IEEE Std 1277-2020 pdf download – IEEE Standard General Requirements and Test Code for Dry-Type and Oil-Immersed Smoothing Reactors and for Dry-Type Converter Reactors for DC Power Transmission.
5.2.1 Unusual ambient temperature conditions The temperature-rise limits of reactors should be adjusted if the cooling air ambient temperature exceeds the limits described in 5.1.2. If the cooling air ambient temperature at site exceeds either of the limits, then the specified temperature-rise limits for the reactor shall be reduced by the same amount as the excess. The adjusted temperature-rise limits shall be rounded to the nearest whole number of degrees Celsius. Minimum ambient temperatures below –40 °C should be specifed as they may have an impact on the reactor. If a particular current rating versus ambient temperature performance is required without additional loss of life, this shall be clearly defned in the specifcation. For indoor reactors, the ambient temperature inside the reactor hall usually exceeds the limits described in 5.1.2 Higher ambient air temperature results in lower air density that contributes to reduce the dielectric withstand of air insulation. Thus, the specifed dielectric withstand voltages shall be associated with the reactor hall ambient air conditions (e.g., maximum air temperature and associated minimum air humidity). If dielectric tests are performed at usual laboratory ambient air conditions, correction factors shall be applied to test voltages in order to take into account the most stringent ambient conditions prevailing in the reactor hall. Correction factors shall be calculated according to the methodology defned in IEEE Std 4™. NOTE—Smoothing and converter reactors may be uniquely (custom) specifed and designed for a specifc location and set of operating conditions and, therefore, loading versus ambient temperature condition may be the norm. Establishing a current rating versus ambient temperature, etc., involves a number of considerations such as the thermal capability of the insulation system versus the winding operating temperature under rated conditions.