CN115327307B - Photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device and method - Google Patents
Photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device and method Download PDFInfo
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- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1263—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation
- G01R31/1272—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of solid or fluid materials, e.g. insulation films, bulk material; of semiconductors or LV electronic components or parts; of cable, line or wire insulation of cable, line or wire insulation, e.g. using partial discharge measurements
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Abstract
The invention relates to a wire and cable live detection technology, in particular to a photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device and method, wherein the device comprises an electromagnetic radiation detection device and a processor; the electromagnetic radiation detection device comprises a detection probe, a probe front end and a main body long handle, wherein the bottom of the detection probe is connected with the front end probe, a longitudinal grip is arranged at the top end of the main body long handle, the lower end of the main body long handle is connected with the detection probe, a transverse grip is arranged in the middle of the main body long handle, a plug is arranged near the top end of the main body long handle, the plug is connected with the top of the detection probe through a signal wire and a power wire, and the signal wire and the power wire are arranged in the main body long handle; the first Hall element, the second Hall element and the third Hall element are orthogonally arranged in the detection probe; the processor is connected with the electromagnetic radiation detection device through a plug; the processor includes a signal processing unit and an arc fault diagnosis module. The device can conveniently carry out nondestructive test on the cable pipeline, determines the position of the series arc fault, and improves the safety and reliability of the photovoltaic cable.
Description
Technical Field
The invention belongs to the technical field of live detection of wires and cables, and particularly relates to a device and a method for nondestructive detection of flux leakage of a series arc fault of a photovoltaic direct current cable.
Background
The photovoltaic power generation adopts a direct current cable to collect electric energy, and the direct current cable series arc fault is a main cause of the fire disaster of the photovoltaic power station. The direct current arc temperature is high, no voltage zero crossing point exists, the arc is difficult to extinguish by itself, the arc path impedance is equivalent to the load impedance, the arc is difficult to cut off through overcurrent protection, and the technology for detecting the series arc faults of the photovoltaic direct current cable is needed to be developed. The prior art mainly comprises two methods, namely an inverter-end high-frequency current component detection method based on conductive coupling and a high-frequency electromagnetic wave component detection method based on radiation coupling. Dc arcs are essentially low voltage, high current gas discharge processes, with severe near field magnetic field distortion and high energy, high frequency magnetic field components. The method for accurately detecting the series arc faults in real time and cutting off the fault circuit is an effective way for avoiding the occurrence of fire accidents caused by continuous burning of the arcs. When a dc series arc fault occurs, the load current is reduced, and is more difficult to discriminate than other arcs. In order to solve the problem of detecting the series arc of the photovoltaic direct current cable, the invention provides a method and a device for detecting the fault of the series arc of the cable by utilizing the magnetic field distortion characteristic of the arc field entering area of the direct current cable.
Disclosure of Invention
Aiming at the problems existing in the background technology, the invention provides a photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device and method.
In order to solve the technical problems, the invention adopts the following technical scheme: a photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device comprises an electromagnetic radiation detection device and a processor; the electromagnetic radiation detection device comprises a detection probe, a probe front end and a main body long handle, wherein the bottom of the detection probe is connected with the front end probe, a longitudinal grip is arranged at the top end of the main body long handle, the lower end of the main body long handle is connected with the detection probe, a transverse grip is arranged in the middle of the main body long handle, a plug is arranged near the top end of the main body long handle, the plug is connected with the top of the detection probe through a signal wire and a power wire, and the signal wire and the power wire are arranged in the main body long handle; the first Hall element (A), the second Hall element (B) and the third Hall element (C) are orthogonally arranged in the detection probe; the processor is connected with the electromagnetic radiation detection device through a plug; the processor includes a signal processing unit and an arc fault diagnosis module.
In the photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device, the first Hall element (A), the second Hall element (B) and the third Hall element (C) are respectively arranged on the z, y and x axes of an orthogonal coordinate system.
In the photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device, the processor also comprises an image processing module, a denoising analysis module and a display device arranged on the longitudinal grip; the processor is connected with the display device in a wireless way.
A method for a photovoltaic dc cable series arc fault magnetic leakage nondestructive testing device, the method comprising the steps of:
step 1, an electromagnetic radiation detection device collects data;
b is measured by a first Hall element (A), a second Hall element (B) and a third Hall element (C), respectively z Direction, B y Direction and B x Transmitting a voltage signal generated by the magnetic field intensity in the direction to a signal processing unit;
step 2, signal processingThe unit will measure B as measured in step 1 z Direction, B y Direction and B x The voltage signals generated in the direction are processed according to the relation between the magnetic field direction and the signal magnitude, and the voltage signals corresponding to the magnetic vectors of the measuring points are returned; the method comprises the following specific steps:
step 2.1, processing the voltage signals measured in the step 1 to obtain voltage signals and directions corresponding to the magnetic vectors;
the measured magnetic field strength is:
wherein B is the voltage signal of the measured magnetic vector, B x 、B y 、B z Voltage signals corresponding to the orthogonal magnetic field intensities measured by the three Hall elements are respectively obtained; wherein B is x 、B y For the components orthogonal to each other in the x-y plane, i.e. the plane of the detection probe, B z Is a component perpendicular to the plane of the detection probe along the long handle of the main body;
the direction angle relative to the magnetic field strength at the probe satisfies:
wherein θ is the angle between the magnetic vector and the x-axis on the x-y plane, i.e. the probe plane,the included angle between the magnetic vector and the z axis, namely the long handle of the main body;
step 2.2, performing fast Fourier transform processing on the voltage signal to judge arc faults;
extracting a high-frequency part of the voltage signal corresponding to the magnetic vector obtained in the step 2.1 by utilizing fast Fourier transform FFT, and if the high-frequency signal of 2 MHz-30 MHz exists, considering that an arc is generated, wherein the position where the arc is generated is the cable wounded position; the formula for the discrete fourier transform DFT and the fast fourier transform FFT is as follows
Discrete fourier transform, DTF:
x is sampled data, N is sampling point number, X is data after Fourier transformation, N and k represent subscripts of X and X, j is complex unit, the value ranges of N and k are 0-N-1, and each data sequence number of X and X is represented;
the Euler expansion can be obtained by:
fast fourier transform FFT:
for polynomialWithout loss of generality, let n=2 s s.epsilon.N, N being taken as the first integer power of 2 or more, considered as a i The parity of the subscript divides the term in f (x) into two parts, i.e
Order the
Then
f(x)＝f 1 (x 2 )+xf 2 (x 2 ) (8)
Carry-inThe method can obtain:
carry-inIs available in the form of
Compared with the prior art, the invention has the beneficial effects that: the magnetic field detection probe is a Hall element with three magnetic field measurement directions being orthogonal in pairs, the signals measured in the three directions are synthesized by the processor, and the detection return result is a signal corresponding to the magnitude of the magnetic vector of the detected position, so that the real situation of the magnetic field of the detected position is reflected. The problem that the magnetic field intensity direction measured by a single Hall element is single, the measured signal is only projected in a single direction, and the reflected cable fault condition is limited due to different magnetic field directions at the detected position is avoided. The method can effectively and accurately detect the local curve of the cable conductor in the outlet pipe, thereby providing effective equipment and method for detecting the series arc faults of the photovoltaic direct current cable.
The arc fault is estimated by adopting a Hall element magnetic field detection mode, and a cable manufacturing loop is not required to be additionally arranged, so that the cable size and the environment in which the cable is positioned are not limited. The nondestructive testing can be conveniently carried out on the cable pipeline so as to determine the position of the series arc fault, countermeasures can be timely taken, and the safety and reliability of the photovoltaic cable are improved.
The detection device does not directly contact with the fault cable, can realize the non-contact detection of the series arc fault of the photovoltaic direct current cable, and ensures the safety of the convenience of the photovoltaic system and operation and maintenance personnel during the fault detection of the photovoltaic cable.
Drawings
FIG. 1 is a schematic diagram of an electromagnetic radiation detecting apparatus according to an embodiment of the present invention;
the device comprises a 1-longitudinal handle, a 2-plug, a 3-signal line power line, a 4-transverse handle, a 5-detection probe, a 6-probe front end, a 7-first Hall element A, an 8-second Hall element B and a 9-third Hall element C;
FIG. 2 is a schematic diagram showing the positioning of the first, second, and third Hall elements in the probe according to one embodiment of the present invention;
wherein, 10-measured magnetic field B z Direction, angle between 11-magnetic vector and main body long handle12-measured magnetic field B y Direction, projection of 13-magnetic vector on probe plane and B x Angle of direction θ, 14-measured magnetic field B x A direction;
FIG. 3 is a schematic diagram showing the connection of an electromagnetic radiation detecting apparatus and a processor according to an embodiment of the present invention;
wherein, 15-electromagnetic radiation detection device, 16-processor;
FIG. 4 is a flow chart of the operation of the photovoltaic DC cable series arc fault magnetic leakage nondestructive testing device according to one embodiment of the present invention;
FIG. 5 is a graph of spectral analysis before arc faults in series of a photovoltaic DC cable according to one embodiment of the present invention;
fig. 6 is a graph of a spectrum analysis after a series arc fault of a photovoltaic dc cable according to an embodiment of the present invention.
Detailed Description
The technical solutions of the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
The invention will be further illustrated, but is not limited, by the following examples.
The series arc fault is the fault type with the highest duty ratio of the photovoltaic direct current cable, and contains rich leakage magnetic field components. The electromagnetic radiation detection device is used for fixing the electronic device and transmitting signals to the processor; the processor is used for receiving and processing the voltage signal returned by the magnetic vector. And obtaining the direction and the size of the magnetic vector of the target position, and generating a detection result. The electromagnetic radiation detection device comprises a detection probe and a probe front end, wherein the detection probe comprises three first Hall elements, second Hall elements and third Hall elements which are orthogonally placed, magnetic vectors are returned in a voltage signal mode, a processor synthesizes the voltage signals and then carries out fast Fourier transform, and fault arc characteristic frequency of 2 MHz-30 MHz is adopted as a judgment basis to identify a series arc fault.
In specific implementation, the photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device comprises an electromagnetic radiation detection device 15 and a processor 16, as shown in fig. 3; the electromagnetic radiation detection device 15 comprises a detection probe 5, a probe front end 6 and a main body long handle, wherein the bottom of the detection probe 5 is connected with the front end probe 6, the top end of the main body long handle is provided with a longitudinal grip 1, the lower end of the main body long handle is connected with the detection probe 5, the middle of the main body long handle is provided with a transverse grip 4, the top end of the main body long handle is provided with a plug 2, the plug 2 is connected with the top of the detection probe 5 through a signal wire and a power wire 3, and the signal wire and the power wire 3 are arranged in the main body long handle; the first Hall element A7, the second Hall element B8 and the third Hall element C9 are orthogonally arranged in the detection probe 5; the processor 16 is connected with the electromagnetic radiation detection device 15 through the plug 5; the processor 16 includes a signal processing unit and an arc fault diagnosis module; as shown in fig. 1.
The electromagnetic radiation detecting device 15 is used for detecting a leakage magnetic field generated at a cable fault, and the first hall element A7, the second hall element B8 and the third hall element C9 measure the magnetic field intensity on an orthogonal three-dimensional coordinate of the position and return in a voltage signal mode.
The main body long handle is used for fixing the detection probe 5, the signal wire, the power wire 3 and the plug 2 can be contained to transmit signals to the processor 16, and the longitudinal handle and the transverse handle which are fixedly arranged on the main body long handle are used for being carried by a person.
The processor 16 includes a signal processing unit and an arc fault diagnosis module for receiving and processing the voltage signal returned by the magnetic vector, and generating a detection result according to the voltage signal. The processor processes according to the relationship of the magnetic field intensity on the orthogonal three-dimensional coordinates, and returns the magnetic vector of the point, including the specific direction and the specific size of the magnetic vector. And judging whether the series arc fault occurs in the target direct current cable according to the obtained magnetic vector direction and the obtained magnetic vector size.
The signal output by the detection probe 5 includes position information for judging the corresponding position of the voltage signal.
Moreover, the processor 16 may also include an image processing module to visualize the resulting voltage signals and form a waveform map of magnetic fields and locations for image acquisition, image analysis, and image preservation.
Moreover, the processor 16 may further include a denoising analysis module, which performs denoising processing on the obtained voltage signal, removes the influence of noise, combines with the image processing module, optimizes the visualization result, and evaluates the cable fault condition according to the signal characteristics after denoising processing.
In addition, a display device can be arranged on the longitudinal handle 1, and a real-time image can be directly displayed at the front end of the device for observing the condition of the cable in real time.
The processor 16 is connected to a display device on the vertical grip, and detects wireless connection of the probe 5. The output result is a real-time image, and the method can be used for observing the condition of the cable in real time.
As shown in fig. 4, in the method for the photovoltaic dc cable series arc fault magnetic leakage nondestructive detection device, the surface through which the magnetic fields detected by the three hall elements provided in the detection probe 5 pass is in an orthogonal form, and the installation is performed in the manner shown in fig. 1. The magnetic field generated by arc fault passes through the first Hall element A7, and the magnetic field is measured at B z DirectionThe generated voltage signal passes through the second Hall element B8 to measure the magnetic field in B y The voltage signal generated in the direction passes through the third Hall element C9 to measure the magnetic field in B x A voltage signal generated in the direction. The three directions conform to the orthogonal three-dimensional coordinate relationship. In an embodiment, the voltage signals are transmitted to the processor 16 through the connection lines, and the three voltage signals are processed according to the relationship between the magnetic field direction and the signal magnitude, and the voltage signals corresponding to the magnetic vector returned to the position specifically include magnitude and direction. The principle of processing the measured values to obtain voltage signals and directions corresponding to magnetic vectors and performing fast fourier transform processing on the signals to determine arc faults is described with reference to fig. 2:
the Hall elements are orthogonally arranged, so that the measured magnetic field intensity is orthogonal, and the measured magnetic field intensity is respectively arranged on the x, y and z axes of an orthogonal coordinate system. Therefore, the magnetic field strength is:
wherein B is the voltage signal of the measured magnetic vector, B x 、B y 、B z Voltage signals corresponding to the orthogonal magnetic field intensities measured by the three Hall elements are respectively obtained. Wherein B is x 、B y For components orthogonal to each other in the x-y plane, i.e. the probe plane, B z Is the component along the probe shaft perpendicular to the probe plane.
Thus, there is a direction angle relative to the magnetic field strength at the probe that satisfies:
where θ is the angle of the magnetic vector to the x-axis in the x-y plane i.e. the probe plane,is the angle between the magnetic vector and the z-axis, i.e. the probe rod.
The high frequency part of the voltage signal corresponding to the magnitude of the magnetic vector obtained after the processing is extracted by utilizing Fast Fourier Transform (FFT), and if the high frequency signal of 2 MHz-30 MHz exists, the electric arc is considered to be generated, so the position where the electric arc is generated is the cable wounded position. Formulas of DFT (discrete fourier transform) and FFT (fast fourier transform) are given below.
For DFT (discrete fourier transform):
x is sampled data, N is sampling point number, X is data after Fourier transformation, N and k represent subscripts of X and X, j is complex unit, the value ranges of N and k are 0-N-1, and each data sequence number of X and X is represented;
the Euler expansion can be obtained by:
in FFT (fast fourier transform) using a fast algorithm:
for polynomialWithout loss of generality, let n=2 s s.epsilon.N (since in the multiplication of polynomials we can equivalently consider a polynomial as the higher order polynomial coefficients are zero, N can be considered the first integer power of 2 or more), consider a as per a i The parity of the subscript divides the term in f (x) into two parts, i.e
Order the
Then
f(x)＝f 1 (x 2 )+xf 2 (x 2 ) (18)
Carry-inIs available in the form of
Carry-inIs available in the form of
By iterating the above process, the time complexity can be reduced, and the final result is shown in fig. 5 and 6.
Note that: since only the high frequency part is focused, the former low frequency part is not considered, and thus the operation is facilitated by reducing the amount of data and thereby reducing the resolution.
In an embodiment, for a known destination cable, the probe is moved in the cable direction, and the magnitude and direction of the corresponding voltage of the magnetic vector at the corresponding position can be read after the processor is processed. And the fault arc characteristic frequency is 2 MHz-30 MHz as a judgment basis, so that the fault position is displayed.
The photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device can further comprise an image processing module, the obtained voltage signals are visualized, a waveform diagram of a magnetic field and a position is formed, and image acquisition, image analysis and image storage are achieved.
The photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device can further comprise a denoising analysis module, the obtained voltage signal is subjected to denoising treatment, the influence of noise is removed, the image processing module is combined, the visual result is optimized, and the cable fault condition is estimated according to the signal characteristics after denoising treatment.
The photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device can further comprise a display device, and can directly display real-time images at the front end of the device for observing the condition of the cable in real time.
The foregoing is merely illustrative of the preferred embodiments of the present invention and is not intended to limit the embodiments and scope of the present invention, and it should be appreciated by those skilled in the art that equivalent substitutions and obvious variations may be made using the teachings of the present invention, which are intended to be included within the scope of the present invention.
Claims (3)
1. The detection method of the photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device comprises an electromagnetic radiation detection device and a processor, wherein the detection device is used for detecting a magnetic leakage field generated at a cable series arc fault; the electromagnetic radiation detection device comprises a detection probe, a probe front end and a main body long handle, wherein the bottom of the detection probe is connected with the front end probe, a longitudinal grip is arranged at the top end of the main body long handle, the lower end of the main body long handle is connected with the detection probe, a transverse grip is arranged in the middle of the main body long handle, a plug is arranged near the top end of the main body long handle, the plug is connected with the top of the detection probe through a signal wire and a power wire, and the signal wire and the power wire are arranged in the main body long handle; the first Hall element (A), the second Hall element (B) and the third Hall element (C) are orthogonally arranged in the detection probe; the processor is connected with the electromagnetic radiation detection device through a plug; the processor comprises a signal processing unit and an arc fault diagnosis module; the three magnetic field measuring directions are two-by-two orthogonal Hall elements, the processor is used for synthesizing signals measured in the three directions, and the detection return result is a signal corresponding to the size of the magnetic vector at the detected position; characterized in that the method comprises the following steps:
for the cable to be detected, the probe is moved along the cable direction, and the processor reads the voltage and the direction corresponding to the magnetic vector of the corresponding position after processing; and the fault arc characteristic frequency is 2 MHz-30 MHz as a judgment basis, so that the fault position is displayed; the method comprises the following steps:
step 1, an electromagnetic radiation detection device collects data;
b is measured by a first Hall element (A), a second Hall element (B) and a third Hall element (C), respectively z Direction, B y Direction and B x Transmitting a voltage signal generated by the magnetic field intensity in the direction to a signal processing unit;
step 2, the signal processing unit measures the B measured in the step 1 z Direction, B y Direction and B x The voltage signals generated in the direction are processed according to the relation between the magnetic field direction and the signal magnitude, and the voltage signals corresponding to the magnetic vectors of the measuring points are returned; the method comprises the following specific steps:
step 2.1, processing the voltage signals measured in the step 1 to obtain voltage signals and directions corresponding to the magnetic vectors;
the measured magnetic field strength is:
wherein B is the magnetic field strength of the measured magnetic vector, B x 、B y 、B z The orthogonal magnetic field intensities measured by the three Hall elements are respectively; wherein B is x 、B y For the components orthogonal to each other in the x-y plane, i.e. the plane of the detection probe, B z Is a component perpendicular to the plane of the detection probe along the long handle of the main body;
the direction angle relative to the magnetic field strength at the probe satisfies:
wherein θ is a magnetic vectorThe angle between the x-y plane and the x-axis on the probe plane,the included angle between the magnetic vector and the z axis, namely the long handle of the main body;
step 2.2, performing fast Fourier transform processing on the voltage signal to judge arc faults;
extracting a high-frequency part of the voltage signal corresponding to the magnetic vector obtained in the step 2.1 by utilizing fast Fourier transform FFT, and if the high-frequency signal of 2 MHz-30 MHz exists, considering that an arc is generated, wherein the position where the arc is generated is the cable wounded position; the formula for the discrete fourier transform DFT and the fast fourier transform FFT is as follows
Discrete fourier transform, DTF:
x is sampled data, N is sampling point number, X is data after Fourier transformation, N and k represent subscripts of X and X, j is complex unit, the value ranges of N and k are 0-N-1, and each data sequence number of X and X is represented;
the Euler expansion can be obtained by:
fast fourier transform FFT:
for polynomialWithout loss of generality, let n=2 s s.epsilon.N, N being taken as the first integer power of 2 or more, considered as a i The parity of the subscript divides the term in f (x) into two parts, i.e
Order the
Then
f(x)＝f 1 (x 2 )+xf 2 (x 2 ) (8)
Carry-inThe method can obtain:
carry-inIs available in the form of
Through the iteration, the fault position is obtained.
2. The detection method of the photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device according to claim 1, wherein the detection method comprises the following steps: the first hall element (a), the second hall element (B) and the third hall element (C) are respectively arranged on the orthogonal coordinate system z, y and x axes.
3. The detection method of the photovoltaic direct-current cable series arc fault magnetic leakage nondestructive detection device according to claim 1, wherein the detection method comprises the following steps: the processor also comprises an image processing module and a denoising analysis module, and a display device is arranged on the longitudinal handle; the processor is connected with the display device in a wireless way.
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