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.     

Development of discone antenna for noncontact partial discharge detection

To realize the noncontact detection of partial discharge of electrical equipment within some range,a wideband,good gain and horizontal plane omnidirectional ultra-high frequency antenna is researched,and it is used as detecting sensor of partial discharge(PD) signals. Characteristic radiation and characteristic impedance of discone antenna are analyzed,and it is found that it is dominant to design the dicone antenna as UHF signal detecting antenna. Then the structure of the antenna is optimized via calculate simulation. The band of the discone antenna is from 200 MHz to above 2 GHz and its average gain is above 4 dB. It is made via discrete method according to the analysis and simulation result,satisfying the design demand. The discone antenna shows good performance to detect analog discharge signals and PD signals in substation from far away. Fixed and mounted PD monitoring system can be developed based on this antenna,and the system can monitor PD of electrical equipment within substation without contacting equipment.     

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.     

Study on the testing device for simulating the partial discharges of different defects in gas insulated switchgear

To overcome the shortage of existing experimental device for partial discharges in gas insulated switchgear(GIS),an installation for testing PD in GIS with multi-structures is designed, which can simulate T-type,L-type and line-type configurations of GIS expediently. The physical dimension and material parameter are given by calculating the characteristic of the propagation of ultra-high frequency electromagnetic waves and the stress of materials. The experiments under single defect and multiple insulation defects are carried on by using the designed 4 physical models of typical insulated defects for GIS. The results show that the built device can simulate the PD,TE mode and TM mode waves with different wave bands in GIS. The system makes a foundation for the further investigation of the electromagnetic waves propagation,the conditions of generating electromagnetic waves,testing method and pattern recognition of the PD in GIS.     

PD Online Measurement of Transformers with Wide Frequency Band System and the Noise Eliminating Method by Cascaded IIR Lattice Notch Digital Filter

The frequency band of conventional partial discharge (PD) measurement systems is selected just within several ten kilohertz. With the development of computer and digital signal processing techniques, wide frequency band (WFB) measurement systems have been used to detect PD in electrical equipment for its higher sensitivity. Nevertheless, the WFB measurement systems are easy suffered from the interference of strong field electromagnetism noises. A set of PD online monitoring system with frequency band from 50 kHz to 1 megahertz used for transformer is developed, in which pre-processing device and cascaded 2nd order IIR lattice notch digital filter are mainly used to suppress periodic narrow-band interference. With analysis of field monitored signal at a 220 kV substation, it is shown that the monitoring system not only can detect and extract the discharge pulse signal effectively, but also has the powerful capability of suppressing interference.     

The fractal characterization of pore structure for some numerical rocks and prediction of permeabilities

This paper uses the fractal theory of pore structures for porous media to study the fractal characterization of pore structure for nine numerical rocks. The results show that the fractal dimension of solid phase is usually greater than the pore fractal dimension, and its fractal scaling regions is less than the one of pore phase. This indicates that the numerical rock is an approximate two-phase fractal porous media. The porosities, volume fractions and permeabilities of nine numerical rocks are predicted. The results show that the fractal theory about pore structures of numerical rocks is effective in describing the porosity and permeability. Moreover, it seems to be more effective for solid phase in approximate two-phase fractal porous media. When predicting permeability using the fractal theory, it is very important to accurately determine the maximum pore size and the range of statistical self-similarity. By comparing the two kinds of predicted permeabilities,it is found that the FT method used by this paper is more accurate, more general and less computational cost than the PNEM method which has been worldwide used.     

Analysis on the ultrasonic online location for partial discharge in the stator winding of generator

The propagation characteristics of the partial discharge’s ultrasonic signal in the stator of generator and the difference between the ultrasonic signal and the running background noise are analyzed with experiments. Ultrasonic online location for partial discharge is proven to be feasible. For non blind area monitoring, the stator is divided into several equal parts. Locating equations are established with electroacoustic detection method and optimized with genetic algorithm. The simulation results indicate that the proposed method of ultrasonic online location for the partial discharge in the stator of generator is correct.     

Adsorption Characteristics of Pb ~(2+) in Pb-Zn Mine Rock of Yunnan

Under the condition of static state, adsorption characteristics of rock in Pb Zn mine of Yunnan have been studied by using conductance method and fractal geometry theory. For sand rock and breccia , the pH of solution in the process of dissolving increases and finally approaches 7, and pH increases slowly for the later because of the compaction of breccia . The conductivity of solution increases with the increase of time when the concentration of Pb 2+ is lower, whereas when the concentration of Pb 2+ is higher. In the process of adsorption ions in rock are entered in solution. Adsorption capacities ( Q ) of two rocks are bigger, and the Q of Pb 2+ in them obey Freundlich experiential formula. The process of adsorption is fractal like, and mean while the kinetics equation is derived.Ability of adsorption of sand rock is weakened while the temperature of the solution is increased.     

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.     

Characteristics of UHF partial discharge signal waveforms of typical insulated defects in GIS

In order to analyze the discharge features of different insulation defects in various experimental conditions, according to characteristics of partial discharge (PD) from the insulation defects in gas insulated switchgear (GIS)) and using ultra high frequency (UHF) method, a lot of PD experiments are carried out based on the designed four typical physical models of insulation defects of GIS in the simulation device, and the real samples of UHF PD waveforms are recorded. The features of UHF PD waveforms in the different situations are discussed and analyzed in detail, which include different sizes or positions of the physical models or under the different voltages and so on. The results show that in low voltage, regardless of types of UHF electromagnetic wave excited by PD sources, the shapes of PD waveform changed little before the changes of waveform. The remaining time is about several nanoseconds.     

Study on separation algorithm of convolutive mixing model and separation of mixing signals of multiple partial discharges

To identify individual partial discharges(PD)signals produced by multiple insulation defects in gas insolated switchgear (GIS),this paper analyses the mechanism of propagation and mixing of multiple PD electromagnetic wave signals in GIS cylinder and proposes the convolutive mixing model to describe it for a separation algorithm to acquire individual PD signals. With the non-stationary property,mixing PD signals are changed at time domain into a set consisting of short-time stationary PD signals and then the Molgedey-Schuster decorrelation approach is employed to separate these stationary PD signals at frequency domain. The correlation of the envelope of separated PD signals in this set is used to reconstruct PD signals to realize the separation of non-stationary UHF PD mixtures. The effective separation of actual UHF PD mixing signals validates the assumption of convolutive mixing process in GIS and also offers a new approach to the identification of mixing PD signals by external ultra-high frequency detection scheme from multiple insulation defects in GIS.     

Deductive Models of Concentration Field for Locating the Death in Mine and Its Application

Based on the idea of locating the death in the collapsed area of mine by the gas released from the organism decomposition proposed by the authors, this paper presents the Least Multiply Square (LMS) model for the location and develops two kinds of ANN models for the locating computation. The results of the organism decomposition experiment indicates that the Back Propagation (BP) is better for locating the death in mine. Above works are set up the foundation of the theoretical analysis and the technical development for locating the death by analyzing the concentration distribution of the marker gas, mercaptans, in mine. Based on the technology developed, the period, for the rescue team members staying in that risk area, can be shorten. The rescue work achieve a step forward for more reasonable, feasible and efficient.     

Application of Self-tuning Models to Air Handling Units for Fault Detection

Building management control systems (BMCS) are widely employed in modern buildings. The huge amount of data available on central stations and outstations provide rich information for fault diagnosis of HVAC systems. An online fault diagnosis method for variable air volume air handling units was presented using self-tuning HVAC component models. The model parameters are tuned online by using a genetic algorithm (GA) which minimizes the error between measured and estimated performance data, so high modeling accuracy is assured. If the error between measured and estimated performance data exceeds preset thresholds, it means the occurrence of faults or abnormalities in the air handling unit system. The statistical method of selecting thresholds also is presented. The fault detection method was tested and validated using data collected from real HVAC systems. The results of validation show that the fault detection method can be integrated in BMCS systems to detect faults in air handling unit systems efficiently.     

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.     

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.     

Design of GIS-based monitoring and maintenance decision support system for urban sewage pipe network

Monitoring and maintenance of sewer system is important to city water environmental management. A method for pipeline monitoring and maintenance decision support system (PMMDSS) based on geologic information system (GIS) and decision making system (DSS) is developed for upgrading sewer system maintaining efficiency. Visual basic (VB) and standardized Active X components are employed in PMMDSS, which selected SuperMap Objects as the development platform. PMMDSS integrates the spatial and model system to achieve the decision analysis for the sewer system monitoring and maintenance. An application Software is developed based on a case study in Yuechi Country of Sichuan Province. The software can be used to dynamically monitor the heath condition and provide an optimum visual decision making platform for the city sewer system.     

Fractal Characteristic of Electric Polarization Feature of Coal

The dielectric response of charge carriers in disordered materials results from the process of fractal time and the conductance of the fractal structure. The medium metamorphism coal is one kind of structural disordered materials . So, electric polarization feature of coal has been further studied by using fractal geometry theory of time. The result shows that electric polarization property of coal in direct current electric field has fractal characteristic. The relation between b constant of polarization and fractal time dimension is:D t=kb, and the constant k may be relevant to metamorphism degree of coal.     

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.     

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.     

The Geometric precision and Performance Analysis for machining Surface based on Fractals

A new analysis method for machining surface profile error is presented in this paper.The linear regression and nonlinear regression are first applied respectively,and then the Weierstrass Mandebrot fractal function is used to obtain the fractal parameters of machining profiles.A minimal parameter set which depicts the machining surface geometric precision is set up,and the surface profile can be reconstructed using these parameters,and an analysis method for part performance and its tolerance structure is proposed.Examples are provided to illustrate the method is feasible and effective.