Electronics

Main characteristics of Circuit Breaker

The main characteristics of the circuit breaker are: rated voltage Ue; rated current In; the range of off-load current adjustment for overload protection (Ir or Irth) and short-circuit protection (Im); rated short-circuit breaking current (industrial circuit breaker Icu; household circuit breaker Icn), etc.

Rated operating voltage (Ue): This is the voltage at which the circuit breaker operates under normal (uninterrupted) conditions.

Rated current (In): This is the maximum current value that a circuit breaker equipped with a special overcurrent detrashing relay can infinitely withstand at the ambient temperature specified by the manufacturer, without exceeding the temperature limit specified for the current bearing components.

Short-circuit relay detrashing current rectification value (Im): short-circuit detrashing relay (instantaneous or short delay) for high fault current values appear, so that the circuit breaker quickly tripped, its trip limit Im.

Rated short-circuit breaking capacity (Icu or Icn): the rated short-circuit breaking current of the circuit breaker is the highest (expected) current value that the circuit breaker can break without damage. The current value provided in the standard is the root-mean-square value of the AC component of the fault current, and the DC transient component (always present in the worst case short circuit) is assumed to be zero when calculating the standard value. Industrial circuit breaker ratings (Icu) and domestic circuit breaker ratings (Icn) are usually given in the form of kA rms values.

Short-circuit breaking capacity (Ics): the rated breaking capacity of circuit breakers is divided into two types of rated limit short-circuit breaking capacity and rated operating short-circuit breaking capacity. National standard “low-voltage switchgear and control equipment low-voltage circuit breakers” (GB14048.2-94) on the rated limit short-circuit breaking capacity and rated operating short-circuit breaking capacity of circuit breakers are explained as follows.

1, the rated limit short-circuit breaking capacity of the circuit breaker: the conditions specified in accordance with the prescribed experimental procedures, excluding the breaking capacity of the circuit breaker to continue to carry its rated current capacity.

2, the rated operating short-circuit breaking capacity of the circuit breaker: the conditions specified in accordance with the prescribed experimental procedures, including the breaking capacity of the circuit breaker to continue to carry its rated current capacity.

3, the rated limit short-circuit breaking capacity of the test procedure for O-t-CO.

Its specific test is: adjust the line current to the expected short-circuit current value (for example, 380V , 50kA), and the test button is not closed, the circuit breaker under test in the closed position, press the test button, the circuit breaker through 50kA short-circuit current, the circuit breaker immediately open (open referred to as O), the circuit breaker should be intact, and can close again. t for the interval, generally 3min, when the line is still In the hot standby state, the circuit breaker and then a turn-on (close referred to as C) and immediately after the open (O), (turn-on test is to assess the electrical and thermal stability of the circuit breaker at peak current). This procedure is CO. circuit breaker can be completely broken, then its limit short circuit breaking capacity qualified.

4, the rated operating short-circuit breaking capacity of the circuit breaker (Icn) test procedure for O-t-CO-t-CO. It is more than the Icn test procedure once CO, after the test, the circuit breaker can completely break, extinguish the arc, it is determined that its rated operating short-circuit breaking capacity qualified.

Therefore, it can be seen that the rated limit short-circuit breaking capacity Icn refers to the low-voltage circuit breaker in the breakout of the maximum three-phase short-circuit current at the circuit breaker out of the normal operation and then break this short-circuit current once, as to whether the subsequent normal connection and breakout, the circuit breaker does not guarantee; while the rated operating short-circuit breaking capacity Ics refers to the maximum three-phase short-circuit current at the circuit breaker out of its occurrence can be Multiple normal interruptions.

IEC947-2 “low-voltage switchgear and control equipment low-voltage circuit breakers” standard: Class A circuit breakers (referring to only overload long-delay, short-circuit transient circuit breakers) Ics can be 25%, 50%, 75% and 100%. class B circuit breakers (circuit breakers with overload long-delay, short-circuit short-delay, short-circuit transient three-stage protection) Ics can be 50%, 75% and 100% of the Ics. Therefore, it can be seen that the rated operating short-circuit breaking capacity is a smaller breaking current value than the rated limit short-circuit breaking current. [1]

In general, the circuit breaker with three protection functions of overload long delay, short circuit short delay and short circuit transient can achieve selective protection, and most main lines (including the outgoing end of the transformer) use it as the main protection switch. IEC92 “Marine Electrical” points out that: circuit breakers with three stages of protection, in favor of its operating short-circuit breaking capacity value, while the use of circuit breakers for branch lines, should ensure that it has sufficient limit short-circuit breaking capacity value.

No matter what kind of circuit breaker, although all have Icu and Ics these two important technical indicators. However, as a branch line on the use of circuit breakers, can only meet the rated limit short-circuit breaking capacity can be. A more common bias is rather to take large, not to take the right fit, that take large insurance. But obtain too large, will cause unnecessary waste (the same type of circuit breaker, its H-type – high breaking type, than S-type – ordinary type of price to 1.3 times ~ 1.8 times more expensive). Therefore, the circuit breaker on the branch line is not necessary to pursue its operating short-circuit breaking capacity indicators. For the use of circuit breakers on the trunk line, not only to meet the requirements of the rated limit short-circuit breaking capacity, but also should meet the requirements of the rated operating short-circuit breaking capacity, if only the rated limit short-circuit breaking capacity Icu to measure its breaking capacity qualified or not, will bring unsafe hidden danger to the user.

Circuit breaker is a basic low-voltage electrical appliances, circuit breakers with overload, short-circuit and under-voltage protection functions, the ability to protect the line and power supply.

The main technical indicators are rated voltage and rated current. Circuit breakers have different functions according to different applications, many varieties and specifications, and many specific technical indicators.

Circuit breaker free release: circuit breaker in the process of closing at any moment, if the protection action is connected to the tripping circuit, the circuit breaker can completely and reliably disconnect, which is called free release. Circuit breakers with free release can ensure that the circuit breaker closed short-circuit fault, can quickly disconnect, can avoid expanding the scope of the accident.

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