The connection of an electrical installation to a MV utility distribution network is always realized by means of a dedicated MV substation usually designated ‘Main substation’. Depending on its size and specific criteria, mainly related to the loads (rated voltage, number, power, location, etc.), the installation may include additional substations designated ‘Secondary substations’. The locations of these substations are carefully selected in order to optimize the budget dedicated to MV and LV power cables. These secondary substations are supplied from the main substation through the internal MV distribution.
Generally, most of the loads are supplied in low voltage by means of MV/LV step down transformers. Large loads such as asynchronous motors above or around 120 kW are supplied in MV. MV/LV step down power transformers are located either in the main substation or in the secondary substations. Small installations may only include a single MV/LV transformer, installed in the main substation in most cases.