The process of calculating electrical losses (the difference between incoming and outgoing energy) in a power system must take into consideration the energy consumed by substations for their own operation (maneuvering equipment, power and lighting). This energy is typically called "substation self consumption". As the power system expands, the process used to measure this energy grows increasingly complex and costly. This paper focuses on the characteristics of the substations in La Electricidad de Caracas (EDC) and attempts to demonstrate that, by applying random sampling, optimal Stratified random sampling and simple random sampling techniques, it is possible to determine energy consumption in each substation and in the power system as a whole