I have 3-phase power in the building, what is the recommended way to
set up a balanced technical power system?
Most 3-phase systems operate at either 208 Volts or 240 Volts, but sometimes
at 480 Volts phase-to-phase. In any case, Using a single isolation transformer
with sufficient capacity to operate the entire facility is the optimum
approach to designing a technical power system. If this is not possible,
3 or more single-phase transformers loaded evenly across the 3-phase source
will also work. This application could include use of rack-type systems
plugged into 120- or 208/240-volt single-phase outlets on a 3-phase distribution
3-phase power operates most cleanly and efficiently when the load current
is balanced across all three power legs of the system. If current is too
unbalanced, current distortion will be the result.
The major drawback to using one single phase transformer on a 3-phase grid
is a tendency to unbalance the 3-phase system's current if particular care
is not taken in evening out the load with careful electrical distribution
planning. For this reason, a single transformer with a 3-phase primary
and a balanced single phase secondary is recommended. Conventional 3-phase
to single-phase isolation transformers help to some extent, but they fail
to evenly balance the load current across the 3-phase system's primary
to the desired degree.
The best distribution method for a 3-phase system involves the use of a
3-phase to 6-phase "wye" isolation transformer. The 6-phase "wye" secondary
has three single-phase outputs -- all are balanced 120-volt outputs with
60 Volts to ground. Each output circuit is rotated 120 degrees from the
adjacent output circuits. All three single-phase outputs share a common
grounding reference. This configuration resembles a 6-point starburst.
The advantages to this design are simple. There is but a single grounding
reference point for all three output circuits. This insures that there
will be no variation in grounding potentials across the system. Secondly,
all three outputs are coupled to the same magnetic flux field insuring
a more stable current alignment -- this stabilizes the power factor in
a 6-phase system.
In either case, whether using a 3-phase to 6-phase system or just a simple
single-phase set up, balancing all 120 volt circuits will dramatically
reduce noise and harmonic power distortion.
(Note: Some equipment requiring a 208-volt single phase circuit for power
supply power requires a 208-volt balanced circuit -- 104 Volts to ground.
3-phase transformers can be engineered to output multiple voltages from
a single secondary coil array when required under these conditions.)
For more information, see the page on Equi=Tech Isolation
Transformers in the products section.
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