CN112014768B

CN112014768B - Method and system for detecting faults of underground power-losing circuit based on additional power supply

Info

Publication number: CN112014768B
Application number: CN202010934290.2A
Authority: CN
Inventors: 张超; 侯良霄; 刘兆栋; 宋娜; 吴旋旋; 张术鹏; 孙泉; 张国超; 杜晓光; 刘梦瑶; 王怀宇; 李润
Original assignee: Shandong University of Science and Technology
Current assignee: Shandong University of Science and Technology
Priority date: 2020-09-08
Filing date: 2020-09-08
Publication date: 2021-05-25
Anticipated expiration: 2040-09-08
Also published as: CN112014768A

Abstract

The fault detection system comprises a control module, a trigger module and a power electronic power supply, wherein the output end of the power electronic power supply is respectively connected with each phase line to be detected, the control module is respectively connected with the output end of the power electronic power supply in a control mode through the trigger module, and is used for analyzing detection signals to obtain the line fault of the line to be detected. The power electronic switch circuit is used as a controllable disturbance source, a power electronic switch device is converted into an independent controllable signal source from the traditional energy conversion role, the power electronic switch has high withstand voltage, large capacity and flexible and controllable conduction state, a detection signal is injected into a system, and the system response can be analyzed to realize fault diagnosis.

Description

Method and system for detecting faults of underground power-losing circuit based on additional power supply

Technical Field

The disclosure relates to the technical field of line fault detection, in particular to a method and a system for detecting faults of an underground power-off line based on an additional power supply.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

As the underground operation environment of the coal mine is more than that of the well, a lot of inflammable and explosive gases exist, the underground operation environment has great importance for strengthening the safety production work of the mine, the leakage protection is an important condition for realizing the safety production of the mine, the underground operation environment is effectively implemented, and the safety of the mine can be well ensured. However, in daily work, when many underground equipment or lines have faults, mine power supply accidents can be caused, particularly, under the condition of collision or extrusion, electric leakage faults are easily caused to the electric and electrical equipment during operation, once the electric leakage is caused, sparks can be formed, when the sparks meet gas such as gas and methane, explosion accidents can be caused, the safety of workers is threatened, and meanwhile, the normal production of underground coal mines is influenced, so that the fault detection of underground power supply lines is particularly important. The underground power supply line has severe operating environment and complex line faults, so that the tripping of a main feeder switch occurs occasionally. The inventor finds that the current common road pulling method is more complicated and time-consuming, the power failure time is often prolonged, and the influence on the mine production and safety is caused.

Disclosure of Invention

In order to solve the problems, the invention provides a method and a system for detecting faults of an underground power-losing line based on an additional power supply.

In order to achieve the purpose, the following technical scheme is adopted in the disclosure:

one or more embodiments provide a system for detecting faults of a power-down line in a well based on an additional power supply, which comprises a control module, a trigger module and a power electronic power supply, wherein the output end of the power electronic power supply is respectively connected with each phase line to be detected, the control module respectively controls and connects the output end of the power electronic power supply through the trigger module, detection signals injected into the corresponding phase lines are detected, and the line faults of the lines to be detected are obtained through analyzing the detection signals.

One or more embodiments provide a method for downhole power loss line fault detection based on an additional power source, comprising the steps of;

acquiring operation data of a circuit to be detected in real time, identifying whether the circuit to be detected is powered off or not, and executing the next step after the power is off;

for leakage and ground fault detection, outputting a control signal to control and trigger an injection thyristor of a switch unit of the power electronic power supply so that the power electronic power supply injects a detection signal to a line to be detected, and analyzing the detection signal to obtain a fault detection result;

for the inter-phase fault detection, a control signal is output to control and trigger the injection thyristor of the switch unit connected with one phase line, so that the power electronic power supply injects a detection signal to the phase line to be detected, the grounding thyristors of the switch units connected with other phase lines are controlled and triggered, and the detection signal is analyzed to obtain a fault detection result.

Compared with the prior art, the beneficial effect of this disclosure is:

(1) the power electronic switch circuit is used as a controllable disturbance source, a power electronic switch device is converted into an independent controllable signal source from the traditional energy conversion role, the power electronic switch is high in voltage resistance, large in capacity and flexible and controllable in conduction state, a detection signal is injected into a system, and system response can be analyzed to realize fault diagnosis.

(2) According to the system, after the main feeder switch of the underground power supply system is tripped, an additional power supply is arranged to inject signals into the circuit, different detection loops can be formed by the detection signals injected into the power-losing circuit by controlling the conduction of different thyristors in the additional power electronic power supply, and the detection signals are analyzed to realize the fault detection of the power-losing circuit. The method can realize fault detection of the underground power-off line in a short time, and greatly reduces the power-off time of a mine.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and not to limit the disclosure.

Fig. 1 is a schematic structural diagram of a detection system according to embodiment 1 of the present disclosure;

fig. 2 is a schematic diagram illustrating a detection principle of a leakage fault and a ground fault according to embodiment 2 of the present disclosure;

fig. 3 is an equivalent circuit diagram of the detection current loop flowing through the phase a according to embodiment 2 of the present disclosure;

fig. 4 is an equivalent circuit diagram of a detection current loop when a single-phase ground fault exists in a line according to embodiment 2 of the present disclosure;

fig. 5 is a simulation diagram of a detected current waveform when an a-phase leakage fault exists in a line according to embodiment 2 of the present disclosure;

fig. 6 is a schematic diagram illustrating a principle of a method for detecting an asymmetric inter-phase fault according to embodiment 2 of the present disclosure;

fig. 7 is an equivalent circuit diagram of a detection current loop when an AB phase-to-phase fault exists in a line according to embodiment 2 of the present disclosure;

fig. 8 is a simulation diagram of a detected current waveform when an AB phase-to-phase fault exists in a line according to embodiment 2 of the present disclosure;

fig. 9 is a schematic diagram illustrating a principle of a method for detecting a three-phase interphase short-circuit fault according to example 2 of the present disclosure;

fig. 10 is an equivalent circuit diagram of a detection current loop when a three-phase interphase short-circuit fault exists in the circuit described in example 2 of the disclosure;

fig. 11 is a schematic diagram illustrating a principle of a detection method in the case of a three-phase interphase short-circuit ground fault according to example 2 of the present disclosure;

fig. 12 is an equivalent circuit diagram of a detection current loop during a three-phase interphase short-circuit ground fault according to example 2 of the present disclosure;

fig. 13 is an interphase equivalent circuit diagram when the line described in example 2 of the present disclosure is free from a three-phase interphase short-circuit ground fault;

fig. 14 is an inter-phase equivalent circuit diagram of the circuit of example 2 of the present disclosure in the presence of a three-phase inter-phase short-circuit ground fault;

fig. 15 is a simulation diagram of harmonic reactance values when a symmetric fault exists on a line and when the line is normal according to example 2 of the present disclosure;

fig. 16 is a graph comparing the slope of a straight line fitted to a symmetric fault according to example 2 of the present disclosure with the slope of a straight line fitted to a normal line.

The specific implementation mode is as follows:

the present disclosure is further described with reference to the following drawings and examples.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise. It should be noted that, in the case of no conflict, the embodiments and features in the embodiments in the present disclosure may be combined with each other. The embodiments will be described in detail below with reference to the accompanying drawings.

Example 1

In the technical solutions disclosed in one or more embodiments, as shown in fig. 1, the system for detecting faults of a power-down line in a well based on an additional power supply includes a control module, a trigger module, and a power electronic power supply, where an output end of the power electronic power supply is connected to each phase line to be detected, the control module controls and connects an output end of the power electronic power supply through the trigger module, respectively, and analyzes a detection signal injected into the corresponding phase line to obtain a line fault of the line to be detected.

A control module: the control instruction is used for generating a control instruction of the power electronic switching power supply and analyzing a line fault.

A triggering module: and the power electronic device is used for generating a trigger signal according to the control instruction of the control module and triggering the power electronic switching power supply to work.

Optionally, the power electronic power supply includes an alternating current power supply and a switch circuit, the switch circuit includes a plurality of connected switch tubes, the output end of the switch tube is connected to each phase line to be detected, and the trigger end of the switch tube is connected to the trigger module.

The structure and application position of the additional power electronic power supply described in this embodiment are shown in fig. 1.

The power electronic power supply comprises an alternating current power supply and a switch circuit connected to two ends of the alternating current power supply, wherein the switch circuit comprises six thyristors, every two thyristors are connected in series and then connected in parallel to form three thyristor branches, the middle point of each branch is an output end and is respectively connected to an A phase, a B phase and a C phase of the three-phase circuit, two thyristors are arranged on each branch, one thyristor is a signal injection thyristor and is used for being connected with the output end of the alternating current power supply, and the other thyristor is a grounding thyristor and is used for being connected with a grounding end.

Specifically, in this embodiment, the thyristor branch connected to the phase a includes a first injection thyristor T1 and a first grounding thyristor T2 connected in series, the thyristor branch connected to the phase B includes a second injection thyristor T3 and a second grounding thyristor T4 connected in series, and the thyristor branch connected to the phase C includes a third injection thyristor T5 and a third grounding thyristor T6 connected in series.

The detection signal provided by the AC power supply is injected into the power-losing circuit through the thyristor unit, passes through the insulation resistor and the ground capacitor of the cable, and finally flows into the grounding point of the AC power supply to form a loop.

And the current transformer and the voltage transformer are arranged on a line, and the current transformer is connected with the voltage transformer control module and used for detecting the injected current detection signal and the injected voltage detection signal. The injected detection signal is detected by a current transformer installed on the line, and whether a leakage fault exists in the line is judged by analyzing the detection current and voltage signals.

The design of this embodiment adopts power electronic switch circuit as controllable disturbance source, changes the power electronic switch device into independent controllable signal source from traditional energy conversion role, and power electronic switch withstand voltage is high, and the capacity is big, and the conducting state is nimble controllable, injects detected signal into the system, can the analytic system response realize failure diagnosis.

According to the system, after a main feeder switch of the underground power supply system is tripped, an additional power supply is arranged to inject signals into a circuit, different detection loops can be formed by injecting detection signals into a power-losing circuit by controlling the conduction of different thyristors in the additional power electronic power supply, and the detection signals are analyzed to realize the fault detection of the power-losing circuit. The method can realize fault detection of the underground power-off line in a short time, and greatly reduces the power-off time of a mine.

Example 2

Based on the system of embodiment 1, this embodiment provides a method for detecting a fault of a power loss line in a well based on an additional power supply, which may be implemented in a control module, including the following steps;

step 1, acquiring operation data of a circuit to be detected in real time, identifying whether the circuit to be detected is powered off, and executing the next step if the circuit to be detected is powered off;

step 2, for electric leakage and ground fault detection, outputting a control signal to control and trigger an injection thyristor of a switch unit of the power electronic power supply so that the power electronic power supply injects a detection signal to a line to be detected, and analyzing the detection signal to obtain a fault detection result;

In step 1, the operation data may include line voltage, line current, feeder switch signal, and the like.

Different thyristor conduction strategies are needed for different line faults, and a thyristor conduction scheme is formulated according to the different thyristor conduction strategies. And step 2 is a thyristor conduction scheme, the control signal of the control module is output to the trigger module, and the trigger module conducts the thyristor of the switch unit. As shown in table 1, in the different types of fault detection, the conduction condition table of each thyristor specifically adopts the following trigger control method, which includes the following steps:

since the detection signal is a sinusoidal signal and the conduction of the thyristor needs to be within the positive half cycle of the signal, for convenience of description, a signal period is defined, which refers to a period of the sinusoidal detection signal.

The first stage is as follows: duration is 2 signal cycles, this phase is for thyristor T₁，T₃，T₅A trigger pulse is applied once per signal period and the remaining thyristors are turned off. The first trigger at this stage is used to detect symmetric faults, and the second trigger is used for leakage faults, including single-phase leakage, two-phase leakage and three-phase leakage.

And a second stage: duration is 1 signal cycle, this stage is to the thyristor T₁，T₄，T₆And applying trigger pulse, and turning off the rest thyristors to detect the AB phase-to-phase and AC phase-to-phase faults.

And a third stage: duration is 1 signal cycle, this stage is to the thyristor T₃，T₆And applying a trigger pulse, and turning off the rest thyristors to detect the BC phase-to-phase fault.

Alternatively, the firing angle may be set to 30 °.

TABLE 1

Step 2 is an identification process for various faults. The following description will be made separately according to the types of failures.

Leakage and ground fault detection.

In step 2, the method for outputting the control signal to control and trigger the injection thyristor of the switch unit of the power electronic power supply and analyzing the electric leakage and the ground fault comprises the following steps:

21) when the obtained detection current injected into a certain phase line is larger than the detection current in normal insulation or normal phase, judging that the phase line has electric leakage or ground fault;

22) setting a first comparison threshold I of a ground fault₁Second comparison threshold value of leakage fault I₂Wherein a first comparison threshold I₁Is far greater than the second comparison threshold I₂(ii) a The far greater can be set by setting a threshold difference.

Specifically, the threshold value is obtained according to specific line detection, for example, the magnitude range of the fault current is determined according to a simulated leakage fault or a ground fault, and the threshold value is set according to the magnitude of the fault current.

23) When the magnitude of the detected current I is between the first comparison threshold I₁And a second comparison threshold I₂When the phase line has the leakage fault, the phase line is judged to have the leakage fault, and when the phase line is larger than a first comparison threshold I₁And judging that the phase line has a ground fault.

The principle of leakage and ground fault detection is described below with specific examples, which include the conduction of the thyristor and the flow of the detection current, as shown in fig. 2.

The control module controls the trigger module to enable the thyristor T₁，T₃，T₅Are simultaneously on, and T₂，T₄，T₆And closing. Current signal passing through thyristor T₁，T₃，T₅And the current is injected into a three-phase line to form a current loop, and the detection of the leakage fault is realized by analyzing the waveform characteristics of the detected current signal.

For an example of phase a, an equivalent circuit diagram of the detection current loop flowing through phase a is shown in fig. 3. In the figure E is the effective value of the voltage of the additional ac power source,

for the current flowing through the phase A line transformer, X_lineIs line impedance, R_JTo ground resistance, R_A，C_AThe phase A is the insulation resistance to ground and the capacitance to ground.

Has effective values of:

line impedance X in formula_lineGround resistance R_JCompared with the insulation resistance R_ANegligible further rewriteable is:

when the A phase circuit has leakage fault, the insulation resistance value R_ADecrease, as can be derived from the above formula, I_AWill follow R_AIs increased, and the insulation resistance at the time of line leakage is greatly different from that at the normal time, so that I_AThe current can be obviously larger than the detection current when the line insulation is normal, and whether the A-phase line has a leakage fault can be detected accordingly. Similarly, leakage faults in the B-phase and C-phase lines can be detected. Because mutual inductors are arranged on the phase circuits and the phase detection circuits are mutually independent, the multi-phase leakage fault can be accurately detected.

Most of power supply lines of mines are neutral point ungrounded systems, and for the neutral point ungrounded systems, only small short-circuit current can occur when single-phase grounding faults occur. And the resistance value of the fault resistor is smaller, so the single-phase earth fault can be regarded as a special leakage fault with a very low insulation resistor resistance value. Therefore, the detection method is the same as that of the leakage fault, and the detection method can be performed simultaneously with the detection of the leakage fault. The equivalent circuit diagram is shown in FIG. 4, when the line impedance X is_lineAnd a ground resistance R_JCan not be ignored any more, and can be equivalent to R_∑At this time

Has effective values of:

value of fault resistance R in the formula_gAnd R_∑The sum of (a) and (b) is small, so that the effective value of the current when a single-phase earth fault exists in the line is far larger than that when a leakage fault exists in the line, so that the current I can be analyzed_AWhether the single-phase earth fault exists in the line or not is judged, and the detection principle is completely the same as that of electric leakage fault detection. The problem with this is how to distinguish between the two types of faults, i.e. the currents under two types of faults_AThe difference between the values of (a) and (b) is large, and a proper threshold value can be set to distinguish the two values.

According to the leakage fault detection principle, the detection current in the line with the leakage fault is obviously larger than that of the normal phase, and accordingly, a criterion for leakage fault detection is established. If leakage fault occurs in phase A, the insulation resistance of phase B and phase C is normal. The simulated waveform of the sense current is shown in fig. 5. Within the electric leakage fault detection time period of 0.02 s-0.04 s, the waveform amplitude of the phase A current is obviously greater than that of the phase BC, and the electric leakage fault detection method can realize the fault detection of the line.

Specifically, the leakage or ground fault can be judged by a graphical method, when the single-phase current waveform area S is larger than the detected current waveform area of a normal phase or normal insulation, the phase has a fault, a waveform area threshold value is set, and the waveform area threshold value S of the ground fault is judged_NGreater than the detection current waveform area threshold S of the leakage fault_MWhen S > S_MAnd S > S_NWhen the phase line has a ground fault; when S > S_MAnd S is less than S_NIn time, the phase circuit has a leakage fault.

The three-phase detection current waveform is positioned above the X axis, because the thyristor is subjected to back pressure and is automatically turned off, and no waveform exists in the negative half shaft of the Y axis. According to the characteristics of the three waveforms in fig. 5, an area method criterion can be considered. That is, the area S enclosed by the waveform of the detected current and the X-axis is obtained, and S is compared with the value S_MAnd (6) carrying out comparison. S_MNamely, a value is determined by considering a certain margin according to the area enclosed by the current waveform and the X axis when the line is normal. The criterion is that S is greater than S_MIf so, a leakage fault exists on the line; if S is less than or equal to S_MThen, thenThere is no leakage fault in the line.

However, as described above, the fault characteristics of the ground fault are the same as those of the leakage fault, and a criterion needs to be set to distinguish the two. When earth fault occurs in the line, the effective value of current is greater than that of leakage fault, so that S can be re-set_NAnd S is_N＞S_M. Then the final criterion is arranged to be: when S is greater than S_MAnd S > S_NWhen the fault occurs, the line has a ground fault; when S is greater than S_MAnd S is less than S_NWhen the circuit is in a leakage fault, the circuit is in a leakage fault.

In step 2, the control signal is output to control and trigger the injection thyristor of the switch unit connected with one phase line, so that the power electronic power supply injects the detection signal to the phase line to be detected, the grounding thyristors of the switch units connected with other phase lines are controlled and triggered, and the detection signal is analyzed to obtain a fault detection result, wherein the phase-to-phase faults comprise symmetrical phase-to-phase faults and asymmetrical phase-to-phase faults.

(II) asymmetric interphase fault detection

The method for detecting the fault of the asymmetric phase-to-phase fault specifically controls a trigger signal to trigger a thyristor of any two-phase line, wherein a switch unit connected with one phase line triggers an injection thyristor, and a switch unit connected with the other phase line triggers a grounding thyristor, and the analysis method can be as follows:

2.1) acquiring detection current data of a two-phase line to be detected;

and 2.2) judging that an inter-phase fault exists when the directions of the detection currents flowing through the two-phase lines are opposite.

Further, in order to realize more accurate judgment, the step 2.2 further comprises the following steps: when the detected currents of the two phases are approximately equal and far larger than the detected current of the normal phase or the detected current of the normal phase, the asymmetric interphase fault between the two phases to be detected is further determined. The comparison of the detected current with the detected current of the normal phase may be achieved by setting a threshold value.

The asymmetric phase-to-phase fault detection method, as shown in fig. 6, includes the conduction condition of the thyristor and the flow direction of the detection current.

Taking the detection of the AB phase-to-phase fault as an example, the thyristor T₁，T₄Conducting and the rest are closed. There are three flow directions after the current injection system is detected: the first is to detect the current flowing through the fault resistor R_fThen flows through the thyristor T₄Then, the current flows into the negative electrode of the detection power supply; the second is direct flow through parallel R_A，C_AThen, the current enters the ground and then flows into the negative electrode of the detection power supply; the third is the current flowing through the fault resistor R_fThen flows through R in parallel_B，C_BAnd finally, the current flows into the negative electrode of the detection power supply, and the asymmetric inter-phase fault can be detected by analyzing the waveform characteristics of the detection current.

The equivalent circuit diagram is shown in FIG. 7, in which X_{line_a}Is the A-phase line impedance, X, of the thyristor cell to the point of failure_{line_b}Is the B-phase line impedance, Z, of the thyristor cell to the point of failure_{eq_A}Is R_A，C_AThe sum of the impedance after parallel connection and the impedance of other detection signals flowing through the line, same Z_{eq_B}Is R_B，R_CThe impedance after parallel connection and the sum of the impedances of other detection signals flowing through the line, and so on.

As referred to above, the currents flowing through the phase a and phase B mutual sensors, respectively.

Has effective values of:

line impedance X in the formula_{line_a}，X_{line_b}Compared with | Z_{eq_A}I and I Z_{eq_B}L, its size is negligible, and can be further written as:

also, without counting the line impedance, there are:

fault resistance R in formula_fThe resistance value is usually much smaller than | Z_{eq_A}I, it can be seen that when the phase AB is in fault, the effective value of the current flowing through the mutual inductor B is I_BEffective value of current I flowing through A mutual inductor_AThe sizes are approximately equal and the directions are opposite. And in the normal line without phase-to-phase fault, the current I flowing through the mutual inductor A_{normal_A}Comprises the following steps:

similarly, the current I flowing through the mutual inductor B on the normal line_{normal_B}Comprises the following steps:

in the effective value expression of (A) in which R is_fIs compared with | Z_{eq_A}L is much smaller. Therefore | Z_{eq_A}//R_fThe value of | is greater than R_fYet to be small, and R_A//jωC_A＝Z_{eq_A}Then has | Z_{eq_A}//R_f|＜|R_A//jωC_AL. Effective value I of current vector under the condition of same voltage_A＞I_{normal_A}Same principle as I_B＞I_{normal_B}. That is, the detection current flowing through the fault phase is much larger than the detection current flowing through the normal phase, the detection current flowing through the a and B phases is the same in the normal phase, and the detection current flowing through the a and B phases is opposite in the direction when the phase-to-phase fault occurs.

In conclusion, when the AB phase-to-phase fault is detected, the thyristor T is used₁，T₄Conducting and the rest are closed. When there is an AB phase fault in the line, I_AAnd I_BWill be significantly larger than the current I on the non-faulted phase_CAnd the two directions are opposite. Therefore, the AB interphase fault existing in the line can be judged.

In the same way, the thyristor T₁，T₆And the switch is switched on, and the rest are switched off, so that the AC phase-to-phase fault can be detected. The detection principle is basically the same as that of the detection principle, and the difference is that if the line has AC phase-to-phase fault, I_AAnd I_CWill be significantly larger than the current I on the non-faulted phase_BAnd the two directions are opposite. Finally, the T is put₃，T₆The thyristor is switched on, and the rest are switched off, so that the phase-to-phase fault of the BC can be detected, and if the phase-to-phase fault exists between the BC, I_BAnd I_CWill be significantly larger than the current I on the non-faulted phase_AAnd the two directions are opposite.

According to the analysis of the interphase fault detection principle, when an interphase fault occurs, the detection currents on the two fault phases are approximately equal in magnitude and obviously higher than those on the normal phase in the same time period, and the directions of the detection currents on the two fault phases are opposite. Suppose that the phases A and B have phase-to-phase faults and the phase C is a normal phase.

The simulation waveform of the detected current is shown in fig. 8. In the AB phase-to-phase fault detection time period of 0.04 s-0.06 s, the waveform amplitude of the phase A current and the waveform amplitude of the phase B current are approximately equal and are both larger than the waveform amplitude of the phase C detection current, and the directions of the phase A current and the phase B current are opposite, so that the asymmetrical phase-to-phase fault detection method can be used for detecting the AB phase-to-phase fault of the line. In the same way, the detection of the AC phase-to-phase fault and the BC phase-to-phase fault can be realized.

Specifically, the inter-phase fault analysis may further perform a judgment by a graphical method, and when one of the two phases of the detected current waveforms is above the X axis and the other phase is below the X axis, and the two phases of the detected current waveforms are symmetrical about the X axis, an inter-phase fault exists.

Further, in order to more accurately judge whether the phase-to-phase fault occurs, the method further comprises the step of judging the change of the detected current waveform: the waveform areas of the detected currents of the two phases are larger than the areas of the normal phase or the normal phase during normal insulation, and the directions of the detected currents of the two phases are opposite, so that an asymmetric interphase fault exists.

As can be seen from fig. 8, the waveform of the a-phase detection current is located above the X-axis, and the waveform of the B-phase detection current is located below the X-axis, both waveforms being substantially symmetrical about the X-axis. And the detected current on the non-failed phase C phase is much smaller than the two phases AB. Therefore, the area method criterion can be also adopted according to the characteristics of the detected current waveform. The waveform of the detected current on the three phases and the area surrounded by the X axis are obtained and are respectively S_A，S_B，S_C. Similarly, the waveform of the detection current flowing when the line is normal and the area surrounded by the X axis are calculated, and S is obtained by considering a certain margin_M. It can be concluded that if AB has phase-to-phase failure, then there is S_A＞S_M，S_B＞S_M. But this cannot be used as a criterion for phase-to-phase failure of the AB. If the AB phase-to-phase fault does not occur in the line, but the A phase and the B phase have leakage faults, S also occurs_A＞S_M，S_B＞S_MThus, it is impossible to accurately determine whether the phase-to-phase fault or the two-phase leakage fault is present. The direction of the current flowing through the transformer can be detected to help the discrimination. Setting the bus flow direction to the line as a positive direction, and the line flow direction to the bus as a negative direction, and formulating an interphase fault criterion as follows: if S_A＞S_M，S_B＞S_MAnd if the direction of the B-phase detection current is negative, the AB phase-to-phase fault can be judged to occur. If S_A＞S_M，S_B＞S_MAnd the direction of the phase B detection current is positive, then leakage faults exist in the phase A and the phase B.

It is noted with respect to the above criteria that only one phase has an area greater than S_MWhen the area of the three phases is larger than S, the leakage fault is determined_MAnd if the current directions are positive, the three-phase leakage fault is determined (the three-phase-to-phase fault has an independent criterion). When two phase areas are larger than S_MIt may not be possible to determine accurately and it is also necessary to further determine the direction of the detected current. Secondly, the above criterion distinguishes the fault only by detecting the current direction of the B phase, which is determined by the structure of the thyristor unit, namely A, BWhen the phase-to-phase fault occurs in the C three phases, the leakage and the phase-to-phase fault can be distinguished only by detecting the detection current direction on the lag phase.

And (III) a detection method of symmetrical interphase faults.

The symmetrical interphase faults comprise three-phase interphase short circuit and three-phase interphase short circuit grounding, the fault detection method of the symmetrical interphase short circuit faults controls trigger signals to trigger thyristors of three-phase lines, a switch unit connected with one phase line triggers an injection thyristor, switch units connected with other two-phase lines trigger a grounding thyristor, and the analysis method can be as follows:

21-1) acquiring detection current data of a three-phase line to be detected;

21-2) judging that the three-phase interphase short-circuit fault exists when the detection current flowing through one phase is opposite to the detection current of the other two-phase line and the current of each phase is respectively larger than the detection current of the line in normal insulation.

Further, in order to realize more accurate judgment, the step 2.2 further comprises the following steps: and if the sum of the currents of the two phases in the same direction is approximately equal to the magnitude of the detected current of the third phase line with the opposite current direction, namely if the difference between the sum of the currents of the two phases in the same direction and the detected current of the third phase line with the opposite current direction is less than a set threshold value, further determining that the three-phase interphase short-circuit fault exists.

Referring to fig. 9, the thyristor conduction strategy is the same as that for diagnosing AB and AC phase faults, and is the same as that for thyristor T₁，T₄，T₆And simultaneously conducting, and an equivalent circuit diagram is shown in figure 10. X in the figure_{line_a}，X_{line_b}，X_{line_c}Respectively corresponding line impedance, Z, on three-phase lines_{eq_A}Is the impedance corresponding to the insulation resistance of the A-phase line and the capacitance to ground after being connected in parallel,

for the current flowing through the A-phase current transformer, and so on, R_fIs the transition resistance. According to fig. 10, get

Has effective values of:

will I_AComparing the expression with the expression when the line is normal, it can be seen that when the line has three-phase interphase short-circuit fault, the effective value of the current I flowing through the A-phase current transformer_AMuch larger than normal. Then according to I_BExpression and I_CExpression and FIG. 10 it can be seen that I_B，I_CAre approximately equal in magnitude and have a value of about I_AHalf of the total current and is also larger than the current flowing through the two phases B and C under normal conditions. However, the judgment is made based on the magnitude relation of the effective value, which is confused with the leakage fault, and it should be noted that fig. 11 does not show the current

The flow direction of (c) is shown. Referring to the analysis of the asymmetrical phase-to-phase fault, when the three-phase-to-phase fault exists in the line, the current

Is in a positive direction, and

is negative. Then the three-phase-to-phase fault in the line can be realized according to the magnitude relation of the three currents and the combination of the flow directions of the three currentsAnd (6) diagnosis. The detection criterion is similar to the detection of interphase fault, namely when S_A＞S_M，S_B＞S_M，S_B＞S_MAnd is

The direction is positive, and the direction is positive,

when the direction is negative, the three-phase interphase short-circuit fault of the line can be judged.

The fault detection method of the three-phase interphase short circuit grounding fault comprises the following steps that a specific trigger signal triggers an injection thyristor of a three-phase line, and the analysis method comprises the following steps:

22-1) acquiring detection signal data of a three-phase line to be detected, wherein the detection signal comprises detection current and detection voltage;

22-2) carrying out Fourier transformation on the detection signal to obtain components of a plurality of frequencies, and calculating harmonic impedance of the line under each frequency according to each component;

22-3) if the imaginary part of the harmonic impedance varies in direct proportion to the increase in frequency, there is no three-phase fault in the line; if the imaginary part of the harmonic impedance changes less than a set threshold with increasing frequency, then the line has a three-phase fault.

The detection method in this example is as follows: firstly, the thyristor T₁，T₃，T₅And simultaneously conducting, injecting a detection signal into the circuit, carrying out Fourier transform on the detection voltage signal, obtaining harmonic impedance under each frequency, and analyzing an imaginary part of the harmonic impedance, namely harmonic reactance X (f). If x (f) varies proportionally with the increase in frequency, there is no three-phase fault in the line; if there is no significant change in x (f) with increasing frequency, then there is a three-phase fault with the line. The simulation diagram of the harmonic reactance value when the line has a symmetric fault and when the line is normal is shown in the attached figure 15.

The method for detecting the short-circuit ground fault between the three phases is shown in the attached figure 11.

The three-phase interphase short circuit earth fault can not be detected by analysisOther methods are needed to diagnose the magnitude and flow direction of the current. Thyristor T₁，T₃，T₅And simultaneously conducting, and turning off the rest. Three-phase failure of the line in the diagram, R_fIs the transition resistance. By using the controllable characteristic of the thyristor, the inverter power supply is instantaneously applied to the circuit, and the excitation generates a transient current response signal in the system. Because the signal contains abundant frequency components, the harmonic impedance of the line under each frequency can be accurately obtained by combining the harmonic impedance theory. An equivalent circuit diagram of the detection method is shown in fig. 12. X_{line_1}Is to detect the line impedance, X, from the power supply to the fault point_{line_2}Is the impedance between the point of failure and the load, Z_GThe impedance, Z, of the line insulation resistance in parallel with the capacitance to ground_loadIs the load impedance. dV and dI are components of a plurality of frequencies of voltage and current pulse signals generated under the control of the thyristor after fourier transform.

As shown in fig. 12, the line can be viewed as a port network. A stimulus at a particular frequency can be applied to the system and the response measured to derive the harmonic impedance of the network at that frequency. At the moment of the conduction of the thyristor, a short pulse intercepted on the basis of a sine wave, namely an instantaneous voltage pulse, is injected into a line, the instantaneous voltage pulse is subjected to Fourier transform according to a superposition principle, namely, a plurality of voltages with different frequencies are superposed on the position of the thyristor at the moment, and current pulse responses of the frequencies are generated at two ends of a system to be tested.

Establishing an equation describing the network impedance according to the aperiodic Fourier transform:

dV(jω)＝Z(jω)×dI(jω)

in the formula, dV (j ω) and dI (j ω) are transient voltages and currents of ω at a specific frequency after fourier transform. Z (j ω) is the harmonic impedance at frequency ω. The harmonic impedance can be expressed as:

in the formula of omega₁＝2πf₁,f₁The harmonic impedance frequency characteristic of the line to be tested can be obtained by calculating voltage and current vectors under different frequencies, namely, the frequency characteristic of the harmonic impedance of the underground power-loss line can be obtained by Fourier transformation of the transient voltage and the transient current. The harmonic impedance z (f) can be decomposed into a representation in terms of resistance and reactance:

where the real part of Z (f) is the harmonic resistance and the imaginary part is the harmonic reactance.

If no three-phase fault exists in the line, an equivalent circuit diagram of the phases is shown in the attached figure 13.

Wherein, X_{line_1}，X_{line_2}Is line reactance, R_G，X_GIs the impedance of the insulation resistance of the line and the capacitance to ground. R_load，X_loadThe equivalent resistance and impedance (inductive load) of the load carried by the line, and the expression of the harmonic impedance at this time is:

Z(f)＝R(f)+jX(f)＝j(X_{line_1}+X_{line_2})+(R_G+jX_G)//(R_load+jX_load)

due to line impedance X_{line_1}，X_{line_2}Much less than the load impedance, can be further written as:

Z(f)＝R(f)+jX(f)＝(R_G+jX_G)//(R_load+jX_load)

then the harmonic resistance and harmonic reactance under normal line are respectively:

the harmonic resistance r (f) has an expression in which the highest order of f in the denominator and the numerator is 2, and therefore, the degree of variation of r (f) with frequency is small. X (f) is expressed in terms of an exponent of f in the denominator of 2 and an exponent of f in the numerator of 3, so that x (f) increases approximately proportionally with increasing frequency f.

The equivalent circuit diagram of the interphase with the three-phase fault in the line is shown in the attached figure 14. Wherein, X_{line_1}，X_{line_2}，X_{line_3}，X_{line_4}Is line reactance, R_G，X_GIs the susceptance, R, of the insulation resistance and the capacitance to ground of the A-phase line_fIs a fault point transition resistance. The expression for the system harmonic impedance Z' (f) is:

Z’(f)＝j(X_{line_1}+X_{line_2})+R_f//[j(X_{line_3}+X_{line_4})+(R_G+jX_G)//(R_load+jX_load)]

and (3) decomposing the harmonic impedance into a real part and an imaginary part to obtain a harmonic resistance R '(f) and a harmonic reactance X' (f) in the three-phase fault:

in the formula

At lower frequencies, it is much smaller than (R)_f+R_G+R_load)²Therefore, R' (f) basically does not change along with the change of frequency at the low frequency of 0-300 Hz; and wherein X' (f) consists of two parts, the first part being 2 π f (L)_{line_1}+L_{line_2}) Due to L_{line_1}，L_{line_2}The values are small and negligible in variation with frequency; the second part is a fraction, the f index in the denominator is 2, the f index in the numerator is 1, and the coefficient difference between the two is small, so that the second part can be reduced along with the increase of the frequency, but the second part can be reduced along with the increase of the frequencySince the variation of the frequency f is limited in the low frequency range and is (R) in the denominator_f+R_{G_1}+R_{load_1})²Much larger than the other terms, the second part is completely negligible in decreasing frequency, and thus, X₁(f) Increases with increasing frequency.

According to a simulation diagram of the three-phase interphase short circuit grounding fault, least square method criterion is considered. Connecting harmonic reactances corresponding to the frequencies in two states, namely, the state with three-phase fault and the state without three-phase fault into a straight line, and fitting the slope corresponding to the straight line by using a least square method. From the above analysis, it can be seen that the slope corresponding to the three-phase fault condition is smaller than the slope corresponding to the no three-phase fault condition, as shown in fig. 16. Therefore, the slope magnitude can be compared to be used as a criterion for detecting the three-phase fault. The slope k when there is no symmetric fault in the line is used as a reference slope, and the calculated slope is detected to be k'. If k 'is less than k, the three-phase fault exists in the line, and if k' is more than or equal to k, the three-phase fault does not exist in the line. However, in practical application, it is difficult to determine the accurate reference slope k considering that the loads of each line are different and the loads of each line vary during operation. However, the slope when there is a three-phase fault is much smaller than that when there is no three-phase fault, and a suitable k can be selected according to the change condition of the load and the change range, and a certain margin is considered.

The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.

Claims

1. A fault detection system for a downhole power-off line based on an additional power supply is characterized in that: the circuit fault detection device comprises a control module, a trigger module and a power electronic power supply, wherein the output end of the power electronic power supply is respectively connected with each phase circuit to be detected, the control module is respectively connected with the output end of the power electronic power supply in a control mode through the trigger module, detection signals injected into the corresponding phase circuits are obtained, and the circuit fault of the circuit to be detected is obtained through analyzing the detection signals;

the control module is used for generating a control instruction of the power electronic switching power supply and analyzing a line fault; the method comprises the steps of outputting a control signal to control and trigger an injection thyristor of a switch unit of the power electronic power supply, analyzing leakage and ground faults, obtaining detection current injected into a certain phase circuit, and judging whether the phase circuit has leakage or ground faults if the detection current is larger than the detection current in normal insulation or normal phase;

setting a first comparison threshold I of a ground fault₁Second comparison threshold value of leakage fault I₂Wherein a first comparison threshold I₁Greater than a second comparison threshold I₂；

When the magnitude of the detected current I is between the first comparison threshold I₁And a second comparison threshold I₂When the phase line has the leakage fault, the phase line is judged to have the leakage fault, and when the phase line is larger than a first comparison threshold I₁And judging that the phase line has a ground fault.

2. The system of claim 1 for downhole lost power line fault detection based on an additional power source, wherein: the power electronic power supply comprises an alternating current power supply and a switch circuit, wherein the switch circuit comprises six thyristors, every two of the thyristors are connected in series and then connected in parallel, the middle point of the serial branch of every two thyristors is an output end, one thyristor on each serial branch is a signal injection thyristor, and the other thyristor is a grounding thyristor.

3. The system of claim 1 for downhole lost power line fault detection based on an additional power source, wherein: the intelligent control system is characterized by further comprising a current transformer and a voltage transformer which are arranged on the line, wherein the current transformer and the voltage transformer are respectively connected with the control module.

4. The system of claim 1 for downhole lost power line fault detection based on an additional power source, wherein: a triggering module: and the power electronic device is used for generating a trigger signal according to the control instruction of the control module and triggering the power electronic switching power supply to work.

5. The method for detecting the fault of the underground power-losing line based on the additional power supply is characterized by comprising the following steps;

for inter-phase fault detection, outputting a control signal to control and trigger an injection thyristor of a switch unit connected with one phase line so as to enable a power electronic power supply to inject a detection signal into the phase line to be detected, controlling and triggering grounding thyristors of switch units connected with other phase lines, and analyzing the detection signal to obtain a fault detection result;

the method for outputting the control signal to control and trigger the injection thyristor of the switch unit of the power electronic power supply and analyzing the leakage and the ground fault comprises the following steps:

acquiring detection current injected into a certain phase line, and if the detection current is larger than the detection current in the normal insulation state or the detection current in the normal phase, judging that the phase line has electric leakage or ground fault;

When the magnitude of the detected current I is between the first comparison threshold I₁And a firstTwo comparison threshold values I₂When the phase line has the leakage fault, the phase line is judged to have the leakage fault, and when the phase line is larger than a first comparison threshold I₁And judging that the phase line has a ground fault.

6. The method for detecting faults of a power-losing circuit in a well based on an additional power supply as claimed in claim 5, wherein: the interphase faults comprise symmetrical interphase faults and asymmetrical interphase faults;

the method for detecting the faults of the asymmetric interphase faults comprises the following steps that a trigger signal triggers thyristors of any two-phase lines, a switch unit connected with one phase line triggers an injection thyristor, and a switch unit connected with the other phase line triggers a grounding thyristor, and the analysis method comprises the following steps:

acquiring detection current data of a two-phase line to be detected;

and when the directions of the detection currents flowing through the two-phase lines are opposite, and the difference value between the detection currents and the normal detection currents or the difference value between the detection currents of the normal phases is larger than a set threshold value, judging that the phase-to-phase fault exists.

7. The method for detecting faults of a power-losing circuit in a well based on an additional power supply as claimed in claim 6, wherein: the symmetrical interphase fault comprises a three-phase interphase short circuit and a three-phase interphase short circuit grounding, the fault detection method of the symmetrical interphase short circuit fault controls a trigger signal to trigger thyristors of three-phase lines, a switch unit connected with one phase line triggers an injection thyristor, switch units connected with other two-phase lines trigger a grounding thyristor, and the symmetrical interphase short circuit analysis method comprises the following steps:

acquiring detection current data of a three-phase line to be detected;

and when the detection current flowing through one phase is opposite to the detection current of the other two-phase line, and the current of each phase is respectively larger than the detection current of the line in normal insulation, judging that the three-phase interphase short-circuit fault exists.

8. The method for detecting faults of a power-losing circuit in a well based on an additional power supply as claimed in claim 6, wherein: the method for judging the symmetrical interphase short-circuit fault further comprises the following steps: and if the sum of the currents of the two phases in the same direction and the difference of the detected currents of a third phase line with the opposite current direction are smaller than a set threshold value, further determining that the three-phase interphase short-circuit fault exists.

9. The method for detecting faults of a power-losing circuit in a well based on an additional power supply as claimed in claim 7, wherein: the three-phase interphase short circuit grounding fault detection method comprises the following steps of triggering an injection thyristor of a three-phase line by a specific trigger signal, wherein the analysis method comprises the following steps:

acquiring detection signal data of a three-phase line to be detected, wherein the detection signal comprises detection current and detection voltage;

carrying out Fourier transform on the detection signal to obtain components of a plurality of frequencies, and calculating harmonic impedance of the line under each frequency according to each component;

if the imaginary part of the harmonic impedance varies in direct proportion to the increase in frequency, then there is no three-phase fault in the line; if the imaginary part of the harmonic impedance changes less than a set threshold with increasing frequency, then the line has a three-phase fault.

10. The method for detecting faults of a power-losing circuit in a well based on an additional power supply as claimed in claim 5, wherein: the operational data includes line voltage, line current, and feeder switch signals.