RCDs Tripping in the Range from DC to AC 50 kHz for Slowly Rising Residual Current

The wide use of power electronic converters means that in many low-voltage systems earth fault currents containing components from DC to AC of various frequencies have to be taken into account. Due to the tendency to increase the modulation frequency in converters, components of higher frequencies may be in the order of several tens of kilohertz. Therefore, it is very important to verify the behavior of devices for protection against electric shock in the presence of earth currents with frequencies other than the nominal frequency of the network, as well as for a DC component. The paper presents the results of tests of residual current devices (RCDs), with slowly rising earth/residual current at selected frequencies within the range 1 Hz - 50 kHz, and at pure DC. Tests have shown that RCDs may not respond to certain frequencies and pure DC, which carries a risk of electric shock.