Upon the date 11:21 AM 2/3/99 +0100, Philip.Belben_at_pgen.com said something
like:
>
>
>
>> so don't get the idea that you can
>> run it in your house or garage.
>
>My parents have 3-phase electricity at home, but I don't (yet). But I
>think it's more common in the UK than in the US. (BTW my parents have a
>16th century farmhouse which they heat electrically during the winter.
>Maximum load we've measured, 36kW.)
36kW!! Ouch! And cost of electricity is, I understand, higher than in the
US, true? Except Jamestown, we pay only $0.03565 per KWH :-) so electric
heat is not such a financial killer for homeowners (or for nuts like me
with working big iron computers in the basement).
Yes, very few private residences in North America have 3 ph power _unless_
it was asked for and installed, of course at an extra co$t. If someone has
a garage or machine shop at home (and the local zoning laws permit it) then
3 ph can be installed. Otherwise, bigger apartment buildings, larger
offices and factory buildings are usually wired for 3 ph at 240 volts or
480 volts.
Anyway, figure that we're stuck with 230 volt single phase (115 volts from
either leg to earth) at our NA homes, while as I've seen for example
normally in Southern Germany at least, 380 volt 3 ph (220 volts from either
leg to earth) is the norm in most other modernized parts of the world.
>
>I am told (I think it was Toy Duell first pointed it out to me) you can get
>reasonable 3-phase using a largeish induction motor (say a mechanical
>rating 2 or 3 times the electrical load you want to connect), without a
>mechanical load: wiring one phase to ground, a second to line, and the
>third to line through a capacitor for an approximate 60 degree phase shift.
>The induction motor will also act as a generator, and produce enough emf to
>tidy up the phase relationships and voltage imbalance. But be warned - you
Yes, I've heard of this often being used for machine shops which are not
wired for 3 ph (such as those garage-based shops in an area where no 3 ph
power is distributed). Good for only inductive loads such as the machine
motors found in a shop. Our computers may not tolerate this though,
especially switching PSUs. Tony? Have you thought about that aspect much?
>will not have the right voltage, and one of the phases (rather than the
>star point) will be at ground potential. A bank of three single-phase
>isolating transformers should do the trick if either of these is critical
>(a single autotransformer, upstream of the converter, will also work if
>only voltage is critical.)
If the rotary converter system discussed above could be used for non-motor
loads such as computers with switchmode PSUs, then one _should_ use
isolation transformers to avoid accidents if parts of the line side of the
PSU is touched to earth or by one's hand.
--Chris
-- --
Christian Fandt, Electronic/Electrical Historian
Jamestown, NY USA cfandt_at_netsync.net
Member of Antique Wireless Association
URL:
http://www.ggw.org/freenet/a/awa/
Received on Wed Feb 03 1999 - 09:57:22 GMT