IEEE C57.12.00-1987 pdf free.IEEE Standard General Requirements for Liquid-Immersed Distribution, Power,and Regulating Transformers.
IEEE C57.12.00 Transformers conforming tothis standard shall be suitable for operation atrated kilovoltamperes under the following usualservice conditions.When air cooled, the temperature ofthe cooling air (ambient temperature) shall notexceed 40 Cand the average temperature of thecooling air for any 24 h period shall not exceed30 °℃.
The top liquid temperature of thetransformer (when operating)shall not be lowerthan -20℃. Starting temperatures below-20 C are not considered as usual service conditions.When water cooled, the temperatureof the cooling water (ambient temperature)shallnot exceed 30 C and the average temperatureof the cooling water for any 24 h period shallnot exceed 25 C. Minimum water temperatureshall not be lower than 1 ‘C, unless the coolingwater includes antifreeze suitable for -20 C operation.
Altitude.The altitude shall not exceed3300 ft (1000 m).Supply Voltage. The supply-voltagewave shape shall be approximately sinusoidal,and the phase voltages supplying a polyphasetransformer shall be approximately equal inmagnitude and time displacement.
Load Current. The load current shallbe approximately sinusoidal. The harmonic fac-tor shall not exceed 0.05 per unit.
NOTE: harmonic factor is defined in ANSI/IEEEC57.12.80-1978 (R 1986) [24].
Operation Above Rated Voltage orBelow Related Frequency
Transformers shall be capable of(1) Operating continuously above rated voltage or below rated frequency, at maximum ratedkilovoltamperes for any tap, without exceedinglimits of observable temperature rise in accord-ance with 5.11.1 when all of the following conditions prevail:
(a) Secondary voltage and volts per hertz donot exceed 105% of rated values
(b) Load power factor is 80% or higher(c)Frequency is at least 95% of rated value(2) Operating continuously above rated volt-age or below rated frequency on any tap at noload, without exceeding limits of observable tem-perature rise in accordance with 5.11.1 whenneither the voltage nor volts per hertz exceed110% of rated values.Unusual Service Conditions. Conditionsother than those described in 4.1 are consideredunusual service and when prevalent should bebrought to the attention of those responsible forthe design and application of the apparatus.Ex-amples of some of these conditions are listed in4.3.1.Unusual Temperature and AltitudeCondtions.Transformers may be used at higheror lower ambient temperatures or at higher altitudes than those specified in 4.1.3 but specialconsideration must be given to these applications. ANSI/IEEE C57.91-1981[29] and ANSI/IEEE C57.92-1981[30],provide information onrecommended practices.Insulation at High Altitude. The dielectric strength of transformers,which dependin whole or in part upon air for insulation, de-creases as the altitude increases due to the effectof decreased air density. When specified,trans-formers shall be designed with larger air spacings using the correction factors of Table i toobtain adequate air dielectric strength at altitudes above 3300 ft (1000 m).IEEE C57.12.00 pdf download.