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Ender.uNF posted:Thanks for the info; I'm still trying to understand reactive and PF and revise it into a layman's explanation. I've used this analogy a few times in real life, I hope it work as good on the internet. Imagine a theoretical small village with a single well in the center of town. every resident has a 10 gallon bucket that they fill in the morning. They use water from the bucket all day and at the end of the day they bring their bucket back and return the extra water. An attendant measures how much water they used and charges them accordingly, say 10 cents a gallon, and then dumps the rest back down the well. the person who used 5 gallons pays 50 cents. the person who used all 10 gallons pays 1 dollar. at first this sounds fair. until you realize that it took equal amounts of work to supply each person with their daily water. In fact, it actually took more work to supply the 5 gallon person with water because the well attendant had to handle their return in the evening, yet the 5 gallon person pays less. If theres 100 citizens and each fills a 10 gallon bucket, the well must be able to supply 1000 gallons even if only 500 are actually used. Imagine the above scenario happening 60 times a second and replace the water with electricity and the well with the electric grid. Thats power factor. A customer with low power factor is basically taking more current than needed, using some of its energy, returning the rest, and only being billed for their consumed kilowatts. The utilities compensate by having meters that can read PF and then they add a surcharge for low PF customers. In the above well scenario, the citizens could improve their "power factor" by taking only the amount of water they will need for the day. Then the load on the well its operator would be representative of the actually needs of the community and more customers could be served by the same well.
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Sep 8, 2011 05:13
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grover posted:I think you're confusing delta with center-tap delta, which is a special case and not all that common. Delta and Wye are a lot simpler than that: I'm in Chicago and a significant portion of our services here are center tap delta. by significant I mean 90% of anything more than 20 years old. this gives you 2 legs of 120 volts for your everyday 120V stuff and one leg of WTF for letting the smoke out of your everyday 120 volt stuff. But between any two legs you get 230 volts, great for running large single or 3-phase motors. The slightly higher voltage makes motors start easier and run cooler. It seems like the majority of new buildings are using 120Y/208 service now. Drheat fucked around with this message at 02:56 on Sep 16, 2011 |
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Sep 16, 2011 02:54
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movax posted:
Better yet, some industrial Delta systems are Corner Grounded. I've only seen one, and it will really throw you for a loop. Its a 3 phase system, but your main panel will only have 2 bus bars, and will use 2-pole breakers rather than 3-pole. you connect two phases from your load to the breaker, and the 3rd phase connects to the grounded "neutral bar" you cannot get multiple voltages from this system and its more dangerous due to the higher phase to ground voltages versus 120Y/208 As for ungrounded delta it has an interesting advantage that is also a hazard. In the event that a piece of equipment or wire "shorts" to ground, nothing will happen. Everything continues operating as normal. however if a second short to ground occurs on a second phase, all hell breaks loose. in a facility using this type of power there will normally be a ground detector, which is just some light bulbs hooked up in a fashion that will alert the facility operators that a ground fault has occurred and the equipment needs attention. This makes ungrounded delta nice for critical equipment because it can continue to run with a single ground fault. Drheat fucked around with this message at 03:16 on Sep 16, 2011 |
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Sep 16, 2011 03:10
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Nerobro posted:They are, they are also typically reciprocating pumps, so the same action that actually pumps the fuel is not wasted on "moving the armature" through the fluid. It's a clever set of design choices! I have changed many fuel pumps on American and Japanese cars and have never seen a a reciprocating pump. they have all been standard brushed DC motors that drive a gear type positive displacement pump. A few years ago the fuel pump on my Caravan died after 250,000 miles. I cut the pump apart expecting to find worn out brushes. I was shocked to find the brushes still at 50%, but the commutator had worn away to the point there was no more copper left, just the fiber insulating material.
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Sep 30, 2011 04:19
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I live in an older neighborhood with lots of trees and all of our power is overhead wires. Last spring we had some bad storms and were without power for 6 days one week and 4 days 2 weeks later. This spring the utility is doing some work that I'm guessing has to do with getting the system ready for spring storms. the main streets have 3 phase medium voltage service on the poles and between each side street is a single phase branch that runs down the back yards to feed transformers for the houses on those streets. Where the branch line ties into the main line theres a fuse/switch device. Over the last few weeks they've been replacing these fuses with new ones that have a big canister hanging off the bottom. It appears to be about the size of a 1 liter bottle. They seem to attach to the existing fuse holders. Any idea what this is.
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Mar 29, 2012 03:48
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Three-Phase posted:Sounds like a single-phase recloser. Thats exactly what it is. In fact its exactly that model. Interesting idea, but I don't think its going to help much in our area. We don't have issues with nusance outages due to animals or rubbing tree branches. All of our outages are due to the wires being on the ground and I don't see a recloser helping with that situation.
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Apr 1, 2012 04:46
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