Feeder terminal device with dual-mode zero-sequence current protection
By combining the traditional zero-sequence current transformer detection and three-phase current calculation modes in the feeder terminal device, the precise protection and rapid response of zero-sequence current faults are achieved, and the problem of insufficient monitoring accuracy and response speed of traditional devices in complex power grid environments is solved, and the accuracy and reliability of protection are improved.
Patent Information
- Application Number
- CN202411789133.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-06
- Publication Date
- 2025-03-21
AI Technical Summary
In the complex and changing power grid environment, the single zero-sequence current detection mode cannot effectively identify and isolate faults, resulting in limited monitoring accuracy, slow response speed, insufficient redundancy, and difficult to meet the high requirements of modern smart grids for rapid identification and isolation of faults.
A feeder terminal device with dual-mode zero-sequence current protection is designed. By combining the traditional zero-sequence current transformer detection and zero-sequence current detection based on three-phase current calculation, the fast Fourier transform algorithm is used to calculate the vector sum of the three-phase current to obtain the zero-sequence current, and the results of the two calculation methods are compared and checked, tripping or alarm operations are performed.
It realizes accurate protection and rapid response to zero-sequence current faults in the power system, improves the accuracy and reliability of protection, and judges single-phase grounding faults through the transient method, enhancing fault detection capabilities.
Smart Images
Figure CN119667375A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of power system automation, and in particular to a feeder terminal device with dual-mode zero-sequence current protection. Background Art
[0002] The statements in this section merely provide background technical information related to the present application and do not necessarily constitute prior art.
[0003] Feeder terminal unit (FTU) is an important equipment in the power system, used for fault identification, fault location, fault isolation and power restoration of feeder lines. Traditional feeder terminal units usually only have a single zero-sequence current detection mode, which cannot adapt to complex and changeable grid conditions. They mainly use zero-sequence current transformers to detect zero-sequence current for fault detection and location. However, zero-sequence current transformers may fail due to various reasons on site (such as aging, damage, etc.), resulting in the failure of zero-sequence current protection to work properly.
[0004] At present, zero-sequence current monitoring in power systems mainly relies on traditional current transformers (CTs) and relay protection devices, but traditional methods have problems such as limited monitoring accuracy, slow response speed, and insufficient redundancy, making it difficult to adapt to the high requirements of modern smart grids for rapid fault identification and isolation. Especially in complex and changeable power grid environments, single-phase grounding faults occur frequently. How to efficiently and accurately capture and analyze zero-sequence current has become the key to improving power grid security. Summary of the invention
[0005] In order to solve or partially solve the problems in the background technology, the present application proposes a feeder terminal device with dual-mode zero-sequence current protection.
[0006] The present application provides a feeder terminal device with dual-mode zero-sequence current protection, comprising:
[0007] A set of pole switches for section points, each pole switch is equipped with a power PT, which is used to convert the 10kV line voltage into an AC 220v output power supply voltage;
[0008] AC sampling integrated circuit, including current transformer CT and voltage transformer PT, used to collect current and voltage of A, B, C three-phase and zero-sequence current;
[0009] The control circuit includes a dual-mode zero-sequence current detection module, which detects zero-sequence current through a zero-sequence current transformer, collects three-phase current data, calculates the vector sum of the three-phase current using a fast Fourier transform algorithm, obtains zero-sequence current, compares and verifies the results of two zero-sequence current calculation methods, and performs tripping or alarm operations according to a preset protection strategy.
[0010] Preferably, the control circuit includes a processor, an AD sampling circuit, a filter capacitor, an optical coupling isolation module, and a switch-off circuit, and the dual-mode zero-sequence current detection module is arranged in the processor;
[0011] The processor monitors the AD sampling circuit, calculates the zero-sequence current, and performs tripping or alarming operations according to the preset protection strategy.
[0012] Preferably, the specific method for the processor to calculate the zero-sequence current is:
[0013] S101: collecting the output current of the corresponding zero-sequence CT in real time through an AD sampling circuit to obtain a discrete sample signal;
[0014] S102: Use a sliding window to truncate the sample signal in real time, set the window opening time in advance, select a preset number of windows as sample windows, and average all sample points in the sample window to obtain the first zero-sequence current I0 1 ;
[0015] S103: synchronously collect the A, B, and C phase currents through the AD sampling circuit, and convert the amplitudes and angles of the three-phase currents into complex forms:
[0016] Ia=Ia m *cos(φa)+j*Ia m *sin(φa)
[0017] Ib=Ib m *cos(φb)+j*Ib m *sin(φb)
[0018] Ic=Ic m *cos(φc)+j*Ic m *sin(φc),
[0019] Among them, Ia m , Ib m 、Ic m are the amplitudes of the three-phase currents, φa, φb, φc are the phase angles of the three-phase currents, and the second zero-sequence current is calculated: I0 2 =|Ia+Ib+Ic|.
[0020] Preferably, the specific method for the control circuit to perform a tripping or alarming operation according to a preset protection strategy is:
[0021] The zero-sequence current values in the two modes are monitored in real time and compared with the preset zero-sequence overcurrent setting values respectively. When the zero-sequence current values in both modes are greater than the zero-sequence overcurrent setting values, a tripping operation is performed and an alarm message is sent. When the zero-sequence current value in only one mode is greater than the zero-sequence overcurrent setting value, only an alarm message is sent and the tripping operation is not performed.
[0022] Preferably, the method for the control circuit to perform a tripping or alarming operation according to a preset protection strategy also includes the logic of using a transient method to perform a single-phase grounding fault judgment, and the specific steps are as follows:
[0023] S201: Record two zero-sequence current waveforms and zero-sequence voltage derivatives;
[0024] S202: Determine whether the two zero-sequence current waveforms maintain opposite polarity to the zero-sequence voltage derivative;
[0025] S203: When both zero-sequence current waveforms maintain opposite polarity to the zero-sequence voltage derivative, a tripping operation is performed and a fault message is sent;
[0026] When only one zero-sequence current waveform maintains opposite polarity with the zero-sequence voltage derivative, only an alarm message is sent.
[0027] Preferably, the processor is a STM32F407I GT6 processor.
[0028] Compared with the prior art, the beneficial effects of this application are:
[0029] (1) The present application combines the two modes of traditional zero-sequence current transformer detection and zero-sequence current detection based on three-phase current calculation. By comparing and verifying the results of the two zero-sequence current calculation methods, accurate protection and rapid response to zero-sequence current faults in the power system are achieved, thereby improving the accuracy and reliability of protection.
[0030] (2) The present application utilizes the transient method to determine single-phase grounding faults, further enhancing the fault detection capability of the feeder terminal device. BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.
[0032] Figure 1 The circuit diagram of this application is shown below.
[0033] Figure 2 This is the dual-mode zero-sequence overcurrent protection flow chart of this application,
[0034] Figure 3 This is a flow chart of the unidirectional ground fault protection of this application. DETAILED DESCRIPTION
[0035] The present application is further described below in conjunction with the accompanying drawings and embodiments.
[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.
[0037] In the present disclosure, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom" and the like indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present disclosure, and do not specifically refer to any part or element in the present disclosure and should not be understood as limitations on the present disclosure.
[0038] Example 1
[0039] like Figures 1 to 3 As shown, the present application provides a feeder terminal device with dual-mode zero-sequence current protection, comprising:
[0040] A set of pole switches for segmentation points, each pole switch is equipped with a power PT, which is used to convert the 10kV line voltage into an AC 220v output power supply voltage to power each module of the device;
[0041] AC sampling integrated circuit, including current transformer CT and voltage transformer PT, used to collect current and voltage of A, B, C three-phase and zero-sequence current;
[0042] The control circuit includes a dual-mode zero-sequence current detection module, which detects zero-sequence current through a zero-sequence current transformer, collects three-phase current data, calculates the vector sum of the three-phase current using a fast Fourier transform algorithm, obtains zero-sequence current, compares and verifies the results of two zero-sequence current calculation methods, and performs tripping or alarm operations according to a preset protection strategy.
[0043] Specifically, the control circuit includes a processor, an AD sampling circuit, a filter capacitor, an optical coupling isolation module, and a switch-off circuit, and the dual-mode zero-sequence current detection module is arranged in the processor;
[0044] The processor monitors the AD sampling circuit, calculates the zero-sequence current, and performs tripping or alarming operations according to the preset protection strategy.
[0045] Typically, an STM32F407I GT6 processor is used as the processor of the control circuit. Preferably, the control circuit also includes a communication interface and a device panel.
[0046] When this device is used, the STM32F407I GT6 processor in the control circuit is initialized, the functions of each pin, clock frequency and other parameters are set, the filter capacitor is checked to see if it is working properly to filter out interference, the electrical isolation function of the optocoupler isolation module is confirmed to be normal, the reliability of the opening circuit action is tested, and the AC sampling circuit is started to prepare for collecting current data.
[0047] When the device is powered on, the AD sampling circuit is started to collect the output current of the corresponding zero-sequence CT in real time with the preset sampling frequency and accuracy, obtain the discretized sample signal, ensure that the signal fully and accurately reflects the zero-sequence current information, and use the sliding window technology to truncate the sample signal in real time. In this embodiment, a 5-sample point window is used to accurately calculate the average value of all sample points in each window, and the new average value is used as the denoised value of the target sample point. This value is used as the first zero-sequence current I0 1 .
[0048] The A, B, and C phase currents are collected synchronously through the AD sampling circuit, so that the timer TI M8 in the STM32F407I GT6 processor runs stably at a frequency of 42MHz, and outputs the PWM signal through the PC8 pin. The automatic reload value (ARR) of the PWM signal is set to 6561 through calculation to ensure that 128 data points can be collected evenly every 20 milliseconds. The collection interval of each data point is 0.15625 milliseconds, so as to accurately trigger the ADC for data collection and obtain high-precision three-phase current data.
[0049] The collected three-phase current data is processed and the amplitude and angle of the three-phase current are converted into complex form, that is, the amplitude and angle of the calculated current are first converted into complex form:
[0050] Ia=Ia m *cos(φa)+j*Ia m *sin(φa)
[0051] Ib=Ib m *cos(φb)+j*Ib m *sin(φb)
[0052] Ic=Ic m *cos(φc)+j*Ic m *sin(φc)
[0053] Among them, Ia m , Ib m 、Ic mare the amplitudes of the three-phase currents, φa, φb, φc are the phase angles of the three-phase currents, and the zero-sequence current is calculated as: I0 2 =|Ia+Ib+Ic|.
[0054] The zero-sequence current information is obtained by calculating the vector sum, and the computing power of the processor is used to accurately and quickly complete complex number operations to ensure the real-time and accuracy of the zero-sequence current calculation.
[0055] During operation, keep the two zero-sequence current calculation methods working continuously, monitor the zero-sequence voltage values in the two modes in real time, and set the appropriate zero-sequence overcurrent setting I0 over , when (I0 1 >I0 over )&(I0 2 >I0 over ), the processor immediately sends a trip signal, triggers the trip circuit to trip the pole switch, cuts off the fault line, and sends an alarm message to the monitoring system through the communication interface to notify the operation and maintenance personnel of the zero-sequence overcurrent fault; when (I0 1 >I0 over )|(I0 2 >I0 over ) condition, the processor only sends an alarm message to the operation and maintenance personnel through the communication interface, indicating that there may be a line fault or a transformer fault, which needs to be checked, but does not perform a tripping operation; when it is met! ((I0 1 >I0 over )&(I0 2 >I0 over )), the system is judged to be operating normally and continues to maintain normal monitoring status.
[0056] This device is also used to use the transient method to judge the logic of single-phase grounding fault. When judging the single-phase grounding fault, both zero-sequence current calculation methods are in working state, and the transient method is used to judge and record the zero-sequence current waveform I0 detected by the traditional zero-sequence current transformer by the feeder terminal device. b1 , the zero-sequence current calculated by the symmetrical component method is recorded as I0 b2 , record the zero-sequence voltage derivative and judge I0 b1 Whether it maintains the opposite polarity with the zero-sequence voltage derivative, that is, judging:
[0057]
[0058] Where (I0 b1 ≠0 and ), when both conditions are met, it is determined that a single-phase grounding fault occurs in the line, and the alarm and tripping operations are executed. When one of the conditions is met, only the alarm operation is executed, and the operation and maintenance personnel are notified to check and analyze the transformer and the line.
[0059] The above are only preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.
[0060] Although the above describes the specific implementation methods of the present application in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present application. Technical personnel in the relevant field should understand that on the basis of the technical solution of the present application, various modifications or deformations that can be made by technical personnel in this field without creative work are still within the scope of protection of the present application.
Claims
1. A feeder terminal device with dual-mode zero-sequence current protection, characterized in that: include: A set of pole switches for section points, each pole switch is equipped with a power PT, which is used to convert the 10kV line voltage into an AC 220v output power supply voltage; AC sampling integrated circuit, including current transformer CT and voltage transformer PT, used to collect current and voltage of A, B, C three-phase and zero-sequence current; The control circuit includes a dual-mode zero-sequence current detection module, which detects zero-sequence current through a zero-sequence current transformer, collects three-phase current data, calculates the vector sum of the three-phase current using a fast Fourier transform algorithm, obtains zero-sequence current, compares and verifies the results of two zero-sequence current calculation methods, and performs tripping or alarm operations according to a preset protection strategy.
2. A feeder terminal device with dual-mode zero-sequence current protection according to claim 1, characterized in that: The control circuit includes a processor, an AD sampling circuit, a filter capacitor, an optical coupling isolation module, and a switch-off circuit, and the dual-mode zero-sequence current detection module is arranged in the processor; The processor monitors the AD sampling circuit, calculates the zero-sequence current, and performs tripping or alarming operations according to the preset protection strategy.
3. A feeder terminal device with dual-mode zero-sequence current protection according to claim 2, characterized in that: The specific method for the processor to calculate the zero-sequence current is: S101: collecting the output current of the corresponding zero-sequence CT in real time through an AD sampling circuit to obtain a discrete sample signal; S102: Using a sliding window to perform real-time truncation of the sample signal, the window opening time is preset, a preset number of windows are selected as sample windows, and all sample points in the sample window are averaged to obtain a first zero-sequence current I01; S103: synchronously collect the A, B, and C phase currents through the AD sampling circuit, and convert the amplitudes and angles of the three-phase currents into complex forms: Take=Take m *cos(φa)+j*Ia m *sin(φa) One=One m *cos(φb)+j*Ib m *sin(φb) Ic=Ic m *cos(φc)+j*Ic m *sin(φc), Among them, Ia m , Ib m 、Ic m are the amplitudes of the three-phase currents, φa, φb, φc are the phase angles of the three-phase currents, and the second zero-sequence current is calculated: I02=|Ia+Ib+Ic|.
4. A feeder terminal device with dual-mode zero-sequence current protection according to claim 3, characterized in that: The specific method for the control circuit to perform tripping or alarming operations according to the preset protection strategy is: The zero-sequence current values in the two modes are monitored in real time and compared with the preset zero-sequence overcurrent setting values respectively. When the zero-sequence current values in both modes are greater than the zero-sequence overcurrent setting values, a tripping operation is performed and an alarm message is sent. When the zero-sequence current value in only one mode is greater than the zero-sequence overcurrent setting value, only an alarm message is sent and the tripping operation is not performed.
5. A feeder terminal device with dual-mode zero-sequence current protection according to claim 4, characterized in that: The method for the control circuit to perform tripping or alarming operations according to a preset protection strategy also includes the logic of using a transient method to perform single-phase grounding fault judgment, and the specific steps are as follows: S201: Record two zero-sequence current waveforms and zero-sequence voltage derivatives; S202: Determine whether the two zero-sequence current waveforms maintain opposite polarity to the zero-sequence voltage derivative; S203: When both zero-sequence current waveforms maintain opposite polarity to the zero-sequence voltage derivative, a tripping operation is performed and a fault message is sent; When only one zero-sequence current waveform maintains opposite polarity with the zero-sequence voltage derivative, only an alarm message is sent.
6. A feeder terminal device with dual-mode zero-sequence current protection according to claim 2, characterized in that: The processor is an STM32F407 IGT6 processor.