rofessional Answer: A single-line diagram (SLD), or one-line diagram, is a simplified representation of a complex electrical system. For overhead transmission lines, an SLD is crucial for visualizing the power flow from generation to distribution. It uses standard symbols to illustrate key components like transformers, circuit breakers, and protective relays, providing a quick and easy-to-understand overview of the entire network. This is essential for system planning, maintenance, and safety procedures.