The accuracy class has no phase angle error restriction and its percentage ratio correction factor (FCRp) must be between 103 and 97% so that it can be estimated within its accuracy class. A current transformer for measuring service is considered to be within its nominal accuracy class when the points determined by the percentage ratio correction factors (FCRp) and the phase angles are within the accuracy.
The accuracy class nominally shows the expected current transformer error taking into account the transformation ratio error and the mismatch error between the primary and secondary currents. Leeson 103085.00
Depending on the instruments connected to the secondary terminals of the current transformers, the accuracy classes of this equipment must be:
– Power supply of indicator ammeters, graphic registers, impedance relays, differential relays, directional relays: 1,2.
– For verification and calibration of instruments of laboratory measurements: 0,1
– Meter supply for the purposes of monitoring industrial costs: 0.6;
– Supply of direct – acting relays, for example, applied to primary substation circuit breakers: 3.