What is a three-line diagram in power systems?

[Passacaglia]

Hi all, is anyone familiar with the term 'three-line diagram'? I've been searching and googling up the wazoo, but all I've uncovered so far is that "A three-line diagram is more detailed than a one-line diagram," which is frustratingly vague. I'm guessing that this term is an alternate one for a more commonly-used term.

(I'm a three-year EE student working an informal internship at a small hydroelectric facility. My 'bosses' have asked me to look into reconnecting to the NYS grid via the NYSEG power company, but neither of them are engineers so I'm mostly on my own. A three-line diagram is one of the first steps that NYSEG documentation requires to connect to the grid. I've been trying to reach NYSEG, but I figured I'd ask the good PF folks instead of sitting on my hands.)

 

[berkeman]

Hi all, is anyone familiar with the term 'three-line diagram'? I've been searching and googling up the wazoo, but all I've uncovered so far is that "A three-line diagram is more detailed than a one-line diagram," which is frustratingly vague. I'm guessing that this term is an alternate one for a more commonly-used term.

(I'm a three-year EE student working an informal internship at a small hydroelectric facility. My 'bosses' have asked me to look into reconnecting to the NYS grid via the NYSEG power company, but neither of them are engineers so I'm mostly on my own. A three-line diagram is one of the first steps that NYSEG documentation requires to connect to the grid. I've been trying to reach NYSEG, but I figured I'd ask the good PF folks instead of sitting on my hands.)

Welcome to the PF.

Others will give you better answers, but I'm guessing they mean the 3-phase power wiring diagram? The utility is definitely the best to talk to. They will need to do inspections and approve your interconnect circuitry/modules.

 

[dlgoff]

... I've uncovered so far is that "A three-line diagram is more detailed than a one-line diagram," which is frustratingly vague.

A one-line diagram:

A three-line diagram:

 

[berkeman]

See, like I said. There's a *better* answer!

 

[Passacaglia]

Thank you all!

 

[sophiecentaur]

You get the same sort of 'abbreviation' with layout diagrams of complex digital circuits where 16 or 32 lines get drawn as one. Really essential at times.

 

[psparky]

We also use the words "one line" or "single line".

Single lines are typically used for overall power distribution like in factory substations...or a single line to describe say 100 or more substations in a factory.

Instead of using three lines, they just use one line to represent three phase power. Makes sense when you have multiple loads to keep track of on one single page or drawing.

In the drawing above, three line makes more sense because they are showing details of how to wire it.
Single lines are more of an overall view to the electrician or plant engineer.

 

[dlgoff]

A one-line diagram:

A three-line diagram:

Lost the three-line diagram as Hot Linking is Dis-allowed. So here's another one:
image compliments of http://www.electrical-installation.org/enwiki/LV_distribution_networks

 

[Passacaglia]

This has all been very helpful, and I got a good start on this diagram yesterday!

Can anyone recommend a pdf with all of the common circuit symbols and labels? Not necessarily with every single symbol under the sun, but enough so that I don't have to invent symbols for stuff. (An asynchronous generator with a Y-connection and a motor starter have already come up.)