Escalating Global GDP (Gross Domestic Product) rate and Global Primary energy consumption demand reliable, uninterrupted and adequate power with high transmission efficiency. In the transmission system, Transformers have the highest population with the highest energy efficiency amongst all other electric devices. Transformers practically operate throughout the year at various load conditions. Therefore, the Total losses in transformers are core loss/no-load loss + I2R Losses + stray losses (due to the linkage of stray flux in structural parts like core clamping structure, tank, etc). Out of these losses in transformer, Stray loss (undesirable) component is more than 20% of the total load loss. Loss capitalization is an important factor in Transformer owning cost which depends on losses and other parameters. Therefore, reduction of stray losses gives the advantage in lower owning cost as well increase in the transmission line efficiency. The paper presents the use of UDEL (Unimpregnated densified electrical grade laminated) wood as a core clamping structure to reduce stray losses and subsequent reduction in heating effects with further advantage in owning cost of the transformer. Development of 15 MVA, 66/11.55 kV transformer with use of UDEL wood core clamp structure against conventional mild steel core clamp is discussed. Results show that there is a 28.2% reduction of stray loss and 4.5% reduction of total losses using the proposed method. The use of UDEL wood also reduces the partial discharges in magnitude (average 27% reduction) by avoiding magnetic material in the vicinity of high voltage leads and yoke shunts. Structural analysis was also performed using Finite Element Method (FEM) based software to check the suitability of wood core clamp structure under dynamic short circuit test condition. To ascertain the ability of UDEL wood core clamping structure, dynamic short circuit withstand test is conducted at the national laboratory and transformer has successfully withstood the test.
transformer, stray loss, leakage flux, Partial Discharge (PD), energy efficient, Finite Element Method (FEM)
Authors are thankful for the management of M/s. Transformers & Rectifiers India Limited to facilitate and allow redesign, modify and test the transformer.
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