Substation Question

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Substation Question

Post by VJR85 » Sat Feb 16, 2008 7:35 pm

I'm doing a project for school that involves designing a substation. I am having a difficult time deciding on the loads to use. I plan to have it power a small residential area and gather the data for the average power consumption of a neighborhood like this.

I would like to have another load that is fairly large. The only thing I can think of is a large synchronous motor driving a cooling tower for a warehouse or something. I found some motors used for this application on GE's site, but they don't seem to provide any specs on the motors.

Are there any other manufacturers that will provide a good amount of data on their websites that will allow me to calculate the load/PF/etc on the substation?

Do you know of any links that provide some good info on cooling towers and the construction involved? I've found nothing on this subject.

Do you have any other ideas for the load? The professor wants us to keep it simple, so a motor is the only large electrical load I can think of.

Thanks for any advice.

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Re: Substation Question

Post by Bigglez » Sat Feb 16, 2008 7:47 pm

Greetings (No Name Supplied),
VJR85 wrote:I'm doing a project for school that involves designing a substation. I am having a difficult time deciding on the loads to use.

Do you have any other ideas for the load? The professor wants us to keep it simple, so a motor is the only large electrical load I can think of.
That sounds like an interesting project!

Most residential loads are non-reactive (lighting, heating, cooking).
Some light industrial loads are reactive, as you pointed out,
mostly electric motors.

So how about escalators, elevators (lifts), commercial
refrigerators, compressors, machine shops? (Mills,
lathes, stamps, presses - all with 1 to 10hp motors).

In the real world nothing is more annoying that sharing
utility power with a factory that does welding!

How about a broadcast transmitter? Should be good
for 100kVA or similar?

Comments Welcome!

Robert Reed
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Post by Robert Reed » Sat Feb 16, 2008 8:39 pm

Not to forget heavy industry such as steel mills- megawatts of power, enough that Q and S lines are run directly to them (138 & 345 KV). But to clarify your post, in the utility industry the term SUBSTATION only deals with high voltage branching - 138 Kv/345KV feeding into them and as low as 33KV running out of them. They generally feed moderate industry directly but primarily feed DISTRIBUTION STATIONS. This is where light industry and residential recieve their power from. Their out put is almost always 13.2KV 'Y' connected lines you see running down your street. Older and rural neighborhoods will still have 5 KV delta connected lines in lieu of that.
There are a horde of trade magazines available free of charge (if you don't mind telling them a few white lies) that have a lot of info and product manufacturer ads in them. I did receive 'Transmission and Distribution' for several years when I worked in the utility industry. Try Googling them up as usually one hit leads to dozens of others.

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Post by jollyrgr » Sun Feb 17, 2008 6:22 am

How about this.

A Data Center with two 100KVA UPS units with a 0.9 PF; one UPS at 80% load, the other at 43% load. UPS units are 75% efficient. Four 15 Ton dual compressor air conditioners. Thirty four tube light fixtures. Seven high volume laser printers (HP 8000) not supported by the UPS units.
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

Dean Huster
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Location: Harviell, MO (Poplar Bluff area)

Post by Dean Huster » Sun Feb 17, 2008 2:05 pm

Go to your local Target store and count the number of light fixtures they have just in the public area. Multiply by the number of tubes per fixture (ours uses 4-foot tubes, 4 per fixture) and then by the number of watts per tube. Multiply this number by the number of hours per month the store is open, divide by 1000 and you'll have kilowatt hours. Multiply that figure by your local electric rate (ours is around 7¢/KWH). Just the lighting bill for the month will take your breath away. And you're using the residental rate. Commercial and industrial customers usually pay a bit more, maybe another 1¢ or 2¢. And they still have to pay the A/C and heating bill and pay for all the POS terminals, box crusher, telephone, computer, alarm systems, video surveillance system, etc. Besides the building costs proper, we call that "overhead". Wow.

I think that you'll find a LOT of reactive loads in most industrial settings as motors are a primary user. Incandescent lighting is nil. On the other hand, the commercial users (merchants and shops) are mostly lighting with some HVAC. When the industrial power factor starts going wild, they have to start hanging capacitors on the higher voltage lines to bring things in check or the power company starts to get their panties in a wad. Once you get down to a residential area, it's resistive loads are the major contributing factor. When you see the power factor twist, it's always going to be inductive reactance, not capacitive reactance unless someone's overcompensated for the PF somewhere.

Don't forget that you have several tier of substations. The final feed line around here to farms and residential areas is around 9.6KV.

Good luck on your project!

Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).


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