What is an airfield substation single-line diagram?
One line for the whole three-phase system, showing how power gets from the utility to the airfield lighting.
A single-line diagram draws a three-phase electrical system as one line, with a symbol for each device. An airfield substation single-line diagram shows how power gets from the utility supply to the airfield lighting: the incoming breaker and transformer, the standby generator and changeover switch, the low-voltage main bus, and the protected feeders that leave it.
It is the first drawing to read before isolating a circuit, tracing an outage or planning an extension, because it shows where each circuit comes from and which device protects it. The changeover on the diagram is also where the switchover time arises. A diagram that no longer matches the site is dangerous, because isolation and fault-finding decisions are made from it.
- Start at the source. Find the utility supply and the standby generator.
- Follow the incoming line. Note the breaker and the transformer between the utility and the changeover.
- Find the changeover. This is where the load moves between the two sources.
- Read the bus and feeders. See which loads are fed, and which breaker protects each one.
- Note protection and earthing. Check the protective devices and the earthing arrangement shown.
- Check against the site. Confirm the drawing is as-built and mark the isolation points before work starts.
Frequently Asked Questions
Q1What is a single-line diagram?
A single-line diagram draws a three-phase electrical system as one line, with a symbol for each device such as a source, breaker, transformer, switch or bus. It leaves out the detail of the individual phases so the whole system can be read on one page.
Q2What does an airfield substation single-line diagram show?
It shows how power gets from the utility supply to the airfield lighting: the incoming supply and breaker, the transformer, the standby generator and changeover switch, the low-voltage main bus, and the protected feeders to the regulators, the UPS and the building services.
Q3Why is the single-line diagram useful for AGL work?
It is the first drawing used to understand what feeds what. It is used to plan isolation before work, to trace the cause of an outage, and to plan an extension, because it shows where each circuit comes from and which device protects it.
Q4Which loads are on the standby side of the changeover?
That depends on the design and the authority's requirement. Annex 14 Volume I lists the facilities that need a secondary power supply, and the diagram shows which feeders are connected after the changeover. Check the electrical design for your site.
Q5How do I keep the diagram up to date?
Update it after every change, mark it as-built, give it a date and revision, and check it against the site. A diagram that no longer matches the installation is dangerous, because isolation and fault-finding decisions are made from it.
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