A new line protection setting optimization method for power system

Abstract

The application relates to a novel line protection setting optimization method for a power system, wherein by establishing a fault transient model of an equivalent power source of new energy, new energy output fluctuation and fault characteristic change can be included in protection setting calculation, thereby solving the problem of mismatch of traditional fixed setting values under a new energy scene; by construction of a self-adaptive compensation angle calculation model, self-adaptive compensation angle calculation can be carried out, thereby real-time correction of a distance protection action boundary is realized, and the problem of decline of protection sensitivity caused by unstable positive sequence voltage phase on a weakly-fed side of new energy is solved; by a fault distance acceleration protection strategy, the speed of protection can be maximally improved under the premise of ensuring selectivity; by construction of a multi-stage protection collaborative setting model, stage-type distance protection and zero sequence protection can be uniformly optimized, thereby the problem of invalidation of original coordination after new energy access is solved; the application has the advantages of accurate detection, strong applicability and convenient and efficient operation.

Description

Technical Field

[0001] This invention belongs to the field of power line protection technology, specifically relating to a novel method for optimizing line protection settings in power systems. Background Technology

[0002] With the rapid growth of installed capacity of new energy power generation, represented by wind power and photovoltaics, the power system is accelerating its transformation towards a new type of power system with a high proportion of new energy integration. New energy power sources are connected to the grid via power electronic converters, and their fault characteristics differ significantly from those of traditional synchronous generators. Specifically, new energy power sources have limited short-circuit current, output voltage and frequency shifts during faults, and nonlinear changes in the equivalent power source's internal impedance. These new characteristics pose serious challenges to traditional line protection methods based on power frequency steady-state quantities and fixed settings. Currently, traditional line protection setting methods suffer from several problems in practical applications: fixed settings cannot adapt to changes in operating modes, positive sequence voltage polarization distance protection has poor adaptability on weak feeder sides, and high-resistance fault detection capabilities are insufficient. To address these issues, it is essential to develop a new, accurate, widely applicable, convenient, and efficient optimized method for line protection settings in power systems. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a new type of power system line protection setting optimization method that is accurate in detection, highly applicable, convenient and efficient.

[0004] The objective of this invention is achieved as follows: a novel method for optimizing line protection settings in power systems, comprising the following steps: Step 1: Obtain the characteristic parameters of the equivalent renewable energy source of the target transmission line, and based on the above parameters, establish a fault transient equivalent model of the renewable energy source. This model uses the form of a controlled current source in series with equivalent impedance to characterize the output characteristics of the renewable energy source during the fault. The output amplitude of the controlled current source is limited by the fault current limit of the renewable energy source, and the output phase is controlled by the control strategy of the renewable energy source and the voltage phase at the grid connection point. Then, extract the output voltage amplitude, phase, and current limiting characteristics of the renewable energy source during the fault as the basic data for protection setting. Step 2: Based on the positive sequence voltage polarization principle, construct an adaptive compensation angle calculation model. Then, collect the instantaneous values ​​of three-phase voltage and current at the protection installation location to extract the positive sequence voltage component. Subsequently, calculate the adaptive compensation angle based on the fault characteristics of the new energy equivalent power source, and use the adaptive compensation angle to correct the action boundary of the distance protection in real time. Step 3: Collect voltage and current data after the fault occurs, and use the fault location algorithm to calculate the electrical distance between the fault point and the protection installation location. Then, compare the fault distance with the preset distance segment threshold, determine the acceleration factor according to the fault distance segment, and execute the acceleration protection strategy based on the fault distance. Step 4: Optimize the coordination between zero-sequence overcurrent protection and staged distance protection, and construct a multi-level protection coordinated setting model. The multi-level protection coordinated setting model is constrained by the four characteristics of relay protection and takes the matching degree between the protection action range and the action time as the objective function. At the same time, the model is solved by optimization algorithm to output the optimal combination of setting values ​​that meet the constraints. Step 5: Coordinate the full-line fast distance protection method with the inverse time-limited distance protection method. Based on the fault type and fault distance, adaptively switch between the full-line fast distance protection method and the inverse time-limited distance protection method, and output the optimized protection setting scheme.

[0005] Furthermore, in step 2, the adaptive compensation angle is calculated using the square method, and is dynamically updated by identifying the phase angle of the equivalent power supply impedance of the new energy source in real time online.

[0006] Furthermore, the fault location in step 3 can be accurately calculated using a dual-end location method that is resistant to load and system oscillation.

[0007] Furthermore, the four requirements for relay protection in step 4 are selectivity, speed, sensitivity, and reliability.

[0008] Furthermore, the optimization algorithm in step 4 is either a particle swarm optimization algorithm or a genetic algorithm.

[0009] Furthermore, the protection setting scheme in step 5 includes the following: impedance setting value and operating time limit of each protection segment, adjustment range and correction coefficient of adaptive compensation angle, segmented threshold and acceleration factor of fault distance acceleration strategy, setting value and coordination relationship of each segment of zero-sequence protection, switching logic and parameters of full-line fast distance protection and inverse time segment distance protection, high-resistance fault identification threshold and acceleration zero-sequence protection parameters, direction discrimination threshold value and adaptive adjustment coefficient.

[0010] The beneficial effects of this invention are as follows: By establishing a fault transient model of an equivalent power source for new energy, this invention can incorporate the power output fluctuations and fault characteristic changes of new energy sources into the protection setting calculation, thereby solving the problem of mismatch between traditional fixed setting values ​​and new energy scenarios, and significantly improving the adaptability of protection settings. This invention constructs an adaptive compensation angle calculation model based on the positive sequence voltage polarization principle, which can calculate the adaptive compensation angle and thereby correct the action boundary of the distance protection in real time. This effectively solves the problem of reduced protection sensitivity caused by the unstable positive sequence voltage phase on the weak feeder side of new energy sources, and improves the reliability of the distance protection. This invention employs an accelerated protection strategy based on fault distance and sets acceleration factors in segments according to the location of the fault point, which can maximize the speed of protection while ensuring selectivity. This invention, through the construction of a multi-level protection collaborative setting model, can uniformly optimize staged distance protection and zero-sequence protection, thereby solving the problem of the failure of the original coordination relationship after the access of new energy sources, and ensuring the coordinated cooperation of protection at all levels in terms of action range and time limit; at the same time, through the coordinated cooperation of full-line fast distance protection and inverse time-limited distance protection, adaptive switching of protection methods under different fault scenarios can be achieved; in summary, this invention has the advantages of accurate detection, strong applicability, and convenience and efficiency. Detailed Implementation

[0011] The present invention will now be further described.

[0012] Example: A novel method for optimizing line protection settings in power systems, comprising the following steps: Step 1: Obtain the characteristic parameters of the equivalent renewable energy source of the target transmission line, and based on the above parameters, establish a fault transient equivalent model of the renewable energy source. This model uses the form of a controlled current source in series with equivalent impedance to characterize the output characteristics of the renewable energy source during the fault. The output amplitude of the controlled current source is limited by the fault current limit of the renewable energy source, and the output phase is controlled by the control strategy of the renewable energy source and the voltage phase at the grid connection point. Then, extract the output voltage amplitude, phase, and current limiting characteristics of the renewable energy source during the fault as the basic data for protection setting. Step 2: Based on the positive sequence voltage polarization principle, an adaptive compensation angle calculation model is constructed. Then, the instantaneous values ​​of three-phase voltage and current at the protection installation point are collected to extract the positive sequence voltage component. Subsequently, based on the fault characteristics of the new energy equivalent power source, the adaptive compensation angle is calculated by the square method. The action boundary of the distance protection is corrected and dynamically updated in real time by using the online real-time identification of the impedance phase angle of the new energy equivalent power source. Step 3: Collect voltage and current data after the fault occurs, and use the fault location algorithm to calculate the electrical distance between the fault point and the protection installation location. Then, compare the fault distance with the preset distance segment threshold, and determine the acceleration factor according to the fault distance segment to execute the accelerated protection strategy based on the fault distance. Among them, the fault location can be accurately calculated using the double-end location method that resists load and system oscillation. Step 4: Optimize the coordination between zero-sequence overcurrent protection and staged distance protection, and construct a multi-level protection coordinated setting model. This model is constrained by the four characteristics of relay protection, with the matching degree between the protection's operating range and operating time as the objective function. The four characteristics of relay protection are selectivity, speed, sensitivity, and reliability. The model is solved using a particle swarm optimization algorithm or a genetic algorithm, outputting the optimal combination of setting values ​​that satisfies the constraints. Step 5: Coordinate the full-line fast distance protection method with the inverse-time distance protection method. Based on the fault type and fault distance, adaptively switch between the full-line fast distance protection method and the inverse-time distance protection method, and output the optimized protection setting scheme. The protection setting scheme includes the following: impedance setting value and operating time of each protection segment, adjustment range and correction coefficient of adaptive compensation angle, segment threshold and acceleration factor of fault distance acceleration strategy, setting value and coordination relationship of each segment of zero-sequence protection, switching logic and parameters of full-line fast distance protection and inverse-time distance protection, high-resistance fault identification threshold and acceleration zero-sequence protection parameters, direction discrimination threshold value and adaptive adjustment coefficient.

[0013] In use, this invention first acquires the characteristic parameters of the equivalent renewable energy source of the target transmission line to establish a fault transient equivalent model of the renewable energy source. Then, this model incorporates renewable energy output fluctuations and fault characteristic changes into the protection setting calculation, thus solving the mismatch problem of traditional fixed setting values ​​in renewable energy scenarios and improving the adaptability of the protection settings. Next, an adaptive compensation angle calculation model is constructed based on the positive sequence voltage polarization principle to calculate the adaptive compensation angle, thereby correcting the action boundary of the distance protection in real time. This avoids the problem of decreased protection sensitivity due to unstable positive sequence voltage phase on the weak renewable energy feed side, improving the reliability of the distance protection. Then, voltage and current data after a fault occur are collected, and the electrical distance between the fault point and the protection installation location is calculated using a fault location algorithm. The fault distance is then compared with a preset distance segment threshold, and an acceleration factor is determined based on the fault distance segment. This maximizes the protection's speed of action while executing an accelerated protection strategy based on the fault distance. Finally, zero-sequence overcurrent protection and staged distance protection are optimized for coordination, and a multi-level protection collaborative setting model is constructed. This addresses the issue of the failure of existing coordination relationships after the integration of new energy sources, ensuring coordinated cooperation among protection systems at all levels in terms of operating range and time limit. In this process, the multi-level protection collaborative setting model is constrained by the selectivity, speed, sensitivity, and reliability requirements of relay protection, with the matching degree between protection operating range and operating time limit as the objective function. It is solved using particle swarm optimization or genetic algorithms to output the optimal combination of setting values ​​that satisfy the constraints. Finally, through the coordinated cooperation of full-line fast distance protection and inverse time distance protection, based on the fault type and fault distance, it completes the protection settings under different fault scenarios. The invention provides adaptive switching of protection methods and outputs an optimized protection setting scheme, which includes the following: impedance setting values ​​and operating time limits for each protection segment, adjustment range and correction coefficient of adaptive compensation angle, segmented threshold and acceleration factor of fault distance acceleration strategy, setting values ​​and coordination relationships of each segment of zero-sequence protection, switching logic and parameters of full-line fast distance protection and inverse time segment distance protection, high-resistance fault identification threshold and acceleration zero-sequence protection parameters, direction discrimination threshold value and adaptive adjustment coefficient. In summary, this invention has the advantages of accurate detection, strong applicability, and convenient and efficient operation.

[0014] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A novel method for optimizing line protection settings in power systems, characterized in that, Includes the following steps: Step 1: Obtain the characteristic parameters of the equivalent renewable energy source of the target transmission line, and based on the above parameters, establish a fault transient equivalent model of the renewable energy source. This model uses the form of a controlled current source in series with equivalent impedance to characterize the output characteristics of the renewable energy source during the fault. The output amplitude of the controlled current source is limited by the fault current limit of the renewable energy source, and the output phase is controlled by the control strategy of the renewable energy source and the voltage phase at the grid connection point. Then, extract the output voltage amplitude, phase, and current limiting characteristics of the renewable energy source during the fault as the basic data for protection setting. Step 2: Based on the positive sequence voltage polarization principle, construct an adaptive compensation angle calculation model. Then, collect the instantaneous values ​​of three-phase voltage and current at the protection installation location to extract the positive sequence voltage component. Subsequently, calculate the adaptive compensation angle based on the fault characteristics of the new energy equivalent power source, and use the adaptive compensation angle to correct the action boundary of the distance protection in real time. Step 3: Collect voltage and current data after the fault occurs, and use the fault location algorithm to calculate the electrical distance between the fault point and the protection installation location. Then, compare the fault distance with the preset distance segment threshold, determine the acceleration factor according to the fault distance segment, and execute the acceleration protection strategy based on the fault distance. Step 4: Optimize the coordination between zero-sequence overcurrent protection and staged distance protection, and construct a multi-level protection coordinated setting model. The multi-level protection coordinated setting model is constrained by the four characteristics of relay protection and takes the matching degree between the protection action range and the action time as the objective function. At the same time, the model is solved by optimization algorithm to output the optimal combination of setting values ​​that meet the constraints. Step 5: Coordinate the full-line fast distance protection method with the inverse time-limited distance protection method. Based on the fault type and fault distance, adaptively switch between the full-line fast distance protection method and the inverse time-limited distance protection method, and output the optimized protection setting scheme.

2. The novel power system line protection setting optimization method as described in claim 1, characterized in that: In step 2, the adaptive compensation angle is calculated using the square method, and is dynamically updated by identifying the phase angle of the equivalent power supply impedance of the new energy source in real time.

3. The novel power system line protection setting optimization method as described in claim 1, characterized in that: The fault location in step 3 can be accurately calculated using a double-ended location method that is resistant to load and system oscillation.

4. The novel power system line protection setting optimization method as described in claim 1, characterized in that: The four requirements for relay protection in step 4 are selectivity, speed, sensitivity, and reliability.

5. The novel power system line protection setting optimization method as described in claim 1, characterized in that: The optimization algorithm in step 4 is either particle swarm optimization or genetic algorithm.

6. The novel power system line protection setting optimization method as described in claim 1, characterized in that: The protection setting scheme in step 5 includes the following: impedance setting value and operating time limit of each protection segment, adjustment range and correction coefficient of adaptive compensation angle, segment threshold and acceleration factor of fault distance acceleration strategy, setting value and coordination relationship of each segment of zero-sequence protection, switching logic and parameters of full-line fast distance protection and inverse time segment distance protection, high impedance fault identification threshold and acceleration zero-sequence protection parameters, direction discrimination threshold value and adaptive adjustment coefficient.