All:
Many thanks all for the replies, and the very good points made. The general
consensus seems to be 'Don't use a Sola transformer if it's the last thing
in the world!'
I should perhaps explain the situation a little more clearly. My remote
station is set up at a disused broadcast tower, which was originally one of
seven. The other six were removed. The orginal lighting power to the towers
was daisy chained from a 120kVA 3phase 208V transformer in the station
house. The cable reduces in size between each tower, and after paralleling
everything possible I have the situation:
About 500' each of: #6; #8//2x#12; #10//2x#12; //3x#12 for each phase and
neutral. Neutral is connected to ground at each end, and ground resistance
is effectively zero due to miles of copper in the ground.
I do not own the site (unfortunately) and the owner uses the tower for his
business radio. There is also nearly 2.5kW of tower lighting in two strings.
I have put both of these onto one phase, and they pull the 120V down to
about 105 which seems satisfactory as it's very bright anyway, and that
should mean the bulbs will last longer.... I think that the size of the
primary transformer means that I don't have to be overly concerned about
balance between phases.
I am using the 208V between the other two phases. I have set the transformer
taps for a compromise between over-voltage off load and undervoltage on
load, and the low voltage part of the circuitry is well stabilised anyway.
The volt drop is such that I get less than a kW out of an 8877 which is
rather disappointing! The HV supply uses choke input filtering (with ~30uF
of output C) which should improve the Sola waveform somewhat.
I do appreciate that Sola transformers are expensive, heavy, noisy and hot.
The hot is probably quite good in Northern Ontario and Sola's application
engineers tell me they should be better than 95% efficient. There is nobody
to hear the noise, and all this has to be complete in the next few weeks
because it's impossible to get there when the snow flies. The heavy and
expensive are totally bad.
I can't realistically change the power wiring any more than I already have.
The front part of the site will be developed in a couple of years and then I
expect a proper supply will be taken to the tower, but that is not now.
I have used motor driven voltage stabilisers in my (distant) youth. Where
the load fluctuates rapidly, as with keying, my experience was that they
hunt furiously, they lag the demand, the brushes don't last, and they fail
at an overvoltage condition which destroys the equipment they were intended
to protect! The Sola at least reacts almost instantaneously.
More help would be greatly appreciated.
73 Roger
VE3ZI
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