DISTRIBUTION SUBSTATIONSDistribution substations are one of the components were often visually exposed to in the local power distribution system. Some distribution substations take up to one acre of land. Substations supply the source of energy for local area distribution and select user sites or a specific customer. The main purpose of the distribution substation is to step down voltage from the transmission or sub transmission level to the distribution level. To accomplish this purpose, substations use various devices for safety, switching and voltage regulation, and measurement. Substations are usually located at or near the center of the distribution area and may be indoors or outdoors. Some substations are operated manually, while others are operated automatically. Substations are designed so that most of the functions are electromechanical, such as relaying and switching, while interfacing with computers for monitoring purposes. The computer systems may be programmed to instruct faulty circuits to shut down or switch to other circuits. This type of interface of computer systems with electromechanical devices is referred to as programmed logic control, or PLC, and is very common in all sectors of power distribution. The computers for these systems may be located onsite within the control building, or may be remotely located in the main station of the power company that owns the substation. A substation thats centrally located within the area it serves is called a distribution substation. Distribution substations may be as close as two miles from each other in densely populated areas. These substations may also be located near a large industrial facility or inside a high rise building to supply high load customers needs. Distribution substations usually contain many components, including bus bars, power transformers, circuit breakers, and voltage regulators. During normal, automatic operation, the voltage in the local distribution system is controlled by monitoring and balancing the inputs from the transmission networks and local generation facilities.

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