A circuit breaker is a switching device that can close, load, and open the current in a normal loop condition and hold and break the abnormal circuit in a specified time. The circuit breaker can be divided into high voltage circuit breaker and low voltage circuit breaker according to its use range.
Circuit breaker can be used to allocate electricity, not frequent start asynchronous motor, the protection of power line and motor, when they happen serious overload or short circuit and under-voltage fault can automatically cut off the circuit, its function is equivalent to fuse switch to owe the combination of thermal relay, etc. Moreover, the parts should not be changed after breaking the current. At present, it has been widely used.
Distribution is an extremely important link in the generation, delivery and use of electricity. The distribution system includes transformers and various high and low voltage electrical equipment, and the low voltage circuit breaker is a widely used electric appliance.
The circuit breaker is composed of contact system, arc extinguishing system, operating mechanism, tripping device and shell.
When short circuit, the magnetic field generated by the large current (usually 10 to 12 times) overcomes the anti-force spring, the tripping device pulls the operating mechanism action, and the switch is instantaneous trip. When overloaded, the current becomes larger, the heat is increased, and the deformation of the bimetal plate is to a certain degree to promote the movement of the body (the larger the current is, the shorter the action time is).
With the electronic type, the size of each phase current is collected by means of the transformer. Compared with the set value, the microprocessor sends out the signal when the current is abnormal, so that the electronic tripping device drives the operation mechanism.
The function of the circuit breaker is to cut off and connect the load circuit, and to cut off the fault circuit to prevent the accident from expanding and ensure the safe operation. The high voltage circuit breaker will open 1500V and the current will be 1500-2000a. The arc can be extended to 2m and continue to burn. So the arc suppression is the problem that the high voltage circuit breaker must solve.
Blow the principle of arc arc mainly cooling arc thermal dissociation, on the other hand stretched by blowing arc arc strengthen composite and diffusion of charged particles, the charged particles in the arc gap blows away at the same time, quickly recover dielectric strength of the medium.
Low-voltage circuit breakers, also known as automatic air switches, can be used to plug and break the load circuit, or to control the motor that does not start frequently. Its function is equal to the knife switch, over-current relay, relay, thermal relay, pressure loss and leakage protector electrical part or all of the functions such as sum, it is a kind of important in the low voltage distribution network protection appliances.
Low voltage circuit breaker has many advantages such as protection function (overload, short circuit, undervoltage protection, etc.), adjustable action value, high breaking ability, convenient operation and safety, so it is widely used. The structure and working principle low voltage circuit breaker consists of operating mechanism, contact, protection device (various kinds of tripping device), and arc extinguishing system.
The main contact of the low voltage circuit breaker is operated by hand or electric switchgear. After the main contact is closed, the free trip mechanism locks the main contact lock in the lock position. The coil of the overcurrent tripping device and the thermal element of the thermal release are in series with the main circuit, and the coil of the undervoltage trip is connected in parallel with the power supply. When the circuit is short circuited or seriously overloaded, the armature of the overcurrent tripping device is absorbed and the free tripping mechanism is made, and the main contact is disconnected from the main circuit. When the circuit is overloaded, the heat element of the thermostat causes the bimetal to bend and move the free trip mechanism. When the circuit is under voltage, the arrester of the undervoltage release is released. Also make free trip mechanism action. The shunt tripping device is used as a remote control. When working normally, its coil is without power, and when it needs distance control, press the start button to make the coil energize.
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With circuit breaker auxiliary contacts: main circuit points and institutions on the mechanical gearing contact, it is mainly used for circuit breaker points and state display, meet in breaker control circuit by circuit breaker points, for the related electrical control and interlock. For example, signal to signal lamp, relay, etc. The rated current 100A of the shell breaker shell is a single breakpoint switch contact, 225A and above is the bridge type contact structure, and the heating current is 3A; The rated current of the shell frame rated current 400A and above can be opened for two or more times. The heating current is 6A. The operating performance is the same as the operating performance of the circuit breaker.
Alarm contacts, alarm contacts for circuit breaker accident, and the contact only when the circuit breaker points break off, is mainly used for load circuit breaker overload short circuit or under voltage and failures, and sometimes free trip, alarm contacts from the original into a normally open position close position, through to auxiliary line indicator or bell, buzzer, etc., in the display or remind the fault tripping circuit breaker status. Because of the failure of the circuit breaker, the probability of free trip is not too high, so the life of alarm contact is 1/10 of the breaker's life. The working current of alarm contact is generally not greater than 1A.
Shunt trip: shunt tripping device is a kind of actuator with voltage source, which is independent of the main circuit voltage. The shunt tripping device is a kind of remote control. When the power supply voltage is equal to the voltage of 70% to 110% of the rated control power voltage, it can reliably break the circuit breaker. The shunt tripping device is a short-time working system, and the coil can not exceed the 1S, otherwise the line will be burned. Molded case circuit breaker to prevent coil burned, the shunt trip coils in series a micro switch, when the shunt tripping device through the armature and, micro switch from into a normally open normally closed state, as a result of the shunt tripping device power supply control circuit is cut off, even if people hold down the button, the shunt coil is never again electrify coil of this avoids damage situation. When the circuit breaker is closed again, the micro switch is in the constant closed position.
Undervoltage tripping device, undervoltage tripping device is at its terminal voltage drop to a prescribed scope, make the circuit breaker with delay or without delay disconnect a trip, when the power supply voltage drop (or even slow down) to 70% and 35% of the rated voltage range, undervoltage tripping device should operate, undervoltage tripping device in power supply voltage is equal to 35% of the rated working voltage trip, undervoltage tripping device should be able to prevent the breaker closing; When the voltage of the power supply is equal to or greater than 85% of the rated working voltage of the arrester, under the condition of the thermal condition, the circuit breaker can be reliably closed. Therefore, when the protected circuit power supply voltage in a voltage drop occurs, can automatically disconnect circuit breaker to cut off the power supply, make the circuit breaker under the load of electrical or electrical equipment from the damage of under voltage. When used, the under-voltage trip coil is connected to the circuit breaker power supply side, and the circuit breaker can be switched on when the undervoltage trip is energized. 
Electric operator: this is one kind is used for automatic remote gate and a switching circuit breaker accessories, electric operation mechanism, which has two kinds of operating mechanism of the motor and electromagnet operating mechanism, motor operating mechanism for molded case circuit breaker shell frame level rated current 400 a and above circuit breaker, electromagnet operation mechanism suitable for molded case circuit breaker shell frame level rated current under 225 a and circuit breaker, whether electromagnet or motor, their absorption and rotation direction is the same, only by the electric operating mechanism within the location of the CAM to achieve, and when used in electric institutions operating circuit breakers, at between 85% and 110% of the rated control voltage under any of the voltage, should ensure reliable circuit breaker closed.
Rotating handles: suitable for molded case circuit breaker, the breaker cover jacket of rotational operating handle, the handle of the shaft is installed in its institutions cooperate with hole, the other side of the rotating shaft through the drawer cabinet door hole, put his hand in the door of the complete sets of equipment of rotating the handle shaft head, above the handle round or square on the door with screws, the installation of this can make the operator at the door by the handle knob clockwise or counterclockwise rotation, to ensure that the circuit breaker closing or brake. At the same time, the turning handle ensures that the circuit breaker is in the lock, and the door cannot be opened; Only the rotating handle is in the split or rebutton, the door of the switch board can be opened. In case of emergency, the circuit breaker is in the "closing" and needs to open the door panel, which can rotate the red release button on the edge of the handle seat.
Extended handle: a kind of external extension handle, which is directly mounted on the handle of the circuit breaker. It is used in the large-capacity circuit breaker for 600A and above.
Handle lock device: it is installed on the handle frame, the handle is punched and padlocked. Mainly used for circuit breaker in closing.
In the working state, no other person will be allowed to split the switch to cause a power failure, or the circuit breaker load side circuit will need to be repaired or not allowed to be charged, in case the circuit breaker will be closed by mistake.