A circuit breaker refers to a switching device that can conduct, carry and break current under normal circuit conditions, and conduct, carry and break current under abnormal circuit conditions within a specified period of time. Circuit breakers are divided into high-voltage circuit breakers and low-voltage circuit breakers according to the scope of application, and the boundaries between high and low voltage are relatively vague. Generally more than 3kV is called high-voltage electrical appliances.
Circuit breakers can be used to distribute electric energy, start asynchronous motors infrequently, protect power lines and motors, and automatically cut off circuits in the event of severe overload, short circuit, undervoltage and other faults. Its function is equivalent to a combination of a fuse switch and an overheat and underheat relay. Moreover, it is generally not necessary to replace parts after breaking the fault current. It has been widely used now.
Power distribution is an extremely important link in the generation, transmission and consumption of electricity. The power distribution system includes transformers and various high and low voltage electrical equipment. Low voltage circuit breakers are electrical appliances with a large amount of use and a wide range of applications.
A circuit breaker is generally composed of a contact system, an arc extinguishing system, an operating mechanism, a release, and a casing.
In the event of a short circuit, the magnetic field generated by the large current (usually 10 to 12 times) overcomes the reaction force spring, the release pulls the operating mechanism to act, and the switch trips instantaneously. When overloaded, the current increases, the heat generation increases, and the bimetal deforms to a certain extent to promote the movement of the mechanism (the greater the current, the shorter the action time).
For the electronic type, the transformer is used to collect the magnitude of each phase current and compare it with the set value. When the current is abnormal, the microprocessor sends a signal to make the electronic release drive the operating mechanism to act.
The function of the circuit breaker is to cut off and connect the load circuit, cut off the fault circuit, prevent the accident from expanding, and ensure safe operation. The high-voltage circuit breaker needs to break the arc of 1500V and the current of 1500-2000A. These arcs can be stretched to 2m and continue to burn. Therefore, arc extinguishing is a problem that high-voltage circuit breakers must solve.
The principle of arc extinguishing is mainly to cool the arc to weaken thermal dissociation. On the other hand, arc blowing elongates the arc, strengthens the recombination and diffusion of charged particles, and at the same time blows away charged particles in the arc gap, quickly restoring the dielectric strength.
Low voltage+, also known as automatic air switch, can be used to switch load circuits on and off, and can also be used to control motors that start infrequently. Its function is equivalent to the sum of part or all of the functions of the knife switch, overcurrent relay, voltage loss relay, thermal relay and leakage protector, and is an important protective appliance in the low-voltage distribution network.
Low-voltage circuit breakers have many protection functions (overload, short-circuit, under-voltage protection, etc.), adjustable action value, high breaking capacity, convenient operation, safety and other advantages, so they are widely used. Structure and working principle The low-voltage circuit breaker is composed of operating mechanism, contacts, protection devices (various releases), and arc extinguishing system.
The main contacts of the circuit breaker voltage are manually operated or closed electrically. After the main contacts are closed, the free trip mechanism locks the main contacts in the closed 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 is connected in parallel with the power supply. When the circuit is short-circuited or severely overloaded, the armature of the overcurrent release is pulled in, so that the free release mechanism operates, and the main contact disconnects the main circuit. When the circuit is overloaded, the thermal element of the thermal trip unit will heat up, bending the bimetal, thereby pushing the free trip mechanism to act. When the circuit is undervoltage, the armature of the undervoltage release is released. And the free trip mechanism is also actuated. A parallel trip device is used for remote control. During normal operation, its coil is de-energized. When distance control is required, press the start button to energize the coil.
Post time: Oct-15-2022