Patent ID: 7103485

Claim:
A method of compensating for secondary currents of current transformers due to saturation, comprising the steps of: (a) determining a saturation starting moment of a current transformer by calculating difference values having at least second order for sampled secondary currents and comparing absolute values of the difference values with a predetermined critical value; (b) obtaining a secondary current value consistent with a current transformation ratio where the effects of the saturation are removed, at a time after the saturation starting moment by: (i) obtaining a magnetizing current at the saturation starting moment using the difference values if the saturation starting moment is determined, and obtaining a magnetic flux value in a steel core of the current transformer from a magnetization curve using the magnetizing current; (ii) calculating a magnetic flux value at a time after the saturation starting moment using a secondary current value measured at that time and the magnetic flux value obtained at the saturation starting moment; (iii) obtaining a magnetizing current at that time from the magnetization curve using the magnetic flux value calculated at that time; and (iv) adding the obtained magnetizing current to the measured secondary current value at that time.