This paper describes self-consumption systems that provide energy in a switchgear to power relay protection, monitoring, control, signaling, blocking and lighting systems. A calculation was performed for the dimensioning of the AC and DC power supply system equipment using the example of a 110/20(10) kV transformer station. Based on the calculation, transformers for powering domestic consumption and batteries and rectifiers in the 110 V and 48 V auxiliary DC power supply system were selected. Short-circuit current, selectivity control and voltage drop calculations were performed for the selected equipment.