Single-phase grounding fault processing method and system for small-resistance grounding system

Abstract

The invention discloses a single-phase grounding fault processing method and system for a small-resistance grounding system. The method at least comprises the following steps: collecting a zero-sequence current signal in real time; identifying a fault and determining a loop and a phase based on the amplitude or change characteristics; judging according to a pre-stored loop type (configuration based on load continuity and the like), if immediate tripping is allowed, cutting off a circuit breaker, and if not, switching off a neutral point quick switch within 20ms and converting into non-grounding operation; when arc light is grounded, a bus-side switch is switched on for arc extinction. According to the invention, on the basis of keeping the accuracy of small resistance grounding line selection, differentiation processing of different types of outgoing line loops is realized, the power supply continuity of the type of load which does not allow immediate tripping is improved, arc overvoltage can be actively inhibited, and the operation reliability of the system is improved.

Description

Technical Field

[0001] This invention relates to the field of power system grounding protection technology, and in particular to a method and system for handling single-phase grounding faults in a low-resistance grounding system. Background Technology

[0002] In medium and low voltage power distribution systems, single-phase grounding faults are one of the most common types of faults, accounting for more than 70% of all faults. Low-resistance grounding methods are widely used due to their larger zero-sequence current and more accurate fault location, making them particularly suitable for industrial power distribution systems with numerous cable lines. This method limits the grounding current by connecting a small resistor in series at the neutral point, while simultaneously utilizing zero-sequence protection to quickly identify and disconnect the faulty circuit, offering advantages such as reliable operation and accurate fault location.

[0003] However, traditional protection strategies require the fault circuit breaker to trip immediately upon detection of a single-phase ground fault to limit the damage of the ground current to the equipment, which results in the loss of power to the load in that circuit. For continuous production loads (such as chemical production lines and steel smelting equipment), immediate power loss can cause product waste disposal, process interruption, equipment damage, and significant economic losses, and may even affect production safety.

[0004] In existing technologies, grounding or ungrounding arc suppression coils allow the system to operate with a single-phase ground fault for a period of time (typically 2 hours), which is beneficial for load transfer or fault handling. However, this approach suffers from problems such as low zero-sequence current, difficulty in fault location, and the potential for generating high-amplitude arc overvoltages, threatening the safety of insulated equipment. Some technical solutions attempt to connect a small resistor in parallel with the arc suppression coil. During a fault, the small resistor is applied to increase the zero-sequence current to assist in fault location and ultimately disconnect the faulty circuit. However, this approach still focuses on disconnection and cannot completely address the continuous power supply requirements of loads that cannot be immediately de-energized. Furthermore, existing flexible grounding or active intervention solutions are often structurally complex, involve inverters or injected power supplies, are costly, and difficult to maintain, making them unsuitable for large-scale application.

[0005] Therefore, there is an urgent need for a single-phase grounding fault handling method and system that can take into account the accuracy of line selection, the continuity of power supply to loads that do not allow immediate power loss, and the suppression of arc overvoltage in low-resistance grounding systems, so as to meet the high reliability power supply requirements of modern industrial enterprises. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for handling single-phase grounding faults in a low-resistance grounding system, which solves the problems of important loads being unable to continue operating with faults and the risk of arcing overvoltage under existing low-resistance grounding methods.

[0007] The "permitted immediate tripping type" and "non-permitted immediate tripping type" described in this invention refer to pre-set operating attributes of outgoing circuits based on load process characteristics, power outage consequences, and operating procedures. These attributes indicate whether immediate disconnection of the corresponding outgoing circuit is permitted in the event of a single-phase ground fault. For example, circuits with minor power outage consequences, such as those for lighting, office equipment, and auxiliary equipment, are set to the "permitted immediate tripping type," while circuits where power outages would result in significant economic losses or safety risks, such as those for continuous chemical production lines, precision manufacturing equipment, and critical medical equipment, are set to the "non-permitted immediate tripping type." These attributes are pre-stored in the controller and can be dynamically adjusted according to actual operational needs.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows: A method for handling single-phase grounding faults in a low-resistance grounding system includes at least the following steps: S1: Real-time acquisition of zero-sequence current signals from the neutral point, busbar, and each outgoing circuit; high-precision current transformers and signal conditioning circuits ensure the accuracy and real-time performance of the acquired data. S2: Based on the zero-sequence current mutation, steady-state amplitude, phase characteristics or harmonic components, identify whether a single-phase ground fault has occurred. If a fault has occurred, further determine the fault circuit and fault phase by comparing the zero-sequence current distribution and phase, thereby improving the timeliness and reliability of fault identification and line selection. S3: Determine the fault circuit type based on the pre-stored outgoing circuit type information. This type information includes at least the types that allow immediate tripping and the types that do not allow immediate tripping, and supports multi-level classification expansion. S4: If it is a type that allows immediate tripping, then output a control command to trip the corresponding outgoing circuit breaker, quickly clear the fault, and prevent the fault from escalating. S5: If the type of tripping is not allowed immediately, a grounding alarm signal will be issued first, and then a control command will be output within a preset time (preferably no more than 20ms) to disconnect the single-phase fast switch of the neutral point, so that the grounding impedance element is taken out of operation, and the system is switched from the low resistance grounding mode to the neutral point ungrounded operation mode, thereby allowing the system to continue to operate with a single-phase grounding fault for a period of time. By disconnecting the neutral point grounding impedance within a preset time when a single-phase grounding fault is detected in an outgoing circuit of a type that is not allowed to trip immediately, the system switches from a low-resistance grounding mode to a neutral point ungrounded operation mode. This invention avoids the problem of this type of load being disconnected due to zero-sequence protection operation, thus achieving continuous operation with faults without affecting the overall system safety. This switching process fully utilizes the tolerance characteristics of the ungrounded mode to single-phase grounding faults, while retaining the line selection advantages of the original low-resistance mode, realizing dynamic complementarity between the two grounding methods.

[0009] S6: Optionally, after switching to neutral-point ungrounded operation mode, continue monitoring the zero-sequence current. If periodic changes are detected, it is determined to be an intermittent arcing ground fault. A control command is output to close the single-phase fast switch of the corresponding faulty phase on the busbar, causing the faulty phase to be directly metallically grounded on the busbar side. This forces the original grounding point current to zero, quickly extinguishing the arc and suppressing arcing overvoltage. This step can respond in milliseconds after the fault characteristics appear, further reducing the threat of overvoltage to equipment insulation.

[0010] Accordingly, the present invention also provides a system for performing the above method. The system includes a neutral point grounding unit, a bus grounding unit, an outgoing circuit detection unit, and a zero-sequence current acquisition and processing controller. The controller integrates fault identification, type judgment, timing control, and output modules, and supports remote configuration, fault recording, and event logging functions, which facilitates operation, maintenance, and post-event analysis.

[0011] Compared with the prior art, the beneficial effects of the present invention are: It retains the advantages of accurate line selection and rapid action of the low-resistance grounding method. At the same time, for outgoing circuits that do not allow immediate tripping, it achieves the ability to continue operating with faults by quickly switching to the neutral point ungrounded operation mode, which significantly improves the power supply continuity of this type of load and reduces the economic losses caused by production interruption. By pre-storing configurable loop type information, differentiated control strategies can be implemented, which can flexibly adapt to the load characteristics of different industrial enterprises and have strong engineering applicability. In ungrounded operation mode, intermittent arcing ground faults are characterized and actively and directly grounded to extinguish the arc quickly, effectively suppress arcing overvoltage, prevent the fault from developing into a phase-to-phase short circuit, and further improve system safety. It operates quickly (critical switching is completed within 20ms), without affecting the original zero-sequence protection as a backup protection action, and is easy to implement in engineering and coordinate with existing protection devices. Attached Figure Description

[0012] To illustrate the technical solutions in the embodiments of the present invention or the prior art more specifically and intuitively, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0013] Figure 1 This is a schematic diagram of the system structure proposed in this invention; Figure 2 This is a circuit diagram for the zero-sequence current signal processing of the present invention. Detailed Implementation

[0014] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0015] Combined with appendix Figure 1-2 A specific embodiment of the present invention will be described in detail below.

[0016] This implementation takes a 10kV industrial enterprise power distribution system as an example. The system includes a main transformer and multiple outgoing circuits (taking circuit 1, circuit 2, and circuit 3 as examples). Circuit 1 is for auxiliary loads (such as lighting), while circuits 2 and 3 are for continuous production line loads. The system is suitable for scenarios with many cable lines and large capacitive currents. The grounding impedance element R value is selected based on the system capacitive current calculation, typically in the range of 10~50Ω. The preset switching time is preferably 15~20ms.

[0017] Example 1: System Structure and Normal Operating Status like Figure 1 As shown, this system includes a neutral point grounding unit (single-phase fast switch VOFCd, grounding impedance element R, zero-sequence current transformer LHd), a bus grounding unit (VOFCa, VOFCb, VOFCc and LH30), an outgoing circuit detection unit (LH1~LH3 and DL1~DL3), and a zero-sequence current acquisition and processing controller ZK. The controller ZK integrates a microprocessor, A / D conversion circuit, communication module, and human-machine interface, supporting local touchscreen operation and remote SCADA access.

[0018] During normal operation, VOFCd is closed, and the system operates with low-resistance grounding; VOFCa to VOFCc are open. Controller ZK collects each zero-sequence current signal in real time. The system's zero-sequence current is essentially zero, and no control action is required. In this state, the accuracy of line selection in the traditional low-resistance grounding method is preserved, and a reliable data foundation is provided for subsequent differentiated processing, thereby ensuring stable system operation in fault-free conditions.

[0019] Example 2: Fault Handling of Circuits Allowing Immediate Tripping Circuit 1 is pre-stored as allowing immediate tripping. When a metallic ground fault occurs in phase A of circuit 1, the zero-sequence current rapidly increases through R. Controller ZK determines that the fault occurs in circuit 1 based on the sudden change (preferably a threshold of 0.5 times the rated zero-sequence current) and the steady-state amplitude, confirms its type, and then outputs a trip command, causing DL1 to trip, circuit 1 is disconnected, and the remaining circuits continue to operate. This process is usually completed within 30~50ms, achieving rapid isolation and preventing fault escalation. At the same time, the original integrated protection serves as a backup to ensure system safety, thereby maintaining rapid response capability in the event of non-critical load faults.

[0020] Example 3: Fault Handling of Circuits Where Immediate Tripping Is Not Allowed Circuit 2 is pre-programmed for a type that does not allow immediate tripping. When a single-phase ground fault occurs in phase B of circuit 2, controller ZK identifies the faulty circuit and phase. After confirming the type, it first issues an alarm signal and transmits it to the backend. Then, within 20ms, it disconnects VOFCd, R exits operation, and the system switches to a neutral-point ungrounded mode. At this time, the three-phase voltage symmetry is basically maintained, and the load of circuit 2 can continue to operate for 2 hours (in accordance with power regulations), avoiding the difficulties of production line shutdown, waste disposal, and process restart caused by immediate power loss. This switch fully utilizes the fault-tolerant operation characteristics of the ungrounded mode while maintaining the overall stability of the system, thereby significantly improving the power supply continuity of critical loads.

[0021] Example 4: Active intervention for intermittent arcing ground faults In the ungrounded operation state of Example 3, if the ground fault is an intermittent arcing ground fault, the zero-sequence current will exhibit a periodic change characteristic of repeated appearance and disappearance (the period is usually on the order of tens of milliseconds to seconds). After the controller ZK detects this characteristic, it determines that there is a risk of arcing ground fault and immediately closes the single-phase fast switch VOFCb of the bus corresponding to the faulty phase (phase B), so that the phase B bus is directly grounded. At this time, the original grounding point is at the same potential as the bus, the grounding current is transferred to the bus side, the fault point current is zero, the arc is quickly extinguished, the arcing overvoltage is effectively suppressed, and it is prevented from developing into a phase-to-phase short circuit.

[0022] Unlike existing technologies that only detect or adjust parameters for arcing grounding, this invention actively alters the system's equipotential conditions and current path by implementing direct metallic grounding of the faulty phase on the bus side, fundamentally eliminating the conditions for arc generation and achieving rapid arc extinguishing. This intervention can be completed within milliseconds after the fault characteristics appear, further reducing system risk. After arc extinguishing, the system can be restored to its monitoring state by automatically or manually resetting the switch based on the zero-sequence current.

[0023] Example 5: Presetting and Management of Outgoing Circuit Type Information Before system commissioning or during operation and maintenance, maintenance personnel configure the type information of each outgoing circuit through the human-machine interface or remote communication interface (such as RS485, Ethernet, 4G / 5G module) of the controller ZK. For example, auxiliary circuits such as lighting and office circuits can be set to the type that allows immediate tripping, while critical circuits such as continuous chemical and steel production lines can be set to the type that does not allow immediate tripping. This information is stored in the controller's non-volatile memory, which is automatically loaded upon power-on. It supports online modification, version management, and operation log recording, ensuring flexible and traceable configuration and facilitating system expansion to more outgoing circuits or multi-section busbar structures. This preset mechanism improves the system's adaptability and maintainability.

[0024] Example 6: Coordination with other protection systems and multi-fault scenarios This system coordinates with existing integrated protection devices: when a circuit fault does not allow immediate tripping, this system prioritizes switching within 20ms to avoid activation of the existing zero-sequence protection (whose setting time is typically over 100ms); if switching fails, multiple grounding occurs, or the system capacitive current is too large, the existing protection acts as a backup trip. Simultaneously, in high-resistance grounding scenarios, this system can still identify and execute corresponding strategies based on zero-sequence current characteristics; in the case of transient faults, it can automatically record and reset. This coordination mechanism and multi-scenario adaptability further improve system reliability and robustness, supporting integration with intelligent distribution terminals to achieve advanced functions such as fault recording, sequence of events (SOE), and remote diagnostics, thereby meeting the comprehensive protection needs of complex distribution environments.

[0025] Example 7: System Applicability Expansion and Optimization This invention is applicable to power distribution systems with voltage levels ranging from 3kV to 35kV and mixed cable and overhead lines, particularly suitable for scenarios with capacitive currents exceeding 10A. For systems of different scales, further optimization can be achieved by adjusting the R value of the grounding impedance element (linear or nonlinear resistance), adding parallel branches, or optimizing the controller algorithm. The system also supports compatibility with distributed power generation scenarios. When photovoltaic or wind power is connected to the grid, dynamic adjustment of type information and switching thresholds ensures that grounding fault handling does not affect the absorption of new energy. This scalability makes the invention applicable to traditional industrial parks, chemical systems, county-level power distribution networks, and power distribution systems with high penetration rates of new energy. In smart grid construction, AI fault prediction modules can be further integrated to improve preventative maintenance levels, thereby achieving higher system intelligence and economic benefits.

[0026] Example 8: Complete Fault Handling Process Example Assuming an intermittent arcing ground fault occurs in phase A of loop 2 (a type where immediate tripping is not permitted) during normal system operation: Controller ZK first collects the zero-sequence current in real time, identifies the fault based on the abrupt change, and confirms the type; after issuing an alarm, it disconnects VOFCd within 18ms, switching the system to ungrounded operation, while loop 2 continues to supply power; subsequently, it detects the recurring and disappearing periodic variation characteristics, closes VOFCa to achieve direct grounding of the bus, and extinguishes the arc; after the fault is cleared, maintenance personnel manually or automatically reset the switch, and the system returns to low-resistance grounding mode. This complete process demonstrates the end-to-end advantages of this invention from fault identification to differentiated processing to active arc suppression, ensuring high-reliability operation of the system under complex fault conditions.

[0027] like Figure 2As shown, the zero-sequence current signal is linearly reduced to a mA-level current signal by the current transformer CT. This current signal is converted into a voltage signal by resistor R1. TVS diode D1 limits the over-limit voltage value caused by external interference to protect the safety of the downstream circuit. The voltage signal converted by resistor R1 is isolated by operational amplifier U1-1 and transmitted to the filter circuit composed of resistor R2 and capacitor C1 for filtering. The processed signal is adjusted to a suitable amplitude by the amplification circuit composed of resistors R3, R4, R5 and operational amplifier U1-2. The amplified voltage signal is filtered again by the filter circuit composed of resistor R6 and capacitor C2. Finally, the voltage signal is clamped within the allowable acquisition voltage range by diodes D2 and D3 and output to the digital-to-analog converter unit.

[0028] The main function of this zero-sequence current signal processing circuit is to safely and accurately convert the raw current signal acquired by the zero-sequence current transformer into a voltage signal suitable for processing by the controller's digital-to-analog converter unit, while providing multi-level protection and anti-interference capabilities. Specifically: the current transformer (CT) achieves linear reduction and electrical isolation of large current signals to mA level; the load resistor R1 completes the current-to-voltage conversion; the TVS diode D1 limits transient overvoltages and protects subsequent circuits from external interference; the isolation operational amplifier U1-1 performs signal buffering and common-mode interference suppression; the two-stage RC filter circuit (R2 / C1 and R6 / C2) effectively removes high-frequency noise; the amplifier circuit (R3, R4, R5, U1-2) adjusts the signal to the optimal amplitude range for A / D conversion; and the clamping diodes D2 and D3 ensure that the output voltage is strictly within the safe range.

[0029] This circuit has a critical impact on the entire system: it significantly improves the signal-to-noise ratio and fidelity, ensuring that the controller ZK can quickly and accurately extract zero-sequence current surges, steady-state amplitudes, and periodic variation characteristics under strong electromagnetic interference environments. This enables the system to complete fault identification, loop type determination, and neutral point switching actions within 20ms. The circuit's anti-interference and protection design further enhances the system's robustness and engineering practicality, providing crucial guarantees for achieving accurate line selection, continuous operation of critical loops with faults, and active suppression of arc overvoltage.

[0030] This invention overcomes the limitations of traditional low-resistance grounding methods through the above-mentioned methods and systems, achieving a balance between accurate line selection and continuous power supply, while effectively suppressing the risk of arc overvoltage. It is particularly suitable for 3kV to 35kV industrial power distribution systems with many cable lines and high requirements for power supply reliability.

[0031] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A single-phase ground fault processing method of a low resistance grounded system, characterized by, At least comprising the following steps: S1: collecting zero sequence current signal in real time; S2: identifying whether single-phase grounding fault occurs based on zero sequence current amplitude or variation characteristics, and if so, identifying fault loop and fault phase; S3: judging fault loop type according to pre-stored outgoing line loop type information, which is pre-configured based on load continuity requirement, production influence degree and / or operation regulation; S4: if fault loop is of type allowing immediate tripping, outputting control instruction to trip circuit breaker of corresponding outgoing line loop; S5: if fault loop is of type not allowing immediate tripping, outputting control instruction to open neutral point single-phase fast switch within preset time, so that system is switched from small resistance grounding operation mode to neutral point ungrounded operation mode.

2. The single-phase earth fault processing method of a low resistance grounding system according to claim 1, characterized in that, Further comprising step S6: after step S5, if it is detected that zero sequence current has periodic variation characteristics of repeated appearance and disappearance, it is judged as intermittent arc grounding fault, and control instruction is outputted to close bus single-phase fast switch of corresponding fault phase, so that fault phase bus is directly grounded.

3. The single-phase earth fault processing method of a low resistance grounding system according to claim 1 or 2, characterized in that, The preset time is not more than 20 ms.

4. The single-phase earth fault processing method of a low resistance grounding system according to claim 1 or 2, characterized in that, The outgoing line loop type information at least comprises type allowing immediate tripping and type not allowing immediate tripping, and the type information is pre-configured and stored through human-computer interface or communication interface.

5. The single-phase earth fault processing method of a low resistance grounding system according to claim 1 or 2, characterized in that, Before step S5, it further comprises sending grounding alarm signal to background.

6. The single-phase earth fault processing method of a low resistance grounding system according to claim 1 or 2, characterized in that, In step S2, identifying single-phase grounding fault comprises judging based on zero sequence current abruptness, steady-state amplitude or phase characteristics.

7. A single phase to ground fault handling system for a low resistance grounded system, characterized by, Comprise: A neutral point grounding unit arranged between neutral point of main transformer and ground, the neutral point grounding unit comprising single-phase fast switch, grounding impedance element and zero sequence current transformer arranged in series; Bus grounding unit arranged between each phase bus A, B, C and ground, each phase bus grounding unit comprising single-phase fast switch and corresponding zero sequence current transformer; Outgoing line loop detection unit arranged on each outgoing line loop for detecting zero sequence current of each outgoing line loop; Zero sequence current acquisition processing controller electrically connected with the neutral point grounding unit, bus grounding unit and outgoing line loop detection unit, for executing the method of any one of claims 1 to 6.

8. The single phase-to-ground fault processing system of low resistance grounding system according to claim 7, characterized in that, The grounding impedance element is linear resistance, non-linear resistance or inductive element.

9. The single phase-to-ground fault processing system of low resistance grounding system according to claim 7, characterized in that, The action time of the single-phase fast switch is not more than 20 ms.

10. The single phase-to-ground fault processing system of low resistance grounding system according to claim 7, characterized in that, The system is suitable for 3kV-35kV three-phase power system.

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