Grid-connected test system and method for asynchronous generators with different capacities

Abstract

The invention discloses a grid-connected test system and method for asynchronous generators with different capacities, and belongs to the field of asynchronous generators, the grid-connected test system comprises a speed regulation dragging source, an asynchronous generator and a magnetizing loop alternating current switch, the input end of the speed regulation dragging source is electrically connected with the input end of the asynchronous generator; the output end of the asynchronous generator is connected with one end of the magnetizing loop alternating current switch and one end of the grid-connected switch KM at the same time, and the other end of the magnetizing loop alternating current switch and the other end of the grid-connected switch KM are both connected with a three-phase alternating current power grid terminal. According to the grid-connected test system and method for the asynchronous generators with different capacities, the test investment is greatly reduced, the economic value is great, and the large test capacity can be achieved. The impulse current amplitude during grid connection of asynchronous generators with different capacities is greatly improved, and the test capability is effectively improved.

Description

Technical Field

[0001] The invention relates to the field of asynchronous generators, in particular to a grid-connected test system and method for asynchronous generators with different capacities. Background Art

[0002] The asynchronous generator is the core equipment in the wind power generation system. Whether it can operate safely and reliably is directly related to the safety of the wind power generator power grid. The asynchronous generator accident in the wind power generation system is something that the wind farm tries to avoid but cannot completely avoid. In particular, due to the large size of the generator, it is inconvenient to disassemble and assemble, and it is not easy to repair on site, it is very difficult to repair. Exiting operation and disassembling the wind tower are destructive, which will cause huge economic losses. Therefore, before the asynchronous generator leaves the factory, whether it can be tested at full power load, the most direct way is to effectively verify it according to the requirements of the national military standard before leaving the factory. Usually, the asynchronous generator grid-connected test is to directly connect to the grid using an AC switch, which will generate a surge current of 5-6 times the rated current. The instantaneous surge current will affect the normal operation of the generator and other equipment in the large power grid system, so the test requires sufficient power capacity as support. Therefore, there are usually two ways to test the power supply. One is to use the power grid for grid connection, but the capacity of the power grid must meet the surge current of 5-6 times the rated current of the asynchronous generator without tripping. The second method is to use a voltage regulator to generate voltage through step-down excitation to make the generator generate voltage, and then steadily adjust the voltage to the rated voltage of the generator. However, due to the characteristics of the voltage regulator, primary and secondary currents, heat generation and other factors, a voltage regulator is generally used to test asynchronous generators. The capacity of the voltage regulator needs to be 1-2 times larger than that of the asynchronous generator, and there are different requirements for generators of different capacities, and the cost is too high.

[0003] When the asynchronous generator is connected to the grid, the impact current generated when the magnetic flux is established will generate a large impact current to the motor and the grid. If it is not operated properly, it will affect the safe operation of the grid and damage the generator, causing economic losses. Therefore, a reasonable method is needed to reduce the impact current when the asynchronous generator is connected to the grid. Summary of the invention

[0004] With regard to the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a grid-connected test system and method for asynchronous generators of different capacities, so as to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A grid-connected test system for asynchronous generators of different capacities includes a speed regulating drag source, an asynchronous generator and a magnetizing circuit AC switch. The speed regulating drag source and the input end of the asynchronous generator are electrically connected to each other, and the output end of the asynchronous generator is simultaneously connected to one end of the magnetizing circuit AC switch and one end of the grid-connected switch KM, and the other end of the magnetizing circuit AC switch and the other end of the grid-connected switch KM are both connected to the connection terminal of the three-phase AC power grid.

[0007] As a further solution of the present invention: the three-phase AC power grid terminal is connected to the three-phase AC power grid.

[0008] As a further solution of the present invention: the grid-connected switch KM is composed of three groups of large-capacity switches connected in parallel.

[0009] As a further solution of the present invention: the magnetizing circuit AC switch includes three groups of bypass switches and three groups of current limiting devices, each group of bypass switches and a corresponding group of current limiting devices are connected in series to form a safety switch structure, and the three groups of safety switch structures are connected in parallel.

[0010] The method of the grid-connected test system of asynchronous generators of different capacities has the following steps:

[0011] S1. Use the speed regulating drag source to drag the asynchronous generator to the synchronous state. At this time, the rotor should be in the open circuit state, and the grid-connected switch KM is not closed. Close the bypass switch connected to the current limiting device in the AC switch of the magnetizing circuit. Under the action of the current limiting device, the asynchronous generator begins to build up voltage. Then, adjust the current limiting device to continuously increase the excitation current so that the voltage at both ends of the grid-connected switch KM is consistent. Then close the grid-connected switch KM and disconnect the bypass switch.

[0012] S2. After closing the grid-connected switch KM, adjust the speed of the asynchronous generator and use the slip to adjust the power of the generator, so as to complete the verification of the generator in accordance with the national standard requirements.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] The invention adopts a grid-connected test system and method for asynchronous generators of different capacities, greatly reduces the test investment, has great economic value, and can achieve a larger test capacity. It greatly improves the impulse current amplitude when asynchronous generators of different capacities are connected to the grid, and effectively improves the test capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the framework of the grid-connected test system of asynchronous generators with different capacities disclosed in the embodiment.

[0016] The reference numerals in the figure are: 1, speed regulating traction source; 2, asynchronous generator; 3, magnetizing circuit AC switch; 4, three-phase AC grid terminal; 31, bypass switch; 32, current limiting device. DETAILED DESCRIPTION

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", and "connected" should be understood in a broad sense; for example, it can be a fixed connection, a detachable connection, or an integral connection, a mechanical connection, or an electrical connection, a direct connection, or an indirect connection through an intermediate medium, or the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] See also Figure 1 , a grid-connected test system for asynchronous generators of different capacities, comprising a speed regulating drag source 1, an asynchronous generator 2 and a magnetizing circuit AC switch 3, wherein the input ends of the speed regulating drag source 1 and the asynchronous generator 2 are electrically connected to each other, and the output end of the asynchronous generator 2 is simultaneously connected to one end of the magnetizing circuit AC switch 3 and one end of the grid-connected switch KM, and the other end of the magnetizing circuit AC switch 3 and the other end of the grid-connected switch KM are both connected to a three-phase AC grid terminal 4, and the three-phase AC grid terminal 4 is connected to the three-phase AC grid;

[0020] The grid-connected switch KM is composed of three sets of large-capacity switches connected in parallel;

[0021] The magnetizing circuit AC switch 3 includes three groups of bypass switches 31 and three groups of current limiting devices 32. Each group of bypass switches 31 and a corresponding group of current limiting devices 32 are connected in series to form a safety switch structure. The three groups of safety switch structures are connected in parallel.

[0022] Use the drag source to drag the asynchronous generator to the synchronous state. Because the asynchronous motor stator is not excited, the asynchronous generator does not generate electricity at this time, and the stator current is zero. After the asynchronous generator is normally connected to the grid, the rotor of the asynchronous generator is similar to an open circuit. At this time, the generator is approximately in a no-load state, and the stator current is the no-load current I0. Therefore, before and after the asynchronous generator is connected to the grid, the stator current is not large. Only at the moment of grid connection, according to the conservation of flux, the flux of each winding of the asynchronous generator is the sum of its own self-inductance flux and the mutual inductance flux of other windings. Therefore, the six windings are calculated through the following formula:

[0023] Therefore, when the stator establishes magnetic flux, the grid-connected impact current will reach 2-3 times the rated current.

[0024] According to the grid-connected test system for asynchronous generators of different capacities of the present invention, after the asynchronous generator is dragged to the synchronous state by the drag source, the magnetizing circuit AC switch 3 is closed, and the generator is excited by the magnetizing circuit using a controllable current, and the asynchronous generator is subjected to the action of the exciting current to establish a magnetic field to generate a voltage, and the output voltage of the generator is adjusted by adjusting the magnitude of the exciting current, and when the monitored grid voltage and the voltage at both ends of the generator are almost the same, the grid-connected switch KM is closed, and after the grid-connected switch is closed, the bypass switch 31 is disconnected. Then the loading is completed by adjusting the speed of the prime mover.

[0025] The current limiting device in the present invention is limited to changing the magnitude of the current, but cannot change the phase of the grid transmission. If the phase is changed, the internal circulating current of the motor generated at the moment of closing the grid-connected switch will have an impact on the generator.

[0026] According to the embodiment of the present invention, the test of an asynchronous generator with a power of 4.87MW was successfully completed on a test power grid with a capacity of 5MW, effectively solving the problem that the power grid cannot work normally due to the large current impact of magnetic flux established when a large-capacity asynchronous generator is connected to the grid, and expanding the test capacity of the test site. It only needs to modify the grid-connected switch in the loop, which is convenient and simple to operate and reliable in operation.

[0027] If the traction system is large enough, then by using the present invention, the capacity of the asynchronous generator to be tested will also become larger.

[0028] The method of the grid-connected test system of asynchronous generators of different capacities has the following steps:

[0029] S1. Use the speed regulating drag source 1 to drag the asynchronous generator 2 to the synchronous state. According to the equivalent circuit principle of the asynchronous generator 2, the rotor should be in an open circuit state at this time. The asynchronous generator 2 is not connected to the three-phase AC power grid at this time, so the magnetic flux is not established. If the grid-connected switch KM is directly closed, an impact current for establishing the magnetic flux will be generated. Therefore, the grid-connected switch KM is not closed, and the bypass switch 31 connected to the current limiting device 32 in the magnetizing circuit AC switch 3 is closed. Under the action of the current limiting device, the asynchronous generator 2 starts to build voltage, and then the current limiting device is adjusted to continuously increase the excitation current so that the voltages at both ends of the grid-connected switch KM are consistent, and then the grid-connected switch KM is closed, and the bypass switch 31 is disconnected;

[0030] S2. After closing the grid-connected switch KM, adjust the speed of the asynchronous generator 2 and use the slip to adjust the power of the generator, so as to complete the verification of the generator in accordance with the national standard requirements.

[0031] The grid-connected test system and method for asynchronous generators of different capacities provided by the present invention can test asynchronous generators of different capacities, greatly improving the test capability. The grid-connected technology is simple, applicable, and easy to operate. It is only necessary to modify the existing test circuit grid-connected switch of the test station, and there is no need to purchase other equipment to increase the capacity, thus saving economic costs.

[0032] The present invention uses a grid-connected test system and method for asynchronous generators of different capacities to greatly reduce the test investment. For the test of asynchronous generators of different capacities, if the test anti-shock capacity is insufficient under the existing conditions, there is no need to expand the test power supply capacity, so the present invention has great economic value; the grid-connected test system and method for asynchronous generators of different capacities of the present invention are easy to operate. The test system of the present invention can be based on the existing test system, and only the grid-connected switch needs to be modified to limit the excitation current during excitation. After the excitation is completed, the magnetization and grid-connected switches are switched and the test can be carried out; the grid-connected test system and method for asynchronous generators of different capacities of the present invention can be applied to the test of asynchronous generators of different capacities, and can achieve a larger test capacity.

[0033] The invention relates to a test system for connecting asynchronous generators of different capacities to the grid, which greatly improves the impact current amplitude when connecting asynchronous generators of different capacities to the grid, effectively improves the test capability, and belongs to the technical field of test devices necessary for medium and high voltage asynchronous generator test sites.

[0034] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive from any point of view. The scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention, and any reference numerals in the claims should not be considered as limiting the claims involved.

[0035] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. Asynchronous generator grid-connected test system with different capacities, characterized by: The invention comprises a speed regulating drag source (1), an asynchronous generator (2) and a magnetizing circuit AC switch (3); the input ends of the speed regulating drag source (1) and the asynchronous generator (2) are electrically connected to each other; the output end of the asynchronous generator (2) is simultaneously connected to one end of the magnetizing circuit AC switch (3) and one end of a grid-connected switch KM; the other end of the magnetizing circuit AC switch (3) and the other end of the grid-connected switch KM are both connected to a three-phase AC power grid connection terminal (4).

2. The grid-connected test system for asynchronous generators of different capacities according to claim 1 is characterized in that: The three-phase AC power grid connection terminal (4) is connected to the three-phase AC power grid.

3. The grid-connected test system for asynchronous generators of different capacities according to claim 2 is characterized in that: The grid-connected switch KM is composed of three groups of large-capacity switches connected in parallel.

4. The grid-connected test system for asynchronous generators of different capacities according to claim 3 is characterized in that: The magnetizing circuit AC switch (3) comprises three groups of bypass switches (31) and three groups of current limiting devices (32), each group of bypass switches (31) and a corresponding group of current limiting devices (32) are connected in series to form a safety switch structure, and the three groups of safety switch structures are connected in parallel.

5. The method for grid-connected test system of asynchronous generators with different capacities according to any one of claims 1 to 4, characterized in that: The method steps are as follows: S1. Use the speed regulating drag source (1) to drag the asynchronous generator (2) to a synchronous state. At this time, the rotor should be in an open circuit state. The grid-connected switch KM is not closed, and the bypass switch (31) connected to the current limiting device (32) in the magnetizing circuit AC switch (3) is closed. Under the action of the current limiting device, the asynchronous generator (2) starts to build up voltage. Then, the current limiting device is adjusted to continuously increase the excitation current so that the voltages at both ends of the grid-connected switch KM are consistent. Then, the grid-connected switch KM is closed and the bypass switch (31) is disconnected. S2. After closing the grid-connected switch KM, adjust the speed of the asynchronous generator (2) and use the slip to adjust the power of the generator, thereby completing the verification of the generator in accordance with the national standard requirements.

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