Most current generation facilities produce electricity at 25,000 volts, or 25 kilovolts. Having producers generate a standard level like this helps keep the electric system stable and predictable. After that stable supply of electricity is produced at generation facilities across the state, it must be moved from those facilities to distribution points throughout the system of transmission and distribution facilities and wires commonly referred to as “the grid.”
As generation facilities are not typically located immediately beside the customers for whom they produce electricity, electricity must be fed into high voltage transmission lines that transport it, at least part of the way, from the generator to the customer.
One of the challenges of moving electricity over long distances like this is that electric current traveling through transmission lines causes the lines to heat up, resulting in a phenomenon known as “line loss.” The primary way to fight line loss is to use higher voltages. Therefore, the electricity is “stepped up” by transformers to much higher voltages — 115kV, 138kV, 230kV, 345kV, 500kV or 765kV. These higher voltages allow the electricity to be transmitted over long distances far more efficiently, but residential and commercial consumers cannot safely use electricity at these high voltages. So before it reaches the final distribution points, such as homes and businesses, substations and transformers “step-down” the voltage depending on the requirements of the end user. Subtransmission systems and customers receive electricity at 26kV and 69kV; primary, or industrial customers receive 13kV and 4kV; and secondary customers, or businesses and residential homes receive 120 volt and 240 volt.[*] 
[*]Subtransmission systems are used to supply distribution substations within the grid. Edvard Csanyi, “Basics Of Subtransmission Systems” (Electrical Engineering Portal, Dec. 17, 2010), https://perma.cc/M5UB-ZK8G.