The improvement of the digital differential relay in on-load tap changer transformer

An advanced method for improving the sensitivity of the digital differential protection is presented in this paper. The new approach based on adaptive adjustment of the percentage differential protection takes into account the tap position of the power transformer with on-load tap changer. The digital differential protection can be more sensitive to the faults of transformer by reducing the unbalance current caused by the tap changing. The presented method has been tested by the internal fault of transformer model set up with PSCAD, which is proved to be suitable for sensitivity improvement.