Detection of disturbance of working conditions of current transformer in energy meters for reduction of unauthorized current consumption

Some current transformers can be very easily affected by dc component of primary current. The behavior of such transformers can be different in comparison with normal conditions. The errors of power measurements arise in order of units of percent and can be both positive and negative according to the type of load for some type of current transformers. The errors are mainly caused by change of phase shift between primary and secondary current. The source of the problem is dc magnetic flux in the ferromagnetic core of the current transformer. The presence of dc magnetic field in ferromagnetic core of current transformer can be, in some cases, detected by analyzing the frequency spectrum of current signal using a microcontroller, usually by measuring the second harmonic. According to these results the microcontroller is able to decide about possibility of unauthorized current consumption. This paper presents the problem about unauthorized power consumption and defines the possibilities to detect interferences caused by users.