Electricity sub-station. Sub-stations are used to convert electricity from the form used in long- distance power lines to a form appropriate to domestic use. Electricity is most easily transported at extremely high voltages. In this way power loss, which is related to current flowing, can be minimised. High voltages are not suitable for use in the home though. The sub- station contains a transformer which converts the high-voltage low-current electricity to low- voltage high-current electricity.