CHAPTER-3 SUB-STATION & SUB-STATION EQUIPMENT 3.1. Sub-Station: A substation is a part of an electrical generation , transmission , and distribution system. Substations transform voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltages and lower distribution voltages, or at the interconnection of two different transmission voltages. 3.2. Classification of Sub-Station: Substations are classified in many ways such as on the basis of- Nature of Duties Service rendered Operating Voltage Importance Design 3.2.1 Substation on The Basis of Nature of Duties: In this basis Substations may classified into Three Categories as follows: Step-Up or Primary Substation: These are usually associated with generating stations. The generated voltages are usually low such as 3.3KV, 6.6KV, 11KV or 33KV is stepped up to primary transmission voltage so that huge power can be transmitted over long distance to the load center. 15