Multi-fault single-phase grounding identification, loop closing operation and load transfer method and system considering distributed power supply

Abstract

The invention discloses a multi-fault single-phase grounding identification, loop closing operation and load transfer method and system considering a distributed power supply, and the method comprises the following steps: eliminating the interference of resonance and the fusing of a high-voltage side of a voltage transformer according to a voltage amplitude and a real-time fluctuation condition under the condition of considering multiple faults of a power distribution system; identifying whether the power distribution system is in a single-phase earth fault state; calculating equilibrium power flow after loop closing according to the equivalent circuit before loop closing operation of the power distribution system with the single-phase earth fault; according to the power distribution system, a neutral point is grounded through an arc suppression coil, and the current increment margin of a grounding fault is determined according to the capacitive current of an inductive current part or all compensation line flowing through the arc suppression coil when a single-phase grounding fault occurs; calculating the sum of the current of each line after loop closing according to the equilibrium power flow and the earth fault current increment margin; calculating an impact current generated at the moment of loop closing during loop closing operation of the power distribution network; if the sum of the currents of all the circuits after loop closing does not exceed the circuit current limiting value and the effective value of the impact current is smaller than the quick-break protection constant value of the corresponding circuit, the loop closing condition is met, and loop closing operation is allowed; and if the sum of the current of each line after loop closing exceeds the current limiting value of the line, or the effective value of the impact current is not smaller than the quick-break protection constant value of the corresponding line, the loop closing condition is not met, and power failure operation under the scene of considering the distributed power supply is adopted. The method can accurately identify the single-phase earth fault of the power distribution network, is used for mode adjustment and fault processing of the power distribution network with the single-phase earth fault, and can improve the accuracy of loop closing verification under the earth fault condition and the safety of power failure load transfer under the participation of a distributed power supply.

Description

Technical Field

[0001] This invention relates to the field of distribution network maintenance, and in particular to a method and system for identifying single-phase grounding, loop closing operation, and load transfer under multiple faults of distributed generation. Background Technology

[0002] Power distribution systems typically employ closed-loop wiring and open-loop operation. Closed-loop power dispatching is not only crucial for improving power supply reliability but also an important tool for dispatchers in handling power distribution system faults.

[0003] Currently, most 10kV distribution systems adopt a neutral point non-direct grounding method, meaning the neutral point is either ungrounded or grounded via an arc suppression coil. Under this grounding method, the system can continue operating without disconnecting the faulty line when a single-phase ground fault occurs, improving power supply reliability. Single-phase ground faults are among the most frequent faults in distribution systems. When handling single-phase ground faults, dispatchers need to perform loop-locking operations based on the distribution system's operating mode, disconnecting the grounded bus or transferring loads to uninterrupted branch lines of the grounded line. This ensures reliable power supply while narrowing the fault area, quickly identifying the faulty line and section, and restoring normal operation to the non-faulty sections.

[0004] However, in distribution systems where the neutral point is not directly grounded, open circuits, blown high-voltage fuses in voltage transformers, and ferroresonance can all cause zero-sequence voltage rises and abnormal phase voltages, leading to false single-phase grounding signals and making single-phase grounding fault identification difficult. For distribution networks operating under single-phase grounding faults, the loop current and the single-phase grounding fault current affect system stability and the safety of loop-closing operations. For example, looping between different main transformers via distribution lines creates a loop current flow; excessive loop current can cause overload of related equipment or even tripping of protection devices. In the case of a single-phase grounding fault, the unbalanced current in the distribution lines also increases the danger of loop-closing power regulation operations. Especially in special operating modes, such as when distribution lines transfer power to the busbar and its outgoing lines via tie switches, a single-phase grounding fault requires multiple tie switches on different distribution lines to loop-close the grounded busbar, making the operation and related electrical quantity changes more complex. This makes it difficult for control personnel to confirm the safety of the corresponding loop-closing power regulation operations during fault handling, hindering timely and correct responses. In addition, if the traditional power outage transfer method is used under a single-phase grounding fault, the access of distributed power sources also poses a challenge to the safety of the operation. Dispatchers urgently need the support of new methods and systems to properly handle the transfer operation under a single-phase grounding fault.

[0005] According to the superposition principle, the power flow after the distribution line is closed in a loop consists of the original power flow of each line before the loop closure and the balanced power flow caused by the voltage difference across the loop closure switch. The original power flow of each line before the loop closure is determined by the line load, and the balanced power flow caused by the loop closure operation can be calculated using Thevenin's equivalent principle.

[0006]

[0007] ΔU and The voltage difference on both sides of the loop closure point The real and imaginary parts. Equilibrium current. It can be represented as:

[0008]

[0009] Because the reactance of lines and transformers in a power distribution system is relatively large and the resistance is relatively small, the above formula can be simplified to:

[0010]

[0011] Chinese patent 201210257852X proposes a method for controlling the closed-loop operation of a distribution network based on the measurement and verification of the voltage magnitude and phase angle difference on both sides of the closed-loop point. This method verifies whether the distribution network meets the closed-loop conditions by checking the voltage amplitude and phase angle and their changes on both sides of the closed-loop point. However, it does not address the verification of current and other electrical quantities caused by the closed-loop, and therefore cannot guarantee that changes in current and other electrical quantities during and after the closed-loop process meet the requirements of equipment capacity and system stability.

[0012] Chinese patent 2011103528519 proposes a distribution network loop closing method based on synchronous phasor measurement and loop power flow calculation. However, this method only considers the normal operation of the system and does not involve the impact of single-phase grounding of the distribution network, so it cannot guarantee the accuracy of the verification under the condition of single-phase grounding of the distribution network. Summary of the Invention

[0013] The main objective of this invention is to propose a method for identifying single-phase grounding faults, performing loop closing operations, and transferring loads under multiple faults of distributed power sources, which can accurately identify single-phase grounding faults, meet equipment capacity and system stability requirements, improve the accuracy of loop closing verification and the safety of power outage transfer in the case of single-phase grounding in the distribution network, and meet the requirements of equipment capacity and system stability.

[0014] The technical solution adopted in this invention is:

[0015] This invention provides a method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources, including the following steps:

[0016] Based on the voltage amplitude and real-time fluctuations, eliminate interference from resonance and high-voltage side fuses of voltage transformers, and identify whether the power distribution system is in a single-phase grounding fault state.

[0017] Calculate the balanced power flow after loop closure based on the equivalent circuit of the power distribution system before loop closure operation in the event of a single-phase ground fault.

[0018] The power distribution system adopts a neutral point grounded through an arc suppression coil. The ground fault current increment margin is determined based on the inductive current flowing through the arc suppression coil during a single-phase ground fault, which partially or completely compensates for the capacitive current of the line.

[0019] The sum of the currents of each line after loop closure is calculated based on the balanced power flow and the margin of the ground fault current increment.

[0020] Calculate the inrush current that will be generated at the moment of loop closure during the operation of the distribution network;

[0021] If the sum of the currents of all lines after the loop is closed does not exceed the line current limit value, and the effective value of the inrush current is less than the corresponding line instantaneous overcurrent protection setting value, then the loop closing condition is met, and the loop closing operation is allowed.

[0022] Following the above technical solution, the ground fault current increment margin is less than or equal to 10A.

[0023] According to the above technical solution, if the conditions for loop closure are not met, loop closure operation is not allowed.

[0024] Following the above technical solution, when loop-closing operations are not permitted, a power outage transfer operation considering distributed power supply scenarios is adopted.

[0025] Following the above technical solution, the voltage difference across the switch before loop closure is used as the equivalent power source of the Thevenin equivalent circuit, and the Thevenin equivalent impedance after loop closure is calculated. The balanced power flow after loop closure is calculated based on the equivalent power source and the Thevenin equivalent impedance.

[0026] Following the above technical solution, the voltage across the switch before loop closure is obtained through the distribution automation SCADA system, the distribution automation system telemetry device, or through the power flow calculation results before loop closure.

[0027] Following the above technical solution, the Thevenin equivalent impedance of the closed loop is the sum of the equivalent impedances of each line and the corresponding transformer in the entire closed loop circuit.

[0028] Following the above technical solution, the voltage after loop closure is considered to be 0.

[0029] This invention also provides a system for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources, comprising:

[0030] The multi-fault identification module is used to eliminate interference from resonance and high-voltage side fuse of voltage transformer under multiple faults, and to identify whether the power distribution system is in a single-phase ground fault state.

[0031] The balanced power flow calculation module is used to calculate the balanced power flow after the loop is closed based on the equivalent circuit of the power distribution system before the loop closure operation when a single-phase ground fault occurs.

[0032] The current increment margin determination module is used to determine the ground fault current increment margin when the power distribution system adopts neutral point grounding through arc suppression coil, based on the inductive current flowing through the arc suppression coil during a single-phase ground fault, which partially or completely compensates for the capacitive current of the line.

[0033] The loop current calculation module is used to calculate the sum of the currents of each line after loop closure based on the balanced power flow and the margin of the ground fault current increment.

[0034] The loop-closing inrush current calculation module calculates the inrush current that will be generated at the moment of loop closure during the operation of the distribution network.

[0035] The loop closure judgment module is used to determine if the sum of the currents of each line after loop closure does not exceed the line current limit value, and the effective value of the inrush current is less than the corresponding line instantaneous overcurrent protection setting value, then the loop closure condition is met and the loop closure operation is allowed.

[0036] A load transfer module for power outages considering distributed power sources is used to safely transfer loads during power outages if the loop closure condition is not met, while considering the connection of distributed power sources.

[0037] Following the above technical solution, the loop closure judgment module is also used to disallow loop closure operations if the loop closure conditions are not met.

[0038] Following the above technical solution, the ground fault current increment margin is less than or equal to 10A.

[0039] The beneficial effects of this invention are as follows: For distribution systems with neutral points grounded via arc suppression coils, this invention can accurately identify whether the system is in a single-phase ground fault state; based on the calculation of the balanced power flow, it determines the ground fault current increment margin by considering the influence of the ground fault current, and calculates the sum of the currents of each line after loop closure based on the balanced power flow and the ground fault current increment margin; simultaneously, it verifies the inrush current after loop closure, and determines whether the loop closure conditions are met by judging the sum of the loop currents and the inrush current, thereby improving the accuracy of loop closure verification under ground fault conditions; if the loop closure conditions are not met, it provides a method for power outage load transfer operation considering distributed power source access, thereby improving the safety of power outage transfer under distributed power source access; this method can be applied to the mode adjustment and fault handling of distribution networks with single-phase ground faults.

[0040] Furthermore, the process of calculating the equalization current is simplified by using Thevenin's equivalence principle.

[0041] Furthermore, for power distribution systems that use a neutral point grounded through an arc suppression coil, when a single-phase ground fault occurs, the inductive current flowing through the arc suppression coil partially or completely compensates for the capacitive current of the line, controlling the ground fault current below 10A, thereby improving the accuracy of loop closing verification under ground fault conditions.

[0042] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart of a method for identifying single-phase grounding, loop closing operation, and load transfer under multiple faults of distributed power sources, according to an embodiment of the present invention.

[0045] Figure 2 This is a flowchart of another embodiment of the present invention considering a single-phase grounding identification, loop closing operation and load transfer method under multiple faults of distributed power sources;

[0046] Figure 3 This is a flowchart of the single-phase grounding fault identification method under multiple faults according to an embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of a 220kV system operating in a ring network according to the present invention;

[0048] Figure 5 This is a flowchart of a power outage transfer method considering distributed power source access under the condition of loop closure in an embodiment of the present invention;

[0049] Figure 6 This is a schematic diagram of the system structure of single-phase grounding identification, loop closing operation and load transfer under multiple faults of distributed power sources in an embodiment of the present invention;

[0050] Figure 7 This is a schematic diagram of a system structure for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources, according to another embodiment of the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0052] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0053] In this invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0054] This invention primarily addresses single-phase grounding fault identification, loop-closing operation, and load transfer methods and systems for distribution networks with non-directly grounded neutral points under multiple fault conditions. This method not only considers the requirements for single-phase grounding fault identification under multiple fault conditions and the current changes in the loop-closing distribution system caused by the balanced power flow, but also takes into account the impact of the grounding fault current. Based on the load and power flow distribution of the distribution system before loop-closing operation under a grounding fault, the balanced power flow after loop-closing is calculated using the superposition principle and Thevenin's theorem. Based on the balanced power flow calculation results, the impact of the grounding fault current is considered through the distribution network grounding fault current increment margin. Combining the load conditions of each distribution network branch before loop-closing, the load current of each line after loop-closing is verified. If the load of each line after loop-closing does not exceed its current limit value, the grounded distribution network meets the loop-closing operation conditions; if the load of any related line exceeds its current limit value after loop-closing, the grounded distribution network does not meet the loop-closing operation conditions.

[0055] Example 1

[0056] like Figure 1 As shown, the method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources in this embodiment mainly includes the following steps:

[0057] S1. Identify whether the power distribution system is in a single-phase ground fault state;

[0058] S2. Calculate the balanced power flow after loop closure based on the equivalent circuit of the power distribution system before the loop closure operation in the event of a single-phase ground fault.

[0059] S3. The power distribution system adopts a neutral point grounded through an arc suppression coil. The ground fault current increment margin is determined based on the inductive current flowing through the arc suppression coil during a single-phase ground fault, which partially or completely compensates for the capacitive current of the line.

[0060] S4. Calculate the sum of the currents of each line after loop closure based on the balanced power flow and the margin of the ground fault current increment.

[0061] S5. Calculate the inrush current that will be generated at the moment of closing the loop during the operation of the distribution network;

[0062] S6. If the sum of the currents of each line after the loop is closed does not exceed the line current limit value, and the effective value of the inrush current is less than the corresponding line instantaneous overcurrent protection setting value, then the loop closing condition is met and the loop closing operation is allowed.

[0063] S7. If the loop closure condition is not met, adopt the power outage transfer operation that considers the access of distributed power sources.

[0064] For power distribution systems with neutral point grounded via an arc suppression coil, when a single-phase ground fault occurs, the inductive current flowing through the arc suppression coil partially or completely compensates for the capacitive current of the line, thus controlling the ground fault current below 10A. Therefore, in power distribution systems with neutral point grounded via an arc suppression coil, a ground fault current increment margin ΔI is set. FG ≤10A.

[0065] Furthermore, if the conditions for closing the loop are not met, the loop closing operation is not allowed.

[0066] When loop closing is not permitted, a load transfer operation that considers distributed generation and disconnection is used to restore the non-faulty section.

[0067] In step S1, the amplitude of the three-phase voltage of the power distribution system bus is obtained and the fluctuation is checked. If the phase voltage rises but does not exceed the line voltage, the possibility of high-frequency resonance fault is ruled out.

[0068] If the voltage drop is not in one phase but is approximately equal to the phase voltage in the other two phases, then the possibility of a blown fuse in the voltage transformer can be ruled out.

[0069] If both of the above fault possibilities can be ruled out, it can be determined that a single-phase grounding fault has occurred in the power distribution system.

[0070] In step S2, the voltage difference across the switch before loop closure is used as the equivalent power source of the Thevenin equivalent circuit, and the Thevenin equivalent impedance after loop closure is calculated. The balanced power flow after loop closure is calculated based on the equivalent power source and the Thevenin equivalent impedance.

[0071] The voltage across the switch before loop closure is obtained through the SCADA system of power distribution automation, the telemetry device of the power distribution automation system, or the power flow calculation results before the loop closure operation.

[0072] The Thevenin equivalent impedance of the closed loop is the sum of the equivalent impedances of all lines and corresponding transformers in the entire closed loop. The voltage after the loop is closed can be considered as 0.

[0073] This invention considers the impact of ground fault current on the relevant line currents after the distribution network is closed-loop while calculating the loop balancing current. For distribution networks with single-phase ground faults, this verification method has higher accuracy and reliability. For distribution networks with single-phase ground faults, a reasonable "ground fault current increment margin" is determined based on the compensation capability of the arc suppression coil. The "ground fault current increment margin" is used to represent the impact of the ground fault current on the relevant line currents after the distribution network is closed-loop, so that the impact of the ground fault current can be quantitatively reflected in the verification and calculation of the closed-loop operation.

[0074] Example 2

[0075] like Figure 2 As shown, the process for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources in this embodiment specifically includes the following steps:

[0076] (1) Single-phase grounding fault identification: The process for identifying multiple faults in a power distribution system is as follows: Figure 3 As shown, the core is to eliminate interference from resonance and high-voltage side fuses of voltage transformers based on voltage amplitude and real-time fluctuations, so as to accurately identify whether the power distribution system is in a single-phase ground fault state.

[0077] (2) Obtaining the closing point voltage: It can be obtained through the distribution automation SCADA system, the distribution automation system telemetry device, or through the power flow calculation results before the closing operation.

[0078] (3) Calculation of equivalent resistance of closed loop: The equivalent resistance of closed loop is the Thevenin equivalent impedance Z Σ =R Σ +jX Σ The sum of the equivalent impedances of all lines and corresponding transformers in the entire closed loop. For a regional power grid with a typical 220kV system operating in a ring network and a 110kV (or 35kV) system radiating power to the 10kV system, the 220kV system operating in a ring network is considered as an infinite system, and the equivalent resistance Z of the closed loop is... Σ The package is the sum of the equivalent impedances of the 110kV (35kV), 220kV transformers, 110kV (35kV) lines, and 10kV lines in the closed loop.

[0079] If the 220kV system operating in a ring network is considered as an infinitely large system, such as Figure 3 The equivalent impedance of the closed loop of the 220-110-10 transformer system shown is:

[0080] Z Σ =Z T(220) +Z L(110) +Z T(110) +Z L(10) Among them, Z T(220) Z is the equivalent impedance of a 220 kV main transformer. L(110) Z is the equivalent impedance of a 110 kV line. T(110) Z is the equivalent impedance of a 110 kV main transformer. L(10) This is the equivalent impedance of a 10 kV line.

[0081] (4) Calculate the loop equalization power flow: Use the voltage difference across the switch before loop closure as the equivalent power supply of the Thevenin equivalent circuit. Let be the voltage across the closing switch before closing the loop. If the voltages at the closing switch for loop branches i and j are respectively... The voltage difference is

[0082]

[0083] According to Thevenin's equivalence principle, the equilibrium current during loop closure is:

[0084]

[0085] For a regional power grid with a typical transmission and distribution structure, the Thevenin equivalent impedance Z of a 220kV system looped through a 10kV line is... Σ =R Σ +jX Σ Generally, the parameters of each component must satisfy R. Σ < <X Σ Therefore, the equalization current during loop closure can be simplified to:

[0086]

[0087] This only considers the voltage before the loop is closed; the voltage difference after the loop is closed is 0.

[0088] (5) Determining the ground fault current increment margin: For a distribution system with a neutral point grounded through an arc suppression coil, when a single-phase ground fault occurs, the inductive current flowing through the arc suppression coil partially or completely compensates for the capacitive current of the line, controlling the ground fault current below 10A. Therefore, for a distribution system with a neutral point grounded through an arc suppression coil, the ground fault current increment margin ΔI is... FG =10A.

[0089] (6) Verification of the inrush current during loop closure: During the loop closure operation of the distribution network, a large inrush current will be generated instantaneously due to the presence of inductive components in the system. If the initial phase angle of the Thevenin equivalent electromotive force E at the instant of loop closure is α, and the power factor angle arctan(X / R) of the loop impedance is... Taking phase A as an example, the steady-state closed-loop current value i CL The expression is Since the magnetic flux linkage does not change abruptly at the moment the loop closes, the expression for the resultant current is:

[0090]

[0091] Excluding the steady-state circulation periodic component The closed-loop inrush current also includes an exponentially decaying aperiodic component. In the most severe case, the maximum instantaneous and effective values ​​of the inrush current are as follows:

[0092]

[0093] In the formula, T a The decay time constant of the non-periodic component, L and R are the equivalent inductance and resistance of the equivalent circuit at the loop closing point, respectively. For the loop closing operation of a 220kV system through a 10kV distribution line, T a X can be obtained through the Thevenin equivalent circuit Σ and R Σ Approximately obtained.

[0094] T a =R Σ / X Σ , where R Σ For Z Σ Real part, for Z Σ Imaginary part, Z Σ This is the equivalent impedance of the closed loop. m The magnitude of the steady-state closed-loop equilibrium current can be obtained from the following formula using the closed-loop steady-state current I. CL Find:

[0095]

[0096] During the loop-closing operation of a distribution network, a large inrush current is generated. If the instantaneous inrush current is too large and exceeds the instantaneous overcurrent protection setting of the line, it will cause the relevant distribution line to trip. Therefore, verifying the inrush current at the moment of loop closure ensures that the effective value of the inrush current is less than the instantaneous overcurrent protection setting of the corresponding line, so as not to cause the instantaneous overcurrent protection of the closed distribution line to trip. The inrush current at the moment of loop closure then meets the loop closure condition.

[0097] (7) Verify the current of each line after loop closure: Due to the existence of the ground fault current, it is impossible to accurately calculate the accurate value of the current after loop closure under ground fault conditions through prior verification. However, since the ground fault current is ΔI FG Generally, the current is no more than 10A. Therefore, the feasibility of the current after closing the loop can be verified by the current before closing the loop, the equalization current after closing the loop, and the fault current margin.

[0098] For distribution lines i and j that are closed in a loop, if their load currents before the loop closure are respectively The currents in lines i and j after loop closure can be verified using the superposition principle, as well as the steady-state currents in lines i and j after loop closure. satisfy

[0099]

[0100] If the calculation yields If none of them exceed the current limit of the line, then the steady-state current of the line after loop closure satisfies the loop closure condition.

[0101] If the steady-state current and the instantaneous impact current after loop closure both meet the corresponding loop closure conditions, then the loop closure operation verification result for the ground fault distribution network is that the loop closure conditions are met, and the loop closure operation can be performed.

[0102] (8) Power outage transfer operation with distributed power source participation: If either the steady-state current after loop closure or the instantaneous impact current after loop closure does not meet the corresponding loop closure conditions, the loop closure operation verification result for the distribution network with ground fault is that the loop closure conditions are not met. The loop closure operation may cause the relevant line current to exceed the limit or even the protection to trip. The loop closure operation is not allowed. In this case, the load can be transferred by power outage.

[0103] For distribution network lines without distributed generation, if the loop-closing conditions are not met, power can be cut off and supplied to non-faulty sections and isolated grounded sections by directly remotely opening the sectionalizing switches and closing the tie switches. However, for distribution network lines containing distributed generation, because they constitute a multi-side power supply structure, the distributed generation must be disconnected before power outage and connected in parallel after power restoration, such as... Figure 4 As shown.

[0104] As can be seen, this invention provides a scheme for verifying the safety and feasibility of loop-closing operations during a single-phase ground fault in a power distribution system with a neutral point grounded via an arc suppression coil. While accurately identifying the single-phase ground fault and calculating the loop-closing equalization current, it also considers the response of the ground fault current to the relevant line currents after the loop-closing operation. For power distribution networks with single-phase ground faults, this verification method offers higher accuracy and reliability; furthermore, it enables safe load transfer during power outages when the loop-closing conditions are not met under distributed power source integration.

[0105] Example 3

[0106] like Figure 6 As shown, the single-phase ground fault identification, loop closing operation, and load transfer system under multiple faults of distributed power sources in this embodiment includes:

[0107] The multi-fault identification module is used to eliminate interference from resonance and high-voltage side fuse of voltage transformer under multiple faults, and to identify whether the power distribution system is in a single-phase ground fault state.

[0108] The balanced power flow calculation module is used to calculate the balanced power flow after the loop is closed based on the equivalent circuit of the power distribution system before the loop closure operation when a single-phase ground fault occurs.

[0109] The current increment margin determination module is used to determine the ground fault current increment margin when the power distribution system adopts neutral point grounding through arc suppression coil, based on the inductive current flowing through the arc suppression coil during a single-phase ground fault, which partially or completely compensates for the capacitive current of the line.

[0110] The loop current calculation module is used to calculate the sum of the currents of each line after loop closure based on the balanced power flow and the margin of the ground fault current increment.

[0111] The loop-closing inrush current calculation module calculates the inrush current that will be generated at the moment of loop closure during the operation of the distribution network.

[0112] The loop closure judgment module is used to determine if the sum of the currents of each line after loop closure does not exceed the line current limit value, and the effective value of the inrush current is less than the corresponding line instantaneous overcurrent protection setting value, then the loop closure condition is met and the loop closure operation is allowed.

[0113] The loop closure judgment module is also used to disallow loop closure operations if the loop closure conditions are not met.

[0114] Furthermore, such as Figure 7 As shown, the single-phase grounding fault identification, loop closing operation and load transfer system under multiple faults also includes a power outage transfer module with distributed power source participation, which is used to perform power outage transfer considering the participation of distributed power source when loop closing operation is not allowed.

[0115] Furthermore, for power distribution systems that use a neutral point grounded through an arc suppression coil, when a single-phase ground fault occurs, the inductive current flowing through the arc suppression coil partially or completely compensates for the capacitive current of the line, controlling the ground fault current below 10A, thereby improving the accuracy of loop closing verification under ground fault conditions.

[0116] Each module is mainly used to implement the various steps of the above method embodiments, which will not be described in detail again.

[0117] In summary, this system for identifying, closing, and transferring single-phase ground faults under multiple fault conditions is designed for distribution systems with a neutral point grounded via an arc suppression coil. Based on accurate identification of the single-phase ground fault state, it calculates the balanced power flow after closing the loop. By considering the influence of the ground fault current, it determines the ground fault current increment margin. Based on the balanced power flow and the ground fault current increment margin, it calculates the sum of the currents in each line after closing the loop. Simultaneously, it verifies the inrush current after closing the loop. By judging the sum of the closed loop currents and the inrush current, it determines whether the closing conditions are met, thereby improving the accuracy of the closing verification under ground fault conditions. This method can be applied to the mode adjustment and fault handling of distribution networks with single-phase ground faults.

[0118] Furthermore, the process of calculating the equalization current is simplified by using Thevenin's equivalence principle.

[0119] Furthermore, when the conditions for loop closure are not met and loop closure is not permitted, power outages and power transfers from distributed power sources should be considered to ensure operational safety.

[0120] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0121] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0122] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method and system for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources, characterized in that, Includes the following steps: Based on the voltage amplitude and real-time fluctuations, eliminate interference from resonance and high-voltage side fuses of voltage transformers, and identify whether the power distribution system is in a single-phase grounding fault state. Calculate the balanced power flow after loop closure based on the equivalent circuit of the power distribution system before loop closure operation in the event of a single-phase ground fault. The power distribution system adopts a neutral point grounded through an arc suppression coil. The ground fault current increment margin is determined based on the inductive current flowing through the arc suppression coil during a single-phase ground fault, which partially or completely compensates for the capacitive current of the line. The sum of the currents of each line after loop closure is calculated based on the balanced power flow and the margin of the ground fault current increment. Calculate the inrush current that will be generated at the moment of loop closure during the operation of the distribution network; If the sum of the currents of all lines after the loop is closed does not exceed the line current limit value, and the effective value of the inrush current is less than the corresponding line instantaneous overcurrent protection setting value, then the loop closing condition is met and the loop closing operation is allowed. If the sum of the currents of all lines after the loop is closed exceeds the line current limit, or the effective value of the inrush current is not less than the corresponding line instantaneous overcurrent protection setting, then the loop closure condition is not met, and a power outage operation considering the distributed power source scenario is adopted.

2. The method for identifying, closing looping, and transferring loads under multiple faults of distributed power sources according to claim 1 is characterized in that if the two-phase voltage of the power distribution system bus does not exceed the line voltage and is not approximately equal to the phase voltage, it is judged as a single-phase ground fault.

3. The method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources as described in claim 1, characterized in that, The ground fault current increment margin is less than or equal to 10A.

4. The method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources as described in claim 1, characterized in that, If the conditions for closing the loop are not met, the loop closing operation is not allowed.

5. The method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources as described in claim 4, characterized in that, When loop closing is not permitted, the loop closing operation should be re-verified by adjusting the voltage or load of the relevant lines in the distribution network.

6. The method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources as described in claim 1, characterized in that, The voltage difference across the switch before loop closure is used as the equivalent power source of the Thevenin equivalent circuit, and the Thevenin equivalent impedance after loop closure is calculated. The balanced power flow after loop closure is calculated based on the equivalent power source and the Thevenin equivalent impedance.

7. The method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources as described in claim 6, characterized in that, The voltage across the switch before loop closure is obtained through the SCADA system of power distribution automation, the telemetry device of the power distribution automation system, or the power flow calculation results before the loop closure operation.

8. The method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources as described in claim 6, characterized in that, The Thevenin equivalent impedance of the closed loop is the sum of the equivalent impedances of all lines and corresponding transformers in the entire closed loop.

9. The method for single-phase grounding identification, loop closing operation, and load transfer under multiple faults of distributed power sources as described in claim 1, characterized in that, The voltage after the loop is closed is considered to be 0.

10. A system for single-phase ground fault identification, loop closing operation, and load transfer under multiple faults of distributed power sources, characterized in that, include: The multi-fault identification module is used to eliminate interference from resonance and high-voltage side fuse of voltage transformer under multiple faults, and to identify whether the power distribution system is in a single-phase ground fault state. The balanced power flow calculation module is used to calculate the balanced power flow after the loop is closed based on the equivalent circuit of the power distribution system before the loop closure operation when a single-phase ground fault occurs. The current increment margin determination module is used to determine the ground fault current increment margin when the power distribution system adopts neutral point grounding through arc suppression coil, based on the inductive current flowing through the arc suppression coil during a single-phase ground fault, which partially or completely compensates for the capacitive current of the line. The loop current calculation module is used to calculate the sum of the currents of each line after loop closure based on the balanced power flow and the margin of the ground fault current increment. The loop-closing inrush current calculation module calculates the inrush current that will be generated at the moment of loop closure during the operation of the distribution network. The loop closing judgment module is used to determine if the sum of the currents of each line after loop closing does not exceed the line current limit value, and the effective value of the inrush current is less than the corresponding line instantaneous overcurrent protection setting value, then the loop closing condition is met and the loop closing operation is allowed. A load transfer module for power outages considering distributed power sources is used to safely transfer loads during power outages if the loop closure condition is not met, while considering the connection of distributed power sources.

Images