A circuit breaker is a switching device capable of closing, carrying and breaking current under normal circuit conditions and capable of carrying and interrupting current under abnormal circuit conditions for a specified period of time. Circuit breaker according to its use is divided into high-voltage circuit breakers and low-voltage circuit breakers, high and low pressure line division is more fuzzy, generally more than 3kV called high-voltage electrical appliances.
Circuit breakers can be used to distribute power, not frequently start the asynchronous motor, the power lines and motors to protect, when they have a serious overload or short circuit and undervoltage problems such as failure to automatically cut off the circuit, its function is equivalent to fuse switch And a combination of overheat relays and the like. And generally do not need to change the parts after breaking the fault current. At present, has been widely used.
Electricity generation, transportation, use, distribution is an extremely important part. Power distribution system, including transformers and a variety of high and low voltage electrical equipment, low-voltage circuit breaker is a wide range of electrical appliances.
Circuit breakers generally by the contact system, arc system, operating mechanism, release, shell and other components.
When the short circuit, the high current (usually 10 to 12 times) to produce the magnetic field to overcome the reaction of the spring, the release device pull the operating mechanism, the switch instantaneous trip. When the overload, the current becomes larger, heat increased, bimetallic deformation to a certain extent to promote the action of the body (the greater the current, the shorter the action time).
There are electronic type, the use of the transformer to collect the current size of each phase, compared with the set value, when the current is abnormal when the microprocessor sends a signal, so that the electronic release device to drive the operating mechanism.
The role of the circuit breaker is to cut off and turn on the load circuit, and cut off the fault circuit to prevent the accident to expand and ensure safe operation. The high-voltage circuit breaker to break 1500V, current 1500-2000A of the arc, these arc can be extended to 2m still continue to burn does not go out. So the arc is high voltage circuit breaker must solve the problem.
The principle of blowing arc is mainly to cool the arc to reduce the heat dissipation, on the other hand through the arc of the arc to enhance the charge of the composite particles and diffusion, while the air gap in the charged particles blowing, the rapid recovery of dielectric dielectric strength.
Low-voltage circuit breakers, also known as automatic air switches, can be used to turn on and off the load circuit, can also be used to control the motor is not frequent start. It is equivalent to the knife switch, over-current relay, loss of stress relays, thermal relays and leakage protector and other electrical parts of the sum of all the functions of low-voltage distribution network is an important protection of electrical appliances.
Low-voltage circuit breaker with a variety of protection functions (overload, short circuit, under voltage protection, etc.), adjustable action value, breaking capacity, easy operation, security, etc., it is widely used. Structure and working principle Low-voltage circuit breaker by the operating mechanism, contacts, protection devices (a variety of release), arc system and other components.
Low-voltage circuit breaker main contact is by manual operation or electric closing. When the main contact is closed, the free trip mechanism locks the main contact in the closing position. The coil of the overcurrent release and the thermal element of the thermal release are connected in series with the main circuit, and the coil of the undervoltage release and the power supply are connected in parallel. When the circuit occurs short circuit or serious overload, the over-current release of the armature pull, so that the free trip mechanism, the main contact disconnect the main circuit. When the circuit is overloaded, the thermal element of the thermal release heats the bimetallic sheet to bend and push the free trip mechanism. When the circuit is undervoltage, the armature of the undervoltage release is released. Also let the free trip mechanism action. Shunt release is used as a remote control, in normal operation, the coil is power, in the need for distance control, press the start button to make the coil power.
Key Features Editor
The characteristics of the circuit breaker are: rated voltage Ue; rated current In; overload protection (Ir or Irth) and short circuit protection (Im) trip current setting range; rated short-circuit breaking current (industrial circuit breaker Icu; home circuit breaker Icn )Wait.
Rated operating voltage (Ue): This is the voltage at which the circuit breaker operates in normal (uninterrupted) conditions.
Rated current (In): This is the maximum current value that can be infinitely tolerated by the circuit breaker with a special overcurrent trip relay at the ambient temperature specified by the manufacturer and does not exceed the temperature limit specified by the current receiving part.
Short-circuit relay trip current setting (Im): Short-circuit trip relay (instantaneous or short delay) for high fault current value when the circuit breaker to quickly trip, the 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 being damaged. The current value provided in the standard is the rms value of the AC component of the fault current. When calculating the standard value, the DC transient component (always occurring in the worst case short circuit) is assumed to be zero. Industrial circuit breaker ratings (Icu) and household circuit breaker ratings (Icn) are usually given in the form of kA rms values.
Short-circuit breaking capacity (Ics): rated breaking capacity of the circuit breaker is divided into the rated limit short-circuit breaking capacity and rated running short-circuit breaking capacity of two. GB "low-voltage switchgear and control equipment, low-voltage circuit breaker" (GB14048.2-94) on the circuit breaker rated short-circuit breaking capacity and rated operation of short-circuit breaking capacity made the following explanation:
1, the rated limit of the circuit breaker short circuit breaking capacity: according to the provisions of the provisions of the experimental procedures, does not include the circuit breaker to continue to carry its rated current capacity of the breaking capacity;
2, the rated operating circuit breaker breaking capacity: according to the provisions of the provisions of the experimental procedures, including the circuit breaker to continue to carry its rated current capacity of the breaking capacity;
3, the rated limit short-circuit breaking capacity of the test procedure for the O-t-CO.
The test is: the circuit current is adjusted to the expected short-circuit current value (such as 380V, 50kA), while the test button is not closed, the circuit breaker is in the closing position, press the test button, the circuit breaker through 50kA short-circuit current, Circuit breaker immediately break (open referred to as O), the circuit breaker should be intact, and can then close. t is the intermittent time, usually 3min, then the line is still in the hot standby state, the circuit breaker and then connected once (close) C and immediately after the break (O), (connected to the test is to check the circuit breaker in the peak Current under electrical and thermal stability). This procedure is CO The circuit breaker can be completely broken, then the limit short-circuit breaking capacity qualified.
4, the rated run of the circuit breaker short circuit breaking capacity (Icn) test procedure for the O-t-CO-t-CO. It is more than Icn test program more than a CO, after the test, the circuit breaker can be completely broken off, extinguish the arc, it is determined that its rated running short circuit breaking capacity qualified.
Therefore, it can be seen, the rated limit short-circuit breaking capacity Icn refers to the low-voltage circuit breaker in the circuit breaker breaking the maximum three-phase short-circuit current can also be normal operation and then break the short-circuit current once, as to whether the normal The circuit breaker is not guaranteed by the circuit breaker.
IEC947-2 Low Voltage Switchgear and Control Equipment Low Voltage Circuit Breakers Standard: Ics for Class A Circuit Breakers (only overloaded long delays, short circuit breakers) may be 25%, 50%, 75% and 100%. Ics of class B circuit breakers (circuit breakers with overloaded long delay, short circuit short delay, short circuit transient) can be 50%, 75% and 100% of Ics. Therefore, it can be seen that the rated run short circuit breaking capacity is a breaking current value that is smaller than the rated limit short circuit breaking current. 
In general, circuit breakers with overloaded long delay, short-circuit short delay and short-circuit transient protection can be selectively protected. Most main lines (including the outlet of the transformer) are used as main protection switches The Do not have short-circuit short-circuit function of the circuit breaker (only overload long delay and short-circuit instantaneous two-stage protection), can not be selective protection, they can only be used in the slip. IEC92 "ship electrical" pointed out: a three-stage protection of the circuit breaker, emphasis on its operating short-circuit breaking capacity value, and used in the branch circuit breaker, should ensure that it has sufficient limit short-circuit breaking capacity value.
No matter what kind of circuit breakers, although both Icu and Ics these two important technical indicators. However, as a circuit breaker used on the branch line, it is possible to satisfy only the rated limit short-circuit breaking capacity. The more common bias is rather take big, do not take the right, that take big insurance. But made too large, will cause unnecessary waste (the same type of circuit breaker, the H-type - high breaking type, than the S-type - ordinary type of expensive to 1.3 times to 1.8 times). So the circuit breaker on the feeder line is not necessary to blindly pursue its operating short-circuit breaking capacity index. For the use of circuit breakers on the trunk, not only to meet the requirements of the rated limit short-circuit breaking capacity requirements, 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 give users a sense of insecurity.
Circuit breaker is a basic low-voltage electrical appliances, circuit breakers with overload, short circuit and undervoltage protection, the ability to protect lines and power.
The main technical indicators are the rated voltage, rated current. Circuit breaker according to different applications have different functions, variety, specifications a lot, the specific technical indicators are also many.
Circuit breaker free trip: circuit breaker in the closing process at any time, if the protection action connected to the trip circuit, the circuit breaker can be completely disconnected, which is called free tripping. With a free trip circuit breaker, you can ensure that the circuit breaker closing short circuit failure, can quickly disconnect, to avoid the scope of the accident to expand