Temperature Comparisons Between
Transformer Standard and Bushing
Standard
There is no conflict between the transformer standard and the bushing standard. The bushing standard C57.19.00 states that
the transformer oil should not exceed an average of 95°C over a 24 hour period. The transformer standard C57.12.00 states
that the ambient shall average 30°C and the average winding temperature rise shall not exceed 65°C. This would mean the
top oil will average 95°C in a 24 hour period and can reach 105°C at times. If you are going to subject a bushing to a
constant top oil temperature of 65°C in an ambient of 40°C, we would recommend using a bushing with viton gaskets and
Nomex windings. A bushing of this type can withstand temperatures of 125°C continuously. With a bushing of this type the
oil becomes the limiting factor. On the standard O Plus C bushing, the insulation class is 105°C.
ANSI/IEEE C57.19.00-1991
(1) The temperature of the ambient air is not above 40 °C or below -30 °C
(3) The temperature of the transformer insulating oil in which the lower end of the bushing is immersed and the bushing
mounting surface does not exceed 95 °C averaged over a 24 h period
ANSI/IEEE C57.12.00-1993
4.1.2.1 Cooling air temperature limit
When air-cooled, the temperature of the cooling air (ambient temperature) shall not exceed 40°C, and the average
temperature of the cooling air for any 24 h period shall not exceed 30°C.
5.11.1.1 Winding temperature rises
The average winding temperature rise above ambient temperature shall not exceed 65 °C at rated kVA when tested
in accordance with C57.12.90-1999 using the particular combination of connections and taps that give the highest
average winding temperature rise. This will generally involve those connections and taps resulting in the highest
losses.
ANSI/IEEE C57.12.10-1997
4.7 Top-liquid temperature-range limits
The transformer shall be suitable for operation over a range of top-liquid temperatures from -20°C to +105°C, provided
the liquid level has been properly adjusted to the indicated 25°C level.
ABB Inc.
Components & Insulation
Material
Address
1128 S. Cavalier Drive
Alamo, TN 38001-3813
Telephone
731-696-5561
Toll free: 1-800-955-8399
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731-696-5269
Web address
http://www.abb.com/electricalcomponents