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1

A Study on the Low Frequency Transients in Power Transformers and Some Protection-Related Issues

Saied M. M.

Electrical Power Quality and Utilisation. Journal

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2014

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Vol. 17, iss. 2

9--16

EN

This paper presents typical results for the non-linear low frequency transients following the energization of power transformers. The three operating conditions of no-load, full-load and internal faults are considered. A direct analytical procedure is applied for solving the corresponding set of differential equations describing the transformers equivalent circuit. The core representation is based on the use of curve fitting applied to their magnetization curves. The results include plots versus time for the supply current, the core flux, the magnetizing current as well as the internal induced voltage. Moreover, graphs for the hysteresis loops relating the instantaneous values of both the excitation current and the core flux are given. An approach is also presented for the numerical determination of the amplitudes of the different harmonics existing in any of these signals utilizing the corresponding equidistant samples. As examples, the DC offset as well as harmonics up to the fourth order are considered. It is shown that several useful features can be extracted from the results in both the time and harmonic domains that can assist in differentiating between overcurrents resulting from short-circuits or inrush phenomena.

2

Zastosowanie magnetyków amorficznych przy budowie transformatorów

Zieliński M.

Wiadomości Elektrotechniczne

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2011

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R. 79, nr 3

17-19

PL

Przedstawiono wykorzystanie materiałów magnetycznych o strukturze amorficznej przy budowie transformatorów.

EN

The paper presents using amorphous magnetic materials in construction of transformers.

3

Magnetic material performance of transformers in common mode active EMI filters for bearing current suppression

Di Piazza M., Ragusa A., Vitale G.

Przegląd Elektrotechniczny

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2011

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R. 87, nr 6

198-201

EN

This paper analyses the performance of two magnetic materials used in the active filters for Common Mode (CM) electromagnetic interference (EMI) reduction in induction motor drives. In particular, active filters based on CM voltage compensation, very useful in bearing current suppression, are considered. The magnetic material is exploited for the core of the common mode transformer (CMT) that it is a crucial part of such devices because it performs the injection of the compensation voltage into the power connections between the inverter and the motor. The issues regarding the choice of the CMT core magnetic material and the windings design are discussed. The problem of the magnetic saturation, related to the desired high power/weight ratio is investigated. Furthermore, the power losses in the magnetic material under non-sinusoidal supply condition are evaluated through a suitable measurement system. A comparison of two CMTs, realized with ferrite and with nanocrystalline material cores, respectively, which are designed to perform the same filtering effect, is presented.

PL

W artykule przedstawiono analizę właściwości dwóch materiałów magnetycznych stosowanych w aktywnych filtrach EMI. Przedstawiono zalecenia dotyczące doboru materiału (głównie indukcji nasycenia) jak i konstrukcji dławików i transformatorów. Zmierzono także straty mocy w warunkach zasilania niesinusoidalnego. Porównano dwa materiały – ferryty i materiały nanokrystaliczne.

4

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.

5

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.

6

Harmonic domain modelling of transformer core nonlinearities using the DIgSILENT powerfactory software

Wiechowski W., Bak-Jensen B., Bak C. L., Lykkegaard J.

Electrical Power Quality and Utilisation. Journal

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2008

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Vol. 14, iss. 1

3-11

EN

This paper demonstrates the results of implementation and verification of an already existing algorithm that allows for calculating saturation characteristics of singlephase power transformers. The algorithm was described for the first time in 1993. Now this algorithm has been implemented using the DIgSILENT Programming Language (DPL) as an external script in the harmonic domain calculations of a power system analysis tool PowerFactory [10]. The algorithm is verified by harmonic measurements on a single-phase power transformer. A theoretical analysis of the core nonlinearities phenomena in single and three-phase transformers is also presented. This analysis leads to the conclusion that the method can be applied for modelling nonlinearities of three-phase autotransformers.

7

Zastosowanie materiałów amorficznych do budowy rdzeni transformatorów specjalnych

Dałek J, Ostrowski J., Stegliński Z.

Nowa Elektrotechnika

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2006

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nr 3 (19)

16--17