What percentage tolerance is assumed for transformer impedance in fault current calculations?

In fault current calculations, a tolerance of 10% for transformer impedance is commonly assumed. This percentage accounts for variations that can occur in transformer manufacturing and operational conditions. It allows engineers to consider potential discrepancies that could affect the actual impedance, thereby ensuring that the calculations for fault current are conservative and reliable.

Using a 10% tolerance recognizes the importance of accounting for these variations without being overly conservative or restrictive, balancing safety and efficiency in system design. This tolerance is essential for accurate protective device settings and system stability during fault conditions, leading to improved operational safety and performance in electrical installations.