Raising or lowering the voltage: the same device, not the same use. The distinction turns concrete the moment a renewable plant connects to the grid.
A step-down transformer reduces the voltage: classic distribution, from MV (15 / 20 kV) to LV (400 / 230 V) to supply a site. The vast majority of installed transformers are step-down units.
A step-up transformer raises the voltage. The typical case: generation (a solar or wind park, cogeneration) producing in LV or MV that must inject into a higher-voltage network. The voltage is then raised to the level of the connection point.
For a renewable park, the step-up unit sits at the heart of the evacuation substation: it raises the generation voltage towards the network operator's grid. Depending on the power, the connection is made:
Connecting a generation installation follows the technical prescriptions of the network operator concerned, to be framed upstream of the project.
Step-down to consume, step-up to generate and inject. If your project is a renewable evacuation substation, state the power, the target connection voltage (MV or HV) and the operator concerned: we design the step-up unit and, if needed, the complete substation. See also the renewables sector and the solar transformers guide.
General overview; exact connection and protection modalities are defined with the network operator (Enedis / RTE) and per the regulation in force.
The direction depends on the connection. In practice a unit is specified and used in one given direction; to evacuate generation, it is designed for that flow and for the constraints of a producer connection.
It depends on the voltage level: the distribution network (MV) belongs to Enedis or a local distribution company; the transmission network (HV), for high powers, belongs to RTE.
A protection that disconnects the generation from the network in case of a grid fault, so the plant does not feed a faulty or isolated network. It is defined with the network operator.
A site with storage draws and injects: the transformer must then be designed for genuinely bidirectional flow, and the case must be announced from the first exchange. See the battery storage page.