The Impact of the Inclusion of MgO Nano-Fillers in a Polyethylene Matrix on Dielectric Strength and Resistance to Partial Discharges

One commonly used strategy to enhance polymers specific properties such as the resistance to partial discharges erosion is the incorporation into the polymeric matrix of inorganic micro or nanoparticles. This study focused on the dielectric properties of Low-Density Polyethylene (LDPE) filled with nano-sized Magnesium Oxide (MgO) particles compounded by thermo-mechanical process and one of the purposes was to establish appropriate processing parameters in order to reach the desired dielectric properties. LDPE was used as a matrix and was reinforced by MgO particles having a nominal average size of 30 nm. The MgO nanoparticles were treated with a silane coupling agent (3-Glycidyloxypropyl Trimethoxysilane). The samples were initially prepared in a melt-mixing chamber with a MgO content of 1% wt. These pre-mixed samples were further treated by the means of thermo-mechanical mixing in a conical co-rotating twin-screw extruder in order to improve the dispersion and distribution of the MgO particles. In this report, both lifetime under a PD activity and AC dielectric strength of pure and nano-filled LDPE samples have been measured and compared. Nano-filled LDPE samples were found to exhibit an improve lifetime, without any detrimental impact on their short-term dielectric strength. This suggests that nano-filled LDPE may be for electric applications for which the dielectric materials may be exposed to partial discharge activities. This is significant result for the use of MgO-reinforced PE as an insulating material for HV cables since the resistance to PD is closely related to treeing resistance which is the main electrical degradation mechanism that leads to failure for shielded extruded power cables.

GIS partial discharge data enhancement method based on self attention mechanism VAE-GAN

The reliability of gas-insulated switchgear(GIS)partial discharge fault diagnosis is crucial for the safe and stable operation of power grids.This study proposed a data enhancement method based on a self-attention mechanism to optimize the VAE-GAN method and solve the problem of the lack of partial discharge samples and the unbalanced distribution between different defects.First,the non-subsampled contourlet transform(NSCT)algorithm was used to fuse the UHF and optical partial discharge signals to obtain a photoelectric fusion phase resolved partial discharge(PRPD)spectrum with richer information.Subsequently,the VAE structure was introduced into the traditional GAN,and the excellent hidden layer feature extraction ability of the VAE was used to guide the generation of the GAN.Then,the self-attention mechanism was integrated into the VAE-GAN,and the Wasserstein distance and gradient penalty mechanisms were used to optimize the network loss function and expand the sample sets to an equilibrium state.Finally,the KAZE and polar coordinate distribution entropy methods were used to extract the expanded samples.The eigenvectors of the sets were substituted into the long short-term memory(LSTM)network for partial discharge fault diagnosis.The experimental results show that the sample generation quality and fault diagnosis results of this method were significantly better than the traditional data enhancement method.The structure similarity index measure(SSIM)index is increased by 4.5%and 21.7%,respectively,and the average accuracy of fault diagnosis is increased by 22.9%,9%,5.7%,and 6.5%,respectively.The data enhancement method proposed in this study can provide a reference for GIS partial discharge fault diagnosis.

Ni/MgO catalyst prepared using atmospheric high-frequency discharge plasma for CO_2 reforming of methane

A new type of Ni/MgO catalyst was prepared using atmospheric high-frequency discharge cold plasma. The influences of conventional method, plasma method, and plasma plus calcination method on the catalytic activity were studied and the CO2 reforming of methane was chosen as the probe reaction. The catalysts were characterized by X-ray diffraction （XRD）, transmission electron microscope （TEM）, X-ray photoelectron spectroscopy, and CO2 temperature-programmed surface reaction techniques. The results suggested that the nickel-based catalyst prepared by plasma plus calcination method possessed a smaller particle size and a higher dispersion of active component, better low-temperature activity and enhanced anti-coking ability. The conversion of CO2 and CH4 was 90.70% and 89.37%, respectively, and the reaction lasted for 36 h without obvious deactivation under 101.325 kPa and 750°C with CO2/CH4 = 1/1.

Characteristics of the propagation of partial discharge ultrasonic signals on a transformer wall based on Sagnac interference

The acoustic emission(AE)method has been widely recognized for the detection of incipient insulation fault phenomenon(partial discharge,PD)in power transfomiers,nevertheless,the installation and placement of AE sensors should be taken into full consideration.In this manuscript,a three-dimensional multiphysics model was established and simulated to research the characteristics of the propagation in the transformer wall.Furthermore,a piezoelectric transducer was used to detect PD ultrasonic signals and verify the simulation results in the laboratory.To ensure the accuracy of the detection,an optical fiber sensor based on the Sagnac interference principle was designed and adopted.The variation of the amplitude of the ultrasonic signal with distance reveals the characteristics of the ultrasonic signal propagating in the transformer wall.The distribution of sound pressure on the upper and lower surfaces of the simulation model proved that ultrasonic waves propagate in the form of symmetrical Lamb waves in the transformer wall.Moreover,the amplitude of the AE attenuates due to absorption and refraction loss,and local fluctuations on account of acoustic interference.Thus,a stable signal detected by an AE sensor does not represent the absence of PD in a transfomier.To improve the reliability of AE detection,it is proposed in this manuscript that repeated movement of the AE sensor is necessary to obtain a suitable measurement position.Similarly,it is necessary to adjust the position of the AE sensor in order to locate the PD source well.In addition,this study is expected to provide a theoretical analysis and a fiber sensor to address the problem of sensor placement in AE detection.

Study on Intermittent Discharge Characteristics of Typical Solid Insulation Defects in Gas Insulated Switchgear

In response to the problem of frequent leakage and false alarm of partial discharge insulation defects in GIS,this paper conducts experimental research on intermittent discharge characteristics of common solid insulation defects in GIS.Using true GIS to build amulti-source testing platform for intermittent discharge of solid insulation defects,and using pulse current method,ultra-high frequency method,ultrasonic method,and gas characteristic component detectionmethod to study the variation law of intermittent discharge characteristics of solid insulation defects.The results showthat:the intermittent discharge state of metal fouling defects on the solid insulation surface decreases with the extension of the discharge time,the discharge time interval as a whole shows an increasing trend,and the metal fouling defects on the solid insulation surface in the intermittent discharge state is difficult to develop into a breakdown discharge fault.The overall discharge amount of air gap defects inside solid insulation also shows the law of increasing first and then decreasing,and the discharge amount of air gap defects inside solid insulation stays at a large level for a long time during intermittent discharge,and there is a risk of breakdown,and the discharge will gradually evolve into continuous discharge;ultrasonic method and characteristic component detection method cannot realize the effective perception of intermittent discharge of metal fouling.The 50-period mapping information commonly used in the power field cannot reflect the intermittent discharge variation law of solid insulation,and the 200-period UHF mapping composed of four groups of 50-period UHF mapping data can initially derive the intermittent discharge distribution law of solid insulation defects.The research results of this paper are of great significance to expand the knowledge of intermittent discharge characteristics and the detection of GIS discharge defects in the field.

Analysis of capacitive voltage rise during off-line partial discharge tests on power transformers

Partial discharge test on a transformer is carried out according to the items in IEC 60. During the test, unproved measuring system is calibrated by proved system at a voltage no less than 50% the rated testing voltage. The result is then extrapolated linearly, leading to an error related to the distribution of stray capacitance, which varies with the testing frequency, especially to large transformers. In this paper a factor, named the capacitive rise fact, is introduced to assess the rise. The factor can be adjusted to some extent by changing the reactance that is connected to the LV side of the testing circuit to lower the capacity of the power source. However, the factor changes when the voltage divider on the high voltage side is removed after the voltage ratio has been calculated, and a great error is resulted under unfavorable conditios.

ANN based pattern recognition of partial discharge in power transformer

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Study of partial discharge characteristics in HFO-1234ze(E)/N2 mixtures

HFO-1234 ze(E)(trans-1,3,3,3-tetrafluoropropene,chemical formula:C3H2F4)is an extremely environmentally friendly SF6 alternative gas with high electrical strength.In this paper,the partial discharge(PD)characteristics of HFO-1234 ze(E)/N2 mixtures were studied using the gas insulation test platform.The PD inception voltage of insulating gas under positive and negative half cycles of power frequency was tested.Using SF6/N2 mixtures as a control group,the effects of electrode spacing,mixing ratio and pressure on the insulation performance of HFO-1234 ze(E)/N2 mixtures were explored.The test results show that the PD inception voltage of the negative half-cycle of pure HFO-1234 ze(E)under short electrode spacing can reach 0.96-1.04 times of pure SF6 under different pressures;the PD inception voltage of40%HFO-1234 ze(E)/60%N2 mixtures at 0.3 MPa is 0.67-0.89 times that of SF6/N2 mixtures under the same conditions,which has great application prospect.

THE STUDY ON MEASURING TECHNIQUE OF PARTIAL DISCHARGE IN GAS INSULATED SWITCHGEAR USING ULTRA HIGH FREQUENCY METHOD WITH EXTERNAL SENSORS

Objective In order to find early latent faults and prevent catastrophic failures, diagnosis of insulation condition by measuring technique of partial discharge(PD) in gas insulated switchgear (GIS) is applied in this paper, which is one of the most basic ways for diagnosis of insulation condition. Methods Ultra high frequency(UHF) PD detection method by using internal sensors has been proved efficient, because it may avoid the disturbance of corona, but the sensor installation of this method will be limited by the structure and operation condition of GIS. There are some of electromagnetic (E-M) waves leak from the place of insulation spacer, therefore, the external sensors UHF measuring PD technique is applied, which isn't limited by the operation condition of GIS. Results This paper analyzes propagated electromagnetic (E-M) waves of partial discharge pulse excited by using the finite-difference time-domain (FDTD) method. The signal collected at the outer point is more complex than that of the inner point, and the signals' amplitude of outer is about half of the inner, because it propagates through spacer and insulation slot. Set up UHF PD measuring system. The typical PD in 252kV GIS bus bar was measured using PD detection UHF technique with external sensors. Finally, compare the results of UHF measuring technique using external sensors with the results of FDTD method simulation and the traditional IEC60270 method detection. Conclusion The results of experiment shows that the UHF technique can realize the diagnosis of insulation condition, the results of FDTD method simulation and the result UHF method detection can demonstrate each other, which gives references to further researches and application for UHF PD measuring technique.

A Study on the Mobile Partial Discharge Locating System

This paper studies on the Partial Discharge (PD) Locating System based on a mobile array of ultra-high frequency (UHF) antennas and a vehicle-mounted PD locating system is established. The system consists of omni-directional antenna array for receiving UHF PD signals, a pre-processing circuit for signal amplification and filtering and the high- speed acquisition and control unit of PD pulse signals. The developed locating system is able to simultaneously record the PD pulse signals received by the antenna array. By assessing the time difference of arrival (TDOA), the two-dimensional hyperbolic locating model quickly locates the PD source. Based on the software developed by LabVIEW, it is also possible to display, store and further analyze the acquired signals. Through the simulation of PD signals and the locating experiments with the system, it is proved that the PD locating system possesses the features of rapidity and precision in determining the bearing of PD source.

Design of DC Partial Discharge Detecting System for Electrical Equipment

A balancing method was used to build a DC partial discharge （PD） testing circuit for electrical equipment,and a narrow-band detection system was designed using detection resistance and a filter. After signal accessed a high-speed digital acquisition （DAQ） card,the system was triggered to extract a single partial discharge （PD） signal. To eliminate the interference pulses caused by power supply ripple,etc.,the time domain and frequency domain features of pulses were extracted. Based on the features,cluster analysis was used to exclude interference pulses. Two-dimensional and three-dimensional histograms were obtained by use of the Δt method. Then,22 discharge statistical operators were calculated for the two-dimensional charts. Lastly,the defective capacitors were tested to verify the system＇s ability. The results show that the system is capable of PD detection in electrical equipment.

Effects of packing particles on the partial discharge behavior and the electrical characterization of oxygen PBRs

Packed-bed reactors(PBRs)hold great promise for environmental applications,but a deeper understanding of the behavior of plasma discharge within PBRs is required.To this end,a partial-discharge alternative equivalent circuit for PBRs was established in this work.Dielectric particles(glass beads or glass sand)were used to place focus on the effects of the particle size and shape on the partial discharge behavior of the oxygen PBRs.Some electrical characterizations were explored(e.g.the effective dielectric capacitance,partial discharge coefficient,and corrected burning voltage)that may differ from long-standing interpretations.The findings indicate that the suppressive effect of surface discharge on filament discharge is stronger with the decrease of the particle size.For partial discharge,the effective dielectric capacitance is always less than the dielectric capacitance.The corrected burning voltage and partial discharge tendency increase with the decrease of the particle size.As compared to an empty reactor,the average electric field in the PBR was found to be improved by 3–4 times,and the ozone energy efficiency and production were promoted by more than 20%and 15%,respectively.The plasma processing capacity can therefore be improved by choosing a relatively large size or a complex,irregularly-shaped packing material that is suitable for the discharge gap.

Partial Discharge Source Classification and De-Noising in Rotating Machines Using Discrete Wavelet Transform and Directional Coupling Capacitor

This paper introduces a new method to separate PD1 from other disturbing signals present on the high voltage genera-tors and motors. The method is based on combination of a pattern classifier, the Discrete Wavelet Transform (DWT), to de-noise PD and Time-Of-Arrival method to separate PD sources. Furthermore, it will be shown that it can recognize PD sources including rotating machine’s internal and external discharge pulses (e.g. on the bus bar).

Denoising Method for Partial Discharge Signal of Switchgear Based on Continuous Adaptive Wavelet Threshold

Partial discharge(PD)is an important reason for the insulation failure of the switchgear.In the process of PD detection,PD signal is often annihilated in strong noise.In order to improve the accuracy of PD detection in power plant switchgear,a method based on continuous adaptive wavelet threshold switchgear PD signals denoising is proposed in this paper.By constructing a continuous adaptive threshold function and introducing adjustment parameters,the problems of over⁃processing of traditional hard threshold functions and incomplete denoising of soft threshold functions can be improved.The analysis results of simulated signals and measured signals show that the continuous adaptive wavelet threshold denoising method is significantly better than the traditional denoising method for the PD signal.The proposed method in this paper retains the characteristics of the original signal.Compared with the traditional denoising methods,after denoising the simulated signals,the signal⁃to⁃noise ratio(SNR)is increased by more than 30%,and the root⁃mean⁃square error(RMSE)is reduced by more than 30%.After denoising the real signal,the noise suppression ratio(NRR)is increased by more than 40%.The recognition accuracy rate of PD signal has also been improved to a certain extent,which proves that the method has a certain practicability.

A Novel Method of Newton Iteration in Complex Field and Lattice Search for Locating Partial Discharges in Transformers

在变压器局部放电特高频定位的多传感器时间差测量中不可避免地存在误差,这往往导致时间差方程组在实数域内无解。为了得到时间差方程组的最优近似解,提出了复数域牛顿迭代网格搜索方法。该方法在复数域内进行迭代;当迭代结果为实数时就将其作为定位结果;当迭代结果为复数时,以其实部为中心点坐标,在该点周围局部区域内采用网格搜索法计算最优近似解。通过在变压器上开展试验检验了该方法的可行性和准确性。研究表明,在一定时间误差下,在实数域采用牛顿迭代法计算时不收敛,而在复数域可以收敛,平均定位误差为0.20 m。复数域牛顿迭代网格搜索方法能够在一定时间误差下求解时间差方程组,给出最优近似解,实现局部放电定位。

Surface Partial Discharge Characteristics of Oil-paper Insulation Under Combined AC-DC Voltage

The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.

Chromatic Mapping of Partial Discharge Signals

This contribution describes the use of chromatic techniques for quantifying signatures of partial discharges(PD).A brief description of the basis of chromatic monitoring is given along with explanations of how the approach may be applied for addressing signals produced by PDs.Laboratory test data from several sources for different types of PDs,operating conditions and geometries have been subjected to the chromatic procedures.These include a point-plane gap,a sphere in a liquid and treeing in a cable.Chromatic changes in PD signals have been investigated as a function of the amplitude of the alternating voltage producing the PD,the time duration before full electrical breakdown and for different forms of PDs.Results of the chromatic processing of these data are presented in the form of a number of chromatic maps relating to different quarter cycles of the alternating voltage producing the PDs.The results show the potential of the chromatic techniques for indicating the likelihood of full electrical breakdown and for distinguishing between certain forms of PDs.A summary of the chromatic processing procedures is presented for producing chromatic maps and for adaptation in further exploring PD signal features.

Application of Complex Daubechies Wavelet in UHF Partial Discharge Measurements

On-line partial discharge(PD)detection still remains a very challenging task because of the strong electromagnetic interferences.In this paper,a new method of de-noising,using complex Daubechies wavelet(CDW)transform,has been proposed.It is a relatively recent enhancement to the real-valued wavelet transform because of tow important properties,which are nearly shift-invariant and availability of phase information.Those properties give CDW transform superiority over other real-valued wavelet transform,and then the construction algorithm of CDW is introduced in detail.Secondly,based on the real threshold algorithm of real-valued wavelet transform,complex threshold algorithm is devised.This algorithm take the different characteristics of real part and imaginary part of complex wavelet coefficients into account,it modifies the real and imaginary parts of complex wavelet coefficients respectively.Thirdly,to obtain a real de-noised signal,new combined information series is devised.By applying different combination of real part and imaginary part of de-noised complex signal,a real de-noised signal can be restored with higher peak signal-to-noise ratio(PSNR)and less distortion of original signals.Finally,On-site applications of extracting PD signals from noisy background by the optimal de-noising scheme based on CDW are illustrated.The on-site experimental results show that the optimal de-noising scheme is an effective way to suppress white noise in PD measurement.