New algorithms to improve the sensitivity of differential protection of regulating transformers

Early detection of incipient failures is an important issue on the way to improve the reliability of energy supply and reduces the cost of maintenance activities. In this paper an advanced method of digital protection will be demonstrated. The new approach based on adaptive adjustment of percentage differential characteristic takes into account the current tapping position of regulating transformers and so provides the timely recognition of low-current faults being undetected before due to insufficient sensitivity to small current magnitude. The presented adjustment algorithm has been tested for two different transformer models set up using ATP-EMTP. Both of them are proved to be suitable for sensitivity improvement, which leads to enhanced information quality regarding the risk assessment of supply breakdown.