Economic analysis of distribution transformers under harmonic distortion

Abstract

This thesis’s aim is to investigate how much of total transformer losses in the distribution system of Sweden is due to harmonic losses, in comparison to the remaining other losses. Use of non-linear loads in power systems is increasing, and this has become a power quality problem for both electric companies and customers. Non-linear load not only increase the distribution transformer operational costs, it causes an increase in losses as well also create additional heating in power system components. Hence, this thesis will cover the basic losses in distribution transformers mainly due to non-linear loads, cost analysis of the total transformer losses and lastly the savings that can be gained respectively. One way to increase the efficiency is to change the transformer to low-loss transformers. Operating losses are less, causing less heat generation and increasing life-time. In conventional loss-analysis, harmonic distortion is not taken into consideration; even though it is of consequence in applications where high harmonic power is observed. There are a number of ways to decreasing transformer harmonics. In this thesis, an analysis has been conducted relating transformer efficiency to its load; as well as concluding an energy saving of 1.52TWh per year by replacing old equipment sensitive to non-linear loads with better transformers. The calculation and the interview show that the average transformer losses due to harmonics in distribution transformers is lower than 4%.