A reliable microcomputer type excitation regulator synchronous generator grid-connected comprehensive judgment method

Abstract

A reliable comprehensive judgment method for grid connection of microprocessor-based excitation regulator synchronous generators, wherein the circuit breaker position input signal circuit connected to the excitation regulator is controlled by the three-phase normally open auxiliary contact DL of the high-voltage side circuit breaker of the main transformer. A DL B and DL C After being connected in series, it is then connected in series with the normally open auxiliary contact GCB of the generator terminal circuit breaker. When the input signal circuit is closed, the generator is determined to be in grid-connected state; when the circuit breaker position input signal circuit is open and the generator stator current is less than 10% of the rated stator current, the generator is determined to be disconnected, i.e., in no-load state. Improvements are made to three aspects of the microprocessor-based excitation regulator generator grid connection determination: the wiring of the input circuit, the stator current analog threshold setting value, and the logic relationship of generator grid connection and disconnection; this can greatly improve the reliability of the microprocessor-based excitation regulator generator grid connection determination criteria.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and specifically to a reliable comprehensive judgment method for grid connection of a microprocessor-based excitation regulator synchronous generator. Background Technology

[0002] The basic tasks of the excitation system are: to maintain a constant generator terminal voltage (within a given value) by adjusting the magnitude of the excitation current to change the strength of the generator rotor magnetic field; to stably (reasonably) distribute reactive power among parallel-operating units; and to improve the stability of the power system, including static, transient, and dynamic stability. For the commonly used static rectifier excitation system, the regulator controls the magnitude of the excitation current by changing the firing angle of the thyristor.

[0003] Taking the IAEC-2000 excitation regulator as an example, the basic principle of its volt-hertz limiting is explained below. [1] as follows:

[0004] When the generator operating frequency is higher than 47Hz, the regulator's terminal voltage reference value remains at the normal setpoint and is unaffected by the volt-hertz limiting function. When the generator is in the low-speed range (47-45Hz), the volt-hertz limiting circuit activates to reduce the voltage setpoint and excitation current, ensuring that the ratio of the generator terminal voltage per unit value to the frequency per unit value (U* / f*) is 1.095, i.e., satisfying U* / f*=1.095. When f≤45Hz, if the generator is in no-load operation, the regulator issues an inverter command to automatically demagnetize; if the generator is in grid-connected operation, the volt-hertz limiting function should automatically block the inverter command. In other words, the regulator only issues an inverter command to demagnetize when the generator is in no-load operation; when the generator is under load, the regulator automatically blocks the inverter command.

[0005] It is evident that the regulator's ability to accurately and reliably determine whether a generator is in grid-connected operation is crucial for the proper functioning of the regulator's volt-hertz limiting function.

[0006] However, years of practical operating experience have shown that the generator grid connection criterion of the IAEC-2000 excitation regulator is not perfect and reliable, and has the following problems: For the case of generator-transformer unit connection, and circuit breakers are installed at both the generator terminal and the high-voltage side of the main transformer, when the high-voltage side circuit breaker of the main transformer is disconnected for load shedding test, or during normal operation, if the high-voltage side circuit breaker of the main transformer trips unexpectedly, the volt-hertz limit function of the regulator will fail, and the excitation transformer overcurrent protection will be activated, resulting in GCB false tripping, false shutdown, and false demagnetization. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a reliable comprehensive judgment method for grid connection of microprocessor-based excitation regulator synchronous generator, which solves the problem that the volt-hertz limit function of the excitation regulator fails under the existing conditions, causing the excitation transformer overcurrent protection to trip, stop, and de-excite the generator.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A reliable comprehensive judgment method for grid connection of microprocessor-based excitation regulator synchronous generators, wherein the circuit breaker position input signal circuit connected to the excitation regulator is controlled by the three-phase normally open auxiliary contact DL of the high-voltage side circuit breaker of the main transformer. A DL B and DL C After being connected in series, it is then connected in series with the normally open auxiliary contact GCB of the generator terminal circuit breaker. When the input signal circuit is turned on, it is determined that the generator is in grid-connected state.

[0010] When the circuit breaker position input signal circuit is disconnected and the generator stator current is less than 10% of the rated stator current, the generator is determined to be disconnected, i.e., in an unloaded state.

[0011] This invention provides a reliable comprehensive judgment method for grid connection of microprocessor-based excitation regulator synchronous generators. It improves three aspects of the grid connection judgment method: the wiring of the input circuit, the stator current analog threshold setting value, and the logical relationship between generator grid connection and disconnection. This method can greatly improve the reliability of the grid connection judgment criteria for microprocessor-based excitation regulator generators and avoid the occurrence of generator-related abnormalities. Attached Figure Description

[0012] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0013] Figure 1 The wiring diagram of the original input circuit in the existing technology;

[0014] Figure 2 This is the wiring diagram of the improved input circuit of the present invention;

[0015] Figure 3 The above is a waveform recording of the frequency changes of the five generators before the improvement in the embodiment;

[0016] Figure 4 The waveforms of the excitation regulators of generator No. 5 before the improvement in the embodiment are shown.

[0017] Figure 5 The above is a waveform recording of the relay protection fault of generator No. 5 before the improvement in the embodiment;

[0018] Figure 6 The waveform diagram shown in the example is when the generator sheds 100% of its rated active load. Detailed Implementation

[0019] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0020] A reliable comprehensive judgment method for grid connection of microprocessor-based excitation regulator synchronous generators, wherein the circuit breaker position input signal circuit connected to the excitation regulator is controlled by the three-phase normally open auxiliary contact DL of the high-voltage side circuit breaker of the main transformer. A DL B and DL C After being connected in series, it is then connected in series with the normally open auxiliary contact GCB of the generator terminal circuit breaker. When the input signal circuit is turned on, it is determined that the generator is in grid-connected state.

[0021] When the circuit breaker position input signal circuit is disconnected and the generator stator current is less than 10% of the rated stator current, the generator is determined to be disconnected, i.e., in an unloaded state.

[0022] Example:

[0023] I. Electrical main wiring and load shedding test of generator unit No. 5 at a certain hydropower station

[0024] The rated active power of generator No. 5 (hereinafter referred to as 5F) of a certain hydropower station is 150MW. 5F is connected to the 220kV switchyard via the generator terminal current transformer, generator terminal circuit breaker (805DL), main transformer, high-voltage side overhead line, and main transformer high-voltage side circuit breaker (05DL), i.e., the generator-transformer unit connection is adopted. After the generator terminal current transformer, the excitation transformer (2100kVA) and the self-use transformer (315kVA) are connected in parallel. Between the generator terminal circuit breaker (805DL) and the low-voltage side of the main transformer, the plant service transformer (4000kVA) is connected in parallel. The generator stator current sampled by the excitation regulator is taken from the 5F generator terminal current transformer.

[0025] During the 100% rated active load (150MW) shedding test of the 5F transformer, after the high-voltage side circuit breaker 05DL of the main transformer opened, the unit frequency rose to 68Hz and then quickly dropped to below 40Hz. At this time, the 5F transformer was already in an unloaded state, and the unit frequency had dropped to below 45Hz. According to the aforementioned volt-hertz limiting principle of the regulator, inverter de-excitation should have been performed under these circumstances. However, the 5F regulator did not perform inverter de-excitation at this time, meaning the regulator's volt-hertz limiting function failed. Subsequently, the 5F excitation transformer overcurrent protection (using the excitation transformer high-voltage side current transformer) tripped, and after a 0.5-second delay, the circuit breaker 805DL was tripped, the unit stopped, and de-excited. Figure 3 It can be seen that after the circuit breaker 05DL trips, the generator frequency increases and then decreases to 45Hz in about 15 seconds.

[0026] II. Analysis of the causes of regulator volt-herm limit function failure and excitation transformer overcurrent protection operation during 5F load shedding test

[0027] The 5F generator of this power station uses an IAEC-2000 excitation regulator. Its generator grid connection criteria are as follows: it adopts an "OR" logic of the normally open auxiliary contact of the high-voltage side circuit breaker of the main transformer being closed and the generator stator current being greater than 5% of the rated stator current; that is, as long as one of the conditions is met, the generator is determined to be in grid connection state. The generator disconnection (no-load) criteria are: the normally open auxiliary contact of the high-voltage side circuit breaker of the main transformer is in the open state, and the generator stator current is less than 5% of the rated stator current, that is, an "AND" logic relationship.

[0028] from Figure 4 As can be seen from the data, after the circuit breaker 05DL trips, the generator rotor voltage drops rapidly and then rises slowly. The rotor current also rises slowly after changing downwards, while the generator stator voltage remains relatively stable (the generator's reactive power also begins to increase after about 15 seconds). This is because the excitation regulator adjusts the generator to maintain a constant stator voltage after the generator sheds its load.

[0029] Fault waveform recording of generator No. 5 relay protection and analysis of the cause of excitation transformer overcurrent protection operation:

[0030] like Figure 5 As shown in the diagram, when the excitation regulator maintains a stable generator stator voltage, the generator stator current steadily increases, reaching 4312A at the generator terminals (maximum secondary current of the terminal current transformer is 2.54A, transformation ratio: 12000 / 5A). This is because when the regulator is in "constant terminal voltage" control mode, and the excitation regulator determines that the generator is in grid-connected status, the generator stator voltage will also drop rapidly when the generator frequency (speed) drops rapidly. To maintain the generator terminal voltage at the given value, the excitation current must be increased (therefore, the generator stator current also increases), eventually reaching... The overcurrent protection setting value of the excitation transformer is as follows: the overcurrent protection output after delay is: tripping circuit breaker 805DL, tripping FMK, and the unit is shut down; the current transformer ratio used for the overcurrent protection of the excitation transformer of generator #5 is 600 / 5A, the setting value is: , and the operating time is 0.5 seconds; because the core magnetic flux of generator #5, main transformer, excitation transformer, plant service transformer, and self-service transformer is higher than or close to saturation at normal frequency during this low-frequency process, the excitation impedance of the four transformers will be greatly reduced, and their excitation current will be greatly increased than normal, resulting in a large part of the stator current of generator #5 being diverted by the excitation current of the four transformers.

[0031] Based on a comprehensive analysis of the basic principles of the IAEC-2000 excitation regulator's volt-Hertz limiting function, generator grid connection criteria, and field test results, the reasons for the failure of the 5F regulator's volt-Hertz limiting function and the activation of the 5F excitation transformer's overcurrent protection are as follows:

[0032] 1. The reason why the regulator's volt-hertz limiting function fails during the 5F load shedding process is as follows: When the 5F frequency drops to 45Hz, due to the low frequency state of 5F, the core magnetic flux of the main transformer, station service transformer, self-service transformer, and excitation transformer all increase significantly or become saturated compared to normal values, resulting in a significant reduction in their excitation impedance and causing their excitation current to be much larger than normal. Since the stator current sampled by the IAEC-2000 excitation regulator at this time includes the current of the above four transformers, when the stator current sampled by the regulator is greater than the threshold value of 5% of the rated stator current, the regulator judges the generator to be in "grid-connected" state, and the regulator cannot issue an inverter command, causing the regulator's volt-hertz limiting function to fail.

[0033] 2. The reason for the tripping and shutdown of the 5F excitation transformer overcurrent protection is as follows: When the 5F frequency drops to 45Hz or below, the stator current sampled by the regulator is greater than the threshold value of 5% of the rated stator current. The regulator has determined that the generator is in grid-connected state, and the regulator's volt-hertz limiting function is locked. Since the regulator is operating in the "constant generator terminal voltage" control mode, in order to maintain the generator terminal voltage at the rated voltage value, the regulator will increase the 5F excitation current, and the excitation transformer current will also increase accordingly. On the other hand, since 5F is still in a low frequency state, the core flux of the excitation transformer will increase much more than the normal value or become saturated, which will greatly reduce its excitation impedance, resulting in its excitation current being much larger than the normal excitation current. Due to these two reasons, when the excitation transformer current increases to the excitation transformer overcurrent protection setting value, the protection will trip the circuit breaker 805DL, shut down, and de-excite via a time delay output.

[0034] III. Comprehensive Criteria for Grid Connection of Regulator Generator Using This Patent

[0035] 1. The position input signal of the IAEC-2000 microprocessor-based regulator circuit breaker, which originally only used the three-phase normally open auxiliary contacts of the high-voltage side circuit breaker of the main transformer in series, is changed as follows: Figure 1 As shown in the diagram, the normally open auxiliary position contact of the generator terminal circuit breaker is changed to be connected in series with the three-phase normally open auxiliary position contact of the existing high-voltage side circuit breaker of the main transformer, as shown in the diagram. Figure 2 As shown in the figure; when the input is connected, it is determined that the generator is in grid-connected state.

[0036] 2. Because the IAEC-2000 microcomputer-based excitation regulator program does not consider factors such as the connection of plant service transformers, self-service transformers, and excitation transformers between the generator terminal and the low-voltage side of the main transformer, the stator current threshold value in its generator grid connection criterion is relatively small. Therefore, it is necessary to modify the stator current threshold value of the generator disconnection (no-load) criterion in the regulator program, increasing the original stator current threshold value from 5% of the rated stator current to 10% of the rated stator current. In this way, when the above-mentioned improved input is disconnected and the generator stator current is less than 10% of the rated stator current, the generator is judged to be in a disconnection (no-load) state.

[0037] This invention improves three aspects of the IAEC-2000 microprocessor-based excitation regulator's generator grid connection criteria: the wiring of the input circuit, the stator current analog threshold setting value, and the logic relationship for generator grid connection and disconnection. In recent years, multiple generator tests and numerous load shedding tests have proven that the microprocessor-based excitation regulator produced using this patent can reliably maintain the generator terminal voltage at its rated value after the generator load shedding test, and the excitation transformer overcurrent protection no longer trips or shuts down. When the generator sheds 100% of its rated active load, the relevant generator terminal voltage (U...)... AB Waveforms showing changes in analog quantities, such as... Figure 6 As shown in the figure, it can be seen that using this patent can greatly improve the reliability of the grid connection criterion for microprocessor-based excitation regulator generators.

[0038] The microprocessor-based excitation regulator manufactured using this patent has the following advantages:

[0039] 1. Operational experience proves that if the microcomputer-based excitation regulator produced by this patent is used, for situations where a generator-transformer unit is connected and circuit breakers are installed at both the generator terminal and the high-voltage side of the main transformer, when the high-voltage side circuit breaker of the main transformer is disconnected for load shedding tests, or during normal operation when the high-voltage side circuit breaker of the main transformer trips unexpectedly, the regulator's volt-hertz limiting function can be reliably prevented from failing, and the excitation transformer overcurrent protection will not be triggered. This will prevent the generator terminal circuit breaker from tripping, stopping, or de-exciting incorrectly.

[0040] 2. It can effectively avoid the generator's accidental shutdown and demagnetization under the above circumstances, and can reduce the time required for restarting the generator after accidental shutdown and demagnetization, as well as the pressure building time. This is conducive to the generator quickly reconnecting to the grid and generating electricity, thereby reducing the generator's no-load water wastage loss, increasing power generation, and having good economic benefits.

[0041] 3. This patent can provide reference for the program design or optimization of circuit breaker position input and synchronous generator grid connection criteria for various microcomputer-based excitation regulators, and has broad application value.

Claims

1. A reliable comprehensive judgment method for grid connection of a microprocessor-based excitation regulator synchronous generator, characterized in that, The circuit breaker position input signal circuit connected to the excitation regulator is via the three-phase normally open auxiliary contact DL of the high-voltage side circuit breaker of the main transformer. A DL B and DL C After being connected in series, it is then connected in series with the normally open auxiliary contact GCB of the generator terminal circuit breaker. When the input signal circuit is turned on, it is determined that the generator is in grid-connected state. When the circuit breaker position input signal circuit is disconnected and the generator stator current is less than 10% of the rated stator current, the generator is determined to be disconnected, i.e., in an unloaded state.

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