The decision to use transformers, to step the voltage up and down,
rather than larger wire for a long circuit is more complicated than
simply comparing the cost of the wire to the cost of transformers and
smaller wire. Even with good toroidal transformers, the transformer pair
is adding about 10% loss in the system. And while the transformer
hysteresis losses may be a less than 1% of the transformer capacity,
they are 24/7 independent of the load. The supply side costs to provide
for the lost energy in the transformers needs to be considered too.
Kent Osterberg
Blue Mountain Solar
On 1/10/2022 6:24 AM, Hilton Dier wrote:
So you have a client with clever ideas - my deepest sympathies. The five most
frightening words from a client are “I am a retired engineer.”
DC transmission is theoretically more efficient due to the surface conduction
effects of AC. However, this is only true in a practical sense at
utility/megawatt scale. At residential scale you will have losses in the
electronics at either end that will negate the wire savings.
Get some toroidal transformers and go to 480 and back. Fat wire is kind of
expensive, but really it’s the trench (and these days, pvc conduit) that cost
the money. Fat wire in conduit is solid state and will never blow a capacitor.
Transformers, if not overloaded, last.
On that last point, 2x oversize the transformers for the load. There will be
“mission creep” while you aren’t looking. “Oh, we didn’t think that half a
dozen 1500 watt resistance heaters scattered around would make any difference.”
Good luck.
Hilton Dier III
Renewable Energy Design
Missisquoi River Hydro LLC
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