial phase into phasor
20＝U20∠ 0 DEG, the phasor value of the voltage of the first and second sampling resistors R01, R02 is
As shown in fig. 3, the current flowing through the non-faulted phase
I22＝U22cosβ2/R12(5)
The current flowing through the failed phase is,
I21＝U21cosα2/R11(6)
the equations are set forth below in the following table,
U21cosα2+I21Rak＝U22cosβ2+I22(Rak+2Rkb) (7)
substituting the formula (5) and the formula (6) into the formula (7),
U21cosα2+(U21cosα2/R11)Rak＝U22cosβ2+(U22cosβ2/R12)(Rak+2Rkb) (8)
and d, listing equations, namely equation (4) and equation (8), according to the electrical parameters collected in step b and step c. The resistances of the front-stage resistor Rak and the rear-stage resistor Rkb are solved according to a system of linear equations composed of the formula (4) and the formula (8). Since the length of the wire is proportional to the resistance value of the wire, the ratio of the distance between the fault point and the two ends of the monitoring line to the total length of the overhead line can be calculated. And calculating the length of the ground fault point from one end of the injected low-frequency alternating-current power supply signal according to the ratio and the known length of the overhead line.
In order to facilitate calculation and measurement and obtain higher calculation accuracy, the first sampling resistor R01 and the second sampling resistor R02 are precision resistors.
It is also possible to calculate using a phasor method, where the reactance value of the line impedance front-end Xak from the ground fault point to the head-end of the ground fault phase is assumed to be
The line impedance from the ground fault point to the end of the ground fault phase is assumed to be the impedance value of the back-end impedance Xkb
Calculated by using the principles of the above column equation
And
after resistance value, the reactance is separated
The real part of, i.e. the resistance of, the line being
Example two
In step c, according to the first embodiment:
and the voltage between the sampling circuit and the fault phase connection point and the voltage between the sampling circuit and the non-fault phase connection point are also acquired, so that the influence of the partial pressure generated by the contact resistance of the sampling circuit and the fault phase connection point and the contact resistance of the sampling circuit and the non-fault phase connection point on the measurement result is avoided.
As shown in FIG. 4, the collected phasor value of the voltage output by the signal source is
The collected phasor values of the voltages of the first sampling resistor R01 and the second sampling resistor R02
The phasor value of the voltage between the first sampling resistor R01 and the non-fault phase connection point and the head end short contact A is
The voltage between the second sampling resistor R02 and the fault phase connection point and the head end short contact A is
Wherein
Wherein the resistance value of the first sampling resistor R01 is R11The resistance value of the second sampling resistor R02 is R12The equations listed are:
U13cos1+(U11cosα1/R11)(Rak+2Rkb)＝U14cos1+(U12cosβ1/R12)Rak(9)
adjusting the resistance of the first sampling resistor R01 to R21The resistance of the second sampling resistor R02 is not changed, and the phasor values of the voltages of the first sampling resistor R01 and the second sampling resistor R02 are acquired at the time
The phasor value of the voltage between the first sampling resistor R01 and the non-fault phase connection point and the head end short contact A is
The voltage between the second sampling resistor R02 and the fault phase connection point and the head end short contact A is
Wherein
The equations are set forth:
U23cos2+(U21cosα2/R21)(Rak+2Rkb)＝U24cos2+(U22cosβ2/R12)Rak(10)
the equations (9) and (10) form an equation set and the resistances of the front-stage resistor Rak and the rear-stage resistor Rkb are solved. And then a calculation is made using the solved resistance value. The embodiment can effectively avoid the influence of the contact resistance on the voltage acquisition, and improves the operation precision.
In summary, the present invention is only a preferred embodiment, and is not intended to limit the scope of the present invention, and various changes and modifications can be made by workers in the light of the above description without departing from the technical spirit of the present invention. The technical scope of the present invention is not limited to the content of the specification, and all equivalent changes and modifications in the shape, structure, characteristics and spirit described in the scope of the claims of the present invention are included in the scope of the claims of the present invention.
Claims (9)
1. A power overhead line ground fault distance measurement method is characterized by comprising the following steps:
a. the fault phase of the line with the ground fault and the head end of any non-fault phase of the fault line are short-circuited through a sampling circuit, the sampling circuit comprises a first sampling resistor (R01, R02) and a second sampling resistor (R02) which are connected in series,
the connection point of the first and second sampling resistors (R01, R02) is formed as a head end short-circuit point A,
a fault phase of a line with a ground fault being generated is short-circuited with the end of the non-fault phase of the fault line to form an end short-circuit point B,
the fault phase and the non-fault phase after short circuit form a fault distance measuring loop;
b. injecting a high-voltage low-frequency alternating current power supply signal between the head end short contact A and the earth grounding system to the fault distance measuring loop, and collecting the electrical quantity parameters of the fault distance measuring loop and the electrical parameters of the high-voltage low-frequency alternating current power supply signal;
c. changing the resistance values of the first sampling resistor and the second sampling resistor (R01 and R02), injecting a high-voltage low-frequency alternating current power supply signal between the head-end short contact A and the earth grounding system to the fault distance measuring loop again, and collecting the electrical quantity parameters of the fault distance measuring loop and the electrical parameters of the high-voltage low-frequency alternating current power supply signal;
d. and c, calculating the resistance of the power transmission line before and after the ground fault point by using the electrical parameters acquired in the steps b and c and according to an impedance method, and calculating the length of the fault point at one end of the high-voltage low-frequency alternating current power supply signal injected into the power transmission line according to the total length of the power transmission line.
2. The power overhead line ground fault location method of claim 1, wherein:
the maximum output voltage of the high-voltage low-frequency alternating current power supply signal is 80% -110% of the rated voltage of the overhead loop.
3. The power overhead line ground fault distance measurement method according to claim 2, characterized in that:
the maximum output voltage of the high-voltage low-frequency alternating current power supply signal is 85% -100% of the rated voltage of the overhead loop.
4. The power overhead line ground fault location method of claim 1, wherein:
the frequency of the high-voltage low-frequency alternating current power supply signal is 0.5-15 Hz.
5. The power overhead line ground fault location method of claim 4, wherein:
the frequency of the high-voltage low-frequency alternating current power supply signal is 1-5 Hz.
6. An electric power overhead line ground fault location method according to claim 1, 2 or 4, characterized in that:
the resistance from the earth fault point of the earth fault phase to the head end short contact point A is a front section resistance (Rak),
the resistance of the ground fault point to the end short B of the ground fault phase is the back-end resistance (Rkb),
the step b is operated as follows: measuring voltage values of the first sampling resistor (R01), the second sampling resistor (R02) and a high-voltage low-frequency alternating current power supply signal, and listing a first equation of a fault distance measuring loop according to ohm's law and kirchhoff's voltage law;
the step c is operated as follows: adjusting the resistance values of the first sampling resistor (R01) and the second sampling resistor (R02) to make the resistance values of the first sampling resistor (R01) and the second sampling resistor (R02) after adjustment different from the resistance values before adjustment,
then, measuring the voltage values of the first sampling resistor and the second sampling resistor (R01 and R02) and the voltage value of the high-voltage low-frequency alternating-current power supply signal, and listing a second equation of the fault distance measuring loop according to ohm's law and kirchhoff's voltage law;
the step d is operated as follows: solving the resistance values of a front-stage resistor (Rak) and a rear-stage resistor (Rkb) according to a linear equation of two-dimensional system consisting of a first equation and a second equation, calculating the length of one end of a fault point at which a high-voltage low-frequency alternating-current power supply signal is injected according to the principle that the resistance value of a lead is in direct proportion to the length and the total length of a transmission line,
the first and second sampling resistors (R01, R02) are precision resistors.
7. The power overhead line ground fault location method of claim 6, wherein:
in the step b, when the voltage values of the first sampling resistor (R01) and the second sampling resistor (R02) are measured and recorded, the first sampling resistor (R01) is connected with the fault,
in step c, when the measurement is recorded, the second sampling resistor (R02) is connected with the fault.
8. The power overhead line ground fault location method of claim 6, wherein:
the sampling circuits are provided with two sampling circuits, the resistance values of a first sampling resistor (R01) and a second sampling resistor (R02) in the two sampling circuits are different,
in the step b, a first sampling circuit is used for short circuit during measurement and recording;
in step c, a second sampling circuit is used for short circuit during measurement and recording.
9. The power overhead line ground fault location method of claim 6, wherein:
in step b and step c: and the voltage between the connection point of the sampling circuit and the fault phase and the head end short contact A is also acquired, and the voltage between the connection point of the sampling circuit and the non-fault phase and the head end short contact A is also acquired so as to avoid the influence of contact resistance.
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