Longitudinal protection method and device based on instantaneous power total and incremental waveform similarity

Abstract

The invention discloses a pilot protection method and device based on instantaneous power total and incremental waveform similarity, and belongs to the technical field of power systems. According to the method, fault detection is started through voltage or current abrupt change, differential capacitance current compensation is carried out based on a full current sampling value, and a compensated voltage value is calculated by combining an electromagnetic wave transmission equation and a line Bergeron model so as to eliminate the influence of line parameters; and judging a passive load branch fault through a current amplitude and an integral value, otherwise, synchronously adopting an instantaneous power full-quantity waveform cosine similarity longitudinal main protection criterion and an instantaneous power increment waveform cosine similarity criterion to identify an internal fault, and overcoming a reliability'dead zone 'defect caused by near-zone fault voltage drop. The method does not need to depend on power frequency phasor calculation, and can improve the sensitivity and reliability of protection in scenes of a high-proportion new energy power grid, a micro-grid and the like.

Description

Technical Field

[0001] This invention relates to the field of power system technology, specifically to a longitudinal protection method and device based on the similarity between instantaneous full power and incremental waveforms. Background Technology

[0002] With the large-scale integration of new energy sources into the power system, the power system is gradually transforming into a high-proportion new energy power system. However, the short-circuit currents of new energy power sources and converter equipment have characteristics such as limited amplitude and large phase variation range. In addition, the interference of harmonic components and transient regulation of converters on the accuracy of power frequency phasor extraction leads to a significant reduction in the sensitivity of traditional differential protection based on power frequency phasors, and even failure to operate. Especially in scenarios such as new energy sending to the AC grid via flexible DC systems and fully electronic power grids, the differential protection faces a serious problem of insufficient sensitivity due to the lack of traditional synchronous motor support on both sides.

[0003] Existing technologies have proposed various improvement schemes to address the above-mentioned problems: for example, to address the impact of high harmonics and frequency shifts, a longitudinal protection method for the transmission lines of new energy power plants based on the correlation of transient current waveforms has been proposed; to address the problem of limited short-circuit current in islanded power grids, a differential protection scheme injecting specific frequencies has been adopted; and to address the insufficient sensitivity caused by loads and distributed power sources (T) connecting to the distribution network, a differential protection scheme based on active power characteristics has been proposed. However, all these methods rely on current components as the core criterion. When the voltage of the fault phase drops significantly, the active power signal is weak, which can easily lead to deterioration of protection performance.

[0004] To address this, this invention combines the full power frequency and non-power frequency information of fault electrical quantities and proposes a protection method that integrates voltage and current sample values ​​based on the principle of instantaneous power conservation. By introducing a voltage component, the protection sensitivity can be significantly improved; simultaneously, it eliminates the need for power frequency phasor calculations, reducing the impact of short-circuit current transient characteristics on protection performance. Furthermore, to address the reliability "dead zone" problem that may occur in the full instantaneous power criterion under low-voltage scenarios of faults within the fault zone, a cosine similarity criterion for the instantaneous power increment waveform is further constructed to overcome the protection failure defects caused by voltage drops in near-field faults. This method is applicable to new power system scenarios such as high-proportion renewable energy grids, microgrids, and AC grids with flexible direct transmission. Summary of the Invention

[0005] To address the issue of insufficient differential protection sensitivity in scenarios such as high-proportion renewable energy power grids, microgrids, and AC power grids transmitting renewable energy via flexible DC systems, this invention provides a longitudinal protection method and device based on waveform similarity of instantaneous power total and incremental values, based on the principle of instantaneous power conservation. By constructing a longitudinal protection criterion based on the cosine similarity of the instantaneous power total waveform based on voltage and current sampling values, and considering the low voltage drop in the near-field fault zone, a longitudinal protection method based on the cosine similarity of the instantaneous power incremental waveform is added. This overcomes the "dead zone" defect when the fault voltage is low, changing the traditional approach based on current-based differential protection or waveform similarity longitudinal protection, and effectively ensuring the high sensitivity requirements of protection in scenarios such as high-proportion renewable energy power grids and microgrids.

[0006] To achieve the above objectives, according to one aspect of the present invention, a waveform similarity longitudinal protection method based on instantaneous full power and incremental power is provided, comprising the following steps:

[0007] Step 1: Initiate fault detection by voltage or current surges and proceed with the fault handling process;

[0008] Step 2: Perform capacitor current compensation based on the full current sampling value to obtain the compensated current sampling value;

[0009] Step 3: Based on the compensated current sampling value obtained in Step 2, and combining the electromagnetic wave propagation equation and the line Berylon model, calculate the compensated voltage sampling value to eliminate the influence of line parameters;

[0010] Step 4: Based on the compensated current sampling value obtained in Step 2, compare the current amplitude with the current setting value to determine whether the passive side of the single power supply line provides short-circuit current. If the passive load branch conditions are met, further compare the current sampling integral values ​​to determine whether it is an internal fault of the line; otherwise, execute Step 5 and Step 6 simultaneously.

[0011] Step 5: Using the compensated current sampling value from Step 2 and the compensated voltage sampling value from Step 3, calculate the total instantaneous power value and construct the cosine similarity longitudinal main protection criterion. When the similarity result is greater than the first similarity criterion setting value, it is determined to be an intra-zone fault.

[0012] Step 6: Using the current sampling value after compensation in Step 2 and the voltage sampling value after compensation in Step 3, calculate the instantaneous power increment value and construct the cosine similarity criterion of the instantaneous power increment waveform. When the increment similarity result is greater than the second similarity criterion setting value, it is determined to be an in-zone fault, so as to overcome the reliability "dead zone" defect caused by the voltage drop of near-zone faults.

[0013] Furthermore, in step 2, when performing capacitor current compensation based on the full current sampling value, a differentiated compensation strategy is adopted for different line types: high-voltage power grid lines consider compensation for ground capacitance and phase-to-phase capacitance, 110kV~220kV overhead lines ignore phase-to-phase capacitance compensation, 35kV~10kV overhead lines do not perform capacitance compensation, and cable lines are compensated according to the π-type equivalent circuit.

[0014] 2. Further, step 2 specifically includes:

[0015] Considering the effects of ground capacitance and phase-to-phase capacitance, the capacitor compensation current for phase a at both ends of line i and j is shown in equation (1):

[0016] (1);

[0017] In the formula, , These are the sampled values ​​of the capacitor current for compensation on the i-side and j-side, respectively; Let a be the capacitance relative to ground. Let be the interphase capacitance of phase a; a, b, c represent the three phases a, b, c; u represents voltage, and i represents current; Indicates the protection sampling period; , Indicates in , The sampling value of the capacitor compensation current of phase a on side i at time; similarly, the capacitor compensation currents of phase b and phase c at both ends of the line on side i and side j are obtained.

[0018] According to equation (2), the current sampling values ​​after compensation capacitor current on the i-side and j-side of the line are obtained:

[0019] (2);

[0020] In the formula, and These are the sampled current values ​​on the i-side and j-side after compensating for the capacitor current; and These are the current sampling values ​​of the i-side and j-side before the compensation capacitor current, respectively; similarly, the current sampling values ​​of the i-side and j-side after the compensation capacitor current of phase b and phase c can be obtained.

[0021] 3. Further, step 3 specifically includes:

[0022] Obtain the full voltage sample values ​​of the j-side and i-side after compensating for impedance voltage drop according to equation (3):

[0023] (3);

[0024] In the formula, and These represent the compensated full-sample voltage values ​​on the i-side and j-side of the line, respectively. and These are the full sampled voltage values ​​of sides i and j before compensation; and These represent the equivalent positive-sequence inductance and resistance of the circuit; the subscript "0" indicates the zero-sequence component.

[0025] 4. Further, step 4 specifically includes:

[0026] The current sampling values ​​of the i-side and j-side after compensation capacitor current are used to determine whether they are greater than the current setting value, as shown in equation (4):

[0027] (4);

[0028] When equation (4) is satisfied, it is determined to be a passive load branch, where, This is the current setting value, with a typical value of 0.1 pu; x represents the three phases a, b, and c. and The sampled integral values ​​of each phase current after compensation on the i-side and j-side are respectively; otherwise, proceed to steps (5) and (6).

[0029] When the fault is determined to be a passive load branch, further judgment is made according to equation (5) to determine whether it is an internal fault of the line. If equation (5) is satisfied, it is an internal fault of the line; otherwise, it is determined to be an external fault.

[0030] (5).

[0031] 5. Further, step 5 specifically includes:

[0032] Cosine similarity is selected as the waveform similarity comparison method. The longitudinal protection criterion for the instantaneous power full waveform cosine similarity on the i-side of the line is shown in equation (6):

[0033] (6);

[0034] If equation (6) is satisfied, an internal fault is considered to have occurred, and a trip command is issued; otherwise, it is an external fault; where c set This represents the first similarity criterion setting value based on the total instantaneous power; r Φ This indicates the similarity calculation results; the time window length is T / 2. The number of sampling points within the time window; and Let i and j represent the instantaneous power values ​​after the compensation capacitor current on side i and the instantaneous power values ​​after the compensation capacitor current and impedance voltage drop on side j, respectively. Their expressions are obtained from equation (7).

[0035] (7).

[0036] Furthermore, the first similarity criterion setting value is -0.5.

[0037] Furthermore, step 6 specifically includes:

[0038] The longitudinal protection criterion for the cosine similarity of the instantaneous power increment waveform on the i-side of the line is shown in equation (8):

[0039] (8);

[0040] If equation (8) is satisfied, an intra-zone fault is considered to have occurred, and a trip command is issued. Otherwise, it is...

[0041] External fault; where the subscript Δ represents the increment; and These represent the instantaneous power increment after the compensation capacitor current on side i, and the instantaneous power increment on side i after the compensation capacitor current and impedance voltage drop on side j, respectively. The number of sampling points within the time window; c set-Δ This represents the second similarity criterion setting value based on the instantaneous power increment; r ΔΦ This represents the cosine similarity calculation result based on the instantaneous power increment waveform; the time window length is taken as T / 2.

[0042] Furthermore, the second similarity criterion setting value is -0.5.

[0043] A longitudinal protection device based on the similarity between instantaneous full power and incremental waveforms includes:

[0044] The fault detection initiation module is used to initiate fault detection and enter the fault handling process based on voltage or current surges.

[0045] The capacitor current compensation module is used to perform capacitor current compensation based on the full current sampling value to obtain the compensated current sampling value.

[0046] The compensated voltage sample value calculation module is used to calculate the compensated voltage sample value based on the obtained compensated current sample value, combined with the electromagnetic wave propagation equation and the line Berylon model, in order to eliminate the influence of line parameters.

[0047] The passive load branch judgment module is used to determine whether the passive side of the single power supply line provides short-circuit current based on the obtained compensated current sampling value and by comparing the current amplitude with the current setting value. If the passive load branch condition is met, the module further determines whether it is an internal fault of the line by comparing the current sampling integral value; otherwise, the first fault judgment module and the second fault judgment module are executed simultaneously.

[0048] The fault judgment module in the first zone is used to calculate the instantaneous power full value and construct the cosine similarity longitudinal main protection criterion by using the compensated current sampling value and the compensated voltage sampling value. When the similarity result is greater than the first similarity criterion setting value, it is judged as a fault in the zone.

[0049] The second fault detection module is used to calculate the instantaneous power increment value and construct the cosine similarity criterion of the instantaneous power increment waveform using the current sampling value and voltage sampling value after compensation in the first step. When the increment similarity result is greater than the second similarity criterion setting value, it is determined to be an in-zone fault, so as to overcome the reliability "dead zone" defect caused by the voltage drop of near-zone faults.

[0050] The main innovations and beneficial effects of this invention are as follows:

[0051] 1. Based on the principle of instantaneous power conservation, a voltage component is introduced to construct the protection criterion, changing the traditional differential protection approach that relies solely on current, and significantly improving protection sensitivity, especially suitable for scenarios where the short-circuit current of new energy power sources is limited.

[0052] 2. Integration of full and incremental waveform similarity criteria: The cosine similarity of the instantaneous power full waveform is used as the main protection, while the instantaneous power incremental waveform criterion is added to effectively overcome the "dead zone" defect when the voltage drops in the near-zone fault, and ensure the reliability of fault identification.

[0053] 3. Differentiated capacitive current compensation strategy: Different compensation methods are adopted for high-voltage power grids, 110kV~220kV overhead lines, 35kV~10kV overhead lines and cable lines to accurately eliminate the influence of line capacitive current and improve protection accuracy.

[0054] 4. No power frequency phasor calculation required: Analysis is performed directly based on voltage and current sampling values, reducing the interference of short-circuit current transient characteristics on protection performance and adapting to the complex transient environment of new power systems such as high-proportion new energy grids and microgrids. Attached Figure Description

[0055] Figure 1 This is a logical schematic diagram of the longitudinal main protection method based on the cosine similarity of instantaneous power full quantity and incremental waveform of the present invention;

[0056] Figure 2 This is a flowchart illustrating the principle and logic of the longitudinal protection based on the cosine similarity of instantaneous power full and incremental waveforms under power grid faults according to the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] Please see Figure 1 and Figure 2 This invention provides a longitudinal protection method based on waveform similarity between instantaneous full power and incremental power, comprising the following steps:

[0059] Step 1: Initiate fault detection by voltage or current surges and proceed with the fault handling process;

[0060] Step 2: Perform capacitor current compensation based on the full current sampling value to obtain the compensated current sampling value;

[0061] In this embodiment, taking the π-type equivalent circuit as an example, considering the influence of ground capacitance and phase-to-phase capacitance, the compensation current of phase a capacitor at both ends of line i and j is as shown in equation (1).

[0062] (1)

[0063] In the formula, , These are the sampled values ​​of the capacitor current for compensation on the i-side and j-side, respectively; Let a be the capacitance relative to ground. Let be the interphase capacitance of phase a; a, b, c represent the three phases a, b, c; u represents voltage, and i represents current; Indicates the protection sampling period; , Indicates in , The sampling value of the phase a capacitor compensation current on the i-side at time j is obtained. Similarly, the phase b and phase c capacitor compensation currents at both ends of the line on the i-side and j-side can be obtained.

[0064] Based on this, the current sampling values ​​after compensation capacitor current on the i-side and j-side of the line can be obtained according to equation (2):

[0065] (2)

[0066] In the formula, and These are the sampled current values ​​on the i-side and j-side after compensating for the capacitor current; and These are the sampled current values ​​on the i-side and j-side before the compensation capacitor current is applied, respectively. Similarly, the sampled current values ​​on the i-side and j-side after the compensation capacitor current is applied to phases b and c can be obtained.

[0067] It should be noted that if it is a high-voltage power grid line, the capacitor current compensation method in formula (1) can be used; if it is a 110kV~220kV overhead line, the compensation effect of phase-to-phase capacitance in formula (1) can be ignored; if it is a 35kV~10kV overhead line, it is not necessary to compensate for the ground capacitance and phase-to-phase capacitance current; if it is a cable line, it can be compensated according to formula (1).

[0068] Step 3: Select an appropriate equivalent model based on different line lengths, and then calculate the compensated voltage sampling value based on the full voltage and current sampling values ​​to eliminate the adverse effects of line parameters such as capacitance. For example, the distributed voltage of a long-distance transmission line can be solved according to the electromagnetic wave propagation equation and the line Berylon model. In this embodiment, taking the π-type equivalent circuit as an example, the full voltage sampling values ​​of the j-side and i-side after compensating for the impedance voltage drop can be obtained according to equation (3).

[0069] (3)

[0070] In the formula, and These represent the compensated full-sample voltage values ​​on the i-side and j-side of the line, respectively. and These are the full sampled voltage values ​​of sides i and j before compensation; and These represent the equivalent positive-sequence inductance and resistance of the circuit; the subscript "0" indicates the zero-sequence component.

[0071] Step 4: To address the issue that the passive side of a single-power supply line does not provide short-circuit current, which may cause the instantaneous power and instantaneous power increment cosine similarity comparison method to fail, a protection additional criterion (see Equation (4)) based on the comparison of short-circuit current amplitudes on both sides of the line (comparison of sampled integral values) is used to determine whether the line has a fault. Otherwise, proceed to steps 5 and 6 simultaneously;

[0072] In this embodiment, the current sampling values ​​of the i-side and j-side after compensation capacitor current are used to determine whether they are greater than the current setting value, as shown in equation (4). When equation (4) is satisfied, it is determined to be a passive load branch; otherwise, proceed to steps (5) and (6). When it is determined to be a passive load branch, it is further determined whether it is an internal line fault according to equation (5). If equation (5) is satisfied, it is an internal line fault; otherwise, it is an external fault.

[0073] (4)

[0074] In the formula, is the current setting value, with a typical value of 0.1pu; x represents the three phases a, b, and c. and These are the sampled integral values ​​of the phase currents after compensation on the i-side and j-side, respectively.

[0075] (5)

[0076] Step 5: Based on the voltage and current sampling values, construct the cosine similarity longitudinal protection criterion of the instantaneous power full waveform; in this embodiment, cosine similarity is selected as the waveform similarity comparison method, and the cosine similarity longitudinal protection criterion of the instantaneous power full waveform on the i-side is shown in equation (6). When equation (6) is satisfied, it is considered that an intra-zone fault has occurred and a trip command is issued; otherwise, it is an external fault.

[0077] (6)

[0078] In the formula, c set This represents the similarity criterion setting value based on the total instantaneous power, and its typical value can be expressed as -0.5; r Φ This indicates the similarity calculation result; the time window length is T / 2. The table shows the number of sampling points within the time window. and Let i and j represent the instantaneous power values ​​after the compensation capacitor current on side i and the instantaneous power values ​​after the compensation capacitor current and impedance voltage drop on side j, respectively. Their expressions can be obtained from equation (7).

[0079] (7)

[0080] Similarly, the longitudinal protection criterion for the instantaneous power full waveform similarity on side j can be obtained.

[0081] Step 6: To address the reliability "dead zone" defect faced by near-area power grid faults, a longitudinal protection criterion based on the cosine similarity of instantaneous power increment waveforms is constructed. In this embodiment, the longitudinal protection criterion based on the cosine similarity of instantaneous power increment waveforms on the i-th side of line is shown in equation (8). If equation (8) is satisfied, an intra-area fault is considered to have occurred, and a tripping command is issued. Otherwise, it is an external fault.

[0082] (8)

[0083] In the formula, the subscript Δ represents the increment (fault component). and These represent the instantaneous power increment after the compensation capacitor current on side i, and the instantaneous power increment on side i after the compensation capacitor current and impedance voltage drop on side j, respectively. The number of sampling points within the time window; c set-ΔThis represents the similarity criterion setting value based on instantaneous power increment, and its typical value can be expressed as -0.5; r ΔΦ This represents the cosine similarity calculation result based on the waveform of the instantaneous power increment (fault component); the time window length is taken as T / 2.

[0084] Step 7: End.

[0085] This invention provides a longitudinal protection device based on the similarity between instantaneous full power and incremental waveforms, comprising:

[0086] The fault detection initiation module is used to initiate fault detection and enter the fault handling process based on voltage or current surges.

[0087] The capacitor current compensation module is used to perform capacitor current compensation based on the full current sampling value to obtain the compensated current sampling value.

[0088] The compensated voltage sample value calculation module is used to calculate the compensated voltage sample value based on the obtained compensated current sample value, combined with the electromagnetic wave propagation equation and the line Berylon model, in order to eliminate the influence of line parameters.

[0089] The passive load branch judgment module is used to determine whether the passive side of the single power supply line provides short-circuit current based on the obtained compensated current sampling value and by comparing the current amplitude with the current setting value. If the passive load branch condition is met, the module further determines whether it is an internal fault of the line by comparing the current sampling integral value; otherwise, the first fault judgment module and the second fault judgment module are executed simultaneously.

[0090] The fault judgment module in the first zone is used to calculate the instantaneous power full value and construct the cosine similarity longitudinal main protection criterion by using the compensated current sampling value and the compensated voltage sampling value. When the similarity result is greater than the first similarity criterion setting value, it is judged as a fault in the zone.

[0091] The second fault detection module is used to calculate the instantaneous power increment value and construct the cosine similarity criterion of the instantaneous power increment waveform using the current sampling value and voltage sampling value after compensation in the first step. When the increment similarity result is greater than the second similarity criterion setting value, it is determined to be an in-zone fault, so as to overcome the reliability "dead zone" defect caused by the voltage drop of near-zone faults.

[0092] The longitudinal protection method based on waveform similarity of instantaneous full and incremental power proposed in the embodiments of this invention can avoid the severe sensitivity deficiencies faced by traditional current differential protection or current waveform similarity protection in AC grids at the sending end of high-proportion renewable energy power grids, microgrids, or renewable energy transmission systems via flexible direct current transmission, thus meeting the protection sensitivity requirements of high-proportion renewable energy power grids and microgrids. Specifically, based on the principle of instantaneous power conservation, this invention provides a longitudinal protection method based on the cosine similarity of instantaneous full and incremental waveforms of voltage and current samples, introducing a voltage component and significantly improving protection sensitivity. Simultaneously, since no power frequency phasor calculation is required, the protection performance is less affected by the complex transient characteristics of short-circuit current, further improving protection performance. Furthermore, considering the potential reliability "dead zone" problem of instantaneous power waveform cosine similarity longitudinal protection when the fault voltage is low, an additional instantaneous power incremental waveform cosine similarity longitudinal protection is constructed to overcome the "dead zone" defect at low fault voltages. With the continuous construction of new power systems and the increasing proportion of renewable energy, the method proposed in this invention should have broad application prospects.

[0093] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A longitudinal protection method based on the similarity between instantaneous full power and incremental waveforms, characterized in that, Includes the following steps: Step 1: Initiate fault detection by voltage or current surges and proceed with the fault handling process; Step 2: Perform capacitor current compensation based on the full current sampling value to obtain the compensated current sampling value; Step 3: Based on the compensated current sampling value obtained in Step 2, and combining the electromagnetic wave propagation equation and the line Berylon model, calculate the compensated voltage sampling value to eliminate the influence of line parameters; Step 4: Based on the compensated current sampling value obtained in Step 2, compare the current amplitude with the current setting value to determine whether the passive side of the single power supply line provides short-circuit current. If the passive load branch conditions are met, further compare the current sampling integral values ​​to determine whether it is an internal fault of the line; otherwise, execute Step 5 and Step 6 simultaneously. Step 5: Using the compensated current sampling value from Step 2 and the compensated voltage sampling value from Step 3, calculate the total instantaneous power value and construct the cosine similarity longitudinal main protection criterion. When the similarity result is greater than the first similarity criterion setting value, it is determined to be an intra-zone fault. Step 6: Using the current sampling value after compensation in Step 2 and the voltage sampling value after compensation in Step 3, calculate the instantaneous power increment value and construct the cosine similarity criterion of the instantaneous power increment waveform. When the increment similarity result is greater than the second similarity criterion setting value, it is determined to be an in-zone fault, so as to overcome the reliability "dead zone" defect caused by the voltage drop of near-zone faults.

2. The method according to claim 1, characterized in that, In step 2, when performing capacitor current compensation based on the full current sampling value, a differentiated compensation strategy is adopted for different line types: high-voltage power grid lines consider compensation for ground capacitance and phase-to-phase capacitance, 110kV~220kV overhead lines ignore phase-to-phase capacitance compensation, 35kV~10kV overhead lines do not perform capacitance compensation, and cable lines are compensated according to the π-type equivalent circuit.

3. The method according to claim 1, characterized in that, Step 2 specifically includes: Considering the effects of ground capacitance and phase-to-phase capacitance, the capacitor compensation current for phase a at both ends of line i and j is shown in equation (1): （1）； In the formula, , These are the sampled values ​​of the capacitor current for compensation on the i-side and j-side, respectively; Let a be the capacitance relative to ground. Let be the interphase capacitance of phase a; a, b, c represent the three phases a, b, c; u represents voltage, and i represents current; Indicates the protection sampling period; , Indicates in , The sampling value of the capacitor compensation current of phase a on side i at time; similarly, the capacitor compensation currents of phase b and phase c at both ends of the line on side i and side j are obtained. According to equation (2), the current sampling values ​​after compensation capacitor current on the i-side and j-side of the line are obtained: （2）； In the formula, and These are the sampled current values ​​on the i-side and j-side after compensating for the capacitor current; and These are the current sampling values ​​of the i-side and j-side before the compensation capacitor current, respectively; similarly, the current sampling values ​​of the i-side and j-side after the compensation capacitor current of phase b and phase c can be obtained.

4. The method according to claim 3, characterized in that, Step 3 specifically includes: Obtain the full voltage sample values ​​of the j-side and i-side after compensating for impedance voltage drop according to equation (3): （3）； In the formula, and These represent the compensated full-sample voltage values ​​on the i-side and j-side of the line, respectively. and These are the full sampled voltage values ​​of sides i and j before compensation; and These represent the equivalent positive-sequence inductance and resistance of the circuit; the subscript "0" indicates the zero-sequence component.

5. The method according to claim 4, characterized in that, Step 4 specifically includes: The current sampling values ​​of the i-side and j-side after compensation capacitor current are used to determine whether they are greater than the current setting value, as shown in equation (4): （4）； When equation (4) is satisfied, it is determined to be a passive load branch, where, This is the current setting value, with a typical value of 0.1 pu; x represents the three phases a, b, and c. and The sampled integral values ​​of each phase current after compensation on the i-side and j-side are respectively; otherwise, proceed to steps (5) and (6). When the fault is determined to be a passive load branch, further judgment is made according to equation (5) to determine whether it is an internal fault of the line. If equation (5) is satisfied, it is an internal fault of the line; otherwise, it is determined to be an external fault. （5） 。 6. The method according to claim 5, characterized in that, Step 5 specifically includes: Cosine similarity is selected as the waveform similarity comparison method. The longitudinal protection criterion for the instantaneous power full waveform cosine similarity on the i-side of the line is shown in equation (6): （6）； If equation (6) is satisfied, an internal fault is considered to have occurred, and a trip command is issued; otherwise, it is an external fault; where c set This represents the first similarity criterion setting value based on the total instantaneous power; r Φ This indicates the similarity calculation results; the time window length is T / 2. The number of sampling points within the time window; and Let i and j represent the instantaneous power values ​​after the compensation capacitor current on side i and the instantaneous power values ​​after the compensation capacitor current and impedance voltage drop on side j, respectively. Their expressions are obtained from equation (7): （7）。 7. The method according to claim 6, characterized in that, The first similarity criterion setting value is -0.

5.

8. The method according to claim 5, characterized in that, Step 6 specifically includes: The longitudinal protection criterion for the cosine similarity of the instantaneous power increment waveform on the i-side of the line is shown in equation (8): （8）； If equation (8) is satisfied, an intra-zone fault is considered to have occurred, and a trip command is issued; otherwise, it is considered that an intra-zone fault has occurred. External fault; where the subscript Δ represents the increment; and These represent the instantaneous power increment after the compensation capacitor current on side i, and the instantaneous power increment on side i after the compensation capacitor current and impedance voltage drop on side j, respectively. The number of sampling points within the time window; c set-Δ This represents the second similarity criterion setting value based on the instantaneous power increment; r ΔΦ This represents the cosine similarity calculation result based on the instantaneous power increment waveform; the time window length is taken as T / 2.

9. The method according to claim 8, characterized in that, The second similarity criterion setting value is -0.

5.

10. A longitudinal protection device based on the similarity between instantaneous full power and incremental waveforms, characterized in that, include: The fault detection initiation module is used to initiate fault detection and enter the fault handling process based on voltage or current surges. The capacitor current compensation module is used to perform capacitor current compensation based on the full current sampling value to obtain the compensated current sampling value. The compensated voltage sample value calculation module is used to calculate the compensated voltage sample value based on the obtained compensated current sample value, combined with the electromagnetic wave propagation equation and the line Berylon model, in order to eliminate the influence of line parameters. The passive load branch judgment module is used to determine whether the passive side of the single power supply line provides short-circuit current based on the obtained compensated current sampling value and by comparing the current amplitude with the current setting value. If the passive load branch condition is met, the module further determines whether it is an internal fault of the line by comparing the current sampling integral value; otherwise, the first fault judgment module and the second fault judgment module are executed simultaneously. The fault judgment module in the first zone is used to calculate the instantaneous power full value and construct the cosine similarity longitudinal main protection criterion by using the compensated current sampling value and the compensated voltage sampling value. When the similarity result is greater than the first similarity criterion setting value, it is judged as a fault in the zone. The second fault detection module is used to calculate the instantaneous power increment value and construct the cosine similarity criterion of the instantaneous power increment waveform using the current sampling value and voltage sampling value after compensation in the first step. When the increment similarity result is greater than the second similarity criterion setting value, it is determined to be an in-zone fault, so as to overcome the reliability "dead zone" defect caused by the voltage drop of near-zone faults.

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