Patent ID: 8395373

Claim:
A method for determining at least one property of a current (I P ) running through a primary winding of a transformer operating in saturation using an unreliable detected current (I S ) running through a secondary winding of said transformer, comprising the steps of: detecting a first reliable extreme point (EP 1 ) of a cycle of the current in the secondary winding, comparing the occurrence in time of the reliable extreme point (EP 1 ) with an absolute time reference (CL), where the absolute time reference (CL) is a reference associated with a period of a periodic signal (U P ) measured at the primary winding at least before the transformer started to operate in saturation, determining a first property of the current running through the primary winding in the form of a phase angle (α 1 ) based on the comparison, obtaining a second extreme point (EP 2 ) in said cycle of the current in the secondary winding, and determining a second property of the current running through the primary winding in the form of an amplitude based on the two extreme points (EP 1 , EP 2 ) of the cycle, wherein the step of obtaining a second extreme point comprises determining a second reconstructed extreme point (EP 2 ) in said cycle of the current in the secondary winding, which second extreme point occurs during a first intermittent time interval (TI 1 ) of the cycle when the transformer is in a saturated state and which determination is made through predicting the current running in the secondary winding from the start of the first intermittent time interval and the prediction is stopped as soon as the second extreme point (EP 2 ) has been determined.