Substation single-phase earth fault line selection discrimination method based on phase current change characteristics

Abstract

The invention discloses a transformer substation single-phase earth fault line selection discrimination method based on phase current change characteristics. The method comprises the following steps: acquiring three-phase current instantaneous values of each feeder switch of a transformer substation before and after a fault occurs; respectively calculating a first characteristic value before a fault and a second characteristic value after the fault for each switch, wherein the characteristic value is the sum of absolute values of differences of instantaneous values of every two phases of current in the three-phase current of the switch; calculating the break variable of each switch, wherein the break variable is the absolute value of the difference between the first characteristic value and the second characteristic value; the feeder line where the switch with the maximum break variable is located is judged to be a fault feeder line; on the fault feeder line, traversing adjacent switches which are directly and electrically connected from upstream to downstream: when the ratio of the break variable of the upstream switch to the break variable of the downstream switch is greater than or equal to a threshold value K, judging that a fault point is located between the two switches; and when all adjacent switches do not meet the conditions, determining that the fault point is located at the downstream of the tail end of the feeder line.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system fault detection, and particularly relates to a substation single-phase grounding fault line selection and discrimination method based on phase current change characteristics. BACKGROUND

[0002] With the popularization of new energy technology and the wide application of power electronic equipment, modern power distribution systems are undergoing profound changes: on the one hand, the high proportion of distributed power sources (such as photovoltaic and wind power) has significantly improved the flexibility of the system, but also makes the topology of the power grid dynamic and variable; on the other hand, the use of a large number of power electronic converters (such as inverters and rectifiers) has realized efficient conversion of electric energy, but has injected rich harmonics and high-frequency noise into the system. Such changes, while promoting the intelligent upgrading of distribution networks, have also significantly increased the probability of single-phase grounding faults and caused the fault current to exhibit complex distortion characteristics (such as increased harmonic content and shortened transient process), posing new challenges to traditional fault identification techniques.

[0003] At present, the most widely used technology in the field of single-phase grounding fault line selection and discrimination is the analysis method based on transient zero-sequence current characteristics. The core logic of this method is that when a single-phase grounding fault occurs, the zero-sequence currents of the fault line and the non-fault line differ in amplitude, phase or frequency characteristics, and by extracting these characteristics, the fault line can be located. However, in new power distribution systems, the limitations of this method are gradually emerging: firstly, inherent problems such as system three-phase imbalance and asymmetric distribution of line parameters can increase the background noise of zero-sequence currents, making it difficult to extract features; secondly, the nonlinear characteristics of a large number of power electronic devices can further distort the zero-sequence current waveform, reducing the stability and distinguishability of transient characteristics; thirdly, in actual engineering, some substations do not have zero-sequence current transformers, or there are problems such as inconsistent transformer ratios and incorrect wiring, which directly lead to missing or abnormal zero-sequence current data, making this method completely ineffective in these scenarios.

[0004] To overcome the limitations of the zero-sequence current method, single-phase grounding fault line selection methods based on phase current change characteristics have gradually gained attention. This method analyzes the change characteristics of three-phase currents themselves (rather than zero-sequence currents) to achieve fault discrimination, avoiding the dependence on zero-sequence transformers, and requiring less synchronization of data collection from different phases or different monitoring points, effectively reducing the difficulty and cost of engineering implementation. However, existing phase current methods mostly focus on transient characteristic analysis (such as current mutation in the initial stage of the fault), and transient signals are easily disturbed by harmonics and noise, requiring high-frequency sampling equipment, resulting in a large amount of data processing and insufficient timeliness. In addition, how to extract effective features from three-phase current waveforms that can reflect the nature of the fault and exclude the interference of load fluctuations is still a key problem that hinders the further development of this technology. SUMMARY

[0005] In view of the defects and deficiencies of the prior art, the application provides a substation single-phase grounding fault line selection method based on phase current change characteristics, three-phase current steady-state values (non-transient mutation values) of each feeder switch before and after the fault are collected, the absolute value sum of the difference between each two-phase current is calculated as the characteristic value before and after the fault respectively; further, the mutation variable reflecting the fault influence is obtained through the absolute difference of the characteristic value; the fault feeder is quickly positioned based on the size difference of the mutation variable of each switch (the feeder where the switch with the largest mutation variable is located is the fault feeder); and the fault interval is accurately positioned through the ratio relationship of the mutation variables of adjacent switches on the fault feeder (the ratio of the upstream switch mutation variable to the downstream switch mutation variable reaches a preset threshold value), if all adjacent switches do not meet the condition, it is determined that the fault is located at the downstream of the feeder end.

[0006] Compared with the prior art, the innovative advantages of the application are as follows: first, the characteristic value is extracted based on the steady-state current characteristic, which avoids the problem that the transient signal is easily disturbed by harmonics and noise, and has low requirements for synchronous data collection; second, the mutation variable calculation eliminates the baseline influence of long-term three-phase imbalance of the system through the difference between the characteristic values before and after the fault, only the imbalance degree of the fault itself is retained, and the anti-interference ability is significantly improved; third, the method does not need to rely on the zero sequence current transformer, and solves the line selection failure problem caused by the absence of the transformer, inconsistent transformer ratio or wiring error; fourth, the method is suitable for various systems such as neutral point not grounded and grounded through arc suppression coil, and can be applied to new distribution network scenes containing distributed power access (by adjusting the threshold parameter to adapt to different system characteristics).

[0007] It solves the problems of zero sequence current dependence, transient interference and three-phase imbalance through the following innovative design:

[0008] 1. The "sum of absolute differences of three-phase current instantaneous values" is proposed as a characteristic variable to avoid the failure of the zero sequence transformer;

[0009] 2. The current value after the fault steady state is used to suppress transient harmonic interference;

[0010] 3. The baseline imbalance degree before the fault is deducted through the mutation variable ΔS to realize high-precision positioning in a high three-phase imbalance system;

[0011] 4. The "feeder-section" two-level positioning is created:

[0012] Line selection layer: the switch with the largest mutation variable locks the fault feeder;

[0013] Section selection layer: the ratio threshold (K=3) of the mutation variables of adjacent switches is used to determine the fault interval, and the measured ratio can reach 2216 times;

[0014] 5. The threshold value K is dynamically adjusted for the arc suppression coil system, and the fault line can still be accurately positioned in the high resistance grounding scene.

[0015] The application specifically adopts the following technical solutions:

[0016] A substation single-phase grounding fault line selection and discrimination method based on phase current change characteristics:

[0017] The three-phase current instantaneous values of each feeder switch of the substation before and after the fault occurrence are collected;

[0018] The first feature value before the fault and the second feature value after the fault are calculated for each switch, and the feature value is the sum of the absolute values of the difference between the two-phase current instantaneous values in the three-phase current of the switch;

[0019] The mutation value of each switch is calculated, and the mutation value is the absolute value of the difference between the first feature value and the second feature value;

[0020] The feeder where the switch with the largest mutation value is located is determined as the fault feeder;

[0021] On the fault feeder, the adjacent switches directly electrically connected are traversed in the order from upstream to downstream:

[0022] When the ratio of the mutation value of the upstream switch to the mutation value of the downstream switch is greater than or equal to the threshold value K, it is determined that the fault point is located between the two switches;

[0023] When all adjacent switches do not satisfy the above condition, it is determined that the fault point is located downstream of the end of the feeder.

[0024] Further, the threshold value K=3.

[0025] Further, in the mutation value calculation, the three-phase current instantaneous values after the fault are the current values after the fault enters the steady state.

[0026] Further, when the system is neutral point grounded through an arc suppression coil, the threshold value K is in the range of 2.0 to 8.0.

[0027] Further, the adjacent switches directly electrically connected are adjacent switches on the same feeder without branch connection.

[0028] Further, it is suitable for distribution network systems with distributed power supply access.

[0029] Further, the mutation value calculation suppresses the influence of long-term three-phase imbalance by deducting the baseline imbalance before the fault.

[0030] Further, a current collection module is used to collect the three-phase current instantaneous values of each feeder switch of the substation before and after the fault occurrence;

[0031] a feature value calculation module configured to calculate a first feature value before the fault and a second feature value after the fault for each switch, the feature value being the sum of absolute values of differences between instantaneous values of each two-phase current in the three-phase current of the switch;

[0032] a mutation value calculation module configured to calculate a mutation value of each switch, the mutation value being the absolute value of the difference between the first feature value and the second feature value;

[0033] a fault line selection module configured to determine the feeder in which the switch with the largest mutation value is located as the fault feeder;

[0034] a fault section selection module configured to traverse, in the fault feeder, adjacent switches directly electrically connected in an order from upstream to downstream:

[0035] when the ratio of the mutation value of the upstream switch to the mutation value of the downstream switch is greater than or equal to a threshold value K, determining that the fault point is located between the two switches;

[0036] when all adjacent switches do not satisfy the above condition, determining that the fault point is located downstream of the end of the feeder.

[0037] and a computer device comprising a processor and a memory, wherein the memory stores a computer program, and wherein when the program is executed by the processor, the steps of the method described above are implemented.

[0038] a non-transitory computer readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the steps of the method described above are implemented.

[0039] Compared with the prior art, the present application and the preferred solutions thereof at least have the following beneficial effects:

[0040] 1. Completely get rid of the dependence on zero sequence current:

[0041] By constructing a feature value through the sum of absolute differences of three-phase currents, without zero sequence transformer data, the line selection failure problem caused by the absence of zero sequence collection devices or abnormal transformers in old substations is fundamentally solved, and the universality of the method is significantly improved.

[0042] 2. Overall improvement of anti-interference ability:

[0043] Transient interference suppression: the feature value is calculated by using the fault steady-state current, which effectively avoids transient harmonic and noise interference and improves the reliability in the scene with a high proportion of power electronic equipment;

[0044] Long-term imbalance compatibility: the baseline imbalance before the fault is deducted through the mutation value calculation, which eliminates the influence of inherent asymmetry of the system and makes the method maintain stable accuracy in long-term three-phase imbalance systems.

[0045] 3. Breakthrough of fault location hierarchy:

[0046] Innovative "feeder-section" two-level positioning mechanism:

[0047] Based on the maximum switching variable, the fault feeder is quickly locked;

[0048] Through the adjacent switching variable ratio threshold (K=3), the fault section is accurately located, breaking the limitation of traditional methods that can only determine the fault direction.

[0049] 4. Self-adaptive optimization in complex scenarios:

[0050] In arc suppression coil grounding system, by dynamically adjusting the threshold range (K=2.0-8.0), the problem of weakening of fault characteristics after compensation is solved;

[0051] Compatible with new distribution network with distributed power supply access, overcoming harmonic pollution and power fluctuation disturbance caused by new energy grid connection.

[0052] 5. Reduced engineering implementation cost:

[0053] Low requirement for data collection synchronization, no need for strict alignment of multiple monitoring point clocks, reducing terminal equipment transformation cost and operation and maintenance difficulty. BRIEF DESCRIPTION OF DRAWINGS

[0054] The present application will be further described in detail below in combination with the drawings and specific embodiments:

[0055] Figure 1 The figure is a technical route diagram of the embodiment of the present application.

[0056] Figure 2 The figure is a current change characteristic diagram of line1 switch K1 before and after fault in the embodiment of the present application.

[0057] Figure 3 The figure is a phase current change characteristic diagram of line2 switch K2 before and after fault in the embodiment of the present application.

[0058] Figure 4 The figure is a phase current change characteristic diagram of line3 switch K3 before and after fault in the embodiment of the present application.

[0059] Figure 5 The figure is a neutral point through arc suppression coil grounding system diagram in the embodiment of the present application. DETAILED DESCRIPTION

[0060] In the following, specific embodiments of the present application will be described in detail with reference to the accompanying drawings, according to which those skilled in the art can clearly understand the present application and can implement the present application. The features in various different embodiments can be combined to obtain new implementations, or to replace certain features in certain embodiments to obtain other preferred implementations, without departing from the principles of the present application.

[0061] In order to make the features and advantages of the present application more obvious and easy to understand, specific examples are given below, and are described in detail as follows with reference to the accompanying drawings:

[0062] The embodiment of the present application proposes a new method for substation single-phase grounding fault line selection and discrimination based on phase current change characteristics, which is based on the steady-state characteristics of three-phase current. The method is divided into fault line selection stage and fault section selection stage. First, the three-phase current values of each switch of each feeder of the substation are collected. Then, the phase current change characteristic value of each switch before and after the fault is calculated, which is equal to the sum of the absolute difference between the two-phase current of each switch. Next, the absolute value of the difference between the phase current change characteristic value of each switch before and after the fault is taken, which is defined as the mutation variable of the phase current change characteristic value. Finally, the fault is judged, in the fault line selection stage, the mutation variables of the phase current change characteristic values of each switch are compared, and the feeder where the switch with the largest mutation variable is located is the fault feeder. In the fault section selection stage, each switch of the fault feeder is traversed from upstream to downstream, and in two adjacent switches, the mutation variable of the phase current change characteristic value of the upstream switch is divided by the mutation variable of the phase current change characteristic value of the downstream switch. If the result is greater than the threshold value (empirical value 3), the fault is between the two switches; if all the switches of the fault feeder do not satisfy this condition, it is judged that the fault is located downstream of the terminal switch of the fault feeder.

[0063] It is based on the analysis of the steady-state characteristics of three-phase current, and the technical route is as shown in Figure 1

[0064] First, the feeder current data is obtained by using the substation terminal data acquisition system, mainly the cross-section value I a ’ , I b ’ , I c ’ before the fault for a period of time, and the actual value of the phase current I a , I b , I c after the fault.

[0065] The current change characteristic value △i ’ before the fault is defined as:

[0066] (1)​

[0067] The current change characteristic value Δi after the fault is:

[0068] (2)

[0069] The mutation value ΔI of the phase current change characteristic before and after the fault is defined as:

[0070] (3)

[0071] The mutation value ΔI represents the change in unbalance degree caused by the fault, and the larger ΔI is, the greater the impact of the fault on the measurement point.

[0072] The principle of judging single-phase ground fault according to ΔI is as follows: in single-phase ground fault, the phase current of the line upstream of the fault point will superimpose zero sequence component, resulting in significant increase of the current change characteristic upstream of the fault point. Taking single-phase ground fault of phase C as an example, due to the low impedance path formed by the fault phase to the ground, the phase current of the fault phase superimposes zero sequence component, and the phase current increases; while the phase current values of non-fault phases (i.e. phases A and B) are still mainly determined by the load current, and change little. Therefore, the last two terms of the current change characteristic value Δi = |I a -I b |+|I a -I c |+|I c -I b | will significantly increase, resulting in larger Δi. Therefore, for the fault line, the switch ΔI value is significantly larger than that of the non-fault line, which can be used as the basis for fault line selection.

[0073] After completing fault line selection, the next stage is fault section selection. If it is determined that the fault feeder is line1, all switches (denoted as K i , K i1 , K i2 , …, K in ) of line1 are traversed from upstream to downstream, and the ΔI of adjacent switches is compared: let the mutation value of the upstream switch be ΔI 上游 , and the mutation value of the downstream switch be ΔI 下游 , the proposed section selection rule is as follows:

[0074] (4)

[0075] (5)

[0076] If none of the switches of the fault feeder satisfies formula (4) after traversing all the switches, it is determined that the fault point is located at the end of the feeder, and the feeder end switch is the upper boundary of the fault interval.

[0077] The principle of this fault section is as follows: the upstream and downstream switches of the feeder fault point have different fault current sizes, the fault current flows through all the upstream switches at the upstream of the fault point, resulting in a large increase in the △I of the switch; at the downstream of the fault point, the fault current is "cut off" by the short-circuit point, and the current of the downstream switch is mainly determined by the load, and the change of the △I is small. This difference provides a basis for locating the fault section. Taking the feeder line1 as an example, assuming that the fault point is located between switches K 11 and K 12 : the upstream switches K1, K 11 flow through the fault current, and the △I value is large; the fault current of the downstream switch K 12 is isolated by the short-circuit point, and the △I value is much smaller. Therefore, if the upstream switch △I≥threshold value*downstream switch △I, the fault is located between the two; if all the switch △I does not satisfy this condition, the fault is located downstream of the terminal switch.

[0078] The innovation of the scheme in this embodiment mainly lies in:

[0079] (1) Strong universality, applicable to single-phase grounding fault scenarios of various grounding systems, such as 1) neutral point ungrounded system: the sum of the sudden changes of the three-phase current differences is large, and it is easy to distinguish the fault line from the non-fault line. 2) neutral point grounded through arc suppression coil system: although the distribution of the zero sequence current becomes complex after compensation through the arc suppression coil, the sudden change of the sum of the three-phase current differences of the fault line is still obvious.

[0080] (2) Strong anti-interference, the method can eliminate the influence of synchronous load changes and suppress the influence of long-term three-phase imbalance. 1) Eliminate synchronous load changes: when the system is normally running, △i depends on the load fluctuation, but the synchronous increase and decrease of the three-phase current caused by the load fluctuation has little effect on △i. Single-phase grounding fault selectively amplifies the current of one phase, resulting in a large increase in △i. By calculating the difference between △i before and after the fault, the fault and the load fluctuation can be effectively distinguished. 2) Suppress three-phase imbalance: if there is a long-term three-phase imbalance in the system, i a ’ ≠I b ’ ≠I c ’ , the sum of the phase current differences △i ’ =|I a ’ -I b ’ |+|I a ’ -I c ’ |+|I c ’ -I b ’| is the sum of the phase current difference △i after the fault, and is called the baseline unbalance degree. The unbalance degree of the long-term three-phase unbalance is included in the baseline unbalance degree, and △i = |I a -I b | is the sum of the phase current difference △i after the fault, and is called the baseline unbalance degree. The unbalance degree of the long-term three-phase unbalance is included in the baseline unbalance degree, and △i = |I a -I c | is the sum of the phase current difference △i after the fault, and is called the baseline unbalance degree. The unbalance degree of the long-term three-phase unbalance is included in the baseline unbalance degree, and △i = |I c -I b | is the sum of the phase current difference △i after the fault, and is called the baseline unbalance degree. The unbalance degree of the long-term three-phase unbalance is included in the baseline unbalance degree, and △i = |I ’ - △i | deducts the influence of the baseline unbalance degree and only retains the unbalance degree caused by the fault itself, so the new phase current method can be applied to fault positioning under long-term three-phase unbalance.

[0081] A specific implementation case is provided below to further demonstrate and introduce the scheme of the application:

[0082] It is assumed that the substation structure is a three-feeder structure, each feeder includes a first-end feeder switch K i , two feeder subordinate switches K i1 and K i2 , and there are a total of 9 switches, as shown in Figure 5 . The three-phase power supply parameters are as follows: power supply frequency 50HZ, line voltage 10kv, and Y-type ungrounded connection mode is adopted. Three-phase symmetrical loads are arranged at the ends of the three feeders, and the active power is P=10kW and the reactive power is Q L =Q C =100var. The three-phase current values measured by each feeder switch are input into the selected section and line selection measurement module for processing.

[0083] The line parameter settings simulate overhead lines, and the positive sequence, zero sequence resistance, capacitance and inductance per unit length are set as shown in Table 1.

[0084] Table 1 Line parameter settings

[0085] Line type Phase sequence Resistance Ω / km Inductance H / km Capacitance F / km Feeder length km Overhead line Positive sequence 0.01273 0.9337e-3 12.74e-9 40、40 Zero sequence 0.3864 4.1264e-3 7.751e-9 40

[0086] In the simulation process, first, a single-phase ground fault occurs in the first-end switch K1 of line1: the fault phase is set to A phase to ground, Rg=0.001Ω to simulate a metallic full ground, the fault time is set to 0.5s to 1s, and the simulation duration is 1s. The three-phase currents I a ’ , I b ’ , I c ’ , I a , I b , I c, taking the switch K1 of line 1 as an example, its current change characteristic value can be calculated according to formulas (1) and (2), as follows: Figure 2 shown.

[0087] After the fault occurs, phase A is disturbed the most and the peak value of phase current changes the most. The phase voltage of the non-fault phases B and C increases to the line voltage. Although the phase currents of the two increase, the values ​​remain close. Therefore, after the fault The sum of the first two differences in |I increases. c -I b |Still keep the value small. Combined Figure 2 Before the fault, the current change characteristic value of the feeder switch K1 is very small, and the amplitude is stable at around 5A, while the current change characteristic value after the fault is around 25A (ignoring the transient mutation after the fault occurs), and the amplitude mutation before and after the fault can reach 20A.

[0088] In addition, the phase current variation characteristic values ​​of switches K2 and K3 of line2 and line3 are analyzed, such as Figure 3 and Figure 4 As shown in the figure, the current variation characteristic values ​​of K2 and K3 are almost unchanged before and after the fault. Therefore, the sudden change in the sum of the phase current differences of each feeder switch before and after the fault is calculated and sorted from largest to smallest. The feeder with the switch ranked first is the fault feeder, thus verifying the line selection logic of the new phase current method.

[0089] Next, we verify the fault segment selection logic of the proposed method. Figure 1 It can be seen that the K1 feeder switch is located upstream of the fault point, K 11 , K 12 Located downstream of the fault point. Since the fault component is "cut off" by the fault point and will not flow downstream of the fault point, the phase current value of the switch downstream of the fault point is less affected by the fault, so K 11 With K 12 The mutation amount is close to zero before and after the fault. According to formula (4) and (5), it can be used to realize fault segment selection. For the two adjacent switches upstream and downstream of the fault point, the mutation amount of the upstream switch should be significantly greater than that of the downstream switch. According to formula (4), the mutation amount of the current change characteristics of the two adjacent switches is divided, △I 上游 / △I 下游 The resulting threshold should be significantly greater than 1. If the threshold is assumed to be 3, once the difference between the mutation values ​​of two adjacent switches is greater than 3, the fault is determined to be located on the line between the two switches, completing the fault section selection. If the difference between the mutation values ​​of two adjacent switches is near 1, this indicates that the mutation values ​​of the two switches are similar, meaning they are both upstream of the fault point and have large mutation values; or that they are both downstream of the fault point and have mutation values ​​approaching zero.

[0090] But when all the fault feeder switches are traversed, none of the two adjacent feeder switches has a mutation value greater than 3, that is, the fault interval is located at the end of the fault feeder. The end line switch is the upper boundary of the fault interval. In this case, all the switches of the fault feeder are located upstream of the fault point, and the mutation values of the current before and after the fault are both a larger value.

[0091] Table 2 lists the mutation values of the current variation characteristics of each switch after a single-phase ground fault of Figure 1 . It can be seen that the mutation value of the fault feeder switch K1 is the largest, so the fault feeder can be determined to be line1 according to the line selection principle; and then according to the section selection principle, the multiple relationship of the adjacent switch mutation values of line1 is compared, and it is found that the ratio of K1 to K 12 is much greater than 3, so the fault is between K1 and K 12 according to the section selection principle.

[0092] Table 2 K1 and K 12 mutation values of phase current variation characteristics of single-phase ground fault in section

[0093] Row Feeder switch K i ]]> Subordinate line switch K i1 ]]> Subordinate line switch K i2 <!-- 6 -->]]> Feeder 1 13.75107924 0.006204676 0.00553652 Feeder 2 0.008927743 0.006032198 0.004386376 Feeder 3 0.008927743 0.006032198 0.004386376

[0094] The final determination result of single-phase ground fault in K1 and K 12 section is as follows:

[0095] The branch with the largest change in phase current difference value: branch 1, change amount: 13.7511 A

[0096] Comparison of actual values of phase current variation of each branch head (arranged in descending order according to numerical value):

[0097] Branch Delta(A) 1 13.7511 2 0.0089 3 0.0089

[0101] Fault location analysis:

[0102] Branch 1 fault is located at the head K1 section (d1_1=2216.24).

[0103] In addition, if a single-phase ground fault is set downstream of the feeder line2 end switch K 22 , the mutation values of the current variation characteristics of each switch are shown in Table 3. The fault feeder switch K 22The maximum mutation quantity is line2, so according to the selected line principle, the fault feeder is line2; at the same time, according to the selected section principle, the multiple relationship of the adjacent switch mutation quantities of line2 is found to be around 1, which does not reach the set threshold value 3, and the mutation quantities of the three switches are all much larger than 0, so according to the selected section principle, it can be judged that the three switches of line2 are located upstream of the fault point, and the fault occurs at the line end of line2.

[0104] Table 3 K 22 The mutation quantity of the phase current change characteristics of the downstream single-phase ground fault

[0105] Row Feeder switch K i ]]> Subordinate line switch K i1 ]]> Subordinate line switch K i2 ]]> Feeder 1 0.006739199 0.004204135 0.003267691 Feeder 2 13.85363389 13.95737289 13.97939558 Feeder 3 0.006739199 0.004204135 0.003267691

[0106] The final K 22 The single-phase ground fault discrimination result of the section is as follows:

[0107] The branch with the largest phase current difference change value is branch 2, and the change value is 13.8536 A

[0108] Comparison of actual values of phase current change quantities of each branch (arranged in descending order according to numerical value):

[0109] Branch Delta(A) 2 13.8536 1 0.0067 3 0.0067

[0113] Fault location analysis:

[0114] The fault of branch 2 is located at the end k22 section (d2_1 = 0.99, d2_2 = 1.00).

[0115] In order to offset the ground capacitance current flowing through the fault point after the single-phase ground fault occurs, an arc suppression coil can be inserted into the neutral point of the distribution network for compensation, so that the arc cannot be maintained and self-extinguishes. However, after the system is compensated by the arc suppression coil, the steady-state component amplitude characteristics of the single-phase ground fault are not obvious, and the fault line and non-fault line cannot be distinguished according to the phase difference of the zero sequence current, which makes the detection effect of the traditional steady-state detection method not ideal. Therefore, the following analyzes the judgment effect of the embodiment scheme in the neutral point grounded by the arc suppression coil. The model built and the related parameter settings are as follows, in which there are three cable outgoing lines, and three switch sections are set for each feeder, and the line length of each switch section is 5km. The compensation mode of the arc suppression coil in this model is over-compensation, and the compensation degree is 10%, and the inductance L of the arc suppression coil is 0.244H.

[0116] Table 5 Cable line parameter settings

[0117] Line type Phase sequence Resistance Ω / km Inductance H / km Capacitance F / km Feeder length km Cable line Positive sequence 0.2700 0.2550e-3 339e-9 15、15 Zero sequence 2.700 1.0490e-3 280e-9 15

[0118] Suppose a single-phase ground fault occurs between K2 and K 21 The phase current variation characteristic values and the mutation values of each switch before and after the fault are shown in Table 5, and the switches are arranged in order according to the mutation values from large to small:

[0119] Table 5: Sum of phase current difference values and mutation values of single-phase ground fault of K2 section

[0120] Row Phase current variation eigenvalue Phase current variation eigenvalue Sudden change variable K2 46.42420779 67.51918886 21.09498107 K22 15.72086601 15.64226576 0.07860025 K21 31.03622866 30.96284115 0.073387513 K12 15.72088722 15.65231495 0.068572273 K32 15.72088722 15.65231495 0.068572273 K3 46.42174709 46.36708355 0.054663536 K1 46.42174709 46.36708355 0.054663536 K11 31.03627057 30.99675034 0.039520224 K31 31.03627057 30.99675034 0.039520224

[0121] According to the above mutation value data, the switch with the maximum mutation value is K2, it can be determined that the fault feeder is line2, and the mutation value of the K2 switch is 287.45 times the mutation value of the K 21 switch, which is much larger than the set threshold of 3 times, and the fault characteristics are obvious, and according to the selected section, it can be determined that the fault interval is between K2 and K 21 .

[0122] Based on the same inventive concept, the application further provides a computer device, which comprises one or more processors and a memory for storing one or more computer programs; the program comprises program instructions, and the processor is configured to execute the program instructions stored in the memory. The processor can be a central processing unit (CPU), and can also be other general-purpose processors, digital signal processors (DSP), application specific integrated circuits (ASIC), field programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., which are the computing core and control core of the terminal, and are configured to implement one or more instructions, and are specifically configured to load and execute one or more instructions in the computer storage medium to implement the above method.

[0123] It should be further explained that based on the same inventive concept, the present application also provides a computer storage medium, which stores a computer program, and the computer program is executed by a processor to perform the above method. The storage medium can adopt any combination of one or more computer readable media. The computer readable medium can be a computer readable signal medium or a computer readable storage medium. The computer readable storage medium may, for example, but is not limited to, an electrical, magnetic, optical, infrared, or semiconductor system, device or apparatus, or any combination of the above. More specific examples (non-exhaustive list) of the computer readable storage medium include: electrical connections having one or more wires, portable computer disks, hard drives, random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM or flash memory), optical fibers, portable compact disk read-only memories (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the above. In the present application, the computer readable storage medium can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, device or apparatus.

[0124] In the description of the present application, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0125] The above shows and describes the basic principles, main features and advantages of the present disclosure. Those skilled in the art should understand that the present disclosure is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present disclosure. Without departing from the spirit and scope of the present disclosure, various changes and improvements can be made to the present disclosure, and these changes and improvements all fall within the scope of the claimed present disclosure.

[0126] The present application is not limited to the above best mode, and anyone can derive other various forms of a substation single-phase grounding fault line selection method based on phase current change characteristics under the inspiration of the present application. Any equivalent changes and modifications made within the scope of the present application application patent range shall fall within the scope of the present application.

Claims

1. A method for identifying single-phase ground fault line in a substation based on phase current variation characteristics, characterized by: Collect the instantaneous three-phase current values ​​of each feeder switch in the substation before and after a fault occurs; Calculate a first characteristic value before a fault and a second characteristic value after a fault for each switch, wherein the characteristic value is the sum of the absolute values ​​of the difference between the instantaneous values ​​of each two phase currents in the three-phase current of the switch; Calculating a mutation amount of each switch, where the mutation amount is the absolute value of the difference between the first eigenvalue and the second eigenvalue; The feeder where the switch with the largest mutation amount is located is determined to be the faulty feeder; On the faulted feeder, traverse the directly electrically connected adjacent switches from upstream to downstream: When the ratio of the mutation amount of the upstream switch to the mutation amount of the downstream switch is greater than or equal to the threshold K, it is determined that the fault point is located between the two switches; When all adjacent switches do not meet the above conditions, it is determined that the fault point is located downstream of the feeder end.

2. A method for identifying a single-phase ground fault line in a substation based on phase current variation characteristics according to claim 1, characterized in that: The threshold K=3.

3. The method for determining the line selection of a single-phase grounding fault in a substation based on phase current variation characteristics according to claim 1, characterized in that: In the calculation of the sudden change amount, the instantaneous value of the three-phase current after the fault is the current value after the fault enters the steady state.

4. The method for determining the line selection of a single-phase grounding fault in a substation based on phase current variation characteristics according to claim 1, characterized in that: When the neutral point of the system is grounded via an arc suppression coil, the threshold value K ranges from 2.0 to 8.

0.

5. The method for determining line selection for a single-phase grounding fault in a substation based on phase current variation characteristics according to claim 1, characterized in that: The directly electrically connected adjacent switches are adjacent switches on the same feeder without branch connection.

6. The method for determining line selection for a single-phase grounding fault in a substation based on phase current variation characteristics according to claim 1, characterized in that: Applicable to distribution network systems with distributed power access.

7. The method for identifying a single-phase ground fault line in a substation based on phase current variation characteristics according to claim 1, characterized in that: The sudden change calculation suppresses the influence of long-term three-phase imbalance by deducting the baseline imbalance before the fault.

8. The method for determining line selection for a single-phase grounding fault in a substation based on phase current variation characteristics according to claim 1, characterized in that: The current acquisition module is used to collect the instantaneous three-phase current values ​​of each feeder switch in the substation before and after a fault occurs; A characteristic value calculation module is used to calculate a first characteristic value before a fault and a second characteristic value after a fault for each switch, wherein the characteristic value is the sum of the absolute values ​​of the difference between the instantaneous values ​​of each two phase currents in the three-phase current of the switch; A mutation amount calculation module, used to calculate the mutation amount of each switch, where the mutation amount is the absolute value of the difference between the first eigenvalue and the second eigenvalue; A fault line selection module is used to determine the feeder where the switch with the largest mutation amount is located as the fault feeder; The fault section selection module is used to traverse the adjacent switches that are directly electrically connected on the fault feeder in order from upstream to downstream: When the ratio of the mutation amount of the upstream switch to the mutation amount of the downstream switch is greater than or equal to the threshold K, it is determined that the fault point is located between the two switches; When all adjacent switches do not meet the above conditions, it is determined that the fault point is located downstream of the feeder end.

9. A computer device comprising a processor and a memory, wherein the memory stores a computer program, wherein: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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