Transformer used in rated voltage not more than 0.66 KV AC circuit, long-term working current not more than 1.2 times the rated value; The total impedance (including wiring) of the instrument should not exceed the rated load of the transformer when the measuring instrument is connected to the S1 and S2 terminals. 

A LOW-VOLTAGE CURRENT TRANSFORMER CONVERTS HIGH AC current into low current that can be easily controlled.