Meaning of Single line diagram: The single line diagram of a power system is the network which shows the main connections and arrangement of the system components along with their data (such as output rating, voltage, resistance and reactance, etc.).
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In power engineering, a one-line diagram or single-line diagram (SLD) is a simplified notation for representing a three-phase power system. Electrical elements such as circuit breakers, transformers, capacitors, bus bars, and conductors are shown by standardized schematic symbols.