On Ambient Temperature of Transformer Substations in Desert Climates

Ambient temperatures used as inputs for transformer prediction, monitoring, or aging algorithms are normally obtained from the atmospheric data available from local and international meteorological agencies. While easy to obtain and certainly useful, this data source may lead to erroneous readings as the ambient temperature, such as the proposed in the standard IEEE C57.91-2011, should be based on the air temperature in contact with the radiator of the transformer, which might divert considerably from the atmospheric temperature measured by a weather station on the vicinity. Differences can be attributed to several factors such as the distance to the meteorological stations, architectural constraints, reduced ventilation, and/or exposure to direct sunlight. These variations could affect the outcome and accuracy of algorithms used for aging prediction, maintenance, and planning. This matter is of additional importance in regions with extremely high temperatures, as transformers ratings are based on the assumption of an ambient temperature of 30 °C. To investigate this effect, this paper studied the difference between the recorded atmospheric and substation temperatures under extreme hot climates. Measurements were performed at a standard outdoor transformer station in the middle east for a year, including the summer months' harsh meteorological conditions and the milder winter, to capture significant temperature fluctuations. The data presented can provide insights for more accurate equipment aging modeling and maintenance planning.