IEEE c57.12.00-2015 pdf free download.Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers.
3. Definitions Standard transformer terminology available in IEEE Std C57.12.80 shall apply. 8 The IEEE Standards Dictionary Online should be consulted for terms not defined in this clause. 9 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 126.96.36.199 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. 188.8.131.52 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.
184.108.40.206 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, which is suitable for –20 o C operation. 4.1.3 Altitude The altitude shall not exceed 1000 m (3300 ft). 4.1.4 Supply voltage The supply-voltage wave shape shall be approximately sinusoidal. The phase voltages supplying a polyphase transformer shall be approximately equal in magnitude and time displacement. 4.1.5 Load current The load current shall be approximately sinusoidal. The harmonic factor shall not exceed 0.05 per unit. Harmonic factor is defined in IEEE Std C57.12.80. Refer to IEEE Std C57.110™ [B21] for information on establishing transformer capability when supplying nonsinusoidal load currents. 10 4.1.6 Operation above rated voltage or below rated frequency 220.127.116.11 Capability Transformers shall be capable of the following: a) Operating continuously above rated voltage or below rated frequency, at maximum rated kVA for any tap, without exceeding the limits of observable temperature rise in accordance with 18.104.22.168 when all of the following conditions prevail: 1) Secondary voltage and volts per hertz do not exceed 105% of rated values 2) Load power factor is 80% or higher 3) Frequency is at least 95% of rated value
NOTE—For generator step-up transformers, the maximum value of the primary voltage would be limited by the magnitude of the highest voltage the generator can supply at full load. For all other step-up transformers, the maximum value of the primary voltage would be limited by the highest system voltage at the primary of the transformer. In either case, these levels should be provided by the user and must be indicated on the nameplate of the transformer. If not provided by user, for generator step-up transformers assume 105% of rated voltage, and for all other step-up transformers, use the maximum system voltage as listed in Table 3 column 1 for distribution and Class I power transformers, and Table 4 column 1 for Class II power transformers, for the applicable nominal system voltage. 11
For multi-winding transformers or autotransformers, 22.214.171.124 applies only to specific loading conditions used as the basis of design. These loading conditions involve simultaneous coordination of kVA input and output, load power factors, and winding voltage combinations [see item j) of 4.3.3]. Differences in loading and voltage regulation for various output windings may prevent simultaneous achievement of 105% voltage on all output terminals. In no case shall the kVA outputs specified for any loading condition require continuous loading of any input winding in excess of its rating. 126.96.36.199 Maximum continuous transformer operating voltage The maximum continuous transformer operating voltage should not exceed the levels specified in ANSI C84.1. System conditions may require voltage transformation ratios involving tap voltages higher than the maximum system voltage for regulation purposes. However, the appropriate maximum system voltage should be observed under operating conditions. 4.1.7 Outdoor operation Unless otherwise specified, transformers shall be suitable for outdoor operation. 4.1.8 Step-down operation Unless otherwise specified, transformers shall be designed for step-down operation.