IEEE C57.12.00-2006 IEEE Standard for Standard General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.
3. Definitions Standard transformer terminology available in IEEE Std C57.12.80 6 shall apply. Other electrical terms are defined in The Authoritative Dictionary of IEEE Standards Terms and Definitions, Seventh Edition [B14]. 7 4. Service conditions 4.1 Usual service conditions 4.1.1 General Transformers conforming to this standard shall be suitable for operation at rated kVA under the following usual service conditions. 4.1.2 Temperature 184.108.40.206 Cooling air temperature limit When air-cooled, the temperature of the cooling air (ambient temperature) shall not exceed 40 o C, and the average temperature of the cooling air for any 24 h period shall not exceed 30 o C. 220.127.116.11 Liquid temperature limit The top liquid temperature of the transformer (when operating) shall not be lower than –20 o C. Liquid temperatures below –20 o C are not considered as usual service conditions. 18.104.22.168 Cooling water temperature limit When water-cooled, the temperature of the cooling water (ambient temperature) shall not exceed 30 o C, and the average temperature of the cooling water for any 24 h period shall not exceed 25 o C. Minimum water temperature shall not be lower than 1 o C, unless the cooling water includes antifreeze suitable for –20 o C operation.
6.6 Liquid insulation system 6.6.1 Insulating liquids Transformers shall be filled with a suitable insulating liquid such as a) Mineral oil. New, unused mineral oil shall meet the requirements of ASTM D3487. NOTE—IEEE Std C57.106 [B35] provides information concerning the acceptance and maintenance of mineral oil, including dielectric test breakdown criteria according to oil application, age, and test method. b) Less flammable hydrocarbon fluid. New, unused less flammable hydrocarbon fluid shall meet the requirements of ASTM D5222-92. NOTE—IEEE Std C57.121 [B43] provides information concerning the acceptance and maintenance of less-flammable fluid in transformers. c) Silicone fluid. New, unused silicone fluid shall meet the requirements of ASTM D2225-92 NOTE—IEEE Std C57.111 [B38] provides information concerning the acceptance and maintenance of silicone insulating fluid in transformers. There are other insulating fluids that may be suitable and are commercially available. At the time of this revision, neither ASTM specifications nor IEEE guides for use in transformers exist.
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