Zero line disconnection detection method and device

Abstract

The invention relates to the technical field of power systems, and discloses a null line disconnection detection method and device, and the method comprises the steps: calculating a three-phase voltage unbalance degree according to a negative sequence voltage and a zero sequence voltage; judging whether the three-phase voltage unbalance degree exceeds a first preset threshold value or not; if the three-phase voltage unbalance degree exceeds the first preset threshold value, whether the difference value between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold value or not continues to be judged; and if the difference value between the third harmonic content and the second harmonic content exceeds a second preset threshold value, determining that the zero line is disconnected. As the null line is disconnected, the third harmonic is obviously increased, and the second harmonic is slightly changed, the neutral line fault and other disturbances can be effectively distinguished through the difference between the third harmonic and the second harmonic. The zero-sequence component and the negative-sequence component are coupled, the three-phase voltage unbalance degree is calculated, the unbalance state of a three-phase system is represented more comprehensively and accurately, and the harmonic characteristic difference of each split-phase voltage is combined and can be effectively applied to neutral line fault detection.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and in particular to a method and device for detecting a neutral line drop. Background Art

[0002] Current mainstream energy metering and power monitoring devices generally employ hardware-based anti-interference measures and simple voltage threshold detection strategies to address neutral line disconnection. These solutions lack highly sensitive detection algorithms for neutral line disconnection and high-resistance faults, which pose serious safety risks in real-world projects, potentially leading to power theft, equipment overheating, and even electrical fires. Therefore, there is an urgent need to develop a novel method that combines high-precision voltage imbalance calculation with sensitive neutral line fault detection. This approach holds significant engineering value for improving the safety and reliability of power system operations. Summary of the Invention

[0003] In view of this, the present invention provides a method and device for detecting a drop in the neutral line, so as to solve the problem of how to improve the sensitivity of detecting a drop in the neutral line fault.

[0004] In a first aspect, the present invention provides a method for detecting a neutral line drop, the method comprising: calculating a three-phase voltage imbalance based on a negative-sequence voltage and a zero-sequence voltage; determining whether the three-phase voltage imbalance exceeds a first preset threshold; if the three-phase voltage imbalance exceeds the first preset threshold, determining whether the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold; if the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds the second preset threshold and lasts for a preset time, determining that the neutral line is dropped.

[0005] The present invention couples the zero-sequence component and the negative-sequence component, calculates the three-phase voltage imbalance, and more comprehensively and accurately characterizes the imbalance state of the three-phase system. It is combined with the preset harmonic state and can be effectively applied to neutral line fault detection.

[0006] In an optional embodiment, calculating the three-phase voltage unbalance degree according to the negative-sequence voltage and the zero-sequence voltage includes: calculating the three-phase voltage unbalance degree according to the negative-sequence voltage and the zero-sequence voltage using a Euclidean norm; The calculation formula for three-phase voltage unbalance is:

[0007] in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage.

[0008] In an optional embodiment, calculating the three-phase voltage imbalance according to the negative-sequence voltage and the zero-sequence voltage includes: assigning different weights to the negative-sequence voltage and the zero-sequence voltage, and calculating the three-phase voltage imbalance using a weighted calculation method; The calculation formula for three-phase voltage unbalance is:

[0009] in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage; ω 1. ω 2 are the weight coefficients of zero-sequence voltage and negative-sequence voltage respectively.

[0010] In an optional embodiment, calculating the three-phase voltage unbalance degree according to the negative-sequence voltage and the zero-sequence voltage includes: assigning different combination coefficients to the negative-sequence voltage and the zero-sequence voltage, and calculating the three-phase voltage unbalance degree using a linear combination calculation method; The calculation formula for three-phase voltage unbalance is:

[0011] in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage; k 1. k 2 are the combination coefficients of zero-sequence voltage and negative-sequence voltage respectively.

[0012] In an optional embodiment, before calculating the three-phase voltage imbalance, it also includes: detecting whether zero-sequence current exists; if zero-sequence current exists, calculating the three-phase voltage imbalance based on negative-sequence voltage and zero-sequence voltage; if zero-sequence current does not exist, determining that the neutral line is disconnected.

[0013] In an optional embodiment, the neutral line drop detection method also includes: if the three-phase voltage imbalance exceeds a first preset threshold, determining whether the phase angle difference of the three-phase voltage exceeds a second preset threshold; if the phase angle difference of the three-phase voltage exceeds the second preset threshold and lasts for more than a preset time, determining that the neutral line is dropped.

[0014] In a second aspect, the present invention provides a neutral line drop detection device, which includes: a calculation module for calculating the three-phase voltage imbalance based on the negative-sequence voltage and the zero-sequence voltage; a first judgment module for judging whether the three-phase voltage imbalance exceeds a first preset threshold; a second judgment module for judging whether the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold if the three-phase voltage imbalance exceeds the first preset threshold; a third judgment module for judging that the neutral line is dropped if the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds the second preset threshold and lasts for a preset time.

[0015] In a third aspect, the present invention provides a computer device comprising: a memory and a processor, the memory and the processor being communicatively connected to each other, the memory storing computer instructions, and the processor executing the zero line drop detection method of the first aspect or any corresponding embodiment thereof by executing the computer instructions.

[0016] In a fourth aspect, the present invention provides a computer-readable storage medium having computer instructions stored thereon, the computer instructions being used to enable a computer to execute the neutral line drop detection method of the first aspect or any corresponding embodiment thereof.

[0017] In a fifth aspect, the present invention provides a computer program product, comprising computer instructions for causing a computer to execute the neutral line drop detection method of the first aspect or any corresponding embodiment thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 is a flowchart of a method for detecting a zero line drop according to an embodiment of the present invention; Figure 2 is a flow chart of another method for detecting a neutral line drop according to an embodiment of the present invention; Figure 3 is a structural block diagram of a neutral line drop detection device according to an embodiment of the present invention; Figure 4 Schematic diagram of the hardware structure of a computer device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0020] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative efforts shall fall within the scope of protection of the present invention.

[0021] Existing methods for calculating three-phase system imbalance have significant theoretical flaws, specifically the difficulty in fully characterizing the imbalance state of the system during actual operation. This is particularly true in the case of a neutral line break. Traditional calculation models overlook the crucial role of the zero-sequence component in energy distribution and space vector characteristic analysis, leading to inaccurate assessments of system imbalance.

[0022] According to an embodiment of the present invention, an embodiment of a neutral line drop detection method is provided. It should be noted that the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and although a logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0023] In this embodiment, a method for detecting a zero line drop is provided, which can be used in the above-mentioned mobile terminals, such as mobile phones, tablet computers, etc. Figure 1 FIG. 1 is a flow chart of a method for detecting a zero line drop according to an embodiment of the present invention. Figure 1 As shown, the process includes the following steps: Step S1: Calculate the three-phase voltage unbalance according to the negative-sequence voltage and the zero-sequence voltage.

[0024] In a three-phase power system, the three-phase voltages are symmetrical under normal operation. However, when a system fault or load imbalance occurs, the voltage decomposes into positive-sequence, negative-sequence, and zero-sequence components. Voltage imbalance is a key parameter for power quality. In a power system, severe voltage imbalance can lead to abnormal operation of three-phase loads, heating of electrical equipment, and additional losses and vibration in motors.

[0025] According to international standards such as IEC 61000-4-30, traditional voltage unbalance calculation is mainly based on the symmetrical component method, which expresses it by calculating the ratio of the negative sequence component and the zero sequence component to the positive sequence component: (1) (2) in, u 2 is the negative sequence voltage component; u 0 is the zero-sequence voltage component; U 0 is the zero-sequence voltage; U1 is the positive sequence voltage; U 2 is the negative sequence voltage.

[0026] The zero-sequence component is composed of three voltage components with equal amplitude and identical phase. Simply put, the zero-sequence component is the "average" of the three-phase current or voltage. The positive-sequence component consists of three voltage components with equal amplitude and a phase difference of 120°, representing the "ideal balance" of the three-phase current or voltage. The negative-sequence component consists of three voltage components with equal amplitude and a phase difference of -120°, reflecting the "unbalanced state" of the three-phase current or voltage.

[0027] Existing imbalance calculation methods fail to fully reflect the actual imbalance state of a three-phase system, especially in the case of a dropped neutral line. They also ignore the importance of the zero-sequence component when considering energy distribution and space vector characteristics, resulting in theoretical flaws. Therefore, this step extracts the negative-sequence voltage and zero-sequence voltage, combines them with the positive-sequence voltage, and uses the industry-standard voltage imbalance calculation formula. The specific calculation method is as follows: (1) Three-phase voltage asymmetry sampling The three-phase voltage sampling resistors must be distributed in a stepped pattern. For example, the sampling resistor for phase A should be 1920K, the sampling resistor for phase B should be 5180K, and the sampling resistor for phase C should be 4020K. This ensures that the three-phase neutral points can be significantly offset after the neutral line is dropped. After digital-to-analog conversion and calibration, digital values ​​are obtained for analysis and calculation.

[0028] (2) Calculate the positive sequence, negative sequence, and zero sequence components of the three-phase voltage Based on the symmetrical component theory, the three-phase voltage is converted into positive sequence, negative sequence, and zero sequence components: (3) in, 、 、 represents the complex voltage coupled with the phase angle; a is the rotation factor, whose value is (4) (3) Calculation of voltage imbalance ① Calculate the three-phase voltage unbalance using the Euclidean norm based on the negative-sequence voltage and zero-sequence voltage; The calculation formula for three-phase voltage unbalance is: (5) in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage.

[0029] Based on Equation (5), the zero-sequence component and the Euclidean norm calculation method are introduced. The square sum square root method is used to comprehensively consider the influence of the negative-sequence and zero-sequence components, reflecting the physical nature of vector superposition. Including the zero-sequence component in the imbalance calculation effectively improves the sensitivity to the zero-line drop fault.

[0030] ② Assign different weights to the negative sequence voltage and zero sequence voltage, and calculate the three-phase voltage imbalance using a weighted calculation method; The calculation formula for three-phase voltage unbalance is: (6) in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage; ω 1. ω 2 are the weight coefficients of zero-sequence voltage and negative-sequence voltage respectively.

[0031] Can be adjusted according to different application scenarios ω 1. ω 2, in order to more accurately reflect the influence of each component.

[0032] ③ Assign different combination coefficients to the negative sequence voltage and zero sequence voltage, and calculate the three-phase voltage unbalance using the linear combination calculation method; The calculation formula for three-phase voltage unbalance is: (7) in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage; k 1. k 2 are the combination coefficients of zero-sequence voltage and negative-sequence voltage respectively.

[0033] Step S2: Determine whether the three-phase voltage imbalance exceeds a first preset threshold.

[0034] Specifically, the first preset threshold is a reference value set based on the operating standards of the power system and actual engineering experience, and is typically selected within the range specified by national standards. For example, the normal operating threshold for three-phase voltage imbalance is generally set at 2%, and the short-term permissible threshold is set at 4%. This step compares the three-phase voltage imbalance calculated in step S1 with the pre-set first threshold. If the three-phase voltage imbalance is less than or equal to the first preset threshold, it indicates that the current three-phase voltage is within the normal imbalance range, the system is operating well, and no further troubleshooting is required. If the three-phase voltage imbalance exceeds the first preset threshold, it indicates that the three-phase voltage is abnormally unbalanced, and there may be a potential fault hazard, requiring further analysis and judgment, at which point the process proceeds to step S3.

[0035] Step S3: If the three-phase voltage imbalance exceeds the first preset threshold, determine whether the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds the second preset threshold.

[0036] Step S4: If the preset order harmonic amount in the three-phase voltage exceeds a second preset threshold value and lasts for a preset time, it is determined that the neutral line is disconnected.

[0037] When the three-phase voltage imbalance exceeds a first preset threshold, specific harmonic levels in the three-phase voltage are tested to further determine whether the cause is a neutral line drop. A neutral line drop can cause characteristic harmonics in the system. Generally, the third harmonic level increases significantly during a neutral line failure, while the second harmonic level changes little. Therefore, the third harmonic is often selected as a preset detection target.

[0038] This step uses harmonic analysis algorithms such as fast Fourier transform (FFT) to perform spectral decomposition on the three-phase voltage signal to determine whether the preset harmonic quantity in the three-phase voltage exceeds a second preset threshold. If it does not exceed the second preset threshold, it means that although there is voltage imbalance, it may be caused by other non-neutral line drop factors (such as three-phase load imbalance). If it exceeds the second preset threshold, it is highly suspected that the system has a neutral line drop fault.

[0039] In some optional real-time modes, such as Figure 2 As shown, before calculating the three-phase voltage imbalance, the following steps are also included: detecting whether zero-sequence current exists; if zero-sequence current exists, calculating the three-phase voltage imbalance according to negative-sequence voltage and zero-sequence voltage; if zero-sequence current does not exist, determining that the neutral line is disconnected.

[0040] In the power system's zero-line drop fault detection process, it is necessary to first conduct zero-sequence current related detection and judgment to prepare for the subsequent three-phase voltage imbalance calculation. The specific logic is as follows: Before entering the three-phase voltage imbalance calculation phase, the zero-sequence current detection operation must be performed first. With the help of the corresponding current detection device, the zero-sequence current signal in the system is obtained.

[0041] If zero-sequence current is detected, the system calculates the three-phase voltage imbalance based on the collected data of negative-sequence voltage and zero-sequence voltage, using the calculation formula of three-phase voltage imbalance, and uses the calculation result in the subsequent zero-line fault judgment process, such as comparing it with the set threshold to assist in determining the fault situation.

[0042] If it is detected that zero-sequence current does not exist, this feature indicates that the system neutral circuit is likely to be abnormally disconnected, which is directly determined to be a neutral line disconnection fault. It can trigger the corresponding alarm or protection action, and promptly remind the operation and maintenance personnel to check the neutral line connection problem to avoid more serious power accidents such as equipment damage and voltage abnormalities caused by neutral line disconnection.

[0043] In some optional real-time methods, in order to prevent the harmonic content of some scenes from being inaccurate, such as Figure 2 As shown, the neutral line drop detection method also includes: if the three-phase voltage imbalance does not exceed the first preset threshold, judging whether the phase angle difference of the three-phase voltage exceeds the second preset threshold; if the phase angle difference of the three-phase voltage exceeds the third preset threshold, judging that the neutral line is dropped.

[0044] After calculating the three-phase voltage imbalance, the next step is to determine the cause of the problem. The calculated three-phase voltage imbalance results are checked. If the value exceeds a pre-set first threshold, the phase angle difference between the three-phase voltages is further detected and determined. If the phase angle difference also exceeds a second pre-set threshold, a neutral drop has occurred. High-precision phase detection equipment is used to obtain phase information for each of the three phase voltages, and the phase angle difference between them is calculated. The calculated phase angle difference is then compared with a third pre-set threshold. If the phase angle difference exceeds the third pre-set threshold, this indicates a significant anomaly in the phase relationship of the three-phase voltages. Based on the overall neutral drop fault detection logic, this phase relationship anomaly matches the electrical characteristics of a neutral drop fault, thus confirming a neutral drop fault. This determination can then trigger appropriate fault alarms, protective actions, or maintenance prompts, ensuring prompt troubleshooting and repair of the neutral drop problem, ensuring stable operation of the power system.

[0045] In a practical application scenario, in a three-phase smart energy meter, the above method and Figure 2 The process shown in the figure realizes the neutral line fault detection function.

[0046] Hardware configuration: The sampling resistor for phase A is 1920K, the sampling resistor for phase B is 5180K, and the sampling resistor for phase C is 4020K. The main control chip uses HT6033, which has sufficient neutral point offset and computing power to complete symmetrical component conversion and imbalance calculation.

[0047] Specific implementation steps: ① Set the standard meter voltage to an extremely unbalanced state of 175.5V for phase A and 220V for phase B, and 265V for phase C at 50Hz. Check whether there is a false alarm when the neutral wire is not unplugged.

[0048] ② Use fixed-point numbers instead of floating-point numbers to calculate positive-sequence, negative-sequence, and zero-sequence components.

[0049] ③ Apply the Euclidean norm formula to calculate the enhanced imbalance degree.

[0050] ④ When the imbalance exceeds the preset threshold (15%) and the difference between the 3rd harmonic content and the 2nd harmonic content exceeds the threshold (4%) for more than 10 seconds, a neutral line fault event is triggered.

[0051] ⑤ The host computer checks the event records of the electricity meters with the algorithm version of the present invention and other traditional algorithm versions.

[0052] This embodiment also provides a neutral line drop detection device for implementing the above-mentioned embodiments and preferred implementations. Details already described will not be repeated here. As used below, the term "module" may refer to a combination of software and / or hardware that implements a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, implementation using hardware, or a combination of software and hardware, is also possible and contemplated.

[0053] This embodiment provides a zero line drop detection device, such as Figure 3 As shown, the device includes: Calculation module 1, used for calculating the three-phase voltage unbalance according to the negative sequence voltage and the zero sequence voltage; A first judgment module 2 is used to judge whether the three-phase voltage imbalance exceeds a first preset threshold; The second judgment module 3 is used to judge whether the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold if the three-phase voltage imbalance exceeds the first preset threshold; The third judgment module 4 is configured to determine that the neutral line is disconnected if the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold and lasts for a preset time.

[0054] The further functional description of each of the above modules and units is the same as that of the above corresponding embodiments and will not be repeated here.

[0055] The neutral line drop detection device in this embodiment is presented in the form of a functional unit, where the unit refers to an ASIC (Application Specific Integrated Circuit) circuit, a processor and memory that executes one or more software or fixed programs, and / or other devices that can provide the above functions.

[0056] The embodiment of the present invention also provides a computer device having the above Figure 3 The neutral line drop detection device shown.

[0057] See also Figure 4 , Figure 4 is a structural diagram of a computer device provided by an optional embodiment of the present invention, such as Figure 4 As shown, the computer device includes: one or more processors 10, memory 20, and interfaces for connecting various components, including high-speed interfaces and low-speed interfaces. Various components utilize different buses to communicate with each other and can be installed on a common mainboard or installed in other ways as needed. The processor can process the instructions executed in the computer device, including instructions stored in the memory or on the memory to display the graphical information of the GUI on an external input / output device (such as, a display device coupled to the interface). In some optional embodiments, if necessary, multiple processors and / or multiple buses can be used together with multiple memories and multiple memories. Equally, multiple computer devices can be connected, and each device provides part of the necessary operations (for example, as a server array, a group of blade servers, or a multi-processor system). Figure 4 A processor 10 is taken as an example.

[0058] The processor 10 may be a central processing unit, a network processor, or a combination thereof. The processor 10 may further include a hardware chip. The hardware chip may be an application-specific integrated circuit, a programmable logic device, or a combination thereof. The programmable logic device may be a complex programmable logic device, a field programmable gate array, a general purpose array logic, or any combination thereof.

[0059] The memory 20 stores instructions that can be executed by at least one processor 10, so as to enable at least one processor 10 to execute the method shown in the above embodiment.

[0060] The memory 20 may include a program storage area and a data storage area, wherein the program storage area may store an operating system and application programs required for at least one function; the data storage area may store data created based on the use of the computer device, etc. In addition, the memory 20 may include a high-speed random access memory, and may also include a non-transient memory, such as at least one disk storage device, a flash memory device, or other non-transient solid-state storage device. In some optional embodiments, the memory 20 may optionally include a memory remotely located relative to the processor 10, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0061] The memory 20 may include a volatile memory, such as a random access memory; the memory may also include a non-volatile memory, such as a flash memory, a hard disk or a solid-state drive; the memory 20 may also include a combination of the above types of memory.

[0062] The computer device further includes an input device 30 and an output device 40. The processor 10, the memory 20, the input device 30 and the output device 40 may be connected via a bus or other means. Figure 4 The bus connection is taken as an example.

[0063] The input device 30 can receive input digital or character information and generate key signal input related to user settings and function control of the computer device. Examples include a touch screen, keypad, mouse, trackpad, touchpad, pointing stick, one or more mouse buttons, trackball, joystick, etc. The output device 40 may include a display device, auxiliary lighting devices (e.g., LEDs), and tactile feedback devices (e.g., vibration motors). Such display devices include, but are not limited to, liquid crystal displays, light emitting diodes, monitors, and plasma displays. In some optional embodiments, the display device may be a touch screen.

[0064] The embodiment of the present invention also provides a computer-readable storage medium. The above-mentioned method according to the embodiment of the present invention can be implemented in hardware, firmware, or implemented as a computer code that can be recorded in a storage medium, or implemented as a computer code that is originally stored in a remote storage medium or a non-temporary machine-readable storage medium and downloaded through a network and will be stored in a local storage medium, so that the method described herein can be stored in such software processing on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only storage memory, a random access memory, a flash memory, a hard disk or a solid-state drive, etc.; further, the storage medium can also include a combination of the above-mentioned types of memory. It can be understood that a computer, a processor, a microprocessor controller or programmable hardware includes a storage component that can store or receive software or computer code. When the software or computer code is accessed and executed by a computer, a processor or hardware, the method shown in the above embodiment is implemented.

[0065] A portion of the present invention may be applied as a computer program product, such as a computer program instruction, which, when executed by a computer, can call or provide the method and / or technical solution according to the present invention through the operation of the computer. Those skilled in the art should understand that the form in which the computer program instruction exists in a computer-readable medium includes, but is not limited to, a source file, an executable file, an installation package file, etc. Accordingly, the way in which the computer program instruction is executed by the computer includes, but is not limited to: the computer directly executes the instruction, or the computer compiles the instruction and then executes the corresponding compiled program, or the computer reads and executes the instruction, or the computer reads and installs the instruction and then executes the corresponding installed program. Here, the computer-readable medium may be any available computer-readable storage medium or communication medium that can be accessed by the computer.

[0066] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A method for detecting a zero line drop, characterized in that: The method comprises: Calculate the three-phase voltage unbalance based on the negative sequence voltage and zero sequence voltage; Determining whether the three-phase voltage imbalance exceeds a first preset threshold; If the three-phase voltage imbalance exceeds a first preset threshold, determining whether the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold; If the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold and lasts for a preset time, it is determined that the neutral line is disconnected.

2. The method for detecting a zero line drop according to claim 1, wherein: Calculating the three-phase voltage unbalance degree according to the negative-sequence voltage and the zero-sequence voltage includes: According to the negative sequence voltage and zero sequence voltage, the three-phase voltage unbalance is calculated using the Euclidean norm; The calculation formula for three-phase voltage unbalance is: in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage.

3. The method for detecting a zero line drop according to claim 1, wherein: Calculating the three-phase voltage unbalance degree according to the negative-sequence voltage and the zero-sequence voltage includes: Different weights are assigned to negative sequence voltage and zero sequence voltage, and the three-phase voltage unbalance is calculated using a weighted calculation method; The calculation formula for three-phase voltage unbalance is: in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage; ω 1. ω 2 are the weight coefficients of zero-sequence voltage and negative-sequence voltage respectively.

4. The method for detecting a zero line drop according to claim 1, wherein: Calculating the three-phase voltage unbalance degree according to the negative-sequence voltage and the zero-sequence voltage includes: Different combination coefficients are assigned to the negative sequence voltage and zero sequence voltage, and the three-phase voltage unbalance is calculated using a linear combination calculation method; The calculation formula for three-phase voltage unbalance is: in, U p is the three-phase voltage unbalance; U 0 is the zero-sequence voltage; U 1 is the positive sequence voltage; U 2 is the negative sequence voltage; k 1. k 2 are the combination coefficients of zero-sequence voltage and negative-sequence voltage respectively.

5. The method for detecting a zero line drop according to claim 1, wherein: Before calculating the three-phase voltage unbalance, it also includes: Detect whether zero-sequence current exists; If zero-sequence current exists, the three-phase voltage unbalance is calculated based on the negative-sequence voltage and zero-sequence voltage; If the zero-sequence current does not exist, it is determined that the neutral line is disconnected.

6. The method for detecting a zero line drop according to claim 1, wherein: Also includes: If the three-phase voltage imbalance exceeds a first preset threshold, determining whether the phase angle difference of the three-phase voltage exceeds a second preset threshold; If the phase angle difference of the three-phase voltages exceeds a second preset threshold and lasts for more than a preset time, it is determined that the neutral line is disconnected.

7. A zero line drop detection device, characterized in that: The device comprises: A calculation module is used to calculate the three-phase voltage unbalance based on the negative sequence voltage and the zero sequence voltage; A first judging module, configured to judge whether the three-phase voltage imbalance exceeds a first preset threshold; a second judgment module, configured to judge whether a difference between a third harmonic content and a second harmonic content in the three-phase voltage exceeds a second preset threshold value if the three-phase voltage imbalance exceeds the first preset threshold value; The third judgment module is used to determine that the neutral line is disconnected if the difference between the third harmonic content and the second harmonic content in the three-phase voltage exceeds a second preset threshold and lasts for a preset time.

8. A computer device, characterized in that: include: A memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the zero line drop detection method according to any one of claims 1 to 6 by executing the computer instructions.

9. A computer-readable storage medium, characterized in that The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a computer to execute the neutral line drop detection method according to any one of claims 1 to 6.

10. A computer program product, characterized in that The method comprises computer instructions, wherein the computer instructions are used to enable a computer to execute the neutral line drop detection method according to any one of claims 1 to 6.

Images