Fault phase selection method suitable for high-voltage transmission line of high-proportion new energy system

Abstract

The application discloses a fault phase selection method suitable for a high-voltage transmission line of a high-proportion new energy system, and comprises the following steps: S1, calculating the phase voltage and phase-to-phase voltage amplitude of a protection installation, the phase compensation voltage and phase-to-phase compensation voltage variation, and the zero sequence current amplitude; S2, if the zero sequence current amplitude is greater than a threshold value, entering S3; otherwise, entering S5; S3, if the intermediate value and the minimum value of the phase voltage amplitude meet a preset condition, determining that a single-phase ground fault occurs in the phase corresponding to the minimum value; otherwise, entering S4; S4, if the two phases corresponding to the minimum value of the phase-to-phase compensation voltage variation are different from the phase corresponding to the maximum value of the phase compensation voltage variation, and the preset condition is met, determining that a single-phase ground fault occurs in the phase corresponding to the maximum value; otherwise, determining that a two-phase ground fault occurs in the two phases corresponding to the minimum value of the phase-to-phase voltage amplitude of the protection installation; and S5, determining that a multi-phase fault occurs in the power grid. The single-phase fault and the multi-phase fault can be accurately distinguished.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection, and more specifically, relates to a fault phase selection method applicable to high-voltage transmission lines in high-proportion new energy systems. Background Technology

[0002] In high-proportion renewable energy systems, the fault characteristics of renewable energy sources differ from those of traditional synchronous generators, making the system's fault features more complex and causing adaptation issues in the protection of transmission lines.

[0003] In high-voltage lines, phase selection elements provide phase selection results for distance protection, reclosing, and fault location. Traditional phase selection methods mainly include abrupt change phase selection and steady-state phase selection. The abrupt change phase selection method relies on the premise that the positive-sequence impedance and negative-sequence impedance of the back-side system are equal. However, the fault characteristics of renewable energy sources are complex and variable. Influenced by low-voltage control strategies, the positive and negative-sequence impedances are often no longer equal. Especially when the control objective is to suppress the negative-sequence component, the short-circuit current on the renewable energy side contains only the positive-sequence component, while the negative-sequence component is essentially zero, resulting in infinite negative-sequence impedance. This causes the abrupt change in the healthy phase to no longer be zero, and there is no clear relationship between the magnitudes of these abrupt changes, leading to incorrect phase selection. When the feed current from the renewable energy side does not contain a negative-sequence component, the phase selection method based on steady-state sequence components fails. Furthermore, the fluctuations and frequency shifts in the transient processes of faults in high-proportion renewable energy systems render the fundamental phasor extraction based on the Fourier algorithm inaccurate. Therefore, a new fault phase selection method is needed that is applicable to high-voltage transmission lines with a high proportion of renewable energy systems. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention provides a fault phase selection method for high-voltage transmission lines in high-proportion new energy systems. The purpose is to solve the problem that existing methods for phase selection based on sudden changes and steady-state sequence components cannot correctly select the phase.

[0005] To achieve the above objectives, on the one hand, the present invention provides a fault phase selection method applicable to high-voltage transmission lines in high-proportion renewable energy systems, the method comprising the following steps:

[0006] S1. When a line fault occurs, based on the real-time acquired sequence of measured voltage and measured current samples at the protection installation point, calculate the amplitude of each phase voltage and phase-to-phase voltage, the change in phase compensation voltage and phase-to-phase compensation voltage, and the amplitude of zero-sequence current at the protection installation point.

[0007] S2. If the zero-sequence current amplitude is greater than the threshold value, proceed to step S3; otherwise, proceed to step S5.

[0008] S3. Sort the voltage amplitudes of each phase at the protection installation location, and if the median value is... and minimum value satisfy Then determine the minimum value If a single-phase ground fault occurs in the corresponding phase, proceed to step S4; otherwise, proceed to step S4; where m is 0.5 to 0.7, n is 2 to 4, and U N This is the rated phase voltage amplitude;

[0009] S4, if the inter-phase compensation voltage change is at its minimum value The corresponding two-phase phase and the maximum value of the phase compensation voltage change The corresponding phases are all different, and satisfy the following conditions: Then determine If a single-phase ground fault occurs in the corresponding phase, otherwise, it is determined that a two-phase ground fault occurs in the two phases corresponding to the minimum phase-to-phase voltage amplitude at the protection installation location; where i is 4 to 6.

[0010] S5. Sort the phase-to-phase voltage amplitudes at the protection installation location and determine the two phases corresponding to the minimum phase-to-phase voltage amplitudes that have experienced phase-to-phase faults.

[0011] Further, in step S1, the sequence of measured voltage and measured current samples obtained in real time at the protection installation point is processed by low-pass filtering, and the phase voltage drop and phase-to-phase voltage drop from the protection installation point to the line setting point are calculated according to the line RL differential equation; then the difference between the phase voltage measured at the protection installation point and the phase voltage drop is used as the phase compensation voltage, and the difference between the phase-to-phase voltage measured at the protection installation point and the phase-to-phase voltage drop is used as the phase-to-phase compensation voltage.

[0012] Furthermore, in step S1, the instantaneous value integration algorithm is used to calculate the amplitude of each phase voltage and the phase-to-phase voltage at the protection installation location:

[0013]

[0014] in, The phase voltage amplitude, This refers to the phase-to-phase voltage amplitude. To protect the phase voltage measured at the installation location, To protect the phase-to-phase voltage measured at the installation location; k0 is the sampling point corresponding to a certain moment after a line fault occurs, Δt is the sampling interval, T is the time corresponding to a data window, and N is the number of sampling points within a data window.

[0015] Furthermore, the compensation voltage change is the difference between the instantaneous value at the current moment and the instantaneous value at the two preceding fundamental moments. The formula for calculating the amplitude of the compensation voltage change is:

[0016]

[0017] in, The magnitude of the phase compensation voltage change. This represents the amplitude of the phase-to-phase compensation voltage change. For phase compensation voltage, This is the phase-to-phase compensation voltage.

[0018] On the other hand, the present invention provides a fault phase selection device suitable for high-voltage transmission lines in high-proportion new energy systems, comprising:

[0019] The calculation module is used to calculate the phase voltage and phase-to-phase voltage amplitude, phase compensation voltage and phase-to-phase compensation voltage change, and zero-sequence current amplitude at the protection installation point based on the real-time acquired sequence of measured voltage and current sampling values ​​at the protection installation point when a line fault occurs.

[0020] The first discrimination module is used to perform the following operations: if the zero-sequence current amplitude is greater than the threshold value, the operation of the second discrimination module is executed; otherwise, the operation of the fourth discrimination module is executed.

[0021] The second discrimination module is used to sort the voltage amplitudes of each phase at the protection installation location, and if the median value is... and minimum value satisfy Then determine the minimum value If a single-phase ground fault occurs in the corresponding phase, then the operation of the third discrimination module is executed; otherwise, m is 0.5 to 0.7, n is 2 to 4, and U N This is the rated phase voltage amplitude;

[0022] The third discrimination module is used to perform the following operation: if the phase-to-phase compensation voltage change is at its minimum value... The corresponding two-phase phase and the maximum value of the phase compensation voltage change The corresponding phases are all different, and satisfy the following conditions: Then determine If a single-phase ground fault occurs in the corresponding phase, otherwise, it is determined that a two-phase ground fault occurs in the two phases corresponding to the minimum phase-to-phase voltage amplitude at the protection installation location; where i is 4 to 6.

[0023] The fourth discrimination module is used to sort the phase-to-phase voltage amplitudes at the protection installation location and determine that the two phases corresponding to the minimum phase-to-phase voltage amplitudes have experienced phase-to-phase faults.

[0024] Furthermore, the calculation module is also used to process the real-time acquired sequence of measured voltage and measured current values ​​at the protection installation point through low-pass filtering, and then calculate the phase voltage drop and phase-to-phase voltage drop from the protection installation point to the line setting point according to the line RL differential equation; then, the difference between the phase voltage measured at the protection installation point and the phase voltage drop is used as the phase compensation voltage, and the difference between the phase-to-phase voltage measured at the protection installation point and the phase-to-phase voltage drop is used as the phase-to-phase compensation voltage.

[0025] Furthermore, the calculation module is also used to calculate the phase voltage and phase-to-phase voltage amplitude at the protection installation location using an instantaneous value integration algorithm:

[0026]

[0027] in, The phase voltage amplitude, This refers to the phase-to-phase voltage amplitude. To protect the phase voltage measured at the installation location, To protect the phase-to-phase voltage measured at the installation location; k0 is the sampling point corresponding to a certain moment after a line fault occurs, Δt is the sampling interval, T is the time corresponding to a data window, and N is the number of sampling points within a data window.

[0028] Furthermore, the calculation module is also used to calculate the compensation voltage change, which is the difference between the instantaneous value at the current moment and the instantaneous value at the two preceding fundamental moments. The formula for calculating the amplitude of the compensation voltage change is:

[0029]

[0030] in, The magnitude of the phase compensation voltage change. This represents the amplitude of the phase-to-phase compensation voltage change. For phase compensation voltage, This is the phase-to-phase compensation voltage.

[0031] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0032] This invention utilizes the voltage and current measured at the protection installation point, calculates the compensation voltage based on the line RL differential equation, and calculates the phase voltage and phase-to-phase voltage amplitude, compensation phase voltage and phase-to-phase voltage variation, and zero-sequence current amplitude at the protection installation point using an instantaneous value integration algorithm. First, it determines whether there is a ground fault based on the zero-sequence current. If the zero-sequence current is greater than a threshold value, it is determined to be a ground fault. Single-phase ground fault selection is performed by sorting the phase voltage amplitudes and comparing the ratio of the median to the minimum value. If phase selection fails, single-phase ground fault selection is performed using the relationship between the maximum and minimum phase compensation voltage variation. If both methods fail, it is determined to be a two-phase ground fault; if the zero-sequence current is less than the threshold value, it is determined to be a multi-phase fault, and the two phases corresponding to the minimum phase-to-phase voltage amplitude at the protection installation point are the faulty phases. The fault phase selection method proposed in this invention uses the integral value of the instantaneous voltage and current, which is not affected by the system frequency offset; it uses the relationship between the voltage amplitude at the protection installation point to select the phase, which is not affected by the complex fault current characteristics of new energy sources, and effectively solves the problem that existing abrupt change phase selection elements and steady-state sequence component phase selection methods are not applicable to new energy transmission lines; it uses compensated voltage change phase selection, which is suitable for various operating modes of high-proportion new energy systems and has high sensitivity. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a high-proportion new energy power system structure provided in an embodiment of the present invention;

[0034] Figure 2 This is a flowchart of the fault phase selection method provided in the embodiments of the present invention;

[0035] Figure 3 This is the zero-sequence current amplitude curve under a single-phase ground fault provided in the embodiments of the present invention;

[0036] Figure 4 This is a curve showing the relationship between the phase voltage amplitude and time at the protection installation point under a single-phase ground fault, provided in an embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] The specific implementation method is illustrated using a high-proportion renewable energy power system as an example, such as... Figure 1 As shown, the system includes a 110kV high-proportion new energy system 1, a transformer 3, an external power grid 2, a transformer 4, and relay protection devices 5 and 6 on both sides of the line.

[0039] This invention provides a fault phase selection method, the flowchart of which is shown below. Figure 2 As shown, the specific steps are as follows:

[0040] S1. When a line fault occurs, based on the real-time acquired sequence of measured voltage and measured current samples at the protection installation point, calculate the amplitude of each phase voltage and phase-to-phase voltage, the change in phase compensation voltage and phase-to-phase compensation voltage, and the amplitude of zero-sequence current at the protection installation point.

[0041] Specifically, the formula for calculating the voltage drop from the protection installation point to the line setting point is:

[0042]

[0043] Where, Δu a (k), Δu b (k), Δu c (k) represents the phase voltage drop, Δuab(k), Δubc(k), and Δuca(k) represent the phase-to-phase voltage drop, and ia(k), ib(k), and ic(k) represent the three-phase currents, L zs and L zm To protect the self-inductance and mutual inductance of the line from the installation point to the setting point, R zs and R zm To protect the self-resistance and mutual resistance of the line from the installation point to the setting point, the setting distance is set to 0.7 times the total length of the line.

[0044] Specifically, the formula for calculating the compensation voltage is:

[0045]

[0046] in, These represent phase compensation voltage and inter-phase compensation voltage, respectively. These represent the phase voltage and phase-to-phase voltage measured at the protection installation location, respectively. These represent the phase voltage drop and phase-to-phase voltage drop from the protection installation point to the setting point, respectively.

[0047] In this embodiment, the instantaneous value integration algorithm is used to calculate the amplitude of each phase voltage and the phase-to-phase voltage at the protection installation location. Compensation for phase voltage and phase-to-phase voltage variations The zero-sequence current amplitude 3I0 is calculated from the three-phase measured current at the protection installation point.

[0048] Specifically, the amplitudes of the phase voltage and phase-to-phase voltage at the protection installation point are:

[0049]

[0050] The data window is set to one fundamental frequency cycle, T = 0.02s.

[0051] Specifically, the compensation voltage change is the difference between the instantaneous value at the current moment and the instantaneous value at the two previous fundamental frequency cycles, and the formula for calculating the amplitude of the change is:

[0052]

[0053] Specifically, the formula for calculating the zero-sequence current amplitude is:

[0054]

[0055] S2. If the zero-sequence current amplitude is greater than the threshold value, proceed to step S3; otherwise, proceed to step S5.

[0056] Specifically, if the zero-sequence current 3I0 satisfies equation (6), then it is determined that a ground fault has occurred in the power grid, and the process proceeds to step S3; otherwise, it is determined that a phase-to-phase fault has occurred in the power grid, and the process proceeds to step S5.

[0057] 3I0>I0set (6)

[0058] Among them, I 0set The setting is based on avoiding the maximum unbalanced current.

[0059] S3. Sort the voltage amplitudes of each phase at the protection installation location, and if the median value is... and minimum value satisfy Then determine the minimum value If a single-phase ground fault occurs in the corresponding phase, proceed to step S4; otherwise, proceed to step S4; where m is 0.5 to 0.7, n is 2 to 4, and U N This is the rated phase voltage amplitude.

[0060] In this embodiment, U N Take as The threshold m is set to 0.5 and n is set to 3.

[0061] S4, if the inter-phase compensation voltage change is at its minimum value The corresponding two-phase phase and the maximum value of the phase compensation voltage change The corresponding phases are all different, and satisfy the following conditions: Then determine If a single-phase ground fault occurs in the corresponding phase, then a two-phase ground fault occurs in the two phases corresponding to the minimum phase-to-phase voltage amplitude at the protection installation location; where i is 4 to 6. High-proportion renewable energy systems have variable operating modes, and the strong short-circuit current on the grid side has a certain boosting effect on the fault phase voltage, which may increase the ratio between the fault phase voltage and the non-fault phase voltage amplitude, thus causing a single-phase fault to be selected as a multi-phase fault. This invention utilizes the compensation voltage change for fault phase selection, playing a phase selection role when phase selection fails in step S3, and has higher sensitivity.

[0062] For example, the minimum value of inter-phase compensation voltage variation The corresponding two-phase phase and the maximum value of the phase compensation voltage change The corresponding phases are all different, which can be understood as: minimum value The two corresponding phases are phase a and phase b, and the maximum value of the phase compensation voltage change is... The corresponding phase is phase c.

[0063] In this embodiment, the threshold i is set to 4.

[0064] S5. Sort the phase-to-phase voltage amplitudes at the protection installation location and determine the two phases corresponding to the minimum phase-to-phase voltage amplitudes that have experienced phase-to-phase faults.

[0065] To further illustrate the effectiveness of the fault phase selection method provided in the embodiments of the present invention, it is now described in detail below with reference to the accompanying drawings and specific examples:

[0066] In this embodiment, the high-proportion new energy power system model experiences a phase A ground fault at point f, the midpoint of the line. The zero-sequence current amplitude of the line relay protection device 5 is as follows: Figure 3 As shown, after a fault, the amplitude quickly reaches 1.2kA after passing through a data window, which is greater than the threshold value of 0.093kA, thus triggering the ground fault phase selection step. The median and minimum values ​​of the phase voltage amplitude at the protection installation location in step S3 are as follows: Figure 4 As shown, and The single-phase grounding fault criterion is met, and it is determined that an A-phase grounding fault has occurred in the power grid.

[0067] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A fault phase selection method applicable to high-voltage transmission lines in high-proportion renewable energy systems, characterized in that, The method includes the following steps: S1. When a line fault occurs, based on the real-time acquired sequence of measured voltage and measured current samples at the protection installation point, calculate the amplitude of each phase voltage and phase-to-phase voltage, the change in phase compensation voltage and phase-to-phase compensation voltage, and the amplitude of zero-sequence current at the protection installation point. S2. If the zero-sequence current amplitude is greater than the threshold value, proceed to step S3; otherwise, proceed to step S5. S3. Sort the voltage amplitudes of each phase at the protection installation location, and if the median value is... and minimum value satisfy Then determine the minimum value If a single-phase ground fault occurs in the corresponding phase, proceed to step S4; otherwise, proceed to step S4; where m is 0.5 to 0.7, n is 2 to 4, and U N This is the rated phase voltage amplitude; S4, if the inter-phase compensation voltage change is at its minimum value The corresponding two-phase phase and the maximum value of the phase compensation voltage change The corresponding phases are all different, and satisfy the following conditions: Then determine If a single-phase ground fault occurs in the corresponding phase, otherwise, it is determined that a two-phase ground fault occurs in the two phases corresponding to the minimum phase-to-phase voltage amplitude at the protection installation location; where i is 4 to 6. S5. Sort the phase-to-phase voltage amplitudes at the protection installation location and determine the two phases corresponding to the minimum phase-to-phase voltage amplitudes that have experienced phase-to-phase faults.

2. The fault phase selection method according to claim 1, characterized in that, In step S1, the sequence of measured voltage and measured current samples obtained in real time at the protection installation point is processed by low-pass filtering and then the phase voltage drop and phase-to-phase voltage drop from the protection installation point to the line setting point are calculated according to the line RL differential equation. The difference between the phase voltage measured at the protection installation point and the phase voltage drop is taken as the phase compensation voltage, and the difference between the phase-to-phase voltage measured at the protection installation point and the phase-to-phase voltage drop is taken as the phase-to-phase compensation voltage.

3. The fault phase selection method according to claim 2, characterized in that, In step S1, the instantaneous value integration algorithm is used to calculate the voltage amplitude of each phase and the voltage amplitude between phases at the protection installation location: in, The phase voltage amplitude, This refers to the phase-to-phase voltage amplitude. To protect the phase voltage measured at the installation location, To protect the phase-to-phase voltage measured at the installation location; k0 is the sampling point corresponding to a certain moment after a line fault occurs, Δt is the sampling interval, T is the time corresponding to a data window, and N is the number of sampling points within a data window.

4. The fault phase selection method according to claim 3, characterized in that, The compensation voltage change is the difference between the instantaneous value at the current moment and the instantaneous value at the two preceding fundamental moments. The formula for calculating the amplitude of the compensation voltage change is: in, The magnitude of the phase compensation voltage change. This represents the amplitude of the phase-to-phase compensation voltage change. For phase compensation voltage, This is the phase-to-phase compensation voltage.

5. A fault phase selection device suitable for high-voltage transmission lines in high-proportion new energy systems, characterized in that, include: The calculation module is used to calculate the phase voltage and phase-to-phase voltage amplitude, phase compensation voltage and phase-to-phase compensation voltage change, and zero-sequence current amplitude at the protection installation point based on the real-time acquired sequence of measured voltage and current sampling values ​​at the protection installation point when a line fault occurs. The first discrimination module is used to perform the following operations: if the zero-sequence current amplitude is greater than the threshold value, the operation of the second discrimination module is executed; otherwise, the operation of the fourth discrimination module is executed. The second discrimination module is used to sort the voltage amplitudes of each phase at the protection installation location, and if the median value is... and minimum value satisfy Then determine the minimum value If a single-phase ground fault occurs in the corresponding phase, then the operation of the third discrimination module is executed; otherwise, m is 0.5 to 0.7, n is 2 to 4, and U N This is the rated phase voltage amplitude; The third discrimination module is used to perform the following operation: if the phase-to-phase compensation voltage change is at its minimum value... The corresponding two-phase phase and the maximum value of the phase compensation voltage change The corresponding phases are all different, and satisfy the following conditions: Then determine If a single-phase ground fault occurs in the corresponding phase, otherwise, it is determined that a two-phase ground fault occurs in the two phases corresponding to the minimum phase-to-phase voltage amplitude at the protection installation location; where i is 4 to 6. The fourth discrimination module is used to sort the phase-to-phase voltage amplitudes at the protection installation location and determine that the two phases corresponding to the minimum phase-to-phase voltage amplitudes have experienced phase-to-phase faults.

6. The fault phase selection device according to claim 5, characterized in that, The calculation module is also used to process the real-time acquired sequence of measured voltage and measured current at the protection installation point through low-pass filtering, and then calculate the phase voltage drop and phase-to-phase voltage drop from the protection installation point to the line setting point based on the line RL differential equation. The difference between the phase voltage measured at the protection installation point and the phase voltage drop is taken as the phase compensation voltage, and the difference between the phase-to-phase voltage measured at the protection installation point and the phase-to-phase voltage drop is taken as the phase-to-phase compensation voltage.

7. The fault phase selection device according to claim 6, characterized in that, The calculation module is also used to calculate the phase voltage and phase-to-phase voltage amplitude at the protection installation location using an instantaneous value integration algorithm: in, The phase voltage amplitude, This refers to the phase-to-phase voltage amplitude. To protect the phase voltage measured at the installation location, To protect the phase-to-phase voltage measured at the installation location; k0 is the sampling point corresponding to a certain moment after a line fault occurs, Δt is the sampling interval, T is the time corresponding to a data window, and N is the number of sampling points within a data window.

8. The fault phase selection device according to claim 7, characterized in that, The calculation module is also used to calculate the compensation voltage change, which is the difference between the instantaneous value at the current moment and the value at the two previous fundamental moments. The formula for calculating the amplitude of the compensation voltage change is: in, The magnitude of the phase compensation voltage change. This represents the amplitude of the phase-to-phase compensation voltage change. For phase compensation voltage, This is the phase-to-phase compensation voltage.

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