CN113794191A - Arc extinction control method and system for ground fault of power distribution network - Google Patents
Arc extinction control method and system for ground fault of power distribution network Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/08—Limitation or suppression of earth fault currents, e.g. Petersen coil
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
- H02J3/0012—Contingency detection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
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Abstract
The invention discloses a power distribution network ground fault arc extinction control method and a power distribution network ground fault arc extinction control system, which comprise the following steps: s1, measuring the three-phase power supply voltage and the neutral point voltage of the power distribution network; s2, judging whether the power distribution network has a single-phase earth fault, if so, entering the step S3; otherwise, returning to step S1; s3, acquiring fault earth voltage, distribution network earth parameters, neutral point voltage and three-phase currents before and after the fault of the distribution network when the fault occurs, and calculating line impedance and fault earth resistance of the distribution network according to the fault earth voltage, the distribution network earth parameters, the neutral point voltage and the three-phase currents before and after the fault of the fault; and S4, calculating the voltage drop on the line impedance according to the line impedance, and correcting the neutral point voltage to enable the neutral point voltage to be equal to a preset specified value so that the fault point voltage is compensated to zero to realize arc extinction. The invention corrects the arc extinction method for controlling the neutral point voltage by using the zero sequence voltage, and realizes full arc extinction in the true sense.
Description
Technical Field
The invention relates to the technical field of power systems, in particular to a power distribution network ground fault arc extinction control method and system.
Background
The distribution network is as the terminal part that structure and operational environment are the most complicated and changeable among the electric power system, and its safety and stability operation is direct to be concerned with the power consumption quality of vast user. But the distribution network is easy to have various random faults, wherein the single-phase earth fault has bad influence and is most frequently generated, and the probability is as high as 80%.
The mechanism of arc extinction of the power distribution network ground fault is as follows: after the alternating current passes through zero point and is extinguished, the recovery speed of the insulating medium is higher than that of the voltage at the fault point, and the electric arc is effectively prevented from reigniting. The main factors influencing arc extinction are as follows: magnitude of residual current, magnitude of recovery voltage, and rate of rise of recovery voltage. The smaller the fault current is, the smaller the medium damage is, and the more favorable the insulation medium recovery and fault arc extinction are; the smaller the amplitude of the fault point recovery voltage is, the slower the initial recovery speed is and the longer the recovery time is, so that the insulation medium is difficult to be punctured again, the electric arc reignition is prevented, and the fault arc extinction is facilitated. The fault arc extinction of the flexible ground control is based on Pulse Width Modulation (PWM) and an active inverter injects zero-sequence current into a power distribution network to control zero-sequence voltage, so that the recovery voltage of a fault point is close to zero, and the instantaneous ground fault is prompted to realize arc extinction. After the ground fault occurs, the current injection is controlled through a certain time delay, the fault residual current is reduced, the zero sequence voltage and the zero sequence current variable quantity of each feeder line are accurately measured, and the dynamic sensing and the reliable protection of the ground fault are realized.
The traditional arc suppression coil can only compensate reactive current in a power distribution network, the active injection type arc suppression method can solve the problems, but line impedance in the power distribution network is not considered in the analysis process, and large residual voltage and residual current still exist in the power distribution network after arc suppression is finished. In practical applications, the problem of line impedance is unavoidable, and many uncertain factors are not considered to be generated, wherein the most fatal point is that when the fault ground resistance is small and much smaller than the line impedance, the fault current and the load current are approximately equal. However, load current is usually large, so that the voltage arc suppression method cannot reduce the ground fault current but increases the ground fault current under the condition, so that the arc suppression does not achieve the expected effect. And when the line impedance is not considered when the injected current is theoretically analyzed, the value of the injected current has a great relationship with the line impedance, the injected current is inaccurate, the full arc extinction of the fault phase cannot be accurately achieved, and the fault phase has larger voltage after the arc extinction, so that great hidden danger is brought to subsequent operation.
Disclosure of Invention
In view of the above, the invention provides a method and a system for arc extinction control of a power distribution network ground fault under the condition of considering the impedance of a power distribution network line, wherein the line impedance is calculated by using parameters which can be obtained in real time in the power distribution network, then the voltage drop on the line impedance is obtained, and based on the voltage drop, an arc extinction method for controlling neutral point voltage by using zero sequence voltage can be corrected, and full arc extinction in a true sense can be realized by the method.
On one hand, the invention provides a power distribution network ground fault arc extinction control method, which comprises the following steps:
s1, measuring the three-phase power supply voltage and the neutral point voltage of the power distribution network;
s2, judging whether the power distribution network has a single-phase earth fault, if so, entering the step S3; otherwise, returning to step S1;
s3, acquiring fault earth voltage, distribution network earth parameters, neutral point voltage and three-phase currents before and after the fault of the distribution network when the fault occurs, and calculating line impedance and fault earth resistance of the distribution network according to the fault earth voltage, the distribution network earth parameters, the neutral point voltage and the three-phase currents before and after the fault of the fault;
and S4, calculating the voltage drop on the line impedance according to the line impedance, and correcting the neutral point voltage to enable the neutral point voltage to be equal to a preset specified value so that the fault point voltage is compensated to zero to realize arc extinction.
Further, the formulas of the line impedance and the fault ground resistance are respectively as follows:
in which the instantaneous distribution network load at which a fault is assumed to occur remains unchanged, ZeqIs line impedance, RfFor fault ground resistance, UNIs neutral point voltage, UiFor fault phase-to-ground voltage of i phase, Z0Is a ground parameter of the distribution network, and
R0、C0respectively fault-to-ground resistance and capacitance to ground, Ii0For i-phase fault to earth currents, UN、Ui、R0、C0The phase I is obtained by measurement and is A phase, B phase or C phase, wherein the I phasei0The current before and after the i-phase fault is obtained by adopting a difference method, and the expression is as follows:
Ii0＝Ii2-Ii1
in the formula Ii2Representing the pre-fault current of the I-phase of the distribution network, Ii1Indicating post-fault current of I-phase of distribution network, Ii2、Ii1Obtained by measurement.
Further, in the step S4, the neutral point voltage is corrected by the double closed loop control method so that the neutral point voltage is equal to the preset specified value.
Further, the double closed-loop control method is controlled based on a double closed-loop controller of a voltage outer loop and a current inner loop, the double closed-loop controller is composed of an external 380v three-phase power supply, an inverter, an uncontrollable rectifier, an LC filter and a grounding transformer Ti, wherein the inverter and the rectifier are jointly used as the voltage outer loop, the LC filter is the current inner loop, and the double closed-loop control method is characterized in that: the power distribution network provides current, three-phase power supply voltage, fault phase voltage and neutral point voltage of fault phases before and after a fault of the power distribution network for the double closed-loop controller, the double closed-loop controller obtains voltage drop on line impedance through real-time data of the power distribution network during the fault, corrected neutral point voltage is obtained through calculation, the corrected neutral point voltage is used as a reference value of a voltage outer ring of the double closed-loop controller, the voltage outer ring provides a current reference value for a current inner ring, output voltage is corrected in real time through feedback of capacitance voltage and inductance current in an LC filter, and finally the output voltage is equal to a preset specified value to achieve arc extinction, wherein the real-time data of the power distribution network comprises the current, the fault phase voltage and the neutral point voltage of the fault phase.
Further, the step S4 modifies the neutral point voltage so that the neutral point voltage is equal to a preset specified value, which is embodied by: correcting the neutral point voltage so that the neutral point voltage is equal to the difference between the voltage across the line impedance and the supply voltage of the faulted phase of the power distribution network by the expression:
UN＝Uzeq-Ei
in the formula of UzeqRepresenting the voltage over the line impedance, EiI-phase supply voltage indicating failure of the distribution network, wherein Uzeq＝Ii0*Zeq。
And further, when the measured neutral point voltage is greater than 15% of the three-phase power supply voltage of the power distribution network, the power distribution network is judged to have the single-phase earth fault.
In another aspect, the present invention also provides a power distribution network ground fault arc suppression control system comprising a microprocessor and a memory connected to each other, the microprocessor being programmed or configured to perform the steps of any of the power distribution network ground fault arc suppression control methods described herein.
The invention provides a power distribution network ground fault arc extinction control method and system, firstly, measuring three-phase power supply voltage and neutral point voltage of a power distribution network; secondly, judging whether the power distribution network has single-phase earth faults or not, and if so, entering the next step; otherwise, returning to the previous step; thirdly, acquiring the fault voltage to ground, the distribution network ground parameter, the neutral point voltage and the three-phase current before and after the fault of the distribution network when the fault occurs in the distribution network, and calculating the line impedance and the fault ground resistance of the distribution network according to the fault voltage to ground, the distribution network ground parameter, the neutral point voltage and the three-phase current before and after the fault of the fault phase; and finally, calculating the voltage drop on the line impedance according to the line impedance, and correcting the neutral point voltage to enable the neutral point voltage to be equal to a preset specified value so as to facilitate the compensation of the fault point voltage to zero and realize arc extinction. Under the condition of considering the line impedance of the power distribution network, the line impedance is calculated according to the fault earth voltage of a fault phase when the power distribution network has a fault, the power distribution network earth parameter, the neutral point voltage and the three-phase current before and after the fault, then the voltage drop on the line impedance is obtained, and the arc extinction method for controlling the neutral point voltage by using the zero-sequence voltage is used for correction based on the voltage drop, so that the full arc extinction in the true sense can be realized.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a flowchart of an arc extinction control method for a power distribution network ground fault according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a dual closed-loop controller;
FIG. 3 is a schematic diagram of a single-phase earth fault occurring in the C phase of a power distribution network;
FIG. 4 is an equivalent sequence diagram of the distribution network at the moment of the C-phase fault of the distribution network;
FIG. 5 is a simplified diagram of a power distribution network circuit according to the present invention;
FIG. 6 is a failed phase C circuit diagram;
FIG. 7 is a schematic diagram of an arc extinction structure of a 10KV power distribution network with a neutral point not grounded;
fig. 8 is a modeling simulation result diagram of the power distribution network ground fault arc extinction control method provided by the invention.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict. The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
Fig. 1 is a flowchart of a power distribution network ground fault arc extinction control method provided according to an embodiment of the invention.
As shown in fig. 1, a power distribution network ground fault arc extinction control method includes the following steps:
s1, measuring the three-phase power supply voltage and the neutral point voltage of the power distribution network;
it should be noted that when the measured neutral point voltage is greater than 15% of the three-phase power supply voltage of the power distribution network, it is determined that a single-phase ground fault occurs in the power distribution network; on the contrary, when the measured neutral point voltage is less than or equal to 15% of the three-phase power voltage of the power distribution network, the power distribution network is judged not to have single-phase earth fault;
s2, judging whether the power distribution network has a single-phase earth fault, if so, entering the step S3; otherwise, returning to step S1;
s3, acquiring fault earth voltage, distribution network earth parameters, neutral point voltage and three-phase currents before and after the fault of the distribution network when the fault occurs, and calculating line impedance and fault earth resistance of the distribution network according to the fault earth voltage, the distribution network earth parameters, the neutral point voltage and the three-phase currents before and after the fault of the fault;
specifically, the formulas of the line impedance and the fault ground resistance are respectively as follows:
in which the instantaneous distribution network load at which a fault is assumed to occur remains unchanged, ZeqIs line impedance, RfFor fault ground resistance, UNIs neutral point voltage, UiFor fault phase-to-ground voltage of i phase, Z0Is a ground parameter of the distribution network, and
R0、C0respectively fault-to-ground resistance and capacitance to ground, Ii0For i-phase fault to earth currents, UN、Ui、R0、C0Measured, I phase is A phase, B phase or C phase, wherein I phasei0The current before and after the i-phase fault is obtained by adopting a difference method, and the expression is as follows:
Ii0＝Ii2-Ii1
in the formula Ii2Representing the pre-fault current of the I-phase of the distribution network, Ii1Indicating post-fault current of I-phase of distribution network, Ii2、Ii1Obtained by measurement;
and S4, calculating the voltage drop on the line impedance according to the line impedance, and correcting the neutral point voltage to enable the neutral point voltage to be equal to a preset specified value so that the fault point voltage is compensated to zero to realize arc extinction. It should be noted that the voltage drop of the line impedance can be calculated according to the line impedance because the distribution network is coupled to the ground parameter Z0It is known that when the line impedance Z is obtainedeqAnd a ground fault resistance value RfIn time, a power distribution network ground parameter Z exists among the three0And fault ground resistance RfAfter being connected in parallel with the line impedance ZeqIn series relation, the total voltage is the fault voltage to earth UiI.e. the line impedance Z can be calculated by using the voltage division law of ohm's laweqPressure drop over the pressure drop.
In a further technical solution, in step S4, the neutral point voltage is corrected by a double closed-loop control method so that the neutral point voltage is equal to a preset specified value, specifically, the neutral point voltage is corrected so that the neutral point voltage is equal to a difference between a voltage across the line impedance and a power supply voltage of a failed phase of the power distribution network, and an expression of the neutral point voltage is:
UN＝Uzeq-Ei
in the formula of UzeqRepresenting the voltage over the line impedance, EiIndicating a faulty i-phase mains voltage of the distribution network.
In addition, it is worth mentioning that the above-mentioned double closed-loop control method is controlled based on a double closed-loop controller of a voltage outer loop and a current inner loop, and the double closed-loop controller is composed of an external 380v three-phase power supply, an inverter, an uncontrollable rectifier, an LC filter and a voltage transformerThe double-closed-loop control method comprises the following steps that a grounding transformer Ti is formed, wherein an inverter and a rectifier are jointly used as a voltage outer loop, an LC filter is used as a current inner loop, and the double-closed-loop control method is characterized in that: the power distribution network provides current, three-phase power supply voltage, fault phase voltage and neutral point voltage of fault phases before and after a fault of the power distribution network for the double closed-loop controller, the double closed-loop controller obtains voltage drop on line impedance through real-time data of the power distribution network during the fault, corrected neutral point voltage is obtained through calculation, the corrected neutral point voltage is used as a reference value of a voltage outer ring of the double closed-loop controller, the voltage outer ring provides a current reference value for a current inner ring, output voltage is corrected in real time through feedback of capacitance voltage and inductance current in an LC filter, and finally the output voltage is equal to a preset specified value to achieve arc extinction, wherein the real-time data of the power distribution network comprises the current, the fault phase voltage and the neutral point voltage of the fault phase. Referring specifically to fig. 2, fig. 2 is a block diagram of a dual closed-loop controller. The power distribution network provides corresponding data for the controller, the data comprises current of fault phases before and after a fault of the power distribution network, three-phase power supply voltage, fault phase voltage and neutral point voltage during the fault, real-time data of the power distribution network during the control and passing the fault are obtained, and corrected neutral point voltage U is obtainedN＝Uzeq-EC. Will Uzeq-ECAs a reference value of a voltage outer ring of the controller, the voltage outer ring provides a current reference value for a current inner ring, and the current reference value is obtained through a capacitor C1Voltage and inductance L0Current feedback, real-time correction of output voltage UNSFinally, make the output voltage equal to Uzeq-ECAnd by controlling the grounding transformer TiSo that U is changedNS＝Uzeq-EC＝UNAnd arc extinction is realized.
The working principle of the power distribution network ground fault arc extinction control method is further explained below, and a single-phase ground fault occurring in the phase C of the power distribution network is taken as an example for explanation.
Fig. 3 is a schematic diagram of a single-phase earth fault occurring in the phase C of the power distribution network. E in FIG. 3A、EB、ECThree-phase supply voltage, U, of the distribution network, respectivelyNIs neutral point voltage, IipIs outsideConnected to the injection current of the double closed-loop controller, R0、C0For single phase to earth leakage resistances and capacitances in three-phase circuits, RfTransition resistance to earth for fault phase, R0、C0Being capacitors and inductors of filter circuits, UCIs C relative ground voltage, where R is a ground reference0、C0The parameter obtained after parallel connection is set as Z0Then Z is0For distribution network ground reference, ZeqIs the power distribution network line impedance. U shapeA、UB、UCIs a three-phase voltage to earth, RfFault ground resistance, IipIs a neutral point injected current, UfIs the fault point to ground voltage. Writing kirchhoff's law of current to the column of fig. 3, the formula of the injected current can be obtained as follows:
in the formula of Ui＝Ei+Ui(i-A, B or C), EA+EB+EC＝0。
Fig. 4 is an equivalent sequence diagram of the distribution network when the phase C fault of the distribution network occurs. When the C phase of the power distribution network has no fault, the system only has a positive sequence, and has no negative sequence and zero sequence. The current I before the fault can be obtainedC1As in equation (4):
IC1＝EC/(Zeq+Zload3) (4)
in the formula IC1For the pre-fault current, Z, of the C-phase of the distribution networkloadRepresenting the load impedance of the C phase of the distribution network, there are three load impedances, Z, due to the invention assuming three branchesload3Three load impedances are represented;
after the fault occurs, the system has three sequence currents, and the current I after the fault can be obtained according to the graph 4C2As shown in formula (5):
IC2＝EC/(Zeq+Zload//Z0//(3Rf+Z0+Zeq/n+Zeq//Zload//Z0)) (5)
in the formula IC1For post-fault currents, Z, of C-phase of the distribution networkloadRepresenting the load impedance of the C phase of the distribution network, wherein the resistance value of the load is unchanged at one moment before and after the fault occurs;
because the instant time before and after the fault is very short, the load is not changed at the moment, the system only has load current before the fault, and the ground capacitance current, the fault grounding current and the load current exist after the fault, so that when a difference method is adopted, the I only having the ground capacitance current and the fault grounding current can be obtainedC0As shown in formula (6):
IC0＝IC2-IC1＝EC/(Zeq+(Z0//Rf)) (6)
fig. 5 is a simplified diagram of a power distribution network circuit according to the present invention. Fig. 5 shows a case where the arc is not extinguished when a fault occurs. Since the invention researches that the neutral point of the power distribution network is not grounded, the column of fig. 4 is written with kirchhoff's current law to obtain (7):
due to Ui＝Ei+Ui(i-A, B or C), EA+EB+ECWhen equal to 0, then U is addedA＝EA+UA、UB＝EB+UBAnd UC＝EC+UCSubstituting the formula (7) for simplification to obtain a formula (8):
to simplify the calculation, the equation (8) is simplified, and since U is usedzeq＝IC0*ZeqTo obtain formula (9):
in the distribution network of formula (9), due to IC0＝IC2-IC1，UC、UN、IC2、IC1The values of (A) and (B) can be obtained through measurement, only two unknowns exist in the formula (9), the two unknowns of the two equations inevitably have solutions, and Z can be obtainedeq、ZfThe expression (2) is as follows (10) (11):
at this time, it is known that a voltage drop across the line impedance is also obtained, and fig. 6 is a failure phase C-phase circuit diagram. In fig. 6, the failed phase C-phase voltage UFTo zero, equation (13) can be derived from kirchhoff's law:
UN＝Uzeq+UF-EC＝Uzeq-EC (13)
namely, the invention can make the voltage of the fault phase zero by only controlling the voltage of the neutral point to be equal to the difference between the voltage on the equivalent impedance and the voltage of the C-phase voltage source, and can complete the arc suppression.
Fig. 7 is a schematic diagram of an arc extinction structure of a 10KV power distribution network with a neutral point not grounded. Fig. 7 is a general schematic diagram for implementing active voltage arc extinction by using a dual closed-loop controller. The principle is that the quantity obtained by direct measurement in a power distribution network is utilized, other unknown parameters are obtained by utilizing the existing rules and criteria, specifically, when the equivalent impedance of the power distribution network is considered, the ground parameters of the power distribution network are obtained or the line impedance value and the fault grounding resistance of the power distribution network are obtained through the three-phase power voltage, the neutral point voltage and the amplitude phase of the power voltage of the power distribution network, then the voltage drop of the line impedance is calculated according to the line impedance, the neutral point voltage is corrected to enable the neutral point voltage to be equal to a preset specified value, so that the fault point voltage is compensated to zero, and arc extinction is realized.
The method of the present invention is modeled and simulated, and the simulation result is shown in fig. 8, where the abscissa in fig. 8 represents the time interval and the ordinate represents the voltage amplitude, specifically, fig. 8 (a) represents the corrected neutral point voltage UNAnd fault phase supply voltage EcRelationship between, light grey wave line indicates faulted phase supply voltage EcBlack wavy line indicates UN-UzeqThe value of (a) is the voltage U across the line impedance of the distribution networkzeqAnd (c) a fault point-to-ground voltage UFAnd the enlarged view in (c) is the enlargement of the post-arc-extinction fault point to ground current simulation waveform. Fault ground resistance R in fig. 8fSetting the voltage to 10 omega, grounding the C phase of the power distribution network through a 10 omega grounding resistor at 0.1s, and connecting the double closed-loop controller at 0.25s to the ground voltage U at the fault pointFReduced to 23.6V, voltage U on line impedance of power distribution networkzeqWhen the voltage drops to 50.5V and the double closed-loop controller is not switched in, the fault phase-to-ground voltage UFThe peak value is 657.5V, and the peak value of the voltage drop on the line impedance of the power distribution network is 1958V.
In another aspect, the present invention also provides a power distribution network ground fault arc suppression control system comprising an interconnected microprocessor and memory, the microprocessor being programmed or configured to perform the steps of the power distribution network ground fault arc suppression control method described above. The system can realize full arc extinction in a true sense obviously.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (7)
1. An arc extinction control method for a power distribution network ground fault is characterized by comprising the following steps:
s1, measuring the three-phase power supply voltage and the neutral point voltage of the power distribution network;
s2, judging whether the power distribution network has a single-phase earth fault, if so, entering the step S3; otherwise, returning to step S1;
s3, acquiring fault earth voltage, distribution network earth parameters, neutral point voltage and three-phase currents before and after the fault of the distribution network when the fault occurs, and calculating line impedance and fault earth resistance of the distribution network according to the fault earth voltage, the distribution network earth parameters, the neutral point voltage and the three-phase currents before and after the fault of the fault;
and S4, calculating the voltage drop on the line impedance according to the line impedance, and correcting the neutral point voltage to enable the neutral point voltage to be equal to a preset specified value so that the fault point voltage is compensated to zero to realize arc extinction.
2. An arc extinction control method for a power distribution network ground fault according to claim 1, wherein formulas of the line impedance and the fault ground resistance are respectively:
in which the instantaneous distribution network load at which a fault is assumed to occur remains unchanged, ZeqIs line impedance, RfFor fault ground resistance, UNIs neutral point voltage, UiFor fault phase-to-ground voltage of i phase, Z0Is a ground parameter of the distribution network, and
R0、C0respectively fault-to-ground resistance and capacitance to ground, Ii0For i-phase fault to earth currents, UN、Ui、R0、C0The phase I is obtained by measurement and is A phase, B phase or C phase, wherein the I phasei0The method is characterized in that the current before and after the i-phase fault of the power distribution network is obtained by adopting a difference method, and the expression is as follows:
Ii0＝Ii2-Ii1
in the formula Ii2Representing the pre-fault current of the I-phase of the distribution network, Ii1Indicating post-fault current of I-phase of distribution network, Ii2、Ii1Obtained by measurement.
3. The power distribution network ground fault arc extinction control method according to claim 2, wherein in the step S4, the neutral point voltage is corrected through a double closed loop control method so that the neutral point voltage is equal to a preset specified value.
4. An arc extinction control method for power distribution network ground faults is characterized in that the double closed-loop control method is controlled based on a double closed-loop controller of a voltage outer loop and a current inner loop, the double closed-loop controller is composed of an external 380v three-phase power supply, an inverter, an uncontrollable rectifier, an LC filter and a grounding transformer Ti, the inverter and the rectifier are used as the voltage outer loop, the LC filter is the current inner loop, and the double closed-loop control method is characterized in that: the power distribution network provides current, three-phase power supply voltage, fault phase voltage and neutral point voltage of fault phases before and after a fault of the power distribution network for the double closed-loop controller, the double closed-loop controller obtains voltage drop on line impedance through real-time data of the power distribution network during the fault, corrected neutral point voltage is obtained through calculation, the corrected neutral point voltage is used as a reference value of a voltage outer ring of the double closed-loop controller, the voltage outer ring provides a current reference value for a current inner ring, output voltage is corrected in real time through feedback of capacitance voltage and inductance current in an LC filter, and finally the output voltage is equal to a preset specified value to achieve arc extinction, wherein the real-time data of the power distribution network comprises the current, the fault phase voltage and the neutral point voltage of the fault phase.
5. The power distribution network ground fault arc extinction control method according to claim 4, wherein the step S4 modifies the neutral point voltage so that the neutral point voltage is equal to a preset specified value, which is embodied by: correcting the neutral point voltage so that the neutral point voltage is equal to the difference between the voltage across the line impedance and the supply voltage of the faulted phase of the power distribution network by the expression:
UN＝Uzeq-Ei
in the formula of UzeqRepresenting the voltage over the line impedance, EiI-phase supply voltage indicating failure of the distribution network, wherein Uzeq＝Ii0*Zeq。
6. An arc extinction control method for a power distribution network ground fault according to claim 5, wherein when the measured neutral point voltage is greater than 15% of a three-phase power supply voltage of the power distribution network, it is determined that a single-phase ground fault occurs in the power distribution network.
7. An electrical distribution network ground fault arc extinction control system comprising a microprocessor and a memory interconnected, wherein the microprocessor is programmed or configured to perform the steps of the electrical distribution network ground fault arc extinction control method of any one of claims 1 to 6.
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