接地故障保护的设置和整定(三)

Setting and Arrangement of Earthing-breakdown Protection

（接2002年第1期第14页） 7 TT 系统接地故障保护 TT系统的电源中性点直接接地,而电气设备的外露可导电部分则经各自的PE线接地.这样在大多数情况下,由于故障回路包括两个接地电阻,使接地故障电流太小,不足以使过电流保护动作切断接地故障电流.而且由于故障电流小,故障点未被熔焊,故障点阻抗是难以估计的接触电阻.因此,TT系统接地故障回路阻抗和故障电流难以估算.所以,必须设置漏电电流动作保护.

Based on the body resistance, physiological reaction while current passed through body, permitted maxium current-action time under variable contacing voltage,the paper presents the following technique issues:earthing-breakdown current and body contacting voltage, eastimation of normal leakage current, earthing-breakdown protection of TN, TT, IT system, earthing-breakdown protection of pre-guard fire,earthing-breakdown protection of far-end line, main e-quivalent potential bonding and auxiliary equivalent potential bonding.