Regional protection method suitable for double-fed wind turbine generator tie line

Abstract

The invention discloses a regional protection method suitable for a double-fed wind turbine generator tie line. The regional protection method comprises the following steps that each in-situ protection device is configured with overcurrent protection and a positive sequence direction element judgment formula; collecting the voltage of each line connected with the double-fed wind power plant bus and the zero sequence voltage, the negative sequence voltage and the magnitude of current of a current transformer; the in-situ protection device judges a three-phase fault, a ground fault or a two-phase inter-phase fault according to the phase voltage, the zero-sequence voltage and the negative-sequence voltage collected by each line, and after the tie line area protection device collects information uploaded by the in-situ protection device of each line, the uploaded information is subjected to centralized judgment by using the in-situ protection device. According to the method, the protection requirement under the weak feed power grid can be met, the influence of crowbar activation of the doubly-fed wind turbine generator and the RSC rotor excitation control strategy is considered, the fault line can be accurately recognized, the problem that under the crowbar activation condition of the doubly-fed wind turbine generator, the grid-connected line of the doubly-fed wind turbine generator is misjudged is avoided, and the utilization level of new energy is improved.

Description

Technical Field

[0001] The invention relates to the field of electrical engineering relay protection, and in particular to a regional protection method suitable for a double-fed wind turbine group tie line. Background Art

[0002] At present, with the continuous development of new power systems, the number of photovoltaic and wind turbines has continued to increase, forming a high proportion of new energy power systems in some local areas, and even forming full-power electronic power grids such as "Gaohaibei No" microgrids and "Shagohuang" new energy DC transmission systems in some scenarios. Compared with traditional power grids, this grid shows obvious weak feedback characteristics. At the same time, doubly fed wind turbines, as the main model of current wind turbines, have been widely used in the construction of new power systems.

[0003] However, the fault characteristics of doubly-fed wind turbines are complex, and they present different fault characteristics under severe faults and minor faults. Under minor faults, they are in the excitation control stage, and their fed short-circuit current is related to the rotor converter control strategy; under severe faults, the crowbar protection of the doubly-fed wind turbine is activated due to rotor overcurrent and DC overvoltage, and the doubly-fed wind turbine is an equivalent motor model. Therefore, the above characteristics bring new challenges to relay protection. In particular, in weakly-fed power grids, the system provides a small short-circuit current, and the current protection setting will be greatly reduced. The fault characteristics of the doubly-fed wind turbine after the crowbar is activated may cause the grid current protection to be misjudged, and then the doubly-fed wind turbine is mistakenly cut off. This seriously limits the application of doubly-fed wind turbines in weakly-fed distribution networks and non-hydro renewable energy power grids such as "high seaside without".

[0004] Therefore, it is urgent to propose a new solution to solve the above problems. Summary of the invention

[0005] The invention provides a regional protection method adapted to a double-fed wind turbine group tie line to solve the problems existing in the prior art.

[0006] The present invention provides a regional protection method adapted to a doubly-fed wind turbine group tie line, comprising the following steps:

[0007] Each local protection device is equipped with overcurrent protection and positive sequence direction element judgment formula, wherein the local protection device on the double-fed wind turbine group tie line is also equipped with a negative sequence direction element judgment formula, and the system-side protection device on the double-fed wind turbine group tie line is equipped with an overcurrent protection setting value judgment formula;

[0008] Collect the voltage of each line connected to the busbar of the double-fed wind farm and the zero-sequence voltage, negative-sequence voltage and current of the current transformer;

[0009] The local protection device determines whether it is a three-phase fault, a ground fault or a two-phase interphase fault according to the phase voltage, zero-sequence voltage and negative-sequence voltage collected from each line, sends the fault judgment result to the judgment element of the local protection device on each line for judgment, and uploads the obtained judgment information to the tie line area protection device;

[0010] After the tie line area protection device collects the information uploaded by the local protection devices of each line, the local protection device is used to make a centralized judgment on the uploaded information, and the information of the busbar incoming line, the grid-connected line of the doubly-fed wind turbine group and the grid-connected line of the non-doubly-fed wind turbine group is obtained through the judgment formula of the positive sequence directional element and the negative sequence directional element, so as to perform tripping actions respectively.

[0011] Furthermore, the judgment element includes a voltage starting element, an overcurrent protection, a positive sequence direction element and a negative sequence direction element, wherein the voltage starting element, overcurrent protection and positive sequence direction element are arranged in an on-site protection device on the grid-connected line and the busbar incoming line of a non-doubly fed wind turbine group, and the voltage starting element, overcurrent protection, positive sequence direction element and negative sequence direction element are arranged in an on-site protection device on the grid-connected line of a doubly fed wind turbine group.

[0012] Furthermore, the step of sending the fault judgment result to the judgment element of the local protection device on each line for judgment includes the following steps:

[0013] If the local protection devices of the non-doubly-fed wind turbine grid-connected lines judge that the overcurrent protection and positive sequence direction elements meet the conditions, the information of the uploaded regional protection is 1; otherwise, it is 0;

[0014] The local protection device of the grid-connected line of the doubly-fed wind turbine generator set has the sensitivity to judge the fault line according to the two-phase metallic fault at the end of the line under three-phase fault. The expression is as follows:

[0015]

[0016] Among them, I W1 Indicates the measured current; I set1 Indicates the current setting value used to judge the fault direction under three-phase fault; Indicates rated current; Represents the system equivalent impedance; Z L Indicates the equivalent impedance of the grid-connected line of the doubly-fed wind farm; K r is the reliability coefficient;

[0017] If the fault line identification criteria meet the conditions and the directional element meets the conditions, it means that the fault occurs in the grid-connected line of the doubly-fed wind turbine generator set, and the uploaded information is 1; otherwise, it means that the fault is not in the grid-connected line of the doubly-fed wind turbine generator set, and the uploaded information is 0.

[0018] Furthermore, the negative sequence directional element judgment formula is as follows:

[0019]

[0020] in, and denote the negative sequence voltage and current respectively; is the negative sequence direction sensitivity angle.

[0021] Furthermore, the positive sequence direction element judgment formula is as follows:

[0022]

[0023] in: and are the pre-fault memory voltage and pre-fault memory current respectively; the subscript "1" of each variable indicates positive sequence, is the sensitive angle of the directional element.

[0024] Furthermore, the overcurrent protection judgment formula is as follows:

[0025]

[0026] in, Indicates the phase overcurrent protection setting value; I min_sc Indicates the minimum short-circuit current value calculated based on the system short-circuit current; k l Represents the sensitivity coefficient.

[0027] Furthermore, for a three-phase fault, the fault judgment result is sent to the judgment element of the local protection device on each line for judgment, and the obtained judgment information is uploaded to the tie line area protection device, including the following steps:

[0028] Each local protection device generates (1,0) information according to the overcurrent and positive sequence directional element criteria and sends it to the tie line area protection device;

[0029] If the regional protection device determines that the bus information is 1 and the other line information is 0, it indicates a bus fault, and the circuit breakers of each line connected to the bus are tripped;

[0030] If the regional protection device determines that the bus information is 1, the line information of a non-doubly-fed unit is 1, and the other line information is 0, then the circuit breaker on the line system side of the non-doubly-fed unit is tripped;

[0031] If the regional protection device determines that the bus information is 1, the line information of the doubly-fed generator set is 1, and other line information is 0, the circuit breaker on the line system side of the doubly-fed generator set is tripped.

[0032] Furthermore, for a ground fault or a two-phase-to-phase fault, the fault judgment result is sent to the judgment element of the local protection device on each line for judgment, and the obtained judgment information is uploaded to the tie line area protection device, including the following steps:

[0033] Each local protection device generates (1,0) information from the overcurrent and positive sequence directional element criteria, and the double-fed line includes a negative sequence directional element, and sends it to the tie line area protection device;

[0034] If the regional protection device determines that the bus information is 1 and the other line information is 0, and the first uploaded information of the double-fed line is 0, it indicates a bus fault, and the circuit breakers of each line connected to the bus are tripped;

[0035] If the regional protection device determines that the bus information is 1, the line information of a non-doubly-fed unit is 1, and the other line information is 0, then the circuit breaker on the line system side of the non-doubly-fed unit is tripped;

[0036] If the regional protection device determines that the bus information is 1, the first information of the double-fed unit line is 1, the second information is -1, and the other line information is 0, then the circuit breaker on the double-fed unit line system side is tripped;

[0037] If the regional protection device determines that the busbar information is 1, the first information of the double-fed unit line is 1, the second information is 0, and the other line information is 0, then the circuit breakers of the lines connected to the busbar are tripped.

[0038] Furthermore, the local protection device determines whether it is a three-phase fault, a ground fault or a two-phase interphase fault according to the phase voltage, zero-sequence voltage and negative-sequence voltage collected from each line, including the following steps:

[0039] min(|U a |,|U b |,|U c |) s ; (5)

[0040] In the above formula, U a , U b and U c Represent the three-phase voltage, U s Represents the voltage setting value. Through calculation, if it satisfies the above formula (5), it is judged that a ground fault occurs. If not, proceed to the next step.

[0041]

[0042] In the above formula, a represents the operator, U 2s It represents the negative sequence voltage setting value. Through calculation, if it satisfies the above formula (6), it is judged that a two-phase phase-to-phase fault occurs. If not, it proceeds to the next step.​

[0043] |U a +U b +U c |>U 0.set (7)

[0044] In the above formula, U 0.set It represents the zero-sequence voltage setting value. Through calculation, if it satisfies the above formula (7), it is judged that a three-phase fault has occurred. If it does not satisfy it, it means that no fault has occurred.

[0045] Compared with the prior art, the regional protection method for the interconnection line of the doubly-fed wind turbine generator system of the present invention can not only adapt to the protection requirements under the weakly-fed power grid, but also take into account the influence of the crowbar activation and RSC rotor excitation control strategy of the doubly-fed wind turbine generator system, and can accurately identify the faulty line, avoid the problem of misjudgment of the grid-connected line of the doubly-fed wind turbine generator system under the condition of the crowbar activation of the doubly-fed wind turbine generator system, and improve the utilization level of new energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 A flow chart of a regional protection method for a tie line of a doubly-fed wind turbine generator system adapted to the present invention;

[0047] Figure 2 A diagram of a power distribution system according to an embodiment of the present invention;

[0048] Figure 3 are the fault current and overcurrent protection settings of the circuit breaker K10 in the embodiment of the present invention when the crowbar of the doubly-fed wind turbine generator set is activated or not activated;

[0049] Figure 4 are the fault current and overcurrent protection settings of the circuit breaker K11 in the embodiment of the present invention when the crowbar of the doubly-fed wind turbine generator set is activated or not activated;

[0050] Figure 5 are the fault current and overcurrent protection settings of the circuit breaker K12 in the embodiment of the present invention when the crowbar of the doubly-fed wind turbine generator set is activated or not activated;

[0051] Figure 6 It is the fault current and overcurrent protection setting value of the circuit breaker K13 in the embodiment of the present invention when the crowbar of the doubly-fed wind turbine is activated or not activated. DETAILED DESCRIPTION

[0052] In order to further understand the content, features and effects of the present invention, the following embodiments are given together with the attached Figures 1 to 6 The detailed instructions are as follows.

[0053] The present invention provides a regional protection method adapted to a doubly-fed wind turbine group tie line, comprising the following steps:

[0054] Each local protection device is equipped with overcurrent protection and positive sequence direction element judgment formula, wherein the local protection device on the double-fed wind turbine group tie line is also equipped with a negative sequence direction element judgment formula, and the system-side protection device on the double-fed wind turbine group tie line is equipped with an overcurrent protection setting value judgment formula;

[0055] Collect the voltage of each line connected to the busbar of the double-fed wind farm and the zero-sequence voltage, negative-sequence voltage and current of the current transformer;

[0056] The local protection device determines whether it is a three-phase fault, a ground fault or a two-phase interphase fault according to the phase voltage, zero-sequence voltage and negative-sequence voltage collected from each line, sends the fault judgment result to the judgment element of the local protection device on each line for judgment, and uploads the obtained judgment information to the tie line area protection device;

[0057] After the tie line area protection device collects the information uploaded by the local protection devices of each line, the local protection device is used to make a centralized judgment on the uploaded information, and the information of the busbar incoming line, the grid-connected line of the doubly-fed wind turbine group and the grid-connected line of the non-doubly-fed wind turbine group is obtained through the judgment formula of the positive sequence directional element and the negative sequence directional element, so as to perform tripping actions respectively.

[0058] In this embodiment, the judgment element includes a voltage starting element, an overcurrent protection, a positive sequence direction element and a negative sequence direction element, wherein the voltage starting element, the overcurrent protection and the positive sequence direction element are arranged in the local protection device on the grid-connected line and the bus incoming line of the non-doubly fed wind turbine group, and the voltage starting element, the overcurrent protection, the positive sequence direction element and the negative sequence direction element are arranged in the local protection device on the grid-connected line of the doubly fed wind turbine group.

[0059] In this embodiment, the step of sending the fault judgment result to the judgment element of the local protection device on each line for judgment includes the following steps:

[0060] If the local protection devices of the non-doubly-fed wind turbine grid-connected lines judge that the overcurrent protection and positive sequence direction elements meet the conditions, the information of the uploaded regional protection is 1; otherwise, it is 0;

[0061] The local protection device of the grid-connected line of the doubly-fed wind turbine generator set has the sensitivity to judge the fault line according to the two-phase metallic fault at the end of the line under three-phase fault. The expression is as follows:

[0062]

[0063] Among them, I W1 Indicates the measured current; I se t1 represents the current setting value used for fault direction judgment under three-phase fault; Indicates rated current; Represents the system equivalent impedance; ZL Indicates the equivalent impedance of the grid-connected line of the doubly-fed wind farm; K r is the reliability coefficient, and its typical value is generally 1.5;

[0064] If the fault line identification criteria meet the conditions and the directional element meets the conditions, it means that the fault occurs in the grid-connected line of the doubly-fed wind turbine generator set, and the uploaded information is 1; otherwise, it means that the fault is not in the grid-connected line of the doubly-fed wind turbine generator set, and the uploaded information is 0.

[0065] In this embodiment, the negative sequence directional element judgment formula is as follows:

[0066]

[0067] in, and denote the negative sequence voltage and current respectively; is the negative sequence direction sensitivity angle; the current flowing from the doubly fed wind turbine to the grid is defined as positive. If the above formula is satisfied, the negative sequence current is in the same direction as the defined direction; otherwise, the negative sequence current is opposite to the defined direction.

[0068] In this embodiment, the positive sequence directional element judgment formula is as follows:

[0069]

[0070] in: and are the pre-fault memory voltage and pre-fault memory current respectively; the subscript "1" of each variable indicates positive sequence, is the sensitivity angle of the directional element; when the above formula is satisfied, it means that the positive sequence current is in the positive direction; otherwise, the positive sequence current is in the reverse direction.

[0071] In this embodiment, the overcurrent protection judgment formula is as follows:

[0072]

[0073] in, Indicates the phase overcurrent protection setting value; I min_sc Indicates the minimum short-circuit current value calculated based on the system short-circuit current; k l Represents the sensitivity coefficient.

[0074] In this embodiment, for a three-phase fault, the method of sending the fault judgment result to the judgment element of the local protection device on each line for judgment, and uploading the obtained judgment information to the tie line area protection device includes the following steps:

[0075] Each local protection device generates (1,0) information according to the overcurrent and positive sequence directional element criteria and sends it to the tie line area protection device;

[0076] If the regional protection device determines that the bus information is 1 and the other line information is 0, it indicates a bus fault, and the circuit breakers of each line connected to the bus are tripped;

[0077] If the regional protection device determines that the bus information is 1, the line information of a non-doubly-fed unit is 1, and the other line information is 0, then the circuit breaker on the line system side of the non-doubly-fed unit is tripped;

[0078] If the regional protection device determines that the bus information is 1, the line information of the doubly-fed generator set is 1, and other line information is 0, the circuit breaker on the line system side of the doubly-fed generator set is tripped.

[0079] In this embodiment, for a ground fault or a two-phase-to-phase fault, the fault judgment result is sent to the judgment element of the local protection device on each line for judgment, and the obtained judgment information is uploaded to the tie line area protection device, including the following steps:

[0080] Each local protection device generates (1,0) information from the overcurrent and positive sequence directional element criteria, and the double-fed line includes a negative sequence directional element, and sends it to the tie line area protection device;

[0081] If the regional protection device determines that the bus information is 1 and the other line information is 0, and the first uploaded information of the double-fed line is 0, it indicates a bus fault, and the circuit breakers of each line connected to the bus are tripped;

[0082] If the regional protection device determines that the bus information is 1, the line information of a non-doubly-fed unit is 1, and the other line information is 0, then the circuit breaker on the line system side of the non-doubly-fed unit is tripped;

[0083] If the regional protection device determines that the bus information is 1, the first information of the double-fed unit line is 1, the second information is -1, and the other line information is 0, then the circuit breaker on the double-fed unit line system side is tripped;

[0084] If the regional protection device determines that the busbar information is 1, the first information of the double-fed unit line is 1, the second information is 0, and the other line information is 0, then the circuit breakers of the lines connected to the busbar are tripped.

[0085] In this embodiment, the local protection device determines whether a three-phase fault, a ground fault or a two-phase interphase fault is present according to the phase voltage, zero-sequence voltage and negative-sequence voltage collected from each line, and includes the following steps:

[0086] min(|U a |,|U b |U c |) s ; (5)

[0087] In the above formula, U​a , U b and U c Represent the three-phase voltage, U s Represents the voltage setting value. Through calculation, if the above formula (5) is satisfied, it is judged that a ground fault has occurred; if not, proceed to the next step;

[0088]

[0089] In the above formula, a represents the operator, U 2s It represents the negative sequence voltage setting value. Through calculation, if it satisfies the above formula (6), it is judged that a two-phase phase-to-phase fault occurs; if not, it proceeds to the next step;

[0090] |U a +U b +U c |>U 0.set ; (7)

[0091] In the above formula, U 0.set represents the zero-sequence voltage setting value; through calculation, if the above formula (7) is satisfied, it is judged that a three-phase fault has occurred; if not, it means that no fault has occurred.

[0092] The embodiment of the present invention builds a typical distribution network model including a double-fed wind turbine, a distributed power source and electric vehicles. Figure 2 As shown, the model parameters are as follows.

[0093] like Figure 2 As shown in the figure, the system voltage is 35kV, and loads 1 to 4 are 4MW+j2Mvar, 8MW+j6Mvar, 3MW+j2Mvar and 12MW+j6Mvar respectively. The capacity of the charging stations is 6MVA. DG is a 6MVA photovoltaic power source. S1 represents the system power supply; Z sys Represents the system equivalent impedance. Both EV and DG adopt the control strategy of suppressing negative sequence current, where EV is an electric vehicle device, DG is a distributed generation device, and LD1~LD4 represent the four connected loads. The double-fed wind turbine is 12MW and also adopts the control strategy of suppressing negative sequence current. The crowbar resistance is 0.06767 ohms, the equivalent impedance of the line where the circuit breakers K1, K4, and K9 are located is 4.5Ω, and the inductance is 0.016H. The equivalent impedance of the line where the circuit breakers K2, K5, and K7 are located is 2.25Ω, and the inductance is 0.00508H. The equivalent impedance of the line where the circuit breakers K3, K6, K11 and K12 are located is 2.25Ω, the inductance is 0.00508H, and the transition resistance is 0.1Ω.

[0094] by Figure 2 The fault points F1 and F2 in FIG. 1 are respectively faulty for explanation.

[0095] min(|U a |,|U b |,|U c |) s ; (5)

[0096] In the above formula, U a , U b and U c Represent the three-phase voltage, U s Represents the voltage setting value. If the above formula (5) is not satisfied by calculation, proceed to the next step;

[0097]

[0098] In the above formula, a represents the operator, U 2s Represents the negative sequence voltage setting value. By calculation, if the result satisfies the above formula (6), it is judged that a two-phase phase-to-phase fault has occurred, indicating that a two-phase phase-to-phase fault has occurred at the fault point F1 or F2.

[0099] A regional protection method for a doubly-fed wind turbine tie line according to this embodiment includes the following steps:

[0100] The voltage and current transformers of the lines where S1, circuit breakers K10, K11 and K12 are located collect voltage and current, and send them to the local protection devices of K10, K11 and K12. Individual circuit breakers are set in their respective local protection devices.

[0101] The voltage starting elements, overcurrent protection, positive sequence directional elements and negative sequence current directional elements in the local protection devices of S2, circuit breakers K10, K11 and K12 are configured.

[0102] S3, judging that an asymmetric fault has occurred in the power grid according to the magnitude of the negative sequence voltage, and proceeding to step S4;

[0103] S4, the local protection device at circuit breaker K10 obtains the upload information of F1 and F2 faults as 1 and 1 according to the overcurrent protection and positive sequence direction element criteria. The local protection device at circuit breaker K11 obtains the upload information of F1 and F2 faults as 0 and 0 according to the current and positive sequence direction element criteria. The local protection device at circuit breaker K12 obtains the upload information of F1 and F2 faults as 1 according to the current and positive sequence direction element criteria (such as Figure 5 At the same time, the local protection device at the circuit breaker K12 obtains the negative sequence current upload information of -1 and 1 under F1 and F2 faults according to the negative sequence current direction element criterion.

[0104] S5, the tie line area protection device determines that an asymmetric fault occurs in the power grid according to the information uploaded by the circuit breakers K10, K11 and K12, and enters S6; ​

[0105] S6. When F1 fails, the fault information of circuit breakers K10, K11 and K12 obtained by the tie-line area protection device is [1, 0, 1], but the negative sequence current information of circuit breaker K12 is 1, then it is judged that the fault occurs in the busbar area, and then the circuit breakers K10, K11 and K12 are tripped; when F2 fails, the fault information of circuit breakers K10, K11 and K12 obtained by the tie-line area protection device is [1, 0, 1], but the negative sequence current information of circuit breaker K12 is -1, then it is judged that the fault occurs in the tie-line of the doubly-fed wind farm, and then the circuit breaker K12 is tripped.

[0106] Figure 5 It shows that under the fault at F1, the short-circuit current of circuit breaker K12 briefly exceeds the protection setting value, causing the protection at circuit breaker K12 to malfunction (under normal circumstances, the protection at K12 should not operate, and only the protection at K10 trips); Figure 6 At the same time, it is shown that if there is a fault at F1, the short-circuit current will also flow, which will cause the protection at the circuit breaker K13 to trip incorrectly (under normal circumstances, K13 should not operate, and only the protection at K10 will trip).

[0107] The invention described above only expresses the implementation methods of the embodiments of the present invention, and cannot be understood as limiting the scope of the invention patent, nor does it impose any form of limitation on the structure of the embodiments of the present invention. It should be pointed out that for ordinary technicians in this field, several changes and improvements can be made without departing from the concept of the embodiments of the present invention, which all belong to the protection scope of the embodiments of the present invention.

Claims

1. A regional protection method for a doubly-fed wind turbine tie line, characterized in that: The following steps are involved: Each local protection device is equipped with overcurrent protection and positive sequence direction element judgment formula, wherein the local protection device on the double-fed wind turbine group tie line is also equipped with a negative sequence direction element judgment formula, and the system-side protection device on the double-fed wind turbine group tie line is equipped with an overcurrent protection setting value judgment formula; Collect the voltage of each line connected to the busbar of the double-fed wind farm and the zero-sequence voltage, negative-sequence voltage and current of the current transformer; The local protection device determines whether it is a three-phase fault, a ground fault or a two-phase interphase fault according to the phase voltage, zero-sequence voltage and negative-sequence voltage collected from each line, sends the fault judgment result to the judgment element of the local protection device on each line for judgment, and uploads the obtained judgment information to the tie line area protection device; After the tie line area protection device collects the information uploaded by the local protection devices of each line, the local protection device is used to make a centralized judgment on the uploaded information, and the information of the busbar incoming line, the grid-connected line of the doubly-fed wind turbine group and the grid-connected line of the non-doubly-fed wind turbine group is obtained through the judgment formula of the positive sequence directional element and the negative sequence directional element, so as to perform tripping actions respectively.

2. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: The judgment element includes a voltage starting element, an overcurrent protection, a positive sequence direction element and a negative sequence direction element, wherein the voltage starting element, the overcurrent protection and the positive sequence direction element are arranged in an on-site protection device on the grid-connected line and the busbar incoming line of a non-doubly fed wind turbine group, and the voltage starting element, the overcurrent protection, the positive sequence direction element and the negative sequence direction element are arranged in an on-site protection device on the grid-connected line of a doubly fed wind turbine group.

3. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: The method of sending the fault judgment result to the judgment element of the local protection device on each line for judgment comprises the following steps: If the local protection devices of the non-doubly-fed wind turbine grid-connected lines judge that the overcurrent protection and positive sequence direction elements meet the conditions, the information of the uploaded regional protection is 1; otherwise, it is 0; The local protection device of the grid-connected line of the doubly-fed wind turbine generator set has the sensitivity to judge the fault line according to the two-phase metallic fault at the end of the line under three-phase fault. The expression is as follows: Among them, I W1 Indicates the measured current; I set1 Indicates the current setting value used to judge the fault direction under three-phase fault; Indicates rated current; Represents the system equivalent impedance; Z L Indicates the equivalent impedance of the grid-connected line of the doubly-fed wind farm; K r is the reliability coefficient; If the fault line identification criteria meet the conditions and the directional element meets the conditions, it means that the fault occurs in the grid-connected line of the doubly-fed wind turbine generator set, and the uploaded information is 1; otherwise, it means that the fault is not in the grid-connected line of the doubly-fed wind turbine generator set, and the uploaded information is 0.

4. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: The negative sequence directional element judgment formula is as follows: in, and denote the negative sequence voltage and current respectively; is the negative sequence direction sensitivity angle.

5. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: The positive sequence direction element judgment formula is as follows: in: and are the pre-fault memory voltage and pre-fault memory current respectively; the subscript "1" of each variable indicates positive sequence, is the sensitive angle of the directional element.

6. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: The overcurrent protection judgment formula is as follows: in, Indicates the phase overcurrent protection setting value; I min_sc Indicates the minimum short-circuit current value calculated based on the system short-circuit current; k l Represents the sensitivity coefficient.

7. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: For a three-phase fault, the method of sending the fault judgment result to the judgment element of the local protection device on each line for judgment, and uploading the obtained judgment information to the tie line area protection device, includes the following steps: Each local protection device generates (1,0) information according to the overcurrent and positive sequence directional element criteria and sends it to the tie line area protection device; If the regional protection device determines that the bus information is 1 and the other line information is 0, it indicates a bus fault, and the circuit breakers of each line connected to the bus are tripped; If the regional protection device determines that the bus information is 1, the line information of a non-doubly-fed unit is 1, and the other line information is 0, then the circuit breaker on the line system side of the non-doubly-fed unit is tripped; If the regional protection device determines that the bus information is 1, the line information of the doubly-fed generator set is 1, and other line information is 0, the circuit breaker on the line system side of the doubly-fed generator set is tripped.

8. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: For a ground fault or a two-phase-to-phase fault, the fault judgment result is sent to the judgment element of the local protection device on each line for judgment, and the obtained judgment information is uploaded to the tie line area protection device, including the following steps: Each local protection device generates (1,0) information from the overcurrent and positive sequence directional element criteria, and the double-fed line includes a negative sequence directional element, and sends it to the tie line area protection device; If the regional protection device determines that the bus information is 1 and the other line information is 0, and the first uploaded information of the double-fed line is 0, it indicates a bus fault, and the circuit breakers of each line connected to the bus are tripped; If the regional protection device determines that the bus information is 1, the line information of a non-doubly-fed unit is 1, and the other line information is 0, then the circuit breaker on the line system side of the non-doubly-fed unit is tripped; If the regional protection device determines that the bus information is 1, the first information of the double-fed unit line is 1, the second information is -1, and the other line information is 0, then the circuit breaker on the double-fed unit line system side is tripped; If the regional protection device determines that the bus information is 1, the first information of the double-fed unit line is 1, the second information is 0, and the other line information is 0, then the circuit breakers of the lines connected to the bus are tripped.

9. A regional protection method for a doubly-fed wind turbine tie line according to claim 1, characterized in that: The local protection device determines whether a three-phase fault, a ground fault or a two-phase interphase fault is present according to the phase voltage, zero-sequence voltage and negative-sequence voltage collected from each line, and includes the following steps: min(|U a |,|U b |,|U c |)<U s ; (5) In the above formula, U a , U b and U c Represent the three-phase voltage, U s Represents the voltage setting value. Through calculation, if it satisfies the above formula (5), it is judged that a ground fault occurs. If not, proceed to the next step; In the above formula, a represents the operator, U 2s It represents the negative sequence voltage setting value. Through calculation, if it satisfies the above formula (6), it is judged that a two-phase phase-to-phase fault occurs. If not, it proceeds to the next step. |In a +U b +U c |>U 0.set ; (7) In the above formula, U 0.set It represents the zero-sequence voltage setting value. Through calculation, if it satisfies the above formula (7), it is judged that a three-phase fault has occurred. If it does not satisfy it, it means that no fault has occurred.

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