On Mon, 29 Feb 2016 05:38:39 +0000 (UTC), you wrote:
since the two lines are 180 degrees out of phase with each other, thus
adding (120-0-120) give 240.
True three phase power is three lines, each 120 degrees apart. You'll
find it in aircraft and industrial plants. It can be wired with a
common (wye) or with an implied center (delta). It does require
special transformers, and the voltages are not always what you expect.
You'll frequently find military surplus/aviation equipment with true 3
phase power, and it's annoying to convert *IF* it will even run on
60/50 Hz. Some test equipment is rated to run from 50/60 to 400 Hz,
but that was generally an option.
BTW: the whine you might hear when boarding a commercial aircraft
frequently comes from the 400 Hz power, not the engines (although that
can be there, too).
Harvey
>Stefan Trethan:In the US, Line, neutral, line is not three phase, it's more two phase
>
>I don't know how often the members of this group will encounter the type of industrial transformers that
>you describe. But I do know that isolation (not insulation) is a factor to be considered,,,,,,,,,often when
>connecting your test equipment up to equipment that you might be troubleshooting, designing, etc.
>
>Refer to the conventional three-phase configuration that most of us encounter.
since the two lines are 180 degrees out of phase with each other, thus
adding (120-0-120) give 240.
True three phase power is three lines, each 120 degrees apart. You'll
find it in aircraft and industrial plants. It can be wired with a
common (wye) or with an implied center (delta). It does require
special transformers, and the voltages are not always what you expect.
You'll frequently find military surplus/aviation equipment with true 3
phase power, and it's annoying to convert *IF* it will even run on
60/50 Hz. Some test equipment is rated to run from 50/60 to 400 Hz,
but that was generally an option.
BTW: the whine you might hear when boarding a commercial aircraft
frequently comes from the 400 Hz power, not the engines (although that
can be there, too).
Harvey
>
>Regards,
>
>Roland F. Harriston, P.D.
>
>----- Original Message -----
>
>From: "Stefan Trethan stefan_trethan@... [Homebrew_PCBs]" <Homebrew_PCBs@yahoogroups.com>
>To: "Homebrew PCBs" <Homebrew_PCBs@yahoogroups.com>
>Sent: Sunday, February 28, 2016 10:14:10 PM
>Subject: Re: [Homebrew_PCBs] Re: drill pcb
>
>
>
>Strictly speaking there are differences between an industrial control
>transformer and an isolation transformer.
>The isolation is often stronger with a dedicated isolation
>transformer, sometimes the windings are even physically separated in
>different chambers or on different shanks, instead of on top of each
>other.
>As a result coupling capacitance is lower with an isolation
>transformer, but also magnetic coupling is worse.
>
>So in some situations you may require an actual isolation transformer.
>
>Many high quality control transformers fulfill the minimum
>requirements for a safety isolation transformer, but always check the
>datasheet.
>
>ST
>
>On Thu, Feb 25, 2016 at 5:15 PM, Brad Thompson
>brad.thompson@... [Homebrew_PCBs]
><Homebrew_PCBs@yahoogroups.com> wrote:
>> If you need to power a 120VAC item from a 240 VAC
>> line (or vice versa), you can use
>> a transformer **with isolated windings** designed exactly for this
>> purpose. These are sometimes referred to as
>> "industrial control transformers".
>>
>> 73--
>>
>> Brad AA1IP
>>
>>
>