Generator self-excitation protection method and device based on reverse reactive power
By monitoring and calculating the voltage, current and power of the generator in a small hydropower station in real time, determining whether self-excitation occurs, and de-arrange the generator in a delayed manner when it occurs, the generator damage and power loss caused by self-excitation overvoltage of small hydropower stations is solved, and cost reduction and power generation efficiency are achieved.
Patent Information
- Application Number
- CN202510425903.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-07
- Publication Date
- 2025-06-24
AI Technical Summary
When small hydropower stations are connected to large hydropower stations, they are prone to overvoltage of generator self-excitation by running with high voltage and long lines, causing generator damage. At the same time, existing solutions are costly and easily lead to power loss.
By obtaining the generator terminal voltage and terminal current in real time, the computer terminal looks at the apparent power and reactive power of the system, and synchronizes the reactance unit value based on the reactive power, the generator rated capacity and the generator straight axis equal to determine whether self-excitation occurs. If it occurs, the generator will be de-listed and an alarm signal will be issued.
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 leakage.
Smart Images
Figure CN120200181A_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 reverse reactive power. 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 a large hydropower station are taken 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 unloaded 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, there are the following two existing solutions: 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, so as to achieve the purpose of suppressing the self-excitation of small hydropower stations; The second solution is to configure a tripping connection circuit. By monitoring the grid connection switch conditions of the units of large hydropower stations, if all the units of a large hydropower station are taken out of operation and all the grid connection switches of the units of the large hydropower station are disconnected, the switches connecting small hydropower stations to large hydropower stations are instantaneously tripped to avoid the operation condition of small units with a high voltage and a long line.
[0004] In the first solution, although the problem of self-excited 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 for the small hydropower station to connect to the large power station are instantaneously tripped. 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 situation of self-excitation generated 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 results in the small hydropower station being unable to operate in parallel for power generation, causing power loss. At the same time, some small hydropower stations also undertake the task of ecological flow. Once tripped, 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 method for small hydropower stations, and proposes a generator self-excitation protection method and device based on reverse reactive power.
[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows:
[0007] In a first aspect, the present invention provides a generator self-excitation protection method based on reverse reactive power. 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 apparent power seen from the terminal to the system according to the terminal voltage and terminal current, and calculate the reactive power seen from the terminal to the system according to the apparent power and the active power on the system side;
[0010] Judge whether self-excitation occurs according to the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and determine whether to disconnect the generator according to the judgment result.
[0011] Further, the calculation formula of the apparent power is as follows:
[0012] S = TV × CT;
[0013] Wherein, S represents the apparent power, TV represents the terminal voltage, and CT represents the terminal current.
[0014] Furthermore, the calculation formula of the reactive power is as follows:
[0015] S = P + jQ;
[0016] Wherein, S represents the apparent power, P represents the active power, Q represents the reactive power, and j represents the imaginary unit.
[0017] Furthermore, determining whether self-excitation occurs according to the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator includes:
[0018] If Then it is determined that self-excitation does not occur in the generator; if Then it is determined that self-excitation will occur in the generator; wherein, Q represents the reactive power, W H represents the rated capacity of the generator, represents the per-unit value of the direct-axis synchronous reactance of the generator.
[0019] Furthermore, determining whether to disconnect the generator according to the judgment result includes:
[0020] After determining 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 reverse reactive power. 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 apparent power looking from the terminal of the generator to the system according to the terminal voltage and terminal current, and calculating the reactive power looking from the terminal of the generator to the system according to the apparent power and the active power on the system side;
[0025] A control module for determining whether self-excitation occurs according to the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and determining whether to disconnect the generator according to the judgment result.
[0026] Furthermore, the calculation formula of the apparent power is as follows:
[0027] S = TV × CT;
[0028] The calculation formula of the reactive power is as follows:
[0029] S = P + jQ;
[0030] Among them, S represents apparent power, TV represents terminal voltage, CT represents terminal current, P represents active power, Q represents reactive power, and j represents the imaginary unit.
[0031] Further, determining whether self-excitation occurs according to the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator includes:
[0032] If then it is determined that self-excitation of the generator does not occur; if then it is determined that self-excitation of the generator will occur; where Q represents reactive power, W H represents the rated capacity of the generator, represents the per-unit value of the direct-axis synchronous reactance of the generator.
[0033] Further, determining whether to disconnect the generator according to the judgment result includes:
[0034] 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.
[0035] The beneficial effects of the present invention are as follows: The method and device for generator self-excitation protection based on reverse reactive power provided by the present invention look at the reactive power of the system from the computer terminal, and judge whether self-excitation of the generator occurs according to the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and disconnect the generator according to the judgment result. The present invention does not require additional reactors and switchgear, reduces costs, and the present invention 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, 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 flow chart of a method for generator self-excitation protection based on reverse reactive power provided by the embodiment;
[0037] Figure 2 It is a schematic principle diagram of a method for generator self-excitation protection based on reverse reactive power provided by the embodiment;
[0038] Figure 3 It is a schematic structural diagram of a device for generator self-excitation protection based on reverse reactive power 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 embodiments will be clearly and completely described below with reference to the accompanying drawings in the embodiments.
[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 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 generators of small hydropower stations connected to the grid channels of large hydropower stations, such as generators of ecological small hydropower stations. Since the current self-excitation protection methods for generators of small hydropower stations usually adopt the scheme of configuring reactors or the scheme of tripping in series, 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 acquired in real time; the apparent power seen from the terminal to the system is calculated according to the terminal voltage and terminal current, and the reactive power seen from the terminal to the system is calculated according to the apparent power and the active power on the system side; it is judged whether self-excitation occurs according to the reactive power, the rated capacity of the generator and the per-unit value of the direct-axis equivalent 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 phenomenon of generator self-excitation is essentially the interaction between capacitive loads and the direct-axis synchronous reactance of the generator. That is, under capacitive load conditions, the generator emits reactive power and establishes a steady-state operation mode corresponding to a certain saturated direct-axis synchronous reactance. When the reactive power at the terminal is less than 0, it indicates that the system sends capacitive reactive power back to the terminal (such as a long line with light load), resulting in a decrease in the system capacitive reactance, and then an excess of capacitive reactive power causes the terminal voltage to rise out of control, and self-excitation is likely to occur; the smaller the rated capacity of the generator, or the larger the per-unit value of the direct-axis synchronous reactance, the larger the direct-axis synchronous reactance, and the easier it is to meet the self-excitation critical condition. Based on this, the present invention calculates the reactive power seen from the terminal to the system through the terminal voltage, terminal current of the generator and the active power on the system side, determines whether self-excitation occurs according to the reactive power, the rated capacity of the generator and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and disconnects the generator only when self-excitation is determined to occur. Through the above method, the self-excitation protection of the generator can be realized without adding additional reactors and switching equipment, reducing the cost, and only disconnecting when the generator has self-excitation, ensuring the normal operation of small hydropower stations connected to the grid with high-voltage long lines, and improving the power generation and power generation efficiency.
[0044] Next, the technical solutions in this embodiment will be clearly and completely described in conjunction with 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 flowchart of a generator self-excitation protection method based on reverse reactive power is shown. Please refer to Figure 1 This method includes the following steps:
[0046] Step 1: Real-time obtain the terminal voltage and terminal current of the generator.
[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 apparent power seen from the terminal to the system according to the terminal voltage and terminal current, and calculate the reactive power seen from the terminal to the system according to the apparent power and the active power on the system side.
[0050] Among them, the apparent power seen from the terminal to the system refers to the apparent power transmitted from the generator terminal to the power system direction, which characterizes the total power capacity under the joint action of voltage and current in the power system. By measuring the terminal voltage and terminal current, the product of the effective value of the voltage and the effective value of the current is the apparent power. Please refer to Figure 2 The calculation formula is as follows:
[0051] S = TV × CT;
[0052] Among them, S represents the apparent power, TV represents the terminal voltage, and CT represents the terminal current.
[0053] After obtaining the apparent power through calculation, the reactive power seen from the terminal to the system can be calculated. The reactive power seen from the terminal to the system refers to the direction and magnitude of the reactive power exchanged between the generator and the power system. When the reactive power seen from the terminal to the system is greater than 0, it represents positive reactive power. At this time, when the generator is in the lagging phase operation (over-excitation) state, it acts as a capacitive element and outputs inductive reactive power to the system; when the reactive power seen from the terminal to the system is less than 0, it represents reverse reactive power. At this time, when the generator is in the leading phase operation (under-excitation) or the loss-of-excitation asynchronous operation state, it acts as an inductive element and absorbs inductive reactive power from the system.
[0054] In this embodiment, the calculation formula for the reactive power seen by the generator terminal looking at the system is as follows:
[0055] S = P + jQ;
[0056] Wherein, S represents apparent power, P represents active power, Q represents reactive power, and j represents the imaginary unit.
[0057] Step 3: Determine whether self-excitation occurs based on the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and determine whether to disconnect the generator according to the judgment result.
[0058] Among them, the rated capacity of the generator can be obtained through the equipment nameplate. If the nameplate information is missing, the rated capacity can be obtained through the technical specification or design drawing provided by the generator manufacturer. The per-unit value of the direct-axis synchronous reactance is directly marked in the nameplate or technical document of some generators. If it is not marked, it can be calculated and converted through no-load and short-circuit tests. The relevant method belongs to the prior art and will not be elaborated in this embodiment.
[0059] After obtaining the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, it is possible to determine whether self-excitation occurs in the unit according to the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator.
[0060] Please refer to Figure 2 , in this embodiment, if then it is determined that the generator does not undergo self-excitation; if then it is determined that the generator will undergo self-excitation; where Q represents reactive power, W H represents the rated capacity of the generator, represents the per-unit value of the direct-axis synchronous reactance of the generator.
[0061] Specifically, when it means that 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 undergo self-excitation; when it means that the system may cause the voltage to continue to rise due to the magnetizing effect of the capacitive current. At this time, the generator is prone 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 undergo self-excitation. After determining that the generator will undergo 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 undergo self-excitation, disconnecting the generator and giving an alarm can avoid damage to the unit caused by self-excitation overvoltage of the generator, and can timely remind the staff, further ensuring the safety of the hydropower station.
[0062] In summary, the generator self-excitation protection method based on reverse reactive power provided in this embodiment looks at the reactive power of the system from the computer side, and determines whether the generator has self-excitation based on the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and disconnects the generator according to the judgment result. This embodiment does not require additional reactors and switchgear, reducing costs. Moreover, this embodiment determines 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 the ecological flow discharge.
[0063] Figure 3 The structural schematic diagram of a generator self-excitation protection device based on reverse reactive power is shown. Please refer to Figure 3 , where 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:
[0064] A sensor module for real-time acquisition of the terminal voltage and terminal current of the generator;
[0065] A calculation module for calculating the apparent power of the system seen from the terminal of the generator based on the terminal voltage and terminal current, and calculating the reactive power of the system seen from the terminal based on the apparent power and the active power on the system side;
[0066] A control module for determining whether self-excitation occurs based on the reactive power, the rated capacity of the generator, and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and determining whether to disconnect the generator according to the judgment result.
[0067] It can be understood that since the generator self-excitation protection device based on reverse reactive power described in this embodiment is used to implement the 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 the relevant parts, please refer to the partial description of the method and will not be elaborated here.
Claims
1. A generator self-excitation protection method based on reverse reactive power, characterized in that: The generator is a generator of a first hydropower station, the first hydropower station is connected to the grid through a second hydropower station, and the method comprises: Obtain the generator terminal voltage and current in real time; The computer terminal looks at the apparent power of the system according to the machine-side voltage and the machine-side current, and the computer terminal looks at the reactive power of the system according to the apparent power and the active power on the system side; Whether self-excitation occurs is determined based on the reactive power, the rated capacity of the generator and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and whether the generator is de-energized is determined based on the determination result.
2. The generator self-excitation protection method based on reverse reactive power according to claim 1, characterized in that: The calculation formula of the apparent power is as follows: S = TV × CT; Among them, S represents apparent power, TV represents terminal voltage, and CT represents terminal current.
3. The generator self-excitation protection method based on reverse reactive power according to claim 1, characterized in that: The reactive power calculation formula is as follows: S = P + jQ; Among them, S represents apparent power, P represents active power, Q represents reactive power, and j represents imaginary unit.
4. The generator self-excitation protection method based on reverse reactive power according to claim 1, characterized in that: Judging whether self-excitation occurs according to the reactive power, the rated capacity of the generator and the per-unit value of the direct-axis equivalent synchronous reactance of the generator includes: like It is determined that the generator does not self-excite; if It is determined that the generator will be self-excited; where Q represents reactive power, W H Indicates the rated capacity of the generator, Indicates the per unit value of the generator direct-axis synchronous reactance.
5. The generator self-excitation protection method based on reverse reactive power according to claim 4, characterized in that: Determine whether to disconnect the generator based on the judgment result, including: After determining that the generator will self-excite, the generator will be de-energized after a preset delay and an alarm signal will be issued.
6. The generator self-excitation protection method based on reverse reactive power according to claim 5, characterized in that: The preset duration is 0.2 seconds.
7. A generator self-excitation protection device based on reverse reactive power, characterized in that: The generator is a generator of a first hydropower station, the first hydropower station is connected to the grid through a second hydropower station, and the device comprises: A sensor module is used to obtain the generator terminal voltage and current in real time; A calculation module, used for calculating the apparent power of the system from the computer end according to the machine end voltage and the machine end current, and calculating the reactive power of the system from the computer end according to the apparent power and the active power of the system side; The control module is used to judge whether self-excitation occurs according to the reactive power, the rated capacity of the generator and the per-unit value of the direct-axis equivalent synchronous reactance of the generator, and determine whether to de-energize the generator according to the judgment result.
8. The generator self-excitation protection device based on reverse reactive power according to claim 7, characterized in that: The calculation formula of the apparent power is as follows: S = TV × CT; The reactive power calculation formula is as follows: S = P + jQ; Among them, S represents apparent power, TV represents terminal voltage, CT represents terminal current, P represents active power, Q represents reactive power, and j represents imaginary unit.
9. The generator self-excitation protection device based on reverse reactive power according to claim 7, characterized in that: Judging whether self-excitation occurs according to the reactive power, the rated capacity of the generator and the per-unit value of the direct-axis equivalent synchronous reactance of the generator includes: like It is determined that the generator does not self-excite; if It is determined that the generator will be self-excited; where Q represents reactive power, W H Indicates the rated capacity of the generator, Indicates the per unit value of the generator direct-axis synchronous reactance.
10. The generator self-excitation protection device based on reverse reactive power according to claim 9, characterized in that: Determine whether to disconnect the generator based on the judgment result, including: After determining that the generator will self-excite, the generator is de-energized after a preset delay and an alarm signal is issued, wherein the preset delay is 0.2 seconds.