CN-121978473-A - Pulse width modulation optical time domain reflection detection device for discharge pressure wave in transformer oil

CN121978473ACN 121978473 ACN121978473 ACN 121978473ACN-121978473-A

Abstract

The invention provides a pulse width modulation optical time domain reflection detection device for discharge pressure waves in transformer oil. Based on the heterodyne coherent optical time domain reflectometer, three time sequence pulse modulation continuous optical signals are adopted to enter an optical fiber to generate a backward Rayleigh scattering signal, the optical fiber is placed into transformer oil to measure pressure waves generated by partial discharge, and the phase is extracted through wavelet denoising, least square smoothing and Hilbert demodulation through the mathematical relationship between the pressure waves and the backward Rayleigh scattering signal, so that the measurement of the partial discharge pressure waves in the transformer is finally realized.

Inventors

ZHANG CHENG
WANG HANG
WANG XUAN
SHAO TAO

Assignees

中国科学院电工研究所
国网山西省电力有限公司电力科学研究院

Dates

Publication Date: 20260505
Application Date: 20260114

Claims (10)

1. The pulse width modulation optical time domain reflection detection device for the discharge voltage wave in the transformer oil is characterized in that the output end of a narrow linewidth laser is divided into a sensing arm and a reference arm through a first coupler; In the sensing arm, the input end of the acousto-optic modulator is optically connected with the pulse light output end of the first coupler, the electric driving end of the acousto-optic modulator is electrically connected with the time sequence square wave output end of the function generator, the pulse light output end of the acousto-optic modulator is optically connected with the first port of the three-port circulator through the erbium-doped optical fiber amplifier, the second port of the three-port circulator is optically connected with the sensing optical fiber laid in transformer oil, and the third port of the three-port circulator is optically connected with the first input end of the second coupler; in the reference arm, the continuous light output end of the first coupler is directly and optically connected with the second input end of the second coupler; The beat frequency output end of the second coupler is optically connected with the optical input end of the balance optical detector, and the electric output end of the balance optical detector is connected with the data acquisition system; The function generator generates pulse sequence units with the time sequence of 400 ns, 200 ns and 100 ns pulse widths and 50 ns intervals; The backward Rayleigh scattered light generated in the sensing optical fiber returns through the three-port circulator and then is subjected to beat frequency with the continuous light of the reference arm in the second coupler, the continuous light is converted into an electric signal by the balance optical detector, and the electric signal is processed, so that the phase change caused by the discharge voltage wave in the transformer oil is extracted.
2. The apparatus of claim 1, wherein the sensing fiber is connected to the second port of the three port circulator via an FC/APC interface, and the sensing fiber is immersed entirely within the transformer oil and is in close proximity to the winding surface.
3. The apparatus of claim 1, wherein the function generator outputs 100 sets of pulse trains.
4. The apparatus of claim 1, wherein a delay fiber is interposed between the third port of the three port circulator and the second coupler.
5. The device of claim 1, wherein the processing of the electrical signal comprises performing wavelet denoising, filtering interference and noise components, obtaining flatter data, sending the flatter data to a phase meter, performing waveform statistics and feature quantity extraction according to the correlation of light intensity and phase with time, and finally completing the partial discharge diagnosis.
6. The apparatus of claim 5, wherein each set of measured waveforms is denoised by wavelet, the phase information of the signals is demodulated using Hilbert transform, and the waveforms are processed by sliding time window least squares polynomial smoothing for the light intensity and phase data of a set of signals, wherein the data mean value in the time window is calculated, the window width is 1000 ns, and then the hundred sets of data are classified, i.e., the signals of the fiber cores are counted.
7. The apparatus of claim 6, wherein the characteristic values of each window, i.e., average value, deviation, maximum slope of waveform, are extracted in the form of sliding time window, and the change rates of each parameter with respect to the adjacent window are compared, and if two of the three parameters have a relative deviation exceeding 50%, an abnormal time window is determined.
8. The apparatus of claim 7, wherein after all waveforms are processed, 1s is used as an analysis interval, 3 groups of tracks are compared with each other to form an abnormal time window distribution within 1s, and if 3 or more tracks contain abnormal time windows, partial discharge is determined to occur in the interval.
9. The apparatus of claim 8, wherein the pressure wave generated by the discharge in the transformer oil causes the optical fiber to microstrain by changing the refractive index by Δn and the length by ΔL, and wherein the relationship between the optical phase shift Δφ and the vibration acceleration a is a linear proportional relationship: ; Wherein a is vibration acceleration, t is pressure wave propagation time, L is optical fiber length, and n is optical fiber refractive index.
10. The apparatus of claim 1, wherein the time delay T is set between pulse train units to a value that is greater than the round trip time of the signal in the fiber, depending on the length of the sensing fiber.

Description

Pulse width modulation optical time domain reflection detection device for discharge pressure wave in transformer oil Technical Field The invention belongs to the field of extra-high voltage transformers, and particularly relates to a pulse width modulation optical time domain reflection detection device for discharge voltage waves in transformer oil. Background The large-scale oil-filled equipment such as an extra-high voltage transformer is used as a key energy conversion hub of an extra-high voltage alternating current/direct current transmission system, and the safe and stable operation of the equipment is critical for the safe and reliable supply of energy. The main protection of the existing oil immersed transformer is current quick break protection, differential protection and heavy gas protection, and the identification of the protection is often about 10 ms. Moreover, the sensitivity of these protection devices is low, especially when insulation faults occur between winding turns. The severe faults of the transformer often originate from internal insulation discharge defects, so that in order to prevent the explosion of the transformer, sensitive, effective and reliable detection of discharge signals in transformer oil is urgently needed, so that protection measures are taken for the transformer at the initial stage of the discharge of the transformer or when severe discharge occurs before severe arc faults occur, even at the moment when the severe arc faults occur, thereby avoiding equipment damage and reducing economic losses. Compared with the detection method, the vibration signal generated by the discharge in the oil is very obvious, and the distributed optical fiber technology is adopted for vibration monitoring, so that the instant measurement and identification of arc faults can be realized. At present, a few patents introduce an optical fiber sensing detection system realized by using heat or vibration and the like, and a monitoring system based on Brillouin scattering and Rayleigh scattering principles is mainly adopted, for example, CN201911175481 is an all-fiber temperature on-line monitoring system and a monitoring method for submarine cables. Such patents mainly employ a certain technology to design a related monitoring system. The intensity of the back Rayleigh scattering is highest in various scattering signals, so that vibration detection based on the back Rayleigh scattering has higher accuracy. However, there is a technical bottleneck in this scattered light intensity increase, and the signal-to-noise ratio is limited by the recognition method simply relying on intensity analysis. The application of the phase sensitive optical time domain reflectometry (phi-OTDR) technology obviously improves the detection sensitivity and the spatial resolution of the system. However, the technology faces the random fluctuation of the signal caused by the coherent fading effect, and can realize the effective identification of the continuous vibration signal through a large amount of statistical processing. In view of the transient nature of the arcing process, the limited sample of vibration coupling data captured by conventional methods results in reduced state identification efficiency. At present, the related invention of accurate monitoring of the discharge in the oil inside the transformer is few, and similar patents mainly monitor the external means such as cables and the like, and no application method capable of being placed inside the transformer to realize accurate detection exists. At present, similar vibration monitoring methods mainly adopt single Brillouin scattering, raman scattering and Rayleigh scattering principles, and no related technology is used for comprehensively applying various principles. The existing technology based on the Brillouin scattering mechanism is mainly aimed at vibration signal detection, however, the intensity of the Brillouin scattering light is extremely low, and the effective information capturing difficulty is remarkable. The signal is simultaneously interfered by multiple physical field coupling such as stress, temperature and the like, and a high-coherence light source and a precise demodulation device are needed to be relied on, so that the system has the highest realization cost. The current patent technology based on raman scattering mechanism mainly focuses on temperature parameter monitoring. The technology is difficult to effectively characterize the arcing phenomenon in oil through temperature change characteristics. In addition, the system needs to be provided with a high-coherence light source and a precise demodulation unit, and the structural complexity and the implementation cost are obviously higher than those of a conventional sensing scheme. The current part of the patent realizes vibration parameter monitoring (namely Optical Time Domain Reflectometry (OTDR)) based on Rayleigh scattering mechanism. Rayleigh scattering has the largest