Primary substations are the first stage in the process of transmitting electrical energy from the grid to the end user. Due to its strategic location within the system, a primary substation and switchgear are designed so that layout, design and operation ensure maximum availability and reliability.

Since the system impedance is lower in the primary substation than further up the grid, the fault level tends to be higher than in other parts of the grid, usually between 25 and 50 kA.