RE: 3 phase power for pole pigs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>

Hi Allen,

> Hello All,
>
> I just went down to the local power company depot to get some 0.276 inch
> solid copper wire, I saw a yard full of old power distribution
> transformers,
> most of which work, but have been rendered obsolete. I live in a
> residential
> area of a small city,
> and I would very much like to upgrade my 15kV 120mA NST farm to a pole pig
> soon. However, I am wondering how I will power the transformer when (if) I
> get it.
> Our house only has single phase power, but there is a massive 3 phase
> terminal block in a green box on the footpath right outside our house.
>
> Questions -
>
> 1. *Must* you run a pole pig on 3 phase power, or can you use single phase
> for lower power levels like I will be running (under 20 Amps)?
>
Most pole pigs, i.e. distribution transformers that hang on poles, are
single phase.
When they are used in three phase configuration there are three transformers
connected together to provide the individual phases. Sometimes there are
only
two transformers, they are connected in a special way to provide psudo three
phase.
If the transformer is pad mount, it could be either single or three phase
depending
on the application.

> 2. Assuming you do need 3 phase for a pole pig, do you have to
> pay the power
> company to install hardwired 3 phase power to your house for a power
> distribution transformer?
>
I don't know how it is where you are, but here the power company will send
an engineer to do a survey. Then they tell you how much it will cost and
if you can get it. Assuming all is well then, you have to get a licensed
electrician to install a new service. Then you can get hooked up.
How much it will cost depends a lot on how the engineer feels about your
application. They are looking at cost vs. payback, or will you be using
enough electricity for them to recover their investment. A lot of times
they will make you pay for the transformers outright.

> 3. Assuming you do need 3 phase, can you use capacitors on a single phase
> line to fool the transformer into thinking it has 3 phase power for lower
> power levels (~20 Amps)
>
There are such things as phase converters. Capacitive, (cheapest but not
that efficient)
rotary, (expensive, but pretty efficient) and now days solid state.

> I have no experience of 3 phase transformers, but I have played with up to
> 10 MOT's at a few kVA power levels, as well as the 15kV 120mA NST's.
>
> Thank you very much,
>
> Alan Williams
>
later,
deano