Ground fault detection method, power distribution terminal and power distribution network system

Abstract

The application discloses a grounding fault detection method, a power distribution terminal and a power distribution network system, and belongs to the technical field of electric power detection. In the application, firstly, a zero sequence voltage mutual inductor and two zero sequence current mutual inductors with different transformation ratios are arranged on a power distribution line; then, a voltage steady-state value of a zero sequence voltage output by the zero sequence voltage mutual inductor is detected, and a current steady-state value of a zero sequence current output by each zero sequence current mutual inductor is detected; then, for each zero sequence voltage mutual inductor, when the voltage steady-state value of the zero sequence voltage is out of limit and the current steady-state value of the zero sequence current is out of limit, power is determined according to a transient value of the zero sequence voltage and a transient value of the zero sequence current, and a detection result is obtained according to the corresponding power and the transient value of the zero sequence current; finally, a grounding fault detection result of the power distribution line is obtained according to detection results corresponding to the two zero sequence current mutual inductors, and the anti-transition resistance capability of a small-current grounding system can be improved.

Description

Technical Field

[0001] This application relates to the field of power detection technology, specifically to a ground fault detection method, a power distribution terminal, and a power distribution network system. Background Technology

[0002] In low-current grounding systems, when a ground fault occurs in a distribution line, the grounding resistance generated by the conductor falling to the ground is very large, which may produce a transition resistance, resulting in a relatively small fault current. At this time, ground fault detection based on the zero-sequence current output by a fixed-ratio current transformer (CT) may not be able to effectively detect the ground fault caused by this transition resistance, making the low-current grounding system have poor resistance to transition resistance. Summary of the Invention

[0003] The main objective of this application is to provide a ground fault detection method, a power distribution terminal, and a power distribution network system, which aims to at least partially solve the aforementioned technical problems.

[0004] To achieve the above objectives, in a first aspect, a ground fault detection method is provided, applied to a distribution network system. The distribution network system includes a distribution terminal, a zero-sequence voltage transformer located on the distribution line, a first zero-sequence current transformer, and a second zero-sequence current transformer. The first and second zero-sequence current transformers have different transformation ratios. The distribution terminal includes a first current sampling channel, a second current sampling channel, a first logic module, a second logic module, and a third logic module. The first current sampling channel and the first logic module correspond one-to-one with the first zero-sequence current transformer, and the second current sampling channel and the second logic module correspond one-to-one with the second zero-sequence current transformer. The transformation ratios of the first and second current sampling channels are different. The method includes: The first zero-sequence current collected by the first zero-sequence current transformer is sampled through the first current sampling channel; The second zero-sequence current collected by the second zero-sequence current transformer is sampled through the second current sampling channel; The first logic module acquires the first steady-state voltage value of the zero-sequence voltage and the first steady-state current value of the first zero-sequence current from the zero-sequence voltage transformer. When the first steady-state voltage value is greater than a preset steady-state voltage threshold and the first steady-state current value is greater than a preset steady-state current threshold, the first transient voltage value of the zero-sequence voltage and the first transient current value of the first zero-sequence current acquired within a first preset time period before the current moment are acquired, and the first power is determined based on the first transient voltage value and the first transient current value. The first detection result is obtained based on the first power and the first transient current value. The second logic module acquires the second steady-state value of the zero-sequence voltage and the second steady-state value of the zero-sequence current from the zero-sequence voltage transformer. When the second steady-state value of the voltage is greater than a preset steady-state voltage threshold and the second steady-state value of the current is greater than a preset steady-state current threshold, the module acquires the second transient value of the zero-sequence voltage and the second transient value of the zero-sequence current collected within a first preset time period before the current moment, and determines the second power based on the second transient value of the voltage and the second transient value of the current. Based on the second power and the second transient value of the current, the module obtains the second detection result. The third logic module determines the grounding fault detection result of the power distribution line based on the first and second detection results.

[0005] Secondly, a power distribution terminal is also provided, including a first current sampling channel, a second current sampling channel, a memory, and a processor. The processor includes a first logic module, a second logic module, and a third logic module. The transformation ratios of the first current sampling channel and the second current sampling channel are different. The first current sampling channel is used to sample the first zero-sequence current on the power distribution line where the power distribution terminal is located, and the second current sampling channel is used to sample the second zero-sequence current on the power distribution line. The memory stores a computer program, and when the computer program is executed by the processor, it implements the ground fault detection method as described above.

[0006] Thirdly, a power distribution network system is also provided, including: Load switches located on power distribution lines; The zero-sequence voltage transformer, the first zero-sequence current transformer, and the second zero-sequence current transformer are located on the incoming side of the load switch. The zero-sequence voltage transformer is used to collect the zero-sequence voltage of the distribution line, the first zero-sequence current transformer is used to collect the first zero-sequence current of the distribution line, and the second zero-sequence current transformer is used to collect the second zero-sequence current of the distribution line. As described above, the power distribution terminal is connected to the zero-sequence voltage transformer, the first zero-sequence current transformer, and the second zero-sequence current transformer.

[0007] Therefore, in this application, firstly, a zero-sequence voltage transformer and a first zero-sequence current transformer and a second zero-sequence current transformer with different turns ratios are installed on the power distribution line. Then, the first zero-sequence current collected by the first zero-sequence current transformer is sampled through a first current sampling channel, and the second zero-sequence current collected by the second zero-sequence current transformer is sampled through a second current sampling channel. Next, the first logic module performs over-limit detection based on the first steady-state value of the zero-sequence voltage collected by the zero-sequence voltage transformer and the first steady-state value of the first zero-sequence current collected by the first current sampling channel. When both the first steady-state value of the voltage and the steady-state value of the zero-sequence current exceed the limit, the first transient value of the zero-sequence voltage and the first steady-state value of the zero-sequence current collected within a first preset time period before the current moment are used for over-limit detection. The first power is determined by the first current transient value. Based on the first power and the first current transient value, the first detection result is obtained. Then, the second logic module performs over-limit detection based on the second steady-state value of the zero-sequence voltage collected by the zero-sequence voltage transformer and the second steady-state value of the second zero-sequence current collected by the second current sampling channel. When both the second steady-state value of the voltage and the steady-state value of the zero-sequence current exceed the limit, the second power is determined based on the second transient value of the zero-sequence voltage and the second transient value of the zero-sequence current collected within the first preset time period before the current moment. Based on the second power and the second current transient value, the second detection result is obtained. Finally, the third logic module obtains the grounding fault detection result of the power distribution line based on the first detection result of the first logic module and the second detection result of the second logic module. In this way, ground fault detection is performed based on the zero-sequence current output by two zero-sequence current transformers with different turns ratios. When the ground fault caused by the transition resistance cannot be detected based on the zero-sequence current output by the zero-sequence current transformer with a larger turns ratio, the ground fault caused by the transition resistance can be detected based on the zero-sequence current output by the zero-sequence current transformer with a smaller turns ratio, thereby improving the transition resistance resistance capability of the low-current grounding system.

[0008] Other features and advantages of this application will be described in detail in the following detailed description section. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of this application, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of the structure of a power distribution network system provided in an exemplary embodiment of this application; Figure 2This is a schematic diagram of the structure of the power distribution terminal provided in an exemplary embodiment of this application; Figure 3 This is a schematic flowchart of a grounding fault detection method provided in an exemplary embodiment of this application; Figure 4 This is another schematic flowchart of the grounding fault detection method provided in an exemplary embodiment of this application.

[0011] The realization of the objectives, functional features and advantages of the embodiments of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0013] In the embodiments of this application, "at least one" refers to one or more; "multiple" refers to two or more. The terms "first," "second," "third," etc., are used only for descriptive purposes and should not be construed as indicating or implying relative importance or order.

[0014] References such as “one embodiment” or “some embodiments” as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the terms “comprising,” “including,” “having,” and variations thereof, as used in this specification, mean “including, but not limited to,” unless otherwise specifically emphasized.

[0015] It should be noted that in the embodiments of this application, "and / or" describes the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. In addition, the character " / ", unless otherwise specified, generally indicates that the associated objects before and after it are in an "or" relationship.

[0016] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0017] Furthermore, the use of "applies to" or "configured to" in this application implies open and inclusive language, which does not exclude the applicability to or configuration to devices performing additional tasks or steps. Additionally, the use of "based on" implies openness and inclusivity, because processes, steps, calculations, or other actions "based on" one or more of the stated conditions or values ​​may in practice be based on additional conditions or values ​​beyond those stated.

[0018] In this application, the term "exemplary" is used to mean "used as an example, illustration, or description." Any embodiment described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other embodiments. The following description is provided to enable any person skilled in the art to make and use this application. Details are set forth in the following description for purposes of explanation. It should be understood that those skilled in the art will recognize that this application can be made without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but is consistent with the broadest scope of the principles and features disclosed in this application.

[0019] First, the background technology related to the grounding fault detection method, distribution terminal and distribution network system of this application will be further introduced.

[0020] In low-current grounding systems, it is required to isolate low-current grounding faults as quickly and as close as possible. However, when a grounding fault occurs in a distribution line, the grounding resistance generated by the fallen conductor is very high, which may create a transition resistance, resulting in a relatively small fault current. In this case, grounding fault detection based on the zero-sequence current output of a fixed-ratio current transformer (CT) may not be effective in detecting the grounding fault caused by this transition resistance, making the low-current grounding system's resistance to transition resistance poor. For example, when a grounding fault with a transition resistance of 5000Ω occurs in a low-current grounding system, calculated with a CT ratio of 100 / 1, the zero-sequence current output by the CT at the time of the fault is approximately 0.4A, which translates to a secondary value of 4mA. If the small CT inside the distribution terminal is configured with a ratio of 20 / 3.53, the zero-sequence current value of the distribution terminal will be approximately 5, which is insufficient for detecting low-current grounding faults. Therefore, grounding fault detection based on the zero-sequence current output of a fixed-ratio CT can detect grounding faults with a transition resistance of less than 5000Ω, but it is difficult to detect intermittent grounding faults.

[0021] Based on this, this application provides a ground fault detection method, a power distribution terminal, and a power distribution network system. First, a zero-sequence voltage transformer and a first zero-sequence current transformer and a second zero-sequence current transformer with different turns ratios are installed on the power distribution line. Then, the first zero-sequence current collected by the first zero-sequence current transformer is sampled through a first current sampling channel, and the second zero-sequence current collected by the second zero-sequence current transformer is sampled through a second current sampling channel. Next, a first logic module performs over-limit detection based on the first steady-state value of the zero-sequence voltage collected by the zero-sequence voltage transformer and the first steady-state value of the first zero-sequence current collected by the first current sampling channel. When both the first steady-state value of the voltage and the steady-state value of the zero-sequence current exceed the limit, the first steady-state value of the zero-sequence voltage collected within a first preset time period before the current moment is used for over-limit detection. The first power is determined by the voltage transient value and the first current transient value of the first zero-sequence current. Based on the first power and the first current transient value, a first detection result is obtained. Then, the second logic module performs over-limit detection based on the second steady-state value of the zero-sequence voltage collected by the zero-sequence voltage transformer and the second steady-state value of the second zero-sequence current collected by the second current sampling channel. When both the second steady-state value of the voltage and the steady-state value of the zero-sequence current exceed the limit, the second power is determined based on the second voltage transient value of the zero-sequence voltage and the second current transient value of the zero-sequence current collected within a first preset time period before the current moment. Based on the second power and the second current transient value, a second detection result is obtained. Finally, the third logic module obtains the grounding fault detection result of the power distribution line based on the first detection result of the first logic module and the second detection result of the second logic module. In this way, ground fault detection is performed based on the zero-sequence current output by two zero-sequence current transformers with different turns ratios. When the ground fault caused by the transition resistance cannot be detected based on the zero-sequence current output by the zero-sequence current transformer with a larger turns ratio, the ground fault caused by the transition resistance can be detected based on the zero-sequence current output by the zero-sequence current transformer with a smaller turns ratio, thereby improving the transition resistance resistance capability of the low-current grounding system.

[0022] Furthermore, in the embodiments of this application, when performing power detection and current transient value detection, a transient method is used to perform zero-sequence power detection and current transient value detection at multiple points within a second preset time period. This can improve the accuracy of the transient method through multi-point redundant detection.

[0023] In addition, this application embodiment also achieves intermittent ground fault detection by determining whether the first detection result or the second detection result indicates a ground fault has occurred multiple times within a third preset time period. This can avoid safety problems caused by intermittent ground faults and improve the safety of the power distribution network system.

[0024] Next, we will provide a detailed introduction to the power distribution network system and power distribution terminal involved in the grounding fault detection method of this application.

[0025] On the one hand, this embodiment provides a power distribution network system, such as Figure 1 As shown, the power distribution network system may include a load switch FS1 located on the distribution line, a zero-sequence voltage transformer PT located on the incoming side of the load switch FS1, a first zero-sequence current transformer CT1 and a second zero-sequence current transformer CT2, and a distribution terminal. The zero-sequence voltage transformer PT is used to collect the zero-sequence voltage of the distribution line, the first zero-sequence current transformer CT1 is used to collect the first zero-sequence current of the distribution line, and the second zero-sequence current transformer CT2 is used to collect the second zero-sequence current of the distribution line. The distribution terminal is connected to the zero-sequence voltage transformer PT, the first zero-sequence current transformer CT1, and the second zero-sequence current transformer CT2 respectively to implement the ground fault detection method of any of the embodiments described below.

[0026] On the other hand, this embodiment provides a power distribution terminal, such as Figure 2 As shown, the power distribution terminal may include a first current sampling channel, a second current sampling channel, a memory, and a processor. The processor may include a first logic module, a second logic module, and a third logic module. The first and second current sampling channels have different transformation ratios. The first current sampling channel is used to sample the first zero-sequence current on the power distribution line where the power distribution terminal is located, and the second current sampling channel is used to sample the second zero-sequence current on the power distribution line. The memory stores a computer program, which, when executed by the processor, implements the ground fault detection method as described in any of the embodiments in this context.

[0027] In this embodiment, both the first current sampling channel and the second current sampling channel are ADC (Analog-to-Digital Conversion) sampling channels. The distribution terminal may also include a voltage sampling channel, which is used to sample the zero-sequence voltage output by the zero-sequence voltage transformer. The turns ratio of the first zero-sequence current transformer CT1 and the second zero-sequence current transformer CT2 can be set according to factors such as the maximum fault zero-sequence residual current of the system. The turns ratio of the first current sampling channel can be set according to the turns ratio of the first zero-sequence current transformer and the channel's rated secondary current, and the turns ratio of the second current sampling channel can be set according to the turns ratio of the second zero-sequence current transformer and the channel's rated secondary current. For example, the turns ratio of the first zero-sequence current transformer CT1 is 100 / 1, and the corresponding turns ratio of the first current sampling channel in the distribution terminal is 20 / 3.53. The transformation ratio of the second zero-sequence current transformer CT2 is 100 / 5, and the transformation ratio of the corresponding second sampling channel in the power distribution terminal is 5 / 3.53. Therefore, the second current sampling channel can improve the zero-sequence current code value obtained after AD conversion compared with the first current sampling channel, so that the acquired second zero-sequence current can meet the requirements of extremely small current acquisition.

[0028] Furthermore, the processor can implement ground fault detection through a first logic module, a second logic module, and a third logic module. Specifically, the first current sampling channel and the first logic module correspond one-to-one with the first zero-sequence current transformer to form one detection line, and the second current sampling channel and the second logic module correspond one-to-one with the second zero-sequence current transformer to form another detection line. The two detection lines are electrically isolated from each other. The first logic module performs ground fault detection based on the zero-sequence voltage collected by the voltage acquisition channel and the first zero-sequence current collected by the first current acquisition channel. The second logic module performs ground fault detection based on the zero-sequence voltage collected by the voltage acquisition channel and the second zero-sequence current collected by the second current sensor. Thus, the first and second logic modules can use different detection algorithms to obtain their respective first and second detection results. The third logic module can then determine the ground fault detection result based on the first detection result of the first logic module and the second detection result of the second logic module. This dual-redundant ground fault detection improves the detection success rate of small-current ground faults in low-current grounding systems with transition resistance grounding.

[0029] Based on the aforementioned power distribution network system and distribution terminal, this embodiment provides a ground fault detection method, such as... Figure 3 As shown, the ground fault detection method may include the following steps: S301: The first zero-sequence current collected by the first zero-sequence current transformer is sampled through the first current sampling channel. In this embodiment, the first current sampling channel can perform analog-to-digital conversion on the first zero-sequence current according to its own transformation ratio, and output the first current code value corresponding to the first zero-sequence current to the first logic module.

[0030] S302: The second zero-sequence current collected by the second zero-sequence current transformer is sampled through the second current sampling channel. In this embodiment, the second current sampling channel can perform analog-to-digital conversion on the second zero-sequence current according to its own transformation ratio, and output the second current code value corresponding to the second zero-sequence current to the second logic module.

[0031] S303: The first logic module acquires the first steady-state value of the zero-sequence voltage and the first steady-state value of the first zero-sequence current from the zero-sequence voltage transformer. When the first steady-state value of the voltage is greater than a preset steady-state voltage threshold and the first steady-state value of the current is greater than a preset steady-state current threshold, the first transient value of the zero-sequence voltage and the first transient value of the first zero-sequence current acquired within a first preset time period before the current moment are acquired, and the first power is determined based on the first transient value of the voltage and the first transient value of the current. A first detection result is obtained based on the first power and the first transient value of the current. In this embodiment, the voltage sampling channel can perform analog-to-digital conversion on the zero-sequence voltage acquired by the zero-sequence voltage transformer to obtain a voltage code value, and output it to the first logic module and the second logic module. Therefore, firstly, the first logic module can determine a first steady-state voltage value based on the voltage code value received during the fault stable operation phase, and compare it with a preset steady-state voltage threshold to detect whether the first steady-state voltage value exceeds the limit; secondly, it can determine a first steady-state current value based on the first current code value received during the fault stable operation phase, and compare it with a first steady-state current threshold to detect whether the first steady-state current value exceeds the limit; and if both the first steady-state voltage value and the first steady-state current value exceed the limit, it can determine that there may be a ground fault in the power distribution system and initiate a ground fault detection process. Then, after initiating the ground fault detection process, the first logic module can use a transient method to determine a first transient voltage value based on the voltage code value at the instant of the ground fault within a first preset time period, and determine a first transient current value based on the first current code value at the instant of the ground fault within the first preset time period, to determine a first power based on the first transient voltage value and the first transient current value, to determine whether the ground fault meets the characteristics of an in-zone ground fault of the first zero-sequence current transformer CT1 based on the first power, and to determine whether the ground fault is reliable based on the first transient current value. Finally, the first logic module can set the "within the zone" flag to 1 when it determines that the ground fault meets the characteristics of an in-zone ground fault, set the "trustworthy" flag to 1 when it determines that the ground fault is trustworthy, set the "within the zone" flag to 0 when it determines that the ground fault does not meet the characteristics of an in-zone ground fault, and set the "trustworthy" flag to 0 when it determines that the ground fault is untrustworthy, thus obtaining the first detection result. The preset voltage steady-state threshold and the first current steady-state threshold can be preset according to the actual usage scenario. The first preset duration can be two cycles of data window prior to the current moment. The voltage steady-state value is the zero-sequence voltage value that persists during the stable operation phase after a ground fault occurs, and the current steady-state value is the zero-sequence current value that persists during the stable operation phase after a ground fault occurs. The voltage transient value is the zero-sequence voltage component that is generated instantaneously when a ground fault occurs and decays rapidly over time, and the current transient value is the zero-sequence current component that is generated instantaneously when a ground fault occurs and decays rapidly over time. When the "within the zone" flag and the "trustworthy" flag of the first logic module are both 1, the first detection result is that a ground fault has occurred; when the "within the zone" flag or the "trustworthy" flag of the first logic module is 0, the first detection result is that no ground fault has occurred.

[0032] In some embodiments, the number of first power values ​​is four, and the first current transient value includes the first maximum current transient value I0(k)_1 of the first zero-sequence current collected within a first preset time period, the first adjacent current transient value I0(k-1)_1 and the second adjacent current transient value I0(k+1)_1 adjacent to the first maximum current transient value I0(k)_1, and the third adjacent current transient value I0(k-2)_1 before the first adjacent current transient value I0(k-1)_1, wherein the first adjacent current transient value I0(k-1)_1 is the current transient value before the first maximum current transient value I0(k)_1; the first... A voltage transient value includes a first synchronous voltage transient value U0(k)_1 corresponding to the first maximum current transient value I0(k)_1, a second synchronous voltage transient value U0(k-1)_1 corresponding to the first adjacent current transient value I0(k-1)_1, a third synchronous voltage transient value U0(k+1)_1 corresponding to the second adjacent current transient value I0(k+1)_1, a fourth synchronous voltage transient value U0(k-2)_1 corresponding to the third adjacent current transient value I0(k-2)_1, and a first adjacent voltage transient value U0(k-3)_1 preceding the fourth synchronous voltage transient value U0(k-2)_1. In step S303, a first voltage difference between the first and second synchronous voltage transient values ​​can be determined, and a first power is obtained based on the first voltage difference and the first maximum current transient value; a second voltage difference between the second and fourth synchronous voltage transient values ​​can be determined, and a first power is obtained based on the second voltage difference and the first adjacent current transient value; a third voltage difference between the third and first synchronous voltage transient values ​​can be determined, and a first power is obtained based on the third voltage difference and the second adjacent current transient value; a fourth voltage difference between the fourth and first adjacent voltage transient values ​​can be determined, and a first power is obtained based on the fourth voltage difference and the third adjacent current transient value.In this embodiment, the first logic module can first determine the first maximum current transient value I0(k)_1, the first adjacent current transient value I0(k+1)_1, the second adjacent current transient value I0(k-1)_1, and the third adjacent current transient value I0(k-2)_1 based on the first current code value received within the first preset time period; then, based on the voltage code value received within the first preset time period, determine the voltage code value relative to the first maximum current transient value I0(k)_1, the first adjacent current transient value I0(k+1)_1, and the second adjacent current transient value I0(k-2)_1, respectively. The first synchronous voltage transient value U0(k)_1, the second synchronous voltage transient value U0(k+1)_1, the second adjacent current transient value U0(k-1)_1, and the fourth synchronous voltage transient value U0(k-2)_1 at the same time as the third adjacent current transient value I0(k-2)_1 are determined, and the first adjacent voltage transient value U0(k-3)_1 before the fourth synchronous voltage transient value U0(k-2)_1 is determined. Finally, the four first powers are calculated according to the following zero-sequence power calculation formula. The zero-sequence power calculation formula is: ρ(k) = ΔU0(k) × I0(k); ΔU0(k)=U0(k)-U0(k-1); ρ is the zero-sequence power.

[0033] In some embodiments, in step S303, each first power can be compared with a first preset power, and each first current transient value can be compared with a first current transient threshold. Then, when at least a first preset number of first powers are all less than the first preset power, and at least one first current transient value is greater than the first current transient threshold, the first detection result is determined to be a ground fault. In this embodiment, the first logic module can compare each first power with the first preset power to determine whether the ground fault meets the characteristics of an in-zone ground fault, and compare each first current transient value with the first current transient threshold to determine whether the ground fault is reliable, thus obtaining a first detection result based on the first zero-sequence current transformer CT1. Specifically, when at least a first preset number of first powers are all less than the first preset power, the first logic module can determine that the ground fault meets the characteristics of an in-zone ground fault and set the in-zone flag to 1; when at least one first current transient threshold is greater than the first current transient threshold, the ground fault is determined to be reliable and the reliable flag is set to 1, thus obtaining a first detection result of a ground fault. Additionally, the first preset quantity can be 3; the first preset power can be 0; the first current transient threshold can be determined based on the trusted flag current threshold. For example, when the trusted flag current threshold is 10A, if the first sampling channel is configured as a 16-bit ADC with a full-scale input voltage of 5V, the corresponding code value range is 2. 15=32768, then the effective value of the secondary zero-current value of the first logic module is 10 / (100 / 1) = 0.1A, and the zero-current peak code value corresponding to the first current transient threshold is 0.1× / (20 / 3.53) × (32768 / 5) = 163; that is, the first logic module can compare each first current transient value with 163 to determine whether the ground fault is reliable.

[0034] S304: The second logic module acquires the second steady-state value of the zero-sequence voltage and the second steady-state value of the second zero-sequence current from the zero-sequence voltage transformer. When the second steady-state value of the voltage is greater than a preset steady-state voltage threshold and the second steady-state value of the current is greater than a preset steady-state current threshold, the second transient value of the zero-sequence voltage and the second transient value of the zero-sequence current acquired within a first preset time period before the current moment are acquired, and the second power is determined based on the second transient value of the voltage and the second transient value of the current. A second detection result is obtained based on the second power and the second transient value of the current. In this embodiment, firstly, the second logic module can determine the second steady-state value of the voltage based on the voltage code value received during the fault stable operation phase, and compare it with the preset steady-state voltage threshold to detect whether the second steady-state value exceeds the limit; secondly, the second steady-state value of the current is determined based on the second current code value received during the fault stable operation phase, and compared with the second steady-state current threshold to detect whether the second steady-state value exceeds the limit; and if both the second steady-state value and the second steady-state value exceed the limit, it is determined that there may be a ground fault in the power distribution system, and the ground fault detection process is initiated. Then, after initiating the ground fault detection process, the second logic module can use a transient method to determine a second voltage transient value based on the voltage code value at the instant of the ground fault occurring within a first preset time period, determine a second current transient value based on the first current code value at the instant of the ground fault occurring within the first preset time period, and determine a second power based on the second voltage transient value and the second current transient value. The second power is then used to determine whether the ground fault meets the characteristics of an in-zone ground fault of the second zero-sequence current transformer CT2, and the second current transient value is used to determine whether the ground fault is reliable. Finally, the second logic module can set the in-zone flag to 1 when it determines that the ground fault meets the characteristics of an in-zone ground fault, set the reliable flag to 1 when it determines that the ground fault is reliable, set the in-zone flag to 0 when it determines that the ground fault does not meet the characteristics of an in-zone ground fault, and set the reliable flag to 0 when it determines that the ground fault is unreliable, thus obtaining the first detection result. The second current steady-state threshold can be preset according to the actual usage scenario. When the zone flag of the second logic module is 1 and the trusted flag is 1, the second detection result is that a ground fault has occurred; when the zone flag of the second logic module is 0 or the trusted flag is 0, the second detection result is that no ground fault has occurred. It can be understood that the first steady-state voltage value is determined by the first logic module based on the voltage code value acquired by the voltage acquisition channel, and the second steady-state voltage value is determined by the second logic module based on the voltage code value acquired by the voltage acquisition channel. Therefore, at the same time, the first steady-state voltage value and the second steady-state voltage value are the same.

[0035] In some embodiments, the number of second power values ​​is four, and the second current transient value includes the second maximum current transient value I0(k)_2 of the second zero-sequence current collected within a first preset time period, the fourth adjacent current transient value I0(k-1)_2 and the fifth adjacent current transient value I0(k+1)_2 adjacent to the second maximum current transient value I0(k)_2, and the sixth adjacent current transient value I0(k-2)_2 before the fourth adjacent current transient value I0(k-1)_2, wherein the fourth adjacent current transient value I0(k-1)_2 is the current transient value before the second maximum current transient value I0(k)_2; the second power value I0(k-1)_2 is the second maximum current transient value I0(k)_2. The two voltage transient values ​​include the fifth synchronous voltage transient value U0(k)_2 corresponding to the second maximum current transient value I0(k)_2, the sixth synchronous voltage transient value U0(k-1)_2 corresponding to the fourth adjacent current transient value I0(k-1)_2, the seventh synchronous voltage transient value U0(k+1)_2 corresponding to the fifth adjacent current transient value I0(k+1)_2, the eighth synchronous voltage transient value U0(k-2)_2 corresponding to the sixth adjacent current transient value I0(k-2)_2, and the second adjacent voltage transient value U0(k-3)_2 preceding the eighth synchronous voltage transient value U0(k-2)_2. In step S304, a fifth voltage difference between the fifth and sixth synchronous voltage transient values ​​can be determined, and a second power is obtained based on the fifth voltage difference and the second maximum current transient value; a sixth voltage difference between the sixth and eighth synchronous voltage transient values ​​can be determined, and a second power is obtained based on the sixth voltage difference and the fourth adjacent current transient value; a seventh voltage difference between the seventh and fifth synchronous voltage transient values ​​can be determined, and a second power is obtained based on the seventh voltage difference and the fifth adjacent current transient value; an eighth voltage difference between the eighth and second adjacent voltage transient values ​​can be determined, and a second power is obtained based on the eighth voltage difference and the sixth adjacent current transient value.In this embodiment, the second logic module can first determine the second maximum current transient value I0(k)_2, the fifth adjacent current transient value I0(k+1)_2, the fourth adjacent current transient value I0(k-1)_2, and the sixth adjacent current transient value I0(k-2)_2 based on the second current code value received within the first preset time period; then, based on the voltage code value received within the first preset time period, determine the voltage code value relative to the second maximum current transient value I0(k)_2, the fifth adjacent current transient value I0(k+1)_2, and the fourth adjacent current transient value I0(k-2)_2, respectively. The fifth synchronous voltage transient value U0(k)_2, the seventh synchronous voltage transient value U0(k+1)_2, the fifth adjacent current transient value U0(k-1)_2, and the eighth synchronous voltage transient value U0(k-2)_2 at the same time as the sixth adjacent current transient value I0(k-2)_2, as well as the second adjacent voltage transient value U0(k-3)_2 before the eighth synchronous voltage transient value U0(k-2)_2; finally, according to the zero-sequence power calculation formula above, four second powers are calculated.

[0036] In some embodiments, in step S304, each second power can be compared with a second preset power, and each second current transient value can be compared with a second current transient threshold. Then, when at least a first preset number of second powers are all less than the second preset power, and each second current transient value is less than the second current transient threshold, the second detection result is determined to be a ground fault. In this embodiment, as... Figure 4 As shown, the second logic module can compare each second power with a second preset power to determine whether the ground fault meets the characteristics of an in-zone ground fault, and compare each second current transient value with a second current transient threshold to determine whether the ground fault is reliable, thus obtaining a second detection result based on the second zero-sequence current transformer CT2. Specifically, the second logic module can determine that the ground fault meets the characteristics of an in-zone ground fault and set the in-zone flag to 1 when at least a first preset number of second powers are less than the second preset power; and determine that the ground fault is reliable and set the reliable flag to 1 when each second current transient threshold is less than the second current transient threshold, thus obtaining a second detection result indicating that a ground fault has occurred. Furthermore, the second preset power can be 0; the second current transient threshold can be determined based on the reliable flag current threshold. For example, when the reliable flag current threshold is 10A, if the second sampling channel is configured as a 16-bit ADC with a full-scale input voltage of 5V, the corresponding code value range is 2. 15 =32768, then the effective value of the secondary zero-current value of the second logic module is 10 / (100 / 5) = 0.5A, and the zero-current peak code value corresponding to the second current transient threshold is 0.1× / (5 / 3.53) × (32768 / 5) = 3271; that is, the second logic module can compare each second current transient value with 3271 to determine whether the ground fault is reliable.

[0037] S305: The ground fault detection result of the power distribution line is determined by the third logic module based on the first detection result and the second detection result. In this embodiment, the third logic module can obtain the ground fault detection result of the power distribution line based on the zone flag and trust flag of the first logic module, and the zone flag and trust flag of the second logic module. Specifically, when the trust flag of the first logic module is 1, the third logic module trusts the first detection result of the first logic module and uses the first detection result as the ground fault detection result; when the trust flag of the second logic module is 1, the third logic module trusts the second detection result of the second logic module and uses the second detection result as the ground fault detection result.

[0038] In other embodiments, when the first detection result indicates a ground fault, the first logic module can further perform fault type detection. The fault type detection process of the first logic module may include: starting a timer when the first logic module determines that the first detection result is a ground fault; and when the timer reaches a second preset duration, comparing the third steady-state value of the zero-sequence voltage collected within the second preset duration with a preset steady-state voltage threshold to obtain the first fault type detection result of the power distribution line. In this embodiment, the first logic module can detect whether the first fault type detection result is a persistent ground fault by detecting whether the third steady-state value of the zero-sequence voltage within the second preset duration is greater than the preset steady-state voltage threshold. The second preset duration can be set according to the actual power distribution scenario.

[0039] In some specific examples, the fault type detection process of the first logic module may further include: when the third steady-state value of the zero-sequence voltage collected within a second preset time period is greater than a preset steady-state voltage threshold, determining that the first fault type detection result is a persistent ground fault. In this embodiment, the first logic module can determine that the first fault type detection result is a persistent ground fault when it detects that the third steady-state voltage value is greater than the preset steady-state voltage threshold.

[0040] In some other embodiments, the fault type detection process of the first logic module may further include: when the third steady-state voltage value is less than or equal to a preset steady-state voltage threshold, based on the zero-sequence voltage and the first zero-sequence current collected when the timing reaches the third preset duration, re-execute the step of acquiring the first steady-state voltage value of the zero-sequence voltage collected by the zero-sequence voltage transformer and the first steady-state current value of the first zero-sequence current collected by the first current sampling channel, to obtain multiple first detection results within the third preset duration; then, when at least a second preset number of first detection results are detected as grounding faults within the third preset duration, determine that the first fault type detection result is an intermittent grounding fault. In this embodiment, when the first logic module detects that the first fault type detection result is not a continuous grounding fault, it can determine whether the fault type of the grounding fault is an intermittent grounding fault by detecting whether the first detection result of a grounding fault is detected multiple times within the third preset duration after the time when the first detection result is a grounding fault. The first logic module can, according to the method in S303, obtain multiple first detection results based on the zero-sequence voltage and first zero-sequence current collected within a third preset time period. It then determines whether the grounding fault type is an intermittent grounding fault based on whether the number of areas with a flag of 1 and a reliable flag of 1 within the third preset time period is greater than a second preset number. Furthermore, the third preset time period and the second preset number can be set according to the actual power distribution scenario. For example, when the third preset time period is 10 seconds, the second preset number can be 3; when the third preset time period is 30 seconds, the second preset number can be 5. That is, the first logic module can start timing when the first setting of the zone flag is 1 and the setting of the trust flag is 1, count the number of times the grounding is detected to be 1, and restart the grounding detection when the zero-sequence voltage and the first zero-sequence current exceed the limit again during the fault process; if the second setting of the zone flag is 1 and the setting of the trust flag is 1, the number of times the grounding is detected to be 2; if the second setting of the zone flag is 0 or the setting of the trust flag is 0, the number of times the grounding is detected to be 1, and so on. If the number of times the grounding is detected to be 3 or more within 10 seconds, or if the number of times the grounding is detected to be 3 or more within 30 seconds, the first fault type detection result is determined to be an intermittent grounding fault, and a grounding action flag is output.

[0041] Furthermore, if the first fault type detection result is not a persistent ground fault, the fault type detection process of the first logic module may further include: when the third steady-state voltage value is less than or equal to a preset steady-state voltage threshold, determining whether the first zero-sequence current collected within a third preset time period is greater than or equal to a preset zero-sequence current; if the first zero-sequence current collected within a third preset time period is greater than or equal to the preset zero-sequence current, re-executing the steps of acquiring the second voltage transient value of the zero-sequence voltage and the second current transient value of the second zero-sequence current collected within the first preset time period before the current moment, and determining the second power based on the second voltage transient value and the second current transient value, thereby obtaining multiple first detection results within the third preset time period. In this embodiment, the first logic module can initiate the ground fault detection process based on the first zero-sequence current exceeding the limit collected within the third preset time period after detecting for the first time that a ground fault has occurred. The preset zero-sequence current can be set according to actual usage conditions; for example, the preset zero-sequence current can be 15mA.

[0042] Understandably, when the second detection result indicates a ground fault, the second logic module can further perform fault type detection. The fault type detection process of the second logic module may include: starting a timer when the second logic module determines that a ground fault has occurred; and when the timer reaches a second preset duration, comparing the fourth steady-state value of the zero-sequence voltage collected within the second preset duration with a preset steady-state voltage threshold to obtain the second fault type detection result for the distribution line. When the fourth steady-state value of the zero-sequence voltage detected within the second preset duration is greater than the preset steady-state voltage threshold, the second fault type detection result is determined to be a persistent ground fault. When the fourth steady-state voltage value is less than or equal to the preset steady-state voltage threshold, the steps of acquiring the second steady-state voltage value of the zero-sequence voltage acquired by the zero-sequence voltage transformer and the second steady-state current value of the second zero-sequence current acquired by the second current sampling channel are re-executed based on the zero-sequence voltage and the second zero-sequence current acquired when the timing reaches the third preset time, to obtain multiple second detection results within the third preset time. Then, when at least a second preset number of second detection results within the third preset time are detected to indicate a ground fault, the second fault type detection result is determined to be an intermittent ground fault. The method of fault type detection implemented by the second logic module is the same as that of the first logic module, and for the sake of brevity, will not be described in detail here.

[0043] Therefore, in S305, the third logic module can determine that a continuous ground fault has occurred in the power distribution line when the detection result of the first fault type or the second fault type is a continuous ground fault. When the detection result of the first fault type or the second fault type is an intermittent ground fault, it can determine that an intermittent ground fault has occurred in the power distribution line.

[0044] In one example, such as Figure 1 and Figure 4 As shown, the incoming side of load switch FS1 is equipped with one zero-sequence PT and two CTs. CT1 has a transformation ratio of 100 / 1, and CT2 has a transformation ratio of 100 / 5. When a ground fault occurs downstream of load switch FS1 at F1, the zero-sequence current is large. First, the first logic module corresponding to CT1 can detect the ground fault in the distribution line based on the zero-sequence current, setting the zone flag to 1 and the confidence flag to 1. The second logic module corresponding to CT2 cannot detect the ground fault in the distribution line based on the zero-sequence current, setting the confidence flag to 0. Then, the first logic module detects that the steady-state value of the zero-sequence voltage is continuously greater than the preset steady-state voltage threshold, determines the ground fault type as a persistent ground fault, and outputs a ground fault action flag. Finally, the third logic module, based on the first logic module's zone flag being 1, the confidence flag being 1, and the presence of a ground fault action flag, reports a ground fault action signal. When a ground fault occurs downstream of load switch FS1 at F2, the zero-sequence current is small. First, the first logic module corresponding to CT1 cannot detect the ground fault based on this zero-sequence current and sets the confidence flag to 0. The second logic module corresponding to CT2 can detect the ground fault based on this zero-sequence current and sets both the zone flag and the confidence flag to 1. Then, if the second logic module detects at least three instances of the zone flag and the confidence flag being 1 within 10 seconds, it outputs a ground fault action flag. Finally, the third logic module, based on the second logic module's zone flag being 1, the confidence flag being 1, and the presence of the ground fault action flag, reports a ground fault action signal.

[0045] In addition, this embodiment also provides a computer-readable storage medium storing a computer program thereon, which is loaded by a processor to execute the steps in any of the ground fault detection methods described above.

[0046] In the embodiments of this application, the storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM), etc.

[0047] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0048] The above provides a detailed description of a ground fault detection method, distribution terminal, and distribution network system provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A ground fault detection method, characterized in that, The method is applied to a power distribution network system, which includes a distribution terminal, a zero-sequence voltage transformer located on a distribution line, a first zero-sequence current transformer, and a second zero-sequence current transformer. The first and second zero-sequence current transformers have different transformation ratios. The distribution terminal includes a first current sampling channel, a second current sampling channel, a first logic module, a second logic module, and a third logic module. The first current sampling channel and the first logic module correspond one-to-one with the first zero-sequence current transformer, and the second current sampling channel and the second logic module correspond one-to-one with the second zero-sequence current transformer. The transformation ratios of the first and second current sampling channels are different. The method includes: The first zero-sequence current collected by the first zero-sequence current transformer is sampled through the first current sampling channel; The second zero-sequence current collected by the second zero-sequence current transformer is sampled through the second current sampling channel; The first logic module acquires the first steady-state value of the zero-sequence voltage and the first steady-state value of the first zero-sequence current from the zero-sequence voltage transformer. When the first steady-state value of the voltage is greater than a preset steady-state voltage threshold and the first steady-state value of the current is greater than a first steady-state current threshold, the first transient value of the zero-sequence voltage and the first transient value of the first zero-sequence current acquired within a first preset time period before the current moment are acquired, and four first powers are determined based on the first transient voltage value and the first transient current value. Each first power is compared with a first preset power, and each first transient current value is compared with a first transient current threshold. When at least a first preset number of first powers are less than the first preset power, and at least one first transient current value is greater than the first transient current threshold, the first detection result is determined to be a ground fault. The second logic module acquires the second steady-state value of the zero-sequence voltage and the second steady-state value of the zero-sequence current collected by the zero-sequence voltage transformer. When the second steady-state value of the voltage is greater than the preset steady-state voltage threshold and the second steady-state value of the current is greater than the second steady-state current threshold, the second transient value of the zero-sequence voltage and the second transient value of the zero-sequence current collected within the first preset time period before the current moment are acquired, and the second power is determined based on the second transient value of the voltage and the second transient value of the current. The second detection result is obtained based on the second power and the second transient value of the current. The third logic module determines the grounding fault detection result of the power distribution line based on the first detection result and the second detection result.

2. The grounding fault detection method according to claim 1, characterized in that, The first power has four values. The first current transient value includes the first maximum current transient value of the first zero-sequence current collected within the first preset time period, the first adjacent current transient value and the second adjacent current transient value adjacent to the first maximum current transient value, and the third adjacent current transient value before the first adjacent current transient value. The first adjacent current transient value is the current transient value before the first maximum current transient value. The first voltage transient value includes the first synchronous voltage transient value corresponding to the first maximum current transient value, the second synchronous voltage transient value corresponding to the first adjacent current transient value, the third synchronous voltage transient value corresponding to the second adjacent current transient value, the fourth synchronous voltage transient value corresponding to the third adjacent current transient value, and the first adjacent voltage transient value before the fourth synchronous voltage transient value. Determining the first power based on the first voltage transient value and the first current transient value includes: A first voltage difference is determined between the first transient value of the synchronization voltage and the second transient value of the synchronization voltage, and a first power is obtained based on the first voltage difference and the first maximum current transient value; A second voltage difference is determined between the second synchronous voltage transient value and the fourth synchronous voltage transient value, and a first power is obtained based on the second voltage difference and the first adjacent current transient value; A third voltage difference is determined between the third synchronous voltage transient value and the first synchronous voltage transient value, and a first power is obtained based on the third voltage difference and the second adjacent current transient value; A fourth voltage difference is determined between the fourth synchronous voltage transient value and the first adjacent voltage transient value, and a first power is obtained based on the fourth voltage difference and the third adjacent current transient value.

3. The grounding fault detection method according to claim 1, characterized in that, After determining that the first detection result indicates a ground fault has occurred, the method further includes: When the first logic module determines that the first detection result is a ground fault, it starts timing; and when the timing reaches the second preset duration, it compares the third steady-state value of the zero-sequence voltage collected within the second preset duration with the preset steady-state voltage threshold to obtain the first fault type detection result of the power distribution line.

4. The grounding fault detection method according to claim 3, characterized in that, The step of comparing the third steady-state value of the zero-sequence voltage collected within the second preset time period with the preset steady-state voltage threshold to obtain the first fault type detection result of the power distribution line includes: When the third steady-state value of the zero-sequence voltage collected within the second preset time period is greater than the preset steady-state voltage threshold, the first fault type detection result is determined to be a persistent grounding fault.

5. The grounding fault detection method according to claim 4, characterized in that, The step of comparing the third steady-state value of the zero-sequence voltage collected within the second preset time period with the preset steady-state voltage threshold to obtain the first fault type detection result of the power distribution line further includes: When the third steady-state voltage value is less than or equal to the preset steady-state voltage threshold, the steps of obtaining the first steady-state voltage value of the zero-sequence voltage collected by the zero-sequence voltage transformer and the first steady-state current value of the first zero-sequence current collected by the first current sampling channel are re-executed based on the zero-sequence voltage and the first zero-sequence current collected when the timing reaches the third preset time, so as to obtain multiple first detection results within the third preset time. When at least a second preset number of the first detection results are detected as grounding faults within the third preset time period, the first fault type detection result is determined to be an intermittent grounding fault.

6. The grounding fault detection method according to claim 1, characterized in that, The second power has four values. The second current transient value includes the second maximum current transient value of the second zero-sequence current collected within the first preset time period, the fourth adjacent current transient value and the fifth adjacent current transient value adjacent to the second maximum current transient value, and the sixth adjacent current transient value before the fourth adjacent current transient value, wherein the fourth adjacent current transient value is the current transient value before the second maximum current transient value. The second voltage transient value includes the fifth synchronous voltage transient value corresponding to the second maximum current transient value, the sixth synchronous voltage transient value corresponding to the fourth adjacent current transient value, the seventh synchronous voltage transient value corresponding to the fifth adjacent current transient value, the eighth synchronous voltage transient value corresponding to the sixth adjacent current transient value, and the second adjacent voltage transient value before the eighth synchronous voltage transient value. The step of determining the second power based on the second voltage transient value and the second current transient value includes: A fifth voltage difference is determined between the fifth synchronous voltage transient value and the sixth synchronous voltage transient value, and a second power is obtained based on the fifth voltage difference and the second maximum current transient value; A sixth voltage difference is determined between the sixth synchronous voltage transient value and the eighth synchronous voltage transient value, and a second power is obtained based on the sixth voltage difference and the fourth adjacent current transient value; A seventh voltage difference is determined between the seventh synchronous voltage transient value and the fifth synchronous voltage transient value, and a second power is obtained based on the seventh voltage difference and the fifth adjacent current transient value; Determine the eighth voltage difference between the eighth synchronous voltage transient value and the second adjacent voltage transient value, and obtain a second power based on the eighth voltage difference and the sixth adjacent current transient value.

7. The grounding fault detection method according to claim 1, characterized in that, The number of second powers is four, and the second detection result is obtained based on the second power and the second current transient value, including: Each of the second power values ​​is compared with the second preset power, and each of the second current transient values ​​is compared with the second current transient threshold. When at least a first preset number of the second power values ​​are all less than the second preset power, and each of the second current transient values ​​is less than the second current transient threshold, the second detection result is determined to be a ground fault.

8. A power distribution terminal, characterized in that, The system includes a first current sampling channel, a second current sampling channel, a memory, and a processor. The processor includes a first logic module, a second logic module, and a third logic module. The transformation ratios of the first current sampling channel and the second current sampling channel are different. The first current sampling channel is used to sample the first zero-sequence current on the distribution line where the distribution terminal is located, and the second current sampling channel is used to sample the second zero-sequence current on the distribution line. The memory stores a computer program, which, when executed by the processor, implements the ground fault detection method as described in any one of claims 1-7.

9. A power distribution network system, characterized in that, include: Load switches located on power distribution lines; The zero-sequence voltage transformer, the first zero-sequence current transformer, and the second zero-sequence current transformer are located on the incoming side of the load switch. The zero-sequence voltage transformer is used to collect the zero-sequence voltage of the power distribution line, the first zero-sequence current transformer is used to collect the first zero-sequence current of the power distribution line, and the second zero-sequence current transformer is used to collect the second zero-sequence current of the power distribution line. The power distribution terminal as described in claim 8 is connected to the zero-sequence voltage transformer, the first zero-sequence current transformer, and the second zero-sequence current transformer, respectively.

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