电力专业英语4--继电保护2继电保护2GroundingSystemTheCTactstostepthecurrentdown,sayfrom1000Aontheprimaryto5Aonthesecondary.ThiswouldgiveaCTratioof1000:5Aor200:1A,andwouldrequire200turnsonthesecondary(assumingoneprimary“turn”).CT的作用是降低电流，例如将原边1000A的电流降至副边的5A。则CT的变比为1000:5A或200:1A，副边绕组的匝数为200（假设原边绕组匝数为1）Currenttransformersforrelayingpurposesaregivenaccuracyclassratings,suchasC400orT400(sometimeswrittenas10C400or10T400).TheletterCindicatesthatitsperformancemaybecalculatedfromitsmagnetizationcurve.TheletterTindicatesthatitsperformancemustbedeterminedbytest.保护用电流互感器均给出其（测量）精度等级，例如C400或T400（有些标为10C400或10T400）。字母C表示其特性通过其磁化曲线计算出来。字母T表示其特性由实验决定。