Fast Time-Domain Distance Protection Method and System Based on Random Correction of Zero-Sequence Current

Abstract

The present invention discloses a fast time-domain distance protection method and system based on random correction of zero-sequence current. Sampling is performed on a new energy grid-connected line system to obtain the three-phase voltage, three-phase current, and zero-sequence current at one end of the line. If the zero-sequence current is greater than the threshold value, zero-sequence current compensation is carried out. If the zero-sequence current is less than the threshold value, random correction is performed on the zero-sequence current, and zero-sequence current compensation is not carried out currently. Using the voltage / current sampling of a unit data window, a voltage / current information matrix within the unit data window is constructed, and the least squares method is used to calculate the single-fitting distance result and the fitting error and calculate the weight. The final cumulative weighted distance result is calculated. If the cumulative distance calculation result continuously and stably is less than the fixed value, it is judged that a fault occurs within the zone, and the distance protection operates to trip. Otherwise, it is judged that a fault occurs outside the zone, and the distance protection does not operate. Compared with the prior art, the present invention realizes weighted summation type fast time-domain distance protection based on random correction of zero-sequence current.

Description

Technical Field

[0001] The present invention relates to the fields of relay protection for AC power transmission systems and new energy grid-connected systems, and particularly to a single-ended distance protection method. Background Art

[0002] In order to address environmental pollution and energy shortage problems, countries around the world are accelerating the process of replacing traditional fossil energy power generation with renewable energy. As the main power source, new energy will become an inevitable trend in the development of future new power systems. However, compared with traditional synchronous power sources, new energy power sources have significant weak-feed and frequency deviation response characteristics, which seriously affect the operating performance of traditional power-frequency-based protection principles. Among them, distance protection, as the main protection or backup protection for some new energy grid-connected lines, has been widely applied in actual power systems. However, the significantly different fault response characteristics of new energy power sources will lead to a serious deterioration of its operating performance. The high harmonic and frequency deviation characteristics of wind power systems result in significant errors in the extraction of power-frequency phasors for distance protection during the initial stage of a fault, thus causing it to fail to operate reliably.

[0003] Traditional time-domain distance protection designs protection criteria using the inherent characteristics of the line model and is not affected by the back-side power source in principle. However, traditional time-domain distance protection has large transient errors under the action of high harmonics. The fast time-domain distance protection algorithm based on least squares fitting error improves the accuracy and convergence speed of the algorithm through weighted summation and accumulation calculation. However, due to the storage and calculation of integer values in actual protection devices, integer rounding errors will occur. Especially during normal operation, the zero-sequence current is small and will be rounded to a constant value in the device, which will cause the weighted summation type fast time-domain distance protection device to malfunction during normal operation. There is an urgent need in the prior art for a fast time-domain distance protection algorithm that is not affected by rounding errors. Summary of the Invention

[0004] In view of the above-mentioned defects existing in the prior art of single-ended distance protection, the present invention proposes a fast time-domain distance protection method and system based on random correction of zero-sequence current, realizing weighted summation type fast time-domain distance protection based on random correction of zero-sequence current.

[0005] The present invention is realized by the following technical solutions:

[0006] In a first aspect, the present invention provides a fast time-domain distance protection method based on random correction of zero-sequence current, including:

[0007] Sampling the new energy grid-connected line system to obtain the three-phase voltage, three-phase current, and zero-sequence current at one end of the line;

[0008] When the zero-sequence current is less than the threshold value, randomly correct all zero-sequence currents affected by integer rounding errors;

[0009] Using the voltage / current sampling of the unit data window, construct the voltage / current information matrix within the unit data window, and calculate the single - fitting distance result and fitting error using the least - squares method based on the obtained voltage / current information matrix within the unit data window, and obtain the weight according to the fitting error;

[0010] Using the single - fitting result and weight within the unit data window, calculate the final cumulative weighted distance result by means of weighted summation within the cumulative data window;

[0011] Conduct an analysis of the cumulative distance calculation result, and determine the type of fault according to the cumulative distance calculation result.

[0012] In some embodiments, if the zero - sequence current is greater than the threshold value, zero - sequence current compensation is performed. The steps of performing zero - sequence current compensation further include:

[0013] Perform zero - sequence current compensation on the measured current according to the three - phase voltage, three - phase current, and zero - sequence current to obtain the compensated resistance current i mr and the compensated inductive current i ml , as shown in the following formula:

[0014] i mr = i m + 3k r i0, i ml = i m + 3k l i0

[0015] In the formula, k r =(r0 – r1) / 3r1 is the resistance zero - sequence compensation coefficient, where r0 and r1 are the zero - sequence resistance and positive - sequence resistance per unit length of the line respectively, and k l =(l0 – l1) / 3l1 is the inductance zero - sequence compensation coefficient, where l0 and l1 are the zero - sequence inductance and positive - sequence inductance per unit length of the line respectively; i mr represents the sampled current after resistance zero - sequence compensation; i ml represents the sampled current after inductance zero - sequence compensation;

[0016] Thus, the compensated resistance current i mr (n) and the compensated inductive current i ml (n) at the sampling point n are obtained.

[0017] In some embodiments, voltage and current sampling are performed using the unit data window determined by s previous points of the sampling point n to construct the voltage information matrix U(n) and the current information matrix I(n), as shown in the following formula:

[0018]

[0019] In the formula, pm () is the line voltage drop per unit length at sampling points n - s + 2, n - s + 3, ..., n - 2, n - 1, i0() is the zero - sequence current at sampling points n - s + 2, n - s + 3, ..., n - 1, u m () is the sampling voltage at sampling points n - s + 2, n - s + 3, ..., n - 1.

[0020] In some embodiments, the single - fit result β(n) is shown as follows:

[0021]

[0022] In the formula, and are the fault distance and the equivalent transition resistance obtained by least - squares fitting solution respectively, I(n) T is the current information transpose matrix;

[0023] The weight W(n) is the reciprocal of the fitting error E rr (n), W(n)=1 / E rr (n);

[0024] The fitting error E rr (n) is shown as follows:

[0025]

[0026] In the formula,. / represents the division of the corresponding elements in the vector. ||·||2 represents the 2 - norm of the vector.

[0027] In some embodiments, using the single - fit result and weight within the unit data window, calculating the final cumulative weighted distance result by weighted summation within the cumulative data window further includes: performing data sampling using the cumulative data window determined by q previous points including sampling point n, and the weighted distance is shown as follows:

[0028]

[0029] In the formula, j represents the sampling point number, taking values from n - q + 1 to n. W(j) and represent the weight and the fault distance calculated for the j - th unit data window respectively.

[0030] In a second aspect, the present invention provides a fast time-domain distance protection system based on random correction of zero-sequence current, including a sampling module, a zero-sequence current random correction module, a cumulative weighted distance calculation module, and a distance protection analysis module; wherein, the sampling module is used to sample the new energy grid-connected line system to obtain the three-phase voltage, three-phase current, and zero-sequence current at one end of the line; the zero-sequence current random correction module is used to perform random correction on all zero-sequence currents affected by integer rounding errors when the zero-sequence current is less than the threshold value; the cumulative weighted distance calculation module is used to construct a voltage / current information matrix within a unit data window by using voltage / current sampling of a unit data window, calculate the single-fitting distance result and fitting error using the least squares method based on the obtained voltage / current information matrix within the unit data window and calculate the weight, and calculate the final cumulative weighted distance result by weighted summation within the cumulative data window using the single-fitting result and weight within the unit data window; the distance protection analysis module is used to analyze the cumulative distance calculation result and determine the fault type according to the cumulative distance calculation result.

[0031] In some embodiments, the step of performing zero-sequence current compensation further includes:

[0032] Performing zero-sequence current compensation on the measured current according to the three-phase voltage, three-phase current, and zero-sequence current to obtain the compensated resistance current i mr and the compensated resistance current i ml , as shown in the following formula:

[0033] i mr = i m + 3k r i0, i ml = i m + 3k l i0

[0034] In the formula, k r =(r0 – r1) / 3r1 is the resistance zero-sequence compensation coefficient, r0 and r1 are the zero-sequence resistance and positive-sequence resistance per unit length of the line respectively, k l =(l0 – l1) / 3l1 is the inductance zero-sequence compensation coefficient, l0 and l1 are the zero-sequence inductance and positive-sequence inductance per unit length of the line respectively; i mr represents the sampled current after resistance zero-sequence compensation; i ml represents the sampled current after inductance zero-sequence compensation.

[0035] Thus, the compensated resistance current i mr (n) and the compensated inductance current i ml (n) at the sampling point n are obtained.

[0036] In some embodiments, voltage and current sampling are performed using a unit data window determined by s previous points of sampling point n to construct a voltage information matrix U(n) and a current information matrix I(n) as shown in the following formula:

[0037]

[0038] where p m () is the voltage drop per unit length of the line at sampling points n-s+2, n-s+3,..., n-2, n-1, i0() is the zero-sequence current at sampling points n-s+2, n-s+3,..., n-1, and u m () is the sampled voltage at sampling points n-s+2, n-s+3,..., n-1.

[0039] In some embodiments, the single-fitting result β(n) is as shown in the following formula:

[0040]

[0041] where and are the fault distance and equivalent transition resistance obtained by least squares fitting respectively, I(n) T is the transposed matrix of current information;

[0042] The weight W(n) is the reciprocal of the fitting error E rr (n), W(n)=1 / E rr (n);

[0043] The fitting error E rr (n) is as shown in the following formula:

[0044]

[0045] where. / represents the division of elements at corresponding positions in the vector. ||·||2 represents the 2-norm of the vector.

[0046] In some embodiments, using the single-fitting result and weight within the unit data window, calculating the final cumulative weighted distance result by weighted summation within the cumulative data window further includes: performing data sampling using a cumulative data window determined by q previous points including sampling point n, and the weighted distance is as shown in the following formula:

[0047]

[0048] where j represents the sampling point number, taking values from n-q+1 to n. W(j) and represent the weight and fault distance calculated for the j-th unit data window respectively.

[0049] Compared with the prior art, the advantages and positive technical effects achieved by the present invention are as follows:

[0050] 1) The steps of zero-sequence current compensation are designed to ensure that the zero-sequence current is not affected by rounding errors, thereby realizing a fast time-domain distance protection algorithm based on the compensated current;

[0051] 2) Through the random correction of the zero-sequence current, it is ensured that all zero-sequence currents affected by integer rounding errors can be randomly corrected to ensure that the corrected zero-sequence current is within a reasonable range, thus ensuring the efficient and reliable operation of the fast time-domain distance protection in the actual relay protection device;

[0052] 3) Using the single fitting result and weight within the unit data window, the final cumulative weighted distance result is calculated by the method of weighted summation within the cumulative data window, providing an important criterion for judgment analysis for the fast time-domain distance protection analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is the overall flowchart of a fast time-domain distance protection method based on random correction of zero-sequence current according to the present invention;

[0054] Figure 2 is the module diagram of a fast time-domain distance protection system based on random correction of zero-sequence current according to the present invention;

[0055] Figure 3 is the specific implementation flowchart of a fast time-domain distance protection method based on random correction of zero-sequence current according to the present invention;

[0056] Figure 4 is the schematic diagram of the test system of the embodiment of the present invention;

[0057] Figure 5 is the schematic diagram of the zero-sequence current rounding error result and the random correction effect of the zero-sequence current;

[0058] Figure 6 is the oscillogram of the protection device and the operation tripping situation when a phase A solid grounding fault occurs at 8 km from the M end of the line. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0059] The technical solutions will be clearly described below in conjunction with the drawings and embodiments.

[0060] As Figure 1 shown, the overall process of a fast time-domain distance protection method based on random correction of zero-sequence current according to the present invention is as follows:

[0061] S1. Sample the new energy grid-connected line system to obtain the three-phase voltage, three-phase current, and zero-sequence current at one end of the line;

[0062] S2. If the zero-sequence current is greater than the threshold value, zero-sequence current compensation is performed. If the zero-sequence current is less than the threshold value, the zero-sequence current is randomly corrected, and zero-sequence current compensation is not performed currently.

[0063] S3. Use the voltage / current sampling of the unit data window to construct the voltage / current information matrix within the unit data window. According to the obtained voltage / current information matrix within the unit data window, use the least squares method to calculate the single-fitting distance result and the fitting error, and calculate the weight based on the fitting error.

[0064] S4. Use the single-fitting result and the weight within the unit data window to calculate the final cumulative weighted distance result by weighted summation within the cumulative data window.

[0065] S5. If the calculated result of the cumulative distance is continuously and stably less than the fixed value for 5 milliseconds, it is judged that a fault occurs within the zone, and the distance protection operates to trip; otherwise, it is judged that a fault occurs outside the zone, and the distance protection does not operate.

[0066] As Figure 2 shown, a fast time-domain distance protection system based on random correction of zero-sequence current of the present invention includes a sampling module, a zero-sequence current random correction module, a cumulative weighted distance calculation module, and a distance protection analysis module. Among them, the sampling module is used to sample the new energy grid-connected line system to obtain the three-phase voltage, three-phase current, and zero-sequence current at one end of the line. The zero-sequence current random correction module is used to perform zero-sequence current compensation if the zero-sequence current is greater than the threshold value, randomly correct the zero-sequence current if the zero-sequence current is less than the threshold value, and not perform zero-sequence current compensation currently. The cumulative weighted distance calculation module is used to use the voltage / current sampling of the unit data window to construct the voltage / current information matrix within the unit data window, calculate the single-fitting distance result and the fitting error using the least squares method based on the obtained voltage / current information matrix within the unit data window and calculate the weight, and use the single-fitting result and the weight within the unit data window to calculate the final cumulative weighted distance result by weighted summation within the cumulative data window. The distance protection analysis module is used to analyze that if the calculated result of the cumulative distance is continuously and stably less than the fixed value for 5 milliseconds, it is judged that a fault occurs within the zone, and the distance protection operates to trip; otherwise, it is judged that a fault occurs outside the zone, and the distance protection does not operate.

[0067] As Figure 3 shown, the implementation process of a weighted summation type fast time-domain distance protection method based on random correction of zero-sequence current of the present invention is specifically described as follows:

[0068] Step 1: Sample the new energy grid-connected line system to obtain the three-phase voltages u ma (n), u mb (n), umc (n) and three-phase current i ma (n), i mb (n), i mc (n), calculate the zero-sequence current i0(n) of sampling point n as shown in the following formula:

[0069] i0(n) = i ma (n) + i mb (n) + i mc (n)

[0070] Step 2: Compare the absolute value of the zero-sequence current i0(n) of sampling point n with the threshold value γ. If the absolute value is greater than γ, perform Step 3 for zero-sequence current compensation; if the absolute value is less than or equal to γ, perform random correction on the zero-sequence current: keep the sign unchanged and change the absolute value to a random value within the range of 0 to Γ, skip Step 3, and perform Step 4; where the threshold value γ is selected to be greater than the zero-sequence current that is uniformly rounded to an integer value in the actual relay protection device to ensure that all zero-sequence currents affected by the rounding error can be randomly corrected. Specifically, it can be selected as one percent of the rated current amplitude during normal system operation; the random correction upper limit value Γ for zero-sequence current random correction can be selected as the maximum value of the zero-sequence current after adding 20 dB noise during normal operation to ensure that the corrected zero-sequence current is within a reasonable range;

[0071] Step 3: Perform zero-sequence current compensation on the measured current according to the three-phase voltage, three-phase current, and zero-sequence current in Step 1 to obtain the compensated resistance current i mr and the compensated inductance current i ml as shown in the following formula:

[0072] i mr = i m + 3k r i0, i ml = i m + 3k l i0

[0073] In the formula, k r = (r0 – r1) / 3r1 is the resistance zero-sequence compensation coefficient, where r0 and r1 are the zero-sequence resistance and positive-sequence resistance per unit length of the line respectively, and k l = (l0 – l1) / 3l1 is the inductance zero-sequence compensation coefficient, where l0 and l1 are the zero-sequence inductance and positive-sequence inductance per unit length of the line respectively; i mr represents the sampled current after resistance zero-sequence compensation; i ml represents the sampled current after inductance zero-sequence compensation;

[0074] Thus, the compensated resistance current i mr (n) and the compensated inductance current iml (n);

[0075] Step 4: Use the unit data window determined by s pre - order points of sampling point n to sample voltage and current, so as to construct a voltage information matrix U(n) and a current information matrix I(n), as shown in the following formula:

[0076]

[0077] In the formula, p m () is the voltage drop of the unit - length line at sampling points n - s + 2, n - s + 3,..., n - 2, n - 1, i0() is the zero - sequence current at sampling points n - s + 2, n - s + 3,..., n - 1, u m () is the sampling voltage at sampling points n - s + 2, n - s + 3,..., n - 1, p m (n) is as shown in the following formula:

[0078]

[0079] In the formula, Δt is the sampling interval, which is the reciprocal of the sampling frequency f s , that is, Δt = 1 / f s ;

[0080] Step 5: Use the voltage and current information matrices U(n) and I(n) described in Step 4, and use the least - squares algorithm to calculate the single - fitting result β(n) and the corresponding fitting error E rr (n). The number of data window points s is related to the fixed - value unit data window length t s , s = t s / Δt; where,

[0081] The single - fitting result β(n) is as shown in the following formula:

[0082]

[0083] In the formula, and are the fault distance and the equivalent transition resistance obtained by least - squares fitting solution respectively, I(n) T is the transposed matrix of the current information;

[0084] The fitting error E rr (n) is as shown in the following formula:

[0085]

[0086] In the formula, the. / symbol represents the element - by - element division of the corresponding positions in the vector, and ||·||2 represents the 2 - norm of the vector;

[0087] Step 6: Perform data sampling using the cumulative data window determined by q previous points including the sampling point n, and calculate the weight W(n) and the weighted distance

[0088] The weight W(n) is the reciprocal of the fitting error E rr (n) in Step 5, W(n) = 1 / E rr (n);

[0089] Weighted distance As shown in the following formula:

[0090]

[0091] In the formula, j represents the sampling point number, taking values from n - q + 1 to n. W(j) and respectively represent the weight and the fault distance calculated from the j-th unit data window;

[0092] Specifically, the number of points q in the cumulative data window is related to the fixed cumulative data window length t q , q = t q / D t ;

[0093] Step 7: If the weighted distance obtained through Step 6 is less than the fixed value x within 5 ms set , and the difference between the maximum value and the minimum value is less than 0.1 km, then the distance protection operates and trips, and the fault handling program ends; otherwise, let n = n + 1, return to Step 1, and repeat the above process using n + 1 sampling points until the obtained weighted distance meets the distance protection operation criterion; the criterion for distance protection operation is specifically shown in the following formula:

[0094] Within 5 consecutive ms:

[0095] In summary, the present invention realizes a weighted summation type fast time-domain distance protection based on random correction of zero-sequence current, randomly corrects the zero-sequence current less than the threshold value and locks its zero-sequence compensation. According to the information matrix composed of sampling values, calculates the single-time fitting distance and the cumulative weighted distance, and constructs a protection criterion according to the relationship between the weighted distance and the setting distance, realizing a single-terminal quantity time-domain distance protection strategy that is not affected by zero-sequence current rounding deviation and new energy characteristics

[0096] Such as Figure 4As shown in the figure, it is a test system according to an embodiment of the present invention, specifically a grid-connected system of a wind farm established through a real-time digital simulation platform (RTDS). The wind farm consists of 20 doubly-fed wind turbines with a rated capacity of 3 MW each, and the total capacity is 60 MW. After two-stage boosting, it is sent into the AC main grid through a 110 kV line, and the total length of the line is 15 km. Taking the line protection M on the wind farm side as the observation object, the sampling rate is 4 kHz. The parameters of the line are as follows: the line length is 15 km, the positive and negative sequence resistances are 0.1111 Ω / m; the positive and negative sequence inductances are 1.2685 mH / km; the positive and negative sequence capacitances are 0.01629 F / km; the zero-sequence resistance is 0.3334 Ω / m; the zero-sequence inductance is 3.552 mH / km; the zero-sequence capacitance is 5.2 F / km. The unit fitting data window length is selected as 2.5 ms, and the cumulative data window length is selected as 10 ms. During the normal operation of the system, the rated current amplitude is about 0.5 kA. Therefore, the threshold value g for random correction of zero-sequence current is 1% * 0.5 = 5 * 10 -3 kA. The upper limit of random correction is taken as 10 -1 kA. The I-section protects 80% of the total length of the line, that is, the I-section distance setting value x set = 12 km.

[0097] As Figure 5 shown, taking the case of a solid A-phase ground fault occurring 8 km away from the M terminal as an example, the actual zero-sequence current i 0re of the system during normal operation before the fault, the zero-sequence current i 0err affected by the rounding error of the protection device, and the zero-sequence current i 0rd after random correction are respectively as Figure 5 (a), Figure 5 (b) and Figure 5 (c) shown. It can be seen that the effect of zero-sequence current correction can change the constant zero-sequence current affected by rounding error into a zero-sequence current fluctuating similar to that during normal operation.

[0098] As Figure 6 shown, recording the fault moment as 0 ms, from 50 ms before the fault to 50 ms after the fault, the voltages and currents sampled by the protection on the M side are as Figure 6 (a) and Figure 6 (b) shown. The trip signals of the traditional time-domain distance protection algorithm without using random zero-sequence current and the algorithm of the present invention are trip0 and trip c respectively, as Figure 6 (c) shown. It can be seen that the algorithm of the present invention can solve the problem of misoperation of the protection during normal operation caused by the rounding error of the zero-sequence current of the actual device, and can correctly judge the actual line fault.

[0099] In addition, based on a similar inventive concept, an embodiment of the present invention further provides an electronic device, including: a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor implements the above method when executing the computer program.

[0100] It should be noted that although the technical solutions have been shown and described with reference to specific exemplary embodiments of the present invention, those skilled in the art should understand that the present invention is not limited to the above embodiments. Any replacement, improvement, or supplement made without departing from the spirit of the present invention and without creative efforts falls within the protection scope of the present invention application.

[0101] Based on the embodiments of the present invention, all other embodiments and technical replacements and deformations of the embodiments obtained by those of ordinary skill in the art without departing from the spirit of the present invention and without creative efforts fall within the protection scope of the present invention.

Claims

1. A fast time-domain distance protection method based on random correction of zero-sequence current, characterized in that It includes the following steps: Sample the new energy grid-connected line system to obtain the three-phase voltage, three-phase current, and zero-sequence current at one end of the line; Under the condition that the zero-sequence current is less than the threshold value, randomly correct all zero-sequence currents affected by integer rounding errors; Use the unit data window determined by s previous points among n sampling points to sample voltage and current to construct the voltage information matrix U(n) and the current information matrix I(n): where p m () is the line voltage drop per unit length at sampling points n - s + 2, n - s + 3,..., n - 2, n - 1, i0() is the zero - sequence current at sampling points n - s + 2, n - s + 3,..., n - 1, u m () is the sampled voltage at sampling points n - s + 2, n - s + 3,..., n - 1; Calculate the single - fitting distance result β(n) and fitting error E using the least - squares method, and obtain the weight W(n) according to the fitting error; rr (n), In the formula, and are the fault distance and equivalent transition resistance obtained by solving the least - squares fitting respectively, and I(n) T is the transposed matrix of current information; In the formula,. / represents the division of the corresponding elements in the vector, ||·||2 represents the 2 - norm of the vector; W(n)=1 / E rr (n); Data sampling is performed using an accumulated data window determined by q previous points among n sampling points, and the weighted distance is calculated Where j represents the sampling point number, taking values from n-q+1 to n, W(j) and respectively represent the weight calculated for the j-th unit data window and the fault distance; Analyze the cumulative distance calculation results and determine the type of fault according to the cumulative distance calculation results.

2. The fast time-domain distance protection method based on random correction of zero-sequence current according to claim 1, characterized in that When the zero-sequence current is greater than the threshold value, zero-sequence current compensation is performed. The steps of zero-sequence current compensation further include: Compensate the measured current i according to the three-phase voltage, three-phase current and zero-sequence current m to obtain the compensated resistance current i mr and the compensated inductance current i ml : i mr = i m + 3k r i0, i ml = i m + 3k l i0 where k r = (r0 – r1) / 3r1 is the zero-sequence compensation coefficient of resistance, r0 and r1 are the zero-sequence resistance and positive-sequence resistance per unit length of the line respectively, k l = (l0 – l1) / 3l1 is the zero-sequence compensation coefficient of inductance, l0 and l1 are the zero-sequence inductance and positive-sequence inductance per unit length of the line respectively, i mr represents the sampled current after zero-sequence compensation of resistance, i ml represents the sampled current after zero-sequence compensation of inductance; Thus, the compensated resistance current i mr (n) and the compensated inductance current i ml (n) are obtained.

3. A fast time-domain distance protection system based on random correction of zero-sequence current, characterized in that, It includes a sampling module, a zero-sequence current random correction module, a cumulative weighted distance calculation module, and a distance protection analysis module; among them, the sampling module is used to sample the new energy grid-connected line system to obtain the three-phase voltage, three-phase current, and zero-sequence current at one end of the line; the zero-sequence current random correction module is used to perform random correction on all zero-sequence currents affected by integer rounding errors under the condition that the zero-sequence current is less than the threshold value; the cumulative weighted distance calculation module is used to use the unit data window determined by s previous points among n sampling points to sample voltage and current to construct the voltage information matrix U(n) and the current information matrix I(n): where p m () is the line voltage drop per unit length at sampling points n - s + 2, n - s + 3,..., n - 2, n - 1, i0() is the zero - sequence current at sampling points n - s + 2, n - s + 3,..., n - 1, u m () is the sampling voltage at sampling points n - s + 2, n - s + 3,..., n - 1; the single - fitting distance result β(n) and fitting error E rr (n) are calculated using the least - squares method, and the weight W(n) is obtained according to the fitting error; where and are the fault distance and equivalent transition resistance obtained by least - squares fitting solution respectively, I(n) T is the current information transpose matrix; where. / represents the element - by - element division of the corresponding positions in the vector, ||·||2 represents the 2 - norm of the vector; W(n) = 1 / E rr (n); Data sampling is performed using an accumulated data window determined by q previous points among n sampling points, and the weighted distance is calculated where j represents the sampling point number, ranging from n-q+1 to n, W(j) and respectively represent the weight calculated by the j-th unit data window and the fault distance; the distance protection analysis module is used to analyze the cumulative distance calculation result and determine the fault type according to the cumulative distance calculation result.

4. A fast time-domain distance protection system based on random correction of zero-sequence current according to claim 3, characterized in that, When the zero-sequence current is greater than the threshold value, zero-sequence current compensation is performed. The steps of zero-sequence current compensation further include: The steps of zero-sequence current compensation further include: Compensate the measured current for zero-sequence current according to three-phase voltage, three-phase current and zero-sequence current to obtain the compensated resistance current i mr and the compensated inductance current i ml : i mr = i m + 3k r i0, i ml = i m + 3k l i0 where k r = (r0 – r1) / 3r1 is the zero-sequence compensation coefficient of resistance, r0 and r1 are the zero-sequence resistance and positive-sequence resistance per unit length of the line respectively, and k l = (l0 – l1) / 3l1 is the zero-sequence compensation coefficient of inductance, l0 and l1 are the zero-sequence inductance and positive-sequence inductance per unit length of the line respectively, and i mr represents the sampled current after zero-sequence compensation of resistance, and i ml represents the sampled current after zero-sequence compensation of inductance; Thus, the compensated resistance current i mr (n) of the sampling point n and the compensated inductance current i ml (n) are obtained.

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