A wind power plant station outgoing line differential protection method and system

Abstract

The application provides a wind power station outgoing line differential protection method and system, the method comprises the following steps: configuring a set of protection devices containing sudden change energy operator algorithm on both sides of the wind power station outgoing line, the protection device can obtain the current sampling value on the side, and the current sampling value on the opposite side is obtained through the optical fiber; the time domain current energy operators on both sides are calculated by using the current signal sampling values on both sides, the differential quantity and the braking quantity are calculated according to the energy operators on both sides; the fault type and the internal and external faults are determined by comparing the size relationship between the ratio of the energy operator differential quantity and the braking quantity of each phase and the setting value. The application does not depend on the power frequency characteristic quantity, and ensures the reliability and the rapidity of the wind power station outgoing line protection.

Description

Technical Field

[0001] This invention belongs to the field of wind power grid connection protection technology, and relates to a differential protection method and system for wind farm transmission lines. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] As wind power generation has rapidly developed into the most technologically mature new energy power generation method, large-scale wind farms have been established in many places in recent years. Centralized grid connection of wind power generation is gradually becoming the development trend of new energy power transmission systems. However, unlike the fault characteristics of traditional power systems, considering the low-voltage ride-through control strategy and high-proportion power electronic topology used by wind turbine power supplies when faults occur, the wind farm side exhibits fault characteristics with limited amplitude and non-power frequency components. This leads to a decrease in the operating performance of traditional differential protection, and even the risk of failure to operate. At the same time, in order to prevent large-scale wind power disconnection from the grid, it is urgent to improve the speed of protection.

[0004] The randomness and volatility of wind power output make it difficult for traditional protection to extract power frequency fault characteristics. Furthermore, the phase angle of the fault current on the wind farm side is controlled, and the phase angle difference between the fault current provided by the system side and the fault current on the wind farm side makes it impossible for traditional differential protection, which serves as the main protection, to reliably identify faults and ensure the safety of the wind farm's power transmission system. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a differential protection method and system for wind farm transmission lines. This invention does not rely on power frequency characteristic quantities, ensuring the reliability and speed of wind farm transmission line protection.

[0006] According to some embodiments, the present invention adopts the following technical solution:

[0007] A differential protection method for transmission lines from a wind farm includes the following steps:

[0008] Acquire the sampled current values ​​on this side and the sampled current values ​​on the opposite side;

[0009] The time-domain current energy operators on both sides are calculated based on the sampled values ​​of the current signals on both sides, and the differential and braking quantities are calculated based on the energy operators on both sides.

[0010] By comparing the ratios of differential momentum and braking quantity of each phase energy operator with the set values, the fault type and fault location are determined based on the comparison results.

[0011] As an alternative implementation, the protection device is used to obtain the sampled current values ​​on the local side and the sampled current values ​​on the opposite side.

[0012] As a further step, the protection device consists of two sets, which are respectively installed on both sides of the wind farm's transmission line.

[0013] As a further step, the protection device is pre-configured with a sampling window length and a sampling frequency.

[0014] As an alternative implementation method, the specific process of calculating the time-domain current energy operator based on the sampled values ​​of the current signals on both sides includes:

[0015] ψ φ =x(ni) 2 -x(n-2i)x(n)

[0016] In the formula, ψ φ Let x(n) be the energy operator for each phase, x(n) be the sampled current value for each phase, and i be the interval point. Interval sampling is used to improve the noise resistance of the energy operator.

[0017] As an optional implementation method, the calculation process for the ratio of differential momentum and braking quantity of each phase energy operator includes:

[0018]

[0019] In the formula, K φ ψ is the ratio of the differential momentum and braking force of the three-phase energy operators A, B, and C. sφ ψ is the energy operator for the system-side current sampling signal. wφ This is the energy operator for the wind farm side current sampling signal.

[0020] As an alternative implementation, if the ratio of the differential momentum and braking amount of the corresponding phase energy operator is greater than or equal to the set value, then the phase is a faulty phase and is a fault within the zone.

[0021] As a further step, after determining the fault within the zone and the faulty phase, the protection device issues a trip command.

[0022] As an alternative implementation method, if a fault is detected and the ratio of the differential momentum and braking amount of each phase energy operator is less than the set value, then it is an external fault.

[0023] As an alternative implementation method, the protection device is reset after an external fault is detected.

[0024] A differential protection system for wind farm transmission lines includes:

[0025] Protection devices are installed on both sides of the transmission line of the wind farm to obtain the current sampling value on this side and the current sampling value on the opposite side;

[0026] The calculation module is used to calculate the time-domain current energy operators on both sides based on the sampled values ​​of the current signals on both sides, and to calculate the differential and braking quantities based on the energy operators on both sides.

[0027] The judgment module is used to compare the ratio of the differential momentum and braking of each phase energy operator with the set value, and to determine the fault type and fault location based on the comparison results.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention utilizes time-domain signals to extract time-frequency domain features, enabling it to operate correctly during high-resistance faults; it is unaffected by changes in wind farm capacity and can still operate correctly even when the wind farm has low output; it has full-line speed capability and can correctly identify faults within a short time. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 This is a schematic diagram of the time-domain current energy operator differential protection principle proposed in this invention;

[0032] Figure 2 A schematic diagram showing the location and topology of the power transmission line fault at the wind farm station;

[0033] Figure 3 A graph showing the time-frequency characteristics of the faulty phase and the non-faulty phase when a BC phase fault occurs within the area.

[0034] Figure 4 A schematic diagram of the differential value of the three-phase energy operator in a single-phase fault;

[0035] Figure 5 A schematic diagram of the differential value of the three-phase energy operator in a two-phase interphase fault;

[0036] Figure 6 A schematic diagram of the differential values ​​of the three-phase energy operator for a two-phase ground fault;

[0037] Figure 7 This is a schematic diagram of the differential value of the three-phase energy operator in a three-phase fault. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0039] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0040] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0041] Figure 1 This invention presents a schematic diagram of the differential protection principle based on the time-domain current energy operator. The invention proposes a differential protection method for wind farm transmission lines based on the time-domain current energy operator, comprising the following steps:

[0042] Step 1: Configure a protection device containing a sudden energy operator algorithm on both sides of the wind farm's transmission line. The protection device can obtain the current sampling value on its own side and obtain the current sampling value on the opposite side through optical fiber.

[0043] Step 2: Calculate the time-domain current energy operators on both sides using the sampled values ​​of the current signals on both sides, and calculate the differential and braking quantities based on the energy operators on both sides;

[0044] Step 3: Determine the fault type and whether the fault is inside or outside the zone by comparing the ratio of the differential momentum and braking amount of each phase energy operator with the setting value.

[0045] In step 1, the protection device can acquire current sampling values ​​from both the local and the opposite side, and perform energy operator calculations on the current sampling data from both sides. The energy operator formula is as follows:

[0046] ψ φ =x(ni) 2 -x(n-2i)x(n)

[0047] In the formula, ψ φ Let x(n) be the energy operator for each phase, x(n) be the sampled current value for each phase, and i be the interval point. Interval sampling is used to improve the noise resistance of the energy operator.

[0048] The energy operator can be used to reflect the time-frequency domain characteristics of the current using the current time-domain signal. In order to accurately identify the time-frequency domain characteristics of the current, the sampling window length of the protection device is set to 10ms and the sampling frequency is set to 10kHz. The high sampling rate enables accurate characterization of the energy operator.

[0049] In step 2, since the fault characteristics exhibited by the new energy side and the system side differ significantly in the time-frequency domain, the energy operators on both sides will differ significantly after a fault occurs. This difference is determined by comparing the ratio of the energy operator differential momentum to the braking amount.

[0050]

[0051] In the formula, K φ ψ is the ratio of the differential momentum and braking force of the three-phase energy operators A, B, and C. sφ ψ is the energy operator for the system-side current sampling signal. wφ This is the energy operator for the wind farm side current sampling signal.

[0052] There is a significant difference in the energy operator ratio when faults occur inside or outside the zone:

[0053] 1) When there is a fault outside the zone or during normal operation, the influence of distributed capacitance is ignored. The line flows through current. The current sampling values ​​detected by the protection devices on both sides are similar. The energy operators on both sides are similar, and the energy operator ratio is close to 0.

[0054] 2) When a fault occurs within the zone, the current sampling values ​​detected by the protection devices on both sides show a significant difference in both amplitude and frequency, and the energy operator ratio is greater than 0.

[0055] Step 3 proposes a differential protection method for wind farm transmission lines based on time-domain current energy operators. The specific setting criteria are as follows:

[0056] K φ ≥K set φ = A, B, C

[0057] In the formula, K φ K is the ratio of the differential momentum and braking force of the three-phase energy operators A, B, and C. set The setpoint is 0.1, taking into account the discharge frequency of the distributed capacitor.

[0058] In step 3, when a fault occurs, the protection device is activated. When an external fault occurs, the ratio of the three-phase energy operators is lower than the set value, and the protection is reset. When an internal fault occurs, the ratio of the energy operator of the faulty phase is higher than the set value, and the ratio of the energy operator of the non-faulty phase is lower than the set value, and the protection device issues a trip command.

[0059] Figure 2 This diagram shows the location and topology of a fault in the transmission line of a wind farm. The wind farm in the diagram is a doubly fed wind farm. Figure 2 The wind farm shown has a total capacity of 100MW, with each doubly-fed induction generator (DFIG) having a capacity of 3MW. The wind farm has 33 turbines, with a turbine terminal voltage of 0.69kV. The transformer substation has a transformation ratio of 35kV / 0.69kV, uses a Dyn connection, and has a short-circuit impedance of 8.42%. The main transformer has a transformation ratio of 220kV / 35kV, uses a YNd connection, and has a short-circuit impedance of 7.28%. The positive and negative sequence impedances per kilometer of the transmission line are both 0.028 + j0.147Ω, and the unit zero-sequence impedance is 0.144 + j0.746Ω. The transmission line length is 20km. Figure 2The topology and parameters mentioned above were used to build a transient model of the wind farm's collection and transmission system in a real-time digital simulator (RTDS) to verify the protection algorithm proposed in this invention.

[0060] There are a total of 5 fault locations: K1, K2, K3, K4, and K5. K1 and K5 are external faults (K1 is on the wind farm side, and K5 is on the system side). K2, K3, and K4 are internal faults (K3 is at the line midpoint, and K2 and K4 are located at the internal near-end). Fault types include single-phase faults, two-phase faults, two-phase ground faults, and three-phase faults. The above four fault types are illustrated using AG, BC, BCG, and ABC faults as examples.

[0061] Figure 3 This diagram illustrates the time-frequency characteristic differences between the faulty phase and the non-faulty phase during a BC-phase fault within the area. Wavelet transform is used to extract the time-frequency characteristics of the fault current on both sides after the fault. Figure 3 It can be seen that the time-frequency characteristics of the faulty phase are significantly different due to the large differences in fault characteristics between the wind field side and the system side, while the time-frequency characteristics of the non-faulty phase are almost the same on both sides without considering the influence of distributed capacitance, and there is no significant difference.

[0062] Figure 4 , Figure 5 , Figure 6 , Figure 7 These are schematic diagrams illustrating the differential values ​​of the energy operator when different types of intra-regional faults occur. Figure 4 This is a schematic diagram of the differential values ​​of the three-phase energy operator in a single-phase fault. Figure 5 This is a schematic diagram of the differential values ​​of the three-phase energy operator in a two-phase interphase fault. Figure 6 This is a schematic diagram of the differential values ​​of the three-phase energy operator in a two-phase ground fault. Figure 7 This diagram illustrates the differential values ​​of the three-phase energy operators during a three-phase fault. The red line represents the differential value of phase A, the blue line represents the differential value of phase B, the yellow line represents the differential value of phase C, and the purple line represents the setting value. The diagram shows that 0ms represents the fault occurrence time, demonstrating that the proposed protection can correctly identify the fault within 5ms, exhibiting good operational performance.

[0063] To further verify the effectiveness of the energy operator differential protection method proposed in this invention, simulation verification was conducted. Table 1 shows the calculated values ​​of the three-phase energy operator differential value at 5ms under different fault types at different fault locations (including inside and outside the fault zone). Table 2 shows the calculated values ​​of the three-phase energy operator differential value at 5ms under single-phase ground faults, where the transition resistance is selected to be as high as 100Ω. Table 3 shows the calculated values ​​of the three-phase energy operator differential value at 5ms under different fault types when wind farms of different capacities are connected.

[0064] Table 1

[0065]

[0066]

[0067] Table 2

[0068]

[0069]

[0070] Table 3

[0071]

[0072]

[0073] Simulation verification shows that the proposed new protection principle can quickly and reliably identify faults inside and outside the protection zone. Within 5ms after a fault occurs inside the zone, the differential value of the fault phase energy operator is greater than the protection setting value, demonstrating good protection speed. The new protection principle can withstand high-resistance faults and remains reliable even when the transition resistance reaches 100Ω. The proposed protection is not affected by the capacity of the new energy source. When the output of the new energy source is weak, the proposed protection can still correctly identify various types of faults, demonstrating good operating performance.

[0074] Given the analytical basis and conditions of this method, the application of the method described in this invention utilizes the time-frequency characteristics difference of the current signals on both sides, and is not affected by the wind turbine control strategy, thus avoiding the situation where the performance of existing differential protection deteriorates or even fails to operate.

[0075] The parameters mentioned above are merely illustrative. In other embodiments, they may be adjusted or changed according to the specific circumstances of the wind farm system and are not limited to the example values ​​mentioned above.

[0076] The present invention also provides the following product examples:

[0077] A differential protection system for wind farm transmission lines includes:

[0078] Protection devices are installed on both sides of the transmission line of the wind farm to obtain the current sampling value on this side and the current sampling value on the opposite side;

[0079] The calculation module is used to calculate the time-domain current energy operators on both sides based on the sampled values ​​of the current signals on both sides, and to calculate the differential and braking quantities based on the energy operators on both sides.

[0080] The judgment module is used to compare the ratio of the differential momentum and braking of each phase energy operator with the set value, and to determine the fault type and fault location based on the comparison results.

[0081] A computer-readable storage medium storing a plurality of instructions adapted for loading by a processor of a terminal device and executing steps in the method.

[0082] A terminal device includes a processor and a computer-readable storage medium, the processor being configured to implement instructions; the computer-readable storage medium being configured to store a plurality of instructions adapted to be loaded by the processor and executed in accordance with the steps of the method.

[0083] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0084] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0085] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0086] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0088] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A differential protection method for transmission lines from wind farms, characterized in that, Includes the following steps: Acquire the sampled current values ​​on this side and the sampled current values ​​on the opposite side; The time-domain current energy operators on both sides are calculated based on the sampled values ​​of the current signals on both sides, and the differential and braking quantities are calculated based on the energy operators on both sides. Compare the ratios of the differential momentum and braking quantities of the energy operators of each phase with the set values, and determine the fault type and location based on the comparison results; The specific process of calculating the time-domain current energy operator based on the sampled values ​​of the current signals on both sides includes: In the formula, For the energy operators of each phase, x (n) represents the sampled current values ​​for each phase. i Using interval sampling as the interval point, the noise resistance of the energy operator is improved; The calculation process for the ratio of differential momentum and braking force of each phase energy operator includes: In the formula, This represents the ratio of the differential momentum and braking force of the three-phase energy operators A, B, and C. The energy operator for the system-side current sampling signal. This is the energy operator for the wind farm side current sampling signal.

2. The differential protection method for wind farm transmission lines as described in claim 1, characterized in that, The protection device is used to obtain the sampled current values ​​of the local side and the opposite side.

3. The differential protection method for wind farm transmission lines as described in claim 2, characterized in that, The protection device consists of two sets, which are respectively installed on both sides of the wind farm's transmission line.

4. A differential protection method for wind farm transmission lines as described in claim 2, characterized in that, The protection device is pre-configured with a sampling window length and a sampling frequency.

5. A differential protection method for wind farm transmission lines as described in claim 1, characterized in that, If the ratio of the differential momentum and braking quantity of the corresponding phase energy operator is greater than or equal to the set value, then the phase is a faulty phase and is a fault within the zone.

6. A differential protection method for wind farm transmission lines as described in claim 5, characterized in that, After determining the fault within the zone and the faulty phase, the protection device issues a trip command.

7. A differential protection method for wind farm transmission lines as described in claim 1, characterized in that, If a fault is detected, and the ratios of differential momentum and braking quantity of each phase energy operator are all less than the set values, then it is an external fault.

8. A differential protection method for wind farm transmission lines as described in claim 7, characterized in that, After determining that the fault is outside the designated area, the protection device is reset.

9. A differential protection system for transmission lines of a wind farm, characterized in that, A differential protection method for wind farm transmission lines according to any one of claims 1-8 includes: Protection devices are installed on both sides of the transmission line of the wind farm to obtain the current sampling value on this side and the current sampling value on the opposite side; The calculation module is used to calculate the time-domain current energy operators on both sides based on the sampled values ​​of the current signals on both sides, and to calculate the differential and braking quantities based on the energy operators on both sides. The judgment module is used to compare the ratio of the differential momentum and braking of each phase energy operator with the set value, and to determine the fault type and fault location based on the comparison results.

10. A differential protection system for wind farm transmission lines as described in claim 9, characterized in that, The protection device is used to obtain the sampled current values ​​of the local side and the opposite side.

11. A differential protection system for wind farm transmission lines as described in claim 10, characterized in that, The protection device consists of two sets, which are respectively installed on both sides of the wind farm's transmission line.

12. A differential protection system for wind farm transmission lines as described in claim 10, characterized in that, The protection device is pre-configured with a sampling window length and a sampling frequency.

13. A differential protection system for wind farm transmission lines as described in claim 9, characterized in that, If the ratio of the differential momentum and braking quantity of the corresponding phase energy operator is greater than or equal to the set value, then the phase is a faulty phase and is a fault within the zone.

14. A differential protection system for wind farm transmission lines as described in claim 13, characterized in that, After determining the fault within the zone and the faulty phase, the protection device issues a trip command.

15. A differential protection system for wind farm transmission lines as described in claim 9, characterized in that, If a fault is detected, and the ratios of differential momentum and braking quantity of each phase energy operator are all less than the set values, then it is an external fault.

16. A differential protection system for wind farm transmission lines as described in claim 15, characterized in that, After determining that the fault is outside the designated area, the protection device is reset.

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