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Decoding Icw: The Core Essentials and Selection Guide for Breaker Short-Time Withstand Current
Concept: What is Icw?
Short-time withstand current (Icw) refers to the ability of a circuit breaker to withstand a specified short-duration current (e.g., 0.05, 0.1, 0.25, 0.5, or 1 second) under defined voltage, short-circuit current, and power factor conditions without tripping. The rated short-time withstand current typically refers to the RMS current value the equipment can withstand for a longer duration, commonly 3 or 4 seconds.
Core Purpose & Standards
Icw is a key parameter for evaluating the electrical and thermal stability of Type B circuit breakers (e.g., air circuit breakers), aiming to ensure power supply continuity and system selectivity. Standard GB14048.2 recommends preferred durations from 0.05s to 1s. Selection must be based on the maximum prospective short-circuit current at the installation point and the permissible thermal withstand time of system conductors/equipment.
Selection Calculation & Engineering Practice
The approximate thermal withstand time of a conductor can be estimated using t = (k * S / I)². In modern practice, blindly pursuing extremely high Icw values over long durations is not meaningful. To balance safety and cost-effectiveness, designers often set the short-time delay of breakers to 0.3s or 0.5s. Thus, evaluating and selecting based on the Icw value at 0.5s typically achieves optimal economic efficiency while ensuring system safety.
Key Requirements for Different Equipment
● Busbars, Switchgear, Disconnectors: Icw value ≥ Prospective short-circuit current; Withstand duration ≥ Upstream protection operating time.
● Type B Circuit Breakers: Icw value ≥ Prospective short-circuit current; Withstand duration ≥ Downstream protection operating time to ensure selective coordination.
About Us:
Mingri Electric Co., Ltd. is a leading provider of high-quality electrical components and solutions, specializing in switchgear,circuit breakers,switches, etc. We are dedicated to delivering innovative products that meet the evolving needs of the global power industry.