The full title is: "Power transformers – Part 6: Reactance" (formerly known as "Determination of transformer and reactor short-circuit reactance").
Reactance is calculated at reference temperature (usually 75°C). But during a fault, winding temperatures can rise from 75°C to 250°C in 100 ms, increasing copper resistivity by 3×. This changes the resistance (which damps DC offset), but the standard's reactance formulas assume constant resistivity. For very short faults (< 5 cycles), this is fine. For longer duration faults (e.g., backup protection delays), the error grows.
Here are the three conceptual shifts it introduced:
The full title is: "Power transformers – Part 6: Reactance" (formerly known as "Determination of transformer and reactor short-circuit reactance").
Reactance is calculated at reference temperature (usually 75°C). But during a fault, winding temperatures can rise from 75°C to 250°C in 100 ms, increasing copper resistivity by 3×. This changes the resistance (which damps DC offset), but the standard's reactance formulas assume constant resistivity. For very short faults (< 5 cycles), this is fine. For longer duration faults (e.g., backup protection delays), the error grows. iec 60076-6
Here are the three conceptual shifts it introduced: The full title is: "Power transformers – Part