The article presents the results of testing the resilience of power supplies of digital protection relays to the effects of short high-voltage pulses. A strange fenomenon of the sensitivity of one of the relay types to standard nanosecond pulses5/50 ns with 1kV amplitude (EFT) and simultaneous resistance to more powerful standard microsecond pulses 1.2/50 μs with amplitude 6 kV μs was detected. By using standard EMC filters, it is not possible to increase the stability of this digital relay to EFT.