An evaluation device and method for the slow fuse discrimination performance of an excitation system PT

Abstract

The present invention discloses a device and method for evaluating the slow fuse discrimination performance of a PT in an excitation system. The device includes a slow fuse simulator, and the slow fuse simulator includes an isolation transformer PT3. The excitation system includes a generator G, a potential transformer PT1, a potential transformer PT2, and an excitation regulator AVR. The three-phase input terminals of the potential transformer PT1 are respectively connected to the three phases of the generator G, the three-phase output terminals of the potential transformer PT1 are respectively connected to the three-phase input terminals of the isolation transformer PT3, the three-phase output terminals of the isolation transformer PT3 are respectively connected to the three-phase input terminals of the first channel of the excitation regulator AVR, and a potential transformer PT2 is connected between the second channel of the excitation regulator AVR and the generator G. The advantages of the present invention are as follows: evaluate the PT slow fuse discrimination performance of the excitation regulator AVR, rectify the excitation regulator in time, and avoid the unplanned outage of the unit.

Description

Technical Field

[0001] The present invention relates to the field of electrical equipment testing and detection, and more specifically to a device and method for evaluating the performance of PT slow-fuse discrimination of an excitation system. Background Art

[0002] When the primary fuse of the voltage transformer (referred to as "PT") for generator output excitation slowly blows (referred to as "PT slow blow"), the resistance of the PT primary fuse increases slowly and continuously, and finally disconnects completely. When observed at the PT secondary voltage sampling end, the sampling voltage of the excitation regulator decreases slowly and continuously.

[0003] When the PT is slow to melt, if the excitation regulator cannot timely and effectively identify the "PT slow to melt" phenomenon, cannot issue a "PT disconnection" alarm, and cannot implement channel switching or control loop switching, the following consequences may occur:

[0004] a) The excitation regulator will mistakenly judge that the generator outlet voltage Ug is reduced, but at this time the voltage set value Uref of the excitation regulator has not changed (because the DCS and AVC devices have no increase or decrease magnetic field instruction output), which will cause the difference between the sampled voltage value and the voltage set value (Uref-Ug) to continue to increase. Due to the PID closed-loop control, the excitation system continues to increase the excitation, and the excitation current continues to increase, which eventually causes the actual primary voltage at the generator end to continue to increase until the "overexcitation" protection action of the generator-transformer group is triggered.

[0005] b) If the unit operator can intervene in time to demagnetize (i.e., reduce the voltage set value Uref of the excitation regulator) during the "PT slow melting" process, there is a certain probability to avoid the unit tripping caused by the action of the "overexcitation" protection device of the generator-transformer group. However, the "PT slow melting" process has a great deal of randomness. During the demagnetization process, if the slow melting process of the PT primary fuse used for sampling the current channel is restored in a short time (i.e., the fuse resistance is reduced again), the sampling voltage of the current channel of the excitation regulator will inevitably rise sharply, and the excitation system will be demagnetized, causing the reactive power of the generator to drop sharply. The generator may enter the leading phase operation range, and even cause the demagnetization protection of the generator-transformer group to act and cause the generator to trip.

[0006] c) During the slow melting process of the PT primary fuse in the current operating channel of the excitation regulator, due to the low sampled voltage in the current channel while the PT primary fuse in the standby channel is intact and the sampled voltage is normal, there will be a large deviation in the sampled voltages between the current channel and the standby channel. If during the slow melting process of the PT in the current channel, the operator manually switches the regulator channel (from the current channel to the standby channel), it will inevitably quickly pull down the generator terminal voltage, which is equivalent to making a step-down of the generator terminal voltage under the generator load condition. When the step amount is small, the generator voltage will stabilize after several cycles, but when the step amount exceeds 3% or more, due to different operating points of the generator itself (i.e., different active and reactive powers generated by the generator during the step) and many factors such as the overshoot of voltage regulation, it will cause the generator to operate in the leading power factor and result in generator instability; when the generator is at the end of the power grid or other reasons cause the loss-of-excitation protection criterion of the generator to adopt a static stability circle (not an asynchronous circle), it is very easy to cause the loss-of-excitation protection of the generator to act.

[0007] Whether the "PT disconnection" logic of the excitation regulator is reliable and reasonable mainly examines whether the excitation regulator can timely identify the "slow melting of PT" phenomenon before the relay protection device operates and switch to the standby regulation channel or switch to the constant excitation current control mode during the slow melting of the PT primary fuse used for sampling in the current channel of the excitation regulator, and there will be no large fluctuations in the reactive power, excitation current, and generator terminal voltage of the unit during this process.

[0008] Currently, the detection methods of PT disconnection for excitation regulators in China are all based on the change of the secondary-side voltage vector state after the complete disconnection of the voltage circuit, and the slow melting state where the high-voltage fuse on the PT side is not completely disconnected is not included in the detection range of PT disconnection. Since 2017, there have been many cases of unplanned outages of units caused by "slow melting of PT" in the industry, and cases recording such accidents are common. Among them, for the excitation regulators of some manufacturers (such as the ABB Unitrol series), it has been clearly proven from the principle that they cannot effectively monitor the "slow melting of PT" phenomenon. There are also some excitation regulators (such as those of Nanrui Electric Control and Nanrui Relay Protection manufacturers) that use the "negative-sequence voltage criterion with negative-sequence current blocking" to distinguish the slow melting of PT, and at this time, how to reasonably calculate and set the negative-sequence voltage setting value has also become a difficult problem in the industry.

[0009] Based on the above background, it is particularly important to conduct an effective evaluation on whether the "PT disconnection" discrimination logic of the excitation regulators of each manufacturer is reliable under the slow melting of the fuse.

[0010] Chinese Patent Publication No. CN209311643U discloses a comprehensive detector for an excitation system, which includes a DSP core controller and an ARM chip connected to each other. The DI input module and the DO output module are both connected to the DSP core controller. The filtering module is connected to the DSP core controller through a first digital-to-analog conversion module. The DSP core controller is connected to a matching circuit module through a second digital-to-analog conversion module. The ARM chip is connected to a MODBUS communication interface for connecting to the main controller of the excitation system, and the ARM chip is also connected to a communication interface for connecting to a host computer. This device completes data sampling and transmission, and can also accurately identify the PT slow fuse fault of the excitation system. However, it cannot evaluate the PT slow fuse discrimination performance of the existing excitation system, nor can it give guiding opinions on whether the existing excitation regulator needs to be rectified for the "PT slow fuse" problem. Summary of the Invention

[0011] The technical problem to be solved by the present invention is that the prior art cannot evaluate the "PT slow fuse" discrimination performance of the existing excitation system, so it cannot give guiding opinions on whether the existing excitation regulator needs to be rectified for the "PT slow fuse" problem, resulting in the risk of unplanned outage of the unit.

[0012] The present invention solves the above technical problems through the following technical means: An evaluation device for the PT slow fuse discrimination performance of an excitation system includes a slow fuse simulator. The slow fuse simulator includes an isolation transformer PT3. The excitation system includes a generator G, a voltage transformer PT1, a voltage transformer PT2, and an excitation regulator AVR. The three phases of the generator G are connected to the three-phase power grid, and a relay protection device is also connected in the three-phase power grid. The three-phase input terminals of the voltage transformer PT1 are respectively connected to the three phases of the generator G, and the three-phase output terminals of the voltage transformer PT1 are respectively connected to the three-phase input terminals of the isolation transformer PT3. The three-phase output terminals of the isolation transformer PT3 are respectively connected to the three-phase input terminals of the first channel of the excitation regulator AVR. A voltage transformer PT2 is connected between the second channel of the excitation regulator AVR and the generator G. During the process of the slow fuse simulator simulating the PT slow fuse, if the relay protection device acts first, it means that the excitation regulator AVR cannot effectively identify the PT slow fuse phenomenon. If the excitation regulator AVR switches channels first, it means that the excitation regulator AVR can effectively identify the PT slow fuse phenomenon.

[0013] The present invention designs a slow fuse simulator for simulating the slow fuse of a PT, and connects the slow fuse simulator to the excitation system. During the process of simulating the slow fuse of the PT, it is judged whether the excitation regulator AVR can effectively distinguish the slow fuse phenomenon of the PT, and the performance of the PT slow fuse discrimination of the excitation regulator AVR is evaluated. When the evaluation result shows that the excitation regulator AVR can effectively distinguish the slow fuse phenomenon of the PT, it indicates that the existing excitation regulator does not need to be rectified for the "PT slow fuse" problem. When the evaluation result shows that the excitation regulator AVR cannot effectively distinguish the slow fuse phenomenon of the PT, it indicates that the existing excitation regulator needs to be rectified for the "PT slow fuse" problem, and rectification measures should be taken in a timely manner to avoid the unplanned outage of the unit.

[0014] Further, the slow fuse simulator further includes a dual-winding potentiometer, a control circuit, a motor, a speed reducer, and a coupling. Any one of the three-phase input terminals of the isolation transformer PT3 is connected to the first winding of the dual-winding potentiometer, the second winding of the dual-winding potentiometer is connected to the control circuit, the control circuit is connected to the motor, the motor is connected to the first winding of the dual-winding potentiometer through the speed reducer and the coupling, the control circuit collects the resistance value fed back by the dual-winding potentiometer and the rotation speed of the motor and compares them with the preset resistance change rate and resistance target value, and generates a control pulse to drive the motor to rotate so as to adjust the resistance value of the dual-winding potentiometer, simulating the slow melting of the fuse in any one of the three-phase input terminals of the isolation transformer PT3.

[0015] Furthermore, the control circuit includes a main control module, a voltage stabilization module, a filtering module, a sampling module, a communication module, a storage module, an optocoupler isolation module, a motor drive module, and a host computer. The main control module is respectively connected to the voltage stabilization module, the sampling module, the optocoupler isolation module, the storage module, and the communication module. The communication module is connected to the host computer. The filtering module is connected to the sampling module. The optocoupler isolation module is connected to the motor through the motor drive module. The potentiometer is connected to the sampling module.

[0016] Still further, the model of the main control module is STM32F103VET6.

[0017] Still further, the voltage stabilization module includes a chip U1, a capacitor C29, a polarized capacitor C5, a polarized capacitor C6, and a capacitor C7. The model of the chip U1 is AMS1117-3.3. One end of the capacitor C29 and the positive electrode of the polarized capacitor C5 are connected to the third pin of the chip U1 and connected to the power supply VCC. The second pin and the fourth pin of the chip U1 are connected and connected to the power supply VCC33. The positive electrode of the polarized capacitor C6 and one end of the capacitor C7 are both connected to the power supply VCC33. The other end of the capacitor C29, the negative electrode of the polarized capacitor C5, the first pin of the chip U1, the negative electrode of the polarized capacitor C6, and the other end of the capacitor C7 are all grounded.

[0018] Further, the filtering module includes a light-emitting diode DS1, a resistor R1, capacitors C1 to C4 with sequential numbers, and an inductor L1. The anode of the light-emitting diode DS1, one end of the capacitor C2, one end of the capacitor C1, and one end of the inductor L1 are all connected to the power supply VCC. The other end of the inductor L1, one end of the capacitor C3, and one end of the capacitor C4 are all connected to the power supply VCC5A. The cathode of the light-emitting diode DS1, the other end of the capacitor C2, and the other end of the capacitor C1 are all grounded to GND. The other end of the capacitor C3 and the other end of the capacitor C4 are both grounded to CNDA.

[0019] Furthermore, the sampling module includes two identical sampling circuits. The input of one sampling circuit is connected to one end of the capacitor C4 in the filtering module, and its output is connected to an AD sampling port of the main control module. The input of the other sampling circuit is connected to the second winding of the dual-winding potentiometer, and the output of the other sampling circuit is connected to another AD sampling port of the main control module. The other sampling circuit includes a resistor R6, a resistor R8, a resistor R10, an amplifier U2B, a capacitor C16, and a resistor R4. One end of the resistor R6 is grounded to GNDA, and the other end of the resistor R6 is respectively connected to one end of the resistor R4, one end of the capacitor C16, and the inverting input end of the amplifier U2B. One end of the resistor R8 is connected to the second winding of the dual-winding potentiometer, and the other end of the resistor R8 is respectively connected to one end of the resistor R10 and the non-inverting input end of the amplifier U2B. The other end of the resistor R10 is grounded to GNDA. The other end of the capacitor C16 and the other end of the resistor R4 are both connected to the output end of the amplifier U2B.

[0020] Furthermore, the opto-isolation module includes two structurally identical first isolation units for driving the start and stop of the motor drive module, a second isolation unit for sending drive pulses, and a third isolation unit for speed feedback. The first isolation unit includes a resistor R23, a chip U6, and a resistor R25. The model of the chip U6 is TLP291-1. One end of the resistor R23 is connected to the eighty-first pin of the main control module, and the other end of the resistor R23 is connected to the first pin of the chip U6. The second pin of the chip U6 is grounded, the fourth pin of the chip U6 is connected to the power supply VCC, the third pin of the chip U6 is respectively connected to a gate pin of the motor drive module and one end of the resistor R25, and the other end of the resistor R25 is grounded to GND;

[0021] The second isolation unit includes a resistor R33, a resistor R34, a resistor R32, and a chip U10. The model of the chip U10 is HCPL0631. One end of the resistor R33 is connected to the ninety-first pin of the main control module. The other end of the resistor R33 is connected to one end of the resistor R34 and the power supply VCC33. The other end of the resistor R34 is connected to the first pin of the chip U10. The second pin of the chip U10 is connected to one end of the resistor R33. The fifth pin of the chip U10 is grounded to GND. The eighth pin of the chip U10 is connected to the power supply VCC. One end of the resistor R32 is connected to the power supply VCC. The other end of the resistor R32 is respectively connected to the seventh pin of the chip U10 and the power drive end of the motor drive module;

[0022] The third isolation unit includes a resistor R36, a resistor R35, and a triode Q1. One end of the resistor R35 is connected to the Hall sensor installed on the motor. The other end of the resistor R35 is connected to the base of the triode Q1. The collector of the triode Q1 is connected to one end of the resistor R36 and the eighty-sixth pin of the main control module. The other end of the resistor R36 is connected to the power supply VCC33. The emitter of the triode Q1 is grounded to GND.

[0023] Furthermore, the model of the motor drive module is IR2136. The motor drive module is connected to the windings of the motor through MOS transistors.

[0024] Even further, the storage module includes a chip U5 and a resistor R20. The model of the chip U5 is AT25256BSSHL. One end of the resistor R20 is connected to the power supply VCC33. The other end of the resistor R20 is connected to the third pin of the chip U5. The fourth pin of the chip U3 is grounded. The seventh and eighth pins of the chip U5 are both connected to the power supply VCC33. The fifth pin of the chip U5 is connected to the fifty-third pin of the main control module. The sixth pin of the chip U5 is connected to the fifty-second pin of the main control module.

[0025] Further, the communication module includes a chip U4 and capacitors C17 to C21 with sequential numbers. The model of the chip U4 is MAX3232IDR. The first pin of the chip U4 is connected to one end of the capacitor C17, the other end of the capacitor C17 is connected to the third pin of the chip U4, the fourth pin of the chip U4 is connected to one end of the capacitor C19, the other end of the capacitor C19 is connected to the fifth pin of the chip U4, the tenth pin of the chip U4 is connected to the sixty-eighth pin of the main control module, the ninth pin of the chip U4 is connected to the sixty-ninth pin of the main control module, the fifteenth pin of the chip U4 is grounded to GND, the sixth pin of the chip U4 is grounded to GND through the capacitor C21, the eighth pin and the seventh pin of the chip U4 are respectively connected to the data communication interface of the host computer, the second pin of the chip U4 is connected to one end of the capacitor C18, the other end of the capacitor C18 is connected to the sixteenth pin of the chip U4, the other end of the capacitor C18 is connected to the power supply VCC33, one end of the capacitor C20 is connected to the power supply VCC33, and the other end of the capacitor C20 is grounded to GND.

[0026] The present invention also provides a method for evaluating the performance of the slow fuse discrimination of the excitation system PT. The method includes: connecting a slow fuse simulator to the excitation system, performing zeroing initialization on the slow fuse simulator, putting into the relay protection device, and the unit is impulse-started until the generator reaches the rated speed. The excitation regulator AVR is put into the constant voltage control mode, and the slow fuse simulator is adjusted to slowly reduce the voltage of any one phase of the three-phase output terminal of the potential transformer PT1 to simulate the slow fuse of the PT. If the relay protection device acts first, it indicates that the excitation regulator AVR cannot effectively discriminate the slow fuse phenomenon of the PT. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively discriminate the slow fuse phenomenon of the PT.

[0027] Furthermore, the PT slow fuse discrimination performance evaluation device for the excitation system further includes a generator-transformer unit, which includes a generator G, a generator excitation winding ROTOR, a voltage transformer bank PT4, a current transformer bank CT, an excitation transformer ET, a generator outlet circuit breaker GCB, a main transformer, and an excitation system. The excitation system includes an excitation regulator AVR, a rectifier bridge RB, and a field breaker FMK. The high-voltage side of the excitation transformer ET is connected to the machine terminal of the generator G, and the low-voltage side is connected to the AC side of the rectifier bridge RB to provide AC power for the rectifier bridge RB. The excitation regulator AVR collects the terminal voltage and terminal current of the generator G through the voltage transformer bank PT4 and the current transformer bank CT respectively, and controls the rectification of the rectifier bridge RB by sending trigger pulses to the thyristor gate of the rectifier bridge RB, thereby controlling the amplitude of the DC voltage output by the rectifier bridge RB. The positive output of the rectifier bridge RB is connected to the positive pole of the generator excitation winding ROTOR through a series-connected field breaker FMK, and the negative output of the rectifier bridge RB is connected to the negative pole of the generator excitation winding ROTOR to provide excitation for the generator excitation winding ROTOR. The outlet of the generator G is connected to the low-voltage side of the main transformer through the circuit breaker GCB, and the high-voltage side of the main transformer is connected to the power grid.

[0028] Still further, the method further includes:

[0029] Step 1: Apply three-phase balanced voltage to the three-phase input terminals of the isolation transformer PT3 with a relay protection tester, and observe that the three sets of line voltages at the three-phase input terminals of the isolation transformer PT3 are consistent with the displayed values of the three sets of line voltages at the three-phase output terminals of the isolation transformer PT3, then the zeroing initialization of the slow fuse simulator is completed.

[0030] Step 2: Before starting the unit of the excitation system, put the relay protection device into operation, disconnect the wiring between the secondary side of a set of excitation voltage transformer PT1 and the excitation regulator AVR, connect the secondary side of the voltage transformer PT1 to the three-phase input terminals of the isolation transformer PT3, and connect the three-phase output terminals of the isolation transformer PT3 to the first channel of the excitation regulator AVR.

[0031] Step 3: The unit is impulse-rotated until the generator G reaches the rated speed. The excitation regulator AVR is put into the constant voltage control mode, set the target value of the terminal voltage of the generator G during starting excitation to 30% of the rated terminal voltage, close the field breaker, and the excitation regulator AVR starts to excite and boost the voltage.

[0032] Step 4: After starting excitation, the excitation current and the terminal voltage start to rise until the secondary value of the terminal voltage of the generator displayed on the excitation regulator AVR reaches 30V, and observe that the displayed values of the three sets of voltages at the input terminals and the three sets of voltages at the output terminals of the slow fuse simulator are both 30V.

[0033] Step 5: Manually increase the excitation after confirmation until the terminal voltage of generator G reaches the rated value. Observe that the display values of the excitation regulator AVR, the three sets of input voltages, and the three sets of output voltages on the slow fuse simulator are all 100V. Do not close the generator outlet circuit breaker GCB, keep the generator in no-load state, and withdraw the "trip main steam valve" pressure plate of the generator-transformer unit protection;

[0034] Step 6: Enter the voltage regulation link. Slowly reduce the voltage of any one of the three-phase output terminals of the potential transformer PT1 by adjusting the slow fuse simulator to simulate the slow melting of the primary side A-phase fuse of the potential transformer PT1. During the voltage regulation process, the voltage regulation can be paused at any time;

[0035] Step 7: Continuously regulate the voltage until the relay protection device operates or the excitation regulator AVR switches channels. If the relay protection device operates first, it indicates that the excitation regulator AVR cannot effectively discriminate the slow melting phenomenon of PT. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively discriminate the slow melting phenomenon of PT.

[0036] The advantages of the present invention are as follows: The present invention designs a slow fuse simulator to simulate the slow melting of PT, and connects the slow fuse simulator to the excitation system. During the process of simulating the slow melting of PT, it is judged whether the excitation regulator AVR can effectively discriminate the slow melting phenomenon of PT, and the discrimination performance of the excitation regulator AVR for the slow melting of PT is evaluated. When the evaluation result shows that the excitation regulator AVR can effectively discriminate the slow melting phenomenon of PT, it indicates that the existing excitation regulator does not need to be rectified for the "slow melting of PT" problem. When the evaluation result shows that the excitation regulator AVR cannot effectively discriminate the slow melting phenomenon of PT, it indicates that the existing excitation regulator needs to be rectified for the "slow melting of PT" problem, and rectification measures should be taken in a timely manner to avoid unplanned shutdown of the unit. Description of the Drawings

[0037] Figure 1 It is the actual application layout diagram of an evaluation device for the discrimination performance of slow melting of PT in the excitation system provided by the embodiment of the present invention;

[0038] Figure 2 It is the principle block diagram of an evaluation device for the discrimination performance of slow melting of PT in the excitation system provided by the embodiment of the present invention;

[0039] Figure 3 It is the principle block diagram of the control circuit in an evaluation device for the discrimination performance of slow melting of PT in the excitation system provided by the embodiment of the present invention;

[0040] Figure 4 It is the schematic diagram of the voltage stabilization module of the control circuit in an evaluation device for the discrimination performance of slow melting of PT in the excitation system provided by the embodiment of the present invention;

[0041] Figure 5Schematic diagram of the filtering module of the control circuit of a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention;

[0042] Figure 6 Schematic diagram of the sampling module of the control circuit of a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention;

[0043] Figure 7 Schematic diagram of the first isolation unit of the control circuit of a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention;

[0044] Figure 8 Schematic diagram of the second isolation unit of the control circuit of a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention;

[0045] Figure 9 Schematic diagram of the third isolation unit of the control circuit of a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention;

[0046] Figure 10 Schematic diagram of the storage module of the control circuit of a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention;

[0047] Figure 11 Schematic diagram of the communication module of the control circuit of a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention;

[0048] Figure 12 Schematic diagram of the generator-transformer unit in a PT slow fuse discrimination performance evaluation device for an excitation system provided by an embodiment of the present invention. Detailed implementation manners

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0050] Such as Figure 1 and Figure 2As shown, a performance evaluation device for discriminating slow fusing of PT in an excitation system includes a slow fusing simulator 1. The slow fusing simulator 1 includes an isolation transformer PT3. The excitation system includes a generator G, a voltage transformer PT1, a voltage transformer PT2, and an excitation regulator AVR. The three phases of the generator G are connected to a three-phase power grid, and a relay protection device is also connected to the three-phase power grid. The three-phase input terminals of the voltage transformer PT1 are respectively connected to the three phases of the generator G, and the three-phase output terminals of the voltage transformer PT1 are respectively connected to the three-phase input terminals of the isolation transformer PT3. The three-phase output terminals of the isolation transformer PT3 are respectively connected to the three-phase input terminals of the first channel of the excitation regulator AVR. A voltage transformer PT2 is connected between the second channel of the excitation regulator AVR and the generator G. During the process of the slow fusing simulator 1 simulating slow fusing of PT, if the relay protection device operates first, it indicates that the excitation regulator AVR cannot effectively discriminate the slow fusing phenomenon of PT. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively discriminate the slow fusing phenomenon of PT.

[0051] Continue to refer to Figure 2, the slow fuse simulator 1 further includes a dual-winding potentiometer 2, a control circuit 3, a motor M, a speed reducer 4, and a coupling 5. Any one of the three-phase input terminals of the isolation transformer PT3 is connected to the first winding of the dual-winding potentiometer 2, the second winding of the dual-winding potentiometer 2 is connected to the control circuit 3, the control circuit 3 is connected to the motor M, and the motor M is connected to the first winding of the dual-winding potentiometer 2 through the speed reducer 4 and the coupling 5. The control circuit 3 collects the resistance value fed back by the dual-winding potentiometer 2 and the rotational speed of the motor M, and compares them with the preset resistance change rate and resistance target value, generating a control pulse to drive the motor M to rotate, thereby adjusting the resistance value of the dual-winding potentiometer 2 to simulate the slow melting of any one of the three-phase input terminals of the isolation transformer PT3. Among them, the motor M is a right-angle worm and wheel brushless DC reduction motor M controlled by duty cycle, with a rated speed of 30 r / min, supporting forward and reverse rotation, and the rated voltage of this motor M is 24 VDC. A speed reducer 4 driven by a gear set is added between the motor M and the dual-winding potentiometer 2 to further improve the resistance control accuracy of the dual-winding potentiometer 2. The speed ratio of the speed reducer 4 is 30 / 1, thereby achieving an adjustment speed of 1 r / min (i.e., 6° / s) for the potentiometer. The potentiometer adopts a dual-winding structure, the resistance values of the two windings are the same, and the sliding contacts of the two windings are linked. One winding is connected in series to the primary side of the isolation transformer PT3 for adjusting the secondary side voltage. The other winding is used to generate a position feedback for the control circuit 3, facilitating the control circuit 3 to collect the current resistance value and resistance change rate. Considering the short-circuit impedance of the isolation transformer PT3 and the input impedance of the excitation regulator AVR voltage sampling circuit comprehensively, the maximum resistance value of the dual-winding potentiometer 2 is selected to be 10 kΩ. For precise voltage regulation, the effective rotation angle of the dual-winding potentiometer 2 is 3600° (i.e., 10 turns), and the resistance adjustment accuracy reaches 0.02%, to ensure the precise control of the resistance value of the dual-winding potentiometer 2. As can be seen from the above, the rotational speed of the dual-winding potentiometer 2 can be adjusted to 6° / s, so the adjustment speed of the resistance of the dual-winding potentiometer 2 is about 16.7 Ω / s. The isolation transformer PT3 adopts a customized sampling transformer, with a YY connection method, a voltage ratio of 380 V / 380 V, and a maximum capacity of 50 VA. Generally, the secondary rated output capacity of voltage transformers is above 300 VA, so it can fully meet the normal working requirements of the isolation transformer. To simulate the characteristics of the voltage transformer as accurately as possible, the excitation circuit impedance of the isolation transformer PT3 is controlled at a relatively high level, thereby controlling the excitation current of the isolation transformer PT3 at the microamp level to ensure that the voltage characteristics of the primary and secondary sides are close to those of an ideal transformer.

[0052] Such as Figure 3As shown, the control circuit 3 includes a main control module 301, a voltage stabilization module 302, a filtering module 303, a sampling module 304, a communication module 305, a storage module 306, an optocoupler isolation module 307, a motor drive module 308, and a host computer 309. The main control module 301 is respectively connected to the voltage stabilization module 302, the sampling module 304, the optocoupler isolation module 307, the storage module 306, and the communication module 305. The communication module 305 is connected to the host computer 309. The filtering module 303 is connected to the sampling module 304. The optocoupler isolation module 307 is connected to the motor M through the motor drive module 308. The potentiometer is connected to the sampling module 304. The model of the main control module 301 is STM32F103VET6.

[0053] As Figure 4 shown, the voltage stabilization module 302 includes a chip U1, a capacitor C29, a polarized capacitor C5, a polarized capacitor C6, and a capacitor C7. The model of the chip U1 is AMS1117-3.3. One end of the capacitor C29 and the positive electrode of the polarized capacitor C5 are connected to the third pin of the chip U1 and connected to the power supply VCC. The second pin and the fourth pin of the chip U1 are connected and connected to the power supply VCC33. The positive electrode of the polarized capacitor C6 and one end of the capacitor C7 are both connected to the power supply VCC33. The other end of the capacitor C29, the negative electrode of the polarized capacitor C5, the first pin of the chip U1, the negative electrode of the polarized capacitor C6, and the other end of the capacitor C7 are all grounded.

[0054] As Figure 5 shown, the filtering module 303 includes a light-emitting diode DS1, a resistor R1, capacitors C1 to C4 numbered in sequence, and an inductor L1. The anode of the light-emitting diode DS1, one end of the capacitor C2, one end of the capacitor C1, and one end of the inductor L1 are all connected to the power supply VCC. The other end of the inductor L1, one end of the capacitor C3, and one end of the capacitor C4 are all connected to the power supply VCC5A. The cathode of the light-emitting diode DS1, the other end of the capacitor C2, and the other end of the capacitor C1 are all grounded to GND. The other end of the capacitor C3 and the other end of the capacitor C4 are all grounded to CNDA.

[0055] As Figure 6As shown, the sampling module 304 includes two identical sampling circuits. One sampling circuit has its input connected to one end of the capacitor C4 in the filtering module 303, and its output connected to an AD sampling port of the main control module 301. The input of the other sampling circuit is connected to the second winding of the dual-winding potentiometer 2, and the output of the other sampling circuit is connected to another AD sampling port of the main control module 301. The main control module 301 acquires the current resistance value and the resistance change rate. The other sampling circuit includes a resistor R6, a resistor R8, a resistor R10, an amplifier U2B, a capacitor C16, and a resistor R4. One end of the resistor R6 is grounded to GNDA, and the other end of the resistor R6 is connected to one end of the resistor R4, one end of the capacitor C16, and the inverting input terminal of the amplifier U2B. One end of the resistor R8 is connected to the second winding of the dual-winding potentiometer 2, and the other end of the resistor R8 is connected to one end of the resistor R10 and the non-inverting input terminal of the amplifier U2B. The other end of the resistor R10 is grounded to GNDA. The other end of the capacitor C16 and the other end of the resistor R4 are both connected to the output terminal of the amplifier U2B.

[0056] The opto-isolation module 307 includes two structurally identical first isolation units for driving the start and stop of the motor drive module 308, a second isolation unit for sending drive pulses, and a third isolation unit for speed feedback, as Figure 7 shown. The first isolation unit includes a resistor R23, a chip U6, and a resistor R25. The model of the chip U6 is TLP291-1. One end of the resistor R23 is connected to the eighty-first pin of the main control module 301, and the other end of the resistor R23 is connected to the first pin of the chip U6. The second pin of the chip U6 is grounded, the fourth pin of the chip U6 is connected to the power supply VCC, the third pin of the chip U6 is connected to a gate pin of the motor drive module 308 and one end of the resistor R25, and the other end of the resistor R25 is grounded to GND. The third pin of the chip U6 in the first isolation unit is connected to a gate pin of the motor drive module 308 to drive the start and stop of the motor drive module 308.

[0057] As Figure 8As shown, the second isolation unit includes resistor R33, resistor R34, resistor R32, and chip U10. The model of chip U10 is HCPL0631. One end of resistor R33 is connected to the ninety - first pin of the main control module 301. The other end of resistor R33 is connected to one end of resistor R34 and power supply VCC33. The other end of resistor R34 is connected to the first pin of chip U10. The second pin of chip U10 is connected to one end of resistor R33. The fifth pin of chip U10 is grounded to GND. The eighth pin of chip U10 is connected to power supply VCC. One end of resistor R32 is connected to power supply VCC. The other end of resistor R32 is respectively connected to the seventh pin of chip U10 and the power drive end of the motor drive module 308, for outputting a pulse control signal to control the motor drive module 308;

[0058] As Figure 9 shown, the third isolation unit includes resistor R36, resistor R35, and triode Q1. One end of resistor R35 is connected to the Hall sensor installed on the motor M. The other end of resistor R35 is connected to the base of triode Q1. The collector of triode Q1 is connected to one end of resistor R36 and the eighty - sixth pin of the main control module 301. The other end of resistor R36 is connected to power supply VCC33. The emitter of triode Q1 is grounded to GND. The data of the Hall sensor is the speed data of the motor M. Therefore, the speed of the motor M is fed back to the main control module 301 through the third isolation unit.

[0059] The model of the motor drive module 308 is IR2136. The motor drive module 308 is connected to the windings of the motor M through MOS tubes.

[0060] As Figure 10 shown, the storage module 306 includes chip U5 and resistor R20. The model of chip U5 is AT25256BSSHL. One end of resistor R20 is connected to power supply VCC33. The other end of resistor R20 is connected to the third pin of chip U5. The fourth pin of chip U3 is grounded. The seventh and eighth pins of chip U5 are both connected to power supply VCC33. The fifth pin of chip U5 is connected to the fifty - third pin of the main control module 301. The sixth pin of chip U5 is connected to the fifty - second pin of the main control module 301. The storage module 306 is used for storing data.

[0061] As Figure 11As shown, the communication module 305 includes a chip U4 and capacitors C17 to C21 numbered in sequence. The model of the chip U4 is MAX3232IDR. The first pin of the chip U4 is connected to one end of the capacitor C17, the other end of the capacitor C17 is connected to the third pin of the chip U4, the fourth pin of the chip U4 is connected to one end of the capacitor C19, the other end of the capacitor C19 is connected to the fifth pin of the chip U4, the tenth pin of the chip U4 is connected to the sixty-eighth pin of the main control module 301, the ninth pin of the chip U4 is connected to the sixty-ninth pin of the main control module 301, the fifteenth pin of the chip U4 is grounded to GND, the sixth pin of the chip U4 is grounded to GND through the capacitor C21, the eighth pin and the seventh pin of the chip U4 are respectively connected to the data communication interface of the upper computer 309, the second pin of the chip U4 is connected to one end of the capacitor C18, the other end of the capacitor C18 is connected to the sixteenth pin of the chip U4, the other end of the capacitor C18 is connected to the power supply VCC33, one end of the capacitor C20 is connected to the power supply VCC33, and the other end of the capacitor C20 is grounded to GND. The communication module 305 is used to transmit data to the upper computer 309 for display. At the same time, the upper computer 309 can also set some parameter values or commands and transmit them to the main control module 301 through the communication module 305.

[0062] The present invention also provides a method for evaluating the performance of slow fuse discrimination of an excitation system PT. The method includes: connecting the slow fuse simulator 1 to the excitation system, performing zero adjustment initialization on the slow fuse simulator 1, putting into the relay protection device, and performing unit impulse rotation until the generator G reaches the rated speed. The excitation regulator AVR is put into the constant voltage control mode, and the slow fuse simulator 1 is adjusted to slowly reduce the voltage of any one phase of the three-phase output terminal of the potential transformer PT1 to simulate PT slow fuse. If the relay protection device acts first, it indicates that the excitation regulator AVR cannot effectively discriminate the PT slow fuse phenomenon. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively discriminate the PT slow fuse phenomenon.

[0063] As Figure 12As shown, the PT slow fuse discrimination performance evaluation device of the excitation system further includes a generator-transformer unit, which includes a generator G, a generator excitation winding ROTOR, a voltage transformer bank PT4, a current transformer bank CT, an excitation transformer ET, a generator outlet circuit breaker GCB, a main transformer, and an excitation system. The excitation system includes an excitation regulator AVR, a rectifier bridge RB, and a field circuit breaker FMK. The high-voltage side of the excitation transformer ET is connected to the machine terminal of the generator G, and the low-voltage side is connected to the AC side of the rectifier bridge RB to provide AC power for the rectifier bridge RB. The excitation regulator AVR collects the terminal voltage and terminal current of the generator G through the voltage transformer bank PT4 and the current transformer bank CT respectively, and controls the rectification of the rectifier bridge RB by sending trigger pulses to the thyristor gate of the rectifier bridge RB, so as to control the amplitude of the DC voltage output by the rectifier bridge RB. The positive output of the rectifier bridge RB is connected to the positive pole of the generator excitation winding ROTOR through a series-connected field circuit breaker FMK, and the negative output of the rectifier bridge RB is connected to the negative pole of the generator excitation winding ROTOR to provide excitation for the generator excitation winding ROTOR. The outlet of the generator G is connected to the low-voltage side of the main transformer through the circuit breaker GCB, and the high-voltage side of the main transformer is connected to the power grid.

[0064] The excitation transformer ET is used to provide excitation power for the rectifier bridge RB. The rectifier bridge RB converts the three-phase alternating current provided by the excitation transformer ET into direct current through rectification. The excitation regulator AVR is connected to the rectifier bridge RB, indicating that the excitation regulator AVR sends trigger pulses to the rectifier bridge RB to control the DC voltage output by the rectifier bridge RB. The alternating current output by the generator G should be three-phase current, and only one line is drawn in the figure for illustration. The excitation regulator AVR collects the terminal voltage of the generator G from the voltage transformer bank PT4 and the current of the generator G from the current transformer bank CT, and sends trigger pulses to the rectifier bridge RB through the PID control method to control the magnitude of the DC voltage output by the rectifier bridge RB, so as to control the magnitude of the current on the generator excitation winding ROTOR, and thus control the terminal voltage of the generator G, forming a closed-loop control under the no-load condition of the generator G. Since there is a risk of tripping when conducting this evaluation test provided by the present invention after the unit is connected to the grid, the power generation enterprise needs to apply for test permission from the dispatching department in advance. Therefore, the generator outlet circuit breaker GCB is disconnected during the operation of the evaluation device of the present invention to avoid direct connection to the three-phase power grid. Of course, if it is necessary to conduct the test after being connected to the grid, the test permission can be applied for from the dispatching department in advance for the test after being connected to the grid.

[0065] The above is only a simple summary of the method of the PT slow fuse discrimination performance evaluation device of the excitation system of the present invention. The following details this method, and the method further includes:

[0066] Step 1: Apply three-phase balanced voltage to the three-phase input terminals Xa, Xb, and Xc of the isolation transformer PT3 using a relay protection tester. Observe that the three sets of line voltages at the three-phase input terminals of the isolation transformer PT3 are consistent with the display values of the three sets of line voltages at the three-phase output terminals of the isolation transformer PT3, and the zero adjustment initialization of the slow fuse simulator 1 is completed.

[0067] Step 2: Before starting the unit of the excitation system, put the relay protection device into operation, disconnect the connection between the secondary side of a set of excitation voltage transformer PT1 and the excitation regulator AVR, connect the secondary side of the voltage transformer PT1 to the three-phase input terminals Xa, Xb, and Xc of the isolation transformer PT3, and connect the three-phase output terminals X’a, X’b, and X’c of the isolation transformer PT3 to the first channel of the excitation regulator AVR.

[0068] Step 3: The unit is rotated until the generator G reaches the rated speed. The excitation regulator AVR is put into the constant voltage control mode. Set the target value of the terminal voltage of the generator G at the time of starting excitation to 30% of the rated terminal voltage. Close the field breaker, and the excitation regulator AVR starts to boost the voltage.

[0069] Step 4: After starting excitation, the excitation current and the terminal voltage start to rise until the secondary value of the terminal voltage of the generator G displayed on the excitation regulator AVR reaches 30V. Observe that the display values of the three sets of voltages at the input terminals and the three sets of voltages at the output terminals of the slow fuse simulator 1 are all 30V.

[0070] Step 5: After confirmation, manually increase the excitation until the terminal voltage of the generator G reaches the rated value. Observe that the display values of the excitation regulator AVR, the three sets of voltages at the input terminals of the slow fuse simulator 1, and the three sets of voltages at the output terminals are all 100V. The generator outlet circuit breaker GCB is not closed, and the generator G is kept in the no-load state. Withdraw the "trip main steam valve" pressure plate of the generator-transformer unit protection.

[0071] Step 6: Enter the voltage regulation link, set a certain voltage regulation speed (such as 0.1V / s), and adjust the slow fuse simulator 1 to slowly reduce the voltage of any one phase (such as phase A) at the three-phase output terminal of the voltage transformer PT1 to simulate the slow melting of the fuse of phase A on the primary side of the voltage transformer PT1. Observe the changes of the following analog quantities during the voltage regulation process: evaluate the input and output terminal voltages Uab, Ubc, Uca, U’ab, U’bc, U’ca of the device; the terminal voltages collected by the two channels of the excitation regulator AVR; the excitation voltage and excitation current. At the same time, observe the following digital quantities: the action conditions of the "generator G over-excitation protection" and "main transformer over-excitation protection" of the relay protection device; the "PT disconnection" alarm signal of the excitation regulator, the channel switching action conditions, and the control mode switching action conditions. Among them, the voltage regulation can be paused at any time during the voltage regulation process to confirm whether the change trend of the analog quantity and the action conditions of the digital quantity are consistent with the expectation.

[0072] Step 7: Continuously adjust the voltage until the relay protection device operates or the excitation regulator AVR switches channels. If the relay protection device operates first, it indicates that the excitation regulator AVR cannot effectively identify the slow fuse phenomenon of the PT. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively identify the slow fuse phenomenon of the PT.

[0073] Through the above technical solutions, the present invention designs the slow fuse simulator 1 to simulate the slow fuse of the PT, and connects the slow fuse simulator 1 to the excitation system. During the process of simulating the slow fuse of the PT, it is judged whether the excitation regulator AVR can effectively identify the slow fuse phenomenon of the PT, and the performance of the excitation regulator AVR in identifying the slow fuse of the PT is evaluated. When the evaluation result is that the excitation regulator AVR can effectively identify the slow fuse phenomenon of the PT, it indicates that the existing excitation regulator does not need to be rectified for the "slow fuse of the PT" problem. When the evaluation result is that the excitation regulator AVR cannot effectively identify the slow fuse phenomenon of the PT, it indicates that the existing excitation regulator needs to be rectified for the "slow fuse of the PT" problem, and rectification measures should be taken in a timely manner to avoid the unplanned outage of the unit. The way to rectify the excitation regulator can adopt the patent literature technology recorded in the background technology or other existing technologies. The specific rectification content is not within the protection scope of the present invention and will not be elaborated here.

[0074] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An evaluation device for the slow fuse discrimination performance of the PT in an excitation system, characterized in that, it includes a slow fuse simulator. The slow fuse simulator includes an isolation transformer PT3. The excitation system includes a generator G, a potential transformer PT1, a potential transformer PT2, and an excitation regulator AVR. The three phases of the generator G are connected to a three-phase power grid, and a relay protection device is also connected in the three-phase power grid. The three-phase input terminals of the potential transformer PT1 are respectively connected to the three phases of the generator G, the three-phase output terminals of the potential transformer PT1 are respectively connected to the three-phase input terminals of the isolation transformer PT3, the three-phase output terminals of the isolation transformer PT3 are respectively connected to the three-phase input terminals of the first channel of the excitation regulator AVR, and a potential transformer PT2 is connected between the second channel of the excitation regulator AVR and the generator G. During the process of the slow fuse simulator simulating the slow fuse of the PT, if the relay protection device acts first, it indicates that the excitation regulator AVR cannot effectively discriminate the slow fuse phenomenon of the PT. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively discriminate the slow fuse phenomenon of the PT; the slow fuse simulator further includes a dual-winding potentiometer, a control circuit, a motor, a speed reducer, and a coupling. Any one of the three-phase input terminals of the isolation transformer PT3 is connected to the first winding of the dual-winding potentiometer, the second winding of the dual-winding potentiometer is connected to the control circuit, the control circuit is connected to the motor, the motor is connected to the first winding of the dual-winding potentiometer through the speed reducer and the coupling, the control circuit collects the resistance value feedback by the dual-winding potentiometer and the rotation speed of the motor and compares them with the preset resistance change rate and resistance target value, and generates a control pulse to drive the motor to rotate so as to adjust the resistance value of the dual-winding potentiometer, simulating the slow fuse of any one of the three-phase input terminals of the isolation transformer PT3.

2. The evaluation device for the slow fuse discrimination performance of the PT in an excitation system according to claim 1, characterized in that, the control circuit includes a main control module, a voltage stabilization module, a filtering module, a sampling module, a communication module, a storage module, an opto-isolation module, a motor drive module, and a host computer. The model of the main control module is STM32F103VET6. The main control module is respectively connected to the voltage stabilization module, the sampling module, the opto-isolation module, the storage module, and the communication module. The communication module is connected to the host computer. The filtering module is connected to the sampling module. The opto-isolation module is connected to the motor through the motor drive module. The potentiometer is connected to the sampling module.

3. The evaluation device for the slow fuse discrimination performance of the PT in an excitation system according to claim 2, characterized in that, The voltage stabilization module includes chip U1, capacitor C29, polarized capacitor C5, polarized capacitor C6, and capacitor C7. The model of chip U1 is AMS1117-3.

3. One end of capacitor C29 and the positive electrode of polarized capacitor C5 are connected to the third pin of chip U1 and connected to power supply VCC. The second pin and the fourth pin of chip U1 are connected and connected to power supply VCC33. The positive electrode of polarized capacitor C6 and one end of capacitor C7 are both connected to power supply VCC33. The other end of capacitor C29, the negative electrode of polarized capacitor C5, the first pin of chip U1, the negative electrode of polarized capacitor C6, and the other end of capacitor C7 are all grounded; The filtering module includes light-emitting diode DS1, resistor R1, capacitors C1 to C4 with sequential numbers, and inductor L1. The anode of light-emitting diode DS1, one end of capacitor C2, one end of capacitor C1, and one end of inductor L1 are all connected to power supply VCC. The other end of inductor L1, one end of capacitor C3, and one end of capacitor C4 are all connected to power supply VCC5A. The cathode of light-emitting diode DS1, the other end of capacitor C2, and the other end of capacitor C1 are all grounded to GND. The other end of capacitor C3 and the other end of capacitor C4 are all grounded to CNDA.

4. An excitation system PT slow fuse discrimination performance evaluation device according to claim 3, characterized in that The sampling module includes two identical sampling circuits. The input of one sampling circuit is connected to one end of capacitor C4 in the filtering module, and its output is connected to an AD sampling port of the main control module; the input of the other sampling circuit is connected to the second winding of the dual-winding potentiometer, and the output of the other sampling circuit is connected to another AD sampling port of the main control module; the other sampling circuit includes resistor R6, resistor R8, resistor R10, amplifier U2B, capacitor C16, and resistor R4. One end of resistor R6 is grounded to GNDA, and the other end of resistor R6 is respectively connected to one end of resistor R4, one end of capacitor C16, and the inverting input end of amplifier U2B. One end of resistor R8 is connected to the second winding of the dual-winding potentiometer, and the other end of resistor R8 is respectively connected to one end of resistor R10 and the non-inverting input end of amplifier U2B. The other end of resistor R10 is grounded to GNDA. The other end of capacitor C16 and the other end of resistor R4 are both connected to the output end of amplifier U2B.

5. An excitation system PT slow fuse discrimination performance evaluation device according to claim 2, characterized in that The optocoupler isolation module includes two first isolation units with the same structure for driving the start and stop of the motor drive module, a second isolation unit for sending drive pulses, and a third isolation unit for speed feedback. The model of the motor drive module is IR2136, and the motor drive module is connected to the windings of the motor through MOS transistors; the first isolation unit includes a resistor R23, a chip U6, and a resistor R25. The model of the chip U6 is TLP291-1. One end of the resistor R23 is connected to the eighty-first pin of the main control module, the other end of the resistor R23 is connected to the first pin of the chip U6, the second pin of the chip U6 is grounded, the fourth pin of the chip U6 is connected to the power supply VCC, the third pin of the chip U6 is respectively connected to a gate pin of the motor drive module and one end of the resistor R25, and the other end of the resistor R25 is grounded to GND; The second isolation unit includes a resistor R33, a resistor R34, a resistor R32, and a chip U10. The model of the chip U10 is HCPL0631. One end of the resistor R33 is connected to the ninety-first pin of the main control module, the other end of the resistor R33 is connected to one end of the resistor R34 and the power supply VCC33, the other end of the resistor R34 is connected to the first pin of the chip U10, the second pin of the chip U10 is connected to one end of the resistor R33, the fifth pin of the chip U10 is grounded to GND, the eighth pin of the chip U10 is connected to the power supply VCC, one end of the resistor R32 is connected to the power supply VCC, and the other end of the resistor R32 is respectively connected to the seventh pin of the chip U10 and the power drive end of the motor drive module; The third isolation unit includes a resistor R36, a resistor R35, and a triode Q1. One end of the resistor R35 is connected to the Hall sensor installed on the motor, the other end of the resistor R35 is connected to the base of the triode Q1, the collector of the triode Q1 is connected to one end of the resistor R36 and the eighty-sixth pin of the main control module, the other end of the resistor R36 is connected to the power supply VCC33, and the emitter of the triode Q1 is grounded to GND.

6. An excitation system PT slow fuse discrimination performance evaluation device according to claim 2, characterized in that, The storage module includes a chip U5 and a resistor R20. The model of the chip U5 is AT25256BSSHL. One end of the resistor R20 is connected to the power supply VCC33, the other end of the resistor R20 is connected to the third pin of the chip U5, the fourth pin of the chip U3 is grounded, the seventh and eighth pins of the chip U5 are both connected to the power supply VCC33, the fifth pin of the chip U5 is connected to the fifty-third pin of the main control module, and the sixth pin of the chip U5 is connected to the fifty-second pin of the main control module; The communication module includes a chip U4 and capacitors C17 to C21 with sequential numbers. The model of the chip U4 is MAX3232IDR. The first pin of the chip U4 is connected to one end of the capacitor C17, the other end of the capacitor C17 is connected to the third pin of the chip U4, the fourth pin of the chip U4 is connected to one end of the capacitor C19, the other end of the capacitor C19 is connected to the fifth pin of the chip U4, the tenth pin of the chip U4 is connected to the sixty-eighth pin of the main control module, the ninth pin of the chip U4 is connected to the sixty-ninth pin of the main control module, the fifteenth pin of the chip U4 is grounded to GND, the sixth pin of the chip U4 is grounded to GND through the capacitor C21, the eighth pin and the seventh pin of the chip U4 are respectively connected to the data communication interface of the upper computer, the second pin of the chip U4 is connected to one end of the capacitor C18, the other end of the capacitor C18 is connected to the sixteenth pin of the chip U4, the other end of the capacitor C18 is connected to the power supply VCC33, one end of the capacitor C20 is connected to the power supply VCC33, and the other end of the capacitor C20 is grounded to GND.

7. The method for an excitation system PT slow fuse discrimination performance evaluation device according to any one of claims 1-6, characterized in that, the method includes: connecting a slow fuse simulator to the excitation system, performing zeroing initialization on the slow fuse simulator, putting into the relay protection device, and the unit is impulse-started until the generator reaches the rated speed. The excitation regulator AVR is put into the constant voltage control mode, and the slow fuse simulator is adjusted to slowly reduce the voltage of any one of the three-phase output terminals of the potential transformer PT1 to simulate PT slow fuse. If the relay protection device acts first, it indicates that the excitation regulator AVR cannot effectively discriminate the PT slow fuse phenomenon. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively discriminate the PT slow fuse phenomenon.

8. The method for an excitation system PT slow fuse discrimination performance evaluation device according to claim 7, characterized in that, The PT slow fuse discrimination performance evaluation device of the excitation system further includes a generator-transformer unit, which includes a generator G, a generator excitation winding ROTOR, a voltage transformer bank PT4, a current transformer bank CT, an excitation transformer ET, a generator outlet circuit breaker GCB, a main transformer, and an excitation system. The excitation system includes an excitation regulator AVR, a rectifier bridge RB, and a field circuit breaker FMK. The high-voltage side of the excitation transformer ET is connected to the machine terminal of the generator G, and the low-voltage side is connected to the AC side of the rectifier bridge RB to provide AC power for the rectifier bridge RB. The excitation regulator AVR collects the machine terminal voltage and machine terminal current of the generator G through the voltage transformer bank PT4 and the current transformer bank CT respectively, and controls the rectification of the rectifier bridge RB by sending trigger pulses to the thyristor gate of the rectifier bridge RB, so as to control the amplitude of the DC voltage output by the rectifier bridge RB. The positive output of the rectifier bridge RB is connected to the positive pole of the generator excitation winding ROTOR through the series field circuit breaker FMK, and the negative output of the rectifier bridge RB is connected to the negative pole of the generator excitation winding ROTOR to provide excitation for the generator excitation winding ROTOR. The outlet of the generator G is connected to the low-voltage side of the main transformer through the circuit breaker GCB, and the high-voltage side of the main transformer is connected to the power grid.

9. The method for a PT slow fuse discrimination performance evaluation device of an excitation system according to claim 8, characterized in that, the method further includes: Step 1: Apply three-phase balanced voltage to the three-phase input terminals of the isolation transformer PT3 with a relay protection tester, and observe that the display values of the three groups of line voltages at the three-phase input terminals of the isolation transformer PT3 are consistent with those of the three groups of line voltages at the three-phase output terminals of the isolation transformer PT3, then the zeroing initialization of the slow fuse simulator is completed; Step 2: Before starting the unit of the excitation system, put the relay protection device into operation, disconnect the connection between the secondary side of a group of excitation voltage transformers PT1 and the excitation regulator AVR, connect the secondary side of the voltage transformer PT1 to the three-phase input terminals of the isolation transformer PT3, and connect the three-phase output terminals of the isolation transformer PT3 to the first channel of the excitation regulator AVR; Step 3: The unit is rotated up to the rated speed of the generator G. The excitation regulator AVR is put into the constant voltage control mode. Set the target value of the machine terminal voltage of the generator G at the time of starting excitation to 30% of the rated machine terminal voltage, close the field circuit breaker, and the excitation regulator AVR starts to boost the voltage; Step 4: After starting excitation, the excitation current and the machine terminal voltage start to rise until the secondary value of the machine terminal voltage of the generator displayed on the excitation regulator AVR reaches 30V, and it is observed that the display values of the three groups of voltages at the input terminal and the three groups of voltages at the output terminal of the slow fuse simulator are both 30V; Step 5: After confirmation, manually increase the excitation until the machine terminal voltage of the generator G reaches the rated value. Observe that the display values on the excitation regulator AVR, the three groups of voltages at the input terminal of the slow fuse simulator, and the three groups of voltages at the output terminal are all 100V. The generator outlet circuit breaker GCB is not closed, and the generator is kept in the no-load state. Withdraw the "trip main steam valve" pressure plate of the generator-transformer unit protection; Step 6: Enter the voltage regulation link, adjust the slow fuse simulator to slowly reduce the voltage of any one of the three-phase output terminals of the potential transformer PT1, and simulate the slow melting of the primary side A-phase fuse of the potential transformer PT1. During the voltage regulation process, the voltage regulation can be paused at any time; Step 7: Continuously regulate the voltage until the relay protection device operates or the excitation regulator AVR switches channels. If the relay protection device operates first, it indicates that the excitation regulator AVR cannot effectively distinguish the slow fuse phenomenon of the PT. If the excitation regulator AVR switches channels first, it indicates that the excitation regulator AVR can effectively distinguish the slow fuse phenomenon of the PT.

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