CALIBRATION OF CURRENT TRANSFORMER

PURPOSE:To assure the accurate measurement despite the application of split cores by a method wherein the coupled state of split cores is adjusted to the specified values during the term of current in measured line maintained in almost constant values to create the calibration state substantially equivalent to the initial state. CONSTITUTION:A pair of circular cores 2, 3 encircling a DC line 1 is provided while a switch 39 is turned on to supply calibrating coils 35, 36 with known current from a DC power supply 40 to measure the value A corresponding to the known current by an ampere meter. Next, the switch 39 is turned off during the term subject to less change in the current in line 1 to measure the value B corresponding to the current in line 1 by the ampere meter 8. Finally, the switch 39 is turned on so that the calibrating coils 35, 36 may be supplied with the known current to generate magnetic flux similar to or reverse to the magnetic flux according to the current in line 1 from the DC power supply 40 in the cores 2, 3 as well as to measure the value B+A1 or B-A1 correspondto the sum of or the difference between the current in line 1 and the calibrating current further to adjust the joint of parts 9, 10 and 11, 12 for making B+A1=B+A or B-A1=B-A.