Going against the Current: Short Circuit Force Background

Electrical faults can generate significant electromagnetic forces on substation conductors and stresses in supporting insulators and structures. Typically, IEEE 605 simplified calculations are used to design for these forces. However, simplified methods and conservative assumptions often lead to overdesign or unnecessary retrofit or replacement. Structural engineers’ lack of knowledge of the fault current and force waveforms, force formulation, correct application of forces, and dynamic response of structural systems can lead to design inaccuracies. This paper/presentation summarizes research into standards and papers on electromagnetic fault forces, load application, and structural response to these dynamic forces. Attention is paid to the difference between the common design method, where the peak fault forces are applied in a static analysis, and the realistic dynamic loading and structural response to this dynamic loading. Comparisons are made between IEEE 605-2008 design methods, IEC 60865 methods, and time history analysis. The capacity of station post insulators is discussed as this often drives yard layout. Applicable standards and recommended safety factors are discussed. Analysis shows that simplified methods are often overly-conservative, though they can be unconservative in common cases. Background knowledge of these topics can have immediate impacts on designs and the more sophisticated methods discussed can be used where warranted.