Technical Data
Effective: May 1998 Page 11
TD.44A.01.T.E
Cutler-Hammer
Magnum DS
Metal-Enclosed
Low-Voltage Switchgear
Application
Unit Substations
Most Magnum DS Switchgear Assem-
blies are configured as unit substations.
A Unit Substation, as referred to in this
publication, is defined as a coordinated
assembly consisting of 3-phase trans-
formers with high-voltage incoming
line sections and an assembly of low-
voltage distribution sections, with the
following parameters:
Transformer kVA – 112.5 through 3750
Low-Voltage – 208, 240, 480 or 600 V
Unit Substations may be indoor or out-
door, with a selection of high-voltage
incoming sections, a choice of trans-
former types and an arrangement of
Magnum DS Switchgear to suit the
application.
Why Unit Substations?
Unit substations follow the system
concept of locating transformers as
close as practicable to areas of load
concentration at utilization voltages,
thus minimizing the lengths of
secondary distribution cables and
buses. This concept provides several
basic advantages, such as:
■ Reduced power losses
■ Improved voltage regulation
■ Improved service continuity
■ Reduced likelihood of faults
■ Increased flexibility
■ Minimized installation expense
■ Availability of non-flammable types
of transformers eliminates necessity
of vaults
■ Efficient space utilization
Advantages of Magnum DS Unit
Substations
■ Complete coordination, both
mechanical and electrical
■ Extreme flexibility with wide choice
of components and ratings to meet
exact application requirements
■ Optimum safety to operators
■ Modern design
■ Meets all applicable ANSI, IEEE,
NEMA and UL Standards
Transition Sections
All indoor Unit Substations utilizing
liquid filled transformers require an
11-inch (279 mm) or 22-inch (559 mm)
wide transition section. The center-line
location of the Iow-voltage throat is
based upon the depth of the Magnum
DS assembly.
In many indoor applications, it is desir-
able to minimize floor space by elimi-
nating the need for a transformer
transition section. For these situations,
Magnum DS switchgear is designed to
accommodate close coupling to dry
type transformers if their low-voltage
terminations conform to a specific ver-
tically oriented arrangement. This con-
figuration may be provided if: (1)
additional space is not required for
auxiliary devices such as grounding
resistors, instrumentation, etc.; (2) zero
sequence ground fault is not applied
on main breakers; (3) connection to
assemblies with no main breaker do
not utilize “A” or “B” position feeder
breakers; (4) adequate conduit space is
available for any top exit cable connec-
tions in this section.
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