Magnetic “Field Method” for Loss Inspection in Electric Steel—A Review and Proposal for Standardization

This paper addresses the long-term delay of standardization of a physically acceptable tester for magnetic energy loss P (in W/kg) in electric steel. A single, uniform and correct tester is needed for exact comparisons of electric energy systems versus fossil ones. Worldwide percentage comparison data are published with two digits after the decimal point. This is in contrast to the fact that standard testers (Epstein Frame and Single Sheet Tester) can determine P with errors up to ten percent. Such errors result from the application of the so-called Current Method (CM), which eliminates the measurement of magnetic field strength H(t) by assuming that it is proportional to the magnetization current i(t). For about 40 years, introduction of the physically correct Field Method (FM) has been blocked. The corresponding argument is that a reliable sensor for H that meets the stability, sensitivity and accuracy standards is not available. Here, we point to the fact that modern micro-mechanic methodologies offer sensors of optimum performance. After a brief review of the present situation, we suggest the rapid standardization of the so-called “Narrow Sheet Tester” (NST) with FM. With a printed H-sensor, it would replace the conventional EF and SST, offering high repeatability, reproducibility and accuracy.