280V motor on 230V circuit

| Professional washing machines. One of my very first days 'in the field' was | to connect some of them. They have a large heating element, you can connect | it single phase, or 3 phase, it just heats up faster (of course) when you | connect it 3 phase. (they have a single phase motor, so it works also in | pure 230 V).

If it has 3 elements rated for 230 volts, with 3 separate connections that would be to three separate phase for a three phase feed, and all connected to the one phase for a single phase feed, then it should heat up at the same speed, while drawing three times the current (not accounting for the motor).

I don't know why it should heat up faster in three phase, or why you would say "of course" about it. I would think it would heat up faster if you took it over to London and hooked it up to a 240 volt supply.

| Since I'm posting from GoogleGroups I can't respond to Phil, but the | rest of you can be enlightened.

Actually, I do see the ones the respond to my own posts. I think the reader does that to keep the threading intact. New posts I won't see. And that is what most of the spam is (I've seen some spammers that do followups to other posts).

| In 120/240 or similar systems there is not the freedom to choose this | ratio. The wiring of the source transformer determines it. As others | have noted, in the "Edison" U.S. system the source is a center tapped | transformer with the center tap grounded. This makes a two phase | system with each 120v "leg" 180 degrees out of phase with the other | one. The ratio of the high voltage (240v) and the low voltage (120v) | is always therefore 2:1. | | In a three phase system there will be three transformers with | secondaries (one for each phase) wired in a "star" or "Y" | configuration. This is necessary because you need the center point of | the "star" or "Y" to be ground for each low voltage phase. If you wire | with a "delta" configuration there is no central grounding point | available for the individual phases. IN three phase circuits the | relationship between that individual phases to ground (say 120v) and | the voltage measured between phases is not arbitrary. It is always | determined by the square root of 3. Hence the between phase voltages | being sqrt 3 x 120 = 208V. Just like the two phase system these | ratios are determined by physics and can't be arbitrarily set.

There is no more or less option to choose once you have either system. The choice you have is between the systems. If you have single phase, you only get 2.0 as a ratio. If you have three phase, you only get 1.7320508 as a ratio.

| Of course there is the issue that electric companies often will name a | voltage one thing while actually supplying an other for small | variations about the "standard" voltage.

They call it 208 volts, but it's closer to 207.8460969 :-)

Precise voltage is not really practical. The voltage standard is a target to stay near.

In alt.engineering.electrical Thomas Tornblom wrote: | snipped-for-privacy@ipal.net writes: | |> In alt.engineering.electrical Thomas Tornblom wrote: |>

|> | Residential power in Norway is normally 230V three phase btw, instead |> | of 400V three phase. Their 230V outlets are two phase and ground |> | instead of one phase, neutral and ground. Their three phase outlets |> | therefore are blue instead of red and have four prongs instead of five. |>

|> Is this the system where the voltage is 133 volts relative to ground and 230 |> volts between phases (and formerly 127 volts relative to ground and 220 volts |> between phases)? | | Yes. | |>

|> If they still use that system, then I'm interested in buying a UPS designed |> for that. But it is my understanding it is phased out in cities and hard to |> find anymore in rural locations. | | It seems they are moving to 400V as well, but I know many Norwegians | are paying a hefty premium on their three phase equipment, like | heatpumps. | | My heatpump use an internally star configured 3x400V compressor, and | it would have been easy to wire it for 3x230V if they had brought out | all the leads.

If all 6 leads of the 3 windings are brought out separate, then it can be wired in star for 400/230 volt systems, and in delta for 230/133 volt systems. But for Europe in general there would be little reason to do that. There is also no reason to do that in North America, as we don't have any 360/208 volt systems at all.

If I were in Europe I'd rather than the 400/230 volt system. In North America I'd rather have the 480/277 volt system.

There is little doubt that electric trains are faster than other types as far as acceleration and overall speed. :-)

I'm quite aware of how a 2-stroke works, as the large EMD's (654 series, up to V-20 cylinder) that have been around for years are exactly that. Also how the turbo-charger works, the four different lube-oil pumps (scavenging, piston-cooling, main, and soak-back). Not to mention the fuel injectors, overspeed trip, high-crankcase pressure shutdown, and air-start systems to name a few of the various components. And Westinghouse air brakes with several variations, and the MU (multi-unit) interface used to connect several locomotives together and allow them all to be 'driven' from one cab.

But the trouble with overall weight is the combination of weight, power and rail capacity. When you get to larger units, the rail used on a lot of roads can't handle more than about 50,000 lbm per wheel set. That means you're limited to about 100 tons for a unit with just 2 axles per truck (4 total). Go up to a 120 ton and you need 3 axles per truck. But a 100 ton,

4-axle unit has 12,500 lbm per axle, while a 120 ton, 6-axle unit has only 10,000 lbm per axle. If the wheel friction coefficients are the same, the 4-axle unit can develop 25% more tractive effort when starting before slipping wheels.

Of course if the 120 ton, 6-axle unit has more overall horsepower, then even though it develops less tractive effort at low speeds, it can achieve a higher speed when loaded to it's rated tractive effort. Below a certain speed, the maximum you can pull is dictated by wheel slip. Then you're limited by tractive motor cooling up to a second point. Beyond that, the overall horsepower becomes the limit. Once you're 'horsepower limited', you can go faster, but only if you can reduce the amount of tractive effort needed (i.e. you want to go faster, you have to pull fewer cars or not climb as steep a grade). This 'hp limited speed' is in the range of just 15 to 20 mph for a lot of 4-axle units, somewhat faster for 6-axle units.

With typical freight trains in the US, they look at the steepest grade on the road and figure out enough locomotive units and maximum cars to just be horsepower limited on that grade. So while the train may go faster on less steep sections or level grade, it'll be at notch 8 (full throttle) and struggling to make about 15 mph up the steepest part of the route. And stalled if one of the locomotive units dies.

So more hp means you may be able to pull it faster, but you can't always pull as much.

Kind of 'weird' until you work out a few problems, but that's how it works.

daestrom

So when one is set for say 118V and the other is set for 120V, you have a

118V source connected in parallel with a 120V source and the only impedance is the transformer windings??

OUCH!!! I think the magic smoke will be spewing in no time

daestrom

That's still essentially a shorted turn (or set of turns).

Phil, did you see daestrom's excellent explanation how they use an inductor to prevent a dead short but in a way such that the inductor is virtually not there during normal operation (counterflowing currents)?

If these tap changers are rather expensive, I'm wondering what those pole pig "voltage regulators" I mentioned are. I thought they were just tapped autotransformers.

It would allow the Norwegians to buy less expensive heatpumps from Sweden :-)

It seems like a very simple and cheap thing to do.

-------------- If I read you correctly, you want to use a second secondary (lower power rating) which is tapped and put in series with the main secondary. Now once you do this, you have in effect a single secondary with taps just as in a conventional tapped secondary. Sure the "tapped section" is lower power- because it is a lower voltage but it still has to handle the same current. Nothing is gained. The problem in tap changing is not "power" but the current being switched.

In either case the voltage driving short circuit current on tap changing is that between taps Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in turns between taps. The short circuit current on such a change will be proportional to 1/(delta n).

If you want fine control, then you could go to sliding carbon brush as in a variac. The first idea of a separate transformer feeding a variac will not solve the "too low" voltage problem of the variac because you are still dealing with an autotransformer.

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer

-------------

Just a bitch that we have dealt with before:

Phil- please realize that 207.846096....... is meaningless except that it is "about 208". 208V is correct to 3 significant figures which is actually better than one can assume to be true in practice. If the voltage line to neutral is actually 120.V (note the decimal) then we have 3 significant digits implying something between 119.5 Vand 120.5.V Then all you can truly claim is 208.V If it is 120.0V then there is reason to assume 208.0 V but no more decimals than that. If you have a meter which gives you 120.000000V with less than 1 part in 120 million error then you can claim 207.846097V for line to line voltage Do you have such a meter?

Engineering and physics students who ignore the principle of "significant digits" lose marks for this "decimal inflation".

Sure- you can let the calculator carry the extra digits (as it will do internally) but accepting these as gospel truth to the limit of the calculator or computer display is simply not on as you can't get better accuracy from a calculation than the accuracy of the original data (actually you will lose a bit). All that you get rid of is round off errors in calculations.

Since, as you say, precise voltage is not really practical, then multi-decimal point numbers are meaningless. If we say 120V +/-10% then we are talking about 108-132V which for line to line becomes 187-229V (average

208V) and any extra decimal points don't mean anything.

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer

------------ So you have a differential voltage producing a circulating current through both windings leading to losses and heating due to circulating currents. In addition, there would be shifts in the load sharing between the two secondaries- with the possibility of overloading one of them. Also, you still haven't solved the problem of switching the current from one tap to another Note also to shift 2% you would have to make two 2% shifts, one on each winding so that you are essentially doubling the work and tap changing equipment while introducing other problems as Daestrom has indicated.

-

--

Don Kelly snipped-for-privacy@shawcross.ca remove the X to answer

| If I read you correctly, you want to use a second secondary (lower power | rating) which is tapped and put in series with the main secondary. Now once | you do this, you have in effect a single secondary with taps just as in a | conventional tapped secondary. Sure the "tapped section" is lower power- | because it is a lower voltage but it still has to handle the same current. | Nothing is gained. | The problem in tap changing is not "power" but the current being switched.

No, that is not what I tried to explain. I'll try again:

The main transformer would have 2 secondaries. These 2 secondaries are NOT wired in series with each other. The smaller of these secondaries will have taps. The tapped smaller secondary feeds another smaller transformer. The larger secondary of the main transformer, and the only secondary of the smaller auxiliary transformer, would be wired in series. So the taps are only dealing with the current of the lower power "tapping section". The smaller secondary of the main transformer, and the primary of the auxiliary transformer, can be wired for whatever voltage/current works out best.

| In either case the voltage driving short circuit current on tap changing is | that between taps | Delta V =A(delta n) Delta Z =B(delta n)^2. where delta n is the change in | turns between taps. The short circuit current on such a change will be | proportional to 1/(delta n). | | If you want fine control, then you could go to sliding carbon brush as in a | variac. The first idea of a separate transformer feeding a variac will not | solve the "too low" voltage problem of the variac because you are still | dealing with an autotransformer.

In that first scheme, adjusting the variac to the lowest voltage would be reducing the voltage contributed by the boost transformer. There is still the original supply voltage going around the variac, "plus" (actually minus) the buck voltage (to select the range I want). Since the variac is an autotransformer itself, it merely feeds the primary of the boost transformer. Note that in this case the "boost" transformer is wired as an isolation transformer. I should have mentioned that. If needed, I guess I could draw some ASCII diagrams or try to get something made graphically (all the tools I have to do that suck, except for Visio which needs Windows to run and I don't have a spare machine to do that at the moment).

|> | Yes -you are shorting a part of the winding but the switching is a bit |> more |> | complex than that so that short circuit currents are limited to |> reasonable |> | values. It is a multistep operation with reactor switching. On-load tap |> | changers are expensive and are generally limited to applications where |> this |> | is absolutely needed (I have seen one where the tap changer was nearly |> as |> | large as the transformer). |>

|> What about multiple parallel transformers, or at least multiple parallel |> windings on the same core (on whichever side the tapping is to be done), |> where the taps are stepped incrementally on each winding? Instead of a |> shorted winding segment, you'd have windings of differing voltage in |> parallel as each of the windings change their taps one at a time. |>

| | So when one is set for say 118V and the other is set for 120V, you have a | 118V source connected in parallel with a 120V source and the only impedance | is the transformer windings?? | | OUCH!!! I think the magic smoke will be spewing in no time

I was afraid of that.

That also means if you are going to parallel 2 transformers, they better have exactly the same winding ratio.

| Phil, did you see daestrom's excellent explanation how they use an | inductor to prevent a dead short but in a way such that the inductor is | virtually not there during normal operation (counterflowing currents)?

I believe I missed that.

| If these tap changers are rather expensive, I'm wondering what those | pole pig "voltage regulators" I mentioned are. I thought they were just | tapped autotransformers.

Sounds like they may be more of a voltage selector.

One set of transformers I saw once had a voltage selector which also revealed the voltage to me. Even those these huge things were well guarded behind a chainlink fence with barbed wire on top, I could clearly read the instructions on the voltage taps. It listed 5 or 6 different voltages in the 4160 volt range (I believe that was a middle one). The secondaries were a thick bundle of insulated wires not on insulator standoffs, so obviously LV, possibly 480V or 208V. These were 3 single tank transformers in roughly the design style of a pole pig (round tank) with a control panel on them with the tap control and some gauge I guessed may be temperature (but I could not see it clear enough at the distance I was at to be sure). The instructions did indicate that the transformer must be de-energized (not just unloaded) when making the change. So I'm guessing they were just to compensate for variations in the delivered voltage. These transformers were about 1 meter wide and 2.5 meters high, each (3 of them). I did not see any reference to a kVA rating. They were also very old looking (pre-WWII). They were humming.

In alt.engineering.electrical Don Kelly wrote:

| Just a bitch that we have dealt with before: | | Phil- please realize that 207.846096....... is meaningless except that it is | "about 208". 208V is correct to 3 significant figures which is actually | better than one can assume to be true in practice. If the voltage line to | neutral is actually 120.V (note the decimal) then we have 3 significant | digits implying something between 119.5 Vand 120.5.V | Then all you can truly claim is 208.V | If it is 120.0V then there is reason to assume 208.0 V but no more decimals | than that. | If you have a meter which gives you 120.000000V with less than 1 part in 120 | million error then you can claim 207.846097V for line to line voltage Do | you have such a meter? | | Engineering and physics students who ignore the principle of "significant | digits" lose marks for this "decimal inflation". | | Sure- you can let the calculator carry the extra digits (as it will do | internally) but accepting these as gospel truth to the limit of the | calculator or computer display is simply not on as you can't get better | accuracy from a calculation than the accuracy of the original data (actually | you will lose a bit). All that you get rid of is round off errors in | calculations. | | Since, as you say, precise voltage is not really practical, then | multi-decimal point numbers are meaningless. If we say 120V +/-10% then we | are talking about 108-132V which for line to line becomes 187-229V (average | 208V) and any extra decimal points don't mean anything.

You didn't notice the :-) I put on the number?

We've been over this. I know the practice of significant digits, and how the voltages are designated (two different reasons you can get 208). I do follow the practice of carrying exactly the result of calculations into other calculations. I also use over significance in comparison of numbers.

But I also know that rounding is a form of noise. So I avoid it until the time I end up with the final result. So if I multiply 120 by the square root of three I do get a number like 207.84609690826527522329356 which is either carried as-is into the next calculation, or rounded if it is the final answer. If some other strange calculation happens to give me the value 207.84609690826527522329356 then I know it is effectively equivalent to 120 times the square root of three in some way. But if what I get is

208.455732193971783228 then I know it has nothing to do with 120 times the square root of three, even though it, too, would end up as 208 if rounded to 3 significant digits.

When it comes to _measured_ amounts, as opposed to synthetic ones, then the significance rules dictate how to round the results. With synthetic numbers (e.g. numbers I can just pick), I can also pick the rounding rules for the final results. But if I don't know that the calculations are done (e.g. I am not merely giving a designation for a voltage system), where someone else may take those numbers and do more calculations and round the results, then I do use more significance. But that is no different to me than just carrying that number from one calculation stage to another.

In alt.engineering.electrical Thomas Tornblom wrote: | snipped-for-privacy@ipal.net writes: | |> In alt.engineering.electrical Thomas Tornblom wrote: |> | snipped-for-privacy@ipal.net writes: |> | |> |> In alt.engineering.electrical Thomas Tornblom wrote: |> |>

|> |> | Residential power in Norway is normally 230V three phase btw, instead |> |> | of 400V three phase. Their 230V outlets are two phase and ground |> |> | instead of one phase, neutral and ground. Their three phase outlets |> |> | therefore are blue instead of red and have four prongs instead of five. |> |>

|> |> Is this the system where the voltage is 133 volts relative to ground and

230 |> |> volts between phases (and formerly 127 volts relative to ground and 220 volts |> |> between phases)? |> | |> | Yes. |> | |> |>

|> |> If they still use that system, then I'm interested in buying a UPS designed |> |> for that. But it is my understanding it is phased out in cities and hard to |> |> find anymore in rural locations. |> | |> | It seems they are moving to 400V as well, but I know many Norwegians |> | are paying a hefty premium on their three phase equipment, like |> | heatpumps. |> | |> | My heatpump use an internally star configured 3x400V compressor, and |> | it would have been easy to wire it for 3x230V if they had brought out |> | all the leads. |>

|> If all 6 leads of the 3 windings are brought out separate, then it can be wired |> in star for 400/230 volt systems, and in delta for 230/133 volt systems. But |> for Europe in general there would be little reason to do that. There is also |> no reason to do that in North America, as we don't have any 360/208 volt systems |> at all. | | It would allow the Norwegians to buy less expensive heatpumps from Sweden :-) | | It seems like a very simple and cheap thing to do.

My guess is that in the cities, they have already changed over to a 400/230 system, or at least a 380/220 system that hasn't been voltage adjusted, yet. What I've heard is the 220/127 system was a leftover in some rural areas of Norway, and also in Spain. Apparently Suadi Arabia has this system so they can make use of both European and American single phase appliances. Mexico also has 220/127 but primarily uses the 127 volt connection (and it's 60 Hz). The really strange thing is Brazil has 220 volts all around the country, with 60 Hz in some parts and 50 Hz in others, and used to use the American

120 volt 2-blade outlet/plug with 220 volts (you can be in for a surprise with that).

All distribution transformers, sometimes called "pole pigs", that I have seen had some sort of voltage adjusting system, usually referred to as taps. Usually they are an actual bolted "tap" and you open the transformer and set the output voltage by making the proper tap connection when the transformer is installed and frankly it is usually ignored thereafter.

The other "cans" you often see on poles are capacitors used to adjust the power factor on some secondaries.

Bruce-in-Bangkok (correct Address is bpaige125atgmaildotcom)

lbm?

I'm not sure on your units.

In another life I used to calibrate railroad electronic weigh bridges.

4 axle locomotives were about 265,000 pounds (US).

6 axle locomotives were about 360,000 pounds.

One 3 axle drive truck weighed 65,000 pounds. (In a second other life, hauled it on a flatbed truck.)

? "daestrom" ?????? ??? ?????? news:482b50d2$0$31739$ snipped-for-privacy@roadrunner.com...

Yes, because as the germans say-"Sie nehmen Strom direct aus der Leitung"-They draw power directly from the wire. So it's a higher impulse current than any on board diesel can provide;_)

Of course you are, but I thought there might be other members of the group, that don't. I didn't know until I read the article. The large, 15,000 HP, 11 MW diesels we have here at our local power station, have a final steam stage, for better efficiency. The URL of our local college, where I got my degree, is

, but I'm not sure if they got an english version.

In Germany, they have special locomotives for freight trains, and special for passenger ones. The former desingned for larger traction power, the latter for higher speed. I have more experience with ships, since there are no railroads in Crete, but there's a lot of sea, and islands in Greece:-) I'll never forget my trip to Rhodes, where my batallion was situated, by rail from Korinthos (the infamous boot camp) and with ship to Rhodes. She was full of soldiers and commuters:-) NB.:There are railroads in continental Greece.

? "Bruce in Bangkok" ?????? ??? ?????? news: snipped-for-privacy@4ax.com...

Or disconnect switches, plain or with high-voltage fuses.