A method for judging ground fault of power distribution network and centralized protection monitoring device

Abstract

The application discloses a kind of grounding fault determination method and centralized protection control device of distribution network.Belongs to the technical field of intelligent distribution system.The grounding fault determination method includes: according to the zero sequence current of ring-in interval unit, the zero sequence current of ring-out interval unit and the zero sequence current of each branch line interval unit, the size and mutation direction of the zero sequence current mutation variable of each interval unit, and the size and mutation direction of bus zero sequence difference flow mutation variable;With the mutation direction of the zero sequence current mutation variable of ring-in interval unit as benchmark, according to the size and mutation direction of the zero sequence current mutation variable of each interval unit, and the size and mutation direction of bus zero sequence difference flow mutation variable, determine the grounding fault as in-zone grounding fault or out-zone grounding fault.The application can solve the technical problem of high misjudgment rate, and further improve the accuracy and reliability of single-phase grounding fault determination of distribution network.

Description

Technical Field

[0001] This invention relates to the field of intelligent power distribution system technology, and in particular to a method for judging grounding faults in power distribution networks and a centralized protection and control device. Background Technology

[0002] Most of my country's power distribution network systems operate with an ungrounded neutral point or a neutral point grounded via an arc suppression coil, i.e., a low-current grounding system. This system is an important component of intelligent power distribution systems. In low-current grounding systems, single-phase grounding faults are the most common temporary faults, accounting for more than 70% of all power distribution network faults. Because the fault current at the fault point is very small during a single-phase grounding fault, especially in power distribution networks with a neutral point grounded via an arc suppression coil, the fault characteristics are further weakened, making fault location extremely difficult and a long-standing technical challenge in the field of intelligent power distribution system protection.

[0003] To address the aforementioned issues, existing technologies typically incorporate low-current grounding protection functionality into centralized or distributed protection and control devices. This function monitors the zero-sequence current and system zero-sequence voltage of the line in real time, analyzing their transient or steady-state characteristics to determine if a grounding fault has occurred on that line. If the fault is determined to be on the line itself, it is classified as an intra-zone grounding fault, the device issues a grounding fault alarm, and disconnects the line's switch; otherwise, it is classified as an inter-zone grounding fault, and the device does not operate. Specifically, grounding protection for a single line generally achieves fault location through direct or indirect analysis of zero-sequence voltage and zero-sequence current.

[0004] However, due to the unbalanced zero-sequence voltage in the power supply system itself, and the very small steady-state current at the fault point when a single-phase grounding occurs, and the extremely short duration of the fault transient process, the grounding protection method based on single-line electrical quantity analysis has poor resistance to transition resistance and a high misjudgment rate. Summary of the Invention

[0005] This invention provides a method for judging ground faults in power distribution networks and a centralized protection and control device to solve the technical problem of high misjudgment rate in the prior art.

[0006] In a first aspect, embodiments of the present invention provide a method for determining ground faults in a distribution network. The protection zone of the distribution network includes a busbar, an incoming loop bay unit, an outgoing loop bay unit, and at least one branch bay unit. The ground fault determination method includes: acquiring the zero-sequence current of the incoming loop bay unit, the zero-sequence current of the outgoing loop bay unit, and the zero-sequence current of each branch bay unit; and determining the magnitude and direction of the zero-sequence current mutation in each bay unit, as well as the zero-sequence difference of the busbar, based on the zero-sequence current of the incoming loop bay unit, the zero-sequence current of the outgoing loop bay unit, and the zero-sequence current of each branch bay unit. The magnitude and direction of the sudden change in current; wherein, each bay unit includes the incoming bay unit, the outgoing bay unit, and each branch bay unit; taking the direction of the sudden change in the zero-sequence current of the incoming bay unit as the reference, and based on the magnitude and direction of the sudden change in the zero-sequence current of the outgoing bay unit and each branch bay unit, as well as the magnitude and direction of the sudden change in the zero-sequence differential current of the busbar, the grounding fault is determined to be either an intra-zone grounding fault or an extra-zone grounding fault; wherein, an intra-zone grounding fault includes any one of the following: busbar grounding fault, branch bay unit grounding fault, and outgoing bay unit grounding fault.

[0007] Optionally, the step of determining the magnitude and direction of the zero-sequence current mutation in each bay unit, and the magnitude and direction of the zero-sequence differential current mutation in the busbar, based on the zero-sequence current of the incoming bay unit, the outgoing bay unit, and the branch bay units, includes: determining the magnitude and direction of the zero-sequence current mutation in the incoming bay unit based on the zero-sequence current sampled values ​​of the incoming bay unit at the current sampling time, one power frequency cycle ago, and two power frequency cycle ago; determining the magnitude and direction of the zero-sequence current mutation in the outgoing bay unit based on the zero-sequence current sampled values ​​of the outgoing bay unit at the current sampling time, one power frequency cycle ago, and two power frequency cycle ago. The magnitude and direction of the zero-sequence current mutation in the fixed loop-out interval unit are determined; based on the zero-sequence current sampling values ​​of each branch interval unit at the current sampling time, one power frequency cycle ago, and two power frequency cycle ago, the magnitude and direction of the zero-sequence current mutation in each branch interval unit are determined; based on the vector sum of the zero-sequence current sampling values ​​of the loop-in interval unit, the loop-out interval unit, and each branch interval unit at the current sampling time, the bus zero-sequence differential current is determined; based on the calculated values ​​of the bus zero-sequence differential current at the current sampling time, one power frequency cycle ago, and two power frequency cycle ago, the magnitude and direction of the bus zero-sequence differential current mutation are determined.

[0008] Optionally, before determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault based on the direction of the zero-sequence current mutation of the looping interval unit and the magnitude and direction of the zero-sequence differential current mutation of each interval unit and the bus zero-sequence differential current mutation, the ground fault determination method further includes: determining whether the absolute value of the zero-sequence current mutation of the looping interval unit is greater than a preset mutation value; if the absolute value of the zero-sequence current mutation of the looping interval unit is greater than the mutation value, then recording the direction of the zero-sequence current mutation of the looping interval unit.

[0009] Optionally, the step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: if the absolute value of the bus zero-sequence differential current mutation is greater than the mutation value set, and the mutation direction of the bus zero-sequence differential current mutation is consistent with the mutation direction of the zero-sequence current mutation in the loop-in bay unit; and if there are other bay units where the absolute value of the zero-sequence current mutation is greater than the mutation value set, and the mutation direction of the zero-sequence current mutation in the other bay units is the same as the mutation direction of the zero-sequence current mutation in the loop-in bay unit, then it is determined to be a bus ground fault.

[0010] Optionally, the step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: determining that a ground fault has occurred in a certain branch bay unit when the following conditions are met simultaneously: the absolute value of the bus zero-sequence differential current mutation is less than the mutation value set; there exists a branch bay unit whose absolute value of the zero-sequence current mutation is greater than the mutation value set, and the mutation direction of the zero-sequence current mutation of the branch bay unit is opposite to the mutation direction of the zero-sequence current mutation of the looping bay unit; if there are other bay units whose absolute value of the zero-sequence current mutation is greater than the mutation value set, then the mutation direction of the zero-sequence current mutation of the other bay units is the same as the mutation direction of the zero-sequence current mutation of the looping bay unit.

[0011] Optionally, the step of determining whether a ground fault is an in-zone ground fault or an out-of-zone ground fault includes: when the following conditions are met simultaneously, it is determined that a ground fault has occurred in the loop-out interval unit: the absolute value of the bus zero-sequence differential current mutation is less than the mutation value set; the absolute value of the zero-sequence current mutation of the loop-out interval unit is greater than the mutation value set; the mutation direction of the zero-sequence current mutation of the loop-out interval unit is opposite to the mutation direction of the zero-sequence current mutation of the loop-in interval unit; if there is a branch interval unit where the absolute value of the zero-sequence current mutation is greater than the mutation value set, then the mutation direction of the zero-sequence current mutation of the branch interval unit is the same as the mutation direction of the zero-sequence current mutation of the loop-in interval unit.

[0012] Optionally, the step of determining whether a ground fault is an in-zone ground fault or an out-of-zone ground fault includes: when the following conditions are met simultaneously, it is determined to be an out-of-zone ground fault: the absolute value of the bus zero-sequence differential current mutation is less than the mutation value set; there is a loop-out interval unit or branch interval unit with an absolute value of zero-sequence current mutation greater than the mutation value set; all loop-out interval units and branch interval units with an absolute value of zero-sequence current mutation greater than the mutation value set have the same mutation direction of zero-sequence current mutation and are all opposite to the mutation direction of zero-sequence current mutation of the loop-in interval unit.

[0013] Optionally, the step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: determining whether it is a bus ground fault based on the bus ground fault criterion; if the bus ground fault criterion cannot determine whether it is a bus ground fault, the bus ground fault criterion is exited, and at least one of the branch bay unit ground fault criterion, the loop-out bay unit ground fault criterion, and the extra-zone ground fault criterion is continued; if the extra-zone ground fault criterion cannot determine whether it is an extra-zone ground fault, the extra-zone ground fault criterion is exited, and at least one of the bus ground fault criterion, the branch bay unit ground fault criterion, and the loop-out bay unit ground fault criterion is continued; if the ground fault type cannot be determined based on the branch bay unit ground fault criterion or the loop-out bay unit ground fault criterion, the process is transferred to the single-line ground fault judgment procedure.

[0014] Optionally, after determining whether the ground fault is an intra-zone ground fault or an extra-zone ground fault, the ground fault determination method further includes: determining whether the system zero-sequence voltage is greater than a preset zero-sequence voltage setting; if the system zero-sequence voltage is greater than the zero-sequence voltage setting, the determination of whether the ground fault is intra-zone or extra-zone is valid, and a trip command is sent to the circuit breaker of the corresponding line to disconnect the faulty line, and an alarm signal is issued at the same time; if the system zero-sequence voltage is less than the zero-sequence voltage setting, fault handling is prohibited, and the process returns to continue executing the steps of obtaining the zero-sequence current of the loop-in bay unit, the zero-sequence current of the loop-out bay unit, and the zero-sequence current of each branch bay unit.

[0015] Secondly, embodiments of the present invention provide a centralized protection and control device for executing the ground fault judgment method for power distribution networks provided in any embodiment of the present invention.

[0016] The ground fault judgment method provided in this invention obtains the zero-sequence current of the incoming, outgoing, and branch line bay units within the protected area. This allows for the determination of the magnitude and direction of the zero-sequence current mutation in each bay unit, as well as the magnitude and direction of the busbar zero-sequence differential current mutation. Using the mutation direction of the incoming zero-sequence current mutation in each bay unit as a benchmark, the method determines whether the ground fault is an in-zone or out-of-zone ground fault based on the magnitude and direction of these mutations. This method introduces the incoming bay unit as a unified reference benchmark, incorporating the previously isolated zero-sequence current information of each bay unit into the same comparison system, thus achieving collaborative analysis and mutual verification of multi-bay data. Compared to traditional single-line protection methods that rely solely on the relationship between the zero-sequence voltage and zero-sequence current of the line for judgment, this method, by comparing the mutation directions of the zero-sequence current mutations in other bay units with those in the incoming bay unit, can more accurately capture the distribution pattern of the fault current and effectively distinguish between in-zone and out-of-zone ground faults. This effectively solves the technical problems of poor resistance to transition resistance and high misjudgment rate of existing grounding protection methods based on single-line electrical quantity analysis. It meets the high reliability requirements of intelligent power distribution systems, facilities and other power distribution switch control equipment manufacturing, and can also provide technical support for the supporting protection of intelligent large-scale DC converter transformers, intelligent reactors and other transformers, rectifiers and inductors.

[0017] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a protection zone of a power distribution network provided in an embodiment of the present invention;

[0020] Figure 2 This is a flowchart of a grounding fault judgment method provided in an embodiment of the present invention;

[0021] Figure 3 This is a flowchart of another ground fault judgment method provided by an embodiment of the present invention;

[0022] Figure 4This is a flowchart of another ground fault judgment method provided by an embodiment of the present invention. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0025] To address the problems in the prior art, this application provides a ground fault judgment method and a centralized protection and control device for a power distribution network. The following is a description of a power distribution network that can apply the ground fault judgment method provided in this application. The power distribution network is a component of an intelligent power distribution system.

[0026] Figure 1 This is a schematic diagram of the structure of a protection zone in a power distribution network provided by an embodiment of the present invention, as shown below. Figure 1 As shown, the protection zone of the power distribution network includes bus 1, incoming loop bay unit 2, outgoing loop bay unit 3, and at least one branch bay unit 4.

[0027] In the distribution network protection area to which this invention applies, the ring-in interval unit refers to the incoming line channel that connects to the upstream power supply and allows energy to flow into this protection area (such as a ring main unit or switchgear). The change in its zero-sequence current can reflect the fault energy input situation of the entire protection area.

[0028] The loop-out interval unit is the outgoing line channel that supplies power to other downstream protected areas.

[0029] Branch bay units refer to power distribution lines that directly supply power to end users.

[0030] Figure 2 This is a flowchart of a ground fault judgment method provided by an embodiment of the present invention. The method in this embodiment can be executed by a centralized protection and control device, which can be implemented in software and / or hardware and integrated into the distribution switch control equipment of distribution network nodes such as ring main units and switching stations in intelligent power distribution systems. Figure 2 As shown, the ground fault detection method includes:

[0031] S101. Obtain the zero-sequence current of the loop-in interval unit, the zero-sequence current of the loop-out interval unit, and the zero-sequence current of each branch interval unit.

[0032] Specifically, each bay unit is equipped with a zero-sequence current transformer (ZCT) to sense the zero-sequence current signal of the current line. After sampling and analog-to-digital conversion, this signal forms a digitized sequence of zero-sequence current sample values, which are then used by the centralized protection and control device for subsequent calculations. Each bay unit includes a loop-in bay unit 2, a loop-out bay unit 3, and each branch bay unit 4.

[0033] It should be noted that although this embodiment uses a zero-sequence current transformer as the signal acquisition method, the present invention is not limited thereto. Any measurement method that can reflect the zero-sequence current information of the line, such as current measurement based on Rogowski coils, or current data obtained from other intelligent electronic devices based on digital communication, can be used as an alternative implementation scheme for this step, as long as the synchronization and accuracy of multi-interval data can be guaranteed.

[0034] S102. Based on the zero-sequence current of the loop-in bay unit, the zero-sequence current of the loop-out bay unit, and the zero-sequence current of each branch bay unit, determine the magnitude and direction of the zero-sequence current mutation of each bay unit, as well as the magnitude and direction of the bus zero-sequence differential current mutation.

[0035] Zero-sequence current mutation refers to the change in zero-sequence current over a short period of time. Its physical nature reflects the transient change in current at the moment a ground fault occurs.

[0036] In practical implementation, the zero-sequence current surge can be determined using a differential algorithm, which calculates the surge using sampled values ​​from several power frequency cycles before and after the fault. Taking the loop-in interval unit as an example, its zero-sequence current surge ΔI0a can be determined as follows: obtain the instantaneous zero-sequence current value I0a(K) at the current sampling time K, the instantaneous value I0a(KN) at the sampling time KN one power frequency cycle ago, and the instantaneous value I0a(K-2N) at the sampling time K-2N two power frequency cycles ago. By calculating the difference between (I0a(K)-I0a(KN)) and (I0a(KN)-I0a(K-2N)), the change in current relative to historical trends at the current moment can be obtained. This calculation method can effectively eliminate the influence of slow changes such as load fluctuations and highlight the current surge caused by the fault.

[0037] It should be noted that the differential algorithm based on historical data from two power frequency cycles described above is only a preferred implementation. Its design is based on the fact that data from one power frequency cycle can reflect the current fundamental component, while data from two power frequency cycles can further eliminate the influence of trend changes. However, this invention is not limited to this. Those skilled in the art can employ other forms of mutation extraction algorithms according to different requirements for response speed and anti-interference capability in practical applications, such as methods based on short-window integration, transient extraction methods based on wavelet transform, or edge detection methods based on morphological filtering. Any mutation feature quantity reflecting the transient process of the fault can be effectively extracted from the zero-sequence current sequence should be considered an equivalent implementation of this invention.

[0038] The method for determining the direction of mutation is related to the sign of the mutation amount itself. If the calculated value of the mutation amount is positive, the direction of mutation is defined as positive; if it is negative, it is defined as negative.

[0039] Busbar zero-sequence differential current refers to the vector sum of all zero-sequence currents flowing into the busbar, i.e., the sum of the instantaneous values ​​of the zero-sequence currents in the incoming and outgoing bay units and each branch bay unit. Under normal conditions where the busbar itself is fault-free, according to Kirchhoff's current law, the zero-sequence current flowing into the busbar should equal the zero-sequence current flowing out of the busbar, meaning the busbar zero-sequence differential current should theoretically be zero. However, when a ground fault occurs on the busbar itself, a portion of the current will flow directly into the ground through the fault point, disrupting the original balance. In this case, the busbar zero-sequence differential current is not equal to zero.

[0040] In some embodiments, at the current sampling time K, the zero-sequence current I0a(K) of the loop-in interval unit, the zero-sequence current I0b(K) of the loop-out interval unit, and the zero-sequence current I0i(K) of each branch interval unit are vector-summed to obtain the bus zero-sequence differential current I0C(K).

[0041] The bus zero-sequence differential current mutation is the transient change in the bus zero-sequence differential current. Its determination method is similar to that of the zero-sequence current mutation in each bay unit, that is, it is calculated based on the bus zero-sequence differential current value at the current moment and several power frequency cycles ago. For example, the bus zero-sequence differential current mutation ΔI0C can be obtained by differential combination of I0C(K), I0C(KN), and I0C(K-2N).

[0042] S103. Based on the direction of the change in the zero-sequence current of the ring-in interval unit, and according to the magnitude and direction of the change in the zero-sequence current of the ring-out interval unit and each branch interval unit, as well as the magnitude and direction of the change in the zero-sequence differential current of the bus, determine whether the grounding fault is an internal or external grounding fault.

[0043] Specifically, in a typical distribution network ring main unit or switching station structure, the loop-in bay unit is the only entry point for external electrical energy into this protected area. When a ground fault occurs at any location within the protected area, the zero-sequence current of the loop-in bay unit is superimposed with a fault current on top of the original load current, thus presenting a sudden change in the zero-sequence current. The direction of the sudden change in the zero-sequence current of the loop-in bay unit is a digital representation of the flow direction of this fault component, that is, the polarity characteristic extracted by the device through the calculation of the sudden change. This polarity may be positive or negative, depending on the installation polarity of the zero-sequence current transformer and the symbol definition of the sudden change calculation algorithm. However, regardless of whether the actual recorded direction is positive or negative, the recorded direction is established as the absolute reference benchmark for this judgment cycle. The sudden change direction of the zero-sequence current of all other bay units is compared with this reference direction to determine whether the current flows normally to the load or abnormally to the fault point.

[0044] An intra-zone grounding fault refers to a grounding fault located within the protection zone (i.e., the busbar, the downstream end of the loop-out bay, and each branch bay under the jurisdiction of the current ring main unit or switching station). Intra-zone grounding faults include any one of the following: busbar grounding faults, branch bay unit grounding faults, and loop-out bay unit grounding faults.

[0045] External grounding faults refer to grounding faults located outside the protection zone. These mainly include grounding faults upstream of the loop entry bay (such as outgoing lines from the upstream substation) and grounding faults on other main lines on the same busbar that are not directly electrically connected to this protection zone. For external grounding faults, this centralized protection and control device only monitors the faults and does not perform tripping operations to avoid expanding the power outage area.

[0046] The ground fault judgment method provided in this invention obtains the zero-sequence current of the incoming, outgoing, and branch line bay units within the protected area. This allows for the determination of the magnitude and direction of the zero-sequence current mutation in each bay unit, as well as the magnitude and direction of the busbar zero-sequence differential current mutation. Using the mutation direction of the incoming zero-sequence current mutation in each bay unit as a benchmark, the method determines whether the ground fault is an in-zone or out-of-zone ground fault based on the magnitude and direction of these mutations. This method introduces the incoming bay unit as a unified reference benchmark, incorporating the previously isolated zero-sequence current information of each bay unit into the same comparison system, thus achieving collaborative analysis and mutual verification of multi-bay data. Compared to traditional single-line protection methods that rely solely on the relationship between the zero-sequence voltage and zero-sequence current of the line for judgment, this method, by comparing the mutation directions of the zero-sequence current mutations in other bay units with those in the incoming bay unit, can more accurately capture the distribution pattern of the fault current and effectively distinguish between in-zone and out-of-zone ground faults. This effectively solves the technical problems of poor resistance to transition resistance and high misjudgment rate in existing grounding protection methods based on single-line electrical quantity analysis.

[0047] In some embodiments, the magnitude and direction of the zero-sequence current mutation of the loop-in interval unit are determined based on the zero-sequence current sampling values ​​of the loop-in interval unit at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago.

[0048] Based on the zero-sequence current sampling values ​​of the loop-out interval unit at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, determine the magnitude and direction of the zero-sequence current mutation of the loop-out interval unit.

[0049] Based on the zero-sequence current sampling values ​​of each branch interval unit at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, determine the magnitude and direction of the zero-sequence current mutation of each branch interval unit.

[0050] The zero-sequence differential current of the busbar is determined by the vector sum of the zero-sequence current sampled values ​​of the ring-in interval unit, the ring-out interval unit, and each branch interval unit at the current sampling time.

[0051] Based on the calculated values ​​of the zero-sequence differential current of the bus at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, determine the magnitude and direction of the change in the zero-sequence differential current of the bus.

[0052] Specifically, the magnitude and direction of the zero-sequence current mutation in each interval unit, as well as the magnitude and direction of the zero-sequence differential current mutation in the bus, can be determined using the following calculation formulas.

[0053] First, determine the magnitude and direction of the zero-sequence current mutation ΔI0a of the loop-in interval unit. Specifically, based on the zero-sequence current sampled value I0a(K) of the loop-in interval unit at the current sampling time K, the zero-sequence current sampled value I0a(KN) at the sampling time KN one power frequency cycle ago, and the zero-sequence current sampled value I0a(K-2N) at the sampling time K-2N two power frequency cycles ago, calculate the zero-sequence current mutation ΔI0a of the loop-in interval unit according to the following formula:

[0054] ΔI0a=[I0a(K)-I0a(KN)]-[I0a(KN)-I0a(K-2N)];

[0055] Where N is the number of sampling points within one power frequency cycle. The calculation result of ΔI0a reflects the change of the zero-sequence current of the loop-in interval unit relative to the historical trend at the current moment. The sign of its value corresponds to the direction of the abrupt change: if ΔI0a>0, the direction of the abrupt change of the zero-sequence current of the loop-in interval unit is defined as positive; if ΔI0a<0, the direction of the abrupt change of the zero-sequence current of the loop-in interval unit is defined as negative.

[0056] Similarly, based on the zero-sequence current sampled value I0b(K) of the loop-out interval unit at the current sampling time K, the zero-sequence current sampled value I0b(KN) at the sampling time KN one power frequency cycle ago, and the zero-sequence current sampled value I0b(K-2N) at the sampling time K-2N two power frequency cycles ago, the zero-sequence current abrupt change ΔI0b of the loop-out interval unit is calculated according to the following formula:

[0057] ΔI0b=[I0b(K)-I0b(KN)]-[I0b(KN)-I0b(K-2N)];

[0058] The calculation result of ΔI0b reflects the abrupt change characteristics of the zero-sequence current of the loop-out interval unit, and the positive or negative value corresponds to the abrupt change direction of the zero-sequence current abrupt change of the loop-out interval unit.

[0059] For each branch bay unit, based on the zero-sequence current sampled value I0i(K) of the i-th branch bay unit at the current sampling time K, the zero-sequence current sampled value I0i(KN) at the sampling time KN one power frequency cycle ago, and the zero-sequence current sampled value I0i(K-2N) at the sampling time K-2N two power frequency cycles ago, the zero-sequence current mutation ΔI0i of the branch bay unit is calculated according to the following formula:

[0060] ΔI0i=[I0i(K)-I0i(KN)]-[I0i(KN)-I0i(K-2N)];

[0061] Where i represents the sequence number of the branch interval unit, i = 1, 2, ..., n, and n is the total number of branch interval units. ΔI0i represents the zero-sequence current mutation of the i-th branch interval unit, and the sign of its value corresponds to the mutation direction of the zero-sequence current mutation of the i-th branch interval unit.

[0062] The bus zero-sequence differential current refers to the vector sum of all zero-sequence currents flowing into the bus. At the current sampling time K, based on the zero-sequence current sampling values ​​I0a(K) of the incoming loop bay unit, I0b(K) of the outgoing loop bay unit, and I0i(K) of each branch bay unit, the bus zero-sequence differential current I0C(K) is calculated according to the following formula:

[0063] I0C(K)=I0a(K)+I0b(K)+ΣI0i(K);

[0064] Wherein, ΣI0i(K) represents the vector summation of the zero-sequence current sampled values ​​of all branch interval units at the current sampling time K.

[0065] Furthermore, based on the calculated value I0C(K) of the zero-sequence differential current of the bus at the current sampling time K, the calculated value I0C(KN) of the sampling time KN one power frequency cycle ago, and the calculated value I0C(K-2N) of the sampling time K-2N two power frequency cycles ago, the sudden change in the zero-sequence differential current of the bus is calculated according to the following formula:

[0066] ΔI0C=[I0C(K)-I0C(KN)]-[I0C(KN)-I0C(K-2N)];

[0067] The calculation results of ΔI0C reflect the transient change characteristics of the zero-sequence differential current of the bus, and the positive or negative value corresponds to the direction of the abrupt change in the zero-sequence differential current of the bus.

[0068] Understandably, centralized protection and control devices need to calculate the zero-sequence current surge in each bay unit in real time. Since the surge calculation uses a differential algorithm based on the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, the centralized protection and control device is required to have caching capabilities, that is, to save at least the zero-sequence current sampling data of the previous two power frequency cycles for each protection cycle.

[0069] Figure 3 This is a flowchart of another ground fault judgment method provided by an embodiment of the present invention. Figure 3 As shown, the ground fault detection method includes:

[0070] S201. Obtain the zero-sequence current of the loop-in interval unit, the zero-sequence current of the loop-out interval unit, and the zero-sequence current of each branch interval unit.

[0071] S202. Based on the zero-sequence current of the loop-in bay unit, the zero-sequence current of the loop-out bay unit, and the zero-sequence current of each branch bay unit, determine the magnitude and direction of the zero-sequence current mutation of each bay unit, as well as the magnitude and direction of the bus zero-sequence differential current mutation.

[0072] S203. Determine whether the absolute value of the zero-sequence current mutation of the loop-in interval unit is greater than the preset mutation value.

[0073] Specifically, the sudden change setting I0d is a pre-set threshold value, the magnitude of which can be adjusted according to the system parameters of the protected area, the accuracy of the zero-sequence current transformer, and the required protection sensitivity. For example, for systems with large capacitive currents, the sudden change setting I0d can be appropriately increased to avoid frequent starts; for scenarios with high detection requirements for high-resistance grounding faults, the sudden change setting I0d can be appropriately decreased to improve sensitivity. Those skilled in the art can flexibly determine the specific value of the sudden change setting I0d according to actual needs.

[0074] If the absolute value of the zero-sequence current mutation in the loop-in interval unit is greater than the mutation set value, then step S204 is executed. When the determination condition is met, it indicates that a noteworthy fault event has occurred within the protected area, and the centralized protection and control device then enters the subsequent judgment process. At this time, the value of the zero-sequence current mutation ΔI0a of the loop-in interval unit is not only used to initiate the judgment, but its mutation direction will also serve as the absolute reference benchmark for all subsequent comparisons, so it is necessary to proceed to the next step for recording.

[0075] If the absolute value of the zero-sequence current mutation in the loop-in interval unit is less than or equal to the mutation threshold, the system returns to step S201 to continue monitoring. When the absolute value of the zero-sequence current mutation in the loop-in interval unit is not greater than the mutation threshold, it indicates that no fault event warranting further judgment has occurred. This could be due to the system being in normal operation, or the absolute value of the disturbance or interference signal being too small to trigger protection. In this case, the centralized protection and control device does not execute any fault judgment logic and directly returns to step S201 to continue data acquisition and monitoring for the next protection cycle. This design effectively avoids frequent activation of the protection process due to minor fluctuations or noise interference, ensuring the stable operation of the centralized protection and control device and the rational utilization of judgment resources.

[0076] The protection cycle refers to the time interval set by a centralized protection and control device to execute a complete ground fault judgment process. Unlike the power frequency cycle determined by the rated frequency of the power system (20ms for a 50Hz system), the protection cycle is the time step of the device's software logic operation. Its length depends on the device's hardware processing capabilities, software algorithm efficiency, and the requirements for the speed of protection action. The historical data relied upon for abrupt change calculation (such as sampled values ​​from one or two power frequency cycles ago) spans the power frequency cycle, while the decision to execute a new round of judgment is based on the protection cycle as the time node.

[0077] S204. Record the direction of the change in the zero-sequence current change of the loop-in interval unit.

[0078] This step is used to save the direction information of the sudden change in the zero-sequence current of the loop-in interval unit. This information will serve as a unified reference standard in subsequent fault type determination. Specifically, if the calculated value of the sudden change in the zero-sequence current ΔI0a of the loop-in interval unit is positive, the direction of the sudden change is recorded as positive; if the calculated value of the sudden change in the zero-sequence current ΔI0a of the loop-in interval unit is negative, the direction of the sudden change is recorded as negative. After recording, the centralized protection and control device continues to execute step S205.

[0079] S205. Based on the direction of the change in zero-sequence current of the ring-in interval unit, and according to the magnitude and direction of the change in zero-sequence current of the ring-out interval unit and each branch interval unit, as well as the magnitude and direction of the change in zero-sequence differential current of the bus, determine whether the grounding fault is an internal or external grounding fault.

[0080] In some embodiments, whether it is a bus grounding fault is determined according to the bus grounding fault criterion. The bus grounding fault criterion includes: if the absolute value of the bus zero-sequence differential current change is greater than the change value set, and the change direction of the bus zero-sequence differential current change is consistent with the change direction of the zero-sequence current change of the loop-in interval unit.

[0081] Furthermore, if there are other interval units where the absolute value of the zero-sequence current mutation is greater than the mutation value, and the mutation direction of the zero-sequence current mutation in other interval units is the same as the mutation direction of the zero-sequence current mutation in the looping interval unit, then it is determined to be a bus grounding fault.

[0082] Specifically, the zero-sequence differential current ΔI0C of the busbar is defined as the vector sum of all zero-sequence currents flowing into the busbar, i.e., I0C = I0a + I0b + ΣI0i. According to Kirchhoff's current law, under the condition that the busbar itself is fault-free, the current flowing into the busbar should be equal to the current flowing out of the busbar. Therefore, the zero-sequence differential current of the busbar should theoretically be zero (or only a small imbalance). When |ΔI0C| > I0d, it indicates that a significant zero-sequence current imbalance has occurred at the busbar node. This means that a portion of the current is either flowing in but not out, or flowing out but not in. This unbalanced current can only flow into the ground through the fault point of the busbar itself.

[0083] When a ground fault occurs on the busbar, the path of the fault current is as follows: it flows into the busbar from the system side (through the loop-in bay) and then directly to ground at the fault point. At this time, the fault current only flows up to the busbar and does not flow to any outgoing lines. The direction of the change in the busbar zero-sequence differential current change ΔI0C reflects the direction of change in the difference between the current flowing into the busbar and the current flowing out of the busbar. Since the fault current flows entirely to ground through the busbar, and the current flowing out of the busbar is much smaller than the current flowing into the busbar, the direction of the change in the busbar zero-sequence differential current change ΔI0C must be consistent with the direction of the change in the zero-sequence current change ΔI0a of the loop-in bay unit.

[0084] When a ground fault occurs in a branch bay unit, the fault current path is as follows: from the system side, it flows into the busbar through the incoming bay unit, and from the busbar, it flows to the ground point through the faulty branch. In this path, the fault current only flows through the incoming bay unit and the faulty branch bay unit; no fault current flows through other non-faulty branch bay units or the outgoing bay units. Therefore, the direction of the zero-sequence current mutation in the faulty branch bay unit should be opposite to the direction of the zero-sequence current mutation ΔI0a in the incoming bay unit, while the direction of the zero-sequence current mutation in other non-faulty branch bay units and the outgoing bay units should be the same as the direction of the zero-sequence current mutation ΔI0a in the incoming bay unit. In this case, the entire protection area exhibits a situation where "there is a bay unit whose zero-sequence current mutation direction is opposite to that of the incoming bay unit," which contradicts the bus ground fault criterion requirement that "the direction of the zero-sequence current mutation in other bay units is the same as the incoming reference direction," thus eliminating the possibility of a bus fault.

[0085] When a ground fault occurs in the outgoing loop unit, the fault current path is as follows: from the system side, it flows into the busbar through the incoming loop unit, and from the busbar, it flows to the ground at the fault point through the outgoing loop unit. The fault current does not flow through any branch loop units. Therefore, the direction of the zero-sequence current mutation in the outgoing loop unit should be opposite to the direction of the zero-sequence current mutation ΔI0a in the incoming loop unit, while the direction of the zero-sequence current mutation in each branch loop unit should be the same as the direction of the zero-sequence current mutation ΔI0a in the incoming loop unit. However, this also results in a loop unit where the direction of the zero-sequence current mutation is opposite to that of the incoming loop unit, contradicting the condition that "the direction of the zero-sequence current mutation in all other loop units is the same as that of the incoming loop unit."

[0086] In the case of an external ground fault, the fault current path is as follows: from the system side, it flows into this protection zone through the loop-in bay unit; after passing the busbar, it flows out of this protection zone from all outgoing lines (loop-out and branch lines) and finally flows to the external fault point. Therefore, the direction of the change in zero-sequence current variation in all loop-out bay units and branch bay units is opposite to the direction of the change in zero-sequence current variation ΔI0a in the loop-in bay unit. This obviously contradicts the condition that "the direction of the change in zero-sequence current variation in other bay units is the same as the direction of the change in zero-sequence current variation in the loop-in bay unit".

[0087] At this point, none of the outgoing or branch bay units exhibits a change in the direction of its zero-sequence current mutation that is opposite to that of the incoming bay unit. This "opposite direction of the zero-sequence current mutation" is precisely the identifying characteristic of a branch bay unit grounding fault or an outgoing bay unit grounding fault. It indicates that the current in the line containing the outgoing or branch bay unit has reversed, meaning the fault current flows from the line to the busbar. Since the change direction of the zero-sequence current mutation in all outgoing and branch bay units is the same as that in the incoming bay unit (i.e., the fault current flows normally from the busbar to the line), the fault cannot occur on any of the outgoing or branch bay units' lines. Therefore, the fault point can only be located at the common connection point of these bay units, i.e., the busbar itself.

[0088] In some embodiments, it is determined whether there is a grounding fault in the branch interval unit according to the grounding fault criterion of the branch interval unit. The grounding fault criterion of the branch interval unit includes: when the following conditions are simultaneously satisfied, it is determined that a grounding fault has occurred in a certain branch interval unit: the absolute value of the sudden change of the zero-sequence differential current of the bus is less than the sudden change setting value; there is a branch interval unit, the absolute value of the sudden change of its zero-sequence current is greater than the sudden change setting value, and the mutation direction of the sudden change of the zero-sequence current of this branch interval unit is opposite to the mutation direction of the sudden change of the zero-sequence current of the incoming loop interval unit; if there are other interval units with the absolute value of the sudden change of the zero-sequence current greater than the sudden change setting value, then the mutation directions of the sudden change of the zero-sequence current of the other interval units are all the same as the mutation direction of the sudden change of the zero-sequence current of the incoming loop interval unit.

[0089] Specifically, the absolute value of the sudden change of the zero-sequence differential current of the bus is less than the sudden change setting value. This condition is used to confirm that no grounding fault has occurred in the bus itself. As mentioned above, when a grounding fault occurs in the bus, the absolute value of the sudden change of the zero-sequence differential current ΔI0C of the bus must be greater than the sudden change setting value (|ΔI0C|>I0d). Therefore, the condition |ΔI0C|<I0d first excludes the possibility of a bus fault and guides the fault location direction to the outgoing line side (i.e., the outgoing loop interval unit or the branch interval unit).

[0090] If there are other interval units with the absolute value of the sudden change of the zero-sequence current greater than the sudden change setting value, then the mutation directions of the other interval units are all the same as the mutation direction of the sudden change of the zero-sequence current of the incoming loop interval unit. This condition is used to verify that all other interval units except the suspected fault branch interval unit are non-fault lines. Specifically, the other interval units include the outgoing loop interval unit and the remaining branch interval units except the suspected fault branch. If there is a situation where the absolute value of the sudden change of the zero-sequence current in these interval units is greater than the sudden change setting value I0d, then the mutation direction of the sudden change of their zero-sequence current must be the same as the mutation direction of the sudden change of the zero-sequence current of the incoming loop interval unit, that is, their fault current shows the normal direction from the bus to the line.

[0091] The logical meaning of this condition is to exclude the following interference situations:

[0092] If the mutation direction of the sudden change of the zero-sequence current of another branch interval unit is also opposite to the mutation direction of the sudden change of the zero-sequence current of the incoming loop interval unit, then it may involve a multi-point grounding fault, exceeding the single-point fault assumption of this criterion;

[0093] If the mutation direction of the sudden change of the zero-sequence current of the outgoing loop interval unit is opposite to the mutation direction of the sudden change of the zero-sequence current of the incoming loop interval unit, then the fault type should be a grounding fault of the outgoing loop interval unit rather than a grounding fault of the branch interval unit;

[0094] If the mutation directions of the sudden change in zero-sequence current of all other interval units are all opposite to the mutation direction of the sudden change in zero-sequence current of the incoming loop interval unit, the fault type should be an external grounding fault.

[0095] In some embodiments, it is determined whether there is a grounding fault in the outgoing loop interval unit according to the grounding fault criterion of the outgoing loop interval unit. The specific conditions of this criterion are: when the following conditions are simultaneously met, it is determined that there is a grounding fault in the outgoing loop interval unit. The absolute value of the sudden change in zero-sequence differential current of the bus is less than the sudden change setting value; the absolute value of the sudden change in zero-sequence current of the outgoing loop interval unit is greater than the sudden change setting value; the mutation direction of the sudden change in zero-sequence current of the outgoing loop interval unit is opposite to the mutation direction of the sudden change in zero-sequence current of the incoming loop interval unit; if there is a branch interval unit with the absolute value of the sudden change in zero-sequence current greater than the sudden change setting value, the mutation directions of the sudden change in zero-sequence current of the branch interval units are all the same as the mutation direction of the sudden change in zero-sequence current of the incoming loop interval unit.

[0096] Specifically, the absolute value of the sudden change in zero-sequence differential current of the bus is less than the sudden change setting value. This condition is used to confirm that there is no grounding fault in the bus itself. As mentioned above, when there is a grounding fault in the bus, the absolute value of the sudden change in zero-sequence differential current ΔI0C of the bus must be greater than the sudden change setting value. Therefore, the condition |ΔI0C| < I0d first excludes the possibility of a bus fault and guides the fault location direction to the outgoing line side, that is, the line where the outgoing loop interval unit or the branch interval unit is located.

[0097] The absolute value of the sudden change in zero-sequence current of the outgoing loop interval unit is greater than the sudden change setting value. This condition is used to confirm that the outgoing loop interval unit has a significant response to this fault event. As the outgoing line channel for the downstream power supply in this protection area, the absolute value of the sudden change in zero-sequence current of the outgoing loop interval unit being greater than the sudden change setting value indicates that this line participates in the distribution of the fault current and is a potential fault line.

[0098] The mutation direction of the sudden change in zero-sequence current of the outgoing loop interval unit is opposite to the mutation direction of the sudden change in zero-sequence current of the incoming loop interval unit. This condition is the core criterion for identifying the outgoing loop interval unit as a fault line. When there is a grounding fault in the downstream line under the jurisdiction of the outgoing loop interval unit, the path of the fault current is: from the system side, through the incoming loop interval unit, into the bus, and then from the bus, through the outgoing loop interval unit, to the fault point. This is exactly opposite to the fault current direction of the incoming loop interval unit (from the system side to the bus). Therefore, the mutation direction of the sudden change in zero-sequence current of the outgoing loop interval unit being opposite to the mutation direction of the sudden change in zero-sequence current of the incoming loop interval unit is the essential feature of the grounding fault in the outgoing loop interval unit.

[0099] If there are branch interval units where the absolute value of the sudden change in zero-sequence current is greater than the sudden change setting value, then the sudden change directions of the zero-sequence current sudden changes of these branch interval units are all the same as the sudden change direction of the zero-sequence current sudden change of the incoming loop interval unit. This condition is used to verify that all branch interval units with significant responses are non-faulty lines, thus excluding the possibility of other fault types.

[0100] Specifically, if there are branch interval units where the absolute value of the sudden change in zero-sequence current is greater than the sudden change setting value I0d, then the sudden change direction of the zero-sequence current sudden change of these branch interval units must be the same as the sudden change direction of the zero-sequence current sudden change of the incoming loop interval unit, that is, the fault current shows the normal direction from the bus to the line. The logical significance of this condition is to exclude the following interference situations:

[0101] If the sudden change direction of the zero-sequence current sudden change of any one branch interval unit is opposite to the sudden change direction of the zero-sequence current sudden change of the incoming loop interval unit, it indicates that this branch interval unit may be a faulty line. At this time, the fault type should be the grounding fault of the branch interval unit rather than the grounding fault of the outgoing loop interval unit;

[0102] If the sudden change directions of the zero-sequence current sudden changes of all branch interval units are all opposite to the sudden change direction of the zero-sequence current sudden change of the incoming loop interval unit, the fault type should be an external grounding fault; this condition ensures that except for the outgoing loop interval unit, no branch interval unit shows fault characteristics, thus uniquely pointing the fault to the outgoing loop interval unit.

[0103] In some embodiments, it is judged whether it is an external grounding fault according to the external grounding fault criterion. The specific conditions of this criterion are: when the following conditions are simultaneously met, it is determined as an external grounding fault: the absolute value of the sudden change in bus zero-sequence differential current is less than the sudden change setting value; there are outgoing loop interval units or branch interval units where the absolute value of the sudden change in zero-sequence current is greater than the sudden change setting value; for all outgoing loop interval units and branch interval units where the absolute value of the sudden change in zero-sequence current is greater than the sudden change setting value, the sudden change directions of their zero-sequence current sudden changes are consistent and all opposite to the sudden change direction of the zero-sequence current sudden change of the incoming loop interval unit.

[0104] Specifically, the absolute value of the sudden change in bus zero-sequence differential current is less than the sudden change setting value. This condition is used to confirm that no grounding fault has occurred on the bus itself. As mentioned before, when a grounding fault occurs on the bus, the absolute value of the sudden change in bus zero-sequence differential current ΔI0C is greater than the sudden change setting value. Therefore, the condition |ΔI0C| < I0d first excludes the possibility of a bus fault, indicating that the fault point is not on the bus.

[0105] There exists a loop-out or branch-line bay unit whose absolute value of the zero-sequence current mutation is greater than the mutation value setpoint. This condition confirms that at least one outgoing-side bay unit (loop-out or branch-line bay unit) within this protection area has a significant response to the fault event. If the absolute value of the zero-sequence current mutation is greater than the mutation value setpoint in any loop-out or branch-line bay unit, it indicates that no line within this protection area sensed the fault, which does not meet the basic premise that an external fault affects this area. Therefore, this condition ensures that the fault event did indeed affect the current distribution within this protection area.

[0106] When the fault point is located outside the protection zone (such as the outgoing line of the upstream substation of the loop-in bay unit, or other main lines on the same busbar that are not directly electrically connected to the protection zone), the distribution of the fault current exhibits a special pattern. Specifically, the fault current flows from the system side into the protection zone through the loop-in bay unit, flows through the busbar, and then flows out of the protection zone from all outgoing lines (loop-out bay units and each branch bay unit), eventually flowing to the external fault point.

[0107] Under this fault current path, the fault current flow direction of each bay unit has the following characteristics: the fault current flow direction of the loop-in bay unit is from the system side to the busbar; the fault current flow direction of the loop-out bay unit and each branch bay unit is from the busbar to the line.

[0108] According to the unified convention of the zero-sequence current transformer installation direction of the present invention (the zero-sequence current transformers of each bay unit face the busbar), the relationship between the fault current flow direction and the transformer installation direction determines the sign of the calculated value of the zero-sequence current mutation in each bay unit:

[0109] The fault current flow direction of the loop-in interval unit is consistent with the installation direction of its zero-sequence current transformer. Therefore, the sign (positive or negative) of the calculated value of its zero-sequence current mutation ΔI0a is recorded as the reference direction for this judgment cycle.

[0110] The fault current flow direction of the outgoing interval unit and each branch interval unit is opposite to the installation direction of their zero-sequence current transformers. Therefore, the calculated signs of their zero-sequence current mutations ΔI0b and ΔI0i are opposite to the mutation direction of the zero-sequence current mutation of the incoming interval unit.

[0111] Meanwhile, since the fault current of all outgoing lines is driven by the same external fault source, the direction of the change of the zero-sequence current change of all loop-out bay units and each branch bay unit with significant response must be consistent. That is, the signs of their change value calculations are all the same (both positive or both negative), and they are all opposite to the direction of the change of the zero-sequence current change of the loop-in bay unit.

[0112] In some embodiments, it is determined whether it is a bus grounding fault based on the bus grounding fault criterion; if it cannot be determined to be a bus grounding fault based on the bus grounding fault criterion, the bus grounding fault criterion is exited, and at least one of the branch bay unit grounding fault criterion, the loop-out bay unit grounding fault criterion, and the external zone grounding fault criterion is continued to be executed; if it cannot be determined to be an external zone grounding fault based on the external zone grounding fault criterion, the external zone grounding fault criterion is exited, and at least one of the bus grounding fault criterion, the branch bay unit grounding fault criterion, and the loop-out bay unit grounding fault criterion is continued to be executed; if the grounding fault type cannot be determined based on the branch bay unit grounding fault criterion or the loop-out bay unit grounding fault criterion, the process is transferred to the single-line grounding fault judgment process.

[0113] Specifically, the meaning of exiting the busbar grounding fault criterion is that the currently collected electrical quantity characteristics do not match the typical profile of a busbar grounding fault, therefore, the continued attempt to assume a busbar fault is abandoned. However, abandoning this criterion does not mean the judgment process ends, but rather that it moves to examining other possible fault types. Specifically, the device will continue to execute one or more of the following criteria: branch bay unit grounding fault criterion, loop-out bay unit grounding fault criterion, and external area grounding fault criterion. These criteria can be executed sequentially (tried one by one in a preset order) or in parallel (simultaneously calculating the matching degree of each criterion and determining the most likely fault type through a comprehensive score). This embodiment does not limit this, as long as accurate identification of the grounding fault type can be achieved.

[0114] The external grounding fault criterion is also used as an independent criterion in the judgment. When an external grounding fault cannot be determined based on this criterion, it means that the current electrical quantity characteristics do not meet the feature that "the change direction of the zero-sequence current change in all outgoing side bay units with significant response is consistent and opposite to the loop reference direction." Therefore, the assumption of an external grounding fault is abandoned, and other possible fault types are examined. This design ensures that the criteria complement and corroborate each other, avoiding omissions due to the limitations of a single criterion.

[0115] When there is only one load line in the protection area (e.g., only one branch bay unit), which makes the basic conditions for "multi-bay" comparison not available, the centralized protection and control device will no longer forcibly apply the multi-bay comparison criteria, but will switch to the single-line grounding fault judgment process.

[0116] The single-line grounding fault judgment process adopts well-known single-line grounding protection algorithms in the field, such as methods based on the phase relationship between zero-sequence voltage and zero-sequence current, methods based on the fifth harmonic component, and methods based on the transient first half-wave principle. These single-line algorithms rely only on the zero-sequence voltage and zero-sequence current information of the line for judgment. Although the accuracy is relatively limited, they can serve as an effective backup solution when multi-interval comparison conditions are not available, ensuring that centralized protection and control devices can still respond in most scenarios.

[0117] Figure 4 This is a flowchart of another ground fault judgment method provided by an embodiment of the present invention. Figure 4 As shown, the ground fault detection method includes:

[0118] S301. Obtain the zero-sequence current of the loop-in interval unit, the zero-sequence current of the loop-out interval unit, and the zero-sequence current of each branch interval unit.

[0119] S302. Based on the zero-sequence current of the loop-in bay unit, the zero-sequence current of the loop-out bay unit, and the zero-sequence current of each branch bay unit, determine the magnitude and direction of the zero-sequence current mutation of each bay unit, as well as the magnitude and direction of the bus zero-sequence differential current mutation.

[0120] S303. Based on the direction of the change in zero-sequence current of the ring-in interval unit, and according to the magnitude and direction of the change in zero-sequence current of the ring-out interval unit and each branch interval unit, as well as the magnitude and direction of the change in zero-sequence differential current of the bus, determine whether the grounding fault is an internal or external grounding fault.

[0121] S304. Determine whether the system zero-sequence voltage is greater than the preset zero-sequence voltage setting value.

[0122] This step is used to verify the ground fault judgment result. Its purpose is to confirm that the electrical quantity changes on which the aforementioned fault type judgment is based are indeed caused by a real ground fault, rather than unbalanced voltage fluctuations, voltage transformer interference or other transient disturbances during normal system operation.

[0123] The system zero-sequence voltage U0 is a global characteristic quantity reflecting whether a ground fault has occurred. When a single-phase ground fault occurs in the power grid, a zero-sequence voltage will appear in the system, and its amplitude is positively correlated with the severity of the fault. Therefore, using whether the system zero-sequence voltage U0 exceeds the preset zero-sequence voltage setting U0d as the criterion for finally confirming the validity of the fault can effectively filter out misjudgments caused by factors such as load fluctuations, switching operations, or measurement errors.

[0124] If it is determined that the system zero-sequence voltage is greater than the zero-sequence voltage setpoint, then step S305 is executed. If it is determined that the system zero-sequence voltage is less than the zero-sequence voltage setpoint, then step S306 is executed, and the process returns to continue executing the steps of obtaining the zero-sequence current of the loop-in interval unit, the zero-sequence current of the loop-out interval unit, and the zero-sequence current of each branch interval unit.

[0125] S305. Confirm that the judgment of grounding fault within or outside the zone is valid, and issue a trip command to the circuit breaker of the corresponding line to disconnect the faulty line, and issue an alarm signal at the same time.

[0126] When the system zero-sequence voltage exceeds the zero-sequence voltage setting, it indicates that the current electrical anomaly is indeed caused by a ground fault, and the aforementioned fault type judgment result is valid. At this time, the centralized protection and control device enters the fault handling process. For ground faults within the zone (including bus ground faults, branch bay unit ground faults, and loop-out bay unit ground faults), the centralized protection and control device issues a trip command to the circuit breaker of the corresponding line to quickly disconnect the faulty line, and simultaneously issues an audible and visual alarm signal to inform maintenance personnel of the location and type of the fault. It should be noted that for loop-out bay unit ground faults (i.e., downstream faults in this protection zone), the trip command is also sent to the circuit breaker of the loop-out bay unit to isolate the downstream faulty line.

[0127] For grounding faults outside the zone, although the centralized protection and control device confirms that the fault judgment is valid, it does not perform a trip operation, but only records the fault information and issues an alarm signal to avoid expanding the power outage area due to faults outside the zone.

[0128] S306. Troubleshooting is prohibited.

[0129] When the system zero-sequence voltage is less than the zero-sequence voltage setting, it indicates that the current electrical abnormality may originate from non-fault factors (such as system imbalance, measurement interference, etc.), and the aforementioned fault type judgment result should not be used as the basis for protection execution. At this time, the centralized protection and control device is prohibited from performing any tripping operation and returns to step S301 to restart data acquisition and monitoring for the next protection cycle. This setting ensures that real faults can be quickly cleared while effectively avoiding malfunctions under non-fault conditions.

[0130] It should be noted that the zero-sequence voltage setting U0d and the sudden change setting I0d need to be comprehensively adjusted based on the single-phase grounding capacitance current level of the power supply system where the protection device is located, the accuracy class of the zero-sequence current transformer used, and the actual requirements of the protection device for sensitivity and selectivity, so as to ensure that the optimal protection performance can be achieved under different operating conditions.

[0131] Based on the same inventive concept, this embodiment of the invention also provides a centralized protection and control device. This centralized protection and control device is a core product of intelligent power distribution systems. It can be used in conjunction with intelligent large-scale DC converter transformers, intelligent reactors, and other transformers, rectifiers, and inductors to execute the ground fault judgment method for power distribution networks provided in any embodiment of the invention. It has the beneficial effects of the ground fault judgment method provided in any embodiment of the invention, which will not be described in detail here.

[0132] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0133] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for determining grounding faults in a power distribution network, characterized in that, The protection zone of the distribution network includes the busbar, the incoming loop bay unit, the outgoing loop bay unit, and at least one branch bay unit. The ground fault detection method includes: The zero-sequence current of the loop-in interval unit, the zero-sequence current of the loop-out interval unit, and the zero-sequence current of each branch interval unit are obtained. Based on the zero-sequence current of the incoming loop interval unit, the zero-sequence current of the outgoing loop interval unit, and the zero-sequence current of each branch interval unit, the magnitude and direction of the zero-sequence current mutation in each interval unit, as well as the magnitude and direction of the zero-sequence differential current mutation in the busbar, are determined; wherein, each interval unit includes the incoming loop interval unit, the outgoing loop interval unit, and each branch interval unit. Based on the direction of the zero-sequence current mutation in the ring-in interval unit and a preset mutation value, and according to the magnitude and direction of the zero-sequence current mutation in the ring-out interval unit and each branch interval unit, as well as the magnitude and direction of the zero-sequence differential current mutation in the busbar, the ground fault is determined to be either an intra-zone ground fault or an extra-zone ground fault; wherein, the intra-zone ground fault includes any one of the following: busbar ground fault, branch interval unit ground fault, and ring-out interval unit ground fault. The aforementioned ring-in interval unit refers to the incoming channel that connects to the upstream power supply and allows energy to flow into the distribution network protection area; The aforementioned loop-out interval unit refers to the outgoing channel for power supply from the distribution network protection area to other downstream protection areas; The branch interval unit refers to the power distribution line that directly supplies power to end users within the protection zone of the power distribution network.

2. The method for determining grounding faults in a power distribution network according to claim 1, characterized in that, The step of determining the magnitude and direction of the zero-sequence current mutation in each bay unit, and the magnitude and direction of the bus zero-sequence differential current mutation, based on the zero-sequence current of the incoming bay unit, the zero-sequence current of the outgoing bay unit, and the zero-sequence current of each branch bay unit, includes: Based on the zero-sequence current sampling values ​​of the loop-in interval unit at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, determine the magnitude and direction of the zero-sequence current mutation of the loop-in interval unit. Based on the zero-sequence current sampling values ​​of the loop-out interval unit at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, determine the magnitude and direction of the zero-sequence current mutation of the loop-out interval unit. Based on the zero-sequence current sampling values ​​of each branch interval unit at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, determine the magnitude and direction of the zero-sequence current mutation of each branch interval unit. The zero-sequence differential current of the bus is determined by the vector sum of the zero-sequence current sampled values ​​of the ring-in interval unit, the ring-out interval unit, and each branch interval unit at the current sampling time. Based on the calculated values ​​of the bus zero-sequence differential current at the current sampling time, the sampling time one power frequency cycle ago, and the sampling time two power frequency cycles ago, the magnitude and direction of the change in the bus zero-sequence differential current are determined.

3. The method for determining grounding faults in a power distribution network according to claim 1, characterized in that, Before the step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault, the ground fault determination method further includes: Determine whether the absolute value of the zero-sequence current mutation of the loop-in interval unit is greater than a preset mutation value; If the absolute value of the zero-sequence current mutation of the loop-in interval unit is greater than the mutation value, then the mutation direction of the zero-sequence current mutation of the loop-in interval unit is recorded.

4. The method for determining grounding faults in a distribution network according to any one of claims 1-3, characterized in that, The step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: If the absolute value of the bus zero-sequence differential current mutation is greater than the mutation value, and the mutation direction of the bus zero-sequence differential current mutation is consistent with the mutation direction of the zero-sequence current mutation of the loop-in interval unit; Furthermore, if there are other interval units where the absolute value of the zero-sequence current mutation is greater than the mutation value, and the mutation direction of the zero-sequence current mutation in the other interval units is the same as the mutation direction of the zero-sequence current mutation in the looping interval unit, then it is determined to be a bus grounding fault.

5. The method for determining grounding faults in a distribution network according to any one of claims 1-3, characterized in that, The step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: A ground fault is determined to have occurred in a branch bay unit when all of the following conditions are met: The absolute value of the zero-sequence differential current mutation in the busbar is less than the mutation constant value. There exists a branch interval unit whose absolute value of zero-sequence current mutation is greater than the mutation value setpoint, and the mutation direction of the zero-sequence current mutation of the branch interval unit is opposite to the mutation direction of the zero-sequence current mutation of the loop interval unit. If there are other interval units where the absolute value of the zero-sequence current mutation is greater than the mutation value, then the mutation direction of the zero-sequence current mutation of the other interval units is the same as the mutation direction of the zero-sequence current mutation of the looping interval unit.

6. The method for determining grounding faults in a distribution network according to any one of claims 1-3, characterized in that, The step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: A ground fault is determined to have occurred in the loop-out bay unit when all of the following conditions are met: The absolute value of the zero-sequence differential current mutation in the busbar is less than the mutation constant value; The absolute value of the zero-sequence current mutation in the loop-out interval unit is greater than the mutation value setpoint. The direction of the abrupt change of the zero-sequence current mutation of the loop-out interval unit is opposite to the direction of the abrupt change of the zero-sequence current mutation of the loop-in interval unit. If there is a branch interval unit whose absolute value of the zero-sequence current mutation is greater than the mutation value, then the mutation direction of the zero-sequence current mutation of the branch interval unit is the same as the mutation direction of the zero-sequence current mutation of the loop interval unit.

7. The method for determining grounding faults in a distribution network according to any one of claims 1-3, characterized in that, The step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: A ground fault outside the designated area is determined when all of the following conditions are met: The absolute value of the zero-sequence differential current mutation in the busbar is less than the mutation constant value; There are loop-out interval units or branch interval units where the absolute value of the zero-sequence current mutation is greater than the mutation value setpoint. All loop-out and branch-line interval units whose absolute values ​​of zero-sequence current mutations are greater than the mutation value have the same mutation direction and are opposite to the mutation direction of the zero-sequence current mutation of the loop-in interval unit.

8. The method for determining grounding faults in a distribution network according to any one of claims 1-3, characterized in that, The step of determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault includes: Determine whether it is a bus grounding fault based on the bus grounding fault criteria; If the bus grounding fault cannot be determined according to the bus grounding fault criterion, the bus grounding fault criterion is exited, and at least one of the branch bay unit grounding fault criterion, the loop-out bay unit grounding fault criterion, and the external grounding fault criterion continues to be executed. If the external grounding fault cannot be determined according to the external grounding fault criterion, the external grounding fault criterion is terminated, and at least one of the bus grounding fault criterion, the branch bay unit grounding fault criterion, and the loop-out bay unit grounding fault criterion continues to be executed. If the ground fault type cannot be determined based on the ground fault criterion of the branch interval unit or the ground fault criterion of the loop-out interval unit, then the single-line ground fault judgment process is initiated.

9. The method for determining grounding faults in a power distribution network according to claim 1, characterized in that, After determining whether a ground fault is an intra-zone ground fault or an extra-zone ground fault, the ground fault determination method further includes: Determine whether the system zero-sequence voltage is greater than the preset zero-sequence voltage value; If the zero-sequence voltage of the system is greater than the zero-sequence voltage setting value, the judgment of the ground fault in the zone or the ground fault outside the zone is confirmed to be valid, and a trip command is sent to the circuit breaker of the corresponding line to disconnect the faulty line and at the same time an alarm signal is issued. If the zero-sequence voltage of the system is less than the zero-sequence voltage setpoint, fault handling is prohibited, and the process returns to continue executing the steps of obtaining the zero-sequence current of the loop-in interval unit, the zero-sequence current of the loop-out interval unit, and the zero-sequence current of each branch interval unit.

10. A centralized protection and control device, characterized in that, The method for determining ground faults in a power distribution network as described in any one of claims 1-9.

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