240 volts

snipped-for-privacy@ipal.net writes:


I was remembering a discussion from a few weeks ago about 3 phase power on utility poles. However, I now see that I confused you with "krw". It was him who was being unpleasant to people (including me), *not* you.
So my comments about your debating style are unjustified, and I apologize for them. It's my fault for not checking who said what before writing.
On the other hand, my more general point still stands. Because someone (not you) was throwing around unjustified personal insults in a previous discussion, I was reluctant to join this one. I imagine there are other people with technical knowledge that also avoid contributing because of the tone. Thus, it's naive to suggest that anyone who disagreed with you would have posted an article saying that, and to take the fact that no one disagreed with you publically as evidence that no one disagrees. It only takes one unreasonable person to create an unpleasant atmosphere.
    Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| snipped-for-privacy@ipal.net writes: | |>Are you making that determination about debating style based on how I answer |>posts that fail to point out specific errors? You cannot conclude what the |>style would be for specific topical challenges when what you see is how I |>respond to personal attacks from people who have a history of doing so. | | I was remembering a discussion from a few weeks ago about 3 phase power | on utility poles. However, I now see that I confused you with "krw". | It was him who was being unpleasant to people (including me), *not* you. | | So my comments about your debating style are unjustified, and I | apologize for them. It's my fault for not checking who said what | before writing.
Accepted. N/P
| On the other hand, my more general point still stands. Because someone | (not you) was throwing around unjustified personal insults in a | previous discussion, I was reluctant to join this one. I imagine there | are other people with technical knowledge that also avoid contributing | because of the tone. Thus, it's naive to suggest that anyone who | disagreed with you would have posted an article saying that, and to | take the fact that no one disagreed with you publically as evidence | that no one disagrees. It only takes one unreasonable person to create | an unpleasant atmosphere.
What I guess I need to learn is to just "let them win" and move on. I would prefer that someone who finds something wrong in what I say go ahead and point it out. So finding some way to end the flame fests (that Usenet is infamous for) early would help.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
daestrom wrote:

I took the P.E. exam before there were hand calculators, so we all used slide rules. One advantage was they were perfectly suited for engineering work without ever needing to be pedantic. ;-)
I've seen more measurements screwed up by lack of knowledge than by insufficient number of decimal places.
--
Virg Wall, P.E.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| daestrom wrote: | |> Most of us skimp on the rules a bit, but taking a number like 120 * |> sqrt(3) and claiming the answer to seven significant digits is over the |> top. |> |> daestrom |> I told you I was going to be pendantic .... :-) | | I took the P.E. exam before there were hand calculators, so we all used | slide rules. One advantage was they were perfectly suited for | engineering work without ever needing to be pedantic. ;-) | | I've seen more measurements screwed up by lack of knowledge than by | insufficient number of decimal places.
Using the wrong formula can do that.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

In many engineering fields (outside of electronics), it's also easy to use the wrong engineering units. Or use the inverse of the conversion from one to another. ;-)
Some 'units-phobics' proclaim how metric is so much easier than our (the US) units of measurements. But in actuality, it's just that you can still get the right answer a lot of times because the conversion factors are often just 1. For example, Push with a force of 12 Newtons for a distance of 30 meters over a period of 10 seconds. How many Watts? Play around for a minute or so and you can come up with 12*30/10 = 36. But in actuality, one is converting Newton-meters to Joules (1) and Joules/sec to Watts (1).
12 Newtons * 30 meters / 10 seconds * [(1 Joule) / (1 Newton-meter)] * [(1 Watt-second) / (1 Joule)] = 36 Watt
This is all to often forgotten in the simplicity of just ignoring the conversion factors (because they're always '1').
In US units, if the problem is 'Push with a force of 12 lbf for a distance of 30 feet over a period of 10 seconds, how many horsepower?', you have to actually understand the system of units, and how to apply them.
12 lbf * 30 feet / 10 seconds * [(1 hp) / (550 ft-lbf/s)] = 0.065 horsepower
In a way, our system of units, because it is so bizarre, helps teach us to follow through with the units and understand the relationship between force, distance, time and power.
(note: I did *not* say 0.065455 horsepower :-)
daestrom
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote: |
| wrote: |> | daestrom wrote: |> | |> |> Most of us skimp on the rules a bit, but taking a number like 120 * |> |> sqrt(3) and claiming the answer to seven significant digits is over the |> |> top. |> |> |> |> daestrom |> |> I told you I was going to be pendantic .... :-) |> | |> | I took the P.E. exam before there were hand calculators, so we all used |> | slide rules. One advantage was they were perfectly suited for |> | engineering work without ever needing to be pedantic. ;-) |> | |> | I've seen more measurements screwed up by lack of knowledge than by |> | insufficient number of decimal places. |> |> Using the wrong formula can do that. |> | | In many engineering fields (outside of electronics), it's also easy to use | the wrong engineering units. Or use the inverse of the conversion from one | to another. ;-) | | Some 'units-phobics' proclaim how metric is so much easier than our (the US) | units of measurements. But in actuality, it's just that you can still get | the right answer a lot of times because the conversion factors are often | just 1. For example, Push with a force of 12 Newtons for a distance of 30 | meters over a period of 10 seconds. How many Watts? Play around for a | minute or so and you can come up with 12*30/10 = 36. But in actuality, one | is converting Newton-meters to Joules (1) and Joules/sec to Watts (1).
Now if only they would just get the rest of the time units metrificated to powers of 10 ... 1 day is 86.4 kiloseconds.
I remember in the mid 1970's I saw a TV PSA (because I was working at a TV station at the time ... master control op) that promoted metrification. They showed a bunch of different symbols of things they claimed were already metric. They showed a clock as one of them I and I noted that was not correct.
| 12 Newtons * 30 meters / 10 seconds * [(1 Joule) / (1 Newton-meter)] * [(1 | Watt-second) / (1 Joule)] = 36 Watt | | This is all to often forgotten in the simplicity of just ignoring the | conversion factors (because they're always '1').
Yes, I would agree. The units are quite well correlated. If we just learn it this way, though, I think it works well.
| In US units, if the problem is 'Push with a force of 12 lbf for a distance | of 30 feet over a period of 10 seconds, how many horsepower?', you have to | actually understand the system of units, and how to apply them. | | 12 lbf * 30 feet / 10 seconds * [(1 hp) / (550 ft-lbf/s)] = 0.065 horsepower | | In a way, our system of units, because it is so bizarre, helps teach us to | follow through with the units and understand the relationship between force, | distance, time and power.
But I think the metric system makes more sense. We just have to learn the simplicity of it in a different way. it would certainly be hard for someone accustomed to having to always apply a non-unity conversion. I'm glad we didn't have a different set of imperial units for volts, amps, watts, ohms, henries, farads, etc.
| (note: I did *not* say 0.065455 horsepower :-)
:-)
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@ipal.net wrote:

Many mid to high end multimeters are more accurate than that.

You are only talking about 1ppm or 0.1ppm. A lot of equipment exists with that accuracy. I have calibration instruments in my lab that will do it. However, that is several orders of magnitude better than any field measurements that I make. Even if you did make measurements with that accuracy on an electrical power system , it would be meaningless from a practical standpoint. It would be difficult to measure the difference in winding temperatures, for example, with a voltage variation of 0.0001%.
You are presenting a great mental excercize, but if you need to go that far down to differentiate between the results of two formulas, then as a practical matter in most power work, they are the same.
--
Benjamin D Miller, PE
www.bmillerengineering.com
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| snipped-for-privacy@ipal.net wrote: |> If I measure a voltage with a voltmeter, I will express it as |> precisely |> as the device is capable of accurately measuring and precisely |> displaying. If it has an accuracy of 1/10 of a volt in a 200 volt |> range (rather good) I'll use that and might state the voltage as |> "119.1" or "121.0". But if | | Many mid to high end multimeters are more accurate than that.
I'm happy with a 4 digit voltmeter. But I want 1 Hz tuning steps on my SSB ham rig, even to the high end of the UHF band.
|> it only has an accuracy of 1 volt, I'll state it as "119" or "121". |> |> So when you see me use a highly precise expression like "235.5589", |> it is coming from a mathematical calculation done with at least 6 or |> 7 digits |> of precision (probably more since I default to using the double type |> which has 14 or so digots), using a formula I believe to be accurate. |> |> If I ever manage to make a real physical measurement with such |> accuracy, I'll be sure to let you know about that miracle device |> capable of doing such a thing. |> | | You are only talking about 1ppm or 0.1ppm. A lot of equipment exists with | that accuracy. I have calibration instruments in my lab that will do it. | However, that is several orders of magnitude better than any field | measurements that I make. Even if you did make measurements with that | accuracy on an electrical power system , it would be meaningless from a | practical standpoint. It would be difficult to measure the difference in | winding temperatures, for example, with a voltage variation of 0.0001%.
If you measure the voltage and find it is 278.415 volts, it could be just a bit different in a few seconds. At this level of accuracy and precision we're into line noise levels :-) But, my mathematical model calculations don't have line noise to worry about (unless I am doing noise modeling).
| You are presenting a great mental excercize, but if you need to go that far | down to differentiate between the results of two formulas, then as a | practical matter in most power work, they are the same.
I want to be able to recognize them in the mathematical model sense, too.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Do your own homework.
Bill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| wrote: | |> You have a machine that requires 240 volt three phase power. It requires |> connection to 3 phase lines and ground, but not neutral. You ask your |> utility to supply 240 volt delta and they say no. The machine fails to |> operate on 208 volts. What do you do? How many different solutions could |> you think of to explore? | | Do your own homework.
I already did. I'm just checking to see if I missed any creative ideas and to see what kind of diversity others as a group would have.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
|

|------------------------------------/-------------------------------------|
I actually have this issue Phil. I used a buck boost transformer. This is a light and intermittent load. A bank of relays at the end of a long cable run.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote: |
| | | |> | |------------------------------------/-------------------------------------| | | | I actually have this issue Phil. I used a buck boost transformer. This is a | light and intermittent load. A bank of relays at the end of a long cable | run.
I'm curious what the configuration is. I have a list of many different configurations near to, and far from, 240 volts, than can be derived from 208Y/120.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

|------------------------------------/-------------------------------------|
is a

It would have to be sized and configured for each real world aplication. In my case 208 is actully 201 most days at most of the locations I have to deal with.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@ipal.net wrote:

Option 1: Fire the purchasing manager who changed my spec and bought something that I specified to work on a voltage I know I have in the plant.
Option 2: if it's just a motor, get it rewound for 208 3 Phase, replace control transformers, replace fuses, replace (adjust) overload heaters, quick check that the panel wiring is heavy enough. I assume we're talking a few hundred kVA here, not something passing thousands of amps.
Option 3: Autotransformer, or if it really needs the isolation, transformer.
Option 4: Build a methane cracker connected to the natural gas supply, use the hydrogen made to run a fuel cell stack producing 400 V DC, then devise a 12-pulse near-sine-wave variable frequency inverter (and birdbath) to power said machine.
These are the solutions that I've used. OK, not the last one, but I once ran a TV set on a variable-frequency drive.
Bill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.