Cutler Hammer, Div of Eaton Corp General-Purpose Encapsulated Transformers Technical Data
Transformers
General-Purpose Encapsulated Transformers
9.4
Accessories
Please refer to Section 9.7 Page 319.
Technical Data and Specifications
Frequency
Eaton standard dry-type
distribution transformers are
designed for 60 Hz operation.
Transformers required for
other frequencies are
available and must be
specifically designed.
Overload Capability
Short-term overload is
designed into transformers as
required by ANSI. Dry-type
distribution transformers will
deliver 200% nameplate load
for one-half hour, 150% load
for one hour and 125% load
for four hours without being
damaged, provided that a
constant 50% load precedes
and follows the overload.
See ANSI C57.96-01.250 for
additional limitations.
Continuous overload capacity
is not deliberately designed
into a transformer because
the design objective is to be
within the allowed winding
temperature rise with
nameplate loading.
Insulation System and
Temperature Rise
Industry standards classify
insulation systems and rise
as shown below:
Insulation System
Classification
+
Ambient
40°C 55°C 10°C 105°C
40°C 80°C 30°C 150°C
25°C 135°C 20°C 180°C
40°C 115°C 30°C 185°C
40°C 150°C 30°C 220°C
The design life of transformers
having different insulation
systems is the same—the
lower-temperature systems
are designed for the same life
as the higher-temperature
systems.
Winding
Rise
+
Hot
Spot
=
Temp.
Class
Enclosures
Eaton encapsulated
transformers, Types EP and
EPT, use a NEMA 3R rated
enclosure as standard.
Winding Terminations
Primary and secondary
windings are terminated in
the wiring compartment.
Encapsulated units have
copper leads or stabs
brought out for connections.
Ventilated transformers
have leads brought out to
aluminum pads that are predrilled to accept Cu/Al lugs.
Lugs are not supplied with
these transformers. Eaton
recommends that external
cables be rated 90°C
(sized at 75°C ampacity) for
encapsulated designs and
75°C for ventilated designs.
Series-Multiple Windings
Series-multiple windings
consist of two similar coils
in each winding that can be
connected in series or parallel
(multiple). Transformers with
series-multiple windings are
designated with an “x” or
“/” between the voltage
ratings, such as voltages of
“120/240” or “240 x 480.”
If the series-multiple winding
is designated by an “x,” the
winding can be connected
only for a series or parallel.
With the “/” designation,
a mid-point also becomes
available in addition to the
series or parallel connection.
As an example, a 120 x 240
winding can be connected
for either 120 (parallel) or
240 (series), but a 120/240
winding can be connected for
120 (parallel), 240 (series) or
240 with a 120 mid-point.
Sound Levels
All Eaton 600 volt class
general-purpose dry-type
distribution transformers are
designed to meet NEMA
ST-20 sound levels listed
here. These are the sound
levels measured in a
soundproof environment.
Actual sound levels
measured at an installation
will likely be higher due to
Average Sound Levels
NEMA ST-20 Average Sound Level in dB
Up to 1.2 kV Above 1.2 kV
kVA
0–9 40 45 45
10–50 45 50 50
51–150 50 55 55
151–300 55 57 58
301–500 60 59 60
501–700 62 61 62
701–1000 64 63 64
1001–1500 65 64 65
Notes
Currently being reviewed and revised by NEMA.
For other ratings or styles not shown, or for special enclosure types (including stainless steel),
refer to Eaton.
Ventilated Encapsulated Ventilated
electrical connections and
environmental conditions.
Lower sound levels are
available and should be
specified when the
transformer is going to be
installed in an area where
sound may be a concern.
For additional information,
please refer to Section 9.7
Page 322.
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Volume 2—Commercial Distribution CA08100003E—December 2010 www.eaton.com 237
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