N. K. Kishore

A wavelet multiresolution analysis for location of faults on transmission lines

Faults on EHV lines are quite common. They cause disruption in power supply. Accurate location of faults will result in faster maintenance and restoration of supply. This paper presents a new method for the location of faults based on wavelet multiresolution analysis (MRA). EMTP (Microtran) is employed to generate the time domain input signal. Daubechies eight (D-8) wavelet transforms of the three phase currents on transmission lines from both the ends are used. The effects of fault inception angle and fault impedance are examined. Extensive simulation work has been carried out and results indicate that the proposed method is very effective in locating the fault with a high accuracy.

A wavelet multiresolution-based analysis for location of the point of strike of a lightning overvoltage on a transmission line

Lightning flashes on extremely high voltage lines are quite common and can lead to insulation breakdown or other line hardware failure causing disruption in supply. An accurate location of the site of failure will result in faster maintenance and restoration of supply. In this paper, a novel technique based on the wavelet multiresolution analysis (MRA) for locating the point of strike of a lightning overvoltage on a transmission line is presented. Lightning strikes at different points on a 400-kV transmission line of different line lengths are simulated by shifting the point of strike of the lightning impulse every 5 km. The Electromagnetic Transient Program (EMTP) [Microtran] is employed to generate the time-domain input signal. Daubechies eight (D8) Wavelet transform is used to analyze lightning overvoltages. The tenth level output of MRA detail signals extracted from the original signals is used as the criterion for the analysis. Extensive simulation work has been done and results indicate that the proposed scheme is very effective in locating the point of strike with reasonable accuracy.

Uniform electric-field-induced lateral migration of a sedimenting drop

We investigate the motion of a sedimenting drop in the presence of an electric field in an arbitrary direction, otherwise uniform, in the limit of small interface deformation and low-surface-charge convection. We analytically solve the electric potential in and around the leaky dielectric drop, and solve for the Stokesian velocity and pressure fields. We obtain the correction in drop velocity due to shape deformation and surface-charge convection considering small capillary number and small electric Reynolds number which signifies the importance of charge convection at the drop surface. We show that tilt angle, which quantifies the angle of inclination of the applied electric field with respect to the direction of gravity, has a significant effect on the magnitude and direction of the drop velocity. When the electric field is tilted with respect to the direction of gravity, we obtain a non-intuitive lateral motion of the drop in addition to the buoyancy-driven sedimentation. Both the charge convection and shape deformation yield this lateral migration of the drop. Our analysis indicates that depending on the magnitude of the tilt angle, conductivity and permittivity ratios, the direction of the sedimenting drop can be controlled effectively. Our experimental investigation further confirms the presence of lateral migration of the drop in the presence of a tilted electric field, which is in support of the essential findings from the analytical formalism.

Simulation and Analysis of Acoustic Wave Propagation due to Partial Discharge Activity

Acoustic detection of partial discharges is based on the retrieval and analysis of mechanical signals produced by partial discharges. Acoustic method is widely used in locating partial discharge sources in transformers. For source location constant velocity of acoustic signals is used. Acoustic method also has potential to classify the partial discharges for better assessment of insulation condition. This paper presents a computer simulation of acoustic signal and analysis of its propagation behavior. It is found that acoustic velocity is not constant over distances of practical interest. An algorithm proposed for source location with distance dependent acoustic velocity leads to reduction in location error. Acoustic pulse produced by partial discharges is deformed and attenuated while propagating through transformer to sensor. This change depends on propagation distance and medium. So, frequency spectrum of sensor output AE pulse is not true representation of source pulse frequency spectrum. Partial discharge classification based on the output acoustic signal can lead to wrong classification. Knowing the location of partial discharge source, frequency dependent attenuation characteristics and output acoustic signals frequency spectrum, an estimation of input pulse frequency spectrum and its parameters is made for the classification of partial discharges

Identification and Classification of Faults on Transmission Lines Using Wavelet Multiresolution Analysis

This article presents a new method for identification and classification of faults based on wavelet multiresolution analysis (MRA). Daubechies eight (D-8) wavelet transforms of the three phase currents on a transmission line are used. The peak absolute value, the mean of the peak absolute values, and summation of the third level output of MRA detail signals of current in each phase extracted from the original signals are used as the criterion for the analysis. The effects of fault distance, fault inception angle and fault impedance are examined. Extensive simulations are carried out to generate time domain input signal using EMTP (Microtran) on a 400 kV, 300 km long line and simulation results show that the proposed method is a simple, effective and robust method suitable for high impedance faults also.

Frequency domain analysis of acoustic emission signals for classification of partial discharges

Online monitoring of partial discharges (PD) can reduce the risk of catastrophic failure of power apparatus. Acoustic emission technique is advantageous for online PD measurement and is adopted here. Partial discharges are classified according to the origin of discharges and their effects on insulation deterioration are also different. This paper reports experimental results and analysis for classification of partial discharges using acoustic emission signal. Acoustic emission signal produced by PD are detected by sensors mounted on the experimental tank surface, stored on an oscilloscope and fed to computer for analysis. The AE signals are analyzed in frequency domain for classification. Amplitude spectrum and power spectrum of acoustic signals are examined. The frequency domain parameters calculated are frequency at peak magnitude, median frequency & percentage signal energy in frequency band. These parameters are used for classification of partial discharges.

Sparkover in sphere gaps with alternating voltages and perturbed electric fields

Quasi uniform field gaps, namely sphere gaps are quite often used in high voltage laboratories. In the present work, both simulation and experimental results to see the electric stress distribution on breakdown voltage are presented. Considering commonly used vertical arrangement of sphere gaps, disruptive discharge voltages are measured experimentally. These experiments are with one sphere grounded. In order to study the redistribution of electric stresses, experiments have been conducted by placing a hemi-spherically tipped rod (needle), near the gap axis. This rod is placed vertically on the ground plane being at ground potential. Experimental results are reported with the rod diameter of 3 mm and its height 10 cm as a function of sphere-gap separation. Experimental results reported are with power frequency alternating voltages. The simulations corresponding to these experimental conditions are reported to correlate the change in electric field distribution obtained by charge simulation models (CSM). Interpreting the experimental breakdown results in relation with simulation results of geometric electric field is attempted. The results with rod in the vicinity of sphere gap results in to a non axi-symmetric field. These are simulated to obtain the maximum stress on the electrodes.

Identification and Localization of Multi-source Partial Discharges by Acoustic Measurements in Oil-pressboard Insulation System

Partial discharges (PD) deteriorate insulation of power apparatus and lead to final failure. Early detection and localization of PD can avoid unwanted failure of power apparatus. There are different techniques for PD detection. Acoustic emission technique for partial discharge detection is advantageous for online detection and source location. Normally, acoustic PD detection and location is based on the assumption of a single PD source. But in practice, more than one source of PD is present and they may be active simultaneously in a power apparatus. This paper addresses the identification and localization of two simultaneous PD sources employing acoustic emission technique in oil pressboard insulation system. The PDAE signals from two simultaneous PD sources are analyzed using wavelet analysis with time frequency resolution and Independent Component Analysis for identification and localization.

Studies on Pulsed Electric Field applications for food sterilization

The present investigation studies the effects of application of repetitive micro-second duration high-voltage double-exponential shaped pulses on water samples containing E. Coli. A high-voltage repetitive pulse generator has been developed to apply these pulses. The design of chamber, operational parameters, and their optimization for the process, the wave-shaping circuitry and the switching circuitry is given utmost importance. It is suggested that repetitive pulse application of the order of about 25-kV/cm electric field intensity be employed for the purpose. Pulsed electric field processing is nonthermal energy efficient alternative to thermal pasteurization techniques. It is applicable in many liquid food processing industries like drinking water segment, beer & beverages, fruit juices and milk.

Detection of electrical discharges in DC accelerator using photomultiplier tubes

Detection of Electrical Discharges using chemical, electrical, acoustic and optical techniques holds key to the protection of any high voltage (HV) system. DC Accelerator, being a HV system is prone to various electrical discharges. In DC Accelerators, optical technique promises better performance than other detection techniques due to its fast response and inherent immunity to electromagnetic noises. Photomultiplier tubes (PMT) are used for collecting the discharge signatures. Experimental prototypes of the accelerator discharges are developed. PMTs are used to detect the signals from these discharges.