Reliable electric power systems serve customer loads without interruptions at different voltage levels. Power plants are meant to generate enough power to meet the customer demand. At the same time, transmission systems are responsible for transporting bulk power over long distances without compromising voltage & frequency stability. Ultimately, distribution systems must deliver electricity to each customer’s service entrance. Therefore, a typical power system is consisted of several sub-systems, including power stations, transmission lines, transmission switching stations, transmission substations, sub-transmission systems, and distribution systems.
Figure 1 shows a simplified drawing of a typical power system and its subsystems.
Transmission systems are responsible for transferring electric power over long distances from generation substations (where step-up transformers are installed). Transmission substations, however, step down the voltage to sub-transmission levels. Hence, sub-transmission systems transport electricity from transmission substations to distribution substations. Most transmission lines are overhead.
From here, the importance of transmission and zone substations becomes very clear. Substations are therefore facilitators between generation, transmission, and distribution systems in HVAC systems, by means of which, system operators are able to control the variations of voltage and power. In other words, substations play a decisive role in creating a smooth power flow, power factor compensation, and they help improving the system voltage profile. Above all, substations are considered as the main switching and voltage transformation points in a power system via their power transformers and switchgear. Substations also accommodate protection and control panels, cap banks, reactors, and voltage regulation facilities.
Figure 2 – A typical transmission substation (courtesy of Electra Net)
Obviously, due to the very important role of substations in power transmission and delivery, power companies are now making efforts to modernize their substations via employing modern power transformers, advanced protection and control schemes and gears, sophisticated switchgears and their associated building and cabling, and flexible panel arrangements. The new advancements in the future will be more focused on efficient switching between zone substations, wide coverage of COMMS networks to support tele-protection and intertripping schemes, and employment of new generations of numerical relays to facilitate for a very reliable and stable power systems.