Relay protection cooperation relation evaluation method and system for intermittent faults

Abstract

The invention discloses a relay protection cooperation relation evaluation method and system for intermittent faults, and the method comprises the steps: constructing a multi-scene intermittent fault current model library, applying current with the amplitude and duration dynamically changing to an upper-stage relay protection device and a lower-stage relay protection device, so as to simulate a single-time intermittent fault, a multiple intermittent fault and a high-resistance intermittent fault, the minimum return intervals T21 and T22 of the upper-level overcurrent protection and the lower-level overcurrent protection are obtained in combination with environment correction; the T21 and the T22 are integrated, and the maloperation risk of the upper-stage relay protection cooperation relation and the lower-stage relay protection cooperation relation is evaluated; if the maloperation risk exists, upper and lower level overcurrent protection constant value parameters are adaptively adjusted, and the upper and lower level relay protection cooperation relation is optimized. By simulating the occurrence process of the intermittent fault in a real power grid, whether each protection device can meet the requirements of selectivity, quickness and reliability according to set logic or not is tested, and the coordination and response capability of the relay protection device under the intermittent fault can be systematically verified and evaluated in a standardized mode.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection evaluation, and relates to a method and system for evaluating the coordination relationship of relay protection for intermittent faults. Background Art

[0002] Relay protection is a key component of the power system, mainly used to quickly isolate the faulty part when an abnormality or fault occurs in the power system, so as to prevent the further expansion of the fault and ensure the safe and stable operation of the power grid. Traditional relay protection devices are based on the detection of physical quantities such as current and voltage, and can quickly act when a fault occurs to cut off the faulty line or equipment.

[0003] In modern power systems, relay protection technology has been very mature after years of development and is widely used in various links such as power generation, transmission, distribution, and power consumption. However, with the complexity and intelligence of the power grid structure, especially the popularization of new energy access, distributed generation, and smart grids, relay protection devices are facing increasingly complex fault modes, among which intermittent faults are particularly prominent.

[0004] Intermittent faults refer to faults in the power system where the fault state does not exist continuously, but occurs intermittently. Such faults may be caused by reasons such as line aging, poor equipment contact, external environmental impacts (such as lightning strikes, tree contact with wires, etc.), and are manifested as sudden changes in fault current or voltage, but will quickly return to normal. Therefore, intermittent faults have the following significant characteristics: the fault state does not exist continuously, but shows short-term, periodic, or random characteristics. Due to the short fault occurrence time, traditional relay protection devices may be difficult to complete fault detection and judgment within a short time, resulting in the fault being ignored or misjudged. After the fault disappears, the system can quickly resume normal operation, making fault troubleshooting more complex. Although intermittent faults seemingly do not cause continuous impacts on the system, their frequent occurrence and disappearance will have negative impacts on aspects such as the insulation of the system, the life of equipment, and the stability of the system. The overstepping operation of relay protection will also cause an expansion of the power outage range.

[0005] Due to its intermittency and instability, this type of fault poses a great challenge to traditional relay protection devices. In recent years, relay protection overstepping operation events caused by intermittent faults have occurred from time to time. Therefore, the coordination and cooperation of different relay protection devices in the power system are required to ensure effective and reliable fault detection and isolation when intermittent faults occur. Therefore, it is particularly necessary to develop an effective evaluation method.

[0006] The coordination relationship of relay protection devices means that when a fault occurs in the power system, each protection device can operate according to the established sequence and logic to ensure that the fault is removed in time without affecting the normal operation of the non-faulty part. Specifically, the coordination relationship of relay protection devices should meet the following basic principles: Selectivity: When a fault occurs, the protection device closest to the fault point should act first to cut off the faulty part, while the protection devices of other non-faulty parts should not act; Quick-acting property: When a fault occurs, the protection device should complete the fault judgment and act within the shortest time to reduce the impact of the fault on the system; Sensitivity: The protection device should have sufficient sensitivity to accurately detect the fault when it occurs and make a correct judgment; Reliability: The protection device should have high reliability to ensure stable operation under various complex working conditions and avoid misoperation or refusal to operate. However, the existence of intermittent faults makes the coordination relationship of relay protection devices more complex. The main reason is that traditional relay protection devices rely on continuous fault current or voltage signals to make judgments, while the current or voltage signals of intermittent faults are instantaneous and difficult to be stably captured.

[0007] Intermittent faults have many impacts on the coordination relationship of relay protection: Due to the shortness and randomness of intermittent faults, it may lead to chaotic action sequences of relay protection devices. For example, some devices may misoperate when the fault appears briefly, while other devices fail to detect the fault in time and thus fail to act as planned. This will result in the failure to isolate the fault in time and may even trigger cascading faults. The electrical characteristics of intermittent faults may cause the protection devices close to the fault point to fail to correctly identify the fault, while the devices far from the fault point misoperate, violating the selectivity principle that protection devices should follow and causing the loss of selectivity. This situation not only cannot effectively isolate the fault but may also lead to an unnecessary expansion of the power outage range. Due to its instantaneous nature, intermittent faults may cause the fault signal to fail to reach the action threshold of the relay protection device, resulting in a decrease in the sensitivity of the protection device and the inability to respond correctly to the fault. The electrical quantity fluctuations caused by intermittent faults may cause the relay protection equipment to misoperate or refuse to operate. In the initial stage of an intermittent fault, due to the low amplitude of the fault current, the relay protection may not be able to act in time; while after the fault disappears, the relay protection may misoperate due to the presence of the recovery signal.

[0008] The technical challenges in evaluating the coordination relationship of relay protection for intermittent faults are as follows: Complexity of fault simulation: Intermittent faults are characterized by instantaneousness and randomness, making it very difficult to simulate intermittent faults in the laboratory or on-site. Traditional fault simulation methods cannot accurately reflect the actual characteristics of intermittent faults, leading to a decrease in the credibility of test results. Validity of test data: Due to the short occurrence time and randomness of intermittent faults, the collected fault data is often not representative and difficult to be used for the commissioning and optimization of relay protection devices. Unclear evaluation criteria for coordination relationship: Existing evaluation methods for the coordination relationship of relay protection devices mostly target continuous faults, and there is no unified standard for evaluating intermittent faults, resulting in the difficulty of quantifying test results. Dynamic response ability of protection devices: The dynamic response ability of traditional relay protection devices is limited, and problems such as response lag or overresponse may occur when facing intermittent faults. Therefore, new relay protection evaluation methods need to be developed to evaluate the dynamic response characteristics of devices under intermittent fault conditions.

[0009] Regarding the relay protection evaluation methods for intermittent faults, there have been some studies and practices. For example, some researchers have tried to improve the sensitivity of relay protection devices to cope with intermittent faults; some other researchers have adopted advanced technologies such as intelligent algorithms and pattern recognition, attempting to judge the occurrence of intermittent faults by analyzing the instantaneous change characteristics of fault current and voltage. However, these solutions still have the following limitations in practical applications: Although improving the sensitivity of relay protection devices can, to a certain extent, improve the detection ability of intermittent faults, it will also increase the risk of misoperation of the equipment in non-fault states. Although intelligent algorithms and pattern recognition technologies can theoretically effectively identify intermittent faults, their algorithm complexity is high, real-time performance is poor, and in practical applications, it is difficult to set and optimize the parameters of the algorithms, restricting their large-scale application. There are differences between the tests in the existing laboratory environment and the actual power grid operating conditions, resulting in the difficulty of reflecting the problems in actual applications with test results. Summary of the Invention

[0010] To address the deficiencies in the existing technology, the present invention provides a method and system for evaluating the coordination relationship of relay protection for intermittent faults. By simulating the occurrence process of multi-scenario intermittent faults in a real power grid, it tests whether each protection device can meet the requirements of selectivity, quick operation, and reliability according to the established logic, and can systematically and standardly verify and evaluate the coordination and response ability of relay protection devices under intermittent faults. This not only helps to improve the performance of relay protection devices but also can optimize their coordination relationship in complex fault situations, reduce misoperation and refusal to operate, and ultimately enhance the safety and stability of the power system.

[0011] The present invention adopts the following technical solutions.

[0012] The first aspect of the present invention proposes a method for evaluating the coordination relationship of relay protection against intermittent faults, including:

[0013] S1: Construct a multi-scenario intermittent fault current model library for the downstream overcurrent protection according to the downstream overcurrent protection setting parameters. Based on this fault current model library, apply currents with dynamically changing amplitudes and durations to the downstream relay protection device to simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults, and combine environmental correction to obtain the minimum return interval T22 of the downstream overcurrent protection;

[0014] S2: Construct a multi-scenario intermittent fault current model library for the upstream overcurrent protection according to the upstream overcurrent protection setting parameters. Based on this fault current model library, apply currents with dynamically changing amplitudes and durations to the upstream relay protection device to simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults, and combine environmental correction to obtain the minimum return interval T21 of the upstream overcurrent protection;

[0015] S3: Considering T21 and T22 comprehensively, use statistical analysis method to calculate the misoperation risk probability and evaluate whether there is a misoperation risk in the coordination relationship between the upstream and downstream relay protections;

[0016] S4: If there is a misoperation risk, adaptively adjust the upstream and downstream overcurrent protection setting parameters to optimize the coordination relationship between the upstream and downstream relay protections.

[0017] Preferably, S1 specifically includes:

[0018] S1.1: Construct a multi-scenario intermittent fault current model library for the downstream overcurrent protection according to the downstream overcurrent protection setting parameters, including a single intermittent fault current model, a multiple intermittent fault current model, and a high-resistance intermittent fault current model;

[0019] S1.2: Dynamically adjust the upstream fault current multiple coefficient K according to the low-load, medium-load, and high-load operating conditions of the power grid, and adjust the currents in the multi-scenario intermittent fault current model library of the downstream overcurrent protection according to K;

[0020] S1.3: Based on S1.2, apply the current sequence of the intermittent fault current model of a single scenario of the downstream overcurrent protection to the downstream relay protection device. If the protection device correctly issues a tripping command, extend the interruption time in the model through the adaptive step size algorithm, repeat applying this current sequence until the protection does not operate, and record the last interruption time as the minimum return interval of a single test of the downstream overcurrent protection;

[0021] S1.4: Repeat S1.2 and S1.3 multiple times under different scenarios of the intermittent fault current model and load levels of the downstream overcurrent protection, take the statistical average of the minimum return intervals of all single tests of the downstream overcurrent protection and apply the environmental correction coefficient to obtain the final minimum return interval T22 of the downstream overcurrent protection.

[0022] Preferably, the single intermittent fault current model is: I1 = I3 = 1.05 * Iset, I2 = 0; T1 = T3 = Tset - ΔT, T2 = 0, where I1, I2, and I3 are the currents in the first, second, and third stages respectively; T1, T2, and T3 are the application durations of I1, I2, and I3 respectively; Iset and Tset are the lower overcurrent protection amplitude setting value and the lower overcurrent protection delay setting value respectively; ΔT is the short delay, and ΔT < 0.5 * Tset.

[0023] Preferably, the multiple intermittent fault current model is:

[0024] The test window Ttotal = 3 * Tset;

[0025] Period 1: I1 = 1.1Iset, T1 = Tset - ΔT; I2 = 0.5Iset, T2 = ΔT / 2; I3 = 1.1 * Iset, T3 = ΔT / 2;

[0026] Period 2: I4 = 1.15Iset, T4 = Tset - ΔT; I5 = 0.4Iset, T5 = ΔT / 2; I6 = 1.15 * Iset, T6 = ΔT / 2;

[0027] Period 3: I7 = 1.2Iset, T7 = Tset - ΔT; I8 = 0.3Iset, T8 = ΔT / 2; I9 = 1.2 * Iset, T9 = ΔT / 2;

[0028] Among them, I4, I5, I6, I7, I8, and I9 are the currents in the fourth, fifth, sixth, seventh, eighth, and ninth stages respectively; T4, T5, T6, T7, T8, and T9 are the application durations of I4, I5, I6, I7, I8, and I9 respectively; and T2, T5, and T8 are all used as interruption times.

[0029] Preferably, the high - resistance intermittent fault current model is: I1 = I3 = 1.2Iset, I2 = 0.2Iset;

[0030] T1 = T3 = Tset - ΔT, T2 = ΔT.

[0031] Preferably, S2 specifically includes:

[0032] S2.1: Adjust the lower overcurrent protection setting parameters in the lower overcurrent protection multi - scenario intermittent fault current model library to the upper overcurrent protection setting parameters to obtain the upper overcurrent protection multi - scenario intermittent fault current model library;

[0033] S2.2: Dynamically adjust the fault current multiple coefficient K' of the lower level according to the voltage fluctuation amplitude on the power supply side, and adjust the current in the intermittent fault current model library for multi-scenario overcurrent protection of the lower level according to K';

[0034] S2.3: Based on S2.2, apply the current sequence of the intermittent fault current model for a single scenario of overcurrent protection of the upper level to the upper-level relay protection device. If the protection device correctly issues a tripping command, extend the interruption time in the model through the adaptive step-size algorithm, and repeat applying this current sequence until the protection does not operate. Record the last interruption time as the minimum return interval for a single test of the upper-level overcurrent protection;

[0035] S2.4: Repeat S2.2 and 2.3 multiple times under the intermittent fault current models and voltage fluctuations of different scenarios of the upper-level overcurrent protection. Take the statistical average of the minimum return intervals for all single tests of the upper-level overcurrent protection and apply the environmental correction coefficient to obtain the minimum return interval T22 of the lower-level overcurrent protection.

[0036] Preferably, S3 specifically includes:

[0037] Comprehensively consider T21 and T22, and use statistical analysis method to calculate the misoperation risk probability P of the coordination relationship between the upper and lower level relay protections:

[0038] P = Φ(ΔTmin / √(σT21² + σT22²))

[0039] where, Φ is the cumulative function of the standard normal distribution; ΔTmin is the difference between T21 and T22; σT21² and σT22² are the variances of T21 and T22 obtained from multiple simulation tests;

[0040] If P > P0, it is determined that there is a misoperation risk in the coordination relationship between the upper and lower level relay protections, otherwise it is determined that the coordination relationship between the upper and lower level relay protections is reliable, where P0 is the misoperation risk threshold.

[0041] Preferably, S4 specifically includes:

[0042] If there is a misoperation risk, adaptively adjust the setting parameters of the overcurrent protection of the upper and lower levels according to ΔTmin:

[0043] If ΔTmin > 0, shorten the delay setting value of the upper-level overcurrent protection to reduce T21, and the shortening amplitude is ΔTmin / 10;

[0044] If ΔTmin < 0, extend the delay setting value of the lower-level overcurrent protection to increase T22, and the extension amplitude is |ΔTmin| / 10;

[0045] where, ΔTmin is the difference between T21 and T22;

[0046] Repeat S1 to S3 after adjustment until the coordination relationship between the primary and secondary relay protections is reliable, and output the adjusted setting value suggestions.

[0047] The second aspect of the present invention proposes a relay protection coordination relationship evaluation system for intermittent faults, including:

[0048] A secondary protection test module, which is used to construct a multi-scenario intermittent fault current model library for the secondary overcurrent protection according to the secondary overcurrent protection setting value parameters, apply currents with dynamically changing amplitudes and durations to the secondary relay protection device based on this fault current model library to simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults, and combine environmental correction to obtain the minimum return intermittent time T22 of the secondary overcurrent protection;

[0049] A primary protection test module, which is used to construct a multi-scenario intermittent fault current model library for the primary overcurrent protection according to the primary overcurrent protection setting value parameters, apply currents with dynamically changing amplitudes and durations to the primary relay protection device based on this fault current model library to simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults, and combine environmental correction to obtain the minimum return intermittent time T21 of the primary overcurrent protection;

[0050] An evaluation module, which is used to comprehensively consider T21 and T22, calculate the misoperation risk probability using statistical analysis methods and evaluate whether there is a misoperation risk in the coordination relationship between the primary and secondary relay protections. If there is a misoperation risk, it adaptively adjusts the primary and secondary overcurrent protection setting value parameters to optimize the coordination relationship between the primary and secondary relay protections.

[0051] The third aspect of the present invention proposes a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0052] The fourth aspect of the present invention proposes a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the method are implemented.

[0053] Compared with the prior art, the beneficial effects of the present invention at least include:

[0054] 1. Multi-scenario intermittent fault simulation and evaluation: By applying currents with dynamically changing amplitudes and durations to the secondary relay protection device, single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults are accurately simulated. Through the adjustment of the current amplitude and time length in the multi-scenario intermittent fault current model library, it is ensured that the response of the primary and secondary relay protection devices under intermittent fault conditions can be tested. Multi-scenario tests are carried out for different current amplitude and time combinations, and environmental correction is combined to determine the minimum return action intermittent time of the protection device.

[0055] 2. Verification of coordination between upper and lower level relay protection devices: Statistical analysis is used to calculate the probability of false operation risk and evaluate whether there is a false operation risk in the coordination relationship between the upper and lower level relay protections. This provides a standardized means to accurately determine whether there is a risk of over-level operation or false operation in the upper and lower level relay protections.

[0056] 3. Dynamic adjustment mechanism: By dynamically adjusting the upper and lower level fault current multipliers according to the operating conditions of the power grid and the voltage fluctuation amplitude on the power supply side, the test current is adjusted in real time, and the intermittent time parameters are adaptively adjusted through an adaptive step algorithm, so that the test can adapt to intermittent faults in different situations, ensuring that the coordination and reliability of the protection device in various complex situations are verified.

[0057] 4. Systematic evaluation: Systematically evaluate the protection device. If there is a risk of false operation, the upper and lower level overcurrent protection setting parameters are adaptively adjusted to optimize the coordination relationship between the upper and lower level relay protections to ensure that they can meet the requirements of selectivity, speed and reliability under intermittent faults. This helps to improve the performance of relay protection devices and optimize the protection coordination of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a flow chart of a relay protection coordination relationship evaluation method for intermittent faults according to the present invention;

[0059] Figure 2 It is a current schematic diagram of the phased changes in amplitude and duration of a single intermittent fault model;

[0060] Figure 3 Simulate the test process for a single intermittent fault of the lower protection level;

[0061] Figure 4 Simulate the test process for a single intermittent fault of the upper protection. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0063] like Figure 1 As shown, Embodiment 1 of the present invention provides a method for evaluating the coordination relationship of relay protection for intermittent faults, including:

[0064] S1: Build a multi-scenario intermittent fault current model library. By applying currents with dynamically changing amplitudes and durations to the subordinate relay protection devices, simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults and perform environmental correction to test the minimum return interval T22 of the subordinate overcurrent protection.

[0065] Further preferably, use a relay protection tester to apply a test current to the subordinate protection device to test the minimum return interval of the subordinate overcurrent protection, specifically including:

[0066] S1.1: Build an intermittent fault current model, including the following three fault types:

[0067] Single intermittent fault: I1 = I3 = 1.05 * Iset, I2 = 0; T1 = T3 = Tset - ΔT, T2 = 0; The test current is divided into three stages as shown, and its amplitude and time length are I1, I2, I3 and T1, T2, T3 respectively; Figure 2 as shown

[0068] Multiple intermittent faults:

[0069] Test window Ttotal = 3 * Tset;

[0070] Period 1: I1 = 1.1Iset, T1 = Tset - ΔT; I2 = 0.5Iset, T2 = ΔT / 2; I3 = 1.1 * Iset, T3 = ΔT / 2;

[0071] Period 2: I4 = 1.15Iset, T4 = Tset - ΔT; I5 = 0.4Iset, T5 = ΔT / 2; I6 = 1.15 * Iset, T6 = ΔT / 2;

[0072] Period 3: I7 = 1.2Iset, T7 = Tset - ΔT; I8 = 0.3Iset, T8 = ΔT / 2; I9 = 1.2 * Iset, T9 = ΔT / 2;

[0073] High-resistance intermittent fault: I1 = I3 = 1.2Iset, I2 = 0.2Iset; T1 = T3 = Tset - ΔT, T2 = ΔT;

[0074] Among them, ΔT is a short delay to ensure that the protection does not operate under T1 and T3, ΔT < 0.5 * Tset; Iset and Tset are the settings of the subordinate overcurrent protection, representing the amplitude setting and delay setting respectively;

[0075] S1.2: Dynamically adjust the fault current multiple coefficient K (range 1.0 - 1.5) according to the grid operation conditions (low load, medium load, high load), for example:

[0076] Low load: K = 1.0;

[0077] Medium load: K = 1.25;

[0078] High load: K = 1.5;

[0079] Multiply the adjusted fault current amplitudes I1, I3, etc. by K. For example, in a single intermittent fault, I1 = I3 = 1.05KIset;

[0080] S1.3: Apply the current sequence corresponding to the fault model to the lower-level relay protection device:

[0081] Single intermittent fault: Apply I1 → I2 → I3;

[0082] Multiple intermittent faults: Apply I1 → I2 → I3 → I4 → I5 → I6 → I7 → I8 → I9;

[0083] High-resistance intermittent fault: Apply I1 → I2 → I3;

[0084] If the protection device correctly issues a trip command, then increase all interruption times (such as T2, T5, T8) through the adaptive step-size algorithm (initial step size 1 ms, gradually decreasing to 0.1 ms), repeat applying the current sequence until the protection does not operate, and record the last interruption time (such as T8 in multiple faults) as the minimum return intermittent T22i for a single test;

[0085] For example, the test process of the lower-level protection for a single intermittent fault is as Figure 3 shown. Continuously apply current with amplitude I1 for duration T1, current with amplitude I2 for duration T2, and current with amplitude I3 for duration T3 to the lower-level relay protection device through a protection tester. If the lower-level relay protection device correctly issues a trip command, then increase T2 (initially increase by 1 ms), and repeat the current application process until the protection does not operate. Record the current T2 as the minimum return operating intermittent T22 of the lower-level relay protection. Specifically, during implementation, the initial T2 = 0. Continuously apply current I1 for duration T1, I2 for duration T2, and I3 for duration T3 through the protection tester. The lower-level protection should be able to correctly issue a trip command. Compensate and increase T2 with an initial step size of 1 ms, and repeat the test process until the protection does not operate. Record the corresponding T2 as the minimum return operating intermittent T22 of the lower-level protection.

[0086] S1.4: Repeat S1.2 and S1.3 N times (N ≥ 5) under different fault models and load levels, take the statistical average of T22i, and apply the environmental correction factor α (based on temperature and humidity, range 0.9 - 1.1) to calculate the final T22 = α * mean(T22i).

[0087] S2: Based on the fault model library, apply currents with dynamically changing amplitudes and durations to the upper-level relay protection device to simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults and perform environmental correction, and test the minimum return interval T21 of the upper-level overcurrent protection;

[0088] Further preferably, apply a test current to the lower-level protection device through a relay protection tester to test the minimum return interval of the upper-level protection device, specifically including:

[0089] S2.1: Adopt the same fault model library as S1.1 and set the initial current parameters of the upper-level protection:

[0090] Single intermittent fault: I1 = I3 = 1.05 * I’set, I2 = 0; T1 = T3 = T’set - ΔT, T2 = 0;

[0091] Multiple intermittent faults:

[0092] Test window Ttotal = 3 * T’set;

[0093] Period 1: I1 = 1.1I’set, T1 = T’set - ΔT; I2 = 0.5I’set, T2 = ΔT / 2; I3 = 1.1 * I’set, T3 = ΔT / 2;

[0094] Period 2: I4 = 1.15I’set, T4 = T’set - ΔT; I5 = 0.4I’set, T5 = ΔT / 2; I6 = 1.15 * I’set, T6 = ΔT / 2;

[0095] Period 3: I7 = 1.2I’set, T7 = T’set - ΔT; I8 = 0.3I’set, T8 = ΔT / 2; I9 = 1.2 * I’set, T9 = ΔT / 2;

[0096] High-resistance intermittent fault: I1 = I3 = 1.2I’set, I2 = 0.2I’set; T1 = T3 = T’set - ΔT, T2 = ΔT;

[0097] Wherein, I’set and T’set are respectively the amplitude setting value and delay setting value of the upper-level overcurrent protection, and ΔT < 0.5 * T’set;

[0098] S2.2: Dynamically adjust the fault current multiple coefficient K’ (range 1.0 - 1.5) according to the voltage fluctuation amplitude on the power supply side. For example:

[0099] Voltage fluctuation < 5%: K’ = 1.0;

[0100] Voltage fluctuation 5% - 10%: K’ = 1.25;

[0101] Voltage fluctuation > 10%: K' = 1.5;

[0102] Multiply the adjusted fault current amplitudes I1, I3, etc. by K', for example, in a single intermittent fault, I1 = I3 = 1.05 * K' * I'set;

[0103] S2.3: Apply the current sequence corresponding to the fault model to the upper-level relay protection device:

[0104] Single intermittent fault: Apply I1 → I2 → I3;

[0105] Multiple intermittent faults: Apply I1 → I2 → I3 → I4 → I5 → I6 → I7 → I8 → I9;

[0106] High-resistance intermittent fault: Apply I1 → I2 → I3;

[0107] If the protection device correctly issues a tripping command, increase all interruption times (such as T2, T5, T8) through the adaptive step-size algorithm, repeat applying the current sequence until the protection does not operate, and record the last interruption time as the minimum return intermittent time T21i for a single test.

[0108] For example, in a single intermittent fault, the corresponding test current is also divided into three stages, and its amplitude and time length are I1, I2, I3 and T1, T2, T3 respectively; as Figure 4 shown, the upper-level protection test process is: continuously apply current with an amplitude of I1 and a duration of T1, current with an amplitude of I2 and a duration of T2, and current with an amplitude of I3 and a duration of T3 to the upper-level relay protection device. If the upper-level relay protection device correctly issues a tripping command, increase T2, and repeat the current application process until the protection does not operate, and record the current T2 as the minimum return operating intermittent time T21 of the upper-level relay protection. Specifically, when implementing, the initial T2 = 0, continuously apply current I1 for a duration of T1, I2 for a duration of T2, and I3 for a duration of T3 through the protection tester, and the lower-level protection should be able to correctly issue a tripping command. Compensate and increase T2 with an initial step size of 1 ms, and repeat the test process until the protection does not operate. Record the corresponding T2 as the minimum return operating intermittent time T21 of the upper-level protection.

[0109] S2.4: Repeat S2.2 and 2.3 at least 5 times (N ≥ 5) under different fault models and voltage fluctuations, take the statistical average value of T21i, and apply the environmental correction coefficient α to calculate the final T21 = α * mean(T21i).

[0110] S3: Considering T21 and T22 corrected for environmental factors, use statistical analysis methods to evaluate the misoperation risk of the coordination relationship between the upper and lower levels of relay protection, and output the risk probability P, specifically including:

[0111] S3.1: Calculate the difference ΔTmin = T21 - T22 between T21 and T22, and construct a maloperation risk probability model P by combining the variances σT212 and σT222 of multiple tests:

[0112] P = Φ(ΔTmin / √(σT212 + σT222)), where Φ is the cumulative function of the standard normal distribution;

[0113] S3.2: Set a maloperation risk threshold P0 (e.g., 0.05):

[0114] If P > P0, it is determined that there is a maloperation risk caused by intermittent faults in the coordination relationship between the upper and lower relay protections;

[0115] If P ≤ P0, there is no risk of overstepping operation between the two-level protections, and the coordination relationship is considered reliable;

[0116] S3.3: Output an evaluation report, including T21, T22, ΔTmin, the P value, and the risk level (e.g., low, medium, high).

[0117] S4: According to the evaluation results, adaptively adjust the setting parameters of the upper and lower protection values to optimize the coordination relationship between the upper and lower relay protections to reduce the maloperation risk, specifically including:

[0118] If S3 determines that there is a maloperation risk (P > P0), adaptively adjust the protection setting according to the magnitude of ΔTmin:

[0119] If ΔTmin > 0, shorten the upper-level delay setting value T’set to reduce T21, and the adjustment range is ΔTmin / 10;

[0120] If ΔTmin < 0, extend the lower-level delay setting value Tset to increase T22, and the adjustment range is |ΔTmin| / 10;

[0121] After adjustment, repeat S1 to 3 until P ≤ P0;

[0122] Output the optimized setting suggestions, including the adjusted Iset, Tset, I’set, and T’set.

[0123] Embodiment 2 of the present invention provides a relay protection coordination relationship evaluation system for intermittent faults, including:

[0124] A lower-level protection test module, which is used to construct a multi-scenario intermittent fault current model library for the lower-level overcurrent protection according to the lower-level overcurrent protection setting parameters, apply currents with dynamically changing amplitudes and durations to the lower-level relay protection device based on this fault current model library to simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults, and combine environmental correction to obtain the minimum return interval T22 of the lower-level overcurrent protection;

[0125] The upper-level protection test module is used to construct a multi-scenario intermittent fault current model library for the upper-level overcurrent protection based on the upper-level overcurrent protection setting parameters, apply currents with dynamically changing amplitudes and durations to the upper-level relay protection device based on this fault current model library to simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults, and combine environmental correction to obtain the minimum return intermittent time T21 of the upper-level overcurrent protection.

[0126] The evaluation module is used to comprehensively consider T21 and T22, calculate the misoperation risk probability using statistical analysis methods, and evaluate whether there is a misoperation risk in the coordination relationship between the upper and lower levels of relay protection. If there is a misoperation risk, it adaptively adjusts the setting parameters of the overcurrent protection at the upper and lower levels to optimize the coordination relationship between the upper and lower levels of relay protection.

[0127] Embodiment 3 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 used to operate according to the instructions to execute the steps according to the method.

[0128] Embodiment 4 of the present invention provides a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the steps of the method are implemented.

[0129] Compared with the prior art, the beneficial effects of the present invention at least include:

[0130] 1. Multi-scenario intermittent fault simulation and evaluation: By applying currents with dynamically changing amplitudes and durations to the lower-level relay protection device, accurately simulate single intermittent faults, multiple intermittent faults, and high-resistance intermittent faults. By adjusting the current amplitude and time length of the multi-scenario intermittent fault current model library, ensure that the response of the upper and lower levels of relay protection devices under intermittent fault conditions can be tested, conduct multi-scenario tests for different current amplitude and time combinations, and combine environmental correction to determine the minimum return action intermittent time of the protection device.

[0131] 2. Coordination verification of the upper and lower levels of relay protection devices: Calculate the misoperation risk probability using statistical analysis methods and evaluate whether there is a misoperation risk in the coordination relationship between the upper and lower levels of relay protection, providing a standardized means to accurately judge whether there is a risk of overstepping or misoperation in the upper and lower levels of relay protection.

[0132] 3. Dynamic adjustment mechanism: Dynamically adjust the upper and lower fault current multiple coefficients according to the operating conditions of the power grid and the voltage fluctuation amplitude on the power supply side, and then adjust the test current in real time. And adaptively adjust the intermittent time parameters through the adaptive step size algorithm, so that the test can adapt to intermittent faults in different situations, and ensure that the coordination and reliability of the protection device under various complex conditions are verified.

[0133] 4. Systemic evaluation: Systematically evaluate the protection device. If there is a risk of maloperation, adaptively adjust the overcurrent protection setting parameters of the upper and lower levels, optimize the coordination relationship between the upper and lower levels of relay protection, ensure that it can meet the requirements of selectivity, quick operation and reliability under intermittent faults, help improve the performance of the relay protection device, and optimize the protection coordination of the power system.

[0134] The present disclosure may be a system, a method, and / or a computer program product. The computer program product may include a computer-readable storage medium having thereon computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0135] The computer-readable storage medium may be a tangible device that can retain and store instructions for use by an instruction execution device. The computer-readable storage medium may be, for example, but is not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), a memory stick, a floppy disk, a mechanically encoded device such as a punch card or raised structures in grooves having instructions stored thereon, and any suitable combination of the foregoing. The computer-readable storage medium as used herein is not construed as being a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated through a waveguide or other transmission medium (e.g., an optical pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0136] The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium to various computing / processing devices, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in a computer-readable storage medium in each computing / processing device.

[0137] The computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine - related instructions, microcode, firmware instructions, state - setting data, or source code or object code written in any combination of one or more programming languages, including object - oriented programming languages such as Smalltalk, C++, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer - readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand - alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider). In some embodiments, by using the state information of the computer - readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field - programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer - readable program instructions to implement various aspects of the present disclosure.

[0138] 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 them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent substitutions can still be made to the specific embodiments of the present invention. Any modification or equivalent substitution that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A method for evaluating the coordination relationship of relay protection for intermittent faults, characterized in that: include: S1: Construct a multi-scenario intermittent fault current model library of the lower-level overcurrent protection according to the set value parameters of the lower-level overcurrent protection. Based on the fault current model library, a current with dynamically changing amplitude and duration is applied to the lower-level relay protection device to simulate a single intermittent fault, multiple intermittent faults and high-resistance intermittent faults, and the minimum return interval T22 of the lower-level overcurrent protection is obtained in combination with environmental correction; S2: According to the upper-level overcurrent protection setting parameters, a multi-scenario intermittent fault current model library of the upper-level overcurrent protection is constructed. Based on the fault current model library, a current with dynamically changing amplitude and duration is applied to the upper-level relay protection device to simulate a single intermittent fault, multiple intermittent faults and high-resistance intermittent faults, and the minimum return interval T21 of the upper-level overcurrent protection is obtained in combination with environmental correction; S3: Comprehensively consider T21 and T22, use statistical analysis method to calculate the probability of false operation risk and evaluate whether there is a false operation risk in the coordination relationship between the upper and lower levels of relay protection; S4: If there is a risk of false operation, the upper and lower level overcurrent protection setting parameters are adaptively adjusted to optimize the coordination relationship between the upper and lower level relay protections.

2. The method for evaluating the coordination relationship of relay protection for intermittent faults according to claim 1 is characterized in that: S1 specifically includes: S1.1: Construct a multi-scenario intermittent fault current model library of the lower-level overcurrent protection according to the lower-level overcurrent protection setting parameters, including a single intermittent fault current model, a multiple intermittent fault current model and a high-resistance intermittent fault current model; S1.2: Dynamically adjust the upper fault current multiplier coefficient K according to the low-load, medium-load and high-load operating conditions of the power grid, and adjust the current in the multi-scenario intermittent fault current model library of the lower overcurrent protection according to K; S1.3: Based on S1.2, the current sequence of the intermittent fault current model of the single scenario of the lower-level overcurrent protection is applied to the lower-level relay protection device. If the protection device correctly issues a trip command, the interruption time in the model is extended by the adaptive step algorithm, and the current sequence is repeatedly applied until the protection does not operate. The last interruption time is recorded as the minimum return interval of the single test of the lower-level overcurrent protection; S1.4: Repeat S1.2 and S1.3 multiple times under the intermittent fault current model and load level of different scenarios of the lower-level overcurrent protection, take the statistical average of the minimum return interval of all single tests of the lower-level overcurrent protection, and apply the environmental correction coefficient to obtain the final minimum return interval T22 of the lower-level overcurrent protection.

3. The method for evaluating the coordination relationship of relay protection for intermittent faults according to claim 2 is characterized in that: The single intermittent fault current model is: I1=I3=1.05*Iset, I2=0; T1=T3=Tset-ΔT, T2=0, wherein I1, I2, I3 are the first, second, and third stage currents respectively; T1, T2, T3 are the application time of I1, I2, I3 respectively; Iset and Tset are the lower-level overcurrent protection amplitude constant and the lower-level overcurrent protection delay constant respectively; ΔT is the short delay, ΔT<0.5*Tset.

4. The method for evaluating the coordination relationship of relay protection for intermittent faults according to claim 3 is characterized in that: The multiple intermittent fault current model is: Test window Ttotal = 3*Tset; Period 1: I1=1.1Iset, T1=Tset-ΔT; I2=0.5Iset, T2=ΔT / 2; I3=1.1*Iset, T3=ΔT / 2; Period 2: I4=1.15Iset, T4=Tset-ΔT; I5=0.4Iset, T5=ΔT / 2; I6=1.15*Iset, T6=ΔT / 2; Period 3: I7=1.2Iset, T7=Tset-ΔT; I8=0.3Iset, T8=ΔT / 2; I9=1.2*Iset, T9=ΔT / 2; Among them, I4, I5, I6, I7, I8, and I9 are the fourth, fifth, sixth, seventh, eighth, and ninth stage currents respectively; T4, T5, T6, T7, T8, and T9 are the application durations of I4, I5, I6, I7, I8, and I9 respectively; and T2, T5, and T8 are all used as interruption times.

5. The method for evaluating the coordination relationship of relay protection for intermittent faults according to claim 4 is characterized in that: The high-resistance intermittent fault current model is: I1=I3=1.2Iset, I2=0.2Iset; T1=T3=Tset-ΔT, T2=ΔT.

6. The method for evaluating the coordination relationship of relay protection for intermittent faults according to claim 1, characterized in that: S2 specifically includes: S2.1: adjusting the lower-level overcurrent protection fixed value parameters in the lower-level overcurrent protection multi-scenario intermittent fault current model library to the upper-level overcurrent protection fixed value parameters to obtain the upper-level overcurrent protection multi-scenario intermittent fault current model library; S2.2: Dynamically adjust the lower-level fault current multiplier coefficient K' according to the voltage fluctuation amplitude on the power supply side, and adjust the current in the lower-level overcurrent protection multi-scenario intermittent fault current model library according to K'; S2.3: Based on S2.2, apply the current sequence of the intermittent fault current model of the upper overcurrent protection single scenario to the upper relay protection device. If the protection device correctly issues a trip command, extend the interruption time in the model through the adaptive step algorithm, and repeat the current sequence until the protection does not operate. Record the last interruption time as the minimum return interval of the upper overcurrent protection single test; S2.4: Repeat S2.2 and 2.3 multiple times under the intermittent fault current model and voltage fluctuation of different scenarios of the upper overcurrent protection, take the statistical average of the minimum return interval of all single tests of the upper overcurrent protection and apply the environmental correction coefficient to obtain the minimum return interval T22 of the lower overcurrent protection.

7. A method for evaluating relay protection coordination relationship for intermittent faults according to claim 1, characterized in that: S3 specifically includes: Taking T21 and T22 into consideration, the false operation risk probability P of the upper and lower level relay protection coordination relationship is calculated using the statistical analysis method: P=Φ(ΔTmin / √(σT212+σT222)) Among them, Φ is the cumulative function of the standard normal distribution; ΔTmin is the difference between T21 and T22; σT212 and σT222 are the variance of T21 and T22 obtained from multiple simulation tests; If P>P0, it is determined that there is a risk of false operation in the coordination relationship between the upper and lower relay protections; otherwise, it is determined that the coordination relationship between the upper and lower relay protections is reliable, where P0 is the false operation risk threshold.

8. The method for evaluating the coordination relationship of relay protection for intermittent faults according to claim 1, characterized in that: S4 specifically includes: If there is a risk of false operation, the upper and lower level overcurrent protection setting parameters are adaptively adjusted according to ΔTmin: If ΔTmin>0, shorten the delay setting of the upper overcurrent protection to reduce T21 by ΔTmin / 10; If ΔTmin<0, extend the delay setting of the lower overcurrent protection to increase T22 by |ΔTmin| / 10; Among them, ΔTmin is the difference between T21 and T22; After adjustment, repeat S1 to S3 until the coordination between the upper and lower level relay protections is reliable, and output the adjusted set value recommendations.

9. A relay protection coordination relationship evaluation system for intermittent faults, used to run the method according to any one of claims 1 to 8, characterized in that: The system comprises: The lower-level protection test module is used to construct a lower-level overcurrent protection multi-scenario intermittent fault current model library according to the lower-level overcurrent protection setting parameters. Based on the fault current model library, a current with dynamically changing amplitude and duration is applied to the lower-level relay protection device to simulate a single intermittent fault, multiple intermittent faults and high-resistance intermittent faults, and the minimum return interval T22 of the lower-level overcurrent protection is obtained in combination with environmental correction; The upper protection test module is used to build an upper overcurrent protection multi-scenario intermittent fault current model library according to the upper overcurrent protection setting parameters. Based on the fault current model library, a current with dynamically changing amplitude and duration is applied to the upper relay protection device to simulate a single intermittent fault, multiple intermittent faults and high-resistance intermittent faults, and the minimum return interval T21 of the upper overcurrent protection is obtained in combination with environmental correction; The evaluation module is used to comprehensively consider T21 and T22, calculate the probability of false operation risk by using statistical analysis method, and evaluate whether there is a false operation risk in the coordination relationship between the upper and lower levels of relay protection. If there is a false operation risk, the upper and lower levels of overcurrent protection setting parameters are adaptively adjusted to optimize the coordination relationship between the upper and lower levels of relay protection.

10. 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 execute the steps of the method according to any one of claims 1-8.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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