Secondary rated current: the primary induced current allowed to pass through the secondary winding of the current transformer. Rated current ratio (transformation ratio): the ratio of the primary rated current to the secondary rated current. Rated voltage: The maximum voltage that the primary winding can withstand to the ground for a long time (the effective value is in kV), which should not be lower than the rated phase voltage of the connected line. The rated voltage of current transformer is divided into several voltage levels such as 0.5, 3, 6, 10, 35, 110, 220, 330, 500kV. Under the specified secondary load and any power factor, when the current error of the current transformer is -10%, the primary current is a multiple of its rated value. The 10% multiple is a technical indicator related to relay protection.