New energy line protection method based on estimating the arrival time of current traveling waves

Abstract

The present invention provides a new energy line protection method based on estimating the arrival time of current traveling waves and its application. The method derives the relationship between the arrival time of the traveling wave and the transmission path by analyzing the refraction and reflection process of the current traveling wave when faults occur at different locations. Since each traveling wave arrives at the protection installation in a certain order when faults occur at different locations, the arrival time of the third wave head is estimated by the arrival time of the first two wave heads. The wavelet transform modulus maximum is used to calibrate the arrival time of the traveling wave. If the estimated value of the arrival time of the third wave head is equal to the measured value, it can be judged as an in-zone fault. If the estimated value is not equal to the measured value, it can be judged as an out-of-zone fault. This method is a single-ended quantity protection, which has the advantages of no need for communication and fast action speed. At the same time, it does not need to introduce voltage quantity, eliminates the influence of the transmission characteristics of the capacitive voltage transformer, and can effectively identify faults.

Description

Technical Field

[0001] The present invention relates to the field of AC line fault identification, and in particular to a new energy line protection method based on estimating the arrival time of a current traveling wave and its application. Background Art

[0002] In order to solve the increasingly severe fossil energy crisis and environmental problems, new energy generation technologies such as wind power and photovoltaics have developed rapidly. Most of them are connected to the grid through high-voltage transmission lines after being collected at stations. Since areas rich in wind and solar energy are usually far away from the load center, the correct action of AC transmission line protection is a prerequisite for the efficient use of new energy. However, the new energy system contains a large number of power electronic devices. When a transmission line fails, its fault characteristics are affected by the control strategy, which is significantly different from the fault characteristics of traditional synchronous power supplies. It is mainly manifested in unstable sequence impedance, controlled phase angle, frequency offset, high-order harmonics and other characteristics, which makes the traditional protection method based on power frequency quantity inapplicable. Traveling wave protection can ignore the influence of control strategy and has a fast action speed. It is one of the effective ways to solve the protection problems of new power systems.

[0003] At present, there are related traveling wave protection methods, but most of them are two-terminal protection schemes. Among them, the application number 201510811828.X and the name of "Single-ended traveling wave ranging reflection wave identification algorithm based on spectrum similarity evaluation" proposed to intercept the appropriate traveling wave characteristic time window according to the high-frequency characteristics of the traveling wave, use the spectrum analysis method to analyze the fault transient traveling wave, and identify the fault transient traveling wave through the optimization method of similar spectrum. However, the threshold of this scheme is difficult to determine and mainly relies on simulation. There is a problem that the near-end fault is difficult to accurately identify. At the same time, the algorithm is complex and the calculation is large. The application number 201410409106.7 and the name of "Fault ranging method based on dual symmetric detection points" proposed to judge the fault in the area by comparing the traveling wave time difference at the detection point with the energy of the first wave of the current traveling wave. However, this scheme is a two-terminal protection, which requires strict synchronization and communication, and has poor speed performance. The application number is 201510146674.7 and the name is "A single-phase ground fault location device and method for distribution network". It uses the arrival time of the traveling waves at both ends and uses GPS for dual-end positioning. However, this solution needs to be able to accurately extract the arrival time of the fault traveling wave, and the information exchange at both ends has high requirements for synchronization and timing, which is difficult to achieve with existing protection devices. The application number is 201510624109.7 and the invention name is "A traveling wave comprehensive ranging method combining impedance method and traveling wave method". It proposes to use the traveling wave method to measure the distance of the high-frequency current recording data by the traveling wave method with the fault line and fault time provided by the impedance method as a reference to obtain the traveling wave ranging length. However, this type of solution requires dual-end synchronization and has high requirements for the synchronization and timing of the device. Application No. 202011213166.3, entitled "A Line Fault Location Method Based on Wavelet Transform", application No. 201810027051.1, entitled "Dual-terminal Traveling Wave Ranging Method Based on Fault Waveform Starting Point Arrival Time Difference", and application No. 201911165839.X "A DC Distribution Line Multi-terminal Traveling Wave Fault Location Method and Location Device" all belong to two-terminal protection. Therefore, there are currently many two-terminal protection schemes, but such methods have high requirements for communication and synchronization, and their speed is reduced.

[0004] There are also several single-ended protection schemes as follows: Application number 201911223016.8, named "A single-ended traveling wave ultra-high-speed protection system and method for flexible DC transmission lines" Application number 201911221690.2, named "Single-ended adaptive traveling wave ultra-high-speed protection system and method for high-resistance faults". This invention uses different methods to fit the zero-mode current traveling wave, and can effectively identify the fault location based on the value of the fitting coefficient. However, this method requires advance detection of data when faults occur at different locations under different circumstances, and the amount of calculation is large. Application No. 201810512316.7, titled "A Fault Location Method for Asynchronous Sampling of Transient Traveling Wave Modulus Time Difference in Power Grid" and Application No. 202111391311.1, titled "A Multi-Terminal Fusion Distribution Network Fault Location Method Based on Traveling Wave Modulus Transmission Time Difference", obtain the fault distance through the distance measurement principle based on the time difference between the line mode and zero mode components of the fault traveling wave, but the zero mode wave velocity is seriously affected by dispersion, resulting in a large distance measurement error. If the zero mode wave velocity is obtained by fitting, it is necessary to train different fault locations in advance, which requires a large amount of calculation. Application No. 201711397294.6, titled "A Single-End Section Location Method for Single-Phase Grounding Fault in Distribution Network", proposes to locate the fault location by comparing the arrival time of the line mode traveling wave, but this scheme has a dead zone when there is a midpoint fault in the line and a reverse fault, resulting in the inability of the protection to operate accurately. Application No. 201811154145.1 Invention Name "A Single-Ended Traveling Wave Distance Measurement Method for T-Connected Transmission Lines Based on Section Matching Algorithm" proposes to use the line segment matching method based on the fault window waveform to achieve the fault section and distance measurement of T-connected transmission lines, but this scheme is limited to the length of the research line, so it cannot be applied to all transmission lines. Application No. 201910548908.9 Invention Name "A Single-Ended Traveling Wave Fault Distance Measurement Method Based on MMC-HVDC" proposes to use empirical mode decomposition-Hilbert Huang transform to analyze the voltage traveling wave after the phase mode change, and calibrate the reflected wave head of the fault point; the fault is measured according to the calibrated wave head, but the AC line has the characteristics of uncertain initial phase angle of the fault and sinusoidal voltage change compared to the DC line, so whether this scheme can be directly applied to the AC line needs further study. The application number is 202210596379.1 and the name of the invention is "Protection method for new energy lines with a high proportion based on the polarity difference of the first four voltage traveling waves". It proposes to use the polarity difference of the first four voltage traveling waves for fault identification. However, after the refraction and reflection of the traveling waves and the attenuation of the lines, whether the first four traveling waves can be accurately identified is a prerequisite for the current solution to be realized. The present invention identifies faults based on the arrival time of the first three traveling waves, which has certain feasibility.

[0005] At present, there are some protection schemes based on estimating the waveform of traveling waves and the arrival time of traveling waves. Application number 201910970933.6 is named "A fault location method for predicting the arrival time of the wave head based on the NARNN model". The invention first preliminarily determines the arrival time of the first wave head at both ends, and then uses the voltage traveling waves at both ends as the training set to predict the waveform through the NARNN model, and obtains the accurate arrival time of the voltage traveling waves at both ends, and uses the double-end ranging formula to calculate the fault location. This invention requires a large amount of data training for different fault locations, different fault types, etc. The process is complex and the amount of calculation is large. At the same time, the use of double-end quantity protection has high requirements for communication and synchronization. Application number 201810541591.1 is named "A distribution network fault location method based on wavelet transform and CNN". A fault location method based on wavelet transform and CNN is proposed. This scheme also needs to train sample data to adapt to the situation of faults in different locations. The process is complex and the amount of calculation is large. Application No. 201811492951.X, named "A method for measuring the distance between transmission line faults based on ARIMA wave head prediction". This invention uses the initial data of the first wave head for training, and then uses ARIMA to predict the waveform, and determines the precise wave head position by the difference between the predicted waveform and the actual waveform, and uses the double-terminal method to determine the fault location. This type of invention that uses sample training for prediction has the disadvantage of large amount of calculation. Application No. 201610209799.4, named "A method for calculating and measuring fault distance based on a single-ended traveling wave that is not affected by the speed of the traveling wave" proposes a solution for measuring the distance of the fault location based on the arrival time of the traveling wave by analyzing the expression of the fault location when faults occur at different locations in the area. However, this invention only analyzes the process of the traveling wave when a fault occurs in the area and then derives the fault location. However, for faults outside the area, there is a similar refraction and reflection phenomenon as the faults within the area, which may lead to misjudgment of protection and produce large errors in the distance measurement results. In summary, there is still a lack of reliable protection principles for the transmission lines of new energy stations. Therefore, it is urgent to study the traveling wave protection scheme based on single-ended quantities for the transmission lines of new energy to further improve the speed and reliability of protection. This invention analyzes in detail the refraction and reflection process of traveling waves when faults occur at different locations inside and outside the area, and then proposes a protection scheme based on the estimated arrival time of traveling waves. This scheme only needs to effectively extract the arrival time of traveling waves, without the need for double-end synchronization, and can effectively identify faults inside and outside the area. Summary of the invention

[0006] The purpose of the present invention is to provide a new energy line protection scheme based on estimating the arrival time of current traveling waves to ensure the safe operation of new energy transmission lines. In order to achieve the above purpose, the present invention provides a new energy line protection method based on estimating the arrival time of current traveling waves. The method analyzes the refraction and reflection process of current traveling waves when faults occur at different locations, and uses the arrival time of traveling waves to characterize the transmission path of fault traveling waves. When faults occur at different locations, the relationship between the transmission paths of the waves leads to a certain relationship between the arrival times of the wave heads, so the arrival time of the third wave head can be estimated by the arrival time of the first two wave heads. Through analysis, it can be known that when a fault occurs within the area, whether it is the first half of the fault or the second half of the fault, the estimated arrival time of the third wave head remains unchanged, so the fault can be identified by detecting the size of the estimated value and the actual value. Within the error range, if the estimated value is equal to the measured value, it can be judged as an in-area fault, and if the estimated value is significantly different from the measured value, it can be judged as an out-of-area fault.

[0007] A new energy line protection method based on estimating the arrival time of a current traveling wave comprises the following steps:

[0008] Step (1) analyzing the refraction and reflection process of traveling waves when faults occur at different locations;

[0009] Step (2) deriving the relationship between the arrival time of the traveling wave and the transmission path;

[0010] Step (3) calibrating the arrival time of the traveling wave head using the wavelet transform modulus maximum;

[0011] Step (4) estimating the arrival time of the third traveling wave based on the arrival times of the first two traveling waves;

[0012] Step (5) compares the measured value with the estimated value to determine whether it is an in-zone fault.

[0013] Preferably, when faults occur at different locations in step (1), the first traveling wave arriving at the protection installation must be the first traveling wave from the fault point, but the transmission path and arrival time of subsequent traveling waves are related to the fault location.

[0014] Preferably, in step (2), the transmission path of the traveling wave is proportional to the transmission time, and the time it takes for the traveling wave to reach the protection installation is obtained by analyzing the transmission path of the traveling wave; when a fault occurs in the first half of the area, the first current traveling wave that arrives at the protection installation must be the initial traveling wave of the fault, and the arrival time is t1; due to the constraint of the line length, the second current traveling wave that arrives at the protection installation must be the reflected wave from the fault point, and the arrival time is t2; since the amplitude of the traveling wave after three reflections is approximately 0, the third traveling wave that arrives at the protection installation must be the reflected wave from the opposite bus, and the arrival time is t3. The relationship between the arrival time of the traveling wave and the transmission path satisfies:

[0015]

[0016] Where: v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, x represents the distance between the fault point and the protection installation, and L1 represents the length of the study line.

[0017] Preferably, in step (3), the modulus maximum of wavelet transform is used to extract the wave head of the current traveling wave; the amplitude of the modulus maximum represents the mutation strength of the signal, and the polarity represents the mutation direction of the signal;

[0018] The maximum modulus of the wavelet transform is defined as: Let Wsf(x) be the wavelet transform of the function f(x), and for all x in a neighborhood of x0 at scale s, we have:

[0019] |W s f(x)|≤|W s f(x0)|

[0020] Where: x0 is the modulus maximum point of wavelet transform; W sf (x0) is the modulus maximum of the wavelet transform.

[0021] Preferably, in step (4), the arrival time of the third traveling wave is calculated by extracting the arrival time of the first two traveling waves:

[0022]

[0023] Where: L1 represents the length of the research line, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, and t2 represents the arrival time of the second traveling wave.

[0024] Preferably, in step (5), the arrival time of the third traveling wave is estimated by the arrival time of the first two traveling waves. By analysis, it can be known that the arrival time of the third traveling wave is different when the fault is within the zone and when the fault is outside the zone; the fault is identified by comparing the estimated value with the actual value: within the error range, if the estimated value is equal to the actual value, it is judged to be an intra-zone fault; if the estimated value is not equal to the actual value, it is an outside-zone fault.

[0025] The present invention also discloses a protection system for a new energy AC transmission line, which is characterized in that: the protection system includes the above-mentioned new energy line protection method based on the estimated current traveling wave arrival time.

[0026] The present invention also discloses a new energy station, including a power supply protection system, which is characterized in that: the power supply protection system is a protection system for the above-mentioned new energy AC transmission line.

[0027] Beneficial Effects

[0028] The present invention is a single-ended protection, which has the advantages of no need for communication and fast action speed. At the same time, it does not need to introduce voltage, eliminates the influence of the transmission characteristics of the capacitive voltage transformer, and can effectively identify faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 This is the diagram of the refraction and reflection process of the traveling wave when a fault occurs in the first half of the area;

[0031] Figure 2 This is the diagram of the refraction and reflection process of the traveling wave when a fault occurs in the second half of the area;

[0032] Figure 3 This is the diagram of the refraction and reflection process of the traveling wave when a fault occurs in the first half of the area outside the zone;

[0033] Figure 4 This is the diagram of the refraction and reflection process of the traveling wave when a fault occurs in the second half of the area;

[0034] Figure 5 This is the diagram of the refraction and reflection process of the traveling wave when a fault occurs in the second half of the area;

[0035] Figure 6 This is the diagram of the refraction and reflection process of the traveling wave when a fault occurs in the second half of the area;

[0036] Figure 7 This is the simulation result diagram when a single-phase grounding fault occurs in the area, where Figure 7 (a) is the reverse current traveling wave detected at the protection installation; (b) is the wavelet transform result of the current traveling wave;

[0037] Figure 8 Figure 2 is a simulation result diagram when a single-phase grounding fault occurs outside the zone, where (a) is the reverse current traveling wave detected at the protection installation; (b) is the wavelet transform result of the current traveling wave.

[0038] Fig. 9 The figure is a schematic diagram of a new energy line protection circuit based on estimating the arrival time of a current traveling wave according to the present invention. DETAILED DESCRIPTION

[0039] The specific structure and method implementation of the present invention are described in detail below in conjunction with the accompanying drawings. The following detailed exemplary embodiments are disclosed only for the purpose of describing the exemplary embodiments. However, the present invention is not limited to the disclosed specific exemplary embodiments, but can cover all modifications, equivalents and alternatives falling within the scope of the present disclosure.

[0040] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] A new energy line protection method based on estimating the arrival time of a current traveling wave comprises the following steps:

[0042] Step 1: Analyze the refraction and reflection process of traveling waves when faults occur at different locations

[0043] Since the present invention relates to the field of fault identification, it is necessary to reliably identify faults inside and outside the zone. Therefore, when analyzing the refraction and reflection process, the faults inside the zone and the faults outside the zone are analyzed separately. When a fault occurs at a different location, the first current traveling wave that arrives at the protection installation must be the initial traveling wave of the fault, but the arrival timing and refraction and reflection process of the subsequent current traveling waves are related to the fault location, so several fault conditions are described separately. Since the reflection coefficient is less than 1, the reflection process will cause a large amount of energy consumption. After multiple refractions and reflections, the amplitude of the traveling wave is very small. Therefore, the amplitude of the traveling wave that is reflected more than three times is approximately 0. The present invention does not consider the reflection process more than three times.

[0044] Step 2: Derive the relationship between the transmission path and the arrival time of the traveling wave

[0045] When a fault occurs in the first half of the line and the second half of the line, the second traveling wave reaching the protection installation is different, so the first half and the second half are discussed separately. Figure 1 As shown, L, M, N, and O represent the busbars at each end, and f represents the fault point. The ports at both ends of the line studied in this paper are MN. When a fault occurs in the first half of the area, the first current traveling wave that arrives at the protection installation must be the initial traveling wave of the fault, and the arrival time is t1; since the fault point is close to the protection installation, the second current traveling wave that arrives at the protection installation in this case is the reflected wave from the fault point, and the transmission path of the traveling wave is fMfM, and the arrival time is t2; since the amplitude of the traveling wave after three reflections can be approximated to 0, the third traveling wave that arrives at the protection installation must be the reflected wave from the opposite busbar, and the transmission path of the traveling wave is fNfM, and the arrival time is t3. The relationship between the arrival time and the transmission path of the traveling wave satisfies:

[0046]

[0047] Where: L1 represents the length of the studied line MN, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, and x represents the distance between the fault point and the protection installation.

[0048] The above formula can be used to obtain the expression of t3:

[0049]

[0050] Through the above derivation, it is found that the arrival time of the third traveling wave can be estimated based on the arrival time of the first two traveling waves alone, and the fault can be effectively identified by comparing the estimated value with the actual value.

[0051] like Figure 2 As shown, L, M, N, and O represent the busbars at each end, and f represents the fault point. The ports at both ends of the line studied in this paper are MN. When a fault occurs in the second half of the area, the first current traveling wave that arrives at the protection installation must be the initial fault traveling wave, and the arrival time is t1; at this time, the fault point is close to the opposite busbar. At this time, the second current traveling wave that arrives at the protection installation is the reflected wave of the opposite busbar, and the transmission path of the traveling wave is fNfM, and the arrival time is t2; the third traveling wave that arrives at the protection installation is the reflected wave of the fault point, and the transmission path of the traveling wave is fMfM, and the arrival time is t3. The relationship between the arrival time and the transmission path of the traveling wave satisfies:

[0052]

[0053] Where: L1 represents the length of the studied line MN, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, and x represents the distance between the fault point and the protection installation.

[0054] The above formula can be used to obtain the expression of t3:

[0055]

[0056] Therefore, through the above analysis, it can be concluded that the arrival time t3 of the third traveling wave measured at the protection installation when a fault occurs in the zone can be estimated through the arrival times of the first two traveling waves, and the expression of the estimated t3 is the same.

[0057] In line with the analysis of faults within the area, the line is also divided into the first half and the second half for discussion when faults occur outside the area. Figure 3As shown, L, M, N, and O represent the busbars at each end, and f represents the fault point. The ports at both ends of the line studied in this paper are MN. When a fault occurs in the first half of the outer zone, the first current traveling wave arriving at the protection installation must be the initial fault traveling wave, and the arrival time is t1; due to the constraint of the line length, the second current traveling wave measured must be the reflected wave of the fault point transmitted through the busbar to the protection installation, and the transmission path of the traveling wave is fNfNM, and the arrival time is t2; the third traveling wave arriving at the protection installation is the reflected wave of the busbar at the opposite end of the next-level line, and the transmission path of the traveling wave is fOfNM, and the arrival time is t3. The relationship between the arrival time and the transmission path of the traveling wave satisfies:

[0058]

[0059] Where: L1 represents the length of the studied line MN, L2 represents the length of the next level line NO, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, and x represents the distance between the fault point and the protection installation.

[0060]

[0061] It can be seen that when a fault occurs in the first half outside the zone, the estimated arrival time of the third traveling wave is significantly different from that when a fault occurs inside the zone.

[0062] like Figure 4 As shown, L, M, N, and O represent the busbars at each end, and f represents the fault point. The ports at both ends of the line studied in this paper are MN. When a fault occurs in the second half of the outer zone, the first current traveling wave arriving at the protection installation must be the initial traveling wave of the fault, and the arrival time is t1; at this time, there are three situations for the second and third traveling waves arriving at the protection installation that need to be discussed separately. When the second traveling wave arriving at the protection installation is the reflected wave of the opposite busbar, the transmission path of the traveling wave is fOfNM; when the third traveling wave arriving at the protection installation is the reflected wave of the fault point, the transmission path of the traveling wave is fNfNM, and the relationship between the arrival time of the traveling wave and the transmission path satisfies:

[0063]

[0064] Where: L1 represents the length of the studied line MN, L2 represents the length of the next level line NO, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, and x represents the distance between the fault point and the protection installation.

[0065] The above formula can be used to obtain the expression of t3:

[0066]

[0067] It can be seen that when a fault occurs in the second half outside the zone, the estimated arrival time of the third traveling wave is significantly different from that when a fault occurs inside the zone.

[0068] like Figure 5 As shown in the figure, L, M, N, and O represent the busbars at each end, and f represents the fault point. The ports at both ends of the line studied in this paper are MN. When the second traveling wave arriving at the protection installation is the reflected wave of the opposite busbar, the wave transmission path is fOfNM, and the arrival time is t2; when the third traveling wave arriving at the protection installation is the reflected wave of the local busbar, the wave transmission path is fNMNM, and the arrival time is t3, the relationship between the arrival time of the traveling wave and the transmission path satisfies:

[0069]

[0070] Where: L1 represents the length of the studied line MN, L2 represents the length of the next level line NO, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, and x represents the distance between the fault point and the protection installation.

[0071] The above formula can be used to obtain the expression of t3:

[0072]

[0073] like Figure 6 As shown in the figure, L, M, N, and O represent the busbars at each end, and f represents the fault point. The ports at both ends of the line studied in this paper are MN. When the second traveling wave arriving at the protection installation is the reflected wave of the busbar at this end, and the wave transmission path is fNMNM, the arrival time is t2; the third traveling wave arriving at the protection installation is the reflected wave of the busbar at the opposite end, and the wave transmission path is fOfNM, and the arrival time is t3. In this case, the relationship between the arrival time of the traveling wave and the transmission path satisfies:

[0074]

[0075] Where: L1 represents the length of the studied line MN, L2 represents the length of the next level line NO, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, and x represents the distance between the fault point and the protection installation.

[0076] The above formula can be used to obtain the expression of t3:

[0077]

[0078] From the above analysis, we can know that the expression of t3 is different when the fault is inside the area and outside the area. Therefore, as long as the above expression is not equal to the expression of t3 when the fault is inside the area, it can be judged as an outside area fault. Therefore, it only needs to satisfy

[0079]

[0080] It can be concluded that:

[0081] x≠L1+L2

[0082] Where: L1 represents the length of the studied line MN, L2 represents the length of the next level line NO, v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, and x represents the distance between the fault point and the protection installation.

[0083] That is, except when a fault occurs at the end of the next-level line, the fault can be effectively identified by estimating the value of t3 and comparing the measured value with the estimated value. Since the probability of a fault occurring at the busbar is small, and when a fault occurs at the busbar, the protection at the busbar can be used to identify the fault due to the selectivity of the protection, so this special situation will not affect this protection.

[0084] In summary, when a fault occurs within the zone, the arrival time of the third traveling wave can be estimated by the arrival time of the first two traveling waves. When a fault occurs outside the zone, the arrival time of the third traveling wave is different from the estimated time within the zone. Therefore, the fault can be identified by comparing whether the measured value is equal to the estimated value.

[0085] Step 3: Use the wavelet transform modulus maximum to calibrate the arrival time of the traveling wave head

[0086] The solution adopted by the present invention is to use the measured arrival time of the first two traveling waves to estimate the arrival time of the third traveling wave, and compare the estimated value of t3 with the actual value to identify the faults inside and outside the zone. However, in traveling wave protection, the line mode traveling wave propagates quickly, and the traveling wave contains a large number of high-frequency components. Therefore, whether the arrival time of the first two traveling waves can be reliably identified is the difficulty in implementing this solution. The wavelet transform modulus maximum (WTMM) under discrete binary wavelet transform can quantitatively describe the local steepness of the signal. The present invention uses the modulus maximum of the wavelet transform to calibrate the arrival time of the wave head. The amplitude of the modulus maximum characterizes the mutation strength of the signal, and the polarity characterizes the mutation direction of the signal.

[0087] The maximum value of wavelet transform modulus is defined as: Let W sf(x) is the wavelet transform of the function f(x), and for all x in a certain neighborhood of x0 at scale s, we have:

[0088] |W s f(x)|≤|W s f(x0)|

[0089] Where: x0 is the modulus maximum point of wavelet transform; W sf (x0) is the modulus maximum of the wavelet transform.

[0090] Step 4: Estimate the arrival time of the third wave based on the arrival times of the first two waves

[0091] From the above analysis, it can be seen that when an internal fault occurs and an external fault occurs, the estimated arrival time of the third traveling wave based on the arrival time of the first two traveling waves is significantly different. Therefore, the measured value of t3 and the estimated value can be compared to determine whether an internal fault has occurred. 3set The expression is:

[0092]

[0093] Step 5: Compare the measured value with the estimated value to determine whether it is an in-zone fault

[0094] The measured arrival time t3 of the third traveling wave obtained by using the wavelet transform modulus maximum is compared with the estimated value t 3set Compare, within the error range, if t3 and t 3set相 It can be judged as an internal fault; if t3 and t 3set If they are not equal, it is judged as an out-of-zone fault.

[0095] Figure 7 The current traveling wave simulation diagram and its wavelet transform modulus maximum value of a single-phase grounding fault on a line MN with a length of 100 km and a distance of 10 km from the M end are given. The fault occurs at 0.5 ms. From the results of the wavelet transform modulus maximum value in Figure (b), it can be seen that the arrival time t1 of the first traveling wave reaching the protection installation is 0.533 ms, and the arrival time t2 of the second traveling wave is 0.601 ms. Substituting the data into t 3set =2L1 / v1+2t1-t2 to get the estimated arrival time of the third traveling wave t 3set =1.138ms. Observe that the arrival time t3 of the third traveling wave calibrated by the wavelet transform modulus maximum value in Figure (b) is 1.140ms. At this time, t3 = t 3set , so it can be determined as an internal fault.

[0096] Figure 8The current traveling wave simulation diagram and wavelet transform modulus maximum of a single-phase grounding fault on a line MN with a length of 100 km and a distance of 90 km from the N end are given. The fault occurs at 0.5 ms. From the results of the wavelet transform modulus maximum in Figure (b), it can be seen that the arrival time t1 of the first traveling wave reaching the protection installation is 1.140 ms, and the arrival time t2 of the second traveling wave is 1.298 ms. Substituting the data into t 3set =2L1 / v1+2t1-t2 to get the estimated arrival time of the third traveling wave t 3set =1.654ms. Observe that the arrival time t3 of the third traveling wave calibrated by the wavelet transform modulus maximum in Figure (b) is 1.812ms. At this time, t3≠t 3set , so it can be determined as an out-of-zone fault.

[0097] It can be seen from the above simulation analysis that when a fault occurs inside or outside the zone, the present invention can effectively identify the fault.

[0098] The present invention provides a new energy line protection method based on the arrival time of current traveling waves. The method analyzes the refraction and reflection process of current traveling waves when faults occur at different locations, and uses the arrival time of traveling waves to characterize the transmission path of fault traveling waves. When faults occur at different locations, the relationship between the transmission paths of the waves leads to a certain relationship between the arrival times of the wave heads, so the arrival time of the third wave head can be estimated by the arrival time of the first two wave heads. Through analysis, it can be known that when a fault occurs within the zone, whether it is the first half of the fault or the second half of the fault, the estimated arrival time of the third wave head remains unchanged, so the fault can be identified by detecting the size of the estimated value and the actual value. If the estimated value is equal to the measured value, it can be judged as an in-zone fault. If the estimated value is significantly different from the measured value, it can be judged as an out-of-zone fault. This method is a single-ended quantity protection, which has the advantages of no need for communication and fast action speed. At the same time, it does not need to introduce voltage quantity, eliminates the influence of the transmission characteristics of the capacitive voltage transformer, and can effectively identify faults.

[0099] This article uses specific examples to illustrate the principles and implementation methods of the invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. The described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

Claims

1. A new energy line protection method based on estimating the arrival time of current traveling waves. When a new energy line fails at different locations, each traveling wave arrives at the protection installation in a certain order. This method analyzes the refraction and reflection process of current traveling waves when a fault occurs at different locations to derive the relationship between the arrival time of the traveling wave and the transmission path. Its characteristics are: The arrival time of the third wave head is estimated by the arrival time of the first two wave heads; the arrival time of the traveling wave is calibrated by the wavelet transform modulus maximum value; if the estimated value of the arrival time of the third wave head is equal to the measured value, it is judged as an internal fault; if the estimated value is not equal to the measured value, it is judged as an external fault; it is characterized by: comprising the following steps: Step (1) analyzing the refraction and reflection process of traveling waves when faults occur at different locations; when faults occur at different locations, the first traveling wave arriving at the protection installation is the first traveling wave from the fault point, and the transmission path and arrival time of subsequent traveling waves are related to the fault location; Step (2) derives the relationship between the arrival time of the traveling wave and the transmission path; the relationship between the arrival time of the traveling wave and the transmission path satisfies: Where: v1 represents the wave velocity of the line mode traveling wave, t1 represents the arrival time of the first traveling wave, t2 represents the arrival time of the second traveling wave, t3 represents the arrival time of the third traveling wave, x represents the distance between the fault point and the protection installation, and L1 represents the length of the research line; Step (3) uses the wavelet transform modulus maximum to calibrate the arrival time of the traveling wave head; the wavelet transform modulus maximum is defined as: Let W s f(x) is the wavelet transform of the function f(x), and for all x in a certain neighborhood of x0 at scale s, we have: |W s f(x)|≤|W s f(x0)| Where: x0 is the modulus maximum point of wavelet transform; W s f(x0) is the modulus maximum of the wavelet transform; Step (4) estimates the arrival time of the third traveling wave according to the arrival time of the first two traveling waves; by analyzing the refraction and reflection process of the traveling wave when the fault occurs in the area, the expression of the estimated third traveling wave is obtained: Where: v1 represents the wave velocity of the line mode traveling wave, L1 represents the length of the research line, t1 represents the time when the first traveling wave arrives, t2 represents the time when the second traveling wave arrives, t 3set It represents the estimated arrival time of the third traveling wave when there is a fault in the area; Step (5) compares the measured value with the estimated value to determine whether it is an internal fault; 3set The fault is identified by comparing with the actual value t3: within the error range, if the estimated value is equal to the actual value, it is judged as an in-zone fault; if the estimated value is not equal to the actual value, it is judged as an out-of-zone fault.

2. A protection system for a new energy AC transmission line, characterized by: The protection system includes the new energy line protection method based on the estimated current traveling wave arrival time as described in claim 1.

3. A new energy station, including a power supply protection system, characterized by: The power supply protection system is the protection system for the new energy AC transmission line as described in claim 2.

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