When a silicon steel sheet is magnetized to a specific magnetic flux density under an AC magnetic field of a certain frequency, the energy lost per unit weight of the silicon steel sheet is called the iron loss value. The frequency of the AC magnetic field usually used is 50 or 60 Hz, and the magnetic flux density achieved is usually 1.5 or 1.7 Tesla. The commonly used unit of iron loss value is the watt value lost per kilogram or per pound of silicon steel sheet, expressed in Watt/kg or Watt/lb. The sources of iron loss value of silicon steel sheets include hysteresis loss, eddy current loss and abnormal eddy current loss. During the magnetization process of silicon steel sheets, hysteresis will occur. Hysteresis loss is the area covered by the B-H hysteresis curve.
The eddy current loss of the silicon steel sheet originates from the alternating magnetic field. Due to the influence of Faraday's theorem, an induced voltage is generated inside the silicon steel sheet. According to Ohm's law, the voltage causes an induced current inside the silicon steel sheet, which in turn causes Joule heat of the silicon steel sheet. This This energy loss is called eddy current loss.
According to classical electromagnetic theory, eddy current loss is related to the thickness, resistivity, magnetic flux density and frequency of the steel sheet. The eddy current loss is proportional to the square of the thickness of the steel sheet and inversely proportional to the resistance coefficient of the steel sheet. Therefore, the thickness of high-grade silicon steel sheets tends to be thinner. In order to increase the resistance coefficient of the steel sheet, silicon steel sheets are added Silicon, aluminum and other elements.
The energy loss after subtracting hysteresis loss and eddy current loss from the iron loss value is called abnormal eddy current loss. Scholars believe that the abnormal eddy current loss is caused by the microscopic eddy current loss caused by the movement and rotation of the magnetic domain. Therefore, the abnormal eddy current loss is related to the size of the magnetic domain.
If the magnetic domain of the silicon steel sheet is large, it will rotate faster when magnetized and the microscopic eddy current loss will increase. Iron loss value is the most important property indicator of silicon steel sheets, and it is also the specification basis for grading silicon steel sheets according to various industrial standards. The lower the iron loss value, the higher the grade and the higher its energy efficiency.