Wikipedia:Reference desk/Archives/Science/2016 November 21

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November 21

About Transformers

Hi, We know that the number turns in primary coil, in comparison to the otherone, play the role of determining input/output in terms of voltages. My question is that can the thickness of wire on either side cause difference in output of power coming out, in terms of voltage or in any other terms ?124.253.244.210 (talk) 10:16, 21 November 2016 (UTC)

The thickness of the wire determines the resistance of each winding. The resistance of the winding affects the current that flows in that winding. The current flowing in one winding affects the current flowing in the other winding. But apart from that important consideration, the thickness of the wires is not a primary cause of difference. Dolphin (t) 11:31, 21 November 2016 (UTC)

The article Transformer explains that the windings in a real transformer have finite non-zero resistances. Winding resistance is inversely proportional to the cross-sectional area of the wire used. Consider the winding resistance $R$ as a resistor in series with an ideal winding. Any current $I$ in the winding causes a voltage drop according to

$V=IR$

and loss of power as heat according to

$P=IV$.

Power transformers are usually wound with sufficiently thick wire to make these losses negligible. If the wire diameters of the primary and secondary windings are inversely proportional to the voltage (turns) step-down ratio, the joule losses in the windings will be approximately equal. However in transformers for high frequency currents the effective wire resistance is increased by the Skin effect. At high frequencies a braided bundle of thin wires or Litz wire can achieve lower loss than a single round wire. DaDoRonRon (talk) 11:39, 21 November 2016 (UTC)

DaDoRonRon, it is not true that winding resistance is inversely proportional to the cross-sectional area of the wire (except for direct current). For alternating current, which is the kind you make go through transformers, skin effect applies.

To answer the question, in the ideal-transformer model (zero resistance), thickness does not matter, but for the real thing Joule effect is of course taken into consideration in the design. Tigraan^{Click here to contact me} 11:49, 21 November 2016 (UTC)

Our article states that "An object of uniform cross section has a resistance proportional to its resistivity and length and inversely proportional to its cross-sectional area." which is consistent with resistance normally being specified at DC. DaDoRonRon (talk) 12:31, 21 November 2016 (UTC)

...and when it isn't DC, we can calculate how different it will be at whatever frequency we are using. See Skin effect. --Guy Macon (talk) 15:22, 21 November 2016 (UTC)

DaDoRonRon does have a point that there is no textbook definition of "wire resistance" that depends on frequency. I think their original answer did not insist enough on that crucial point, but there is no need to argue when everyone seems to agree on the physics. Tigraan^{Click here to contact me} 15:38, 21 November 2016 (UTC)

DaDoRonRon can have points all day, but I don't think he'll be replying anymore to this (or any other thread). It's an old friend coming back for a visit. He's been shown the door. --Jayron32 16:29, 21 November 2016 (UTC)

Also, there most certainly is a textbook definition of "wire resistance" that depends on frequency. See Impedance. --Guy Macon (talk) 16:55, 21 November 2016 (UTC)

Oh well. WP:DENY, I guess. Tigraan^{Click here to contact me} 17:33, 21 November 2016 (UTC)

High wattage circuit breakers

Orders of magnitude (current) confirms 15 or 20 Amps is the typical North American circuit breaker rating. At a nominal 120 Volts that's about 1.8 or 2.4 kilowatts. It says 10 and 20 Amps for Europe which is about 2.3 and 4.6 kilowatts since 230 Volts is the nominal standard. Why is Europe so awesome? Do any parts of the world exceed 2300/4600W? What part of the 230+ Volt world has the lowest percentage of sub-20 Amp circuits? Do these high wattage countries have more powerful microwaves, hotplates, vacuum cleaners, blenders etc? Are some electrics like blankets, lawnmowers or chainsaws more common there? Does a higher wattage common socket enable uses/inventions that North America doesn't even use? Sagittarian Milky Way (talk) 19:23, 21 November 2016 (UTC)

I'm on 240V. The only appliance I have that is rated over 1.8 kW is my immersion heater for hot water at 3.2 kW, and that is on its own circuit breaker, hard wired in. The most powerful plug in motors I have on a standard 10A plug are 1.8 kW on my electric chainsaw,rotary saw table and log splitter. Judging by the current load the vacuum cleaner must be about 1.8 kW as well. In Australia we also have 15A plugs, but they don't tend to be used in houses. So, it would appear that the USA's inferior electrical system (designed by politicians) sets the standard for the world. Funny dat. UK fuses (in the plugs) used to be 13A, at 240V. Greglocock (talk) 20:18, 21 November 2016 (UTC)

Hot water heaters here have two circuit breakers connected together with one handle. That's the only way we can get 240V in the home (connect a +120V wire and -120V wire to each other instead of to neutral) Sagittarian Milky Way (talk) 21:36, 21 November 2016 (UTC)

Wait, an immersion heater is a rod you stick in something instead of putting the something on the stove? American water heaters are tanks in the basement fed by water mains. See, you have appliances I've never heard of. Sagittarian Milky Way (talk) 21:57, 21 November 2016 (UTC)

Immersion heaters are generally installed within the hot water tank, so that you can switch them on to provide a boost to water heating when needed (e.g. when you want a shower at a time when the normal water heating from the boiler is off). It's to make the water that comes out of the hot tap hot, rather than to replace heating water on the stove (we use electric kettles for that, which are technically similar to immersion heaters but would not be referred to as such). While the portable ones shown in the article exist, they'd be just as confusing to someone in the UK as they are to you (and I suspect they would have standard fuses/wiring). MChesterMC (talk) 09:14, 22 November 2016 (UTC)

Or in the garage or (as in my house) an outside closet. We don't have basements in Southern California! Also here all the central heating, water heaters, ovens, etc. use natural gas, because that's cheap while electricity is expensive. As mentioned by others, we have 240V split-phase for some heavy-duty appliances. My house has 240V hookups for the central air conditioning compressor, electric clothes dryer, and electric oven. (As I said, most people here use gas ovens instead, but they still seem to build most homes with the electric oven socket.) Also my home has a few 20A sockets, though I don't think I have anything that uses the 20A hookup. Luckily the NEMA 5-20 socket is "downwards-compatible", so you can use it like a plain 15A socket and plug in regular appliances. --47.138.163.230 (talk) 19:04, 22 November 2016 (UTC)

In the UK, high-power individual plug-in appliances are limited by a 13A fuse (just over 3 kilowatts) to protect the socket and flex from overheating, but a typical ring circuit is protected by a 30A circuit breaker (7.2 kilowatts or 7.5 at the 250v that I usually get). 3 kilowatt kettles and portable heaters are common here. Dbfirs 20:25, 21 November 2016 (UTC)

In NZ, where many appliances sold here are also sold in Australia, I've owned a few plug in portable room heaters that are specced over 1800W. (These may be less common in Australia given climate and house design differences.) My kettle is also 2000-2400W and IIRC many kettles are at least 2000W. Home deep fryers also tend to be 2000W-2400W (although probably not that many homes have these). IIRC the wall paper remover I used a few years back was also 2400W. In other words IMO home appliances where you want significant heat are often rated above 1.8kW and I expect more common also in Australia than Greglocock suggests. But the 2.4kW/10 amp limit I agree with. I've never seen a 15 amp plug and they almost never occur in houses. Nil Einne (talk) 12:33, 22 November 2016 (UTC)

It is correct that the typical circuit in North America is 15 A or 20 A at 120 V, but it is standard to provide for higher power levels for appliances that require them such as electric stoves, central air conditioners, etc. My house has four such circuits, as large as 40 A at 240 V. We just don't have that much power at ordinary outlets. --76.71.5.45 (talk) 21:23, 21 November 2016 (UTC)

Yes, we have higher power for hard-wired appliances here in the UK too, including power showers up to 10.8 kilowatts with a 50 amp circuit breaker. (I don't have anything so decadent!) Dbfirs 00:18, 22 November 2016 (UTC)

Do you have plug-in railguns and hobby woodcarving lasers? Sagittarian Milky Way (talk) 01:01, 22 November 2016 (UTC)

Not personally. Are they common in your part of the galaxy? Dbfirs 08:48, 22 November 2016 (UTC)

Our article on this: split-phase electric power. Other articles of potential (heh) interest: mains electricity by country, AC power plugs and sockets. --47.138.163.230 (talk) 19:04, 22 November 2016 (UTC)

There's an interesting article on the reasons for the different voltages at http://www.worldstandards.eu/electricity/why-no-standard-voltage/ I hadn't realised until reading it that the US system used a compromise of 240v split into two to provide the 120v supply. Back in the 50s and 60s before domestic central heating systems became affordable, 3Kw electric radiant heaters were quite common in the UK homes. You can still buy 3Kw fan heaters that plug into a 13 amp socket. [1]Richerman (talk) 13:04, 22 November 2016 (UTC)

Typical circuit breakers used in Germany are 6, 10, 15 (old), 16 (most common), for Industry and stove and pre fuse: 20, 25, 32 A. Germany does not use split-phase electric power. Each phase is 230 V AC to neutral and 400 VAC to other Phase. Such three-phase electric power allows Sternschaltung and Dreieckschaltung to start a three phase motors at 230 V and change to 400 V to operate. 115 V AC equpment can not be used in Germany without reconfiguration or additional transformer. In switching mode power supplies PFCs or delon circuits can help. Heaters sometimes use 2 separate 115 V heaters to use in parallel or in row to fit the 230 V power grid. --Hans Haase (有问题吗) 15:42, 23 November 2016 (UTC)

• US homes come in all sizes from hovels to mega-mansions. Larger homes may have a 400 Amp split-phase service entrace, or larger. the mains breaker is a split-phase breaker with a pair of 400 Amp breakers mechanically tied together. A big house may have one or more sub-panels with branch circuts from the main panel. These breakers can be (e.g.) 200A, 100A, or lower. The home may have fixed appliances (stove, range top, HVAC compressors, etc) with sizes typically up to 60A. I have never personally seen a circuit with a receptacle larger than 30A (typical for a clothes dryer), but they do exist. Some luxury homes have 3-phase power to the home, which us used for a (very few) 3-phase circuits and also used to create split-phase panels for the normal stuff. In one such installation I have seen a 3-phase plug for a Tesla car charger at 50A -Arch dude (talk) 19:46, 23 November 2016 (UTC)

Note the wire gauge needs to fit circuit breakers maximum current. Aware such risks at migrated equipment. Using analog signals, 230 V in Europe make You hear the power grids frequency in double that loud than use at 115 V due installed Y-capacitors deliver half of the grid voltage to the equipment. Using it on a split phase 230 V, both pins required to have a circuit braker behind, but wiping out their sine waves each other, no noise from the grid is in the spakers. Impossible in Europe. --Hans Haase (有问题吗) 01:40, 25 November 2016 (UTC)

X and Y capacitors are explained here and here. I never heard of them before, so I'll pause a moment before making these shortcuts - also, do we have any better target than this article? Wnt (talk) 19:44, 26 November 2016 (UTC)