Correction of Errors Introduced by Instrument Transformers - Digital Signal Processing in Power System Protection and Control - page 106

Fig. 7.6 Block scheme of the CT saturation correction procedure

fundamental frequency component T 1 ; either calculating the non-rotating or

rotating phasor components.
The above considerations show how digital representation of the secondary
current may be efficiently used to determine fractions of the period when the CT
magnetic core is not saturated, thus transformation is correct, and how distorted
waveshape may be processed to determine phasors. The presented methods are not
unique, but perhaps represent the best compromise between the accuracy and
efficiency. More details as well as simulative examples of the CT saturation
detection/correction procedures operation can be found in [ 13 ]. Slightly modified
version of the procedure for CT saturation is presented in [ 11 ], where an approach
based on numerical solution of the differential equation describing the saturated
current transformer is adopted.

7.2.4 Other Methods of CT Saturation Detection
and Secondary Current Reconstruction

A large number of journal and conference papers, which dealt with the CT satu-
ration detection and correction issue, may be divided into three groups:

• no CT current correction is performed, but the information on CT saturation is
used for other purpose, e.g. for adaptation of protection settings [ 9 ] or per-
forming calculations during CT unsaturated periods only [ 1 ],