Method and system for open distance protection of line protection device

Abstract

The invention discloses a method and system for opening distance protection of a line protection device, and the method comprises the steps: enabling the line protection device to judge whether the function state of longitudinal current differential protection is effective or not in real time, calculating the differential current in real time if the function state is effective after the protection is started, enabling the distance protection to select the fault phase in real time, and judging the direction, judging whether the differential current of the fault phase is greater than or equal to a threshold, if so, directly opening distance protection, and if not, opening distance protection when the distance protection judgment direction is a positive direction after delaying threshold time; if the function state is invalid, the distance protection selects the fault phase in real time and discriminates the direction, the fault after coincidence and the fault after manual closing are distinguished, and the distance protection is opened under other conditions. The condition of incorrect action of distance protection is effectively prevented.

Description

Technical Field

[0001] This invention belongs to the field of power transmission line fault identification technology, and relates to a method and system for open distance protection of a line protection device. Background Technology

[0002] The distance protection phase selection element and directional element of a typical line protection device are designed based on the transient equivalent circuit of a synchronous generator, the symmetrical component method, and the superposition principle line characteristics. With the rapid promotion and application of new power systems, the connection of a large number of power electronic devices has greatly changed the transient characteristics of traditional synchronous generator power grids.

[0003] The characteristics of power electronic equipment are determined by the control strategy, exhibiting nonlinear features such as limited current amplitude, controlled current phase, and suppression of negative sequence current. Traditional typical phase selection elements and directional elements are difficult to adapt to, and distance protection may malfunction.

[0004] Furthermore, for short lines less than 10km in length, if the measured impedance is significantly less than the system impedance when a fault occurs at the end of the line, the Distance Section I protection will have difficulty determining whether the fault is within or outside the line zone, which may lead to false tripping due to exceeding the limit. If a transient single-phase ground fault occurs within the zone on this line, the protection will trip a single phase, cutting off the current of the faulty phase. After reclosing, the Distance Section II reclosing acceleration element will be activated. However, the Distance Section II acceleration element currently operates rapidly without delay. If a transient fault of the same phase occurs at the outlet of an adjacent line at this time, it may cause the line to trip three phases falsely, resulting in failure to reclose and expanding the scope of the accident.

[0005] Therefore, it is urgent to study methods to prevent incorrect operation of distance protection. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method and system for open distance protection of line protection devices.

[0007] The present invention adopts the following technical solution.

[0008] The first aspect of this invention provides a method for open distance protection of a line protection device, comprising:

[0009] Step 1: The line protection device determines in real time whether the function status of the longitudinal current differential protection is effective. After the protection is started, proceed to Step 2.

[0010] Step 2: If the longitudinal current differential protection is effective, the differential current is calculated in real time, the distance protection selects the fault phase and determines the direction in real time, and proceeds to Step 3; otherwise, the distance protection selects the fault phase and determines the direction in real time, and proceeds to Step 4.

[0011] Step 3: Determine whether the differential current of the faulty phase selected by the distance protection is greater than or equal to the threshold. If so, directly open the distance protection; otherwise, proceed to step 5.

[0012] Step 4: Analyze the fault scenario. If it is a fault after reclosing, proceed to step 5. If it is a fault after manual closing, directly open the distance protection and continue for the set opening time. If it is a fault other than the fault after reclosing or the fault after manual closing, open the distance protection when the voltage and current constraints are met and the direction of the distance protection judgment is positive.

[0013] Step 5: After a delay threshold time, activate distance protection when the direction of distance protection determination is positive.

[0014] Preferably, the line protection device determines in real time whether the functional status of the longitudinal current differential protection is effective, including:

[0015] If the following conditions are met simultaneously, the function of the longitudinal current differential protection is deemed valid; otherwise, the function of the longitudinal current differential protection is deemed invalid:

[0016] The sampling current value is valid, both fiber optic channel pressure plates are engaged, the differential protection function on both sides is engaged, there is no CT disconnection alarm, no device fault, no current inconsistency, and no fiber optic channel fault.

[0017] Preferably, the threshold is the smaller of the primary current and the differential operating current setting.

[0018] Preferably, the criterion for the fault after re-coincidence is: the detected secondary current threshold is greater than 0.08In and is not the capacitor current, where In is the secondary rated current.

[0019] Preferably, the set opening time is 0.5s.

[0020] Preferably, the voltage and current constraint is: when all three phase voltages are less than 1V, the current of the faulty phase is greater than the secondary rated current.

[0021] Preferably, the threshold time is greater than the sum of the phase current differential protection operation time and the circuit breaker fault clearing time.

[0022] Preferably, when the distance protection is opened, for a line not exceeding 10km, if the line length l is between 5km and 10km, the protection range of distance I is reduced by (1-5 / l) times before being opened; if the line length l is less than 5km, distance I protection is deactivated.

[0023] A second aspect of the present invention provides a system for open distance protection of a line protection device, comprising:

[0024] The functional status determination module is used by the line protection device to determine in real time whether the functional status of the longitudinal current differential protection is effective.

[0025] The protection start-up discrimination module is used to determine whether the protection has started and whether it will enter the phase selection and direction discrimination module.

[0026] The phase selection and direction discrimination module is used to calculate the differential current in real time when the function of the longitudinal current differential protection is effective, and the distance protection selects the fault phase and determines the direction in real time, and then enters the differential current discrimination module; otherwise, the distance protection selects the fault phase and determines the direction in real time, and then enters the fault scenario analysis module.

[0027] The differential current discrimination module is used to determine whether the differential current of the fault phase selected by the distance protection is greater than or equal to the threshold. If it is, the distance protection is opened directly; otherwise, it enters the delayed opening module.

[0028] The fault scenario analysis module is used to analyze fault scenarios. If it is a fault after reclosing, it will enter the delayed opening module. If it is a fault after manual closing, it will directly open the distance protection and continue to open for the set time. If it is a fault other than the fault after reclosing and the fault after manual closing, it will open the distance protection when the voltage and current constraints are met and the direction of the distance protection judgment is positive.

[0029] The delayed opening module is used to open the distance protection when the direction of the distance protection determination is positive after a delay threshold time.

[0030] A third aspect of 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.

[0031] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0032] This invention utilizes the characteristic that longitudinal current differential protection is unaffected by power electronic equipment to determine the effectiveness of the longitudinal current differential protection function in real time. After the protection is started, if the longitudinal current differential protection function is ineffective, the distance protection is opened through fault scenario analysis; if the longitudinal current differential protection function is effective, the differential current is calculated, and the distance protection is opened through differential current analysis.

[0033] This invention analyzes fault scenarios when opening distance protection, determining whether to open the protection based on post-reclosing faults, manual closing faults, and other conditions to prevent false tripping and failure to operate. For post-reclosing faults, a delayed opening time is introduced to effectively prevent false tripping caused by rapid operation of the distance protection acceleration element after reclosing due to faults at adjacent line outlets before the system has fully stabilized, thus preventing the accident from escalating. Conditions for identifying post-reclosing faults are set to further prevent protection false tripping and to prevent capacitive current from causing misjudgment and restoration of full-phase operation. A distance protection opening time is set for manual closing faults so that if no fault occurs after the opening time, the protection exits the manual closing acceleration logic and normally engages all protection elements, operating according to the normal set time. Voltage and current constraints are set for other conditions to effectively prevent distance protection false tripping due to three-phase voltage loss caused by secondary circuit problems after protection startup.

[0034] This invention utilizes differential current analysis to open distance protection. When the differential current of the selected fault phase is greater than or equal to a threshold, the distance protection is directly opened. When the differential current of any selected fault phase is less than the threshold, a delayed opening method is used. The delay time t is greater than the operating time of the phase-specific current differential protection plus the circuit breaker fault clearing time. During the fault period, the distance protection remains closed, preventing maloperation due to incorrect phase selection or direction judgment during faults within the same line zone. This addresses the potential maloperation problem during faults within the zone in new power systems. Similarly, when the differential current of any selected fault phase is less than the threshold, a delayed opening method is used. The delay time t is greater than the operating time of the phase-specific current differential protection of adjacent lines plus the circuit breaker fault clearing time. During the fault period, the distance protection remains closed, preventing maloperation due to incorrect direction judgment during faults on adjacent lines. This addresses the potential maloperation problem during faults outside the zone in new power systems.

[0035] This invention addresses short lines less than 10km by dynamically adjusting the protection range of distance I or disabling the protection of distance I, fundamentally avoiding protection overruns caused by measurement impedance errors during faults at the end of short lines, and significantly improving the power supply reliability of short lines. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the protection range during a line fault.

[0037] Figure 2 This is a schematic diagram of the typical polygonal distance protection action characteristics;

[0038] Figure 3 This is a flowchart of a method for open distance protection of a line protection device according to the present invention. Detailed Implementation

[0039] 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 embodiments described in this application 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.

[0040] Embodiment 1 of this invention provides a method for enabling distance protection in a line protection device. The line protection device determines the status of the longitudinal current differential protection function in real time. After the protection is started, if the longitudinal current differential protection function is effective, the protection calculates the differential current of phases A, B, and C in real time. The distance protection selects the phase and determines the direction in real time, selecting the differential current of the faulty phase that meets the threshold threshold I. fz When the distance protection is activated, the differential current of any selected fault phase is less than the threshold value I. fz When the distance protection meets the delay threshold time t, it is activated in the positive direction. If the longitudinal current differential protection function is ineffective, the distance protection selects the phase and determines the direction in real time, activating the distance protection according to the fault scenario. This can be applied to various situations. Figure 1 The protection range during line faults is as follows. Taking a double busbar connection as an example, the MN and NP lines are adjacent lines, and each line has a dual-protection system (Line Protection 1 and Line Protection 2) installed on both sides; CT1, CT2, CT3, and CT4 are current transformers on each side of the line, providing AC current to the line protection device; PT1, PT2, PT3, and PT4 are voltage transformers on each side of the line, providing AC voltage to the protection device; B1, B2, B3, and B4 are circuit breakers on each side of the line, which trip when the protection operates to disconnect the fault; F1 is the midpoint fault in the MN line area, F2 is the N-side outlet fault in the NP line area, and F3 is the M-side reverse outlet fault of the MN line.

[0041] Line protection 1 and line protection 2 are equipped with the same protection elements. The main protection is longitudinal current differential protection, including phase current differential protection and zero-sequence current differential protection. Zero-sequence current differential protection is mainly used for high-resistance grounding faults. It is a double-ended quantity protection and protects the fault within the line area.

[0042] The protection range of the longitudinal current differential protection on both sides of the MN line is the line fault between CT1 and CT2, such as the fault at point F1; the protection range of the longitudinal current differential protection on both sides of the NP line is the line fault between CT3 and CT4, such as the fault at point F2.

[0043] Distance protection typically includes Distance Section I, Distance Section II, and Distance Section III. Distance Section I is generally set with a protection range of 0.8 times the total length of the line; Distance Section II is generally set with a protection range extending to 0.3 times the total length of the adjacent line; and Distance Section III is generally set with a protection range extending to 0.8 times the total length of the adjacent line. Currently, the common practice is that if a fault occurs within Distance Section III or is reclosed within Distance Section II, the distance protection will activate with no delay; if a fault occurs during operation, the distance protection will activate according to the set time.

[0044] The set time for distance protection can be either instantaneous or delayed. Distance protection is a single-ended quantity protection. The impedance is calculated based on the voltage and current at the installation location of the protection device, and the protection range is determined based on the reactance setting. It includes faults at points F1 or F2 in the forward direction, and point F3 is a fault in the reverse direction of the line, in which case the distance protection will not operate.

[0045] For lines with voltage levels of 220kV and above, phase-separated circuit breakers of phases A, B, and C are usually configured. When the protection operates, it is required to correctly select the faulty phase. In single-phase mode or single-phase fault, the faulty phase will be tripped. If the wrong phase is selected, the non-faulty phase or all three phases will be tripped, resulting in false tripping.

[0046] Longitudinal current differential protection based on Kirchhoff's laws is currently the only protection element that is largely unaffected by power electronic equipment; the current in the faulty branch is essentially the differential current. However, the calculation of the differential current relies on fiber optic channels to facilitate information exchange between the protection devices on both sides of the line. In extreme cases, such as when the fiber optic channel is interrupted or the longitudinal current differential protection on either side is deactivated, the differential protection functions on both sides will be disabled, making it impossible to calculate the differential current correctly. However, the distance protection may not be deactivated, primarily to prevent failure to operate; the phase selection and direction elements of the distance protection will still be used. When the longitudinal current differential protection function is active, the phase-specific differential current can be calculated, and the distance protection can be activated via the differential current.

[0047] Figure 2 This is a schematic diagram of the typical polygonal distance protection action characteristics, where X DZ The distance protection reactance setting reflects the range of protected line length; R DZ The distance protection resistor setting reflects the ability to handle transition resistance. Operation is only permitted if the measured impedance Z = R + jX of the selected phase falls within the polygonal distance protection operating characteristic zone.

[0048] Distance protection is typically activated when the conditions of positive direction of memory voltage, negative sequence positive direction, or zero sequence positive direction are met. Distance protection can operate after the selected phase is within the operating range and the set delay time is met.

[0049] Figure 3The flowchart of the open distance protection method of the line protection device of the present invention is as follows:

[0050] Step 1: The line protection device determines in real time whether the function status of the longitudinal current differential protection is effective. After the protection is started, proceed to Step 2.

[0051] (1) The line protection determines the functional status of the longitudinal current differential protection in real time and enters (2).

[0052] The longitudinal current differential protection is considered to be in a valid state if the following conditions are met simultaneously: the sampled current value is valid, both fiber optic channel pressure plates are engaged, the differential protection function on both sides is engaged, there is no CT disconnection alarm, there is no device fault, there is no current inconsistency, and there is no fiber optic channel fault.

[0053] If any of the above conditions are not met, the function of the longitudinal current differential protection is deemed invalid.

[0054] The longitudinal current differential protection of the line protection device is the main protection, which strictly guarantees the normal communication of the fiber optic channel. Only under special circumstances may the channel be abnormal, causing the longitudinal current differential protection to become ineffective.

[0055] (2) If the protection is activated, proceed to step 2; otherwise, return to (1).

[0056] According to conventional protection requirements, if any one of the following conditions is met—current surge start, zero-sequence auxiliary start, overcurrent auxiliary start, weak feeder start, remote call start, or static stability / instability start—the protection will start and enter the fault discrimination logic.

[0057] Step 2: If the function of the longitudinal current differential protection is effective, calculate the differential current of phases A, B, and C in real time, and the distance protection selects the phase and determines the direction in real time. Proceed to Step 3. Otherwise, the distance protection selects the phase and determines the direction in real time. Proceed to Step 4.

[0058] When the longitudinal current differential protection is in a valid state, the differential current of phases A, B, and C is calculated in real time, and the distance protection selects the phase and determines the direction in real time.

[0059] When the function of the longitudinal current differential protection is invalid, the distance protection selects the phase and determines the direction in real time.

[0060] The calculation results of differential current are largely unaffected by the control strategy of nonlinear power electronic components.

[0061] Backup protection uses single-ended current for phase selection. Due to the influence of the nonlinear power electronic component control strategy of the new power system, the current amplitude is limited, the phase angle is controlled, and the negative sequence current is suppressed. The phase selection element with inter-phase current mutation, the phase selection element with steady-state zero negative sequence current, and the phase selection element with weak feed low voltage are affected to varying degrees, which may lead to phase selection errors.

[0062] In new power systems, fault current amplitude is limited, phase angle is controlled, negative sequence current is suppressed, and negative sequence direction is unstable. The renewable energy side exhibits weak feeder characteristics, which may lead to maloperation of distance protection in the opposite direction or outside the positive direction fault zone. Therefore, accurate direction determination is still required. The memory voltage direction determination element and the negative sequence direction element are affected to varying degrees, potentially resulting in incorrect direction selection.

[0063] Step 3: The differential current of the faulty phase selected by the distance protection meets the threshold threshold I. fz If the distance protection is enabled, then proceed to step 5; otherwise, proceed to step 5.

[0064] Distance protection selects the differential current of the faulty phase to meet the threshold threshold I. fz At that time, the distance protection is directly judged as positive and the distance protection is activated.

[0065] The phase selection results for distance protection include: single-phase fault (A, B, C), phase-to-phase fault (AB, BC, CA), and three-phase fault (ABC).

[0066] If the selected phase is a single-phase fault, for example, a phase A fault, the differential current of phase A must meet the threshold threshold I. fz ;

[0067] If the selected phase is an inter-phase fault, such as a BC phase fault, the differential current of phase B and the differential current of phase C must both meet the threshold threshold I. fz ;

[0068] If the selected phase is a three-phase fault, the differential current of phase A, phase B, and phase C must all meet the threshold threshold I. fz .

[0069] The typical formula for calculating differential current is as follows:

[0070]

[0071] In the formula, The currents on the M side and N side are respectively. For phases A, B, and C, or zero-sequence current, I fz This is the differential current threshold.

[0072] Based on the requirement that a single fault current of 800A can correctly select the phase, the differential current threshold I... fzThe preferred value is the smaller of the primary current of 300A and the differential operating current setting, which fully meets the phase selection requirements. The differential operating current setting is a protection setting given based on the field conditions. The zero-sequence current differential protection can only operate when it exceeds this setting, providing a certain capacity to handle transition resistance. If this setting is larger than the primary current of 300A, I... fz A single current of 300A provides high sensitivity.

[0073] Step 4: Analyze the fault scenario. If it is a fault after reclosing, proceed to step 5. If it is a fault after manual closing, directly open the distance protection and continue for the set opening time. If it is a fault other than the fault after reclosing or the fault after manual closing, open the distance protection when the voltage and current constraints are met and the direction of the distance protection judgment is positive.

[0074] When the function of the longitudinal current differential protection is deemed invalid, backup protection still needs to operate under certain operational requirements. In this case, the distance protection needs to determine whether to activate based on the fault after reclosing, the manual closing fault, and other situations to prevent false tripping and failure to operate.

[0075] After a system fault, the protection system activates, sends a trip command, clears the fault, and the fault current disappears. When the protection system retracts the trip command, reclosing is initiated. Alternatively, if the protection system does not activate, a trip position is entered, and there is no current in the corresponding phase, reclosing is initiated. After a single-phase trip, if there is current in the original faulty phase, the reclosing logic is accelerated. After a three-phase trip, if any phase has current, the reclosing logic is accelerated. If there is an adjacent line fault at this time, the acceleration element after reclosing in distance II will operate rapidly, leading to maloperation. Therefore, step 5 is required to determine if the distance protection meets the threshold time t before opening the distance protection.

[0076] The secondary current threshold for determining whether a fault has entered reclosing mode is greater than 0.08In, and it must not be capacitive current, where In is the rated secondary current. When the circuit breaker on one side closes but the circuit breaker on the other side does not, capacitive current will occur. The longer the line and the higher the voltage level, the larger the capacitive current will be. If the voltage has not yet returned to normal, it may cause the protection to malfunction. The characteristic of capacitive current is that the current of the same phase leads the voltage by approximately 90°. To prevent capacitive current from causing the protection to misjudge and restore full-phase operation, it is necessary to determine whether it is capacitive current. If it exhibits capacitive current characteristics, the protection will not determine whether to enter the reclosing acceleration logic. The minimum accurate operating current of the protection is 0.08In; it needs to be greater than this value for the protection to reliably determine whether to restore full-phase operation and enter the reclosing acceleration logic.

[0077] After manual closing, to ensure rapid protection action in case of a fault, the distance protection does not distinguish direction and enters the manual closing acceleration logic, rapidly operating within the protection action zone and directly opening the distance protection. However, if there is no fault after 0.5 seconds, the protection needs to exit the manual closing acceleration logic and normally engage all protection components, operating according to the normal set time. That is, the opening time for a manual closing fault is 0.5 seconds.

[0078] This is neither a reclosing acceleration logic nor a manual closing acceleration logic. The protection is in normal operating condition. Distance protection is activated when the direction determined by the distance protection is positive, and tripping occurs according to the selected phase. However, after protection activation, if a three-phase voltage loss occurs due to secondary circuit issues, the distance protection may malfunction due to a certain load current, requiring preventative measures. The preventative method is to activate the distance protection only after all three-phase voltages are less than 1V and the current in the faulty phase is greater than In. During a fault, if the voltage is very low, less than 1V, it indicates a metallic short circuit near the output. In this case, the distance protection must activate only after the current in the faulty phase is greater than In to prevent maloperation under this condition.

[0079] For short lines less than 10km, if the line length l is between 5km and 10km, the protection range of distance section I is reduced by (1-5 / l) times before being opened. If the line length is less than 5km, distance section I protection is deactivated to prevent the problem of exceeding distance section I protection.

[0080] Step 5: After determining that the distance protection meets the threshold time t, activate the distance protection.

[0081] When the longitudinal current differential protection is in a valid state, if the differential current of any fault phase selected by the distance protection is less than the threshold threshold I... fz If the longitudinal current differential protection is ineffective, and the fault is caused by reclosing, in order to prevent the distance protection from mis-selecting phase or misjudging direction, a delayed opening method for the distance protection is adopted. The distance protection is only opened after the distance protection is determined to meet the threshold time t.

[0082] The threshold time t should be greater than the operating time of the phase current differential protection plus the fault clearing time of the circuit breaker.

[0083] For the threshold time t, considering that the typical operating time of the phase current differential protection is 0.02s and the typical operating time of the circuit breaker is 0.04s, and taking into account a certain time margin, a threshold time t of 0.1s can meet the condition for delayed operation.

[0084] When a fault occurs within the line area, misselection of phase or misjudgment of direction by the distance protection may lead to maloperation. The method of delaying the opening of the distance protection is adopted. The delay time is greater than the threshold time t, and the distance protection does not open during the fault period, which can solve the problem of possible maloperation during faults within the line area under the new power system.

[0085] For distance protection, only a certain transition resistance capability needs to be considered. For ground faults with a large transition resistance, both zero-sequence current differential protection and zero-sequence overcurrent protection can operate. When distance protection operates, phase-specific current differential protection will also operate.

[0086] When the differential current of any fault phase selected by the distance protection is less than the threshold threshold, in order to prevent the distance protection from misjudging the direction and causing false tripping when the next level line fault occurs, a delayed opening distance protection method is adopted. The delay time is greater than the threshold time t, and the distance protection does not open during the fault period. This can solve the problem of possible false tripping due to faults outside the zone in the new power system.

[0087] In summary, the open distance protection strategy is as follows:

[0088] When the longitudinal current differential protection function is active, and the differential current of the fault phase selected by the distance protection meets the threshold, the distance protection is directly opened.

[0089] When the longitudinal current differential protection function is effective, and the differential current of the fault phase selected by the distance protection is less than the threshold threshold, the time delay is greater than the threshold time t, and the distance protection is opened after the positive direction discrimination condition is met.

[0090] When the longitudinal current differential protection function is invalid, the distance protection is judged according to the following conditions: reclosing fault, manual closing fault, and other conditions. If the reclosing fault is judged, the distance protection is opened after the threshold time t is met and the positive direction judgment condition is met. If the manual closing fault is judged, the distance protection is opened directly and continues to be open for the set time. Otherwise, the distance protection is opened after the voltage and current constraints and the positive direction judgment condition are met.

[0091] Embodiment 2 of the present invention provides a system for open distance protection of a line protection device, comprising:

[0092] The functional status determination module is used by the line protection device to determine in real time whether the functional status of the longitudinal current differential protection is valid. Specifically, the longitudinal current differential protection is considered valid if the following conditions are met simultaneously: the sampled current value is valid, both fiber optic channel pressure plates are engaged, the differential protection function on both sides is engaged, there is no CT disconnection alarm, there is no device fault, there is no current inconsistency, and there is no fiber optic channel fault. If any of the above conditions are not met, the longitudinal current differential protection is considered invalid.

[0093] Protection start-up discrimination module: When protection is started, the phase selection and direction discrimination module is entered to execute the fault discrimination logic.

[0094] The phase selection and direction discrimination module is used to calculate the differential current in real time when the function status of the longitudinal current differential protection is valid. The distance protection selects the fault phase and determines the direction in real time, and then enters the differential current discrimination module. Otherwise, the distance protection selects the fault phase and determines the direction in real time, and then enters the fault scenario analysis module to distinguish between reclosing fault, manual closing fault and other situations. After discrimination, it enters the distance protection opening module.

[0095] Differential current discrimination module: When the differential current of the fault phase selected by the distance protection meets the threshold, the distance protection directly judges it as positive and enters the distance protection opening module; when the differential current of any fault phase selected by the distance protection is less than the threshold, it enters the delayed opening module.

[0096] The fault scenario analysis module is used to analyze fault scenarios. If it is a fault after reclosing, it will enter the delayed opening module. If it is a fault after manual closing, it will directly open the distance protection and continue to open for the set time. If it is a fault other than the fault after reclosing and the fault after manual closing, it will open the distance protection when the voltage and current constraints are met and the direction of the distance protection judgment is positive.

[0097] Delayed opening module: After the distance protection meets the threshold time t, the distance protection is opened when the direction of the distance protection is positive.

[0098] The specific opening strategy is as follows: When the longitudinal current differential protection function is effective and the differential current of the faulty phase selected by the distance protection meets the threshold, the distance protection is directly opened; when the longitudinal current differential protection function is effective and the differential current of the faulty phase selected by the distance protection is less than the threshold, the distance protection is opened after the distance protection meets the threshold time t and the positive direction discrimination condition is met; when the longitudinal current differential protection function is ineffective, if it is determined to be a reclosing fault, the distance protection is opened after the distance protection meets the threshold time t and the positive direction discrimination condition is met; if it is determined to be a manual closing fault, the distance protection is directly opened and continues for the set opening time; otherwise, the distance protection is opened after the voltage and current constraints and the positive direction discrimination condition are met.

[0099] Embodiment 3 of 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.

[0100] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0101] This invention utilizes the characteristic that longitudinal current differential protection is unaffected by power electronic equipment to determine the effectiveness of the longitudinal current differential protection function in real time. After the protection is started, if the longitudinal current differential protection function is ineffective, the distance protection is opened through fault scenario analysis; if the longitudinal current differential protection function is effective, the differential current is calculated, and the distance protection is opened through differential current analysis.

[0102] This invention analyzes open distance protection through fault scenarios and determines the open distance protection based on post-reclosing faults, manual closing faults, and other situations to prevent false operation and failure to operate.

[0103] For reclosing faults, a delayed opening is introduced to effectively prevent the rapid action of the acceleration element after reclosing in distance II due to the fault at the outlet of the adjacent line when the system has not fully recovered. This prevents the accident from escalating. Furthermore, conditions for judging the entry of reclosing faults are set to further prevent protection maloperation and prevent capacitive current from causing protection misjudgment and restoring full-phase operation.

[0104] After manual closing, a fault-free distance protection opening time is set so that if there is no fault after the opening time, the protection exits the manual closing acceleration logic, and the protection components are put into normal operation according to the normal set time.

[0105] Voltage and current constraints are set for other situations besides reclosing faults and manual closing faults to effectively prevent distance protection from maloperating due to three-phase voltage loss caused by secondary circuit problems after protection starts.

[0106] This invention utilizes differential current analysis to open distance protection. When the differential current of the selected fault phase is greater than or equal to a threshold, the distance protection is directly opened. When the differential current of any selected fault phase is less than the threshold, a delayed opening method is used. The delay time t is greater than the operating time of the phase-specific current differential protection plus the circuit breaker fault clearing time. During the fault period, the distance protection remains closed, preventing maloperation due to incorrect phase selection or direction judgment during faults within the same line zone. This addresses the potential maloperation problem during faults within the zone in new power systems. Similarly, when the differential current of any selected fault phase is less than the threshold, a delayed opening method is used. The delay time t is greater than the operating time of the phase-specific current differential protection of adjacent lines plus the circuit breaker fault clearing time. During the fault period, the distance protection remains closed, preventing maloperation due to incorrect direction judgment during faults on adjacent lines. This addresses the potential maloperation problem during faults outside the zone in new power systems.

[0107] This invention addresses short lines less than 10km by dynamically adjusting the protection range of distance I or disabling the protection of distance I, fundamentally avoiding protection overruns caused by measurement impedance errors during faults at the end of short lines, and significantly improving the power supply reliability of short lines.

[0108] 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 method for open distance protection of a line protection device, characterized in that, include: Step 1: The line protection device determines in real time whether the function status of the longitudinal current differential protection is effective. After the protection is started, proceed to Step 2. Step 2: If the longitudinal current differential protection is effective, the differential current is calculated in real time, the distance protection selects the fault phase and determines the direction in real time, and proceeds to Step 3; otherwise, the distance protection selects the fault phase and determines the direction in real time, and proceeds to Step 4. Step 3: Determine whether the differential current of the faulty phase selected by the distance protection is greater than or equal to the threshold. If so, directly open the distance protection; otherwise, proceed to step 5. Step 4: Analyze the fault scenario. If it is a fault after reclosing, proceed to step 5. If it is a fault after manual closing, directly open the distance protection and continue for the set opening time. If it is a fault other than the fault after reclosing or the fault after manual closing, open the distance protection when the voltage and current constraints are met and the direction of the distance protection judgment is positive. Step 5: After a delay threshold time, activate distance protection when the direction of distance protection determination is positive.

2. The method for open distance protection of a line protection device according to claim 1, characterized in that: The line protection device determines in real time whether the function of the longitudinal current differential protection is effective, including: If the following conditions are met simultaneously, the function of the longitudinal current differential protection is deemed valid; otherwise, the function of the longitudinal current differential protection is deemed invalid: The sampling current value is valid, both fiber optic channel pressure plates are engaged, the differential protection function on both sides is engaged, there is no CT disconnection alarm, no device fault, no current inconsistency, and no fiber optic channel fault.

3. The method for open distance protection of a line protection device according to claim 1, characterized in that: The threshold is the smaller of the primary current and the differential operating current setting.

4. The method for open distance protection of a line protection device according to claim 1, characterized in that: The criterion for determining the fault after re-coincidence is: the detected secondary current threshold is greater than 0.

08. I n is not the capacitive current, where... I n is the secondary rated current.

5. The method for open distance protection of a line protection device according to claim 1, characterized in that: The set opening time is 0.5 seconds.

6. The method for open distance protection of a line protection device according to claim 1, characterized in that: The voltage and current constraints are as follows: when all three phase voltages are less than 1V, the current of the faulty phase is greater than the secondary rated current.

7. The method for open distance protection of a line protection device according to claim 1, characterized in that: The threshold time is greater than the sum of the phase current differential protection operation time and the circuit breaker fault clearing time.

8. The method for open distance protection of a line protection device according to claim 1, characterized in that: When implementing open distance protection, for lines not exceeding 10km, if the line length... Between 5km and 10km, the protection range of section I is reduced. After doubling, if the line length is... If the distance is less than 5km, then the first stage of distance protection will be discontinued.

9. A system for open distance protection of a line protection device, operating the method described in any one of claims 1-8, characterized in that, The system includes: The functional status determination module is used by the line protection device to determine in real time whether the functional status of the longitudinal current differential protection is effective. The protection start-up discrimination module is used to determine whether the protection has started and whether it will enter the phase selection and direction discrimination module. The phase selection and direction discrimination module is used to calculate the differential current in real time when the function of the longitudinal current differential protection is effective, and the distance protection selects the fault phase and determines the direction in real time, and then enters the differential current discrimination module; otherwise, the distance protection selects the fault phase and determines the direction in real time, and then enters the fault scenario analysis module. The differential current discrimination module is used to determine whether the differential current of the fault phase selected by the distance protection is greater than or equal to the threshold. If it is, the distance protection is opened directly; otherwise, it enters the delayed opening module. The fault scenario analysis module is used to analyze fault scenarios. If it is a fault after reclosing, it will enter the delayed opening module. If it is a fault after manual closing, it will directly open the distance protection and continue to open for the set time. If it is a fault other than the fault after reclosing and the fault after manual closing, it will open the distance protection when the voltage and current constraints are met and the direction of the distance protection judgment is positive. The delayed opening module is used to open the distance protection when the direction of the distance protection determination is positive after a delay threshold time.

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 1-8.

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