Adaptive evaluation method for incremental differential protection of new energy delivery system and computer storage medium

Abstract

The invention relates to the technical field of differential protection, and provides an adaptive evaluation method for incremental differential protection of a new energy delivery system and a computer storage medium. The data in the line comprises an included angle between power supply potentials of a new energy side and a system side, a short-circuit current of the system side and a rated current of the new energy side; then the operation data are substituted into an established braking risk assessment equation, if the equation is met, it is indicated that the incremental differential motion of the new energy delivery system can act correctly, and if not, the operation refusal risk exists; wherein the braking risk assessment equation is obtained according to an increment differential equation and the relation between the current after the system side fault and the load current before the new energy side fault. According to the method, the risk of action delay or action rejection of differential protection is effectively avoided, and the reliability of line differential protection is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of differential protection, and in particular to an adaptability evaluation method and a computer storage medium for incremental differential protection of a new energy transmission system. Background Art

[0002] Differential protection is the main protection for current high-voltage power grids. Incremental differential is a type of differential protection. Incremental differential uses the current change before and after the fault to construct protection, which can eliminate the influence of load current and is more sensitive than traditional differential protection methods.

[0003] With the rapid development of new energy photovoltaic and wind power in my country, the installed capacity of new energy is constantly increasing. However, the power supply characteristics of new energy are very different from those of traditional synchronous power supplies, showing the characteristics of limited amplitude and controlled phase angle, which has an adverse effect on the sensitivity of incremental differential protection. In extreme cases, the incremental differential protection may even refuse to operate, threatening the safety of the power grid. Therefore, a method that can evaluate the adaptability of incremental differential protection is needed.

[0004] In the prior art, the accuracy of the differential protection method for the new energy transmission line is low, and the influence of the characteristics of the limited amplitude and controlled phase angle of the new energy power source on the sensitivity of the differential protection is not taken into account. For example, the invention patent publication with the publication number CN115632384A proposes a method, device and equipment for differential protection of new energy transmission lines. The application mentions that the fault current in the new energy transmission line is difficult to be continuously greater than the braking current or the differential current threshold, resulting in delays or even refusal of differential protection. Therefore, the application samples the differential current data in the line at a fixed time interval, and counts the sampling points that meet the differential current to meet the differential protection criterion. At the same time, the incremental count value is calculated based on the duration of the differential current first meeting the differential protection criterion and the duration of the differential current first not meeting the differential protection criterion. When the sum of the incremental count value and the number of sampling points reaches the threshold, it is determined to perform the differential protection action. However, the application does not take into account that due to the characteristics of the new energy power source itself, there may be a situation where the differential current does not meet the differential protection criteria but the system has already failed. Therefore, this method cannot completely avoid the situation where the differential protection is delayed or even refuses to operate. Summary of the invention

[0005] The purpose of the present invention is to provide an adaptability evaluation method and computer storage medium for incremental differential protection of a new energy transmission system, so as to solve the technical problem that the risk of refusal to operate of a new energy transmission system cannot be evaluated in the prior art, resulting in delayed action or even refusal of differential protection in the new energy transmission system.

[0006] In order to solve the above technical problems, the present invention provides an adaptability evaluation method for incremental differential protection of a new energy transmission system, the steps comprising:

[0007] 1) Obtaining the operating data of the new energy transmission system, the operating data including: the angle between the power supply potentials on the new energy side and the system side, the short-circuit current on the system side and the rated current on the new energy side;

[0008] 2) Substitute the operating data into the established braking risk assessment equation. If the braking risk assessment equation is satisfied, it means that the incremental differential of the new energy delivery system can operate correctly, otherwise there is a risk of refusal to operate; the braking risk assessment equation is obtained by the incremental differential equation and the relationship between the current after the fault on the system side and the load current before the fault on the new energy side.

[0009] Furthermore, the braking risk assessment equation is:

[0010]

[0011] Among them, α is the angle between the potential of the new energy side and the system side, is the current angle before and after the fault on the new energy side, k scr It is the ratio of the short-circuit current on the system side to the rated current of the new energy station. is the determination equation, k is the braking coefficient.

[0012] Furthermore, when there is a risk of failure of differential protection, the installed capacity of the renewable energy side is reduced and / or

[0013] Or increase the short-circuit capacity on the system side so that the operating data of the new energy delivery system after adjustment meets the braking risk assessment equation.

[0014] Furthermore, when judging whether the braking risk assessment equation is satisfied, the operating data is substituted into the established braking risk assessment equation to obtain a variation curve of the current angle before and after the fault on the new energy side, and the minimum point is found from the variation curve. The minimum point is compared with the braking coefficient k to judge whether the new energy delivery system satisfies the braking risk assessment equation.

[0015] Furthermore, the incremental differential equation is:

[0016]

[0017] in, is the sum of the current mutations on both sides of the line, k is the braking coefficient, is the synthetic braking current, is the sudden change of current on the system side, is the sudden change of current on the new energy side.

[0018] Furthermore, the braking coefficient k∈[0.5, 0.8].

[0019] A computer storage medium stores a computer program to implement the adaptability evaluation method for incremental differential protection of a new energy transmission system as described above.

[0020] The beneficial effects of the present invention are as follows: as an improved invention, the present invention combines the characteristics of new energy power sources, derives a braking risk assessment equation based on the incremental differential equation and the relationship between the current after the system side fault and the load current before the new energy side fault, and uses the braking risk assessment equation to determine whether there is a risk of refusal to operate in the new energy transmission system. This method can realize the incremental differential protection risk assessment of the new energy transmission system, determine whether there is a risk of refusal to operate, effectively avoid delayed action or refusal of differential protection, and improve the reliability of line differential protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Send out line models for new energy sources;

[0022] Figure 2 is the voltage vector diagram of the incremental differential;

[0023] Figure 3 For example 1 The value of The change curve of

[0024] Figure 4 For Example 2 The value of The change curve. DETAILED DESCRIPTION

[0025] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0026] The present invention uses data in the system lines to calculate whether there is a risk of incremental differential protection rejection in the new energy transmission system, effectively avoiding the risk of delayed action or rejection of differential protection due to the characteristics of the new energy power source itself.

[0027] Embodiment of the adaptability evaluation method of incremental differential protection of new energy transmission system

[0028] In the renewable energy transmission system, due to the characteristics of limited amplitude and controlled phase angle of renewable energy power sources, the incremental differential protection method commonly used in traditional circuit systems will have low sensitivity when applied to the renewable energy transmission system, and there is even a risk of refusal to operate.

[0029] The typical model of new energy transmission line is shown in the figure below: Figure 1As shown, in the traditional circuit, when the sudden change in the circuit satisfies the incremental differential equation, the incremental differential protection will be triggered.

[0030] In the new energy transmission line, the incremental differential equations are:

[0031]

[0032] in, is the sum of the current mutations on both sides of the line, I set is the differential constant, k is the braking coefficient, generally k = 0.5 ~ 0.8, It is the difference between the sudden change in current on the system side and the sudden change in current on the new energy side.

[0033] In traditional circuits, the incremental differential protection is triggered only when both equations (1) and (2) are satisfied. In the new energy transmission system, equation (1) can be directly applied to the incremental differential protection. The specific analysis is as follows:

[0034]

[0035] in, and is the current after the fault on both sides of the transmission line, and is the load current on both sides before the fault, that is and For the through current, it satisfies: therefore: It can be seen that the differential current of the incremental differential is exactly the same as the differential current of the traditional differential, so the adaptability evaluation of the traditional differential current setting can be directly used for the adaptability evaluation of the incremental differential setting. After the new energy is connected to the line, formula (1) can be used to calculate whether the line measured differential current meets the setting.

[0036] For equation (2), when both sides of the line are traditional power lines, due to the inertia support of the synchronous generator, it is considered to remain unchanged at the beginning of the fault. and Approximately same direction, differential current Very large, and the braking current Very small, the amplitude ratio of the two is much larger than the braking coefficient k.

[0037] However, for the renewable energy transmission line, due to the influence of the converter control strategy of the renewable energy power source, during the fault period It presents the fault characteristics of limited amplitude and controlled phase angle. When the angle changes to a certain extent, it may cause Less than This causes the differential protection to fail to operate.

[0038] Use Figure 2 The incremental differential voltage vector diagram shown analyzes the currents in the new energy transmission line. is the sudden change of the current on the system side. When a fault occurs on the system side, the current after the fault on the system side The direction is fixed, according to the system side pre-fault current Direction and system side post-fault current The direction of the system side current mutation can be obtained Since the short-circuit current direction is controlled before and after the new energy failure, Figure 2 There are three short-circuit current situations listed: is the current mutation amount on the new energy side corresponding to these three situations.

[0039] and are the power supply potentials on the new energy side and the system side, and are the voltages measured at the protection installations on the new energy side and the system side, respectively; α is the current collected by the protection on the new energy side and the system side, and the voltage angle measured at the voltage transformer installation, which can be approximately taken as the angle between the power potentials on both sides, that is, the power angle of the power sources on both sides. The power angle of the line can be obtained in real time through power flow calculation in the circuit system. Among them, the power source on the new energy side can be a power source with a converter such as photovoltaic, wind turbine, and energy storage, and the power source on the system side is a power source with synchronous machine characteristics. For the convenience of calculation, the resistance in the transmission line is ignored, and the transmission line is considered to be purely inductive, with a positive sequence impedance angle of 90°.

[0040] by As the phase reference, let:

[0041]

[0042] From this we can conclude that:

[0043]

[0044]

[0045] Due to the current limiting effect of the power electronic device on the renewable energy side, the fault current provided by the power supply on the renewable energy side does not change much compared to before the fault. The fault current on the renewable energy side can be approximately considered as:

[0046]

[0047] in, is the angle between the current after the fault on the new energy side and the current before the fault. Due to the regulation of the converter on the new energy side, the angle between the current after the fault on the new energy side and the current before the fault is The value range of cannot be determined, so the maximum range [0°, 360°] is taken.

[0048] Therefore, the incremental differential braking coefficient equation can be written as follows:

[0049]

[0050] Definition of new energy short circuit ratio k scr as follows:

[0051]

[0052] Among them, S ac is the system short-circuit capacity of the AC grid on the system side, P w is the installed capacity of new energy, U n is the rated voltage of the system, I sf is the short-circuit current of the S-side system, I wn It is the rated current of the new energy station on the W side.

[0053] Assume that the new energy source is in full power state before the fault, that is,

[0054] so:

[0055]

[0056] Further, there are:

[0057]

[0058] Among them, only the angle between the current after the fault and the current before the fault on the new energy side is One parameter is a variable, and the values ​​of the remaining parameters can be obtained from the new energy delivery system.

[0059] Braking risk assessment equation for:

[0060]

[0061] If the braking risk assessment equation satisfies:

[0062]

[0063] Then the braking equation of the incremental differential can operate correctly, otherwise there is a risk of the incremental differential refusing to operate.

[0064] Based on the above analysis, this application proposes an adaptability evaluation method for incremental differential protection of a renewable energy transmission system to evaluate the risk of incremental differential protection rejection. The specific steps include:

[0065] First, in Figure 1 The data in the line are obtained before the operation of the new energy transmission system shown, wherein the data in the line include: the angle between the power supply potential of the new energy side and the system side, the short-circuit current of the system side and the rated current of the new energy station. The new energy side refers to the new energy station side.

[0066] Substitute the operating data into the established braking risk assessment equation. If the equation is satisfied, it means that the incremental differential of the new energy transmission system can operate correctly. Otherwise, there is a risk of refusal to operate. At this time, it is necessary to adjust the parameters of the new energy transmission system to prevent the differential protection from refusal to operate.

[0067] According to the above, the braking risk assessment equation is derived from equation (2) in the incremental differential equation group combined with the actual situation of the renewable energy transmission system and the renewable energy short-circuit ratio (i.e., the relationship between the current after the fault on the system side and the load current before the fault on the renewable energy side).

[0068] The braking risk assessment equation is:

[0069]

[0070] Among them, α is the angle between the potential of the new energy side and the system side, is the current angle before and after the fault on the new energy side. Due to the regulation of the converter on the new energy side, the current angle before and after the fault on the new energy side is The value range of cannot be determined, so the maximum range is taken k scr It is the ratio of the short-circuit current on the system side to the rated current of the new energy station. When the minimum absolute value of the braking risk assessment equation is less than the braking coefficient of the incremental differential equation, the parameters of the new energy transmission system are adjusted to prevent the differential protection from refusing to operate.

[0071] Subsequently, the operating data is substituted into the established braking risk assessment equation to obtain a variation curve of the current angle before and after the fault on the new energy side, the minimum point is found from the variation curve, and the minimum point is compared with the braking coefficient k to realize the judgment of whether the new energy transmission system meets the braking risk assessment equation.

[0072] In order to obtain the braking risk assessment equation more intuitively and accurately The minimum absolute value, in this embodiment, the braking risk assessment equation And the corresponding new energy short-circuit ratio k in this refusal risk assessment scr The angle α between the electric potential on the new energy side and the system side is input into the function image drawing software to obtain the current angle before and after the fault on the new energy side. Take the braking risk assessment equation from 0° to 360° The change curve can be intuitively obtained through the change curve The minimum value of .

[0073] As another embodiment, it can be directly calculated by other software The minimum value of, or by taking the derivative, calculate the reciprocal zero point at The value in gets the minimum value.

[0074] Specifically, according to the formula: It can be seen that the parameter that affects the short-circuit ratio of renewable energy is the system short-circuit capacity S of the AC power grid on the system side. ac and the installed capacity of new energy sources P w By increasing the installed capacity of new energy sources P w Adjust and reduce the short-circuit capacity S on the system side ac Adjust to increase, or only adjust the system short-circuit capacity S of the system side AC power grid ac Reduce or only adjust the installed capacity P of the new energy side w Increase so that the minimum absolute value of the braking risk assessment equation is greater than the braking coefficient of the incremental differential equation.

[0075] When the minimum absolute value of the braking risk assessment equation is greater than the braking coefficient of the incremental differential equation, the system line protects the system according to the incremental differential equation. When the situation in the system line satisfies the incremental differential equation, the system is differentially protected. That is, when the differential current in the new energy transmission system The absolute value is greater than the differential setting I set , at the same time, the differential current The absolute value of the braking coefficient is greater than the sum of the braking current The product of the absolute values ​​of and , the new energy transmission system triggers the differential protection action. Among them, the synthetic braking current It is the difference between the sudden change in current on the system side and the sudden change in current on the new energy side.

[0076] The specific steps of the incremental differential protection method proposed in this application are more intuitively demonstrated through the following two examples.

[0077] In Example 1, the short-circuit ratio k of the renewable energy transmission system is calculated based on the data in the renewable energy transmission system. scr =1.5, the angle between the potential of the new energy side and the system side is α = 20°, The value of the current angle before and after the fault on the new energy side The change curve of Figure 3 As shown by Figure 3 It can be seen that the current angle before and after the fault on the new energy side is hour, At this time, as long as the braking coefficient k of the incremental differential is less than 0.968, there is no risk of refusal to operate the incremental differential, and the differential protection is triggered when the new energy delivery system satisfies the incremental differential equation.

[0078] In Example 2, the short-circuit ratio k of the renewable energy transmission system is calculated based on the data in the renewable energy transmission system. scr =1.0, the angle between the potential of the new energy side and the system side is α=10°, The value of the current angle before and after the fault on the new energy side The change curve of Figure 4 As shown by Figure 4 It can be seen that the current angle before and after the fault on the new energy side is hour, Since the braking coefficient k is generally in the range of 0.5 to 0.8, the new energy delivery system has the risk of refusal to operate. At this time, it is only necessary to reduce the installed capacity of the new energy side or increase the short-circuit capacity of the system side, or adjust both at the same time, so that the adjusted operating data meets the braking risk assessment equation.

[0079] Computer Storage Medium Embodiments

[0080] The present invention provides a computer storage medium, in which a computer program is stored. The computer program includes a data collection module, a data analysis module and a control module.

[0081] The data collection module is mainly used to collect data in the new energy transmission system line. The data analysis module is mainly used to calculate and determine whether there is a differential refusal risk in the new energy transmission system. If there is a risk, the information is output to the control module so that the control module can adjust the parameters of the new energy transmission system to eliminate the refusal risk.

[0082] The computer storage medium embodiments described above are merely illustrative, and the module division is merely a logical function division. There may be other division methods in actual implementation, such as combining or integrating multiple modules into another system, or some features may be ignored or not executed.

[0083] The specific implementation process has been described in detail in the method embodiment and will not be repeated here.

Claims

1. A method for evaluating the adaptability of incremental differential protection of a new energy transmission system, characterized in that the steps include: 1) Obtaining the operating data of the new energy transmission system, the operating data including: the angle between the power supply potentials on the new energy side and the system side, the short-circuit current on the system side and the rated current on the new energy side; 2) Substitute the operating data into the established braking risk assessment equation. If the braking risk assessment equation is satisfied, it means that the incremental differential of the new energy delivery system can operate correctly, otherwise there is a risk of refusal to operate; the braking risk assessment equation is obtained by the incremental differential equation and the relationship between the current after the fault on the system side and the load current before the fault on the new energy side.

2. The adaptability evaluation method for incremental differential protection of a new energy transmission system according to claim 1 is characterized in that: The braking risk assessment equation is: Among them, α is the angle between the potential of the new energy side and the system side, is the current angle before and after the fault on the new energy side, k scr It is the ratio of the short-circuit current on the system side to the rated current of the new energy station. is the determination equation, k is the braking coefficient.

3. The adaptability evaluation method for incremental differential protection of a new energy transmission system according to claim 1 is characterized in that: When there is a risk of refusal to operate of the differential protection, the installed capacity on the renewable energy side is reduced and / or the short-circuit capacity on the system side is increased so that the operating data of the renewable energy transmission system after adjustment satisfies the braking risk assessment equation.

4. The adaptability evaluation method for incremental differential protection of a new energy transmission system according to claim 2 is characterized in that: When judging whether the braking risk assessment equation is satisfied, the operating data is substituted into the established braking risk assessment equation to obtain a variation curve of the current angle before and after the fault on the new energy side, the minimum point is found from the variation curve, and the minimum point is compared with the braking coefficient k to judge whether the new energy delivery system satisfies the braking risk assessment equation.

5. The adaptability evaluation method of incremental differential protection of a new energy transmission system according to claim 1 is characterized in that: The incremental differential equation is: in, is the sum of the current mutations on both sides of the line, k is the braking coefficient, is the synthetic braking current, is the sudden change of current on the system side, is the sudden change of current on the new energy side.

6. The adaptability evaluation method for incremental differential protection of a new energy transmission system according to claim 2 is characterized in that: The braking coefficient k∈[0.5, 0.8].

7. A computer storage medium, characterized in that: The computer storage medium stores a computer program to implement the adaptability assessment method for incremental differential protection of a new energy transmission system as described in any one of claims 1 to 6 above.

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