A single-phase grounding fault location system and method for power distribution networks

Abstract

A single-phase ground fault location system and method for power distribution networks is disclosed. The system includes: a vacuum contactor for switching or external protection tripping low-resistance circuits; a low-resistance circuit that temporarily amplifies the zero-sequence current of the ground fault line by temporarily changing the zero-sequence impedance of the low-current grounding system, thereby improving the sensitivity of zero-sequence overcurrent protection of substation outgoing switches, distribution network line sectionalizing, branching, and demarcating switches; a current transformer for recording the low-resistance current and providing low-resistance overcurrent protection; a low-resistance controller for diagnosing ground faults, outputting control commands to achieve automatic opening and closing of the vacuum contactor, and providing an operation interface for external equipment to enable or disable the low-resistance circuit; a user terminal for users to issue operation commands to enable or disable the low-resistance circuit; and a low-resistance status indicator light to display whether the low-resistance function is enabled and the opening / closing status of the vacuum contactor. This invention features a reasonable control logic that amplifies the zero-sequence current of the ground fault line in a timely manner, significantly improving the sensitivity of the location equipment.

Description

Technical Field

[0001] This invention relates to the field of single-phase grounding fault location technology in power distribution networks, and in particular to a single-phase grounding fault location system and method for power distribution networks. Background Technology

[0002] Currently, most of my country's 3-66kV power grids use either ungrounded neutral points or grounded via arc suppression coils. The main function of the arc suppression coil is to generate inductive current to compensate for the grid's capacitive current when a single-phase ground fault occurs, thereby reducing the residual current at the fault point and achieving self-extinguishing of the arc and elimination of the fault. The use of arc suppression coils effectively prevents reignition of the arc after it crosses zero, and pre-adjusted arc suppression coils can also eliminate ferroresonant overvoltages caused by the saturation of electromagnetic transformers.

[0003] Chinese Invention Patent Title: A Method for Selecting Lines of an Active Intervention Arc Suppression Device Considering Busbar Grounding Faults, Patent No.: CN114966462A, discloses a method for selecting lines of an active intervention arc suppression device considering busbar grounding faults, which uses a single-phase grounding fault initiation criterion composed of zero-sequence voltage 3U0 and minimum line voltage Ulwin.

[0004] Once a line grounding occurs, regardless of compensation or arc suppression, the fault point must ultimately be isolated, and the isolation of the fault point should be accurate and fast. However, while the use of arc suppression coils effectively reduces the arc current of the grounding line and the grounding point, it also changes the polarity of the zero-sequence current of the grounding line, making the fault characteristics of the grounding line in a low-current grounding system less obvious, resulting in a decrease in the accuracy of grounding line selection. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a single-phase grounding fault location system and method for power distribution networks. With increasingly stringent power supply safety requirements, it is necessary to implement immediate arc suppression for instantaneous grounding in low-current grounding systems and rapid isolation for permanent grounding. This requires adding a parallel automatic switching low-resistance mode to the arc suppression coil. Through reasonable control logic, the arc suppression coil can be activated immediately upon instantaneous grounding, quickly compensating for grid capacitive current and even restoring insulation at the grounding point, thus restoring the grid to normal. For grounding that persists for more than a certain time limit, it is judged as permanent grounding, and a low-resistance circuit is pre-activated or temporarily activated, connected in parallel across the arc suppression coil. This temporarily amplifies the zero-sequence current of the grounding line, making the grounding characteristics significant within a limited and controllable current range. The zero-sequence overcurrent protection of the outgoing line switch and distribution network switch is used for alarm location or rapid tripping. For high-resistance grounding, the temporary activation of low resistance can assist conventional grounding fault location devices based on lateral amplitude and phase comparison in accurate fault location, providing a reliable basis for dispatchers to accurately disconnect faults.

[0006] The technical solution adopted in this invention is as follows:

[0007] A single-phase ground fault location system for a power distribution network includes:

[0008] Vacuum contactors, matched with low resistance, are used for switching or external protection tripping of low resistance.

[0009] Low resistance, by temporarily changing the zero-sequence impedance of the low-current grounding system, provides a temporarily amplified zero-sequence current for the ground fault line, improves the sensitivity of the zero-sequence overcurrent protection of the substation outgoing switches, distribution network line section, branch, and boundary switches, so that they can operate reliably and achieve accurate alarm or tripping of the fault line.

[0010] Current transformers, configured with a current ratio matching low-resistance current limiting, are used for recording low-resistance current and providing low-resistance overcurrent protection.

[0011] The low-resistance controller is used to diagnose grounding faults, output control commands, realize the automatic opening and closing of vacuum contactors, and provide a low-resistance operation interface for external equipment, completing functions such as remote signaling and remote control with the back-end unit, remote control unit, etc.

[0012] The user terminal can execute user commands to enable or disable the low resistance function; the low resistance status indicator shows whether the low resistance function is enabled and the vacuum contactor's open / closed status; the over-temperature alarm light indicates an abnormal low resistance over-temperature state; the low resistance action counter records the number of low resistance actions; the low resistance remote / local handle is used to enable or disable the low resistance function locally or remotely; the low resistance enable / disable handle enables or disables the low resistance function when operating locally; and the low resistance temperature setting panel allows setting the low resistance over-temperature temperature.

[0013] A method for locating a single-phase ground fault in a distribution network includes:

[0014] When the power grid is operating normally, the low resistance function is activated and the vacuum contactor is in the closed state. If a ground fault occurs in the distribution network, the zero-sequence current of the system is directly amplified, so that the zero-sequence overcurrent protection of the distribution network switches from the fault line substation to the fault point can be successfully activated. Through reasonable setting and timing coordination, the zero-sequence overcurrent protection of each level of switch selectively trips to isolate the grounding point or issues a zero-sequence overcurrent protection alarm signal to determine the ground fault conductor segment. If a permanent ground fault occurs in the distribution network, the vacuum contactor will automatically disconnect after a set delay. After the grounding point disappears and the fault characteristic quantity 3U0 is lower than the set value, the vacuum contactor will return to the closed state.

[0015] When the power grid is operating normally, the low resistance function is engaged, but the vacuum contactor is in the open state, and the arc suppression coil is in normal operation. If a ground fault occurs in the distribution network, the fault characteristic quantity 3U0 exceeds the set value. If the ground fault is a transient ground fault, the vacuum contactor remains in the open state and only performs arc suppression. After the fault point is restored to insulation, the power grid returns to normal. If the ground fault is a permanent ground fault, the vacuum contactor automatically closes after the set time, amplifying the zero-sequence current of the system. This allows the zero-sequence overcurrent protection of the distribution network switches from the fault line substation to the fault point to be successfully activated. Through reasonable setting and timing coordination, the zero-sequence overcurrent protection of each level of switch selectively trips to isolate the grounding point or issues a zero-sequence overcurrent protection alarm signal to determine the ground fault conductor segment. After the grounding disappears and the fault characteristic quantity 3U0 is lower than the set value, the vacuum contactor automatically returns to the open state.

[0016] The beneficial effects of this invention are as follows:

[0017] The low resistance of this invention is directly connected in parallel to both sides of the original grounding transformer arc suppression coil, with independent control logic, does not interfere with the normal operation of the arc suppression coil system, and does not require modification of the original arc suppression coil system.

[0018] This method flexibly assists the selective tripping or alarm operation of zero-sequence overcurrent protection on the power grid for line and section selection. After a ground fault occurs, it can first extinguish the arc, and for permanent faults, it can automatically and briefly switch to low resistance to reduce the system's zero-sequence impedance and amplify the zero-sequence current. It can also switch to low resistance during normal operation, directly amplifying the zero-sequence current for transient ground faults, and automatically deactivating low resistance for permanent faults after a delay to enter arc extinguishing operation. By utilizing the principle of changing the zero-sequence impedance in a low-current grounding system, and through reasonable control logic, it amplifies the zero-sequence current of the faulty line in a timely manner, significantly improving the sensitivity of the line selection equipment. Through setting values, it can flexibly realize the alarm or tripping of zero-sequence overcurrent protection for grounded lines, significantly improving the accuracy of line selection, reducing the workload of dispatchers, and further improving the reliability of power supply in the distribution network. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a single-phase grounding fault location system for a power distribution network according to the present invention.

[0020] Figure 2 This is a schematic diagram of the system wiring according to an embodiment of the present invention;

[0021] Figure 3 This is the operating timing diagram for Mode 1 of the present invention;

[0022] Figure 4 This is the working timing of Mode 2 in the embodiment of the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments: To clearly illustrate the technical features of this solution, the present invention will be described in detail below through specific embodiments and with reference to the accompanying drawings. The following disclosure provides many different embodiments or examples for implementing different structures of the present invention. To simplify the disclosure of the present invention, components and arrangements of specific examples are described below. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. It should be noted that the components shown in the drawings are not necessarily drawn to scale. Descriptions of well-known components and processing techniques and processes are omitted in the present invention to avoid unnecessarily limiting the present invention.

[0024] like Figure 1 or Figure 2 As shown, the present invention provides a single-phase grounding fault location system for a distribution network, comprising:

[0025] Vacuum contactors, matched with low resistance, are used for switching or external protection tripping of low resistance.

[0026] Low resistance, by temporarily changing the zero-sequence impedance of the low-current grounding system, provides a temporarily amplified zero-sequence current for the ground fault line, improves the sensitivity of the zero-sequence overcurrent protection of the substation outgoing switches, distribution network line section, branch, and boundary switches, so that they can operate reliably and achieve accurate alarm or tripping of the fault line.

[0027] Current transformers, configured with a current ratio matching low-resistance current limiting, are used for recording low-resistance current and providing low-resistance overcurrent protection.

[0028] The low-resistance controller is used to diagnose grounding faults, output control commands, realize the automatic opening and closing of vacuum contactors, and provide an operation interface for low-resistance activation and deactivation for external equipment. It enables functions such as remote signaling and remote control with the back-end control unit and remote control units. The low-resistance controller has a built-in vacuum contactor closing timeout limit. If the automatic low-resistance disconnection fails, the low-resistance controller will activate according to the set timeout limit to control the automatic deactivation of the low-resistance device, or connect to the high-voltage side switch of the grounding transformer via the trip output to achieve the tripping of the high-voltage side switch. The low-resistance controller has built-in interlocking input and output nodes, and introduces sectionalizing switch position nodes, enabling automatic blocking of subsequent low-resistance functions during parallel bus operation, ensuring that only one low-resistance device operates on the same bus. The low-resistance controller can also achieve remote control and remote signaling, and, in conjunction with the station's measurement and control devices, achieve information exchange with the back-end control unit and remote control units.

[0029] The user terminal allows the user to issue operation commands to enable or disable the low resistance function and displays the low resistance operating status.

[0030] The low resistance status indicator shows whether the low resistance function is engaged and the vacuum contactor is open or closed; the over-temperature alarm light indicates an abnormal low resistance over-temperature condition; the low resistance action counter records the number of low resistance actions; the low resistance remote / local handle is used to enable or disable the low resistance function locally or remotely; the low resistance enable / disable handle enables or disables the low resistance function when operating locally; and the low resistance temperature setting panel allows setting the low resistance over-temperature temperature.

[0031] In the single-phase grounding fault location system of the power distribution network, a low resistor is connected in parallel at the arc suppression coil of the neutral point of the grounding transformer in the primary system.

[0032] Figure 2 The specific meanings of the parameters are as follows: 1TV: grounding transformer neutral point voltage transformer; 1TA: low resistance current transformer; KM: vacuum contactor; R: low resistance.

[0033] The remote signaling quantities of the low-resistance controller of this invention are as follows: Low-resistance main contactor closing remote signal: issued when the low-resistance vacuum contactor is closed. Low-resistance function activation remote signal: issued when the low-resistance function is activated. Low-resistance zero-sequence voltage continuous over-limit remote signal: issued when a permanent ground fault occurs and the number of low-resistance actions reaches the set number. Low-resistance operating timeout remote signal: issued when the low-resistance current-carrying time reaches the low-resistance current-carrying timeout tripping setting value. External low-resistance trip remote signal: issued when other protection or automatic devices cause the low-resistance to deactivate and trip. Low-resistance over-temperature remote signal: when the low-resistance reaches its rated design temperature due to excessive current, excessive time, etc., this signal is issued when the low-resistance is automatically disconnected; the signal returns after the temperature drops to normal. Low-resistance interlocking remote signal: when multiple low-resistance units in the same substation are running in parallel on the bus, the preset preceding low-resistance is the main activated unit, and the subsequent low-resistance is interlocked and its function is blocked; this remote signal is issued when a low-resistance is interlocked by the preceding low-resistance.

[0034] The remote control parameters of the low-resistance controller of this invention are as follows: Remote control to activate low resistance: When the dispatching terminal remotely activates low resistance, the low resistance function is enabled. If a ground fault occurs at this time, the low resistance will operate according to normal logic. Remote control to deactivate low resistance: When the dispatching terminal remotely deactivates low resistance, the low resistance function is deactivated. If a ground fault occurs at this time, the low resistance will no longer operate.

[0035] In this embodiment of the invention, the preset values ​​for the low-impedance controller include:

[0036] 3U0: Ground fault characteristic quantity, i.e., zero-sequence voltage of the neutral point of the grounding transformer, recommended 20V;

[0037] T1: Low resistance delay tripping time, used in mode one. It starts timing from 3U0 over-limit and automatically trips when the set value is reached. This value should be greater than the sum of the time of the first action, reclosing and second action of the zero-sequence overcurrent protection of the outgoing switch and distribution switch. 4.5S is recommended.

[0038] T u0 Low resistance delay activation time, used in mode 2, starts timing from 3U0 over-limit, and the vacuum contactor automatically closes when the set value is reached, used to avoid transient ground faults, 2S recommended;

[0039] T2: Low resistance closing holding time, used in mode two. It starts timing after the low resistance vacuum contactor automatically closes and automatically opens when the set value is reached. This value should be greater than the sum of the time for the first action, reclosing, and second action of the zero-sequence overcurrent protection of the outgoing switch and distribution network switch. 4.5S is recommended.

[0040] T sr Low-resistance heat dissipation lock-up time: This ensures safe and stable heat dissipation for low-resistance applications. 600 seconds is recommended.

[0041] T R The thermal stability time for low resistance is determined by the thermal stability characteristics when a large current passes through a low resistance; 10 seconds is recommended.

[0042] T5: Low-resistance current-carrying timeout tripping time, collected from the vacuum contactor position signal, as an additional measure for the low-resistance vacuum contactor failing to trip automatically after a preset time. It must not exceed the low-resistance thermal stability time and should meet the following requirements: T1 <T5<T R (Mode 1) or T2 <T5<T R (Mode 2), 5.5S recommended;

[0043] T set Low resistance and over-temperature alarm setting, recommended value is 450℃;

[0044] Twin: This is the open window time for allowing the low-resistance contactor to switch on and off n times. It is used to prevent frequent switching of the low-resistance contactor when it is permanently grounded. When the fault characteristic value 3U0 exceeds the limit and exceeds the open window time, the low-resistance vacuum contactor is blocked from closing. The number of times the low-resistance contactor can be preset by setting this time. 604.5S (Mode 1) or 606.5S (Mode 2) is recommended, which means that the low-resistance contactor can close twice. The calculation method is Twin = (n-1)*Tsr + T1 (Mode 1) or Twin = (n-1)*Tsr + Tu0 + T2 (Mode 2), where n is the number of times the low-resistance contactor can close.

[0045] This invention provides a method for locating single-phase ground faults in a distribution network, comprising:

[0046] The vacuum contactor is initially in the closed position (mode 1) or open position (mode 2). After the device collects the ground fault characteristic quantity 3U0 and starts beyond the limit, it enters the action sequence.

[0047] In Mode 1, when the power grid is operating normally, the low resistance function is activated and the vacuum contactor is in the closed state. If a ground fault occurs in the distribution network, the zero-sequence current of the system is directly amplified, so that the zero-sequence overcurrent protection of the distribution network switch from the fault line station to the fault point can be successfully activated. Through reasonable setting and timing coordination, the zero-sequence overcurrent protection of each level of switch selectively trips to isolate the grounding point or issues a zero-sequence overcurrent protection alarm signal to determine the ground fault conductor segment. If a permanent ground fault occurs in the distribution network, the vacuum contactor will automatically disconnect after a set delay. After the grounding point disappears and the fault characteristic quantity 3U0 is lower than the set value, the vacuum contactor will return to the closed state.

[0048] By coordinating reasonable settings and timing, the circuit breaker can be flexibly adjusted according to the substation capacitor current in actual operation. For example, if there are four circuit breakers with zero-sequence overcurrent protection from the substation switch to the fault point, such as the substation switch, section, branch, and boundary circuit breakers, their zero-sequence overcurrent protection can be set to 40A, 0.8s; 30A, 0.6s; 20A, 0.4s; and 15A, 0.2s respectively. Through the coordination of protection at different levels, selective isolation of faults can be achieved.

[0049] like Figure 3 The diagram shows the working timing of Mode 1 in this embodiment of the invention. The moment 3U0 exceeds the limit is taken as the zero point. At this time, the low-resistance delayed tripping time relay, the allowable switching open window time relay, and the current-overtime tripping time relay all start timing. Within the T1 time limit, if the fault is successfully isolated (e.g., zero-sequence overcurrent protection trips), the low-resistance delayed tripping time relay, the allowable switching open window time relay, and the current-overtime tripping time relay all reset to their pre-fault state. If the fault is not isolated (e.g., zero-sequence overcurrent protection trips without alarm activation, switch malfunction, etc.), when the T1 time limit is reached, the low-resistance vacuum contactor automatically trips, and the low-resistance device enters a heat dissipation lockout state. After heat dissipation ends, 3U0 continues to exceed the limit. At this time, the vacuum contactor automatically closes, and the low-resistance delayed tripping time relay and the allowable switching open window time relay start timing. When the T1 time limit is reached, the low-resistance vacuum contactor automatically trips and enters a heat dissipation lockout state. At this point, the open window time allowing for two switching operations of the low-resistance circuit is reached, locking the low-resistance vacuum contactor from closing. This means the low-resistance contactor will no longer close during this fault until the fault is cleared (the fault characteristic quantity 3U0 disappears from the limit). Then, the lockout is released, and the system returns to its pre-fault state. Throughout this process, if the low-resistance vacuum contactor does not trip after time T1, the low-resistance controller will automatically trip the vacuum contactor at time T5. Figure 3The specific parameters are as follows: Twin: the opening time window allowing n low-resistance switching operations, Twin = (n-1)*Tsr + T1; T1: low-resistance delay opening time; T sr T1: Low resistance heat dissipation lockout time; T5: Low resistance current carrying timeout tripping time; T1: Low resistance current carrying timeout tripping time. <T5<T R ;T R Low resistance thermal stability time.

[0050] For Mode 2, when the power grid is operating normally, the low resistance function is engaged, but the vacuum contactor is in the open state, and the arc suppression coil is in normal operation. If a ground fault occurs in the distribution network, the fault characteristic quantity 3U0 exceeds the set value. If the ground fault is a transient ground fault, the vacuum contactor remains in the open state and only performs arc suppression. After the fault point is restored to insulation, the power grid returns to normal. If the ground fault is a permanent ground fault, the vacuum contactor automatically closes after the set time, amplifying the zero-sequence current of the system. This allows the zero-sequence overcurrent protection of the distribution network switches from the fault line substation to the fault point to start smoothly. Through reasonable setting and timing coordination, the zero-sequence overcurrent protection of each level of switch selectively trips to isolate the grounding point or issues a zero-sequence overcurrent protection alarm signal to determine the ground fault conductor segment. After the grounding disappears and the fault characteristic quantity 3U0 is lower than the set value, the vacuum contactor automatically returns to the open state.

[0051] By appropriately coordinating setpoints and timing, the system can be flexibly adjusted manually based on the substation capacitor current during actual operation. The setpoints can be set according to actual needs.

[0052] like Figure 4 The diagram shows the working timing of Mode 2 in this embodiment of the invention. The moment 3U0 exceeds the limit is taken as the zero point. At this time, the low-impedance delay-activated time relay starts timing. If it is a transient fault, 3U0 will no longer exceed the limit after the fault disappears, the low-impedance delay-activated time relay will reset, and the system will return to its pre-fault state. If it is a permanent fault, then T... u0When the time limit is reached, the low-resistance vacuum contactor automatically closes. The low-resistance closing holding time relay, the allowable switching open window time relay, and the current overtime tripping time relay start timing. Within the T2 time limit, if the fault is successfully isolated (e.g., zero-sequence overcurrent protection trips), the low-resistance closing holding time relay, the allowable switching open window time relay, and the current overtime tripping time relay all reset to their pre-fault states. If the fault is not isolated (e.g., zero-sequence overcurrent protection trips without alarm, switch malfunction, etc.), when the T2 time limit is reached, the low-resistance vacuum contactor automatically trips, and the low-resistance enters a heat dissipation lockout state. When heat dissipation ends, 3U0 continues to exceed the limit. At this time, the vacuum contactor automatically closes, and the low-resistance closing holding time relay and the allowable switching open window time relay start timing. When the T2 time limit is reached, the low-resistance vacuum contactor automatically trips and enters a heat dissipation lockout state. At this point, the open window time allowing for two switching operations of the low-resistance circuit is reached, locking the low-resistance vacuum contactor from closing. This means the low-resistance contactor will no longer close during this fault until the fault is cleared (the fault characteristic quantity 3U0 disappears from the limit). Then, the lockout is released, and the system returns to its pre-fault state. Throughout this process, if the low-resistance vacuum contactor does not trip after time T2, the low-resistance controller will automatically trip the vacuum contactor at time T5. Figure 4 The specific parameters are as follows: Twin: the opening time window allowing n low-resistance switching operations, Twin = (n-1)*Tsr + T2; T2: the low-resistance closing hold time; T sr T1: Low resistance heat dissipation lockout time; T5: Low resistance current carrying timeout tripping time; T1: Low resistance current carrying timeout tripping time. <T5<T R ;T R Low resistance thermal stability time; T u0 Low resistance delay time is used to avoid instantaneous ground faults.

[0053] If the distribution network switch of the grounded line does not trip, and the zero-sequence overcurrent protection of the substation outgoing switch also does not trip, the low-resistance vacuum contactor will automatically trip after a set delay for low-resistance heat dissipation. After heat dissipation is complete, it will automatically close and reconnect. If a permanent grounding fault or other grounding fault occurs that cannot be isolated by the tripping of the zero-sequence overcurrent protection of the outgoing or distribution network switch, the low-resistance controller will deactivate its low-resistance function and be used for equipment protection after the maximum number of switching cycles set for a single fault.

[0054] For high-resistance grounding, the zero-sequence impedance of the system decreases during the period when low resistance is applied. However, due to the presence of high resistance, the zero-sequence current of the faulty line may not be amplified sufficiently. The zero-sequence overcurrent protection of the outgoing switch and distribution network switch may not reach the set value and will not start. However, the resistive current generated by the short-term low resistance can correct the polarity of the zero-sequence current of the grounded line. The faulty line can also be accurately selected by conventional line selection devices based on transverse amplitude and phase comparison.

[0055] When a ground fault occurs in the system, after the low-resistance vacuum contactor closes, the zero-sequence current flowing through the low-resistance contactor is connected to the high-voltage side protection device of the grounding transformer. The zero-sequence overcurrent protection of the high-voltage side of the grounding transformer can be used as the main backup protection for the zero-sequence overcurrent of the system. The low-resistance vacuum contactor is tripped in the first time limit and the high-voltage side switch of the grounding transformer is tripped in the second time limit to prevent the low-resistance contactor from burning out or causing a fire in the system due to excessive zero-sequence current and long duration when the low-resistance contactor cannot be disconnected and the fault is not isolated.

[0056] To prevent situations where permanent grounding of the busbar or other grounding faults cannot be isolated by the zero-sequence overcurrent protection of the outgoing line or distribution network switch, resulting in the continuous existence of the fault characteristic quantity 3U0 and causing frequent switching of the low-resistance vacuum contactor, the low-resistance controller is equipped with an open window time that allows the low-resistance to be switched n times. This allows the low-resistance to be switched according to the set number of times when the above situation occurs. After the set number of times is reached, it will not be switched again during this fault period, thus avoiding damage or reduced service life of the equipment due to frequent switching.

[0057] The low-resistance controller is equipped with an external trip input. During the continuous closed position of the low-resistance vacuum contactor, the external protection can disconnect the low-resistance and disconnect the control power supply circuit of the low-resistance vacuum contactor via the trip low-resistance input until a manual inspection confirms that there is no problem, and then it can be manually put back on.

[0058] The low-resistance controller is equipped with a low-resistance current-carrying timeout tripping time. In case of failure of automatic low-resistance disconnection, the controller can automatically disconnect the low-resistance circuit through the timeout tripping input, or it can be connected to the high-voltage side switch of the grounding transformer through the tripping output of the high-voltage side switch of the grounding transformer to achieve low-resistance disconnection, thus preventing the failure of low-resistance disconnection from causing the accident to escalate.

[0059] The low-resistance controller has a debugging drive function. By shorting the output node of the 3U0 zero-sequence voltage relay, the timing and logic function of the line selection system can be verified without applying the fault characteristic quantity 3U0.

[0060] The low-resistance vacuum contactor closing circuit is connected in series with an infrared temperature controller node. When the low resistance is detected to exceed the set temperature (the temperature can be set via the low resistance temperature setting panel), the infrared temperature relay will disconnect the low-resistance vacuum contactor control circuit, illuminate the "over-temperature alarm light", and send a "low resistance over-temperature" remote signal. When the temperature drops to a safe temperature, the vacuum contactor control circuit will automatically be restored.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A power distribution network single-phase ground fault line selection system, characterized in that, Comprise: Vacuum contactor, matched with low resistance, used for switching or external protection tripping low resistance; Low resistance, by temporarily changing the small current grounding system zero sequence impedance, provides temporary amplified zero sequence current for the grounding fault line, improves the zero sequence overcurrent protection sensitivity of substation outgoing switch, distribution network line section, branch, boundary switch, realizes accurate alarm or tripping of fault line; Current transformer, configured with current ratio matched with low resistance current limiting, used for low resistance current recording and low resistance overcurrent protection; Low resistance controller, used for diagnosing grounding fault, outputting control command, realizing automatic switching of vacuum contactor, and providing operation interface for external device to put in or take out low resistance, completing remote signaling and remote control function with background machine and remote machine; Low resistance controller is provided with vacuum contactor closing time limit, used for starting low resistance controller according to set time limit when low resistance automatic disconnection fails, controlling low resistance to automatically exit, or connecting to grounding transformer high voltage side switch through tripping outlet to realize opening of grounding transformer high voltage side switch; The low resistance controller is internally provided with an open window time for allowing low resistance switching Twin , for preventing low resistance from being frequently switched on when permanent grounding occurs, and when the fault characteristic quantity 3U0 exceeds the open window time, the low resistance vacuum contactor is locked to prevent closing, and the specific calculation method is: wherein, n is the number of reclosing times; Tsr is the low resistance heat dissipation lockout time; T is the low resistance delay opening time or low resistance reclosing holding time; User terminal, used for issuing operation command by user to realize putting in or taking out of low resistance function, and displaying low resistance running state; The working principle of the system is: The initial state of vacuum contactor is mode one or mode two respectively, after the device collects grounding fault characteristic quantity 3U0 exceeding limit to start, enters action sequence; For mode one, low resistance function is put in when power grid is normally operated, and vacuum contactor is in closing state, if grounding fault occurs in distribution network, the system zero sequence current is directly amplified, so that zero sequence overcurrent protection of distribution network switch from fault line station switch to fault point is started smoothly, through reasonable setting value and time cooperation, zero sequence overcurrent protection of switches at all levels selectively trips to isolate grounding point or sends zero sequence overcurrent protection alarm signal to determine grounding fault wire segment; if permanent grounding fault occurs in distribution network, vacuum contactor is automatically disconnected after setting delay, after grounding point disappears and fault characteristic quantity 3U0 is lower than setting value, vacuum contactor is restored to closing state again; For mode two, low resistance function is put in when power grid is normally operated, but vacuum contactor is in opening state, arc suppression coil is normally put into operation, if grounding fault occurs in distribution network, fault characteristic quantity 3U0 exceeds limit to reach setting value; if grounding fault is transient grounding fault, vacuum contactor remains opening state, only arc suppression works, after fault point restores insulation, power grid restores normal; if grounding fault is permanent grounding fault, vacuum contactor is automatically closed after setting time, amplifies system zero sequence current, so that zero sequence overcurrent protection of distribution network switch from fault line station switch to fault point is started smoothly, through reasonable setting value and time cooperation, zero sequence overcurrent protection of switches at all levels selectively trips to isolate grounding point or sends zero sequence overcurrent protection alarm signal to determine grounding fault wire segment, after grounding disappears and fault characteristic quantity 3U0 is lower than setting value, vacuum contactor is automatically restored to opening state; The system further comprises: Low resistance state indicator, used for displaying whether low resistance function is put in or not, and opening and closing state of vacuum contactor; Over temperature alarm lamp, used for indicating over temperature abnormal state of low resistance; Low resistance action counter, used for recording low resistance action times; Low resistance remote / local handle, used to realize the local or remote on / off of low resistance function; Low resistance on / off handle, used to realize the on or off of low resistance function when operated locally; Low resistance temperature setting panel, used to set the over-temperature temperature of low resistance.

2. The single-phase-to-ground fault line selection system of the electrical distribution network of claim 1, wherein, The low resistance controller is provided with an external tripping input, which is used to exit the low resistance and disconnect the control power loop of the vacuum contactor when the external protection is tripped during the closing of the vacuum contactor.

3. The single-phase-to-ground fault line selection system of the electrical distribution network of claim 1, wherein, The low resistance controller is provided with interlocking inputs and outputs, and the position nodes of sectional switches are introduced, so that the low resistance function can be automatically locked after the bus parallel operation, and only one low resistance is kept running on the bus.

4. The single-phase-to-ground fault line selection system of the electrical distribution network of claim 1, wherein, The low resistance controller can realize remote control and remote signaling, and interact with the background machine and the remote machine through the station measurement and control device.

5. A method for single-phase earth fault line selection of a power distribution network, characterized in that, When the power grid is in normal operation, the low resistance function is turned on, and the vacuum contactor is in the closed state. If a grounding fault occurs in the distribution network, the system zero sequence current is amplified, so that the zero sequence overcurrent protection of the distribution network switch from the station switch to the fault point is started smoothly. Through reasonable setting of the value and time, the zero sequence overcurrent protection of each level of switch selectively trips the isolation point or sends an alarm signal, and determines the grounding fault wire segment. If a permanent grounding fault occurs in the distribution network, the vacuum contactor is automatically disconnected after a set delay, and the vacuum contactor returns to the closed state after the fault characteristic 3U0 is lower than the set value. When the power grid is in normal operation, the low resistance function is turned on, but the vacuum contactor is in the open state, and the arc suppression coil is normally put into operation. If a grounding fault occurs in the distribution network, the fault characteristic 3U0 exceeds the set value. If the grounding fault is a transient grounding fault, the vacuum contactor remains in the open state and only works for arc suppression. After the fault point restores insulation, the power grid returns to normal. If the grounding fault is a permanent grounding fault, the vacuum contactor automatically closes after a set time, amplifies the system zero sequence current, and enables the zero sequence overcurrent protection of the distribution network switch from the station switch to the fault point to start smoothly. Through reasonable setting of the value and time, the zero sequence overcurrent protection of each level of switch selectively trips the isolation point or sends an alarm signal, and determines the grounding fault wire segment. After the grounding disappears and the fault characteristic 3U0 is lower than the set value, the vacuum contactor automatically returns to the open state. If the distribution network switch of the grounding line does not trip, and the zero sequence overcurrent protection of the substation outlet switch also does not trip, the low resistance vacuum contactor automatically opens after a set delay, which is used for low resistance heat dissipation, and automatically closes after the heat dissipation is completed. If a bus permanent grounding or other grounding fault cannot be isolated by the outlet and distribution network switch zero sequence overcurrent protection, the low resistance controller exits the low resistance after a set maximum number of single fault switching, which is used to protect the equipment. Twin The low resistance controller is internally provided with an open window time for allowing low resistance switching Tsr , for preventing low resistance from being frequently switched when permanent grounding occurs, and when the fault characteristic quantity 3U0 exceeds the open window time, the low resistance vacuum contactor is locked for closing, and the specific calculation method is: wherein, n is the number of reclosing times; ​ is the low resistance heat dissipation lockout time; T is the low resistance delay opening time or low resistance reclosing holding time.

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