A backup protection method and system for new energy power systems

Abstract

This invention discloses a backup protection method and system for new energy power systems, belonging to the field of power system relay protection technology. Considering that in new energy power grids, the zero-sequence voltage and current may be very small after a fault, and zero-sequence overcurrent protection cannot identify the fault, after a line fault occurs, in addition to distance protection and zero-sequence overcurrent protection judgment, weak fault identification is further performed to make a judgment in cases where the zero-sequence voltage and current are small. Considering that the zero-sequence voltage and current are very small, a new criterion of the ratio of phase-to-phase voltage to phase voltage after the fault is added to the weak fault identification. The criterion is further supplemented by amplifying the zero-sequence voltage and current, thereby achieving a more comprehensive judgment. This invention utilizes the cooperation between protection systems to reliably clear faults in scenarios where new energy is connected. Moreover, the criterion is simple, the protection action speed is fast, and the safety and stability margin of the hierarchical protection system can be improved.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, and more specifically, relates to a backup protection method and system for new energy power systems. Background Technology

[0002] In recent years, the construction of smart substations characterized by IEC61850 has provided new opportunities for the development of relay protection. Substation-area protection, wide-area protection, and hierarchical protection have become research hotspots in the field of relay protection in recent years. However, with the continuous expansion of the power grid, the setting and coordination of backup protection is becoming increasingly difficult, while higher requirements are being placed on the reliability and speed of transmission line protection.

[0003] Furthermore, the integration of new energy sources also presents new requirements for the coordination between protection systems. In a 110kV power grid, the neutral point is generally directly grounded. When a three-phase asymmetrical fault occurs, the system will generate a large zero-sequence current, thus using the zero-sequence current to construct ground fault protection. However, in a fully renewable energy power grid, the zero-sequence voltage and current after a fault may be very small, and the zero-sequence overcurrent protection may not be able to identify the fault, leading to the relay protection device failing to operate and the fault not being reliably cleared. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a backup protection method and system for new energy power systems, which solves the technical problem that the existing technology cannot reliably isolate faults in the scenario of connecting new energy.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a backup protection method for a new energy power system, comprising: performing the following operations after a line fault occurs in the new energy power system:

[0006] S1. Determine whether the time interval between the current time and the time when the fault occurred is greater than the distance protection activation time t1 = t' + Δt1. If so, control the relay protection device to execute distance protection; otherwise, wait until the time interval between the current time and the time when the fault occurred is greater than the distance protection activation time t1. Where t' is the longest delay of the hierarchical protection of the system, and Δt1 is the first preset time.

[0007] S2. Distance protection: If the distance between the fault point and the relay protection device is less than the preset distance, proceed to step S5; otherwise, if the fault is a ground fault, proceed to step S3; if the fault is a phase-to-phase fault, proceed to step S4.

[0008] S3. Zero-sequence overcurrent protection: Control the relay protection device to perform zero-sequence overcurrent protection, and in this process determine whether the current zero-sequence current is greater than the first preset current value. If yes, proceed to step S5; otherwise, proceed to step S4.

[0009] S4. Weak Fault Identification: Determine whether the three-phase voltage and three-phase current at the relay protection device in the system at the current moment meet the weak fault identification criteria. If they do, proceed to step S5; otherwise, determine that the fault has been cleared and the backup protection is completed.

[0010] Among them, the weak fault identification criteria include: within the first preset time period, the effective value of each phase voltage is within the preset voltage range, and the larger of the effective value and the maximum value of each phase current is greater than the second preset current value, and the ratio of the maximum phase voltage to the maximum phase voltage is greater than the preset ratio.

[0011] Alternatively, the effective value of the zero-sequence voltage is 3 times greater than the preset voltage value, and the larger of the effective value and the maximum value of the phase current within the preset time period is greater than the preset current value.

[0012] Alternatively, the effective value of the zero-sequence current is greater than the preset current value;

[0013] S5. The circuit breaker is controlled to clear the fault, and backup protection is completed.

[0014] More preferably, the weak fault identification criteria include: a first action criterion, a second action criterion, and a third action criterion;

[0015] The first action criterion is:

[0016]

[0017] The second action criterion is:

[0018]

[0019] The third action criterion is:

[0020]

[0021] Where t0 is the sampling start time; T is the power frequency period; u a (t) represents the phase a voltage at the relay protection device in the system at time t; u b (t) represents the phase b voltage at the relay protection device in the system at time t; u c (t) represents the c-phase voltage at the relay protection device in the system at time t; Δt is the sampling interval; α is the first preset coefficient; U N β is the rated phase voltage of the line; β is the second preset coefficient; γ is the third preset coefficient; This represents the maximum value of the three-phase current on the corresponding side; For the corresponding side Phase current sampling value, I set There is a current threshold; i0(t) is the zero-sequence current value at time t, I0set This is the threshold value for zero-sequence current.

[0022] More preferably, step S2 includes:

[0023] Based on the three-phase voltage and three-phase current at the relay protection device in the system at the current moment, calculate the operating voltage and polarization voltage of the line;

[0024] If the distance between the fault point and the relay protection device is less than the preset distance, and the amplitudes of the operating voltage and polarization voltage are both greater than the preset voltage values ​​within the second preset time period, and their polarities are opposite, then proceed to step S6; otherwise, if the fault is a ground fault, proceed to step S4; if the fault is a phase-to-phase fault, proceed to step S5.

[0025] More preferably, step S3 further includes: before executing zero-sequence overcurrent protection, determining whether the time interval between the current time and the time when the fault occurred is greater than the zero-sequence overcurrent protection activation time t2 = t1 + Δt2; if so, executing zero-sequence overcurrent protection; otherwise, waiting until the time interval between the current time and the time when the fault occurred is greater than the zero-sequence overcurrent protection activation time t2; wherein, Δt2 is a second preset time.

[0026] More preferably, step S4 further includes: before performing weak fault identification, determining whether the time interval between the current time and the time when the fault occurred is greater than the weak fault identification input time t3 = t2 + Δt3; if so, performing weak fault identification; otherwise, waiting until the time interval between the current time and the time when the fault occurred is greater than the weak fault identification input time t3; wherein, Δt3 is a third preset time.

[0027] In a second aspect, the present invention provides a backup protection system for a new energy power system, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the backup protection method provided in the first aspect of the present invention when executing the computer program.

[0028] Thirdly, the present invention provides a relay protection system for a new energy power system, comprising: a relay protection device and a backup protection controller;

[0029] The backup protection controller is used to execute the backup protection method provided in the first aspect of the present invention.

[0030] Fourthly, the present invention also provides a computer-readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls the device in which the storage medium is located to perform the backup protection method provided in the first aspect of the present invention.

[0031] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0032] 1. This invention provides a backup protection method for new energy power systems. Considering that in new energy power grids, the zero-sequence voltage and current may be very small after a fault, and zero-sequence overcurrent protection cannot identify the fault, after a line fault occurs, in addition to distance protection and zero-sequence overcurrent protection judgment, weak fault identification is further performed to make a judgment in cases where the zero-sequence voltage and current are small. Considering that the zero-sequence voltage and current are very small, a new criterion of the ratio of phase-to-phase voltage to phase voltage after the fault is first added to the weak fault identification, and then the criterion is supplemented by amplifying the zero-sequence voltage and current, thereby achieving a more comprehensive and sufficient judgment. This invention utilizes the cooperation between protection systems to reliably disconnect faults in scenarios where new energy is connected.

[0033] 2. Furthermore, the backup protection method for new energy power systems provided by the present invention, in addition to determining whether the distance between the fault point and the relay protection device is less than a preset distance, also needs to determine whether the amplitude of the working voltage and the polarization voltage are both greater than the preset voltage value and the polarities of the two are opposite during the second preset time period, which is beneficial to improving the situation of failure to operate or false operation when a fault occurs at the output of the protection device.

[0034] 3. Furthermore, the backup protection method for new energy power systems provided by the present invention executes zero-sequence overcurrent protection only after the time interval between the current time and the time of the fault occurrence is greater than the zero-sequence overcurrent protection activation time, which is beneficial to the coordination between different protections and ensures the selectivity of relay protection.

[0035] 4. Furthermore, the backup protection method for new energy power systems provided by the present invention performs weak fault identification only after determining whether the time interval between the current time and the time of the fault occurrence is greater than the weak fault identification activation time. This is beneficial for the coordination between different protection systems and ensures the selectivity of relay protection.

[0036] 5. The backup protection method for new energy power systems provided by this invention has simple criteria and fast protection action speed, effectively solving the problems of difficult coordination of backup protection for transmission lines and the inability to reliably clear faults caused by protection device failure to operate, and can improve the safety and stability margin of the hierarchical protection system. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the 110kV high-proportion new energy power system structure provided by the present invention;

[0038] Figure 2 A flowchart of the backup protection method for reliably clearing faults provided by the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0040] Firstly, this invention addresses the problems of difficult coordination of backup protection for transmission lines and the inability to reliably clear faults caused by protection device malfunctions. It proposes a backup protection method for reliably clearing faults. By utilizing the coordinated operation of distance protection, zero-sequence overcurrent protection, and weak fault identification criteria, the problem of traditional line backup protection failing to accurately identify faults can be solved, effectively improving the system's safety and stability margin.

[0041] This will be illustrated using a high-proportion renewable energy power system as an example. Figure 1 As shown, the system includes: a 110kV high-proportion renewable energy system 1, a transformer 2, a first relay protection device 3, a transmission line 4, a second relay protection device 5, a transformer 6, and an external power grid 7. Figure 1 A phase A short circuit fault occurred at 50% of the forward protected line of the first relay protection device in the 110kV system shown. Figure 1 Taking point f (with a transition resistor of 150Ω) as an example. Figure 2 As shown, when a line fault occurs in the new energy power system, the following operations shall be performed:

[0042] S1. Determine whether the time interval between the current moment and the fault occurrence moment is greater than the distance protection activation time t1 = t' + Δt1. If so, control the relay protection device to execute distance protection; otherwise, wait until the time interval between the current moment and the fault occurrence moment is greater than the distance protection activation time t1. Wherein, t' is the longest delay of the hierarchical protection of the system, and Δt1 is the first preset time, which is used to represent the coordination time of the longest delay of distance protection and hierarchical protection, and is generally related to the circuit breaker operation time. In this embodiment, t' is taken as 1.8s and Δt1 is taken as 0.5s.

[0043] S2. Distance protection: If the distance between the fault point and the relay protection device is less than the preset distance (distance protection criterion), proceed to step S5; otherwise, if the fault is a ground fault, proceed to step S3; if the fault is a phase-to-phase fault, proceed to step S4.

[0044] It should be noted that the expression for the distance protection criterion is as follows:

[0045] |l|<l set

[0046] Where |l| is the distance between the fault point and the relay protection device; l set The preset distance is specifically the distance between the installation point of the relay protection device and the setting point. The sensitivity is set according to the total length of the protection line. In this embodiment, the value is 0.8L, where L is the total length of the line.

[0047] This is beneficial for improving the situation where the protection device fails to operate or operates erroneously when there is a fault at the outlet. Preferably, in an optional implementation, the distance protection criterion further includes: determining whether the working voltage and polarization voltage amplitudes are both greater than the preset voltage value and the polarities of the two are opposite within a second preset time period.

[0048] Specifically, in this embodiment, step S2 includes:

[0049] Based on the three-phase voltage and current at the relay protection device in the system at the current moment, calculate the operating voltage and polarization voltage of the line.

[0050] If the distance between the fault point and the relay protection device is less than the preset distance, and the amplitudes of the operating voltage and polarization voltage are both greater than the preset voltage values ​​within the second preset time period, and their polarities are opposite, then proceed to step S6; otherwise, if the fault is a ground fault, proceed to step S4; if the fault is a phase-to-phase fault, proceed to step S5.

[0051] It should be noted that before calculating the line's operating voltage and polarization voltage, it is necessary to determine whether the fault is a ground fault or a phase-to-phase fault. This involves the following steps:

[0052] The three-phase voltage and three-phase current at the relay protection device are filtered in real time; the phase operating voltage change and phase-to-phase operating voltage change are calculated using the filtered three-phase voltage and three-phase current, and phase selection calculation is performed to determine whether it is a ground fault or a phase-to-phase fault.

[0053] Specifically, the formulas for calculating the magnitude of the phase operating voltage and the phase-to-phase operating voltage variation are as follows:

[0054]

[0055]

[0056] in, The amplitude of the phase operating voltage change; k0 is the current sampling point; N is the number of sampling points in one cycle; The phase operating voltage is denoted by Δt; Δt is the sampling interval; and T is the power frequency period. This refers to the amplitude of the phase-to-phase operating voltage change. Let be the phase-to-phase operating voltage of the k-th sample; where, Indicates phase; It indicates any two phases alternating.

[0057] The method for phase selection calculation is as follows:

[0058] First, compare the changes in the operating voltage of the three phases. Take the largest phase The change in interphase operating voltage between the other two phases If the ratio is greater than a preset multiple, it is judged as a single-phase fault (i.e., a ground fault); if it does not meet the requirement, it is judged as a phase-to-phase fault. The largest of the three is the phase with the phase-to-phase fault being measured.

[0059] Specifically, regarding the criterion that the amplitudes of both the operating voltage and the polarization voltage are greater than the preset voltage value and their polarities are opposite during the second preset time period, when the fault is a ground fault or a phase-to-phase fault, the specific expressions are as follows: Determine whether the following condition is met at any time t during the second preset time period:

[0060] Grounding criterion:

[0061] Alternating Criteria:

[0062] in, These represent the operating voltage and polarization voltage at time t during a ground fault, respectively. These are the operating voltage and polarization voltage at time t during a phase-to-phase fault, U set1 and U set2 The preset voltage value is the low voltage threshold setting. When all voltage and current samples within a time window meet the criteria, the protection element trips. In this embodiment, the duration of the second preset time period is 5ms. set1 and U set2 The values ​​are 6V and 8V respectively.

[0063] S3. Zero-sequence overcurrent protection: Control the relay protection device to perform zero-sequence overcurrent protection, and in this process determine whether the current zero-sequence current is greater than the first preset current value. If yes, proceed to step S5; otherwise, proceed to step S4.

[0064] Specifically, the expression for the zero-sequence overcurrent protection criterion is as follows:

[0065] I0>I set.0

[0066] Where I0 is the zero-sequence current, I set.0 The first preset current value is the zero-sequence current threshold value, which is higher than the unbalanced current during normal operation. In this embodiment, the value is 0.5kA.

[0067] Furthermore, in order to optimize the coordination between different protections and ensure the selectivity of relay protection, preferably, in an optional implementation, step S3 above further includes: before executing zero-sequence overcurrent protection, determining whether the time interval between the current time and the time of the fault occurrence is greater than the zero-sequence overcurrent protection activation time t2 = t1 + Δt2; if so, executing zero-sequence overcurrent protection; otherwise, waiting until the time interval between the current time and the time of the fault occurrence is greater than the zero-sequence overcurrent protection activation time t2; wherein, Δt2 is a second preset time, representing the set coordination time between zero-sequence overcurrent protection and distance protection; in this embodiment, Δt2 is taken as 0.5s.

[0068] S4. Weak Fault Identification: Determine whether the three-phase voltage and three-phase current at the relay protection device in the system at the current moment meet the weak fault identification criteria. If they do, proceed to step S5; otherwise, determine that the fault has been cleared and the backup protection is completed.

[0069] Considering that the zero-sequence voltage and current after a fault may be very small, and the zero-sequence overcurrent protection cannot identify the fault, a weak fault identification process is further performed when the zero-sequence overcurrent protection criterion is not met. This is achieved by first adding a new criterion—the ratio of phase-to-phase voltage to phase voltage after a fault—to the weak fault identification process, and then supplementing the criterion by amplifying the zero-sequence voltage and current, thus achieving a more comprehensive and sufficient judgment. Specifically, the weak fault identification criteria include: a first action criterion, a second action criterion, and a third action criterion; meeting any one of these criteria is sufficient.

[0070] First action criterion: Within a first preset time period, the effective value of each phase voltage is within a preset voltage range, and the larger of the effective value and the maximum value of each phase current is greater than a second preset current value, and the ratio of the maximum phase-to-phase voltage to the maximum phase voltage is greater than a preset ratio; specifically:

[0071]

[0072] The second action criterion is: the effective value of the zero-sequence voltage is three times greater than the preset voltage value, and the larger of the effective value and the maximum value of the phase current within the preset time period is greater than the preset current value; specifically:

[0073]

[0074] The third criterion is: the effective value of the zero-sequence current is greater than the preset current value; specifically:

[0075]

[0076] Where t0 is the sampling start time; T is the power frequency period; u a (t) represents the phase a voltage at the relay protection device in the system at time t; u b(t) represents the phase b voltage at the relay protection device in the system at time t; u c (t) represents the c-phase voltage at the relay protection device in the system at time t; Δt is the sampling interval; α is the first preset coefficient, preferably 0.1; U N β is the rated phase voltage of the line; β is the second preset coefficient (waveform similarity coefficient), preferably 0.15; γ is the third preset coefficient, preferably 0.75. This represents the maximum value of the three-phase current on the corresponding side; For the corresponding side Phase current sampling value, I set There is a current threshold; i0(t) is the zero-sequence current value at time t, I 0set This is the zero-sequence current threshold value. In this embodiment, the first preset time period is 5ms; Δt is 250μs, T is 50Hz, and U is 0.1. N The value is 110kV; I set The value is 0.2kA; I 0set The value is 0.5kA.

[0077] Furthermore, to optimize the coordination between different protection systems and ensure the selectivity of relay protection, preferably, in an optional implementation, step S4 further includes: before performing weak fault identification, determining whether the time interval between the current time and the fault occurrence time is greater than the weak fault identification activation time t3 = t2 + Δt3; if so, performing weak fault identification; otherwise, waiting until the time interval between the current time and the fault occurrence time is greater than the weak fault identification activation time t3; wherein, Δt3 is a third preset time, representing the set waiting time for the system to enter a steady state. In this embodiment, Δt3 is taken as 0.5s.

[0078] S5. The circuit breaker is controlled to clear the fault, and backup protection is completed.

[0079] In this embodiment, the calculation is based on the three-phase voltage and three-phase current at the relay protection device in the system after the fault occurs. The distance protection criterion and the zero-sequence overcurrent protection criterion are not met. The weak fault identification criterion is met 3.3s after the fault occurs, and the circuit breaker is controlled to clear the fault, thus reliably clearing the fault.

[0080] In summary, this invention provides a reliable backup protection method for fault clearing. After a line fault occurs, the three-phase voltage and three-phase current at the corresponding protection installation point are processed by the same low-pass filter and then phase selection calculation is performed. Based on the phase selection calculation results and measured voltage and current, it is sequentially determined whether the distance protection, zero-sequence overcurrent protection, and weak fault identification criteria are met. If they are met, the corresponding protection operates; if not, the operation conditions are continuously checked, and the fault is reliably cleared by coordinating the protections. The backup protection method for reliable fault clearing proposed in this invention has simple criteria and fast protection operation speed. It can reliably clear metallic faults and high-resistance grounding faults on the line, effectively solving the problems of difficult coordination of backup protection for transmission lines and the inability to reliably clear faults caused by protection device failure to operate. It provides reliable backup protection for the line and effectively improves the safety and stability margin of the hierarchical protection system.

[0081] In a second aspect, the present invention provides a backup protection system for a new energy power system, comprising: a memory and a processor, wherein the memory stores a computer program, and the processor executes the backup protection method provided in the first aspect of the present invention when executing the computer program.

[0082] The relevant technical solutions are the same as the backup protection method provided in the first aspect of this invention, and will not be described in detail here.

[0083] Thirdly, the present invention provides a relay protection system for a new energy power system, comprising: a relay protection device and a backup protection controller;

[0084] The backup protection controller is used to execute the backup protection method provided in the first aspect of the present invention.

[0085] The relevant technical solutions are the same as the backup protection method provided in the first aspect of this invention, and will not be described in detail here.

[0086] Fourthly, the present invention also provides a computer-readable storage medium comprising a stored computer program, wherein the computer program, when executed by a processor, controls the device in which the storage medium is located to perform the backup protection method provided in the first aspect of the present invention.

[0087] The relevant technical solutions are the same as the backup protection method provided in the first aspect of this invention, and will not be described in detail here.

[0088] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A backup protection method for a new energy power system, characterized in that, include: When a line fault occurs in a new energy power system, perform the following operations: S1. Determine whether the time interval between the current time and the time when the fault occurred is greater than the distance protection activation time t1 = t' + Δt1. If so, control the relay protection device to execute distance protection; otherwise, wait until the time interval between the current time and the time when the fault occurred is greater than the distance protection activation time t1. Where t' is the longest delay of the hierarchical protection of the system, and Δt1 is the first preset time. S2. Distance protection: If the distance between the fault point and the relay protection device is less than the preset distance, proceed to step S5; otherwise, if the fault is a ground fault, proceed to step S3; if the fault is a phase-to-phase fault, proceed to step S4. S3. Zero-sequence overcurrent protection: Control the relay protection device to perform zero-sequence overcurrent protection, and in this process determine whether the current zero-sequence current is greater than the first preset current value. If yes, proceed to step S5; otherwise, proceed to step S4. S4. Weak Fault Identification: Determine whether the three-phase voltage and three-phase current at the relay protection device in the system at the current moment meet the weak fault identification criteria. If they do, proceed to step S5; otherwise, determine that the fault has been cleared and the backup protection is completed. Among them, the weak fault identification criteria include: within the first preset time period, the effective value of each phase voltage is within the preset voltage range, and the larger of the effective value and the maximum value of each phase current is greater than the second preset current value, and the ratio of the maximum phase voltage to the maximum phase voltage is greater than the preset ratio. Alternatively, the effective value of the zero-sequence voltage is 3 times greater than the preset voltage value, and the larger of the effective value and the maximum value of the phase current within the preset time period is greater than the preset current value. Alternatively, the effective value of the zero-sequence current is greater than the preset current value; S5. The circuit breaker is controlled to clear the fault, and backup protection is completed.

2. The backup protection method according to claim 1, characterized in that, The weak fault identification criteria include: a first action criterion, a second action criterion, and a third action criterion; The first action criterion is: The second action criterion is: The third action criterion is: Where t0 is the sampling start time; T is the power frequency period; u a (t) represents the phase a voltage at the relay protection device in the system at time t; u b (t) represents the phase b voltage at the relay protection device in the system at time t; u c (t) represents the c-phase voltage at the relay protection device in the system at time t; Δt is the sampling interval; α is the first preset coefficient; U N β is the rated phase voltage of the line; β is the second preset coefficient; γ is the third preset coefficient; This represents the maximum value of the three-phase current on the corresponding side; For the corresponding side Phase current sampling value, I set There is a current threshold; i0(t) is the zero-sequence current value at time t, I 0set This is the threshold value for zero-sequence current.

3. The backup protection method according to claim 1, characterized in that, Step S2 includes: Based on the three-phase voltage and three-phase current at the relay protection device in the system at the current moment, calculate the operating voltage and polarization voltage of the line; If the distance between the fault point and the relay protection device is less than the preset distance, and the amplitudes of the operating voltage and polarization voltage are both greater than the preset voltage values ​​within the second preset time period, and their polarities are opposite, then proceed to step S6; otherwise, if the fault is a ground fault, proceed to step S4; if the fault is a phase-to-phase fault, proceed to step S5.

4. The backup protection method according to any one of claims 1-3, characterized in that, Step S3 further includes: Before executing zero-sequence overcurrent protection, determine whether the time interval between the current time and the time when the fault occurred is greater than the zero-sequence overcurrent protection activation time t2 = t1 + Δt2. If so, execute zero-sequence overcurrent protection; otherwise, wait until the time interval between the current time and the time when the fault occurred is greater than the zero-sequence overcurrent protection activation time t2. Wherein, Δt2 is the second preset time.

5. The backup protection method according to any one of claims 1-3, characterized in that, Step S4 further includes: Before performing weak fault identification, determine whether the time interval between the current time and the time when the fault occurred is greater than the weak fault identification input time t3 = t2 + Δt3. If so, perform weak fault identification; otherwise, wait until the time interval between the current time and the time when the fault occurred is greater than the weak fault identification input time t3. Here, Δt3 is the third preset time.

6. A backup protection system for a new energy power system, characterized in that, include: A memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to perform the backup protection method according to any one of claims 1-5.

7. A relay protection system for a new energy power system, characterized in that, include: Relay protection devices and backup protection controllers; The backup protection controller is used to execute the backup protection method according to any one of claims 1-5.

8. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored computer program, wherein when the computer program is executed by a processor, it controls the device containing the storage medium to perform the backup protection method according to any one of claims 1-5.

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