Naslov
Concepts for Research of Combined Electric Field at Lightning Impulse Test for HV Windings

Autori
Banović, Mladen ; Mikulecky, Antun

Vrsta, podvrsta i kategorija rada
Radovi u zbornicima skupova, cjeloviti rad (in extenso), znanstveni

Izvornik
Proceedings of the International Colloquium Transformer Research and Asset Management, Cavtat, 12.-14.11.2009 / - , 2009

Skup
International Colloquium Transformer Research and Asset Management

Mjesto i datum
Cavtat, Hrvatska, 12.11.2009. - 14.11.2009

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
transformer windings; lightning impulse test; combined electric field; experiments; FEM modeling; optimal paper thickness

Sažetak
Transformer designers usually consider axial stresses between discs (coils) in HV windings and radial stresses between windings in separate manner - as two mutually independent properties, which transformer should withstand both. That is so because of historical reasons: withstand voltages between discs and withstand voltages between windings where investigated on separate models that exclude one another. On another side, high paper thickness increases withstand voltage between discs but decrease their cooling properties. In that sense, the optimal paper thickness should be used. This work can give contribution to that. The goal of this research is to qualify and to quantify the influence of radial stress on axial stress of transformer coil insulation at lightning impulse (LI) test. Combined electric field is investigated experimentally by using complex models, Figure 1, that simulate both radial and axial stresses. They will be placed in special test tank, and will be tested in high voltage (HV) laboratory using LI impulses in appropriate steps. Models are vacuum dried and oil impregnated. Models made of flat wire and CTC wire, with different insulation increases and different spacer heights will be investigated. Because of statistical evaluation, 12 identical models of the same size and type will be tested. During LI testing partial discharges (PD) will be checked too. Two basic types of models will be investigated: models with usual magnitude of radial electric field stress used in transformer design, and models with negligible radial stress. Total planed number of models as shown in Figure 1 will be greater than 500. Special consideration is paid to electric field evaluation. Electric field in each model type is calculated using appropriate 2D FEM program. Because of huge number of different types of models and type of used copper shape, and because of problems with geometry generation a special program for automatic generation of models is developed. Obtained data will be analysed correlating testing results with different characteristics of electric field in model, such is maximum value of electric field, stressed space, stressed field line and simply obtained combined el. field. Paper describes all basic steps in experimental investigation of combined stresses in transformer HV winding including models design and LI testing procedure.

Izvorni jezik
Engleski

Znanstvena područja
Elektrotehnika

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