Electrical devices in transmission and distribution networks are submitted to
fast front transients. These transients are often a cause of a failure in the power
system. To simulate these phenomena, ...it is necessary to detailly model all the
components of the power system. This paper concentrates on studding transformer
internal failures due to voltage stress that can occur when fast front
electromagnetic wave travels through the transformer. To prevent a failure, an
internal insulation of the transformer has to be dimensioned to sustain these
transient phenomena. Therefore, it is necessary to use advanced wideband
transformer models for its dimensioning.
In this paper, a wide band transformer model based on limited transformer
geometry is used to simulate evaluate the stresses on internal transformer
insulation in the case of fast front transients. The model is validated for calculation
of internal overvoltages with the test case from CIGRE brochure.
Nekompaktna lijeva klijetka (NLK) rijetka je kardiomiopatija, koja se danas znatno češće otkriva u kliničkoj praksi zahvaljujući suvremenoj ultrazvučnoj dijagnostici. Bolest je uzrokovana zastojem ...normalne embrionalne pretvorbe endomiokarda iz mreže isprepletenih mišićnih vlakana u zreli kompaktni miokard. Morfološki se manifestira jedinstvenom dvoslojnom strukturom miokarda, koju čine unutarnji hipertrofični nekompaktni i subepikardijalni tanki kompaktni sloj, najčešće u inferiolateralnim i apikalnim segmentima lijeve klijetke. Unutarnji sloj tvori isprepletena masa mišićnih niti i trabekula s protočnim intertrabekularnim recesusima. Dijagnosticira se u infantilnom i adultnom obliku, koji se javljaju sporadično ili u obitelji, spolno vezano, odnosno autosomno dominantno. Prepoznavanje ove bolesti bitno je zbog visokog pobola i smrtnosti uzrokovanih progresivnim zatajivanjem srca, tromboembolijskim incidentima i malignim aritmijama. Ehokardiografija je metoda izbora u dijagnozi i praćenju bolesnika s NLK. U radu su sažeti najnoviji literaturni podatci o patogenezi, dijagnostičkim postupcima i liječenju ove bolesti.
Events such as lightning, switching of vacuum circuit breaker or switching operations in gas
insulated substation (GIS) generate high frequency overvoltages. An equipment in a transmission or a
...distribution system has to be protected against such phenomena.
Unfortunately, the traditional transformer models available in Electromagnetic transient simulations
program (EMTP-like) software packages are not capable of representing transformer behavior in a transient
state, which includes high frequencies. Moreover, high frequency transformer models are often too complex
or require confidential information on transformer geometry. However, in the design stage of insulation
coordination it is particularly important to accurately calculate transmitted overvoltages through
transformers.
In the scope of this paper two different transformer models for high frequency, are developed in an
EMTP-type software program. The first model named “Black box” derives solely from the values measured
on the transformer terminals and does not require any knowledge of the transformer inner geometry. The
second model named “Grey box”, is based on a lumped RLC parameters network, whose values are
derived from the simple geometry of the transformer window and from the nameplate data. Furthermore,
the models’ capabilities to characterize a transformer at high frequencies are analyzed. The case study is
done on a distribution transformer which is to be located inside a power plant. The transmitted overvoltages
calculated with the models in the EMTP-type software program are compared with measurements.
The paper describes the fatigue strength assessment of ship hull girder according to Common Structural Rules for Oil Tankers (CSR). Additional criteria for hull girder fatigue calculation have ...recently been introduced into CSR because of frequent crack appearances on the main deck structure of large tankers. Hull girder fatigue check in CSR is performed in two steps: preliminary “fatigue section modulus” verification and detail fatigue calculation of deck longitudinals. The analysis is performed for an Aframax oil tanker fully complying with “old” rules of classification societies. Since the results of fatigue calculation for initial structure have not been found acceptable, a significantly increased hull section modulus is necessary as the only practical way for the deck longitudinal fatigue life improvement. In practice, the vertical wave bending moment at midship, as the primary cause of hull girder fatigue damage, is calculated according to a simplified CSR formula. In order to improve the knowledge of its influence on the calculated fatigue life, the wave bending moment is also determined directly by a hydrodynamic and statistical analysis.
In that analysis, the North Atlantic navigation is assumed as design wave environment for three predominant loading conditions. It is obvious that such an approach enables a more detailed and rational fatigue analysis than the one carried out according to the CSR rules.
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