CLICK IMAGE TO ENLARGE The illustration above shows a simple power system one-line diagram. A power system network usually begins in the generation side.In the case of a distribution utility, their system starts at the connection point which is normally a mesh of transmission lines called a "grid". Bulk power is delivered through transmission line with a typical voltage rating ranging from 138kV and above. A power substation receives this power and then brings down the voltage level from 138kV to 69kV through the use of power transformers. A distribution substation then receives again this power to be transformed into a voltage level that can be distributed to distribution transformers before it can be utilized by commercial and residential customers. This diagram not only shows the path where the power flow but it also shows all the electrical components where power losses occur. Later we will discuss this components and how they contribute losses in the system.