Bus low residual voltage full frequency limit PT cabinet control system

Abstract

The utility model discloses a bus low residual voltage full frequency limit harmonic PT cabinet control system relates to low voltage circuit protection technical field, including the isolation handcart, high voltage current -limiting fuse and voltage transformer, the positive pole of high voltage current -limiting fuse is connected with low voltage power grid bus, through the active current -limiting harmonic eliminator and microcomputer secondary harmonic eliminator of setting, wherein the primary harmonic elimination of active current -limiting harmonic eliminator can eliminate high frequency resonance voltage, and microcomputer secondary harmonic eliminator can effectively eliminate low frequency resonance voltage, so can realize full frequency limit harmonic function, the resonance elimination and protection effect of this control system to low voltage circuit has been improved to the maximum degree to the active current -limiting harmonic eliminator thermosensitive type harmonic elimination module's resistance value is kiloohm level when normal work, and voltage transformer primary winding's resistance value is megaohm level when normal work, therefore will not produce the influence to each performance of voltage transformer.

Description

Technical Field

[0001] This utility model relates to the field of medium and low voltage circuit protection technology, and in particular to a busbar low residual voltage full-frequency harmonic limiting PT cabinet control system. Background Technology

[0002] 3-35kV (including 66kV) power grids belong to medium- and low-voltage transformer and distribution networks. The absolute value of internal overvoltages in such grids is not high. Therefore, the main factor endangering the insulation safety level of the grid is not internal overvoltage, but atmospheric overvoltage (i.e., lightning overvoltage). Consequently, the overvoltage protection measures adopted for a long time have only been to prevent damage to equipment from atmospheric overvoltages. The main technical measures are limited to installing various types of surge arresters. The discharge voltage of surge arresters is more than four times the phase voltage, therefore they are only effective in protecting against lightning strikes and have no protective effect against internal overvoltages.

[0003] In my country, most systems below 35kV adopt a neutral point non-effective grounding operation mode. The neutral point of the primary winding of the electromagnetic voltage transformer (PT) on the bus becomes the only metal channel between the power grid and the ground. The charging and discharging path of the power grid's capacitance to ground must pass through the primary winding of the voltage transformer. The above circuit structure will cause the equivalent excitation reactance of the PT to form a special resonant circuit with the equivalent capacitance of the system to ground when certain equipment switching operations or single-phase grounding faults disappear. This will excite various harmonic ferroresonant overvoltages, thereby causing PT saturation. This can easily cause serious damage to the circuit and PT cabinet, thus triggering a circuit safety accident.

[0004] In existing technologies, to eliminate resonance and prevent circuit damage caused by overvoltage, a silicon carbide resistor is typically connected in series on the neutral point side of the high-voltage side of the PT (potential transformer). This increases the damping of the resonant circuit to eliminate resonance. However, the silicon carbide resistor is a varistor similar to that of a zinc oxide surge arrester, exhibiting nonlinear volt-ampere characteristics: under normal operating conditions, it exhibits high resistance (approximately 100 kΩ); when ferroresonance or charge transfer causes an increase in zero-sequence current, its resistance drops rapidly (tens of kΩ). These resistor characteristics have two drawbacks: firstly, excessively high resistance during normal operation may lead to three-phase voltage imbalance in the PT; secondly, when the PT is over-excited, the resistance becomes too low, reducing the harmonic suppression and current-limiting functions, which is detrimental to suppressing PT faults. Utility Model Content

[0005] The purpose of this invention is to provide a busbar low residual voltage full-frequency harmonic limiting PT cabinet control system to solve the problems mentioned in the background art. In existing medium and low voltage circuits, when a silicon carbide resistor is connected in series on the neutral point side of the PT high voltage side to increase the damping of the resonant circuit to eliminate resonance, the resistance value of the silicon carbide resistor itself is too large during normal operation, which may lead to unbalanced three-phase voltage of the PT. At the same time, when the PT is over-excited, the resistance value is too small, and the harmonic elimination and current limiting functions are reduced, which is not conducive to suppressing the occurrence of PT faults.

[0006] To achieve the above objectives, this utility model provides the following technical solution: a busbar low residual voltage full-frequency harmonic limiting PT cabinet control system, including an isolation trolley, a high-voltage current-limiting fuse, and a voltage transformer. The positive terminal of the high-voltage current-limiting fuse is connected to the medium- and low-voltage power grid busbar, and the negative terminal of the high-voltage current-limiting fuse is connected to the positive terminal of the voltage transformer. The negative terminal of the high-voltage current-limiting fuse is also connected to the voltage transformer. An active current-limiting harmonic suppressor is connected to the primary winding of the voltage transformer. A microcomputer secondary harmonic suppressor is connected to the open delta winding of the active current-limiting harmonic suppressor. An intelligent microcomputer harmonic limiting controller is connected to the negative terminal of the active current-limiting harmonic suppressor. The negative terminal of the intelligent microcomputer harmonic limiting controller is grounded. The active current-limiting harmonic suppressor includes a thermistor-type harmonic suppressor module.

[0007] The resistance of the thermistor-type harmonic elimination module is in the kiloohm range during normal operation, and the resistance drops to the hundredohm range after the temperature rises above the threshold.

[0008] Preferably, the high-voltage current-limiting fuse is connected in parallel with a lightning rod, and the high-voltage current-limiting fuse is also connected in parallel with a high-capacity overvoltage absorption device. The lightning rod and the high-capacity overvoltage absorption device are connected in parallel, and the positive terminals of both the lightning rod and the high-capacity overvoltage absorption device are connected to the medium- and low-voltage power grid busbar. The negative terminals of both the lightning rod and the high-capacity overvoltage absorption device are grounded. The advantage of this arrangement is that the lightning rod can prevent overvoltage caused by external lightning and other factors from damaging the circuit. The high-capacity overvoltage absorption device can effectively smooth the rising edge of the overvoltage and eliminate voltage spikes. It can withstand the huge energy generated by the overvoltage and make the residual voltage value after the overvoltage is eliminated lower than that of the lightning arrester, thereby avoiding damage to the circuit due to excessive residual voltage.

[0009] Preferably, the high-capacitance overvoltage absorption device adopts a structure combining a high-capacitance zinc oxide resistor and a discharge gap. The advantage of this configuration is that the high-capacitance zinc oxide resistor and the discharge gap can protect each other, thereby ensuring that the discharge value is equal under various voltage waveforms and is not affected by various operational overvoltage waveforms. The overvoltage protection value is accurate and the protection performance is excellent.

[0010] Preferably, the intelligent microcomputer harmonic limiter controller adopts MICROCHIP core technology. The intelligent microcomputer harmonic limiter controller includes a high-speed DSP core processor, and the DSP core processor is connected to an FPGA coprocessor and a FLASH memory. The DSP core processor is also connected to an SDRAM memory, and the FPGA coprocessor is also connected to an AD acquisition chip. The advantage of this configuration is that the high-speed DSP core processor can ensure the real-time performance of the operation and the accuracy of the action, thereby enabling real-time monitoring of the system status, accurate judgment of the resonance fault, and timely action. This effectively improves the control system's ability to detect and handle circuit faults in a timely manner, and enhances the safety and reliability of the control system.

[0011] Preferably, the active current limiting harmonic suppressor further includes a voltage and current acquisition circuit and a temperature sampling circuit. The voltage and current acquisition circuit is used to acquire the analog voltage signal and analog current signal of the voltage transformer, and the temperature sampling circuit is used to acquire the temperature value of the thermistor-type harmonic suppressor module. The voltage and current acquisition circuit and the temperature sampling circuit are connected to a filter computer, which is connected to the AD acquisition chip in the intelligent microcomputer harmonic suppressor controller. The advantage of this configuration is that the voltage and current acquisition circuit can continuously monitor the voltage signal provided by the voltage transformer in real time. Once phenomena such as voltage transformer disconnection, overvoltage, undervoltage, low voltage, resonance, or arcing grounding occur, the intelligent microcomputer harmonic suppressor controller utilizes the high-speed, repetitive data processing capabilities of the DSP to perform Fourier analysis and determine the fault type of the system. It displays fault conditions and alarms, outputs corresponding switching node signals, and simultaneously acquires and feeds back the current in the neutral point circuit of the voltage transformer in real time. It also tracks the entire voltage and current change process from the start of current limiting to completion of current limiting after the current limiting device detects an abnormal increase in the neutral point current of the voltage transformer. The temperature acquisition circuit monitors the temperature signal in real time to monitor the temperature of the thermal harmonic suppression module of the current limiting harmonic suppression device. When the temperature continuously exceeds the set threshold, the intelligent microcomputer harmonic limiting controller will issue an alarm signal, indicating that the thermal harmonic suppression module 31 has deteriorated and needs to be replaced in time. This avoids the failure of the active current limiting harmonic suppression device due to aging, which would lead to the failure of the primary harmonic suppression function and threaten the safe operation of the circuit, thus improving the safety and reliability of the control system.

[0012] Preferably, the intelligent microcomputer harmonic limiter controller is also connected to an LCD touch screen and LED indicator lights. The advantage of this configuration is that the LCD touch screen allows staff to more flexibly and efficiently export and read the required parameters as well as input the required parameters, improving the convenience and reliability of the control system. The LED indicator lights can promptly detect the operating status of the control system itself, thus facilitating staff to promptly detect abnormalities and take timely measures.

[0013] In summary, the technical effects and advantages of this utility model are as follows:

[0014] 1. In this utility model, by setting an active current-limiting harmonic suppressor and a microcomputer-based secondary harmonic suppressor, the active current-limiting harmonic suppressor can eliminate medium- and high-frequency resonant voltages, while the microcomputer-based secondary harmonic suppressor can effectively eliminate medium- and low-frequency resonant voltages. This achieves full-frequency harmonic limiting, maximizing the control system's resonance elimination and protection effect on medium- and low-voltage circuits. Furthermore, the active current-limiting harmonic suppressor's thermistor module has a resistance value in the kiloohm range during normal operation, while the voltage transformer's primary winding has a resistance value in the megaohm range during normal operation. Therefore, it will not affect the voltage transformer's performance or significantly change the system's parameters, ensuring stable circuit operation. Moreover, the thermistor module's resistance value drops to the hundred-ohm range after the temperature rises above a threshold, thus enabling rapid and reliable dissipation of resonant energy and quick elimination of resonant voltage, improving circuit protection.

[0015] 2. In this utility model, the high-capacitance overvoltage absorption device adopts a structure combining a high-capacitance zinc oxide resistor and a discharge gap. The high-capacitance zinc oxide resistor and the discharge gap can protect each other, so that the discharge value is equal under various voltage waveforms and is not affected by various operational overvoltage waveforms. The overvoltage protection value is accurate and the protection performance is excellent. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is the primary harmonic elimination circuit diagram of the low residual voltage full-frequency harmonic limiting PT cabinet control system of the busbar in this utility model;

[0018] Figure 2 This is a block diagram of the primary harmonic elimination structure of the low residual voltage full-frequency harmonic limiting PT cabinet control system of the busbar in this utility model;

[0019] Figure 3 The waveform diagram shows the inrush current suppression at the neutral point of the voltage transformer during operation of the low residual voltage full-frequency harmonic limiting PT cabinet control system of this utility model.

[0020] In the diagram: 1. High-voltage current-limiting fuse; 2. Voltage transformer; 3. Active current-limiting harmonic suppressor; 31. Thermistor-type harmonic suppressor module; 4. Microcomputer secondary harmonic suppressor; 5. Intelligent microcomputer harmonic limiting controller; 6. Lightning rod; 7. High-capacity overvoltage absorption device. Detailed Implementation

[0021] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0022] Example 1

[0023] Please refer to Figures 1-3 The busbar low residual voltage full-frequency harmonic limiting PT cabinet control system shown includes an isolation handcart, a high-voltage current-limiting fuse 1, and a voltage transformer 2. The positive terminal of the high-voltage current-limiting fuse 1 is connected to the medium and low voltage power grid busbar, and the negative terminal of the high-voltage current-limiting fuse 1 is connected to the positive terminal of the voltage transformer 2. The primary winding of the voltage transformer 2 is connected to an active current-limiting harmonic suppressor 3. The open delta winding of the active current-limiting harmonic suppressor 3 is connected to a microcomputer secondary harmonic suppressor 4. The negative terminal of the active current-limiting harmonic suppressor 3 is connected to an intelligent microcomputer harmonic limiting controller 5. The negative terminal of the intelligent microcomputer harmonic limiting controller 5 is grounded. The active current-limiting harmonic suppressor 3 includes a thermistor-type harmonic suppressor module 31.

[0024] The resistance of the thermistor-type harmonic elimination module 31 is in the kiloohm range during normal operation, and drops to the hundredohm range after the temperature rises above the threshold.

[0025] refer to Figure 1 A high-voltage current-limiting fuse 1 is connected in parallel with a lightning rod 6. The high-voltage current-limiting fuse 1 is also connected in parallel with a high-capacity overvoltage absorption device 7. The lightning rod 6 and the high-capacity overvoltage absorption device 7 are connected in parallel. The positive terminals of the lightning rod 6 and the high-capacity overvoltage absorption device 7 are both connected to the medium- and low-voltage power grid busbars, and the negative terminals of the lightning rod 6 and the high-capacity overvoltage absorption device 7 are both grounded.

[0026] Specifically, the lightning rod 6 can prevent overvoltage caused by external lightning and other factors from damaging the circuit. The high-capacity overvoltage absorption device 7 can effectively smooth the rising edge of the overvoltage and eliminate voltage spikes. It can withstand the huge energy generated by the overvoltage and make the residual voltage value after the overvoltage is eliminated lower than that of the surge arrester, thereby avoiding damage to the circuit due to excessive residual voltage.

[0027] refer to Figure 1 The high-capacitance overvoltage absorption device 7 adopts a structure combining a high-capacitance zinc oxide resistor and a discharge gap.

[0028] Specifically, the high-capacity zinc oxide resistor and the discharge gap can protect each other, so that the discharge value is equal under various voltage waveforms and is not affected by various operating overvoltage waveforms. The overvoltage protection value is accurate and the protection performance is excellent.

[0029] refer to Figure 2 The intelligent microcomputer harmonic limiter controller 5 adopts MICROCHIP core technology. The intelligent microcomputer harmonic limiter controller 5 includes a high-speed DSP core processor, and the DSP core processor is connected to an FPGA coprocessor and FLASH respectively. The DSP core processor is also connected to SDRAM, and the FPGA coprocessor is also connected to an AD acquisition chip.

[0030] Specifically, the high-speed DSP core processor can ensure real-time operation and accuracy of action, thereby enabling real-time monitoring of system status, accurate judgment of resonance faults, and timely action. This effectively improves the control system's ability to detect and handle circuit faults in a timely manner, and enhances the safety and reliability of the control system.

[0031] refer to Figure 2 The active current limiting harmonic suppressor 3 also includes a voltage and current acquisition circuit and a temperature sampling circuit. The voltage and current acquisition circuit is used to acquire the voltage analog signal and current analog signal of the voltage transformer 2. The temperature sampling circuit is used to acquire the temperature value of the thermistor-type harmonic suppressor module 31. The voltage and current acquisition circuit and the temperature sampling circuit are connected to a filter computer, which is connected to the AD acquisition chip in the intelligent microcomputer harmonic suppressor controller 5.

[0032] Specifically, the voltage and current acquisition circuit can continuously monitor the voltage signal provided by the voltage transformer 2 in real time. If phenomena such as voltage transformer 2 disconnection, overvoltage, undervoltage, low voltage, resonance, or arcing occur, the intelligent microcomputer harmonic limiting controller 5 utilizes the high-speed, repetitive data processing capabilities of the DSP to perform Fourier analysis, determine the system fault type, display the fault status and alarms, and output corresponding switching node signals. Simultaneously, the voltage and current acquisition circuit can collect and provide real-time feedback on the current in the neutral point circuit of the voltage transformer 2 and the current limiting harmonic suppressor's response when voltage is detected. During the entire voltage and current change process from the start of current limiting to the completion of current limiting after the abnormal increase in neutral point current of transformer 2, the temperature acquisition circuit monitors the temperature signal in real time to monitor the temperature of the thermal harmonic suppression module 31 of the current limiting harmonic suppressor. When the temperature continues to exceed the set threshold, the intelligent microcomputer harmonic suppressor controller 5 will issue an alarm signal, indicating that the thermal harmonic suppression module 31 has deteriorated and needs to be replaced in time. This avoids the failure of the active current limiting harmonic suppressor 3 due to aging, which would lead to the failure of the primary harmonic suppression function and threaten the safe operation of the circuit. This improves the safety and reliability of the control system.

[0033] Generally, when the thermistor-type harmonic suppression module 31 reaches the Curie temperature of 75℃, the impedance rises rapidly, limiting the neutral point current of the voltage transformer 2. After the current is limited, the internal temperature of the active current-limiting harmonic suppressor 3 will tend to reach equilibrium after a certain period of time. The temperature after equilibrium will not exceed 100℃. If the temperature rises to 100℃, the controller will alarm, indicating that the thermistor-type harmonic suppression module 31 has deteriorated and the user needs to be notified in time to replace it.

[0034] refer to Figure 2 The intelligent microcomputer harmonic limiter controller 5 is also connected to an LCD touch screen and LED display lights.

[0035] Specifically, the LCD touchscreen allows staff to export and read required parameters more flexibly and efficiently, improving the convenience and reliability of the control system. The LED indicator can promptly detect the operating status of the control system, making it easier for staff to identify abnormalities and take timely measures.

[0036] The intelligent microcomputer harmonic limiter controller 5 is also connected to an output circuit, an input signal acquisition circuit, and serial and network ports, enabling comprehensive and thorough monitoring of the circuit and the operating status of the control system.

[0037] Working principle: During normal operation of the medium and low voltage power grid and this control system, the intelligent microcomputer harmonic limiter controller 5 continuously monitors the voltage signal provided by the voltage transformer 2 in real time. Once phenomena such as voltage transformer 2 disconnection, overvoltage, undervoltage, low voltage, resonance, arcing grounding, etc. occur, the intelligent microcomputer harmonic limiter controller 5 uses the high-speed and repetitive data processing capability of DSP to perform Fourier analysis, determine the fault type of the system, display the fault status and alarm, and output the corresponding switch node signals.

[0038] Meanwhile, the microcomputer secondary harmonic suppressor 4 can work with the active current-limiting harmonic suppressor 3 to eliminate the resonant voltage across the entire frequency range, thus improving the protection effect on the circuit.

[0039] Furthermore, the high-capacity overvoltage absorption device 7 can effectively smooth out the rising edge of the overvoltage and eliminate voltage spikes. It can withstand the huge energy generated by the overvoltage and make the residual voltage value after the overvoltage is eliminated lower than that of the surge arrester, thereby avoiding damage to the circuit due to excessive residual voltage value.

[0040] Meanwhile, the intelligent microcomputer harmonic limiting controller 5 can collect and provide real-time feedback on the current in the neutral point circuit of the voltage transformer 2 and the entire voltage and current change process from the start of current limiting to completion after the current limiting device detects an abnormal increase in the neutral point current of the voltage transformer 2. Furthermore, the temperature acquisition circuit monitors the temperature signal to monitor the temperature of the thermal harmonic limiting module 31 of the current limiting harmonic limiting device in real time. When the temperature continuously exceeds the set threshold, the intelligent microcomputer harmonic limiting controller 5 will issue an alarm signal, indicating that the thermal harmonic limiting module 31 has deteriorated and needs to be replaced promptly. This prevents the active current limiting harmonic limiting device 3 from aging and failing, which could lead to the failure of the primary harmonic limiting function and threaten the safe operation of the circuit, thus improving the safety and reliability of the control system.

[0041] Finally, it should be noted that the above are merely preferred embodiments of the present utility model and are not intended to limit the present utility model. Although the present utility model has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A busbar low residual voltage full-frequency harmonic limiting PT cabinet control system, comprising an isolating handcart, a high-voltage current-limiting fuse (1), and a voltage transformer (2), characterized in that: The positive terminal of the high-voltage current-limiting fuse (1) is connected to the medium- and low-voltage power grid busbar. The negative terminal of the high-voltage current-limiting fuse (1) is connected to the positive terminal of the voltage transformer (2). The negative terminal of the high-voltage current-limiting fuse (1) is connected to the voltage transformer (2). The primary winding of the voltage transformer (2) is connected to an active current-limiting harmonic suppressor (3). The open delta winding of the active current-limiting harmonic suppressor (3) is connected to a microcomputer secondary harmonic suppressor (4). The negative terminal of the active current-limiting harmonic suppressor (3) is connected to an intelligent microcomputer harmonic suppressor (5). The negative terminal of the intelligent microcomputer harmonic suppressor (5) is grounded. The active current-limiting harmonic suppressor (3) includes a thermistor-type harmonic suppressor module (31). The resistance of the thermistor-type harmonic elimination module (31) is in the kiloohm range when it is working normally, and the resistance of the thermistor-type harmonic elimination module (31) drops to the hundredohm range after the temperature rises above the threshold.

2. The busbar low residual voltage full-frequency harmonic limiting PT cabinet control system according to claim 1, characterized in that: The high-voltage current-limiting fuse (1) is connected in parallel with a lightning rod (6), and the high-voltage current-limiting fuse (1) is also connected in parallel with a high-capacity overvoltage absorption device (7). The lightning rod (6) and the high-capacity overvoltage absorption device (7) are connected in parallel. The positive poles of the lightning rod (6) and the high-capacity overvoltage absorption device (7) are both connected to the medium and low voltage power grid bus, and the negative poles of the lightning rod (6) and the high-capacity overvoltage absorption device (7) are both grounded.

3. The busbar low residual voltage full-frequency harmonic limiting PT cabinet control system according to claim 2, characterized in that: The high-capacity overvoltage absorption device (7) adopts a structure that combines a high-capacity zinc oxide resistor and a discharge gap.

4. The busbar low residual voltage full-frequency harmonic limiting PT cabinet control system according to claim 3, characterized in that: The intelligent microcomputer harmonic limiter controller (5) adopts MICROCHIP core technology. The intelligent microcomputer harmonic limiter controller (5) includes a high-speed DSP core processor, and the DSP core processor is connected to an FPGA coprocessor and a FLASH. The DSP core processor is also connected to an SDRAM, and the FPGA coprocessor is also connected to an AD acquisition chip.

5. The busbar low residual voltage full-frequency harmonic limiting PT cabinet control system according to claim 4, characterized in that: The active current limiting harmonic suppressor (3) also includes a voltage and current acquisition circuit and a temperature sampling circuit. The voltage and current acquisition circuit is used to acquire the voltage analog signal and current analog signal of the voltage transformer (2). The temperature sampling circuit is used to acquire the temperature value of the thermistor-type harmonic suppressor module (31). The voltage and current acquisition circuit and the temperature sampling circuit are connected to a filter computer. The filter computer is connected to the AD acquisition chip in the intelligent microcomputer harmonic suppressor controller (5).

6. The busbar low residual voltage full-frequency harmonic limiting PT cabinet control system according to claim 5, characterized in that: The intelligent microcomputer harmonic limiter controller (5) is also connected to an LCD touch screen and an LED display.

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