Circuit breaker breaking capacity and short-time withstand current - News - Global IC Trade Starts Here Free Join

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The ultimate short-circuit breaking capacity, short-circuit breaking capacity and short-time withstand current limit short-circuit breaking capacity (Icu) of the circuit breaker refers to certain tests under certain test parameters (voltage, short-circuit current, power factor). The program, the short-circuit current that can be turned on and off, after which it is turned on, does not continue to carry the breaking capacity of its rated current. Its test procedure is 0-t (on line) C0 ("0" is break, t is intermittent time, generally 3min, "C0" means break immediately after turning on). After the test, verify the tripping characteristics and power frequency withstand voltage.

The operation short-circuit breaking capacity (Ics) refers to the short-circuit current that can be turned on and off after a certain test procedure under certain test parameters (voltage, short-circuit current and power factor). After this on-off, continue Carrying the breaking capacity of its rated current, its test procedure is 0-t (on line) C0-t (on line) C0.

Short-time withstand current (Icw) refers to the ability of a circuit breaker to withstand 0.05, 0.1, 0.25, 0.5 or 1 s under certain voltage, short-circuit current and power factor, and the circuit breaker is not allowed to trip. Icw is in short delay. When tripping, the evaluation index of the electric stability and thermal stability of the circuit breaker is for the class B circuit breaker. Generally, the minimum value of Icw is: when In≤2500A, it is 12In or 5kA, and In> At 2500A, it is 30kA (Iww of DW45_2000 is 400V, 50kA, and Icw of DW45_3200 is 400V, 65kA).

The test conditions for running the short-circuit breaking capacity are extremely demanding (one-time breaking, two-on-off), and since it continues to carry the rated current (the number of times is 5% of the life) after the test, it is not only necessary to verify the tripping characteristics, Frequency withstand voltage, but also verify the temperature rise. IEC947_2 (and 1997 new IEC60947_2) and China's national standard GB140482, Ics can be 25%, 50%, 75% and 100% of the ultimate short-circuit breaking capacity Icu value (B class circuit breaker is 50%, 75% and 100%, 25% of Class B is in view of the fact that most of it is used for mainline protection).

An important principle of the circuit breaker mentioned above is that the short-circuit breaking capacity of the circuit breaker ≥ the expected short-circuit current of the circuit. The short-circuit breaking capacity of this circuit breaker usually refers to its ultimate short-circuit breaking capacity.

Regardless of the Class A or Class B circuit breakers, their ability to operate short-circuit breaking is mostly less than its ultimate short-circuit breaking capacity Icu.

Class A: DZ20 series Ics = 50% ~ 77% Icu, CM1 series Ics = 58% ~ 7 2% Icu, TM30 series Ics = 50% ~ 75% Icu, (individual product Ics = Icu).

Class B: DW15 series Ics=60% Icu, (individual such as 630AIcs=Icu, but short circuit breaking capacity is only 30V when 30kA), DW45 series Ics=62.5%~80%Icu.

Regardless of the Class A or Class B circuit breaker, as long as its Ics meets the Icu percentage values ​​specified in the IEC947_2 (or GB14048.2) standard, it is a qualified product.

When designing and selecting, the user only needs to meet the limit short-circuit breaking capacity of the circuit breaker ≥ the expected short-circuit current of the line can meet the requirements. For the line itself, for example, the circuit with the transformer capacity of 1600kVA as exemplified above may have a short-circuit current of about 43kA. It is calculated only by the distance of the transformer from the transformer of 5m, and the internal resistance of the knife switch, the transformer and the circuit breaker are all regarded as zero (the short-circuit current is therefore larger than the actual situation). The probability of such a short circuit is extremely small. When selecting a circuit breaker, as long as its ultimate short-circuit breaking capacity is >43kA, for example, 50kA is sufficient. After "0" and "C0" once, its mission was completed. A new circuit breaker must be replaced, and the short-circuit breaking capability, for example 50% Icu, also reaches 25kA, which can achieve one break, two The secondary on-off (at 25kA short-circuit current) fault current then carries its rated current, the task is very difficult. Some users believe that it is a misunderstanding and unnecessary to design the circuit breaker's short-circuit breaking capacity (Ics) ≥ line expected short-circuit current.

Some manufacturers have advertised in the sample, its product Ics=Icu, if it is true, it indicates that its I cu indicator has a margin, if it is not true, it indicates that it has water, not all believe, and Ics=Icu Circuit breakers, the price is much higher, not worthwhile.

It should be mentioned that the short-circuit breaking capability of all circuit breakers (whether Icu or Ics) is the periodic component rms value. The current of C (close-on) of "C0" in the short-circuit test is the peak current Ich. When the test station performs the short-circuit breaking test, the voltage, short-circuit current (effective value) and power factor (cos) have been adjusted, and its on-current is also determined. The on-current test ("C" test) is the ability to assess the electrical repulsion and thermal stability of the contacts and other electrical conductors with peak currents. What is the rms current (breaking current) in its corresponding Under power factor, there is a peak current, and the user does not need to consider the peak current parameter.

To help the user understand, the relationship between the peak current and the periodic component rms current is listed below.

Peak current (impact current)  ich = kch (root) 2Ic

Where Ic is the periodic component effective value, kch is the impact coefficient 1<kch<2, and kch×2 is the peak coefficient.