Impedance-based generator self-excitation protection method and device
By calculating the terminal impedance and system capacitive reactance of a small hydropower station generator in real time, determining the self-excitation and delaying the generator, the problems of high cost and power loss in the existing technology are solved, and efficient self-excitation protection is achieved.
Patent Information
- Application Number
- CN202510425814.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-07
- Publication Date
- 2025-07-08
AI Technical Summary
The self-excitation protection methods of existing small hydropower stations have problems such as high cost and easy power loss.
By obtaining the generator's terminal voltage and terminal current, the computer terminal impedance and the system capacitive reactance in real time, combining the generator's direct axis synchronous reactance to determine whether self-excitation occurs, and de-arrange the generator delays after determining that self-excitation occurs.
There is no need to add additional reactors and switching equipment, which reduces costs, avoids power loss, improves power generation efficiency, and avoids the impact on ecological flow.
Smart Images
Figure CN120280863A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of hydropower stations, and particularly relates to a generator self-excitation protection method and device based on impedance. Background Art
[0002] Due to environmental protection requirements, some hydropower stations have built ecological small hydropower stations, and these ecological small hydropower stations are often connected to the grid through their main power stations. In addition, some small hydropower stations are also connected to the grid through relatively large nearby hydropower stations. As a result, a situation has emerged: small hydropower stations are connected to the grid connection channels of nearby large hydropower stations and share their transmission lines and grid interfaces. This mode is similar to the "surplus power grid connection" method of distributed photovoltaic power stations, that is, small hydropower stations give priority to self-use or supply local loads, and the remaining power is transmitted to the main power grid through the facilities of large hydropower stations. Since the capacity of the generators of small hydropower stations is small, while the outgoing line voltage level of large power stations is high and the line is long, the charging power is relatively large. When all the units of large hydropower stations are out of operation and the outgoing line at the opposite end trips, it is easy to cause the units of small hydropower stations to operate with a high voltage and an empty long line, thereby causing self-excitation overvoltage of the units of small hydropower stations and resulting in damage to the generator sets of small hydropower stations.
[0003] For the above problems, the existing solutions are as follows: The first solution is to configure reactors. By adding high-voltage reactor intervals on long lines or buses, or connecting low-voltage reactors in parallel on the outgoing lines of small hydropower stations, the charging power on high-voltage long lines is absorbed by the reactors, thereby achieving the purpose of suppressing self-excitation of small hydropower stations. The second solution is to configure a tripping connection circuit. By monitoring the grid connection switches of the units of large hydropower stations, if all the units of large hydropower stations are out of operation and all the grid connection switches of the units of large hydropower stations are disconnected, then the switches connecting small hydropower stations to large hydropower stations are instantaneously tripped to avoid the operating condition of small units operating with a high voltage and a long line.
[0004] In the first solution, although the problem of self-excitation overvoltage can be solved from the mechanism by configuring reactors, additional reactors and switching equipment need to be added, increasing the cost and affecting the commissioning time of the unit to a certain extent. In the second solution, by monitoring that all grid-connected switches of the large power station are disconnected, the switches connecting the small hydropower station to the large power station are tripped instantaneously. This tripping scheme adopts the measure of pre-control operation mode to avoid the operation mode of the small hydropower station operating with a high-voltage long line under no-load. Although it can avoid the self-excitation situation caused by the small hydropower station operating with a high-voltage long line under no-load alone, it also reduces the situation of the small hydropower station operating in parallel with a high-voltage long line. Because the small hydropower station can operate safely when operating in parallel with a high-voltage long line and will not generate self-excitation phenomenon, and self-excitation phenomenon will only occur when operating with a high-voltage long line under no-load. However, due to the pre-control operation mode measure, the small hydropower station is also tripped after all units of the large hydropower station are disconnected from the grid, which causes the small hydropower station to be unable to generate electricity and operate in parallel, resulting in power loss. At the same time, some small hydropower stations also undertake the task of ecological flow. Once they are disconnected from the grid, it will also affect the discharge of ecological flow. Summary of the Invention
[0005] The present invention aims to solve the problems of high cost and easy power loss existing in the existing self-excitation protection methods for small hydropower stations, and proposes a generator self-excitation protection method and device based on impedance.
[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:
[0007] In a first aspect, the present invention provides a generator self-excitation protection method based on impedance. The generator is a generator of a first hydropower station, and the first hydropower station is connected to the grid through a second hydropower station. The method includes:
[0008] Obtain the terminal voltage and terminal current of the generator in real time;
[0009] Calculate the terminal impedance according to the terminal voltage and terminal current, and calculate the system capacitive reactance according to the terminal impedance and the equivalent resistance on the external system side of the generator;
[0010] Judge whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator, and determine whether to disconnect the generator according to the judgment result.
[0011] Further, the calculation formula of the terminal impedance is as follows:
[0012]
[0013] Wherein, Z represents the terminal impedance, TV represents the terminal voltage, and CT represents the terminal current.
[0014] Furthermore, the calculation formula for the system capacitive reactance is as follows:
[0015] Z = R + jX;
[0016] Wherein, X represents the system capacitive reactance, Z represents the terminal impedance of the machine, R represents the equivalent resistance on the external system side of the generator, and j represents the imaginary unit.
[0017] Furthermore, determining whether self-excitation occurs based on the system capacitive reactance and the direct-axis synchronous reactance of the generator includes:
[0018] If -X > X d , it is determined that self-excitation does not occur in the generator; if 0 > X > -X d , it is determined that self-excitation will occur in the generator; wherein, X represents the system capacitive reactance, and X d represents the direct-axis synchronous reactance of the generator.
[0019] Furthermore, determining whether to disconnect the generator according to the judgment result includes:
[0020] After it is determined that self-excitation will occur in the generator, the generator is disconnected after a preset time delay, and an alarm signal is sent.
[0021] Furthermore, the preset time delay is 0.2 seconds.
[0022] In a second aspect, the present invention provides a generator self-excitation protection device based on impedance. The generator is a generator of the first hydropower station, and the first hydropower station is connected to the grid through the second hydropower station. The device includes:
[0023] A sensor module for real-time acquisition of the terminal voltage and terminal current of the generator;
[0024] A calculation module for calculating the terminal impedance according to the terminal voltage and terminal current, and calculating the system capacitive reactance according to the terminal impedance and the equivalent resistance on the external system side of the generator;
[0025] A control module for determining whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator, and determining whether to disconnect the generator according to the judgment result.
[0026] Furthermore, the calculation formula for the terminal impedance is as follows:
[0027]
[0028] The calculation formula for the system capacitive reactance is as follows:
[0029] Z = R + jX;
[0030] Among them, Z represents the terminal impedance, TV represents the terminal voltage, CT represents the terminal current, X represents the system capacitive reactance, R represents the equivalent resistance on the external system side of the generator, and j represents the imaginary unit.
[0031] Furthermore, determining whether self-excitation occurs based on the system capacitive reactance and the direct-axis synchronous reactance of the generator includes:
[0032] If -X > X d , it is determined that self-excitation does not occur in the generator; if 0 > X > -X d , it is determined that self-excitation will occur in the generator; where X represents the system capacitive reactance, and X d represents the direct-axis synchronous reactance of the generator.
[0033] Furthermore, determining whether to disconnect the generator according to the judgment result includes:
[0034] After it is determined that self-excitation will occur in the generator, the generator is disconnected after a preset time delay and an alarm signal is sent, and the preset time delay is 0.2 seconds.
[0035] The beneficial effects of the present invention are as follows: The impedance-based generator self-excitation protection method and device provided by the present invention calculate the system capacitive reactance, judge whether self-excitation occurs in the generator according to the magnitude of the system capacitive reactance and the direct-axis synchronous impedance of the generator, and disconnect the generator according to the judgment result. The present invention does not require additional reactors and switching equipment, reducing costs. Moreover, the present invention judges whether self-excitation occurs from the mechanism of self-excitation itself. When a small hydropower station operates in parallel with a high-voltage long line, the corresponding generator will not be disconnected, thereby avoiding power loss, improving power generation efficiency, and also avoiding the impact on ecological flow discharge. Description of the Drawings
[0036] Figure 1 It is a schematic flowchart of an impedance-based generator self-excitation protection method provided by the embodiment;
[0037] Figure 2 It is a schematic diagram of the principle of an impedance-based generator self-excitation protection method provided by the embodiment;
[0038] Figure 3 It is a schematic structural diagram of an impedance-based generator self-excitation protection device provided by the embodiment. Detailed Embodiments
[0039] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the present embodiment will be clearly and completely described below in conjunction with the accompanying drawings in the present embodiment.
[0040] In some of the processes described in the specification of the present invention and the above-mentioned drawings, a plurality of operations appear in a specific order. However, it should be clearly understood that these operations may not be executed in the order in which they appear herein or may be executed in parallel. The serial numbers of the operations are only used to distinguish the different operations, and the serial numbers themselves do not represent any execution order. In addition, these processes may include more or fewer operations, and these operations may be executed in sequence or in parallel.
[0041] The technical solution of the present invention is applicable to the self-excitation protection of the generators of small hydropower stations connected to the grid channels of large hydropower stations, such as the generators of ecological small hydropower stations. At present, the common solutions for the self-excitation protection of the generators of small hydropower stations are the configuration of reactors or the tripping connection scheme. The inventors have found through research that these methods have at least the problems of high cost and power loss.
[0042] Based on this, the technical solution of the present invention is proposed. In the present invention, the terminal voltage and terminal current of the generator are obtained in real time; the terminal impedance is calculated according to the terminal voltage and terminal current, and the system capacitive reactance is calculated according to the terminal impedance and the equivalent resistance on the external system side of the generator; it is judged whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator, and it is determined whether to disconnect the generator according to the judgment result.
[0043] Specifically, starting from the mechanism of self-excitation itself, the self-excitation phenomenon of the generator is essentially the interaction between the capacitive load and the direct-axis synchronous reactance of the generator. That is, under the condition of a capacitive load, the generator emits reactive power and establishes a steady-state operation mode corresponding to a certain saturated direct-axis synchronous reactance. When the generator is unloaded or lightly loaded with a long line (equivalent to a capacitive load), the ratio of the system capacitive reactance to the direct-axis synchronous reactance of the generator determines whether a positive feedback loop is formed. The direct-axis synchronous reactance of the generator is the core parameter to measure the ability of the generator to establish a magnetic field. If the system shows too strong capacitive characteristics, the magnetizing effect generated by the capacitive current will cause the terminal voltage to continue to rise, leading to positive feedback and thus triggering self-excitation. Based on this, the present invention calculates the system capacitive reactance through the terminal voltage, terminal current of the generator and the equivalent resistance on the external system side of the generator, determines whether self-excitation occurs according to the system capacitive reactance and the synchronous reactance of the generator, and disconnects the generator only when it is determined that self-excitation occurs. Through the above method, the self-excitation protection of the generator can be realized without adding additional reactors and switching devices, reducing the cost, and only disconnecting the generator when self-excitation occurs in the generator, ensuring the normal operation of the small hydropower station connected to the grid with a high-voltage long line, and improving the power generation and power generation efficiency.
[0044] Next, the technical solutions in this embodiment will be described clearly and completely with reference to the accompanying drawings in this embodiment. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.
[0045] Figure 1 The flow schematic diagram of a generator self-excitation protection method based on impedance is shown. Please refer to Figure 1 , and this method includes the following steps:
[0046] Step 1: Obtain the terminal voltage and terminal current of the generator in real time.
[0047] In this embodiment, the generator is the generator of the first hydropower station, and the first hydropower station is connected to the grid through the second hydropower station. Usually, this generator is the generator of a small hydropower station, and this small hydropower station is connected to the grid connection channel of a large hydropower station and shares its transmission line and grid interface.
[0048] It can be understood that the terminal voltage of the generator is the voltage at the output end of the generator, and the terminal current is the current at the output end of the generator. In practical applications, a voltage transformer and a current transformer can be used to detect the terminal voltage and terminal current in real time respectively.
[0049] Step 2: Calculate the terminal impedance according to the terminal voltage and terminal current, and calculate the system capacitive reactance according to the terminal impedance and the equivalent resistance on the external system side of the generator.
[0050] Among them, the terminal impedance refers to the equivalent impedance (i.e., input impedance) seen by the generator towards the system side, which is used to characterize the comprehensive impedance characteristic of the generator to alternating current. By measuring the terminal voltage and terminal current and combining the system equivalent model, the terminal impedance can be calculated. Please refer to Figure 2 , and the calculation formula is as follows:
[0051]
[0052] Among them, Z represents the terminal impedance, TV represents the terminal voltage, and CT represents the terminal current.
[0053] After obtaining the terminal impedance, the system capacitive reactance can be calculated according to the following formula:
[0054] Z = R + jX;
[0055] Among them, X represents the system capacitive reactance, Z represents the terminal impedance, R represents the equivalent resistance on the external system side of the generator, and j represents the imaginary unit.
[0056] Step 3: Judge whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator, and determine whether to disconnect the generator according to the judgment result.
[0057] Among them, the direct-axis synchronous reactance of the generator can be measured through no-load test and short-circuit test. After obtaining the system capacitive reactance and the direct-axis synchronous reactance of the generator, it is possible to determine whether self-excitation occurs in the unit by comparing the capacitive reactance value with the synchronous impedance of the unit.
[0058] Please refer to Figure 2 , in this embodiment, if -X > X d , it is determined that the generator does not have self-excitation; if 0 > X > -X d , it is determined that the generator will have self-excitation; where X represents the system capacitive reactance, and X d represents the direct-axis synchronous reactance of the generator.
[0059] Specifically, when -X > X d , the inductive impedance of the generator dominates, the voltage fluctuation is small, and the system is in a stable state. At this time, it is determined that the generator does not have self-excitation; when 0 > X > -X d , the system may cause the voltage to continuously rise due to the magnetizing effect of the capacitive current. At this time, the generator is likely to enter the self-excitation state, resulting in no-load operation at a high voltage. At this time, it is determined that the generator will have self-excitation. After determining that the generator will have self-excitation, the generator is disconnected after a preset time delay and an alarm signal is sent. The preset time delay can be set according to the actual situation, and this embodiment does not limit it. For example, the preset time delay is 0.2 seconds. After determining that the generator will have self-excitation, disconnecting the generator and giving an alarm can avoid damage to the unit caused by generator self-excitation overvoltage, and can timely remind the staff, further ensuring the safety of the hydropower station.
[0060] In summary, the impedance-based generator self-excitation protection method provided in this embodiment calculates the system capacitive reactance, and determines whether the generator has self-excitation according to the magnitude of the system capacitive reactance and the direct-axis synchronous impedance of the generator, and disconnects the generator according to the judgment result. The present invention does not require additional reactors and switchgear, reducing costs. And this embodiment judges whether self-excitation occurs from the mechanism of self-excitation itself. When a small hydropower station is connected to the grid with a high-voltage long line, the corresponding generator will not be disconnected, thus avoiding power loss, improving power generation efficiency, and also avoiding the impact on ecological flow discharge.
[0061] Figure 3 The structure diagram of an impedance-based generator self-excitation protection device is shown. Please refer to Figure 3 , the generator is the generator of the first hydropower station, and the first hydropower station is connected to the grid through the second hydropower station. The device includes:
[0062] A sensor module for real-time acquisition of the terminal voltage and terminal current of the generator;
[0063] A calculation module for calculating the terminal impedance according to the terminal voltage and terminal current, and calculating the system capacitive reactance according to the terminal impedance and the equivalent resistance on the external system side of the generator;
[0064] A control module, configured to determine whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator, and determine whether to disconnect the generator according to the determination result.
[0065] It can be understood that since the impedance-based generator self-excitation protection device described in this embodiment is a device for implementing the impedance-based generator self-excitation protection method described in the embodiment, for the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple. For relevant parts, refer to the partial description of the method, and details are not elaborated here.
Claims
1. An impedance-based self-excitation protection method for generators, characterized in that The generator is the generator of the first hydropower station, and the first hydropower station is interconnected to the grid through the second hydropower station. The method includes: Obtaining the terminal voltage and terminal current of the generator in real time; Calculating the terminal impedance according to the terminal voltage and terminal current, and calculating the system capacitive reactance according to the terminal impedance and the equivalent resistance on the external system side of the generator; Judging whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator, and determining whether to disconnect the generator according to the judgment result.
2. The impedance-based generator self-excitation protection method according to claim 1, characterized in that, The calculation formula of the terminal impedance is as follows: Wherein, Z represents the terminal impedance, TV represents the terminal voltage, and CT represents the terminal current.
3. The impedance-based generator self-excitation protection method according to claim 1, wherein, The calculation formula of the system capacitive reactance is as follows: Z = R + jX; Wherein, X represents the system capacitive reactance, Z represents the terminal impedance, R represents the equivalent resistance on the external system side of the generator, and j represents the imaginary unit.
4. The impedance-based generator self-excitation protection method according to claim 1, wherein Judging whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator includes: If -X > X d , it is determined that the generator does not experience self-excitation; if 0 > X > -X d , it is determined that the generator will experience self-excitation; where X represents the system capacitive reactance, and X d represents the direct-axis synchronous reactance of the generator.
5. The impedance-based generator self-excitation protection method according to claim 4, characterized in that Determining whether to disconnect the generator according to the judgment result includes: After it is determined that self-excitation of the generator will occur, the generator is disconnected after a preset time delay and an alarm signal is sent.
6. The impedance-based generator self-excitation protection method according to claim 5, characterized in that The preset time delay is 0.2 seconds.
7. Impedance-based generator self-excitation protection device, characterized in that, The generator is the generator of the first hydropower station, and the first hydropower station is interconnected to the grid through the second hydropower station. The device includes: A sensor module for obtaining the terminal voltage and terminal current of the generator in real time; A calculation module for calculating the terminal impedance according to the terminal voltage and terminal current, and calculating the system capacitive reactance according to the terminal impedance and the equivalent resistance on the external system side of the generator; A control module for judging whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator, and determining whether to disconnect the generator according to the judgment result.
8. The impedance-based generator self-excitation protection device according to claim 7, characterized in that, The calculation formula of the terminal impedance is as follows: The calculation formula of the system capacitive reactance is as follows: Z = R + jX; Wherein, Z represents the terminal impedance, TV represents the terminal voltage, CT represents the terminal current, X represents the system capacitive reactance, R represents the equivalent resistance on the external system side of the generator, and j represents the imaginary unit.
9. The impedance-based generator self-excitation protection device according to claim 7, wherein Judging whether self-excitation occurs according to the system capacitive reactance and the direct-axis synchronous reactance of the generator includes: If -X > X d , it is determined that the generator does not experience self-excitation; if 0 > X > -X d , it is determined that the generator will experience self-excitation; where X represents the system capacitive reactance and X d represents the direct-axis synchronous reactance of the generator.
10. The impedance-based generator self-excitation protection device according to claim 9, characterized in that, Determining whether to disconnect the generator according to the judgment result includes: After it is determined that self-excitation of the generator will occur, the generator is disconnected after a preset time delay and an alarm signal is sent, and the preset time delay is 0.2 seconds.