A flexible excitation structure for connecting a high-voltage side of a main transformer

Abstract

The utility model discloses a kind of main transformer high voltage side access flexible excitation structure, belong to generator excitation technical field.The structure includes generator set;Flexible excitation system is connected with the high voltage side of main transformer through excitation transformer, flexible excitation system is connected with excitation winding, excitation winding is matched with generator set and is connected, and main transformer is connected with power system through high voltage side transmission line.The utility model accesses flexible excitation system in main transformer high voltage side, compared with traditional machine end access mode, significantly reduce the network side impedance, improve the proportion of reactive current flowing to system side, give full play to the double-channel reactive power injection advantage of flexible excitation system, enhance the reactive power control effect and transient voltage support capability, can quickly realize reactive power compensation, effectively maintain power system voltage level, improve power system operation stability, applicable to new energy high proportion power grid scene.

Description

Technical Field

[0001] This utility model relates to the field of excitation technology, and in particular to a flexible excitation structure for the high-voltage side of a main transformer. Background Technology

[0002] The excitation system is a core component of a synchronous generator, playing a crucial role in maintaining stable generator operation and ensuring a safe and reliable power supply to the power system. Its main functions include maintaining stable generator terminal voltage and achieving a rational distribution of reactive power among parallel-operating generators, thereby improving the overall stability of the power system.

[0003] Currently, synchronous generators widely adopt self-excited excitation. This method draws excitation power from the generator terminals, which is supplied to the generator via an excitation transformer and a thyristor rectifier. It offers advantages such as short excitation response time and fast terminal voltage regulation, demonstrating outstanding performance in improving system stability under both small and large disturbances. However, conventional self-excited excitation systems use thyristor rectification. As semi-controlled devices, thyristors have significant limitations: they cannot maintain strong excitation capability when the terminal voltage drops sharply under abnormal grid conditions; they are difficult to improve system damping through power exchange, resulting in limited ability to suppress system oscillations; and they can only absorb reactive power from the system, unable to provide effective reactive power support to the system.

[0004] With the increasing proportion of renewable energy in power grids across various regions, the demand for reactive power support in power systems is rising. Flexible DC excitation systems based on fully controlled devices have emerged to address this need. Building upon self-excited excitation systems, these systems replace thyristor converters with fully controlled device converters, enabling independent control of the exchange of active and reactive power on the grid side, thus providing stronger reactive power support to the system. However, the excitation power supply of existing flexible excitation systems is typically still drawn from the generator terminal. This results in the grid-side impedance including the main transformer impedance and the high-voltage transmission line impedance, leading to a smaller reactive current flowing to the system side. This severely limits the actual reactive power injection effect of flexible excitation systems and makes it difficult to meet the reactive power support requirements of power grids with a high proportion of renewable energy.

[0005] To address this, this invention proposes a flexible excitation structure for the high-voltage side of the main transformer. By optimizing the access method of the excitation system, reducing the grid-side impedance, fully leveraging the dual-channel reactive power injection advantage of the flexible excitation system, improving the reactive power support effect, and ensuring the stable operation of the power system. Summary of the Invention

[0006] The technical problem to be solved by this utility model is to provide a flexible excitation structure for the high voltage side of the main transformer, so as to solve the technical problems of large grid-side impedance and limited reactive power injection effect in the existing excitation system.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows: A flexible excitation structure for high-voltage side connection of a main transformer includes a generator set, a main transformer, a high-voltage side transmission line, an excitation transformer, an excitation winding, and a flexible excitation system. The flexible excitation system is connected to the high-voltage side of the main transformer through the excitation transformer, the flexible excitation system is connected to the excitation winding, the excitation winding is matched and connected to the generator set, and the main transformer is connected to the power system through the high-voltage side transmission line.

[0008] The aforementioned flexible excitation system includes a three-phase converter, a voltage stabilizing capacitor, and a DC chopper; the input terminal of the three-phase converter is connected to the output terminal of the excitation transformer, the output terminal of the three-phase converter is connected to the input terminal of the voltage stabilizing capacitor, the output terminal of the voltage stabilizing capacitor is connected to the input terminal of the DC chopper, and the output terminal of the DC chopper is connected to the excitation winding.

[0009] The three-phase converter mentioned above is a VSC converter, which is used to rectify the three-phase AC power output from the excitation transformer into DC power.

[0010] The aforementioned voltage-stabilizing capacitor is an electrolytic capacitor, which is used to filter and stabilize the DC output of the three-phase converter.

[0011] The aforementioned DC chopper is a DC-DC chopper module. The DC chopper is used to convert the voltage output by the stabilizing capacitor into the excitation voltage required by the excitation winding.

[0012] The primary winding of the excitation transformer is connected to the high-voltage busbar of the main transformer, and the secondary winding of the excitation transformer is connected to the input terminal of the flexible excitation system.

[0013] The low-voltage side of the aforementioned main transformer is connected to the output terminal of the generator set, the high-voltage side of the main transformer is connected to one end of the high-voltage transmission line, and the other end of the high-voltage transmission line is connected to the power system.

[0014] The reactive current output by the aforementioned flexible excitation system is divided into two paths: one path flows through the main transformer to the generator terminal, and the other path flows through the high-voltage side transmission line to the power system.

[0015] The aforementioned flexible excitation system is composed of fully controlled devices, which are IGBT or IGCT power devices.

[0016] The excitation winding mentioned above is the rotor excitation winding of the generator set. The excitation winding is fixedly connected to the output terminal of the DC chopper via a cable.

[0017] The flexible excitation structure connected to the high-voltage side of the main transformer provided by this utility model has the following beneficial effects: 1. This structure connects the flexible excitation system to the high-voltage side of the main transformer. Compared with the traditional generator-end connection method, it significantly reduces the grid-side impedance, resulting in a significant increase in the reactive current flowing to the system side. This effectively enhances the effect of injected reactive power on the system side and fully leverages the advantages of the dual-channel reactive power injection of the flexible excitation system. 2. The flexible excitation system adopts a combination structure of three-phase converter, voltage stabilizing capacitor and DC chopper, which can realize precise control of excitation current and reactive power, improve reactive power control effect, and make the flexible excitation system have better control performance. 3. The three-phase converter, which is composed of fully controlled components, has the ability to boost voltage. When the terminal voltage drops, since the excitation power supply is taken from the high-voltage side of the main transformer, it can quickly achieve strong excitation and effectively restore the system voltage. 4. The flexible excitation system has transient voltage support capability. Through strong excitation and reactive power exchange with the generator terminal, it provides stronger voltage support for the power system, significantly improving the stability of power system operation. It is especially suitable for power grid scenarios with a high proportion of new energy sources. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram of the overall structure of the flexible excitation structure connected to the high-voltage side of the main transformer according to this utility model; Figure 2 A schematic diagram of the equivalent circuit when a flexible excitation is connected to the end of a traditional generator. Figure 3 This is a schematic diagram of the equivalent circuit when the high-voltage side of the main transformer of this utility model is connected to flexible excitation. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments: A flexible excitation structure for high-voltage side connection of a main transformer includes a generator set, a main transformer, a high-voltage side transmission line, an excitation transformer, an excitation winding, and a flexible excitation system; the flexible excitation system is connected to the high-voltage side of the main transformer through the excitation transformer, the flexible excitation system is connected to the excitation winding, the excitation winding is matched and connected to the generator set, and the main transformer is connected to the power system through the high-voltage side transmission line.

[0020] Furthermore, the flexible excitation system includes a three-phase converter, a voltage stabilizing capacitor, and a DC chopper; the input terminal of the three-phase converter is connected to the output terminal of the excitation transformer, the output terminal of the three-phase converter is connected to the input terminal of the voltage stabilizing capacitor, the output terminal of the voltage stabilizing capacitor is connected to the input terminal of the DC chopper, and the output terminal of the DC chopper is connected to the excitation winding.

[0021] Furthermore, the three-phase converter is a VSC converter, which is used to rectify the three-phase AC power output from the excitation transformer into DC power. As a fully controllable converter, the VSC converter has the characteristics of high control precision and fast response speed, and can flexibly realize the AC to DC power conversion, providing a stable DC power supply for subsequent excitation voltage regulation.

[0022] Furthermore, the voltage-stabilizing capacitor is an electrolytic capacitor, which is used to filter and stabilize the DC output of the three-phase converter. Electrolytic capacitors have the advantages of large capacitance and good filtering effect, which can effectively filter out the ripple component in the DC current, ensure the stability of the output DC voltage, and provide a guarantee for the normal operation of the DC chopper.

[0023] Furthermore, the DC chopper is a DC-DC chopper module, which is used to convert the voltage output from the stabilizing capacitor into the excitation voltage required by the excitation winding. The DC-DC chopper module can achieve precise adjustment of the output voltage by adjusting the on and off times of the switching devices, thereby meeting the excitation voltage requirements of the excitation winding under different operating conditions.

[0024] Furthermore, the primary winding of the excitation transformer is connected to the high-voltage busbar of the main transformer, and the secondary winding of the excitation transformer is connected to the input terminal of the flexible excitation system. The excitation transformer is used to reduce the high voltage on the high-voltage side of the main transformer to the input voltage level required by the flexible excitation system, ensuring the safe and stable operation of the flexible excitation system.

[0025] Furthermore, the low-voltage side of the main transformer is connected to the output terminal of the generator set, and the high-voltage side of the main transformer is connected to one end of the high-voltage transmission line, while the other end of the high-voltage transmission line is connected to the power system. The main transformer performs voltage step-up conversion of the generator set's output voltage to meet the requirements of high-voltage transmission, and realizes the exchange of electrical energy between the generator set and the power system through the high-voltage transmission line.

[0026] Furthermore, the reactive current output by the flexible excitation system is divided into two paths: one flows through the main transformer to the generator terminal, and the other flows through the high-voltage transmission line to the power system. This structure enables reasonable diversion of reactive current, significantly increasing the proportion of reactive current flowing to the system side compared to the traditional generator terminal connection method, thus enhancing the reactive power support capability of the power system.

[0027] Furthermore, the flexible excitation system is constructed using fully controllable devices, namely IGBTs or IGCTs. These fully controllable devices are characterized by their ability to control both conduction and shutdown, enabling the flexible excitation system to independently control the exchange of active and reactive power, significantly improving the system's control flexibility and reactive power support capability.

[0028] Furthermore, the excitation winding is the rotor excitation winding of the generator set, and the excitation winding is fixedly connected to the output terminal of the DC chopper via a cable. The rotor excitation winding receives the excitation voltage output from the DC chopper to generate an excitation magnetic field, thereby realizing the electromagnetic energy conversion of the generator set and ensuring the stable operation of the generator set.

[0029] The working principle of this utility model is as follows: During operation, the flexible excitation system draws excitation power from the high-voltage side of the main transformer through the excitation transformer. The excitation transformer steps down the three-phase AC power from the high-voltage side of the main transformer and outputs it to the three-phase converter of the flexible excitation system. The three-phase converter rectifies the stepped-down three-phase AC power into DC power, which is then filtered and regulated by a voltage-stabilizing capacitor before being sent to a DC chopper. The DC chopper converts the regulated DC voltage into the excitation voltage required by the excitation winding according to the operating requirements of the generator set and outputs it to the excitation winding to provide excitation energy for the generator set. At the same time, the reactive current output by the flexible excitation system is divided into two paths: one path flows through the main transformer to the generator set terminals, and the other path flows through the high-voltage side transmission line to the power system, thereby achieving reactive power compensation and voltage support for the power system.

[0030] Example 1: like Figure 1 As shown, a flexible excitation structure for the high-voltage side of a main transformer includes a generator set, a main transformer, a high-voltage transmission line, an excitation transformer, a flexible excitation system, and an excitation winding. The low-voltage side of the main transformer is connected to the output terminal of the generator set, one end of the high-voltage side of the main transformer is connected to the power system through the high-voltage transmission line, and the other end of the high-voltage side of the main transformer is connected to the primary winding of the excitation transformer. The secondary winding of the excitation transformer is connected to the input terminal of the flexible excitation system, and the output terminal of the flexible excitation system is connected to the excitation winding. The excitation winding is the rotor excitation winding of the generator set and is installed in conjunction with the generator set.

[0031] The flexible excitation system includes a three-phase converter, a voltage stabilizing capacitor, and a DC chopper. The three-phase converter is a VSC converter, whose input is connected to the secondary winding of the excitation transformer, used to rectify the three-phase AC power output from the excitation transformer into DC power. The voltage stabilizing capacitor is an electrolytic capacitor, whose input is connected to the output of the three-phase converter, used to filter and stabilize the rectified DC power. The DC chopper is a DC-DC chopper module, whose input is connected to the output of the voltage stabilizing capacitor, and whose output is fixedly connected to the excitation winding via a cable, used to convert the stabilized DC voltage into the excitation voltage required by the excitation winding.

[0032] In this embodiment, the flexible excitation system uses IGBT fully controlled power devices, which can independently control the exchange of active and reactive power on the grid side; the excitation transformer is selected according to the voltage level of the high-voltage side of the main transformer and the input voltage requirements of the flexible excitation system to ensure the matching and safety of voltage conversion.

[0033] like Figure 2 As shown, currently, flexible excitation systems are mostly connected to the excitation power supply from the generator end via an excitation transformer. In this connection scheme, reactive current is injected, part of which flows to the generator end, and the other part flows to the system side through the main transformer and high-voltage transmission lines. Its grid-side impedance... X and reactive current flowing to the system side I qn They are respectively: ; ; in, X T The impedance of the main transformer. X L The impedance of the high-voltage transmission line. X d This represents the generator impedance.

[0034] like Figure 3 As shown, the flexible excitation system is connected to the excitation power supply via the excitation transformer from the high-voltage side of the main transformer. In this connection scheme, reactive current is injected, part of which flows to the generator terminal through the main transformer, and the other part flows to the system side through the high-voltage side transmission line. Its grid-side impedance is... X’ and reactive current flowing to the system side I ’ qn They are respectively: ; ; The comparison shows that: ; ; In summary, the grid-side impedance of flexible excitation connected to the high-voltage side of the main transformer is smaller, the reactive current obtained by shunting is larger, and the advantages of dual-channel reactive power injection of flexible excitation can be better utilized.

[0035] During operation, the excitation power supply is taken from the high-voltage side of the main transformer. After being stepped down by the excitation transformer, it is input to the three-phase converter of the flexible excitation system. The three-phase converter rectifies the three-phase AC power into DC power, which is then filtered and regulated by the voltage-stabilizing capacitor before being sent to the DC chopper. The DC chopper adjusts the voltage to the excitation voltage required by the excitation winding, providing excitation energy for the generator set. At the same time, the reactive current output by the flexible excitation system is divided into two paths: one path flows through the main transformer to the generator set terminals, and the other path flows through the high-voltage side transmission line to the power system, realizing reactive power compensation and voltage support.

[0036] To verify the technical effectiveness of this invention, referring to the excitation system model of Unit 2 of a hydropower station, the structure was connected to the power system via a 50km high-voltage transmission line. The per-unit reactance values ​​of the generator, main transformer, and high-voltage transmission line were selected, and the reactive current flowing to the system side was calculated for both traditional generator-end excitation and the high-voltage side excitation of this invention. The results show that the grid-side impedance of this invention is lower, and the reactive current flowing to the system side is approximately 1.58 times that of the traditional generator-end connection method. This significantly improves the effect of reactive power injection on the system side, enabling rapid reactive power compensation, effectively maintaining the voltage level of the power system, and greatly improving the stability of power system operation.

[0037] The above description is merely a preferred embodiment of this utility model and is not intended to limit the utility model in any way. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A flexible excitation structure connected to the high-voltage side of a main transformer, characterized in that: It includes generator sets, main transformers, high-voltage transmission lines, excitation transformers, excitation windings, and flexible excitation systems. The flexible excitation system is connected to the high-voltage side of the main transformer through the excitation transformer, the flexible excitation system is connected to the excitation windings, the excitation windings are matched with the generator sets, and the main transformer is connected to the power system through the high-voltage transmission lines.

2. The flexible excitation structure connected to the high-voltage side of the main transformer according to claim 1, characterized in that, The flexible excitation system includes a three-phase converter, a voltage stabilizing capacitor, and a DC chopper; the input terminal of the three-phase converter is connected to the output terminal of the excitation transformer, the output terminal of the three-phase converter is connected to the input terminal of the voltage stabilizing capacitor, the output terminal of the voltage stabilizing capacitor is connected to the input terminal of the DC chopper, and the output terminal of the DC chopper is connected to the excitation winding.

3. The flexible excitation structure connected to the high-voltage side of the main transformer according to claim 2, characterized in that, The three-phase converter is a VSC converter, which is used to rectify the three-phase AC power output from the excitation transformer into DC power.

4. The flexible excitation structure connected to the high-voltage side of the main transformer according to claim 2, characterized in that, The voltage-stabilizing capacitor is an electrolytic capacitor, which is used to filter and stabilize the DC output of the three-phase converter.

5. A flexible excitation structure for the high-voltage side of a main transformer according to claim 2, characterized in that, The DC chopper mentioned is a DC-DC chopper module, which is used to convert the voltage output by the stabilizing capacitor into the excitation voltage required by the excitation winding.

6. The flexible excitation structure connected to the high-voltage side of the main transformer according to claim 1, characterized in that, The primary winding of the excitation transformer is connected to the high-voltage busbar of the main transformer, and the secondary winding of the excitation transformer is connected to the input terminal of the flexible excitation system.

7. A flexible excitation structure for the high-voltage side of a main transformer according to claim 1, characterized in that, The low-voltage side of the main transformer is connected to the output terminal of the generator set, the high-voltage side of the main transformer is connected to one end of the high-voltage transmission line, and the other end of the high-voltage transmission line is connected to the power system.

8. A flexible excitation structure for the high-voltage side of a main transformer according to claim 1, characterized in that, The reactive current output by the flexible excitation system is divided into two paths: one path flows through the main transformer to the generator terminal, and the other path flows through the high-voltage side transmission line to the power system.

9. A flexible excitation structure for the high-voltage side of a main transformer according to claim 1, characterized in that, The flexible excitation system is composed of fully controlled devices, which are IGBT or IGCT power devices.

10. A flexible excitation structure for the high-voltage side of a main transformer according to claim 1, characterized in that, The excitation winding is the rotor excitation winding of the generator set, and the excitation winding is fixedly connected to the output terminal of the DC chopper via a cable.

Images