The duration of the fault (longer faults allow more heat to escape, increasing the value of Step-by-Step Engineering Workflow
This is the base rating, assuming no heat escapes the conductor during the short-circuit event. Calculate the Modifying Factor (
Obtain the operating time of your protection device (circuit breaker or fuse) at the prospective fault current. For example, a breaker might trip in 0.2 seconds. iec 949 pdf work
Using the methodology in IEC 60949 allows electrical engineers to:
Multiply the two values to find the actual permissible current: Key Formulas & Parameters Adiabatic Formula: The base short-circuit current is typically calculated as: The duration of the fault (longer faults allow
for XLPE insulation). By taking advantage of heat transfer into adjacent materials, engineers can often justify an increase of in the permissible short-circuit current compared to purely adiabatic calculations. 2. Core Calculation Methodology
To help you apply these principles to your specific engineering task, tell me: Using the methodology in IEC 60949 allows electrical
Requires more complex mathematics and detailed knowledge of the cable's material layers.
Where ( \alpha ) and ( \beta ) are constants derived from the thermal properties of the insulation and sheath materials (PVC, XLPE, EPR, etc.).
I=K×St×ln(θf+βθi+β)cap I equals the fraction with numerator cap K cross cap S and denominator the square root of t end-root end-fraction cross the square root of l n open paren the fraction with numerator theta sub f plus beta and denominator theta sub i plus beta end-fraction close paren end-root : Permissible short-circuit current (A). : Cross-sectional area of the conductor ( mm2m m squared : Duration of the short circuit (maximum 5 seconds). θitheta sub i θftheta sub f : Initial and final conductor temperatures (°C). : Material-dependent constants (e.g., for Copper). Where to Find the Document