A cable seal defect depth detection device and method based on multi-frequency eddy current

Abstract

The present invention relates to a cable seal defect depth detection device based on multi-frequency eddy current, comprising a multi-channel signal acquisition and transmission unit, a signal processing unit and a display unit, wherein the multi-channel signal acquisition and transmission unit comprises an external connector, a sensor internal wiring, a signal transmitting sensor, a signal receiving sensor and a probe body, wherein the signal transmitting sensor and the signal receiving sensor are both installed in the probe body; the external connector is installed in the probe body, the transmitting sensor and the signal receiving sensor are both connected to the sensor internal wiring, and the outer ends of all the sensor internal wirings pass through the external connector and extend outward; the signal transmitting sensor and the signal receiving sensor are both connected to the signal processing unit signal, and the signal processing unit is electrically connected to the display unit. The present invention also includes a cable seal defect depth detection method based on multi-frequency eddy current. The present invention can detect deeper cable seals, has high detection efficiency and is convenient, and belongs to the field of cable non-destructive detection technology.

Description

Technical Field

[0001] The invention relates to the technical field of cable non-destructive detection, and in particular to a cable lead seal defect depth detection device and method based on multi-frequency eddy current. Background Art

[0002] The quality defects of the cable body and accessories are the main causes of high-voltage cable failures. Lead sealing is a key process for the on-site installation of high-voltage cable accessories. The quality of the lead seal directly affects the safe and stable operation of high-voltage cables. Since the traditional lead sealing process can only be handled manually, once the lead seal has cracks, holes and other defects due to inadequate construction technology or force, vibration and other factors during operation, it is easy to cause water ingress and moisture in the accessories or poor electrical connections, and the insulation level is reduced, which can cause high-voltage cable line fault tripping or even cable breakdown accidents.

[0003] Traditional lead seal inspection requires the removal of the cable housing heat shrink sleeve for manual inspection, which is a destructive test with low efficiency. Existing inspection methods can only detect surface defects of lead seals, and traditional eddy current inspection methods can only detect surface or near-surface defects of the test piece.

[0004] At present, it is difficult to detect defects in cable accessories, and lead seals are prone to mechanical damage, corrosion, cracking, sand holes, deformation and other defects. Traditional eddy current testing is limited by factors such as small probe size, low detection efficiency, weak signal penetration, and low sensitivity. Therefore, it is difficult to accurately detect damage inside cable accessories; eddy current testing is used in power cable lead seal depth defect detection. Due to the complex cable operating conditions, the workload of lead seal detection is large.

[0005] Main difficulties: 1. Eddy current array detection technology is applied to cable seal detection in operation, providing a new, faster and more convenient method for detecting cable seal defects. However, there is currently no multi-channel detection probe detection device specifically designed for cable seals, and the detection efficiency is low and the reliability is not high.

[0006] 2. Low-frequency signals have strong penetration and can easily penetrate deeper into cable seals, but the detection sensitivity of low-frequency signals is relatively low. The detection sensitivity of high-frequency signals is relatively high, but its penetration depth is limited. Currently, the two have not been combined and applied in eddy current detection, which makes detection more difficult. Summary of the invention

[0007] In view of the technical problems existing in the prior art, the purpose of the present invention is to provide a cable seal defect depth detection device based on multi-frequency eddy current that can detect deeper cable seals with high detection efficiency and convenience.

[0008] Another object of the present invention is to provide a cable seal defect depth detection method based on multi-frequency eddy current, which is simple to operate and can achieve deeper cable seal detection.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] A cable seal defect depth detection device based on multi-frequency eddy current comprises a multi-channel signal acquisition and transmission unit, a signal processing unit and a display unit, wherein the multi-channel signal acquisition and transmission unit comprises an external connector, a sensor internal wiring, a signal transmitting sensor, a signal receiving sensor and a probe body, wherein the number of the signal receiving sensors is twice the number of the signal transmitting sensors; the signal transmitting sensor and the signal receiving sensor are both mounted at one end of the probe body; the external connector is mounted at the other end of the probe body, a signal transmitting sensor is connected to an internal sensor wiring and the external connector, a signal receiving sensor is connected to an internal sensor wiring, and the outer ends of all the internal sensor wirings pass through the external connector and extend outward; the signal transmitting sensor and the signal receiving sensor are both signal-connected to the signal processing unit, and the signal processing unit is electrically connected to the display unit.

[0011] As a preferred embodiment, the probe body includes a detection probe body and a fixed probe body, the detection probe body is mounted on the fixed probe body, the signal transmitting sensor and the signal receiving sensor are both mounted on the detection probe body, and the external connector is mounted on the fixed probe body.

[0012] As a preferred embodiment, the detection probe body and the fixed probe body are both arc-shaped block structures, the convex end of the detection probe body is attached and fixed to the concave end of the fixed probe body, the external connector is installed at the convex end of the fixed probe body, and the signal transmitting sensor and the signal receiving sensor are both installed at the concave end of the detection probe body.

[0013] As a preferred embodiment, the fixed probe body is a semicircular arc block with a thickness of 180-240 mm and a diameter of 80-120 mm, and the fixed probe body is made of glass fiber reinforced flame retardant PBT.

[0014] As a preferred embodiment, the fixed probe body is provided with a connecting channel, and the external connector is installed in the connecting channel; the detection probe body is provided with connecting holes, the number of the connecting holes corresponds to the number of signal transmitting sensors and signal receiving sensors, and all the connecting holes are the same as the connecting channel; one signal transmitting sensor is installed in one connecting hole, and one signal receiving sensor is installed in one connecting hole, and all the wiring inside the sensors extends from the connecting holes, gathers into the connecting channel and extends outside the connecting channel.

[0015] As a preferred embodiment, the number of signal receiving sensors is four, the number of signal transmitting sensors is two, the number of connecting holes is six, and the six connecting holes are evenly arranged along the circumferential direction at the inwardly concave end of the detection probe body; the two signal transmitting sensors are respectively embedded in the two connecting holes located in the middle, and the four signal receiving sensors are respectively installed in the four connecting holes, and the four signal receiving sensors are respectively distributed on both sides of the two signal transmitting sensors; the two signal transmitting sensors are both connected to the signal processing unit, and the four signal receiving sensors are all connected to the signal processing unit.

[0016] As a preference, among the two signal transmitting sensors, one transmits a signal of 10 KHz, and the other transmits a signal of 10 Hz.

[0017] As a preferred embodiment, the diameter of the transmitting signal sensor and the signal receiving sensor are both 0.4 mm; the number of turns of the coils of the transmitting signal sensor and the signal receiving sensor are both 60-100 turns, and the transmitting signal sensor and the signal receiving sensor are both made of nanocrystalline soft magnetic alloy.

[0018] As a preferred embodiment, among the six connection holes, the included angle of the two connection holes located at the two ends on the detection probe body is 120 degrees.

[0019] A cable seal defect depth detection method based on multi-frequency eddy currents uses a cable seal defect depth detection device based on multi-frequency eddy currents. The method comprises the following steps: two transmitting signal sensors transmit waves of different frequency bands to form a modulated wave, the modulated wave detects the cable seal, a signal receiving sensor receives the cable seal information, the signal receiving sensor transmits the cable seal information to a signal processing unit, and a display unit displays the seal detection information, thereby obtaining the cable seal status.

[0020] Theoretical basis of the present invention:

[0021] 1. Eddy current flaw detection is based on the principle of electromagnetic induction. According to the characteristics of electromagnetic waves, low-frequency electromagnetic waves show low signal attenuation, making them suitable for long-distance transmission and strong penetration, but low accuracy. High-frequency electromagnetic waves have weaker penetration than low-frequency electromagnetic waves, but high accuracy. The electromagnetic waves used for eddy current flaw detection are generally high-frequency electromagnetic waves. In order to better achieve the accuracy of eddy current detection, the principle of superposition of electromagnetic waves of different frequencies is now used. The uplink in the system is first a low-frequency pulse; then the downlink is a high-frequency pulse of equal amplitude. When the low-frequency pulse detects the information of the lead seal and transmits it to the system, it is superimposed with the high-frequency pulse of equal amplitude and transmitted to the system for lead seal analysis, which can detect deeper defect types.

[0022] 2. Signal picking and processing:

[0023] Detection refers to the process of detecting the modulated signal from the modulated signal. Therefore, the purpose of demodulation is to recover the modulated signal. For demodulation, the amplitude modulated wave and the carrier can be multiplied and then filtered through a high-pass filter. The most common demodulation methods are rectification detection and phase-sensitive detection. If the modulated signal is biased and a DC component is superimposed so that the biased signal has a positive voltage, the envelope of the amplitude modulated wave will have the shape of the original modulated signal. The amplitude modulated wave can be simply rectified and filtered by half-wave or full-wave, and the original modulated signal can be recovered by subtracting the bias voltage.

[0024] The eddy current detection signal is generated by the intersection of a changing magnetic field and the cable seal. In short, it is caused by the electromagnetic induction effect. This action generates a current circulating in the conductor. The faster the magnetic field changes, the greater the induced electromotive force and the stronger the eddy current.

[0025] The eddy current signals generated by the high-frequency and low-frequency electromagnetic wave signals act on the sensors in turn. The sensors transmit the collected signal changes to the analysis host, which extracts the characteristic values ​​from the superimposed pulse eddy current signals and maps them to the corresponding thickness information. The Fourier transform is used to perform harmonic analysis on the pulse signal to extract information such as amplitude. The effective measurement signal is obtained through filtering and processed and analyzed. The state of the seal is analyzed by observing the impedance value changes corresponding to the measurement signal.

[0026] In general, the present invention has the following advantages:

[0027] 1. The present invention utilizes high-frequency electromagnetic waves with high accuracy, low-frequency electromagnetic waves suitable for long-distance transmission and strong penetration, and high-frequency and low-frequency electromagnetic wave signals are superimposed to obtain modulated waves, which can detect deeper cable seal information.

[0028] 2. The present invention belongs to non-destructive testing, and can detect the cable seal without destroying the existing structure of the cable, and the operation is convenient and quick.

[0029] 3. The multi-channel probe of the present invention is composed of multiple sensors placed in a distributed manner and driven electronically. Each individual sensor in the probe generates a signal with a phase and amplitude relative to the structure below it. This data is associated with the encoded position and time and is represented in the form of an image. The multi-channel detection probe can improve the detection capability and save a lot of time; through signal coupling, a single probe scan can cover a larger area while maintaining high resolution; complex robotic technology is not required to move the probe, and a simple manual scan is sufficient to complete the detection; the defect detection depth and quantitative performance are improved.

[0030] 4. Both the detection probe body and the fixed probe body are arc-shaped block structures. This design matches the shape of the cable and can achieve the best coupling effect.

[0031] 5. The present invention adopts signal conversion and processing technology, which can effectively suppress interference signals and achieve accurate detection under the operating conditions of cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of a cable lead seal defect depth detection device based on multi-frequency eddy current.

[0033] Figure 2 It is a schematic diagram of a multi-channel signal acquisition and transmission unit.

[0034] Figure 3 It is a perspective view of a multi-channel signal acquisition and transmission unit.

[0035] Figure 4 It is a curve graph of the detection accuracy of lead seal information when electromagnetic wave signals of three different frequencies are at the same depth.

[0036] Figure 5 It is a curve graph of the superposition of two signals emitted by a signal transmitting sensor.

[0037] Among them, 1 is the fixed probe body, 2 is the detection probe body, 3 is the connection hole, 4 is the internal wiring of the sensor, 5 is the external connector, 6 is the signal transmitting sensor, and 7 is the signal receiving sensor. SPECIFIC EMBODIMENTS

[0038] The present invention will be further described in detail below in conjunction with specific embodiments.

[0039] A cable lead seal defect depth detection device based on multi-frequency eddy current includes a multi-channel signal acquisition and transmission unit, a signal processing unit, and a display unit. The multi-channel signal acquisition and transmission unit includes an external connector, internal wiring of the sensor, a signal transmitting sensor, a signal receiving sensor, and a probe body. The number of signal receiving sensors is twice the number of signal transmitting sensors; both the signal transmitting sensor and the signal receiving sensor are installed at one end of the probe body; the external connector is installed at the other end of the probe body. One signal transmitting sensor and one internal wiring of the sensor are connected to the external connector, and one signal receiving sensor is connected to one internal wiring of the sensor. The outer ends of all the internal wirings of the sensors pass through the external connector and extend outward; both the signal transmitting sensor and the signal receiving sensor are signal-connected to the signal processing unit, and the signal processing unit and the display unit are electrically connected.

[0040] The probe body includes a detection probe body and a fixed probe body. The detection probe body is installed on the fixed probe body. Both the signal transmitting sensor and the signal receiving sensor are installed on the detection probe body, and the external connector is installed on the fixed probe body.

[0041] The detection probe body and the fixed probe body are both arc-shaped block structures. The convex end of the detection probe body is attached and fixed to the concave end of the fixed probe body. The external joint is installed at the convex end of the fixed probe body, and the signal transmitting sensor and the signal receiving sensor are both installed at the concave end of the detection probe body.

[0042] The fixed probe body is a semicircular arc block with a thickness of 180-240 mm and a diameter of 80-120 mm, and is made of glass fiber reinforced flame retardant PBT. The fixed probe body of this embodiment has a thickness of 225 mm and a diameter of 100 mm.

[0043] The fixed probe body is provided with a connecting channel, and the external connector is installed in the connecting channel; the detection probe body is provided with connecting holes, and the number of the connecting holes corresponds to the number of the signal transmitting sensors and the signal receiving sensors, and all the connecting holes are the same as the connecting channel; one signal transmitting sensor is installed in one connecting hole, and one signal receiving sensor is installed in one connecting hole, and all the wiring inside the sensors extends from the connecting holes, gathers into the connecting channel and extends outside the connecting channel.

[0044] There are four signal receiving sensors, two signal transmitting sensors, and six connecting holes, which are evenly arranged circumferentially at the inwardly concave end of the detection probe body; two signal transmitting sensors are respectively embedded in the two connecting holes in the middle, and four signal receiving sensors are respectively installed in the four connecting holes, and the four signal receiving sensors are respectively distributed on both sides of the two signal transmitting sensors; the two signal transmitting sensors are both connected to the signal processing unit, and the four signal receiving sensors are both connected to the signal processing unit.

[0045] Of the two signal transmitting sensors, one transmits a signal of 10KHz, and the other transmits a signal of 10Hz.

[0046] The diameters of the transmitting signal sensor and the signal receiving sensor are both 0.4 mm; the coil turns of the transmitting signal sensor and the signal receiving sensor are both 60-100 turns, and the transmitting signal sensor and the signal receiving sensor are both made of nanocrystalline soft magnetic alloy.

[0047] The external connector of this embodiment adopts an external N-type connector.

[0048] Among the six connection holes, the included angle of the two connection holes located at the two ends on the detection probe body is 120 degrees.

[0049] A cable seal defect depth detection method based on multi-frequency eddy currents uses a cable seal defect depth detection device based on multi-frequency eddy currents. The method comprises the following steps: two transmitting signal sensors transmit waves of different frequency bands to form a modulated wave, the modulated wave detects the cable seal, a signal receiving sensor receives the cable seal information, the signal receiving sensor transmits the cable seal information to a signal processing unit, and a display unit displays the seal detection information, thereby obtaining the cable seal status.

[0050] The specific detection steps are:

[0051] Step 1: Select the test method and equipment according to the nature, voltage level, size of the device to be tested, and the type and size of defects to be detected.

[0052] Step 2: Pre-treat the inspected workpiece to remove surface dirt and adsorbed impurities;

[0053] Step 3: Prepare comparison test blocks according to corresponding technical conditions or standards;

[0054] Step 4: Determine the test frequency. The test frequency is generally selected between 10Hz and 10kHz. The selection is based on the thickness of the workpiece to be inspected, the desired penetration depth, the sensitivity to be achieved, etc. The lower the frequency, the greater the penetration concentration, and the appropriate signal is selected for modulation.

[0055] Step 5: Adjust the instrument. Select the instrument balance mode: automatic, manual, or not required; select the sensitivity; adjust the phase; select the filter type and frequency; adjust the alarm battery; adjust the recorder sensitivity; adjust the delay time of the marking device; determine the automatic sorting level.

[0056] Step 6: Start the test. When testing under the selected specification, try to keep the moving speed constant and the distance between the sensor and the test piece constant.

[0057] Step 7: Test records: test piece condition, detection conditions, and detection standards based on the acceptance structure assessment.

[0058] During the detection, the corresponding effects of each step are as follows:

[0059] 1. Signal modulation: According to the thickness of the seal to be inspected and the detection accuracy requirements, adjust the high-frequency and low-frequency signals to obtain the appropriate modulation wave, so that the corresponding depth defects on the test block can be detected and the accuracy requirements can be met at the same time.

[0060] 2. Signal acquisition: Save and call the modulated equipment parameters. Place the probe on the surface of the seal to be inspected, and move it at a uniform speed in the circumferential and longitudinal directions to obtain the seal surface information.

[0061] 3. Signal calibration: When changing the test location during the test or encountering abnormal signals, signal calibration should be performed on the test block to ensure that the test data is true and reliable.

[0062] 4. Signal processing: perform detection processing on the signals collected by the front end to obtain effective detection signals, and conduct comparative analysis to obtain detection results.

[0063] 5. Defect judgment: Compare the impedance changes and combine with the test block data to determine whether there are defects and the severity of the defects, and give corresponding treatment suggestions.

[0064] 6. Conducting on-site cable testing, we found that the modulated wave can penetrate the high-frequency component deep into the cable seal, stimulate the defects deep in the cable, and reflect the amplitude of the defects more intuitively on the display screen. Through experiments, we found that the modulated wave is more sensitive to deeper signal excitation.

[0065] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A cable seal defect depth detection device based on multi-frequency eddy current, Features: It includes a multi-channel signal acquisition and transmission unit, a signal processing unit and a display unit. The multi-channel signal acquisition and transmission unit includes an external connector, a sensor internal wiring, a signal transmitting sensor, a signal receiving sensor and a probe body. The number of signal receiving sensors is twice the number of signal transmitting sensors. The signal transmitting sensor and the signal receiving sensor are both installed at one end of the probe body. The external connector is installed at the other end of the probe body. A signal transmitting sensor is connected to an internal sensor wiring and the external connector, and a signal receiving sensor is connected to an internal sensor wiring. The outer ends of all the internal sensor wirings pass through the external connector and extend outward. The signal transmitting sensor and the signal receiving sensor are both signal-connected to the signal processing unit, and the signal processing unit is electrically connected to the display unit. The probe body includes a detection probe body and a fixed probe body, the detection probe body is installed in the fixed probe body, the signal transmitting sensor and the signal receiving sensor are both installed in the detection probe body, and the external connector is installed in the fixed probe body; The detection probe body and the fixed probe body are both arc-shaped block structures, the outwardly convex end of the detection probe body is attached and fixed to the inwardly concave end of the fixed probe body, the external connector is installed at the outwardly convex end of the fixed probe body, and the signal transmitting sensor and the signal receiving sensor are both installed at the inwardly concave end of the detection probe body; The fixed probe body is provided with a communication channel, and the external connector is installed in the communication channel; the detection probe body is provided with connection holes, the number of which corresponds to the number of signal transmitting sensors and signal receiving sensors, and all the connection holes are connected to the communication channel; one signal transmitting sensor is installed in one connection hole, and one signal receiving sensor is installed in one connection hole, and all the wiring inside the sensors extends from the connection holes to the communication channel and extends outside the communication channel; The number of signal receiving sensors is four, the number of signal transmitting sensors is two, the number of connection holes is six, and the six connection holes are evenly arranged along the circumferential direction at the inwardly concave end of the detection probe body; the two signal transmitting sensors are respectively embedded in the two connection holes located in the middle, and the four signal receiving sensors are respectively installed in the four connection holes, and the four signal receiving sensors are respectively distributed on both sides of the two signal transmitting sensors in pairs; the two signal transmitting sensors are all connected to the signal processing unit, and the four signal receiving sensors are all connected to the signal processing unit; Among the two signal transmitting sensors, one signal transmitting sensor transmits a signal of 10KHz, and the other signal transmitting sensor transmits a signal of 10Hz.

2. A cable seal defect depth detection device based on multi-frequency eddy current according to claim 1, Features: The fixed probe body is a semicircular arc block with a thickness of 180-240mm and a diameter of 80-120mm. The fixed probe body is made of glass fiber reinforced flame retardant PBT.

3. A cable seal defect depth detection device based on multi-frequency eddy current according to claim 1, Features: The diameters of the signal transmitting sensor and the signal receiving sensor are both 0.4 mm; the coil turns of the signal transmitting sensor and the signal receiving sensor are both 60-100 turns, and the signal transmitting sensor and the signal receiving sensor are both made of nanocrystalline soft magnetic alloy.

4. A cable seal defect depth detection device based on multi-frequency eddy current according to claim 1, Features: Among the six connection holes, the included angle of the two connection holes located at the two ends on the detection probe body is 120 degrees.

5. A cable seal defect depth detection method based on multi-frequency eddy current, using a cable seal defect depth detection device based on multi-frequency eddy current according to any one of claims 1 to 4, Features: The method comprises the following steps: transmitting waves of different frequency bands through two signal transmitting sensors to superimpose a modulated wave, the modulated wave detects the cable seal, the signal receiving sensor receives the information of the cable seal, the signal receiving sensor transmits the information of the cable seal to a signal processing unit, and the display unit displays the seal detection information, thereby obtaining the cable seal status.

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