Parts of a Substation – Labeled Diagram of the Yard

All 10 parts on the diagram

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The yard 10

Power transformer Changes the voltage from one level to another.
Transmission line Brings high-voltage power in from far away.
Circuit breaker Switches a circuit off, even with current flowing.
Disconnect switch Isolates equipment. It cannot break load current.
Control house Holds the relays, meters and batteries.
Bus (busbar) Bars that the lines and the transformer connect to.
Lightning arrester Limits surge voltages from lightning, to protect the equipment.
Insulators Hold live wires and bars away from the steel.
Steel structure The frame that carries the wires and equipment.
Feeder (distribution line) Carries lower-voltage power out to the streets.

How this list was compiled: Every name checked on 2026-09-30 and kept only where both of these use it. (1) US Occupational Safety and Health Administration, Electric Power eTool, Illustrated Glossary: Substations, https://www.osha.gov/etools/electric-power/illustrated-glossary/sub-station (a US federal work), with its Distribution System page and its glossary of terms, https://www.osha.gov/etools/electric-power/glossary-terms : power transformers, circuit breakers, disconnect switches, transmission bus and distribution bus, lightning arresters, bus support insulators and suspension insulators, control house, steel superstructures, transmission lines, distribution feeder circuits; what a substation does; the control house contains switchboard panels, batteries, meters and relays; steel superstructures support equipment, lines and switches; lightning arresters limit surge voltages. (2) Wikipedia, Substation, Busbar and Disconnector, https://en.wikipedia.org/wiki/Substation : transmission lines, transformers, circuit breakers, disconnect switch (it cannot interrupt load current), busbars (supported on insulators), lightning arrester, control building, steel lattice structures, feeders. Licence: own work

The drawing: Own drawing from plain geometry; nothing traced. Licence: own work

How it works

A substation switches power lines in and out of the grid and changes the voltage from one level to another. The drawing follows the power from the transmission line at the left to the feeder at the right.

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From the line to the transformer

The transmission line ends on a steel structure, hanging from insulators. A disconnect switch isolates what comes after it, and a circuit breaker switches the circuit off under load. The lightning arrester protects the power transformer from surges.

From the transformer out

The power transformer lowers the voltage. Lines and transformers connect to the bus, and each feeder carries power away to the streets. The control house holds the relays, meters and batteries that run the yard.

Questions and answers

What are the main parts of a substation?

Power transformers, circuit breakers, disconnect switches, buses, lightning arresters and insulators, all carried on steel structures, plus a control house. Transmission lines come in and distribution feeders go out.

What is the difference between a circuit breaker and a disconnect switch?

A circuit breaker can switch a circuit off while current is flowing. A disconnect switch cannot interrupt load current; it isolates equipment once the breaker has opened.

What does the transformer do in a substation?

It changes the voltage from one level to another. In a distribution substation it lowers the transmission voltage to a level the feeders can carry to customers.

What is a bus in a substation?

A bus, or busbar, is a set of bars or wires that lines and transformers connect to. Power is routed in and out of the substation through it.