Its job in the system
Transmission connects major sources and demand areas. It is usually a network with multiple routes, rather than a dedicated wire from one power station to one home. The path highlighted here is a teaching route through the system; it is not a claim that a particular household receives identifiable electricity from a single generator.
How it works
Lines and cables transfer power under electrical and thermal constraints. Increasing the flow raises heating and can bring equipment closer to its operating limits. Voltage and stability constraints matter too, so a line cannot be treated as a pipe with only one simple capacity number. Operators plan and adjust transfers while considering what might happen if equipment becomes unavailable.
In a connected AC network, flows divide among available paths according to the electrical state and impedances of those paths. Operators influence the pattern through generation, network switching, and specialised equipment, but ordinary AC power does not follow a software-selected packet route. Losing a line can redistribute flow onto other lines, which may then become more heavily loaded.
A line becomes unavailable
Illustrative example: two demand areas are connected through several AC transmission paths. If one path becomes unavailable, electrical flows redistribute across the remaining network. Some remaining lines may become more heavily loaded even though customers have not changed their consumption. Operators may need to change generation or other conditions to remain within limits. The example identifies a dependency, not an outage forecast: the actual redistribution requires network impedances, injections, controls, and constraints that this conceptual illustration does not specify.
What it connects to
Transmission is linked to generators at one end and distribution substations at many others. Cross-border interconnectors can connect neighbouring systems. Communication networks carry the measurements and control information that help operators understand the physical network, but those information flows are separate from the energy flow.
Different places, different designs
Overhead AC lines are common, but underground and submarine cables are important in some places. HVDC connections use converter stations and offer different control properties. Islands and remote communities may use smaller systems without a large transmission network at all.
Sources & further reading
Original explanations informed by these sources. Diagrams are conceptual; local systems differ.
- How electricity is delivered to consumers U.S. Energy Information Administration · Not stated · Source & rights record
- Electricity glossary U.S. Energy Information Administration · Not stated · Source & rights record
- Electricity 101 U.S. Department of Energy · Not stated · Source & rights record