Design of a High Frequency Transformer for High Voltage Applications
Examensarbete för masterexamen
Electric power engineering (MPEPO), MSc
Kramadhati Venkatagiri , Vagul
Sharma , Niharika
Abstract An Electrostatic Precipitator is an industrial device that filters exhaust gases from process plants to release clean air into the atmosphere. For its functioning, a suitable high voltage transformer is required which operates under electrical stresses induced by power electronic components. Existing transformers for this application are bulky in size, expensive due to material requirement, and require complex balancing circuitry to operate due to multiple cores. A "planar" transformer is therefore suggested as a suitable replacement. With the secondary consisting of multiple PCBs with deposited traces layered around a single core, it is expected that the size of the transformer can be reduced along with the system complexity and material requirements. This thesis introduces FEM (finite element method)-based simulation model for designing the high-voltage high-frequency planar transformer. Implementation of the model in COMSOL Multiphysics software is presented focusing on application specific aspects such as AC effects at high frequencies, planar PCB design, insulation standards, and the implementation of integrated rectification. In addition, the effect of using dielectric barriers to mitigate high voltage stresses is evaluated based on simulations of the electric fields in the transformer. Furthermore, based on the results of the simulations, a prototype of the transformer was assembled and its efficiency was evaluated. The measurements of core losses were performed to identify limiting operational conditions. It was found that operating the core close to the saturation magnetic flux density should be avoided since this resulted in rapid heating and high steady-state temperatures in the tests. The least losses were obtained by operating at nearly one-third of saturation flux density. The efficiency of the transformer was calculated considering the measured core loss, winding loss and rectification loss. The results of the performed simulations and measurements indicate that a planar transformer can be considered as a promising solution for replacement of traditional transformers used in electrostatic precipitators.