Assessment of the allowable short-term overloads in power transformers including condition management

• Main Authors: Yasuoka, J, Jardini, J.A, Brittes, J.L.P, Magrini, L.C, Kayano, P.S.D, Camargo, J
• Format: Conference Proceeding
• Language: English
• Subjects: Plant engineering, maintenance and safety; Power engineering computing; Substations; Transformers and reactors
• DOI: 10.1049/cp:20051106

The decision about the nominal power of each substation transformer is made based on the peak load value and in the contingency criteria during emergency situations. As emergency criteria, some facilities in Brazil consider that when one transformer is disconnected, the other ones in the same substation need to supply the total load. Others facilities consider that a substation can assume an amount of extra load, up to 30% of its total load from other substations. In both cases, the overload on each transformer must not exceed 20%. This limit of 20% of overloading has been adopted based on a qualitative study about the typical duration of peak load, aiming to not exceed the oil or hot spot limit temperature. This criteria has resulted in a high amount of installed capacity that should be optimized, postponing the construction of future installations. Within CPFL (Companhia Paulista de Forqa e Luz, a Brazilian distribution utility), it is considered that it can be allowed an overload more than 150%, depending on the time interval, if a real time system that stores information about transformer heating variables and conditioning maintenance is available. For such, a real time digital system was developed, and its performance is being evaluated in a group of 3 substations and in the distribution control center (DCC). (4 pages)