A simple method for determination of ratio error and phase angle in current transformers: Correlation of significant constants of current transformers

Up to the present time current transformer performance has been described by curves which show ratio error and phase angle over a range of current at various values of burden, (ohms) power factor, and frequency. The number of curves that are required to cover all possible conditions is so great as to render them, by their very bulk, practically useless. Another limitation is that they do not describe performance under transient conditions. Performance of other types of transformers and certain other apparatus is invariably calculated from a few easily measured constants, according to simple standard formulas. Up to the present time, available methods for calculation of current transformer performance have had the disadvantage of either being difficult to use, or of depending on constants difficult to measure, or else they have not been sufficiently accurate for general use. A method is described which depends on the following constants: 1. Open-circuit saturation curve measured in the usual way. 2. Secondary coil resistance. 3. Equivalent leakage reactance calculated from the voltage of an exploring coil enclosing the maximum value of leakage flux. The method includes several important short cuts in the calculation which reduce the numerical work to a practical minimum. Curves are plotted which allow direct reading of the exact components of exciting current which cause ratio error and phase angle. The objects of the paper are: 1. To present a practical method of calculation. 2. To establish constants (1), (2), and (3) as the fundamental quantities which determine real excellence of the transformer.