What are Variacs?
First of all we would like to mention that we are
speaking of AC voltage, with a normal frequency
at 50 o 60 Hz, and a low or very low voltage
down to 1000 V.
The mains voltage is supplied at a nominal value of 230 V
in single-phase ( 400 V in three-phase) which can
vary of ± 10% in output, respectively to
the nominal values. These values are standard
in Europe, but not worldwide, where nominal values
can vary from 110 V up to 600 V.
These are problems that manufactures must
face when exporting machines worldwide and it becomes
necessary to be able to simulate different
voltages in testing labs.
All Variacs can resolve this problem, since they can
offer a voltage variation, manually or
automatically, from zero to a maximum of a pre-set
value.
In other cases, the Variac is useful for simple jobs
as in slowly increasing or decreasing lamp brilliancies,
as in theatres or in stabilizing current in a
galvanizing bath.
This use might seem a old
fashioned, but has the advantage of feeding
a load with a constant sinusoidal waveform, doesn't
create distortions at high frequency and above all
doesn't pollute the electric network.
The most used Variacs are the toroidals ones with
single-phase powers up to 7 - 8 kVA and
three-phase up to 20 - 25 kVA.
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Standard autotransformer with ratio variable |
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To be more precise, one must speak of voltage
supply, to which these transformers are
limited. The output occurs on copper spirals,
with a carbon brush, which is limited to both the
dimensions and withdrawable surface and cooling
down.
For currents over 30 A one must use parallel
transformers or column-type with a straight line
withdraw.
More than transformers, we are actually speaking of
autotransformers for the majority of the cases.
VARAT has designed a three-phase Variac with
totally static voltage and a power limit of 500 kVA,
which is ideal where difficulties and load losses
are always more frequent with power and voltage
increase.
Along with an automatic regulation, this system
offers a stabilized voltage output on a pre-set value
and is isolated from the network.
This product has become maintenance free due to the
absence of moving parts, brush usage, sparks and
overheating. |
