Temperature influence on core losses and magnetization demand of electrical steel sheets using adapted Epstein frame and ring probe

In this paper, the influence of temperatures up to 250 °C on core losses and magnetization demand of electrical steel sheets is illustrated. Therefore, measurements are made using an adopted high-temperature Epstein frame and a stator core as a ring probe. Three different electrical steel sheet grades, M330-50A, M530-50A and NO20-15, and a stator core are tested. Magnetic property measurements are performed at various frequencies from DC to 1.2 kHz with a defined sinusoidal waveform of magnetic polarization. This covers a wide range of electric motor applications from industrial drives to electric vehicle drives. With increasing temperature, magnetization demand rises significantly in medium polarization range. For specific core losses, a loss separation is performed using the Jordan approach, separating specific hysteresis and specific eddy current losses to determine the temperature influence on each loss component. The temperature behavior of the specific electrical resistivity of electrical steel sheets is measured and used to calculate the physical specific eddy current losses. After separation, specific hysteresis losses also show a significant temperature influence.

I. Introduction

For the efficient operation of electrical drives and power transformers, electrical steel sheet plays a crucial role. Its unique magnetic properties make it an ideal material for applications requiring low core losses and high magnetic permeability. The potential for high ambient temperatures in industrial environments, or highly stressed integrated drive systems, results in high temperatures within the electrical machine and therefore within the electrical sheet metal packages. However, when exposed to high-temperature environments, electrical steel sheet faces several challenges that can affect its performance and longevity. Understanding the behavior of electrical steel at elevated temperatures is essential for optimizing the design and efficiency of electrical machines operating under demanding conditions. The influence of the temperature dependence of electrical steel sheets is the focus of several publications. Some, as in [1] and [2] use a high-temperature Epstein frame test setup. Other publications use ring specimen as in [3]- [5]. All of them deal with the problem of material stability of the measurement setup at higher temperatures and provide appropriate solutions for high temperature measurements. The aim of the following sections is to show how a temperature dependent measurement of the soft magnetic properties of electrical steel sheets can be realized. Therefore, the magnetization demand and the specific core losses considered for a setup of different electrical steel sheet grades at room temperature and up to 250 °C.