Stray loss is mainly caused by leakage flux from winding, but structures closer to the winding will tend to be affected easier by leakage flux.
The ratio of stray loss relative to all losses may not necessarily be large but heat is generated in certain areas and may become an issue in the operation of transformers. In particular, stray loss occurring in the core tends to have effect on not only the core, but insulated items that construct the core, and may result in degradation of insulating oil due to burnout. Stray loss of the core is physically iron loss, but the cause is not the main magnetic flux in the core.
Categorically, it is considered stray loss as it is evaluated from short circuit tests in the actual machine test and because it is caused by leakage flux from winding (Fig. 1).
Fig. 1 Three phase transformers and 3D mesh in JMAG
The short circuit modeling is performed to evaluate stray loss and obtain stray loss distribution in the core close to the winding. Grain oriented laminations are used in the transformer core and it is modeled in the JMAG (Fig. 2).
Fig. 2 B-H curve and iron losses curves in easy and hard axis (top) and easy axis direction in the laminations (bottom) – hard axis is perpendicular to easy axis direction
Fig. 3 show eddy current distributions, hysteresis iron losses density and eddy current loss density. Eddy current losses is much higher because of large induced eddy currents in the solid configuration of lamination for leakage flux. JMAG simulations show the ability to calculate stray losses in 3D for electrical devices.
Fig. 3 Eddy current distribution in the core close to the winding - Hysteresis losses density in the core close to winding - Eddy current losses density in the core close to winding
Induction heating has been used for various purposes from production technology such as quenching and shrink fitting through to the design of home appliances as in Induction cooking system. Induction heating is the technology based on the eddy current, and it becomes a key issue for design to control the eddy current accurately. However, since the eddy current depends on factors such as geometry, material characteristics, frequency, and temperature, its behavior is complicated.
As a precision component, a gear requires an accurate evaluation of dimensional tolerance due to thermal deformation resulting from induction hardening. The main objective of work is a coupled magnetic and thermal analysis of a gear to study elevated temperature process (Fig. 1).
Fig. 1 Gear and induction coil configuration (top) simplified model of the coil for analysis in JMAG (bottom)
Accurate modeling of induction heating requires precise material data versus temperature for magnetic and thermal analysis. Magnetic susceptibility, electrical conductivity, thermal conductivity, specific heat capacity versus temperature for gear iron material are used in the simulations. Magnetic frequency analysis is used for eddy current losses calculations in the gear at source frequency 10 kHz and transient thermal analysis is used for gear temperature calculations. Two way coupled analysis is performed for magneto thermal analysis. Skin mesh elements of JMAG is used in the gear for accurate modeling of eddy currents (Fig. 2).
Fig. 2 3D mesh for gear and induction coil (partial model) using skin mesh element for accurate calculation of eddy currents
Eddy current loss density and eddy currents distribution are shown in Fig. 3 shows temperature distribution in the gear. Temperature variation versus time in one point of gear is shown in Fig. 6. Using JMAG helps to analyze magneto thermal Multiphysics of electrical devices such as induction heating.
Fig. 3 Eddy current loss density in the gear - Eddy currents distribution in the gear - Temperature distribution in the gear
Fig. 6 Temperature versus time for one point in the gear (Point 1 in Fig. 5)