Loading of Substation Electrical Equipment with Emphasis on Thermal Capability Part I-Principles

Nameplate ratings for substation equipment do not always represent the maximum loading capability of the equipment because they do not reflect the influence of the environmental factors and loading patterns which will exist when the equipment is ultimately placed in service. This paper discusses the principles of thermal capability and describes the environmental factors and loading patterns which influence the maximum loading capability of substation equipment. A companion paper, Part II, describes the application of these principles and factors in determining the thermal capability of specific substation equipment.