Single Line Diagram

Power systems are extremely complicated electrical networks that are geographically spread over very large areas. For most part, they are also three phase networks – each power circuit consists of three conductors and all devices such as generators, transformers, breakers, disconnects etc. are installed in all three phases. In fact, the power systems are so complex that a complete conventional diagram showing all the connections is impractical. Yet, it is desirable, that there is some concise way of communicating the basic arrangement of power system components. This is done by using Single Line Diagram. It is also called One Line Diagram.

Single Line Diagrams do not show the exact electrical connections of the circuits. As the name suggests, Single Line Diagrams use a single line to represent all three phases. They show the relative electrical interconnections of generators, transformers, transmission and distribution lines, loads, circuit breakers, etc., used in assembling the power system. The amount of information included in a Single Line Diagrams depends on the purpose for which the diagram is used. For example, if the Single Line Diagrams is used in initial stages of designing a substation, then all major equipment will be included in the diagram – major equipment being generators, transformers, circuit breakers, disconnectors and bus-bars. Normally there is no need to include instrument transformers or protection and metering devices. However, if the purpose is to design a protection scheme for the equipment in the substation, then instrument transformers, metering devices and relays are also included. Any information that is required is added to the Single Line Diagrams. In this case connections of generator and transformer windings, as well as the method of grounding the neutral are indicated

In power engineering, a single-line diagram is a simplified notation for representing a Three Phase power system.The single-line diagram has its largest application in power flow studies. Electrical elements such as Generators, circuit breakers, Isolators, Transformers, Instrumentation transformers, Capacitors, Bus-bars and conductors are shown by standardized schematic symbols.Instead of representing each of three phases with a separate line or terminal, only one conductor is represented. It is a form of block diagram graphically depicting the paths for power flow between entities of the system. Elements on the diagram do not represent the physical size or location of the electrical equipment, but it is a common convention to organize the diagram with the same left-to-right, top-to-bottom sequence as the switchgear or other apparatus represented.


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