Dabop
Master Poster
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120 V or 240 V Mains - which voltage is better?
- Thread starter psionl0
- Start date
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- electricity
Dabop
Master Poster
The problem isn't "armature stress" either, but smooth operation.
um right.....
it certainly can be a problem - esp in heavy duty motors
It can literally tear the insulation to pieces....
thats why 3 phase motors are common, and 180 deg 2 phase motors much less so- they need to be massively overengineered to survive ie very expensive and much less power than similar sized 3 phase motor
um right.....
it certainly can be a problem - esp in heavy duty motors
It can literally tear the insulation to pieces....
thats why 3 phase motors are common, and 180 deg 2 phase motors much less so- they need to be massively overengineered to survive ie very expensive and much less power than similar sized 3 phase motor
psionl0
Skeptical about skeptics
It's interesting to compare the (three phase) motors and generators used on aircraft with normal 50 or 60 Hz stationary ones. For the same power rating, the aircraft units are much smaller and lighter.
The reason is that they run at a higher frequency (400 Hz was common at one time - I don't know if that's still a common aircraft frequency). Because the magnetic flux is changing much faster with the higher frequency, the actual flux strength doesn't need to be so high - so the 'iron' (magnetic) circuit of the units can be much smaller and lighter.
The reason is that they run at a higher frequency (400 Hz was common at one time - I don't know if that's still a common aircraft frequency). Because the magnetic flux is changing much faster with the higher frequency, the actual flux strength doesn't need to be so high - so the 'iron' (magnetic) circuit of the units can be much smaller and lighter.
aleCcowaN
imperfecto del subjuntivo
Three-phase power was always a matter of medium to high power and saving money. Here in Argentina you have a whole bunch of three-phase inverters to use with solar panels, but the high quality ones cost around 500 euro per Kilowatt, and there's no one that I've seen smaller than 4 Kw. One could use one of them to generate three-phase power from a single-phase or split-phase conventional source but, where's the economy in it? The only reason I see to resource to that is the electric company making you pay for the extra two wires if you're, say, 10 miles from the nearest three-phase line. And yet you could manage just with one extra wire and triángulo abierta if the extra charges from unbalanced charge doesn't make it bad business.
Dabop
Master Poster
The reason I've been involved with single-phase to three phase conversion is when I've been using factory equipment in my home workshop - or helping friends to do that. Lathes, milling machines and such often have three phase motors - but when you buy an old one and put it in your home workshop, no three phase is available. Sure, you could ask the electricity company to run three phase to your house, but if you only want to run one or two fairly small machines it's usually easier and cheaper to generate your own local three-phase supply from the single phase one already available in your home.
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aleCcowaN
imperfecto del subjuntivo
Well I can see what was said......
And what about the other post in it where it's refer as "the so-called two-phase system"?
So far it start to emerge the notion of using "two-phase" in a popular setting as a way to say "don't try to mix them, you'll mess everything up", and not for the scientific value of it.
Fortunately nobody can't mess it up with the so-called "two-phase" as to invert the spin of a motor, what would be so easy to do in a real poly-phasic setting.
Dabop
Master Poster
http://www.fcxinc.com/why-the-aviation-industry-operates-on-400-hz-power/
They still do, and it was because the transformers etc would be much smaller and lighter than if they ran at 50 or 60 Hz
The lower frequency is better for longer runs (not usually an issue on aircraft, not even the Antonov An-225 is THAT big) but obviously weight is a major factor on all planes
aleCcowaN
imperfecto del subjuntivo
That's quite true, if you're running those motors for short periods.
Another thing I'd consider here -I don't know if it is the same way elsewhere- is that you have just one metre for one-phase (or two-phase, which is the same thing) and you would have a different metre for three-phase, with duplication of the basic charge, or everything on the three-phase metre. In my country all three-phase metres really measure two phases and multiply by 1.5. They force you to hang your one-phase service to one of the two phases that are measured, so you're instantly paying 150% for your household electricity. Unless you hang your house from the third phase, which is a crime. What means you're either a criminal or an idiot who is paying more than he owes.
In those cases using some capacitors and whatnot to create an inefficient three-phase system that runs one hour a day is the soundest and more economic solution.
psionl0
Skeptical about skeptics
That may be true in the US but here, the cost of a 3 phase meter is only $100 more than that of a single phase meter. Other than that, supply charges are identical.
I doubt that you can get a several kilowatt 3 phase inverter for less than $100.
Dabop
Master Poster
And further down again, the poster you mentioned says....
note the bolded and underlinedRoger said:
Speaking of the 240V/120V three-wire, single-phase, mid-point neutral system used in the US ....
Shortly after I came home from work one afternoon, half the electricity went out in my house. It was very bizarre. Some kitchen appliances were working. Others weren't. There didn't seem to be any logic to what was working and what wasn't.
Even though I have (or should have had) enough knowledge of electrical systems to understand what was happening, with my house seemingly dying around me, my brain wasn't working right.
I called the power company thinking they could, at least, tell me who could fix the problem. One of the selections in the phone menu was "If only one half of your power is out in your home, press ...." Oh ... That's when I realized what must have happened.
In less than an hour, the power company had a service truck at our house. The technician installed some device that attached to our electrical meter sort of like the face-sucking creature in the Alien movie. It restored power to my house until, a few days later, a connection in the box by the curb was repaired.
Shortly after I came home from work one afternoon, half the electricity went out in my house. It was very bizarre. Some kitchen appliances were working. Others weren't. There didn't seem to be any logic to what was working and what wasn't.
Even though I have (or should have had) enough knowledge of electrical systems to understand what was happening, with my house seemingly dying around me, my brain wasn't working right.
I called the power company thinking they could, at least, tell me who could fix the problem. One of the selections in the phone menu was "If only one half of your power is out in your home, press ...." Oh ... That's when I realized what must have happened.
In less than an hour, the power company had a service truck at our house. The technician installed some device that attached to our electrical meter sort of like the face-sucking creature in the Alien movie. It restored power to my house until, a few days later, a connection in the box by the curb was repaired.
psionl0
Skeptical about skeptics
lol
Dabop
Master Poster
Interesting- it must have been basically a miniature 2:1 transformer, but being used as a step UP transformer- ie it was pulling mega amps through the still working phase, stepping the voltage up and then backfeeding it into the defunct phase
I bet the wires leading in from the street on that working phase were running a tad 'warm' lol (as before halving the voltage means doubling the current, so instead of your stove pulling 20a @240v, it was using the transformer and pulling 40A through the working 110v phase.... as an example- actual figures would of course be different, but always twice the rated current on the ratings plate)
psionl0
Skeptical about skeptics
A 1:1 transformer with its secondary winding reversed would be all you need to get the "defunct phase" working. (You could even use a centre tapped auto transformer
) You would just connect the primary across the working side.
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Dabop
Master Poster
hmm yeah- could be-didnt think of that
either way that working phase was working HARD!!!
either way that working phase was working HARD!!!
Lots of factory control systems in the UK run at 110V AC. The idea is that it's safer even though it involves the extra hassle of 240V (or 400V) to 110V transformers.
Unfortunately there are two different ways of doing it that causes much confusion, blown fuses and cursing when connecting different systems together.
One system is to have a centre-tapped transformer with the centre-tap connected to ground and two anti-phase wires of 55V AC each. Very similar to the two-wire 220V USA system. This has the advantage of a lower voltage from any wire to ground - and voltages below 60V used to be considered safe enough that you could touch them without getting a noticeable shock (assuming you weren't standing in a pool of salt water or similar) so you didn't even need to worry too much about shrouding terminals and similar inside control cabinets.
The drawback of this 55V - 0 - 55V idea is that you have to put fuses in both of the 55V wires. When a fuse blows and a panel is apparently 'dead' the other fuse often hasn't blown so you often get people tinkering around trying to find the fault when they suddenly surprise themselves by shorting the remaining wire to ground with the accompanying sparks and curse words!
So the more common system now is to have a single 110V winding on the transformer, connect one side of it to ground, and then you have a more dangerous 110V to ground on the other wire, but you only have to fuse that one wire and when the fuse does blow, the circuit is then really dead and safe to work on until the fuse is replaced even when the maintenance engineers forget to throw the isolator.
As I say - the problems really arise when you have to connect one 110V centre-tapped panel to another single-ended one. It's quite common to see banks of 110V coil relays whose sole function is to convert between the two varieties of 110V signal!
Unfortunately there are two different ways of doing it that causes much confusion, blown fuses and cursing when connecting different systems together.
One system is to have a centre-tapped transformer with the centre-tap connected to ground and two anti-phase wires of 55V AC each. Very similar to the two-wire 220V USA system. This has the advantage of a lower voltage from any wire to ground - and voltages below 60V used to be considered safe enough that you could touch them without getting a noticeable shock (assuming you weren't standing in a pool of salt water or similar) so you didn't even need to worry too much about shrouding terminals and similar inside control cabinets.
The drawback of this 55V - 0 - 55V idea is that you have to put fuses in both of the 55V wires. When a fuse blows and a panel is apparently 'dead' the other fuse often hasn't blown so you often get people tinkering around trying to find the fault when they suddenly surprise themselves by shorting the remaining wire to ground with the accompanying sparks and curse words!
So the more common system now is to have a single 110V winding on the transformer, connect one side of it to ground, and then you have a more dangerous 110V to ground on the other wire, but you only have to fuse that one wire and when the fuse does blow, the circuit is then really dead and safe to work on until the fuse is replaced even when the maintenance engineers forget to throw the isolator.
As I say - the problems really arise when you have to connect one 110V centre-tapped panel to another single-ended one. It's quite common to see banks of 110V coil relays whose sole function is to convert between the two varieties of 110V signal!
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It worked well enough to run our air conditioning - which can be rather important here in Florida.
DGM
Skeptic not Atheist
In the US there might not be 3 phase available in residential areas for miles. In a small shop, generating your own is often the only economically viable choice.
It cost me around $2000usd to bring it to my shop from around 1/4 mile away.
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