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1

3D Stray Field Analysis of Transformer Cores Considering DC-bias

Mulasalihovic E., Pfutzner H., Zanolin P.

Przegląd Elektrotechniczny

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2011

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R. 87, nr 9b

57-60

EN

The paper presents experimental analyses of stray field configurations of a 3-phase/3-limb model transformer core. Core-tank interactions are roughly simulated arranging a steel plate above the core. The paper considers also DC-bias, caused e.g. by geomagnetically induced currents (GICs). For the determination of stray field distributions B(x,y,z,t) an automatic scanning system was applied, based on the 3D Hall sensor method. A sensor with four needle contacts was used for non-destructive 2D analyses of local distributions of eddy current fields E(x,y,t) as arising at the upper and lower surface of the simulated tank material. The results reveal strong increases of stray field through weak bias if arising in a nonbalanced way. In the tank simulation plate, mainly cross-sectional eddy currents are generated, flowing perpendicular to the limbs as a rough tendency. Bias yields very strong enhancements of eddy current losses. Above the tank simulation, a considerably strong rest stray field arises. As a rough tendency, it is directed from one yoke to the other one, however, with complex reconstructions as a function of time. The novel methodology promises to complement traditionally performed numerical analyses in a effective way.

PL

Przedstawiono analizę pola rozproszonego w trzyfazowym modelu rdzenia transformatora podmagnesowanego polem DC. Źródłem takiego pola mogą być na przykład pola geomagnetyczne. Zastosowano automatyczny system skanera wykorzystującego czujnika Halla. Do analizy pola elektrycznego od prądów wirowych wykorzystano czujniki igłowe. Badania wykazały znaczący wpływ podmagnesowania. Zbiornik symulowano przy użyciu płytki stalowej. Podmagnesowanie znacząco zwiększało też straty od prądów wirowych.

2

Investigation of GIC effects on core losses in single phase power transformers

Mousavi S.A., Engdahl G., Agheb E.

Archives of Electrical Engineering

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2011

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Vol. 60, nr 1

35-47

EN

This paper presents a method for estimation of core losses in banks of single phase power transformers that are subjected to an injected DC current such as geomagnetically induced currents (GIC). The main procedure of the core loss calculation is to obtain a magnetic flux density waveform in both time and location by using a novel algorithm based on 3D FEM inside the core and then to calculate the loss distribution based on loss separation theory. Also, a simple and effective method is proposed for estimation of losses of asymmetric minor loops by using combination of symmetric loops. The effect of DC biasing on core losses in single phase power transformers is investigated and the sensitivity of core type and material is evaluated. the results shows that DC current biasing could increase core losses up to 40 percent or even more.

3

Complete surface analysis of model transformer core considering dc-magnetization components

Mulasalihovic E., Pfűtzner H., Zanolin P.

Przegląd Elektrotechniczny

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2009

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R. 85, nr 1

43-46

EN

The paper describes a complete surface analysis of a 3-phase model transformer core considering dc-magnetization, caused e.g. by geo-magnetically induced currents (GICs). A multi-parametric sensor was used for non-destructive analysis of local distributions of magnetic field components, eddy current field components, off-plane flux and classical eddy current losses. Results are given for mere AC excitation and for additional DC excitation of the S-limb. The established data prove to visualize in a most effective way which core regions are affected by phenomena like rotational magnetization or planar eddy currents due to stray flux which tends to be strongly enhanced from GICs.

PL

Artykuł opisuje analizę powierzchni modelu rdzenia transformatora trzyfazowego uwzględniającą magnetyzację DC powodowaną między innymi geomagnetycznymi prądami indukowanymi. Użyto wieloparametrowego czujnika do nieniszczącej analizy lokalnego rozkładu pola magnetycznego, składowych prądów wirowych, strumienia i strat wiroprądowych. Podano rezultaty dla wymuszenia AC i dodatkowego odmagnesowania DC w jarzmie. Otrzymane rezultaty umożliwiają wizualizacje jakie części jarzma są podane magnesowaniu rotacyjnemu oraz prądom wirowym powierzchniowym na skutek strumienia rozproszonego silnie zależnego od składowej DC.

4

Geomagnetic variations and their time derivatives during geomagnetic storms at different levels of intensity

Watermann J., Gleisner H.

Acta Geophysica

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2009

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Vol. 57, no. 1

197-208

EN

The latitudinal distributions of horizontal geomagnetic variations, ΔH, and their time derivatives, ∂H/∂t, were analysed statistically over the three-year period 2003–2005. It appears that the amplitude distributions of horizontal geomagnetic variations and their time derivatives differ systematically between different geomagnetic latitudes and storm intensity levels. We show that the magnetic field variations observed at auroral and polar cap latitudes are under all geomagnetic storm levels comparable in amplitude (in a statistical sense) while they are smaller at subauroral latitudes. In contrast, their time derivatives are clearly the largest at auroral latitudes at all storm levels. These distributions determine in a general sense where and with which probability technological systems and operational procedures may be affected by geomagnetic storms. However, one observes in individual cases that the peak ∂H/∂t (the largest in all horizontal directions) is not necessarily the one which triggers a power system blackout.