Click through the live one-line diagram, then drill the vocabulary with flashcards, a quiz, and a circuit-building game. Includes feeder ties, SCADA/automation, reliability metrics, and rough equipment costs — from the substation fence to the customer's meter.
A one-line diagram draws each circuit as a single line, even when it really carries three phase wires. The conventions below are the ones this diagram uses.
The feeder is the continuous three-phase backbone leaving the substation, labeled “3φ, OH.” It’s the trunk.
A lateral is labeled on the tap conductor itself (“1φ tap, OH”), not on a pole, because a lateral is a circuit, not a piece of hardware. This is usually where a single-phase tap peels off to serve a smaller area or a single large customer.
Solid = overhead, dashed = underground, applied the same way to primary and secondary. Color separates primary (orange, ~12kV) from secondary (blue, 120/240V), so color and line style each carry exactly one meaning.
The riser pole marks the literal point where an overhead conductor becomes a cable and goes into the ground. It’s a real piece of hardware worth knowing, since it’s where crews actually do the transition splice.
“Service drop” is reserved for the overhead conductor from a pole transformer to the customer. The underground equivalent, from a vault or pad-mount transformer, is a service lateral.
Both show their normal state (N.C., normally closed) right in the label. That’s the single most important thing a one-line communicates about a switching device.
A recloser is a self-contained circuit breaker with built-in relaying. It senses fault current, opens automatically, waits a set interval, and recloses to test whether the fault cleared (a tree branch, momentary contact) or persists (a downed conductor). It typically goes through 2–4 operations before locking out and staying open, which is why the lights sometimes blink a few times before an outage actually sticks. That’s the recloser doing its job.
The control center has monitoring/control links (dotted) into the recloser and the switch. Those are the two points where an operator can see status and, for the switch, operate it remotely from the office.
Not every device on a feeder is SCADA-equipped. The fuse and transformers here are not, which is realistic: fuses are purely local, non-communicating protective devices.
Left out on purpose. Ties introduce backfeed and restoration, which are easier to learn once primary vs. secondary and OH vs. UG are solid. You can work with a tie hands-on in the Playground tab, and it’s still in the Glossary.
Feeder A and Feeder B are tied together at a normally-open point. Click any switch, recloser, or the tie to operate it by hand. Hit Insert Fault, then click a spot on the trunk line or on a lateral to simulate a problem — then work out how to isolate it and restore as many customers as you can.
Click the pieces below, in order, to trace power from the substation to a customer's outlet. There's more than one valid full path in real life — build the standard overhead one.
These three numbers are how utilities and regulators score grid reliability. Every capital project you evaluate — a recloser, a feeder tie, an undergrounding program — ultimately gets justified by how much it's expected to move these.
System Average Interruption Duration Index. The average number of outage-minutes a customer experienced over the year. This is the headline number regulators watch.
System Average Interruption Frequency Index. The average number of separate interruptions a customer experienced. Reclosers and feeder ties mainly attack this number.
Customer Average Interruption Duration Index. Of the interruptions a customer did have, how long each one lasted on average — a measure of how fast crews restore power once something fails.
Set your system's total customer count, then add outage events (customers affected × how long it lasted) to see how they move SAIDI/SAIFI/CAIDI. This is the same math utilities run for a whole year of events.