Assuming Icu=60KA, then when a faulty current of 60KA is generated in the line, the circuit breaker can safely cut off the circuit without abnormal conditions such as contact welding and blasting. Note that circuit breakers that have been broken at the limit are not allowed to be used again (often fail) and must be replaced. If Ics=60KA, after the current is broken, the circuit breaker is promised to be closed and reused, but it must also be replaced after emergency. Nowadays many good circuit breakers can do Icu=Ics. VFNC3C inverterOf course, for ICU and Ics, the country has strict definitions and related experiments, and the above is just a brief talk.
Some large systems tend to have large short-circuit currents, and many circuit breakers now have ICUs of more than 100KA or more.
The circuit breaker has the ultimate short-circuit breaking ability, the short-circuit breaking ability of operation and the short-term withstand current
The additional limit short-circuit breaking capacity (ICU) refers to the short-circuit current that can be turned on and broken under certain experimental parameters (voltage, short-circuit current, power factor) under certain experimental procedures, and no longer continues to carry its additional current after this switching ability. Its experimental procedure is 0-t (on-line) CO ("O" is the breaking, t is the intermittent time, generally 3min, and "CO" means that it is broken immediately after being connected). After the test test, the trip characteristics and power frequency withstand voltage should be verified.
The additional operation short-circuit breaking ability (Ics) refers to the short-circuit current that can be turned on and broken under the conditions of certain experimental parameters (voltage, short-circuit current and power factor) through a certain experimental procedure.
Short-time withstand current (Icw) refers to the ability to endure 0.05, 0.1, 0.25, 0.5 or 1s under a certain voltage, short-circuit current and power factor, and the circuit breaker does not agree to trip, Icw is the check target of the electrical stability and thermal stability of the circuit breaker when the circuit breaker is tripped, it is for Class B circuit breakers, and the * small value of Icw is: when the In≤ 2500A, it is 12In or 5kA, and when the In> is 2500A, it is
30 kA (400 V, 50 kA for DW45_2000 and 400 V and 65 kA for DW45_3200).
The experimental conditions for short-circuit breaking are extremely harsh (primary breaking, second on-off), because it has to continue to carry additional current (the number of times is 5% of the lifetime) after the test, so it is necessary to verify not only the tripping characteristics, power frequency withstand voltage, but also the temperature rise. IEC947_2 (and the new version of the IEC60947_2 in 1997) and China's national norms and GB140482 rules, Cs can be 25%, 50%, 75% and 100% of the ICU value for ultimate short-circuit breaking (50%, 75% and 100% for Class B circuit breakers, and 25% for Class B circuit breakers because it is mostly used for trunk line maintenance).
An important principle for the selection of circuit breakers mentioned above is that the short-circuit breaking ability of the circuit breaker can ≥ the expected short-circuit current of the line, and the short-circuit breaking ability of this circuit breaker generally refers to its limit short-circuit breaking ability.
Regardless of Class A or Class B circuit breakers, most of their operating short-circuit breaking ability is less than its limit short-circuit breaking ability to Icu. Class A: DZ20 series Ics=50%-77%Icu, CM1 series Ics=58%-72%Icu, TM30 series Ics=50%-75%Icu, (single product Ics=Icu).
Class B: DW15 series ICS=about 60% Icu, (a single such as 630AIcs=Icu, but the short circuit breaking can only be 30kA at 400V), DW45 series ICS=62.5%-80% Icu.
Regardless of whether it is a Class A or Class B circuit breaker, as long as its ICS meets the IEC947_2 (or GB14048.2) specification rules, the ICU percentage value is a qualified product.
It should be mentioned that the short-circuit breaking capability of all circuit breakers, regardless of ICU or ICS, is a valid value for the weight of the cycle. In the short-circuit test, the current of C (close on) of "C0" is the peak current Ich. When the short-circuit breaking experiment is performed at the experimental station, the voltage, short-circuit current (RMS) and power factor (COS) have been adjusted, and the turn-on current is confirmed. The turn-on current test ("C" experiment) is the ability to check the electrical repulsion and thermal stability of the contacts and other conductors by the peak current, what kind of RMS current (breaking current) the Toshiba inverter has, and what kind of peak current there is under its corresponding power factor, and the user does not need to consider the peak current parameter.
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