A circuit breaker is a switching device that can close, carry and break current under normal circuit conditions and can close and carry current under the abnormal loop conditions within a specified time. Circuit breakers are divided into high-voltage circuit breakers and low-voltage circuit breakers according to their use range. The division of high and low voltage lines is relatively vague. Generally, 3kV or more is called high-voltage electrical equipment.
Circuit breakers can be used to distribute electrical energy, start asynchronous motors infrequently, protect power lines and motors, and automatically cut off circuits when they are severely overloaded or short-circuited or under-voltage faults. Their functions are equivalent to fuse switches. Combined with over-heat relays and the like. Moreover, it is generally not necessary to change parts after breaking the fault current. At present, it has been widely used. In the generation, transmission and use of electricity, power distribution is an extremely important link. The power distribution system includes transformers and various high and low voltage electrical equipment, and the low voltage circuit breaker is a kind of electrical appliance with a large amount of use.
1.Porcelain sleeve: it is insulator and support for connection between main loop and power system. Due to getting through with housing of breaker, it belongs to part of pressure vessel, so it is high strength and good sealing.
2.Arc distinguish chamber is composed of static contactor, dynamic contactor, porcelain sleeve, air cylinder and sprayer.
3.Absorber: material is aluminum alloyed vessel. It has F-03 molecular sieve inside. Its effect is to absorb moisture in the SF6 gas and low fluoride born due to electric arc effect.
Its function is to transfer horizontal movement output to vertical movement of breaker contactor by external connecting lever, shaft and internal connecting lever. There are seal rings on each side of shaft. Buffers are installed up and down of external connecting lever. Self sealing valve is interface for breaker and pipelines air-in and air-out, which is used to measure breaker moisture.
5.Arc distinguish principle
The cabin is single pressure air pressing structure: that is SF6 gas of 0.4-0.5Mpa inside breaker. During switch off, movable air will be effect on static seat, internal air is compressed, and there is air difference with external air. High pressure SF6 gas blow arc to force arc distinguished when current is zero. Once breaking, this pressure will be disappeared and internal and external pressure will be balanced. Due to cut-off valve on the seat, switch on pressure is very small.
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The circuit breaker is generally composed of a contact system, an arc extinguishing system, an operating mechanism, a trip unit, a casing, and the like.
When short-circuited, the magnetic field generated by a large current (generally 10 to 12 times) overcomes the reaction force spring, the trip unit pulls the operating mechanism, and the switch instantaneously trips. When overloaded, the current becomes larger, the heat is increased, and the bimetal is deformed to a certain extent to push the mechanism (the larger the current, the shorter the action time).
If there is an electronic type, the current of each phase is collected by using a transformer, and compared with the set value, when the current is abnormal, the microprocessor sends a signal to cause the electronic trip unit to drive the operating mechanism.
The function of the circuit breaker is to cut off and close the load circuit, and cut off the fault circuit to prevent accidents from expanding and ensure safe operation. The high-voltage circuit breaker is to break 1500V, the current is 1500-2000A arc, these arcs can be extended to 2m and continue to burn without extinguishing. Therefore, arc extinguishing is a problem that must be solved by high voltage circuit breakers.
The principle of arc-extinguishing arc is mainly to cool the arc to attenuate the heat release. On the other hand, the arc is used to stretch the arc to enhance the recombination and diffusion of the charged particles, and at the same time, the charged particles in the arc gap are blown off, and the dielectric strength of the medium is quickly restored.
Low-voltage circuit breakers, also known as automatic air switches, can be used to switch the load circuit on and off, as well as to control motors that are not frequently started. Its function is equivalent to the sum of all or all of the functions of the knife switch, over current relay, voltage loss relay, thermal relay and leakage protector. It is an important protection device in the low voltage distribution network.
Low-voltage circuit breakers are widely used because of their various protection functions (overload, short circuit, under voltage protection, etc.), adjustable action values, high breaking capacity, easy operation and safety. Structure and working principle The low-voltage circuit breaker is composed of operating mechanism, contacts, protection devices (various trip units), arc extinguishing system and so on.
The main contacts of the low voltage circuit breaker are manually operated or electrically closed. After the main contact is closed, the free trip mechanism locks the main contact in the closed position. The coil of the overcurrent release and the thermal element of the thermal trip are connected in series with the main circuit, and the coil of the undervoltage release is connected in parallel with the power supply. When the circuit is short-circuited or severely overloaded, the armature of the overcurrent release pulls in, causing the free trip mechanism to act and the main contact to open the main circuit. When the circuit is overloaded, the heat element of the thermal tripper generates heat to bend the bimetal and push the free trip mechanism. When the circuit is under voltage, the armature of the undervoltage release is released. The free trip mechanism is also actuated. The shunt release is used for remote control. In normal operation, the coil is de-energized. When distance control is required, the start button is pressed to energize the coil.