Generator step-up transformers (GSU) are the critical link between the power station and the transmission network, often operated day and night at full load. They must be built to withstand extreme thermal loading without ageing prematurely.

GSU take the voltage from the generator voltage level up to the suitable transmission voltage level.

These transformers are located in a power station and are built as single-phase or three-phase units.

There are two (2) basic technologies for designing and manufacturing: core and shell. With shell-formed transformers, the primary and secondary are on one leg and surrounded by the core. With a core-formed transformer, cylindrical legs windings cover the core legs.