Direction comparison type traveling wave protection method and system suitable for three-phase alternating current power grid

Abstract

The invention discloses a direction comparison type traveling wave protection method and system suitable for a three-phase alternating current power grid, and belongs to the technical field of power system relay protection. The method comprises the steps that protection devices are installed at the head end and the tail end of a power transmission line, three-phase current signals are obtained based on synchronous unbiased sampling of accurate time synchronization, equivalent values Id and Iq under a synchronous rotating coordinate system are obtained through Park transformation of the three-phase current signals, and then the equivalent values Id and Iq are expressed in the amplitude and angle forms Ir and Itheta through polar coordinate transformation; performing multi-scale cubic B-spline wavelet transform on the single amplitude Ir; marking a modulus maximum moment after wavelet transformation as a traveling wave head arrival moment and marking the polarity of the wave head; and judging a fault area and processing a fault according to the wave head polarity and the arrival time of the two ends. The direction comparison type traveling wave protection method for the three-phase alternating current power grid realizes direction comparison type traveling wave protection for the three-phase alternating current power grid, the calculation data window is only 0.1 millisecond, the consumed time is reduced by two orders of magnitude compared with the traditional power frequency protection, and the protection quickness is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of relay protection for electric power systems, and more specifically, relates to a directional comparison type traveling wave protection method and system suitable for three-phase alternating current power grids. Background Art

[0002] When power lines transmit electric energy, they propagate in the form of electromagnetic waves. When resistance and conductivity are ignored, the propagation speed of the linear traveling wave is:

[0003]

[0004] Substituting the inductance and capacitance of the overhead line into the above formula, it can be found that the traveling wave propagation speed of the overhead line is close to the speed of light. When a fault occurs at point F of the transmission line, the fault point will generate a traveling wave that propagates to both ends of the line at a speed close to the speed of light, so that the traveling wave head can be detected at both ends of the line. According to the time difference of reaching both ends of the line and the known total length of the line, the exact location of the fault point F can be calculated. This is the basic principle of traveling wave ranging distance protection.

[0005] Traveling wave line protection not only has the characteristics of simple principle and much faster action speed than traditional protection based on industrial frequency electrical quantities, but also has the unique advantage of not being affected by transition resistance, current transformer saturation, system oscillation and conductor distributed capacitance. It is particularly suitable for the field of high-voltage and long-distance transmission line protection.

[0006] In the field of HVDC transmission line protection, the more mature traveling wave protection schemes include those of ABB and SIEMENS. These two protection schemes have fast protection actions and can reliably identify various faults within the entire length of the line, but they are susceptible to noise interference and easy to malfunction to varying degrees. This is due to the defects in the protection judgment principle. The voltage and current used in the principle are instantaneous values. The value of the calculation point selected during the calculation directly affects the result of the judgment; secondly, due to the inherent characteristics of differential operations, it is very sensitive to noise and easily interfered by noise.

[0007] In the field of high-voltage AC transmission line protection, China introduced two sets of RALDA type traveling wave polarity comparison directional protection devices from Sweden in the early 1980s, which were installed on the 500kV Jinliao line of the Northeast Power Grid and the 500kV Pingwu line of the Central China Power Grid. However, due to the high-frequency transient nature of the traveling wave itself, principle defects, and limitations of mathematical tools, sensor methods, and technical conditions, the performance of the protection devices developed at this stage was not stable enough, and the reliability was poor. Eventually, they were withdrawn from operation, and the results were not popularized. As a result, there has been no significant progress in the traveling wave protection of AC lines for many years, far behind the DC traveling wave protection.

[0008] In recent years, with the advancement of technology, traveling wave ranging technology for AC transmission lines has made great progress, and valuable experience has been accumulated in the collection of traveling wave signals, detection of traveling wave heads, and precise measurement of arrival times. This has objectively become the technical basis for traveling wave protection of high-voltage AC transmission lines.

[0009] For example, prior art document 1 (CN117761449A) discloses a timing and synchronous sampling method and system for traveling wave ranging, which solves the timing accuracy and sampling synchronization accuracy problems in traveling wave ranging, controls the total ranging error introduced by the timing link and the sampling pulse generation link to within 10 meters, and improves the accuracy of traveling wave ranging. This prior art has become the technical basis for traveling wave protection of high-voltage AC transmission lines in terms of data sampling. Summary of the invention

[0010] In order to solve the backwardness and shortcomings of the traveling wave protection of high-voltage AC transmission lines in the existing technology, the present invention provides a directional comparison traveling wave protection method suitable for three-phase AC power grids, which mainly solves the problems of double-end synchronous unbiased sampling, the normalization problem of three-phase AC system and DC system, and the problem of poor anti-interference of simple differential calculation values. Finally, it integrates the traveling wave directional protection and traveling wave ranging technology, and proposes a complete technical solution for directional comparison traveling wave protection.

[0011] The present invention adopts the following technical solution. A first aspect of the present invention provides a directional comparison type traveling wave protection method applicable to a three-phase AC power grid, comprising the following steps:

[0012] Step 1: Based on accurate time-synchronized unbiased sampling, protection devices are installed at the beginning and end of the transmission line to obtain three-phase current signals Ia, Ib, and Ic. The sampling frequency is greater than or equal to 1 MHz, and the sampled data has an accurate timestamp, and the timestamp deviation is less than 1 microsecond.

[0013] Step 2, based on the three-phase current signals Ia, Ib, Ic collected in step 1, continuous real-time Park transformation is superimposed on polar coordinate transformation to perform continuous real-time Park transformation on the double-end synchronous sampling data to obtain equivalent values ​​Id, Iq in the synchronous rotating rectangular coordinate system, and then expressed in the form of amplitude and angle Ir, Iθ through polar coordinate transformation;

[0014] Step 3, based on the sampling sequence of the current amplitude Ir obtained by the coordinate transformation in step 2, a multi-scale cubic B-spline wavelet transform is performed to output a high-frequency component sequence of each scale space;

[0015] Step 4: Based on the decomposition result of step 3, the wave head of the traveling wave is marked by the modulus maximum method, the modulus maximum time t after wavelet transformation is marked as the arrival time of the traveling wave head, and the polarity of the wave head is marked;

[0016] Step 5, based on the wave head polarity and wave head arrival time obtained in step 4, perform traveling wave polarity direction comparison type traveling wave protection, and judge whether it is an internal fault or an external fault according to the wave head polarity and arrival time at both ends; if it is an internal fault, the protection action will remove the fault; if it is an external fault, the protection will be locked to prevent false operation.

[0017] In step 1, synchronous unbiased sampling based on precise timing specifically includes:

[0018] Step 1.1: Accurately synchronize the time by using the crystal oscillator training algorithm to track the measured frequency of the crystal oscillator, so that the tracking and synchronization accuracy is less than 16 nanoseconds.

[0019] Step 1.2, frequency locking and phase locking. Based on the tracking and timing accuracy achieved in step 1.1, the second cycle count of the crystal oscillator is consistent with the second cycle tracking of the precise timing, so the frequency is locked; the zero pulse edge of the sampling pulse is locked and synchronized with the second pulse edge of the precise timing, so the phase is locked;

[0020] Step 1.3, unbiased sampling, based on the frequency-locked phase-locked method implemented in step 1.2, uses a long-period amortized modulation algorithm. The sampling pulse is periodically generated by the time-synchronized second pulse. After each cycle, it will be re-locked with the second pulse edge to achieve long-term operation without cumulative deviation.

[0021] Step 1.4, high-density sampling, based on the unbiased sampling achieved in step 1.3, using a high sampling rate ADC chip with a sampling rate of at least 1 MHz;

[0022] In step 1.1, the crystal taming algorithm specifically includes:

[0023] The taming cycle needs to be no less than 1 minute;

[0024] The initial taming time needs to be no less than 10 minutes;

[0025] After one cycle is completed, the next taming cycle starts immediately and the iteration continues.

[0026] In step 1.3, the long-period amortized modulation algorithm specifically includes:

[0027] The long-period amortized modulation algorithm is used to modulate the PWM module set in the FPGA to output synchronous sampling pulses;

[0028] The amortization of the long-cycle amortized modulation algorithm is used when the high-frequency phase-locked clock pulse and the synchronous sampling pulse are not integer multiples. The remainder after division is evenly distributed over the entire cycle to control the deviation of the synchronous sampling pulse.

[0029] The dividend of the long-period amortized modulation algorithm is selected as the total number of clock pulses N, rather than the clock pulse frequency value;

[0030] The divisor of the long-period amortized modulation algorithm is selected as the product of the synchronous sampling pulse frequency value Fs and the long-period second number T;

[0031] The calculation formula of the remainder R of the long-period amortized modulation algorithm is:

[0032] R=(N mod(T×Fs)) (6)

[0033] The final implementation result of the long-period amortized modulation algorithm is that, with a total of N phase-locked clock pulses as the description object, exactly (T*Fs) sampling pulses will be output;

[0034] In step 2, the continuous real-time Parker transformation superimposed with polar coordinate transformation specifically includes:

[0035] Step 2.1, based on the three-phase current signal obtained in step 1, the standard 50Hz rotating coordinate system formed by precise timing is selected through the rotating coordinate of Parker transformation. The initial phase angle θ is a constant, and its value does not affect the result, and is usually set to 0. The formula of Parker transformation is:

[0036]

[0037] In the formula,

[0038] i a ,i b ,i c is the input three-phase current signal, per unit value,

[0039] i d ,i q , i0 is the equivalent value in the synchronous rotating rectangular coordinate system, the per unit value,

[0040] θ is the angle between the dq0 rotating coordinate system and the abc stationary coordinate system, in radians;

[0041] Step 2.2, based on the equivalent value in the synchronous rotating rectangular coordinate system obtained by Parker transformation, polar coordinate transformation is performed to extract the relatively stable polar coordinate amplitude value. The formula for calculating the modulus value by polar coordinate transformation is:

[0042]

[0043] In the formula,

[0044] i d ,i q is the equivalent value of the synchronous rotating rectangular coordinate system dq axis, per unit value,

[0045] i r is the equivalent amplitude in the synchronously rotating polar coordinate system, per unit value.

[0046] Step 3 specifically includes:

[0047] Step 3.1, based on the current amplitude obtained in step 2, a partially overlapping sliding window is performed, the sliding window length of the sampled data is 128 microseconds, the step length is 100 microseconds, and 28 microseconds is the overlapping part, which can avoid missing the signal detection of the intersection part of the sliding window;

[0048] Step 3.2, based on the sliding window obtained in step 3.1 and the current amplitude obtained in step 2, a multi-scale cubic B-spline wavelet transform is performed on the sampling sequence of the current amplitude. The wavelet function of the cubic B-spline wavelet transform is:

[0049]

[0050] Step 3.3, use dyadic wavelet to perform multi-scale analysis, decomposing at least 4 scales at a sampling rate of 1 MHz;

[0051] Step 3.4, use FPGA to implement continuous real-time sliding window wavelet analysis algorithm, each sliding window length is 128 microseconds, based on 1MHz sampling rate, there are 128 sampling points.

[0052] In step 4, the algorithm for marking the wave head of the traveling wave by the modulus maximum method specifically includes:

[0053] Step 4.1, based on the decomposition result of step 3, find the high-frequency component modulus maximum point at each scale and its corresponding modulus maximum; the maximum value of the modulus maxima at all scales is the modulus maximum of the traveling wave;

[0054] Step 4.2: If the modulus maximum is greater than the threshold, it is considered to be a traveling wave head; the threshold can be obtained by actual measurement;

[0055] Step 4.3, mark the polarity of the wave head. If the modulus maximum value is greater than 0, the wave head is marked as positive, and if it is less than 0, the wave head is marked as negative;

[0056] Step 4.4, mark the time t of the modulus maximum as the arrival time of the traveling wave head.

[0057] In step 5, the traveling wave polarity direction comparison type traveling wave protection algorithm specifically includes:

[0058] Step 5.1: Based on the wave head polarity and wave head arrival time information obtained in step 4, the traveling wave polarity direction comparison type traveling wave protection is performed. Both end programs receive the wave head information transmitted by the other end, and then compare it with the wave head information of the local end. If the wave head polarity is different, it can be determined as an out-of-zone fault.

[0059] Step 5.2, traveling wave polarity direction comparison type traveling wave protection, if the wave head polarity is the same, it is necessary to further determine whether the arrival time difference of the wave heads on both sides satisfies the formula. The specific formula is:

[0060]

[0061] in,

[0062] t m is the timestamp of the maximum value of the m-side modulus, in microseconds;

[0063] t n is the timestamp of the n-side modulus maximum in microseconds;

[0064] L is the total length of the line in meters;

[0065] v is the speed of the traveling wave;

[0066] 10 is the error constant in microseconds, based on a single-ended maximum of plus or minus 5 microseconds, including engineering error and algorithm error;

[0067] If the conditions are met, it is judged as an in-zone fault.

[0068] Step 5.3: Based on the fault judgment results obtained in steps 5.1 and 5.2, if it is confirmed to be an out-of-zone fault, the protection is locked to prevent false operation. If it is confirmed to be an in-zone fault, the output is operated to cut off the fault.

[0069] The second aspect of the present invention provides a direction comparison type traveling wave protection system suitable for a three-phase AC power grid, comprising: a synchronous unbiased sampling module based on precise timing, a continuous real-time Parker transform superimposed polar coordinate transformation module, a multi-scale cubic B-spline wavelet transform module, a modulus maximum method traveling wave head detection module, and a traveling wave polarity direction comparison type traveling wave protection logic module;

[0070] The synchronous unbiased sampling module based on precise timing is used to receive external timing signals and use the external timing signals to generate high-precision synchronous sampling pulses to achieve long-term unbiased uniform sampling.

[0071] The continuous real-time Parker transformation superimposed polar coordinate transformation module is connected to the synchronous unbiased sampling module based on precise timing. Based on the three-phase current signal obtained from the synchronous unbiased sampling module based on precise timing, it is used to realize the transformation from the static abc coordinate system to the rotating dq0 coordinate system, and then converted into the amplitude and angle in the polar coordinate system; a relatively stable polar coordinate amplitude value is extracted from the three-phase sinusoidal waveform data through the coordinate transformation;

[0072] A multi-scale cubic B-spline wavelet transform module is connected to the continuous real-time Parker transform superimposed polar coordinate transform module. The polar coordinate amplitude quantity obtained by the continuous real-time Parker transform superimposed polar coordinate transform module is used to perform cubic B-spline wavelet transform and scale decomposition from a relatively stable polar coordinate amplitude quantity signal to extract high-frequency components at different scales.

[0073] The module of modulus maximum method for detecting the head of traveling wave is connected with the module of multi-scale cubic B-spline wavelet transform. Based on the decomposition result of the module of multi-scale cubic B-spline wavelet transform, it is used to identify and mark the head information of traveling wave from the high-frequency components of different scales decomposed by wavelet, including the precise time of arrival of the head and the polarity of the head. According to the difference of traveling wave frequency, the head of traveling wave will be reflected in different decomposition scales.

[0074] The traveling wave polarity direction comparison traveling wave protection logic module is connected to the modulus maximum method traveling wave head detection module. Based on the wave head polarity mark information and wave head arrival time information obtained by the modulus maximum method traveling wave head detection module, it is used to receive the wave head arrival time and polarity information of the other end, and compare it with the wave head arrival time and polarity of the local end to determine the fault area and handle it.

[0075] The continuous real-time Parker transformation superimposed polar coordinate transformation module specifically comprises: a Parker transformation unit polar coordinate transformation unit;

[0076] The Parker transformation unit is connected to the synchronous unbiased sampling module based on precise timing, and is used to transform the static abc coordinate system into the rotating dq0 coordinate system through the Parker transformation based on the three-phase current signal obtained by the synchronous unbiased sampling module based on precise timing;

[0077] The polar coordinate transformation unit is connected to the Park transformation unit, and is used to extract relatively stable polar coordinate amplitude quantities through polar coordinate transformation based on the equivalent values ​​Id, Iq in the synchronous rotating rectangular coordinate system obtained by the Park transformation unit.

[0078] The module for detecting the traveling wave head by modulus maximum method specifically comprises: a modulus maximum calculation unit, a traveling wave head judgment unit, a wave head polarity and wave head arrival time marking unit;

[0079] The modulus maximum calculation unit is connected to the multi-scale cubic B-spline wavelet transform module, and is used to solve the modulus maximum point of the high-frequency component at each scale and its corresponding modulus maximum based on the scale decomposed by the multi-scale cubic B-spline wavelet transform module; the maximum value of the modulus maximum at all scales is the modulus maximum of the traveling wave;

[0080] A traveling wave head judging unit is connected to the modulus maximum value calculating unit, and is used to judge the traveling wave head based on the modulus maximum value obtained by the modulus maximum value unit by comparing it with the threshold value obtained by actual measurement. If the maximum value is greater than the threshold value, it is judged as a traveling wave head.

[0081] The wave head polarity and wave head arrival time marking unit is connected with the modulus maximum calculation unit and the traveling wave head judgment unit. Based on the modulus maximum obtained by the modulus maximum calculation unit and the traveling wave head judgment result obtained by the traveling wave head judgment unit, when the modulus maximum is greater than 0, the wave head polarity is marked as positive; when the modulus maximum is less than 0, the wave head polarity is marked as negative; the modulus maximum time t is marked as the traveling wave head arrival time.

[0082] The traveling wave polarity direction comparison type traveling wave protection logic module specifically includes: a fault area judgment unit and a fault processing unit;

[0083] The fault area judgment unit is connected to the modulus maximum method traveling wave head detection module, and compares the opposite end information with the local end information based on the wave head polarity and wave head arrival time obtained by the modulus maximum method traveling wave head detection module to judge the fault area;

[0084] The fault processing unit is connected to the fault area judgment unit, and processes the fault based on the judgment result of the fault area judgment unit on the fault area; when it is judged to be an out-of-area fault, the protection is locked to prevent false operation; when it is judged to be an in-area fault, the protection action cuts off the fault.

[0085] Compared with the prior art, the beneficial effects of the present invention include at least: extracting a relatively stable amplitude signal similar to direct current from the three-phase AC system through Park transform and polar coordinate transform, thereby formally unifying the three-phase AC traveling wave protection and the DC traveling wave protection; multi-scale cubic B-spline wavelet transform and modulus maximum method wave head detection are more accurate than traditional differential component judgment criteria; finally, the traveling wave polarity direction comparison traveling wave protection module finally realizes the transition from traditional power frequency protection to traveling wave protection, and the traveling wave protection logic only needs a single window (about 0.1 milliseconds) of data to complete accurate fault judgment and output tripping, which is 2 orders of magnitude faster than the previous single-cycle 20 milliseconds or half-cycle 10 milliseconds traditional power frequency protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0086] Figure 1 It is a schematic diagram of a directional comparison type travelling wave protection method applicable to three-phase AC power grid;

[0087] Figure 2 It is a schematic diagram of a directional comparison traveling wave protection system suitable for three-phase AC power grid. DETAILED DESCRIPTION

[0088] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0089] The present invention provides a directional comparison type traveling wave protection method applicable to a three-phase AC power grid, comprising the following steps:

[0090] Step 1: Based on accurate time-synchronized unbiased sampling, protection devices are installed at the beginning and end of the transmission line to obtain three-phase current signals Ia, Ib, and Ic. The sampling frequency is greater than or equal to 1 MHz, and the sampled data has an accurate timestamp, and the timestamp deviation is less than 1 microsecond.

[0091] Preferably, in step 1, the synchronous unbiased sampling based on precise timing specifically includes:

[0092] Step 1.1, accurate timing, receiving external timing signals, using crystal oscillator taming algorithm, tracking the measured frequency of the crystal oscillator, so that the tracking timing accuracy is less than 16 nanoseconds;

[0093] Step 1.2, frequency locking and phase locking, based on the tracking and timing accuracy of step 1.1, which is less than 16 nanoseconds, the frequency locking is achieved by making the crystal oscillator second cycle count consistent with the precise timing second cycle tracking; the sampling pulse zero pulse edge is locked and synchronized with the precise timing second pulse edge to achieve phase locking;

[0094] Step 1.3, unbiased sampling, based on the frequency-locked phase-locked method implemented in step 1.2, uses a long-period amortized modulation algorithm. The sampling pulse is periodically generated by the time-synchronized second pulse. After each cycle, it will be re-locked with the second pulse edge to achieve long-term operation without cumulative deviation.

[0095] Step 1.4, high-density sampling, based on the unbiased sampling achieved in step 1.3, using a high sampling rate ADC chip with a sampling rate of at least 1 MHz;

[0096] Preferably, in step 1.1, the crystal oscillator taming algorithm specifically includes:

[0097] Continuous periodic iterative taming: through continuous periodic taming, the frequency of the crystal oscillator is adjusted to be consistent with the nominal frequency;

[0098] The taming cycle needs to be no less than 1 minute, and the typical value is 128 seconds;

[0099] The initial taming time needs to be no less than 10 minutes, and the typical value is 15 minutes;

[0100] After one cycle is completed, the next taming cycle starts immediately and the iteration continues.

[0101] The typical value is 128 seconds, which is used to control the taming error;

[0102] The theoretical maximum error of the double-ended measurement edge is calculated with two measurement pulses, and the pulse width is 8 nanoseconds. If it is tamed with a short period of 1 second, the maximum measurement error of the second period is 16 nanoseconds.

[0103] According to the long period crystal oscillator training, the total maximum deviation of 128 seconds is 16 nanoseconds, so the measurement error of the second period is 0.125 nanoseconds, which is a decrease of two orders of magnitude.

[0104] Preferably, in step 1.3, the long-period amortized modulation algorithm specifically includes:

[0105] The long-period amortized modulation algorithm is used to modulate the PWM module set in the FPGA to output synchronous sampling pulses;

[0106] The amortization of the long-cycle amortized modulation algorithm is used when the high-frequency phase-locked clock pulse and the synchronous sampling pulse are not integer multiples. The remainder after division is evenly distributed over the entire cycle to control the deviation of the synchronous sampling pulse.

[0107] The dividend of the long-period amortized modulation algorithm is selected as the total number of clock pulses N, rather than the clock pulse frequency value;

[0108] The divisor of the long-period amortized modulation algorithm is selected as the product of the synchronous sampling pulse frequency value Fs and the long-period second number T;

[0109] Furthermore, the calculation formula of the remainder R of the long-period amortized modulation algorithm is:

[0110] R=(N mod(T×Fs)) (6)

[0111] In the formula,

[0112] R is the remainder of the long-period amortized modulation algorithm;

[0113] N is the total number of clock pulses;

[0114] T is the long period in seconds;

[0115] Fs is the synchronous sampling pulse frequency value.

[0116] The final implementation result of the long-period amortized modulation algorithm is that, with a total of N phase-locked clock pulses as the description object, exactly (T*Fs) sampling pulses will be output;

[0117] Step 2, based on the three-phase current signal collected in step 1, continuous real-time Park transformation is superimposed on polar coordinate transformation to perform continuous real-time Park transformation on the double-end synchronous sampling data to obtain equivalent values ​​Id, Iq in the synchronous rotating rectangular coordinate system, and then expressed in the form of amplitude and angle Ir, Iθ through polar coordinate transformation;

[0118] Preferably, in step 2, the continuous real-time Parker transformation superimposed with polar coordinate transformation specifically includes:

[0119] Step 2.1, based on the three-phase current signal obtained in step 1, the standard 50Hz rotating coordinate system formed by precise timing is selected through the rotating coordinate of Parker transformation. The initial phase angle θ0 is a constant, and its value does not affect the result, and is usually set to 0. The formula of Parker transformation is:

[0120]

[0121] In the formula,

[0122] i a ,i b ,i c is the input three-phase current signal, per unit value,

[0123] i d ,i q , i0 is the equivalent value in the synchronous rotating rectangular coordinate system, the per unit value,

[0124] θ is the angle between the dq rotating coordinate system and the abc stationary coordinate system, in radians;

[0125] Step 2.2, based on the equivalent values ​​Id, Iq in the synchronous rotating rectangular coordinate system obtained by Parker transformation, polar coordinate transformation is performed to extract relatively stable polar coordinate amplitude values. The formula for calculating the modulus value by polar coordinate transformation is:

[0126]

[0127] In the formula,

[0128] i d ,i q is the equivalent value of the synchronous rotating rectangular coordinate system dq axis, per unit value,

[0129] i r is the equivalent amplitude in the synchronously rotating polar coordinate system, per unit value;

[0130] Preferably, in step 2.2, the sliding window length needs to be greater than the step length, and the number of sampling points is usually an integer power of 2 to facilitate subsequent wavelet transform.

[0131] Step 3, based on the sampling sequence of the current amplitude Ir obtained by the coordinate transformation in step 2, partially overlap the sliding window, perform multi-scale cubic B-spline wavelet transform, only take the sampling sequence of the double-terminal current amplitude Ir for multi-scale cubic B-spline wavelet transform, perform scale decomposition, and output the low-frequency component sequence and high-frequency component sequence of each scale space;

[0132] Preferably, step 3 specifically includes the following steps:

[0133] Step 3.1: Partially overlapping sliding windows. Based on the current amplitude obtained in step 2, a partially overlapping sliding window is performed. The sliding window length of the current amplitude is 128 microseconds, the step length is 100 microseconds, and 28 microseconds is the overlapping part, which can avoid missing signal detection at the intersection of the sliding windows.

[0134] Preferably, the sliding window length needs to be greater than the step length, and the number of sampling points is usually an integer power of 2 to facilitate subsequent wavelet transform.

[0135] Step 3.2, based on the sliding window obtained in step 3.1 and the current amplitude Ir obtained in step 2, a multi-scale cubic B-spline wavelet transform is performed on the sampling sequence of the current amplitude Ir in the sliding window. The wavelet function of the cubic B-spline wavelet transform is for

[0136]

[0137] Step 3.3, use dyadic wavelet to perform multi-scale analysis, decomposing at least 4 scales at a sampling rate of 1 MHz;

[0138] Step 3.4, use FPGA to implement continuous real-time sliding window wavelet analysis algorithm, each sliding window length is 128 microseconds, based on 1MHz sampling rate, there are 128 sampling points.

[0139] Preferably, in step 3.3, the number of scales of the multi-scale analysis is related to the sampling rate. For example, if the sampling rate is doubled from 1 MHz to 2 MHz, the corresponding number of decomposition scales should also be increased by 1 to at least 5 scales.

[0140] Furthermore, in step 3.4, assuming that the sliding window length remains unchanged at 128 microseconds, as the sampling rate increases by an integer power of 2, the number of sampling points in the window will also increase by an integer power of 2, which will bring more arduous calculation requirements and time consumption, but the performance improvement brought by traveling wave protection is not obvious.

[0141] Step 4: Based on the decomposition result of step 3, the wave head of the traveling wave is marked by the modulus maximum method, the modulus maximum time t after wavelet transformation is marked as the arrival time of the traveling wave head, and the polarity of the wave head is marked;

[0142] Preferably, in step 4, the algorithm for marking the wave head of the traveling wave by the modulus maximum method specifically includes:

[0143] Step 4.1, based on the scale decomposed in step 3, find the detail coefficient at each scale, that is, the modulus maximum point of the high-frequency component and its corresponding modulus maximum; the maximum value of the modulus maximum at all scales is the modulus maximum of the traveling wave;

[0144] Taking 1MHz sampling rate as an example, the traveling wave mode maximum usually appears at the 3rd to 4th scale;

[0145] Step 4.2: If the modulus maximum is greater than the threshold, it is considered to be a traveling wave head; the threshold can be obtained by actual measurement;

[0146] Step 4.3, mark the polarity of the wave head. If the modulus maximum value is greater than 0, the wave head is marked as positive, and if it is less than 0, the wave head is marked as negative;

[0147] Step 4.4, mark the time t of the modulus maximum as the arrival time of the traveling wave head;

[0148] Step 5, based on the wave head polarity and wave head arrival time obtained in step 4, perform traveling wave polarity direction comparison type traveling wave protection, and judge whether it is an internal fault or an external fault according to the wave head polarity and arrival time at both ends; if it is an internal fault, the protection action will remove the fault; if it is an external fault, the protection will be locked to prevent false operation.

[0149] Preferably, in step 5, the traveling wave polarity direction comparison type traveling wave protection algorithm specifically includes:

[0150] Step 5.1: Based on the wave head polarity and wave head arrival time information obtained in step 4, the traveling wave polarity direction comparison type traveling wave protection is performed. Both end programs receive the wave head information transmitted by the other end, and then compare it with the wave head information of the local end. If the wave head polarity is different, it can be determined as an out-of-zone fault.

[0151] Step 5.2, traveling wave polarity direction comparison type traveling wave protection, if the wave head polarity is the same, it is necessary to further determine whether the arrival time difference of the wave heads on both sides satisfies the formula. The specific formula is:

[0152]

[0153] In the formula,

[0154] t m is the timestamp of the maximum value of the m-side modulus, in microseconds;

[0155] t n is the timestamp of the n-side modulus maximum in microseconds;

[0156] L is the total length of the line in meters;

[0157] v is the speed of the traveling wave, which is 300 m / μs;

[0158] 10 is the error constant in microseconds, based on a single-ended maximum of plus or minus 5 microseconds, including engineering error and algorithm error;

[0159] If the conditions are met, it is judged as an in-zone fault.

[0160] Step 5.3: Based on the fault judgment results obtained in steps 5.1 and 5.2, if it is confirmed to be an out-of-zone fault, the protection is locked to prevent false operation; if it is confirmed to be an in-zone fault, the output is operated to cut off the fault;

[0161] Among them, for ultra-short lines with a length of less than 3 kilometers, the transmission time of the traveling wave on the entire line is less than 10 microseconds, and this method is not applicable.

[0162] like Figure 2 As shown, embodiment 2 of the present invention provides a direction comparison type traveling wave protection system suitable for a three-phase AC power grid, including: a synchronous unbiased sampling module based on precise timing, a continuous real-time Parker transform superimposed polar coordinate transformation module, a multi-scale cubic B-spline wavelet transform module, a modulus maximum method traveling wave head detection module, and a traveling wave polarity direction comparison type traveling wave protection logic module;

[0163] The synchronous unbiased sampling module based on precise timing is used to receive external timing signals and use the external timing signals to generate high-precision synchronous sampling pulses to achieve long-term unbiased uniform high-density sampling;

[0164] Among them, the synchronous unbiased sampling module based on precise timing specifically includes: precise timing unit, frequency-locked phase-locked unit, unbiased sampling unit, and high-density sampling unit;

[0165] The precise timing unit is used to receive an external timing signal, and adopts a crystal oscillator taming algorithm to track the measured frequency of the crystal oscillator, so that the tracking timing accuracy is less than 16 nanoseconds;

[0166] The frequency-locked phase-locked unit is connected to the precise timing unit, and is used to achieve frequency-locked phase-locked synchronization based on the frequency and phase synchronization of the crystal oscillator in the system and the external timing pulse signal implemented by the precise timing unit;

[0167] The unbiased sampling unit is connected to the frequency-locked phase-locked unit, and the frequency locking and phase locking realized by the frequency-locked phase-locked unit are used to realize long-term operation without accumulated deviation through a long-period amortized modulation algorithm;

[0168] The high-density sampling unit is connected to the unbiased sampling unit, and is used to perform high-density sampling with a sampling rate of at least 1 MHz through a high-sampling-rate ADC chip based on the long-term operation without accumulated deviation achieved by the unbiased sampling unit.

[0169] The continuous real-time Parker transformation superimposed polar coordinate transformation module is connected to the synchronous unbiased sampling module based on precise timing. Based on the three-phase current signal obtained from the synchronous unbiased sampling module based on precise timing, it is used to realize the transformation from the static abc coordinate system to the rotating dq0 coordinate system, and then converted into the amplitude and angle in the polar coordinate system; a relatively stable polar coordinate amplitude value is extracted from the three-phase sinusoidal waveform data through the coordinate transformation;

[0170] Among them, the continuous real-time Parker transformation superimposed polar coordinate transformation module specifically includes: a Parker transformation unit, a polar coordinate transformation unit;

[0171] The Parker transformation unit is connected to the synchronous unbiased sampling module based on precise timing, and the three-phase current signal obtained by the synchronous unbiased sampling module based on precise timing is used to transform the static abc coordinate system into the rotating dq0 coordinate system through the Parker transformation;

[0172] The polar coordinate transformation unit is connected to the Park transformation unit, and is used to extract relatively stable polar coordinate amplitude quantities through polar coordinate transformation based on the equivalent values ​​Id, Iq in the synchronous rotating rectangular coordinate system obtained by the Park transformation unit.

[0173] The multi-scale cubic B-spline wavelet transform module is connected to the continuous real-time Parker transform superimposed polar coordinate transform module. Based on the polar coordinate amplitude obtained by the continuous real-time Parker transform superimposed polar coordinate transform module, a partially overlapping sliding window is used to perform cubic B-spline wavelet transform on the relatively stable polar coordinate amplitude signal, and scale decomposition is used to extract high-frequency components at different scales. The traveling wave signal exists in these high-frequency components.

[0174] The module of modulus maximum method for detecting the head of traveling wave is connected with the module of multi-scale cubic B-spline wavelet transform. It is used to identify and mark the head information of traveling wave from the high-frequency components of different scales decomposed by wavelet based on the scale decomposed by the module of multi-scale cubic B-spline wavelet transform, including the precise time of arrival of the head and the polarity of the head. According to the difference of traveling wave frequency, the peak energy, i.e., the head of traveling wave, will be reflected at different decomposition scales.

[0175] Among them, the modulus maximum method traveling wave head detection module specifically includes: a modulus maximum calculation unit, a traveling wave head judgment unit, a wave head polarity and wave head arrival time marking unit;

[0176] A modulus maximum value calculation unit is connected to the multi-scale cubic B-spline wavelet transform module and is used to solve the modulus maximum value of the traveling wave based on the scale decomposed by the multi-scale cubic B-spline wavelet transform module;

[0177] Specifically, it includes: solving the modulus maximum point of the detail coefficient, i.e. the high-frequency component, at each scale, and its corresponding modulus maximum; the maximum value of the modulus maximum at all scales is the modulus maximum of the traveling wave;

[0178] A traveling wave head judging unit is connected to the modulus maximum value calculating unit, and is used to compare the modulus maximum value obtained by the modulus maximum value unit with a threshold value to judge the traveling wave head;

[0179] Specifically, the method includes: obtaining a threshold value through actual measurement, comparing the threshold value with the modulus maximum value, and if the maximum value is greater than the threshold value, determining it as a traveling wave head;

[0180] The wave head polarity and wave head arrival time marking unit is connected to the modulus maximum value calculation unit and the traveling wave head judgment unit, and marks the wave head polarity and the wave head arrival time based on the modulus maximum value obtained by the modulus maximum value calculation unit and the traveling wave head judgment result obtained by the traveling wave head judgment unit;

[0181] Specifically, when the modulus maximum is greater than 0, the wave head polarity is marked as positive; when the modulus maximum is less than 0, the wave head polarity is marked as negative; the modulus maximum time t is marked as the arrival time of the traveling wave head;

[0182] The traveling wave polarity direction comparison type traveling wave protection logic module is connected to the modulus maximum method traveling wave head detection module, and is used to receive the wave head arrival time and polarity information of the other end based on the wave head polarity mark information and wave head arrival time information obtained by the modulus maximum method traveling wave head detection module, and compare it with the wave head arrival time and polarity of the local end to determine the fault area and handle it;

[0183] Among them, the traveling wave polarity direction comparison type traveling wave protection logic module specifically includes: a fault area judgment unit and a fault processing unit;

[0184] The fault area judgment unit is connected to the modulus maximum method traveling wave head detection module, and compares the opposite end information with the local end information based on the wave head polarity and wave head arrival time obtained by the modulus maximum method traveling wave head detection module to judge the fault area;

[0185] The fault area determination unit specifically includes:

[0186] When the wave head polarity is different, it is determined to be an out-of-zone fault;

[0187] When the wave head polarities are the same, the arrival times of the wave heads on both sides are further compared to determine the fault area;

[0188] When the time difference between the arrival times of the wave heads on both sides satisfies the following formula, it is judged as an internal fault;

[0189] The specific formula is:

[0190]

[0191] In the formula,

[0192] t m is the timestamp of the maximum value of the m-side modulus, in microseconds;

[0193] t n is the timestamp of the n-side modulus maximum, in microseconds;

[0194] L is the total length of the line in meters;

[0195] v is the speed of the traveling wave,

[0196] 10 is the error constant in microseconds, based on a single-ended maximum of plus or minus 5 microseconds, including engineering error and algorithm error;

[0197] A fault processing unit is connected to the fault area determination unit, and processes the fault based on the determination result of the fault area by the fault area determination unit;

[0198] The fault handling unit specifically includes:

[0199] When it is judged as an out-of-zone fault, the lockout protection prevents false operation;

[0200] When it is judged to be an internal fault, the protection action will clear the fault;

[0201] Among them, for ultra-short lines with a length of less than 3 kilometers, the transmission time of the traveling wave on the entire line is less than 10 microseconds, and this system is not applicable.

[0202] Compared with the prior art, the beneficial effects of the present invention include at least: extracting a relatively stable amplitude signal similar to direct current from the three-phase AC system through Park transform and polar coordinate transform, thereby formally unifying the three-phase AC traveling wave protection and the DC traveling wave protection; multi-scale cubic B-spline wavelet transform and modulus maximum method wave head detection are more accurate than traditional differential component judgment criteria; finally, the traveling wave polarity direction comparison traveling wave protection module finally realizes the transition from traditional power frequency protection to traveling wave protection, and the traveling wave protection logic only needs a single window (about 0.1 milliseconds) of data to complete accurate fault judgment and output tripping, which is 2 orders of magnitude faster than the previous single-cycle 20 milliseconds or half-cycle 10 milliseconds traditional power frequency protection.

[0203] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A directional comparison traveling wave protection method suitable for a three-phase AC power grid, characterized in that: The following steps are involved: Step 1: Based on accurate time-synchronized unbiased sampling, protection devices are installed at the beginning and end of the transmission line to obtain three-phase current signals Ia, Ib, and Ic. The sampling frequency is greater than or equal to 1 MHz, and the sampled data has an accurate timestamp, and the timestamp deviation is less than 1 microsecond. Step 2, based on the three-phase current signals Ia, Ib, Ic collected in step 1, continuous real-time Park transformation is superimposed on polar coordinate transformation to perform continuous real-time Park transformation on the double-end synchronous sampling data to obtain equivalent values ​​Id, Iq in the synchronous rotating rectangular coordinate system, and then expressed in the form of amplitude and angle Ir, Iθ through polar coordinate transformation; Step 3, based on the sampling sequence of the current amplitude Ir obtained by the coordinate transformation in step 2, a multi-scale cubic B-spline wavelet transform is performed to output a sequence of high-frequency components in each scale space; Step 4: Based on the decomposition result of step 3, the wave head of the traveling wave is marked by the modulus maximum method, the modulus maximum time t after wavelet transformation is marked as the arrival time of the traveling wave head, and the polarity of the wave head is marked; Step 5, based on the wave head polarity and wave head arrival time obtained in step 4, perform traveling wave polarity direction comparison type traveling wave protection, and judge whether it is an internal fault or an external fault according to the wave head polarity and arrival time at both ends; if it is an internal fault, the protection action will remove the fault; if it is an external fault, the protection will be locked to prevent false operation.

2. A directional comparison type traveling wave protection method applicable to a three-phase AC power grid according to claim 1, characterized in that: The step 1 specifically includes: Step 1.1, accurate timing, receiving external timing signals, using crystal oscillator taming algorithm, tracking the measured frequency of the crystal oscillator, so that the tracking timing accuracy is less than 16 nanoseconds; Step 1.2, frequency locking and phase locking, based on the tracking and timing accuracy of step 1.1, which is less than 16 nanoseconds, the frequency locking is achieved by making the crystal oscillator second cycle count consistent with the precise timing second cycle tracking; the sampling pulse zero pulse edge is locked and synchronized with the precise timing second pulse edge to achieve phase locking; Step 1.3, unbiased sampling, based on the frequency-locked phase-locked method implemented in step 1.2, uses a long-period amortized modulation algorithm. The sampling pulse is periodically generated by the time-synchronized second pulse. After each cycle, it will be re-locked with the second pulse edge to achieve long-term operation without cumulative deviation. Step 1.4, high-density sampling, based on the unbiased sampling achieved in step 1.3, uses a high sampling rate ADC chip with a sampling rate of at least 1 MHz.

3. A directional comparison type traveling wave protection method applicable to a three-phase AC power grid according to claim 1, characterized in that: The step 2 specifically includes: Step 2.1, based on the three-phase current signal obtained in step 1, the standard 50Hz rotating coordinate system formed by precise timing is selected through the rotating coordinate of Parker transformation. The initial phase angle is a constant, and its value does not affect the result, and is usually set to 0. The formula of Parker transformation is: In the formula, i a ,i b ,i c is the input three-phase current signal, per unit value, i d ,i q , i0 is the equivalent value in the synchronous rotating rectangular coordinate system, the per unit value, θ is the angle between the dq0 rotating coordinate system and the abc stationary coordinate system, in radians; Step 2.2, based on the equivalent value in the synchronous rotating rectangular coordinate system obtained by Parker transformation, polar coordinate transformation is performed to extract the relatively stable polar coordinate amplitude. The formula for calculating the amplitude by polar coordinate transformation is: In the formula, i d ,i q is the equivalent value of the synchronous rotating rectangular coordinate system dq axis, per unit value, i r is the equivalent amplitude in the synchronously rotating polar coordinate system, per unit value.

4. A directional comparison type traveling wave protection method applicable to a three-phase AC power grid according to claim 1, characterized in that: The step 3 specifically includes: Step 3.1, based on the current amplitude obtained in step 2, a partially overlapping sliding window is performed, the sliding window length of the current amplitude is 128 microseconds, the step length is 100 microseconds, and 28 microseconds is the overlapping part, which can avoid missing the signal detection of the intersection part of the sliding window; Step 3.2, based on the sliding window obtained in step 3.1 and the current amplitude obtained in step 2, a multi-scale cubic B-spline wavelet transform is performed on the sampling sequence of the current amplitude. The wavelet function of the cubic B-spline wavelet transform is for Step 3.3, use dyadic wavelet to perform multi-scale analysis, decomposing at least 4 scales at a sampling rate of 1 MHz; Step 3.4, use FPGA to implement continuous real-time sliding window wavelet analysis algorithm, each sliding window length is 128 microseconds.

5. The directional comparison traveling wave protection method applicable to a three-phase AC power grid according to claim 1, characterized in that: The step 4 specifically includes: Step 4.1, based on the decomposition result of step 3, find the high-frequency component modulus maximum point at each scale and its corresponding modulus maximum; the maximum value of the modulus maxima at all scales is the modulus maximum of the traveling wave; Step 4.2, if the modulus maximum is greater than the threshold, it is considered to be a traveling wave head; Step 4.3, mark the polarity of the wave head. If the modulus maximum value is greater than 0, the wave head is marked as positive, and if it is less than 0, the wave head is marked as negative; Step 4.4, mark the time t of the modulus maximum as the arrival time of the traveling wave head.

6. A directional comparison type traveling wave protection method applicable to a three-phase AC power grid according to claim 1, characterized in that: The step 5 specifically includes: Step 5.1: Based on the wave head polarity and wave head arrival time information obtained in step 4, the traveling wave polarity direction comparison type traveling wave protection is performed. Both end programs receive the wave head information transmitted by the other end, and then compare it with the wave head information of the local end. If the wave head polarity is different, it can be determined as an out-of-zone fault. Step 5.2, traveling wave polarity direction comparison type traveling wave protection, if the wave head polarity is the same, it is necessary to further determine whether the difference in arrival time of the wave heads on both sides satisfies the formula. The specific formula is: In the formula, t m is the timestamp of the maximum value of the m-side modulus, in microseconds; t n is the timestamp of the n-side modulus maximum in microseconds; L is the total length of the line in meters; v is the speed of the traveling wave; 10 is the error constant in microseconds, based on a single-ended error of plus or minus 5 microseconds, including engineering error and algorithm error; If the conditions are met, it is judged as an in-area fault; Step 5.3, based on the fault judgment results obtained in steps 5.1 and 5.2, if it is confirmed to be an out-of-zone fault, the protection is locked to prevent false operation; if it is confirmed to be an in-zone fault, the output is activated to cut off the fault.

7. A directional comparison type traveling wave protection system applicable to a three-phase AC power grid, running a directional comparison type traveling wave protection method applicable to a three-phase AC power grid as claimed in any one of claims 1 to 6, comprising: Based on the precise timing synchronous unbiased sampling module, the continuous real-time Parker transform superimposed polar coordinate transformation module, the multi-scale cubic B-spline wavelet transform module, the modulus maximum method traveling wave head detection module, the traveling wave polarity direction comparison type traveling wave protection logic module, it is characterized by: The synchronous unbiased sampling module based on precise timing is used to receive external timing signals and use the external timing signals to generate high-precision synchronous sampling pulses to achieve long-term unbiased uniform high-density sampling; The continuous real-time Parker transformation superimposed polar coordinate transformation module is connected to the synchronous unbiased sampling module based on precise timing. Based on the three-phase current signal obtained from the synchronous unbiased sampling module based on precise timing, it is used to realize the transformation from the static abc coordinate system to the rotating dq0 coordinate system, and then converted into the amplitude and angle in the polar coordinate system; a relatively stable polar coordinate amplitude value is extracted from the three-phase sinusoidal waveform data through the coordinate transformation; The multi-scale cubic B-spline wavelet transform module is connected to the continuous real-time Parker transform superimposed polar coordinate transform module. The polar coordinate amplitude quantity obtained by the continuous real-time Parker transform superimposed polar coordinate transform module is used to perform cubic B-spline wavelet transform on the relatively stable polar coordinate amplitude quantity signal, decompose the scale, and extract the high-frequency components at different scales; The module of modulus maximum method for detecting the head of traveling wave is connected with the module of multi-scale cubic B-spline wavelet transform. Based on the decomposition result of the module of multi-scale cubic B-spline wavelet transform, it is used to identify and mark the head information of traveling wave from the high-frequency components of different scales decomposed by wavelet, including the precise time of arrival of the head and the polarity of the head. According to the difference of traveling wave frequency, the head of traveling wave will be reflected in different decomposition scales. The traveling wave polarity direction comparison traveling wave protection logic module is connected to the modulus maximum method traveling wave head detection module. Based on the wave head polarity mark information and wave head arrival time information obtained by the modulus maximum method traveling wave head detection module, it is used to receive the wave head arrival time and polarity information of the other end, and compare it with the wave head arrival time and polarity of the local end to determine the fault area and handle it.

8. A directional comparison type traveling wave protection system suitable for a three-phase AC power grid according to claim 7, characterized in that: The continuous real-time Parker transformation superimposed polar coordinate transformation module specifically includes: a Parker transformation unit and a polar coordinate transformation unit; The Parker transformation unit is connected to the synchronous unbiased sampling module based on precise timing, and is used to transform the static abc coordinate system into the rotating dq0 coordinate system through the Parker transformation based on the three-phase current signal obtained by the synchronous unbiased sampling module based on precise timing; The polar coordinate transformation unit is connected to the Park transformation unit, and is used to extract relatively stable polar coordinate amplitude quantities through polar coordinate transformation based on the equivalent values ​​Id, Iq in the synchronous rotating rectangular coordinate system obtained by the Park transformation unit.

9. A directional comparison type traveling wave protection system suitable for a three-phase AC power grid according to claim 7, characterized in that: The module for detecting the traveling wave head by modulus maximum method specifically comprises: a modulus maximum calculation unit, a traveling wave head judgment unit, a wave head polarity and wave head arrival time marking unit; The modulus maximum calculation unit is connected to the multi-scale cubic B-spline wavelet transform module, and is used to solve the modulus maximum point of the high-frequency component at each scale and its corresponding modulus maximum based on the scale decomposed by the multi-scale cubic B-spline wavelet transform module; the maximum value of the modulus maximum at all scales is the modulus maximum of the traveling wave; A traveling wave head judging unit is connected to the modulus maximum value calculating unit, and is used to judge the traveling wave head based on the modulus maximum value obtained by the modulus maximum value unit by comparing it with the threshold value obtained by actual measurement. If the maximum value is greater than the threshold value, it is judged as a traveling wave head. The wave head polarity and wave head arrival time marking unit is connected with the modulus maximum calculation unit and the traveling wave head judgment unit. Based on the modulus maximum obtained by the modulus maximum calculation unit and the traveling wave head judgment result obtained by the traveling wave head judgment unit, when the modulus maximum is greater than 0, the wave head polarity is marked as positive; when the modulus maximum is less than 0, the wave head polarity is marked as negative; the modulus maximum time t is marked as the traveling wave head arrival time.

10. A directional comparison type traveling wave protection system suitable for a three-phase AC power grid according to claim 7, characterized in that: The traveling wave polarity direction comparison type traveling wave protection logic module specifically includes: a fault area judgment unit and a fault processing unit; The fault area judgment unit is connected to the modulus maximum method traveling wave head detection module, and compares the opposite end information with the local end information based on the wave head polarity and wave head arrival time obtained by the modulus maximum method traveling wave head detection module to judge the fault area; The fault processing unit is connected to the fault area judgment unit, and processes the fault based on the judgment result of the fault area judgment unit on the fault area; when it is judged to be an out-of-area fault, the protection is locked to prevent false operation; when it is judged to be an in-area fault, the protection action cuts off the fault.

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