Harold and Susan Vordos wrote:

"Pete C." wrote in message
...
Harold and Susan Vordos wrote:
snip----

That's how everything used to be and I believe both the wild leg and
open delta configurations were primarily used as a way to save
transformer costs.

Regardless of reason, machine shops are typically provided with this
service. The higher voltage is very desirable, and in some cases mandatory.
I question your logic about saving transformer costs if individual machines
would require buck/boost transformers. Between the area required to store
them, and the increased cost of labor for installing them, seems to me it's
a terrible waste of money when it can be dealt with by installing the delta
system instead of the wye.

The transformer cost savings was for the large oil filled cans on the
pole, by using only two for open delta, or two smaller and one larger
for the unbalanced wild leg.

The buck/boost autotransformers are quite small and inexpensive. They
are dry type autotransformers, not full isolating transformers with
multiple windings so they are much smaller than you would expect for
their capacity. The KVA size required for the autotransformer is not the
full KVA of the load. The sizes you would need for an average machine
are about shoe box size and around $150 new.

http://www1.mscdirect.com/CGI/NNPDFF...PARTPG=NNLMK32

The other point is that many machines have appropriate taps and
connections on their motors and/or internal transformers and would not
require the buck/boost.



A Wye connected transformer does not present this risk since only one
leg of the transformer winding is ties to a hot line with the other at
neutral / ground potential.

But yields only 208 volts. A good friend moved from one shop to
another,
the second serviced by a Y service. His CNC machines didn't like that
one
bit. Regardless of the fact that machine tools should have motors
that
can run on either voltage, I very much prefer to have the higher
voltage,
regardless of the inconvenience of losing the B phase for 120V service.
I've managed to work around that very nicely in all situations.

Nope, a Wye connected transformer yields whatever you spec it to yield,
208/120 is just the most popular for light commercial use, if you need
more power you get 480/277 Wye. Of course if you get the 480/277 then
you also need a transformer to give you 208/120 as well.

But you've overlooked the fact that it does *not* yield 240 volts, the
optimum voltage for machine tools. I'm having more than a little trouble
understanding why you feel delta is such a bad deal when it solves all
problems aside from the wild leg issue. I can't think of one small
machine shop that is wired wye------not one. Many of my friends are still
in business in Utah, all of which have the delta service. Could be it's a
regional thing. Dunno.

How is 240v "optimum" for machine tools? A lot of machines larger than
bench top size can be strapped for operation on 480v input as well. When
I did CNC service, I don't recall seeing a single machine that didn't
have a 480v input option.

I would consider "optimum" voltage for a machine to be any voltage that
it can be strapped for. If it was designed with those taps then it
should operate just as well on any of them.

The "optimum" voltage that you would want to use based on external
factors would be one of the higher voltage options based on smaller
required wire gauge, reduced voltage drop, etc. From that standpoint
208v and 240v are essentially equal.

If a machine has taps for both 208v and 240v then there is no advantage
or disadvantage to either, only the convenience of what you have
available. If there are a sufficient number of machines that can take
480v to fill a decent portion of a 480v panel then that is an even
better choice.

I didn't say that delta was bad, I said that delta with a wild leg was
bad, they are two different things. Take a (pure) delta service for the
three phase and use a proper transformer to provide 208/120 Wye and I'd
be happy. No wild leg anywhere, and you've still got your 240v delta
that you like, as well as the familiar and flexible 208/120. Of course
it would still be preferable to go with the 208/120 Wye to begin with
and save the complexity.

I also didn't say that there were not plenty of shops with the wild leg
service. If it's already in place in a shop and in good condition there
is little reason to change it. I would not use it for a new
installation.


As for the CNC machines, back when I worked on them I seem to recall
every one I worked on could be wired for a pretty wide range of input
voltages. They also have the small buck/boost autotransformers you can
use on the few machines that truly can't be restrapped for 208.

Or you could use 3 phase delta and ignore buying buck/boost transformers and
their inherent problems. I thought that was an excellent idea.

What inherent problems? For the few machines that might require them in
a decent sized shop cost should not be an issue. They are quite small so
space should not be an issue. They are not difficult to wire so
installation should not be an issue.

Many years ago I worked for a mid sized printing company. The building
had 208/120 service, and there was only one machine in the entire
company that required the buck/boost transformers, a press made in
Sweden.


It would certainly be my preference to use a few autotransformers on one
or two problem machines rather than go with a wild leg system.

You keep speaking of these problems, but I've had 3 phase delta systems
since 1967, and aside from the one failure, which would have occurred be it
delta or wye, I've never had any problems. From that I conclude that the
problems, while possibly serious, are highly unlikely to plague the average
person. I'm more than willing to gamble on these ethereal problems than
request wye service and know for damned sure I'm going to face other
problems, which I would. I get the idea you're geared to light commercial,
where wye service is the norm. Machine shops do not use it----for obvious
reasons. Places that have a lighting load that tends to be the largest
power demand is where you find lots of wye service, at least in my
experience.

Failures due to poor maintenance can and will occur with any power
system. Annual IR camera inspections really are cheap insurance since
they can usually spot these problems developing before they can do any
damage.

These days when you can get a handheld IR thermometer for $50 at Sears
you can do the inspections yourself and save even more money. Granted
it's a little slower than with an IR camera, but not that much slower.
Do a monthly scan, input the data to a spreadsheet and pickup problem
trends even faster.

Wye service is indeed good for buildings with a lot of lighting load,
480/277 is particularly good for that.

The main thing is that you are indicating that there is a big
disadvantage to 208v vs. 240v which I just don't see. I think your
making more of the difference between 208v and 240v than there is
justification for.

The allowable voltage range for your 240/120 3ph delta wild leg service
is from 220v-254v at the service entrance (from a chart referencing ANSI
C84.1-1989). If the service is considered acceptable over a range of 34v
I just don't see a 32V difference between services as significant.

Large motors are built to handle widely varying power and load
conditions, and power supplies for controls either have plenty of tap
adjustment range for older machines, or switching supplies for newer
machines that are happy on anywhere from 98v - 250v. Your motors might
run a few degrees warmer but still well within their specified operating
range and your controls should be perfectly happy as well.



Most machines I've seen can accommodate a wide input voltage range, for
the few machines that can't you use the small inexpensive buck/boost
autotransformers.

We've already kicked that around. Why buy more transformers when you can
get the proper voltage?

Again, because not many machines would actually require it, and the fact
that your "proper" 240V service is allowed to vary over a 34v range
anyway.

Basically I think the 14% or so difference is of little to no
significance for 95% of the possible machines you might run, and for
those few the fix is easy and inexpensive.



The utilities aren't that concerned with balance since they can just
switch a few residential streets between phases to balance things. I
just like my power system to be balanced, since that seems to be the
only place in my life where I have any hope of achieving balance. Of
course, not running any large business, I'm still stuck with my rotary
phase converter.

Pete C.

Yeah, the one that puts out 240 volts---------do you get my drift?

Er, no, a couple weeks ago I had 269V! A call to TXU had that fixed in
less than one hour fortunately (good response).

And actually the 240V is some 9% high for the machine, as it's motor is
rated for 220/440.


Funny, I get the distinct idea you think I made a mistake by installing the
delta system. You couldn't be more wrong if you tried. It serves my
purpose perfectly, very unlike a wye system.

I think my main point is that I feel the Wye system would have served
your needs equally well and would have simplified the installation by
avoiding your use of separate panels for your single and three phase
loads to avoid the wild leg issue.

Pete C.