Improving the Error of Time Differences of Arrival on Partial Discharges Measurement in Gas-Insulated Switchgear

Partial Discharge (PD) detection based on Ultra-High-Frequency (UHF) measurements in Gas-Insulated Switchgear (GIS) is often used for fault location based on extraction of Time Differences of Arrival (TDoA), and the core technique is to obtain the precise time difference of each UHF signal. Usually, TDoA extraction algorithms can be categorized as cross-correlation function method (CCF), minimum energy method (ME), and threshold value method (TV) are not qualified to analyze the time difference with high accuracy and efficiency, especially the complicated UHF PD signals in the field. In this paper, multiple tests were carried out based on the real GIS UHF signals. Three typical algorithms (CCF, ME, and TV) were used to extract and calculate the TDoA of UHF signals. Afterwards, depending on the disassembly of equipment, the accuracy and effective range of the algorithms are analyzed by means of error and variance. To minimize the error and the variance, an average method with the combination (CA) and portfolio of traditional algorithms is proposed and verified in different situations. The results demonstrate that the improved algorithm could increase the accuracy of time difference extraction, less than 4.0%.

Localizing Swimming Objects in Noisy Environments by Applying Nearfield Acoustic Holography and Minimum Energy Method

A problem in localizing individual swimming objects acoustically is the high amount of strongly fluctuating ambient noise due to turbulent pressure fluctuations, thermal and seismic noise, motoring vessels, wind and marine mammals. In littoral and other shallow waters additionally the complex boundaries produce absorption of high-frequency components and strong reverberation in other frequency regions, refraction due to sudden changes in temperature and scattering from the rough sea surface and floor. In this paper localization of a single swimming object in presence of disturbing sources and noise is simulated. Low-frequency nearfield acoustic holography (NAH) based on vector hydrophone array measurements is combined with minimum energy method (MEM) to increase detection certainty. This combination of NAH and MEM appears to be a reliable and robust detection method suitable e.g. for sort-range navigation in littoral waters and for iceberg detection in open waters.

Simulation of Two Dimensional Nanoscale Cutting Copper by Quasi-Steady Molecular Statics Method

An orthogonal cutting is a symmetric cutting thus it can be modified as a two dimensional cutting. This paper uses quasi-steady molecular statics method to carry out simulation of two dimensional nanoscale cutting copper work piece by the diamond tools. For the two dimensional quasi-steady molecular statics nanoscale cutting model used by this paper, when the cutting tool moves on a copper work piece, displacement of atoms is caused due to the effects of potential on each other. After a small distance that each atom moves is directly solved by the calculated trajectory of each atom, the concept of force balance is used. The minimum energy method is employed to carry out the search, and obtain the new movement position for each atom. Based on the simulation results, this paper studies the chip formation shape and cutting forces in x direction and y direction.

An experimental and theoretical study of the mixing characteristics of a periodically reoriented irrotational flow

The minimum-energy method to generate chaotic advection should be to use an irrotational flow. However, irrotational flows have no saddle connections to perturb in order to generate chaotic orbits. To the early work of Jones & Aref (Jones & Aref 1988 Phys. Fluids 31 , 469–485 ( doi:10.1063/1.866828 )) on potential flow chaos, we add periodic reorientation to generate chaotic advection with irrotational experimental flows. Our experimental irrotational flow is a dipole potential flow in a disc-shaped Hele-Shaw cell called the rotated potential mixing flow; it leads to chaotic advection and transport in the disc. We derive an analytical map for the flow. This is a partially open flow, in which parts of the flow remain in the cell forever, and parts of it pass through with residence-time and exit-time distributions that have self-similar features in the control parameter space of the stirring. The theory compares well with the experiment.

On the Predictive Power of the Minimum Energy Condition

We reexamine the minimum energy method to determine the magnetic field strength in spiral galaxies from the cosmic ray standpoint of view. It is shown that for example in M51 the estimated field strength is about a factor of 2 lower than obtained with the standard method. As a by-product the corresponding γ-ray flux from the galaxies can be calculated, which will allow further improvement of the method provided reliable γ-ray spectra are at hand.