The Effects of Short Circuits at Medium Voltage Transformers

2019 ◽  
Author(s):  
Alexandru Vasile Hotea ◽  
Radu Adrian Tirnovan ◽  
Liviu Neamt
Keyword(s):  
Medium Voltage ◽  
Short Circuits

scholarly journals Incomplete Cross-Bonding in the MV Line. Experience from the Operation of MV Single Cable Lines

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5292
Author(s):  
Krzysztof Dobrzynski ◽  
Zbigniew Lubosny ◽  
Jacek Klucznik ◽  
Janusz Grala ◽  
Dominik Falkowski
Keyword(s):  
Mathematical Model ◽  
Power Systems ◽  
Power Losses ◽  
Cable Line ◽  
Medium Voltage ◽  
Economic Justification ◽  
Line Section ◽  
Short Circuits ◽  
Cable Lines ◽  
The Mathematical Model

Cable lines are one of the basic components of power systems. Medium and high voltage cables mainly comprise a metallic sheath, which is concentric to the main core conductor. There are several operating schemes of such cable lines, which differ in the place of earthing of sheaths and the possible use of the sheaths and/or conductors crossing. The sheaths cross-bonding is typically done in two places of one cable line section, and it allows to reduce power losses. Nevertheless, the use of incomplete sheaths crossing—only in one place on cable route may have economic justification. The paper presents an incomplete sheaths cross-bonding analysis of an existing medium voltage cable line. The results obtained by the mathematical model are validated by measurements taken on 30 October 2019 on an existing cable line. Measurements recorded on a real object for various systems of crossing sheaths are presented. The influence of incorrect sheaths crossing on the measured quantities was shown. In addition, the risk of excess voltage on the sheaths during short-circuits has been verified using a mathematical model.

scholarly journals General earth fault protection for MV networks using wavelet decomposition and Bayesian criterion

2019 ◽  
Vol 84 ◽  
pp. 02007
Author(s):  
Lubomir Marciniak
Keyword(s):  
High Resistance ◽  
Wavelet Decomposition ◽  
Harmonic Distortion ◽  
Sampling Frequency ◽  
Selective Detection ◽  
Medium Voltage ◽  
Bayesian Criterion ◽  
Fault Protection ◽  
Probability Criterion ◽  
Short Circuits

For selective detection of earth faults in medium voltage networks, the general protection can be used, which unlike individual protections controls earth currents in all lines supplied from the substation. To detect high-resistance and arc faults, it is possible to use in such protections the details from wavelet decomposition of earth currents and the Bayesian conditional probability criterion. The paper presents a protection model using details of earth currents and the Bayesian criterion. Significant parameters of the model were determined: sampling frequency, wavelet types and decomposition levels, parameters of the probability density function and decision conditions. The effectiveness of the protection in the case of non-stationary high-resistance short-circuits in the network with natural asymmetry and harmonic distortion was also assessed.

Prospects for convergent beam electron diffraction with a 200kV cold field-emission transmission electron microscope

1991 ◽  
Vol 49 ◽  
pp. 466-467
Author(s):  
J W Steeds ◽  
R Vincent
Keyword(s):  
Field Emission ◽  
High Performance ◽  
Small Diameter ◽  
Convergent Beam Electron Diffraction ◽  
Zone Axis ◽  
Medium Voltage ◽  
Transmission Electron ◽  
Good Crystallinity ◽  
Special Modification ◽  
Convergent Beam

We review the analytical powers which will become more widely available as medium voltage (200-300kV) TEMs with facilities for CBED on a nanometre scale come onto the market. Of course, high performance cold field emission STEMs have now been in operation for about twenty years, but it is only in relatively few laboratories that special modification has permitted the performance of CBED experiments. Most notable amongst these pioneering projects is the work in Arizona by Cowley and Spence and, more recently, that in Cambridge by Rodenburg and McMullan.There are a large number of potential advantages of a high intensity, small diameter, focussed probe. We discuss first the advantages for probes larger than the projected unit cell of the crystal under investigation. In this situation we are able to perform CBED on local regions of good crystallinity. Zone axis patterns often contain information which is very sensitive to thickness changes as small as 5nm. In conventional CBED, with a lOnm source, it is very likely that the information will be degraded by thickness averaging within the illuminated area.

Atomic structure imaging of the Si/SiO2 interface with high-resolution electron microscopy

1986 ◽  
Vol 44 ◽  
pp. 390-391
Author(s):  
J.L. Batstone ◽  
J.M. Gibson ◽  
Alice.E. White ◽  
K.T. Short
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Atomic Structure ◽  
High Resolution Electron Microscopy ◽  
Medium Voltage ◽  
Voltage Electron ◽  
Resolution Electron ◽  
Structural Image ◽  
Electron Microscopes ◽  
Point To Point

High resolution electron microscopy (HREM) is a powerful tool for the determination of interface atomic structure. With the previous generation of HREM's of point-to-point resolution (rpp) >2.5Å, imaging of semiconductors in only <110> directions was possible. Useful imaging of other important zone axes became available with the advent of high voltage, high resolution microscopes with rpp <1.8Å, leading to a study of the NiSi2 interface. More recently, it was shown that images in <100>, <111> and <112> directions are easily obtainable from Si in the new medium voltage electron microscopes. We report here the examination of the important Si/Si02 interface with the use of a JEOL 4000EX HREM with rpp <1.8Å, in a <100> orientation. This represents a true structural image of this interface.

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