A fault on-line monitoring system and method applied to an excitation power cabinet

Abstract

The application discloses a kind of applied to the fault on-line monitoring system and method of excitation power cabinet, it is related to the technical field of the fault monitoring of excitation power cabinet, the voltage integral value of each thyristor is obtained, the voltage integral value of upper and lower thyristor on the same bridge arm is subtracted to obtain signed integral difference value, integral difference value threshold, voltage integral value upper and lower limit threshold and fluctuation amplitude threshold are set;According to the voltage integral value fluctuation amplitude of the multiple periods of thyristor, the trigger failure fault is judged, according to the integral difference value of two continuous periods of bridge arm, abnormal bridge arm is screened, and then according to the integral difference value sign and the comparison result of single voltage integral value and threshold, short-circuit or open-circuit fault is judged;The application does not need historical fault sample and complex algorithm, and only through voltage integration, subtraction and threshold comparison can realize the detection and positioning of thyristor short-circuit, open-circuit and trigger failure fault.

Description

Technical Field

[0001] This invention relates to the field of fault monitoring technology for excitation power cabinets, specifically to an online fault monitoring system and method for excitation power cabinets. Background Technology

[0002] The excitation power cabinet contains six thyristors connected in a three-phase fully controlled bridge rectifier circuit to provide DC excitation current to the generator rotor. After prolonged operation, the thyristors may experience three typical faults: short-circuit damage, open-circuit damage, or trigger failure. Failure to detect these faults promptly can lead to generator reactive power fluctuations, rotor overheating, and even system shutdown.

[0003] Existing fault monitoring methods use voltage and current waveform analysis and Fast Fourier Transform (FFT) to extract harmonic features to identify faults. However, the waveform fluctuates violently at the moment of a fault, indicating a non-stationary signal. Spectrum analysis cannot accurately pinpoint the exact moment of the fault occurrence, and the computation is complex, requiring dedicated processing chips. Deep learning methods require collecting large amounts of fault data to train neural network models. However, excitation systems are designed and operated to minimize fault occurrences, making it almost impossible to obtain real fault samples in the field. Models trained from simulation data have low accuracy in field applications.

[0004] Meanwhile, neural networks are black-box structures, making it difficult for maintenance personnel to understand the basis of alarms, resulting in insufficient trust. Infrared thermal imaging determines faults by monitoring the surface temperature of thyristors, but there is a significant delay in heat conduction to the surface when the internal junction temperature rises sharply, and changes in ambient temperature and cooling fan speed can interfere with surface temperature measurement, easily leading to missed or false alarms.

[0005] The methods described above either rely on historical fault data or require complex calculations or expensive equipment, making it impossible to achieve an online monitoring solution that can quickly and accurately locate faults without relying on any prior samples and solely on the physical characteristics of the rectifier bridge itself.

[0006] The technical problem to be solved by the present invention is to provide a monitoring method that can diagnose and accurately locate thyristor faults in real time without fault data or complex algorithms, but only through simple voltage comparison. Summary of the Invention

[0007] The purpose of this invention is to provide an online fault monitoring system and method for excitation power cabinets to solve the problems raised in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for online fault monitoring applied to excitation power cabinets includes the following steps: S1. Obtain the voltage signal across each thyristor and take the absolute value of each voltage signal, then integrate it within each power frequency cycle to obtain the voltage integral value of each thyristor. S2. Subtract the integral value of the upper thyristor voltage from the integral value of the lower thyristor voltage in the same bridge arm to obtain the integral difference value of the bridge arm. The integral difference value is a signed numerical value. S3. Set a first threshold, a second threshold, a third threshold and a fourth threshold. The first threshold is the upper limit of the normal fluctuation range of the integral difference, the second threshold is the lower limit of the integral value of a single thyristor voltage, the third threshold is the upper limit of the integral value of a single thyristor voltage, and the fourth threshold is the maximum allowable amplitude of the fluctuation of the integral value of the same thyristor voltage within multiple consecutive cycles. S4. Continuously record the voltage integral value of each thyristor for the most recent N cycles, calculate the difference between the maximum and minimum values ​​of these N values, and if the difference is greater than the fourth threshold, then the thyristor is determined to have a trigger failure fault. S5. For the bridge arm corresponding to the thyristor that has not been determined to have triggered failure, when the voltage integral difference of the bridge arm for two consecutive cycles is greater than the first threshold and the two voltage integral differences have the same sign, the fault type determination is entered. S6. When the sign of the voltage integral difference of the bridge arm is positive, if the voltage integral value of the lower thyristor is less than the second threshold, the lower thyristor is determined to be short-circuited; if the voltage integral value of the upper thyristor is greater than the third threshold, the upper thyristor is determined to be open-circuited. S7. When the voltage integral difference of the bridge arm is negative, if the voltage integral value of the upper thyristor is less than the second threshold, the upper thyristor is determined to be short-circuited; if the voltage integral value of the lower thyristor is greater than the third threshold, the lower thyristor is determined to be open-circuited.

[0009] S1 further includes the following: A low-voltage signal is obtained by connecting a voltage divider resistor network in parallel between the anode and cathode of each thyristor; The low-voltage signal is passed through an isolation amplifier to output a voltage signal that is proportional to the voltage across the thyristor. The voltage signal is input into a precision rectifier circuit to obtain the absolute value signal of the voltage signal; The absolute value signal is input into an integrator and the reset period of the integrator is set to one power frequency cycle; The integrator is reset at the end of each power frequency cycle and outputs the voltage integral value of the thyristor during that power frequency cycle. The six thyristors are processed in the above manner to obtain six voltage integral values, which are then denoted as V1, V2, V3, V4, V5, and V6 respectively. Wherein, V1 corresponds to the voltage integral value of the first thyristor, V2 corresponds to the voltage integral value of the second thyristor, V3 corresponds to the voltage integral value of the third thyristor, V4 corresponds to the voltage integral value of the fourth thyristor, V5 corresponds to the voltage integral value of the fifth thyristor, and V6 corresponds to the voltage integral value of the sixth thyristor.

[0010] S2 further includes the following: Subtracting the integral value V1 of the upper thyristor voltage of the first bridge arm from the integral value V4 of the lower thyristor voltage gives the integral difference D1 of the first bridge arm, where D1 = V1 - V4. Subtracting the integral value V3 of the upper thyristor voltage of the second bridge arm from the integral value V6 of the lower thyristor voltage gives the integral difference D2 of the second bridge arm, where D2 = V3 - V6. Subtracting the integral value V5 of the upper thyristor voltage of the third bridge arm from the integral value V2 of the lower thyristor voltage gives the integral difference D3 of the third bridge arm, where D3 = V5 - V2. Among them, the voltage integral values ​​V1, V2, V3, V4, V5, and V6 correspond to the voltage integral values ​​of the six thyristors, respectively. The first bridge arm consists of a first thyristor and a fourth thyristor, with the first thyristor being the upper thyristor and the fourth thyristor being the lower thyristor. The second bridge arm consists of a third thyristor and a sixth thyristor, with the third thyristor being the upper thyristor and the sixth thyristor being the lower thyristor. The third bridge arm consists of a fifth thyristor and a second thyristor, with the fifth thyristor being the upper thyristor and the second thyristor being the lower thyristor. The integral differences D1, D2, and D3 are all signed values. A positive sign indicates that the integral value of the upper thyristor voltage is greater than that of the lower thyristor voltage, and a negative sign indicates that the integral value of the upper thyristor voltage is less than that of the lower thyristor voltage.

[0011] S3 further includes the following: The first threshold is the maximum absolute value of the voltage integral difference of the same bridge arm during normal operation, multiplied by a preset coefficient; The second threshold is the minimum value of the integral of a single thyristor voltage during normal operation, multiplied by a preset coefficient; The third threshold is the maximum value of the integral value of a single thyristor voltage during normal operation multiplied by a preset coefficient; The fourth threshold is the maximum fluctuation amplitude of the voltage integral value of multiple consecutive power frequency cycles of the same thyristor during normal operation, multiplied by a preset coefficient. The preset coefficient is greater than 1 and is preset according to the monitoring sensitivity requirements.

[0012] S4 further includes the following: For each thyristor, the voltage integral value of the thyristor for the most recent N power frequency cycles is continuously recorded, where N is a preset positive integer; Find the maximum and minimum values ​​from the N voltage integral values ​​and calculate the difference between the maximum and minimum values; The difference is compared with a fourth threshold. If the difference is greater than the fourth threshold, the thyristor is determined to have a trigger failure fault. For thyristors that have not been determined to have triggered a failure, continue with the subsequent steps.

[0013] S5 further includes the following: For each thyristor that has not been determined to have triggered a failure, determine the bridge arm to which the thyristor belongs; For each bridge arm, the voltage integral difference of the bridge arm over two consecutive power frequency cycles is continuously monitored; When the voltage integral difference of a bridge arm in both of the two power frequency cycles is greater than the first threshold and the two voltage integral differences have the same sign, the bridge arm is determined to meet the fault type determination condition and the fault type is determined.

[0014] S6 further includes the following: When the sign of the voltage integral difference of the bridge arm that meets the fault type determination condition is positive, the lower thyristor voltage integral value and the upper thyristor voltage integral value of that bridge arm are obtained. The integrated value of the lower thyristor voltage is compared with the second threshold. If the integrated value of the lower thyristor voltage is less than the second threshold, it is determined that the lower thyristor has a short circuit fault. The integrated value of the upper thyristor voltage is compared with the third threshold. If the integrated value of the upper thyristor voltage is greater than the third threshold, it is determined that the upper thyristor has an open circuit fault.

[0015] The S7 further includes the following: When the sign of the voltage integral difference of the bridge arm that meets the fault type determination condition is negative, the upper thyristor voltage integral value and the lower thyristor voltage integral value of that bridge arm are obtained. The integrated value of the upper thyristor voltage is compared with the second threshold. If the integrated value of the upper thyristor voltage is less than the second threshold, it is determined that the upper thyristor has a short circuit fault. The integrated value of the lower thyristor voltage is compared with a third threshold. If the integrated value of the lower thyristor voltage is greater than the third threshold, it is determined that the lower thyristor has an open circuit fault.

[0016] An online fault monitoring system for excitation power cabinet includes a signal acquisition and integration unit, a difference calculation unit, a threshold setting unit, a trigger failure determination unit, a bridge arm screening unit, and a fault determination unit. The signal acquisition and integration unit is used to obtain the voltage integral value of each thyristor; The difference calculation unit is used to calculate the signed difference between the integral values ​​of the voltages of the upper and lower thyristors in the same bridge arm; The threshold setting unit is used to set the integral difference threshold, the upper and lower limits of the voltage integral value threshold, and the fluctuation amplitude threshold. The trigger failure determination unit is used to determine the trigger failure fault based on the fluctuation range of the voltage integral value of the thyristor over multiple cycles. The bridge arm screening unit is used to screen out abnormal bridge arms based on the integral difference between two consecutive cycles of the bridge arm. The fault determination unit is used to determine whether a short-circuit fault or an open-circuit fault is caused by comparing the integral difference sign of the abnormal bridge arm and the integral value of the upper and lower thyristor voltages with the threshold.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention does not require any historical fault samples or prior data. It utilizes the voltage symmetry of the three-phase fully controlled bridge rectifier circuit itself to complete fault detection through voltage integration, subtraction and threshold comparison, thus fundamentally avoiding the dependence of existing technologies on fault data collection and model training.

[0018] 2. This invention can simultaneously detect thyristor short-circuit faults, open-circuit faults, and trigger failure faults, as well as accurately locate specific faulty thyristors, by comparing voltage integral values ​​and judging thresholds. It does not require complex calculations or expensive equipment such as Fourier transform, neural networks, or infrared thermal imaging, and is low in cost with a response speed of less than one power frequency cycle. Attached Figure Description

[0019] Figure 1 This is a flowchart of a method for online fault monitoring applied to an excitation power cabinet according to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example: Figure 1 As shown, the present invention provides a technical solution. A method for online fault monitoring applied to excitation power cabinets includes the following steps: S1. Obtain the voltage signal across each thyristor and take the absolute value of each voltage signal, then integrate it within each power frequency cycle to obtain the voltage integral value of each thyristor. S2. Subtract the integral value of the upper thyristor voltage from the integral value of the lower thyristor voltage in the same bridge arm to obtain the integral difference value of the bridge arm. The integral difference value is a signed numerical value. S3. Set a first threshold, a second threshold, a third threshold and a fourth threshold. The first threshold is the upper limit of the normal fluctuation range of the integral difference, the second threshold is the lower limit of the integral value of a single thyristor voltage, the third threshold is the upper limit of the integral value of a single thyristor voltage, and the fourth threshold is the maximum allowable amplitude of the fluctuation of the integral value of the same thyristor voltage within multiple consecutive cycles. S4. Continuously record the voltage integral value of each thyristor for the most recent N cycles, calculate the difference between the maximum and minimum values ​​of these N values, and if the difference is greater than the fourth threshold, then the thyristor is determined to have a trigger failure fault. S5. For the bridge arm corresponding to the thyristor that has not been determined to have triggered failure, when the voltage integral difference of the bridge arm for two consecutive cycles is greater than the first threshold and the two voltage integral differences have the same sign, the fault type determination is entered. S6. When the sign of the voltage integral difference of the bridge arm is positive, if the voltage integral value of the lower thyristor is less than the second threshold, the lower thyristor is determined to be short-circuited; if the voltage integral value of the upper thyristor is greater than the third threshold, the upper thyristor is determined to be open-circuited. S7. When the voltage integral difference of the bridge arm is negative, if the voltage integral value of the upper thyristor is less than the second threshold, the upper thyristor is determined to be short-circuited; if the voltage integral value of the lower thyristor is greater than the third threshold, the lower thyristor is determined to be open-circuited.

[0022] S1 further includes the following: A low-voltage signal is obtained by connecting a voltage divider resistor network in parallel between the anode and cathode of each thyristor; The low-voltage signal is passed through an isolation amplifier to output a voltage signal that is proportional to the voltage across the thyristor. The voltage signal is input into a precision rectifier circuit to obtain the absolute value signal of the voltage signal; The absolute value signal is input into an integrator and the reset period of the integrator is set to one power frequency cycle; The integrator is reset at the end of each power frequency cycle and outputs the voltage integral value of the thyristor during that power frequency cycle. The six thyristors are processed in the above manner to obtain six voltage integral values, which are then denoted as V1, V2, V3, V4, V5, and V6 respectively. Wherein, V1 corresponds to the voltage integral value of the first thyristor, V2 corresponds to the voltage integral value of the second thyristor, V3 corresponds to the voltage integral value of the third thyristor, V4 corresponds to the voltage integral value of the fourth thyristor, V5 corresponds to the voltage integral value of the fifth thyristor, and V6 corresponds to the voltage integral value of the sixth thyristor.

[0023] S2 further includes the following: Subtracting the integral value V1 of the upper thyristor voltage of the first bridge arm from the integral value V4 of the lower thyristor voltage gives the integral difference D1 of the first bridge arm, where D1 = V1 - V4. Subtracting the integral value V3 of the upper thyristor voltage of the second bridge arm from the integral value V6 of the lower thyristor voltage gives the integral difference D2 of the second bridge arm, where D2 = V3 - V6. Subtracting the integral value V5 of the upper thyristor voltage of the third bridge arm from the integral value V2 of the lower thyristor voltage gives the integral difference D3 of the third bridge arm, where D3 = V5 - V2. Among them, the voltage integral values ​​V1, V2, V3, V4, V5, and V6 correspond to the voltage integral values ​​of the six thyristors, respectively. The first bridge arm consists of a first thyristor and a fourth thyristor, with the first thyristor being the upper thyristor and the fourth thyristor being the lower thyristor. The second bridge arm consists of a third thyristor and a sixth thyristor, with the third thyristor being the upper thyristor and the sixth thyristor being the lower thyristor. The third bridge arm consists of a fifth thyristor and a second thyristor, with the fifth thyristor being the upper thyristor and the second thyristor being the lower thyristor. The integral differences D1, D2, and D3 are all signed values. A positive sign indicates that the integral value of the upper thyristor voltage is greater than that of the lower thyristor voltage, and a negative sign indicates that the integral value of the upper thyristor voltage is less than that of the lower thyristor voltage.

[0024] The essence of S2 is a three-phase fully controlled bridge rectifier circuit; In a three-phase fully controlled bridge rectifier circuit, six thyristors are divided into three bridge arms according to the phase sequence of the three-phase AC power, and each bridge arm corresponds to one phase of AC input. The first bridge arm consists of the first thyristor and the fourth thyristor. The first thyristor is connected in the positive half-cycle direction of the AC phase and is called the upper thyristor. The fourth thyristor is connected in the negative half-cycle direction and is called the lower thyristor. The second bridge arm consists of a third thyristor and a sixth thyristor. The third thyristor is the upper thyristor, and the sixth thyristor is the lower thyristor. The third bridge arm consists of a fifth thyristor and a second thyristor. The fifth thyristor is the upper thyristor, and the second thyristor is the lower thyristor. During normal operation, the two thyristors on the same bridge arm conduct alternately within one power frequency cycle, and the duration and waveform of each thyristor bearing reverse voltage are basically symmetrical. Therefore, the integral value V1 of the upper thyristor voltage is approximately equal to the integral value V4 of the lower thyristor voltage, and the integral difference D1 obtained by subtracting them is close to zero. Similarly, the difference D2 between V3 and V6 is close to zero, and the difference D3 between V5 and V2 is close to zero; However, when a thyristor experiences a short circuit or open circuit fault, the symmetry is disrupted, and the corresponding integral difference will deviate significantly from zero and have a fixed positive or negative sign. The fault can be located by comparing the difference with the threshold.

[0025] S3 further includes the following: The first threshold is the maximum absolute value of the voltage integral difference of the same bridge arm during normal operation, multiplied by a preset coefficient; The second threshold is the minimum value of the integral of a single thyristor voltage during normal operation, multiplied by a preset coefficient; The third threshold is the maximum value of the integral value of a single thyristor voltage during normal operation multiplied by a preset coefficient; The fourth threshold is the maximum fluctuation amplitude of the voltage integral value of multiple consecutive power frequency cycles of the same thyristor during normal operation, multiplied by a preset coefficient. The preset coefficient is greater than 1 and is preset according to the monitoring sensitivity requirements.

[0026] As described in S2 above, when the three-phase fully controlled bridge rectifier circuit is running normally, the voltage integral values ​​of the upper and lower thyristors of the same bridge arm are approximately equal, and the difference is close to zero. However, due to differences in component parameters and power grid fluctuations, the integral difference will have a normal fluctuation range. Therefore, the first threshold is set to be slightly higher than the upper limit of the normal fluctuation range, in order to distinguish between normal fluctuations and deviations caused by faults; When a single thyristor is working normally, its voltage integral value is stable within a fixed range. Therefore, the second threshold is set below the lower limit of this range to determine whether the voltage integral value of the thyristor is too low due to a short circuit. The third threshold is set above the upper limit of the range to determine whether the voltage integral value of the thyristor is too high due to an open circuit. In the case of trigger failure, the thyristor exhibits intermittent non-conductivity, with its voltage integral value fluctuating greatly over multiple cycles, and the fluctuation range is far greater than that of the normal state. Therefore, the fourth threshold is set to be slightly higher than the upper limit of normal fluctuation range, in order to capture such abnormal fluctuations; Furthermore, all four thresholds are obtained by multiplying the measured normal data when the equipment was first put into operation by a preset coefficient, without requiring any historical fault samples.

[0027] S4 further includes the following: For each thyristor, the voltage integral value of the thyristor for the most recent N power frequency cycles is continuously recorded, where N is a preset positive integer; Find the maximum and minimum values ​​from the N voltage integral values ​​and calculate the difference between the maximum and minimum values; The difference is compared with a fourth threshold. If the difference is greater than the fourth threshold, the thyristor is determined to have a trigger failure fault. For thyristors that have not been determined to have triggered a failure, continue with the subsequent steps.

[0028] The essence of the trigger failure fault is the loss of the thyristor gate trigger signal or the degradation of the gate performance, which causes the thyristor to fail to conduct in some cycles but recover normal in other cycles. When a trigger failure occurs, the voltage integral value during the conduction cycle is close to the normal value, while the voltage integral value during the non-conducting cycle is significantly larger or smaller due to the full reverse voltage. The voltage integral value of multiple cycles will show large jumps. Therefore, the present invention is designed to monitor and continuously record the voltage integral value of the most recent N cycles and calculate the difference between the maximum and minimum values, which can directly reflect the amplitude of this periodic jump. Then compare the difference with the fourth threshold. If the difference is greater than the fourth threshold, it indicates that the conduction state of the thyristor is inconsistent in different cycles, thus determining the trigger failure fault. The method designed in this invention does not rely on fault data and can identify intermittent faults simply through multi-cycle self-comparison.

[0029] S5 further includes the following: For each thyristor that has not been determined to have triggered a failure, determine the bridge arm to which the thyristor belongs; For each bridge arm, the voltage integral difference of the bridge arm over two consecutive power frequency cycles is continuously monitored; When the voltage integral difference of a bridge arm in both of the two power frequency cycles is greater than the first threshold and the two voltage integral differences have the same sign, the bridge arm is determined to meet the fault type determination condition and the fault type is determined.

[0030] According to the characteristics of the three-phase fully controlled bridge rectifier circuit, when a short circuit fault or open circuit fault occurs, the symmetry of the voltage integral values ​​of the upper and lower tubes of the bridge arm where the faulty thyristor is located is permanently destroyed, and the integral difference will continue to be greater than the normal fluctuation range and the sign remains unchanged. External influences, such as sudden load changes and grid harmonics, may also cause the integral difference to exceed the limit for a short period of time, but usually it will not last for two cycles and the sign may change. Therefore, by setting up two continuous monitoring cycles and requiring that the integral difference be greater than the first threshold and have the same sign, the present invention can eliminate false alarms caused by instantaneous disturbances and confirm that the fault does indeed persist. Therefore, when a bridge arm meets this condition, the bridge arm is identified as an abnormal bridge arm and enters the specific fault type determination process.

[0031] S6 further includes the following: When the sign of the voltage integral difference of the bridge arm that meets the fault type determination condition is positive, the lower thyristor voltage integral value and the upper thyristor voltage integral value of that bridge arm are obtained. The integrated value of the lower thyristor voltage is compared with the second threshold. If the integrated value of the lower thyristor voltage is less than the second threshold, it is determined that the lower thyristor has a short circuit fault. The integrated value of the upper thyristor voltage is compared with the third threshold. If the integrated value of the upper thyristor voltage is greater than the third threshold, it is determined that the upper thyristor has an open circuit fault.

[0032] The S7 further includes the following: When the sign of the voltage integral difference of the bridge arm that meets the fault type determination condition is negative, the upper thyristor voltage integral value and the lower thyristor voltage integral value of that bridge arm are obtained. The integrated value of the upper thyristor voltage is compared with the second threshold. If the integrated value of the upper thyristor voltage is less than the second threshold, it is determined that the upper thyristor has a short circuit fault. The integrated value of the lower thyristor voltage is compared with a third threshold. If the integrated value of the lower thyristor voltage is greater than the third threshold, it is determined that the lower thyristor has an open circuit fault.

[0033] The principle behind using symbols to determine short-circuit or open-circuit faults in S6 and S7 is as follows: When the sign of the integral difference of the bridge arm is positive, it means that the integral value of the upper thyristor voltage is greater than the integral value of the lower thyristor voltage, that is, the integral of the upper thyristor is too large and the integral of the lower thyristor is too small. When the integral value is too small and below the second threshold, it indicates that the voltage across the thyristor has been close to zero for a long time. This is because a short circuit fault causes the thyristor to be permanently turned on, and the voltage across its terminals is clamped to zero. Therefore, if the integral value of the lower thyristor voltage is less than the second threshold, the lower thyristor is short-circuited; if the integral value of the upper thyristor voltage is less than the second threshold, the upper thyristor is short-circuited. When the integral value is too large and exceeds the third threshold, it indicates that the thyristor failed to conduct during the period when it should have been conducting and was subjected to the all-reverse voltage spike, which caused the integral value to increase. Therefore, if the integral value of the upper thyristor voltage is greater than the third threshold, it corresponds to the upper thyristor being open, and if the integral value of the lower thyristor voltage is greater than the third threshold, it corresponds to the lower thyristor being open. This invention utilizes this characteristic of the three-phase fully controlled bridge rectifier circuit and employs this method to directly correlate fault types with electrical and physical effects through bidirectional verification of the sign of the integral difference and the magnitude of a single integral value. Compared with the prior art, the ingenuity of this invention lies in the fact that it does not rely on fault data, spectrum transformation or neural networks, but only utilizes the voltage symmetry of the rectifier bridge itself and simple addition and subtraction comparison to simultaneously realize fault detection, classification and location.

[0034] An online fault monitoring system for excitation power cabinet includes a signal acquisition and integration unit, a difference calculation unit, a threshold setting unit, a trigger failure determination unit, a bridge arm screening unit, and a fault determination unit. The signal acquisition and integration unit is used to obtain the voltage integral value of each thyristor; The difference calculation unit is used to calculate the signed difference between the integral values ​​of the voltages of the upper and lower thyristors in the same bridge arm; The threshold setting unit is used to set the integral difference threshold, the upper and lower limits of the voltage integral value threshold, and the fluctuation amplitude threshold. The trigger failure determination unit is used to determine the trigger failure fault based on the fluctuation range of the voltage integral value of the thyristor over multiple cycles. The bridge arm screening unit is used to screen out abnormal bridge arms based on the integral difference between two consecutive cycles of the bridge arm. The fault determination unit is used to determine whether a short-circuit fault or an open-circuit fault is caused by comparing the integral difference sign of the abnormal bridge arm and the integral value of the upper and lower thyristor voltages with the threshold.

[0035] Based on the above technical solution, the present invention now provides the following embodiments to further illustrate the feasibility of the invention, the contents of which are as follows: In the generator excitation system of a hydropower station, the excitation power cabinet adopts a three-phase fully controlled bridge rectifier circuit, with six internal thyristors numbered sequentially from VT1 to VT6. When the power cabinet is first put into operation, a reference state acquisition operation is performed. A voltage divider resistor network is connected in parallel between the anode and cathode of each thyristor to reduce the high voltage signal across the thyristor to a low voltage signal, which is then output as a voltage signal proportional to the voltage across the thyristor through an isolation amplifier.

[0036] The voltage signal is input to a precision rectifier circuit to obtain an absolute value signal, which is then input to an integrator. The integrator's reset period is set to 20 milliseconds per power frequency cycle. At the end of each power frequency cycle, the integrator resets and outputs the voltage integral value of the thyristor within that cycle. This process is performed on each of the six thyristors, resulting in six voltage integral values, which are sequentially denoted as V1, V2, V3, V4, V5, and V6. Actual measurements yielded V1 = 0.85 volt-seconds, V2 = 0.84 volt-seconds, V3 = 0.86 volt-seconds, V4 = 0.85 volt-seconds, V5 = 0.84 volt-seconds, and V6 = 0.85 volt-seconds. These values ​​represent the voltage integral values ​​of each thyristor during normal operation.

[0037] Based on the circuit structure of the three-phase fully controlled bridge, the six thyristors are divided into three bridge arms. The first bridge arm consists of VT1 and VT4, where VT1 is the upper thyristor and VT4 is the lower thyristor. The second bridge arm consists of VT3 and VT6, where VT3 is the upper thyristor and VT6 is the lower thyristor. The third bridge arm consists of VT5 and VT2, where VT5 is the upper thyristor and VT2 is the lower thyristor.

[0038] During normal operation, the upper and lower thyristors of the same bridge arm conduct alternately within one power frequency cycle. The duration and waveform of the reverse voltage they each bear are basically symmetrical. Therefore, the voltage integral value of the upper thyristor is approximately equal to that of the lower thyristor.

[0039] Subtracting the integral value V1 of the upper thyristor voltage of the first bridge arm from the integral value V4 of the lower thyristor voltage gives the integral difference D1 of the first bridge arm: D1 = V1 - V4 = 0.85 - 0.85 = 0 volts / seconds.

[0040] Subtracting the integral value V3 of the upper thyristor voltage of the second bridge arm from the integral value V6 of the lower thyristor voltage gives the integral difference D2 of the second bridge arm: D2 = V3 - V6 = 0.86 - 0.85 = 0.01 volt-seconds.

[0041] Subtracting the integral value V5 of the upper thyristor voltage of the third bridge arm from the integral value V2 of the lower thyristor voltage gives the integral difference D3 of the third bridge arm: D3 = V5 - V2 = 0.84 - 0.84 = 0 volts / seconds.

[0042] All three integral differences are close to zero and have positive and negative signs. A positive sign indicates that the integral value of the upper thyristor voltage is greater than that of the lower thyristor voltage, and a negative sign indicates that the integral value of the upper thyristor voltage is less than that of the lower thyristor voltage.

[0043] Based on data measured during normal operation, four thresholds are set. The first threshold is the maximum absolute value of the voltage integral difference of the same bridge arm during normal operation, multiplied by a preset coefficient. During normal operation, the maximum absolute value of the integral difference of the three bridge arms is 0.01 volt-seconds, and the preset coefficient is 1.5. Therefore, the first threshold is equal to 0.01 multiplied by 1.5, which equals 0.015 volt-seconds.

[0044] The second threshold is the minimum value of the integrated voltage of a single thyristor during normal operation, multiplied by a preset coefficient. During normal operation, the minimum integrated voltage value of the six thyristors is 0.84 volts per second. The preset coefficient is 0.5, so the second threshold is equal to 0.84 multiplied by 0.5, which equals 0.42 volts per second.

[0045] The third threshold is the maximum value of the integrated voltage of a single thyristor during normal operation multiplied by a preset coefficient. During normal operation, the maximum value of the six voltage integrals is 0.86 volts per second. The preset coefficient is 1.5, so the third threshold is equal to 0.86 multiplied by 1.5, which equals 1.29 volts per second.

[0046] The fourth threshold is the maximum fluctuation amplitude of the voltage integral value of the same thyristor in multiple consecutive power frequency cycles during normal operation, multiplied by a preset coefficient.

[0047] During normal operation, the voltage integral value of each thyristor is continuously recorded for 10 cycles, with a maximum fluctuation of 0.02 volts per second. The preset coefficient is 2, so the fourth threshold is equal to 0.02 multiplied by 2, which equals 0.04 volts per second.

[0048] All preset coefficients are greater than 1 and are preset according to monitoring sensitivity requirements, without the need for any historical fault samples.

[0049] Three months after the equipment was put into operation, the system began online monitoring. For each thyristor, the voltage integral value of its most recent N power frequency cycles was continuously recorded, where N is set to 5. Taking the first thyristor VT1 as an example, the voltage integral values ​​of its most recent 5 cycles were recorded as 0.84 volt-seconds, 0.83 volt-seconds, 0.85 volt-seconds, 0.84 volt-seconds, and 0.83 volt-seconds, respectively.

[0050] Find the maximum value of 0.85 volts and the minimum value of 0.83 volts and the difference between them, which is 0.02 volts and the difference between them. Compare this difference of 0.02 volts and the fourth threshold of 0.04 volts and the difference of 0.02 volts and the difference ...

[0051] The same operation was performed on the other five thyristors in sequence, and no thyristor was found to have a voltage integral value with a maximum and minimum difference exceeding the fourth threshold. Therefore, none of the thyristors were determined to be trigger failure faults.

[0052] For each thyristor that has not been determined to have triggered a failure, determine the bridge arm to which it belongs. VT1 belongs to the first bridge arm, and VT4 also belongs to the first bridge arm.

[0053] The voltage integral difference of the first bridge arm was continuously monitored over two consecutive power frequency cycles. In the first cycle, V1 = 0.84 volt-seconds and V4 = 0.33 volt-seconds were measured, and D1 = 0.84 - 0.33 = 0.51 volt-seconds was calculated.

[0054] In the second cycle, V1 = 0.83 volts / second and V4 = 0.32 volts / second were measured, and D1 = 0.83 - 0.32 = 0.51 volts / second was calculated.

[0055] The voltage integral difference between the two cycles is 0.51 volts per second, which is greater than the first threshold of 0.015 volts per second, and both differences are positive.

[0056] Therefore, the first bridge arm is determined to meet the fault type determination conditions, and the fault type determination step is initiated.

[0057] For the second bridge arm, V3 was measured to be 0.86 volts and 0.85 volts and V6 was measured to be 0.85 volts and 0.84 volts for two consecutive cycles. D2 was calculated to be 0.01 volts and 0.01 volts, respectively. Both were less than the first threshold and did not meet the condition.

[0058] For the third bridge arm, V5 = 0.84 volt-seconds, 0.84 volt-seconds, V2 = 0.84 volt-seconds, 0.84 volt-seconds, and D3 was calculated to be 0 volt-seconds, which does not meet the condition.

[0059] Therefore, only the first bridge arm was identified as the abnormal bridge arm.

[0060] For the first bridge arm that meets the fault type determination criteria, its voltage integral difference value is positive. The voltage integral value of the lower thyristor VT4 and the voltage integral value of the upper thyristor VT1 of this bridge arm are obtained. At this time, the voltage integral value of VT4 is measured to be 0.33 volts per second. This value is compared with the second threshold of 0.42 volts per second. 0.33 is less than 0.42, so it is determined that the lower thyristor VT4 has a short circuit fault.

[0061] Meanwhile, the voltage integral value of VT1 was measured to be 0.84 volts per second. This value was compared with the third threshold of 1.29 volts per second. 0.84 is less than 1.29, which does not meet the condition of being greater than the third threshold. Therefore, the upper thyristor is not judged to be open circuit fault.

[0062] At this point, the system outputs a fault alarm message: a short circuit fault has occurred in the lower thyristor VT4 of the first bridge arm.

[0063] If we assume different fault types, for example, when the integral difference of the first bridge arm is positive and the voltage integral value of the upper thyristor VT1 is 1.35 volts / second, which is greater than the third threshold of 1.29 volts / second, while the voltage integral value of the lower thyristor VT4 is 0.85 volts / second, which is greater than the second threshold of 0.42 volts / second, then it is determined that the upper thyristor VT1 has an open circuit fault.

[0064] If the integral difference is negative, for example, D1 = -0.51 volts second, and the voltage integral value of the upper thyristor VT1 is 0.32 volts second, which is less than the second threshold of 0.42 volts second, then the upper thyristor VT1 is determined to be short-circuited; if the voltage integral value of the lower thyristor VT4 is 1.35 volts second, which is greater than the third threshold of 1.29 volts second, then the lower thyristor VT4 is determined to be open-circuited.

[0065] All of the above judgment processes do not rely on any historical fault data or complex algorithms, and can be completed simply through voltage integration, subtraction, and threshold comparison.

[0066] The entire online monitoring system consists of a signal acquisition and integration unit, a difference calculation unit, a threshold setting unit, a trigger failure determination unit, a bridge arm screening unit, and a fault determination unit. The signal acquisition and integration unit is responsible for acquiring the integrated voltage value of each thyristor. The difference calculation unit is responsible for calculating the signed difference between the integrated voltage values ​​of the upper and lower thyristors within the same bridge arm. The threshold setting unit is responsible for setting the threshold values ​​for the integration difference, the upper and lower limits of the integrated voltage value, and the fluctuation amplitude. The trigger failure determination unit is responsible for determining trigger failure faults based on the fluctuation amplitude of the integrated voltage value of the thyristor over multiple cycles. The bridge arm screening unit is responsible for filtering out abnormal bridge arms based on the integration difference between two consecutive cycles. The fault determination unit is responsible for determining short-circuit or open-circuit faults based on the sign of the integration difference of the abnormal bridge arm and the comparison results of the integrated voltage values ​​of the upper and lower thyristors with the threshold values. These units work collaboratively to achieve an online monitoring solution that can diagnose and accurately locate thyristor faults in real time solely through voltage comparison, without requiring fault data or complex algorithms.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for online fault monitoring applied to excitation power cabinets, characterized in that: Includes the following steps: S1. Obtain the voltage signal across each thyristor and take the absolute value of each voltage signal, then integrate it within each power frequency cycle to obtain the voltage integral value of each thyristor. S2. Subtract the integral value of the upper thyristor voltage from the integral value of the lower thyristor voltage in the same bridge arm to obtain the integral difference value of the bridge arm. The integral difference value is a signed numerical value. S3. Set a first threshold, a second threshold, a third threshold and a fourth threshold. The first threshold is the upper limit of the normal fluctuation range of the integral difference, the second threshold is the lower limit of the integral value of a single thyristor voltage, the third threshold is the upper limit of the integral value of a single thyristor voltage, and the fourth threshold is the maximum allowable amplitude of the fluctuation of the integral value of the same thyristor voltage within multiple consecutive cycles. S4. Continuously record the voltage integral value of each thyristor for the most recent N cycles, calculate the difference between the maximum and minimum values ​​of these N values, and if the difference is greater than the fourth threshold, then the thyristor is determined to have a trigger failure fault. S5. For the bridge arm corresponding to the thyristor that has not been determined to have triggered failure, when the voltage integral difference of the bridge arm for two consecutive cycles is greater than the first threshold and the two voltage integral differences have the same sign, the fault type determination is entered. S6. When the sign of the voltage integral difference of the bridge arm is positive, if the voltage integral value of the lower thyristor is less than the second threshold, the lower thyristor is determined to be short-circuited; if the voltage integral value of the upper thyristor is greater than the third threshold, the upper thyristor is determined to be open-circuited. S7. When the voltage integral difference of the bridge arm is negative, if the voltage integral value of the upper thyristor is less than the second threshold, the upper thyristor is determined to be short-circuited; if the voltage integral value of the lower thyristor is greater than the third threshold, the lower thyristor is determined to be open-circuited.

2. The online fault monitoring method for excitation power cabinet according to claim 1, characterized in that: S1 further includes the following: A low-voltage signal is obtained by connecting a voltage divider resistor network in parallel between the anode and cathode of each thyristor; The low-voltage signal is passed through an isolation amplifier to output a voltage signal that is proportional to the voltage across the thyristor. The voltage signal is input into a precision rectifier circuit to obtain the absolute value signal of the voltage signal; The absolute value signal is input into an integrator and the reset period of the integrator is set to one power frequency cycle; The integrator is reset at the end of each power frequency cycle and outputs the voltage integral value of the thyristor during that power frequency cycle. The six thyristors are processed in the above manner to obtain six voltage integral values, which are then denoted as V1, V2, V3, V4, V5, and V6 respectively. Wherein, V1 corresponds to the voltage integral value of the first thyristor, V2 corresponds to the voltage integral value of the second thyristor, V3 corresponds to the voltage integral value of the third thyristor, V4 corresponds to the voltage integral value of the fourth thyristor, V5 corresponds to the voltage integral value of the fifth thyristor, and V6 corresponds to the voltage integral value of the sixth thyristor.

3. The online fault monitoring method for excitation power cabinet according to claim 1, characterized in that: S2 further includes the following: Subtracting the integral value V1 of the upper thyristor voltage of the first bridge arm from the integral value V4 of the lower thyristor voltage gives the integral difference D1 of the first bridge arm, where D1 = V1 - V4. Subtracting the integral value V3 of the upper thyristor voltage of the second bridge arm from the integral value V6 of the lower thyristor voltage gives the integral difference D2 of the second bridge arm, where D2 = V3 - V6. Subtracting the integral value V5 of the upper thyristor voltage of the third bridge arm from the integral value V2 of the lower thyristor voltage gives the integral difference D3 of the third bridge arm, where D3 = V5 - V2. Among them, the voltage integral values ​​V1, V2, V3, V4, V5, and V6 correspond to the voltage integral values ​​of the six thyristors, respectively. The first bridge arm consists of a first thyristor and a fourth thyristor, with the first thyristor being the upper thyristor and the fourth thyristor being the lower thyristor. The second bridge arm consists of a third thyristor and a sixth thyristor, with the third thyristor being the upper thyristor and the sixth thyristor being the lower thyristor. The third bridge arm consists of a fifth thyristor and a second thyristor, with the fifth thyristor being the upper thyristor and the second thyristor being the lower thyristor. The integral differences D1, D2, and D3 are all signed values. A positive sign indicates that the integral value of the upper thyristor voltage is greater than that of the lower thyristor voltage, and a negative sign indicates that the integral value of the upper thyristor voltage is less than that of the lower thyristor voltage.

4. The online fault monitoring method for excitation power cabinet according to claim 1, characterized in that: S3 further includes the following: The first threshold is the maximum absolute value of the voltage integral difference of the same bridge arm during normal operation, multiplied by a preset coefficient; The second threshold is the minimum value of the integral of a single thyristor voltage during normal operation, multiplied by a preset coefficient; The third threshold is the maximum value of the integral value of a single thyristor voltage during normal operation multiplied by a preset coefficient; The fourth threshold is the maximum fluctuation amplitude of the voltage integral value of multiple consecutive power frequency cycles of the same thyristor during normal operation, multiplied by a preset coefficient. The preset coefficient is greater than 1 and is preset according to the monitoring sensitivity requirements.

5. The online fault monitoring method for excitation power cabinet according to claim 1, characterized in that: S4 further includes the following: For each thyristor, the voltage integral value of the thyristor for the most recent N power frequency cycles is continuously recorded, where N is a preset positive integer; Find the maximum and minimum values ​​from the N voltage integral values ​​and calculate the difference between the maximum and minimum values; The difference is compared with a fourth threshold. If the difference is greater than the fourth threshold, the thyristor is determined to have a trigger failure fault. For thyristors that have not been determined to have triggered a failure, continue with the subsequent steps.

6. The online fault monitoring method for excitation power cabinet according to claim 5, characterized in that: S5 further includes the following: For each thyristor that has not been determined to have triggered a failure, determine the bridge arm to which the thyristor belongs; For each bridge arm, the voltage integral difference of the bridge arm over two consecutive power frequency cycles is continuously monitored; When the voltage integral difference of a bridge arm in both of the two power frequency cycles is greater than the first threshold and the two voltage integral differences have the same sign, the bridge arm is determined to meet the fault type determination condition and the fault type is determined.

7. The online fault monitoring method for excitation power cabinet according to claim 6, characterized in that: S6 further includes the following: When the sign of the voltage integral difference of the bridge arm that meets the fault type determination condition is positive, the lower thyristor voltage integral value and the upper thyristor voltage integral value of that bridge arm are obtained. The integrated value of the lower thyristor voltage is compared with the second threshold. If the integrated value of the lower thyristor voltage is less than the second threshold, it is determined that the lower thyristor has a short circuit fault. The integrated value of the upper thyristor voltage is compared with the third threshold. If the integrated value of the upper thyristor voltage is greater than the third threshold, it is determined that the upper thyristor has an open circuit fault.

8. The online fault monitoring method for excitation power cabinet according to claim 6, characterized in that: The S7 further includes the following: When the sign of the voltage integral difference of the bridge arm that meets the fault type determination condition is negative, the upper thyristor voltage integral value and the lower thyristor voltage integral value of that bridge arm are obtained. The integrated value of the upper thyristor voltage is compared with the second threshold. If the integrated value of the upper thyristor voltage is less than the second threshold, it is determined that the upper thyristor has a short circuit fault. The integrated value of the lower thyristor voltage is compared with a third threshold. If the integrated value of the lower thyristor voltage is greater than the third threshold, it is determined that the lower thyristor has an open circuit fault.

9. An online fault monitoring system for excitation power cabinets, applied to the online fault monitoring method for excitation power cabinets as described in any one of claims 1-8, characterized in that: It includes a signal acquisition and integration unit, a difference calculation unit, a threshold setting unit, a trigger failure determination unit, a bridge arm screening unit, and a fault determination unit; The signal acquisition and integration unit is used to obtain the voltage integral value of each thyristor; The difference calculation unit is used to calculate the signed difference between the integral values ​​of the voltages of the upper and lower thyristors in the same bridge arm; The threshold setting unit is used to set the integral difference threshold, the upper and lower limits of the voltage integral value threshold, and the fluctuation amplitude threshold. The trigger failure determination unit is used to determine the trigger failure fault based on the fluctuation range of the voltage integral value of the thyristor over multiple cycles. The bridge arm screening unit is used to screen out abnormal bridge arms based on the integral difference between two consecutive cycles of the bridge arm. The fault determination unit is used to determine whether a short-circuit fault or an open-circuit fault is caused by comparing the integral difference sign of the abnormal bridge arm and the integral value of the upper and lower thyristor voltages with the threshold.

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