CURRENT MEASURING INSTRUMENT

PURPOSE:To measure a current with high accuracy by preventing insulator damage due to a high frequency surge of a current flowing to a bus and eliminating influence of an axial magnetic field. CONSTITUTION:Inner and outer peripheries and both sides of a wound core 2 of an insulator of an annular shape are covered along entire peripheries with conductor plates 5, 5,..., and outsides of the plates 5, 5,... are wound with a winding 3 to form an annular coil 1. A bus 4 to be measured is coaxially inserted inside the coil 1, a voltage induced in the winding 3 by a current flowing to the bus 4 is output between output terminals (a) and (b), and a current flowing to the bus 4 is measured based on the induced current. A high voltage generated by a high frequency surge superposed on the current flowing to the bus 4 is suppressed by a stray electrostatic capacity between the winding 3 and the plates 5, 5,... Eddy currents are produced in the plates 5, 5,... by an operation of an axial magnetic field by the current flowing to the bus 4 to alleviate an operation of the magnetic field to the core 2 and the winding 3.