Loss Analysis and Temperature Measurement of Middle Frequency Transformer Applied for Solid State Transformer

This paper investigates the middle frequency transformer for the solid-state transformer applied for the HVDC transmission from the offshore windfarm. The key component is the middle-frequency transformer. The testing transformer of 3kHz, 5kVA rating with amorphous and nano-crystaline core materials are investigated. Dependency of the loss in the transformer to frequency is measured and estimation of loss and size at higher frequency are realized. To establish the better cooling method, temperature and loss measurement using optical fiber is also performed. This paper reports the first results of this new measurement. The temperature increase in the core and the conductor should be avoided and the cooling of the iron core and copper windings is important. The new temperature distribution measurement is performed and the results show the good coincidence with the analytical results. The analysis of the current distribution of the windings is also shown.