Tripping of F-type RCDs for High-Frequency Residual Currents

Abstract

Residual current devices (RCDs) are apparatus commonly used for protection against electric shock in low-voltage electrical installations. They protect people in the case of an earth fault or even in the case of direct contact with the live parts. However, to be effective protective devices, RCDs have to detect residual currents of various waveform shapes which appear in modern electrical installations. For this purpose, RCDs are classified into four types: AC;A;F and B. This paper is focused on F-type RCDs provided for the detection, in particular, of mixed-frequency residual currents. According to the standard referring to the F-type RCDs, they are tested by manufacturers under the non-sinusoidal waveform having components generated by control equipment supplied from a single-phase. In this paper, results of two tripping tests (other than normative) of F-type RCDs are presented. During the first test, waveforms having components generated by control equipment supplied from three phases were forced. During the second test, high-frequency pure sinusoidal residual currents were generated. Results of these tests have shown that F-type RCDs may detect mixed-frequency residual currents other than the normative but may not react to sinusoidal currents of frequencies higher than 1 kHz.