Electrical substations, being part of the transmission network, are made up of high voltage (HV) components which collectively are called the primary system.
The interconnection between the transmission and distribution networks is achieved through the primary substations. In addition to the HV part, the stations also include a medium voltage (MV) and low voltage (LV) part, which is called the secondary system.
Finally, the primary system control devices constitute the Protection
Command and Control System (SPCC).
