A method, device and computer program product for determining at least one property of a current (Ip) running through the primary winding of a transformer operating in saturation using an unreliable detected current (Is) running through the secondary winding of the transformer. According to the invention a first reliable extreme point (EP1) of a cycle of the current in the secondary winding is detected and compared with an absolute time reference. Based on the comparison a first property of the current running through the primary winding in the form of the phase angle is then determined.