Cutler Hammer, Div of Eaton Corp Distribution Transformers Technical Data
Transformers
Distribution Transformers
9.5
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 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 Terminations
Eaton recommends that
external cables be rated 90°C
(sized at 75°C ampacity) for
encapsulated designs and
75°C for ventilated designs.
Winding
Rise
+
Hot
Spot
=
Temp.
Class
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
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. The following pages provide listings for most standard transformer ratings and
styles. For all-copper and bolt-on-breaker designs, contact Eaton.
Ventilated Encapsulated Ventilated
will likely be higher due to
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.
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Volume 2—Commercial Distribution CA08100003E—December 2010 www.eaton.com 251
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