Evaluation of errors of the wattmeter method for determining magnetic losses in transformers

The problem of the influence of the accuracy of dividing magnetic losses into components in transformers on the efficiency of minimizing these losses is considered. Various methods of studying and evaluating the magnetic properties of electrical steels and the power of magnetic losses are described. It is shown that the use of the wattmeter method for determining the components of magnetic losses in a specific transformer, in contrast to the currently used methods for determining the power of specific magnetic losses, does not require special equipment and software. An assessment of two specific errors of the wattmeter method for determining the magnetic losses in the transformer core is carried out. The first error is associated with the errors of the measuring devices (wattmeter and frequency meter), the second – with electrical losses during an idle experiment. The dependences of the errors of these losses on the accuracy class of the devices (wattmeter and cymometer) are obtained. It was found that for a dry single-phase transformer, the error of hysteresis losses is 19 times higher than the accuracy class of devices, and the error of eddy-current losses is 32 times. For low-power transformers (up to 5 kVA), taking into account electrical losses in the no-load experiment underestimates the losses due to hysteresis and overestimates the losses due to eddy currents, the error in determining which can significantly exceed the total error in determining the magnetic losses. It is shown that for transformers with a capacity of over 25 kVA, the error associated with taking into account electrical losses in the no-load test is negligible.

Magnetic Properties of Rapidly Quenched Ribbons of Soft Magnetic Iron-Based Alloys after Annealing in Air and in Vacuum

The physical reasons of influence of heat treatment in vacuum and air on magnetic properties of ribbon’s of amorphous soft magnetic iron-based alloys were investigated. It is shown that the heat treatment in the air contributes to retrieve the status of a material with lower specific magnetic losses. The reason for this is the formation during annealing of increased concentration along the axis of the ribbon of embedded in the surface atoms of hydrogen and oxygen. In this direction induced pseudo-uniaxial tensile stress, contributing to the reduction of the period of the domain structure and the speed of domain walls motion in the process of magnetization reversal.