The impact of higher-order harmonics on tripping of residual current devices

Distorted line to earth voltage on the output terminals of the inverter of variable speed drives results in an earth fault current comprising harmonics. Higher-order harmonics in the earth fault current have a negative effect on tripping of residual current devices. In some cases sensitivity of residual current devices rapidly decreases and protection against electric shock is not effective. In the paper results of the laboratory testing of residual current devices sensitivity are described.