The pic and this narrative were done to provide a basic understand of electrical distribution systems that I generally install, maintain, train other personnel on, etc.
I’ll try to keep this short to preserve my fingers.
But if you have any questions, fell free ask.
I’m calling the above drawing a Modified One Line Drawing.
We use One Line Drawings all the time; they provide the functional relationship between different pieces of equipment. I added the word Modified because One Lines don’t provide voltages, names, etc. They do provide the Equipment Numbers, which are given to each piece of equipment. These Numbers are generally based on the floor the equipment is on, and either column intersections (letters and numbers), room numbers, etc.
The pic is a composite of the various jobs I’ve worked on.
All the numbers I’ll talk about: Voltage, amps, weight, etc. are real figures, but vary widely depending on the installation.
I’ll start by describing this system, then later walk through its functioning.
On the left top, you’ll see City Power. This is where the power initially comes into the job site, bldg., etc. It may originate from the city, county, etc. The City owns that bldg. and its contents, and they are the ones who come to the jobsite and operate Breaker 1 (Brkr 1).
Switch gear and breakers.
The breakers in there weigh about 250 lbs., and are rated at 13.8KV, 1200 amps. They’re about 3’ x 3’ x 3’. They have motors in them. The motors compress springs (we call it charging). These springs are used to move the fingers of the breakers that make contact with the bus bar. Once the brkr is charged, it can be closed manually by pushing a switch, or by the CMC (later). The brkr closes extremely fast, and it is a loud, equipment shaking event. It is done this way to prevent electrical arcing. The closing mechanism is very strong; it will amputate fingers.
I mentioned CMC - control and monitoring circuits. Generally all swtch gear has this, and the voltages used are 120VAC, 24VDC, and/or 12VCD. This is a system used to control and monitor the brkrs, voltage, amps, HZ, etc. Brkrs talk to each other, and the entire system may be monitored at a remote location. It’s pretty damn elaborate.
Let’s talk about bus bars for a minute, as it applies to Peterle and my conversation in the Radiation thread. The yellow things in my drawing represent the bus. If you have ever looked at a panel at Home Depot, you’ll see 2 pieces of copper about 1/8” thick x 1’ long x 1” wide – this is the bus bar, or bus as we call them. The bus is what applies electricity to the brkr. If you ever see bus, DO NOT TOUCH IT as it may be energized.
In the swtch gear I work in, the bus comes in 8’ x 6” x ¾” sections. I’ve worked on swtch gear that was 52’ long, and they bolted 3 8’ sections of bus together. And they’re worth a fair amount of money. The permanent generators are big, expensive things. At a previous job, the gens were 13.8KV, 1000 amps, burned 175 gallons of diesel per hour at max load, and cost a little over $1,000,000 each – and there were 24 of them. IIRC the max load for the system was 800 amps.
So how does it all work?
Start in the upper left corner where it says City Power, and follow the lines. Power enters the jobsite usually at 13.8KV.
The city supplies the power to the job site through Brkr 1. Brkr 1 feeds Brkr 2 inside a swtch gear. Brkr 2 is the main brkr for that piece of gear. If you want to turn the power off for that piece of gear, open Brkr 2.
Now look at the lower left corner, and you’ll see a Permanent Generator – this generator supplies power in an emergency when City Power is stopped.
It works like this. The CMC sees there is city power to the system, so it stays open. When City Power stops for any reason, the CMC tells Brkr 1 and Brkr 2 to open to prevent back feed to the City’s grid. It also tells Brkr 3 and Brkr 4 to close, and for the Permanent Generator to come one. Then the generator is now supplying power.
Oops; looks like I screwed up the numbering and forgot the number 5.
So now to get power into the bldg. (from either the City or the Generator), we have to close Brkr 6.>> Brkr 6 feeds Brkr 7 in a swtch gear, which is the main Brkr for a 13.8KV to 277/480V transformer. This piece of gear is extremely elaborate, and I could talk at length about how it works, all the breakers, etc.
Previous job I was on this gear was 52’ long. It had a 13.8KV to 277/480 transformer on each end – each transformer weighed more than 16,000 lbs. The gear was fed twice on each end with 138.KV City Power, and had about 20 Brkrs of assorted ampacities .
I think you can follow the rest of the One Line. Again, ask questions if you have them. Let’s talk about the Batteries and the Cooling Pump in the lower right.
The Batteries – we call them UPS – are designed to provide power when City Power and Perm Generator fails. They don’t last a long time, and IRRC the Japan battery system was designed to last 8 hrs. These systems are constantly charging, provided they have City, Generator, etc. going to them.>> Once City or Generator power is stopped to that panel, the batteries will start supplying power to that panel, and keep the Cooling Pump going.
UPS systems are complex and expensive.
Now look at Options 1, 2, and 3.
This is where a Temporary Gen could be attached to provide power when the City, Perm Gen, and Batteries have failed.
It could be attached anywhere in the system depending on what needs to keep running, voltages required, etc.
I basically have no idea what kind of problem they had when the article mentioned they couldn’t use the Temp Gens because the plugs didn’t match.
Say what?
The gens I use for these types of applications don’t use plugs. As Peterle mentioned, we use hydraulic lugs to attach the wires.
This is just an extremely abbreviated version of how these systems work, but maybe it’ll give you an idea of what's going on.
OK, my fingers are toast.
Ask them if you got them.
Last edited by Backstop; March 23rd, 2011 at 14:32.
Reason: New WP is killing me.
It would appear that you and Peterle are in the same line of work. A good friend of mine was a lineman for a good number of years. I have a lot of respect for you fellas who work with high voltage.
As for myself outside of installing some simple 110v outlets my knowledge of electrity is painfully lacking! I spent 2 years building and installing traffic control boxes. Turning stop lights from red to green is more challenging than one might think. I must admit I enjoyed my time as a "cabinet rat" quite a bit. One thing I learned was that a DC spike can be as painful as a 110v spike.
Interesting stuff, I wish I knew more about all the distribution equipment but I only work on 480 down (maintenance electrician) mostly troubleshooting control circuits. I am actually a licensed operating engineer for turbines but I don't do that, so my license just sits....probably a mistake.
Cool pics though, I could look at that stuff all day.
Basic Electrical Distribution System
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Originally Posted by Luke
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