Current transformer leakage current detection method and device capable of overcoming circulating current

Abstract

The invention discloses a current transformer leakage current detection method and device capable of overcoming circulating current, and belongs to the field of current transformer detection. The method comprises the following steps of: respectively mounting the non-contact leakage current detection devices of the current transformer with large and small diameters on a current transformer framework rod and a secondary tube through a cross-core structure design, sending a synchronous signal, and simultaneously collecting a secondary side leakage current signal; large and small current signals are obtained through signal sampling, amplification, filtering and analog-to-digital conversion, and bus secondary voltage is obtained by combining synchronous sampling; extracting power frequency fundamental wave components and fundamental wave phases of the current signal and the voltage signal by using a Fourier analysis method; performing absolute error calibration fitting by taking the primary side current phase as a reference phase, and correcting the phases of the large current and the small current; and calculating the capacitance of the current transformer for monitoring the insulating property of the current transformer. The method can overcome the influence of loop current, guarantees the stability and reliability of a measurement result, and provides a powerful guarantee for the stable operation of a power system.

Description

Technical Field

[0001] The invention belongs to the technical field of current transformer detection, and relates to a current transformer leakage current detection method and device for overcoming circulating current. Background Art

[0002] As a key device in the power system, the current transformer is the main way for secondary devices to collect current. The current transformer transmits electrical quantities through the principle of electromagnetic induction, and according to the transformation ratio of the primary side to the secondary side, it converts the large current on the primary side of the power system into a small current used by the secondary equipment.

[0003] The on-site environment of oil-immersed current transformers is complex, with high electromagnetic field strength, wide distribution, and many interference factors. The leakage current of oil-immersed current transformers has two loops, the frame rod and the secondary tube, which is a tiny signal at the milliampere level, usually in the range of 50mA to 150mA, and is not easy to collect. The Fluke clamp meter used for on-site detection can only detect the current of the small-caliber secondary tube loop. The diameter of the on-site oil-immersed current transformer frame rod is relatively large, usually reaching tens of centimeters, and the diameter size of the detection unit is relatively high. During on-site detection, the loop current between the frame rod and the secondary tube causes phase error in the current measurement. Therefore, how to develop a high-precision, large-caliber, and highly anti-interference non-contact leakage current detection device is the core difficulty of the research. Summary of the invention

[0004] The present invention aims at the deficiencies in the prior art and provides a current transformer leakage current detection method and device which overcome the circulating current.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A current transformer leakage current detection device, comprising:

[0007] A current sensor, used for sampling a leakage current analog signal;

[0008] An adaptive program-controlled amplifier for amplifying leakage current analog signals;

[0009] A multi-stage filter, used for filtering the amplified leakage current analog signal;

[0010] A multi-channel AD converter, used for converting the filtered leakage current analog signal into a digital signal;

[0011] an embedded processor for calculating the capacitance of the current transformer based on the leakage current digital signal;

[0012] The wireless transmission module is used to transmit the current transformer capacitance to the background to monitor the insulation performance of the current transformer.

[0013] To optimize the above technical solutions, the specific measures taken also include:

[0014] Furthermore, it also includes a power supply module, which is used to supply power to the detection device.

[0015] The present invention also proposes a current transformer leakage current detection method for overcoming circulating current, wherein the current transformer leakage current has two loops, a frame rod and a secondary tube, and the method comprises the following steps:

[0016] Step 1: Install the leakage current detection device on the frame rod loop and the secondary tube loop respectively, and use the synchronization signal to make the leakage current detection device collect the frame rod leakage current analog signal and the secondary tube leakage current analog signal at the same time; after the frame rod leakage current analog signal and the secondary tube leakage current analog signal are amplified, filtered and analog-to-digital converted, the frame rod leakage current digital signal and the secondary tube leakage current digital signal are obtained;

[0017] Step 2, combining synchronous sampling to obtain the bus secondary voltage;

[0018] Step 3, delivering a standard primary current through a standard current source;

[0019] Step 4, extracting the power frequency fundamental component and fundamental phase of the frame pole leakage current digital signal, the secondary tube leakage current digital signal and the standard primary current, and extracting the fundamental frequency of the busbar secondary voltage signal;

[0020] Step 5: perform absolute error calibration fitting with the fundamental phase of the standard primary current as the reference phase, and correct the phase of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current; perform waveform superposition of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current after phase correction to obtain a synthetic current as the leakage current of the current transformer under test;

[0021] Step 6: Calculate the capacitance of the current transformer using the leakage current of the current transformer under test, the fundamental frequency of the bus secondary voltage signal, and the bus secondary voltage value, so as to monitor the insulation performance of the current transformer.

[0022] To optimize the above technical solutions, the specific measures taken also include:

[0023] Furthermore, the method adopted in step 4 is Fourier analysis.

[0024] Furthermore, in step 5, the absolute error calibration fitting is performed using the fundamental phase of the standard primary current as the reference phase, and the phases of the digital signal of the rack leakage current and the digital signal of the secondary tube leakage current are corrected as follows:

[0025] The fundamental phases of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current after Fourier decomposition are θ1 and θ2 respectively, and the fundamental phase of the standard primary current is φ. The phase difference between the standard primary current and the digital signal of the pole leakage current, and the phase difference between the standard primary current and the digital signal of the secondary tube leakage current are compared respectively, and the shift point numbers m1 and m2 of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current are obtained. The waveforms of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current are shifted by the corresponding number of points respectively; the formula is:

[0026]

[0027] Wherein, i=1 or 2, m1 represents the number of shift points of the pole leakage current digital signal, m2 represents the number of shift points of the secondary tube leakage current digital signal, N represents the number of sampling points of the pole leakage current digital signal and the secondary tube leakage current digital signal, and 360° / N represents the phase degree represented by one sampling point.

[0028] Further, in step 6, the calculation formula for calculating the capacitance of the current transformer using the leakage current of the current transformer under test, the fundamental frequency of the bus secondary voltage signal and the bus secondary voltage value is:

[0029]

[0030] Among them, I x is the leakage current of the current transformer under test, U is the bus secondary voltage value, and f is the fundamental frequency of the bus secondary voltage signal.

[0031] The beneficial effects of the present invention are as follows: the present invention proposes a current transformer leakage current detection method and device for overcoming circulating current, which can accurately collect the current on the frame pole and the current passing through the secondary tube by developing a high-precision, large-caliber, and highly anti-interference non-contact leakage current detection device; in order to overcome the influence of the loop current, a method of shifting and correcting the phase is adopted to ensure the stability and reliability of the measurement results, providing a strong guarantee for the stable operation of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The present invention is a flow chart of a current transformer detection method for overcoming circulating current.

[0033] Figure 2 The present invention is a schematic diagram of a non-contact leakage current detection device for a current transformer that overcomes circulating current. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] Embodiment 1

[0036] The present invention provides a current transformer leakage current detection device, comprising:

[0037] A current sensor, used for sampling a leakage current analog signal;

[0038] An adaptive program-controlled amplifier for amplifying leakage current analog signals;

[0039] The multi-stage filter is used to filter the amplified leakage current analog signal and remove noise and burrs in the signal.

[0040] A multi-channel AD converter, used for converting the filtered leakage current analog signal into a digital signal;

[0041] an embedded processor for calculating the capacitance of the current transformer based on the leakage current digital signal;

[0042] A wireless transmission module is used to transmit the capacitance of the current transformer to the background to monitor the insulation performance of the current transformer;

[0043] The power module is used to supply power to the detection device.

[0044] Embodiment 2

[0045] The present invention proposes a current transformer leakage current detection method for overcoming circulating current using the detection device of embodiment 1, wherein the current transformer leakage current has two loops, a frame rod and a secondary tube, and the method comprises the following steps:

[0046] Step 1: Install the leakage current detection devices of large and small diameters on the frame rod loop and the secondary tube loop respectively through a through-type structural design, and use a synchronous signal to enable the leakage current detection device to simultaneously collect the frame rod leakage current analog signal and the secondary tube leakage current analog signal; after the frame rod leakage current analog signal and the secondary tube leakage current analog signal are amplified, filtered and analog-to-digital converted, the frame rod leakage current digital signal and the secondary tube leakage current digital signal are obtained;

[0047] For example, when continuous data is collected at the same time period on site, the directly synthesized current waveform has "burr oscillations", and the phase difference between large and small currents is about 180°. After direct addition and fitting, the waveform noise amplification effect is worse, with an error of 2%-5%. After smoothing and filtering through a multi-stage filter, the waveform is smooth with small fluctuations, and the error of the measured data is stable at around 0.7%.

[0048] Step 2, combining synchronous sampling to obtain the bus secondary voltage;

[0049] Step 3, delivering a standard primary current through a standard current source;

[0050] Step 4: Use Fourier analysis to extract the power frequency fundamental component and fundamental phase of the frame rod leakage current digital signal, the secondary tube leakage current digital signal and the standard primary current, and extract the fundamental frequency of the busbar secondary voltage signal;

[0051] The collected current and voltage are periodic signals. The Fourier expansion of the periodic signal s(t) is:

[0052]

[0053] Among them, a0 is the DC component, a n is the amplitude, f is the fundamental frequency 50Hz, is the phase of the corresponding frequency; when n=1, a1 represents the fundamental frequency amplitude, and the corresponding is the fundamental frequency phase; moving the fundamental frequency phase of the current and primary current signals to the same can overcome the influence of the loop current. n represents the order.

[0054] Step 5. To overcome the influence of loop current, absolute error calibration fitting is performed with the fundamental phase of the standard primary current as the reference phase to correct the phase of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current. The fundamental phases of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current after Fourier decomposition are θ1 and θ2 respectively, and the fundamental phase of the standard primary current is φ. The phase difference between the standard primary current and the digital signal of the pole leakage current and the phase difference between the standard primary current and the digital signal of the secondary tube leakage current are compared respectively to obtain the number of shift points m1 and m2 of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current, and the waveforms of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current are moved by the corresponding number of points respectively. The formula is:

[0055]

[0056] Wherein, i=1 or 2, m1 represents the number of shift points of the pole leakage current digital signal, m2 represents the number of shift points of the secondary tube leakage current digital signal, N represents the number of sampling points of the pole leakage current digital signal and the secondary tube leakage current digital signal, and 360° / N represents the phase degree represented by one sampling point.

[0057] The digital signal of the pole leakage current after phase correction and the digital signal of the secondary tube leakage current are waveform superimposed to obtain the synthetic current, which is used as the leakage current I of the current transformer under test. x .

[0058] For example, a standard primary current of 150, 140, 120, 10, and 70 mA is transmitted through a standard current source, and the large and small current signals on the secondary frame rod and the secondary tube are synchronously measured. The fundamental current value and fundamental phase are obtained after Fourier decomposition; compared with the primary current phase, the large current phase difference is about 33.5 degrees, the number of shift points m1=24, and the small current phase difference is about 2 degrees, the number of shift points m2=1; after the large and small currents are shifted, the waveforms are superimposed to calculate the synthetic current I x As shown in Table 1, the error between the synthetic current and the standard current is within 1%. The shift correction method adopted by the present invention is accurate and reliable, and can effectively overcome the influence of the loop current.

[0059] Different levels of primary current are transmitted through a standard current source, and large and small current signals and synthetic current signals are obtained through a non-contact leakage current detection device. Each current level is sampled 20 times continuously, each sampling is 1 cycle, and the sampling interval is 1s. 20 current values ​​are obtained. After sorting, the maximum and minimum values ​​are removed and the average is obtained to obtain the current value, as shown in Table 1. The error between the synthetic current and the standard current is within 1%.

[0060] Table 1 Current transformer displacement correction

[0061]

[0062] Step 6: Calculate the current transformer capacitance C using the leakage current of the current transformer under test, the fundamental frequency of the bus secondary voltage signal, and the bus secondary voltage value to monitor the insulation performance of the current transformer. The calculation formula is:

[0063]

[0064] Among them, I x is the leakage current of the current transformer under test, U is the bus secondary voltage value, and f is the fundamental frequency of the bus secondary voltage signal, 50 Hz.

[0065] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A current transformer leakage current detection device, characterized in that: include: A current sensor, used for sampling a leakage current analog signal; An adaptive program-controlled amplifier for amplifying leakage current analog signals; A multi-stage filter, used for filtering the amplified leakage current analog signal; A multi-channel AD converter, used for converting the filtered leakage current analog signal into a digital signal; an embedded processor for calculating the capacitance of the current transformer based on the leakage current digital signal; The wireless transmission module is used to transmit the current transformer capacitance to the background to monitor the insulation performance of the current transformer.

2. The current transformer leakage current detection device according to claim 1, characterized in that: It also includes a power supply module, which is used to supply power to the detection device.

3. A current transformer leakage current detection method for overcoming circulating current using the detection device of claim 1, wherein the current transformer leakage current has two loops, a frame rod and a secondary tube, and is characterized in that: The method comprises the following steps: Step 1: Install the leakage current detection device on the frame rod loop and the secondary tube loop respectively, and use the synchronization signal to make the leakage current detection device collect the frame rod leakage current analog signal and the secondary tube leakage current analog signal at the same time; after the frame rod leakage current analog signal and the secondary tube leakage current analog signal are amplified, filtered and analog-to-digital converted, the frame rod leakage current digital signal and the secondary tube leakage current digital signal are obtained; Step 2, combining synchronous sampling to obtain the bus secondary voltage; Step 3, delivering a standard primary current through a standard current source; Step 4, extracting the power frequency fundamental component and fundamental phase of the frame pole leakage current digital signal, the secondary tube leakage current digital signal and the standard primary current, and extracting the fundamental frequency of the busbar secondary voltage signal; Step 5: perform absolute error calibration fitting with the fundamental phase of the standard primary current as the reference phase, and correct the phase of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current; perform waveform superposition of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current after phase correction to obtain a synthetic current as the leakage current of the current transformer under test; Step 6: Calculate the capacitance of the current transformer using the leakage current of the current transformer under test, the fundamental frequency of the bus secondary voltage signal, and the bus secondary voltage value, so as to monitor the insulation performance of the current transformer.

4. The current transformer leakage current detection method for overcoming circulating current as claimed in claim 3, characterized in that: The method used in step 4 is Fourier analysis.

5. The current transformer leakage current detection method for overcoming circulating current as claimed in claim 4, characterized in that: In step 5, the absolute error calibration fitting is performed using the fundamental phase of the standard primary current as the reference phase, and the phases of the digital signal of the rack leakage current and the digital signal of the secondary tube leakage current are corrected as follows: The fundamental phases of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current after Fourier decomposition are θ1 and θ2 respectively, and the fundamental phase of the standard primary current is φ. The phase difference between the standard primary current and the digital signal of the pole leakage current, and the phase difference between the standard primary current and the digital signal of the secondary tube leakage current are compared respectively, and the shift point numbers m1 and m2 of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current are obtained. The waveforms of the digital signal of the pole leakage current and the digital signal of the secondary tube leakage current are shifted by the corresponding number of points respectively; the formula is: Wherein, i=1 or 2, m1 represents the number of shift points of the pole leakage current digital signal, m2 represents the number of shift points of the secondary tube leakage current digital signal, N represents the number of sampling points of the pole leakage current digital signal and the secondary tube leakage current digital signal, and 360° / N represents the phase degree represented by one sampling point.

6. The current transformer leakage current detection method for overcoming circulating current as claimed in claim 3, characterized in that: In step 6, the calculation formula for calculating the capacitance of the current transformer using the leakage current of the current transformer under test, the fundamental frequency of the bus secondary voltage signal and the bus secondary voltage value is: Where C is the current transformer capacitance, I x is the leakage current of the current transformer under test, U is the bus secondary voltage value, and f is the fundamental frequency of the bus secondary voltage signal.

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