Electric power is produced at generating stations (GS) and transmitted to consumers through an intricate network of apparatus including transmission lines, transformers, and switching devices. Electric power is generated using synchronous machines that are driven by turbines. Generated power is transmitted from the generating sites over long distances to load centers that are spread over wide areas. Three-phase average cost systems comprise the main means of generation, transmission, and distribution of electric power. Voltage and frequency levels are required to remain within tight tolerance levels to ensure a high-quality product. The transmission system interconnects all major GS and main load centers in the system. It forms the backbone of the integrated power system and operates at the highest voltage levels. The subtransmission system transmits power at a lower voltage and in smaller quantities from the transmission substation to the distribution substations.