Self-adaptive differential protection method based on fault duration

Abstract

The embodiment of the invention discloses a self-adaptive differential protection method based on fault duration, and relates to the technical field of power system relay protection, and the method comprises the steps: obtaining a power system fault signal, and starting timing based on the fault signal, so as to determine the fault duration; if the fault duration does not exceed a first preset threshold value, first protection logic is executed, and the first protection logic is used for conducting rapid fault recognition through a fault transient component; if the fault duration exceeds the first preset threshold value, switching to a second protection logic which is used for performing reliable fault identification by using a fault steady-state component; different logics are adopted in the fault transient state stage and the fault steady state stage, self-adaption of the protection strategy is achieved, protection rapidity and reliability are both considered, and protection accuracy and adaptability to complex working conditions are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system relay protection technology, and in particular to an adaptive differential protection method based on fault duration. BACKGROUND

[0002] Differential protection is the core protection mode of key power equipment such as generator-transformer units, and its basic principle is to determine whether there is an internal fault by comparing the difference of the currents on both sides of the protected equipment. In an ideal case, the differential current is zero when there is an external fault, and the differential current is the fault current when there is an internal fault.

[0003] At present, the differential protection scheme usually adopts fixed protection logic and setting parameters. For example, some schemes use transient components at the initial stage of the fault, such as fault component currents, for fault judgment. The advantage of this method is fast response speed, which can quickly identify and remove faults at the moment of fault occurrence. However, its disadvantage is that as the fault continues, the transient component will quickly decay or become distorted due to system oscillation, which may lead to a decrease in the reliability of the protection, especially in some complex fault conditions. Other schemes are based on steady-state components, such as full-current frequency phasors, for judgment. This method has high reliability and selectivity after the system enters a new steady state, but its disadvantage is that it needs a certain data window to accurately calculate the frequency phasor at the initial stage of the fault, resulting in a relatively slow response speed.

[0004] It can be seen that the current differential protection scheme is difficult to adapt to the dynamic evolution process of the fault, and cannot simultaneously consider the rapidity and reliability of the protection action, especially in complex system conditions, which may lead to the risk of internal fault rejection or external fault misoperation. SUMMARY

[0005] The main purpose of the present application is to provide an adaptive differential protection method based on fault duration, which can solve the technical problem that the fixed protection logic of differential protection cannot simultaneously consider the rapidity and reliability of fault identification.

[0006] To achieve the above-mentioned purpose, the first aspect of the present application provides an adaptive differential protection method based on fault duration, which comprises:

[0007] Obtaining a fault signal of a power system and starting a timer based on the fault signal to determine the fault duration;

[0008] If the fault duration does not exceed a first preset threshold, a first protection logic is executed, which is used to use fault transient components for rapid fault identification;

[0009] If the fault duration exceeds the first preset threshold, switch to the second protection logic, and the second protection logic is used for reliable fault identification using a fault steady-state component.

[0010] The second aspect of the present application provides an adaptive differential protection device, comprising:

[0011] A signal acquisition module is configured to acquire a power system fault signal.

[0012] A timing module is configured to start timing based on the fault signal to determine the fault duration.

[0013] A logic control module is configured to execute the first protection logic if the fault duration does not exceed the first preset threshold, and the first protection logic is used for fast fault identification using a fault transient component.

[0014] The logic control module is further configured to switch to the second protection logic if the fault duration exceeds the first preset threshold, and the second protection logic is used for reliable fault identification using a fault steady-state component.

[0015] The present application provides an adaptive differential protection method based on fault duration, which acquires a power system fault signal, and starts timing based on the fault signal to determine the fault duration. If the fault duration does not exceed the first preset threshold, the first protection logic is executed, and the first protection logic is used for fast fault identification using a fault transient component. If the fault duration exceeds the first preset threshold, the second protection logic is switched to, and the second protection logic is used for reliable fault identification using a fault steady-state component. The present application has the following beneficial effects:

[0016] 1. The accuracy and reliability of the protection are improved. By using more targeted protection logic in the fault transient stage and the steady-state stage, internal faults and external faults can be more accurately distinguished, and fast and reliable action can be achieved in internal faults, and effective blocking can be achieved in external faults to avoid misoperation. 2. The rapidity and selectivity of the protection are considered. The first protection logic based on transient components is used in the early stage of the fault to ensure the instantaneous response ability to internal faults. The second protection logic based on steady-state components is switched to in the later stage of the fault to ensure the selectivity of the protection under complex conditions, and the technical contradiction that the traditional fixed logic protection scheme is difficult to achieve both is solved. 3. The adaptive ability of the protection is enhanced. The present application enables the protection device to actively adapt to the dynamic evolution process of the fault, rather than using a fixed criterion, which significantly improves the intelligent level of the relay protection and the adaptability to complex power grid environments. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the accompanying drawings in the following description only only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0018] Wherein:

[0019] Figure 1 The flow of the adaptive differential protection method based on fault duration provided by the embodiment of the present application;

[0020] Figure 2 The schematic diagram of the adaptive differential protection principle provided by the embodiment of the present application;

[0021] Figure 3 Another schematic diagram of the adaptive differential protection principle provided by the embodiment of the present application;

[0022] Figure 4 The schematic diagram of the action waveform of the fault component current protection within 40ms after the fault occurs provided by the embodiment of the present application;

[0023] Figure 5 Another schematic diagram of the action waveform of the fault component current protection within 40ms after the fault occurs provided by the embodiment of the present application;

[0024] Figure 6 The schematic diagram of the action waveform of the fault component current protection after 40ms after the fault occurs provided by the embodiment of the present application;

[0025] Figure 7 Another schematic diagram of the action waveform of the fault component current protection after 40ms after the fault occurs provided by the embodiment of the present application;

[0026] Figure 8 Another schematic diagram of the action waveform of the fault component current protection after 40ms after the fault occurs provided by the embodiment of the present application;

[0027] Figure 9 The schematic diagram of the structure of the adaptive differential protection device provided by the embodiment of the present application. DETAILED DESCRIPTION

[0028] In the following, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0029] The terms "first", "second", etc. in the specification and claims of the present application and the above drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed or can optionally include other steps or units inherent to the process, method, product or device.

[0030] In this document, the term "embodiment" means that a specific feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive of other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] The embodiments of the present application will be described in conjunction with the drawings in the embodiments of the present application.

[0032] Please refer to Figure 1 , which shows a flowchart of a self-adaptive differential protection method based on fault duration provided by an embodiment of the present application. As Figure 1 shown, the method comprises:

[0033] 101, obtaining a power system fault signal, and starting timing based on the above fault signal to determine the fault duration.

[0034] The execution subject in the embodiments of the present application can be a self-adaptive differential protection device. In actual application, the device can be a self-adaptive differential protection system regarded as a hardware device and software function.

[0035] The self-adaptive differential protection mentioned in the embodiments of the present application mainly dynamically adjusts the protection strategy according to the running state and structural changes of the power equipment and system, so as to realize the best protection function.

[0036] Figure 2 A self-adaptive differential protection principle diagram provided by an embodiment of the present application. AsFigure 2 As shown, the adaptive relay dynamically changes the working characteristics of the relay protection device by adjusting the protection setting value, selecting different protection algorithms and different protection criteria, etc. through the system state parameters, so that the protection can automatically adapt to the current operating state of the system, and improve the sensitivity and accuracy of the protection action.

[0037] For the power system, the line current can be continuously monitored, and the collected data can be analyzed in real time. Specifically, during the operation of the power system, the currents, voltages and other signals of each key node are monitored in real time. When an abnormal signal such as a sudden change in current or abnormal fluctuation in voltage is detected, it is judged that a fault has occurred in the power system, and a timer is immediately started to record the duration after the fault occurs. For example, by setting monitoring devices at the current transformers and voltage transformers of the generator set in the substation, when a sudden increase in current or a sudden drop in voltage is detected, a fault signal is triggered and timing is started to obtain the above-mentioned fault duration.

[0038] In the embodiments of the present application, the first preset threshold can be set in advance. If the fault duration does not exceed the first preset threshold, step 102 can be performed; if it exceeds, step 103 can be performed.

[0039] Optionally, before the first protection logic or the second protection logic is executed, a frequency tracking process can also be performed, including:

[0040] The frequency tracking method based on a short data window is adopted to calculate the system frequency of the power system, and the system frequency is used for subsequent protection logic calculation.

[0041] The conventional phasor calculation method based on Fourier transform will produce a large error when the frequency deviates from the rated value, which will further affect the accuracy of the differential protection. The frequency tracking method proposed in the embodiments of the present application can quickly capture the change of the system frequency with a very short data window, and provide an accurate frequency reference for subsequent protection calculation.

[0042] Generally, frequency tracking adopts a linear fitting zero-crossing point algorithm, which can better meet the error requirement when the system frequency is within the normal range, but for a substation, the frequency changes greatly during the start-stop process. The algorithm requires a complete electrical quantity cycle to obtain a relatively accurate result, and is prone to large calculation errors. Therefore, a frequency tracking technology based on machine learning short data window is proposed in the embodiments of the present application. This method calculates three line electrical quantities using three-phase electrical quantities e a , e b and e c :

[0043]

[0044] In the formula, eab e bc and e ca It represents the electrical quantity between two phases.

[0045] Then, two electrical quantities with shorter phase differences are selected from the three phase electrical quantities and the three line electrical quantities to achieve rapid frequency calculation. The formula for calculating the period of the measured electrical quantity is as follows:

[0046]

[0047] In the formula: T e e is the period of the measured electrical quantity; x and e y Let e ​​be the two selected electrical quantities; Δθ is e x ahead of e y Phase difference; T s Let G be the sampling interval, and e be the value of e. x and e y Number of samples between zero crossings; e x (m-1) is e x A sampling point before the zero-crossing point from negative to positive, e x (m) represents the next sampling point; e y (n-1) is e y A sampling point before the zero-crossing point from negative to positive, e y (n) represents the next sampling point.

[0048] The frequency of the measured electrical quantity is calculated as follows:

[0049]

[0050] In the formula: f e The frequency of the electrical quantity being measured.

[0051] From the above analysis, it can be seen that by using the short data window frequency tracking algorithm, the frequency calculation time is shortened to T. e ·Δθ / 2π. Assume that when e is chosen... ab and e a When performing calculations, the phase difference between the two is Δθ = π / 6, thus reducing the frequency calculation time to T. e / 12 will significantly improve the speed of frequency tracking calculations.

[0052] By adding the above frequency tracking processing, the adaptability and reliability of the system under harsh operating conditions with unstable system frequency can be significantly enhanced, avoiding protection misjudgments caused by frequency mismatch.

[0053] 102. If the duration of the above-mentioned fault does not exceed the first preset threshold, the first protection logic is executed. The first protection logic is used to perform rapid fault identification by utilizing the transient components of the fault.

[0054] Specifically, at each calculation cycle (e.g. 1 millisecond), a judgment can be performed, i.e. comparing whether the current fault duration t exceeds a first preset threshold T1.

[0055] If the judgment result is no (i.e. t < T1), it means that the fault is still in the transient stage, and the first protection logic will be performed. In the embodiment, a composite criterion strategy of parallel operation and segmented investment is adopted in the first protection logic, so as to balance the rapidity and sensitivity of protection.

[0056] In an optional implementation, the above performing the first protection logic comprises:

[0057] using a high-threshold fault component current differential protection based on a first data window in a preset first time period after the fault occurs; and

[0058] parallelly using a low-threshold fault component current differential protection based on a second data window in a preset second time period after the fault occurs, the second data window having a length greater than the first data window.

[0059] The first time period is before the second time period. For example, T1 is 40 ms, the preset first time period after the fault occurs can be 10 milliseconds to 20 milliseconds after the fault occurs, and the preset second time period after the fault occurs can be 20 milliseconds to 40 milliseconds after the fault occurs.

[0060] In the embodiment, in order to wait for confirmation of the fault authenticity, at least 10 ms of disturbance needs to be tolerated without misoperation; and transient interference (such as switch jitter) such as pre-breakdown current when the circuit breaker is closed, transformer excitation inrush current, and line charging capacitor transient process is avoided.

[0061] Specifically, in the first time period after the fault occurs, a high-threshold fault component current differential protection criterion based on a short data window (such as a short data window of 10 milliseconds) can be put into operation. Here, the "fault component current" refers to the current after the fault minus the memory current before the fault, and this method can effectively filter out the influence of load current, thereby highlighting the fault characteristics. The short data window is used to obtain calculation results as soon as possible, so as to realize fast response.

[0062] In the second time period after the fault occurs, another low-threshold fault component current differential protection criterion based on a long data window (such as a long data window of 20 milliseconds) is put into operation in parallel. The long data window (such as 20 milliseconds, corresponding to one complete cycle of 50 Hz power frequency) can more accurately calculate the fault component, thereby improving the sensitivity of the criterion.

[0063] The action equations of the criteria in the two time periods above can be similar, but the parameters in the first time period can be set to a higher start threshold and a larger braking coefficient to ensure rapid action in case of severe internal faults and sufficient anti-saturation capability in case of external faults. In contrast, the parameters in the second time period are set to a lower start threshold and a smaller braking coefficient. This criterion is mainly used to detect internal faults with less obvious characteristics, as a supplement to the previous criterion.

[0064] For example, the action equation for the above criterion can be expressed as:

[0065] |I d.Δ |>K·|I r.Δ |+I start.H ;

[0066] Among them, I d.Δ For the fault component differential current, I r.Δ This is the fault component braking current.

[0067] Table 1 is a comparison table of protection parameters activated within 30ms of a fault occurrence, provided in an embodiment of this application.

[0068]

[0069] Table 1

[0070] For example, as shown in Table 1, the parameters in the first time period are set to a higher start-up threshold I. start.H (For example, the conventional differential starting current I) dz The differential protection (main protection) time in this application embodiment is selected as 20-30ms, and the parameters in the second time period are set to a lower start threshold (e.g., 1 times I). dz And a smaller braking coefficient (e.g., fluctuating between 0.2 and 0.3).

[0071] Figure 3 This is a schematic diagram illustrating another adaptive differential protection principle provided in an embodiment of this application. (See diagram below.) Figure 3 As shown, within 40ms of a fault occurrence, fault component current differential protection is employed because the fault component characteristics are extracted relatively accurately. Furthermore, a combination of long and short data windows is used to improve the selectivity, speed, sensitivity, and reliability of the protection. Within 10–20ms of a fault occurrence, fault component current differential protection with a high threshold and high restraint coefficient is activated. Within 20–40ms of a fault occurrence, fault component current differential protection with a low threshold and low restraint coefficient is activated.

[0072] When the fault is not timely removed within 40 ms, since the fault component cannot be accurately extracted at this time, the protection is adjusted to be a combination of full current, zero sequence current and negative sequence current, thereby improving the accuracy of the protection, and the data window size can be 20 ms.

[0073] At any time t < 40 ms, as long as any one of the above two criteria meets the action condition, the system can determine that it is an internal fault, and a trip command can be sent.

[0074] 103、If the fault duration exceeds the first preset threshold, the second protection logic is switched to, and the second protection logic is used for reliable fault identification using a fault steady-state component.

[0075] If the fault duration exceeds the first preset threshold, the fault has lasted for a period of time, the transient component has basically decayed, and the system has entered a steady state or a quasi-steady state, at which time the second protection logic can be executed.

[0076] In an optional embodiment, the second protection logic specifically includes:

[0077] A protection measure combining full current differential protection, zero sequence current differential protection and negative sequence current differential protection.

[0078] In the second protection logic of the embodiments of the present application, a strategy of parallel operation of multiple mature and reliable steady-state differential protection criteria can be used to improve the reliability and selectivity of the protection. Specifically, the following three protection criteria can be operated in parallel in the second protection logic, and the calculation of the three protection criteria is based on full current frequency phasors extracted by a preset data window (such as 20 ms):

[0079] 1. Full current ratio restraint differential protection: This is the most common form of differential protection, and the action criterion is |I d |>K·|I r |+I start , where I d is a full current differential current phasor, and I r is a full current restraint current phasor. The criterion has good response to various types of phase-to-phase faults.

[0080] 2. Zero sequence current differential protection: This criterion is specifically used for detecting ground faults, and the difference between the zero sequence currents on both sides of the protected equipment is compared to determine the fault, which has high sensitivity and is not affected by load current and system oscillation.

[0081] 3. Negative sequence current differential protection: This criterion is very sensitive to asymmetric faults (such as phase-to-phase faults and single-phase ground faults), and can effectively distinguish between internal faults and external asymmetric faults.

[0082] When the fault duration is monitored to exceed the first preset threshold, for example, any time t≥40 milliseconds, as long as any one of the above three steady-state protection criteria meets its own action condition, the system can determine an internal fault based on the second protection logic and send a trip command. This combination ensures comprehensive coverage and reliable discrimination of various faults.

[0083] In an optional embodiment, the second protection logic is specifically:

[0084] extracting steady-state power frequency phasors of the differential current and the braking current;

[0085] plotting a working point trajectory in a phase space formed by the braking current as the horizontal axis and the differential current as the vertical axis;

[0086] if the working point trajectory enters a preset internal fault region, determining an internal fault.

[0087] Specifically, the second protection logic in the embodiment of the application can also use a protection criterion based on a phase space trajectory, which can extend the action characteristics of the differential protection from a traditional plane curve to a more intuitive area judgment, has good dynamic characteristics and clear physical meaning.

[0088] The specific implementation steps of the second protection logic can include:

[0089] 31, calculating steady-state phasors. Still taking T1 as 40 milliseconds for example, when t≥40 milliseconds, a sliding data window (for example, 20 milliseconds) is used to calculate the steady-state power frequency phasors of the differential current I d and the braking current I r . Among them, the calculation method of the braking current I r may be various, for example, taking the maximum value of the effective values of the currents on each side, or half of the sum of the effective values of the currents on each side, etc., to reflect the load level of the system and the severity of the external fault.

[0090] 32, constructing a phase space. A two-dimensional Cartesian coordinate system is defined as a phase space. The horizontal axis (x-axis) of the phase space represents the amplitude |I r | of the braking current, and the vertical axis (y-axis) represents the amplitude |I d | of the differential current. The running state of the power system at any time can be represented by a working point (|I r |, |I d |) in the phase space.

[0091] 33. Divide the protection region. In the phase space, two non-overlapping regions are divided according to the protection action characteristic: normal operation / external fault region, and internal fault region. The boundary of the two regions is usually defined by one or more curves (i.e. the protection action characteristic curve). For example, a typical ratio braking characteristic boundary can be defined by the following piecewise function:

[0092] When |I r |≤I r1 , the boundary is |I d |=I start (minimum starting current).

[0093] When |I r |>I r1 , the boundary is |I d |=K·(|I r |-I r1 )+I start (K is the braking coefficient).

[0094] All the regions below and to the left of the boundary line are defined as the "normal operation / external fault region"; all the regions above and to the right of the boundary line are defined as the "internal fault region". The parameters I start ,I r1 ,K need to be set according to the characteristics of the protected object and the power grid.

[0095] 34. Draw the working point trajectory and determine. After the protection is put into operation, the current working point (|I r |,|I d |) can be calculated at each calculation period, and plotted in the phase space. With the change of system state, these continuous working points will form a trajectory. If the working point is always located in the "normal operation / external fault region", it is determined that there is no internal fault, and the protection does not act; if the working point trajectory crosses the boundary and enters the "internal fault region", it is determined that an internal fault occurs, and a trip command is issued.

[0096] In the embodiment of the present application, when the normal operation or external fault occurs, the differential current |I d | is very small compared with the braking current |I r |, so the working point will be stably located in the normal operation / external fault region close to the horizontal axis in the phase space. Once the internal fault occurs, the differential current |I d | will increase sharply, and the increase amplitude is much larger than that of the braking current |I r |, which leads to the rapid movement of the working point to the upper or right-up direction, crossing the boundary line and entering the internal fault region, thereby triggering the protection action.

[0097] Further optionally, the method further comprises: performing a corresponding operation according to the decision result.

[0098] Regardless of whether step 102 or step 103 is executed, the decision result will eventually enter the step of outputting a protection result. Specifically, the tripping instruction can be used to trigger tripping, and the blocking instruction can be used to trigger blocking. If the fault is cleared (for example, the current returns to normal after the circuit breaker trips), the starting element returns, the entire flow ends, and the next start is awaited.

[0099] The simulation waveforms of the embodiment under different working conditions are used to verify the beneficial effects of the technical solution.

[0100] Figure 4 and Figure 5 are respectively action waveform diagrams of the fault component current protection provided by the application within 40 ms after the fault occurs.

[0101] Among them, Figure 4 represents the waveform of an internal inter-phase short-circuit fault of a 80 ms unit, Figure 5 represents the waveform of an external single-phase grounding short-circuit fault of a 80 ms unit. When the internal fault of the unit occurs, the action quantity is obviously greater than the braking quantity, and the intelligent differential protection can accurately act. When the external fault of the unit occurs, the action quantity is obviously less than the braking quantity, and the intelligent differential protection can effectively avoid malfunction.

[0102] Figure 6 , Figure 7 , Figure 8 are respectively action waveform diagrams of the fault component current protection provided by the application after 40 ms after the fault occurs.

[0103] Among them, Figure 6 represents the full current differential protection of the external single-phase grounding fault of the unit, Figure 7 represents the zero sequence current differential protection of the external single-phase grounding fault of the unit, Figure 8 represents the negative sequence current differential protection of the external single-phase grounding fault of the unit. It can be seen that, at the initial stage of the external fault of the unit (within 40 ms), the braking quantity of the zero sequence current differential protection and the negative sequence current differential protection is relatively close to the action quantity, and after the fault is stable (after 40 ms), the braking quantity is obviously greater than the action quantity, thereby avoiding the interference of the external unbalanced current and malfunction.

[0104] The embodiment of the application further provides another specific implementation manner of the adaptive differential protection method described in the application. In an optional implementation manner, the implementation manner of the first protection logic can also select other technologies using transient characteristics as needed.

[0105] In an optional implementation manner, the first protection logic is specifically:

[0106] Wavelet transform is performed on the collected current signal to extract high frequency components in a preset frequency band;

[0107] The energy of the high frequency components is calculated;

[0108] If the energy exceeds a preset action threshold, it is determined that there is an internal fault.

[0109] In this embodiment, when the fault duration t is determined to be less than the first preset threshold T1 (for example, still set to 40 milliseconds), the first protection logic performed can adopt a transient energy criterion based on wavelet transform. As a powerful time-frequency analysis tool, wavelet transform can effectively capture the transient and local characteristics in the signal, and is suitable for analyzing the transient signal in the initial stage of the fault.

[0110] The specific implementation steps of the first protection logic can include:

[0111] 21. Signal preprocessing. After collecting the current signals on both sides of the protected equipment, the instantaneous value sequence i d (k) of the differential current is first calculated, where k is the sample point number.

[0112] 22. Wavelet decomposition. The differential current signal i d (k) is subjected to multi-layer discrete wavelet transform. Daubechies series wavelets (such as db4 or db8) can be selected as needed. Through multi-layer decomposition, the original signal can be decomposed into detail components (high frequency parts) and approximation components (low frequency parts) in different frequency bands. For example, 5-layer decomposition can obtain 5 detail components d1, d2, d3, d4, d5 from high to low and one approximation component a5.

[0113] 23. Extracting transient high frequency components. The transient current generated by internal faults of the power system contains much more high frequency components than external faults, and these high frequency components are mainly concentrated in the frequency band of several hundred hertz to several thousand hertz. According to the sampling frequency and the number of decomposition layers, a certain number of detail components can be selected as signals representing transient characteristics. For example, if the sampling frequency is 10 kHz, the first layer detail component d1 corresponds to the frequency band of 2.5 kHz-5 kHz, and the second layer detail component d2 corresponds to the frequency band of 1.25 kHz-2.5 kHz. The sum of the energies of d1 and d2 can be selected as the basis for judgment.

[0114] 24. Calculate transient energy. In a very short time window (for example, the first one or several milliseconds after the fault) after the fault, the energy of the selected detail components (such as d1 and d2) is calculated. The energy can be calculated in the form of the sum of squares, for example, for the detail component d j , the energy E j in N sampling points can be calculated as: total transient energy E total i.e. the sum of the energy of each selected detail component.

[0115] 25, fault discrimination. The calculated total transient energy E total is compared with a preset action threshold E set . If E total >E set , it is determined that an internal fault has occurred, and a trip command is immediately issued. Otherwise, if E total ≤E set , it is determined that an external fault or a non-fault disturbance has occurred, and the protection does not act. The action threshold E set needs to be set by analyzing a large amount of simulation data of different types and locations of internal and external faults, in order to distinguish between internal and external faults.

[0116] The working principle of the above method is mainly as follows: when an internal fault occurs, since the fault point is located inside the protected equipment, a severe electromagnetic transient process will occur, resulting in the appearance of strong high-frequency oscillation components in the differential current. The wavelet transform can accurately capture the energy of these high-frequency components, so that the calculated total transient energy E total can easily exceed the action threshold E set . When an external fault occurs, although the system will also produce a transient process, the high-frequency signals will be significantly attenuated by the line impedance during the propagation from the fault point to the protection installation. Therefore, the calculated total transient energy E total will be much smaller than the action threshold E set , thereby ensuring that the protection reliably does not act.

[0117] When the fault duration t exceeds 40 milliseconds, the embodiment will also switch to the second protection logic, which will not be described again here.

[0118] Based on the description of the foregoing method embodiment, the embodiment of the present application further provides an adaptive differential protection device.

[0119] Figure 9 A structural schematic diagram of an adaptive differential protection device provided by the embodiment of the present application is shown in FIG. 9. As shown in the figure, the adaptive differential protection device 900 includes: Figure 9

[0120] a signal acquisition module 910, configured to acquire a power system fault signal;

[0121] a timing module 920, configured to start timing based on the fault signal to determine a fault duration;

[0122] ​The logic control module 930 is configured to execute a first protection logic if the fault duration does not exceed a first preset threshold, and the first protection logic is configured to use a fault transient component for fast fault identification.

[0123] The logic control module 930 is further configured to switch to a second protection logic if the fault duration exceeds the first preset threshold, and the second protection logic is configured to use a fault steady component for reliable fault identification.

[0124] Optionally, the adaptive differential protection device 900 further comprises a tripping outlet module 940 configured to receive a decision result from the logic control module 930, and output a tripping instruction if the decision result is an internal fault.

[0125] The tripping instruction is usually a strong level signal, which drives an external circuit breaker to act through an outlet relay, so as to disconnect the protected equipment from the power grid to isolate the fault. If the decision result is an external fault or normal operation, a blocking signal is output or no signal is output, so as to ensure that the circuit breaker does not act.

[0126] It can be understood that the related content of each module in Figure 9 has been described in detail in the foregoing method embodiments, and the details can be referred to the content in the method embodiments; that is, Figure 9 The adaptive differential protection device 900 provided in the present application can execute any step in the embodiments shown in Figure 1 , and details are not described herein.

[0127] In one embodiment, a computer readable storage medium is also provided, and the computer readable storage medium stores a computer program. When the computer program is executed by a processor, the processor executes any step in the foregoing method embodiments.

[0128] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program. The program can be stored in a non-volatile computer readable storage medium, and when the program is executed, the processes of the above-mentioned embodiment methods can be included. Any reference to memory, storage, database, or other medium used in the embodiments provided in the present application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration but not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0129] The technical features of the above embodiments can be combined in any way. In order to make the description simple, not all possible combinations of the technical features in the above embodiments are described, but as long as the combination of the technical features does not exist, it should be considered as the scope of the present application.

[0130] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent of the present application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. An adaptive differential protection method based on fault duration, characterized in that, The method includes: Acquire a power system fault signal and start timing based on the fault signal to determine the fault duration; If the duration of the fault does not exceed the first preset threshold, the first protection logic is executed. The first protection logic is used to quickly identify the fault using the transient component of the fault. If the duration of the fault exceeds the first preset threshold, the system switches to the second protection logic, which is used to perform reliable fault identification using the steady-state components of the fault.

2. The adaptive differential protection method based on fault duration according to claim 1, characterized in that, The method further includes: Before executing the first protection logic or the second protection logic, frequency tracking processing is performed, including: The system frequency of the power system is calculated using a frequency tracking method based on a short data window, and the system frequency is then used for subsequent protection logic calculations.

3. The adaptive differential protection method based on fault duration according to claim 2, characterized in that, The method of calculating the system frequency of the power system using a short data window-based frequency tracking method includes: Obtain the three-phase electrical quantities of the power system and calculate the three line electrical quantities; From the three-phase electrical quantities and the three line electrical quantities, select in real time a pair of electrical quantities with the smallest absolute value of phase difference; The system frequency is calculated using the zero-crossing information of the electrical quantities with the smallest absolute value of the phase difference between the two pairs of quantities.

4. The adaptive differential protection method based on fault duration according to claim 1, characterized in that, The execution of the first protection logic includes: Within a preset first time period after a fault occurs, high-threshold fault component current differential protection based on a first data window is employed; and, During a preset second time period after the fault occurs, low-threshold fault component current differential protection based on a second data window is used in parallel, where the length of the second data window is greater than that of the first data window.

5. The adaptive differential protection method based on fault duration according to claim 1, characterized in that, The first protection logic is as follows: Wavelet transform is performed on the acquired current signal to extract high-frequency components within a preset frequency band; Calculate the energy of the high-frequency component; If the energy exceeds a preset action threshold, it is determined to be an internal fault.

6. The adaptive differential protection method based on fault duration according to claim 1, characterized in that, The second protection logic specifically includes: Protection measures combining full-current differential protection, zero-sequence current differential protection, and negative-sequence current differential protection.

7. The adaptive differential protection method based on fault duration according to claim 1, characterized in that, The second protection logic is as follows: Extract the steady-state power frequency phasors of differential current and braking current; In the phase space formed by the braking current as the horizontal axis and the differential current as the vertical axis, draw the trajectory of the operating point; If the working point trajectory enters the preset internal fault area, it is determined to be an internal fault.

8. The adaptive differential protection method based on fault duration according to any one of claims 1-7, characterized in that, The first preset threshold is 40ms.

9. An adaptive differential protection device, characterized in that, include: The signal acquisition module is used to acquire power system fault signals; A timing module is used to start timing based on the fault signal in order to determine the duration of the fault; The logic control module is used to execute the first protection logic if the duration of the fault does not exceed the first preset threshold. The first protection logic is used to perform rapid fault identification using the transient components of the fault. The logic control module is further configured to switch to a second protection logic if the duration of the fault exceeds the first preset threshold. The second protection logic is configured to use the steady-state components of the fault for reliable fault identification.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the adaptive differential protection method based on fault duration as described in any one of claims 1-8.

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