Automatic de-excitation device for large three-machine brushless excitation generator

Abstract

The present invention discloses an automatic de-excitation device for a large three-machine brushless excitation generator, which adjusts the excitation system. The excitation system converts the power output by the permanent magnet machine into an excitation current and transmits it to the generator excitation. The automatic de-excitation device adjusts the magnitude of the excitation current in the excitation system. The automatic de-excitation device also obtains the power supply voltage and power supply frequency output by the permanent magnet machine, and starts the automatic de-excitation program when the power supply voltage is lower than a first preset value or the power supply frequency is lower than a second preset value, thereby controlling the excitation current of the excitation system to achieve demagnetization. Compared with the prior art, the present invention generates an automatic de-excitation signal when the power supply voltage and power supply frequency output by the permanent magnet machine are lower than preset values, thereby automatically starting the de-excitation program, and can de-excite in time when the machine stops due to a fault or the excitation switch refuses to move, thereby ensuring the safe operation of the excitation system.

Description

Technical Field

[0001] The invention relates to a generator excitation system, in particular to an automatic de-excitation device for the excitation of a large three-machine brushless excitation generator. Background Art

[0002] The main excitation methods for large steam turbine generator sets are self-parallel excitation and three-machine brushless excitation. The excitation system 20 of the brushless excitation generator set is shown below Figure 1 As shown. After the excitation system obtains power from the permanent magnet machine 22 coaxial with the generator, it is converted into direct current through a rectifier bridge and output to the main exciter 23 for excitation. The alternating current generated by the main exciter 23 is rectified into direct current through a rotating rectifier bridge and then excites the generator 24, thereby generating a rotating magnetic field of the generator and prompting the steam turbine generator set to convert kinetic energy into electrical energy. The automatic excitation regulator 21 (AVR: automatic voltage regulator) plays a core regulating and controlling role in the generator excitation system. By adjusting the trigger angle of the rectifier bridge to change the magnitude of the excitation winding current output to the main exciter 23, the purpose of adjusting the strength of the generator magnetic field and the generator terminal voltage is achieved.

[0003] At present, there are two ways to de-excite the excitation regulator of the generator set. One is to directly trip the de-excitation switch by the tripping signal of the electrical internal or external protection, and the other is to automatically de-excite by the automatic de-excitation signal sent by the excitation regulator locally or remotely. In the first way, after receiving the tripping command, the excitation regulator directly trips the de-excitation switch and connects the de-excitation resistor, the regulator power supply and the rectifier bridge circuit are disconnected, and the energy of the main exciter field winding circuit is consumed by the de-excitation resistor; in the second way, after receiving the automatic de-excitation signal, the excitation regulator triggers the automatic de-excitation program, and adjusts the trigger angle of the rectifier bridge thyristor according to the internal setting logic, so that it finally runs in the inverter state and achieves the effect of rapid de-excitation.

[0004] The existing automatic de-excitation logic of the excitation regulator is mainly that during the commissioning of the excitation regulator, the regulator is manually operated on-site to automatically de-excite. Some unit regulators are also equipped with remote automatic de-excitation signals, such as program shutdown signals or automatic de-excitation after the generator is disconnected to perform inverter demagnetization. However, when the auxiliary exciter power supply does not meet the requirements, the excitation regulator only sends an alarm, and at this time the excitation system cannot work normally, and even if there is a fault in the auxiliary exciter circuit, continuing to operate will worsen the fault and even endanger the safety of the excitation regulator and excitation system equipment.

[0005] When the auxiliary exciter power supply does not meet the requirements, the existing generator excitation regulator only sends an alarm and cannot automatically de-excite so that the generator excitation system can exit in time. The main risks and shortcomings are as follows:

[0006] 1. When the auxiliary exciter power supply does not meet the requirements, the excitation regulator and its power unit can no longer provide the excitation current required for the normal operation of the generator. If it continues to deteriorate, it may cause the generator to run in phase or lose magnetism for a long time, which is not conducive to the safe and stable operation of the generator and the nearby power grid.

[0007] 2. In the event of failure of the auxiliary exciter and its power supply circuit, if the excitation cannot be stopped in time, the upstream power supply circuit failure may be transmitted or affect the regulator power circuit and control circuit, causing damage to the excitation regulator, and may also further affect the safety of other equipment in the excitation system.

[0008] 3. When the generator set fails and needs to shut down, if the excitation regulator receives the electrical protection tripping demagnetization signal and the demagnetization switch refuses to operate, it will not be conducive to the rapid demagnetization of the generator. The generator will provide fault current to the fault point for a long time, which may cause the fault to worsen and cause damage to the primary equipment.

[0009] Therefore, there is an urgent need for an automatic de-excitation device to solve the above-mentioned problems. Summary of the invention

[0010] The purpose of the present invention is to provide an automatic de-excitation device for a large three-machine brushless excitation generator, which can de-excite in time when the generator stops due to a fault.

[0011] In order to achieve the above purpose, the present invention discloses an automatic de-excitation device for a large three-machine brushless excitation generator, which adjusts the excitation system. The excitation system converts the power output by the permanent magnet machine into an excitation current and transmits it to the generator excitation. The automatic de-excitation device adjusts the magnitude of the excitation current in the excitation system. The automatic de-excitation device also obtains the power supply voltage and power supply frequency output by the permanent magnet machine, and triggers an automatic de-excitation program when the power supply voltage is lower than a first preset value or the power supply frequency is lower than a second preset value, thereby controlling the excitation current of the excitation system to achieve demagnetization.

[0012] Compared with the prior art, the present invention monitors the power supply of the permanent magnet machine in real time. When the power supply of the permanent magnet machine does not meet the requirements, the automatic de-excitation device can automatically de-excite without human intervention, which can effectively avoid the expansion of the impact of the situation caused by the failure of the permanent magnet machine circuit. At the same time, it can also be used as a backup de-excitation means for the unit when the electrical protection needs to shut down and de-excite but the de-excitation switch does not work normally. Specifically, the following situations can be guaranteed: on the one hand, when the power supply of the permanent magnet machine (auxiliary exciter) does not meet the requirements, the excitation is automatically de-excited to avoid the adverse effects caused by the failure of the excitation system output to meet the normal operation requirements of the generator, resulting in the long-term low excitation or leading phase operation of the generator; on the other hand, when the permanent magnet machine (auxiliary exciter) and its circuit fail or the excitation switch refuses to move, the excitation is promptly withdrawn, avoiding the further impact of the auxiliary exciter and its circuit failure on the excitation system; on the other hand, when the generator set fails and needs to trip and de-excite but the de-excitation switch refuses to move, it is used as a backup de-excitation to avoid the adverse effects of the generator continuing to provide current to the fault point for a long time.

[0013] Preferably, the automatic de-excitation device generates a power supply abnormality signal when the power supply voltage is lower than a first preset value or the power supply frequency is lower than a second preset value, and triggers an automatic de-excitation program according to the power supply abnormality signal.

[0014] Specifically, the automatic de-excitation device includes a voltage-frequency relay and an automatic voltage regulator, wherein the voltage-frequency relay is connected to the power supply output by the permanent magnet machine and generates a power supply abnormality signal when the power supply voltage is lower than a first preset value, and generates a power supply abnormality signal when the power supply frequency is lower than a second preset value, and the automatic voltage regulator receives the power supply abnormality signal and triggers the automatic de-excitation program upon receiving the power supply abnormality signal. The voltage-frequency relay determines whether the power supply is abnormal and generates a power supply abnormality signal when the power supply is abnormal. There is no need to re-edit the structure and internal software of the automatic voltage regulator. It is only necessary to connect the power supply abnormality signal to the relevant interface in the automatic voltage regulator that triggers the automatic de-excitation program (for example, the power supply abnormality signal is used as the automatic de-excitation signal to trigger the automatic de-excitation).

[0015] Preferably, the automatic de-excitation device includes an automatic voltage regulator, which is connected to the output power supply of the permanent magnet machine, determines that the power supply is abnormal when the power supply voltage is lower than a first preset value or the power supply frequency is lower than a second preset value, and triggers the automatic de-excitation program when the power supply is abnormal and the automatic excitation regulator operates normally.

[0016] Preferably, the automatic excitation withdrawal device also alarms while triggering the automatic excitation withdrawal procedure.

[0017] Preferably, the excitation system includes a rectifier bridge, a main exciter and a rotating rectifier bridge. The rectifier bridge converts the power output by the permanent magnet machine into a DC power supply and transmits it to the main exciter. The main exciter converts the DC power supply into an AC power supply and rectifies it into DC through a rotating rectifier bridge to excite the generator. The steps of triggering the automatic de-excitation program by the automatic de-excitation device specifically include: adjusting the trigger angle of the rectifier bridge thyristor to make the excitation system operate in an inverter state, thereby achieving demagnetization.

[0018] Preferably, the first preset value is 85% of the rated load voltage, and the second preset value is 90% of the rated frequency. Of course, the first preset value and the second preset value can also be other set values, which can be set as needed. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the excitation system diagram of the brushless excitation generator set.

[0020] Figure 2 The invention discloses a circuit diagram of an automatic de-excitation device for an excitation generator.

[0021] Figure 3 It is a working schematic diagram of the automatic de-excitation device for the excitation generator of the present invention. DETAILED DESCRIPTION

[0022] In order to explain the technical content, structural features, achieved objectives and effects of the present invention in detail, the following is a detailed description in conjunction with the implementation methods and the accompanying drawings.

[0023] refer to Figure 2 and Figure 3 The present invention discloses a large three-machine brushless excitation generator automatic de-excitation device 100, which adjusts the excitation system 20, referring to Figure 1 The excitation system 20 converts the power output by the permanent magnet machine 22 into an excitation current and transmits it to the generator 24 for excitation. The automatic de-excitation device 100 adjusts the magnitude of the excitation current in the excitation system 20. The automatic de-excitation device 100 also obtains the power voltage Umc and the power frequency fmc output by the permanent magnet machine 22. When either the power voltage Umc is lower than a first preset value or the power frequency fmc is lower than a second preset value, the automatic de-excitation program is triggered. The automatic de-excitation device 100 controls the magnitude of the excitation current of the excitation system 20 according to the automatic de-excitation program to achieve demagnetization.

[0024] Specifically, the automatic de-excitation device 100 includes a voltage-frequency relay 11 and an automatic voltage regulator 21. The voltage-frequency relay 11 is connected to the power supply output by the permanent magnet machine 22 and generates a power supply abnormality signal when the power supply voltage Umc is lower than a first preset value, and generates a power supply abnormality signal S1 when the power supply frequency fmc is lower than a second preset value. The automatic voltage regulator 21 is connected to the power supply abnormality signal S1 and triggers the automatic de-excitation program according to the power supply abnormality signal S1. Among them, the voltage-frequency relay 11 is connected to the three-phase power output by the permanent magnet machine 22 according to the fuses F1, F2, and F3 respectively. Since the original automatic voltage regulator 21 can trigger automatic de-excitation according to the command input by the relevant control button, in this scheme, the power supply abnormality signal output by the voltage-frequency relay 11 is connected to the input interface of the above-mentioned control button, so that the automatic voltage regulator 21 triggers the de-excitation logic according to the power supply abnormality signal, and there is no need to re-edit the structure and internal software of the automatic voltage regulator 21, and only the power supply abnormality signal needs to be connected to the relevant interface in the automatic voltage regulator 21.

[0025] Of course, other components may be added between the permanent magnet machine 22 and the automatic voltage regulator 21 to replace the voltage-frequency relay 11. The replacement component may generate a power supply abnormality signal S1 when the power supply voltage Umc is lower than a first preset value or the power supply frequency fmc is lower than a second preset value.

[0026] refer to Figure 1 The automatic voltage regulator 21 adjusts the trigger angle of the rectifier bridge thyristor T according to the automatic de-excitation signal, so that the main exciter 23 operates in the inverter state, thereby achieving de-excitation.

[0027] Among them, the first preset value is 85% of the rated load voltage Un, and the second preset value is 90% of the rated frequency fn. Of course, the first preset value and the second preset value can also be other set values, which can be set as needed. During operation, when the power supply voltage Umc is lower than 85% of the rated load voltage Un, or the power supply frequency fmc is lower than 90% of the rated frequency fn, when either of the two occurs, a power supply abnormality signal is generated.

[0028] Preferably, reference Figure 3Different from the above embodiment, in another embodiment, the automatic de-excitation device 100 includes an automatic voltage regulator 21, which is connected to the output power supply of the permanent magnet machine 22, and determines that the power supply is abnormal when the power supply voltage Umc is lower than the first preset value or the power supply frequency fmc is lower than the second preset value, and triggers the automatic de-excitation program when the power supply is abnormal and the automatic excitation regulator is operating normally. Specifically, the automatic voltage regulator 21 generates a power supply abnormality signal when the power supply voltage Umc is lower than the first preset value or the power supply frequency fmc is lower than the second preset value, generates an automatic de-excitation signal according to the power supply abnormality signal and the AVR normal operation signal, and triggers the automatic de-excitation according to the automatic de-excitation signal.

[0029] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention are still within the scope covered by the present invention.

Claims

1. An automatic de-excitation device for a large three-machine brushless excitation generator, which adjusts the excitation system. The excitation system converts the power output by the permanent magnet machine into an excitation current and transmits it to the generator excitation. The automatic de-excitation device adjusts the magnitude of the excitation current in the excitation system, characterized in that: The automatic de-excitation device also obtains the power supply voltage and power supply frequency output by the permanent magnet machine, and triggers the automatic de-excitation program when the power supply voltage is lower than a first preset value or the power supply frequency is lower than a second preset value, thereby controlling the excitation current of the excitation system to achieve de-excitation.

2. The automatic de-excitation device for a large three-machine brushless excitation generator according to claim 1, characterized in that: The automatic de-excitation device generates a power supply abnormality signal when the power supply voltage is lower than a first preset value or the power supply frequency is lower than a second preset value, and triggers an automatic de-excitation program according to the power supply abnormality signal.

3. The automatic de-excitation device for a large three-machine brushless excitation generator as claimed in claim 2, characterized in that: The automatic de-excitation device includes a voltage-frequency relay and an automatic voltage regulator. The voltage-frequency relay is connected to the power supply output by the permanent magnet machine and generates a power supply abnormality signal when the power supply voltage is lower than a first preset value, and generates a power supply abnormality signal when the power supply frequency is lower than a second preset value. The automatic voltage regulator is connected to the power supply abnormality signal and triggers the automatic de-excitation program when receiving the power supply abnormality signal.

4. The automatic de-excitation device for a large three-machine brushless excitation generator as claimed in claim 1, characterized in that: The automatic de-excitation device includes an automatic voltage regulator, which is connected to the output power supply of the permanent magnet machine. When the power supply voltage is lower than a first preset value or the power supply frequency is lower than a second preset value, it is determined that the power supply is abnormal, and when the power supply is abnormal and the automatic excitation regulator operates normally, an automatic de-excitation program is triggered.

5. The automatic de-excitation device for a large three-machine brushless excitation generator according to claim 1, characterized in that: The automatic de-excitation device also alarms while triggering the automatic de-excitation program.

6. The automatic de-excitation device for a large three-machine brushless excitation generator according to claim 1, characterized in that: The excitation system includes a rectifier bridge, a main exciter and a rotating rectifier bridge. The rectifier bridge converts the power output by the permanent magnet machine into a DC power supply and transmits it to the main exciter. The main exciter converts the DC power supply into an AC power supply and excites the generator after it is rectified into DC through a rotating rectifier bridge. The steps of triggering the automatic de-excitation program by the automatic de-excitation device specifically include: adjusting the trigger angle of the rectifier bridge thyristor to make the excitation system run in an inverter state, thereby achieving de-excitation.

7. The automatic de-excitation device for a large three-machine brushless excitation generator according to claim 1, characterized in that: The first preset value is 85% of the rated load voltage, and the second preset value is 90% of the rated frequency.

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