CN112326591A - Internal defect detection system and detection method for EPR (ethylene propylene rubber) heat-shrinkable cable terminal - Google Patents
Internal defect detection system and detection method for EPR (ethylene propylene rubber) heat-shrinkable cable terminal Download PDFInfo
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Abstract
The invention discloses an EPR (ethylene propylene rubber) heat-shrinkable cable terminal internal defect detection system and a detection method thereof, belongs to the technical field of high voltage and insulation, and aims to solve the problems of poor popularization, poor penetrability, large influence of environmental temperature, damage to a detected object and the like. The system comprises: the terahertz detector comprises a femtosecond laser and a spectroscope which are arranged along a terahertz pulse channel from left to right, a detection optical path system and an excitation optical path system which are arranged behind the spectroscope in parallel, and further comprises a phase-locked amplifier and an acquisition terminal which are connected with each other. The method comprises sample preparation and installation, defect detection, data collection and processing and result application. The combination of the system and the method is a widening of the application of the terahertz nondestructive visual detection technology to the EPR thermal shrinkage cable terminal, the unique combination of the structure and the method can definitely establish the terahertz time-domain spectral characteristics of the internal defects of the EPR thermal shrinkage cable terminal, and finally the terahertz time-domain spectral characteristics are reversely applied to realize the nondestructive visual detection of the internal defects of the composite cable.
Description
Technical Field
The invention belongs to the technical field of high voltage and insulation, and particularly relates to an EPR thermal shrinkage cable terminal internal defect detection system and a detection method thereof.
Background
The EPR thermal shrinkage cable terminal has the characteristics of small volume, light weight, easiness in installation, wide application range and the like, and is widely applied to medium and low voltage power systems and traction power supply systems. But is easily influenced by factors such as an installation process, an operation condition, external force damage and the like in the installation process; in later use and long-term operation, the application scenes are more various and can be in severe application conditions. Therefore, in long-term operation, under the combined action of rapid cold and hot alternation, transient overvoltage impact and long-term high-frequency vibration, the insulation layers in the insulation layers are separated to generate micro air gaps, and partial discharge is initiated; along with the continuous increase of the air gap and the gradual formation of a discharge channel, the material of the internal insulating layer is decomposed due to discharge ablation; as the air gap grows further and the discharge ablates the carbide to accumulate continuously, the discharge increases continuously, the air gap grows continuously and finally forms a discharge channel through the row, resulting in discharge breakdown.
At present, a detection method of an EPR (ethylene propylene rubber) heat-shrinkable cable terminal is only limited to medium loss tangent angle testing, partial discharge detection, infrared temperature measurement and the like adopted in maintenance at all levels, but the defects of internal insulation layering and the like caused by special working conditions of the cable terminal cannot be detected by the detection, and the actual requirements are difficult to meet.
In the prior art, the nondestructive testing method for the internal defects of the cable terminal mainly comprises the following steps: the CT scanning and X-ray scanning technologies based on high-energy rays have been applied to devices such as GIS switchgear, cable terminals, insulators, etc., but are difficult to popularize because of poor detection effects of X-rays, etc., on delamination and cracks, and high-energy free radiation generated by the X-rays, etc., which is harmful to the human body. Other detection methods cannot be applied to the detection of the composite cable terminal due to respective defects. For example, ultrasonic methods have great energy attenuation in composite materials with strong sound absorption property, and are difficult to penetrate through thicker material structures; the infrared wave method is greatly influenced by the environmental temperature; the laser speckle imaging method needs a high-energy laser light source and can damage a measured object.
Based on the problems in the background art, a detection system and a detection method thereof special for the internal defects of the EPR heat-shrinkable cable terminal are urgently needed to overcome the problems of poor popularization, poor penetrability, large influence of environmental temperature, damage to a measured object and the like.
Disclosure of Invention
The invention aims to provide a system and a method for detecting internal defects of an EPR (ethylene propylene rubber) heat-shrinkable cable terminal, which are used for solving various problems in the background technology.
In order to solve the problems, the technical scheme of the invention is as follows:
an EPR thermal shrinkage cable termination internal defect detection system, includes: the terahertz detector comprises a femtosecond laser and a spectroscope which are arranged along a terahertz pulse channel from left to right, a detection optical path system and an excitation optical path system which are arranged behind the spectroscope in parallel, and further comprises a phase-locked amplifier and an acquisition terminal which are connected with each other;
the detection light path system comprises a delay control unit, a photoconductive emitter, eight reflecting mirrors and a two-degree-of-freedom rapid moving platform which are sequentially arranged along the light path from left to right; a photoconductive detector is arranged above the eighth reflecting mirror; the two-degree-of-freedom platform is provided with a sample of the EPR heat shrinkable cable, and the sample can freely move up and down in the vertical direction and freely rotate in the horizontal direction of the two-degree-of-freedom platform;
the excitation light path system comprises a lens, and the lens is arranged above the photoconductive detector;
the photoconductive detector is connected with the phase-locked amplifier.
Furthermore, the reflecting mode is obliquely arranged at an angle of 45 degrees from left to right by using the spectroscope, one surface of the reflecting mode, which can penetrate through the terahertz pulse, faces to the photoconductive emitter, and the other surface, which can penetrate through the terahertz pulse and can reflect the terahertz pulse from the sample to be detected, faces to the photoconductive detector.
Furthermore, a first reflecting mirror is arranged on the light path of the femtosecond laser and the spectroscope; a sixth reflecting mirror is arranged on the light path of the spectroscope and the lens; the light path of the spectroscope and the photoconductive emitter is sequentially provided with a second reflecting mirror, a third reflecting mirror, a fourth reflecting mirror, a fifth reflecting mirror and a seventh reflecting mirror.
Furthermore, the delay control unit is arranged between the third reflector and the fourth reflector.
Further, the femtosecond laser is a titanium-sapphire femtosecond pulse laser, the central wavelength of the femtosecond laser is 810nm, the pulse width of the femtosecond laser is less than 100fs, the repetition frequency of the femtosecond laser is 80MHz, and the output power of the femtosecond laser is 960 mW.
Further, the photoconductive emitter is biased by a direct current voltage; the photoconductive detector is not biased by a direct current voltage.
Further, the sample from outside to inside includes in proper order: the heat-shrinkable tube with the umbrella skirt, the stress tube, the heat-shrinkable tube, the stress tube and the main insulation; its internal defects include: insulation delamination defects, insulation moisture defects, and powdery discharge product agglomeration defects.
The detection method of the internal defect detection system of the EPR heat-shrinkable cable terminal comprises the following steps:
step A, sample preparation and installation:
the sample is arranged in a two-freedom-degree platform, the relative positions of the photoconductive emitter, the reflecting mirror eight, the sample and the photoconductive detector are adjusted, so that the sample is arranged at the focal plane of the photoconductive emitter and the photoconductive detector, and the sample can freely move up and down on the focal plane in the whole test process.
Step B, defect detection:
the method comprises the following steps that a femtosecond laser is started, the generated femtosecond laser excites terahertz pulses, the terahertz pulses advance in two paths under the action of a spectroscope, and the terahertz pulses directly send the terahertz pulses with time domain signals, frequency domain amplitude and phase information to a photoconductive detector in a path of an excitation light path system through a light path reflector six and a focusing lens;
terahertz pulses enter the photoconductive emitter through a delay control unit in a passage of a detection light path system, namely a light path reflector II, a light path reflector III, a light path reflector IV, a light path reflector V and a light path reflector VII, enter a sample to be detected through the spectroscope in a reflection mode, and are reflected to the photoconductive detector through the spectroscope in the reflection mode after being incident on the terahertz pulse scanning on a component to be detected;
the method comprises the steps that a photoconductive detector receives two paths of terahertz pulses, converts the terahertz pulses with time domain signals, frequency domain amplitude and phase information into corresponding current information, transmits the current information to a phase-locked amplifier to obtain the magnitude and direction of driving current of terahertz pulse signals on a photoconductive antenna, improves the signal-to-noise ratio through noise reduction and amplification, and transmits the information to an acquisition terminal;
and D, continuously moving the component to be detected, repeating the steps, carrying out omnibearing point-by-point two-dimensional scanning on the component to be detected, storing the terahertz pulse time-domain waveform obtained by sampling by the photoelectric detector, and collecting and processing the obtained scanning result in the step C.
C, data collection and processing:
b, analyzing and processing all the signals collected in the step B by the acquisition terminal, namely performing Fourier transform on the terahertz pulse time domain waveform to obtain three-dimensional matrix data of a frequency domain, selecting time position amplitude, time domain maximum value and delay time imaging of the time domain pulse in the signal processing process, and selecting amplitude of a frequency point and overlapping value imaging of all frequency point amplitudes in the frequency domain;
and D, performing imaging detection on the sample, acquiring two-dimensional matrix data of the frequency domain, establishing a database, and using the database as an operation basis in the step D.
Step D, result application:
and (3) defining an EPR thermal shrinkage cable terminal sample to be detected as a sample A, repeating the steps A-C on the sample A for detection, and reversely judging the type, the degree and the parameters of the hidden defects of the sample A by using the database established in the step C.
Further, in the step C, the imaging detection is performed on the sample and the correspondence of the two-dimensional matrix data of the frequency domain is obtained as follows:
(a) when the insulation delamination defect exists, the contact surfaces of all insulation layers of the cable terminal can be separated, and an air gap is formed between the insulation layers; the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed and formed on the terahertz imageSpecific peak, peak band of frequency domain spectrum is 30cm-1To 45cm-1Over a wave number of (c).
And (3) performing reverse operation, namely, performing rapid imaging and image reconstruction technology according to the internal terahertz time-domain signal, frequency domain amplitude and phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has an air gap layering defect, parameters of the internal defect and the degree of the internal defect according to the difference of peak values of the reference sample and the sample with the insulation layering defect on a time-domain spectrum and a frequency-domain spectrum.
(b) When the insulation moisture defect exists, a small amount of moisture exists between the insulation layers of the cable terminal; the terahertz image is reflected that the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed to form a specific peak, and the peak spectral band of the frequency domain spectrum is 35cm-1To 55cm-1Over a wave number of (c).
And (3) performing reverse operation, namely performing rapid imaging and image reconstruction technology according to the internal terahertz time-domain signal, the frequency domain amplitude and the phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has an insulation moisture defect, and parameters of the crack defect and the degree of the crack defect according to the difference of peak values of the reference sample and the defective sample on the time-domain spectrum and the frequency-domain spectrum.
(c) When the powdery discharge product is gathered and defective, impurities exist between insulating layers of the cable terminal, which is reflected on the terahertz image, that is, the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed to form a specific peak, and the peak spectrum section of the frequency domain spectrum is 55cm-1To 80cm-1Over a wave number of (c).
And (3) performing reverse operation, namely, performing rapid imaging and image reconstruction technology according to the internal terahertz time-domain signal, frequency-domain amplitude and phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has a powdery discharge product aggregation defect, a parameter of a grid breaking defect and a degree of the grid breaking defect according to the difference of peak values of a reference sample and a defective sample on a time-domain spectrum and a frequency-domain spectrum.
The invention has the following beneficial effects:
(1) the system generates terahertz pulses by arranging a femtosecond laser, the terahertz pulses are split into two paths by a spectroscope, one path of terahertz pulses is used as exciting light, the other path of terahertz pulses is used as detecting light, a photoconductive detector receives the two paths of terahertz pulses, converts the terahertz pulses with time domain signals, frequency domain amplitudes and phase information into corresponding current information, and transmits the current information to a phase-locked amplifier to obtain the magnitude and direction of driving current of terahertz pulse signals on a photoconductive antenna, and meanwhile, the signal-to-noise ratio is improved by noise reduction and amplification; finally, entering an acquisition terminal, and collecting and processing current information of each position of the component to be detected;
the action principle of the spectroscope in the system is that after a beam of light is projected on the coated glass, the beam of light is divided into two beams through reflection and refraction; a lens in the system is used for focusing the terahertz pulse for excitation reflected by the spectroscope; the photoconductive transmitter is used for receiving one path of terahertz pulse for detection of the femtosecond laser; the photoconductive detector is used for receiving the two paths of terahertz pulses.
(2) The two-degree-of-freedom platform is convenient for the samples of the EPR heat-shrinkable cable to be detected in all directions and accurately collect the states and data of the unused positions of the samples; the arrangement of the spectroscope is used for carrying out light splitting on the terahertz pulse emitted by the femtosecond laser, so that the working processes of the photoconductive emitter and the photoconductive detector are ensured; the optical path reflectors are arranged as required, on one hand, the optical path reflectors are used for delaying, and the delaying function is to change the overlapping positions of the terahertz pulses and the femtosecond laser pulses on the test antenna, so that the whole terahertz time-domain pulse signal is sampled and scanned; and on the other hand, the terahertz wave detector is used for reflecting the terahertz wave pulse in the optical path and changing the propagation direction of the terahertz wave pulse.
(3) The terahertz pulse signal adopted by the method is taken as an electromagnetic wave with special properties such as low energy consumption, strong penetrability, high signal-to-noise ratio, fingerprint spectrum and the like, and compared with measuring means such as ultrasonic wave, X ray, infrared measurement and the like, the terahertz pulse signal has the advantages of non-contact, no damage, high penetrability and the like, and has unique advantages in the field of non-metallic materials.
The terahertz wave is extremely sensitive to material molecular changes, and air gaps and discharge decomposition products which appear in the operation process of the EPR heat-shrinkable cable terminal are obviously different from adjacent insulating layer materials in molecular structure and category; meanwhile, the EPR thermal shrinkage cable terminal has a special structure without shielding and armoring, and is extremely adaptive to the terahertz detection method, so that the internal defects of the EPR thermal shrinkage cable terminal can be efficiently and accurately diagnosed.
(4) The combination of the system and the method is a widening of the application of the terahertz nondestructive visual detection technology to the EPR thermal shrinkage cable terminal, the unique combination of the structure and the method can definitely establish the terahertz time-domain spectral characteristics of the internal defects of the EPR thermal shrinkage cable terminal, and finally the terahertz time-domain spectral characteristics are reversely applied, so that the nondestructive visual detection of the internal defects of the composite cable is realized, and the popularization prospect is good.
Drawings
FIG. 1 is a schematic structural diagram of an internal defect detection system of an EPR heat-shrinkable cable terminal;
FIG. 2 is a schematic view of a sample layering structure from outside to the center in an EPR thermal shrinkage cable terminal internal defect detection system.
The reference numbers are as follows: 11-femtosecond laser; 12-a first reflector; 13-a spectroscope; 14-mirror two; 15-mirror three; 16-mirror four; 17-mirror five; 18-a photoconductive emitter; 19-mirror six; 110-the sample; 111-lens; 112-mirror seven; 113-a lock-in amplifier; 114-acquisition terminal; 115-mirror eight; 116-a two degree of freedom platform; 117-photoconductive detector; 118-delay control unit.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
In the present invention, unless otherwise expressly stated or limited, the terms "connected," "connecting," and the like are to be construed broadly, and may, for example, refer to direct connection, indirect connection through intervening media, internal communication between two elements, or interactive relationship between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Examples
As shown in fig. 1-2, an EPR thermal shrinkage cable termination internal defect detection system comprises: the terahertz detector comprises a femtosecond laser 11 and a spectroscope 13 which are arranged along a terahertz pulse channel from left to right, a detection optical path system and an excitation optical path system which are arranged behind the spectroscope 13 in parallel, and further comprises a phase-locked amplifier 113 and an acquisition terminal 114 which are connected with each other;
the detection light path system comprises a delay control unit 118, a photoconductive emitter 18, a reflecting mirror eight 115 and a two-degree-of-freedom rapid moving platform 116 which are sequentially arranged along the light path from left to right; a photoconductive detector 117 is arranged above the eight reflecting mirror 115; the two-degree-of-freedom platform 116 is provided with a sample 110 of an EPR (ethylene-propylene-rubber) heat-shrinkable cable, and the sample 110 can freely move up and down in the vertical direction and freely rotate in the horizontal direction of the two-degree-of-freedom platform 116;
the excitation optical path system comprises a lens 111, and the lens 111 is arranged above the photoconductive detector 117;
the photoconductive detector 117 is connected to the lock-in amplifier 14.
The specific arrangement is described with reference to the following:
the reflection mode spectroscope 115 is disposed at an angle of 45 ° from left to right, and faces the photoconductive emitter 18 through one side of the terahertz pulse, and faces the photoconductive detector 117 through the terahertz pulse and the side that can reflect the terahertz pulse from the sample 110 to be measured.
A first reflecting mirror 12 is arranged on the light path of the femtosecond laser 11 and the spectroscope 13; a reflecting mirror six 19 is arranged on the light path of the spectroscope 13 and the lens 111; a second reflecting mirror 14, a third reflecting mirror 15, a fourth reflecting mirror 16, a fifth reflecting mirror 17 and a seventh reflecting mirror 112 are sequentially arranged on the light path of the spectroscope 13 and the photoconductive emitter 18; the delay control unit 118 is provided between the mirror three 15 and the mirror four 16.
The specific equipment and sample configuration parameters are described below:
the femtosecond laser 11 is a titanium-sapphire femtosecond pulse laser, the center wavelength of which is 810nm, the pulse width of which is less than 100fs, the repetition frequency of which is 80MHz, and the output power of which is 960 mW.
The photoconductive emitter 18 is biased with a dc voltage; the photoconductive detector 117 is not biased with a dc voltage.
The sample 110 comprises, in order from the outside to the inside: the heat-shrinkable tube with the umbrella skirt, the stress tube, the heat-shrinkable tube, the stress tube and the main insulation; its internal defects include: insulation delamination defects, insulation moisture defects, and powdery discharge product agglomeration defects.
The detection method of the internal defect detection system of the EPR heat-shrinkable cable terminal comprises the following steps:
step A, sample preparation and installation:
the sample 110 is mounted in a two-degree-of-freedom platform 116, and the relative positions of the photoconductive emitter 18, the mirror eight 115, the sample 110 and the photoconductive detector 117 are adjusted, so that the sample 110 is arranged at the focal plane of the photoconductive emitter 18 and the photoconductive detector 117, and the sample 110 can freely move up and down on the focal plane all the time during the test.
Step B, defect detection:
the femtosecond laser 11 is turned on, the generated femtosecond laser excites the terahertz pulse, the terahertz pulse advances in two paths under the action of the spectroscope 13, and the terahertz pulse directly sends the terahertz pulse with time domain signals, frequency domain amplitude and phase information to the photoconductive detector 117 through the light path reflector six 19 and the focusing lens 111 in the path of the excitation light path system.
The terahertz pulses enter the photoconductive emitter 18 through the delay control unit 118 in the path of the detection optical path system, namely, the optical path reflector two 14, the optical path reflector three 15, the optical path reflector four 16, the optical path reflector five 17 and the optical path reflector seven 112, enter the sample 116 to be detected through the spectroscope 115 for the reflection mode, and after scanning the terahertz pulses incident on the component 116 to be detected, the terahertz pulses with time domain signals, frequency domain amplitude and phase information are reflected to the photoconductive detector 117 through the spectroscope 115 for the reflection mode.
The photoconductive detector 117 receives the two paths of terahertz pulses, converts the terahertz pulses with time domain signals, frequency domain amplitude and phase information into corresponding current information, transmits the current information to the phase-locked amplifier 113, obtains the magnitude and direction of the driving current of the terahertz pulse signals on the photoconductive antenna, improves the signal-to-noise ratio through noise reduction and amplification, and transmits the information to the acquisition terminal 114.
And (3) continuously moving the component 116 to be tested, repeating the steps, carrying out omnibearing point-by-point two-dimensional scanning on the component 116 to be tested, storing the terahertz pulse time-domain waveform obtained by sampling by the photoconductive detector 117, and collecting and processing the obtained scanning result in the step (C).
C, data collection and processing:
and C, the acquisition terminal 114 analyzes and processes all the signals collected in the step B, namely, Fourier transform is carried out on the terahertz pulse time domain waveform to obtain three-dimensional matrix data of a frequency domain, in the signal processing process, the time position amplitude, the time domain maximum value and the delay time imaging of the time domain pulse are selected, and the frequency domain selects the frequency point amplitude and the superposed value imaging of all the frequency point amplitudes.
And D, performing imaging detection on the sample, acquiring two-dimensional matrix data of the frequency domain, establishing a database, and using the database as an operation basis in the step D.
Step D, result application:
and (3) defining an EPR thermal shrinkage cable terminal sample to be detected as a sample A, repeating the steps A-C on the sample A for detection, and reversely judging the type, the degree and the parameters of the hidden defects of the sample A by using the database established in the step C.
Specifically, the method comprises the following steps: in the step C, the imaging detection is carried out on the sample and the correspondence of the two-dimensional matrix data of the frequency domain is obtained as follows:
(a) when the insulation delamination defect exists, the contact surfaces of all insulation layers of the cable terminal can be separated, and an air gap is formed between the insulation layers; the terahertz image is reflected that the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed to form a specific peak, and the peak spectral band of the frequency domain spectrum is 30cm-1To 45cm-1Over a wave number of (c).
And (3) performing reverse operation, namely, performing rapid imaging and image reconstruction technology according to the internal terahertz time-domain signal, frequency domain amplitude and phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has an air gap layering defect, parameters of the internal defect and the degree of the internal defect according to the difference of peak values of the reference sample and the sample with the insulation layering defect on a time-domain spectrum and a frequency-domain spectrum.
(b) When the insulation moisture defect exists, a small amount of moisture exists between the insulation layers of the cable terminal; the terahertz image is reflected that the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed to form a specific peak, and the peak spectral band of the frequency domain spectrum is 35cm-1To 55cm-1Over a wave number of (c).
And (3) performing reverse operation, namely performing rapid imaging and image reconstruction technology according to the internal terahertz time-domain signal, the frequency domain amplitude and the phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has an insulation moisture defect, and parameters of the crack defect and the degree of the crack defect according to the difference of peak values of the reference sample and the defective sample on the time-domain spectrum and the frequency-domain spectrum.
(c) When the powdery discharge product is gathered to have defects, impurities exist between insulating layers of the cable terminal, and the impurities are reflected on the terahertz image, namely the time domain spectrum of the terahertz waveAnd the frequency domain spectrum is obviously changed to form a specific peak, and the peak spectrum section of the frequency domain spectrum is 55cm-1To 80cm-1Over a wave number of (c).
And (3) performing reverse operation, namely, performing rapid imaging and image reconstruction technology according to the internal terahertz time-domain signal, frequency-domain amplitude and phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has a powdery discharge product aggregation defect, a parameter of a grid breaking defect and a degree of the grid breaking defect according to the difference of peak values of a reference sample and a defective sample on a time-domain spectrum and a frequency-domain spectrum.
Claims (9)
1. The utility model provides a EPR pyrocondensation cable termination internal defect detecting system which characterized in that includes: the terahertz detector comprises a femtosecond laser (11) and a spectroscope (13) which are arranged along a terahertz pulse channel from left to right, a detection optical path system and an excitation optical path system which are arranged behind the spectroscope (13) in parallel, and further comprises a phase-locked amplifier (113) and an acquisition terminal (114) which are connected with each other;
the detection light path system comprises a time delay control unit (118), a photoconductive emitter (18), a reflecting mirror eight (115) and a two-degree-of-freedom rapid moving platform (116) which are sequentially arranged along a light path from left to right; a photoconductive detector (117) is arranged above the eight (115) reflecting mirror; a sample (110) of the EPR heat-shrinkable cable is arranged on the two-degree-of-freedom platform (116), and the sample (110) can freely move up and down in the vertical direction and freely rotate in the horizontal direction of the two-degree-of-freedom platform (116);
the excitation light path system comprises a lens (111), and the lens (111) is arranged above the photoconductive detector (117);
the photoconductive detector (117) is connected with a phase-locked amplifier (14).
2. The system for detecting internal defects in an EPR heat shrinkable cable termination of claim 1, wherein: the reflection mode is obliquely arranged from left to right at an angle of 45 degrees by a spectroscope (115), one side of the reflection mode, which can transmit the terahertz pulse, faces to the photoconductive emitter (18), and the other side, which can transmit the terahertz pulse and can reflect the terahertz pulse from the sample to be detected (110), faces to the photoconductive detector (117).
3. An EPR heat shrinkable cable termination internal defect detection system as claimed in claim 1 or 2, wherein: a first reflecting mirror (12) is arranged on the light path of the femtosecond laser (11) and the spectroscope (13); a reflecting mirror six (19) is arranged on the light path of the spectroscope (13) and the lens (111); and a second reflecting mirror (14), a third reflecting mirror (15), a fourth reflecting mirror (16), a fifth reflecting mirror (17) and a seventh reflecting mirror (112) are sequentially arranged on the light path of the spectroscope (13) and the photoconductive emitter (18).
4. The system for detecting internal defects in an EPR heat-shrinkable cable termination of claim 3, wherein: and the time delay control unit (118) is arranged between the third reflector (15) and the fourth reflector (16).
5. The system for detecting internal defects in an EPR heat shrinkable cable termination of claim 1, wherein: the femtosecond laser (11) is a titanium gem femtosecond pulse laser, the central wavelength of the femtosecond laser is 810nm, the pulse width is less than 100fs, the repetition frequency is 80MHz, and the output power is 960 mW.
6. The system for detecting internal defects in an EPR heat shrinkable cable termination of claim 1, wherein: -said photoconductive emitter (18) is biased with a dc voltage; the photoconductive detector (117) is not biased with a dc voltage.
7. The system for detecting internal defects in an EPR heat shrinkable cable termination of claim 1, wherein: the sample (110) comprises, in order from the outside to the inside: the heat-shrinkable tube with the umbrella skirt, the stress tube, the heat-shrinkable tube, the stress tube and the main insulation; its internal defects include: insulation delamination defects, insulation moisture defects, and powdery discharge product agglomeration defects.
8. A method for detecting a defect detection system in an EPR heat shrinkable cable terminal as claimed in any one of claims 1 to 7, wherein: the method comprises the following steps:
step A, sample preparation and installation:
mounting the sample (110) in a two-degree-of-freedom platform (116), and adjusting the relative positions of the photoconductive emitter (18), the reflecting mirror eight (115), the sample (110) and the photoconductive detector (117) so that the sample (110) is arranged at the focal plane of the photoconductive emitter (18) and the photoconductive detector (117), wherein the sample (110) can freely move up and down in the focal plane during the whole test;
step B, defect detection:
the method comprises the following steps that a femtosecond laser (11) is started, the generated femtosecond laser excites terahertz pulses, the terahertz pulses advance in two paths under the action of a spectroscope (13), and the terahertz pulses directly send the terahertz pulses with time domain signals, frequency domain amplitude and phase information to a photoconductive detector (117) through a light path reflector six (19) and a focusing lens (111) in a path of an excitation light path system;
terahertz pulses enter a photoconductive emitter (18) through a time delay control unit (118) in a passage of a detection light path system, namely a light path reflector II (14), a light path reflector III (15), a light path reflector IV (16), a light path reflector V (17) and a light path reflector seven (112), enter a sample to be detected (116) through a spectroscope (115) for a reflection mode, and are reflected to a photoconductive detector (117) through the spectroscope (115) for the reflection mode after being scanned by the terahertz pulses incident on a component to be detected (116);
the photoconductive detector (117) receives the two paths of terahertz pulses, converts the terahertz pulses with time domain signals, frequency domain amplitude and phase information into corresponding current information, transmits the current information to the phase-locked amplifier (113), obtains the magnitude and direction of driving current of terahertz pulse signals on the photoconductive antenna, improves the signal-to-noise ratio through noise reduction and amplification, and transmits the information to the acquisition terminal (114);
continuously moving the component (116) to be tested, repeating the steps, carrying out omnibearing point-by-point two-dimensional scanning on the component (116) to be tested, storing a terahertz pulse time domain waveform obtained by sampling by a photoelectric detector (117), and collecting and processing an obtained scanning result in the step C;
c, data collection and processing:
b, analyzing and processing all the signals collected in the step B by the acquisition terminal (114), namely performing Fourier transform on the terahertz pulse time-domain waveform to obtain three-dimensional matrix data of a frequency domain, selecting time position amplitude, time domain maximum value and delay time imaging of the time domain pulse in the signal processing process, and selecting amplitude of a frequency point and overlapping value imaging of all frequency point amplitudes in the frequency domain;
performing imaging detection on the sample, acquiring two-dimensional matrix data of a frequency domain, establishing a database, and using the database as an operation basis in the step D;
step D, result application:
and (3) defining an EPR thermal shrinkage cable terminal sample to be detected as a sample A, repeating the steps A-C on the sample A for detection, and reversely judging the type, the degree and the parameters of the hidden defects of the sample A by using the database established in the step C.
9. The method for detecting the internal defect detection system of the EPR heat-shrinkable cable terminal as claimed in claim 8, wherein: in the step C, the imaging detection is carried out on the sample and the correspondence of the two-dimensional matrix data of the frequency domain is obtained as follows:
(a) when the insulation delamination defect exists, the contact surfaces of all insulation layers of the cable terminal can be separated, and an air gap is formed between the insulation layers; the terahertz image is reflected that the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed to form a specific peak, and the peak spectral band of the frequency domain spectrum is 30cm-1To 45cm-1Over the wave number of (c);
performing reverse operation, namely, performing fast imaging and image reconstruction technology according to an internal terahertz time-domain signal, frequency domain amplitude and phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has an air gap layering defect, parameters of the internal defect and the degree of the internal defect according to the difference of peak values of a reference sample and an insulation layering defect sample on a time-domain spectrum and a frequency-domain spectrum;
(b) when the insulation moisture defect exists, a small amount of moisture exists between the insulation layers of the cable terminal; the terahertz image is reflected that the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed to form a specific peak, and the peak spectral band of the frequency domain spectrum is 35cm-1To 55cm-1Over the wave number of (c);
performing reverse operation, namely performing rapid imaging and image reconstruction technology according to an internal terahertz time-domain signal, frequency-domain amplitude and phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has an insulation moisture defect, and parameters of a crack defect and the degree of the crack defect according to the difference of peak values of a reference sample and a defective sample on a time-domain spectrum and a frequency-domain spectrum;
(c) when the powdery discharge product is gathered and defective, impurities exist between insulating layers of the cable terminal, which is reflected on the terahertz image, that is, the time domain spectrum and the frequency domain spectrum of the terahertz wave are obviously changed to form a specific peak, and the peak spectrum section of the frequency domain spectrum is 55cm-1To 80cm-1Over the wave number of (c);
and (3) performing reverse operation, namely, performing rapid imaging and image reconstruction technology according to the internal terahertz time-domain signal, frequency-domain amplitude and phase of the sample A to obtain a 2D or 3D terahertz image of the EPR thermal shrinkage cable terminal sample, and judging whether the sample A has a powdery discharge product aggregation defect, a parameter of a grid breaking defect and a degree of the grid breaking defect according to the difference of peak values of a reference sample and a defective sample on a time-domain spectrum and a frequency-domain spectrum.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113092497A (en) * | 2021-04-20 | 2021-07-09 | 重庆大学 | Nondestructive testing method and system for discharge traces in insulating paperboard |
| CN113237847A (en) * | 2021-05-07 | 2021-08-10 | 西南科技大学 | Nondestructive testing method and system for hexanitrohexaazaisowurtzitane crystal form |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113092497A (en) * | 2021-04-20 | 2021-07-09 | 重庆大学 | Nondestructive testing method and system for discharge traces in insulating paperboard |
| CN113237847A (en) * | 2021-05-07 | 2021-08-10 | 西南科技大学 | Nondestructive testing method and system for hexanitrohexaazaisowurtzitane crystal form |
| CN113237847B (en) * | 2021-05-07 | 2022-09-02 | 西南科技大学 | Nondestructive testing method and system for hexanitrohexaazaisowurtzitane crystal form |
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