LV generator protection - engineering site - Schneider Electric

4.3.1.2. Source Ground Return (SGR)The “Source Ground Return” system directly measures the earth fault current bya specific external sensor.This protection detects faults upstream and downstream of the circuit-breaker.It is only possible at the supply end of the LV installation.E88019 E88018Figure 33.Note: the SGR CT is specific to this application.The Ground protection and Neutral protection are separate and thus can becombined.Setting the protection devicesGround protection can be set for its threshold (limited to 1200 A) by 9 bands andby its time delay (same as the Short Time Delay).To enhance discrimination with fuses or other circuit-breakers, part of the groundprotection curve can be converted into a reverse curve by choosing the l 2 tONsetting.The SGR protection requires use of the MDGF module.4.3.2. Residual current device (RCD) protection or“zero sequence” systemRCD protection is stipulated by installation standards (IEC 60 364) for protectionof people and equipment in the following cases:b TT type grounding systems, in which currents resulting from insulation faultsare smallb TN-S type networks with very long cables, in which the instantaneous thresholdis not sufficient to protect a short-circuit at the end of the lineb IT networks with very long cables.This protection is also used to provide additional fire protection.Its threshold from 500 mA to 30 A and time delay can be set to ensure residualcurrent discrimination.Figure 34.An external rectangular toroid sensor is compulsory.39