1) the connection of the current transformer shall abide by the principle of series connection [8] : That is, the primary winding resistance shall be in series with the circuit under test, and the secondary winding resistance shall be in series with all instrument loads.

2.At the same time, one end of the secondary side must be grounded, in case of insulation damage, the primary side high voltage channeling into the secondary low voltage side, resulting in human and equipment accidents