Single-phase earth fault judgment method based on three-phase current change characteristics

Abstract

A single-phase earth fault judgment method based on three-phase current change characteristics uses a phase current signal as a signal easy to collect, and the phase current signal contains rich fault information after a fault occurs. Meanwhile, the phase current transformer is widely installed in a power distribution network line. The phase current is used as a judgment signal, so that the condition that the applicability of the fault line selection system is influenced due to lack of a zero-sequence current signal acquisition device in the system can be avoided. Moreover, the phase current amplitude variance is adopted as a criterion, the dependence of the algorithm on communication can be reduced, and the method can still finish fault line selection on site under the condition that communication signals are poor or communication is lacked.

Description

Technical Field

[0001] The present invention belongs to the technical field of single-phase grounding fault judgment, and in particular relates to a single-phase grounding fault judgment method based on three-phase current variation characteristics. Background Art

[0002] The distribution network, typically a power grid with a voltage level below 110 kV, is responsible for directly supplying electricity to consumers within the power system. The reliability of the distribution network's power supply directly impacts the safety and affordability of electricity use. Statistics show that over 95% of power outages experienced by consumers are caused by issues within the distribution system, and approximately half of all power system losses occur within the distribution network.

[0003] There are two types of faults in distribution networks: short circuits, including two-phase short circuits, two-phase ground faults, and three-phase short circuits; and single-phase ground faults. The probability of a single-phase ground fault occurring in a distribution network is much higher than that of a short circuit, so identifying single-phase ground faults is essential.

[0004] Currently, single-phase grounding faults are judged by the FTU using the single-phase grounding fault line selection algorithm with zero-sequence voltage or current as the judgment signal. However, due to the lack of zero-sequence voltage or zero-sequence current transformers in some areas of the existing distribution network, the line switches cannot use zero-sequence voltage or current as the judgment signal, resulting in the single-phase grounding fault line selection algorithm not working properly. The line switches in some areas use the phase current physical synthesis method to obtain zero-sequence voltage or zero-sequence current, which is too low in accuracy to meet the judgment of the single-phase grounding fault line selection algorithm. In addition, after compensation by the arc suppression coil grounding system, the zero-sequence current of the fault section is reduced and is difficult to exceed the fixed value, and the zero-sequence current is small under high-resistance grounding faults, which will cause the problem of low accuracy in single-phase grounding fault judgment.

[0005] Currently, field personnel still mostly determine the faulty section by testing the circuit. This involves first disconnecting the outgoing circuit breaker of the faulty line within the substation, then disconnecting the sectionalizer in the middle of the line, and finally reclosing the outgoing circuit breaker of the substation. If no fault occurs, the fault is located behind the sectionalizer, and so on. Each opening and closing of the switch impacts the power grid, easily generating operational overvoltage and resonant overvoltage. Frequent switching operations also shorten the service life of the switch. For unmanned substations, remote control is required via communication. However, because remote communication equipment cannot guarantee the complete accuracy of transmitted signals, this can cause switchgear to fail to operate or malfunction, further increasing the burden on power-consuming equipment. Summary of the Invention

[0006] To address the shortcomings of the existing technology, the present invention aims to provide a single-phase ground fault detection method based on the characteristics of three-phase current variations. Using phase current as the detection signal can avoid the problem of the system's lack of zero-sequence current signal acquisition devices affecting the applicability of the fault line selection system. Furthermore, using phase current amplitude variance as the criterion reduces the algorithm's dependence on communication. Even in the presence of poor or absent communication signals, this method can still complete the fault line selection locally.

[0007] The present invention adopts the following technical solutions.

[0008] A single-phase ground fault judgment method based on three-phase current variation characteristics includes:

[0009] The distribution switch monitoring terminal FTU obtains the fault component amplitude variance information of the three-phase current of the pole switch transmitted by the current transformer through calculation to analyze whether the fault point is upstream or downstream of the pole switch as the detection point.

[0010] Preferably, the fault component amplitude variance information of the three-phase current of the pole-mounted switch obtained by calculating the three-phase current includes:

[0011] The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component upstream of the fault point Var K When , it is obtained according to the following formula:

[0012]

[0013] The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component of the normal line and the line downstream of the fault point Var i When , it is obtained according to the following formula:

[0014] Var i ≈0

[0015] Among them, J is the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point. The fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and zero-sequence current from the three-phase current of the pole-mounted switch. The fundamental amplitude of the positive and negative zero-sequence components of the fault is obtained after the residual current is transformed by Fourier transform.

[0016] Preferably, the fault analysis point is located upstream or downstream of the pole switch serving as the detection point, including:

[0017] Set the threshold Var0 and compare the relationship between the fault component amplitude variance information of each phase current of the pole-mounted switch and the threshold Var0:

[0018] When the amplitude variance information of the fault component of each phase current of the pole switch is greater than the threshold Var0, it is the upstream line of the fault point; when the amplitude variance information of the fault component of each phase current of the pole switch is not greater than the threshold Var0, it is a normal line or the downstream line of the fault point.

[0019] Preferably, the threshold K rel is the reliability coefficient, which is 0.85, and I0 is the fundamental amplitude of the zero-sequence current of the line after the fault occurs.

[0020] A single-phase grounding fault judgment device based on three-phase current variation characteristics of the method includes:

[0021] A calculation module is used to analyze whether the fault point is located upstream or downstream of the pole switch as a detection point by obtaining the fault component amplitude variance information of the three-phase current of the pole switch through calculation based on the three-phase current.

[0022] Preferably, the calculation module is also used for the fault component amplitude variance information of the three-phase current of the pole-mounted switch, which is the variance Var of the fundamental amplitude of the fault component upstream of the fault point. K When , it is obtained according to the following formula:

[0023]

[0024] The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component of the normal line and the line downstream of the fault point Var i When , it is obtained according to the following formula:

[0025] Var i ≈0

[0026] Among them, J is the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point. The fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and zero-sequence current from the three-phase current of the pole-mounted switch. The fundamental amplitude of the positive and negative zero-sequence components of the fault is obtained after the residual current is transformed by Fourier transform.

[0027] Preferably, the operation module is further configured to set a threshold value Var0, and compare the relationship between the fault component amplitude variance information of each phase current of the pole-mounted switch and the threshold value Var0:

[0028] When the amplitude variance information of the fault component of each phase current of the pole switch is greater than the threshold Var0, it is the upstream line of the fault point; when the amplitude variance information of the fault component of each phase current of the pole switch is not greater than the threshold Var0, it is a normal line or the downstream line of the fault point.

[0029] Preferably, the threshold K rel is the reliability coefficient, which is 0.85. I0 is the fundamental amplitude of the zero-sequence current of the line itself after the fault occurs. The fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and zero-sequence current from the three-phase current of the pole switch. The fundamental amplitude of the positive and negative zero-sequence components of the fault is obtained after the residual current is transformed by Fourier transform.

[0030] A terminal includes a processor and a storage medium;

[0031] The storage medium is used to store instructions;

[0032] The processor is configured to operate according to the instruction to execute the steps of the method for determining a single-phase grounding fault based on three-phase current change characteristics.

[0033] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the single-phase grounding fault judgment method based on three-phase current change characteristics.

[0034] The beneficial effect of the present invention is that, compared with the prior art, the phase current signal used in the present invention is an easily collected signal that contains rich fault information after a fault occurs. At the same time, phase current transformers are widely installed in distribution network lines. Using phase current as a judgment signal can avoid the situation where the applicability of the fault line selection system is affected by the lack of a zero-sequence current signal acquisition device in the system. In addition, using the phase current amplitude variance as a judgment criterion can reduce the algorithm's dependence on communication. In the case of poor communication signals or lack of communication, the method can still complete the fault line selection on site. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a flow chart of the single-phase grounding fault judgment method based on three-phase current change characteristics described in the present invention;

[0036] Figure 2 This is the structural diagram of the neutral point grounding system through the arc suppression coil;

[0037] Figure 3 It is the equivalent diagram of single-phase ground fault;

[0038] Figure 4 It is the zero-sequence circuit equivalent diagram;

[0039] Figure 5 This is a schematic diagram of the neutral point grounding system model through the arc suppression coil;

[0040] Figure 6 This is the current waveform upstream of the fault point under the neutral point arc suppression coil grounding system model with the grounding resistance set to 0Ω;

[0041] Figure 7This is the current waveform downstream of the fault point under the neutral point arc suppression coil grounding system model with the grounding resistance set to 0Ω;

[0042] Figure 8 This is the normal line current waveform under the neutral point arc suppression coil grounding system model with the grounding resistance set to 0Ω;

[0043] Figure 9 This is the current waveform upstream of the fault point under the neutral point grounded through arc suppression coil system model with the grounding resistance set to 2000Ω;

[0044] Figure 10 This is the current waveform downstream of the fault point under the condition of the neutral point grounded through the arc suppression coil system model with the grounding resistance set to 2000Ω;

[0045] Figure 11 This is a normal line current waveform diagram under the condition of the neutral point arc suppression coil grounding system model with the grounding resistance set to 2000Ω;

[0046] Figure 12 This is a schematic diagram of the neutral point ungrounded system model;

[0047] Figure 13 This is the current waveform upstream of the fault point under the neutral point ungrounded system model with the grounding resistance set to 0Ω;

[0048] Figure 14 This is the current waveform downstream of the fault point under the neutral point ungrounded system model with the grounding resistance set to 0Ω;

[0049] Figure 15 This is the normal line current waveform under the neutral point ungrounded system model with the grounding resistance set to 0Ω;

[0050] Figure 16 This is the current waveform upstream of the fault point under the condition of the neutral point ungrounded system model with the grounding resistance set to 2000Ω;

[0051] Figure 17 This is the current waveform downstream of the fault point under the condition of the neutral point ungrounded system model with the grounding resistance set to 2000Ω;

[0052] Figure 18 This is a normal line current waveform diagram under the condition of a neutral point ungrounded system model with the grounding resistance set to 2000Ω. DETAILED DESCRIPTION

[0053] Currently, most methods for locating single-phase grounding fault sections in distribution networks, both domestically and internationally, use installed FTUs to collect line information and employ corresponding algorithms or voltage-time switchgear to locate the fault section. Proposed methods for locating distribution network fault sections fall into two main categories: local judgment and control, and centralized information control. Local judgment and control refers to a technique that can locate the fault section independently of a dispatching center (master station) and with little or no reliance on communication systems. Centralized information control involves uploading fault and switch information from an information collection device to a master station. The dispatching center then processes the information, locates the fault section, and issues remote control commands to disconnect the switches at both ends of the faulty feeder.

[0054] Local judgment control does not require a master station and is relatively independent. This type of section location technology has low communication requirements and can meet the needs of faulty section location in weak or no communication conditions. Currently, the most widely used local judgment control section location methods are voltage-time switchgear control and FTU-based local judgment devices. The voltage-time switch control method relies on the coordination of voltage-time switches in the line to locate and isolate the faulty section. No communication is required; the voltage-time switches automatically operate according to a predetermined opening and closing sequence. To ensure the ability to handle multiple faults, each switch is locked or automatically reset after operation. However, this method requires frequent opening and closing operations of the switchgear, resulting in high switching losses. Furthermore, frequent opening and closing may cause operational overvoltages or resonant overvoltages, which can damage line equipment and cause irreversible losses. FTU-based local judgment devices make judgments based on zero-sequence current exceeding a set value. However, due to the zero-sequence current generated in both the non-fault section and the fault section during a single-phase ground fault, the device's location accuracy is low.

[0055] Centralized information control refers to a system where the dispatching center (master station) comprehensively calculates and analyzes line fault information collected from devices such as FTUs and fault indicators installed along the line. After determining the faulty section, the master station issues switch opening and closing commands. Currently, there are two main algorithms for locating the faulty section at the master station under centralized information control: one that relies on artificial intelligence algorithms such as neural networks and genetic algorithms; and another that locates the faulty section based on distribution network topology and fault current information. The former requires a large amount of computation, resulting in slow calculation speed and insufficient practical application. The latter, however, lacks zero-sequence voltage or current transformers on some distribution network lines, making it difficult to obtain the zero-sequence voltage or current on the line, making the algorithm less applicable. Furthermore, centralized information control algorithms all share the limitations of communication systems. When the communication system is disturbed or malfunctions, these algorithms may fail or malfunction, causing damage to power consumption equipment.

[0056] As users' demands for power supply reliability continue to increase, the next step to improving power supply reliability is to accurately locate the fault section and respond to power outages. Based on developments both domestically and internationally, the distribution network is becoming increasingly important in improving power supply reliability, and fault detection is receiving increasing attention.

[0057] Existing fault location technologies cover most grounding schemes and fault conditions, and are suitable for field application. However, in practice, existing fault location technologies often exhibit certain drawbacks due to factors such as harmonics, interference, and signal acquisition difficulties. Currently, fault location in distribution networks is primarily based on algorithms based on voltage-time distributed switches (for local judgment control) and FTU-based local judgment devices, and on centralized information control algorithms that utilize line information and line topology. While the local judgment control algorithm is relatively simple and does not require the installation of distribution terminal equipment, its location method has certain drawbacks: algorithms based on voltage-time distributed switches require a long fault isolation time, and frequent switching operations can cause damage to both consumers and switchgear. FTU-based local judgment devices, based on their algorithms based on zero-sequence current exceeding a set value, have low fault location accuracy due to the presence of zero-sequence current in both faulty and non-faulty sections of the line. While algorithms that leverage line information and line topology offer simple criteria, minimal computational effort, and can quickly locate faulty sections, they suffer from poor fault tolerance. Furthermore, due to the lack of zero-sequence voltage or current transformers on some lines in the distribution network, algorithms that rely on zero-sequence voltage or current as judgment signals are less applicable. Furthermore, the latter single-phase ground fault line selection algorithm requires uploading fault information to a master station via a communication system to determine the fault location. Interference or failure of the communication system can lead to misjudgment or algorithm failure.

[0058] There is an urgent need to develop an algorithm that can utilize the available line information in existing systems to diagnose single-phase grounding faults in distribution networks, making the algorithm highly applicable. This algorithm can be used in systems without zero-sequence current transformers or where the acquired zero-sequence current / voltage values are not highly accurate. Furthermore, it can quickly and accurately diagnose and handle single-phase grounding faults in distribution networks even when communication is poor or unavailable.

[0059] The FTU's fast and accurate fault line selection technology facilitates the maintenance of power grid equipment, extending its service life and reducing the maintenance burden. In other words, the FTU's highly accurate and adaptable single-phase ground fault line selection function for low-current grounding systems can improve power supply reliability, enhance the economic benefits of power supply agencies and users, and maintain power grid equipment, thus being of great significance. Phase current signals, as easily acquired signals, contain a wealth of fault information after a fault occurs. Furthermore, phase current transformers are widely installed in distribution networks. Using phase current as a judgment signal can avoid situations where the applicability of the fault line selection system is affected by the lack of zero-sequence current signal acquisition devices in the system. Furthermore, using phase current amplitude variance as a criterion reduces the algorithm's reliance on communication, allowing the algorithm to perform fault line selection locally even in the presence of poor or absent communication signals. To this end, the present invention proposes a distributed single-phase ground fault line selection algorithm based on phase current variance calculation. This single-phase ground fault line selection algorithm utilizes the relationship between the variance of the phase current fundamental amplitude on the line and a threshold as a criterion to distinguish between faulty and non-faulty sections of the line. It is used to solve single-phase grounding faults in the line and improve the reliability, safety and economy of power supply in the distribution network.

[0060] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0061] The present invention provides a single-phase ground fault judgment method based on three-phase current change characteristics, such as Figure 1 As shown, including:

[0062] Three current transformers are installed on the three-phase lines of the pole switch of the small current grounding system to measure the three-phase current of the pole switch;

[0063] The current transformer sends the measured three-phase current of the pole switch to the distribution switch monitoring terminal FTU;

[0064] Specifically, the current transformer is in communication connection with the distribution switch monitoring terminal FTU, so that the current transformer can send the measured three-phase current of the pole switch to the distribution switch monitoring terminal FTU.

[0065] The distribution switch monitoring terminal FTU obtains the fault component amplitude variance information of the three-phase current of the pole switch through calculation based on the three-phase current to analyze whether the fault point is located upstream or downstream of the pole switch as the detection point.

[0066] Specifically, when a single-phase grounding fault occurs in a low-current grounding system, the phase currents on each line of the low-current grounding system will change. Take the neutral point arc suppression coil grounding system as an example. Figure 2As shown, line 1-N is the outgoing line of the distribution network. A 、e B 、e C is the electromotive force of the power supply; C i is the capacitance to ground of each line (i=1, 2...n); C K C' is the capacitance of the upstream line to ground at the fault point; K is the capacitance of the line downstream of the fault point to ground. A single-phase ground fault occurs on phase A of line K, and the fault occurs before the next section of the line.

[0067] According to the symmetrical component method, when calculating the grounding current, the circuit grounding point can be equivalent to the positive, negative, and zero sequence voltage effects, such as Figure 3 As shown, is the three-phase positive sequence voltage at the fault point; is the three-phase negative sequence voltage at the fault point; is the three-phase zero-sequence voltage at the fault point.

[0068] Therefore, according to the superposition theorem, as shown in formula (1), the three-phase currents on each line of the small current grounding system after the fault are Normal operating load current and fault component current Superposition composition.

[0069]

[0070] At the same time, considering that the power supply electromotive force remains basically unchanged before and after the fault occurs, as shown in formula (2), the load current on the line after the fault is The load current before the fault occurs are roughly equal, and the load current before the fault occurs is the system phase current.

[0071]

[0072] Based on this, as shown in formula (3), the fault component current after the fault can be obtained by subtracting the current values corresponding to the full cycle difference measured by the detection device before and after the fault occurs.

[0073]

[0074] Since the positive and negative sequence currents in the fault current only form a loop between the power supply and the fault point, most of the positive and negative sequence currents are concentrated on the lines upstream of the fault point. However, since the zero sequence current forms a loop between the ground capacitance on each line and the fault point, the zero sequence current will be split at the fault point and flow to all lines in the system. The zero sequence equivalent circuit is as follows: Figure 4 As shown, is the zero sequence voltage; L0 is the arc suppression coil inductance; C i is the capacitance to ground of each line (i=1, 2...n); it should be emphasized that: C K C' is the capacitance of the upstream line to ground at the fault point; K is the capacitance of the line downstream of the fault point to ground.

[0075] Depend on Figure 4 It can be seen that the zero-sequence current is shunted at the fault point, and the zero-sequence current flows to the upstream line of the fault point and the downstream line of the fault point respectively, and then flows to the normal line through the upstream line of the fault point. According to the circuit theorem, the shunting coefficient β of the zero-sequence current on the i-th line can be obtained i As shown in formula (4):

[0076]

[0077] Among them, C m is the capacitance to ground on each line m = 1, 2...n; α is the capacitance to ground on line i or the reactance value of the arc suppression coil.

[0078] It is important to note that since the zero-sequence current in the fault section is the sum of the zero-sequence currents downstream of the fault point, its shunt coefficient is as shown in formula (5):

[0079]

[0080] Since the positive-sequence and negative-sequence currents in the fault current form a loop between the fault point and the power supply through the busbar, and the zero-sequence current in the fault current is composed of the ground capacitance on each line through the busbar and the fault point to form a loop, the current fault component upstream of the fault point contains three types of currents: positive-sequence, negative-sequence and zero-sequence.

[0081] Without loss of generality, assume that the positive and negative sequence currents at the fault point obtained by the symmetrical component method are Then the three-sequence current upstream of the fault point is As shown in formula (6) and formula (7):

[0082]

[0083]

[0084] β K is the shunt coefficient of the zero-sequence current upstream of the fault point, and the direction factor is a=e j120° Therefore, the fault components of each phase on the upstream line of the fault point are As shown in formula (8) to formula (10):

[0085]

[0086]

[0087]

[0088] in, It is the positive sequence component of the three-phase current fault component on the upstream line of the fault point; It is the negative sequence component of the three-phase current fault component on the upstream line of the fault point; It is the zero-sequence component of the three-phase current fault component on the upstream line of the fault point.

[0089] The following analysis shows the normal lines and lines downstream of the fault point. Since the positive- and negative-sequence currents in the fault current form a loop only between the fault point and the power source via the busbar, and do not pass through the normal lines or the lines downstream of the fault point, the zero-sequence current in the fault current is formed by the ground capacitance on each line, through the busbar and the fault point, forming a loop. Therefore, the fault component of the current in the normal lines and the lines downstream of the fault point is mainly composed of the zero-sequence current on the lines themselves.

[0090] To ensure uniformity, assume that the positive and negative sequence currents at the fault point obtained by the symmetrical component method are Then the positive and negative zero-sequence currents on the normal line and the line downstream of the fault point are as shown in formula (11) to formula (12):

[0091]

[0092]

[0093] β i is the shunt coefficient of zero-sequence current on line i. Then the fault component of the three-phase current on the normal line and the line downstream of the fault point is They are shown in formula (13) to formula (15) respectively:

[0094]

[0095]

[0096]

[0097] in, It is the positive sequence component of the three-phase current fault component on the normal line and the line downstream of the fault point; It is the negative sequence component of the three-phase current fault component on the normal line and the line downstream of the fault point; It is the zero-sequence component of the three-phase current fault component on the normal line and the line downstream of the fault point.

[0098] By analyzing the fault components of the three-phase currents of the upstream line of the fault point, the normal line, and the downstream line of the fault point, it can be found that: on the upstream line of the fault point, the fault component of the fault phase is greater than that of the non-fault phase, and the fault components of the non-fault phase are equal; in the normal line and the downstream line of the fault point, the fault components of the three-phase currents are all equal.

[0099] However, the influence of the shunt coefficient β in the results makes the fault characteristics unclear, and when the fault component is small, it is easy to cause malfunction. Therefore, relying solely on numerical equality cannot accurately complete the fault line location.

[0100] Considering that the shunt coefficient β is the effect of the zero-sequence current on the fault component, the zero-sequence current is calculated using the three-phase current and then subtracted from the zero-sequence current on the line from the fault component to eliminate the influence of the shunt coefficient β on the result.

[0101] The three-phase current fault component of the upstream line of the fault point minus the zero-sequence current is as shown in formulas (16) to (18):

[0102]

[0103]

[0104]

[0105] From the results, it can be seen that after subtracting the zero-sequence current, the fault phase is in the opposite direction to the normal direction, the amplitude is twice that of the normal phase, and the fault phase has the largest amplitude.

[0106] The three-phase current fault components of the normal line and the line downstream of the fault point minus the zero-sequence current are shown in formulas (19) to (21):

[0107]

[0108]

[0109]

[0110] It can be seen that after subtracting the zero-sequence current, there is a big difference between the results of the three phases ABC on the fault component of the upstream line of the fault point, the normal line and the line downstream of the fault point: the three-phase results of the normal line and the line downstream of the fault point are basically the same and close to 0, while on the line upstream of the fault point, there is a 2-fold relationship between the fault phase and the non-fault phase.

[0111] At the same time, considering that in actual operating conditions, the quantitative relationship between the amplitudes of the three-phase current fault components may not be completely consistent with theoretical analysis due to interference from harmonics in the system or limited sensitivity of the detection device, it is impossible to make an accurate judgment based solely on the multiple relationship of the amplitudes. Therefore, it is considered to use variance to enhance the difference between the upstream and normal lines of the fault point and the downstream lines of the fault point, thereby improving the accuracy of the judgment criteria.

[0112] The variance of the fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component upstream of the fault point. K As shown in formula (22):

[0113]

[0114] Variance Var of the fundamental amplitude of the fault component between the normal line and the line downstream of the fault point i As shown in formula (23):

[0115] Var i ≈0(23)

[0116] Wherein, J is the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point.

[0117] In order to complete the local fault line selection and location, the relationship between the line variance and the threshold can be compared by setting the threshold Var0. When the variance is greater than the threshold, it is the upstream line of the fault point, otherwise it is a normal line or the downstream line of the fault point. At the same time, considering that the variance calculated for each line is related to the zero-sequence fault component fundamental amplitude J at the fault point when a single-phase grounding fault occurs in the system, in order to make the method more adaptable, the zero-sequence current fundamental amplitude I0 of the line itself after the fault occurs can be used as a parameter. Since I0 is smaller than J, it will not affect the judgment result, so an adaptive threshold can be set according to the line's own zero-sequence current K rel is the reliability coefficient, which can be taken as 0.85.

[0118] After the algorithm determines whether the detection point is upstream or downstream of the fault point or on a normal line, the judgment result can be uploaded to the main station through the communication device or judged on-site by using the signal exchange of adjacent devices. When one of two adjacent devices is judged to be upstream of the fault point and the other is judged to be downstream of the fault point or on a normal line, the location of the fault section can be determined.

[0119] In a preferred but non-limiting embodiment of the present invention, the operation to obtain the fault component amplitude variance information of the three-phase current of the pole-mounted switch includes:

[0120] The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component upstream of the fault point Var KWhen , it is obtained according to the following formula:

[0121]

[0122] The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component of the normal line and the line downstream of the fault point Var i When , it is obtained according to the following formula:

[0123] Var i ≈0

[0124] Among them, J is the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point. The fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and zero-sequence current from the three-phase current of the pole-mounted switch. The fundamental amplitude of the positive and negative zero-sequence components of the fault is obtained after the residual current is transformed by Fourier transform.

[0125] Specifically, the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and the zero-sequence current from the three-phase current of the pole switch. The residual current is transformed by Fourier transform to obtain the fundamental amplitude of the positive and negative zero-sequence components of the fault. Among them, the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point as the fundamental amplitude of the current is three fundamental amplitudes, which are three fundamental amplitudes corresponding to the three-phase current of the pole switch. Each fundamental amplitude is the residual current obtained by subtracting the load current and the zero-sequence current from the corresponding phase current. The residual current is transformed by Fourier transform to obtain the fundamental amplitude of the positive and negative zero-sequence components of the fault corresponding to the phase current.

[0126] In a preferred but non-limiting embodiment of the present invention, the fault analysis point is located upstream or downstream of the pole switch serving as the detection point, and includes:

[0127] Set the threshold Var0 and compare the relationship between the fault component amplitude variance information of each phase current of the pole-mounted switch and the threshold Var0:

[0128] When the amplitude variance information of the fault component of each phase current of the pole switch is greater than the threshold Var0, it is the upstream line of the fault point; when the amplitude variance information of the fault component of each phase current of the pole switch is not greater than the threshold Var0, it is a normal line or the downstream line of the fault point.

[0129] In a preferred but non-limiting embodiment of the present invention, the threshold K rel is the reliability coefficient, which is 0.85, and I0 is the fundamental amplitude of the zero-sequence current of the line after the fault occurs.

[0130] The following simulation experiments are used to verify the single-phase grounding fault judgment method based on three-phase current variation characteristics of the present invention:

[0131] The neutral point arc suppression coil grounding system model is as follows Figure 5 As shown in Figure 1, the fault line is divided into upstream and downstream lines. In this experiment, the ground resistance is set to 0Ω and 2000 ohms, respectively, to test the reliability of the algorithm in the metal grounding and high-resistance grounding conditions.

[0132] Set the grounding resistance to 0Ω, use the algorithm to process the three-phase current of each line, and after subtracting the load current and zero-sequence current, the difference between the fault component current upstream of the fault point and the zero-sequence current is The difference between the fault component current and the zero sequence current of the line downstream of the fault point and the normal line The current waveforms are as follows Figure 6 、 Figure 7 、 Figure 8 As shown, after Fourier transforming the residual current, the fundamental amplitude of the current is extracted and listed in the table, and the variance is calculated using the fundamental amplitude of the three-phase current of the same line and filled in the table below. See Table 1 for the metal grounding test data results of the neutral point arc suppression coil grounding system:

[0133] Table 1

[0134]

[0135]

[0136] Table 1 shows that the variance upstream of the fault point is much greater than that downstream of the fault point and on normal lines. The significant difference between detection points upstream and downstream of the fault point clearly indicates the faulty section for on-site diagnosis. Furthermore, the calculated amplitude of phase A in the line upstream of the fault point is twice as large as that of phases B and C, which indicates the faulty phase. The amplitudes in the remaining lines are extremely small, approximately zero. These experimental results are consistent with the analysis presented above. This algorithm can effectively locate metallic ground faults in neutral-grounded systems with arc suppression coils.

[0137] The grounding resistance is set to 2000Ω, and the three-phase current of each line is processed by the algorithm. After subtracting the load current and zero-sequence current, the difference between the fault component current upstream of the fault point and the zero-sequence current is The difference between the fault component current and the zero-sequence current downstream of the fault point and on the normal line The current waveforms are as follows Figure 9 、 Figure 10 、 Figure 11 As shown:

[0138] After Fourier transforming the residual current, the fundamental amplitude of the current is extracted and listed in the table. The variance is calculated using the fundamental amplitude of the three-phase current of the same line and filled in the table below. See Table 2 for the high-resistance grounding test data results of the neutral point arc suppression coil grounding system:

[0139] Table 2

[0140]

[0141] Table 2 shows that the variance upstream of the fault point is much larger than that downstream and on normal lines. The differences between the detection points on both sides of the fault point are significant, allowing for local identification of the faulty section. Furthermore, the calculated amplitude of phase A in the upstream line is twice as large as that of phases B and C, indicating the faulty phase. The amplitudes in the remaining lines are extremely small, approximately zero. The experimental results are consistent with the aforementioned analysis. This algorithm can be used to locate high-resistance grounding faults in systems where the neutral point is grounded via arc suppression coils.

[0142] Neutral point ungrounded system model Figure 12 As shown in Figure 1, the fault line is divided into upstream and downstream lines. In this experiment, the ground resistance is set to 0Ω and 2000 ohms respectively to test the reliability of the algorithm in the metal grounding and high-resistance grounding conditions.

[0143] Set the grounding resistance to 0Ω, use the algorithm to process the three-phase current of each line, and after subtracting the load current and zero-sequence current, the difference between the fault component current and the zero-sequence current on the upstream line of the fault point is The difference between the fault component current and the zero sequence current on the line downstream of the fault point and the normal line The current waveforms are as follows Figure 13 、 Figure 14 、 Figure 15 As shown:

[0144] After Fourier transforming the residual current, the fundamental amplitude of the current is extracted and listed in the table. The variance is calculated using the fundamental amplitude of the three-phase current of the same line and filled in the table below. See Table 3 for the metal grounding test data results of the neutral point ungrounded system:

[0145] Table 3

[0146]

[0147] Table 3 shows that the variance of the lines upstream of the fault point is much greater than that of the lines downstream and in normal conditions. The differences between the detection points on both sides of the fault point are significant, allowing for the selection of the faulty section for on-site diagnosis. Furthermore, the calculated amplitude of phase A in the line upstream of the fault point is twice as large as that of phases B and C, indicating the faulty phase can be identified. The amplitudes of the remaining lines are extremely small, approximately zero. These experimental results are consistent with the analysis presented above. This algorithm can be used to locate metal-grounded fault lines in systems with an ungrounded neutral point.

[0148] Set the ground resistance to 2000Ω, use the algorithm to process the three-phase current of each line, and subtract the load

[0149] The difference between the fault component current and the zero-sequence current on the upstream line of the fault point is The difference between the fault component current and the zero sequence current on the line downstream of the fault point and the normal line The current waveforms are as follows Figure 16 、 Figure 17 、 Figure 18 As shown:

[0150] After Fourier transforming the residual current, the fundamental amplitude of the current is extracted and listed in the table. The variance is calculated using the fundamental amplitude of the three-phase current of the same line and filled in the table below. See Table 4 for the measurement results of the high-resistance grounding of the neutral point ungrounded system:

[0151] Table 4

[0152]

[0153]

[0154] Table 4 shows that the variance upstream of the fault point is much larger than that downstream and on normal lines. The differences between the detection points on both sides of the fault point are significant, allowing for the selection of the faulty section for on-site diagnosis. Furthermore, the calculated amplitude of phase A in the upstream line is twice as large as that of phases B and C, indicating the faulty phase can be identified. The amplitudes in the remaining lines are extremely small, approximately zero. These experimental results are consistent with the analysis presented above. This algorithm can be used to locate metal-grounded fault lines in systems with an ungrounded neutral point.

[0155] In summary, the fault component current amplitude variance criterion can successfully locate fault sections in both arc suppression coil-grounded and ungrounded low-current grounding systems, including both metallic and high-resistance single-phase grounding faults, clearly distinguishing between faulty sections, non-faulty sections, and normal lines. By analyzing the variance of the three-phase current fault component amplitude at different points along the line, it is possible to determine whether the point is upstream or downstream of the fault. By comprehensively comparing the analysis results from multiple points along the line, fault line selection and fault section location can be achieved.

[0156] The beneficial effect of the present invention is that, compared with the prior art, the phase current signal used in the present invention is an easily collected signal that contains rich fault information after a fault occurs. At the same time, phase current transformers are widely installed in distribution network lines. Using phase current as a judgment signal can avoid the situation where the applicability of the fault line selection system is affected by the lack of a zero-sequence current signal acquisition device in the system. In addition, using the phase current amplitude variance as a judgment criterion can reduce the algorithm's dependence on communication. In the case of poor communication signals or lack of communication, the method can still complete the fault line selection on site.

[0157] A single-phase grounding fault judgment device based on three-phase current variation characteristics of the method described in the present invention includes:

[0158] A calculation module is used to analyze whether the fault point is located upstream or downstream of the pole switch as a detection point by obtaining the fault component amplitude variance information of the three-phase current of the pole switch through calculation based on the three-phase current.

[0159] In a preferred but non-limiting embodiment of the present invention, the calculation module is also used for the fault component amplitude variance information of the three-phase current of the pole switch, which is the variance Var of the fundamental amplitude of the fault component upstream of the fault point. K When , it is obtained according to the following formula:

[0160]

[0161] The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component of the normal line and the line downstream of the fault point Var i When , it is obtained according to the following formula:

[0162] Var i ≈0

[0163] Among them, J is the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point. The fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and zero-sequence current from the three-phase current of the pole-mounted switch. The fundamental amplitude of the positive and negative zero-sequence components of the fault is obtained after the residual current is transformed by Fourier transform.

[0164] In a preferred but non-limiting embodiment of the present invention, the operation module is further configured to set a threshold Var0 and compare the relationship between the fault component amplitude variance information of each phase current of the pole-mounted switch and the threshold Var0:

[0165] When the amplitude variance information of the fault component of each phase current of the pole switch is greater than the threshold Var0, it is the upstream line of the fault point; when the amplitude variance information of the fault component of each phase current of the pole switch is not greater than the threshold Var0, it is a normal line or the downstream line of the fault point.

[0166] In a preferred but non-limiting embodiment of the present invention, the threshold K re l is the reliability coefficient, which is 0.85, and I0 is the fundamental amplitude of the zero-sequence current of the line after the fault occurs.

[0167] A terminal according to the present invention includes a processor and a storage medium;

[0168] The storage medium is used to store instructions;

[0169] The processor is configured to operate according to the instruction to execute the steps of the method for determining a single-phase grounding fault based on three-phase current change characteristics.

[0170] The computer-readable storage medium of the present invention stores a computer program, which, when executed by a processor, implements the steps of the single-phase grounding fault judgment method based on three-phase current change characteristics.

[0171] The beneficial effect of the present invention is that, compared with the existing technology, the present invention is based on the clearing principle and optimization model of my country's typical provincial electricity spot market, adopts the qualitative analysis method of causal analysis, and proposes the relevant factors affecting the clearing of the electricity spot market on the consumption of new energy. The present invention proposes a mathematical modeling method of power grid topology information based on feature extraction, extracts key information of the global topology, and retains detailed information of the local topology. Without losing key topological information, it solves the problem that the conventional mathematical table of the power grid topology is large in scale and sparse. The present invention mathematically models many market factors, performs coupling calculation and information extraction on multiple original factors, numerically represents non-numerical factors, improves the applicability of statistical analysis with causal analysis, and concisely reflects the coupling influence of multiple key factors on the consumption of new energy.

[0172] The applicant of the present invention has made a detailed explanation and description of the implementation examples of the present invention in conjunction with the drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only the preferred implementation schemes of the present invention, and the detailed description is only to help readers better understand the spirit of the present invention, and is not a limitation on the scope of protection of the present invention. On the contrary, any improvements or modifications based on the inventive spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A single-phase ground fault judgment method based on three-phase current change characteristics, characterized in that: include: The distribution switch monitoring terminal FTU obtains the fault component amplitude variance information of the three-phase current of the pole switch transmitted by the current transformer through calculation to analyze whether the fault point is upstream or downstream of the pole switch as the detection point.

2. The single-phase grounding fault judgment method based on three-phase current change characteristics according to claim 1 is characterized in that: The fault component amplitude variance information of the three-phase current of the pole-mounted switch obtained according to the three-phase current calculation includes: The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component upstream of the fault point Var K When , it is obtained according to the following formula: The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component of the normal line and the line downstream of the fault point Var i When , it is obtained according to the following formula: Our i ≈0 Among them, J is the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point. The fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and zero-sequence current from the three-phase current of the pole-mounted switch. The fundamental amplitude of the positive and negative zero-sequence components of the fault is obtained after the residual current is transformed by Fourier transform.

3. The single-phase grounding fault judgment method based on three-phase current variation characteristics according to claim 1 is characterized in that: The fault analysis point is located upstream or downstream of the pole switch serving as the detection point, and includes: Set the threshold Var0 and compare the relationship between the fault component amplitude variance information of each phase current of the pole-mounted switch and the threshold Var0: When the amplitude variance information of the fault component of each phase current of the pole switch is greater than the threshold Var0, it is the upstream line of the fault point; when the amplitude variance information of the fault component of each phase current of the pole switch is not greater than the threshold Var0, it is a normal line or the downstream line of the fault point.

4. The single-phase grounding fault judgment method based on three-phase current variation characteristics according to claim 3 is characterized in that: The threshold K re l is the reliability coefficient, which is 0.85, and I0 is the fundamental amplitude of the zero-sequence current of the line after the fault occurs.

5. A single-phase grounding fault judgment device based on three-phase current change characteristics of the method, characterized in that: include: A calculation module is used to analyze whether the fault point is located upstream or downstream of the pole switch as a detection point by obtaining the fault component amplitude variance information of the three-phase current of the pole switch through calculation based on the three-phase current.

6. The single-phase grounding fault judgment device based on three-phase current variation characteristics according to claim 5, characterized in that: The calculation module is also used for the fault component amplitude variance information of the three-phase current of the pole switch, which is the variance Var of the fundamental amplitude of the fault component upstream of the fault point. K When , it is obtained according to the following formula: The fault component amplitude variance information of the three-phase current of the pole-mounted switch is the variance of the fundamental amplitude of the fault component of the normal line and the line downstream of the fault point Var i When , it is obtained according to the following formula: Our i ≈0 Among them, J is the fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point. The fundamental amplitude of the positive and negative zero-sequence components of the fault at the fault point is the residual current obtained by subtracting the load current and zero-sequence current from the three-phase current of the pole-mounted switch. The fundamental amplitude of the positive and negative zero-sequence components of the fault is obtained after the residual current is transformed by Fourier transform.

7. The single-phase grounding fault judgment device based on three-phase current variation characteristics according to claim 5, characterized in that: The operation module is further configured to set a threshold value Var0 and compare the relationship between the fault component amplitude variance information of each phase current of the pole-mounted switch and the threshold value Var0: When the amplitude variance information of the fault component of each phase current of the pole switch is greater than the threshold Var0, it is the upstream line of the fault point; when the amplitude variance information of the fault component of each phase current of the pole switch is not greater than the threshold Var0, it is a normal line or the downstream line of the fault point.

8. The single-phase grounding fault judgment device based on three-phase current variation characteristics according to claim 7, characterized in that: The threshold K rel is the reliability coefficient, which is 0.85, and I0 is the fundamental amplitude of the zero-sequence current of the line after the fault occurs.

9. A terminal comprising a processor and a storage medium; The storage medium is used to store instructions; It is characterized by: The processor is configured to operate according to the instruction to execute the steps of the single-phase grounding fault judgment method based on three-phase current change characteristics according to any one of claims 1 to 4.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the single-phase grounding fault judgment method based on three-phase current change characteristics according to any one of claims 1 to 4 are implemented.

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