The application of pole mounted amorphous core transformers to the electrical distribution network.

Abstract

With the drive to save money when supplying electricity to customers, utilities are looking for solutions to decrease losses on distribution lines while maintaining good quality of supply. Amorphous core transformers are known for having the lower no-load losses compared to cold rolled grain orientated transformers and hence may be an important technology to decrease losses on the distribution network. The amorphous material is easily magnetised, however this comes at the expense of a lower saturation point and the transformer may need to be designed at a lower peak flux density. Inrush currents are a phenomenon that occurs when a transformer is switched on. The combination of the voltage switching angle and the remnant flux lead to an overflux and subsequent saturation of the core material, this leads to a high current. The purpose of this dissertation is to investigate the performance of amorphous core transformers installed on distribution lines, where they are switched onto the network from the high voltage side, and conclude if they are a suitable replacement for cold rolled grain oriented steel core. Inrush currents have been investigated through a circuit model developed in Alternative Transients Program/Electromagnetic Transients Program (ATP/EMTP) to determine the currents for various designs of transformers. The model consists of the non-linear component related to the core used as well as the air core of the high voltage winding. The circuit model has been validated through an experiment. A study was undertaken to understand the difference in the forces between amorphous core transformers and cold rolled grain orientated, this was investigated in Finite Element Method Magnetics (FEMM) by determining the distribution of magnetic flux. Additionally, as the inrush current is only seen on the high voltage winding and not the low voltage winding, the models were compared to the forces due to short-circuit currents, where there is current on both high voltage and low voltage windings and a different magnetic flux distribution. The position of the tap winding was of interest as it results in an unsymmetrical force distribution.