Mains distribution--general
In most major countries, electricity is supplied on a wide scale by electricity generating and distribution companies (electricity utilities). The distribution network normally consists of a large number of low voltage networks (often termed the mains) to which domestic and small business consumers are connected, with the low voltage networks being supplied through a higher voltage distribution network or system (often termed the grid). The low voltage (consumer) networks may for example operate at 230 V (or 440 V 3-phase).
The distribution network will normally operate at more than one voltage. There is long-distance distribution at voltages of say 132 kV or 275 kV, which we will term high voltages. These high voltages are stepped down (possibly through 2 or more stages) through transformer and switching stations (which we will term primary or high voltage stations) to voltages of say 11 kV or 33 kV, which we will term intermediate voltages. These are in turn stepped down through further transformer and switching stations (which we will term substations) to the final consumer mains voltage.