A transformer core grounding current online monitoring system and device

Abstract

The present invention relates to an online monitoring system and device for transformer core grounding current, comprising a signal acquisition unit, a conditioning unit, a data analysis unit, a storage unit, and a control unit. The control unit receives the measured value and historical data of the core grounding current, the measured value and historical data of the clamp grounding current, the measured value and historical data of the amplitude correlation coefficient, and the measured value and historical coefficient of the phase correlation coefficient, and comprehensively determines the fault state of the transformer core based on the received information. The present invention monitors the core grounding current and the clamp grounding current simultaneously, and after amplifying and filtering the corresponding grounding currents, analyzes the degree of correlation between the core grounding current and the clamp grounding current from different dimensions. By utilizing the principle that the correlation between the two grounding currents is significantly improved when the core and the clamp are turned on, the early insulation fault of the core and the clamp is assisted in the judgment, which can improve the detection rate of early insulation faults with the core grounding current lower than 100mA.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric power monitoring, and in particular relates to an online monitoring system and device for transformer core grounding current. Background Art

[0002] Transformers are core equipment for power transmission, and their operational reliability directly impacts grid security. As the core component of the magnetic circuit, the transformer core requires reliable single-point grounding during normal operation to eliminate floating potentials. However, over long-term operation, insulation aging, mechanical vibration, or foreign object intrusion can lead to multiple grounding faults in the core. This can cause abnormally high ground currents, leading to localized overheating, insulation degradation, and even serious accidents such as core burnout.

[0003] Traditional core grounding fault detection relies primarily on regular manual inspections or offline testing, using a clamp-on ammeter to measure the grounding current. This method has significant drawbacks: poor real-time performance, an inability to capture transient abnormal signals, and susceptibility to human error. With the development of smart grids, some improved solutions have adopted fixed current sensors combined with threshold alarm functions, but the following problems still exist: the threshold of existing online monitoring devices is typically set below 0.1A. When an initial multi-point grounding fault occurs in the core, the grounding current may be below the threshold, making it difficult to effectively identify early faults with the existing threshold setting. Lowering the alarm threshold can also lead to false alarms due to noise interference. Current anomalies caused by external metal foreign objects connecting to the down conductor can also be misjudged as temporary interference due to current amplitude fluctuations. Therefore, it is necessary to design an online transformer core grounding current monitoring device and system that balances sensitivity and false positive rate. Summary of the Invention

[0004] The purpose of the present invention is to provide an online monitoring system for transformer core grounding current to solve the problem in the prior art that it is difficult to identify early transformer faults; the purpose of the present invention is also to provide an online monitoring device for transformer core grounding current using the above monitoring system.

[0005] In order to achieve the above objectives, the present invention adopts the following technical solutions for an online monitoring system of transformer core grounding current:

[0006] A transformer core grounding current online monitoring system, comprising:

[0007] A signal acquisition unit, which is used to detect the iron core grounding current flowing through the iron core grounding lead wire and the clamp grounding current flowing through the clamp grounding lead wire;

[0008] A conditioning unit is used to process the collected signals, and simultaneously process the core grounding current into the core grounding voltage and the clamp grounding current into the clamp grounding voltage;

[0009] A data analysis unit, used for analyzing the measured value of the amplitude correlation coefficient between the core grounding voltage and the clamp grounding voltage and the measured value of the phase correlation coefficient between the core grounding voltage and the clamp grounding voltage at a specific frequency component;

[0010] A storage unit for storing historical data of the amplitude correlation coefficient between the core grounding voltage and the clamp grounding voltage under normal operating conditions, historical data of the phase correlation coefficient between the core grounding voltage and the clamp grounding voltage, and a set of transient waveform templates corresponding to the switch operation modes;

[0011] A control unit, the signal acquisition unit, the data analysis unit and the storage unit are electrically connected to different input ports of the control unit to transmit signals thereto, and the control unit comprehensively determines the transformer core fault state based on the core grounding current, the clamp grounding current, the amplitude correlation coefficient measured value, the phase correlation coefficient measured value, the amplitude correlation coefficient historical data, the phase correlation coefficient historical data, the switch operation status and the operation mode.

[0012] Furthermore, when the core grounding current exceeds the set threshold, the waveform is judged to be consistent with the transient waveform template under the corresponding switching operation mode. If the two are consistent, it is determined that the core grounding current amplitude fluctuation is caused by the switching action; if the two are inconsistent, it is determined that the transformer has an insulation fault;

[0013] When the core grounding current is less than the set threshold, the change of the measured value of the amplitude correlation coefficient relative to the historical data and the change of the measured value of the phase correlation coefficient relative to the historical data are analyzed. When the increase of the measured value of the amplitude correlation coefficient relative to the historical data and the increase of the measured value of the phase correlation coefficient relative to the historical data both exceed the set value, it is determined that the transformer has an early insulation fault.

[0014] Furthermore, the steps of the data analysis unit for performing correlation analysis are as follows:

[0015] Step 1: Acquire the core grounding voltage and the clamp grounding voltage by synchronous sampling;

[0016] Step 2: Perform discrete Fourier transform on the core grounding voltage and the clamp grounding voltage to obtain frequency domain representations of the core grounding voltage and the clamp grounding voltage, and identify the fundamental wave and main harmonic frequencies;

[0017] Step 3: Perform frequency division filtering and Hilbert transformation on the core grounding voltage and the clamp grounding voltage respectively to obtain the instantaneous amplitude and instantaneous phase sequence of the corresponding frequency signal;

[0018] Step 4: Calculate the amplitude correlation between the core grounding voltage and the clamp grounding voltage at the same frequency component and measure it with the amplitude correlation coefficient;

[0019] Step 5: Calculate the phase correlation of the same frequency components of the core grounding voltage and the clamp grounding voltage and measure it with a phase correlation coefficient.

[0020] Furthermore, when the core grounding current is less than the set threshold, the changes in the measured value of the amplitude correlation coefficient under the fundamental component relative to the historical data and the changes in the measured value of the phase correlation coefficient under the harmonic component relative to the historical data are analyzed respectively. When the increase in the amplitude correlation coefficient under the fundamental component and the increase in the phase correlation coefficient under the harmonic component exceed the set value, it is determined that the transformer has an early insulation fault.

[0021] Furthermore, a resistor is connected in series to the core grounding lead and / or the clamp grounding lead, and control switches for controlling the switching state of the resistor are provided on both sides of the resistor; when the increase amplitude of the amplitude correlation coefficient and the increase amplitude of the phase correlation coefficient under only the fundamental component exceed the set value or the increase amplitude of the amplitude correlation coefficient and the increase amplitude of the phase correlation coefficient under only the harmonic component exceed the set value, the resistor on the core grounding lead or the clamp grounding lead is switched into the loop;

[0022] If the measured values ​​of the amplitude correlation coefficient and the phase correlation coefficient under the corresponding frequency component decrease by more than the set value after the resistor is switched on and off, it is determined that an early insulation fault has occurred between the iron core and the clamp; if the measured values ​​of the amplitude correlation coefficient and the phase correlation coefficient under the corresponding component do not exceed the set value after the resistor is switched on and off, it is determined that the transformer is in normal condition.

[0023] Furthermore, the storage unit updates the historical data stored therein in real time.

[0024] Furthermore, in step four, the amplitude correlation coefficient of each frequency component is calculated using the Pearson correlation coefficient formula; in step five, the phase difference between the instantaneous phase of the core grounding voltage and the instantaneous phase of the clamp grounding voltage is directly calculated for each frequency component, and then the standard deviation of the phase difference sequence under the frequency component is calculated, and then the standard deviation is divided by the maximum value of the standard deviation when the phase difference is completely random, and the phase correlation coefficient at each frequency component is constructed by subtracting this value from 1.

[0025] Furthermore, the conditioning unit includes a sampling resistor, a filter circuit, an amplifier circuit and an A / D converter, the amplifier circuit includes a primary amplifier circuit and a secondary amplifier circuit, the primary amplifier circuit is placed between the sampling resistor and the filter circuit, and the secondary amplifier circuit is placed between the filter circuit and the A / D converter, the filter circuit includes a low-pass filter circuit and a high-pass filter circuit, and the primary amplifier circuit and the secondary amplifier circuit both use inverting amplifier circuits; the signal acquisition unit includes a first Hall sensor and a second Hall sensor, and also includes a bracket, a movable plate that can be guided and moved in the up and down directions is provided on the bracket, and two grooves are provided on the movable plate for the corresponding Hall sensors to be inserted so that the two Hall sensors are at the same height.

[0026] Furthermore, when a lightning strike occurs, the control unit determines that an early insulation fault or an insulation fault occurs in the transformer, and the duration of the corresponding judgment criterion is required to be greater than 10ms.

[0027] The present invention provides an online monitoring device for transformer core grounding current using the following technical solutions:

[0028] A transformer core grounding current online monitoring device comprises a shell, in which the transformer core grounding current online monitoring system is integrated.

[0029] The beneficial effects of the present invention are as follows: the present invention simultaneously monitors the core grounding current and the clamp grounding current, and after amplifying and filtering the core grounding current and the clamp grounding current, analyzes the degree of correlation between the core grounding voltage and the clamp grounding voltage. By utilizing the principle that the correlation between the grounding currents of the core and the clamp is low when the insulation between the core and the clamp is good, and the correlation between the core and the clamp is significantly improved when the core and the clamp are in the same circuit when the core and the clamp are turned on, the early insulation faults of the core and the clamp can be assisted in judging. Even when the core grounding current is lower than 100mA, the early insulation faults of the core and the clamp can be successfully identified. The present invention determines the specific criteria for identifying transformer fault risks, which can significantly improve the accuracy of fault identification.

[0030] Furthermore, the present invention measures the correlation between the core and fixture grounding currents using two different dimensions: amplitude correlation and phase correlation at different frequency components. This allows filtering out the common interference source of power grid background harmonics. This is because power grid background harmonics are generally high-frequency harmonics, but the core and fixture have different phase responses to high-frequency harmonics. Therefore, when this interference occurs, the amplitude correlation may increase by more than a set value, while the phase correlation may not.

[0031] Furthermore, when the increase in the amplitude correlation coefficient and the increase in the phase correlation coefficient exceed the set value only under the fundamental component or only under the harmonic component, the present invention judges whether the cause of the deviation in the followability of the fundamental component and the harmonic component is external interference or early insulation fault through the feedback of the system after the resistor is switched, which can further improve the detection rate of the present invention for early insulation faults.

[0032] Furthermore, the historical data stored in the storage unit of the present invention changes in real time, that is, after eliminating abnormal data, the earliest data in the storage unit is replaced by the data processed by the signal acquisition unit and the data analysis unit, thereby compensating for parameter change errors caused by aging of power grid equipment and transformer equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of an online monitoring system for transformer core grounding current according to the present invention;

[0034] Figure 2 A flow chart of correlation analysis for the present invention;

[0035] Figure 3 A flow chart for determining the fault status of the transformer core;

[0036] In the figure: 100, transformer; 200, signal acquisition unit; 300, conditioning unit; 400, data analysis unit; 500, control unit; 11, iron core; 12, clamp; 13, housing; 14, iron core ground lead; 15, clamp ground lead; 16, housing ground lead; 21, first Hall effect sensor; 22, second Hall effect sensor; 23, bracket; 24, movable plate; 25, resistor; 26, control switch; 31, sampling resistor; 32, filter circuit; 34, A / D converter; 321, low-pass filter circuit; 322, high-pass filter circuit; 331, primary amplifier circuit; 332, secondary amplifier circuit. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the embodiments of the present invention and the accompanying drawings.

[0038] Embodiment 1 of a transformer core grounding current online monitoring system of the present invention:

[0039] The transformer core grounding current online monitoring system of the present invention is used to monitor the core grounding current of a transformer 100 in real time. The transformer 100 includes an iron core 11, a clamp 12, and a housing 13. Both the primary winding and the secondary winding are wound around the iron core 11. The clamp 12 is used to fix the iron core 11 and includes an upper clamp and a lower clamp, which are respectively arranged at the upper and lower ends of the transformer 100. The upper clamp and the lower clamp are connected by a connecting rod. The connecting rod is made of a conductive material to enable the upper and lower clamps to conduct electricity. The iron core 11 of the transformer 100 is grounded via a core grounding lead 14, the clamp 12 is grounded via a clamp grounding lead 15, and the housing 13 is grounded via a housing grounding lead 16.

[0040] The transformer core grounding current online monitoring system includes a signal acquisition unit 200, a conditioning unit 300, a data analysis unit 400, a control unit 500 and a storage unit.

[0041] The signal acquisition unit 200 includes a first Hall sensor 21 and a second Hall sensor 22. The first Hall sensor 21 is used to detect the current flowing through the core grounding lead 14, which is the core grounding current. The second Hall sensor 22 is used to detect the current flowing through the clamp grounding lead 15, which is the clamp grounding current. The core grounding lead 14 and the clamp grounding lead 15 are spaced appropriately apart. The first and second Hall sensors 21 and 22 are supported at the same height by a bracket 23 to balance the effects of leakage magnetic flux from the transformer 100 on their detection results. The first and second Hall sensors 21 and 22 use a synchronized clock source to drive multi-channel ADC sampling, ensuring complete synchronization of their sampling results.

[0042] Bracket 23 is made of wood or other non-conductive and non-magnetic materials. A movable plate 24 is mounted on bracket 23 and can slide up and down along bracket 23. The movable plate 24 has two recesses that match the shape of the bottom of the Hall effect sensors for insertion. The first Hall effect sensor 21 and the second Hall effect sensor 22 are inserted into their corresponding recesses. The two recesses are identical in size, so once inserted, the first Hall effect sensor 21 and the second Hall effect sensor 22 are at the same height. This ensures that the leakage magnetic flux from transformer 100 affects both sensors in the same manner. In this embodiment, the two Hall effect sensors inserted into the recesses are raised and lowered synchronously. During measurement, the movable plate 24 is moved up and down, and the point with the lowest noise level is selected as the detection point.

[0043] The signal acquisition unit 200 further includes a resistor 25 and a control switch 26 . The two resistors 25 are respectively connected in series to the core grounding lead 14 and the clamp grounding lead 15 and their switching states are controlled by the corresponding control switch 26 .

[0044] The conditioning unit 300 includes a sampling resistor 31, a filter circuit 32, an amplifier circuit, and an A / D converter 34. The current collected by the first and second Hall sensors 21 and 22 passes through the sampling resistor 31 and is converted into an analog voltage signal. The analog voltage signal is filtered by the filter circuit 32 and then fed into the A / D converter 34, which converts the analog voltage signal into a digital voltage signal. The amplifier circuit, used to amplify the analog voltage signal, includes a primary amplifier circuit 331 and a secondary amplifier circuit 332. The primary amplifier circuit 331 is positioned between the sampling resistor 31 and the filter circuit 32, while the secondary amplifier circuit 332 is positioned between the filter circuit 32 and the A / D converter 34.

[0045] Both the primary amplifier circuit 331 and the secondary amplifier circuit 332 are inverting amplifier circuits with an amplification factor of -R2 / R1. The inverting amplifier circuit introduces voltage negative feedback, belongs to the differential mode signal, has strong anti-interference ability, and is less affected by the external ambient temperature.

[0046] The filter circuit 32 includes a low-pass filter circuit 321 and a high-pass filter circuit 322. When the core is grounded at a single point, the detection current value of the first Hall sensor 21 is extremely small. At this time, harmonics can have a significant impact on the detection results. Therefore, the voltage signal in the present invention is first filtered out by the low-pass filter circuit 321 to remove high-frequency harmonics, and then filtered out by the high-pass filter circuit 322 to eliminate measurement accuracy drift caused by low temperatures. The conditioning unit 300 converts the core grounding current collected by the first Hall sensor 21 into the core grounding voltage, and converts the clamp grounding current collected by the second Hall sensor 22 into the clamp grounding voltage.

[0047] The data analysis unit 400 is used to analyze the correlation between two groups of voltage signals. The specific steps of the data analysis unit 400 for performing the correlation analysis are as follows:

[0048] Step 1: Acquire the core grounding voltage and the clamp grounding voltage by synchronous sampling.

[0049] Step 2: Perform discrete Fourier transform on the core grounding voltage and the clamp grounding voltage respectively to obtain frequency domain representations of the core grounding voltage and the clamp grounding voltage, and identify the fundamental wave and main harmonic frequencies.

[0050] In this step, the main harmonic frequency refers to the harmonic corresponding to the first 90% of the energy.

[0051] Step 3: Perform frequency division filtering and Hilbert transformation on the core grounding voltage and the clamp grounding voltage respectively to obtain the instantaneous amplitude and instantaneous phase sequence of the corresponding frequency signal.

[0052] Frequency division filtering refers to designing bandpass filters for the fundamental frequency and main harmonic frequency components respectively. For the 50HZ fundamental wave, a 50±2HZ bandpass filter is designed, and for the nth harmonic, a 50n±2nHZ bandpass filter is designed. Hilbert transform is performed on the narrowband signal obtained after filtering.

[0053] Specifically, in this step, the instantaneous amplitude and instantaneous phase of the core grounding voltage at the fundamental and main harmonic frequencies, and the instantaneous amplitude and instantaneous phase of the clamp grounding voltage at the fundamental and main harmonic frequencies are calculated respectively.

[0054] Step 4: Calculate the amplitude correlation between the core grounding voltage and the clamp grounding voltage at the same frequency component and measure it with the amplitude correlation coefficient. The amplitude correlation coefficients at different frequency components constitute an amplitude correlation coefficient sequence.

[0055] In this step, the instantaneous amplitude sequences at different frequency components of the core grounding voltage and the clamp grounding voltage are first extracted respectively. After aligning the instantaneous amplitude sequences of the two signals, the correlation coefficient of the two instantaneous amplitudes is calculated for each frequency component using the Pearson correlation coefficient formula.

[0056] Step 5: Calculate the phase correlation of the same frequency components of the core grounding voltage and the clamp grounding voltage and measure it with a phase correlation coefficient. The phase correlation coefficients at different frequency components constitute a phase correlation coefficient sequence.

[0057] In this step, first extract the instantaneous phase sequence of the core grounding voltage and the clamp grounding voltage at different frequency components, directly calculate the phase difference between the instantaneous phase of the core grounding voltage and the instantaneous phase of the clamp grounding voltage for each frequency component, then calculate the standard deviation of the phase difference sequence, and then divide the standard deviation by the maximum value of the standard deviation when the phase difference is completely random, and subtract this value from 1 to construct the phase correlation coefficient at each frequency component. That is, the phase correlation coefficient = , where is the standard deviation of the phase difference sequence, is the theoretical maximum value of the standard deviation of the phase difference sequence.

[0058] It should be emphasized that in both step 4 and step 5, the amplitude correlation coefficient and the phase correlation coefficient are calculated for at least one complete power frequency cycle, and the sampling frequency of the A / D converter 34 is 1024 Hz.

[0059] The storage unit stores historical data on the amplitude correlation coefficient between the core-ground voltage and the clamp-ground voltage during normal operation, historical data on the phase correlation coefficient between the core-ground voltage and the clamp-ground voltage, and a set of transient waveform templates corresponding to each switching operation mode. The control unit 500 determines the operating status of the transformer based on the signals transmitted by the signal acquisition unit 200, the data analysis unit 400, and the storage unit.

[0060] It's important to emphasize that the historical data stored in the storage unit is not static but updated in real time. If the core grounding current and clamp grounding current waveforms within a specific time period are determined to be normal operating conditions, the data for that time period is added to the storage unit, and the oldest data segment in the historical data is deleted accordingly.

[0061] The process of judging the operating status of the transformer is as follows:

[0062] When the amplitude of the core grounding current is greater than 100mA, the waveform change of the core grounding current is analyzed to see whether it is synchronized with the template of the corresponding transient waveform in the transient waveform template set under the corresponding switch operation. If the two are synchronized, it is determined that the amplitude fluctuation of the core grounding current is caused by the switch action, and the control unit 500 does not issue a corresponding alarm instruction.

[0063] If the waveform change of the core grounding current is not synchronized with the switch operation signal, it is determined that an insulation fault occurs in the transformer, and the control unit 500 issues a corresponding alarm triggering instruction.

[0064] When the amplitude of the core grounding current is less than 100mA, analyze the changes in the measured values ​​of the amplitude correlation coefficients under the fundamental component and the main harmonic components relative to the historical data. At the same time, analyze the changes in the measured values ​​of the phase correlation coefficients under the fundamental component and the main harmonic components relative to the historical data. When the measured value increases of the amplitude correlation coefficient and the phase correlation coefficient under the fundamental component and the harmonic component exceed the set values, it is determined that the core has the risk of early insulation failure.

[0065] If the measured values ​​of the amplitude correlation coefficient and phase correlation coefficient for only the fundamental component increase by more than the set value, or if the measured values ​​of the amplitude correlation coefficient and phase correlation coefficient for only the harmonic component increase by more than the set value, resistor 25 is switched on and off via control switch 26. If the measured values ​​of the amplitude correlation coefficient and phase correlation coefficient for the corresponding frequency component decrease by more than the set value (10% in this embodiment) after resistor 25 is switched on, it is determined that an early insulation fault has occurred between the core and the clamp. If the measured values ​​of the amplitude correlation coefficient and phase correlation coefficient for the corresponding component do not change significantly after resistor 25 is switched on, or if the decrease does not exceed the set value, it is determined that the increase in the amplitude correlation coefficient and phase correlation coefficient for the corresponding component is caused by interference, and the transformer is determined to be normal.

[0066] This is because if an insulation failure occurs, switching resistor 25 will force the current of the corresponding frequency component to change its conduction path; however, the switching of resistor 25 is insensitive to external interference. Of course, resistor 25 can be connected in series with the core ground lead 14 or the clamp ground lead 15. In the event of an early insulation failure between the core and the clamp, the on-resistance between them is typically between 1 kilo-ohm and 10 kilo-ohm. Therefore, in this embodiment, the resistance of resistor 25 is 50 kilo-ohm, which is much greater than the on-resistance, thereby forcing the current to change its conduction path.

[0067] Based on multiple practical data, we know that 95% of early insulation faults result in increases in the measured values ​​of the amplitude and phase correlation coefficients exceeding 20%. Therefore, the set value for the increase in the measured values ​​of the amplitude and phase correlation coefficients is 20%. However, if external interference causes deviations in the tracking performance of the fundamental and harmonic components, the amplitude and phase correlation coefficients decrease by less than 10% in 97% of cases after switching a 50 kilo-ohm resistor. Therefore, the set value for the decrease in the measured values ​​of the amplitude and phase correlation coefficients for the corresponding frequency components is 10%.

[0068] The core grounding current is mainly caused by eddy currents and leakage flux caused by changes in magnetic flux, while the main sources of the clamp grounding current are induced currents and leakage currents generated by structural vibration. The fundamental trend of the core grounding current follows the trend of the current flowing through the winding. The fundamental trend of the clamp grounding current should be a low-amplitude industrial frequency sine wave, superimposed with other frequency components caused by mechanical vibration, as well as high-frequency noise and occasional interference pulses. The overall waveform is smooth, without obvious distortion or continuous high-amplitude fluctuations. Therefore, the waveform of the clamp grounding current is similar to a flat noise band with an extremely small amplitude, far smaller than the amplitude of the core grounding current; in the time domain, it has the characteristics of irregular random fluctuations and no periodic pulses; in the frequency domain, it has the characteristics of uniform spectrum distribution and no significant harmonic peaks.

[0069] Therefore, when the insulation between the core and the clamp is intact, the phase difference between the two follows a random distribution and has no fixed relationship. However, when the insulation between the core and the clamp is damaged, the two are connected, forming a loop. At this time, electromagnetic induction dominates the clamp current, and the phase, frequency domain characteristics, and change trends of the clamp current and the core grounding current will be synchronized, and both will be mainly characterized by the power frequency. Therefore, the above criteria can clearly identify early insulation faults between the core and the clamp, and can accurately identify this early multi-point grounding fault even when the core grounding current does not reach 100 mA.

[0070] Embodiment 2 of a transformer core grounding current online monitoring system and device of the present invention:

[0071] The difference between the second embodiment and the first embodiment is that:

[0072] In this embodiment, the influence of external lightning strikes is taken into consideration. Since the duration of the impact caused by lightning strikes is usually 1.2 / 50 microseconds, when lightning strikes, the lightning impulse current makes a major contribution to the core grounding current and the clamp grounding current. Therefore, the correlation between the two will be significantly improved. To avoid misjudgment, when lightning occurs, the control unit 500 judges the operating status of the transformer. The reference basis that the increase in amplitude correlation and phase correlation exceeds the set value for a duration greater than 10ms is introduced into the judgment criteria.

[0073] An embodiment of an online monitoring device for transformer core grounding current of the present invention:

[0074] A transformer core grounding current online monitoring device includes a housing in which is integrated a transformer core grounding current online monitoring system disclosed in an embodiment of the transformer core grounding current online monitoring system. Detailed description is omitted.

[0075] In actual operation, a 220kV transformer experienced nonlinear contact between the core and the clamp due to aging of the clamp insulation pads. After replacing the pads, the transformer returned to normal operation. However, when the fault occurred, the maximum amplitude of the core grounding current was only 43mA, making it impossible to detect the fault using the traditional threshold of 100mA. However, after processing, it was found that the amplitude correlation coefficient between the core grounding voltage and the clamp grounding voltage at the fundamental frequency changed from the historical data of 0.34 to 0.85, and the phase correlation coefficient changed from the historical data of 0.2 to 0.6, which were successfully detected by the monitoring system of the present invention.

Claims

1. A transformer core grounding current online monitoring system, characterized in that: include, A signal acquisition unit, which is used to detect the iron core grounding current flowing through the iron core grounding lead wire and the clamp grounding current flowing through the clamp grounding lead wire; A conditioning unit is used to process the collected signals, and simultaneously process the core grounding current into the core grounding voltage and the clamp grounding current into the clamp grounding voltage; A data analysis unit, used for analyzing the measured value of the amplitude correlation coefficient between the core grounding voltage and the clamp grounding voltage and the measured value of the phase correlation coefficient between the core grounding voltage and the clamp grounding voltage at a specific frequency component; A storage unit for storing historical data of the amplitude correlation coefficient between the core grounding voltage and the clamp grounding voltage under normal operating conditions, historical data of the phase correlation coefficient between the core grounding voltage and the clamp grounding voltage, and a set of transient waveform templates corresponding to the switch operation modes; A control unit, wherein the signal acquisition unit, the data analysis unit, and the storage unit are electrically connected to different input ports of the control unit to transmit signals thereto, and the control unit comprehensively determines the transformer core fault state based on the core grounding current, the clamp grounding current, the amplitude correlation coefficient measured value, the phase correlation coefficient measured value, the amplitude correlation coefficient historical data, the phase correlation coefficient historical data, the switch operation status, and the operation mode; When the core grounding current exceeds the set threshold, the waveform is judged to be consistent with the transient waveform template under the corresponding switch operation mode. If the two are consistent, it is determined that the core grounding current amplitude fluctuation is caused by the switching action; If the two are inconsistent, it is determined that the transformer has an insulation fault; When the core grounding current is less than the set threshold, the change of the measured value of the amplitude correlation coefficient relative to the historical data and the change of the measured value of the phase correlation coefficient relative to the historical data are analyzed. When the increase of the measured value of the amplitude correlation coefficient relative to the historical data and the increase of the measured value of the phase correlation coefficient relative to the historical data exceed the set value, it is determined that the transformer has an early insulation fault; The steps for the data analysis unit to perform correlation analysis are as follows: Step 1: Acquire the core grounding voltage and the clamp grounding voltage by synchronous sampling; Step 2: Perform discrete Fourier transform on the core grounding voltage and the clamp grounding voltage to obtain frequency domain representations of the core grounding voltage and the clamp grounding voltage, and identify the fundamental wave and main harmonic frequencies; Step 3: Perform frequency division filtering and Hilbert transformation on the core grounding voltage and the clamp grounding voltage respectively to obtain the instantaneous amplitude and instantaneous phase sequence of the corresponding frequency signal; Step 4: Calculate the amplitude correlation between the core grounding voltage and the clamp grounding voltage at the same frequency component and measure it with the amplitude correlation coefficient; Step 5: Calculate the phase correlation of the same frequency components of the core grounding voltage and the clamp grounding voltage and measure it with a phase correlation coefficient.

2. The transformer core grounding current online monitoring system according to claim 1, characterized in that: When the core grounding current is less than the set threshold, the changes in the measured value of the amplitude correlation coefficient under the fundamental component relative to the historical data and the changes in the measured value of the phase correlation coefficient under the harmonic component relative to the historical data are analyzed respectively. When the increase in the amplitude correlation coefficient under the fundamental component and the increase in the phase correlation coefficient under the harmonic component exceed the set value, it is determined that the transformer has an early insulation fault.

3. The transformer core grounding current online monitoring system according to claim 2, characterized in that: A resistor is connected in series to the core grounding lead and / or the clamp grounding lead, and control switches for controlling the switching state of the resistor are provided on both sides of the resistor; when the increase amplitude of the amplitude correlation coefficient and the increase amplitude of the phase correlation coefficient under only the fundamental component exceed the set value, or the increase amplitude of the amplitude correlation coefficient and the increase amplitude of the phase correlation coefficient under only the harmonic component exceed the set value, the resistor on the core grounding lead or the clamp grounding lead is switched into the loop; If the measured values ​​of the amplitude correlation coefficient and the phase correlation coefficient under the corresponding frequency component decrease by more than the set value after the resistor is switched on and off, it is determined that an early insulation fault has occurred between the iron core and the clamp; if the measured values ​​of the amplitude correlation coefficient and the phase correlation coefficient under the corresponding component do not exceed the set value after the resistor is switched on and off, it is determined that the transformer is in normal condition.

4. The transformer core grounding current online monitoring system according to claim 3, characterized in that: The storage unit updates the historical data stored therein in real time.

5. The transformer core grounding current online monitoring system according to claim 4, characterized in that: In step 4, the amplitude correlation coefficient of each frequency component is calculated using the Pearson correlation coefficient formula; In step five, the phase difference between the instantaneous phase of the core grounding voltage and the instantaneous phase of the clamp grounding voltage is directly calculated for each frequency component, and then the standard deviation of the phase difference sequence under the frequency component is calculated. The standard deviation is then divided by the maximum value of the standard deviation when the phase difference is completely random, and the phase correlation coefficient at each frequency component is constructed by subtracting this value from 1.

6. A transformer core grounding current online monitoring system according to any one of claims 1 to 5, characterized in that: The conditioning unit includes a sampling resistor, a filter circuit, an amplifier circuit and an A / D converter. The amplifier circuit includes a primary amplifier circuit and a secondary amplifier circuit. The primary amplifier circuit is placed between the sampling resistor and the filter circuit, and the secondary amplifier circuit is placed between the filter circuit and the A / D converter. The filter circuit includes a low-pass filter circuit and a high-pass filter circuit. Both the primary amplifier circuit and the secondary amplifier circuit use an inverting amplifier circuit. The signal acquisition unit includes a first Hall sensor and a second Hall sensor, and also includes a bracket. A movable plate that moves in an up-down direction is provided on the bracket. Two grooves are provided on the movable plate for inserting corresponding Hall sensors so that the two Hall sensors are at the same height.

7. A transformer core grounding current online monitoring system according to any one of claims 1 to 5, characterized in that: When a lightning strike occurs, the control unit determines that the transformer has an early insulation fault or an insulation fault, and the duration of the corresponding judgment criterion is required to be greater than 10ms.

8. A transformer core grounding current online monitoring device, characterized by: The invention comprises a shell, in which a transformer core grounding current online monitoring system according to any one of claims 1 to 7 is integrated.

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