阅读说明：本技术 一种多端混合直流输电线路的保护方法 (Protection method for multi-terminal hybrid direct-current transmission line ) 是由 邢超 王龙 奚鑫泽 何鑫 刘明群 李胜男 马红升 向川 于 2021-08-06 设计创作，主要内容包括：本申请涉及继电保护技术领域,提供一种多端混合直流输电线路的保护方法,当直流输电系统发生故障时,实时采集线路端故障电流,通过计算故障电流线模分量突变量的正负,判断故障方向,防止反向故障引起的保护误动作；利用CEEMDAN算法对故障电流线模分量进行分解,获得各IMF分量；进而,根据Teager能量算子计算高频分量的瞬时幅值,并通过比较高频分量瞬时幅值的最大值与整定值的大小,判断故障位置。当高频分量瞬时幅值的最大值大于整定值时,判定为区内故障,相应保护端执行保护动作；当高频分量瞬时幅值的最大值小于或等于整定值时,判定为区外故障,保护端不动作。本申请能迅速且可靠地执行保护动作,保证最小范围切除故障。(The application relates to the technical field of relay protection, and provides a protection method of a multi-terminal hybrid direct-current transmission line, when a direct-current transmission system breaks down, the fault current of a line terminal is collected in real time, the fault direction is judged by calculating the positive and negative of the fault current line modulus component break variable, and the protection misoperation caused by reverse fault is prevented; decomposing the fault current line-mode components by using a CEEMDAN algorithm to obtain IMF components; and further, calculating the instantaneous amplitude of the high-frequency component according to a Teager energy operator, and judging the fault position by comparing the maximum value of the instantaneous amplitude of the high-frequency component with the setting value. When the maximum value of the instantaneous amplitude of the high-frequency component is greater than the setting value, judging that the fault exists in the area, and executing protection action by a corresponding protection end; and when the maximum value of the instantaneous amplitude of the high-frequency component is less than or equal to the setting value, judging that the fault is outside the area, and keeping the protection end from acting. The method and the device can rapidly and reliably execute the protection action and ensure that the fault is removed in the minimum range.)

1. A protection method for a multi-terminal hybrid direct-current transmission line is characterized by comprising the following steps:

acquiring fault current traveling wave data of a first protection end and a second protection end in a power transmission line;

calculating to obtain the positive and negative of the fault current line mode component variable quantity according to the fault current traveling wave data of the first protection end and the fault current traveling wave data of the second protection end;

judging the fault direction according to the positive and negative of the fault current line modulus component variable quantity;

if the fault direction is at two sides of the T area, decomposing the fault current line mode component to obtain an inherent mode function component;

obtaining a high-frequency component according to the inherent modal function component;

calculating the instantaneous amplitude of the high-frequency component by using a Teager energy operator;

and comparing the maximum value of the instantaneous amplitude with a preset setting value, if the maximum value of the instantaneous amplitude is greater than the setting value, judging that the fault is a fault in the line area, and executing a protection action by the first protection end or the second protection end.

2. The method for protecting the multi-terminal hybrid direct-current transmission line according to claim 1, wherein if the fault direction is on two sides of a T zone, the fault current line-mode component is decomposed by using an adaptive noise ensemble empirical mode decomposition algorithm.

3. The method for protecting the multi-terminal hybrid direct-current transmission line according to claim 1, wherein the fault direction is judged by adopting the following formula according to the positive and negative of the fault current line mode component variation:

wherein x is 1 or 2, K₁Represents the integral of the variation of the fault current line modulus component of the first protection terminal in a 1 millisecond time window, K₂Represents the integral of the variation of the modulus component of the fault current line of the second protection terminal within a time window of 1 millisecond,. DELTA.i_1.1Represents the variation of the modulus component of the fault current line at the first protection terminal, Delta i_1.2Representing the variation of the modulus component of the fault current line at the second protection terminal, t₀For the initial time of the fault, Δ t is the sampling interval, and n Δ t represents the length of the 1 millisecond time data window.

4. The method for protecting the multi-terminal hybrid direct-current transmission line according to claim 3, wherein the criterion for judging the fault direction is as follows:

if K₁>0 and K₂<0, judging that the fault is a left fault of the T area;

if K₁<0 and K₂>0, judging that the fault is a right fault of the T area;

if K₁<0 and K₂<And 0, judging the fault as the fault in the T area.

5. The protection method of the multi-terminal hybrid direct-current transmission line according to claim 4, wherein when the fault is determined to be a left side fault of the T zone, the first protection terminal determines that the fault is an intra-zone fault of the left side of the T zone or an extra-zone fault of the left side of the T zone, and the specific determination method is as follows:

if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the first protection end is larger than the setting value of the first protection end, the fault is judged to be a fault in the left area of the T area;

and if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the first protection end is less than or equal to the setting value of the first protection end, judging that the fault is an external fault on the left side of the T area.

6. The method for protecting the multi-terminal hybrid direct-current transmission line according to claim 5, wherein when the fault is determined to be a fault in a left zone of the T zone, the first protection terminal executes a protection action; and when the fault is judged to be the outside fault on the left side of the T area, the first protection end does not act.

7. The protection method of the multi-terminal hybrid direct-current transmission line according to claim 4, wherein when the fault is determined to be a right side fault of the T zone, the second protection terminal determines that the fault is an intra-zone fault on the right side of the T zone or an extra-zone fault on the right side of the T zone, and the specific determination method is as follows:

if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the second protection end is larger than the setting value of the second protection end, the fault is judged to be a fault in the right area of the T area;

and if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the second protection end is less than or equal to the setting value of the second protection end, judging that the fault is an external fault on the right side of the T area.

8. The method for protecting the multi-terminal hybrid direct-current transmission line according to claim 7, wherein when the fault is determined to be a fault in a right region of the T region, the second protection terminal executes a protection action; and when the fault is judged to be the outside fault on the right side of the T area, the second protection end does not act.

9. The method for protecting a multi-terminal hybrid direct-current transmission line according to claim 5 or 7, wherein the setting value of the first protection terminal and the setting value of the second protection terminal are calculated by using the following formulas:

T_set1＝K_rel×T_{max_out1}

T_set2＝K_rel×T_{max_out3}

in the formula, T_set1Setting value of the first protection end; t is_set2Setting value of the second protection end; k_relIs a reliability factor; t is_{max_out1}When the fault is outside the left side of the T area, the first protection end calculates the instantaneous energy maximum value of a high-frequency component Teager energy operator; t is_{max_out3}And when the fault is an external fault on the right side of the T area, the second protection end calculates the instantaneous energy maximum value of the high-frequency component Teager energy operator.

10. The method according to claim 9, wherein the reliability factor is set to 1.1.

Technical Field

The application relates to the technical field of relay protection, in particular to a protection method for a multi-terminal hybrid direct-current transmission line.

Background

The relay protection of the direct current transmission line is the most important protection in the direct current transmission system and is the key for maintaining the normal work of the direct current transmission line. The direct-current transmission line has long power transmission distance and complex working environment, so the fault occurrence probability is high. Therefore, whether the direct current transmission line can be quickly recovered after a fault occurs directly influences the safety and the stability of the whole power grid.

At present, the relay protection of the direct current transmission line mostly takes traveling wave protection and differential undervoltage protection as main protection, and longitudinal differential protection as backup protection.

The traveling wave protection judges whether a line fault occurs or not by mainly identifying the arrival of a traveling wave head at a measuring end, has ultrahigh-speed action performance, but has the problems of high requirement on sampling rate, limited transition resistance tolerance and lack of setting basis, and also has the problem of poor selectivity when boundary conditions change in a multi-end hybrid direct-current system.

The differential undervoltage protection mainly identifies line faults according to the change rate and amplitude of the measured end voltage, the protection action has high response speed, but the problems of poor transition resistance tolerance and dependence on simulation tests for setting exist, the selectivity is difficult to ensure in a multi-end mixed direct current system, and due to the lack of boundary elements, the differential undervoltage protection is difficult to distinguish the faults at the tail end of the line and the head end of the adjacent line, and the risk of misoperation exists.

The pilot differential protection utilizes the current magnitude at two ends of a line at a measuring end to form protection, but due to the capacitance to ground effect of a long-distance transmission line, when a fault occurs, the rapid voltage drop can cause the capacitance of the line to generate larger transient current, the reliability of the method is seriously influenced, and the probability of protection misoperation is even increased to a certain degree. In practice, the pilot differential protection usually uses a longer delay to avoid the fault transient phase better, but the snap-action is also impaired. In addition, the pilot differential protection requires accurate synchronization of data acquisition moments at two ends of a line, but after the line of the multi-end hybrid direct-current system fails, the current is rapidly increased, and a small synchronization error can cause a large differential error, so that the reliability is reduced.

In summary, the ultra-high voltage multi-terminal hybrid direct current transmission is a trend of development of the current high-voltage direct current transmission system, and the operation modes of the ultra-high voltage multi-terminal hybrid direct current transmission are changeable, so that after a transmission line fails, how a relay protection device can quickly and reliably perform protection actions to ensure that the fault is removed in a minimum range is a direction in which further research is needed for the existing ultra-high voltage multi-terminal hybrid direct current transmission system.

Disclosure of Invention

In order to overcome the defects of the prior art, the application aims to provide a protection method of a multi-terminal hybrid direct-current transmission line, which can quickly and reliably execute protection actions and ensure that faults are removed in a minimum range.

In order to achieve the above object, the present application provides a protection method for a multi-terminal hybrid dc transmission line, which specifically includes:

and acquiring fault current traveling wave data of a first protection end and a second protection end in the power transmission line.

And calculating to obtain the positive and negative of the fault current line mode component variable quantity according to the fault current traveling wave data of the first protection end and the fault current traveling wave data of the second protection end.

And judging the fault direction according to the positive and negative of the fault current line modulus component variable quantity.

And if the fault direction is at two sides of the T area, decomposing the fault current line mode component to obtain the inherent mode function component.

And obtaining a high-frequency component according to the inherent modal function component.

And calculating the instantaneous amplitude of the high-frequency component by using a Teager energy operator.

And comparing the maximum value of the instantaneous amplitude with a preset setting value, if the maximum value of the instantaneous amplitude is greater than the setting value, judging that the fault is a fault in the line area, and executing a protection action by the first protection end or the second protection end.

Further, if the fault direction is on two sides of the T area, the fault current line-mode component is decomposed by using a complete set empirical mode decomposition (CEEMDAN) algorithm of the adaptive noise.

Further, according to the positive and negative of the fault current line modulus component variation, the fault direction is judged by adopting the following formula:

wherein x is 1 or 2, K₁Represents the integral of the variation of the fault current line modulus component of the first protection terminal in a 1 millisecond time window, K₂Represents the integral of the variation of the modulus component of the fault current line of the second protection terminal within a time window of 1 millisecond,. DELTA.i_1.1Represents the variation of the modulus component of the fault current line at the first protection terminal, Delta i_1.2Representing the variation of the modulus component of the fault current line at the second protection terminal, t₀For the initial time of the fault, Δ t is the sampling interval, and n Δ t represents the length of the 1 millisecond time data window.

Further, the criterion for judging the fault direction is as follows:

if K₁>0 and K₂<And 0, judging that the fault is a left fault of the T area.

If K₁<0 and K₂>And 0, judging that the fault is a right fault of the T area.

If K₁<0 and K₂<And 0, judging the fault as the fault in the T area.

Further, when it is determined that the fault is a left side fault of the T zone, the first protection terminal determines that the fault is an intra-zone fault of the left side of the T zone or an extra-zone fault of the left side of the T zone, and the specific determination method is as follows:

and if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the first protection end is greater than the setting value of the first protection end, judging that the fault is a fault in the left area of the T area.

And if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the first protection end is less than or equal to the setting value of the first protection end, judging that the fault is an external fault on the left side of the T area.

Further, when the fault is judged to be a fault in the left area of the T area, the first protection end executes protection action; and when the fault is judged to be the outside fault on the left side of the T area, the first protection end does not act.

Further, when it is determined that the fault is a right side fault of the T zone, the second protection terminal determines that the fault is an intra-zone fault of the right side of the T zone or an extra-zone fault of the right side of the T zone, and the specific determination method is as follows:

and if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the second protection end is greater than the setting value of the second protection end, judging that the fault is a fault in the right area of the T area.

And if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the second protection end is less than or equal to the setting value of the second protection end, judging that the fault is an external fault on the right side of the T area.

Further, when the fault is judged to be a fault in the right area of the T area, the second protection end executes protection action; and when the fault is judged to be the outside fault on the right side of the T area, the second protection end does not act.

Further, the setting value of the first protection end and the setting value of the second protection end are calculated by adopting the following formulas:

T_set1＝K_rel×T_{max_out1}

T_set2＝K_rel×T_{max_out3}

in the formula, T_set1Setting value of the first protection end; t is_set2Setting value of the second protection end; k_relIs a reliability factor; t is_{max_out1}Is the left side of the T zoneWhen an external fault occurs, the first protection end calculates the instantaneous energy maximum value of a high-frequency component Teager energy operator; t is_{max_out3}And when the fault is an external fault on the right side of the T area, the second protection end calculates the instantaneous energy maximum value of the high-frequency component Teager energy operator.

Further, the reliability factor is set to 1.1.

The application provides a protection method of a multi-terminal hybrid direct-current transmission line, when a direct-current transmission system fails, the fault current of a line terminal is collected in real time, the fault direction is judged by calculating the positive and negative of the abrupt change of the modulus component of the fault current line, and the protection misoperation caused by reverse fault is prevented; then, decomposing the fault current line-mode components by using a CEEMDAN algorithm to obtain IMF components; and further, calculating the instantaneous amplitude of the high-frequency component according to a Teager energy operator, and judging the fault position by comparing the maximum value of the instantaneous amplitude of the high-frequency component with the setting value. When the maximum value of the instantaneous amplitude of the high-frequency component is greater than the setting value, judging that the fault is an internal fault of the line area, and executing protection action by a corresponding protection end; and when the maximum value of the instantaneous amplitude of the high-frequency component is less than or equal to the setting value, judging that the fault is an external fault of the line, and keeping the protection end not to act. The method and the device can accurately identify the direction of the fault position, effectively prevent the malfunction of the protection end during reverse fault, and avoid mode aliasing effect. In conclusion, the method and the device can rapidly and reliably execute the protection action and ensure that the fault is removed in the minimum range.

Drawings

In order to more clearly explain the technical solution of the present application, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious to those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic flow chart of a protection method for a multi-terminal hybrid direct-current transmission line according to an embodiment of the present disclosure;

fig. 2 is a schematic diagram of an extra-high voltage multi-terminal hybrid direct-current power transmission topology provided in the embodiment of the present application;

fig. 3 is a schematic diagram of a location of an extra-high voltage multi-terminal hybrid dc fault provided in the embodiment of the present application;

in the figure: the protection circuit comprises a 1-alternating current system, a 2-alternating current filter, a 3-converter transformer, a 4-smoothing reactor, a 5-LCC converter valve, a 6-direct current filter, a 7-MMC converter valve, an 8-direct current circuit, a 9-first protection end and a 10-second protection end.

Detailed Description

The technical solutions in the embodiments of the present application will be fully and clearly described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In order to facilitate understanding of the technical solutions of the embodiments of the present application, some concepts related to the present application are first described below.

Referring to fig. 1, a schematic flow chart of a protection method for a multi-terminal hybrid direct-current transmission line provided in an embodiment of the present application is shown. The embodiment of the application provides a method for protecting a multi-terminal hybrid direct-current transmission line, which specifically comprises the following steps:

step S1: and acquiring fault current traveling wave data of a first protection end and a second protection end in the power transmission line.

Step S2: and calculating to obtain the positive and negative of the fault current line mode component variable quantity according to the fault current traveling wave data of the first protection end and the fault current traveling wave data of the second protection end.

In the embodiment of the application, the specific method for calculating the positive and negative of the fault current line mode component variation is as follows:

step S21: reading the current of the positive and negative lines measured by the measuring end;

step S22: the measured current is decoupled, and the current line mode component is adopted to judge the fault direction, so that the misoperation of the non-fault line protection device due to the influence of electromagnetic coupling is prevented. The decoupling calculation method specifically comprises the following steps:

in the formula i₀、i₁Zero and line-mode components, i, of the decoupled fault current, respectively_p、i_nThe rated currents of the anode and the cathode of the circuit are respectively.

Step S23: by line-mode current i in fault₁Minus the line mode current i during normal operation_{1_N}The fault current change Δ i can be obtained. The calculation formula is as follows:

△i＝i₁-i_{1_N}

step S3: and judging the fault direction according to the positive and negative of the fault current line modulus component variable quantity. Specifically, the fault direction includes the inside of the T zone and both sides of the T zone, and when it is determined that the fault is located in the T zone, the fault belongs to an outside-line fault, and neither the first protection end nor the second protection end performs any protection action.

More specifically, in the embodiment of the present application, the T-zone is two portions between the line outgoing end and two circuit breakers in the connection string.

Further, according to the positive and negative of the fault current line modulus component variation, the fault direction is judged by adopting the following formula:

wherein x is 1 or 2, K₁Represents the integral of the variation of the fault current line modulus component of the first protection terminal in a 1 millisecond time window, K₂Represents the integral of the variation of the modulus component of the fault current line of the second protection terminal within a time window of 1 millisecond,. DELTA.i_1.1Represents the variation of the modulus component of the fault current line at the first protection terminal, Delta i_1.2Representing the variation of the modulus component of the fault current line at the second protection terminal, t₀For the initial time of the fault, Δ t is the sampling interval, and n Δ t represents the length of the 1 millisecond time data window.

Step S4: and if the fault direction is at two sides of the T area, decomposing the fault current line mode component to obtain the inherent mode function component.

Further, if the fault direction is on both sides of the T-zone, the fault current line-Mode component is decomposed by using a Complete Ensemble Empirical Mode Decomposition (CEEMDAN) algorithm of Adaptive Noise.

Specifically, the sequence of Intrinsic Mode Functions (IMFs) decomposed by the CEEMDAN algorithm is the result of multi-pass band filtering, and each separated IMF sequence should be stable. Therefore, the CEEMDAN algorithm is preferably used in the embodiment of the present application to perform the decomposition of the fault current line modulus component.

Further, the criterion for judging the fault direction is as follows:

if K₁>0 and K₂<And 0, judging that the fault is a left fault of the T area.

If K₁<0 and K₂>And 0, judging that the fault is a right fault of the T area.

If K₁<0 and K₂<And 0, judging the fault as the fault in the T area.

Specifically, if the fault direction is on both sides of the T zone, it is further determined whether the fault is located on the left side or the right side of the T zone, so as to narrow the search range for finding the fault location and speed up the fault identification.

Step S5: and obtaining a high-frequency component according to the inherent modal function component.

Specifically, it can be obtained from the decomposition principle and process of the CEEMDAN algorithm that the earlier separated natural mode function (IMF) component has a higher frequency, and the first separated IMF sequence contains the highest frequency component, i.e., a high-frequency component, in the original signal. Therefore, the line mode component signal of the fault circuit can be decomposed into IMF components with instantaneous frequencies from high to low through the CEEMDAN decomposition algorithm, and only the first IMF component needs to be obtained and is the high-frequency component.

Step S6: and calculating the instantaneous amplitude of the high-frequency component by using a Teager energy operator.

In the embodiment of the application, a concrete method for calculating the instantaneous amplitude of the high-frequency component by using a Teager energy operator is as follows:

Ψ[i_(n)]＝[i_(n)]²-i_(n-1)i_(n+1)

in the formula i_(n-1)、i_(n)、i_(n+1)The modulus components of the sampling current lines of the n-1 th sampling point, the n +1 th sampling point and the n +1 th sampling point respectively.

Step S7: comparing the maximum value of the instantaneous amplitude with a preset setting value, if the maximum value of the instantaneous amplitude is greater than the preset setting value, judging that the fault is a fault in the line area, and executing a protection action by the first protection end or the second protection end; if the maximum value of the instantaneous amplitude is smaller than the setting value, the fault is judged to be an external fault of the line area, and the first protection end and the second protection end do not act.

Furthermore, when the fault is determined to be a left side fault of the T zone, the first protection terminal determines that the fault is an internal fault of the left side zone of the T zone or an external fault of the left side zone of the T zone, and the specific determination method is as follows:

and if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the first protection end is greater than the setting value of the first protection end, judging that the fault is a fault in the left area of the T area.

And if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the first protection end is less than or equal to the setting value of the first protection end, judging that the fault is an external fault on the left side of the T area.

In the embodiment of the present application, the method for determining the internal and external faults of the left zone of the T zone is specifically expressed as follows:

in the formula, T₁Calculating the maximum value of the instantaneous amplitude of the high-frequency component for the first protection end; t is_set1The setting value is the setting value of the first protection end.

Furthermore, when the fault is judged to be a fault in the left zone of the T zone, the first protection end executes protection action; and when the fault is judged to be the outside fault on the left side of the T area, the first protection end does not act. Specifically, the first protection end executes a corresponding protection action to indicate that the protection element sends an action instruction, so that the circuit breaker of the circuit is tripped.

Further, when it is determined that the fault is a right side fault of the T zone, the second protection terminal determines that the fault is an intra-zone fault of the right side of the T zone or an extra-zone fault of the right side of the T zone, and the specific determination method is as follows:

and if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the second protection end is greater than the setting value of the second protection end, judging that the fault is a fault in the right area of the T area.

And if the maximum value of the instantaneous amplitude of the high-frequency component calculated by the second protection end is less than or equal to the setting value of the second protection end, judging that the fault is an external fault on the right side of the T area.

In the embodiment of the present application, the method for determining the internal and external faults of the right side area of the T area is specifically expressed as follows:

in the formula, T₂Calculating the maximum value of the instantaneous amplitude of the high-frequency component for the second protection end; t is_set2And setting value of the second protection end.

Furthermore, when the fault is determined to be a fault in the right area of the T area, the second protection terminal executes protection action; and when the fault is judged to be the outside fault on the right side of the T area, the second protection end does not act. Specifically, the second protection end executes a corresponding protection action, and the protection element sends an action instruction to trip the circuit breaker of the circuit.

Further, the setting value of the first protection end and the setting value of the second protection end are calculated by adopting the following formulas:

T_set1＝K_rel×T_{max_out1}

T_set2＝K_rel×T_{max_out3}

in the formula, K_relIs a reliability factor; t is_{max_out1}When the fault is outside the left side of the T area, the first protection end calculates the instantaneous energy maximum value of a high-frequency component Teager energy operator; t is_{max_out3}And when the fault is an external fault on the right side of the T area, the second protection end calculates the instantaneous energy maximum value of the high-frequency component Teager energy operator.

Further, the reliability factor is set to 1.1. Specifically, the setting of the reliability factor may be specifically set according to specific situations, and the setting of the reliability factor of 1.1 in the embodiment of the present application is an optimal setting obtained through repeated experiments, but is not a fixed setting.

In summary, K calculated when the first protection end is used₁>0. K calculated by the second protection terminal₂<When 0, judging that the left side of the T area has a fault, locking the second protection end, unlocking the first protection end, and judging the left side of the T area by the first protection end; k calculated when the first protection end is used₁<0. K calculated by the second protection terminal₂>When 0, judging that the right side of the T area has a fault, locking the first protection end, unlocking the second protection end, and judging that the right side of the T area has the fault by the second protection end; k calculated when the first protection end is used₁<0. K calculated by the second protection terminal₂<And when 0, judging that the T area has a fault, locking the first protection end and the second protection end, and not acting the first protection end and the second protection end.

Compared with the prior art, the embodiment of the application has the following characteristics:

1) according to the method, the fault direction criterion is adopted, the integral value of the modulus components of the fault current lines on the two sides of the T area in 1 millisecond is calculated, and the fault direction is judged according to the positive value and the negative value of the integral value.

2) According to the method, the fault current signal is completely decomposed into a plurality of orders of IMF components by using a decomposition method of complete set empirical mode decomposition (CEEMDAN) of adaptive noise and local adaptive decomposition of the CEEMDAN, so that a modal aliasing effect is avoided.

3) According to the method and the device, the Teager energy operator is used for extracting the instantaneous amplitude of the high-frequency component in the IMF component, the Teager energy operator is used for drawing the energy spectrogram of the high-frequency component, and the internal and external faults of the area can be rapidly identified through the comparison of the setting value and the maximum value of the instantaneous amplitude of the high-frequency component.

The protection method for the extra-high voltage multi-terminal hybrid direct current transmission line provided by the embodiment of the application comprises the following specific implementation steps:

step S21: after the ultrahigh voltage multi-terminal hybrid direct current transmission system breaks down, the first protection terminal and the second protection terminal acquire fault current data within 1 millisecond after the fault.

Step S22: the detected current is subjected to phase mode change, the current abrupt change of a line mode is integrated within 1 millisecond through calculation, and fault direction judgment is carried out according to the positive and negative of the integrated value.

Step S23: when it is determined that the fault is located at the left side of the T zone, step S24 is performed, when it is determined that the fault is located at the right side of the T zone, step S25 is performed, and when it is determined that the fault is located within the T zone, step S26 is performed.

Step S24: and when the fault is judged to be the fault on the left side of the T area, judging the faults inside and outside the left area of the T area by the first protection end, carrying out CEEMDAN decomposition on the fault current line mode component to obtain each IMF component, then calculating the instantaneous amplitude of the high-frequency component by using a Teager energy operator, and judging the faults inside and outside the left area of the T area according to the maximum value of the instantaneous amplitude of the high-frequency component. When the maximum value of the instantaneous amplitude of the high-frequency component is greater than the setting value, judging that the fault is in the left area, and enabling the first protection end to act; and when the maximum value of the instantaneous amplitude of the high-frequency component is smaller than the setting value, judging that the fault is outside the left area, and not acting the first protection end.

Step S25: when the fault is judged to be positioned on the right side of the T area, the second protection end judges the right side fault of the T area, CEEMDAN decomposition is carried out on the fault current line mode component to obtain each IMF component, then the Teager energy operator is used for calculating the instantaneous amplitude and the frequency of the high-frequency component, and the internal and external faults of the right side area of the T area are judged according to the maximum value of the instantaneous amplitude of the high-frequency component. When the maximum value of the instantaneous amplitude of the high-frequency component is greater than the setting value, judging that the fault is in the right area, and enabling the second protection end to act; and when the maximum value of the instantaneous amplitude of the high-frequency component is smaller than the setting value, judging that the fault is outside the right area, and not acting the second protection end.

Step S26: and when the T area is judged to have a fault, the T area fault belongs to an external fault of the line area, and the first protection end and the second protection end do not act.

The protection method for the multi-terminal hybrid direct-current transmission line provided by the embodiment of the present application will be described in detail through specific embodiments.

Referring to fig. 2 and fig. 3, an extra-high voltage multi-terminal hybrid dc power transmission topology schematic diagram and an extra-high voltage multi-terminal hybrid dc fault location schematic diagram provided in the embodiment of the present application are shown. In the embodiment of the application, the transition resistance is set to be a value between 0 and 500 omega, and the protection method can be used for testing different fault positions and different transition resistances of the positive line and the negative line and testing the fault outside the fault area (f) on the left side of the T area by adopting the protection method in the embodiment of the application_out1) Left zone internal fault of zone T (f)_inI1、f_inI2、f_inI3) Right side of zone T internal fault (f)_inII1、f_inII2、f_inII3) Right side out-of-zone fault of zone T (f)_out3) Internal fault of zone T (f)_out2) Simulation tests were performed to obtain simulation results as shown in tables 1 and 2 below. Wherein, Table 1 shows simulation results of the positive electrode, Table 2 shows simulation results of the negative electrode, T_set1＝1.82*10³，T_set2＝9.83*10³. As can be seen from tables 1 and 2, both the first protection terminal and the second protection terminal can operate correctly.

TABLE 1 protection action results (Positive fault)

TABLE 2 protection action results (cathode failure)

The application provides a protection method of a multi-end hybrid direct-current transmission line, which specifically comprises the following steps:

acquiring fault current traveling wave data of a first protection end and a second protection end in a power transmission line;

calculating to obtain the positive and negative of the fault current line mode component variable quantity according to the fault current traveling wave data of the first protection end and the fault current traveling wave data of the second protection end;

judging the fault direction according to the positive and negative of the fault current line modulus component variable quantity;

if the fault direction is at two sides of the T area, decomposing the fault current line mode component to obtain an inherent mode function component;

obtaining a high-frequency component according to the inherent modal function component;

calculating the instantaneous amplitude of the high-frequency component by using a Teager energy operator;

and comparing the maximum value of the instantaneous amplitude with a preset setting value, if the maximum value of the instantaneous amplitude is greater than the setting value, judging that the fault is a fault in the line area, and executing a protection action by the first protection end or the second protection end.

According to the technical scheme, when the direct-current power transmission system fails, the fault current of the line end is collected in real time, the fault direction is judged by calculating the positive and negative of the fault current line modulus component break variable, and the protection misoperation caused by the reverse fault is prevented; then, decomposing the fault current line-mode components by using a CEEMDAN algorithm to obtain IMF components; and further, calculating the instantaneous amplitude of the high-frequency component according to a Teager energy operator, and judging the fault position by comparing the maximum value of the instantaneous amplitude of the high-frequency component with the setting value. When the maximum value of the instantaneous amplitude of the high-frequency component is greater than the setting value, judging that the fault is an internal fault of the line area, and executing protection action by a corresponding protection end; and when the maximum value of the instantaneous amplitude of the high-frequency component is less than or equal to the setting value, judging that the fault is an external fault of the line, and keeping the protection end not to act. The method and the device can accurately identify the direction of the fault position, effectively prevent the malfunction of the protection end when an external fault occurs, and avoid mode aliasing effect. In conclusion, the method and the device can rapidly and reliably execute the protection action and ensure that the fault is removed in the minimum range.

The present application has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the application. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the presently disclosed embodiments and implementations thereof without departing from the spirit and scope of the present disclosure, and these fall within the scope of the present disclosure. The protection scope of this application is subject to the appended claims.