Analysis of internal unbalancing current in distribution transformers

Abstract

Transformers are basically a static device with more than 95% efficiency. The major losses in transformers are copper loss and core loss. The minor losses are frictional and windage losses. But the formation of neutral current in the distribution transformers will create minor loss that will affect the efficiency of the transformer. There are many reasons for the formation of neutral current. In this paper neutral current formation due to changes in constructional parameters is studied i.e., neutral current formed as a part of difficulty in implementing the design values practically. The difference in design values will create an unbalancing current in three limbs and causes neutral current to flow. The factors that have been considered for the study of formation of neutral current in transformers are air gap difference, improper orientation, leakage flux, impedance difference in the winding, change in excitation current in each limb. These design parameters has been analyzed for different transformers and found that a small percentage of neutral current is formed which decreases the efficiency of the transformers significantly. The loss due to unbalancing current in distribution transformer is considered as a minor loss. Unbalancing current flows in 4 wire electric distribution system due to linear load unbalances are considered yet. Index Terms-air gap, magnetic unbalancing, neutral current, stacks difference.978-1-4799-1823-2/15/$31.00 ©2015 IEEE