Fault phase location method for single-phase grounding fault with resistance in distribution network

Abstract

The present invention specifically relates to a method for locating a fault phase of a single-phase grounding fault with resistance in a distribution network, and belongs to the technical field of detecting faults in distribution networks. The present invention comprises the following steps: real-time monitoring of the zero-sequence voltage of the distribution network to determine whether a permanent single-phase grounding fault with resistance occurs in the distribution network; calculating the Euclidean distance between the zero-sequence voltage waveform function of each of the three phases of the distribution network and the actual waveform function of the zero-sequence voltage of the distribution network, normalizing the calculated distance, and selecting the largest phase as the fault phase. The present invention proposes a method for locating a fault phase of a single-phase grounding fault with resistance in a distribution network, which overcomes the problem that the traditional phase selection method is easily affected by the asymmetry of system parameters and is difficult to tolerate high grounding resistance, accurately selects the fault phase in a very short time after the fault occurs, buys time for the fault arc extinguishing, effectively prevents the fault from further deteriorating, and better ensures the reliability and safety of the user's electricity use.

Description

Technical Field

[0001] The present invention specifically relates to a method for locating a fault phase of a single-phase grounding fault in a distribution network with resistance, and belongs to the technical field of fault detection in distribution networks (G01R31 / 08). Background Art

[0002] my country's medium-voltage distribution network mostly adopts a small current grounding method based on ungrounded, arc-extinguishing coil grounding and active flexible grounding, among which the number of single-phase grounding faults with resistance accounts for more than 80% of the total faults. When a low-resistance single-phase grounding fault occurs in the distribution network, the three-phase voltage of the distribution network changes greatly. Through the change of the three-phase voltage, it is relatively easy to find the fault phase of the distribution network where the low-resistance single-phase grounding fault occurs, and then the fault arc is extinguished by determining the fault phase to ensure the safe operation of the distribution network. When a high-resistance single-phase grounding fault occurs in the distribution network, the fault information is weak and is easily affected by the asymmetry of the distribution network, which makes the three-phase voltage of the distribution network less affected. It is easy to misjudge when finding the fault phase when the distribution network has a high-resistance single-phase grounding fault through the change of the three-phase voltage. The error in the phase selection result causes the arc-extinguishing current to be calculated incorrectly, which makes the fault worse, greatly affecting the safe operation of the distribution network. Therefore, how to locate the fault phase when a single-phase grounding fault with resistance occurs in the distribution network has become an important issue to ensure the safe operation of the distribution network.

[0003] The patent application number is CN202010408155.4, the application publication number is CN111551822B, and the patent name is: A method and device for selecting a phase for a single-phase ground fault in a distribution network. The patent uses the change in the neutral point displacement voltage before and after the fault to select the fault phase, but when a high-resistance ground fault occurs in the system, the change is very small and it is easy to cause misjudgment. The patent application number is CN202110037805.3, the application publication number is CN112881858A, and the patent name is: A method for selecting a phase for a single-phase ground fault in a distribution network with asymmetric parameters. The patent injects currents of different amplitudes into the distribution network twice, and uses the change in the injected current and the zero-sequence voltage to select the fault phase. Although this method improves the phase selection sensitivity, the injected current will cause the fault to deteriorate. At the same time, the above method needs to avoid the transient process, which reduces the rapid performance. The active arc extinguishing device can only be put into use after the phase selection is completed, which increases the risk of fault deterioration due to untimely arc extinguishing. Therefore, the phase selection method using transient information is very necessary for the rapidity of fault arc extinguishing and the suppression of fault deterioration. Summary of the invention

[0004] The technical problem to be solved by the present invention is: how to quickly and accurately locate the fault phase of a single-phase grounding fault with resistance in a distribution network.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is: a method for locating a fault phase of a single-phase grounding fault in a distribution network with resistance, comprising the following steps:

[0006] Step 1: Real-time monitoring of the zero-sequence voltage of the distribution network, and defining the time when the waveform of the zero-sequence voltage shows AC attenuation as the start time t of the suspected single-phase grounding fault y , when the t y When the zero-sequence voltage of the distribution network is y Then, the zero-sequence voltage transient attenuation component is separated out; the zero-sequence voltage transient attenuation component includes the transient zero-sequence voltage AC attenuation component and the envelope of the transient zero-sequence voltage AC attenuation component;

[0007] Step 2: From the t y At the beginning, every other power frequency cycle T of the distribution network f The attenuation coefficient δ in the envelope is collected once in real time, and a total of a times are collected and formed into an attenuation coefficient set A, as shown in the following formula (1):

[0008] A={δ1、δ2、...、δ a} (1)

[0009] In formula (1), δ1, δ2, ... to δ a They are respectively the first attenuation coefficient, the second attenuation system to the ath attenuation coefficient collected in real time from the envelope;

[0010] Substituting the data in the attenuation coefficient set A into the following formula (2) in turn, the distribution network is calculated from the t y After starting, each of the power frequency cycles T f The ground resistance inside

[0011] R Ei =1 / (2δ i C Σ -G Σ ),i=1,2,...,a (2)

[0012] In formula (2), R Ei is the distribution network from the t y After starting, at a power frequency cycle T f The ith power frequency cycle T f Ground resistance inside; δ i is the i-th attenuation coefficient among a attenuation coefficients collected in real time from the envelope; C Σ and G Σ They are the total capacitance and conductance to ground of the distribution network respectively;

[0013] All calculated grounding resistances are compared with the resistance single-phase grounding fault judgment threshold in turn. If all calculated grounding resistances are less than the resistance single-phase grounding fault judgment threshold, it indicates that a permanent resistance single-phase grounding fault has occurred in the distribution network. At this time, the start time t of the suspected resistance single-phase grounding fault is y Redefine it as the start time t0 of the single-phase grounding fault with resistance in the distribution network, and continue to execute the following step 3;

[0014] If all the calculated grounding resistances are greater than or equal to the resistance single-phase grounding fault judgment threshold, it indicates that no permanent resistance single-phase grounding fault occurs in the distribution network, and the process returns to step 1;

[0015] Step 3: Starting from t0, a time period of T is selected as the time period for judging the single-phase grounding fault with resistance, and the attenuation coefficient δ of the envelope at the end time t0+T of the time period for judging the single-phase grounding fault with resistance is collected in real time. T And put it into formula (2) to calculate the grounding resistance R of the distribution network within the resistance single-phase grounding fault judgment time. ET ;

[0016] The following formula (3) is used to calculate the grounding resistance of phase A, phase B and phase C of the distribution network within the single-phase grounding fault judgment time. ET The zero-sequence voltage calculation waveform function of a single-phase grounding fault is:

[0017]

[0018] In formula (3), t is the time in the single-phase grounding fault judgment time with resistance, t∈[t0,t0+T]; m=A,B,C represents the phase; u 0m (t) is the zero-sequence voltage calculation waveform function value of the mth phase at time t in the single-phase grounding fault judgment time with resistance after the grounding fault occurs in the distribution network; A m is the attenuation constant of the resistive single-phase grounding fault occurring in the mth phase of the distribution network; ω T is the AC attenuation angular frequency; B m is the attenuation constant of the single-phase grounding fault with resistance occurring in the mth phase of the distribution network; u 0Em (t) is the zero-sequence voltage fundamental frequency calculated waveform function value of the mth phase at time t in the single-phase ground fault judgment time with resistance after the ground fault occurs in the distribution network; L is the inductance value of the arc suppression coil; G ET is the grounding conductivity of the distribution network within the time period for judging the single-phase grounding fault with resistance; i bd(t) is the natural unbalanced current of the distribution network at time t in the determination time of the single-phase grounding fault with resistance; e m (t) is the power supply potential of the mth phase after the ground fault occurs in the distribution network, ω is the angular frequency of the power frequency in the distribution network, u 01 (t) is the natural unbalanced voltage of the distribution network at time t in the determination time of the single-phase grounding fault with resistance;

[0019] Real-time collection of the grounding resistance of the distribution network during the single-phase grounding fault judgment time with resistance is R ET The actual waveform function u1(t) of the zero-sequence voltage of a single-phase grounding fault;

[0020] Step 4: Randomly select N different moments from the single-phase grounding fault judgment time with resistance, namely t1, t2, ... to t N , the t1, t2, ... to t N All belong to the aforementioned [t0, t0+T];

[0021] The said t1, t2, ... to t N Substituting into the zero-sequence voltage calculation waveform function of phase A, phase B and phase C of the distribution network in turn, to obtain N discrete values ​​of the zero-sequence voltage calculation waveform of phase A, discrete values ​​of the zero-sequence voltage calculation waveform of phase B and discrete values ​​of the zero-sequence voltage calculation waveform of phase C;

[0022] The said t1, t2, ... to t N Substitute into the actual waveform function u1(t) of the zero-sequence voltage of the distribution network in sequence to obtain N discrete values ​​of the actual waveform of the zero-sequence voltage of the distribution network;

[0023] The N A-phase zero-sequence voltage calculation waveform discrete values, B-phase zero-sequence voltage calculation waveform discrete values, C-phase zero-sequence voltage calculation waveform discrete values ​​and distribution network zero-sequence voltage actual waveform discrete values ​​are collected to form a distribution network waveform judgment matrix C, as shown in the following formula (4):

[0024]

[0025] In formula (4), u 0A (t1),u 0A (t2), ... to u 0A (t N ) are respectively t1, t2, ... to t N Substitute into the A-phase zero-sequence voltage calculation waveform function of the distribution network in sequence to obtain N A-phase zero-sequence voltage calculation waveform discrete values; u 0B (t1),u 0B (t2), ... to u 0B (t N) are respectively the t1, t2, ... to t N Substitute into the B-phase zero-sequence voltage calculation waveform function of the distribution network in sequence to obtain N B-phase zero-sequence voltage calculation waveform discrete values; u 0C (t1),u 0C (t2), ... to u 0C (t N ) are respectively the t1, t2, ... to t N Substitute them into the C-phase zero-sequence voltage calculation waveform function of the distribution network in sequence to obtain N discrete values ​​of the C-phase zero-sequence voltage calculation waveform; u1(t1), u1(t2), ... to u1(t N ) are respectively the t1, t2, ... to t N Substituting into the actual waveform function of the zero-sequence voltage of the distribution network in turn, N actual waveform discrete values ​​of the zero-sequence voltage of the distribution network are obtained;

[0026] Step 5: Calculate the Euclidean distance between the calculated zero-sequence voltage waveforms of phase A, phase B and phase C of the distribution network and the actual zero-sequence voltage waveform of the distribution network according to the following formula (5):

[0027]

[0028] The Euclidean distance between the actual waveform of the zero-sequence voltage of the distribution network and the calculated waveform of the zero-sequence voltage of the three phases A, B, and C is converted into similarity by the following formula (6):

[0029]

[0030] Step 6: normalize the three similarities obtained in step 5, and select the phase corresponding to the largest similarity after normalization as the fault phase of the distribution network where the single-phase grounding fault with resistance occurs.

[0031] Beneficial effects of the invention: The invention proposes a fault phase locating method for a single-phase grounding fault with resistance in a distribution network, which overcomes the problem that the traditional phase selection method is easily affected by the asymmetry of system parameters and is difficult to tolerate high grounding resistance. The fault phase can be accurately selected in a very short time after the fault occurs, which buys time for fault arc extinguishing, effectively prevents the fault from further deteriorating, and better ensures the reliability and safety of users' electricity use. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a flow chart of a method for locating a fault phase of a distribution network having a single-phase grounding fault with resistance.

[0033] Figure 2 It is a calculation waveform diagram in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following is a further description of a fault phase location method for a single-phase grounding fault in a distribution network with resistance in conjunction with the accompanying drawings and specific embodiments of the present invention.

[0035] The fault phase location method of the distribution network in this embodiment has a single-phase grounding fault with resistance, such as Figure 1 As shown, the following steps are included:

[0036] Step 1: Monitor the zero-sequence voltage of the distribution network in real time, and define the time when the zero-sequence voltage waveform shows AC attenuation as the start time t of the suspected single-phase grounding fault. y , when t appears y When the zero-sequence voltage of the distribution network is y Then the zero-sequence voltage transient attenuation component is separated out; the zero-sequence voltage transient attenuation component includes the transient zero-sequence voltage AC attenuation component and the envelope of the transient zero-sequence voltage AC attenuation component;

[0037] In this embodiment, Figure 2 As shown, at 0.13s, the waveform of the zero-sequence voltage of the distribution network shows AC attenuation.

[0038] Step 2: From t y At the beginning, every power frequency cycle T of the distribution network f The attenuation coefficient δ in the envelope is collected once in real time, and a total of a times are collected and formed into an attenuation coefficient set A, as shown in the following formula (1):

[0039] A={δ1、δ2、...、δ a} (1)

[0040] In formula (1), δ1, δ2, ... to δ a They are the first attenuation coefficient, the second attenuation system to the ath attenuation coefficient collected in real time from the envelope;

[0041] In this embodiment, the power frequency T f It is 0.02s, and a total of 4 acquisitions were performed. The first attenuation coefficient δ1 is 6.991, the second attenuation coefficient δ2 is 6.994, the third attenuation coefficient δ3 is 6.992, and the fourth attenuation coefficient δ4 is 6.995;

[0042] Substitute the data in the attenuation coefficient set A into the following formula (2) to calculate the distribution network from t y After starting, each of the power frequency cycles T f The ground resistance inside

[0043] R Ei =1 / (2δ i C Σ -G Σ ),i=1,2,...,a (2)

[0044] In formula (2), R Ei is the distribution network from t y After starting, at a power frequency cycle T f The ith power frequency cycle T f Ground resistance inside; δ i is the i-th attenuation coefficient among a attenuation coefficients collected in real time from the envelope; C Σ and G Σ They are the total capacitance and conductance to ground of the distribution network respectively;

[0045] All calculated grounding resistances are compared with the resistance single-phase grounding fault judgment threshold in turn. If all calculated grounding resistances are less than the resistance single-phase grounding fault judgment threshold, it indicates that a permanent resistance single-phase grounding fault has occurred in the distribution network. At this time, the suspected resistance single-phase grounding fault start time t y Redefine it as the start time t0 of the single-phase grounding fault with resistance in the distribution network, and continue to execute the following step 3;

[0046] If all the calculated grounding resistances are greater than or equal to the resistance single-phase grounding fault judgment threshold, it indicates that no permanent resistance single-phase grounding fault occurs in the distribution network, and the process returns to step 1.

[0047] Substituting the four attenuation coefficients in this example into formula (2), four grounding resistances are calculated, which are 3003.4Ω, 3001.2Ω, 3002.6Ω, and 3004.7Ω respectively; the threshold for judging a single-phase grounding fault with resistance is 30kΩ; the four grounding resistances are all less than the threshold for judging a single-phase grounding fault with resistance, so it can be judged that a permanent single-phase grounding fault with resistance has occurred in the distribution network.

[0048] Step 3: Starting from t0, select a time period of T [t0, t0+T] as the time period for judging the single-phase grounding fault with resistance, and collect the attenuation coefficient δ of the envelope line at the end time t0+T of the time period for judging the single-phase grounding fault with resistance in real time T And put it into formula (2) to calculate the grounding resistance R of the distribution network within the judgment time of single-phase grounding fault with resistance ET ;

[0049] The time length T selected in this embodiment is 0.02s, so the grounding resistance R of the distribution network within the time length of the single-phase grounding fault judgment with resistance ET The value is 3003.4Ω

[0050] The following formula (3) is used to calculate the grounding resistance of phase A, phase B and phase C of the distribution network within the time of judging the single-phase grounding fault with resistance: R ETThe zero-sequence voltage calculation waveform function of a single-phase grounding fault is:

[0051]

[0052] In formula (3), t is the time in the judgment time of single-phase ground fault with resistance, t∈[t0,t0+T]; m=A,B,C represents the phase; u 0m (t) is the zero-sequence voltage calculation waveform function value of the mth phase at time t in the single-phase grounding fault judgment time with resistance after the grounding fault occurs in the distribution network; A m is the attenuation constant of a single-phase ground fault with resistance occurring in the mth phase of the distribution network; ω T is the AC attenuation angular frequency; B m is the attenuation constant of a single-phase ground fault with resistance occurring in the mth phase of the distribution network; u 0Em (t) is the zero-sequence voltage fundamental frequency calculation waveform function value of the mth phase at time t in the single-phase ground fault judgment time with resistance after the ground fault occurs in the distribution network; L is the inductance value of the arc suppression coil; G ET is the grounding conductivity of the distribution network within the judgment time of a single-phase grounding fault with resistance; i bd (t) is the natural unbalanced current of the distribution network at time t in the judgment time of a single-phase grounding fault with resistance; e m (t) is the power supply potential of the mth phase after the ground fault occurs in the distribution network, ω is the angular frequency of the power frequency in the distribution network, and u 01 (t) is the natural unbalanced voltage of the distribution network at time t in the judgment time of a single-phase grounding fault with resistance;

[0053] In this embodiment, the grounding resistance of phase A, phase B and phase C of the distribution network is calculated to be R within the single-phase grounding fault judgment time. ET The specific process of calculating the zero-sequence voltage waveform function of a single-phase grounding fault is as follows:

[0054] u 0A (t) = e -6.991(t-0.13) (-262.2 sin 336.8(t-0.13)-1427.8 cos 336.8(t-0.13))+579.2 sin(314.2t-1.4)

[0055] u 0B (t) = e -6.991(t-0.13) (-907.4 sin 336.8(t-0.13)+896.7c os 336.8(t-0.13))+1811.4s in(314.2t+1.8)

[0056] u 0C (t) = e -6.991(t-0.13)(1564.5 sin 336.8(t-0.13)+216.4 cos 336.8(t-0.13))+2144.8 sin(314.2t+0.5).

[0057] Real-time collection of distribution network grounding resistance R within the judgment time of single-phase grounding fault with resistance ET The actual waveform function u1(t) of the zero-sequence voltage of a single-phase grounding fault;

[0058] Step 4: Randomly select N different moments from the single-phase ground fault judgment duration with resistance, namely t1, t2, ... to t N , t1, t2, ... to t N All belong to [t0,t0+T];

[0059] Set t1, t2, ... to t N Substitute them into the zero-sequence voltage calculation waveform function of phase A, phase B and phase C of the distribution network in turn, and obtain N discrete values ​​of the zero-sequence voltage calculation waveform of phase A, the discrete values ​​of the zero-sequence voltage calculation waveform of phase B and the discrete values ​​of the zero-sequence voltage calculation waveform of phase C;

[0060] Set t1, t2, ... to t N Substitute them into the actual waveform function u1(t) of the zero-sequence voltage of the distribution network in turn to obtain N discrete values ​​of the actual waveform of the zero-sequence voltage of the distribution network;

[0061] Collect N discrete values ​​of the calculated waveform of the zero-sequence voltage of phase A, the calculated waveform of the zero-sequence voltage of phase B, the calculated waveform of the zero-sequence voltage of phase C, and the actual waveform discrete values ​​of the zero-sequence voltage of the distribution network to form the distribution network waveform judgment matrix C, as shown in the following formula (4):

[0062]

[0063] In formula (4), u 0A (t1),u 0A (t2), ... to u 0A (t N ) are t1, t2, ... to t N Substitute them into the A-phase zero-sequence voltage calculation waveform function of the distribution network in sequence to obtain N discrete values ​​of the A-phase zero-sequence voltage calculation waveform; u 0B (t1),u 0B (t2), ... to u 0B (t N ) are t1, t2, ... to t N Substitute them into the B-phase zero-sequence voltage calculation waveform function of the distribution network in sequence to obtain N discrete values ​​of the B-phase zero-sequence voltage calculation waveform; u 0C (t1),u 0C(t2), ... to u 0C (t N ) are t1, t2, ... to t N Substitute them into the C-phase zero-sequence voltage calculation waveform function of the distribution network in sequence, and obtain N discrete values ​​of the C-phase zero-sequence voltage calculation waveform; u1(t1), u1(t2), ... to u1(t N ) are t1, t2, ... to t N Substitute them into the actual waveform function of the zero-sequence voltage of the distribution network in turn to obtain N discrete values ​​of the actual waveform of the zero-sequence voltage of the distribution network;

[0064] Step 5: Calculate the Euclidean distance between the calculated zero-sequence voltage waveforms of phase A, phase B and phase C of the distribution network and the actual zero-sequence voltage waveform of the distribution network according to the following formula (5):

[0065]

[0066] The Euclidean distance between the actual waveform of the zero-sequence voltage of the distribution network and the calculated waveform of the zero-sequence voltage of the three phases A, B, and C is converted into similarity by the following formula (6):

[0067]

[0068] Step 6: Normalize the three similarities obtained in step 5, and select the phase corresponding to the largest similarity after normalization as the fault phase where the single-phase grounding fault with resistance occurs in the distribution network.

[0069] like Figure 2 As shown, in this embodiment, the portion of the waveform calculated in step 3 at 0.13 to 0.15 s is discretized, the sampling period is 0.08 ms, and the actual zero-sequence voltage in the same time period is collected according to the same sampling period. The actual zero-sequence voltage is substituted into equations (5) and (6) and the normalized similarity is calculated: 98.8%, 0.6%, 0.6%. It can be seen that a fault has occurred in phase A.

Claims

1. A method for locating a fault phase of a single-phase grounding fault in a distribution network, characterized by: The following steps are involved: Step 1: Monitor the zero-sequence voltage of the distribution network in real time, and define the time when the waveform of the zero-sequence voltage shows AC attenuation as the start time of the suspected single-phase grounding fault. , when the When the zero-sequence voltage of the distribution network is Then, the zero-sequence voltage transient attenuation component is separated out; the zero-sequence voltage transient attenuation component includes the transient zero-sequence voltage AC attenuation component and the envelope of the transient zero-sequence voltage AC attenuation component; Step 2: From the At the beginning, every other power frequency cycle of the distribution network The attenuation coefficient in the envelope is collected once in real time , a total of a times are collected and collected to form the attenuation coefficient set A, as shown in the following formula (1): （1） In formula (1), They are respectively the first attenuation coefficient, the second attenuation system to the ath attenuation coefficient collected in real time from the envelope; Substituting the data in the attenuation coefficient set A into the following formula (2) in turn, the distribution network is calculated from After starting, each cycle is a The ground resistance inside （2） In formula (2), The distribution network is from the After starting, at a power frequency cycle The ith power frequency cycle Ground resistance inside; is the i-th attenuation coefficient among a attenuation coefficients collected in real time from the envelope; and They are the total capacitance and conductance to ground of the distribution network respectively; All calculated grounding resistances are compared with the resistance single-phase grounding fault judgment threshold in turn. If all calculated grounding resistances are less than the resistance single-phase grounding fault judgment threshold, it indicates that a permanent resistance single-phase grounding fault has occurred in the distribution network. At this time, the start time of the suspected resistance single-phase grounding fault is Redefined as the start time of single-phase ground fault with resistance in distribution network , and continue to perform step 3 below; If all the calculated grounding resistances are greater than or equal to the resistance single-phase grounding fault judgment threshold, it indicates that no permanent resistance single-phase grounding fault occurs in the distribution network, and the process returns to step 1; Step 3: From the To begin, select a time period of length T The time for judging the single-phase grounding fault with resistance is collected in real time at the end time of the single-phase grounding fault with resistance judgment time. The attenuation coefficient And put it into formula (2) to calculate the grounding resistance of the distribution network within the resistance single-phase grounding fault judgment time: ; The following formula (3) is used to calculate the grounding resistance of phase A, phase B and phase C of the distribution network within the single-phase grounding fault judgment time: The zero-sequence voltage calculation waveform function of a single-phase grounding fault is: （3） In formula (3), t is the time in the single-phase grounding fault judgment time with resistance, ; Indicates phase; is the zero-sequence voltage calculation waveform function value of the mth phase at time t in the single-phase grounding fault judgment time with resistance after the grounding fault occurs in the distribution network; is the attenuation constant of the resistive single-phase grounding fault occurring in the mth phase of the distribution network; is the AC attenuation angular frequency; is the attenuation constant of the resistive single-phase grounding fault occurring in the mth phase of the distribution network; is the zero-sequence voltage fundamental frequency calculation waveform function value of the mth phase at time t in the single-phase grounding fault judgment time with resistance after the grounding fault occurs in the distribution network; L is the inductance of the arc suppression coil; is the grounding conductivity of the distribution network within the resistive single-phase grounding fault judgment time; is the natural unbalanced current of the distribution network at time t during the single-phase grounding fault judgment duration with resistance; is the power supply potential of the mth phase after a ground fault occurs in the distribution network, is the angular frequency of the power supply in the distribution network, is the natural unbalanced voltage of the distribution network at time t in the determination time of the single-phase grounding fault with resistance; The grounding resistance of the distribution network is collected in real time within the time period of the single-phase grounding fault judgment with resistance. The actual waveform function of the zero-sequence voltage of a single-phase ground fault ; Step 4: Randomly select N different moments from the single-phase ground fault judgment duration with resistance, which are , All belong to the ; The Substituting into the zero-sequence voltage calculation waveform function of phase A, phase B and phase C of the distribution network in turn, to obtain N discrete values ​​of the zero-sequence voltage calculation waveform of phase A, discrete values ​​of the zero-sequence voltage calculation waveform of phase B and discrete values ​​of the zero-sequence voltage calculation waveform of phase C; The Substitute the actual waveform function of the zero-sequence voltage of the distribution network into In the above equation, the actual waveform discrete values ​​of zero-sequence voltage of N distribution networks are obtained; The N A-phase zero-sequence voltage calculation waveform discrete values, B-phase zero-sequence voltage calculation waveform discrete values, C-phase zero-sequence voltage calculation waveform discrete values ​​and distribution network zero-sequence voltage actual waveform discrete values ​​are collected to form a distribution network waveform judgment matrix C, as shown in the following formula (4): （4） In formula (4), , ,…arrive They are respectively Substituting them into the A-phase zero-sequence voltage calculation waveform function of the distribution network in sequence, N discrete values ​​of the A-phase zero-sequence voltage calculation waveform are obtained; , ,…arrive They are respectively Substituting them into the B-phase zero-sequence voltage calculation waveform function of the distribution network in sequence, N B-phase zero-sequence voltage calculation waveform discrete values ​​are obtained; , ,…arrive They are respectively Substituting into the C-phase zero-sequence voltage calculation waveform function of the distribution network in sequence, N C-phase zero-sequence voltage calculation waveform discrete values ​​are obtained; , ,…arrive They are respectively Substituting into the actual waveform function of the zero-sequence voltage of the distribution network in turn, N actual waveform discrete values ​​of the zero-sequence voltage of the distribution network are obtained; Step 5: Calculate the Euclidean distances between the calculated zero-sequence voltage waveforms of phases A, B and C of the distribution network and the actual zero-sequence voltage waveforms of the distribution network according to the following formula (5): （5） The Euclidean distance between the actual waveform of the zero-sequence voltage of the distribution network and the calculated waveform of the zero-sequence voltage of the three phases A, B, and C is converted into similarity by the following formula (6): （6） Step 6: normalize the three similarities obtained in step 5, and select the phase corresponding to the largest similarity after normalization as the fault phase of the distribution network where the single-phase grounding fault with resistance occurs.

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