Maker Pro
Maker Pro

280V motor on 230V circuit

T

Thomas Tornblom

Jan 1, 1970
0
| 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.
 
| 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.
 
| [email protected] writes:
|
|>
|> | 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.
 
T

Thomas Tornblom

Jan 1, 1970
0
| [email protected] writes:
|
|>
|> | 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.
 
D

Don Kelly

Jan 1, 1970
0
----------------------------
| 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).

I was thinking of what I might do to get some fine voltage control within
a
very limited range around 120 volts. The obvious option was a 0-140 volt
variable transformer. But I wanted to make sure I had a setup that could
be better limited, for example, to not allow an accidental too low
voltage.
I also didn't want to run all the power through the variable. So what I
was going to do was get a smaller variable transformer, and two buck-boost
transformers. One transformer would be wired 120->16 in buck mode to drop
the voltage down to 104. The other transformer would be wired 120->24 and
supplied via the 0-140 variable transformer, giving me a 0-28 variable
boost.
The end result is 104-132 over the full range of variable transformer
control
(assuming the boost transformer has no issues with being overfed at 140V).

So I might envision a transformer where the taps can be part of a boost
transformer added to the main transformer. The first buck transformer in
my above example would not be needed because the main transformer would be
designed with a 1st secondary at the lowest voltage of the adjustable
range.
A 2nd secondary on the same main transformer would have the adjustable
taps
and it would feed a separate boost transformer which has a secondary wired
in series with the 1st secondary of the main. So the taps would only be
dealing directly with a fraction of the power (assuming there is no back
feed issue involved) based on the needed adjustment range.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to
ignorance |
| by the abuse department, bellsouth.net is blocked. If you post
to |
| Usenet from these places, find another Usenet provider ASAP.
|
| Phil Howard KA9WGN (email for humans: first name in lower case at
ipal.net) |

--------------
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 [email protected]
remove the X to answer
 
D

Don Kelly

Jan 1, 1970
0
----------------------------
| 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.
-------------

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 [email protected]
remove the X to answer
 
D

Don Kelly

Jan 1, 1970
0
----------------------------
| 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.

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to
ignorance |
| by the abuse department, bellsouth.net is blocked. If you post
to |
| Usenet from these places, find another Usenet provider ASAP.
|
| Phil Howard KA9WGN (email for humans: first name in lower case at
ipal.net) |
------------
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.
-
 
| 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.
 
| 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.
 
| [email protected] writes:
|
|> | [email protected] writes:
|> |
|> |>
|> |> | 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).
 
B

Bruce in Bangkok

Jan 1, 1970
0
| 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.


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)
 
T

Tzortzakakis Dimitrios

Jan 1, 1970
0
? "daestrom said:
There is little doubt that electric trains are faster than other types as
far as acceleration and overall speed. :)
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;_)
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.
'
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 www.teiher.gr , but I'm not sure if they got an english version.
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.
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.


--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.
 
T

Tzortzakakis Dimitrios

Jan 1, 1970
0
? "Bruce in Bangkok said:
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.
Or disconnect switches, plain or with high-voltage fuses.
Bruce-in-Bangkok

--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.
 
T

Tzortzakakis Dimitrios

Jan 1, 1970
0
Ï said:
In alt.engineering.electrical Tzortzakakis Dimitrios <[email protected]>
wrote:

| 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.
Maybe you connected with single phase just one element? The rest two
remained unconnected? (3 230 volts elements, connected wye). I'm sure it
heated up faster, in 3 phase connection.





--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.
 
T

Tzortzakakis Dimitrios

Jan 1, 1970
0
Ï said:
| [email protected] writes:
|
|> | [email protected] writes:
|> |
|> |>
|> |> | 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).

--
There should be no problem with the frequency, the local US base (In
Gournes-decomissioned after the end of the Cold War) used a regular 15 kV,
50 Hz feed, from the cretan grid, which was stepped down to 4150 volts and
then to 120/240. All with US switchgear and tranformers! (NB for US guys.#10
wire gauge->10 mm2 main feed of residence, #12 ->6 mm2 stove,#14->4 mm2
water heaters, #16->2.5 mm2 washing machines, dryers, #18->1.5 mm2
lighting.-approximately). I think that the personnel of the base used
standard US fluorescent light fixtures and other equipment, sone of it was
left as some of the buildings "inherited" by the greek state, were converted
by us to 230/400 volts, with regular Schuko receptacles.


--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
NB:I killfile googlegroups.
 
| ? <[email protected]> ?????? ??? ??????
| |> In alt.engineering.electrical Tzortzakakis Dimitrios <[email protected]>
|> wrote:
|>
|> | 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.
|>
| Maybe you connected with single phase just one element? The rest two
| remained unconnected? (3 230 volts elements, connected wye). I'm sure it
| heated up faster, in 3 phase connection.

You were the one who said "it just heats up faster (of course) when you
connect it 3 phase."

I would disagree.

But the fact that you said "(of course)" seems you presume that to be the
general case. Now your most recent comment at least acknowledges that if
not all elements are connected, it won't heat up as fast.

In the simple case, each of 3 elements is individually wired, so you have
a total of 6 leads. When connecting to three phase, one lead of each is
connected to neutral, and each of the other leads is connected to separate
phases. When connecting to single phase, they are all wired in parallel.
Both cases always involve one of the leads from each element connected to
neutral, so those 3 leads can be pre-connected together. So you could have
just 4 leads. The common neutral lead needs to be rated for all the current
together for it to be rated properly for single phase.

It should apply the same voltage (230V) to each element, and they should each
draw the same current. How would you believe this would be slower to heat?

If the 3 elements were wired _internally_ in star without a neutral lead,
it would still work fine on three phase as long as all elements were equal
impedance. But on single phase, you could only activate 2 of the elements,
and that would be 2 in series fed with 230 volts. You'd only get 1/6 the
power that way.

Are you assuming the elements would be wired that way? That would clearly
NOT be intended for single phase connection.

The 3 elements could be wired _internally_ in delta. In this case, these
would have to be 400V elements. Connecting 2 leads to 230 volts would still
give you only 1/6 the power (but more evenly distributed in this case).

So what is the situation that makes _you_ believe that 3 elements connected
to single phase _will_ draw less power to heat the water than when connected
to three phase?
 
D

Don Kelly

Jan 1, 1970
0
| 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).
---------------------------------
Actually I see added complexity without any gain. You may be doing the tap
changing at a lower current and higher voltage but there will be no "lower
Power" switching but there will be more losses during operation even when
not changing taps. I suspect the complexity and the losses together would
cost more than a conventional tap changer. There are some circuit factors
involved which may be undesirable but I haven't done a proper analysis.[/QUOTE]
 
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