Thermal and electromagnetic performance of transformers

The transformers represent a large present value and are of great strategic importance in power systems. While the system ages there is a wish to increase loading. The transformers are threatened by reduced mechanical strength and withstand voltage from a ged materials. Increasingly complex and upgraded grids increase the short circuit forces, inrush currents, and the risk of overvoltages and resonance situations. This all has to be handled by the owner within a frame of cost minimization and steadily stro nger demands for power quality. the projectt adresses: -A survey of available information to identify causes of transformer failure and find if aging dependent failure modes has yet become frequent. Later a scheme for risk management of populations based on operational data, condition monitoring and strategic importance will be established. -Materials ageing and the performance of refurbishment techniques will be studied both in laboratory and in in-service scale to find validity of proposed ageing models . At the same time different diagnostic methods like dielectric response and chemical analysis will used to find the applicability for assessing remaining life and for quality control of refurbishment methods. -Adaptive models for improved control with tr ansformer hot-spot condition during transient overloading will be investigated using CFD- and system-tools that has already been established for studying turbine gas and heat-flow. -Electromagnetic models will be developed to estimate internal stresses a nd interaction with power systems: A detailed model of saturation and inrush currents based on measurements and design data will be established. A high frequency terminal model based on measurements to obtain the stresses in a power system. A detailed phy sical, electromagnetic field model based on loss mechanisms, material behavior, and design to obtain internal stresses. Instrumentation for measuring transformer frequency responses will be developed.