High-resistance grounding fault inverse time limit protection method and system based on dynamic constant value

Abstract

The invention discloses a high-resistance grounding fault inverse time limit protection method and system based on a dynamic constant value, and the method comprises the steps: collecting three-phase current and voltage signals at a protection installation part, and calculating a triple zero-sequence current fundamental wave effective value at the protection installation part as a starting judgment parameter; when the line has a grounding fault and the starting judgment parameter is greater than the starting protection threshold value, starting protection; detecting the phase voltage, the phase current and the zero sequence current of the fault phase at the protection installation position, calculating a high-resistance fault judgment coefficient, and if the calculated value is 1, continuing to start protection judgment; otherwise, designing a dynamic current starting constant value and a dynamic time constant based on the high-resistance fault judgment coefficient, substituting the dynamic current starting constant value and the dynamic time constant into an inverse time limit formula, calculating zero-sequence inverse time limit protection calculation time, and calculating total action time of zero-sequence inverse time limit protection by combining zero-sequence inverse time limit matching time and zero-sequence inverse time limit minimum time; and after the total action time, the inverse-time zero-sequence overcurrent protection action of the line is used for removing the fault. The method is simple in calculation and easy for engineering implementation.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and more specifically, relates to a method and system for high-resistance grounding fault inverse-time protection based on dynamic setting. Background Technology

[0002] The distribution network is the core link connecting end users in the power system, and its operational reliability directly affects the power supply quality and electricity safety of the end users. In the actual operation of the distribution network, high-resistance grounding faults (such as faults grounded through soil, vegetation, insulating media, etc.) are a typical type of fault that is difficult to handle. The fault current amplitude of this type of fault is usually small and the electrical characteristics are relatively hidden. Traditional zero-sequence overcurrent protection is prone to problems such as delayed operation and failure to operate due to fixed settings. This not only delays the fault isolation process but may also lead to the expansion of the fault range, threatening the safe and stable operation of the distribution network.

[0003] Chinese patent application CN119575061A discloses a method and device for detecting high-resistance grounding faults in distribution networks. It improves detection efficiency by acquiring residual current, residual voltage, and the V2 / V1 ratio, and performing fault detection based on preset rules. However, it still has the following shortcomings: its detection rules rely on fixed thresholds or trend judgments of multiple electrical quantities (residual current, residual voltage, and V2 / V1 ratio). These thresholds need to be preset through laboratory testing or simulation, resulting in poor adaptability to different power grid structures, operating modes, or fault conditions. Furthermore, this method does not involve the optimization of protection actions and cannot dynamically adjust protection settings according to fault impedance, which may lead to delayed or failed protection actions during high-resistance grounding faults, affecting rapid fault isolation and system recovery. Chinese patent application CN114895141A discloses a method for identifying and locating high-resistance grounding faults based on composite factors. This method identifies faulty feeders and locates faulty sections by calculating the composite factors of each feeder and the fault location index at each node. However, it still has the following shortcomings: the method relies on complex operations of zero-sequence voltage and zero-sequence current (such as composite factor calculation), which is computationally complex and requires high measurement accuracy. In high-resistance faults, the zero-sequence current amplitude is small and easily affected by interference, potentially leading to identification errors. Furthermore, this method mainly focuses on fault identification and location, without addressing the optimization of protection action logic, and cannot solve the problem of delayed or failed operation of traditional zero-sequence overcurrent protection under high-resistance faults.

[0004] In summary, existing technologies are insufficient to balance the sensitivity, speed, and adaptability of protection in high-resistance grounding fault scenarios. There is an urgent need for a high-resistance grounding fault protection scheme that can adaptively adjust protection parameters, is simple to calculate, and is easy to implement in engineering. Summary of the Invention

[0005] To address the shortcomings of existing technologies, particularly the problems of poor adaptability due to fixed thresholds, complex calculations relying on multiple signals, and delayed or failed action due to the lack of integrated protection action optimization in existing high-resistance grounding fault detection methods, this invention provides a high-resistance grounding fault discrimination and protection scheme that can adaptively adjust protection settings and act quickly. Specifically, it includes a high-resistance grounding fault inverse-time protection method and system based on dynamic settings.

[0006] The present invention adopts the following technical solution.

[0007] In a first aspect, the present invention discloses a high-resistance grounding fault inverse-time protection method based on dynamic setpoints, the method comprising the following steps: Step 1: Real-time acquisition of three-phase current and three-phase voltage signals at the protection installation point, i.e., the beginning of the line, and calculation of the effective value of the fundamental wave of the zero-sequence current at the protection installation point as the start-up judgment parameter; Step 2: When a ground fault occurs on the line and the start-up judgment parameter is greater than the start-up protection threshold, the protection is activated; Step 3: Detect the phase voltage, phase current, and zero-sequence current of the faulty phase at the protection installation point. Combine this with the positive sequence impedance of the line to calculate the high-resistance fault discrimination coefficient. If the high-resistance fault discrimination coefficient is 1, it indicates that a metallic fault has occurred, and return to step 2; otherwise, proceed to step 4. Step 4: Based on the high-resistance fault discrimination coefficient, design an adaptive dynamic current start-up setting and a dynamic time constant, and substitute them into the inverse-time formula. Calculate the zero-sequence inverse-time protection calculation time corresponding to the zero-sequence current measured at the protection installation location at this time. Combine the preset zero-sequence inverse-time coordination time and the preset zero-sequence inverse-time minimum time to calculate the total operating time of the zero-sequence inverse-time protection. After the total operating time, the line inverse-time zero-sequence overcurrent protection of this line will operate to clear the fault.

[0008] More preferably, The activation protection threshold is set to avoid the maximum unbalanced zero-sequence current during normal line operation, specifically:

[0009] in, To activate the protection threshold; The reliability coefficient is given, and it satisfies the following conditions: ; This represents the maximum unbalanced zero-sequence current during normal operation of the line.

[0010] More preferably, The high-resistance fault discrimination coefficient is determined as follows:

[0011] in, Let be the high-resistance fault discrimination coefficient, and satisfy . ; To protect the voltage drop of the line from the installation point to the fault point; To protect the phase voltage of the faulty phase measured at the installation location; To protect the phase voltage of the faulty phase measured at the installation location with vector The included angle, For vectors voltage of the fault phase at the fault point The included angle, The positive sequence impedance angle per unit length of the line; The vector ,in, To protect the phase current of the faulty phase measured at the installation location, To protect the zero-sequence current measured at the installation location, It is a zero-order compensation coefficient, and satisfies , These are the positive-sequence impedance and zero-sequence impedance per unit length of the transmission line, respectively.

[0012] More preferably, The fault phase voltage at the fault point Its phase angle is equal to the phase angle of the zero-sequence current measured at the protection installation point.

[0013] More preferably, The dynamic current starting setpoint changes with the high-resistance fault discrimination coefficient c. When the high-resistance fault discrimination coefficient decreases, the dynamic current starting setpoint decreases to ensure reliable start of the line inverse-time zero-sequence overcurrent protection. When the high-resistance fault discrimination coefficient increases, the dynamic current starting setpoint gradually increases and eventually equals the original current starting setpoint to avoid false tripping. The dynamic current start-up setting value is determined in the following manner:

[0014] in, The dynamic current start-up setting value is set. Set the initial current starting value; The starting current lower limit coefficient determines the minimum percentage that the starting current setting can be reduced to; The adjustment range is controlled by the current adjustment amplitude. The shape coefficient controls the hyperbolic tangent function. The steepness; This is the high-resistance fault discrimination coefficient.

[0015] More preferably, The dynamic time constant changes with the high-resistance fault discrimination coefficient c. When the high-resistance fault discrimination coefficient decreases, the dynamic time constant decreases, accelerating the protection action. When the high-resistance fault discrimination coefficient increases, the dynamic time constant gradually increases and eventually equals the original time constant. The dynamic time constant is determined as follows:

[0016] in, The dynamic time constant, The original time constant; It is the lower limit coefficient of the time constant, which determines the minimum proportion to which the time constant can be shortened; Adjust the time range to control the scope of the adjustment; The shape coefficient controls the hyperbolic tangent function. steepness, This is the high-resistance fault discrimination coefficient.

[0017] More preferably, The total operating time of the zero-sequence inverse time protection is determined as follows:

[0018] in, The total operating time of the zero-sequence inverse-time protection is... To pre-set the zero-sequence inverse time limit for coordination time; The minimum time for the preset zero-sequence inverse time limit; Calculate the time for zero-sequence inverse time protection; The calculation time for the zero-sequence inverse time limit protection is specifically as follows:

[0019] in, The dynamic current start-up setting value is set. The dynamic time constant, To protect the zero-sequence current measured at the installation location.

[0020] Secondly, the present invention discloses a high-resistance grounding fault inverse-time protection system based on the aforementioned method, including a signal acquisition and start-up criterion calculation module, a protection start-up discrimination module, a grounding fault type discrimination module, and an adaptive inverse-time protection action calculation module; The signal acquisition and start-up criterion calculation module acquires the three-phase current and three-phase voltage signals at the protection installation point, i.e., the beginning of the line, in real time, and calculates the effective value of the fundamental wave of the zero-sequence current at the protection installation point as the start-up judgment parameter. The protection activation judgment module activates protection when a ground fault occurs on the line and the activation judgment parameter is greater than the activation protection threshold. The ground fault type discrimination module detects the phase voltage, phase current, and zero-sequence current of the faulty phase at the protection installation point. Combined with the positive sequence impedance of the line, it calculates the high-resistance fault discrimination coefficient. If the high-resistance fault discrimination coefficient is 1, it indicates that a metallic fault has occurred, and the system returns to the protection start discrimination module; otherwise, it enters the adaptive inverse time protection action calculation module. The adaptive inverse-time protection action calculation module, based on the high-resistance fault discrimination coefficient, designs an adaptive dynamic current start-up setting and a dynamic time constant and substitutes them into the inverse-time formula to calculate the zero-sequence inverse-time protection calculation time corresponding to the zero-sequence current measured at the protection installation location at this time. Combining the preset zero-sequence inverse-time coordination time and the preset zero-sequence inverse-time minimum time, the total action time of the zero-sequence inverse-time protection is calculated. After the total action time, the line inverse-time zero-sequence overcurrent protection of this line is activated to clear the fault.

[0021] Thirdly, the present invention provides a terminal, including a processor and a storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of the first aspects of the present invention.

[0022] Fourthly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in any one of the first aspects of the present invention.

[0023] Compared with the prior art, the beneficial effects of the present invention include at least the following: 1. This invention addresses the problem of poor adaptability of fixed threshold values, improving the sensitivity and speed of protection: Addressing the shortcomings of existing technologies (such as CN119575061A) that rely on preset fixed thresholds or trends and lack adaptability under different power grid conditions and faults, this invention introduces a high-resistance coefficient to achieve dynamic and smooth adjustment of the current initiation setting and time constant. This allows the protection to automatically lower the initiation threshold and shorten the action time during high-resistance faults, significantly improving the sensitivity and speed of protection and effectively preventing failure to operate; while during low-resistance faults, it maintains the original setting, ensuring selective coordination with upstream and downstream protection.

[0024] 2. Overcoming the limitations of complex calculations and reliance on multi-terminal signals, and improving engineering practicality: In view of the shortcomings of existing technologies (such as CN114895141A) that require complex number operations, have high requirements for measurement accuracy, and are computationally complex, the discrimination coefficient calculation method proposed in this invention only needs to utilize the fault phase voltage, current and zero-sequence current at the protection installation location. The calculation process is simple, and there is no need for multi-terminal synchronous data or complex system parameters, which reduces the difficulty and cost of implementation and has stronger engineering practicality and reliability.

[0025] 3. Deep integration of fault diagnosis and protection action is achieved, optimizing overall protection performance: Unlike most existing technologies that focus on fault detection or location without deeply optimizing subsequent protection action logic, this invention directly and seamlessly applies the high-resistance fault diagnosis results to the optimization of the inverse-time protection's action characteristics, achieving end-to-end enhancement from "detection" to "action." This fundamentally solves the problem of slow action of traditional zero-sequence overcurrent protection during high-resistance grounding faults, enabling rapid fault isolation, reducing the power outage area, and improving the safe and stable operation of the power grid.

[0026] 4. Wide adaptability to various fault types: The method proposed in this invention, through unified analysis of the voltage phase characteristics at the fault point under single-phase grounding and two-phase grounding fault conditions, enables the dynamic adjustment strategy of protection setting based on high resistance coefficient to have good adaptability to different types of grounding faults, thus expanding the applicability of the method. Attached Figure Description

[0027] Figure 1 This is a flowchart illustrating the high-resistance grounding fault inverse-time protection method based on dynamic setpoints in this invention. Figure 2 This is a system structure diagram of a ground short circuit via a transition resistor provided in Embodiment 1 of the present invention; Figure 3 This is a dynamic trajectory diagram of the protection and fault point voltage vector during a phase A ground fault, provided in Embodiment 1 of the present invention. Figure 4 This is a composite sequence network diagram of a two-phase short circuit to ground via a transition resistor, provided in Embodiment 1 of the present invention. Figure 5 This is a dynamic trajectory diagram of the protection and fault point voltage vector during a BC phase ground fault, provided in Embodiment 1 of the present invention. Figure 6 This is the zero-sequence inverse time overcurrent protection operation logic diagram provided in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram showing the change of dynamic current start-up setting value with high resistance fault discrimination c according to Embodiment 1 of the present invention; Figure 8 This is a schematic diagram showing the change of dynamic time constant with high-resistance fault discrimination c according to Embodiment 1 of the present invention; Figure 9 This is a schematic diagram of a fault circuit provided in Embodiment 2 of the present invention; Figure 10 The variables are provided according to Embodiment 2 of the present invention. A schematic diagram showing how its rate of change varies with the transition resistance; Figure 11 It is provided according to Embodiment 2 of the present invention. , Polar graph of the variable as a function of transition resistance; Figure 12 This is a schematic diagram showing the change of variable c and its rate of change with the transition resistance according to Embodiment 2 of the present invention; Figure 13 This is a typical structure diagram of short-circuit stringing provided in Embodiment 3 of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this invention.

[0029] like Figure 1 As shown, this invention discloses a high-resistance grounding fault inverse-time protection method based on dynamic setpoints, the method comprising the following steps: Step 1: Real-time acquisition of three-phase current and three-phase voltage signals at the protection installation point, i.e., the beginning of the line, and calculation of the effective value of the fundamental wave of the zero-sequence current at the protection installation point as the start-up judgment parameter; Step 2: When a ground fault occurs on the line and the start-up judgment parameter is greater than the start-up protection threshold, the protection is activated; The activation protection threshold is set to avoid the maximum unbalanced zero-sequence current during normal line operation, specifically:

[0030] in, To activate the protection threshold; The reliability coefficient is given, and it satisfies the following conditions: ; This represents the maximum unbalanced zero-sequence current during normal operation of the line.

[0031] Step 3: Detect the phase voltage, phase current, and zero-sequence current of the faulty phase at the protection installation point. Combine this with the positive sequence impedance of the line to calculate the high-resistance fault discrimination coefficient. If the high-resistance fault discrimination coefficient is 1, it indicates that a metallic fault has occurred, and return to step 2; otherwise, proceed to step 4. The high-resistance fault discrimination coefficient is determined as follows:

[0032] in, Let be the high-resistance fault discrimination coefficient, and satisfy . ; To protect the voltage drop of the line from the installation point to the fault point; To protect the phase voltage of the faulty phase measured at the installation location; To protect the phase voltage of the faulty phase measured at the installation location with vector The included angle, For vectors voltage of the fault phase at the fault point The included angle, The positive sequence impedance angle per unit length of the line; The vector ,in, To protect the phase current of the faulty phase measured at the installation location, To protect the zero-sequence current measured at the installation location, It is a zero-order compensation coefficient, and satisfies , These are the positive-sequence impedance and zero-sequence impedance per unit length of the transmission line, respectively.

[0033] The fault phase voltage at the fault point Its phase angle is equal to the phase angle of the zero-sequence current measured at the protection installation point.

[0034] Step 4: Based on the high-resistance fault discrimination coefficient, design an adaptive dynamic current start-up setting and a dynamic time constant, and substitute them into the inverse-time formula. Calculate the zero-sequence inverse-time protection calculation time corresponding to the zero-sequence current measured at the protection installation location at this time. Combine the preset zero-sequence inverse-time coordination time and the preset zero-sequence inverse-time minimum time to calculate the total operating time of the zero-sequence inverse-time protection. After the total operating time, the line inverse-time zero-sequence overcurrent protection of this line will operate to clear the fault.

[0035] The dynamic current starting setpoint changes with the high-resistance fault discrimination coefficient c. When the high-resistance fault discrimination coefficient decreases, the dynamic current starting setpoint decreases to ensure reliable start of the line inverse-time zero-sequence overcurrent protection. When the high-resistance fault discrimination coefficient increases, the dynamic current starting setpoint gradually increases and eventually equals the original current starting setpoint to avoid false tripping. The dynamic current start-up setting value is determined in the following manner:

[0036] in, The dynamic current start-up setting value is set. Set the initial current starting value; The starting current lower limit coefficient determines the minimum percentage that the starting current setting can be reduced to; The adjustment range is controlled by the current adjustment amplitude. The shape coefficient controls the hyperbolic tangent function. The steepness; This is the high-resistance fault discrimination coefficient.

[0037] The dynamic time constant changes with the high-resistance fault discrimination coefficient c. When the high-resistance fault discrimination coefficient decreases, the dynamic time constant decreases, accelerating the protection action. When the high-resistance fault discrimination coefficient increases, the dynamic time constant gradually increases and eventually equals the original time constant. The dynamic time constant is determined as follows:

[0038] in, The dynamic time constant, The original time constant; It is the lower limit coefficient of the time constant, which determines the minimum proportion to which the time constant can be shortened; Adjust the time range to control the scope of the adjustment; The shape coefficient controls the hyperbolic tangent function. steepness, This is the high-resistance fault discrimination coefficient.

[0039] The total operating time of the zero-sequence inverse time protection is determined as follows:

[0040] in, The total operating time of the zero-sequence inverse-time protection is... To pre-set the zero-sequence inverse time limit for coordination time; The minimum time for the preset zero-sequence inverse time limit; Calculate the time for zero-sequence inverse time protection; The calculation time for the zero-sequence inverse time limit protection is specifically as follows:

[0041] in, The dynamic current start-up setting value is set. The dynamic time constant, To protect the zero-sequence current measured at the installation location.

[0042] The present invention also discloses a high-resistance grounding fault inverse-time protection system based on the above method, including a signal acquisition and start-up criterion calculation module, a protection start-up discrimination module, a grounding fault type discrimination module, and an adaptive inverse-time protection action calculation module; The signal acquisition and start-up criterion calculation module acquires the three-phase current and three-phase voltage signals at the protection installation point, i.e., the beginning of the line, in real time, and calculates the effective value of the fundamental wave of the zero-sequence current at the protection installation point as the start-up judgment parameter. The protection activation judgment module activates protection when a ground fault occurs on the line and the activation judgment parameter is greater than the activation protection threshold. The ground fault type discrimination module detects the phase voltage, phase current, and zero-sequence current of the faulty phase at the protection installation point. Combined with the positive sequence impedance of the line, it calculates the high-resistance fault discrimination coefficient. If the high-resistance fault discrimination coefficient is 1, it indicates that a metallic fault has occurred, and the system returns to the protection start discrimination module; otherwise, it enters the adaptive inverse time protection action calculation module. The adaptive inverse-time protection action calculation module, based on the high-resistance fault discrimination coefficient, designs an adaptive dynamic current start-up setting and a dynamic time constant and substitutes them into the inverse-time formula to calculate the zero-sequence inverse-time protection calculation time corresponding to the zero-sequence current measured at the protection installation location at this time. Combining the preset zero-sequence inverse-time coordination time and the preset zero-sequence inverse-time minimum time, the total action time of the zero-sequence inverse-time protection is calculated. After the total action time, the line inverse-time zero-sequence overcurrent protection of this line is activated to clear the fault.

[0043] Example 1: like Figure 1 As shown, this invention provides a high-resistance grounding fault inverse-time protection method based on dynamic setpoints, comprising the following steps: Step 1: Real-time acquisition of three-phase current and three-phase voltage signals at the protection installation point, i.e., the beginning of the line, and calculation of the effective value of the fundamental wave of the zero-sequence current at the protection installation point as the start-up judgment parameter; Three-phase current is synchronously collected using configured current transformers and voltage transformers. and three-phase voltage The zero-sequence current is calculated based on this. To protect the installation location from three times the zero-sequence current. The fundamental effective value is used as the startup judgment parameter. This startup judgment parameter is sensitive to ground faults and its theoretical value is zero during normal system operation, thus exhibiting strong anti-interference capability.

[0044] Step 2: When a ground fault occurs on the line and the start-up judgment parameter is greater than the start-up protection threshold, the protection is activated; The start-up protection threshold To avoid the maximum unbalanced zero-sequence current during normal line operation The tuning is calculated using the following formula:

[0045] in, To activate the protection threshold; The reliability coefficient is given, and it satisfies the following conditions: ; This represents the maximum unbalanced zero-sequence current during normal operation of the line.

[0046] This setting ensures that the protection reliably does not activate during normal operation, but can be sensitively activated in the event of a ground fault. The purpose is to filter out minor disturbances and ensure that the subsequent high-resistance discrimination algorithm only activates when a suspected fault actually exists, thereby improving system reliability.

[0047] Step 3: Detect the phase voltage, phase current, and zero-sequence current of the faulty phase at the protection installation point. Combine this with the positive sequence impedance of the line to calculate the high-resistance fault discrimination coefficient. If the high-resistance fault discrimination coefficient is 1, it indicates that a metallic fault has occurred, and return to step 2; otherwise, proceed to step 4. Specifically, such as Figure 2 As shown, the sequence impedance of each component is currently pure reactance, and the positive sequence impedance of the system is... and negative sequence impedance Equal, that is The per-unit value of the power supply electromotive force of the reference phase relative to the short-circuit point is The positive-sequence and zero-sequence reactances of the power supply are , .

[0048] When on the line f When a ground fault occurs, the fault phase voltage measured at the bus protection installation point voltage at the fault point The relationship is:

[0049] in, The voltage at the fault point. , , These are the fault phase voltage, fault phase current, and zero-sequence current measured at the protection installation location, respectively. This represents the faulty phase, and its value is one of the three phases A, B, and C. To protect the wiring from the installation point to the fault point f The positive sequence impedance of the line at that location; This is the zero-sequence current compensation coefficient. These are the positive-sequence impedance and zero-sequence impedance per unit length of the transmission line, respectively. The distance between the fault point and the protection installation location. To protect the voltage drop of the line from the installation point to the fault point, and to meet the requirements .

[0050] Furthermore, When a single-phase ground fault occurs, assuming that the fault point... f After applying resistance When a phase-A ground fault occurs, the line is unloaded before the fault. ,in, , , Let the grounding resistances of phases A, B, and C be respectively. Then the sequence currents at the fault point are:

[0051] in: These are the positive-sequence, negative-sequence, and zero-sequence currents from the fault point to ground. To view the equivalent positive-sequence and zero-sequence reactances of the system from the fault point; The electromotive force of phase A is the power supply; and And the sequence reactance of each component is constant; such as Figure 3 As shown, the endpoints of the sequence current vector vary with the transition resistance. The trajectory of the change is a semicircle related to the system's equivalent reactance.

[0052] The fault point can be obtained from the sequence currents. f Fault phase voltage for:

[0053] Fault point f The fault phase voltage can also be expressed by the voltage drop across the transition resistor as follows:

[0054] Fault point f A phase-A ground fault occurred at point M, and the fault phase was measured at the protection point on the M side of the busbar. The voltage is:

[0055] In this system, the electromotive force and the sequence reactance are all constants, and the fault phase measured at the protection point is the zero-sequence current. A linear function. For example... Figure 3 As shown, the voltage at the protection point and the voltage vector endpoints at the fault point change with the transition resistance. The trajectory of the changes is always a semicircle.

[0056] When a single-phase ground fault occurs through a transition resistor, for example, when phase A experiences a ground fault through a transition resistor, the fault point... f voltage Sequence currents relative to ground at the fault point , , In phase, satisfying:

[0057] When a two-phase ground fault occurs, assuming that the fault point f After applying resistance When a two-phase-to-ground short circuit occurs between phases B and C, the line is unloaded before the short circuit. Based on the system wiring diagram, the composite sequence network diagram is derived as follows: Figure 4 As shown in (a), to facilitate analysis, it is converted into the form shown in (a). Figure 4 (b) form, as shown in the diagram:

[0058]

[0059] in, This is the equivalent electromotive force after the positive and negative sequences are connected in parallel; It is the equivalent reactance after the positive and negative sequence reactances are connected in parallel.

[0060] Depend on Figure 4 (b) The zero-sequence current at the short-circuit point can be obtained. for:

[0061] in, The equivalent current after positive and negative sequence parallel connection, This is to examine the zero-sequence reactance of the system from the perspective of the fault point.

[0062] By combining the zero-sequence current formula and the composite sequence network diagram at the short-circuit point, the positive-sequence and negative-sequence currents at the short-circuit point can be obtained:

[0063] in, The fault points are respectively f Positive and negative sequence currents at the point; Fault point f The zero-sequence voltage at that point.

[0064] The fault phase voltage can be expressed by the voltage drop across the transition resistor as follows:

[0065] in, , The fault points are respectively f The phase voltages of phases B and C at the location.

[0066] Fault point f When a two-phase B-to-ground fault occurs at the protection installation point, the voltage of phase B at the protection installation point... By synthesizing the sequence voltages, we obtain:

[0067] in, , , These represent the positive sequence, negative sequence, and zero sequence voltages at the protection installation location, respectively. For operator, and , Relationship exists: , ; The negative sequence impedance of the system; This represents the positive sequence electromotive force of phase B of the system.

[0068] The electromotive force and sequence reactance are all constants, and the B-phase voltage at the protection installation point is... It is zero-sequence current Linear functions, such as Figure 5 As shown, the voltage at the protection installation point and the voltage vector endpoints at the fault point vary with the transition resistance. The trajectory of the changes is always a semicircle.

[0069] When a two-phase ground fault occurs through a transition resistor, the phase of the zero-sequence current measured at the protection installation point should theoretically remain in phase with the phase of the fault voltage.

[0070] Based on the above calculations and analysis, it can be seen that the phase angle of the fault phase voltage at the fault point can be obtained by measuring the phase angle of the zero-sequence current at the protection installation point. That is, the phase angle of the fault phase voltage at the fault point is equal to the phase angle of the zero-sequence current measured at the protection installation point.

[0071] Depend on Figure 3 , Figure 5 Obtain the phase voltage at the fault point under single-phase and two-phase grounding conditions via a transition resistor. Fault phase voltage With line voltage drop The vector triangles formed exhibit common characteristics. Applying the triangle sine theorem to these vector triangles, we obtain:

[0072] Define line voltage drop voltage of the fault phase The ratio is the high-resistance fault discrimination coefficient c, which, after simplification, yields:

[0073] in, Let be the high-resistance fault discrimination coefficient, and satisfy . ; To protect the voltage drop of the line from the installation point to the fault point; To protect the phase voltage of the faulty phase measured at the installation location; Phase voltage of the faulty phase measured at the protection point with vector The included angle, For vectors voltage of the fault phase at the fault point The included angle, The positive sequence impedance angle per unit length of the line; Specifically, , , It can be expressed as follows: , ,

[0074] in, To protect the fault phase current measured at the installation location, To protect the zero-sequence current measured at the installation location, The zero-order compensation coefficient is... These are the positive-sequence impedance and zero-sequence impedance per unit length of the transmission line, respectively. Fault point f The phase voltage at point can be set as follows during calculation: It equals the zero-sequence current phase angle measured at the protection installation location.

[0075] Collected fault phase voltage With line voltage drop satisfy When a metallic ground fault occurs, the phase voltage at the fault point... =0, , When a ground fault occurs via a transition resistor, the phase voltage at the fault point... Not 0, , Furthermore, as the transition resistance gradually increases, the phase voltage at the fault point... As the voltage gradually increases, the difference between the collected fault phase voltage and the line voltage drop gradually increases, and in extreme cases, it may... , Therefore, according to The situation is used to determine whether a high-resistance grounding fault has occurred.

[0076] Step 4: Based on the high-resistance fault discrimination coefficient, design adaptive dynamic current start-up setting and dynamic time setting and substitute them into the inverse-time formula. Calculate the zero-sequence inverse-time protection calculation time corresponding to the zero-sequence current measured at the protection installation location at this time. Combine the preset zero-sequence inverse-time coordination time and the preset zero-sequence inverse-time minimum time to calculate the total operating time of the zero-sequence inverse-time protection. After the total operating time, the line inverse-time zero-sequence overcurrent protection of this line will operate to clear the fault.

[0077] When a high-resistance grounding fault is detected, the current start setting and time setting are adjusted, thereby adjusting the inverse time protection action time. The protection action is performed based on the adjusted inverse time limit protection action time.

[0078] Specifically, the general inverse time formula in the IEC standard inverse time characteristic curve is:

[0079] in: Calculation time for zero-sequence inverse time protection, For time constant, Set current starting value, This is three times the measured zero-sequence current.

[0080] like Figure 6 The zero-sequence inverse time protection calculation time is shown. Depend on and The joint decision involves the logic of protective actions. , , , These are the four constant values. This is achieved by integrating current and time; when the accumulated amount reaches a specific action threshold, it meets the requirements. Component activation conditions; To preset the zero-sequence inverse time coordination time, so that the protection maintains its inverse time characteristics within the interval; To preset the minimum time for zero-sequence inverse timing, and Together, they are used to avoid the time constraints of reclosing, distance protection, and three-phase inconsistency protection; the total operating time of zero-sequence inverse time protection is: .

[0081] The adaptive dynamic current start-up setpoint is used to adjust the current start-up setpoint. The obtained dynamic current start-up setpoint ,like Figure 7 As shown, "dynamic" here means that the current starting setpoint changes with the high-resistance fault discrimination coefficient c, automatically lowering the starting threshold when the resistance is high to ensure reliable protection startup; and restoring the original value when the resistance is low to avoid false tripping. This dynamic current starting setpoint... The specific calculation method is as follows:

[0082] In the formula, Set the initial current starting value; The starting current lower limit coefficient determines the minimum proportion to which the current setpoint can be reduced when the resistance is high; The adjustment range is controlled by the current adjustment amplitude. The shape coefficient controls the hyperbolic tangent function. The steepness, i.e., the adjustment process follows The smoothness of the change; This is the high-resistance fault discrimination coefficient.

[0083] The dynamic time constant is obtained by adjusting the time constant. Obtaining dynamic time constant ,like Figure 8 As shown, "dynamic" here means that the time constant changes with the high-resistance fault discrimination coefficient c, significantly shortening the time constant and accelerating the protection action when the resistance is high; and restoring the original value when the resistance is low to maintain coordination with the upstream protection. The specific calculation method for the dynamic time constant is as follows:

[0084] In the formula, The dynamic time constant, The original time constant; It is the lower limit coefficient of the time constant, which determines the minimum proportion that the time constant can be shortened under high resistance; Adjust the time range to control the scope of the adjustment; The shape coefficient controls the hyperbolic tangent function. The steepness of the adjustment process, i.e., how smoothly the adjustment process changes. This is the high-resistance fault discrimination coefficient.

[0085] Adjusted zero-sequence inverse time protection calculation time for:

[0086] The adjusted total operating time of the zero-sequence inverse time protection for:

[0087] in, To pre-set the zero-sequence inverse time limit for coordination time; The minimum time for the preset zero-sequence inverse time limit; The calculation time is for zero-sequence inverse time protection.

[0088] The protection action is performed based on the total operating time of the adjusted zero-sequence inverse time protection.

[0089] Example 2: To more clearly illustrate the outstanding substantive features of this invention and the significant progress it brings to the prior art, an application example of implementing this invention is described below.

[0090] Building such Figure 9 The model shown was simulated, and the variables described in Example 1 were applied respectively. , and The analysis focuses on the changes in transition resistance, namely:

[0091] in, Let be the high-resistance fault discrimination coefficient, and satisfy . ; To protect the voltage drop of the line from the installation point to the fault point; To protect the phase voltage of the faulty phase measured at the installation location; Phase voltage of the faulty phase measured at the protection point with vector The included angle, For vectors voltage of the fault phase at the fault point The included angle, The positive sequence impedance angle per unit length of the line; Specifically, , , It can be expressed as follows: , ,

[0092] in, To protect the fault phase current measured at the installation location, To protect the zero-sequence current measured at the installation location, The zero-order compensation coefficient is... These are the positive-sequence impedance and zero-sequence impedance per unit length of the transmission line, respectively. Fault point f The phase voltage at point can be set as follows during calculation: It equals the zero-sequence current phase angle measured at the protection installation location.

[0093] variable The variation of its rate of change with the transition resistance is as follows: Figure 10 As shown, during normal operation When the angle approaches 90°, a resistive component is introduced due to the transition resistance during a ground fault. It will shift towards 0°, with the rate of change being steep in the early stage and gradual in the later stage.

[0094] With variables In comparison, variables The change in transition resistance is very small, and the polar plots of the two are as follows: Figure 11 As shown, as the transition resistance gradually increases, It plays a dominant role in the process of change, causing the discriminant coefficient to gradually approach 0.

[0095] The final graph showing the variation of the high-resistance fault discrimination coefficient c with the transition resistance is as follows: Figure 12 As shown, as the transition resistance gradually increases, the discrimination coefficient c gradually transitions from 1 to 0, reflecting high resistance fault information.

[0096] Example 3: To more clearly illustrate the outstanding substantive features of this invention and the significant advancements it brings to the prior art, another application example of implementing this invention is described below.

[0097] Build such in PSCAD / EMTDC software Figure 13 The short-circuit string model shown is analyzed. The simulation model parameters of the short-circuit string scenario are shown in Table 1. Zero-sequence inverse time protection is configured on all lines. Multiple types of short-circuit faults are set at the midpoint of line MP. The fault time is 1 second. Protection 1 and protection 2 are selected for analysis. The measured values ​​of the positive direction protection and the action time under different strategies when the short-circuit string scenario is grounded through different transition resistors are shown in Table 2.

[0098] Dynamic current start-up setpoint With dynamic time constant The parameters selected are: current parameters: =0.25, =0.6, =3.5; Time parameter: =0.15, =0.9, =7.0; Table 1. Simulation Model Parameters for Short-Circuit Serial Scenarios

[0099] Table 2. Measurement values ​​of positive direction protection and operating time under different strategies when short-circuit series grounding occurs through different transition resistances.

[0100] This inverse-time protection optimization scheme effectively solves the protection problem of high-resistance grounding faults by introducing a high-resistance coefficient to dynamically adjust the protection setting. Experimental results show that this scheme can automatically adjust the current start-up setting (adjustable from 0.113-0.303kA) and time constant (adjustable from 0.075-0.403s) according to the fault nature, significantly improving protection performance while maintaining selectivity—the operating time is shortened by more than 50% compared to traditional schemes for 90Ω high-resistance grounding faults, with particularly significant optimization effects for BC phase-to-phase faults, reducing the operating time from 16.28s to 7.74s. This scheme covers a transition resistance range of 0-90Ω and has good adaptability to both single-phase and phase-to-phase faults, providing an effective technical approach to solving the high-resistance grounding protection problem in power systems.

[0101] Example 4: An embodiment of the present invention provides a terminal, including a processor and a storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of Embodiment 1.

[0102] Example 5: The present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in any one of the embodiments.

[0103] It is worth noting that in the embodiments of the present invention, "steps + numbers" is only an expression for clearly describing a specific implementation method of a high-resistance grounding fault inverse-time protection method based on dynamic setpoints, and is not an absolute restriction on the order of the steps. Under the guidance of the core concept of the present invention, changing the order of these steps to achieve the same or similar technical effects all fall within the scope of the present invention.

[0104] 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 high-resistance grounding fault inverse-time protection method based on dynamic setting, characterized in that, The method includes the following steps: Step 1: Real-time acquisition of three-phase current and three-phase voltage signals at the protection installation point, i.e., the beginning of the line, and calculation of the effective value of the fundamental wave of the zero-sequence current at the protection installation point as the start-up judgment parameter; Step 2: When a ground fault occurs on the line and the start-up judgment parameter is greater than the start-up protection threshold, the protection is activated; Step 3: Detect the phase voltage, phase current, and zero-sequence current of the faulty phase at the protection installation point. Combine this with the positive sequence impedance of the line to calculate the high-resistance fault discrimination coefficient. If the high-resistance fault discrimination coefficient is 1, it indicates that a metallic fault has occurred, and return to step 2; otherwise, proceed to step 4. Step 4: Based on the high-resistance fault discrimination coefficient, design an adaptive dynamic current start-up setting and a dynamic time constant, and substitute them into the inverse-time formula. Calculate the zero-sequence inverse-time protection calculation time corresponding to the zero-sequence current measured at the protection installation location at this time. Combine the preset zero-sequence inverse-time coordination time and the preset zero-sequence inverse-time minimum time to calculate the total operating time of the zero-sequence inverse-time protection. After the total operating time, the line inverse-time zero-sequence overcurrent protection of this line will operate to clear the fault.

2. The high-resistance grounding fault inverse-time protection method based on dynamic setpoints according to claim 1, characterized in that: The activation protection threshold is set to avoid the maximum unbalanced zero-sequence current during normal line operation, specifically: in, To activate the protection threshold; The reliability coefficient is given, and it satisfies the following conditions: ; This represents the maximum unbalanced zero-sequence current during normal operation of the line.

3. The high-resistance grounding fault inverse-time protection method based on dynamic setpoints according to claim 1, characterized in that: The high-resistance fault discrimination coefficient is determined as follows: in, Let be the high-resistance fault discrimination coefficient, and satisfy . ; To protect the voltage drop of the line from the installation point to the fault point; To protect the phase voltage of the faulty phase measured at the installation location; To protect the phase voltage of the faulty phase measured at the installation location with vector The included angle, For vectors voltage of the fault phase at the fault point The included angle, The positive sequence impedance angle per unit length of the line; The vector ,in, To protect the phase current of the faulty phase measured at the installation location, To protect the zero-sequence current measured at the installation location, It is a zero-order compensation coefficient, and satisfies , These are the positive-sequence impedance and zero-sequence impedance per unit length of the transmission line, respectively.

4. The high-resistance grounding fault inverse-time protection method based on dynamic setpoints according to claim 3, characterized in that: The fault phase voltage at the fault point Its phase angle is equal to the phase angle of the zero-sequence current measured at the protection installation point.

5. The high-resistance grounding fault inverse-time protection method based on dynamic setpoints according to claim 4, characterized in that: The dynamic current starting setpoint changes with the high-resistance fault discrimination coefficient c. When the high-resistance fault discrimination coefficient decreases, the dynamic current starting setpoint decreases to ensure reliable start of the line inverse-time zero-sequence overcurrent protection. When the high-resistance fault discrimination coefficient increases, the dynamic current starting setpoint gradually increases and eventually equals the original current starting setpoint to avoid false tripping. The dynamic current start-up setting value is determined in the following manner: in, The dynamic current start-up setting value is set. Set the initial current starting value; The starting current lower limit coefficient determines the minimum percentage that the starting current setting can be reduced to; The adjustment range is controlled by the current adjustment amplitude. The shape coefficient controls the hyperbolic tangent function. The steepness; This is the high-resistance fault discrimination coefficient.

6. The high-resistance grounding fault inverse-time protection method based on dynamic setpoints according to claim 4, characterized in that: The dynamic time constant changes with the high-resistance fault discrimination coefficient c. When the high-resistance fault discrimination coefficient decreases, the dynamic time constant decreases, accelerating the protection action. When the high-resistance fault discrimination coefficient increases, the dynamic time constant gradually increases and eventually equals the original time constant. The dynamic time constant is determined as follows: in, The dynamic time constant, The original time constant; It is the lower limit coefficient of the time constant, which determines the minimum proportion to which the time constant can be shortened; Adjust the time range to control the scope of the adjustment; The shape coefficient controls the hyperbolic tangent function. steepness, This is the high-resistance fault discrimination coefficient.

7. The high-resistance grounding fault inverse-time protection method based on dynamic setpoints according to claim 6, characterized in that: The total operating time of the zero-sequence inverse time protection is determined as follows: in, The total operating time of the zero-sequence inverse-time protection. To pre-set the zero-sequence inverse time limit for coordination; The minimum time for the preset zero-sequence inverse time limit; Calculate the time for zero-sequence inverse time protection; The calculation time for the zero-sequence inverse time limit protection is specifically as follows: in, The dynamic current start-up setting value is set. The dynamic time constant, To protect the zero-sequence current measured at the installation location.

8. A high-resistance ground fault inverse-time protection system based on dynamic setpoints according to the method of any one of claims 1-7, comprising a signal acquisition and start-up criterion calculation module, a protection start-up discrimination module, a ground fault type discrimination module, and an adaptive inverse-time protection action calculation module, characterized in that: The signal acquisition and start-up criterion calculation module acquires the three-phase current and three-phase voltage signals at the protection installation point, i.e., the beginning of the line, in real time, and calculates the effective value of the fundamental wave of the zero-sequence current at the protection installation point as the start-up judgment parameter. The protection activation judgment module activates protection when a ground fault occurs on the line and the activation judgment parameter is greater than the activation protection threshold. The ground fault type discrimination module detects the phase voltage, phase current, and zero-sequence current of the faulty phase at the protection installation point. Combined with the positive sequence impedance of the line, it calculates the high-resistance fault discrimination coefficient. If the high-resistance fault discrimination coefficient is 1, it indicates that a metallic fault has occurred, and the system returns to the protection start discrimination module. Otherwise, proceed to the adaptive inverse time protection action calculation module; The adaptive inverse-time protection action calculation module, based on the high-resistance fault discrimination coefficient, designs an adaptive dynamic current start-up setting and a dynamic time constant and substitutes them into the inverse-time formula to calculate the zero-sequence inverse-time protection calculation time corresponding to the zero-sequence current measured at the protection installation location at this time. Combining the preset zero-sequence inverse-time coordination time and the preset zero-sequence inverse-time minimum time, the total action time of the zero-sequence inverse-time protection is calculated. After the total action time, the line inverse-time zero-sequence overcurrent protection of this line is activated to clear the fault.

9. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-7.

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