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2017 Sensata Technologies
Installation
2.3.6 Using the MS-PAE with Three-Phase Power
The MS-PAE inverter’s AC input is designed to be connected to 120 VAC single-phase or 120/240
VAC split-phase power. On a 120/240 VAC split-phase power system, there are two 120-voltage
phases (also known as “legs” or “lines”) that are 180° apart with a neutral connection centered
between them. The voltage between the two 120 VAC legs (L-L) is 240 VAC, and the voltage
between each of the legs and neutral (L-N) is 120 VAC.
In industrial and some larger commercial installations, three-phase power is used. On a three-phase
power system (that can be either in a Delta or WYE/Star con
fi
guration), there are three individual
phases (“legs” or “lines”) that are 120° apart. The voltage between any two legs is 208 VAC (L-L),
and if the system has a neutral wire, the voltage between one leg and neutral (L-N) is 120 VAC.
If you only have 208 VAC three-phase power—either from the utility or from a generator—there
are two options to connect this three-phase power to the MS-PAE inverter’s input. Depending on
requirements, you can either use an appropriate buck-boost transformer or you can connect to
the MS-PAE inverter directly.
Note:
Be aware that most buck-boost transformers are not isolated, but are autotransformers—
which will not work. An autotransformer requires fewer windings and has a smaller core, so it is
typically lighter and less costly than a conventional isolation transformer with the same ratings.
However, with an autoformer, the primary (input) and secondary (output) windings are physically
interconnected. Since the primary and secondary windings of an autoformer are not isolated from
each other, and the entire system has a common ground, you would not be able to connect two
legs of the three-phase system to the MS-PAE inverter. When the input (or primary) side and
output (or secondary) side of the autoformer have a common reference (normally ground), a high
in-rush of current will occur after the MS-PAE Series inverter connects to the three phase system.
This excessive current happens when the transformer inside the inverter tries to move the two
incoming legs that are 120° out-of-phase (from the three-phase source input) to 180° out-of-
phase (split-phase inverter output). This phase mismatch will cause the inverter’s input 30-amp
breaker(s) to open and may cause other damage to the inverter.
