Hexaformer Transformer Essay

High Efficiency Transformer Core Design

Abstract— Distribution transformers have inherently high efficiencies of up to 99%, however they are in continuous operation and have a long lifespan. As a result a small efficiency increase can add to significant savings over the lifespan of the transformer. Symmetric core design has the potential to improve transformer efficiency. This paper highlights the key findings of an MSc research topic on High Efficiency Transformer Core Design. The proposal is based on the evaluation of the hexa-transformer for use within Eskom Distribution in South Africa. A three phase 100 kVA unit has been purchased and tested. A 50% transformer no-load loss reduction has been achieved. The transformer was thus opened and examined. The results indicated sound manufacturing quality. It is thus recommended that Eskom consider these units for future implementation in their distribution network. .

Keywords— Hexa-transformer, efficient, no-load loss, symmetric core design.

I. Introduction Transformer core design can be optimised by modifying the core geometry or changing the core material or both. The hexa-transformer is designed for improved core efficiency. It is a transformer with a triangular core configuration. The core consists of nine rolls of laminated steel bands and core legs that have a cross sectional shape of a hexagon, hence the name hexa-transformer or more commonly referred to as the hexaformer. Refer to Figure 1 below 1[1].

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Figure 1: Cross sectional view of the hexa-transformer: Courtesy of Hexaformer AB in Sweden [1]
The hexagonal shape is clearly illustrated.

Conventional transformer cores are constructed using electrical steel laminations. Laminations are used because they restrict the electrical conductance of the core to reduce core losses, and also to increase the magnetic