CN113447772A - High-voltage cable partial discharge online monitoring system and method - Google Patents
High-voltage cable partial discharge online monitoring system and method Download PDFInfo
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Abstract
The invention relates to a high-voltage cable partial discharge on-line monitoring system and a method, wherein the system comprises a first coupler, a scattered signal acquisition module and a position frequency information acquisition module; the first coupler is used for dividing one beam of continuous light into two beams of continuous light; the scattering signal acquisition module is used for modulating one of the two beams of continuous light into a periodic electric pulse sequence and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence; the position frequency information acquisition module is used for determining the position of partial discharge according to the back Rayleigh scattering signal, receiving the other beam of the two beams of continuous light and returning to the reference light, interfering the reference light to generate an interference signal, and acquiring the frequency information of the partial discharge according to the interference signal. The high-voltage cable partial discharge on-line monitoring system provided by the invention can realize high-frequency response to the partial discharge of a long-distance high-voltage cable.
Description
Technical Field
The invention relates to the technical field of high-voltage cable monitoring, in particular to a high-voltage cable partial discharge online monitoring system and method.
Background
The high-voltage power cable is produced and installed in a curved manner or is rented under the stress of electricity, heat, machinery and the like during normal operation to cause the insulation cracking of the cable, generate partial discharge and induce the fault of the cable, thereby bringing serious loss to the country.
The method has the advantages that partial discharge of the cable is discovered as early as possible, and the method has important significance for reducing cable faults, improving power supply reliability and ensuring safe and stable operation of a power system. The high-frequency partial discharge frequency is generally between 1MHz and 300MHz, and the high-frequency partial discharge frequency can be detected by using a conventional high-frequency current transformer and a conventional capacitive coupling sensor, and the high-frequency partial discharge frequency is not suitable for partial discharge of a long-distance cable because the high-frequency partial discharge frequency is detected by a single point and cannot be used for distributed detection of the long-distance cable; the high-frequency pulse current method has high sensitivity and poor positioning precision and is easy to be interfered by electromagnetism; the transient earth electric wave monitoring method is mostly used for monitoring partial discharge of a transformer, GIS and a cable joint, has poor positioning precision and cannot be applied to monitoring partial discharge of a long-term cable. These conventional partial discharge monitoring methods are not suitable for remote distributed partial discharge monitoring.
Distributed sound sensing based on the phase-sensitive OTDR technology is limited by the response range of the optical fiber sensing length to frequency, cannot respond to the partial discharge high-frequency part of a long-distance high-voltage cable, and limits the wide application of the system.
Disclosure of Invention
In view of the above, there is a need to provide an online monitoring system and method for partial discharge of a high-voltage cable, so as to solve the problem in the prior art that the high-frequency part of partial discharge of a long-distance high-voltage cable cannot respond.
The invention provides a high-voltage cable partial discharge online monitoring system which comprises a first coupler, a scattered signal acquisition module and a position frequency information acquisition module, wherein the first coupler is connected with the first coupler;
the first coupler is used for dividing one beam of continuous light into two beams of continuous light; the scattering signal acquisition module is used for modulating one of the two beams of continuous light into a periodic electric pulse sequence and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence; the position frequency information acquisition module is used for determining the position of partial discharge according to the back Rayleigh scattering signal, receiving the other beam of the two beams of continuous light and returning to the reference light, interfering the reference light to generate an interference signal, and acquiring the frequency information of the partial discharge according to the interference signal.
Further, the scattering signal acquisition module comprises an acousto-optic modulator, a circulator and a sensing optical fiber; the scattering signal obtaining module modulates one of the two beams of continuous light into a periodic electric pulse sequence, and generates a backward rayleigh scattering signal according to the periodic electric pulse sequence, and specifically includes:
the acousto-optic modulator modulates one of the two beams of continuous light into a periodic electric pulse sequence, the circulator transmits the periodic electric pulse sequence to the sensing optical fiber, and the sensing optical fiber generates a backward Rayleigh scattering signal according to the periodic electric pulse sequence.
Further, the position frequency information acquisition module comprises a second coupler, a data processing unit and a fan-in fan-out module; the position frequency information obtaining module determines a position of partial discharge according to the back rayleigh scattering signal, receives another beam of the two continuous beams and returns a reference beam, interferes the reference beam to generate an interference signal, and obtains frequency information of partial discharge according to the interference signal, and specifically includes:
the data processing unit determines the position of partial discharge according to the back Rayleigh scattering signal, the fan-in fan-out module receives the other beam of the two beams of continuous light and returns reference light, the second coupler interferes the reference light to generate an interference signal, and the data processing unit also acquires frequency information of the partial discharge according to the interference signal.
Further, the high voltage cable partial discharge on-line monitoring system further includes a first photodetector, and the data processing unit determines the position of partial discharge according to the back rayleigh scattering signal, and specifically includes: the photoelectric detector converts the backward Rayleigh scattering signal into a corresponding first electric signal, and the data processing unit processes the first electric signal by using a sliding difference algorithm to determine the position of partial discharge.
Further, the high voltage cable partial discharge on-line monitoring system further includes a second photodetector, and the data processing unit obtains frequency information of partial discharge according to the interference signal, and specifically includes: the second photoelectric detector converts the interference signal into a corresponding second electric signal, and the data processing unit analyzes the second electric signal by using fast Fourier transform spectrum to obtain frequency information of partial discharge.
Further, the first coupler is a 1 × 2 coupler, and the second coupler is a 2 × 2 coupler.
The invention also provides an online monitoring method for partial discharge of the high-voltage cable, which comprises the following steps:
dividing a beam of continuous light into two beams of continuous light;
modulating one beam of the two beams of continuous light into a periodic electric pulse sequence, and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence;
and determining the position of partial discharge according to the back Rayleigh scattering signal, receiving the other beam of the two beams of continuous light and returning to reference light, interfering the reference light to generate an interference signal, and acquiring frequency information of the partial discharge according to the interference signal.
Further, determining the position of the partial discharge according to the back rayleigh scattering signal specifically includes: and converting the backward Rayleigh scattering signal into a corresponding first electric signal, and processing the first electric signal by using a sliding difference algorithm to determine the position of partial discharge.
Further, acquiring frequency information of the partial discharge according to the interference signal specifically includes: and converting the interference signal into a corresponding second electric signal, and analyzing the second electric signal by using a fast Fourier transform frequency spectrum to obtain frequency information of partial discharge.
Further, the second electrical signal is
Where r is the response coefficient of the second photodetector, As(t) is the amplitude of the probe light, Al(t) is the amplitude of the reference light, Δ w is the frequency shift of the acousto-optic modulator,
back-rayleigh scattering light caused by high frequency acoustic signals generated for partial dischargeIs changed in the phase of the phase-change,
for initiating phase difference between probe light and reference light
Compared with the prior art, the invention has the beneficial effects that: dividing one beam of continuous light into two beams of continuous light through the first coupler; modulating one of the two beams of continuous light into a periodic electric pulse sequence through the scattering signal acquisition module, and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence; determining the position of partial discharge according to the back Rayleigh scattering signal through the position frequency information acquisition module, receiving the other beam of the two beams of continuous light and returning to reference light, interfering the reference light to generate an interference signal, and acquiring frequency information of the partial discharge according to the interference signal; high-frequency response to partial discharge of a long-distance high-voltage cable can be realized.
Drawings
Fig. 1 is a block diagram of a high-voltage cable partial discharge online monitoring system provided by the invention;
FIG. 2 is a schematic diagram of a sequence of electrical pulses provided by the present invention;
fig. 3 is a frequency spectrum diagram obtained by performing fast fourier transform on a high-frequency signal according to the present invention after demodulation;
FIG. 4 is a schematic cross-sectional view of a seven-core optical fiber disposed within a cable according to the present invention;
FIG. 5 is a schematic diagram of the present invention providing the connection of seven-core optical fibers to a fan-in fan-out module;
fig. 6 is a schematic structural diagram of a high-voltage cable partial discharge online monitoring system provided by the invention.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
Example 1
The embodiment of the invention provides an online monitoring system for partial discharge of a high-voltage cable, which has a structural block diagram, and as shown in fig. 1, the system comprises a first coupler 01, a scattered signal acquisition module 02 and a position frequency information acquisition module 03;
the first coupler 01 is used for dividing one continuous light beam into two continuous light beams; the scattering signal acquisition module 02 is configured to modulate one of the two beams of continuous light into a periodic electrical pulse sequence, and generate a backward rayleigh scattering signal according to the periodic electrical pulse sequence; the position frequency information obtaining module 03 is configured to determine a position of partial discharge according to the rayleigh-backscattering signal, receive another beam of the two continuous beams and return to the reference light, interfere the reference light to generate an interference signal, and obtain frequency information of partial discharge according to the interference signal.
Preferably, the scattering signal acquisition module comprises an acousto-optic modulator, a circulator and a sensing optical fiber; the scattering signal obtaining module modulates one of the two beams of continuous light into a periodic electric pulse sequence, and generates a backward rayleigh scattering signal according to the periodic electric pulse sequence, and specifically includes:
the acousto-optic modulator modulates one of the two beams of continuous light into a periodic electric pulse sequence, the circulator transmits the periodic electric pulse sequence to the sensing optical fiber, and the sensing optical fiber generates a backward Rayleigh scattering signal according to the periodic electric pulse sequence.
In a specific embodiment, the continuous light emitted by the narrow linewidth laser is divided into two beams after passing through the 1 × 2 coupler, the continuous light branched from the upper side is modulated into a periodic electric pulse sequence with a specified code by the acousto-optic modulator, the electric pulse sequence is schematically shown in fig. 2, the electric pulse sequence has a period T and is composed of a narrow pulse and a wide pulse, the pulse width of the narrow pulse is τ 1, generally tens of nanoseconds, and the pulse width of the wide pulse is τ 2 — T1, which is the time of one period except for the narrow pulse. The amplitude of the narrow pulse high level is I1, the amplitude of the wide pulse high level is I2, and I1 is greater than I2; the coded light pulse modulated by the acousto-optic modulator AOM passes through a first port of the circulator and then enters the sensing optical fiber through a second port of the circulator, and the generated backward Rayleigh scattering signal passes through a third port of the circulator and enters the Photoelectric Detector (PD) to be converted into an electric signal.
Preferably, the position frequency information acquisition module comprises a second coupler, a data processing unit and a fan-in fan-out module; the position frequency information obtaining module determines a position of partial discharge according to the back rayleigh scattering signal, receives another beam of the two continuous beams and returns a reference beam, interferes the reference beam to generate an interference signal, and obtains frequency information of partial discharge according to the interference signal, and specifically includes:
the data processing unit determines the position of partial discharge according to the back Rayleigh scattering signal, the fan-in fan-out module receives the other beam of the two beams of continuous light and returns reference light, the second coupler interferes the reference light to generate an interference signal, and the data processing unit also acquires frequency information of the partial discharge according to the interference signal.
In a specific embodiment, the data processing unit processes and positions the positions of the partial discharge by using a sliding difference algorithm according to a plurality of groups of collected Rayleigh scattering signals; assuming that the rayleigh scattered signal rl (l is 1, …, N) of the OTDR is acquired N times and the moving average time is M, then
Selecting a sliding reference signal R in consideration of a pulse width time and an attenuation time of the ultrasonic waver＝Rint(i/2M)*M+1Then the sliding differential signal is Δ R ═ Δ R1,ΔR2,...,ΔRi,...,ΔRJ}，ΔRi＝Ri-RrJ-K-1-N-M; the use of the sliding differential averaging can reduce the number of averaging, improve the signal-to-noise ratio without losing high frequency components, and at the same time, identify the position of the vibration signal in the optical fiber by the difference.
Preferably, the high-voltage cable partial discharge online monitoring system further includes a first photodetector, and the data processing unit determines the position of the partial discharge according to the back rayleigh scattering signal, specifically including: the photoelectric detector converts the backward Rayleigh scattering signal into a corresponding first electric signal, and the data processing unit processes the first electric signal by using a sliding difference algorithm to determine the position of partial discharge.
Preferably, the high-voltage cable partial discharge on-line monitoring system further includes a second photodetector, and the data processing unit obtains frequency information of partial discharge according to the interference signal, and specifically includes: the second photoelectric detector converts the interference signal into a corresponding second electric signal, and the data processing unit analyzes the second electric signal by using fast Fourier transform spectrum to obtain frequency information of partial discharge.
Preferably, the first coupler is a 1 × 2 coupler and the second coupler is a 2 × 2 coupler.
In one embodiment, the continuous light output from the branch below the output end of the 1 × 2 coupler enters the reference fiber, the light output from the port of the circulator 2 enters the seven-core fiber core 1 and exits from the core 4, the reference light enters from the core 2 through the fan-out module, and is connected with the core 3 through a jumper wire after passing through the fan-out module at the far end, and interferes with the reference light returned from the core 3 in the 2 × 2 coupler, the interference signal enters the balanced photodetector 2(BPD2) and is converted into an electrical signal, and then enters the data processing unit, the vibration on the fiber is demodulated, the frequency information is obtained through fast fourier transform spectrum analysis, and the electrical signal output by the BPD2 can be expressed as:
wherein r is the response coefficient of BPD, As(t) is the amplitude of the probe light, Al(t) is the amplitude of the reference light,. DELTA.w is the AOM frequency shift,
the high frequency acoustic signals generated for the partial discharge cause phase changes in the back rayleigh scattered light,
the phase difference is initiated for the probe light and the reference light.
A can be demodulated by the following algorithms(t) and
wherein Q (t) is Hilbert transform of I (t), arctan is arctangent operation, and j is imaginary unit. And sending the demodulated signal to an upper computer to carry out fast Fourier transform to obtain corresponding frequency information.
The high frequency signal is demodulated and then subjected to fast fourier transform to obtain a spectrogram, as shown in fig. 3. Fig. 3 shows a frequency spectrum diagram obtained by performing fast fourier transform on a high-frequency signal of 5MHz demodulated by using a high-voltage cable partial discharge online monitoring system, and it is seen from fig. 3 that the frequency response of the system can reach 5MHz, which proves the capability of the system described in this embodiment of the invention to detect high-frequency partial discharge.
A schematic cross-sectional view of a seven-core optical fiber disposed within a cable, as shown in fig. 4; the sensing optical fiber is a seven-core optical fiber, 4 cores of the seven-core optical fiber are selected and marked as a core 1, a core 2, a core 3 and a core 4; the connection diagram of the seven-core optical fiber and the fan-in fan-out module is shown in fig. 5; in fig. 5, core 1 is connected to core 4 as the sensing fiber and sensing arm using a fan-in fan-out module, and core 2 is connected to core 3 as the reference arm; partial discharge occurs at a certain position on the cable, and the inner core 1 and the core 4 of the seven-core optical fiber are influenced by sound waves generated by the partial discharge; the positions of the vibrations occurring on the cores 1 and 4 can be located, and the accuracy of the location can be verified by the result of the location by the following formula:
l1+l2≈2l
where l1 is the vibration position located on core 1, l2 is the vibration position located on core 4, and l is the length of the seven-core fiber.
In another embodiment, as shown in fig. 6, a schematic structural diagram of an online partial discharge monitoring system for a high-voltage cable includes: laser light source 1, 1 x 2 coupler 2, FPGA-based arbitrary waveform generator 3, acousto-optic modulator 4, circulator 5, photodetector 6, first fan-in fan-out module 7, seven-core fiber 8, second fan-in fan-out module 9, 2 x 2 coupler 10, balanced photodetector 11, and digital processing unit 12. The laser light source is a narrow linewidth light source; the 1-to-2 coupler divides the incident light into two light outputs according to a specific power ratio.
An arbitrary waveform generator 3 based on FPGA sends out a periodic electric pulse sequence with specified codes; the single-period electric pulse sequence is composed of a narrow pulse and a wide pulse, wherein the pulse width of the narrow pulse is generally tens of nanoseconds, and the pulse width of the wide pulse is the time of one period except the narrow pulse. The amplitude of the high level of the narrow pulse is greater than the amplitude of the high level of the wide pulse. Four cores of the seven-core optical fiber 8 are connected out by the multi-core optical fiber fan-in fan-out module 7 to serve as sensing optical fibers and reference optical fibers of the system. (four optical fibers may also be used instead of a multi-core fiber).
The detection light enters from the first port of the circulator 5, and is output from the second port to the sensing optical fiber (seven-core optical fiber), and the reflected backward rayleigh scattering light is output from the third port; the signal light and the local oscillator light interfere in the 2-by-2 coupler 10 and are output in two paths after the interference; the photodetector 6(PD) receives and converts the back rayleigh scattered light into an electrical signal, and the balanced photodetector 11(BPD) receives and converts the interfered two optical signals into an electrical signal.
Example 2
The embodiment of the invention provides a high-voltage cable partial discharge online monitoring method, which comprises the following steps:
dividing a beam of continuous light into two beams of continuous light;
modulating one beam of the two beams of continuous light into a periodic electric pulse sequence, and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence;
and determining the position of partial discharge according to the back Rayleigh scattering signal, receiving the other beam of the two beams of continuous light and returning to reference light, interfering the reference light to generate an interference signal, and acquiring frequency information of the partial discharge according to the interference signal.
Preferably, the determining the position of the partial discharge according to the back rayleigh scattering signal specifically includes: and converting the backward Rayleigh scattering signal into a corresponding first electric signal, and processing the first electric signal by using a sliding difference algorithm to determine the position of partial discharge.
Preferably, the acquiring frequency information of the partial discharge according to the interference signal specifically includes: and converting the interference signal into a corresponding second electric signal, and analyzing the second electric signal by using a fast Fourier transform frequency spectrum to obtain frequency information of partial discharge.
Preferably, the second electrical signal is
Where r is the response coefficient of the second photodetector, As(t) is the amplitude of the probe light, Al(t) is the amplitude of the reference light, Δ w is the frequency shift of the acousto-optic modulator,
the high frequency acoustic signals generated for the partial discharge cause phase changes in the back rayleigh scattered light,
the phase difference is initiated for the probe light and the reference light.
The invention discloses a high-voltage cable partial discharge on-line monitoring system and a method, wherein a beam of continuous light is divided into two beams of continuous light by a first coupler; modulating one of the two beams of continuous light into a periodic electric pulse sequence through the scattering signal acquisition module, and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence; determining the position of partial discharge according to the back Rayleigh scattering signal through the position frequency information acquisition module, receiving the other beam of the two beams of continuous light and returning to reference light, interfering the reference light to generate an interference signal, and acquiring frequency information of the partial discharge according to the interference signal; high-frequency response to partial discharge of a long-distance high-voltage cable can be realized.
The technical scheme of the invention can detect the high-frequency acoustic signals caused by partial discharge, can realize remote monitoring and positioning, and realizes remote high-frequency response to the partial discharge of the high-voltage cable. When partial discharge occurs at a certain position of the high-voltage cable, high-frequency ultrasonic signals of the product can be influenced by vibration at two positions of the same cross section area on the sensing optical fiber, and the positioning accuracy can be verified mutually by using the positioning results of the two positions. The sensing optical fiber used in the technical scheme of the invention is the seven-core optical fiber, the requirement of the whole system can be met only by selecting four cores of the seven-core optical fiber, and the other optical fiber can be used for communication or the other optical fiber, so that the use of the optical fiber is greatly reduced. The high-frequency ultrasonic wave attenuation of partial discharge is fast, and transmission distance is short, can fine solution ultrasonic wave's quick attenuation, improves the sensitivity of signal detection, has increased the SNR to the high-frequency acoustic signal that partial discharge produced, can be more effectual to carrying out the office and put and carry out distributed safety monitoring.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A high-voltage cable partial discharge online monitoring system is characterized by comprising a first coupler, a scattered signal acquisition module and a position frequency information acquisition module;
the first coupler is used for dividing one beam of continuous light into two beams of continuous light; the scattering signal acquisition module is used for modulating one of the two beams of continuous light into a periodic electric pulse sequence and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence; the position frequency information acquisition module is used for determining the position of partial discharge according to the back Rayleigh scattering signal, receiving the other beam of the two beams of continuous light and returning to the reference light, interfering the reference light to generate an interference signal, and acquiring the frequency information of the partial discharge according to the interference signal.
2. The high-voltage cable partial discharge online monitoring system according to claim 1, wherein the scattering signal acquisition module comprises an acousto-optic modulator, a circulator and a sensing optical fiber; the scattering signal obtaining module modulates one of the two beams of continuous light into a periodic electric pulse sequence, and generates a backward rayleigh scattering signal according to the periodic electric pulse sequence, and specifically includes:
the acousto-optic modulator modulates one of the two beams of continuous light into a periodic electric pulse sequence, the circulator transmits the periodic electric pulse sequence to the sensing optical fiber, and the sensing optical fiber generates a backward Rayleigh scattering signal according to the periodic electric pulse sequence.
3. The high-voltage cable partial discharge online monitoring system according to claim 2, wherein the position frequency information acquisition module comprises a second coupler, a data processing unit and a fan-in fan-out module; the position frequency information obtaining module determines a position of partial discharge according to the back rayleigh scattering signal, receives another beam of the two continuous beams and returns a reference beam, interferes the reference beam to generate an interference signal, and obtains frequency information of partial discharge according to the interference signal, and specifically includes:
the data processing unit determines the position of partial discharge according to the back Rayleigh scattering signal, the fan-in fan-out module receives the other beam of the two beams of continuous light and returns reference light, the second coupler interferes the reference light to generate an interference signal, and the data processing unit also acquires frequency information of the partial discharge according to the interference signal.
4. The system according to claim 3, further comprising a first photodetector, wherein the data processing unit determines the position of the partial discharge according to the rayleigh backscattering signal, and specifically comprises: the photoelectric detector converts the backward Rayleigh scattering signal into a corresponding first electric signal, and the data processing unit processes the first electric signal by using a sliding difference algorithm to determine the position of partial discharge.
5. The system according to claim 4, further comprising a second photodetector, wherein the data processing unit obtains frequency information of the partial discharge according to the interference signal, and specifically comprises: the second photoelectric detector converts the interference signal into a corresponding second electric signal, and the data processing unit analyzes the second electric signal by using fast Fourier transform spectrum to obtain frequency information of partial discharge.
6. The system of claim 5, wherein the first coupler is a 1 x 2 coupler and the second coupler is a 2 x 2 coupler.
7. A high-voltage cable partial discharge online monitoring method is characterized by comprising the following steps:
dividing a beam of continuous light into two beams of continuous light;
modulating one beam of the two beams of continuous light into a periodic electric pulse sequence, and generating a backward Rayleigh scattering signal according to the periodic electric pulse sequence;
and determining the position of partial discharge according to the back Rayleigh scattering signal, receiving the other beam of the two beams of continuous light and returning to reference light, interfering the reference light to generate an interference signal, and acquiring frequency information of the partial discharge according to the interference signal.
8. The on-line monitoring method for partial discharge of a high-voltage cable according to claim 6, wherein the determining the position of the partial discharge according to the back rayleigh scattering signal specifically comprises: and converting the backward Rayleigh scattering signal into a corresponding first electric signal, and processing the first electric signal by using a sliding difference algorithm to determine the position of partial discharge.
9. The on-line monitoring method for partial discharge of the high-voltage cable according to claim 6, wherein the obtaining of the frequency information of the partial discharge according to the interference signal specifically comprises: and converting the interference signal into a corresponding second electric signal, and analyzing the second electric signal by using a fast Fourier transform frequency spectrum to obtain frequency information of partial discharge.
10. The on-line monitoring method for partial discharge of high voltage cable according to claim 9, wherein the second electrical signal is
Where r is the response coefficient of the second photodetector, As(t) is the amplitude of the probe light, Al(t) is the amplitude of the reference light, Δ w is the frequency shift of the acousto-optic modulator,
the high frequency acoustic signals generated for the partial discharge cause phase changes in the back rayleigh scattered light,
the phase difference is initiated for the probe light and the reference light.
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