Preassembled metal closed primary and secondary integrated ring main unit

Abstract

The application provides a preassembled metal closed primary and secondary fusion complete ring net box, and belongs to the technical field of ring net boxes.The preassembled metal closed primary and secondary fusion complete ring net box comprises a ring net box main body, and further comprises a central processing unit, an electronic mutual inductor and a circuit breaker.Through the introduction of a cross comparison mechanism of three-phase differential sudden change variables, the limitation of blindly blocking a trip signal in traditional technologies is broken.In the variable stage of an electric network, the system can distinguish common mode noise interference from a real short circuit fault.The design enables an intelligent protection device in the ring net box to avoid non-fault misoperation under the strong interference of internal equipment operation arcs and to have instantaneous protection when a real short circuit occurs in an electromagnetic interference blind area, so that the compatibility of the anti-strong electromagnetic interference capability and the protection of an electric network is realized.

Description

Technical Field

[0001] This invention belongs to the field of ring network box technology, specifically relating to a pre-assembled metal-enclosed primary and secondary integrated ring network box. Background Technology

[0002] The integrated primary and secondary ring main unit is a core piece of equipment for the intelligent transformation of power distribution networks. It highly integrates traditional primary power distribution equipment with secondary intelligent terminals. This integration transforms it from a simple power distribution node into an intelligent unit with a wealth of functions, including measurement and control, protection, feeder automation, line loss metering, communication, and status monitoring. When a fault occurs in the power distribution network, it can respond quickly, automatically locate and isolate the faulty area, and restore power supply to non-faulty areas, significantly improving the self-healing capability and power supply reliability of the power grid. Furthermore, its modular and standardized design, along with its telemetry, remote signaling, and remote control capabilities, not only significantly shortens the construction cycle and reduces on-site commissioning and maintenance workload, but also, thanks to its fully sealed and fully insulated enclosure structure, can adapt to various harsh outdoor environments, providing strong support for the safe, reliable, and economical operation of urban power distribution networks.

[0003] In existing distribution network integrated primary and secondary ring main units, protection devices are prone to malfunctions during opening and closing operations, either due to non-fault conditions or failure to operate during fault conditions. This problem arises because the compact architecture of the integrated primary and secondary systems significantly reduces the physical isolation distance between high-voltage and low-voltage equipment. When a circuit breaker opens or closes, the transient arc generated between the contacts radiates a strong electromagnetic pulse into the confined space, causing interference. Since the analog signal output by the electronic instrument transformer is very weak, this strong transient interference can severely distort the originally stable digitally sampled sine wave, masking the crucial zero-crossing characteristics of the waveform. This leads to phase recognition failure of the protection device, resulting in malfunctions.

[0004] Furthermore, to address the aforementioned interference, the current industry standard technical approach typically employs a "dead-zone blocking" strategy: upon detecting an abnormal transition, the system forcibly starts a timer, blocking all tripping signals within a preset range of tens to hundreds of milliseconds. However, if a real short-circuit fault happens to occur on the line during this dead-zone period, the protection device will be unable to respond in time, causing the distribution network to lose its speed in fault clearing and reducing the reliability of power supply to the line.

[0005] Therefore, in order to solve the above problems, it is necessary to provide a pre-assembled metal-enclosed primary and secondary integrated ring network box. Summary of the Invention

[0006] The purpose of this invention is to provide a pre-installed metal-enclosed integrated primary and secondary ring main unit, which aims to solve the problem that in existing integrated primary and secondary ring main units, the strong electromagnetic interference generated by the opening and closing operations can cause the protection device to malfunction. Although the conventional "dead zone blocking" strategy can suppress malfunctions, it can lead to the protection device refusing to operate if a real fault occurs during the blocking period, thereby weakening the reliability of the power distribution network.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A pre-installed metal-enclosed integrated primary and secondary ring main unit includes a ring main unit, and also includes a central processing unit, an electronic instrument transformer, and a circuit breaker. The electronic instrument transformer is provided in multiple forms, each used to detect the signal value of the current in each phase of the three-phase line on the high-voltage side. The normal power frequency cycle of the power grid is obtained. The central processing unit adaptively adjusts the sampling frequency based on the normal power frequency cycle to obtain a constant number of sampling sequences with phase points aligned within each complete power frequency cycle. The difference between the signal value at the current sampling point and the signal value at the corresponding phase in the previous cycle is calculated to obtain the differential mutation amount. Based on the differential mutation amount, it is determined whether it is a calm phase or a changing phase. During the change phase, based on the difference characteristics between the differential abrupt changes of the three phases, short-circuit faults or common-mode noise interference are determined, and the circuit breaker is controlled to perform tripping protection actions based on the results.

[0008] Preferably, the steps for determining a peaceful phase or a changing phase include: Preset mutation threshold; If the absolute values ​​of the differential mutation amounts of the three phase lines are all lower than the mutation threshold, the system is determined to be in a stable operating state, the power frequency cycle is calibrated as a normal cycle, and it is determined to be a peaceful phase. If the absolute value of the differential mutation in any phase is greater than or equal to the mutation threshold, then a transient mutation is determined to have occurred in the power grid, the power frequency cycle is calibrated as a variable cycle, and the variable phase is determined.

[0009] Preferably, the central processing unit includes a data cache module, which is capable of storing signal values ​​of at least N complete power frequency cycles of current, where N≥3.

[0010] Preferably, the number of judgments is preset to M, where M≥2; When a transient change is detected in the power grid, the decision time window H is opened simultaneously. Within the decision time window H, common-mode interference identification logic is executed; When the differential mutation amount of the three phase lines is less than the mutation threshold for M consecutive sampling points, the disturbance is determined to end, and the decision time window H is closed.

[0011] Preferably, the logic for common-mode interference identification is executed as follows: Obtain the differential abrupt changes of the three phase lines at the same sampling point, and denot them as ΔA, ΔB, and ΔC, respectively; Calculate the difference between ΔA and ΔB, and take its absolute value as the abrupt change difference a; Calculate the difference between ΔB and ΔC, and take its absolute value as the abrupt change difference b; Calculate the difference between ΔC and ΔA, and take its absolute value as the mutation difference c.

[0012] Preferably, a preset threshold for variation is used; Determine whether the mutation differences a, b, and c are greater than or equal to a preset change threshold; If any one of the mutation differences a, b, and c is greater than or equal to the change threshold, it is determined that the three-phase line disturbance has lost consistency and a real short-circuit fault is currently superimposed. Control the circuit breaker to perform tripping protection actions.

[0013] Preferably, a severe fault threshold is preset; If the mutation differences a, b, and c are all less than the preset change threshold, it is further determined whether the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are greater than or equal to the preset severe fault threshold. If the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are all greater than or equal to the severe fault threshold, it is determined that a three-phase line symmetrical short-circuit fault has occurred. Control the circuit breaker to perform tripping protection actions.

[0014] Preferably, if it is determined that the mutation differences a, b, and c are all less than a preset change threshold, and the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are all less than the preset severe fault threshold; The disturbances experienced by the three phase lines are determined to be highly consistent and within the range of interference characteristics, and are therefore common-mode noise interference caused by the arc of the switch operation. The circuit breaker is controlled to maintain its original state.

[0015] Preferably, the mutation threshold is set to 5% to 10% of the rated current amplitude.

[0016] Preferably, the variable threshold is set according to the allowable hardware sampling and transmission error range of common-mode interference between the three phases, and is set to 3% to 8% of the rated amplitude; The severe fault threshold is set based on the historical peak values ​​of the line's maximum operating load and arc interference, and is set to 300% to 500% of the rated amplitude.

[0017] Compared with the prior art, the beneficial effects of the present invention are: This invention breaks through the limitations of blindly blocking trip signals in traditional technology by introducing a cross-comparison mechanism of three-phase differential abrupt changes. After the power grid enters a period of change, the system can distinguish between common-mode noise interference and real short-circuit faults. This enables the intelligent protection device in the ring network box to avoid non-fault maloperation under strong interference from the internal equipment operating arc, and to have instantaneous protection when a real short circuit occurs in the electromagnetic interference blind zone. This achieves compatibility between strong electromagnetic interference resistance and power grid protection. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the structural distribution of the present invention; Figure 3 This is a schematic diagram of the overall process of the present invention; Figure 4 This is a schematic diagram of the circuit breaker control process of the present invention.

[0019] In the diagram: 1. Ring main body; 2. Central processing unit; 3. Electronic current transformer; 4. Circuit breaker. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In existing integrated primary and secondary ring main units of distribution networks, protection devices are prone to malfunctions during opening and closing operations, either without faults or malfunctions. This is because the compact architecture of the integrated primary and secondary units significantly reduces the physical isolation distance between high-voltage and low-voltage equipment. When a circuit breaker opens or closes, the transient arc generated between the contacts radiates a strong electromagnetic pulse into the confined space, causing interference. Since the analog signal output by the electronic instrument transformer is very weak, this strong transient interference causes severe distortion of the originally stable digitally sampled sine wave, masking the crucial zero-crossing characteristics of the waveform. This leads to phase recognition failure of the protection device, resulting in malfunctions.

[0022] To address the aforementioned interference, the current industry standard approach typically employs a "dead-zone blocking" strategy: upon detecting an abnormal transition, the system forcibly starts a timer, blocking all tripping signals within a preset range of tens to hundreds of milliseconds. However, if a real short-circuit fault occurs on the line during this dead-zone period, the protection device will be unable to respond in time, causing the distribution network to lose its speed in fault clearing and reducing the reliability of power supply to the line.

[0023] Please see Figures 1 to 4 The present invention provides the following technical solution: a pre-installed metal-enclosed primary and secondary integrated ring network box, including a ring network box body 1, and further including: a central processing unit 2, an electronic current transformer 3 and a circuit breaker 4; Multiple electronic instrument transformers 3 are provided, each used to detect the signal value of the current in each phase of the three-phase line on the high-voltage side; The central processing unit 2 adaptively adjusts the sampling frequency based on the normal power frequency cycle to acquire a constant number of sampling sequences with phase points aligned within each complete power frequency cycle. The difference between the signal value at the current sampling point and the signal value at the corresponding phase in the previous cycle is calculated to obtain the differential mutation amount. Based on the differential mutation amount, it is determined whether it is a calm phase or a changing phase. During the change phase, based on the difference characteristics between the differential abrupt changes of the three phase lines, short-circuit faults or common-mode noise interference are determined, and the circuit breaker 4 is controlled to perform tripping protection actions based on the results.

[0024] When the system is in a stable phase, the central processing unit 2 continuously acquires the power grid's frequency cycle and automatically updates the cached current power grid frequency cycle to the normal frequency cycle. Once the system enters a fluctuating phase, it uses the last normal frequency cycle before the fault, recorded in the cache module, to adaptively adjust the sampling frequency.

[0025] For example, if the power grid's operating frequency is 50Hz, and 10 data points need to be collected within one complete operating frequency cycle, then the actual sampling frequency = 50Hz × 10 times = 500Hz. If the power grid frequency changes and drops to 48Hz, but 10 data points are still collected within each complete operating frequency cycle, then the actual sampling frequency = 48Hz × 10 times = 480Hz.

[0026] Please see Figure 3 The steps to determine whether a phase is peaceful or in a state of flux include: Preset mutation threshold; If the absolute values ​​of the differential mutation amounts of the three phase lines are all below the mutation threshold, the system is determined to be in a stable operating state, the power frequency cycle is calibrated as a normal cycle, and it is judged to be in a peaceful phase. If the absolute value of the differential mutation in any phase is greater than or equal to the mutation threshold, it is determined that a transient mutation has occurred in the power grid, and the power frequency cycle is calibrated as a variable cycle and determined to be a variable phase.

[0027] It should be noted that in actual power grid operation, the current sampling signal is not absolutely smooth due to factors such as peak and off-peak electricity consumption. By setting a threshold for sudden changes, the system can effectively filter out these slight fluctuations under normal operating conditions. When the differential change is below this threshold, the system determines it to be in a stable phase, at which point the control module only performs basic monitoring and data caching, without consuming excessive computing resources. However, once the differential change exceeds the limit, the system determines it has entered a fluctuating phase, and immediately activates a higher-level three-phase difference feature recognition algorithm to improve efficiency.

[0028] In summary, by acquiring the normal power frequency cycle of the power grid through the central processing unit 2 and adaptively adjusting the sampling frequency, a rigorous, phase-aligned sampling sequence can still be obtained even when the power grid frequency drifts. Combined with the comparison logic between differential mutation amount and mutation threshold, the system can quickly and accurately distinguish between calm and fluctuating phases, avoiding misjudgments.

[0029] The central processing unit 2 includes a data cache module, which is capable of storing signal values ​​of at least N complete power frequency cycles of the current, where N≥3, so that sufficient historical data can be available for backtracking.

[0030] Please see Figure 4 The preset number of judgments is M, where M≥2; When a transient change is detected in the power grid, the decision time window H is opened simultaneously. Within the decision time window H, execute the common-mode interference identification logic; When the differential mutation of the three phase lines is less than the mutation threshold for M consecutive sampling points, the disturbance is determined to be over and the decision time window H is closed.

[0031] The logic for performing common-mode interference identification is as follows: Obtain the differential abrupt changes of the three phase lines at the same sampling point, and denot them as ΔA, ΔB, and ΔC, respectively; Calculate the difference between ΔA and ΔB, and take its absolute value as the abrupt change difference a; Calculate the difference between ΔB and ΔC, and take its absolute value as the abrupt change difference b; Calculate the difference between ΔC and ΔA, and take its absolute value as the mutation difference c.

[0032] Preset change threshold; Determine whether the mutation differences a, b, and c are greater than or equal to the preset change threshold; If any one of the mutation differences a, b, and c is greater than or equal to the change threshold, it is determined that the three-phase line disturbance has lost consistency and a real short-circuit fault is currently superimposed. Control circuit breaker 4 to perform trip protection action.

[0033] Preset critical fault threshold; If the mutation differences a, b, and c are all less than the preset change threshold, further determine whether the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are greater than or equal to the preset severe fault threshold. If the absolute values ​​of the differential mutation quantities ΔA, ΔB, and ΔC are all greater than or equal to the severe fault threshold, it is determined that a three-phase line symmetrical short-circuit fault has occurred. Control circuit breaker 4 to perform trip protection action.

[0034] If it is determined that the mutation differences a, b, and c are all less than the preset change threshold, and the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are all less than the preset severe fault threshold; The disturbances experienced by the three phase lines are determined to be highly consistent and within the range of interference characteristics, and are therefore common-mode noise interference caused by the arc of the switch operation. Control circuit breaker 4 to maintain its original state.

[0035] The mutation threshold is set to 5% to 10% of the rated current amplitude.

[0036] The variable threshold is set based on the allowable hardware sampling and transmission error range of common-mode interference between the three phases, and is set to 3% to 8% of the rated amplitude; The severe fault threshold is set based on the line's maximum operating load and the historical peak value of arc interference, and is set to 300% to 500% of the rated amplitude.

[0037] It should be noted that in actual operation, the arc generated by the opening and closing of the circuit breaker inside the primary and secondary integrated ring main unit within a very small space will form a strong electromagnetic pulse radiating throughout the space. The interference caused by this pulse to the electronic instrument transformer 3 often has a high degree of spatial symmetry, that is, it exhibits typical "common-mode noise" characteristics. This means that at the same moment, the differential abrupt changes ΔA, ΔB, and ΔC of the three-phase lines will have extremely similar amplitude jumps, resulting in very small abrupt differences a, b, and c obtained by subtracting them from each other. Conversely, if a real short-circuit fault occurs on the line, such as a single-phase grounding or a two-phase short circuit, the current abrupt change of the faulty phase will surge instantaneously, while the current abrupt change of the non-faulty phase will remain relatively stable. This will lead to a sharp increase in the abrupt differences a, b, and c. Even in the extremely rare case of a three-phase completely symmetrical short circuit, although the abrupt difference is small, the absolute value of its differential abrupt change will show an explosive increase of hundreds or even thousands of times the rated value.

[0038] For example, assume the system's rated current amplitude is 600A. Based on this, the following thresholds are set: sudden change threshold 30A (5%), variation threshold 48A (8%), and severe fault threshold 2400A (400%). In common-mode noise interference, when the system performs a switching operation that generates a strong electromagnetic pulse, all three phases experience the same common-mode interference, causing simultaneous sudden changes in the sampled readings: ΔA = 150A, ΔB = 160A, ΔC = 145A. The absolute values ​​of these values ​​are all greater than the sudden change threshold of 30A, triggering the judgment logic. The calculated differences in sudden changes are a = 10A, b = 15A, and c = 5A, respectively. Clearly, a, b, and c are all less than the variation threshold of 48A, and the absolute values ​​of ΔA, ΔB, and ΔC are far lower than the severe fault threshold of 2400A. Therefore, the system determines that the disturbances experienced by the three phases are highly consistent, confirming it as common-mode noise interference caused by the arc of the switching operation. It then controls circuit breaker 4 to maintain its original state, successfully avoiding false tripping due to interference.

[0039] If a real asymmetrical fault occurs during the switching arc interference, resulting in a true phase A-to-ground short circuit on the line, the current abruptly changes to: ΔA = 1800A, ΔB = 10A, and ΔC = 15A. The calculated difference in current a = 1790A. This value is significantly greater than the fluctuation threshold of 48A. The system immediately determines that the three-phase line disturbance has lost consistency, confirming that a real short-circuit fault has been superimposed. It quickly bypasses the interference shielding logic and controls circuit breaker 4 to perform the tripping protection action, achieving rapid fault clearing.

[0040] This invention overcomes the limitations of blindly blocking trip signals in traditional technologies by introducing a cross-comparison mechanism for three-phase differential abrupt changes. After the power grid enters a period of change, the system can distinguish between common-mode noise interference and actual short-circuit faults. This allows the intelligent protection device within the ring main unit to not only avoid non-fault malfunctions under strong interference from internal equipment operating arcs, but also to provide instantaneous protection in the event of an actual short circuit in the electromagnetic interference blind zone, achieving compatibility between strong electromagnetic interference resistance and power grid protection.

[0041] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention 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 invention should be included within the protection scope of the present invention.

Claims

1. A pre-assembled metal-enclosed primary and secondary fusion ring mesh box, comprising a ring mesh box body (1), characterized in that, Also includes: Central processing unit (2), electronic instrument transformer (3) and circuit breaker (4); The electronic current transformer (3) is provided in multiple forms, which are used to detect the signal values ​​of the current of each phase of the three-phase line on the high-voltage side. The central processing unit (2) adaptively adjusts the sampling frequency based on the normal power frequency cycle to obtain a constant number of sampling sequences with phase points aligned within each complete power frequency cycle. The difference between the signal value at the current sampling point and the signal value at the corresponding phase in the previous cycle is calculated to obtain the differential mutation amount. Based on the differential mutation amount, it is determined whether it is a calm phase or a changing phase. During the change phase, based on the difference characteristics between the differential mutations of the three phases, short-circuit faults or common-mode noise interference are judged, and the circuit breaker (4) is controlled to perform trip protection action based on the result. When faced with common-mode noise interference, execute the common-mode interference identification logic: Obtain the differential abrupt changes of the three phase lines at the same sampling point, and denot them as ΔA, ΔB, and ΔC, respectively; Calculate the difference between ΔA and ΔB, and take its absolute value as the abrupt change difference a; Calculate the difference between ΔB and ΔC, and take its absolute value as the abrupt change difference b; Calculate the difference between ΔC and ΔA, and take its absolute value as the abrupt change difference c; Preset change threshold; Determine whether the mutation differences a, b, and c are greater than or equal to a preset change threshold; If any one of the mutation differences a, b, and c is greater than or equal to the change threshold, it is determined that the three-phase line disturbance has lost consistency and a real short-circuit fault is currently superimposed. Control the circuit breaker (4) to perform the trip protection action; Preset critical fault threshold; If the mutation differences a, b, and c are all less than the preset change threshold, it is further determined whether the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are greater than or equal to the preset severe fault threshold. If the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are all greater than or equal to the severe fault threshold, it is determined that a three-phase line symmetrical short-circuit fault has occurred. Control the circuit breaker (4) to perform the trip protection action; If it is determined that the mutation differences a, b, and c are all less than the preset change threshold, and the absolute values ​​of the differential mutation amounts ΔA, ΔB, and ΔC are all less than the preset severe fault threshold; The disturbances experienced by the three phase lines are determined to be highly consistent and within the range of interference characteristics, and are therefore common-mode noise interference caused by the arc of the switch operation. Control the circuit breaker (4) to maintain its original state.

2. The pre-assembled metal-enclosed primary and secondary fusion ring mesh box according to claim 1, characterized in that, The steps to determine whether a phase is peaceful or in flux include: Preset mutation threshold; If the absolute values ​​of the differential mutation amounts of the three phase lines are all lower than the mutation threshold, the system is determined to be in a stable operating state, the power frequency cycle is calibrated as a normal cycle, and it is determined to be a peaceful phase. If the absolute value of the differential mutation in any phase is greater than or equal to the mutation threshold, then a transient mutation is determined to have occurred in the power grid, the power frequency cycle is calibrated as a variable cycle, and the variable phase is determined.

3. The pre-assembled metal-enclosed primary and secondary fusion ring mesh box according to claim 1, characterized in that: The central processing unit (2) includes a data cache module, which is capable of storing signal values ​​of at least N complete power frequency cycles of current, where N≥3.

4. The pre-assembled metal-enclosed primary and secondary fusion ring mesh box according to claim 2, characterized in that: The preset number of judgments is M, where M≥2; When a transient change is detected in the power grid, the decision time window H is opened simultaneously. Within the decision time window H, common-mode interference identification logic is executed; When the differential mutation amount of the three phase lines is less than the mutation threshold for M consecutive sampling points, the disturbance is determined to end, and the decision time window H is closed.

5. The pre-assembled metal-enclosed primary and secondary fusion ring mesh box according to claim 2, characterized in that: The mutation threshold is set to 5% to 10% of the rated current amplitude.

6. The pre-assembled metal-enclosed primary and secondary fusion ring mesh box according to claim 5, characterized in that: The variable threshold is set based on the allowable hardware sampling and transmission error range of common-mode interference between the three phases, and is set to 3% to 8% of the rated amplitude; The severe fault threshold is set based on the historical peak values ​​of the line's maximum operating load and arc interference, and is set to 300% to 500% of the rated amplitude.

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