Selected protective algorithms of modern IED

The paper presents some aspects of the work IED protection algorithms. These functions are hidden deep in the algorithms, however, very important for the power protection automation during abnormal failure in the MV lines. These functions have not been tested yet. An example of this problem is action of the IDMT overcurrent protection when the input current changes its value after protection start-up. Another example is the work of an earth fault protection based on Y0> criteria, when Y0 signal is distorted. The article is entirely based on the experience and measurements conducted by the author in the laboratories of the Institute of Electrical Power Engineering Poznań University of Technology.