circuit breaker

The circuit breaker has the following features: rated voltage Ue; Rated current In; Setting range of tripping current 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 that the circuit breaker equipped with a special over-current trip relay can withstand indefinitely at the ambient temperature specified by the manufacturer, not exceeding the temperature limit specified by the current bearing component.

Short circuit relay trip current setting (Im) : Short circuit trip relay (instantaneous or short delay) is used to make the circuit breaker trip quickly when the high fault current value occurs. Its trip limit is Im.

Rated short-circuit breaking capacity (Icu or Icn) : The rated short-circuit breaking current of a circuit breaker is the highest (expected) current at which the circuit breaker can be broken without being damaged. 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 (which always occurs 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 as root mean square values of kA.

Short circuit breaking capability (Ics) : The rated breaking capability of a circuit breaker is divided into rated limit short circuit breaking capability and rated operation short circuit breaking capability. The national standard "Low-voltage Switchgear and Control Equipment Low-voltage circuit breaker" (GB14048.2-94) has the following interpretation on the rated limit short-circuit breaking capacity and rated operation short-circuit breaking capacity of circuit breaker:

1, the rated limit of the circuit breaker short circuit breaking capacity: according to the conditions specified in the prescribed experimental procedures, excluding the breaker continues to carry its rated current capacity breaking capacity;

2, the rated operation of the circuit breaker short circuit breaking capacity: according to the conditions specified in the prescribed experimental procedures, including the breaker continues to carry its rated current capacity breaking capacity;

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

The specific test is: adjust the current of the line to the expected short-circuit current value (such as 380V, 50kA), but the test button is not closed, the test circuit breaker is in the closing position, press the test button, the circuit breaker passes the short-circuit current of 50kA, the circuit breaker is immediately opened (open for short as O), the circuit breaker should be intact, and can be closed again. T is the intermittent time, generally 3min. At this time, the line is still in the hot standby state, and the circuit breaker will be switched on again (close C for short) and then switched on (O). (the switch on test is to assess the electric and thermal stability of the circuit breaker at the peak current.) This program is known as CO. If the circuit breaker can be completely broken, its ultimate short-circuit breaking capacity is qualified.

4, the rated operation of the circuit breaker short circuit breaking capacity (Icn) test procedure for O-T-CO-T-CO. It is more than the Icn test procedure of a CO, after the test, the circuit breaker can completely break, extinguished the arc, it is determined that its rated operation 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 circuit breaker outlet end of the maximum three-phase short-circuit current can also be normal operation and then cut off the short-circuit current once, as to whether the future can be normally connected and cut off, the circuit breaker is not guaranteed; Ics for rated operation indicates that the circuit breaker can be normally broken multiple times when the maximum three-phase short circuit current occurs at its outlet end.

Iec947-2 "Low-voltage switchgear and control equipment Low-voltage circuit breakers" standard: Class A circuit breakers (refers to only overload long delay, short circuit transient circuit breakers) the Ics can be 25%, 50%, 75% and 100%. The Ics of Class B circuit breakers (three-section protection circuit breakers with long overload delay, short circuit delay, and short circuit transient) can be 50%, 75%, and 100% of the Ics. Therefore, it can be seen that the rated short-circuit breaking capacity is a kind of breaking current value smaller than the rated limit short-circuit breaking current. [1]

Generally speaking, with overload long delay, short circuit short delay and short circuit transient three protection function of the circuit breaker, can achieve selective protection, most of the main trunk (including transformer outlet end) are used as the main protection switch. The circuit breakers without short circuit delay (only long overload delay and short circuit transient two-stage protection) cannot be used as selective protection. They can only be used in branches. IEC92 "Marine Electrical" points out that: circuit breakers with three-section protection, the emphasis is on its operating short-circuit breaking capacity value, while circuit breakers used in branch lines, it should be ensured that it has sufficient short-circuit breaking capacity value.

No matter what kind of circuit breaker, although have the Icu and Ics this two important technical indicators. However, as a circuit breaker used on the branch line, it can only meet the rated limit short circuit breaking capacity. The more common bias is to prefer to take large, do not take is appropriate, that take large insurance. But if it is too large, it will cause unnecessary waste (the same type of circuit breaker, its H-type - high-score breaking type, is 1.3 times to 1.8 times more expensive than the S-type - ordinary type). Therefore, the circuit breaker on the branch line is not necessary to blindly pursue its operating short-circuit breaking ability index. For circuit breakers used on main lines, they should not only meet the requirements of rated limit short-circuit breaking capacity, but also meet the requirements of rated operation short-circuit breaking capacity. If only rated limit short-circuit breaking capacity Icu is used to measure whether its breaking capacity is qualified or not, it will bring unsafe risks to users.

Circuit breaker is a kind of basic low-voltage appliances, circuit breaker with overload, short circuit and undervoltage protection function, has the ability to protect lines and power supplies.

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

Free trip of circuit breaker: At any time in the closing process of the circuit breaker, if the protection action is connected to the trip circuit, the circuit breaker can be completely and reliably disconnected, which is called free trip. The circuit breaker with free trip can ensure that the circuit breaker can be quickly disconnected when the short circuit fault occurs, which can avoid expanding the scope of the accident.