Harmonic effects on distribution transformers and new design considerations for k-factor transformers

Abstract

This paper presents the effects of harmonic distortion of load current & voltages on distribution transformers, the standard ways of calculating the harmonic effects & design & development of K Factor transformer, which can operate under a specific harmonic environment. The usage of non-linear loads on power systems has increased the awareness of the potential reduction of a transformer's life due to increased heat losses. The performance analysis of transformers in a harmonic environment requires knowledge of the load mix, details of the load current harmonic content & total THD. The additional heating experienced by a transformer depends on the harmonic content of the load current & the design principals of the transformer.// Both No load & Load losses are effected by the presence of harmonics in load currents. But the variation in load losses contributes more to excessive heat generation in distribution transformer. Increment in no load losses in a distribution transformer due to harmonics is less compared to the load loss but it has a significant contribution to the capitalization cost when operating in longer term. The load loss components get affected by the harmonic current loading are the I2R loss, winding eddy current loss & the other stray losses. The methods of predicting extra losses are described in this thesis and standard ways of de-rating transformers are also discussed.// The K-FACTOR method is an approximation of the total stray loss heating effect, including the fundamental and harmonic contributions & finally new design techniques for K-F ACTOR transformers are discussed. In designing of K-F ACTOR transformers different design techniques like parallel conductor arrangement for windings, lower flux density & introduction of static shields are discussed & the estimated results are compared with actual implemented results.