Suppression of Periodic Narrowband Interferences in Cable Partial Discharge Detections

There are background noises and interferences in the signal acquired,due to partial discharge(PD) detection system covers a broad frequency band.To suppress periodic narrowband signal which is a quite serious interference in PD measurement,the existing suppression method is introduced,the new method of wavelet packet transform is mainly studied to de-noise the periodic narrowband in XLPE cable PD detection system,which is based on the db4 basic wavelet using soft threshold.The results of the experiment show that wavelet packet transform is effective in restraining the periodic narrowband interferences to extract the PD pulses in XLPE cable PD monitoring system.     

A Method for Online Measurement of Dielectric Loss of HV Capacitive Equipment Insulation

It is still a major problem for research on online monitor dielectric dissipation factor of high voltage equipment insulation. In the field, new methods are paid attention by researchers especially. At present, there are no methods achieving the satisfactory measurement results. Based on the voltage and current at their respective zero crossed points, this paper proposes the integral measurement method which can be used to measure the dielectric dissipation factor of high voltage capacitive apparatus. The formula for dielectric dissipation factor angle computation is deduced by theoretical analysis and the computation results are achieved by digital simulation. Meanwhile, this paper explains the effect to measurements by system frequency, content of harmonic and zero-drift and draws the relevant error curves. It also proposes the measures to reduce the integral measurement method presented in this paper,which can convert measurement of small signal into that of big signal and accurately measure dielectric loss of capacitive apparatus. It also possesses great anti jamming ability under strong electromagnetic interference environment. The online measurement system can detect the dielectric dissipation factor of high voltage equipment by the integral measurement method.     

Analysis of UHF Method Used in Partial Discharge Detection in GIS

The possibility of UHF (ultra high frequency) method used in partial discharge detection in GIS is analyzed, and the UHF sensor, simulating passive filter, detecting the method of wide-band and narrow-band are studied, in order to avoid interferes of low-frequency. The authors develop an inner loop sensor in GIS model and investigate UHF method detecting partial discharge in GIS. The results indicate that the UHF system of detecting PD can effectively detect partial discharge and avoid outer corona interfere and Periodic pulse interfere. At the same time, narrow-frequency PD detection is an effective detection method to restrain UHF interferes.     

Wavelet Packet Decomposition Based on Entropy Threshold for White-noise Rejection in PD Signal

This paper analyzes the different characteristics of white-noise interference in the signals of partial discharge (PD) after wavelet transform. There is high value in lots of scales for PD and white-noise interference is to zero with increasing scale. The threshold is set for wavelet coefficient in all scales. If the coefficient of signal is higher than the threshold, it is PD signal. Otherwise it is noise interference. A threshold-based wavelet packet transform (WPT) algorithm is put forward to suppress white noise interference in PD signals. The results testifies that it has a favorable adaptability to extract PD signals using WPT.     

Capacitive Coupler Used for Detecting Partial Discharge in GIS

The coaxial configuration of gas-insulated substations is of great advantages transmitting the electromagnetic wave excitated by partial discharge and of great advantages of partial discharge detection. Based the characteristics of configuration of GIS and PD signals inside, the authors design a disc coupler and a loop coupler for continuous monitoring of partial discharge in GIS, and analyze the sensor's characteristics theoretically. The frequency response (FR) characteristics of the disc coupler and the loop coupler are analyzed by the simulation and measurement realistically of square wave response. In addition, the measured results of partial discharge by the sensors designed in GIS are given, and it is shown that the sensors designed are available for the measurement of partial discharge in GIS.     

Application of Wavelet Denoising in Partial Discharge Online Monitoring of Transformer

Because of the strong interferences, such as discrete spectrum interferences (DSI), white noise and pulse-shaped interferences, it is still a difficult work to extract the partial discharge (PD) signal for transformer online monitoring techniques. Through deeply study on the automatic selection of threshold value and mother wavelet, the wavelet-based de-noising method for partial discharge signals is proposed. The analyzing results on simulation signal and field-measured signal indicate that the proposed method is fit for de-noising white noise but for DSI the comparably worse de-noising results is acquired. Hence it is predicted that good de-noising results will be achieved with the wavelet-based de-noising method combined with digital filtering method fitting for de-noising DSI.     

The Application of Narrowband Interference Suppression in Direct Sequence Spread Spectrum

In order to improve the system effect, it is necessary take the technique of digital signal process to suppress interference, because of the finite gain and the narrow-band interference in system of direct sequence spread spectrum. The authors design a new filter structure improving on tunable digital heterodyne adaptive notch filters. This filter can adaptively track the interference frequency and control the bandwidth and depth of notch, which has the excellent agility and utility. The experiment proves this method overcomes limitation of other interference suppressions, hardly weaken the system performances, enhances the stability of the filter system, and can quickly track the interference frequency.     

Application of digital phase-locked loop and filtering technique in PWM rectifier

VHS-ADC high speed digital signal processing platform based on MATLAB and FPGA could be used to build three-phase voltage source rectifier with space voltage vector PWM(SVPWM).The initial phase of coordinate transformation from three phase static coordinate to two phase static coordinate which is called Park transformation and from two phase rotating reference frame to two phase static coordinate is uncertain. There existed noise in acquiring grid voltage and current. Digital phase-locked loop is added to follow the frequency and phase of grid voltage, FIR filter is added to process signal and reduce the interference. External voltage control loop, internal current control loop and the model of coordinate transformation are designed on the VHS-ADC platform. The small power experiment is conducted to verify the stability and feasibility of the control system. The experimental results show that the digital phase-locked loop and FIR digital filter can be applied to three-phase voltage source rectifier.     

A floating threshold quantization algorithm to suppressmixing interferences in partial discharge

Due to the obvious difference of energy distribution frequencies from partial discharge (PD) signal and its mixing interferences (white noise and narrow brand), we uses the characteristic that node decomposition coefficients of wavelet packet transform can effectively show the energy change of signals to build up a floating threshold quantization algorithm (FTQA) varying with the noise energy of PD decomposition coefficients. It makes the node thresholds under the optimal base various with the noise strength in decomposition coefficients to self adaptively reality the choice of optimal threshold to finely partition PD decomposition coefficients. For simulated and real PD signals with mixing interferences, the conditional global threshold quantization algorithm (GTQA) and the proposed floating threshold quantization algorithm are employed to suppress the mixing interferences in PD signals and compared, and the results show that the proposed algorithm has the stronger suppression ability to mixing interference on PD signal and keeps perfect PD waveform via suppression.     

GIS Partial Discharge Signal and Its Internal Sensor Detection

Partial discharge electromagnetic waves in GIS propagate is not only in the transverse electric and magnetic(TEM)mode, but also in transverse electric(TE) and transverse magnetic(TM)mode. The paper deduces out the mathematic expressions transient field excited by PD in GIS anywhere by using dyadic Green function theory. The contributions of TEM mode and all high order modes in the detecting frequency scope should be taken into consideration when calculating the electric field excited by PD in GIS. In simulative GIS laboratory, the designed inner couplers are superior to other outer sensors in detection of partial discharge. Inner couplers for the GIS model are developed and their frequency responses are analyzed in antenna model. At last the PD pulses excited by man-made defect are detected by inner couplers using high parameters oscilloscope.     

Application on Extracting Feature in State Monitoring and Fault Diagnosis

With the development and application of information and internet and virtual instrument technology ,the virtual globular company based on internet arises .To study remote state monitoring, remote fault detection and diagnosis about large scale, complicated and integrative equipment become very important. In the whole fault diagnosis system , the detecting ,data acquisition is original ,processing; transform and extracting features with the signal detected is a key factor. The theories and methods used in mechanical fault diagnosis is stated. The application of signal process and its feature extracting methods is introduced which are time domain, frequency domain and time frequency domain analysis, in state monitoring and fault diagnosis with its signal analysis. The processing method of random time variant special signal is given also.     

Relationship between Partial Discharge and Dissolved Gases Conentration in Oil

Long time partial discharge is bad for transfomers inside insulation and now partial discharge monitoring is not satisfactory because of electromagnetic interference and noise interference .This is a new way via dissolved gases concentration analysis to find partial discharge and acconding to diagnosis system to confirm partial discharge level. A basic research has been carried out to discover the correspondence relationship between partial discharge level and dissolved gases concentration,some valuable laws are gained for the first time.     

A Practical Method of Eliminating the White Noise of Partial Discharge with Wavelet

The white noise of PD(partial discharge) signal brings great difficult to the PD signal's processing, so eliminating the white noise is a necessary section. There are many methods of eliminating white noise, but none of them are suitable to the PD signal processing. Because PD signal and white noise have different Lipschitz exponents and different wavelet transform features in time-scales, a new eliminating white noise method has been brought forward that has simple operation and meets the timing need of PD signal's processing. After the processing with this method, the PD signal is not distortion and the effect of eliminating white noise is very good. This method can be applied to the processing of PD signal gotten from the site.     

THE RESEARCH OF MONITORING AND DIAGNOSING BALL BEARING FATIQUE ON LINE

This paper describes the research work of analyzing vibration signal to monitor and diagnose on line the ball bearing fatique. Carrying out a large mumber of life test on ball bearing test machine, it is discovered that in the so called "second effect" vibration signal as the bearing fatique occurs, apart from the two widely used spetrum charactersof "fraverse frequency" and "high frequency shock pulse" , there is another important but rarely known opcctrum characteristic of high frequency peaks existing in the middle-to-high frequency band.The generating mechanism, effect factors and test method of those high frequency peaks are researched tentativ tentatively. Two binds of device for monitoring abnd diagnos sing ball learing fatique on line are developed based ion this new type spectrum characteristic. One consists of a bandpass filter, the other is based on the spetrum characters which corns from the DDS ( Dynamic Data System ) modeling     

Performance Analysis of Anti-CW Interference in MC-CDMA Systems

The multicarrier-code division multiple access (MC-CDMA),which is the combination of direct sequence CDMA (DS-CDMA) and orthogonal frequency division multiplexing (OFDM) techniques, offers various advantages over single-carrier CDMA system. Some of the advantages are that MC-CDMA systems possess can remove the intersymbol interference (ISI) and enhance narrow-band interference suppression capabilities. So the MC-CDMA technique becomes a focus in the field of mobile communication. The authors introduce the typical MC-CDMA system model, discuss the decision statisticalvariable in Rayleigh fading channel included the CW interference, and give the expressions of probability of error in uplink. An approach is proposed with Modified Equal Gain Combining (MEGC) to decrease the effect of CW interference. Theoretical analysis and numerical results show that the anti-CW interference performance of MC-CDMA system can be improved used the MEGC approach.     

Simulation Propagation of Partial Discharge UHF Signals in Transformer

Many factors affect the propagation of ultra high frequency(UHF) signals caused by partial discharge(PD) on the waveforms and energy of signals in transformer.To investigate the relationshi Pof factors and UHF signals,simulation model of transformer for PD study are established.UHF signals in simulation model of transformer caused by PD are calculated using finite difference time domain method.By means of amplitude and cumulative energy plot of simulation signals,and combing the measured result,the following factors:distance between PD source and detection position,different metallic conductor position around detection position and iron core and winding are researched,which contribute to comprehend the propagation characteristic of UHF signals and detect UHF signals accurately.     

基于广义谐振理论的输电线路中波无源干扰谐振频率预测

现有IEEE（institute of electrical and electronics engineers）标准,目前只能明确0.5~1.7 MHz有限频段的输电线路无源干扰谐振机理。为拓展输电线路无源干扰谐振的研究频率,引入广义谐振理论,提出了一种基于电磁场能量平衡的干扰谐振频率预测构想。将大尺度空间下输电线路铁塔阵列及天线等效为广义封闭系统,从而基于复坡印廷定理,推导了电磁开放系统广义谐振因子的表达式,求解得到的广义谐振因子零值点为无源干扰谐振频点。该方法由于避开了传统将铁塔等效为半波天线的局限,因此可以实现中波频段无源干扰谐振预测。采用IEEE标准算例进行验证,结果表明：1.7 MHz频率以下,基于广义谐振理论的无源干扰谐振频率预测值和缩比模型实测值最大误差不超过±0.169 MHz。     

Impact of Main Factor on Radio Channel of LMDS System

Characteristics of radio channel play a key role in stabilization and reliability of LMCS/LMDS system at centimeter and millimeter. Rain specific attenuation has been recognized as a principal cause for impact system performance in LMDS and satellite communications systems operating in the same frequency band. In contrast to mobile communication system, multipath is not a typically problem for LMDS system, because directional antennas are used and the antennas are sufficiently high providing a line of sight propagation path between the transmitter and receiver. Moreover, the effects of buildings, foliage, and dust storms shouldn't be ignored. The impact of these factors on signal propagation and propose corresponding models is discussed. At the last,antenna height and directivity are used in the classification of statistical channel models for LMDS.     

数字图像监测作物生长特征的研究进展

为对作物进行田间数量化管理以及长势监测,从数字图像监测作物长势的基本原理、数字图像获取方法、图像分析处理技术以及数字图像在作物长势监测方面的应用4个方面进行概述,简要归纳了数字图像基本原理、获取及分析方法,总结出可以利用数字图像实现作物覆盖度、叶面积指数、生物量、氮素营养诊断进行监测,认为对于数字图像的获取应明确获取标准,要根据具体情况选取分析方法,同时在今后可以利用专家模型,多角度评判作物长势,以期为实现作物的精确管理提供参考。     

Numerical analysis on the performance of spiral antennas

The surfaces of the Planar Spiral Antennas and Conical Spiral Antennas are analyzed with planar triangle. The surface currents of the antennas are solved by using the Method of Moment (MoM) based on the RWG basis function. The input impedance, directivity, gain, radiated power and radiation field of the antenna can be found. The results indicate that, in very wide frequency band, the value of the input impedance equals to the theoretical value of Self-Compensated antennas (in agreement with Babinet-booker' principle), which is,188.5 ohm , the half of the wave impedance of free space, while the directivity, gain and radiated power are stable within the frequency band. When the antenna is driven by the signal of derivative Gaussian pulse, the radiating electric field waveform is obtained by the Fourier transform. When the spiral antenna is used as the pulse radiation antenna, the waveform of the radiation electric field shows the characteristics of the Gaussian quadratic differential.