Physically consistent multi-frequency magnetic loss testing of silicon steel

Abstract

For decades, much effort has been made to establish test systems for the determination of magnetic losses of electric steels. However, presently available systems are still associated with considerable deficiencies. Meanwhile, increased awareness of preservation of energy enforces the need to determine losses with absolute accuracy. Furthermore, modern drives yield demand for multi-frequency testing. This paper summarizes a multi-frequency test system that avoids the major physical compromises of conventional methodologies. The paper describes the overall design of “physically consistent magnetic loss testing” (CLT) with preferred sample size of 500 × 170 mm2. Specific emphasis is placed on four crucial features: (i) Practical independency of sample state from an extra-thin yoke. (ii) Effective field detection with consideration of demagnetizing field components. (iii) Effective induction detection with advanced air flux compensation, based on true-field conditions. (iv) Complete suppression of harmonics for unique results. Results for time-averaged losses and for instantaneous power functions of grain-oriented steels are presented for frequencies ranging from 162/3 Hz to 10 kHz. For thermal and practical reasons, loss determination is restricted to a maximum of 100 W/kg. The design of CLT claims to be the first loss test concept with an assessed absolute accuracy of about 2.5%. Considering the benefits of the presented system, the method is proposed as a base for international standardization.