Abstract
A calculable potential transformer(PT) with nominal ratio error in wide range of -10% to +10% has been developed on basis of theoretical calculation of ratio error by the number of windings. The developed PT can be used to evaluate the linearity and accuracy of the PT comparator by comparing both the theoretical and experimental values of the PT which have exactly same ratio errors in nominal and calculated values. The PT has been applied for calibration and correction of the PT comparator up to wide ratio error range of -10% to +10%. This portable PT is very convenient to carry to the power industry for the on-site calibration of the PT comparator.