Numerical research on the losses characteristic and hot-spot temperature of laminated core joints in transformer

The laminated joint model is proposed to solve the losses and hot-spot temperature problems of a transformer core, which are mainly caused by the abnormal magnetic field of joints in the laminated core. The different structures and sizes of the joints are considered when designing the proposed model. An equivalent method of joint building factor (JBF) is presented to compute and clearly reflect the relation between losses and structures. Next, a 3D model of transformer for electromagnetic-thermal coupling is designed, and the heat sources of joints and temperature distribution are calculated by using the equivalent iteration of the JBF. Results show that the heat losses and hot-spot temperature of the joints are higher than those of other regions and increase rapidly with the increasing magnetic flux. Finally, a test system using an infrared thermometer is proposed to analyze the hot-spot temperature of joints and clamps. Results indicate that the hot-spots on the joints have the most abnormal temperatures because of the laminated layers. Furthermore, a relative error of less than 2.59% indicates that the theoretical value agrees well with practical values. Therefore, the validity of this calculating method is demonstrated, along with its significance for monitoring temperature and designing transformers.