A zinc oxide surge arrester type overvoltage protection device based on leakage current

Abstract

The application relates to the technical field of overvoltage protection and monitoring, in particular to a zinc oxide arrester type overvoltage protection device based on leakage current, which comprises a signal acquisition module, a Rogowski coil for acquiring a transient current change rate, and a resistance-capacitance voltage divider in parallel with both ends of a zinc oxide valve through a high-voltage arm, for outputting an analog voltage signal based on a low-voltage arm; a characteristic output unit, which comprises a high-pass filter differentiator, a two-way window voltage comparator and a logic gate circuit; a link configuration unit for determining signal routing, PGA gain value, filtering form and sampling rate based on a trend mark; an event determination unit for starting a timer through a microcontroller to determine the residence time of a digital voltage sequence; a protection execution unit for executing an update log protection strategy; and a monitoring update unit for judging whether to update the voltage reference value of the two-way window voltage comparator. The application improves the reliability of the zinc oxide arrester type overvoltage protection device based on leakage current.

Description

Technical Field

[0001] This invention relates to the field of overvoltage protection and monitoring technology, and in particular to a zinc oxide surge arrester-type overvoltage protection device based on leakage current. Background Technology

[0002] Zinc oxide surge arresters are core devices in power systems for limiting overvoltage and protecting the insulation of power equipment. However, in practical applications, the signal acquisition architecture with a fixed sampling rate and a single gain channel cannot simultaneously meet the requirements of wideband transient capture and high-precision steady-state measurement. Furthermore, the lack of fine-grained classification capabilities for event types leads to the mixed processing of different types of events. Therefore, there is an urgent need for a zinc oxide surge arrester-type overvoltage protection device that can adjust the signal acquisition link according to transient signal characteristics, accurately classify overvoltage events based on transient current steepness and overvoltage residence time, and implement differentiated protection strategies for different classification results.

[0003] Chinese Patent Application Publication No. CN119044644A discloses a digital surge arrester monitor and its operating method, including a voltage limiting protection valve, a voltage divider, a power frequency current isolation circuit, a rectifier bridge, a switching circuit, mechanical meters and counters, an MCU, and a driver. When the monitor is de-energized, the switching circuit switches the mechanical meters and counters to the rectifier bridge, enabling the monitor to display leakage current with a pointer and record lightning strike actions with a counter, similar to a mechanical surge arrester monitor. When the monitor is energized, the power frequency current isolation circuit collects leakage current, the voltage divider collects the valve voltage waveform, the MCU measures and calculates the leakage current value to drive the mechanical meters, and the voltage threshold is used to determine a lightning strike and drive the counter. This monitor can effectively extract power from the high potential when a series gap zinc oxide surge arrester operates, thereby achieving timely monitoring of the impulse current. It is suitable for high-potential operation monitoring of series gap zinc oxide surge arresters and has good application value.

[0004] However, the existing technology still has the following problems: the existing technology does not consider the differentiation of different event types and cannot provide differentiated processing strategies, which leads to poor monitoring and protection effects of surge arresters. Summary of the Invention

[0005] To address this issue, the present invention provides a zinc oxide surge arrester-type overvoltage protection device based on leakage current, which overcomes the problem in the prior art that it does not consider different event types and cannot provide differentiated processing strategies, thus resulting in poor monitoring and protection effects of the surge arrester.

[0006] To achieve the above objectives, the present invention provides a zinc oxide surge arrester-type overvoltage protection device based on leakage current, comprising: The signal acquisition module includes a Rogowski coil connected to the grounding lead of the zinc oxide arrester to acquire the transient current change rate, and a resistive-capacitive voltage divider connected in parallel across the two ends of the zinc oxide valve through the high-voltage arm to output an analog voltage signal based on the low-voltage arm. The intelligent monitoring box, which is connected to the signal acquisition module, includes: The feature output unit includes a high-pass filter differentiator for outputting a pulse flag based on the transient current change rate, a dual-window voltage comparator for outputting a trend flag based on the analog voltage signal, and logic gate circuits. A link configuration unit, which determines the signal route, PGA gain value, filtering method and sampling rate based on the trend flag; An event determination unit is used to convert the analog voltage signal into a digital voltage sequence based on the sampling rate when the trend indicator is a lightning strike trend, start a timer through a microcontroller to determine the dwell time of the digital voltage sequence, and determine an event indicator based on the pulse indicator and the dwell time. The protection execution unit is used to execute an update log protection strategy when the trend indicator is an operational disturbance trend, execute an alarm protection strategy and trigger an overvoltage protection action in response to a lightning strike event, or execute a loss recording protection strategy or trigger an overvoltage protection action in response to a near-field fault event or a pulse interference event. The monitoring and update unit is used to count the total number of operational disturbance trends within a preset period to determine whether to update the voltage reference value of the dual-window voltage comparator.

[0007] Furthermore, the feature output unit includes: A differential calculation subunit is used to determine the differential voltage signal based on the transient current change rate; A pulse output subunit, which is connected to the differential calculation subunit, is used to determine whether the pulse flag is a first steepness flag or a second steepness flag based on the equivalent frequency of the differential voltage signal.

[0008] Furthermore, the feature output unit further includes: A trend output subunit is used to input the comparison result of the first voltage reference value of the first voltage comparator, the second voltage reference value of the second voltage comparator, and the analog voltage peak value into the logic gate circuit to determine the trend flag; The dual-window voltage comparator includes a first voltage comparator and a second voltage comparator. The first voltage reference value is greater than the second voltage reference value. The analog voltage peak value is obtained based on the analog voltage signal. The trend indicators include the lightning strike trend, the operational disturbance trend, and the safety trend.

[0009] Furthermore, the event determination unit includes: A timing recording subunit is used to start a timer when the digital voltage sequence is first detected to be greater than the second voltage reference value and record the timer count value as the start time; and to stop the timer when the digital voltage sequence drops back below the second voltage reference value and record the timer count value as the end time. A time calculation subunit, which is connected to the timing recording subunit, is used to determine the dwell time based on the difference between the end time and the start time.

[0010] Furthermore, the event determination unit also includes: An event analysis subunit, connected to the time calculation subunit, is used to determine that the event flag is the near-field fault event when the pulse flag is the second steepness flag, and to analyze the comparison result between the dwell time and the dwell time reference value when the pulse flag is the first steepness flag. The result determination subunit, which is connected to the event analysis subunit, is used to determine the event flag as the pulse interference event when the dwell time is less than or equal to the dwell time reference value, and to determine the event flag as the lightning strike event when the dwell time is greater than the dwell time reference value.

[0011] Furthermore, the protection execution unit is used to trigger the overvoltage protection action of closing the fast bypass switch connected in parallel with the zinc oxide valve plate when the alarm protection strategy is executed. The protection execution unit is used to calculate the energy integral based on the differential voltage signal under the condition of executing the alarm protection strategy, and to accumulate the energy integral into the energy register, and to light up the LED alarm light; The overvoltage protection action includes outputting a trip command to the circuit breaker operating mechanism and triggering the closure of a fast bypass switch connected in parallel with the zinc oxide valve.

[0012] Furthermore, the protection execution unit responds to a near-zone fault event by executing a loss recording protection strategy and triggering an overvoltage protection action by outputting a trip command to the circuit breaker operating mechanism; The protection execution unit only executes the loss recording protection strategy in response to a pulse interference event; The loss record protection strategy involves sending standard format messages to the backend main station via the communication module.

[0013] Furthermore, the protection execution unit is used to write the original waveform and the time of occurrence of the operation disturbance into the log to update the log when the update log protection strategy is executed; The log uses a cyclic overwrite mechanism, retaining only the most recent 1000 records.

[0014] Furthermore, in response to an operation disturbance ratio being greater than an operation disturbance ratio reference value, the monitoring and updating unit determines to update the voltage reference value of the dual-window voltage comparator; The proportion of operational disturbances is positively correlated with the total number of operational disturbance trends.

[0015] Furthermore, the link configuration unit is used to route the signal into a dedicated lightning strike signal chain when the trend indicator is the lightning strike trend, with the PGA gain set to 0.1, a 5MHz low-pass filter activated, and a sampling rate set to 10MSPS. The link configuration unit is also used to route the signal into the operation wave dedicated signal chain under the condition that the trend indicator is the operation disturbance trend, set the PGA gain to 1, activate the 100kHz low-pass filter, and set the sampling rate to 1MSPS. The link configuration unit is also used to route the signal into a dedicated signal chain for steady-state leakage current when the trend indicator is the safe trend, set the PGA gain to 1000, activate the 100Hz narrowband power frequency filter, and set the sampling rate to 1kSPS.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: after acquiring the transient current change rate and analog voltage signal through the signal acquisition module, the signal is input to the feature output unit to output a trend indicator. The link configuration unit routes the signal to the corresponding dedicated signal chain according to different trend indicators. When the trend indicator is determined to be a lightning strike trend, it is configured with low gain, high frequency filter and high sampling rate to fully capture the details of the lightning strike steep wave. When the trend indicator is determined to be an operational disturbance trend, it is configured with medium gain, intermediate frequency filter and medium sampling rate to adapt to the waveform characteristics of the operational wave. When the trend indicator is determined to be a safety trend, it is configured with high gain, narrowband power frequency filter and low sampling rate to ensure the measurement accuracy of steady-state leakage current. This enables the link to simultaneously meet the requirements of wideband transient capture and high-precision steady-state measurement, thereby further improving the reliability of the zinc oxide surge arrester-type overvoltage protection device based on leakage current.

[0017] Furthermore, this invention classifies overvoltage events into two categories—a second steepness indicator and a first steepness indicator—using pulse flags. The second steepness indicator, due to its relatively gentle wavefront, conforms to the electrical characteristics of fault overvoltage and can be identified as a near-zone fault event. The first steepness indicator further analyzes the comparison between the dwell time and the dwell time reference value. If the dwell time is greater than the dwell time reference value, it indicates that the overvoltage event simultaneously possesses the characteristics of an extremely steep wavefront and continuous energy injection of a lightning strike, and can be identified as a lightning strike event. If the dwell time is less than or equal to the dwell time reference value, it indicates that although the wavefront of the overvoltage event is steep, the energy is fleeting, conforming to the physical nature of interference such as partial discharge or corona discharge, and can be identified as a pulse interference event. By analyzing multidimensional parameters, different event types are effectively distinguished, thereby further improving the reliability of the zinc oxide surge arrester-type overvoltage protection device based on leakage current.

[0018] Furthermore, this invention employs targeted processing measures for different event flags through the protection execution unit. In response to a lightning strike, it executes an alarm protection strategy, illuminating the LED alarm light and accumulating the energy integral into the energy register to promptly determine the total energy absorbed by the surge arrester. In response to near-zone fault events or pulse interference events, it executes a loss recording protection strategy, sending standard format messages to the backend master station via the communication module to continuously record the cumulative loss of the valve plate caused by the corresponding event. In response to operational disturbance trends, it executes an update log protection strategy, writing the original waveform and the time of occurrence into a cyclic log. These differentiated processing measures ensure that alarm resources, communication resources, and storage resources are all used to handle the most critical events, improving the timeliness of response to high-hazard events and avoiding the problem of excessive resource consumption for low-hazard events, thereby further improving the reliability of the zinc oxide surge arrester-type overvoltage protection device based on leakage current.

[0019] Furthermore, by monitoring the total number of times the update unit statistically analyzes the operational disturbance trend within a preset period, the present invention determines to update the voltage reference value of the dual-window voltage comparator when the operational disturbance ratio is greater than the operational disturbance ratio reference value. This allows the triggering condition for event discrimination to be corrected according to changes in the actual operating environment of the surge arrester, ensuring the discrimination accuracy of the device during long-term operation and further improving the reliability of the zinc oxide surge arrester-type overvoltage protection device based on leakage current. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a zinc oxide surge arrester-type overvoltage protection device based on leakage current according to an embodiment of the present invention; Figure 2 This is a block diagram of a zinc oxide surge arrester-type overvoltage protection device based on leakage current, according to an embodiment of the present invention. Figure 3This is a logic decision diagram for determining signal routing, PGA gain value, filtering method, and sampling rate based on trend indicators in an embodiment of the present invention. Figure 4 This is a logic diagram illustrating how the present invention determines an event flag based on a pulse flag and a dwell time. Figure 5 This is a logic diagram for determining whether to update the voltage reference value of the dual-window voltage comparator in an embodiment of the present invention. The components include: 1. Grounding down conductor; 2. Rogowski coil; 3. Zinc oxide surge arrester; 4. RC voltage divider; 5. High-pass filter differentiator; and 6. Intelligent monitoring box. Detailed Implementation

[0021] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0022] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0023] It should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0025] Please see Figure 1As shown, it is a structural schematic diagram of a zinc oxide surge arrester-type overvoltage protection device based on leakage current according to an embodiment of the present invention. The zinc oxide surge arrester 3 includes a grounding lead 1, a Rogowski coil 2 and a resistive-capacitive voltage divider 4. The grounding lead 1 is connected to the Rogowski coil 2; the Rogowski coil 2 is connected to the resistive-capacitive voltage divider 4; the zinc oxide surge arrester 3 is connected to a high-pass filter differentiator 5; and the high-pass filter differentiator 5 is connected to an intelligent monitoring box 6.

[0026] See Figure 2 The diagram shown is a block diagram of a zinc oxide surge arrester-type overvoltage protection device based on leakage current according to an embodiment of the present invention. The device in this embodiment includes: The signal acquisition module includes a Rogowski coil 2, which is sleeved on the grounding lead 1 of the zinc oxide arrester 3 and used to acquire the transient current change rate, and a resistive-capacitive voltage divider 4, which is connected in parallel across the two ends of the zinc oxide valve plate through the high-voltage arm and used to output an analog voltage signal based on the low-voltage arm. The intelligent monitoring box, which is connected to the signal acquisition module, includes: The feature output unit, which is connected to the signal acquisition module, includes a high-pass filter differentiator 5 for outputting pulse flags based on the transient current change rate, and a dual-window voltage comparator and logic gate circuit for outputting trend flags based on analog voltage signals. The link configuration unit, which is connected to the feature output unit, is used to determine the signal route, PGA gain value, filtering method and sampling rate based on the trend flag; The event determination unit, which is connected to the feature output unit and the link configuration unit respectively, is used to convert the analog voltage signal into a digital voltage sequence based on the sampling rate when the trend indicator is a lightning strike trend. The microcontroller starts a timer to determine the dwell time of the digital voltage sequence and determines the event indicator based on the pulse indicator and the dwell time. The protection execution unit is connected to the link configuration unit and the event determination unit respectively. It is used to execute the update log protection strategy when the trend indicator is the operation disturbance trend, execute the alarm protection strategy and trigger the overvoltage protection action in response to the lightning strike event, or execute the loss recording protection strategy or trigger the overvoltage protection action in response to the near-field fault event or the pulse interference event. The monitoring and update unit is connected to the feature output unit and the protection execution unit respectively. It is used to count the total number of operational disturbance trends within a preset period to determine whether to update the voltage reference value of the dual-window voltage comparator.

[0027] Specifically, in this embodiment, the link configuration unit routes the signal to the corresponding dedicated signal chain according to different trend indicators. When the trend indicator is determined to be a lightning strike trend, it is configured with low gain, high frequency filter and high sampling rate to fully capture the details of the lightning strike steep wave. When the trend indicator is determined to be a safe trend, it is configured with high gain, narrowband power frequency filter and low sampling rate to ensure the measurement accuracy of steady-state leakage current, so that the link can simultaneously meet the requirements of wideband transient capture and high-precision steady-state measurement.

[0028] In this embodiment, the feature output unit includes: The differential calculation subunit is used to determine the differential voltage signal based on the transient current change rate; The pulse output subunit, which is connected to the differential calculation subunit, is used to determine whether the pulse flag is the first steepness flag or the second steepness flag based on the equivalent frequency of the differential voltage signal.

[0029] Specifically, the differential calculation subunit is used to convert the transient current rate of change into a differential voltage signal that can determine the steepness of the current wavefront. The differential voltage signal provides a basis for the pulse output subunit to determine the steepness level. The steeper the transient current wavefront and the more rapidly the transient current rate of change rises, the higher the amplitude of the differential voltage signal; the gentler the transient current rate of change, the lower the amplitude of the differential voltage signal.

[0030] Specifically, when determining the differential voltage signal, the voltage signal is amplified by high frequency and shaped by internal circuitry to extract the high frequency component that reflects the rate of change of the current wavefront steepness, thereby obtaining a differential voltage signal whose amplitude is positively correlated with the transient current wavefront steepness. The voltage signal is directly output through the Rogowski coil 2 connected to the grounding lead 1 of the zinc oxide arrester 3.

[0031] In this embodiment, the pulse output subunit is used to determine the equivalent frequency characteristics of the differential voltage signal. The steeper the wavefront of the transient current, the faster the pulse rise speed and the shorter the duration of the differential voltage signal, and the higher the equivalent frequency. Conversely, the gentler the wavefront of the transient current, the slower the pulse rise speed and the longer the duration of the differential voltage signal, and the lower the equivalent frequency. The pulse output subunit has a frequency threshold. The equivalent frequency of the differential voltage signal is compared with the frequency threshold. When the equivalent frequency is greater than the frequency threshold, a first steepness flag is output. When the equivalent frequency is less than or equal to the frequency threshold, a second steepness flag is output.

[0032] Understandably, under extremely steep transient current wavefront conditions, the differential voltage signal rapidly rises to its peak value in a very short time and then rapidly decays. The entire pulse duration is extremely short, and the corresponding equivalent frequency is higher than the preset frequency threshold, indicating that the transient event has the extremely steep wavefront characteristics unique to lightning strikes or steep pulse interference. Based on this, the pulse output subunit outputs the first steepness indicator.

[0033] Under the condition that the transient current wavefront is relatively flat, the rise of the differential voltage signal is slow and the pulse duration is long. The corresponding equivalent frequency will be lower than or equal to the preset frequency threshold, indicating that the wavefront steepness of the transient event conforms to the characteristics of non-lightning events such as near-field faults or operational disturbances. Based on this, the pulse output subunit outputs a second steepness indicator.

[0034] Specifically, the equivalent frequency is the reciprocal of the wavefront time, which is set based on international standards and engineering experience.

[0035] Understandably, for a single pulse signal, its wavefront time corresponds to the time it takes for the signal to rise from the baseline to the peak value, a process that can be considered as one-quarter of an equivalent period. However, in engineering applications, to simplify calculations and maintain consistency with the standard definition of wavefront time, the wavefront time is directly taken as the equivalent period.

[0036] Understandably, for lightning strikes, the wavefront time range specified by international standards is typically 1 to 10 microseconds, corresponding to an equivalent frequency of 100 kHz to 1 MHz. For switching overvoltages and near-field faults, the wavefront time is typically 50 to several hundred microseconds, corresponding to an equivalent frequency of several kilohertz to 20 kHz.

[0037] Specifically, the frequency threshold is used to provide a clear binary classification boundary for the frequency characteristics of the differential voltage signal. Since the equivalent frequency of the differential voltage signal is a continuously changing physical quantity, while the event analysis subunit and the result determination subunit require Boolean input conditions, the frequency threshold is set according to the order of magnitude difference between direct lightning strikes and pulse interference events in the wavefront time. The value selected is the highest equivalent frequency that will be generated by near-field faults, and at the same time, the lowest equivalent frequency that will be generated by lightning strikes, with an appropriate margin.

[0038] In this embodiment, the feature output unit further includes: The trend output sub-unit is used to input the comparison result of the first voltage reference value of the first voltage comparator, the second voltage reference value of the second voltage comparator, and the analog voltage peak value into the logic gate circuit to determine the trend flag. The dual-window voltage comparator includes a first voltage comparator and a second voltage comparator. The first voltage reference value is greater than the second voltage reference value. The analog voltage peak value is obtained based on the analog voltage signal. The trend indicators include lightning strike trend, operational disturbance trend, and safety trend.

[0039] Specifically, the trend output subunit is also used to determine a first voltage reference value and a second voltage reference value. The first voltage reference value is the upper limit of the dual-window voltage comparator, used to distinguish between operational disturbance trends and lightning strike trends. The second voltage reference value is the lower limit of the dual-window voltage comparator, used to distinguish between safety trends and operational disturbance trends. The first voltage reference value can be set as the DC reference voltage of the zinc oxide varistor, which is the transition voltage of the zinc oxide varistor from the low current region to the high current region. The second voltage reference value can be set as the peak power frequency voltage corresponding to the rated voltage of the surge arrester. The rated voltage is the maximum effective value of the power frequency voltage when the zinc oxide varistor maintains normal operation.

[0040] Specifically, when the simulated voltage peak value is less than or equal to the second voltage reference value, it indicates that the voltage across the zinc oxide valve plate is within the normal operating range, and the trend output subunit determines the trend flag as a safe trend; when the simulated voltage peak value is greater than the second voltage reference value but less than the first voltage reference value, it indicates that an operational disturbance has occurred in the system, and the trend output subunit determines the trend flag as an operational disturbance trend; when the simulated voltage peak value is greater than or equal to the first voltage reference value, it indicates that the overvoltage amplitude has reached the level of lightning overvoltage, and the trend output subunit determines the trend flag as a lightning strike trend.

[0041] Specifically, the peak value of the analog voltage is the maximum value of the signal in each cycle that is tracked and maintained in real time by the peak detection circuit after the analog voltage signal enters the intelligent monitoring box.

[0042] Please see Figure 3 As shown, it is a logic decision diagram of determining signal routing, PGA gain value, filtering form and sampling rate based on trend flag in an embodiment of the present invention. The link configuration unit is used to import the signal routing into the lightning strike dedicated signal chain when the trend flag is a lightning strike trend. The PGA gain is set to 0.1, the 5MHz low-pass filter is activated, and the sampling rate is set to 10MSPS. The link configuration unit is also used to route the signal into the operation wave dedicated signal chain when the trend indicator is an operation disturbance trend, with the PGA gain set to 1, the 100kHz low-pass filter activated, and the sampling rate set to 1MSPS. The link configuration unit is also used to route the signal into the steady-state leakage current dedicated signal chain under the condition that the trend indicator is a safe trend, with the PGA gain set to 1000, the 100Hz narrowband power frequency filter activated, and the sampling rate set to 1kSPS.

[0043] In this embodiment, the link configuration unit also includes a lightning strike configuration subunit, which is used to set the PGA gain to 0.1 so that when the signal amplitude after the lightning overvoltage is attenuated by the RC divider 4 is high, the PGA gain ensures that the signal falls completely within the effective input range. It is also used to activate the 5 MHz low-pass filter so that when the equivalent frequency of the lightning overvoltage reaches hundreds of kilohertz to megahertz, the 5 MHz cutoff frequency completely preserves high-frequency characteristics such as wavefront steepness and wave tail oscillation. The sampling rate is set according to the sampling theorem, that is, the sampling rate must be twice the filter cutoff frequency, so the sampling rate is set to 10 mega-samples per second.

[0044] In this embodiment, the link configuration unit further includes a disturbance configuration subunit, which is used to set the PGA gain to 1 to adapt to medium-amplitude operational disturbance signals, requiring neither attenuation nor amplification, allowing them to pass through at their original amplitude; to activate a 100 kHz low-pass filter to filter out high-frequency noise while fully preserving waveform characteristics through a 100 kHz cutoff frequency; and to set the sampling rate to 1 megasamples per second, which is 10 times the filter cutoff frequency, providing sufficiently dense sampling points for the rising and falling edges of the operational wave.

[0045] In this embodiment, the link configuration unit also includes a security configuration subunit, which is used to set the PGA gain to 1000 to ensure that the signal can be effectively distinguished by the analog-to-digital converter when the steady-state leakage current signal is extremely weak, in the range of microvolts to millivolts; to activate the 100 Hz narrowband power frequency filter to suppress high-frequency noise and improve the signal-to-noise ratio of resistive current separation when the useful information of the leakage current is concentrated at or near the power frequency; and to set the sampling rate to 1,000 sampling points per second to meet the minimum requirements of the sampling theorem for 100 Hz signals, while reducing the data throughput to support long-term continuous monitoring.

[0046] In this embodiment, the event determination unit includes: The timing recording subunit is used to start a timer when the digital voltage sequence is first detected to be greater than the second voltage reference value and record the timer count value at this time as the start time. When the digital voltage sequence drops back to below the second voltage reference value, the timer stops timing and records the timer count value at this time as the end time. The time calculation subunit, which is connected to the timing recording subunit, is used to determine the dwell time based on the difference between the end time and the start time.

[0047] Please see Figure 4 As shown, this is a logic diagram for determining an event flag based on a pulse flag and dwell time according to an embodiment of the present invention. The event determination unit further includes: The event analysis subunit, which is connected to the time calculation subunit, is used to determine that the event flag is a near-zone fault event when the pulse flag is the second steepness flag, and to analyze the comparison results between the dwell time and the dwell time reference value when the pulse flag is the first steepness flag. The result determination subunit, which is connected to the event analysis subunit, is used to determine the event flag as an impulse interference event when the dwell time is less than or equal to the dwell time reference value, and to determine the event flag as a lightning strike event when the dwell time is greater than the dwell time reference value.

[0048] In this embodiment, the event analysis subunit is also used to determine the dwell time reference value. The dwell time reference value is the time criterion boundary value for further distinguishing between lightning strike events and pulse interference events under lightning strike trend conditions. According to international standards and power system engineering experience, the standard waveform of direct lightning current is a combination of the wavefront time and the wave tail time, where the wave tail time is usually tens to hundreds of microseconds. At both ends of the zinc oxide valve, the duration of lightning overvoltage corresponds to the wave tail time of the lightning current. The process of overvoltage rising and falling back to a lower level usually lasts at least tens of microseconds. However, pulse interference, whether partial discharge or corona discharge, completes its discharge process in the nanosecond to several microsecond range. The overvoltage duration is extremely short, much shorter than the wave tail time of lightning overvoltage. Therefore, the dwell time reference value should be selected between the shortest possible dwell time of lightning overvoltage and the longest possible dwell time of pulse interference. Preferably, the dwell time reference value can be taken as tens of microseconds based on the minimum wave tail time of the standard lightning current waveform, so that it can effectively distinguish between lightning strike events with continuous energy injection and pulse interference events with instantaneous discharge.

[0049] Specifically, the steepness of the transient current wavefront is the main characteristic that distinguishes lightning strikes from pulse interference events and near-field faults. The wavefront time of lightning strikes is on the order of microseconds, and the corresponding current change rate is extremely high. The wavefront time of near-field faults and pulse interference events is in the range of tens to hundreds of microseconds, and the current change rate is significantly lower. Therefore, the pulse indicator is used as the first distinguishing feature, and the second steepness indicator is used to directly determine the near-field fault event.

[0050] Specifically, in events with equally steep wavefronts, the duration of overvoltage is the main characteristic that distinguishes real lightning strikes from pulse interference. Real lightning strikes are accompanied by continuous injection of lightning current, and the residence time of overvoltage can reach tens of microseconds or more. Pulse interference originates from local breakdown or discharge, and the residence time of overvoltage is only on the order of nanoseconds to several microseconds. Therefore, residence time is used to distinguish between pulse interference events and lightning strike events.

[0051] Specifically, this embodiment classifies overvoltage events into two categories, a second steepness indicator and a first steepness indicator, using pulse flags. When the dwell time is greater than the dwell time reference value, it indicates that the overvoltage event simultaneously possesses the characteristics of an extremely steep wavefront and continuous energy injection of a lightning strike, and can be identified as a lightning strike event. When the dwell time is less than or equal to the dwell time reference value, it indicates that although the wavefront of the overvoltage event is steep, the energy is fleeting, which conforms to the physical nature of interference such as partial discharge or corona, and can be identified as a pulse interference event.

[0052] Specifically, the protection execution unit is used to trigger the overvoltage protection action of closing the fast bypass switch connected in parallel with the zinc oxide valve plate when the alarm protection strategy is executed. The protection execution unit is used to calculate the energy integral based on the differential voltage signal under the condition of executing the alarm protection strategy, accumulate the energy integral into the energy register, and light up the LED alarm light; The overvoltage protection action includes outputting a trip command to the circuit breaker operating mechanism and triggering the closure of the fast bypass switch connected in parallel with the zinc oxide valve.

[0053] In this embodiment, the protection execution unit includes an energy integral calculation subunit, which is used to determine the energy integral. First, the differential voltage signal is mathematically integrated to restore the transient current change rate to the transient current instantaneous value. Then, the amplitude is calibrated according to the mutual inductance coefficient of the Rogowski coil 2 to obtain the actual transient current value flowing through the zinc oxide valve plate. The actual transient current value is multiplied by the analog voltage signal output by the RC voltage divider 4 at the same time to obtain the instantaneous power. The instantaneous power is integrated over the residence time interval, and the result is the energy integral absorbed by the surge arrester in the lightning strike event.

[0054] Specifically, the protection execution unit responds to a near-zone fault event by executing a loss recording protection strategy and triggers an overvoltage protection action by outputting a trip command to the circuit breaker operating mechanism; The protection execution unit only executes the loss recording protection strategy in response to pulse interference events; The loss record protection strategy involves sending standard format messages to the backend master station via the communication module.

[0055] In this embodiment, the protection execution unit includes a message determination subunit, which provides complete data support for the background master station to perform surge arrester loss assessment and lifetime prediction based on standard format messages. The standard format message includes at least the event type, the event occurrence time, the peak value of the differential voltage signal, the peak value of the analog voltage, the energy integral, and the dwell time of the corresponding event. Among them, the event type is used to distinguish between near-zone fault events and pulse interference events, the event occurrence time records the start timestamp of the transient overvoltage, the peak value of the differential voltage signal and the peak value of the analog voltage record the maximum value of the current steepness and the maximum value of the overvoltage in the corresponding event, respectively, the energy integral records the cumulative energy absorbed by the surge arrester in the corresponding event, and the dwell time records the duration of the overvoltage.

[0056] Specifically, the protection execution unit is used to update the log by writing the original waveform and the time of occurrence of the operation disturbance into the log under the condition of executing the update log protection policy; The log uses a circular overwrite mechanism, retaining only the most recent 1000 records.

[0057] In this embodiment, the protection execution unit includes a log update subunit, which is used to determine that the original waveform is a sampled data segment of the analog voltage signal before and after the operation disturbance occurs, each five power frequency cycles. The sampling rate is determined by 1 MHz of the operation wave dedicated signal chain. The recording length of a single original waveform is a total of ten power frequency cycles, or 200 milliseconds. The amount of data recorded is 200,000 sampling points, ensuring that the recording length can completely cover the entire process of a single operation disturbance from its inception, oscillation to decay.

[0058] In this embodiment, the log update subunit is also used to determine the number of log entries to be 1,000 based on the capacity of the non-volatile memory in the intelligent monitoring box and the amount of data in a single log entry. A single log entry contains the original waveform data segment and the corresponding timestamp of the occurrence time. With 1,000 records, the total storage overhead is on the order of millions of sampling points, which matches the memory capacity configured in the intelligent monitoring box. At the same time, 1,000 records can cover the number of pulse interference events that will occur in a typical inspection cycle. When the number of log entries reaches 1,000, the newly written record will automatically overwrite the earliest record.

[0059] Specifically, this embodiment protects the execution unit by taking targeted processing measures for different event flags. The differentiated processing measures ensure that alarm resources, communication resources and storage resources are used to deal with the most important events, which improves the timeliness of response to high-risk events and avoids the problem of low-risk events consuming too many resources.

[0060] Please see Figure 5As shown, it is a logic decision diagram for determining whether to update the voltage reference value of the dual-window voltage comparator in an embodiment of the present invention. The monitoring and update unit determines to update the voltage reference value of the dual-window voltage comparator in response to the operation disturbance ratio being greater than the operation disturbance ratio reference value. The monitoring and update unit determines that the voltage reference value of the dual-window voltage comparator should not be updated if the operation disturbance ratio is less than or equal to the operation disturbance ratio reference value. Among them, the proportion of operational disturbances is positively correlated with the total number of operational disturbance trends.

[0061] Understandably, when the operating disturbance ratio is less than or equal to the operating disturbance ratio reference value, it indicates that the frequency of the operating disturbance trend is within a reasonable range under normal operating conditions. At this time, the second voltage reference value matches the actual operating boundary of the system, and the dual-window voltage comparator can correctly distinguish between the safety trend and the operating disturbance trend without adjusting the voltage reference value.

[0062] When the proportion of operational disturbances exceeds the reference value, it indicates that the frequency of operational disturbance trends has exceeded reasonable expectations under normal operating conditions. This is because the current second voltage reference value is set too high, causing some operational disturbance events with lower amplitudes to fail to reach the second voltage reference value and thus be missed as safe trends. Meanwhile, some operational disturbance events with slightly higher amplitudes that just exceed the threshold are frequently captured, resulting in a false impression of an abnormally high proportion of operational disturbance trends in the statistical results. At this point, the monitoring update unit determines that the second voltage reference value needs to be lowered to improve the detection sensitivity of the dual-window voltage comparator for operational disturbance events, so that missed events are re-included in the statistical range of operational disturbance trends, restoring the consistency between the discrimination results and the actual on-site operating conditions.

[0063] In this embodiment, the monitoring and updating unit is also used to determine the method of updating the voltage reference value of the dual-channel window voltage comparator by reducing the second voltage reference value. When the total number of operation disturbance trends within a preset period is abnormally high, causing the operation disturbance ratio to exceed the operation disturbance ratio reference value, it indicates that the current second voltage reference value is set too high, causing signals with lower amplitude to fail to reach the second voltage reference value, while signals with slightly higher amplitude frequently trigger the operation disturbance trend. By reducing the second voltage reference value, the detection sensitivity of the dual-channel window voltage comparator to the operation disturbance trend is improved.

[0064] Specifically, the preset period is the time window during which the monitoring and updating unit performs statistical calculations and determines whether the voltage reference value needs to be updated. Its length is preset based on engineering experience. The time span required for the log to cycle through 1,000 records under normal operating conditions is used as the basis for the preset period value, so as to balance the sufficiency of the statistical sample and the timeliness of the device's response to changes in operating conditions.

[0065] Specifically, when reducing the second voltage reference value, the operation is performed in a step-by-step manner to ensure the stability of the device's judgment during the adaptive adjustment process. Preferably, the current second voltage reference value is subtracted from a preset fixed step size to obtain the updated second voltage reference value. The preset fixed step size is set according to the initial value of the second voltage reference value and engineering experience, and can be exemplarily taken as five percent to ten percent of the initial value. After the update is completed, the dual-window voltage comparator uses the new second voltage reference value to perform subsequent trend indicator judgment.

[0066] In one specific embodiment, the second voltage reference value is provided with a lower limit protection value. That is, when the preset lower limit protection value is reached after multiple reductions, it will no longer be reduced, so as to avoid the normal power frequency voltage fluctuation being misjudged as an operational disturbance due to the second voltage reference value being too low.

[0067] In this embodiment, the monitoring and update unit further includes an operation disturbance ratio determination subunit, which is used to determine the operation disturbance ratio as the core indicator for judging whether the voltage reference value needs to be adjusted. The operation disturbance ratio is the ratio of the total number of operation disturbance trends to the total number of outputs of all trend flags, wherein the total number of outputs of all trend flags is the sum of the number of outputs of the safety trend, the number of outputs of the operation disturbance trend, and the number of outputs of the lightning strike trend.

[0068] Specifically, the operation disturbance ratio determination subunit is also used to determine whether the frequency of occurrence of the current operation disturbance trend is within the normal range based on the operation disturbance ratio reference value. The operation disturbance ratio reference value is the statistical average of the operation disturbance ratio calculated in the first few preset periods after the device is put into operation, which is used as the initial value of the operation disturbance ratio reference value to reflect the actual frequency of operation disturbance events at the device installation site under normal operating conditions.

[0069] Specifically, this embodiment monitors the total number of times the operation disturbance trend is counted within a preset period by the update unit. When the operation disturbance ratio is greater than the operation disturbance ratio reference value, the voltage reference value of the dual-window voltage comparator is updated. This allows the triggering condition for event discrimination to be corrected according to the changes in the actual operating environment of the surge arrester, ensuring the discrimination accuracy of the device in long-term operation.

[0070] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A zinc oxide surge arrester-type overvoltage protection device based on leakage current, characterized in that, include: The signal acquisition module includes a Rogowski coil connected to the grounding lead of the zinc oxide arrester to acquire the transient current change rate, and a resistive-capacitive voltage divider connected in parallel across the two ends of the zinc oxide valve through the high-voltage arm to output an analog voltage signal based on the low-voltage arm. The intelligent monitoring box, which is connected to the signal acquisition module, includes: The feature output unit includes a high-pass filter differentiator for outputting a pulse flag based on the transient current change rate, a dual-window voltage comparator for outputting a trend flag based on the analog voltage signal, and logic gate circuits. A link configuration unit, which determines the signal route, PGA gain value, filtering method and sampling rate based on the trend flag; An event determination unit is used to convert the analog voltage signal into a digital voltage sequence based on the sampling rate when the trend indicator is a lightning strike trend, start a timer through a microcontroller to determine the dwell time of the digital voltage sequence, and determine an event indicator based on the pulse indicator and the dwell time. The protection execution unit is used to execute an update log protection strategy when the trend indicator is an operational disturbance trend, execute an alarm protection strategy and trigger an overvoltage protection action in response to a lightning strike event, or execute a loss recording protection strategy or trigger an overvoltage protection action in response to a near-field fault event or a pulse interference event. The monitoring and update unit is used to count the total number of operational disturbance trends within a preset period to determine whether to update the voltage reference value of the dual-window voltage comparator.

2. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 1, characterized in that, The feature output unit includes: A differential calculation subunit is used to determine the differential voltage signal based on the transient current change rate; A pulse output subunit, which is connected to the differential calculation subunit, is used to determine whether the pulse flag is a first steepness flag or a second steepness flag based on the equivalent frequency of the differential voltage signal.

3. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 2, characterized in that, The feature output unit further includes: A trend output subunit is used to input the comparison result of the first voltage reference value of the first voltage comparator, the second voltage reference value of the second voltage comparator, and the analog voltage peak value into the logic gate circuit to determine the trend flag; The dual-window voltage comparator includes a first voltage comparator and a second voltage comparator. The first voltage reference value is greater than the second voltage reference value. The analog voltage peak value is obtained based on the analog voltage signal. The trend indicators include the lightning strike trend, the operational disturbance trend, and the safety trend.

4. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 3, characterized in that, The event determination unit includes: A timing recording subunit is used to start a timer when the digital voltage sequence is first detected to be greater than the second voltage reference value and record the timer count value as the start time; and to stop the timer when the digital voltage sequence drops back below the second voltage reference value and record the timer count value as the end time. A time calculation subunit, which is connected to the timing recording subunit, is used to determine the dwell time based on the difference between the end time and the start time.

5. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 4, characterized in that, The event determination unit further includes: An event analysis subunit, connected to the time calculation subunit, is used to determine that the event flag is the near-field fault event when the pulse flag is the second steepness flag, and to analyze the comparison result between the dwell time and the dwell time reference value when the pulse flag is the first steepness flag. The result determination subunit, which is connected to the event analysis subunit, is used to determine the event flag as the pulse interference event when the dwell time is less than or equal to the dwell time reference value, and to determine the event flag as the lightning strike event when the dwell time is greater than the dwell time reference value.

6. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 5, characterized in that, The protection execution unit is used to trigger the overvoltage protection action of closing the fast bypass switch connected in parallel with the zinc oxide valve plate when the alarm protection strategy is executed. The protection execution unit is used to calculate the energy integral based on the differential voltage signal under the condition of executing the alarm protection strategy, and to accumulate the energy integral into the energy register, and to light up the LED alarm light; The overvoltage protection action includes outputting a trip command to the circuit breaker operating mechanism and triggering the closure of a fast bypass switch connected in parallel with the zinc oxide valve.

7. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 6, characterized in that, The protection execution unit responds to a near-zone fault event by executing a loss recording protection strategy and triggers an overvoltage protection action by outputting a trip command to the circuit breaker operating mechanism; The protection execution unit only executes the loss recording protection strategy in response to a pulse interference event; The loss record protection strategy involves sending standard format messages to the backend main station via the communication module.

8. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 7, characterized in that, The protection execution unit is used to update the log by writing the original waveform and the time of occurrence of the operation disturbance into the log when the update log protection strategy is executed. The log uses a cyclic overwrite mechanism, retaining only the most recent 1000 records.

9. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 8, characterized in that, The monitoring and updating unit determines to update the voltage reference value of the dual-window voltage comparator in response to the operation disturbance ratio being greater than the operation disturbance ratio reference value. The proportion of operational disturbances is positively correlated with the total number of operational disturbance trends.

10. The zinc oxide surge arrester-type overvoltage protection device based on leakage current according to claim 9, characterized in that, The link configuration unit is used to route the signal into a dedicated lightning strike signal chain when the trend indicator is the lightning strike trend. The PGA gain is set to 0.1, a 5MHz low-pass filter is activated, and the sampling rate is set to 10MSPS. The link configuration unit is also used to route the signal into the operation wave dedicated signal chain under the condition that the trend indicator is the operation disturbance trend, set the PGA gain to 1, activate the 100kHz low-pass filter, and set the sampling rate to 1MSPS. The link configuration unit is also used to route the signal into a dedicated signal chain for steady-state leakage current when the trend indicator is the safe trend, set the PGA gain to 1000, activate the 100Hz narrowband power frequency filter, and set the sampling rate to 1kSPS.

Images