Coping with abnormal flux conditions when applying transformer protection

In the design and application of biased differential protection to large transformers, some or all of the following overfluxing conditions may require attention. The last condition does not generally receive as much general attention as the first condition: energisation; AC overfluxing; and DC overfluxing. After a brief review of biased differential protection for transformers, each of the above conditions are given some individual consideration with the aid of a spread-sheet transformer model and with reference to real events that have been encountered. The aim is to review the efficacy of new or established relay design features for addressing overfluxing concerns