Temporary grounding fault processing device for medium-voltage power distribution network
The device, which identifies faulty phases and transfers grounding current in medium-voltage distribution networks, solves the problem of unplanned power outages caused by single-phase grounding faults in neutral point low-resistance grounding systems, thus achieving power supply stability and rapid fault handling.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- ANHUI ONESKY ELECTRIC TECH
- Filing Date
- 2025-04-24
- Publication Date
- 2026-04-24
AI Technical Summary
In a medium-voltage distribution network with a neutral point grounded by a small resistor, when a single-phase ground fault occurs, the protection device cannot distinguish between a temporary ground fault and a permanent ground fault, leading to unplanned power outages and affecting the continuity of power supply.
By using the controller to identify the faulty phase and instruct the single-phase circuit breaker to close within the time delay of the protection device, the grounding current at the fault point is transferred to the substation, thus avoiding the temporary grounding fault from triggering the protection device. A current limiting device is used to suppress high-frequency current and limit circulating current.
It enables rapid identification and transfer of fault current without affecting power supply continuity, avoiding power outages caused by temporary grounding faults, ensuring stable system operation, and suppressing high-frequency current and circulating current.
Smart Images
Figure CN224164627U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of temporary grounding fault handling technology in power systems, and more specifically, to a device for handling temporary grounding faults in low-resistance grounding systems. Background Technology
[0002] In the early stages of power distribution system development, medium-voltage distribution networks of 35kV and below operated with the neutral point grounded via an arc suppression coil or without grounding. In ungrounded neutral systems, the fault current is relatively small during single-phase ground faults, generally allowing for continued operation for up to 2 hours. However, with the increase in cable lines, the system capacitive current continuously increases, leading to increasingly serious problems with intermittent arcing grounding overvoltages, potentially damaging equipment insulation and even causing phase-to-phase short circuits. While grounding the neutral point via an arc suppression coil can compensate for capacitive current, reduce fault current, and decrease the possibility of arc reignition, it also presents some problems, such as increased grid investment, decreased selectivity of protection devices, the possibility of resonant overvoltages, and low accuracy in grounding line selection. With the acceleration of urbanization, the scale of urban power distribution networks continues to expand, the proportion of cable lines is increasing, and the system capacitive current is rising significantly. Urban power distribution networks dominated by cable lines and with large system capacitive currents place higher demands on rapid fault clearing and protection selectivity, which the grounding via an arc suppression coil or without grounding methods can no longer meet.
[0003] Neutral point grounding with a low resistance means that the neutral point is grounded through a low-resistance resistor (usually a few ohms to tens of ohms). This method can effectively suppress overvoltage, quickly disconnect faulty lines, and reduce equipment insulation requirements. Therefore, in applications where cables are the main component or where the system has a large capacitive current, neutral point grounding with a low resistance is increasingly being chosen.
[0004] However, operational experience also shows that most single-phase grounding faults in medium-voltage distribution networks are recoverable grounding faults, which can self-heal under certain conditions, i.e., temporary grounding faults. In a neutral-point grounded system with a small resistance, after a single-phase grounding fault occurs, a large current will flow through the faulty line when the grounding impedance at the fault point is small. At this time, the protection device of the faulty line will trip, thus disconnecting the faulty line, without distinguishing between temporary and permanent grounding faults. Handling single-phase grounding faults in this way increases the risk of unplanned power outages and reduces the continuity of power supply. Even if power is subsequently restored through reclosing, it will still cause a short-term power interruption. For situations with high requirements for power supply continuity, such as medical institutions, semiconductor manufacturing, chemical industry, steelmaking, stock exchanges, bank data centers, key laboratories, and military communication networks, this approach is clearly unsuitable. Utility Model Content
[0005] In addressing the problem that in existing medium-voltage distribution networks using neutral point grounded with a small resistance, the protection devices of faulty lines invariably trip when a single-phase ground fault occurs and the grounding impedance at the fault point is low, regardless of whether it is a temporary or permanent ground fault, thus affecting the continuity of power supply, this application provides a single-phase ground fault handling device for medium-voltage distribution networks. This handling device completes the transfer of the grounding current at the fault point within the delay action of the protection device, so that a temporary ground fault will not trigger the operation of the protection device, thereby avoiding the impact of temporary ground faults on the continuity of power supply.
[0006] In one embodiment of this application, a device for handling temporary grounding faults in a medium-voltage distribution network is provided. The medium-voltage distribution network uses a neutral point grounded through a small resistor. The device is located in a substation and connected in parallel to the busbar of the medium-voltage distribution network. The device includes: single-phase circuit breakers, including single-phase circuit breakers Ka, Kb, and Kc, whose first terminals are respectively connected to phases A, B, and C of the medium-voltage distribution network and whose second terminals are grounded through a current-limiting device; a controller is electrically connected to the single-phase circuit breakers Ka, Kb, and Kc. Based on real-time collected electrical quantity data of the medium-voltage distribution network, when a single-phase grounding fault is detected, the controller identifies the faulty phase and instructs the single-phase circuit breaker corresponding to the faulty phase to close, so as to transfer the grounding current at the fault point to the substation.
[0007] In a further embodiment of this application, the electrical quantity data of the medium-voltage distribution network includes the three-phase voltage, zero-sequence voltage, and neutral point current flowing through a small resistor in the medium-voltage distribution network.
[0008] In the above embodiment, the sampling frequency of the controller is further at least 9.6 kHz.
[0009] In a further embodiment of this application, the processing device further includes a current limiting device, and the single-phase circuit breaker Ka, single-phase circuit breaker Kb and single-phase circuit breaker Kc are grounded through the current limiting device.
[0010] In the above embodiment, the current limiting device further includes a single-phase reactor L, and the power frequency inductive reactance Z of the single-phase reactor L is in the range of 10Ω to 100Ω.
[0011] In a further embodiment of this application, the current limiting device further includes a single-phase circuit breaker Kl connected in parallel with the single-phase reactor L, and the single-phase circuit breaker Kl is electrically connected to the controller; the controller commands the single-phase circuit breaker Kl to close within a time t after closing the single-phase circuit breaker corresponding to the faulty phase.
[0012] In the above embodiment, the controller further instructs the single-phase circuit breaker Kl to close within 20ms to 30ms after closing the single-phase circuit breaker corresponding to the faulty phase.
[0013] In the embodiments of this application, the circuit breaker is a vacuum circuit breaker.
[0014] In various embodiments of this application, the controller includes a signal sampling module, a calculation module, and an input / output module. The input / output module is connected to a single-phase circuit breaker. The signal sampling module is used to collect electrical quantity data of the medium-voltage distribution network in real time and transmit the electrical quantity data to the calculation module. The calculation module is used to identify the faulty phase when a single-phase ground fault is detected based on the real-time collected electrical quantity data of the medium-voltage distribution network and output control commands to the input / output module. The input / output module is used to receive control commands and circuit breaker status and output drive signals to the single-phase circuit breaker to control the opening and closing operations of the single-phase circuit breaker.
[0015] In a further embodiment of this application, the controller further includes a human-computer interaction module and a communication module, wherein the communication module is used to realize information interaction between the processing device and the outside; and the human-computer interaction module is used to provide device status display and human-computer interaction interface.
[0016] The beneficial effects of this application are as follows:
[0017] The processing device of this application completes the transfer of the grounding current at the fault point within the time delay of the protection device, so that the temporary grounding fault of the fault phase will not trigger the operation of the protection device, thereby avoiding the impact of the temporary grounding fault on the continuity of power supply.
[0018] The processing device of this application can effectively suppress instantaneous high-frequency current by closing the faulty phase circuit breaker with a reactor, and can limit the circulating current between the non-faulty phase and the faulty phase without causing a phase-to-phase short circuit when the phase is switched. Attached Figure Description
[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application.
[0020] In the attached diagram:
[0021] Figure 1 This is a schematic diagram of one embodiment of the device for handling temporary grounding faults in a medium-voltage power distribution network according to this application;
[0022] Figure 2 This is a schematic diagram of the current flow direction when a temporary grounding fault occurs in a medium-voltage distribution network.
[0023] Figure 3This is a schematic diagram of the current flow after the processing device of this application is activated;
[0024] Figure 4 This is a functional block diagram of the controller in the processing apparatus of this application. Detailed Implementation
[0025] In a medium-voltage distribution network using a neutral point grounded through a small resistor, in one embodiment of this application, the grounding impedance within the substation meets the requirements of GB / T50065-2011 standard, and the line protection devices in the distribution network are required to have zero-sequence overcurrent action set to a time-delay action (e.g., a delay of 100ms). Figure 1 As shown, the temporary grounding fault handling device for medium-voltage distribution networks according to this application is located in a substation and connected in parallel to the busbar of the medium-voltage distribution network. The handling device includes: single-phase circuit breakers, including single-phase circuit breakers Ka, Kb, and Kc, whose first terminals are respectively connected to phases A, B, and C of the medium-voltage distribution network and whose second terminals are grounded through a current limiting device; the controller is electrically connected to the single-phase circuit breakers Ka, Kb, and Kc. Based on the electrical quantity data of the medium-voltage distribution network collected in real time, when a single-phase grounding fault is detected, the controller identifies the faulty phase and instructs the single-phase circuit breaker corresponding to the faulty phase to close, so as to transfer the grounding current of the faulty phase to the substation. The processing device described in this application allows the controller to command the single-phase circuit breaker of the corresponding faulty phase to close when an arcing ground fault occurs. Since the arc resistance during an arcing ground fault is generally not less than 20Ω (except for purely metallic ground faults), and the grounding impedance of the processing device located within the substation is even smaller, the processing device, after closing the single-phase circuit breaker of the corresponding faulty phase, will transfer the grounding current at the fault point to the substation, resulting in almost no current flowing through the fault point, thus allowing the arc to extinguish naturally without triggering the protection device. After a delay (e.g., 2 seconds), the controller reopens the circuit breaker of the faulty phase. If the grounding fault is temporary, the system resumes normal operation, ensuring that the faulty line does not lose power during the entire grounding fault process. However, if the grounding fault is permanent, after the circuit breaker of the corresponding faulty phase trips, a grounding current supplied by a small resistor will flow through the fault point, causing the protection device of the faulty line to continue to activate the zero-sequence overcurrent protection trip, thereby disconnecting the faulty line.
[0026] In various embodiments of this application, the controller collects the three-phase voltage, zero-sequence voltage, and neutral point current flowing through a small resistor in real time from the medium-voltage distribution network to determine whether a single-phase ground fault has occurred, and identifies the faulty phase when a single-phase ground fault is detected. Specifically, the controller is electrically connected to a device for measuring the three-phase voltage, zero-sequence voltage, and neutral point current flowing through a small resistor. For example, a voltage transformer (PT) with a Yyn0 connection can be used to measure the phase voltage. In a Yyn0 connection, the primary winding is connected in a star configuration, the secondary winding is also connected in a star configuration, and the neutral points of both the primary and secondary sides are grounded. This connection method can measure both line voltage and phase voltage. By detecting changes in the three-phase voltage, a preliminary determination can be made as to whether a single-phase ground fault has occurred. When a single-phase ground fault occurs, the voltage of the faulty phase will decrease (approaching zero), while the voltage of the non-faulty phases will rise to near the line voltage. The phase-to-ground voltage can be measured by the PT, and the phase with the lowest voltage is the faulty phase.
[0027] Alternatively or additionally, a three-phase five-limb voltage transformer can be used to measure phase voltage and zero-sequence voltage. A three-phase five-limb voltage transformer has three primary windings and one auxiliary secondary winding. Under normal operation, the three-phase voltages are symmetrical, and the output voltage of the auxiliary secondary winding is zero. When an asymmetry occurs in the distribution network, such as a ground fault, it causes a shift in the neutral point potential, resulting in a zero-sequence voltage, which is induced in the auxiliary secondary winding. When a single-phase ground fault occurs, the zero-sequence voltage changes significantly and is no longer zero. This significant increase in zero-sequence voltage is a direct indicator of a ground fault, and detecting the zero-sequence voltage allows for a more accurate determination of the fault type.
[0028] When a single-phase ground fault occurs, the fault current forms a loop through the neutral point resistor, generating a significantly increased zero-sequence current. The magnitude and direction of the zero-sequence current can help identify the faulty phase. The zero-sequence current can be directly measured using a zero-sequence current transformer (CT), or by measuring the three-phase currents separately and then adding their vectors together. In a distribution network with a neutral point grounded through a small resistor, when a single-phase ground fault occurs, the zero-sequence current of the faulty phase flows from the fault point to the neutral point. If the direction of the zero-sequence current flow in each phase can be determined, the faulty phase can be roughly identified.
[0029] In one embodiment of this application, the processing apparatus further includes a current limiting device, wherein a first terminal of the current limiting device is connected to the second terminal of a single-phase circuit breaker Ka, Kb, Kc, and the second terminal of the current limiting device is grounded. Figure 1As shown, in one embodiment of this application, the current limiting device includes a single-phase reactor L. Preferably, the power frequency inductive reactance Z of the single-phase reactor L is in the range of 10Ω to 100Ω. This is because an inductive reactance that is too small cannot limit the short-circuit current when the phases are switched out, while an inductive reactance that is too large cannot transfer the grounding current at the fault point. Specifically, the single-phase reactor L has the following functions: suppressing the amplitude and rise rate (di / dt) of the high-frequency current at the moment of closing, reducing the impact of sudden current changes, and achieving the purpose of protecting the equipment; when the phases are switched out, it can limit the short-circuit current between the faulty phase and the closed phase, preventing tripping. It is worth noting that when transferring the grounding current at the fault point with the reactor, the transfer current must be measurable to determine whether the phase switching is correct. Therefore, the single-phase reactor L can achieve a balance between suppressing high-frequency current, limiting the two-phase short-circuit current, and transferring the grounding current at the fault point.
[0030] In one embodiment of this application, the current limiting device further includes a single-phase circuit breaker Kl connected in parallel with the single-phase reactor L. The single-phase circuit breaker Kl is electrically connected to the controller. Upon correct closing, the controller will instruct the single-phase circuit breaker Kl to close within time t. Preferably, the time t is in the range of 20ms to 30ms. The delayed closing of the single-phase circuit breaker Kl can lower the grounding impedance within the processing device relative to the grounding impedance at the fault point. Since current always flows along the path of least impedance, the current can be effectively transferred from the fault point to the device. Figure 2 As shown, assuming a ground fault occurs in phase A at point G, the grounding current supplied by the small resistor at the neutral point flows back through the fault point. The current flow direction is illustrated by the dashed line. Figure 3 As shown, after the controller closes the single-phase circuit breakers Ka and Kl, the grounding current at the fault point has been transferred to the processing device, the current at the fault point is effectively cut off, and the arc grounding phenomenon is naturally extinguished.
[0031] Specifically, after the controller detects a ground fault and determines that phase A is grounded, it can instruct the single-phase circuit breaker Ka corresponding to phase A to close. In order to ensure that the total time from the occurrence of the ground fault to the closing position of the single-phase circuit breaker Ka does not exceed 30 milliseconds, the opening and closing time of the single-phase circuit breaker should not exceed 10 milliseconds. Therefore, on the one hand, the sampling frequency of the controller should be at least 9.6kHz to ensure that the ground fault can be quickly identified and the faulty phase can be determined. On the other hand, a single-phase vacuum circuit breaker with fast action time can be selected.
[0032] It is worth noting that a delay of 20ms to 30ms is sufficient for the single-phase reactor L to stabilize its current, preventing high-frequency current from impacting the equipment, and simultaneously determining whether the closing phase is the faulty phase. If not, there is enough time to open the circuit. If the delay is too long, the current may not be transferred in time, affecting fault handling efficiency. Furthermore, the controller needs to complete signal sampling, fault diagnosis, and other operations within this timeframe. If the delay is too short, the controller may not be able to complete all operations.
[0033] like Figure 4 As shown, in various embodiments of this application, the controller may include a signal sampling module, a calculation module, and an input / output module. In another embodiment of this application, the controller may further include a human-computer interaction module and a communication module.
[0034] The signal sampling module is used to collect electrical quantity data of the medium-voltage distribution network in real time and transmit the electrical quantity data to the calculation module. Specifically, the signal sampling module can collect three-phase voltage (voltages of phases A, B, and C), zero-sequence voltage (vector sum of three-phase voltages), and neutral point current flowing through a small resistor. This neutral point current can reflect the ground fault current.
[0035] The calculation module, based on real-time collected electrical quantity data of the medium-voltage distribution network, identifies the faulty phase when a single-phase ground fault is detected and outputs control commands to the input / output modules. Specifically, the calculation module can determine whether a ground fault has occurred based on the zero-sequence voltage amplitude and the neutral point current magnitude. It can also identify the faulty phase by combining the three-phase voltage phase shift and the phase relationship between the zero-sequence current and voltage. After confirming the ground fault and identifying the faulty phase, it can generate circuit breaker opening and closing commands according to preset algorithms (such as fuzzy logic and threshold judgment). In addition, the calculation module can monitor its own and external equipment status (such as reactor abnormalities and circuit breaker jamming), triggering alarms or interlocking when necessary.
[0036] The input / output module receives control commands and circuit breaker status, and outputs drive signals to the circuit breaker to control its opening and closing operations. Specifically, the input / output module can send drive signals (opening / closing signals) to the circuit breakers (Ka, Kb, Kc, Kl) according to the control commands issued by the arithmetic module, and collect the circuit breaker's position signals (opening / closing status), operation completion signals, etc., and can trigger alarms or lockouts in abnormal situations (such as closing failure, failure to operate).
[0037] The communication module is used to enable information exchange between the device and external systems, supporting remote monitoring and fault management. Specifically, the communication module can upload fault information (such as fault phase, occurrence time, and current waveform) to the background monitoring system and receive remote control commands (such as device parameter settings and reset commands). This communication module can support multiple communication protocols (such as Modbus, CDT, IEC61850, etc.) to adapt to different scenario requirements.
[0038] The human-machine interface (HMI) module provides equipment status display and a user interface to facilitate operation and maintenance by maintenance personnel. Specifically, the HMI module can display system voltage, current, fault status, and other information in real time via an LCD screen or indicator lights. It also supports setting device parameters (such as delay time and reactor switching threshold) via buttons or a touch screen, and can provide audible and visual alarms or text prompts for fault events or equipment malfunctions.
[0039] In summary, the controller in the processing device of this application is mainly responsible for real-time monitoring of the system status, quickly determining the grounding fault and identifying the faulty phase, controlling the circuit breaker to transfer the fault current, ensuring the safe and stable operation of the system, and realizing remote monitoring and data transmission through communication with external devices.
Claims
1. A device for handling temporary grounding faults in a medium-voltage distribution network, wherein the medium-voltage distribution network uses a neutral point grounded through a small resistor, characterized in that, The processing device is located within the substation and connected in parallel to the busbar of the medium-voltage distribution network. The processing device includes: A single-phase circuit breaker includes single-phase circuit breaker Ka, single-phase circuit breaker Kb, and single-phase circuit breaker Kc, whose first terminals are respectively connected to phases A, B, and C of a medium-voltage distribution network and whose second terminals are grounded. The controller is electrically connected to single-phase circuit breakers Ka, Kb, and Kc. The controller is configured to: based on real-time collected electrical quantity data of the medium-voltage distribution network, when a single-phase ground fault is detected, identify the faulty phase and instruct the single-phase circuit breaker corresponding to the faulty phase to close, so as to transfer the ground current at the fault point to the substation.
2. The device for handling temporary grounding faults in medium-voltage power distribution networks according to claim 1, characterized in that, The electrical quantity data of the medium-voltage distribution network includes the three-phase voltage, zero-sequence voltage, and neutral point current flowing through a small resistor.
3. The device for handling temporary grounding faults in medium-voltage power distribution networks according to claim 1, characterized in that, The sampling frequency of the controller is at least 9.6 kHz.
4. The device for handling temporary grounding faults in medium-voltage distribution networks according to claim 1, characterized in that, It also includes a current limiting device, through which the single-phase circuit breaker Ka, single-phase circuit breaker Kb and single-phase circuit breaker Kc are grounded.
5. The device for handling temporary grounding faults in medium-voltage distribution networks according to claim 4, characterized in that, The current limiting device includes a single-phase reactor L, and the power frequency inductive reactance Z of the single-phase reactor L is in the range of 10Ω to 100Ω.
6. The device for handling temporary grounding faults in medium-voltage distribution networks according to claim 5, characterized in that, The current limiting device also includes a single-phase circuit breaker Kl connected in parallel with the single-phase reactor L. The single-phase circuit breaker Kl is electrically connected to the controller. The controller commands the single-phase circuit breaker Kl to close within a time t after closing the single-phase circuit breaker corresponding to the faulty phase.
7. The device for handling temporary grounding faults in medium-voltage distribution networks according to claim 6, characterized in that, The time t is in the range of 20ms to 30ms.
8. The device for handling temporary grounding faults in medium-voltage distribution networks according to claim 1, characterized in that, The circuit breaker is a vacuum circuit breaker.
9. The apparatus for handling temporary grounding faults in a medium-voltage distribution network according to any one of claims 1 to 8, characterized in that, The controller includes a signal sampling module, a processing module, and an input / output module. The input / output module is connected to a single-phase circuit breaker. The signal sampling module is used to collect electrical quantity data of the medium-voltage distribution network in real time and transmit the electrical quantity data to the calculation module; The computing module is used to identify the faulty phase when a single-phase grounding fault is detected based on the electrical quantity data of the medium-voltage distribution network collected in real time, and output control commands to the input-output module. The input / output module is used to receive control commands and circuit breaker status, and output drive signals to the single-phase circuit breaker to control the opening and closing operations of the single-phase circuit breaker.
10. The device for handling temporary grounding faults in medium-voltage distribution networks according to claim 9, characterized in that, The controller also includes a human-computer interaction module and a communication module, wherein... The communication module is used to enable information interaction between the processing device and the outside world; The human-computer interaction module is used to provide device status display and human-computer interaction interface.